Multiple-responsive supramolecular vesicle based on azobenzene–cyclodextrin host–guest interaction

Multiple-responsive supramolecular vesicles have been successfully fabricated by the complexation between β-cyclodextrin (β-CD) and a pH/photo dual-responsive amphiphile 4-(4-(hexyloxy)phenylazo)benzoate sodium (HPB) with azobenzene and carboxylate groups. When mixing β-CD with HPB to reach a host/guest molar ratio of 1 : 1, the azobenzene group of HPB could be spontaneously included by β-CD molecules. Then, the formed inclusion complexes (HPB@β-CD) could self-assemble into vesicles, which was driven by the hydrophobic interaction of the alkyl chain of HPB and the hydrogen bonds between neighboring β-CDs. The reversible assembly/disassembly of the vesicles could be simply regulated under UV or visible light irradiation. The reversible phase transformation between vesicles and microbelts could also be realized by adjusting the pH values of the sample. Adding both competitive guest molecules (1-adamantane carboxylic acid sodium (ADA)) and α-amylase would result in the phase transformation from vesicles to micelles. Moreover, the vesicles would be destroyed when β-CD was continuously added until the ratio of host/guest reached 2 : 1. Such an interesting quintuple-responsive vesicle system reported here not only has potential applications in various fields such as controlled release or drug delivery, but also provides a reference for the design and construction of multiple responsive systems.

A quintuple-responsive vesicle system was successfully fabricated by simply mixing HPB with an equal amount of β-CD.     

Functionalization and metathesis polymerization induced self-assembly of an alternating copolymer into giant vesicles

A facile fabrication of spherical vesicles and micelles by acyclic diene metathesis (ADMET) polymerization and alternative metathesis polymerization (ALTMET) was investigated. We utilize fluorine (FL) and perylene diimide-based (PDI) α,ω-dienes and α,ω-diacrylates to provide a series of homopolymers and alternating copolymers. When using α,ω-dienes as model monomers, TEM measurement indicates that the aromatic FL and PDI building block induced polymers to generate medium-sized (30–50 nm and 90–120 nm, respectively) micelles and vesicles. It was amazing that alternating copolymers derived from PDI α,ω-dienes and FL α,ω-diacrylates spontaneously form giant vesicles with sizes in the range of 0.7 μm to 2.5 μm. The controlled self-assembly of the organic polymer mediated by ADMET and ALTMET techniques avoided extremely annoying post treatment. Therefore, this work establishes a new, versatile synthetic strategy to create nanoparticles having tunable morphologies with potential application as molecular payload delivery vehicles.

Fluorine (FL) and perylene diimide-based (PDI) α,ω-dienes and α,ω-diacrylates were used to synthesise a series of homopolymers and alternating copolymers and provide spherical vesicles and micelles by metathesis polymerization.     

Binding model-tuned room-temperature phosphorescence of the bromo-naphthol derivatives based on cyclodextrins

Herein, bromo-naphthol derivatives were synthesized to investigate the influence on their phosphorescence emission efficiency resulting from different binding models with cyclodextrins. And the results indicated that α-cyclodextrin could result in the highest phosphorescence emission efficiency, due to the tight encapsulation of the bromo-naphthol motif into the cavity.

Bromo-naphthol derivatives were synthesized to form host–guest complexation with cyclodextrins with different cavity sizes for the investigation of binding model-mediated room-temperature phosphorescence efficiency.

Organic room-temperature phosphorescence (RTP) materials have received widespread attention in the past decades owing to their potential application in anticounterfeiting,¹ biological imaging,^2,3 and optoelectronic materials.⁴ However, the relatively low intersystem crossing efficiency from singlet state to the triplet state and quenching of the triplet state by external oxygen and water traditionally make it difficult to obtain the RTP materials.^5–8 Therefore, to realize the RTP materials, much effort should be devoted on the enhancement of the intersystem crossing efficiency and shielding from the oxygen and water in the environment. Along with this line, variant methods have been developed, such as polymer matrix,^9–11 crystallization,^12,13 H-aggregation,¹⁴ and noncovalent interactions,^15–17 especially the host-guest interaction,^18–20 which could provide a relatively enclosed environment to stabilize the excited state of the organic molecules and shield them from the external substance. Even though there are many outstanding systems constructed by cucurbituril (CB)^21,22 and cyclodextrin (CD),^23,24 little research has been conducted to investigate the influence resulting from their binding model.CD, as a kind of macrocyclic molecule, has been widely investigated in the fabrication of functional materials.²⁵ Moreover, due to the hydrophobic cavities in this kind of macrocyclic molecule, the phosphors could be shielded from the external environment, and many RTP systems have been successfully constructed.^26–28 However, there are three kinds of CDs with different cavity sizes, which exhibit different binding affinities to the guest molecules. To the best of our knowledge, little research has been conducted to exploit the effects caused by their binding models on the RTP materials. Herein, two bromo-naphthol derivatives (4C and 6C) were synthesized to form host–guest complexation with α-CD, β-CD, and γ-CD (Scheme 1). Due to the different cavity size of these three host molecules, their binding models with bromo-naphthol derivatives were different, resulting in the different RTP properties. The α-CD could partially encapsulate the bromo-substituent motif, resulting in the highest phosphorescence quantum yield, as well as the longest phosphorescence lifetime. This research on tuning the RTP properties of phosphors by the binding models could provide a general guidance in the design of highly efficient RTP materials.Open in a separate windowScheme 1Schematic illustration of cyclodextrin-mediated RTP.The guest molecules of 4C and 6C were successfully synthesized according to synthesis route provided in the ESI^† (Scheme S1 and S2, ESI^†). Firstly, their host–guest properties with cyclodextrins were investigated by the ¹H NMR spectroscopy. As shown in Fig. 1, the protons H_1-6 of the aromatic groups in 4C exhibited obvious shift after the addition of cyclodextrins. Interestingly, different change of the chemical-shift was observed upon the addition of α-CD, β-CD, and γ-CD. The protons showed downfield-shift in the presence of α-CD and β-CD, and the broaden effect could be observed in the presence of α-CD, which might result from the relatively small size of α-CD, leading to the tight encapsulation of 4C into its cavity. And the protons exhibited the upfield-shift upon the addition of γ-CD, which might be caused by the π⋯π stacking interaction in the formed ternary host-guest complex. Moreover, 2D NOESY spectroscopy was employed to further investigate the binding models between 4C and cyclodextrins. As shown in Fig. S8^† in the ESI,^† the corresponding peaks assigned H_1-3 on 4C and H_c on the α-CD were obviously observed, indicating partial aromatic ring was encapsulated into the cavity of α-CD. And the signals between H_1-6 on 4C and H_c and H_e on the β-CD could be observed, indicating the aromatic ring was totally encapsulated into the cavity of β-CD (Fig. S9, ESI^†). However, the observed signals assigned to H_2,3,6 on 4C and C_c on γ-CD indicated the inclusion 4C into the cavity of γ-CD (Fig. S10, ESI^†), and the signals between H₂ and H₄ indicated the π⋯π stacking interaction between the aromatic rings. These results were consistent with the previous conclusions. Also similar phenomena could be observed in the systems of the compound 6C and cyclodextrins with different cavity sizes (Fig. S7, ESI^†). And the 2D NOESY spectra of 6C⊂α-CD, 6C⊂β-CD, and 6C⊂γ-CD also provided the same binding models between 6C and different cyclodextrins with cavity size.Open in a separate windowFig. 1 ¹H NMR (400 MHz, D₂O, 298 K) spectra of 4C (a) after adding 1.0 equivalent α-CD (b), β-CD (c), and γ-CD (d). ([4C] = [α-CD] = [β-CD] = [γ-CD] = 2 mM).Following, the binding stoichiometries between the 4C and cyclodextrins were measured by Job''s plot method using ¹H NMR spectroscopy. As shown in Fig. S14 in the ESI,^† it could be concluded the 1 : 1 binding ratio was determined between 4C and α-CD. Moreover, the binding stoichiometry between 4C and β-CD or γ-CD was determined to be 1 : 1 or 2 : 1 (Fig. S15 and S16, ESI^†), respectively. To determine the binding constants, titration experiments were carried out in aqueous solution containing constant concentration of 4C (2 mM) and varying concentration of cyclodextrins respectively. And the binding constants were calculated to be (2.3 ± 0.45) × 10³ M⁻¹ for 4C between α-CD (Fig. S17, ESI^†), (2.8 ± 0.84) × 10³ M⁻¹ for 4C between β-CD (Fig. S18, ESI^†), and (2.7 ± 0.39) × 10² M⁻¹ and (3.2 ± 0.72) × 10³ M⁻¹ for 4C between γ-CD (Fig. S19, ESI^†). Also due to the main difference between 4C and 6C was the length of alkyl chain, the binding sites between the 6C and cyclodextrins couldn''t be affected, which was also certificated by the ¹H NMR and 2D NOESY spectra (Fig. S7, S11, S12, and S13, ESI^†) between 6C and CDs (α-CD, β-CD and γ-CD), the binding stoichiometries and constants between 6C and CDs were similar with the above results.From the above results, it could be concluded the compound 4C could form the host–guest complexation with cyclodextrins, and due to the different size of the cavities, the binding models were different, which might result in different photoluminescence properties. Firstly, the UV-vis spectra of 4C in the absence or presence of cyclodextrins were recorded in Fig. 2a, from which the obvious increase in the absorption intensity could be observed, indicating the formation of host–guest complexation could affect its photoluminescence properties. Moreover, the decrease of the absorption intensity at 265 and 272 nm, and the increase in the intensity at 345 nm could be observed in the presence of γ-CD (Fig. S20, ESI^†), indicating the tightly stacking occurred between the aromatic rings of 4C, which was consistent with the previous 2D NOSEY spectroscopy results.Open in a separate windowFig. 2(a) UV-vis spectral changes in the aqueous solution of 4C (1.5 × 10⁻³ mM) upon adding equivalent α-CD and β-CD. (b) Solid state phosphorescence spectral changes of 4C, n_4C:n_α-CD = 1 : 1, n_4C:n_β-CD = 1 : 1 and n_4C:n_γ-CD = 1 : 1 (Ex: 280 nm, 298 K). (c)Pictures of 4C (a and e), n_4C:n_α-CD = 1 : 1 (b and f), n_4C:n_β-CD = 1 : 1 (c and g) and n_4C:n_γ-CD = 1 : 1 (d and h) under ambient light (a–d) and 365 nm lamp (e–h).Following, the host–guest complexation 4C⊂α-CD, 4C⊂β-CD, and 4C⊂γ-CD were successfully prepared through the grinding method.^18,19 Then its photoluminescence spectra were recorded, and presented as Fig. S24 in the ESI.^† From these spectra, the chromophore only emitted the blue fluorescence at 380 nm, which was consistent with the fluorescence spectrum in the aqueous solution (Fig. S21, ESI^†). This result also further certificated by the determination of its luminescence lifetime, from the decay curve, its lifetime was determined to be 0.77 ns. However, the addition of cyclodextrins could result in the appearance of the new emission peaks at 518 nm and 548 nm, and the average lifetimes at both 518 nm and 548 nm remarkably improved, indicating the formation of host–guest complexation could stabilize the triplet of 4C (†). This observation was also consistent with the photographs obtained under the UV light irradiation (365 nm). As shown in Fig. 2c, the solid of 4C emitted the violet luminescence, and the yellow luminescence could be observed from 4C⊂α-CD. However, the yellow luminescence was remarkably reduced in the complexation of 4C⊂β-CD, and 4C⊂γ-CD. This observation was also consistent with the previous results, the addition of α-CD could remarkably improve the phosphorescence intensity. Moreover, their quantum yields of luminescence were further determined. As being presented in

Spontaneous catanionic vesicles formed by the interaction between an anionic β-cyclodextrins derivative and a cationic surfactant

The present work shows the synthesis of a new type of catanionic surfactant, ModCD14–BHD, which involves an anionic amphiphilic cyclodextrin and the cationic benzyl-n-hexadecyldimethylammonium (BHD). It is obtained from the simple association of the cationic surfactant benzyl-n-hexadecyldimethylammonium chloride (BHDC) and β-cyclodextrin (β-CD) monosubstituted with an alkenyl succinate group (Mod-β-CD14). ModCD14–BHD form unilamellar vesicles spontaneously in water, while the individual components (BHDC and Mod-β-CD14) do not. The vesicles were character-ized by dynamic light scattering (DLS), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and ¹H NMR techniques. We suggest that the formation of an inclusion complex between some of the cyclodextrins units and the long hydrocarbon moiety of the cationic surfactant play a crucial role in the vesicles formation. Besides, some or the cavities are available to interact with an external guest. We think that the new surfactant molecule has properties that may lead to important applications in biomedical and pharmaceutical sciences.

Catanionic vesicles containing an anionic β-cyclodextrins derivative and a cationic surfactant.     

Cyclodextrin modified niosomes to encapsulate hydrophilic compounds

Niosomes were prepared from equimolar mixtures of two non-ionic surfactants, Span 80 and Tween 80. The capability of the vesicular systems was studied through the encapsulation of two azo dyes as molecular probes of different hydrophobicity (methyl orange (MO) and methyl yellow (MY)). To improve the efficiency of the niosomes to encapsulate the dyes, we employed an additional modification of the vesicular system, adding β-cyclodextrin (β-CD) or a modified amphiphilic β-CD (Mod-β-CD) to the niosomes. Neither the inclusion of dyes nor the incorporation of β-CD to the niosomes produces considerable modifications in size and morphology of the vesicles. However, in the presence of Mod-β-CD the niosomes became smaller, probably due to the anchoring of the cyclodextrin at the surface of vesicles through the hydrophobic chain, altering the curvature of the outer monolayer and reducing the surface charge of the interphase. The entrapment efficiency (EE) for MY was higher than that for MO in niosomes without cyclodextrin, however, the content of MO in the presence of β-CD increased considerably. Besides, the release of this dye under the same conditions was faster and reached 70% in 24 hours whereas in the absence of the macrocycle, the release was 15%, in the same time. UV-visible spectrophotometry and induced circular dichroism analysis allowed it to be established that MO is complexed with cyclodextrins inside vesicles, whereas MY interacts mainly with the niosome bilayer instead of with CD. Besides, the cavity of cyclodextrins is probably located in the interphase and preferably in the polar region of niosomes.

Incorporation of β-cyclodextrin into niosomes considerably increased the encapsulated amount and the delivery rate of a hydrophilic molecular probe.     

Recovery,reusability and stability studies of beta cyclodextrin used for cholesterol removal from shrimp lipid

Beta cyclodextrin (β-CD) was used for cholesterol removal from shrimp lipid using ethyl acetate and water as solvents. The cholesterol incorporating β-CD complex (β-CD–CL) was collected and β-CD recovery was performed using a β-CD–CL : ethanol mixture (1 : 15 ratio) with the aid of ultrasonication and a water bath at 55 °C for 40 min. Recycled β-CD (R-β-CD) was compared with pure β-CD (P-β-CD) for the reusability of cholesterol removal from shrimp lipid. R-β-CD showed 94% cholesterol removal, while 95% was achieved for P-β-CD. Differential Scanning Calorimetry (DSC) showed a slight decrease in the melting point of R-β-CD. Nevertheless, FTIR and NMR results revealed that functional groups and the proton spectrum of R-β-CD was negligibly altered. Fatty acid contents of treated oil were slightly higher when treated with R-β-CD than those of the lipid subjected to P-β-CD treatment. Reusability of β-CD could be achieved as confirmed by the maintained capacity in cholesterol removal and unaltered structure.

Beta cyclodextrin (β-CD) used for cholesterol removal from shrimp lipid was reused after the cholesterol bound with β-CD was removed. Efficenicy of recycled β-CD was similar to pure β-CD.     

Photo-responsive polymeric micelles and prodrugs: synthesis and characterization

Bio-recognizable and photocleavable amphiphilic glycopolymers and prodrugs containing photodegradable linkers (i.e. 5-hydroxy-2-nitrobenzyl alcohol) as junction points between bio-recognizable hydrophilic glucose (or maltose) and hydrophobic poly(α-azo-ε-caprolactone)-grafted alkyne or drug chains were synthesized by combining ring-opening polymerization, nucleophilic substitution, and “click” post-functionalization with alkynyl-pyrene and 2-nitrobenzyl-functionalized indomethacin (IMC). The block-grafted glycocopolymers could self-assemble into spherical photoresponsive micelles with hydrodynamic sizes of <200 nm. Fluorescence emission measurements indicated the release of Nile red, a hydrophobic dye, encapsulated by the Glyco-ONB-P(αN₃CL-g-alkyne)_n micelles, in response to irradiation caused by micelle disruption. Light-triggered bursts were observed for IMC-loaded or -conjugated micelles during the first 5 h. Following light irradiation, the drug release rate of IMC-conjugated micelles was faster than that of IMC-loaded micelles. Selective lectin binding experiments confirmed that glycosylated Glyco-ONB-P(αN₃CL-g-alkyne)_n could be used in bio-recognition applications. The nano-prodrug with and without UV irradiation was associated with negligible levels of toxicity at concentrations of less than 30 μg mL⁻¹. The confocal microscopy and flow cytometry results indicated that the uptake of doxorubicin (DOX)-loaded micelles with UV irradiation by HeLa cells was faster than without UV irradiation. The DOX-loaded Gluco-ONB-P(αN₃CL-g-PONBIMC)₁₀ micelles effectively inhibited HeLa cells'' proliferation with a half-maximal inhibitory concentration of 8.8 μg mL⁻¹.

Bio-recognizable and photocleavable amphiphilic glycopolymers and prodrugs containing photodegradable linkers as junction points between hydrophilic glycose and hydrophobic poly(α-azo-ε-caprolactone)-grafted alkyne or drug chains were synthesized.     

Efficient photoelectrocatalytic performance of beta-cyclodextrin/graphene composite and effect of Cl− in water: degradation for bromophenol blue as a case study

Photoelectrocatalytic technology has proven to be an efficient way of degrading organic contaminants, including dyes. Graphene (GR) -based catalysts have been frequently used in photoelectrocatalysis, due to their excellent catalytic performances. In this work, the GR/beta-cyclodextrin (GR/β-CD) composite was prepared and used for a widely used triphenylmethane dye (bromophenol blue, BPB) photoelectrocatalytic degradation. The results indicated that the degradation of the prepared GR/β-CD composite for BPB was effective with the combination of external bias voltage and simulated sunlight irradiation. Under optimum conditions, the BPB (10 mg L⁻¹) was completely eliminated by GR/β-CD composite within 120 min. ˙O₂⁻ played a prominent role in the BPB photoelectrocatalytic degradation. The time required for the removal of BPB in water to reach 100% can be reduced to 30 min with the presence of Cl⁻, owing to the generation of ˙Cl. Moreover, the toxicity of the degraded system with Cl⁻, predicted by the QSAR (Quantitative Structure–Activity Relationship) model in ECOSAR (Ecological Structure–Activity Relationships) program, was weaker than that without Cl⁻. The prepared GR/β-CD composite revealed great advantages in photoelectrocatalytic degradation of organic pollutants due to its metal-free, low cost, simplicity, and efficient performance. This work provided new insight into the efficient and safe degradation of organic pollutants in wastewaters.

O₂˙⁻ played a crucial role in the photoelectrocatalytic degradation of BPB by the prepared GR/β-CD. Cl⁻ marginally promoted the degradation of BPB and chlorinated intermediates were generated.     

Photostability and antioxidant activity studies on the inclusion complexes of trans-polydatin with β-cyclodextrin and derivatives

The inclusion complexes of trans-polydatin and three cyclodextrins (CDs), namely β-cyclodextrin (β-CD), methyl-β-cyclodextrin (Me-β-CD) and (2-hydroxy) propyl-β-cyclodextrin (HP-β-CD) were prepared. The effects of the inclusion behavior of trans-polydatin with three kinds of CDs were investigated in both solution and the solid state with the following methods: phase-solubility, X-ray diffraction (XRD), thermogravimetric analysis (TG), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM), proton nuclear magnetic resonance (¹H-NMR) and two-dimensional rotational frame nuclear overhauser effect spectroscopy (2D ROESY). The results indicated that trans-polydatin formed a 1 : 1 stoichiometric inclusion complex with CDs. Meanwhile, the solubility and thermal stability of the inclusion complexes were improved after encapsulating by CDs. Furthermore, the photostability of trans-polydatin was enhanced after forming the inclusion complexes. The antioxidant activities results showed that the antioxidant performance of the inclusion complexes was enhanced in comparison to the native trans-polydatin. Therefore, it can be a potentially promising way to promote its drug bioavailability or phytochemical preparations.

The inclusion complexes of trans-polydatin and three cyclodextrins (CDs), namely β-cyclodextrin (β-CD), methyl-β-cyclodextrin (Me-β-CD) and (2-hydroxy) propyl-β-cyclodextrin (HP-β-CD) were prepared.     

Efficient modification of PAMAM G1 dendrimer surface with β-cyclodextrin units by CuAAC: impact on the water solubility and cytotoxicity

The toxicity of the poly(amidoamine) dendrimers (PAMAM) caused by the peripheral amino groups has been a limitation for their use as drug carriers in clinical applications. In this work, we completely modified the periphery of PAMAM dendrimer generation 1 (PAMAM G1) with β-cyclodextrin (β-CD) units through the Cu(i)-catalyzed azide–alkyne cycloaddition (CuAAC) to obtain the PAMAM G1-β-CD dendrimer with high yield. The PAMAM G1-β-CD was characterized by ¹H- and ¹³C-NMR and mass spectrometry studies. Moreover, the PAMAM G1-β-CD dendrimer showed remarkably higher water solubility than native β-CD. Finally, we studied the toxicity of PAMAM G1-β-CD dendrimer in four different cell lines, human breast cancer cells (MCF-7 and MDA-MB-231), human cervical adenocarcinoma cancer cells (HeLa) and pig kidney epithelial cells (LLC-PK1). The PAMAM G1-β-CD dendrimer did not present any cytotoxicity in cell lines tested which shows the potentiality of this new class of dendrimers.

The toxicity of the poly(amidoamine) dendrimers (PAMAM) caused by the peripheral amino groups has been a limitation for their use as drug carriers in clinical applications.     

A green sorbent for CO2 capture: α-cyclodextrin-based carbonate in DMSO solution

Cyclodextrin (α-CD)/KOH pellet dissolved in DMSO was utilized to capture CO₂. KOH has a dual function of enhancing the nucleophilicity of the hydroxyl groups on the α-CD rims and acting as a desiccant. ¹³C NMR spectroscopy provided evidence for the chemisorption of CO₂ through the formation of organic carbonate (RO-CO₂⁻·K⁺). This was supported by the spectral changes obtained using ex situ ATR-FTIR spectroscopy upon bubbling CO₂. Activation of α-CD with NaH or bubbling with ¹³CO₂ verified that chemisorption occurred solely via RO-CO₂⁻·K⁺ rather than inorganic bicarbonate. Volumetric gas uptake demonstrated a sorption capacity of 21.3 wt% (4.84 mmol g⁻¹). To the best of our knowledge, this is the highest chemisorption value reported to date for CD-based sorbents. DFT calculations of the Gibbs free energies indicated that the formation of RO-CO₂⁻·K⁺ was more favoured at the primary carbinol rather than its secondary counterpart.

α-Cyclodextrin dissolved in DMSO is a potential sorbent for CO₂ capture through the exclusive formation of ionic organic carbonate.     

Exploring inclusion complex of an anti-cancer drug (6-MP) with β-cyclodextrin and its binding with CT-DNA for innovative applications in anti-bacterial activity and photostability optimized by computational study

The co-evaporation approach was used to examine the host–guest interaction and to explore the cytotoxic and antibacterial properties of an important anti-cancer medication, 6-mercaptopurine monohydrate (6-MP) with β-cyclodextrin (β-CD). The UV-Vis investigation confirmed the inclusion complex''s (IC) 1 : 1 stoichiometry and was also utilized to oversee the viability of this inclusion process. FTIR, NMR, and XRD, among other spectrometric techniques, revealed the mechanism of molecular interactions between β-CD and 6-MP which was further hypothesized by DFT to verify tentative outcomes. TGA and DSC studies revealed that 6-MP''s thermal stability increased after encapsulation. Because of the protection of drug 6-MP by β-CD, the formed IC was found to have higher photostability. This work also predicts the release behavior of 6-MP in the presence of CT-DNA without any chemical changes. An evaluation of the complex''s antibacterial activity in vitro revealed that it was more effective than pure 6-MP. The in vitro cytotoxic activity against the human kidney cancer cell line (ACHN) was also found to be significant for the IC (IC₅₀ = 4.18 μM) compared to that of pure 6-MP (IC₅₀ = 5.49 μM). These findings suggest that 6-MP incorporation via β-CD may result in 6-MP stability and effective presentation of its solubility, cytotoxic and antibacterial properties.

The complexation of an essential anti-cancer drug called 6-Mercaptopurine monohydrate with β-cyclodextrin was investigated for enhancing bioavailability.     

Preparation of a carboxymethyl β-cyclodextrin polymer and its rapid adsorption performance for basic fuchsin

The presence of dyes in a water system has potential adverse effects on the ecological environment. The conventional cyclodextrin (CD) polymer only has CD cavities as adsorption sites and exhibits slow adsorption for dye removal. In this study, we designed a novel carboxymethyl β-CD polymer (β-CDP-COOH). The structural properties of β-CDP-COOH were characterized as an irregular cross-linked polymer with negative surface charge, and the introduction of carboxymethyl groups greatly enhanced the adsorption ability of the β-CD polymer to basic fuchsin (BF). The maximum removal efficiency of β-CDP-COOH (96%) could be achieved within 1 min, whereas that of conventional β-CD polymer (70%) was achieved after 50 min. The adsorption mechanism revealed that the adsorption behavior of β-CDP-COOH could be effectively fitted with the pseudo-second-order kinetic model and Langmuir isotherm. Both CD cavities and carboxymethyl groups were effective adsorption sites, so β-CDP-COOH had an advantage in adsorption capacity over the conventional β-CD polymer. This study indicated that β-CDP-COOH is a potential highly efficient adsorbent for the removal of cationic dye contaminants.

Introduction of carboxymethyl groups greatly accelerated the adsorption rate of a β-CD polymer, and the removal efficiency reached 96% within 1 minute.     

β-Cyclodextrin functionalized 3D reduced graphene oxide composite-based electrochemical sensor for the sensitive detection of dopamine

A three-dimensional reduced graphene oxide nanomaterial with β-cyclodextrin modified glassy carbon electrode (3D-rGO/β-CD/GCE) was constructed and used to detect the electrochemical behavior of dopamine (DA). The nanocomposite materials were characterized by scanning electron microscopy (SEM), infrared spectrometry (FT-IR), Raman spectrogram and thermogravimetric analysis (TGA), which showed that β-CD was well modified on 3D graphene with a porous structure. The electrochemical properties of different modified electrodes were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), proving the highest electron transfer rate of the 3D-rGO/β-CD modified electrode. The experimental conditions such as scan rate, pH, enrichment time and layer thickness were optimized. Under the best experimental conditions, DA was detected by differential pulse voltammetry (DPV) by 3D-rGO/β-CD/GCE with excellent electrocatalytic ability and satisfactory recognition ability, resulting in a wide linear range of 0.5–100 μM and a low detection limit (LOD) of 0.013 μM. The modified electrode based on 3D-rGO/β-CD nanocomposites is promising in the field of electrochemical sensors due to its high sensitivity and other excellent properties.

A 3D-rGO/β-CD nanocomposite was successfully synthesized and further modified onto the surface of GCE to construct a new biosensor for electrochemically sensing DA.     

Preparation of prolinamide with adamantane for aldol reaction catalysis in brine and separation using a poly(AN-MA-β-CD) nanofibrous film via host–guest interaction

Prolinamides with double-H potential were prepared and employed as organocatalysts in asymmetric aldol reactions. The catalyst with adamantane showed improved catalytic activity, which was further enhanced by using brine as the solvent. A series of aldol reactions in brine at 0 °C provided good yields (up to 98%) with high diastereoselectivities (>99 : 1) and enantioselectivities (>99%). The prepared catalyst was adsorbed by a nanofibrous film of poly(AN-MA-β-CD) via host–guest interaction in the reaction system. The catalyst was separated from the film by applying ultrasound, with a total recovery of 96.2%. The catalyst was reused up to five times without a significant change in diastereoselectivity and enantioselectivity.

Prolinamide with adamantane catalyzed the aldol reaction. The reaction of cyclohexanone with m-nitrobenzaldehyde assessed recyclability of catalyst. After run, the catalyst was adsorbed with nanofibrous of polymer via host–guest interaction.     

Open-tubular capillary electrochromatography with hydroxypropyl-β-cyclodextrin imprinted polymers: hybrid polyhedral oligomeric silsesquioxane as a coating for enantioseparation

A hydroxypropyl-β-cyclodextrin (HP-β-CD) imprinted coating based on polyhedral oligomeric silsesquioxane (POSS) for open tubular electrochromatography was prepared. The mixture of methacryl-POSS (MA0735), HP-β-CD (template), methacrylic acid (MAA, monomer), N,N′-methylenebisacrylamide (MBA, crosslinker) and toluene-dimethyl sulfoxide (porogen) was used to synthesize the chiral selective coating. The influence of synthesis parameters on the imprinting effect and separation performance, including the amount of HP-β-CD, POSS, and MAA, was investigated systemically. The optimum polymerization was prepared by mixing HP-β-CD, MA0735, MAA, and MBA with the molar ratio of 1 : 1.87 : 1.60 : 1.60. Five racemates were separated by the modified capillary columns using aqueous buffer. Column efficiency on the POSS-based MIPs coating column was greater than 22 000 plates/m. MIPs-POSS hybrid coating capillaries had improved resolution (3.36 times) and the greatest resolution was up to 6.15 within 10 min.

A hydroxypropyl-β-cyclodextrin (HP-β-CD) imprinted coating based on polyhedral oligomeric silsesquioxane (POSS) for open tubular electrochromatography was prepared.     

Fullerene–porphyrin hybrid nanoparticles that generate activated oxygen by photoirradiation

The preparation of water-dispersible hybrid nanoparticles comprising fullerene and porphyrin from cyclodextrin complexes is described. In the presence of polyethylene glycol, C₆₀ fullerene and porphyrin were expelled from the cyclodextrin cavity to form fullerene–porphyrin hybrid nanoparticles in water. The fullerene–porphyrin hybrid nanoparticles exhibit improved singlet oxygen generation ability under photoirradiation compared with that of C₆₀ nanoparticles.

Hybrid nanoparticles comprising fullerene and porphyrin are formed via guest exchange reaction of cyclodextrin complexes. The hybrid nanoparticles exhibit singlet oxygen generation ability under photoirradiation.

Water-dispersible colloidal fullerene assemblies, referred to as fullerene nanoparticles (NPs), have recently received increasing attention.^1–3 Fullerene NPs are negatively charged and can be dispersed in water in the absence of any solubilizer. Fullerene NPs demonstrate promise within biological and medical applications, as radical scavengers and photosensitizers for photodynamic therapy. To further extend the applications of fullerene NPs, additional hybridization with desired functional molecules is required. Porphyrin and associated derivatives are highly promising candidates for hybridization with fullerenes to increase photoactivity.⁴ Numerous studies on the complexation of fullerenes with porphyrin molecules using synthetic organic chemistry^5–7 or supramolecular chemistry^8–10 have been reported. Although fullerene NPs have been intensively studied over the last decade, no reliable method to achieve the hybridization of porphyrins with fullerene NPs has been proposed.Poly(ethylene glycol) monomethyl ether (PEG) was recently observed to accelerate the decomposition of fullerene C₆₀–γ-CD complexes in water, which leads to the rapid aggregation of C₆₀ to form water-dispersible C₆₀ NPs.¹¹ In this method, C₆₀–γ-CD complexes can exist as stable isolated molecules in water, enabling the precise size control and step-wise growth of C₆₀ NPs.^12,13 Herein, the preparation of hybrid NPs comprising C₆₀ and hydrophobic porphyrin molecules are reported. C₆₀–γ-CD and porphyrin-trimethyl-β-cyclodextrin (por–TMe-β-CD) complexes are mixed in water in the presence of PEG. Both complexes decompose through the interaction of PEG with the CDs, leading to the formation of C₆₀–porphyrin hybrid NPs (denoted as C₆₀–por NPs). The C₆₀–por NPs are negatively charged and easily disperse in water. Additionally, the ability of C₆₀–por NPs to generate activated oxygen is also evaluated.The C₆₀–γ-CD complex^14,15 and 1–TMe-β-CD complex (Fig. 1)^16–18 were prepared according to a previously described procedure (see the ESI^† for details). The ¹H NMR spectrum of the mixed solution comprising the C₆₀–γ-CD complex and PEG after 1 h incubation at 80 °C shows that the peaks attributed to the C₆₀–γ-CD complexes completely disappeared (Fig. S1^†). Hence, the ¹H NMR data confirm the decomposition of the C₆₀–γ-CD complexes and the formation of water-dispersible C₆₀ NPs, as previously reported.^11–13 The effect of PEG on 1–TMe-β-CD complexes was also investigated by ¹H-NMR as shown in Fig. S2.^† After incubating the mixed solution of 1–TMe-β-CD complex and PEG ([1] = 0.1 mM, [PEG] = 5.0 g L⁻¹) for 1 h at room temperature, peaks attributed to the 1–TMe-β-CD complex were still evident at 4.97 ppm and above 7.7 ppm (Fig. S2(i)^†). Hence, PEG has no influence upon the 1–TMe-β-CD structure at room temperature. Conversely, after incubating for 1 h at 80 °C, a dark purple precipitate formed and the aforementioned ¹H NMR peaks completely disappeared (Fig. S2(ii)^†). In the absence of PEG, the 1–TMe-β-CD complex was stable in water both at room temperature (Fig. S2(iii)^†) and 80 °C (Fig. S2(iv)^†). These results suggest a decomposition route of 1–TMe-β-CD by interaction with PEG at 80 °C, with a concomitant formation of non-dispersible large aggregates.Open in a separate windowFig. 1Chemical structures of porphyrin derivatives used in this study.To obtain hybrid NPs comprising C₆₀ and 1 (C₆₀–1 NPs), PEG (M_w = 2000) was added to an aqueous solution containing C₆₀–γ-CD and 1–TMe-β-CD complexes ([C₆₀] = [1] = 0.1 mM, [PEG] = 5.0 g L⁻¹), which were thereafter incubated at room temperature or 80 °C. The ¹H NMR spectrum of the mixed solution at room temperature shows peaks attributed to γ-CD in the C₆₀–γ-CD complex at 5.03 ppm, TMe-β-CD in the 1–TMe-β-CD complex at 4.97 ppm, and 1 in the 1–TMe-β-CD complex in the region of 7.6–8.5 ppm (Fig. 2a(i)). The data indicate that PEG fails to induce the decomposition of the C₆₀–γ-CD and 1–TMe-β-CD complexes at room temperature. Conversely, after the mixture was heated at 80 °C for 1 h, the peaks attributed to the C₆₀–γ-CD and 1–TMe-β-CD complexes completely disappeared (Fig. 2a(ii)). Hence, C₆₀–γ-CD and 1–TMe-β-CD were decomposed at 80 °C, in the presence of PEG. The solution after being subjected to heat treatment at 80 °C for 1 h, was dark purple in the absence of any precipitate. The hydrodynamic diameter and ζ-potential of the reacted solution were 125 nm (polydispersity index = 0.21) and −20.2 mV, respectively. Water dispersible fullerene NPs typically exhibit negative ζ-potentials, the origin of which still requires elucidating.^19,20 Hence, the formation of water-dispersible nano-composites, C₆₀–1 NPs, is suggested.Open in a separate windowFig. 2(a) ¹H NMR spectra of mixed solutions comprising fullerene C₆₀–γ-cyclodextrin (CD) and 1–trimethyl (TMe)-β-CD complexes ([C₆₀] = [1] = 0.1 mM) (i) before and (ii) after heating at 80 °C for 1 h, in the presence of polyethylene glycol (PEG) (5 g L⁻¹). Open circles: free γ-CD, filled circles: C₆₀–γ-CD, open diamonds: free TMe-β-CD, and filled diamonds: porphyrin–TMe-β-CD (por–TMe-β-CD) complex. The spectra at 7.6–8.5 ppm, are amplified five-fold. (b) Ultraviolet-visible (UV/Vis) absorption spectra of the mixed solution comprising C₆₀–γ-CD and 1–TMe-β-CD complexes ([C₆₀] = [1] = 0.1 mM) with PEG (5 g L⁻¹), before (dashed line) and after (solid line) heating at 80 °C for 1 h. (c) UV/Vis absorption spectra of the mixed solution comprising the C₆₀–γ-CD complex as a function of the 1–TMe-β-CD complex concentration ([C₆₀] = 0.1 mM, [1] = 0–0.2 mM) with PEG (5 g L⁻¹) after heating at 80 °C for 1 h.The por–TMe-β-CD complexes using 2–6 (Fig. 1), were also prepared adopting the same procedure as that for the 1–TMe-β-CD complex. Each por–TMe-β-CD complex solution was mixed with C₆₀–γ-CD and PEG ([C₆₀] = [por] = 0.1 mM, [PEG] = 5.0 g L⁻¹). The ¹H NMR spectrum of each individual mixed solution after being incubated for 1 h at 80 °C, is shown in Fig. S3.^† In the ¹H NMR spectrum of the mixture comprising C₆₀–γ-CD and 2–TMe-β-CD, the peaks attributed to these complexes at 5.03, 4.98, and 7.60–8.50 ppm, completely disappeared after being subjected to incubation for 1 h at 80 °C, without precipitation (Fig. S3a^†). Similar changes in the ¹H NMR spectrum of the mixture comprising C₆₀–γ-CD and 3–TMe-β-CD complexes are observed, as shown in Fig. S3b.^† The data suggest that the 2–TMe-β-CD and 3–TMe-β-CD complexes can be decomposed in a similar manner as the C₆₀–γ-CD complexes, and imply the formation of C₆₀–2 and C₆₀–3 NPs.The ¹H NMR spectra of the mixed solutions comprising C₆₀–γ-CD and 4, 5, or 6–TMe-β-CD complexes failed to show peaks attributed to the C₆₀–γ-CD complex, and peaks associated with the respective por–TMe-β-CD complexes were observed after incubation for 1 h at 80 °C (Fig. S3c–e,^† respectively). Hence, the data suggest that the C₆₀–γ-CD complex decomposed in the presence of PEG, and the 4, 5, and 6–TMe-β-CD complexes were observed to be stable without decomposition at 80 °C. There have been reports suggesting the strong interaction of water-soluble tetraphenyl porphyrins with TMe-β-CDs.^21,22 Polar substituents prompt the penetration of the polarized porphyrin rims into the TMe-β-CD cavity. Porphyrins 4–6 possess polar substituents, which are suggested to enable the formation of stable TMe-β-CD complexes. Furthermore, the size of the β-CD cavity is sufficiently narrow to prevent any strong interaction with PEG.²³ Thus, PEG-induced decomposition of the 4, 5, and 6–TMe-β-CD complexes is not possible.The absorption behavior of C₆₀–1 NPs was investigated using ultraviolet-visible (UV/Vis) spectroscopy. In the UV/Vis spectra, the characteristic peak of solvated C₆₀–γ-CD, at 333 nm shifted to 344 nm after heating at 80 °C for 1 h (Fig. 2b). An additional broad absorption at 400–550 nm is also apparent, which is characteristic of solid-state crystalline C₆₀ and arises from the electronic interactions between adjacent C₆₀ molecules.^24,25 The characteristic peak of the solvated 1–TMe-β-CD complex at 415 nm, shifted to 432 nm, with induced broadening after being subjected to heat treatment at 80 °C for 1 h (Fig. 2b). In the absence of C₆₀–γ-CD complexes, the characteristic absorption peak attributed to the solvated 1–TMe-β-CD complex completely disappeared after heating for 1 h at 80 °C, in the presence of PEG (Fig. S4^†). The data show that 1, when expelled from the TMe-β-CD cavities, forms non-dispersible precipitates in the absence of C₆₀. For 1 dispelled from the TMe-β-CD cavities to be stably dispersed in water, formation of co-aggregates with C₆₀ may be a prerequisite. C₆₀–2 and C₆₀–3 NPs also show similar UV-Vis absorption spectra after being subjected to heating at 80 °C for 1 h, as shown in Fig. S5a and b,^† respectively.To further elucidate the composite formation of C₆₀ and 1, the influence of 1 concentration on C₆₀–1 NP formation was investigated by UV/Vis spectroscopy (Fig. 2c). The intensity of the absorption peak at 432 nm increased as a function of 1 concentration from 0.05 to 0.1 mM. Conversely, the absorption peak at 345 nm, derived from the formation of fullerene NPs, shifted to 338 nm, with increasing concentration of 1. This absorption peak derives from the fullerene nanoparticle size, and as the size decreased (i.e., the NPs became smaller), the peak blue-shifted.¹¹ The results suggest that in the presence of 1, the fullerene interaction might be disturbed, or smaller C₆₀ NPs might form. For C₆₀–1 NPs formulated with 0.2 mM of 1 ([C₆₀] = 0.1 mM, [1] = 0.2 mM), the absorption peak derived from the Soret band of 1 split into two peaks (Fig. 2c). The absorption peak at the shorter wavelength of 415 nm is consistent with that of the 1–TMe-β-CD complex. The absorption peak at the longer wavelength of 431 nm is almost consistent with the absorption peaks in the UV/Vis spectra of C₆₀–1 NPs fabricated with 0.05 and 0.1 mM of 1. The findings indicate that in the sample comprising 0.2 mM of 1, a portion of the 1–TMe-β-CD complexes remained in the complex state after heating for 1 h at 80 °C, in the presence of PEG. The absorption peak at 338 nm, which reflects the state of fullerene NPs, is similar to that of C₆₀–1 NPs fabricated with 0.1 mM of 1. When C₆₀ and 1 form co-aggregated NPs, the ratio of 1 to C₆₀ is thought to be limited to ∼1 : 1.Morphological observations of the hybrid NPs were also undertaken. In the absence of the por–TMe-β-CD complex, C₆₀ NPs possessing fairly monodisperse size distributions were observed (Fig. S6a^†). The average diameter of the individual NPs, determined from the transmission electron microscopy (TEM) images, is 82 nm. C₆₀ NPs have been previously reported to exhibit lattice fringes and diffraction patterns, which suggests that C₆₀ NPs maintain the face-centered cubic (fcc) crystalline structure.¹¹ C₆₀–1 NPs prepared with 0.05 mM C₆₀ and 0.1 mM 1, possessed irregular shapes (Fig. 3a and b, respectively). The average diameter of C₆₀–1 NPs, determined by TEM, is 119 nm (Fig. 3a and S6b^†), demonstrating the larger C₆₀–1 NP size than that of the C₆₀ NPs (82 nm). Increasing the concentration of 1 to 0.1 mM results in the average diameter of C₆₀–1 NPs to increase to 131 nm (Fig. 3b and S6c^†). Similar morphology is observed from the TEM micrographs of C₆₀–2 and C₆₀–3 NPs having average diameters of 109 nm and 144 nm, respectively (Fig. 3c and d, respectively). A lower PEG molecular weight or a lower reaction temperature during C₆₀ NP formation via C₆₀–γ-CD complexes have been reported to induce an increase in the diameter of the C₆₀ NPs.^11,12 Thus, the findings suggest that slower reaction conditions result in less nucleation and a larger NP formation. Porphyrin 3 possesses a methoxy substituent at the para position of the phenyl group and is more polar than 1 or 2. Previous reports have demonstrated that the higher the polarity of the phenyl group, the more stable the complex with TMe-β-CD,^21,22 which indicates that 3–TMe-β-CD is more stable than 1– or 2–TMe-β-CD in water. Thus, the aforementioned decomposition, which results from the interaction with PEG, is slower in 3 with a concomitant increase in the NP size.Open in a separate windowFig. 3Transmission electron microscopy (TEM) images of C₆₀–1 nanoparticles (NPs) prepared with (a) 0.05 and (b) 0.1 mM of the 1–TMe-β-CD complex. TEM images of (c) C₆₀–2 and (d) C₆₀–3 NPs. Scale bars in images (a–d) are 100 nm. (e) High resolution TEM micrograph and selected-area electron diffraction pattern of C₆₀–1 NP. Scale bar is 10 nm. (f) ¹³C NMR spectra of (i) C₆₀ NPs and (ii) C₆₀–1 NPs. (g) Illustration of a C₆₀–por NP. A portion of C₆₀ form crystalline structures, while a portion of the porphyrin molecules interact with C₆₀ at the molecular level.In the high-resolution TEM micrograph (Fig. 3e), the C₆₀–1 NPs only exhibited partial lattice fringes, and hence did not show clear diffraction patterns compared with the C₆₀ NPs (inset in Fig. 3e).¹¹ The findings demonstrate the highly amorphous nature of the C₆₀–1 NPs, and that the C₆₀ crystal structure was only retained in part. ¹³C NMR spectra also provide important information about the structure of the C₆₀–1 NPs. A characteristic C₆₀ cluster signal at 142.4 ppm was detected in both C₆₀ NPs and C₆₀–1 NPs (Fig. 3f).²⁶ The C₆₀–1 NP dispersions also exhibited several small new signals at 141.5, 143.3, and 143.7 ppm, as shown in Fig. 3f(ii). When a fullerene and a porphyrin molecule form a stable complex in solution, the C₆₀ signal shifts depending on the interaction type between the fullerene and the porphyrin molecule.²⁷ Thus, the porphyrin molecule interacted with the aggregate of C₆₀ in C₆₀–1, as illustrated in Fig. 3g.Some porphyrin molecules can form a co-crystal with fullerene C₆₀.²⁸ To form a crystal structure, not only the interaction between molecules but also the relationship with the solvent, such as gradually changing the polarity of the solvent or removing the solvent, are important. In our system, porphyrin molecules that are pseudo-dissolved by TMe-β-CDs are added to water, which is a poor solvent for porphyrins, through the interaction of PEG with TMe-β-CDs. The porphyrin molecule should immediately aggregate and have difficulty forming a crystal structure. Furthermore, because water is also a poor solvent for fullerene C₆₀, C₆₀ also immediately aggregates in water. Thus, it should be extremely difficult for C₆₀ and porphyrin molecules to regularly associate to form a co-crystal structure.The concentration of singlet oxygen molecules (¹O₂, Type-II energy transfer pathway) generated by photoirradiation was measured according to a chemical method using 9,10-anthracenediyl-bis(methylene) dimalonic acid (ABDA)^15,29 as a marker to determine the biological activities of C₆₀ NPs, C₆₀–1 NPs, C₆₀–2 NPs, and C₆₀–3 NPs. The absorption of ABDA at the absorption maximum (380 nm) was monitored as a function of irradiation time ([C₆₀] = 0.1 mM, [por] = 0 or 0.1 mM). Under visible-light irradiation at wavelengths > 620 nm, C₆₀–1 NPs, C₆₀–2 NPs, and C₆₀–3 NPs generated higher levels of ¹O₂ than C₆₀ (Fig. 4a). These results show that the ¹O₂ photoproduction abilities of the C₆₀–por NPs were higher than that of the C₆₀ NPs. There are no significant differences in the ¹O₂ photoproduction abilities of C₆₀–1 NPs, C₆₀–2 NPs, and C₆₀–3 NPs, which suggests that the structure of the porphyrin has an insignificant influence on the ability of the hybrid NPs. The generation of formazan, via the reduction of nitroblue tetrazolium (NBT) by oxygen radicals (O₂˙⁻), is observed as an increase of absorption intensity at 560 nm.³⁰ The reduction of NBT by O₂˙⁻ was scarcely detected in solutions containing C₆₀–1 NPs, C₆₀–2 NPs, and C₆₀–3 NPs under photoirradiation, even though formazan was readily detected in the positive control sample in the presence of reduced nicotinamide adenine dinucleotide (NADH) (Fig. 4b). The results suggest that the reactive oxygen species produced by C₆₀–1 NPs, C₆₀–2 NPs, and C₆₀–3 NPs are predominantly ¹O₂ generated by a Type-II reaction.¹⁸Open in a separate windowFig. 4(a) ¹O₂ generation by NPs. Bleaching of 9,10-anthracenediyl-bis(methylene) dimalonic acid (ABDA) was monitored as a function of the decrease in the absorbance at 380 nm, for C₆₀ NPs (black circles and solid line), C₆₀–1 NPs (red circles and solid line), C₆₀–2 NPs (blue circles and solid line), and C₆₀–3 NPs (green circles and solid line) ([C₆₀] = 15 μM, [por] = 0 or 15 μM, [ABDA] = 25 μM). (b) O₂˙⁻ generation by NPs. The amount of formazan generated by the reduction of nitroblue tetrazolium (NBT) in the presence of O₂˙⁻ was analyzed by the absorbance at 560 nm, of C₆₀–1 NPs (red circles) and C₆₀–2 NPs (blue circles) in the absence (solid lines) and presence (dashed lines) of NADH ([C₆₀] = 15 μM, [por] = 15 μM, [NBT] = 200 μM, [NADH] = 0 or 625 μM). All samples were photoirradiated at >620 nm, in O₂-saturated aqueous solutions.In summary, the preparation of hybrid C₆₀–porphyrin NPs was achieved via a guest exchange reaction comprising porphyrin CD complexes and C₆₀. Seven C₆₀–por NP derivatives with various moieties were prepared. CD porphyrin complexes possessing phenyl and methoxyphenyl moieties were decomposed in the presence of PEG at the same time as C₆₀–γ-CD complexes and formed NPs with C₆₀. Porphyrins containing a hydrophilic moiety form stable complexes with TMe-β-CD and fail to co-aggregate with C₆₀. The C₆₀–por NPs are negatively charged and are easily dispersed and stable in water. The ¹O₂ generation ability of C₆₀–por NPs under photoirradiation (>620 nm) is greater than that of C₆₀ NPs. The findings herein demonstrate a new method to fabricate fullerene–porphyrin composite materials, which provides a route to highly functional fullerene-based materials.     

Enhanced skin adhesive property of electrospun α-cyclodextrin/nonanyl group-modified poly(vinyl alcohol) inclusion complex fiber sheet

Many medical tapes on the market lack sufficient adhesive strength and breathability. Owing to its high biocompatibility, poly(vinyl alcohol) (PVA), a synthetic polymer, has attracted attention in the medical field. In this study, we aimed to prepare an inclusion complex fiber (ICFiber) using α-cyclodextrin (α-CD) and nonanyl-group-modified PVA (C9–PVA) for skin adhesion with improved performance. By changing the concentration of α-CD, six microfiber sheets were fabricated by electrospinning the α-CD/2.3C9–PVA inclusion complex solutions. The bonding strength and energy of the ICFiber sheets on the porcine skin were evaluated. Among the tested ICFiber sheets, the ICFiber-3 (molar ratio of α-CD/C9 groups was 0.612) sheet showed high tensile strength and break strain. The bonding strength and energy of ICFiber-3 sheet on porcine skin were 1.10 ± 0.11 N and 5.07 ± 0.94 J m⁻², respectively, in the presence of water. In addition, ICFiber-3 sheet showed a better water vapor transmission rate (0.95 ± 0.02 mL per day) than commercial tapes. These results demonstrate that the α-CD/2.3C9–PVA ICFiber sheet is a promising adhesive for wearable medical devices.

Inclusion complex fiber (ICFiber) sheets composed of α-cyclodextrin (α-CD) and nonanyl-group-modified poly(vinyl alcohol) (PVA) (C9–PVA) were developed for breathable skin adhesive.     

μ-Oxo-bridged diiron(iii) complexes of tripodal 4N ligands as catalysts for alkane hydroxylation reaction using m-CPBA as an oxidant: substrate vs. self hydroxylation

A series of non-heme μ-oxo-bridged dinuclear iron(iii) complexes of the type [Fe₂(μ-O)(L1–L6)₂Cl₂]Cl₂1–6 have been isolated and their catalytic activity towards oxidative transformation of alkanes into alcohols has been studied using m-choloroperbenzoic acid (m-CPBA) as an oxidant. All the complexes were characterized by CHN, electrochemical, and UV-visible spectroscopic techniques. The molecular structures of 2 and 5 have been determined successfully by single crystal X-ray diffraction analysis and both possesses octahedral coordination geometry and each iron atom is coordinated by four nitrogen atoms of the 4N ligand and a bridging oxygen. The sixth position of each octahedron is coordinated by a chloride ion. The (μ-oxo)diiron(iii) core is linear in 2 (Fe–O–Fe, 180.0°), whereas it is non-linear (Fe–O–Fe, 161°) in 5. All the diiron(iii) complexes show quasi-reversible one electron transfer in the cyclic voltammagram and catalyze the hydroxylation of alkanes like cyclohexane, adamantane with m-CPBA as an oxidant. In acetonitrile solution, adding excess m-CPBA to the diiron(iii) complex 2 without chloride ions leads to intramolecular hydroxylation reaction of the oxidant. Interestingly, 2 catalyzes alkane hydroxylation in the presence of chloride ions, but intramolecular hydroxylation in the absence of chloride ions. The observed selectivity for cyclohexane (A/K, 5–7) and adamantane (3°/2°, 9–18) suggests the involvement of high-valent iron–oxo species rather than freely diffusing radicals in the catalytic reaction. Moreover, 4 oxidizes (A/K, 7) cyclohexane very efficiently up to 513 TON while 5 oxidizes adamantane with good selectivity (3°/2°, 18) using m-CPBA as an oxidant. The electronic effects of ligand donors dictate the efficiency and selectivity of catalytic hydroxylation of alkanes.

The ligand stereoelectronic effect of diiron(iii) complexes determines the efficiency and selectivity of catalytic alkane hydroxylation with m-CPBA as an oxidant.     

A CO2-responsive smart fluid based on supramolecular assembly structures varying reversibly from vesicles to wormlike micelles

CO₂-responsive smart fluids have been widely investigated in the past decade. In this article, we reported a CO₂-responsive smart fluid based on supramolecular assembly structures varying from vesicles to wormlike micelles. Firstly, oleic acid and 3-dimethylaminopropylamine reacted to form a single-chain weak cationic surfactant with a tertiary amine head group, N-[3-(dimethylamino)propyl]oleamide (NDPO). Then, 1,3-dibromopropane was used as the spacer to react with NDPO to form a gemini cationic surfactant, trimethylene α,ω-bis(oleate amide propyl dimethyl ammonium bromide) (GCS). By controlling the feed ratio of 1,3-dibromopropane and NDPO, we found that the mixtures of GCS and NDPO with the molar ratio of 7 : 3 approximately could form vesicles in aqueous solution by supramolecular self-assembly. After bubbling CO₂, the tertiary amine of NDPO was protonated. The packing parameter of the mixed surfactants reduced accordingly, accompanied by the transition of aggregates from vesicles to wormlike micelles. As a result, the zero-shear viscosity of the solution increased by more than four orders in magnitude. When the solid content of GCS/NPDO mixtures was higher than 5 wt% in solution, the sample treated by CO₂ behaved as a gel over a wide frequency range with shear-thinning and self-healing properties. In addition, the sol–gel transition could be repeatedly and reversibly switched by cyclically bubbling CO₂ and N₂. Our effort may provide a new strategy for the design of CO₂-responsive smart fluids, fostering their use in a range of applications such as in enhanced oil recovery.

CO₂-responsive smart fluids have been widely investigated in the past decade. In this article, we reported a CO₂-responsive smart fluid based on supramolecular assembly structures varying from vesicles to wormlike micelles.