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.     

Thiophene-containing tetraphenylethene derivatives with different aggregation-induced emission (AIE) and mechanofluorochromic characteristics

Four thiophene-containing tetraphenylethene derivatives were successfully synthesized and characterized. All these highly fluorescent compounds showed typical aggregation-induced emission (AIE) characteristics and emitted different fluorescence colors including blue-green, green, yellow and orange in the aggregation state. In addition, these luminogens also exhibited various mechanofluorochromic phenomena.

Four thiophene-containing AIE-active TPE derivatives were synthesized. Furthermore, these luminogens exhibited various mechanofluorochromic phenomena.

High-efficiency organic fluorescent materials have attracted widespread attention due to their potential applications in organic light-emitting devices and fluorescent switches.^1–8 Meanwhile, smart materials sensitive to environmental stimuli have also aroused substantial interest. Mechanochromic luminescent materials exhibiting color changes under the action of mechanical force (such as rubbing or grinding) are one important type of stimuli-responsive smart materials, which can be used as pressure sensors and rewritable media.^9–18 Bright solid-state emission and high contrast before and after grinding are very significant for the high efficient application of mechanochromic fluorescence materials.^19–28 However, a majority of traditional emissive materials usually exhibit poor emission efficiency in the solid state due to the notorious phenomenon of aggregation caused quenching (ACQ), and the best way to solve the problem is to develop a class of novel luminescent materials oppositing to the luminophoric materials with ACQ effect. Fortunately, an unusual aggregation-induced emission (AIE) phenomenon was discovered by Tang et al. in 2001.²⁹ Indeed, the light emission of an AIE-active compound can be enhanced by aggregate formation.^30–32 Obviously, it is possible that AIE-active mechanochromic fluorescent compounds can be applied to the preparation of high-efficiency mechanofluorochromic materials. Numerous luminescent materials exhibiting mechanochromic fluorescent behavior have been discovered up to now.³³ Whereas, examples of fluorescent molecules simultaneously possessing AIE and mechanofluorochromic behaviors are still limited, and the exploitation of more AIE-active mechanofluorochromic luminogens is necessary. Organic solid emitters with twisted molecular conformation can effectively prevent the formation of ACQ effect, thus exhibiting strong solid-state luminescence. Tetraphenylethene is a highly twisted fluorophore. Meanwhile, it is also a typical AIE unit, which can be used to construct high emissive stimuli-responsive functional materials.^34–37The design and synthesis of novel organic emitters with tunable emission color has become a promising research topic at present. Only a limited number of organic fluorescent materials with full-color emission have been reported to date.^38,39 For example, in 2018, Tang et al. reported six tetraphenylpyrazine-based compounds. Interestingly, in film states, these luminogens exhibited different fluorescence colors covering the entire visible range, and this is the first example of realizing full-color emission based on the tetraphenylpyrazine unit.⁴⁰ It is still an urgent challenge to develop novel organic luminophors with tunable emission color basing on the same core structure.In this study, four organic fluorophores containing tetraphenylethene unit were successfully synthesized (Scheme 1). Introducing the thiophene and carbonyl units into the molecules possibly promoted the formation of weak intermolecular interactions such as C–H⋯S or C–H⋯O interaction, which was advantageous to the exploitation of interesting stimuli-responsive fluorescent materials. Indeed, all these compounds showed obvious AIE characteristics. Furthermore, these luminogens emitted a series of different fluorescent colors involving blue-green, green, yellow and orange in the aggregation state. In addition, these luminogens also exhibited reversible mechanofluorochromic phenomena involving different fluorescent color changes.Open in a separate windowScheme 1The molecular structures of compounds 1–4.To investigate the aggregation-induced properties of compounds 1–4, the UV-vis absorption spectra of 1, 2, 3 and 4 (20 μM) in DMF–H₂O mixtures of varying proportions were studied initially (Fig. S1^†). Obviously, level-off tails were obviously observed in the long-wavelength region as the water content increased. This interesting phenomenon is generally associated with the formation of nano-aggregates.⁴¹ Next, the photoluminescence (PL) spectra of 1–4 in DMF–H₂O mixtures with various water fraction (f_w) values were explored. As shown in Fig. 1, almost no PL signals were noticed when a diluted DMF solution of luminogen 1 was excited at 365 nm, and thus almost no fluorescence could be observed upon UV illumination at 365 nm, and the corresponding absolute fluorescence quantum yield (Φ) was as low as 0.04%. However, when the water content was increased to 50%, a new blue-green emission band with a λ_max at 501 nm was observed, and a faint blue-green fluorescence was noticed under 365 nm UV light. As the water content was further increased to 90%, a strong blue-green emission (Φ = 30.81%) could be observed. Furthermore, as shown in Fig. S2,^† the nano-aggregates (f_w = 90%) obtained were confirmed by dynamic light scattering (DLS). Therefore, the compound 1 with bright blue-green emission caused by aggregate formation showed typical AIE feature.Open in a separate windowFig. 1(a) Fluorescence spectra of the dilute solutions of compound 1 (2.0 × 10⁻⁵ mol L⁻¹) in DMF–water mixtures with different water contents (0–90%). Excitation wavelength = 365 nm. (b) Fluorescence images of 1 (2.0 × 10⁻⁵ mol L⁻¹) in DMF–water mixtures with different f_w values under 365 nm UV light.Similarly, as can be seen in Fig. 2–4, compounds 2–4 also showed obvious aggregation-induced green emission, aggregation-induced yellow emission, and aggregation-induced orange emission, respectively. When the water content was zero, the quantum yields of compounds 2–4 were 0.04%, 0.05% and 0.46%, respectively, while as the water content increased to 90%, the corresponding quantum yields of compounds 2–4 also increased to 30.67%, 45.57% and 26.53%, respectively. Hence, luminogens 2–4 were also AIE-active species. In addition, as shown in Fig. 5, the DFT calculations for the compounds 1–4 were performed. The calculated energy gaps (ΔE) of four compounds were 3.6178416 eV (compound 1), 3.276084 eV (compound 2), 3.3073755 eV (compound 3) and 3.0766347 eV (compound 4) respectively. Therefore, the various numbers and the various kinds of the substituents had slight effects on their molecular orbital energy levels of 1–4.Open in a separate windowFig. 2(a) Fluorescence spectra of the dilute solutions of compound 2 (2.0 × 10⁻⁵ mol L⁻¹) in DMF–water mixtures with different water contents (0–90%). Excitation wavelength = 365 nm. (b) Fluorescence images of 2 (2.0 × 10⁻⁵ mol L⁻¹) in DMF–water mixtures with different f_w values under 365 nm UV light.Open in a separate windowFig. 3(a) Fluorescence spectra of the dilute solutions of compound 3 (2.0 × 10⁻⁵ mol L⁻¹) in DMF–water mixtures with different water contents (0–90%). Excitation wavelength = 365 nm. (b) Fluorescence images of 3 (2.0 × 10⁻⁵ mol L⁻¹) in DMF–water mixtures with different f_w values under 365 nm UV light.Open in a separate windowFig. 4(a) Fluorescence spectra of the dilute solutions of compound 4 (2.0 × 10⁻⁵ mol L⁻¹) in DMF–water mixtures with different water contents (0–90%). Excitation wavelength = 365 nm. (b) Fluorescence images of 4 (2.0 × 10⁻⁵ mol L⁻¹) in DMF–water mixtures with different f_w values under 365 nm UV light.Open in a separate windowFig. 5(a) HOMO and LUMO frontier molecular orbitals of molecule 1 based on DFT (B3LYP/6-31G*) calculation. (b) HOMO and LUMO frontier molecular orbitals of molecule 2 based on DFT (B3LYP/6-31G*) calculation. (c) HOMO and LUMO frontier molecular orbitals of molecule 3 based on DFT (B3LYP/6-31G*) calculation. (d) HOMO and LUMO frontier molecular orbitals of molecule 4 based on DFT (B3LYP/6-31G*) calculation.Subsequently, the mechanochromic fluorescent behaviors of compounds 1–4 were surveyed by solid-state PL spectroscopy. As shown in Fig. 6, the as-synthesized powder sample 1 exhibited an emission band with a λ_max at 444 nm, corresponding to a blue fluorescence under 365 nm UV light. Intriguingly, a new blue-green light-emitting band with a λ_max at 507 nm was observed after the pristine solid sample was ground. After fuming with dichloromethane solvent vapor for 1 min, the blue-green fluorescence was converted back to the original blue fluorescence. Therefore, luminogen 1 exhibited reversible mechanochromic fluorescence feature. Furthermore, this reversible mechanofluorochromic conversion was repeated many times by grinding-exposure without showing signs of fatigue (Fig. 10).Open in a separate windowFig. 6(a) Solid-state PL spectra of compound 1 before grinding, after grinding, and after treatment with dichloromethane solvent vapor. Excitation wavelength: 365 nm. Photographic images of compound 1 under 365 nm UV light: (b) the as-synthesized powder sample. (c) The ground sample. (d) The sample after treatment with dichloromethane solvent vapor.Open in a separate windowFig. 10Repetitive experiment of mechanochromic behavior for compound 1.Similarly, as evident from Fig. 7–9, luminogens 2–4 also exhibited obvious mechanofluorochromic characteristics. Moreover, the repeatabilities of their mechanochromic behaviors were also satisfactory (Fig. S3^†). Hence, all the compounds 1–4 showed reversible mechanofluorochromic phenomena involving different fluorescent color changes, and the various numbers of the substituents could effectively influence the mechanofluorochromic behaviors of 1–4. Obviously, luminogen 3 or 4 after grinding exhibited more red-shifted fluorescence in comparison with that of the corresponding luminogen 1 or 2 after grinding.Open in a separate windowFig. 7(a) Solid-state PL spectra of compound 2 before grinding, after grinding, and after treatment with dichloromethane solvent vapor. Excitation wavelength: 365 nm. Photographic images of compound 2 under 365 nm UV light: (b) the as-synthesized powder sample. (c) The ground sample. (d) The sample after treatment with dichloromethane solvent vapor.Open in a separate windowFig. 8(a) Solid-state PL spectra of compound 3 before grinding, after grinding, and after treatment with dichloromethane solvent vapor. Excitation wavelength: 365 nm. Photographic images of compound 3 under 365 nm UV light: (b) the as-synthesized powder sample. (c) The ground sample. (d) The sample after treatment with dichloromethane solvent vapor.Open in a separate windowFig. 9(a) Solid-state PL spectra of compound 4 before grinding, after grinding, and after treatment with dichloromethane solvent vapor. Excitation wavelength: 365 nm. Photographic images of compound 4 under 365 nm UV light: (b) the as-synthesized powder sample. (c) The ground sample. (d) The sample after treatment with dichloromethane solvent vapor.In order to further explore the possible mechanism of mechanofluorochromism of 1–4, the powder X-ray diffraction (PXRD) measurements of various solid states of 1–4 were carried out. As depicted in Fig. 11, the pristine solid powder 1 showed many clear and intense reflection peaks, suggesting its crystalline phase. However, after the pristine powder sample was ground, the sharp and intense diffraction peaks vanished, which indicated the crystalline form was converted to the amorphous form. Interestingly, when the ground solid sample was fumigated with dichloromethane solvent vapor for 1 min, the corresponding sample powder exhibited the PXRD pattern of the initial crystalline form. Meanwhile, the structural transformations of the solid samples of 2–4 were similar to that of 1 (Fig. S4–S6^†). Obviously, the morphological changes of solid samples of 1–4 from crystalline state to amorphous state and vice versa could be attributed to the reversible mechanical switching in compounds 1–4, and the mechanofluorochromic phenomena observed in 1–4 were related to the morphological transition involving the ordered crystalline phase and the disordered amorphous phase.Open in a separate windowFig. 11XRD patterns of compound 1: unground, ground and after treatment with dichloromethane solvent vapor.Fortunately, single crystals of compounds 1 and 2 were obtained by slow diffusion of n-hexane into a trichloromethane solution containing small amounts of 1 or 2. As shown in Fig. 12 and ​and13,13, the molecular structures of 1 and 2 exhibited a twisted conformation due to the existence of tetraphenylethene unit. Meanwhile, some weak intermolecular interactions, such as C–H⋯π interaction (d = 2.866 Å) for 1, π⋯π interaction (d = 3.371 Å) for 1, C–H⋯S interaction (d = 2.977 Å) for 2, and π⋯π interaction (d = 3.189 Å) for 2, were observed. These weak intermolecular interactions gave rise to a loose packing motif of 1 or 2, which indicated their ordered crystal packings might readily collapse upon exposure to external mechanical stimulus. Therefore, their solid-state fluorescence could be adjusted by mechanical force.Open in a separate windowFig. 12The structural organization of compound 1.Open in a separate windowFig. 13The structural organization of compound 2.In summary, four fluorescent molecules containing thiophene and tetraphenylethene units were successfully designed and synthesized in this study. All these compounds showed obvious AIE characteristics. Furthermore, these luminogens emitted various fluorescence colors involving blue-green, green, yellow and orange in the aggregation state. Meanwhile, these luminogens basing on the same core structure also exhibited reversible mechanofluorochromic phenomena involving different fluorescent color changes. The results of this study will be beneficial for the exploitation of novel luminophors with full-color emission.     

Ni(ii)-based coordination polymers for efficient electrocatalytic oxygen evolution reaction

The exploration of highly efficient, stable and cheap water oxidation electrocatalysts using earth-abundant elements is still a great challenge. Herein, alkaline-stable cationic Ni(ii) coordination polymers (Ni-CPs) were successfully obtained under hydrothermal conditions, which could stabilize the incorporation of Fe(iii) to form Fe-immobilized Fe@Ni-CPs. The newly developed Ni-based CPs were used for the first time as an effective electrocatalyst for the oxygen evolution reaction in strong alkaline media.

An alkaline-stable cationic Ni(ii) coordination polymer showed remarkable oxygen evolution reaction (OER) catalytic activity due to capturing Fe ions.

The oxygen evolution reaction (OER) plays a vital role in energy storage and conversion applications due to energy issues and the need for sustainable development.^1–4 Because of the sluggish kinetics of the OER, excellent electrocatalysts are required to work in acidic or strong alkaline environments.^5,6 Noble metal-based catalysts like IrO₂ and RuO₂ with high efficiency showed excellent OER catalytic activity.⁷ However, noble metal with high-cost and scarcity are impractical for scale-up applications. Currently, to substitute these precious metal-based materials, transition-metal-based (Fe, Co, Ni and so on) and metal-free (e.g., N, P and S) hybrid materials have been extensively developed.^8–10 For example, metal–organic frameworks (MOFs) such as ZIF-8/67 derived metal–carbon composite materials exhibit promising electrocatalytic performance.^11,12 Unfortunately, the pyrolysis process destroys the framework completely and causes agglomeration of metals, resulting in a decreased number of active sites. Therefore, to explore highly efficient and low-cost OER catalysts that can be directly used in the OER without calcination are desired, including complexes and MOFs.Recently, much of transition bimetallic materials showed excellent electrocatalytic activity.^13–15 However, a handful of examples such as Fe–Co-MOFs or Co–Ni-MOFs have been explored due to instability, poor conductivity and harsh synthesis conditions.^16–20 Notably, the disadvantages of MOFs have limited their usage in the potential OER. Therefore, it is urgent to develop cheap, stable and active OER catalysts to replace the precious metals. However, this is still a great challenge. Coordination polymers (CPs) with a low-dimensional framework similar to MOFs are constructed by metal ion and organic ligands with potential active sites and functional groups, exhibiting wide applications in sensing, photoluminescence and photocatalysis.^21–26 However, rare examples of CPs have been directly explored in the OER. For Fe/Ni-based bimetal electrocatalysts, a novel strategy involves doping Fe(iii) into a functional Ni-based CPs, which could enhance the electrocatalytic OER activities.Herein, we report the hydrothermal synthesis of a Ni-based CPs as a high-performance OER electrocatalyst in strong alkaline solutions (Scheme 1). The blue crystals of [Ni(bp)₃·(H₂O)₂]·(bp)·(ClO₄)₂ (bp = 4,4′-biprydine) were obtained upon the reaction of bp ligands with NiClO₄·6H₂O under hydrothermal systems. Chemical stability tests displayed that Ni-CPs could retain their original framework in water or even a strong alkaline (pH = 14) solution after 12 hours (Fig. S1^†), which is rarely reported for most transition metal CPs. The thermogravimetric analysis (TGA) showed that there is a significant change at about 110 °C due to the weight loss of the partial guest (Fig. S2^†). Interestingly, the cationic Ni-CPs successfully captured the Mohr''s salt (ammonium iron(ii) sulfate) by taking advantage of the post-synthetic strategy. The obtained Fe@Ni-CPs exhibited a high-efficient OER activity under strong alkaline conditions.Open in a separate windowScheme 1Illustration of the synthesis process for Fe doped Ni coordination polymers for the OER.Single-crystal X-ray diffraction analysis revealed that the Ni-CPs crystallized in the C2/c space group (Table S1^†). The obtained Ni coordination polymer was the isostructural compound reported by Talham,²⁷ but their packing modes were distinctly different (Fig. S3–S5^†). It also had a similar coordination environment to the railroad-like double chains synthesized by Yaghi.²⁸ The parallel chains were occupied by 4,4′-bpy, perchlorate and water molecules. In the Ni-CPs, most of the phenyl rings adopted the face-to-face mode. There were evident π⋯π interactions between the adjacent 4,4′-biprydine (Fig. 1a). In addition, there were strong intermolecular hydrogen bonds between 4,4′-bpy and perchlorate (strong Cl–O⋯C amongst adjacent layers) (Fig. 1a). The weak reaction increased the high density of the framework and protected the coordination bonds against external guest attacking. These chains and guests were further packed with a three-dimensional structure along the c-axis (Fig. 1b).Open in a separate windowFig. 1(a) The weak reaction between chains in Ni CPs, showing the Cl–O⋯C (green and black dashed line) and π⋯π interactions (pink dashed line) between the adjacent perchlorate and 4,4′-biprydine, respectively; (b) the packing view of Ni CPs along the c-axis. Cl in green, Ni in pale blue, N in blue, O in red and C in black. H atoms and partial guest molecules were omitted for clarity.The unique cationic Ni-CPs framework has the potential to immobilize some counterpart ions. To demonstrate this, Mohr''s salts were investigated. Most strikingly, the color slowly changed from blue to green in an aqueous solution, given by the optical image (Fig. 2a and b), which not only indicated that Ni-CPs captured Mohr''s salts via ion-exchange, but also suggested an alteration in the valence of Fe ions. It was possible that Fe²⁺ may have been further oxidized to Fe³⁺ under the O₂ and water environment when we prepared the Fe@Ni-CPs (4Fe²⁺ + 2H₂O + O₂ = 4Fe³⁺ + 4OH⁻). The PXRD pattern showed that the frameworks remained unchanged after doping with Fe ions (Fig. S1^†). From the transmission electron microscopy (TEM) images (Fig. 2c), after immobilization, the morphology of the Fe@Ni-CPs was still level and smooth; no ring-like patterns arose corresponding to the selected area for electron diffraction (SAED) (Fig. 2d), indicating that no bulk Fe particles formed during ion-exchange. This was further demonstrated using high resolution TEM (HRTEM) (Fig. 2e), in which there was no lattice fringe of crystallized Fe. The well distribution of C, N, O, Cl, Fe, and Ni in Fe@Ni-CPs was demonstrated by elemental mapping (Fig. 2f–l). Energy-dispersive X-ray spectroscopy (EDX) also agreed well with the above mapping data (Fig. S6^†). In addition, the Fe³⁺ uptake was 4.1 wt%, as determined by inductively coupled plasma atomic emission spectroscopy (ICP). These results showed Fe ions to have been successfully immobilized by the Ni-CPs.Open in a separate windowFig. 2(a–b) The optical image of Ni-CPs and Fe@Ni-CPs; (c) TEM images of Fe@ Ni-CPs; (d–e) the corresponding SAED and HRTEM pattern. (f–l) Element mapping of C, N, O, Cl, Fe, and Ni in Fe@Ni-CPs.The X-ray photoelectron spectroscopy (XPS) survey spectrum of the Fe@Ni-CPs also showed the presence of C, N, O, Cl, Fe, and Ni elements (Fig. 3a). The Fe 2p high resolution XPS spectrum exhibited peaks at 725 eV and 711 eV (Fig. 3b), further indicating the presence of the Fe³⁺ oxidation state. This could be explained by the transformations of Fe²⁺ to Fe³⁺ during the ion-exchange process. Similarly, in the Ni 2p spectra (Fig. 3c), two main peaks located at 855.8 eV and 873.5 eV can be ascribed to Ni²⁺ 2p_3/2 and Ni²⁺ 2p_1/2, respectively. These peaks are associated with two shakeup satellite peaks, indicating that Ni still remained in a divalent state. The Cl 2p and N 1s region could be corresponded to the ClO₄⁻ and biprydine, respectively (Fig. S7^†). The O 1s spectrum (Fig. 3d) was divided into two peaks at 531.7 eV and 533.2 eV, which could be assigned to the OH group from filled H₂O molecules and partial ClO₄⁻, respectively.Open in a separate windowFig. 3(a) XPS survey spectrum of the Ni-CPs; XPS spectra of the Ni-CPs in the (b) Fe 2p, (c) Ni 2p, and (d) O 1s regions.The above Ni-CPs with Fe doping encouraged us to investigate its electrocatalytic application in oxygen evolution reaction. To study the electrocatalytic activity of Fe@Ni-CPs for the OER, linear sweep voltammetry (LSV) was performed in a strong alkaline solution (pH = 14) for Fe@Ni-CPs@GC (fresh samples coated on glassy carbon electrode with Nafion binder). Fe@Ni-CPs@GC directly acted as working electrodes and showed good OER activity with an onset potential of 1.52 V (Fig. 4a), overpotential of 368 mV at 10 mA cm⁻², and a Tafel slope of 59.3 mV dec⁻¹ (Fig. 4b). These OER performances are close to some reported MOFs catalysts (Table S2^†) and even better than commercial benchmark OER catalysts like RuO₂ working at the same condition (Fig. S8^†). In contrast, the electrocatalytic OER activities of the pristine Ni-CPs@GC without Fe incorporation displayed much worse activity. The onset potential, overpotential (at 10 mA cm⁻²), and the Tafel slope reached 1.62 V, 458 mV, and 96.8 mV dec⁻¹, respectively (Fig. 4a and b). In addition, Fe@Ni-CPs showed a strong durability during the OER process. The chronoamperometric response of Fe@Ni-CPs displayed a slight anodic current attenuation within 12 h due to the peeling of samples during the evolution of a large amount of O₂ gas (Fig. S9^†). Furthermore, LSV of Fe@Ni-CPs showed negligible changes after OER tests for 12 h (Fig. S10^†). These results indicate that the Fe-doped Ni-CPs with more active sites could serve as an excellent candidate for OER in strong alkaline conditions.Open in a separate windowFig. 4(a) OER polarization curves and (b) Tafel plots of various electrocatalysts in a 1 M KOH aqueous solution; (c) linear relationship of the current density at 1.1 V (vs. RHE) vs. scan rates for Fe@Ni-CPs@GC and Ni-CPs@GC; (d) EIS of Fe@Ni-CPs and Ni-CPs electrode.When Fe(iii) was introduced, the resulting Fe@Ni-CPs catalysts greatly improved OER catalytic performance. There were dynamic collisions between Fe³⁺ ions and Ni-CPs, which allowed for more accessible catalytic active sites compared to the Ni-CPs. Particularly, Fe(iii) doping can contribute to the adsorption and reaction of OH⁻ groups in OER process.²⁹ As a result, Fe@Ni-CPs enhanced charge transfer under an apt electronic environment of the mixed Fe⋯Ni systems. In addition, electrochemical impedance spectrum and double-layer capacitance (C_dl) of the Fe@Ni-CP were also studied. The C_dl of Fe@Ni-CPs was confirmed to be 269.7 μF cm⁻² (Fig. 4c and S11^†), which is higher than that of Ni-CPs (C_dl = 174.2 μF cm⁻²) (Fig. 4c and S12^†). The semicircular diameter in EIS of Fe@Ni-PCP was smaller than that of Ni-CPS (Fig. 4d). These results further showed that Fe@Ni-CPs were more effective in enlarging the catalytically active surface area, conductivity and synergistic effects between Fe and Ni in comparison to Ni-CPs coated on electrodes.In conclusion, a new alkaline-stable cationic Ni(ii) coordinated polymers was synthesized under hydrothermal conditions. The Ni CPs could quickly interact with Mohr''s salt. Interestingly, the Ni CPs could act as a unique oxidation matrix to realize the transformation of Fe²⁺ to Fe³⁺ during the ion-exchange process. Furthermore, the resulting Fe@Ni-CPs electrode, for the first time, showed an excellent electrocatalytic activity for OER in strong alkaline media. This study provides a new avenue to explore stable coordinated polymers by incorporating the low-cost and high-activity transition metal, Fe, which will substitute the rare noble metals used in energy-related research.     

Crystal structure of a DNA duplex cross-linked by 6-thioguanine–6-thioguanine disulfides: reversible formation and cleavage catalyzed by Cu(ii) ions and glutathione

Herein, we determined the crystal structure of a DNA duplex containing consecutive 6-thioguanine–6-thioguanine disulfides. The disulfide bonds were reversibly formed and cleaved in the presence of Cu(ii) ions and glutathione. To our knowledge, this is the first reaction in which metal ions efficiently accelerated disulfide bond formation between thio-bases in duplexes.

The crystal structure of a DNA duplex cross-linked by 6-thioguanine–6-thioguanine disulfides has been solved.

The reversible cross-linking of nucleic acids has been investigated for use in biochemical and medicinal studies. For instance, a cross-linking reaction through imine bonds that reversibly formed at lower temperatures and dissociated at higher temperatures has been reported.¹ Metal ion-mediated base pairs have recently attracted interest. In DNA and RNA duplexes, metal ions are placed between bases, and coordination bonds between metal ions and bases stabilize the duplexes.² Metal ion-mediated base pairs are reversibly formed at lower temperatures and dissociated at higher temperatures. Oligonucleotides with thiol tethers have been used to cross-link duplexes and hairpin structures by forming disulfide bonds.³ Disulfide bonds are reversibly formed by oxidization and dissociated by reduction. Disulfide bond formation between 4-thiouracil (^4SU) and 6-thiohypoxanthine (^6SH), and between ^4SU and 6-thioguanine (^6SG), has been reported.⁴ Disulfide bond formation between ^4SU and ^6SG in duplexes has been investigated^4f and applied for mechanistic studies of flap endonucleases.^4h In the reports, I₂ (an oxidizing reagent) was used to accelerate disulfide bond formation. In this paper, we report a novel crystal structure of a DNA duplex containing two consecutive cross-linked ^6SG–^6SG pairs. Notably, disulfide bond formation between 6-thioguanine bases in a duplex was accelerated in the presence of Cu(ii) ions.A DNA dodecamer (ODN-I) with a pseudo-self-complementary sequence d(CGCGAXXBCGCG) (X = ^6SG, B = 5-bromouracil) formed a duplex (duplex-I) consisting of C–G and A–B Watson–Crick base pairs and X–X pairs (Fig. 1). The B residue was incorporated in ODN-I to apply single-wavelength anomalous dispersion (SAD) method for crystal structure analysis.Open in a separate windowFig. 1A scheme for preparation of a DNA duplex containing 6-thioguanine–6-thioguanine disulfides.Thiobases, including 2-thiothymine (^2ST), 4-thiothymine (^4ST), and 6-thioguanine (^6SG), form metallo-base pairs.⁵ Duplexes containing ^2ST pairs and ^4ST pairs are stabilized in the presence of Hg(ii) and Ag(i) ions. The formation of the ^4ST–Ag(i)₂–^4ST pair in which two Ag(i) ions are placed between ^4ST bases was revealed by a crystal structure.^5b Additionally, metal ion binding of ^6SG has been reported.^5c,d,e Consequently, it is expected that duplex-I, which contains ^6SG–M–^6SG metallo-base pairs, could be formed by mixing metal ions and ODN-I. However, in the presence of Cu(ii) ions, we observed crystals of duplex-Iss including cross-linked ^6SG–^6SG pairs.Prior to crystallization, 2 mM ODN-1 was mixed with 2 mM CuCl₂ at room temperature. Single crystals of ODN-1 were obtained for a few days in a droplet prepared by merging 1 μl of ODN-1/Cu(ii) mixed solution and 1 μl of crystallization solution containing 50 mM MOPS (pH 7.0), 10 mM spermine, 250 mM ammonium nitrate, and 10% 2-methyl-2,4-pentanediol, which was equilibrated against 250 μl of 40% 2-methyl-2,4-pentanediol. In the crystal, two DNA fragments formed an antiparallel right-handed helix, as expected (Fig. 2a). The DNA duplex contains seven canonical Watson–Crick G–C and two A–B base pairs. At one end, two complementary residues, 5′-end C1 and 3′-end G12′, do not form Watson–Crick G–C base pairs, bulge out from the helix, and are involved in crystal packing contact (Fig. 2b). At the center of the duplex, two contiguous 6-thioG residues, X6 and X7, form disulfide-bonded base pairs with the X7′ and X6′ residues on the opposite strand, respectively (Fig. 2b and d). As a result, the DNA duplex is largely kinked at the center (Fig. 2d) where the minor groove of 6-thioG residues is widely exposed (Fig. 2c). A similar bent structure of a duplex containing an artificial disulfide pair has been solved by NMR spectroscopy.^3g Such structural disorders might be necessary for incorporating the disulfide pairs. Electron density maps clearly indicate the formation of a disulfide bond between the S6 atoms of the X6–X7′ and X7–X6′ base pairs (Fig. S1^†). In the X6–X7′ and X7–X6′ base pairs, two 6-thio-G residues align almost perpendicularly.Open in a separate windowFig. 2Secondary (a) and tertiary (b–d) structures of the DNA duplex containing two disulfide-bonded base pairs between 6-thio-G residues. X and B residues are 2′-deoxy-6-thioguanosine and 2′-deoxy-5-bromouridine, respectively. Views are from a phosphate-ribose backbone (b) and from the minor groove (c and d) of the two consecutive disulfide-bonded base pairs.To investigate disulfide bond formation in solution, solutions containing ODN-I′ in the presence of oxidation reagents, Cu(ii) ions and I₂, were analysed by high-performance liquid chromatography (HPLC) with a reverse-phase silica gel column. In ODN-I′, the B base in ODN-I was replaced by a T base. One minute after Cu(ii) ions were added to the ODN-I′ solution, a peak with a longer retention time was observed (Fig. 3B). The peak was separated and analysed by electron spray ionization time-of-flight mass spectrometry, and the result indicated the formation of duplex-I′ss. The addition of a large excess of I₂ did not induce the formation of duplex-I′ss (Fig. 3C), which differs from previous reports in which I₂ was successfully used for disulfide bond formation between 4-thiouracil and 6-thioguanine residues in DNA and RNA duplexes.^4f,g Also, duplex-I′ss was not generated by using KBrO₃ as an oxidation reagent in 24 h (Fig. S4^†).Open in a separate windowFig. 3HPLC profiles of solutions containing ODN-I′ and Cu(ii) ions and I₂. (A) A solution containing 20 μM ODN-I′ in 400 mM NH₄NO₃, 50 mM MOPS (pH 7.0). (B); 320 μM CuCl₂ was added to the solution. (C); 1 mM I₂ was added to the solution. Reactions were incubated at 4 °C.Glutathione have been used for cleave disulfide bonds and thioethers on nucleobases.⁶ Glutathione was added to the solution containing duplex-I′ss and the reaction was analyzed by HPLC. The peak for duplex-I′ss was immediately diminished and a peak for ODN-I′ was observed (Fig. S2c^†). In contrast, the addition of EDTA to a solution of duplex-I′ss did not alter the HPLC profile (Fig. S2b^†). Consequently, X–X pair formation (disulfide bond formation) was accelerated in the presence of Cu(ii) ions.As duplex-I′ss formed, the thiocarbonyl groups of the 6-thioguanine residues converted into disulfide groups; consequently, the absorbance at approximately 340 nm decreased (Fig. 4).⁷Open in a separate windowFig. 4Absorbance spectra of (A) duplex-I′ (4 μM), (B) duplex-I′ss (approximately 1 μM). (C) The spectra were overlapped. For easily compared, four times lager value of duplex-I′ss''s absorption is plotted.In conclusion, we determined the crystal structure of a DNA duplex containing consecutive 6-thioguanine–6-thioguanine disulfides. This is the first crystal structure of a nucleic acid duplex containing covalently linked bases through disulfide bonds. The DNA duplex is largely kinked at the disulfide base pairs where the minor groove of 6-thioG residues is widely exposed. The disulfide bonds were reversibly formed and cleaved in the presence of Cu(ii) ions and glutathione. Interestingly, oxidizing reagents such as I₂ and KBrO₃ did not accelerate disulfide bond formation. The arrangement of 6-thioguanine residues in the duplex structure may be related to their reactions. To our knowledge, this is the first reaction in which metal ions efficiently accelerated disulfide bond formation between thio-bases in DNA duplexes. Studies of disulfide bond formation of thio-bases (^2ST, ^4ST, ^6SG, etc.) in the presence of metal ions and metallo-base pair formations (interactions of thio–base pairs and metal ions) are currently in progress.     

Correction: Thermodynamically stable vesicle formation of biodegradable double mPEG-tailed amphiphiles with sulfonate head group

Correction for ‘Thermodynamically stable vesicle formation of biodegradable double mPEG-tailed amphiphiles with sulfonate head group’ by Rita Ghosh et al., RSC Adv., 2020, 10, 32522–32531, DOI: 10.1039/D0RA05613H

The authors regret that an incorrect version of Fig. 5 was included in the original article. The correct version of Fig. 5 is presented below.Open in a separate windowFig. 1Upper panel: Size distribution histograms of aggregates in 2.0 mM solutions (pH 7) of (a) (mPEG₄)₂SO₃Na, and (b) (mPEG₂₃)₂SO₃Na at 25 °C; lower panel: unstained HRTEM images of 2 mM (c) (mPEG₄)₂SO₃Na and (d) (mPEG₂₃)₂SO₃Na solutions in phosphate buffer (pH 7.0).The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

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.     

Correction: A guanidyl-functionalized TiO2 nanoparticle-anchored graphene nanohybrid for enhanced capture of phosphopeptides

Correction for ‘A guanidyl-functionalized TiO₂ nanoparticle-anchored graphene nanohybrid for enhanced capture of phosphopeptides’ by Hailong Liu et al., RSC Adv., 2018, 8, 29476–29481.

The authors regret that there was an error in Fig. 3 of the original article, as the three parts of the figure were labelled incorrectly. The correct version of Fig. 3 is presented below.Open in a separate windowFig. 1MALDI-TOF mass spectra of tryptic digests of β-casein: (a) direct analysis and after enriched by (b) GF-TiO₂–GO and (c) TiO₂ (# dephosphorylated fragment).The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Correction: Preparation of glycerol monostearate from glycerol carbonate and stearic acid

Correction for ‘Preparation of glycerol monostearate from glycerol carbonate and stearic acid’ by Li Han et al., RSC Adv., 2016, 6, 34137–34145.

The authors regret that Fig. 6 in the original article was incorrect. The caption referred to ¹³C NMR spectra, whereas the figure itself was an expanded version of the ¹H NMR shown in Fig. 5. The correct version of Fig. 6 is presented below.Open in a separate windowFig. 6 ¹³C NMR spectra of GMS.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

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.     

Correction: Solution-processed Cu2XSnS4 (X = Fe,Co, Ni) photo-electrochemical and thin film solar cells on vertically grown ZnO nanorod arrays

Correction for ‘Solution-processed Cu₂XSnS₄ (X = Fe, Co, Ni) photo-electrochemical and thin film solar cells on vertically grown ZnO nanorod arrays’ by Anima Ghosh et al., RSC Adv., 2016, 6, 115204–115212.

The authors regret that there were two errors in the original article. In the “Experimental details” section on page 115205, “1 M sodium sulfide at 70–80 °C for 24 h” should have read “0.5 M sodium sulfide at 70–80 °C for 24 h”. Additionally, Fig. 3 parts (b)–(d) were mistakenly reproduced from the authors’ previous publication (ref. 33 in the original article). The correct Fig. 3 is presented below.Open in a separate windowFig. 3(a and b) FESEM images of ZnO nanorod arrays, ZnS sensitized ZnO nanorods; (c and d) cross-sectional images of ZnO nanorod arrays and ZnS sensitized ZnO nanorods. The inset in panel (a) shows ZnO nanorod arrays and the inset in panel (b) shows a magnified view.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Correction: High-detectivity perovskite-based photodetector using a Zr-doped TiOx cathode interlayer

Correction for ‘High-detectivity perovskite-based photodetector using a Zr-doped TiO_x cathode interlayer’ by C. H. Ji et al., RSC Adv., 2018, 8, 8302–8309.

The authors regret that the names of the authors are shown incorrectly in the original article. The corrected author list is as shown above.In addition, the authors regret that an incorrect version of Fig. 4b was included in the original article. The correct version of Fig. 4 is as shown below.Open in a separate windowFig. 4Dynamic characteristics of photocurrent response times using a laser diode at a light intensity of 650 μW cm⁻² at 525 nm. (a) Photocurrent response time under −0.1 V at a pulsed frequency of 1 MHz. (b) Cut-off frequency for the perovskite photodetector under −0.1 V.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Correction: Improving the inhibitory effect of CXCR4 peptide antagonist in tumor metastasis with an acetylated PAMAM dendrimer

Correction for ‘Improving the inhibitory effect of CXCR4 peptide antagonist in tumor metastasis with an acetylated PAMAM dendrimer’ by Changliang Liu et al., RSC Adv., 2018, 8, 39948–39956.

The authors regret that the term “CXCL12” was incorrectly displayed as “CXCR12” in Scheme 1 and Fig. 6(a)–(c) in the original article. The correct versions of Scheme 1 and Fig. 6(a)–(c) are presented below.Open in a separate windowScheme 1Schematic illustration of the preparation of the P_AC80–E5 complex and the process of anti-tumor metastasis of the E5 peptide in the presence of P_AC80.Open in a separate windowFig. 6(a–c) The inhibitory effect of E5 and P_AC80–E5 on: (a) MCF-7; (b) MDA-MB-231; and (c) 4T1 cells detected by transwell assay. The CXCL12 supplemented sample without E5 or P_AC80–E5 was set as 100% as the control. Error bars represent the standard deviation (n = 3).The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.