Correction: Efficient removal of cobalt from aqueous solution using β-cyclodextrin modified graphene oxide

Correction for ‘Efficient removal of cobalt from aqueous solution using β-cyclodextrin modified graphene oxide’ by Wencheng Song et al., RSC Adv., 2013, 3, 9514–9521.

The authors regret that Fig. 1 and ​and33 were incorrect in the original article. The SEM images of both GO and β-CD, and the Raman spectra of both, were confused with other samples. The correct versions of Fig. 1 and ​and33 are presented below.Open in a separate windowFig. 1SEM images of (a) GO and (b) β-CD-GO.Open in a separate windowFig. 2Raman spectra of GO and β-CD-GO.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Experimental review of PEI electrodeposition onto copper substrates for insulation of complex geometries

Polyetherimide (PEI) was used for coating copper substrates via electrophoretic deposition (EPD) for electrical insulation. Different substrate preparation and electrical field application techniques were compared, demonstrating that the use of a pulsed voltage of 20 V allowed for the best formation of insulating coatings in the 2–6 μm thickness range. The results indicate that pulsed EPD is the best technique to effectively coat conductive substrates with superior surface finish coatings that could pass a dielectric withstand test at 10 kV mm⁻¹, which is of importance within the EV automotive industry.

Electrophoretic deposition relying on electrodeposition of charged polymers via modulated electrical fields is reported. Superior surface finishes that could pass a dielectric withstand test at 10 kV mm⁻¹ were obtained for pulsed potentials at 20 V.

Electrophoretic deposition (EPD) is a useful and scalable technique for the production of electrically insulating coatings on conductive substrates having irregular shapes, while at the same time allowing a precise control of the coating thickness.^1,2 EPD relies on the preparation of an aqueous colloidal suspensions based on charged polymers that are deposited as particles onto an electrically conductive substrate by an induced electric field.³ In contrast to other electrical field induced deposition methods such as electroplating, EPD does not require the suspension to have high electrical conductivity, allowing for small power losses due to the total current being used for the coating formation.⁴ Advantages also include that more complex shapes/parts can be coated due to the emulsion being able to reach into difficult geometries, consequently covering areas in hard to reach segments that otherwise would remain uncoated in a dip-coating procedure.^1–4To promote high electrophoretic movement of the polymer particles and homogenous formation of the polymer coatings, both high polymer charge and high polymer colloidal suspension concentration are required in the coating system.^5–7 These factors are considered the most important in the selection of polymer for the EPD systems.⁴ The control over the coating quality has shown, however, to rely on several more parameters, including deposition time, electric field strength, suspension viscosity, applied voltage, etc.⁷ To enhance the polymer charge and solubility, functional groups have been added to the polymer structure and/or a mixture of solvents have been utilized, respectively.^8,9 Furthermore, the thermal stability of the selected polymers needs to be considered to withstand the temperature build-up in the conductive substrate (as an applied coating) during regular operations, e.g., in the automotive parts. Here, polyether ether ketone (PEEK) and polyetherimide (PEI) have shown to be useful in terms of producing homogenous coatings and adequately allowing for thermal post-treatments performed. These post treatments are made to ensure uniform concealing and reformation of the insulating polymer characteristics, i.e., post-coating deposition.^10–12 Among the two, the PEI is the most interesting as it is the least expensive.The EPD of PEI requires a quaternization reaction resulting in protonated PEI (qPEI) for the formation of a charged polymer emulsion suspension and subsequent effective electrophoretic deposition of the PEI onto the conductive substrate.^13,14 The PEI''s imide group undergoes a ring-opening reaction by the addition of 1-methylpiperazine, leading to the formation of an amide group in the PEI structure (Fig. 1a and S1^†). The process is followed by acid protonation of lactic acid, and charge neutralization of the amine group, which in turn allow for the preparation of the polymer suspensions (emulsion) required for the EPD process (Fig. 1a). The inset in Fig. 1a shows the resulting polymer emulsion in the round bottom flask. After the EPD emulsion coating was carried out on the substrate, the coated substrate was treated at high temperature to allow the re-imidization of the PEI, producing the insulating coating (Fig. 1a). A challenge in this context is the possible H₂ gas formation on the cathode electrode, from one of the half reactions in the electrolysis of water, and occasional formation of bubbles/voids in the formed PEI coatings.¹⁵ Therefore, alternating currents (AC) and pulsed direct currents (DC) were evaluated as process alternatives to improve the coating properties.¹⁶ However, to our best knowledge, enlightening comparisons between different voltages, current set-ups, surface substrate preparations, and charged polymer suspension formation have previously not been cross-examined, and compared, in terms of finding optimal conditions for generating useful EPD conditions and formation of uniform insulating coatings.Open in a separate windowFig. 1The electrophoretic deposition process from PEI to qPEI followed by re-imidization to PEI (a), and FTIR transmission spectra of the different samples (b). The coated PEI material was scrapped off prior to the FTIR analysis.In this work, copper substrates with different surface treatments (polishing and sandblasting, Fig. S2^†) and acidic cleaning (HCl and HNO₃), were used for the EPD of qPEI under different potentials (2–20 V), see Fig. 2 and S3.^† The selected potentials were obtained from screening useful conditions with associated electrical field strengths, as well as motivated from previous works.^17,18 The qPEI suspension formation was evaluated in terms of lactic acid/water content and mixing temperature of the solution after the addition of water (Table S1^†). The coated copper substrates with qPEI were always identically heat treated to re-imidize the qPEI forming the electrically insulating PEI layer (Fig. S4 and S5^†). To prepare the qPEI, PEI (20 g) was dissolved in an NMP/acetophenone solution and 1-methylpiperazine was added. The solution was treated at 110 °C (2 h), which promoted the ring-opening of the imide ring in the PEI, from the solvated state (sPEI) to the fully protonated state (qPEI) (Fig. 1a and S1^†). The changes in the FTIR spectra for the corresponding sPEI and qPEI is shown in Fig. 1b. The PEI stretching bands at 1780 and 1720 cm⁻¹ (imide carbonyl of the five-member ring) and 1360 cm⁻¹ (carbon–nitrogen vibration of imide five-member ring) were considerably reduced in the sPEI sample, and almost absent in the qPEI sample. Additionally, the strong band observed at 1670 cm⁻¹ (–C O vibration from amide) demonstrated the successful formation of qPEI (Fig. 1b).¹⁴ The band at 1360 cm⁻¹ and the broad shoulder observed for the band at 1670 cm⁻¹ was ascribed to the characteristics bands of acetophenone (Fig. S6^†). The presence of the bands at 1780, 1720 and 1548 cm⁻¹ confirmed the re-imidation of the qPEI forming PEI coating, see Fig. 1b.Open in a separate windowFig. 2Current density decay on the copper substrate during the EPD process using different constant voltages and substrate pretreatments (a), compassion between constant and pulse voltage 20 V (b), and initial current density response when qPEI suspensions of different storage time were used (c). The result in “c” are the average of triplicates and the error bars the standard deviation.The formation of a qPEI polymer suspension was strongly relying on the combined composition of lactic acid, acetophenone, and water, as well as the suspension temperature. The suspensions formed by 0.35 wt% lactic acid, 79.65 wt% acetophenone, and 20 wt% water, mixing temperature = 90 °C, (Suspension 1, Table S1^†), resulted in solid lumps being formed at the bottom of the reactor (Fig. S7a^†). Increasing the water content to 46 wt% on the expense of the combined amount of lactic acid and acetophenone (Suspension 2, Table S1^†) resulted in a more homogenous suspension without apparent particle agglomeration at room temperature if rapid stirring was applied (Fig. S7b^†). An increase of the lactic acid content to 1.3 wt% and water content to 67.5 wt% (Suspension 3, Table S1^†) led to an unstable suspension that immediately phase separated, unless the suspension was stirred rapidly using mechanical stirring (Fig. S7c and d^†). To stabilize the emulsion, the mixing temperature was decreased to 65 °C and the emulsion turned into a milky, highly viscous liquid (Suspension 4). At lower temperatures (23 °C or lower), a milky suspension with lower viscosity was formed (Suspension 5) that was stable for up to 48 h before any phase separation was observed (Fig. S8^†). The pH of this optimized suspension was 4.6 and showed an electrical conductivity of 126 mS m⁻¹. The addition of water to the qPEI was also found necessary to carry out as slow as possible to avoid excessive foam formation in the making of the optimized suspension, see further Fig. S9.^†The EPD process on the copper substrate using Suspensions 1 and 2 did not produce a coating layer on the substrate. Suspension 1 yielded a suspension with lumps formed whereas Suspension 2 appeared more homogenous (Table S1^†) but no coating was formed, possibly due to limited ionic movement, which is a key factor/requirement for producing homogenous EPD coatings.²Trials using Suspensions 3 and 4 for the EPD process revealed that an increased lactic acid content facilitated the formation of the coating, probably due to improved ionic movement, however none of these solutions produced homogenous coatings. Suspension 5 resulted in evenly covered copper substrates (Fig. S5^†). The pH of the qPEI Suspension 3 was 8.6 ± 0.1 while for Suspension 5 was 4.6 ± 0.1. The difference in the pH for the aforementioned suspensions (both having the same lactic acid/water composition, Table S1^†) could result from different zeta potential values, where very low zeta potential values have been previously showed to have a negative effect on the ionic stability/mobility in colloidal dispersions.² Suspension 5 was therefore used for the further EPD of the copper substrates due to its low viscosity, low mixing temperature, and ability to form homogenous qPEI coatings on the substrate (Table S1 and Fig. S5^†). Fig. 2a shows the current density decay of the qPEI suspension during the EPD process for representative samples. The decrease in conductivity shown in Fig. 2a represents the coverage of the copper substrate (electrode) with the insulating qPEI layer. It should be noted that the decrease in current density was not ascribed to a depletion of qPEI in the solution/suspension. The same suspension could be used several times without an evident decrease in the initial current density. Fig. 2a shows that a sandblasted (Sbl) substrate coated at 7 V (constant voltage) resulted in double initial current density compared to the non-sandblasted substrate, independently of the pre-acid treatment used (7 V HCl Sbl – 7 V HNO₃ Sbl vs. 7 V HCl – 7 V HNO₃, respectively). The sandblasting process increased the surface area of the substrate, which was suggested to have favoured a higher exposure of the substrate in the qPEI suspension. Despite the increase in surface for the sandblasted samples, the current density equilibrium was always reached within less than 15 s, similarly to the non-sandblasted samples (Fig. 2a). The lower voltages in Fig. 2a were not further explored due to inefficient formation of the coatings and lack of electric field gradient in the suspension. A higher voltage of 20 V was instead considered but due to the unwanted half reaction, the pulsed voltage setting was explored. Although the use of 20 V pulsed voltage showed similar initial current density, the pulsed case presented a lower current density decay as compared to the constant 20 V settings, and the current density equilibrium was reached beyond 30 s for the pulsed sample (Fig. 2b). Fig. 2c shows the effect of keeping the qPEI suspension stored for extensive time (2 weeks) on the initial current density (prior to initiating the EPD process). The observed decrease in the initial current density for both 7 V and 20 V EPD treatment suggests that the number of charged particles in the suspensions decreased with longer storage times, which was a consequence of the qPEI emulsion aggregation. Accordingly, the initial current density obtained after storing the suspension for 2 weeks and using constant 20 V was similar to 7 V when used fresh (ca. 0.012 mA cm⁻², Fig. 2c). The result show that for a production of qPEI substrate coating by EPD, the quality/thickness of the polymer coating is affected by the qPEI suspension storage time, but this may not be problematic as long as the voltage of the EPD is used to compensate for the reduced total charge of the emulsion. Fig. 3a shows the result of an unsuccessful EPD coating when using the heterogeneous Suspension 3 (Table S1 and Fig. S7c, d^†). The uneven coverage was revealed in the SEM micrographs, and the oxidation of the copper during the thermal treatment (re-imidization step) is visually observed in the image as a yellow/green coat (Fig. 3a). The sandblasting of the copper substrate in combination with coating from Suspension 5 (7 V HCl Sbl) is shown in Fig. 3b. The micrograph of the surface shows a homogenous and complete PEI coverage. No defects from the thermal treatment of the qPEI coated layer (to produce PEI by re-imidization, Fig. 1a) were observed (Fig. 3b). It is noteworthy that the PEI layer coated the rough sandblasted copper substrate perfectly around the periphery of the copper substrate, demonstrating the ability of the EPD process to evenly coat substrates of complex profiles.Open in a separate windowFig. 3Copper substrate after the EPD process and thermal treatment (qPEI re-imidization) and SEM micrographs of the PEI coatings of samples coated (constant voltage) at 7 V HCl – Suspension 3 (a), 7 V HCl Sbl (b), 7 V HCl (c), and 7 V HCl coating layer after being scratched with a scalpel (d). The coatings in (b) and (c) firmly attached to the copper substrates. Fig. 3c shows a copper substrate that was coated identically as Fig. 3b with Suspension 5, but in absence of sandblasting (7 V HCl). The microscopy revealed the smooth and evenly coated substrate obtained, with copper imperfections revealed through the coating (see photo Fig. 3c, left). A micrograph of the same coated 7 V HCl sample display how a scratch on the surface (with a scalpel after the coating procedure) appeared (Fig. 3d, left). The PEI coating layer had a thickness of about 3–4 μm on the copper surface and the coatings was revealed as firmly attached to the copper substrates, as seen from the encircled area shown with higher resolution imaging (Fig. 3d, right). Nano-sized cracks are observed on the coating close to the cut edge (Fig. 3d, right), which resulted from the plastic deformation of the PEI film coating. The results demonstrate the importance of using a homogenous suspension for obtaining well-distributed polymer and properly coated conductive substrates.A typical defect observed in the EPD coated samples with the post-thermal treatment converting the qPEI to PEI (re-imidized) was the formation of bubbles in the coating film, see Fig. 4a. The effect was ascribed to volatiles formed at the surface of the copper as a consequence of hydrolysis occurring during the EPD process, leaving remains of gas (H₂/O₂) and/or hydroxyl groups that during the thermal treatment allowed condensation of water and resulted in poor consolidation of the coating.^15,19 The formation of these bubbles was observed for all the samples after the drying of the coated substrate when using constant voltage for the EPD (60 °C oven for 17 h). On the contrary, the use of pulsed voltage (20 V) favoured the preparation of a smooth coatings on the substrate under the same drying conditions (60 °C oven for 17 h, Fig. 4b). Here, the presence of defects was limited to the edge of the sample (Fig. 4b). It is suggested that the pulsed deposition limited the hydrolysis reactions in the qPEI suspension due to the overall shorter time with applied potential, reducing the formation of hydrolysed fractions trapped between the coating and the substrate.^17,18,20 However, more extensive drying of the coated copper substrate (60 °C oven for 44 h), also resulted in smooth coatings with no apparent defects, both for the constant 20 V and pulsed 20 V depositions (Fig. 4c and d). The longer drying times accordingly favoured the evaporation of the formed hydrolysed species and facilitated the release of entrapped volatiles. In industrial production, long drying times often represents excessive energy costs. The pulsed DC voltage is therefore suggested as a useful condition for generating smoothly coated substrates in short drying times. A stepwise build-up of the coating also enables otherwise entrapped volatiles to dissipate between each pulse when voltage is absent, resulting in a more homogenous morphology. The cross-section of the coated substrates (prepared via constant or pulsed voltage deposition) are shown in Fig. 4c and d, respectively. The EDS mapping of the coatings display the carbon base of the polymer, whereas the thickness could be established to around 4–6 μm.Open in a separate windowFig. 4Shows the copper substrate coated without (a) and with (b) pulsed EPD conditions at 20 V, after for 17 hours of thermal post treatment at 250 °C. Images (c) and (d) show the same substrates after 44 hours 250 °C heat treatment, with accompanying SEM and EDS mapping insets; without pulsed 20 V deposition and with pulsed 20 V deposition, respectively. (e) Schematic representation of the electrical insulation resistance test setup. Note: it is not drawn to scale, as the coating is about 1/1000 the thickness compared to the size of electrode.The DSC and TGA analysis performed on the removed PEI from the copper substrates showed that no significant difference in thermal properties resulted from carrying out the EPD process, i.e. when comparing the thermal characteristics of the virgin PEI before the quaternization reaction and the final PEI from the coating (Fig. S10a and b^†). A slight decrease in the degradation temperature for the PEI retrieved from the coating layer as compared to the raw PEI (528 °C and 541 °C, respectively, Fig. S11 and S12^†) was however observed. Although this could indicate some molecular changes in the PEI polymer on the coating and/or traces of low molecular weight fractions such as lactic acid (Fig. S12a and b^†), these temperatures are well above the service temperature of electrically conductive copper cables (even considering heat build-up).As an example of the insulating characteristics of the PEI coating, the electrical insulation of the coated and re-imidized samples, i.e. 7 V HCl sample (constant voltage), were evaluated using an insulation resistance test at a temperature of 20 °C (see Fig. 4e). The top electrode had a polished surface with a radius of 2 mm and the electrode was kept at a positive potential of 50 V with reference to the negative sample. For automotive applications, this voltage level may fit for VCA-systems (below 60 VDC).²¹ Considering that the coating thickness was on average ca. 5 μm, these conditions yielded a substantial electric stress of 10 kV mm⁻¹ during the test. A Keithley 2450 source-measure-unit (SMU) was used to apply the voltage and to measure the corresponding current and resistance. Non-coated copper substrates showed a resistance of less than 0.1 ohm, essentially a short circuit (the SMU was current limited). The coated samples on the other hand showed an insulation resistance greater than 10⁹ ohm, illustrating the effectiveness of the EDP method and the re-imidization process in forming an insulating polymeric coating.     

Correction: iTRAQ-based quantitative proteomic analysis for identification of biomarkers associated with emodin against severe acute pancreatitis in rats

Correction for ‘iTRAQ-based quantitative proteomic analysis for identification of biomarkers associated with emodin against severe acute pancreatitis in rats’ by Hong Xiang et al., RSC Adv., 2016, 6, 72447–72457.

The authors regret that Fig. 2–4 were shown incorrectly in the original article. An incorrect section of the SAP group in the MPO-immunohistochemical staining (Fig. 2A) and HE staining (Fig. 3) experiments was used in error. In addition, Fig. 4 has been revised to show the zymogen granule, in order to better represent the ultrastructure of the pancreas. The correct versions of Fig. 2–4 are shown below.Open in a separate windowFig. 2Emodin down-regulated the MPO protein expression in pancreas of SAP rats. (A) Effect of emodin on MPO-immunopositive area (brown) staining of pancreatic tissue in SAP rats by immunohistochemical detection. (B) Effect of emodin on MPO-immunopositive area (red) staining of pancreatic tissue in SAP rats by immunofluorescence detection. Images are presented at 200× magnification. The data are presented as the mean ± SD, n = 6. **P < 0.01 versus SO; ^#P < 0.05 versus SAP, ^##P < 0.01 versus SAP.Open in a separate windowFig. 3Emodin improved pancreatic histopathology of SAP rats. Effect of emodin on H&E staining of pancreatic tissue in SAP rats. Images are presented at 200× magnification. The data are presented as the mean ± SD, n = 6. **P < 0.01 versus SO; ^#P < 0.05 versus SAP, ^##P < 0.01 versus SAP.Open in a separate windowFig. 4Emodin attenuated cellular structure changes in pancreas of SAP rats. Representative images of the cells’ ultrastructure in the SO (A), SAP (B), 60 mg kg⁻¹ emodin (C), 30 mg kg⁻¹ emodin (D) and 15 mg kg⁻¹ emodin (E) groups. Images are presented at 25 000× magnification.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Correction: Dipyrrolyl-bis-sulfonamide chromophore based probe for anion recognition

Correction for ‘Dipyrrolyl-bis-sulfonamide chromophore based probe for anion recognition’ by Namdev V. Ghule et al., RSC Adv., 2014, 4, 27112–27115, DOI: 10.1039/C4RA04000G.

The authors regret that an incorrect version of Fig. 1 was included in the original article. The correct version of Fig. 1 is presented below.Open in a separate windowFig. 1Color changes of receptor DPBS in chloroform upon addition of 5 equiv. of F⁻, Cl⁻, Br⁻, I⁻, H₂PO₄⁻, HSO₄⁻, ClO₄⁻ and AcO⁻ (tetrabutylammonium salts).The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Correction: A p-type multi-wall carbon nanotube/Te nanorod composite with enhanced thermoelectric performance

Correction for ‘A p-type multi-wall carbon nanotube/Te nanorod composite with enhanced thermoelectric performance’ by Dabin Park et al., RSC Adv., 2018, 8, 8739–8746.

The authors regret that an incorrect version of Fig. 8 was included in the original article. The correct version of Fig. 8 is presented below.Open in a separate windowFig. 1FE-SEM images of MWCNT/Te nanorod composites with various MWCNT contents (a) 1 wt%, (b) 3 wt%, and (c) 5 wt%.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Nanomaterials and continuous wave laser-based efficient desorption for atmospheric pressure mass spectrometric imaging of live hippocampal tissue slices

Micrometer-resolution mass spectrometric imaging of live hippocampal tissue is achieved with a highly efficient desorption of biomolecules using a 532 nm continuous wave laser and gold nanoparticles or graphene oxide as an energy transporter, which enables clear identification of the distributions of monoacylglycerol, adenine, cholesterol, sphingosine and ceramide.

Micrometer-resolution mass spectrometric imaging of live hippocampal tissue is achieved with a highly efficient desorption of biomolecules using a 532 nm continuous wave laser and gold nanoparticles or graphene oxide as an energy transporter.

There are wide ranges of applications of the atmospheric pressure mass spectrometry (AP-MS) method to detect pesticides or explosive materials or for biological samples that should be analysed in an ambient environment to get more accurate information and/or for real-time analysis.^1–5 AP-MS imaging can provide chemical and spatial information of molecules of interest, which is important for bioimaging applications. The AP-MS method is based on efficient desorption and ionization procedures under open-air atmospheric pressure and ambient temperature conditions.^6–8 Although several methods, such as desorption electro-spray ionization, matrix-assisted laser desorption ionization, or laser ablation electrospray ionization, have been used to obtain MS imaging of biological samples, limited spatial resolution (several-tens-to-hundred micro-meters) and complex instrumental setup have been the main limitations of AP-MS imaging.^9–11 The use of organic or inorganic nanomaterials as an efficient matrix for mass analysis is also a viable approach.^12–18Recently, we reported a high spatial resolution AP-MS imaging system with efficient desorption procedures by use of gold nanorods (AuNRs) and femtosecond (fs) pulsed laser oscillator, and subsequent ionization step with an aid of plasma system (termed AP-nanoPALDI MS system), which showed a micro-meter spatial resolution and detailed chemical information of live mouse hippocampal tissues.¹⁹ However, for more practical applications of AP-MS system, such as endoscopic platform for in situ cancerous cell detection in the clinic, a simple laser setup compatible with normal optical fiber is more desirable. The fs laser oscillator provides high energy sufficient to produce desorption of molecules, but the high peak power (several hundred kW) requires the use of the specific optical fiber and the distorted wave property in the optical fiber is another critical issues for cost-effective in situ endoscopic applications.^20–22In this work, we solved such a problem by using 532 nm-continuous wave (CW) laser for desorption. Although K.-C. Schäfer et al., investigated a CW laser source for in situ realtime identification of biological tissues, it requires high output power (∼W) and visible region wavelength was not possible to produce efficient desorption.²³ Therefore, the use of materials that can respond to a 532 nm laser is essential to facilitate the desorption process. We used spherical gold nanoparticles (AuNPs) as a light absorber to visible wavelength. We also investigated the use of carbon-based nanomaterials, such as graphene, that can respond to multiple wavelengths because of broad and strong light absorption property in the visible and NIR region of light, which can widen the availability of light source for sample desorption.We used the previously developed AP-nanoPALDI MS system with a change of light source. The AP-MS system for this study is described in detail in ESI Note 1 and Fig. S1.^† A 532 nm CW laser beam was introduced into the inverted microscopy by a dichromic beam splitter (NFD01-532-25x36, Semrock, USA) and was focused precisely on the specimen through the objective lens (Scheme 1). Because a visible light laser was employed as the light source for desorption, this configuration enabled both optical imaging monitoring and laser desorption in biological samples through the same objective lens. All the MS images in this study were obtained using a 20× objective lens (NA = 0.45; LUCPlanFLN 20X, Olympus, Japan) to focus the laser beam. The neutral molecule substances desorbed by the focused CW laser compulsorily meet the helium plasma medium by a separate plasma ionization source, and some were ionized by metastable helium atoms with excitation energies of 19.8 eV.Open in a separate windowScheme 1Visible-light-absorbing nanomaterials and CW-laser-based mass spectrometry imaging system for live hippocampal tissue slice. (1) Incubating nanomaterials on tissue, (2) CW-based desorption and ionization with laser and plasma, (3) mass-based spectrometry imaging process.Adult-mouse (7 week old, male, C57BL/6) hippocampal tissue slices were chosen for tissue imaging because of the distinctive structures and functions related with memories. Especially we focused on cornu ammonis 1 (CA1), cornu ammonis 3 (CA3), and dentate gyrus (DG), since the connections among these three regions play an important role in consolidating information of short-term memories to long-term memories and spatial navigation.^24–26 For AP-MS imaging, first, the fresh tissue slice of adult-mouse hippocampus (200 μm thickness) was incubated with AuNPs (0.5 nM, 20 nm) or nanosized graphene oxide (GO) (<100 nm, 0.2 mg mL⁻¹) in the artificial cerebral spinal fluid (ACSF) for 1 h (see ESI Notes 2 & 3^†). After incubation, the tissue was washed 10 times with ACSF, and then placed tissue on the scanning stage for imaging. Transmission electron microscopy analysis showed the relatively uniform distribution of AuNPs on the tissue surface (Fig. S2^†).To examine the possibility of CW laser for efficient desorption, we performed single line scanning for the tissue treated with AuNPs (20 nm, λ_max = 520 nm) and applied a 532 nm CW laser (300 mW, 20×, 0.45 NA objective lens). The results were compared with that of a previous fs laser-based AP-MS system. The helium ion microscopy (HIM) images in Fig. 1A scanned with the fs-based laser AP-MS system show narrow bottom and top widths (3.2, and 2.9 μm, and 4.7 and 5.7 μm, respectively) of desorbed tissue area (Fig. 1C). The line scanned area with the CW-based laser AP-MS system also shows successful desorption with a micrometer resolution (bottom width 5.2, 4.7 μm, top width 10.8, 11.3 μm) indicating the possibility of using the CW-based laser for AP-MS system (Fig. 1C).Open in a separate windowFig. 1Helium ion microscopy (HIM, Orion NanoFab, Carl Zeiss, USA) images of hippocampal tissue after line scanning with 802 nm fs laser (A), or with CW laser (B). (C) Confocal fluorescence images of both samples from the confocal laser scanning microscope (LSM-700, Carl Zeiss, Germany). Scale bar in (A) and (B) is 10 μm.The use of nanomaterial and selection of sufficient input laser power were critical factors for successful desorption and reliable MS imaging. No such clear desorption could be found in case of the absence of nanomaterials (Fig. 2A and S3^†). Only a small part of tissue surface was desorbed when CW laser was applied on the tissues without treating nanomaterials. The tissues treated with AuNPs show uniform and reproducible desorption patterns with application of CW laser with input power higher than 200 mW (Fig. 2B). Applying less than 200 mW is not desirable because of non-uniform desorption patterns shown in Fig. 2B (100 mW, 75 mW). Non-uniform desorption can cause significant defects in MS imaging. The tissue treated with GO solution shows very uniform and sharp desorption, even with a 100 mW input laser application. Interestingly, in spite of stronger light absorption properties of r-GO, the tissue sample treated with r-GO solution shows non-uniform and inefficient desorption patterns compared with the GO-treated tissue sample. As shown in Fig. 2D, applying 100 mW is not sufficient output power to produce uniform desorption. This is possibly due to decreased dispersity of r-GO in aqueous buffer condition and resulting non-uniform distribution of r-GO on tissue samples. In this regard, GO solution is the most desirable nanomaterial in terms of desorption.Open in a separate windowFig. 2Helium ion microscopy (HIM) images of linear craters on hippocampal tissue slices, which desorbed by focused CW laser beam with various output powers and hippocampal tissue slice treated without nanomaterials (A), or with AuNPs (B), GO (C), and r-GO solution (D). (Scale bar = 50 μm).Next, we applied the CW-laser AP-MS system to obtain hippocampal tissue imaging with a narrow pixel size of 4.2 μm × 5.0 μm covering an area of 1800 μm × 1500 μm (433 × 300 pixels) not to make dead pixel in the image. The actual resolution for the image will be about 10 μm based on minimum desorption area shown in Fig. 1 & 2. Total acquisition time was 350 min. The scanning conditions for an accurate timing among scanning stage, laser trigger, and signal acquisition was described in detail in ESI Note 4 and Fig. S4.^† After removing the plasma background, MS spectra of more than 200 specimens were obtained, and some of the detected ions were identified as metabolites, lipids, and their derivatives by a comparison of the measured masses and the calculated chemical formulas (Fig. S5^†). Several saturated and unsaturated monoacylglycerol (MAG) ions could be identified based on chemical formulas, such as MAG 16:0, MAG 18:0, MAG 16:1, MAG 18:1, and MAG 18:2. Other lipid and metabolite ions were identified, such as adenine, cholesterol, sphingosine, sphinganine, and ceramide 18:0.By transforming each MS spectrum with BioMAP software (Novartis Institutes for BioMedical Research, Cambridge, USA), MS-based images for hippocampal tissue were obtained as shown in Fig. 3A. After MS analysis with CW laser, the scanned area showed complete destruction indicating efficient desorption and ionization process occurred in this area. The MS images with selected ion-species for MAGs (16:1, 16:0, 18:1, 18:0), adenine, cholesterol, sphingosine and ceramide are displayed in Fig. 3B, C.Open in a separate windowFig. 3(A) The photo of hippocampal tissue before and after MS analysis with the treatment of AuNPs and 532 nm CW laser (300 mW), (B) ion images for MAGs, (C) ion images for adenine, cholesterol, sphingosine, and ceramide 18:0. In the adenine ion image at m/z = 136.062, (a) represents an apical dendritic area and (b) represents a basal dendritic area.The images constructed with selected ion species exhibited mostly similar spatial distribution with that of our previously reported NIR (802 nm) fs laser and mPEG-AuNRs based ion images displayed in Fig. S6.^† The image obtained with adenine m/z = 136.062 clearly shows the distribution of soma (cell body) of neurons in the tissue specimen that is commonly observed in nucleus is concentrated in the DG (Fig. 3C). Moreover, the ion image of adenine can clearly distinguish the apical and basal dendritic areas, located on the inside and outside of the soma location, respectively (see (a) and (b) in ion image of adenine at m/z = 136.062 in Fig. 3C). As shown in Fig. 3B and C, MAGs, sphingosine, and cholesterol were found to be most abundant in the apical dendritic area of CA1 of the hippocampus tissue. These high-resolution ion images can be used to study the molecular differences between the apical and basal dendrites of the neurons at the tissue level.In addition to the use of AuNPs as an efficient light absorber of 532 nm laser, GO nanosheet is also an excellent nanomaterial for efficient desorption, as demonstrated in Fig. 2C and S3.^† We obtained the AP-MS imaging of the hippocampal tissue slice treated with GO solution (0.2 mg mL⁻¹) and CW laser (Fig. 4). The scanned area shows the completely and uniformly desorbed area. As for this MS analysis method, since the ionization occurs in a separate plasma source after desorption procedure by laser, the obtained mass spectra were not significantly different from those obtained with AuNPs. The MS images constructed with MAG mass spectrum showed uniform distribution of MAG ions in the tissues (Fig. 4B). The adenine distributions in this mass analysis are identical with the image obtained with AuNPs in Fig. 3C. MAGs were found to be most abundant in the apical dendritic area of CA1 of the hippocampus tissue, and ceramide 18:0 and sphingosine were abundant in the basal dendrite area as well as the apical dendrite area in the CA region of the tissue. Overall, the MS images obtained with GO and CW laser showed more reliable information on the spatial distribution of molecules, mainly because of uniform distribution of GO nanosheets on tissue specimen and efficient desorption. Since GO also absorbs the NIR light, the possibility of AP-MS analysis with NIR fs laser was also confirmed (Fig. S7^†). The CA1 region in the tissue was successfully desorbed, showing clear corresponding MS images.Open in a separate windowFig. 4(A) The photo of hippocampal tissue before and after MS analysis with the treatment of GO solution and 532 nm CW laser (300 mW), (B) ion images for MAGs, (C) ion images for adenine, cholesterol, sphingosine, and ceramide.These results indicate the strong potential of GO for wide ranges of light sources for efficient desorption.To accurately compare the performance of r-GO for AP-MS imaging, we performed MS imaging after treating r-GO solution (0.2 mg mL⁻¹) on the hippocampal tissue. Applying 300 mW CW laser was successful based on the scanned bright field image in Fig. 5A. The distribution of MAGs on apical and basal dendrites of hippocampal tissue slice was very similar with the results obtained with AuNPs (Fig. 5B). However, the spatial distribution of mass ion is not regular. The most distinctive result is the distribution of MAG (16:0) (in Fig. 5B) compared with the same ion images in Fig. 3B, ​,4B.4B. The distribution of the MAG (16:0) ion spectrum in the images obtained with AuNPs or GO was quite uniform. Although the distribution of the adenine mass spectrum was visible, the signal intensity was weaker compared with the images obtained with AuNPs or GO (Fig. 5C). The low solubility and non-uniform distribution of r-GO can be assumed the main reasons of these observed irregular distributions of selected mass ions.Open in a separate windowFig. 5(A) The photo of hippocampal tissue before and after MS analysis with the treatment of r-GO solution and 532 nm CW laser (300 mW), (B) ion images for MAGs, (C) ion images for adenine, cholesterol, sphingosine, and ceramide.All these results indicate that the efficient desorption of molecules on the wet-state hippocampal tissue for AP-MS imaging is possible by use of nanomaterials such as AuNPs or carbon nanomaterials. In addition, the CW-laser is also an excellent light source for AP-MS imaging, which can greatly expand the ranges of application of the AP-MS-based analysis method in real-time mass analysis with endoscopic devices.In summary, we demonstrate that CW-laser based AP-MS imaging is possible with the use of nanomaterials. The incubation of tissues with AuNPs or nanosized graphene oxides (<100 nm) was essential to induce efficient desorption of wet-state hippocampal tissue. Because of excellent dispersity of GO in aqueous buffer solution, GO was found to be the most desirable nanomaterials for efficient desorption to increase the sensitivity and reproducibility of the AP-MS imaging system. The successful AP-MS imaging with CW-laser system highlights the advancement of AP-MS imaging technology into future clinical applications. The CW-based AP-MS system can identify lipidomic and metabolic observations in live tissues or detect pathogenic tissues, and opens a new approach to MS endoscopy for in vivo mass spectrometry based diagnosis.     

Correction: Green-synthesised cerium oxide nanostructures (CeO2-NS) show excellent biocompatibility for phyto-cultures as compared to silver nanostructures (Ag-NS)

Correction for ‘Green-synthesised cerium oxide nanostructures (CeO₂-NS) show excellent biocompatibility for phyto-cultures as compared to silver nanostructures (Ag-NS)’ by Qaisar Maqbool, RSC Adv., 2017, 7, 56575–56585, https://doi.org/10.1039/c7ra12082f.

The author regrets that Fig. 4 and ​and55 of the original article did not appropriately represent the findings.Open in a separate windowFig. 4Comparative TGA analysis of CeO₂-NS and Ag-NS.Open in a separate windowFig. 5FTIR spectrum of CeO₂-NS and Ag-NS.The correct version of Fig. 4 is shown below. In addition, the associated text on page 56578 “Experimental findings show total mass loss…” should be changed to “Experimental findings show total mass loss of 57.53% by CeO₂-NS and 61.12% by Ag-NS.” Fig. 5 of the original article shows only the plot of selected data points. In order to provide clarity to readers, it should be replaced with the following original FTIR plots (complete scan).The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Correction: Synthesis and characterization of AFe2O4 (A: Ni,Co, Mg)–silica nanocomposites and their application for the removal of dibenzothiophene (DBT) by an adsorption process: kinetics,isotherms and experimental design

Correction for ‘Synthesis and characterization of AFe₂O₄ (A: Ni, Co, Mg)–silica nanocomposites and their application for the removal of dibenzothiophene (DBT) by an adsorption process: kinetics, isotherms and experimental design’ by Fahimeh Vafaee et al., RSC Adv., 2021, 11, 22661–22676, https://doi.org/10.1039/D1RA02780H.

The authors regret an error in Fig. 4 where a section of the XRD for 4(a) and (b) is identical.Open in a separate windowFig. 4(a) The XRD pattern of sample 3 after adsorption of DBT. (b) The XRD pattern of sample 3 before adsorption of DBT.The authors have repeated the experiment and provided new data for Fig. 4. An independent expert has viewed the new data and has concluded that it is consistent with the discussions and conclusions presented. The correct Fig. 4 is shown below:The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

A julolidine-fused anthracene derivative: synthesis,photophysical properties,and oxidative dimerization

We describe the synthesis and characterization of a julolidine-fused anthracene derivative J-A, which exhibits a maximum absorption of 450 nm and a maximum emission of 518 nm. The fluorescent quantum yield was determined to be 0.55 in toluene. J-A dimerizes in solution via oxidative coupling. Structure of the dimer was characterized using single crystal X-ray diffraction.

A julolidine fused anthracene derivative with unique photophysical and redox properties was presented.

Julolidine¹ is a popular structural subunit in various fluorescent dyes (Chart 1).² The restricted motion and strong electron-donating capability of the fused julolidine moiety are quite effective for improving the photophysical properties. For instance, julolidine-fused fluorophores normally display desirable photophysical characteristics, such as high quantum yield, red-shifted absorption and emission, and good photostability. Recently, julolidine derivatives have been widely exploited in various applications such as sensing,³ imaging,⁴ and nonlinear optical materials.⁵ Several julolidine dyes have been used in dye-sensitized solar cells due to their large π-conjugated system and the promising electron donating property.⁶Open in a separate windowChart 1The structure of julolidine, J-A and DAA.In this paper, we report a julolidine-fused anthracene derivative J-A, which exhibits attractive photophysical properties not observed in DAA, a dimethyl-amino substituted analogue. Both the absorption and emission of J-A show a dramatic red-shift (ca. 74 and 131 nm, respectively), compared with the unmodified anthracene (Fig. 2). The fluorescence quantum yield of J-A was determined to be 0.55 in toluene, while the emission of DAA was completely quenched. The observed spectral properties were rationalized by DFT calculations. In addition, we found that J-A was stable in the solid state, but reactive in solution. J-A dimer was formed through oxidative coupling at the para-position of the N-atom in a dichloromethane solution under air atmosphere. The structure of the dimerized product was characterized using single crystal X-ray diffraction, which unambiguously reveals the structural feature of the julolidine-fused anthracene compound. Preparation of J-A is shown in Scheme 1. Detailed synthesis and characterizations are provided in the ESI.^†Open in a separate windowScheme 1Synthetic route of J-A.Open in a separate windowFig. 2(A) Absorption spectra of J-A, AN, and DAA (1 × 10⁻⁴ mol L⁻¹ in dichloromethane); (B) emission spectra of J-A, AN, and DAA (1 × 10⁻⁵ mol L⁻¹ in dichloromethane). Excitation wavelength: 350 nm. 1 cm cuvette was used in both of the experiments. Inset: visualized fluorescence in solution was shown. ¹H-NMR signals of J-A shift to the high-field significantly, compared with DAA (Fig. 1), which indicates that the fused structure of J-A facilitates electron delocalization from the nitrogen atom to the anthracene moiety, and thus resulting in a stronger shielding effect. In the case of DAA, however, electron delocalization from the dimethyl amino group to the anthracene core is essentially inhibited due to steric hindrance, which will explain the fact that it displays a spectral feature similar to that of the unmodified anthracene.Open in a separate windowFig. 1Comparison of the ¹H-NMR spectrum between J-A and DAA in CDCl₃. Partial resonance signals in aromatic region are shown.Fusing with julolidine will exert significant effects on the photophysical properties of anthracene. The absorption and fluorescence spectra of J-A, DAA, and anthracene are shown in Fig. 2. The maximum absorption of J-A is 450 nm, which displays a red-shift of about 70 nm compared with the unmodified anthracene. J-A emits green light (^maxλ_em = 518 nm, Φ = 0.55), while anthracene emits blue light (^maxλ_em = 380 nm, Φ = 0.22). In contrast, the absorption of DAA essentially overlaps with that of anthracene, with only a minor red shift of ca. 10 nm, but its fluorescence is quenched significantly (Fig. 2). This spectral feature indicates that the dimethyl amino group is electronically separated from the anthracene moiety in the ground state, a result in good accordance with the ¹H-NMR data shown above. The quenched fluorescence of DAA may result from the photo-induced electron transfer⁷ from the lone pair of the nitrogen atom to the anthracene moiety in the excited state.The observed photophysical properties of J-A were reproduced by DFT calculations. The HOMO and LUMO orbitals are evenly distributed over the anthracene moiety and the N-atom in the julolidine, indicating the existence of a conjugated structure. The HOMO–LUMO transition (f = 0.10) corresponds to the absorption band at 450 nm. The sharper absorption at 390 nm can be assigned to the HOMO to LUMO + 1 transition. In contrast, the HOMO and LUMO orbitals of DAA resemble those of anthracene, because the dimethyl-amino group is orthogonal to the conjugated π-system (Fig. 3).Open in a separate windowFig. 3Molecular orbitals of J-A and DAA calculated at the B3LYP/6-31G(d) level of theory (iso value = 0.02). Orbital energies were given in parentheses. Excitation energies were computed by TD-DFT at the same level. Values in parentheses represent the oscillator strengths (f).J-A is stable in the solid state, but reactive in solution. The cyclic voltammetry (CV) diagram of J-A shows an irreversible oxidation potential at 0.007 V (vs. Fc/Fc⁺), indicating that J-A is easy to be oxidized (Fig. S3^†). Single crystals suitable for X-ray diffraction study were obtained by slow evaporation of a dichloromethane solution of J-A under air atmosphere. To our surprise, instead of J-A, X-ray data discloses the formation of a dimeric product (Scheme 2) of J-A. We hypothesized that the dimeric compound 5 formed via oxidative coupling reaction, a mechanism well-documented for the dimerization of the dimethylaniline compounds.⁸ The ¹H-NMR spectrum of 5 is distinct from that of J-A. All protons of the anthracene part (b′–d′) appear as a group of multiplet resonance signals (6.93–7.04 ppm) (Scheme 2). In addition, mass spectrometric analysis indicates that two hydrogen atoms were removed after the dimerization of J-A. Compound 5 exhibits a maximum absorption at 460 nm and a very weak emission (^maxλ_em = 530 nm, Φ = 0.03, Fig. S1^†). Two quasi-reversible oxidation waves were identified in the CV diagram of 5 at −0.010 V and 0.135 V (vs. Fc/Fc⁺), respectively (Fig. S5^†).Open in a separate windowScheme 2Oxidative dimerization of J-A. Inset: partial ¹H-NMR of 5 is shown.X-ray structure of 5 is shown in Fig. 4. The two connected anthracene planes are found to be orthogonal to each other with a dihedral angle of 90.17°, as a result of steric repulsion. Specifically, the bond length of N–C3 is 1.389 Å, which is similar to those of the other reported julolidine compounds (1.359–1.393 Å), while significantly shorter than that of the dimethyl-amino anthracene (1.433 Å).⁹ This result testifies the presence of electron delocalization between the fused julolidine nitrogen and the anthracene π-plane, which is in good agreement with the DFT calculations (Fig. 3). However, the two anthracene π-planes connected by the single bond (C4–C5, 1.489 Å) might not exhibit electron delocalization because of the orthogonal conformation. The fused julolidine ring-i and -ii are symmetric to each other, and both of them adopt an “envelope” conformation. The fused julolidine is nonplanar (bond angle, C3–N–C2, 115.73°, C3–N–C1, 115.92°, C1–N–C2, 113.81°). 5 is closely packed in the crystal (Fig. 4B), and no intercalated solvent molecules were observed. The closest distance between two adjacent anthracene planes is 3.922 Å, indicating a weak π–π stacking. Detailed crystal data are summarized in Table S5.^†Open in a separate windowFig. 4(A) Single crystal X-ray structure of 5. (B) View along a-axis.In summary, we report the synthesis and characterizations of a julolidine-fused anthracene derivative J-A, which demonstrates significantly red-shifted absorption (^maxλ_ab = 450 nm) and emission (^maxλ_em = 518 nm, Φ = 0.55), compared with the unmodified anthracene. The photophysical properties of J-A also contrast dramatically with a dimethyl-amino analogue DAA, which were rationalized by DFT calculations. In addition, J-A could be transformed into 5, a dimeric product, whose single crystal X-ray structure unambiguously confirmed the structural feature of the julolidine-fused anthracene.     

Correction: A sensitive OFF–ON–OFF fluorescent probe for the cascade sensing of Al3+ and F− ions in aqueous media and living cells

Correction for ‘A sensitive OFF–ON–OFF fluorescent probe for the cascade sensing of Al³⁺ and F⁻ ions in aqueous media and living cells’ by Lingjie Hou et al., RSC Adv., 2020, 10, 21629–21635, DOI: 10.1039/D0RA02848G.

The authors regret that an incorrect version of Fig. 4 was included in the original article. The correct version of Fig. 4 is presented below.Open in a separate windowFig. 4The ESI-MS spectrum of Al³⁺–HNS complex.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Enzymatic dephosphorylation-triggered self-assembly of DNA amphiphiles

In this work, phosphorylated lipid-conjugated oligonucleotide (DNA-lipid-P) has been synthesized to develop an enzyme-responsive self-assembly of DNA amphiphiles based on dephosphorylation-induced increase of hydrophobicity. Since elevated ALP level is a critical index in some diseases, ALP-triggered self-assembly of DNA amphiphiles shows promise in disease diagnosis and cancer treatment.

Enzymatic dephosphorylation-triggered self-assembly of DNA amphiphiles is developed by integrating enzymatic dephosphorylation-induced increase of hydrophobicity and intermolecular aggregation of lipid-conjugated oligonucleotides.

Lipid-conjugated oligonucleotides are DNA amphiphiles that can self-assemble into lipid-based DNA micelles. As such, lipid tails act as a hydrophobic core and DNA act as a hydrophilic corona.^1–3 Because of their advantages of facile preparation, programmable design, small size (<100 nm) and biocompatibility, lipid-based DNA micelles show potential in the imaging of intracellular targets (mRNA and small molecules) and drug delivery.^4–6To further improve their potential for better drug delivery and disease diagnosis, stimuli-responsive control of the change of morphology or assembly/disassembly of DNA micelles has attracted enormous attention in practical applications. It was reported that photo-irradiation and nucleic acid hybridization have been used to trigger assembly/disassembly or the change of morphology of DNA micelles.^7–10 For example, Jin et al. developed stability-tunable DNA micelles by using photo-controllable dissociation of an intermolecular G-quadruplex.⁷ The intermolecular parallel G-quadruplexes were introduced into lipid-based DNA micelles to lock the whole structure, resulting in enhanced structural stability against disruption by serum albumin. However, photo-controlled release of complementary DNA blocks the formation of G-quadruplexes and thus leads to the dissociation of micelles by the existence of serum albumin. In addition, Chien et al. reported stimuli-responsive programmable shape-shifting DNA micelles by controlling geometric structure and electrostatics.⁸ DNA hybridization and dissociation change the geometric structure and electrostatics of hydrophilic moiety, leads to the conversion of DNA assemblies between spherical and cylindrical structures.In spite of these advances, enzyme-responsive regulation of self-assembly of DNA amphiphiles has scarcely reported. Since the hydrophobicity of lipid tail plays a critical role in the aggregation of DNA micelles, we speculated that the self-assembly of lipid-conjugated oligonucleotides can be regulated by controlling the hydrophobicity of lipid tails. Carry this idea forward, we noted that ALP is a hydrolase that removes phosphate groups from nucleic acids or proteins.^11,12 Remarkably, ALP has been widely employed to convert hydrophilic phosphorylated small molecules to hydrophobic dephosphorylated products for molecular imaging, disease diagnosis and cancer therapy.^13–16 Herein, therefore, enzymatic dephosphorylation-triggered self-assembly of DNA amphiphile is reported. As shown in Fig. 1, DNA-lipid-P is composed of four segments: DNA, linker, lipid and phosphate groups. Four negatively charged phosphate groups at lipid terminus decrease their hydrophobicity. Therefore, DNA-lipid-P exhibits weak self-assembly. However, ALP converts DNA-lipid-P to DNA-lipid by removing phosphate groups. The newly generated DNA-lipid shows greater hydrophobicity compared to DNA-lipid-P thus enables self-aggregation in aqueous solution.Open in a separate windowFig. 1Schematic illustration of enzymatic dephosphorylation-triggered self-assembly of DNA amphiphile.Lipid-conjugated oligonucleotides are amphiphiles which compose of two segments: hydrophobic lipid tails and hydrophilic oligonucleotides. Generally, lipid-conjugated oligonucleotides can self-assemble into aggregated DNA nanostructures, for example, DNA micelles, in aqueous solution by intermolecular hydrophobic interaction. To investigate whether the hydrophobicity affects the self-assembly of lipid-conjugated oligonucleotides, a series of lipid phosphoramidites with different length of alkyl chains (six, nine, twelve and fifteen) at the lipid tail were conjugated with oligonucleotide on a DNA synthesizer. The obtained lipid-conjugated oligonucleotides named as C6-DNA, C9-DNA, C12-DNA and C15-DNA, respectively (Fig. 2a). High-performance liquid chromatography (HPLC) is a universal tool to assess the hydrophobicity of DNA by comparing their retention times. Greater retention time indicates the stronger hydrophobicity. As shown in Table S2,^† the retention time of DNA, C6-DNA, C9-DNA, C12-DNA and C15-DNA is 10.0, 19.1, 23.8, 27.3 and 30.8 minutes, respectively, suggesting that DNA with longer alkyl chains has stronger hydrophobicity. The result is consistent with the previous report.¹⁷ Next, the self-assembly of these lipid-conjugated oligonucleotides was investigated by agarose gel electrophoresis and dynamic light scattering (DLS) assays. As shown in Fig. 2b, only C15-DNA shows a tailed nucleic acids band which is belongs to the self-assembled nanostructure. In addition, results of DLS assays exhibit that the particle size of 10 μM C6-DNA, C9-DNA, C12-DNA and C15-DNA in buffer solution is 2.7 nm, 4.2 nm, 6.5 nm and 28.2 nm, respectively (Fig. 2c). Besides, the morphology of self-assembled C15-DNA micelles was visualized with atomic force microscopy (AFM) and the result shows the spherical nanostructure with diameter of 36.8 ± 6.1 nm (Fig. S7^†). Both evidences support the self-assembly of C15-DNA in buffer solution. In another word, the self-assembly of lipid-conjugated oligonucleotides into DNA micelles is hydrophobicity-dependent. A greater hydrophobicity indicates a stronger tendency of aggregation.Open in a separate windowFig. 2Hydrophobicity-dependent self-assembly of lipid-conjugated oligonucleotides. (a) Chemical structures of lipid-conjugated oligonucleotides with different length of alkyl chains at the terminus of lipid tail. (b) 1% agarose gel electrophoresis analysis of 1 μM TAMRA-labeled C6-DNA, C9-DNA, C12-DNA and C15-DNA. C15-DNA shows a tailed band in agarose gel which can be attributed to the formation of aggregated micellar nanostructure. (c) DLS size analysis of C6-DNA, C9-DNA, C12-DNA and C15-DNA in buffer solution. The average size of C6-DNA, C9-DNA, C12-DNA and C15-DNA in buffer solution is 2.7 nm, 4.2 nm, 6.5 nm and 28.2 nm, respectively.Next, we further synthesize DNA-lipid-P by solid-phase synthesis and phosphoramidite chemistry. In a previous literature, we developed a novel lipid phosphoramidite in which two DMT-protected hydroxyl groups was modified at the terminus of lipid tails thus enables further chemical phosphorylation during DNA synthesis.¹⁷ As shown in Fig. 3, linker and lipid phosphoramidites were successively conjugated at the 5′-terminus of DNA, followed by coupling with chemical phosphorylation reagent. After deprotection and purification, DNA-lipid-P was obtained and characterized by mass spectrum. As shown in Fig. S8,^† the calculated molecular weight of DNA-lipid-P is 7789.8 Da, and the observed molecular weight is 7792.4 Da. The mass error is 2.6 Da (0.03%) which is within the mass error tolerance (0.03%), suggesting the successful synthesis of DNA-lipid-P. As such, DNA-lipid was also successfully synthesized with high purity (>98%) (Fig. S9^†).Open in a separate windowFig. 3Solid-phase synthesis route of DNA-lipid-P.Having confirmed the successful synthesis of DNA-lipid-P, we further investigate the self-assembly of DNA-lipid and DNA-lipid-P in buffer solution. Nile red, a fluorescent dye that exhibits significant fluorescence in hydrophobic media, but negligible emission in aqueous solution, was used to determine the encapsulation of guest molecules to further assess the formation of the micellar structure.^7,18 Nile red (1 μM) were incubated with various concentrations of DNA, DNA-lipid or DNA-lipid-P and the corresponding fluorescence spectroscopies were recorded. As shown in Fig. 4, both DNA (Fig. 4b) and DNA-lipid-P (Fig. 4c) show weaker fluorescence emission at 630 nm, even the concentration was upper to 10 μM. However, DNA-lipid (Fig. 4d) exhibits a bright fluorescence emission at 630 nm, suggesting the formation of hydrophobic core. After calculation, the critical micelle concentration (CMC) of DNA-lipid is 0.36 μM (Fig. 4e). The remarkable difference of CMC between DNA-lipid and DNA-lipid-P indicates that enzymatic conversion of DNA-lipid-P to DNA-lipid could trigger the spontaneous intermolecular aggregation.Open in a separate windowFig. 4Characterizations of self-assembly of DNA-lipid-P and DNA-lipid. (a) The chemical structures of DNA-lipid and DNA-lipid-P. Fluorescence spectroscopies of Nile red-encapsulated DNA (b), DNA-lipid-P (c) and DNA-lipid (d) in buffer solution. The concentration of Nile red is 1 μM. (e) Fluorescence intensity of Nile red-encapsulated DNA, DNA-lipid-P and DNA-lipid at 630 nm. The CMC of DNA-lipid is 0.36 μM, and the CMC of DNA-lipid-P is larger than 10 μM.Next, ALP was used to convert DNA-lipid-P to DNA-lipid (Fig. 5a). As shown in Fig. 5b (black and red lines), the retention time of DNA-lipid and DNA-lipid-P is 26.5 and 20.9 minutes, respectively, indicates that the phosphorylation of lipid tail indeed decreases the hydrophobicity of lipid-conjugated oligonucleotides. Then, ALP was incubated with DNA-lipid-P (10 μM) at 37 °C for ten minutes and then 75 °C for five minutes to deactivate ALP, followed by subjected to fluorescence measurements. As shown in Fig. 5b (pink line), after the treatment of ALP (2 U), the DNA peak of DNA-lipid-P at 20.9 minutes disappeared; instead, a new DNA peak at 26.5 minutes was observed. Mass spectrum analysis indicates that the molecular weight of newly generated DNA peak is 7474.2 Da, which is consistent with the calculated molecular weight of DNA-lipid (7470.9 Da) (Fig. S10^†). In a word, ALP enables enzymatic dephosphorylation of DNA-lipid-P; and the generated DNA-lipid has greater hydrophobicity than DNA-lipid-P thus facilitates the controllable self-assembly into DNA micelles.Open in a separate windowFig. 5Enzymatic dephosphorylation of DNA-lipid-P. (a) Schematic of ALP-induced conversion of DNA-lipid-P to DNA-lipid. (b) HPLC chromatograms of DNA-lipid-P (black line), DNA-lipid (red line), and DNA-lipid-P treated with ALP (0.1 U (blue line), 1 U (green line) and 2 U (pink line)) in buffer solution.Encouraged by the ALP-induced dephosphorylation of DNA-lipid-P to DNA-lipid, we further assess whether ALP enables activatable self-assembly of DNA-lipid-P. As shown in Fig. 6a, DNA-lipid-P (1 μM) shows weak self-assembly in buffer solution. However, DNA-lipid (1 μM) exhibits obvious aggregation band in gel electrophoresis assay. After incubation with ALP (1 U), DNA-lipid-P + ALP group also shows tailed band which suggests the formation of aggregated nanostructures. In addition, results of Nile red-encapsulated fluorescence experiments also support the conclusion of ALP-activate self-assembly of DNA-lipid-P (Fig. 6b). Therefore, ALP-induced enzymatic dephosphorylation triggers the self-assembly of DNA-lipid-P.Open in a separate windowFig. 6Enzymatic dephosphorylation-triggered self-assembly of DNA-lipid-P. (a) 1% agarose gel electrophoresis analysis of DNA-lipid-P (lane 1), DNA-lipid (lane 2) and DNA-lipid-P treated with ALP (1 U) (lane 3). (b) Fluorescence spectroscopies of Nile red-encapsulated DNA-lipid, DNA-lipid (ALP), DNA-lipid-P or DNA-lipid-P (ALP).In summary, enzymatic dephosphorylation-triggered self-assembly of DNA amphiphile is developed by integrating enzymatic dephosphorylation-induced increase of hydrophobicity and intermolecular aggregation of lipid-conjugated oligonucleotides. The strategy may also suitable for many other amphiphiles. Since elevated ALP level is a critical index in some diseases and even cancers, we believe that ALP-triggered self-assembly of DNA-lipid-P shows potential in disease diagnosis and cancer therapy.     

Correction: A novel biocompatible,simvastatin-loaded,bone-targeting lipid nanocarrier for treating osteoporosis more effectively

Correction for ‘A novel biocompatible, simvastatin-loaded, bone-targeting lipid nanocarrier for treating osteoporosis more effectively’ by Shan Tao et al., RSC Adv., 2020, 10, 20445–20459, DOI: 10.1039/D0RA00685H.

The authors regret that incorrect versions of Fig. 7, ​,99 and ​and1010 were included in the original article. The correct versions of Fig. 7, ​,99 and ​and1010 are presented below.Open in a separate windowFig. 7Histological analysis of organs from all experimental groups. H&E staining of heart, liver, spleen, lung, kidney, indicating the carrier has good biocompatibility. Scale bar = 50 μm.Open in a separate windowFig. 9Alkaline phosphatase (ALP) activity (arrows) and tartrate-resistant acid phosphatase (TRAP) assay results (arrowheads) of bone tissue sections. Scale bar = 50 μm. The ALP activity is much more high in SIM/LNPs and SIM/ASP₆-LNPs groups, while the TRAP activity is the opposite.Open in a separate windowFig. 10Histological assessment of bone formation in all experimental groups. (A) HE staining of femur bone. Scale bar = 50 μm. Histology of bone in the all experimental groups shows all ovariectomized groups had a higher amount of adipose tissue than Sham group. The trabecular bone is much more prominent in SIM/LNPs and SIM/ASP₆-LNPs groups. (B) Immunohistochemical staining for BMP-2 in typical newly-formed bone tissue (red arrows) and immunohistochemical staining for the osteogenic markers osteopontin (OPN, arrows) and osteocalcin (OCN, arrowheads). Scale bar = 50 μm. The BMP-2, OPN, OCN are much more prominent in SIM/LNPs and SIM/ASP₆-LNPs groups.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Colour-tunable ultralong organic phosphorescence upon temperature stimulus

A new class of single-component molecular crystal with colour-tunable ultralong organic phosphorescence (UOP) was designed and synthesized through alkyl chain engineering. Forming a more rigid environment at 77 K, the colour-tunable UOP from yellow-white to blue-green is achieved through dual-emission of crystal and amorphous states.

A new class of single-component molecular crystal with colour-tunable ultralong organic phosphorescence (UOP) was designed and synthesized through alkyl chain engineering.

Ultralong phosphorescence, a kind of phosphorescence that can be observed by the naked eye after removing the excitation source, has received great attention in the fields of sensing,¹ displays,² imaging,³ anti-counterfeiting⁴ and so on during the past years. Unfortunately, it is limited to inorganic materials because of the weak spin–orbit coupling (SOC) and strong non-radiative transition of pure organic materials.⁵ Compared with inorganic materials, however, organic materials have some excellent merits, such as inexpensive cost, relative safety to the environment, and soft preparation conditions.⁶ The realization of UOP becomes very significant. As mentioned above, UOP can be achieved by promoting intersystem crossing (ISC) through enhancing SOC and suppressing non-radiative transitions. In view of these factors, various strategies such as polymerization,⁷ H-aggregation,⁸ crystallization,⁹ host–guest doping,¹⁰ and freezing conditions¹¹ have been explored to achieve UOP with the unremitting efforts of scientific researchers.Intelligent-response organic luminescent materials can change their luminescent properties such as colour, lifetime, intensity, etc. after being stimulated by the external factor, such as mechanical forces, temperature, pH, light, solvent, etc., which have caught great attraction. The sensitivity of luminescent molecule to excitation wavelength, temperature or oxygen can be applied in sensors, optical recording and so on.^12–14However, the luminescence of these materials with intelligent-response are mostly limited to fluorescence or room temperature phosphorescence (RTP) with relatively short lifetimes.^15–18 Few samples display persistent luminescent feature.¹⁹ Most organic compounds can only tune their afterglow properties by changing molecular side groups or multi-component doping.^20–23 Therefore, the development of single component UOP materials with intelligent response remains a challenge. Inspired by the alkyl-chain engineering²⁴ and freezing conditions, herein we speculate that temperature response UOP might be induced by controlling the activity of the alkyl chain to regulate non-radiative transition rate. By means of reducing the temperature to restrict the molecular motions at amorphous state, colour-tunable UOP with temperature-response can be realized by dual-emission of molecules at both amorphous and crystalline states.In our previous study, MCzT crystals showed yellow UOP at RT.²⁵ The crystals showed the same UOP at 77 K with that at RT (Fig. 1a). Here, 9-(2-((4,6-dimethoxy-1,3,5-triazin-2-yl)oxy)ethyl)-9H-carbazole (MTOD) was designed and via alkyl chain attaching carbazole with a triazine core. The target molecule was characterized by ¹H NMR and ¹³C NMR (Fig. S1–S3^†). Its melting point reaches 130 °C. (Fig. S4^†) MTOD achieved a lifetime of up to 860 ms under ambient conditions. Surprisingly, the UOP changed from yellow-white to blue-green after the removal of the UV-lamp for several seconds at 77 K (Fig. 1b), demonstrating colour-tunable property of UOP with a low temperature stimulus.Open in a separate windowFig. 1Molecular structures and UOP photographs of MCzT (a) and MTOD (b).In order to explore the reasons for the colour-tunable UOP of MTOD at low temperature. The photophysical properties of MTOD in the crystal state were first investigated under ambient conditions. As shown in Fig. 2a, the photoluminescence (PL) spectrum of MTOD shows two main emission peaks at 375 and 413 nm and a shoulder at 435 nm. From the lifetime decay profiles (Fig. S5a^†), it was confirmed that they were all assigned to the fluorescence. Notably, the crystals of MTOD presented yellow afterglow after turning off the UV lamp. From the delayed phosphorescence spectrum, the main emission of MTOD was located at 414, 556 and 600 nm with lifetimes of 681.91, 860.56 and 860.59 ms, respectively (Fig. 2b and S5b^†). Among these, the emission around 414 nm is assigned to triplet–triplet annihilation (TTA) fluorescence originating larger π–π overlaps of carbazole groups from the crystal data (Fig. S6^†).²⁶ Remaining two emission peaks are attributed to UOP emission. From the phosphorescence excitation-emission spectra of MTOD, UOP can be efficiently excited from 260 to 380 nm, with the optimal excitation at 360 nm (Fig. S7^†).Open in a separate windowFig. 2Photophysical properties of MTOD at room temperature and at 77 K. (a) Steady-state photoluminescence (PL, blue dashed line) and phosphorescence (red solid line) spectra at RT and 77 K. Inset: photographs taken after removing excitation. (b) Time-resolved phosphorescence decay of the emission bands at 556 and 600 nm at room temperature, respectively. (c) Time-resolved phosphorescence decay of the emission bands at 478, 564 and 612 nm at 77 K, respectively. (d) PL (blue dashed line) and phosphorescence (red solid line) spectra at molten state.Subsequently, we measured the PL and phosphorescence spectra of MTOD at 77 K (Fig. 2a). The steady-state PL spectrum showed four peaks at 361, 376, 410 and 436 nm, with little change compared with its corresponding spectrum at RT. However, a new phosphorescence peak appears at about 480 nm with an intense emission than others, which displays an ultralong lifetime of 2.5 s. Obviously, the new emission peak plays an indispensable role in the colour-changed UOP at 77 K. The yellowish-white UOP observed by naked eyes at 77 K is generated by the combination of three phosphorescence peaks. However, as time goes by, only the blue-green afterglow at about 480 nm due to the shorter lifetime of long-wavelength phosphorescence can be observed.To find out the origin of this new peak at 480 nm, the PL and phosphorescence spectra of MTOD at molten state were measured as amorphous emission. As shown in Fig. 2d, the PL peak is located at 380 nm and the phosphorescence spectrum shows a broad band with a main peak at 484 nm. It is suggested that the new phosphorescence emission peak at 77 K may be attributed to amorphous state. Taken together, we deduce that the colour-tunable property of the crystal is possibly due to the presence of an amorphous state at low temperature.The X-ray single crystal diffraction of MTOD crystal was taken to explore the mechanism of UOP at room temperature. Abundant intermolecular and intramolecular interactions (Fig. 3a, S6, S8 and S9a^†) in the crystals strongly restrict the torsional molecular configuration. The dihedral angle between the triazine and carbazole groups is about 75° (Fig. S10^†). In the crystal of MTOD, the single molecule is limited by multiple intermolecular interactions, including C–H⋯N (2.681 Å), π-H⋯π (2.791, 2.876 Å), π-H⋯N (2.703, 2.711 Å) (Table S3^†). The rich intermolecular interactions are beneficial to limit molecular motions to suppress non-radiative transitions of excited molecules, leading to UOP. However, the amorphous molecules around the crystals with weak restriction displayed negligible phosphorescence at room temperature due to the strong motions of alkyl chains.Open in a separate windowFig. 3Intermolecular interactions (a) at room temperature and (b) at 100 K.Comparatively, the single crystal of MTOD molecule at 100 K was measured in order to explore the colour-changing mechanism of UOP at low temperature (Fig. 3b and S9b^†). By comparison, MTOD crystals exhibit more intermolecular interactions at 100 K and the distance become shorter. Molecular conformation of MTOD changed slightly, the dihedral angle between triazine and carbazole changed from 74.95° to 75.32° (Fig. S10^†). These increased interactions can constrain the molecules more effectively and the stronger restriction of alkyl chain and carbazole will further suppress non-radiative transitions, resulting in the much longer phosphorescence lifetime of over 1.0 s at low temperature. Compared with the molecules in the crystalline state, freezing condition can provide a more rigid environment to minimize the movement of the alkyl chain, greatly reducing the non-radiative transition rate at amorphous state, resulting in the lifetime of short wavelength phosphorescence at 478 nm up to 2.5 s.According to the above results, the photophysical process of colour-tunable phosphorescence can be described by Jablonski diagram as shown in Fig. 4. Upon photoexcitation, both electrons in amorphous and crystalline molecules transforms to lowest singlet states (S₁). Then, the electrons in S₁ would further transform to the lowest triplet (T₁) through ISC. At room temperature, amorphous molecules show strong molecular motions to facilitate the non-radiative transitions. However, crystalline molecules due to closely arrangement can exhibit phosphorescence through radiative decay. At 77 K, both excitons in amorphous and crystal states are dominated by radiative transitions, leading to colour-tunable UOP.Open in a separate windowFig. 4(a) Jablonski diagram of the relevant photophysical processes illustrating amorphous and crystalline UOP process at room temperature (top) and 77 K (bottom). (b) Phosphorescence spectra of MTOD at different temperature and (c) corresponding coordinates in CIE.In view of the interesting luminescent phenomenon, we have investigated a series of phosphorescent spectra of MTOD crystals at different temperatures ranged from 183 to 273 K. As shown in Fig. 4b, as the temperature increases, the phosphorescence intensity of the amorphous molecules gradually decreases. The colour variations of the MTOD crystals in response to the environmental temperatures are shown in the Commission International de l’Eclairage (CIE) coordinate diagram (Fig. 4c). As the temperature was gradually changed from 183 to 273 K, the UOP changed from green to yellow with good linearity of the CIE coordinates. This demonstrated that MTOD crystals may have potential in low temperature sensing.In conclusion, we synthesized a colour-tunable single-component UOP compound through alkyl chain engineering. Combined the spectral and single crystal analyses, it is indicated that colour-tunable UOP comes from dual-emission of molecules at amorphous and crystalline states. Low temperature provides better rigid effect on UOP of amorphous molecules than crystals, resulting in the UOP colour changed from yellow-white to blue-green. More interestingly, red-shifted UOP of MTOD crystals with the increase of temperature can be achieved, demonstrating its potential for temperature sensing. This study will provide a platform for the design of single-component UOP molecules with tunable colour emission and broadens its application field.     

Retracted Article: Facile preparation of bithiazole-based material for inkjet printed light-emitting electrochemical cell

Light-emitting electrochemical cell of bithiazole-based material was fabricated by solution processing rendered high external quantum efficiency over 12.8% and luminance of 1.8 10⁴ cd m⁻².

Light-emitting electrochemical cell of bithiazole-based material was fabricated by solution processing rendered high external quantum efficiency over 12.8% and luminance of 1.8 10⁴ cd m^−2.

It is well known that inkjet printing works as precise and versatile patterning method for printed electronics.^1,2 As for its advantages, it is already being exploited widespread for printing electronics.^3,4 Those merits are easily processed from solutions and conveniently used for air-stable electrodes.^5,6Light-emitting electrochemical cells (LECs) have emerged as an active layer,^7,8 arousing tremendous attention over the years.^9–11 Nevertheless, LECs are simpler than organic light-emitting diodes (OLEDs).^12,13 Due to its single layer architecture, low fabrication price and operating voltages, LECs are considered as a promising, next-generation, emissive thin-film technology.^14–16The most efficient device used to date for LECs are biscyclometalated iridium(iii) (Ir) complexes, because they have highly efficient and stable devices spanning the whole visible range.^17–19 However, avoiding the use of Ir is strongly desired because of its high cost and limited supply.^20–22 Till now, thiazole has worked as active component in a LECs system with a long-lived charge-separation molecule, without additional ions in its active layer.^23–26 As for its advantages, it can reduce recombination of charge carriers and facilitate carrier transfer.^27–29 More and more importance has been attached to thiazole compounds, especially bithiazole-based ones.^30–33 Therefore, these have aroused interest in the syntheses of bithiazoles.^34–36Based on our previous research,^37–41 the use of bithiazole ligands already explored by our group for photocatalytic technology has the advantage of an easy transformation of neutral complexes into charged ones by substitution on the N-atom of the thiazole moiety.^42,43 Furthermore, we demonstrate the fabrication of LEC devices by a combination of inkjet printing and spin coating, on A4 paper substrates for low cost, disposable and flexible conductive pattern.^44,45 Their corresponding material characteristics were closely investigated, a detailed report of the material properties of the resulting coatings, and an envisaged proof of concept application are disclosed in this paper. These fully printed devices demonstrate the potential upscaling of the fabrication of optoelectronic devices.Herein we report the design for a range of bithiazole derivatives 1a–1c (Fig. 1, their synthesis is shown in Scheme S1^†), and explore their properties. First of all, the UV-visible diffuse-reflectance (UV-vis DRS) spectra of those specimens at room temperature are displayed in Fig. 2 and the data are collected in Table S1.^† This enhancement was ascribed to the increase of aromatic rings, which has an intense absorption in the visible-light region. And their bandgap energies (E_g) are between 2.97–3.01 eV (Table S1^†), and are estimated from these absorption spectra according to the Kubelka–Munk method. Expanding the conjugated system and electron density with these donor groups, it can lead to a larger bathochromic shift of the absorption maximum.^46,47Open in a separate windowFig. 1Chemical structures of compounds 1a–1c described in this work.Open in a separate windowFig. 2UV-vis DRS spectra of 1a–1c.All of the three compounds are photoluminescent at room temperature, the relevant fluorescence peak maximum ranges from 360 to 398 nm (Fig. 3). They emit blue light when they are being excited. In agreement with Fig. 3, the presence of electron-releasing groups would shift the emission maximum. Among them, the most electron-donating carbazole unit would give the most red-shifted peak at 398 nm for 1c (Table S1^†). The PL quantum yield (ϕ_PL) studies show that both 1a and 1b are as high as 62 and 78%, while another one is 85% (Table S1^†). The data for their fluorescent quantum yields largely depends on interaction effect with molecules 1a–1c in the crystal packing. In this context, π–π intermolecular interactions can inhibit the fluorescence.⁴⁸Open in a separate windowFig. 3Typical PL spectra of 1a–1c.It may indicate that enlarging the conjugation length and electron density with these donor groups plays an important role in increasing the ϕ_PL.⁴⁹ Moreover, those with high ϕ_PL may be suitable for application as efficient light-emitting material in LECs.⁵⁰In addition, time-resolved measurements of the donor lifetime (τ) in 1a–1c were carried out, and their corresponding values are given in Table S1.^† The bithiazole derivatives 1a–1c showed long-lived singlet fluorescence lifetimes (τ_F), ranging between 1.04 and 9.54 ns (Table S1^†). This was on average more than double the fluorescence lifetime of the bithiazole starting material.⁵¹ These three samples possess relatively high decay time, as a result of their inhomogeneity.⁵² Compound 1c exhibited the longest fluorescence lifetime decay τ_F = 9.54 ns. The sensitivity of the emission to the polarity of the solvent is beneficial for an intramolecular charge transfer (ICT)-like emission.⁵³ This difference probably accounts for the high concentration of donor units in the bithiazole backbone, low rates of intersystem crossing to reactive triplet states.^48,54Consequently, the composite 1c was the best performing LEC and chosen for the below test. The EL spectra obtained for both devices were almost identical, with a main peak at 498 nm and other peak at 504 nm wavelength as illustrated in Fig. 4a. It may account for trapping, cavity, and self-absorption effects from within the LEC device 1c multilayer-structure. The spin-coated emission is quantified by the commission Internationale de L’Eclairage (CIE) coordinates of (0.28, 0.42), and a colour rendering index (CRI) of 65 (Table S2^†). While inkjet-printed light emission with CIE coordinates of (0.34, 0.43) and a CRI value of 83 was achieved for device 1c (Table S2^†). It exhibits good colour rendering indices (CRI > 70), this device exhibited a warm-white appearance, and the colour rendering is considered sufficient for indoor lighting applications.Open in a separate windowFig. 4Comparison of device characteristics with spin-cast and inkjet printer emitting layer for 1c: (a) electroluminescent spectra, (b) luminance vs. voltage, (c) current density vs. voltage, (d) efficiency vs. luminance behaviour.The time-dependent brightness and current density under constant biases of 2.9–3.3 V for device 1c are shown in Fig. 4b and c. Interestingly, the device with the inkjet-printed emitting layer (EML) produced a light output of around 3600 cd m⁻², whereas 4600 cd m⁻² was achieved with the spin-coated EML. In other words, the device with the inkjet printed EML obtained about 78.3% of brightness compared with the reference device. The differences between the two devices regarding current efficiency (J) and power efficiency (PE) were rather closed, as listed in the Table S2.^† A luminous efficiency much larger than 10 cd A⁻¹ was achieved for the inkjet-printed EML, which tended to be 73.9%, and is similar to the spin-coated emitting layer.The performance gap between the devices (Fig. 4d) can be attributed to differences in the height and surface roughness of the emitting layer.⁵⁵ Lateral sizing histograms (Fig. S11^†) show that the spin-coated EML possessed a thickness of 35 nm and a very smooth surface. The inferior performance of the inkjet-printed EML is caused by a less homogeneous surface morphology and an overall fatter layer.⁵⁶ The depth of the inkjet-printed EML ranged from 25 nm (pixel centre) to 35 nm (pixel edges). As a consequence, it is an inkjet deposition process and the related evaporation dynamics reduces the light output and efficiency, but also postpones the stability of the device in the system.^10,57We then shifted our attention to the turn-on kinetics, efficiency and long-term stability of the LEC device for 1c; the typical evolution of current density and light emission is presented in Fig. 5a and b, showing a slow turn-on followed by a progressive decay over time.Open in a separate windowFig. 5(a) Current density (closed symbols) and brightness (open symbols) versus time at 3 V for a device with the representative sample 1c; (b) EQE versus time at an applied voltage of 3 V.The build-up of the light output is synchronous with that of the current density. This time-delayed response is one of the striking features of the operation of an electrochemical cell and reflects the mechanism of device operation.²² The champion device in this set exhibited a peak power efficiency (PE) of 17.4 lm W⁻¹ at a luminance of 18 000 cd m⁻². Meanwhile, the current density began to decrease, possibly due to the electrochemical oxidation or electro corrosion that occurred on component 1c through accumulated electroinduced holes, and then it kept up a durative datum.⁵⁸ Apparently it exhibited outstanding long-term operation stability beyond 40 h (Fig. 5b).The time-dependent external quantum efficiency (EQE) of LEC for the representative substrate 1c are shown in Fig. 5b. It also exhibited similar temporal tendency in device efficiency. When a bias was applied on the LECs, the EQE quickly increased since balanced carrier injection was achieved by the formation of the doped layers.⁵⁹ After attaining the crest value, the device current was still rising while the EQE reduced little by little. It implied that both growing the doped layers and weakening of the EQE was resulting from exciton quenching near the bithiazlole core in persistently extended doped layers.⁶⁰ Doping-induced self-absorption was rather adaptable to the temporal roll-off in device efficiency. This configuration shows the best performance (EQE = 12.8%) compared to those devices prepared with the single compounds, which is given in Table S3.^† The reason may be that the steady-state recombination zone in 1c device was close to the central active layer.⁶¹ Besides it contains fluorenes on its side chains, constructing plane structure, benefiting from good electron injection abilities, leading to enhancing the EQE itself.⁶²The fabrication of inkjet-printed bithiazole interdigitated electrode (IDE) is illustrated in Fig. 6. All the prepared varieties of bithiazole-based ink have been found to be highly stable with nil or miniscule precipitation in over 180 days being stored on the shelf (Fig. 6a). After HCl treatment of the paper substrate, the prepared inks have filled within ink cartridges of a low-cost desktop printer Canon iP1188 (Fig. 6b). Fig. 6c shows the photograph of inkjet-printed conductive patterns.Open in a separate windowFig. 6(a) The representative ink based on sample 1c was stable for 180 days; (b) electrode printing using Canon iP1188 printer; (c) scale showing size of printed electrodes; (d) interdigitated electrode (inset shows small size printed pattern).In addition, the most attractive prospect of the bilayer device structure at this stage is the possibility for patterned emission for the creation of a static display. Fig. 7 presents a photograph of a small portion of a larger static display, with a resolution of 170 PPI, which repeatedly exhibits a message in the form of the word “LEC”. As shown in Fig. 7, the pixel array produced are fairly luminous. The EL spectra were collected from each pixel on the substrate, the emission peak wavelength was about 510 nm and the full width at half maximum was about 170 nm. The low variation in emission intensity in the different pixels implies a small variation in thickness of the solution-coated layers. More specifically, if we assume a minimum diameter of 20 μm for an inkjetted electrolyte droplet, and a smallest inter-droplet distance of 10 μm, we attain a pitch of 30 μm, which corresponds to a high display resolution of 850 PPI. Finally, we draw attention to the herein presented static-display LEC that comprises solely air-stabile materials, and that we routinely fabricate the bilayer stack under ambient atmosphere.Open in a separate windowFig. 7(a) The patterned light emission from a bilayer LEC, with the emission pattern defined by the selected positions of the ink jetted electrolyte droplets. (b) The droplet diameter and pitch were 50 and 150 μm, respectively, and the device was driven at V = 3 V. The scale bar measures 300 μm.     

A stomata-inspired superhydrophobic portable filter system

Stomata, specialized functional openings distributed on the leaf surface, are used for plant respiration by allowing gas exchange, i.e., taking in carbon dioxide and releasing oxygen, and for water content regulation. Their function is vital to plant survival. Leaves with different wettability exhibit different stomata densities. In this study, we find that stomata on Pistia stratiotes L. leaves are protected by superhydrophobic setae, which prevent direct contact between the stomata and water in humid environments by suspending water droplets on the top of the setae. Thus, oxygen and carbon dioxide are freely exchanged through the stomata. This structure inspired us to design and develop a mask for filtering solid particles and noxious gas from the atmosphere. The incoming gas is in convective contact with water, achieving a filtering efficiency. The solid particles and potential harmful gas in air are wetted and captured by water, leaving fresh air for healthy breathing. This novel design has potential applications in the treatment of respiratory diseases.

The bio-fabricated superhydrophobic filter system (a–c). The liquid water is suspended on the top of the papillae surface and hardly contacts the stomata, which filter the incoming air (d).

A stoma is a plant gas exchange channel that is used for carbon dioxide intake and oxygen release, playing a crucial role in plant survival in nature.^1–3 The distribution and density of stomata on the leaf surface may vary with surface wettability. On the hydrophilic leaves of a locust tree, the stomata density on the lower surface is higher than that on the upper surface. This unique design is beneficial for respiration and photosynthesis, even in rainy conditions. Some leaves with superhydrophobic surfaces exhibit a higher stomata density on the upper surface than that on the lower surface, because of their robust water-repellence.^4–7 Rough micro-/nano-topography may allow significantly more air flow between solid–liquid interfaces with water droplets'' suspension on the peak region of the rough solid surface.^8–11 Thus, the superhydrophobic topography suppresses direct contact between the stomata and water, preventing contamination and yielding healthy plants.Many plants in nature possess superhydrophobic leaves, e.g., lotus, taro, and Pistia stratiotes L.^12–14 Different from other superhydrophobic plants with micro/nano-topography, Pistia stratiotes L. plants have millimetre-level superhydrophobic setae. Their high topographical features are especially beneficial for long-lasting and steady breathing in the water environment. Inspired by this natural design, we developed a novel air filtration system. It consists of stomata arrays integrated with superhydrophobic micro-papillae. The micro-hole arrays filter micro-sized solid particles from the air and provide fresh air for breathing. Pistia stratiotes L. is a self-cleaning floating herbaceous plant that lives on the water surface. The plant''s surface is covered with superhydrophobic millimeter-sized setae (mm-setae) arrays for keeping a stable respiration shown in Fig. 1a and b, enabling the plant survival in high-humidity environments. Water droplets with a large surface tension are easily suspended on the surface of setae arrays (Fig. 1c and Movie Online Resource 1^†). Thus, they rarely contact the stomata under the setae arrays, maintaining a layer of flowing air at the solid–liquid interface, further enhancing the leaf survivability. Even when the leaf surface is 1 m below the water level, the leaf can survive for more than 24 h due to the amount of air retained between the mm-setae. The ability of the Pistia stratiotes L. leaf to survive underwater is better than that of the lotus leaf.^5,15 In addition, solid dust may be easily captured by a water droplet, and once it is wetted, it cannot get out of the water droplet due to the large surface tension and excellent wettability of water.^16–20 Fig. S1 and Movie Online Resource 2^† show a captured solid particle that floats in the water droplet. In this process, water filters the air.²¹Open in a separate windowFig. 1The state of a droplet on the surface of Pistia stratiotes L. leaf. (a) An optical image of Pistia stratiotes L. on the water surface. (b and c) The droplet suspends on the surface of mm-setae arrays. The droplet cannot directly contact the leaf base and cover the stomata, maintaining the respiration function. The mm-setae are distributed not only on the upper side but also on the lower side of the leaf. (d–f) The SEM micrograph of the leaf surface. (d–f) The surface is covered by mm-setae arrays. The setae with a height of 600–1400 μm are distributed on the upper side and lower side of the leaf. The setae are covered by nano-petals and wax material, which induce the superhydrophobic function. (f) The distribution of stomata on the leaf surface. The stomata are located at the bottom region of the micro-setae.The surface of the Pistia stratiotes L. leaf is composed of mm-setae and stomata. The mm-setae and stomata play two vital roles for plant survival, i.e., they provide the airflow and serve as a gateway for gas exchange, respectively. Fig. 1d–f shows the SEM micrographs of the leaf surface for better insight into topographical details. The mm-setae, with a height of ∼1 mm, are covered by nano-petals and wax material for achieving the superhydrophobic function, and the stomata are located in the root region of the mm-setae (Fig. 1f). Large setae effectively hinder direct contact between stomata and water. Droplet suspends on the top region of rough surface and shows Cassie''s state.^22,23 The mm-setae are distributed not only on the upper surface but also on the lower surface of the leaf (Fig. S2^†), both playing a significant role in maintaining water-repellence and respiration, further enhancing the survival ability underwater.²⁴The mm-setae on the leaf surface exhibit excellent mechanical properties required to resist the external force exerted by water and avoid wetting. We used a micromechanical balance to test the mechanical properties of mm-setae on the upper and lower surfaces (Fig. 2). A stress of 3.2 × 10–2 N is generated when the mm-setae are bent at a deformation of 1 mm. The relationship between the deformation and the stored elastic energy (Γ) is shown in eqn (1):²²1where K is the elastic modulus of the mm-setae, h₀ and Δh are the initial height and the deformation of mm-setae, respectively. The bending of the mm-setae becomes challenging as the deformation increase.²⁵ The average pressure is larger than 104 Pa, so the water-repellence function is stable even when the structure is soaked in water at a depth of 1 m, making the structure substantially more durable than that of the lotus leaf. As the wetting of stomata is suppressed, the exchange of oxygen and carbon dioxide can take place freely through the stomata even in rainy environment (Fig. 3), resulting in normal respiration. This design improves the vitality and avoids the leaf''s degradation.Open in a separate windowFig. 2The mechanical test of the mm-setae on the upper and lower surfaces. The diameter of the steel bar is 2 mm. When the mm-setae on the upper surface are bent 1 mm (the line consisting of hollow squares), the average pressure acting on the surface is larger than 1 × 104 Pa, which illustrates that superhydrophobic function still exists 1 m below the water level. The results of mechanical testing indicate the pressure necessary for the water intrusion.Open in a separate windowFig. 3Schematic representation of respiration on the surface of the Pistia stratiotes L. leaf. (a and b) The top and side view of the topography. (c) The droplet suspends on the top region of the micro-setae surface. The stomata are located at the bottom of the mm-setae, avoiding direct contact with water.Inspired by the functionality of the combination of stomata and superhydrophobic mm-setae, we designed a superhydrophobic membrane with upper surface composed of superhydrophobic micro-papillae and micro-stomata arrays (Fig. 4). The micro-papillae, with a height of 500 μm and a base diameter of 500 μm, could provide more air flow and induce a liquid droplet suspension on their tips (Fig. 4b). The contact angle of the 10 μL-droplet is larger than 152°, and the droplet quickly sheds off the surface with a tilting angle of 2°, providing a passage for air (inset in Fig. 4b). The micro-stomata are located between the micro-papillae and extend through the membrane. The long and short diameters of elliptical stomata are 1 mm and 500 μm, respectively. The space between two neighboring stomata, with a width of 500 μm, provides the superhydrophobic function and a lot of air between the solid surface and water. The stomatal channels with a length of 4 mm pass through the whole membrane (Fig. S3^†). When the surface is covered by water, the micro-papillae generate small bubbles and air layer at liquid/solid interface (Fig. 4c). The three-phase contact line is very unstable, as it shrinks and detaches from the solid surface when the surface is tilted at an angle of 2° (Fig. 4d). The excellent superhydrophobic performance indues liquid droplet suspension on the tip of micro-papillae, preventing liquid from contacting with the stomata (Fig. 4e and S4^†). In the magnified view of the surface shown in Fig. 5, the surface is covered by micro sphere and ZnO nano-rod, which enhances the roughness and further water-repellence function.Open in a separate windowFig. 4The bio-fabricated gas transmission system. (a and b) The top view and side view of the bio-fabricated surface. The upper surface is composed of superhydrophobic micro-papillae and micro-stomata. The micro-papillae with a height of 500 μm and a base diameter of 500 μm are shown in (b). The inset shows the superhydrophobic state. The droplet suspends on the top of the micro-papillae. The contact angle is larger than 150°. The micro-stomata are located between the micro-papillae and extend through the membrane. (c and d) Top view of the droplet on the bio-fabricated surface. The micro-papillae surfaces generate small bubbles and air layer between the liquid/solid interface. The three-phase contact line (the red curve) is very unstable. (e) The magnified side view of the interface. Liquid suspends on the micro-papillae surface and could not contact the stomata.Open in a separate windowFig. 5The SEM images of the bio-fabricated membrane. (a) The surface is composed by elliptic micro-stomata array and micro-papillae array. (b) The papilla surface is covered by micro sphere and ZnO nano-rod. The diameter and height of nano-rods are 90∼110 nm and 2 μm, respectively. (c and d) The top view and side view of the elliptic stomata.The designed bio-fabricated respiratory system is constructed by this membrane equipped with a polymethyl methacrylate (PMMA) shell, and it is used to capture micro-sized solid particles and gas pollutants from the atmosphere (Fig. 6). The membrane is locked in the PMMA shell as a gate to prevent the infiltration of water as shown in the Movie 3.^† A filter mask is obtained after mounting the respiratory system on a mask. Fig. 7a shows its working schematic. During the breathing process, the air moves through the valley of the superhydrophobic micro-papillae after entering the respiratory system, and it is filtered by water before being transported into the breathing system (Fig. 7b). Most of solid micro particles and odorous gas once contact the water, they are wetted and absorbed by the water. As the stale gas passes through the sample, it turns into cleaner air. Practical application process by medical staff illustrate that the mask system filters not only solid dusts but also harmful gases in the air (Fig. 7c). Most of the solid particles from the air are absorbed due to their excellent water wettability (Fig. S5^†). This design effectively improves respiratory system.Open in a separate windowFig. 6The bio-fabricated respiratory system. (a–d) Different side views of the bio-fabricated system (Movie S3^†). (e) The filter system is implemented in a mask.Open in a separate windowFig. 7The bio-fabricated respiratory system. (a) Schematic drawing of the system. The bio-fabricated surface is embedded in a groove. The groove is filled with water. The air is filtered by water, so the clean air moves through the stomata. (b and c) Practical application process by medical staff. The mask system not only filter the solid dust in atmosphere, but also harmful gases from the air.The water in the PMMA shell could be replaced by a volatile drug to treat diseases. Drugs are transported through the stomata and enter the body by the respiratory tract. The size of stomata controls the drug flowing speed. Moreover, this system can be recycled. When the water/drug solution in the PMMA shell is dry, the shell could be reused after washing with water. The number of reuses can exceed 120 times.In conclusion, inspired by the topography of the natural leaf surface, we developed a novel kind of air filter. The bio-fabricated surface is equipped with superhydrophobic micro-setae and perforating structural micro-stomata. Water suspends on the superhydrophobic micro-setae, providing significantly more flowing air at the valley of the micro-setae. The air is filtered when it goes through the valley and the stomata, providing fresh, comfortable, and moderately humid air for the human respiratory system. This study provides an effective fabrication method for respiratory filtration systems, having potential applications for masks, breather valves, and medical treatment.     

Correction: Bio-conjugation of graphene quantum dots for targeting imaging

Correction for ‘Bio-conjugation of graphene quantum dots for targeting imaging’ by Fei Jia et al., RSC Adv., 2017, 7, 53532–53536.

The authors regret that the versions of Fig. 2 and ​and44 displayed in the original article were incorrect. The loading dye in Fig. 2c should be the artificial marker for molecular weight analysis. The original Fig. 4 did not support the EGFR binding due to the cell endocytosis, and the result has been revised with an improved data set. The correct versions of Fig. 2 and ​and44 are shown below.Open in a separate windowFig. 2(a) The sucrose DGU gradient used for purifying the conjugates. (b) The desired SA@GQDs positions in the DGU column. (c) PL image of the DGU column after ultracentrifuge. (d) Bolt 4–12% Bis–Tris gel electrophoresis analysis of SA@GQDs, anti-mouse@GQDs and Erbitux@GQDs, respectively. The loading dye with confirmed molecule weight was tested as references. (e) The cell viability of conjugate Erbitux@GQDs (SCC cell).Open in a separate windowFig. 4(a) SCC cell imaging by Erbitux@GQDs which is binding to the EGFR receptor of SCC cell membrane. (b) The bright field, and PL picture at different channels. After merging the PL picture of Dapi and GFP channels, the successful staining of membrane and nucleus was observed. The quantum yield of GQDs is much lower than Dapi, and we have to tune the contrast/brightness to reach the same quality between Dapi and GQDs. The emission of Dapi also has some signal in GQDs channel, and we have re-draw the data to get rid of the Dapi signal.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Insight into trifluoromethylation – experimental electron density for Togni reagent I

3,3-Dimethyl-1-(trifluoromethyl)-1,3-dihydro-1-λ3,2-benziodoxole represents a popular reagent for trifluoromethylation. The σ hole on the hypervalent iodine atom in this “Togni reagent” is crucial for adduct formation between the reagent and a nucleophilic substrate. The electronic situation may be probed by high resolution X-ray diffraction: the experimental charge density thus derived shows that the short intermolecular contact of 3.0 Å between the iodine and a neighbouring oxygen atom is associated with a local charge depletion on the heavy halogen in the direction of the nucleophile and visible polarization of the O valence shell towards the iodine atom. In agreement with the expectation for λ3-iodanes, the intermolecular O⋯I–C_aryl halogen bond deviates significantly from linearity.

The experimentally observed electron density for the “Togni reagent” explains the interaction of the hypervalent iodine atom with a nucleophile.

A “halogen bond” denotes a short contact between a nucleophile acting as electron density donor and a (mostly heavy) halogen atom as electrophile;^1,2 halogen bonds are a special of σ hole interactions.^3–5 Such interactions do not only play an important role in crystal engineering;^6–11 rather, the concept of a nucleophile approaching the σ hole of a neighbouring atom may also prove helpful for understanding chemical reactivity.The title compound provides an example for such a σ hole based reactivity: 3,3-dimethyl-1-(trifluoromethyl)-1,3-dihydro-1-λ3,2-benziodoxole, 1, (Scheme 1) commonly known as “Togni reagent I”, is used for the electrophilic transfer of a trifluoromethyl group by reductive elimination. The original articles in which the application of 1¹² and other closely related “Togni reagents”¹³ were communicated have been and still are highly cited. Trifluoromethylation is not the only application for hypervalent iodine compounds; they have also been used as alkynylating¹⁴ or azide transfer reagents.^15,16 The syntheses of hypervalent iodanes and their application in organofluorine chemistry have been reviewed,¹⁷ and a special issues of the Journal of Organic Chemistry has been dedicated to Hypervalent Iodine Catalysis and Reagents.¹⁸ Recently, Pietrasiak and Togni have expanded the concept of hypervalent reagents to tellurium.¹⁹Open in a separate windowScheme 1Lewis structure of the Togni reagent, 1.Results from theory link σ hole interactions and chemical properties and indicate that the electron density distribution associated with the hypervalent iodine atom in 1 is essential for the reactivity of the molecule in trifluoromethylation.²⁰ Lüthi and coworkers have studied solvent effects and shown that activation entropy and volume play relevant roles for assigning the correct reaction mechanism to trifluoromethylation via1. These authors have confirmed the dominant role of reductive elimination and hence the relevance of the σ hole interaction for the reactivity of 1 in solution by ab initio molecular dynamics (AIMD) simulations.^21,22 An experimental approach to the electron density may complement theoretical calculations: low temperature X-ray diffraction data of sufficient resolution allow to obtain the experimental charge density and associate it with intra- and inter-molecular interactions.^23–25 Such advanced structure models based on aspherical scattering factors have also been applied in the study of halogen bonds.^26–30 In this contribution, we provide direct experimental information for the electronic situation in Togni reagent I, 1; in particular, we analyze the charge distribution around the hypervalent iodine atom.Excellent single crystals of the title compound were grown by sublimation.^§ The so-called independent atom model (IAM), i.e. the structure model based on conventional spherical scattering factors for neutral atoms, confirms the solid state structure reported by the original authors,¹² albeit with increased accuracy. As depicted in Fig. 1, two molecules of 1 interact via a crystallographic center of inversion. The pair of short intermolecular O⋯I contacts thus generated can be perceived as red areas on the interaction-sensitive Hirshfeld surface.³¹Open in a separate windowFig. 1Two neighbouring molecules of 1, related by a crystallographic center of inversion. The short intermolecular I⋯O contacts show up in red on the Hirshfeld surface³² enclosing the left molecule. (90% probability ellipsoids, H atoms omitted, symmetry operator 1 − x, 1 − y, 1 − z).The high resolution of our diffraction data ^¶ for 1 allowed an atom-centered multipole refinement^33,34 and thus an improved model for the experimental electron density which takes features of chemical bonding and lone pairs into account. Fig. 2 shows the deformation density, i.e. the difference electron density between this advanced multipole model and the IAM in the same orientation as Fig. 1.^|| The orientation of an oxygen lone pair (blue arrow) pointing towards the σ hole of the heavy halogen in the inversion-related molecule and the region of positive charge at this iodine atom (red arrow) are clearly visible. Single-bonded terminal halides are associated with one σ hole opposite to the only σ bond, thus resulting in a linear arrangement about the halogen atom. Different geometries and potentially more than a single σ hole are to be expected for λ3-iodanes such as our target molecule, and as a tendency, the resulting halogen bonds are expected to be weaker than those subtended by single-bonded iodine atoms.³⁵ In agreement with these theoretical considerations, the closest I⋯O contacts in 1 amount to 2.9822(9) Å. This distance is significantly shorter than the sum of the van-der-Waals radii (I, 1.98 Å; O, 1.52 Å (ref. 36)) but cannot compete with the shortest halogen bonds between iodine and oxygen^37,38 or iodine and nitrogen.^39–41Fig. 1 and ​and22 show that the C_aryl–I⋯O contacts are not linear; they subtend an angle C10–I1⋯O1′ of 141.23(3)° at the iodine atom. On the basis of theoretical calculations, Kirshenboim and Kozuch³⁵ have suggested that the split σ holes should be situated in the plane of the three substituents of the hypervalent atom and that halogen and covalent bonds should be coplanar. Fig. 3 shows that the C_aryl–I⋯O interaction in 1 closely matches this expectation, with the next oxygen neighbour O1′ only 0.47 Å out of the least-squares plane through the heavy halogen I1 and its three covalently bonded partners C1, O1 and C10.Open in a separate windowFig. 2Deformation density for the pair of neighbouring molecules in 1; the dashed blue and red arrows indicate regions of opposite charge. (Contour interval 0.10e Å⁻³; blue lines positive, red lines negative, green lines zero contours, symmetry operator 1 − x, 1 − y, 1 − z).Open in a separate windowFig. 3A molecule of 1, shown [platon] along O1⋯C1, and its halogen-bonded neighbour O1ⁱ. Symmetry operator 1 − x, 1 − y, 1 − z.The Laplacian, the scalar derivative of the gradient vector field of the electron density, emphasizes local charge accumulations and depletions and it allows to assess the character of intra- and inter-molecular interactions. A detailed analysis of all bonds in 1 according to Bader''s Atoms In Molecules theory⁴² is provided in the ESI.^‡ We here only mention that the electron density in the bond critical point (bcp) of the short intermolecular I⋯O contact amounts to 0.102(5)e Å⁻³; we are not aware of charge density studies on λ3-iodanes, but both the electron density and its small positive Laplacian match values experimentally observed for halogen bonds involving O and terminal I in the same distance range.⁴³The crystal structure of 1 necessarily implies additional contacts beyond the short halogen bond shown in Fig. 1 and ​and2.2. The shortest among these secondary interactions is depicted in Fig. 4: it involved a non-classical C–H⋯F contact with a H⋯F distance of 2.55 Å.Open in a separate windowFig. 4C–H⋯F contact in 1; additional information has been compiled in the ESI.^‡ Symmetry operators i = 1 − x, 1 − y, 1 − z; ii = 1 − x, 1 − y, −z.The topological analysis of the experimental charge density reveals that this non-classical C–H⋯F hydrogen bond and all other secondary contacts are only associated with very small electron densities in the bcps. Table S8 in the ESI^‡ provides a summary of this analysis and confirms that the I⋯O halogen bond discussed in Fig. 1 and ​and22 represents by far the most relevant intermolecular interaction.The relevance of this halogen bond extends beyond the crystal structure of 1: Insight into the spatial disposition of electrophilic and nucleophilic regions and hence into the expected reactivity of a molecule may be gained from another electron-density derived property, the electrostatic potential (ESP). The ESP for the pair of interacting molecules in 1 is depicted in Fig. 5.Open in a separate windowFig. 5Electrostatic potential for a pair of molecules in 1 mapped on an electron density isosurface (ρ = 0.5e Å⁻³; program MoleCoolQt^44,45). Fig. 5 underlines the complementary electrostatic interactions between the positively charged iodine and the negatively charged oxygen atoms. One can easily imagine to “replace” the inversion-related partner molecule in crystalline 1 by an incoming nucleophile.The ESP tentatively obtained for a single molecule in the structure of 1 did not differ significantly from that derived for the inversion-related pair (Fig. 5), and even the results from theoretical calculations in the gas phase for an isolated molecule²⁰ are in good qualitative agreement with our ESP derived from the crystal structure. In the absence of very short contacts, polarization by neighbouring molecules only has a minor influence on the ESP. The experimentally observed electron density matches the proven reactivity for the title compound, and we consider it rewarding to extend our charge density studies on related hypervalent reagents.