(25R)-2,3,25,27-Tetrahydrophysalin A dimethanol solvate, C30H42O12, a derivative of 13,14-seco-16,24-cyclosteroid physalin A, crystallizes in the orthorhombic space groupP212121, witha=15.486(5),b=14.794(4), 12.248(6) Å andZ=4. The crystal structure has been solved by direct methods, and refined to an R-value of 0.053 for 2345 observed reflections.1H NMR spectral data of physalin A and its hydrogenated derivatives measured in dimethylsulfoxide-d6 solutions have been elucidated, based on the crystal structure of the tetrahydrophysalin A, enabling the assignment of all the proton signals of physalin A. The-proton of C(11)-methylene has been shown to resonate at remarkably higher field due to anisotropic shielding effect of carbonyl group at C(15). 相似文献
Dendrimer‐based supramolecular hydrogels have gained attention in biomedical fields. While biocompatible dendrimers were used to prepare hydrogels via physical and/or chemical crosslinking, smart functions such as pH and molecular control remain undeveloped. Here, we present polyglycerol dendrimer‐based supramolecular hydrogel formation induced by a specific interaction between the polyglycerol dendrimer and an amino group of glycol chitosan. Gelation was achieved by mixing the two aqueous solutions. Hydrogel formation was controlled by varying the polyglycerol dendrimer generation. The hydrogel showed pH‐dependent swelling; strongly acidic conditions induced degradation via dissociation of the specific interaction. It also showed unique l ‐arginine‐responsive degradation capability due to competitive exchange of the amino groups of glycol chitosan and l ‐arginine. These polyglycerol dendrimer‐based supramolecular characteristics allow multimodal application in smart biomaterials. 相似文献
Supramolecular hydrogels have been prepared on the basis of polymer inclusion complex (PIC) formation between poly(ethylene glycol) (PEG)-modified chitosans and alpha-cyclodextrin (alpha-CD). A series of PEG-modified chitosans were synthesized by coupling reactions between chitosan and monocarboxylated PEG using water-soluble carbodiimide (EDC) as coupling agent. With simple mixing, the resultant supramolecular assembly of the polymers and alpha-CD molecules led to hydrogel formation in aqueous media. The supramolecular structure of the PIC hydrogels was confirmed by differential scanning calorimetry (DSC), X-ray diffraction, and (13)C cross-polarized/magic-angle spinning (CP/MAS) NMR characterization. The PEG side-chains on the chitosan backbones were found to form inclusion complexes (ICs) with alpha-CD molecules, resulting in the formation of channel-type crystalline micro-domains. The IC domains play an important role in holding together hydrated chitosan chains as physical junctions. The gelation property was affected by several factors including the PEG content in the polymers, the solution concentration, the mixing ratio of host and guest molecules, temperature, pH, etc. All the hydrogels in acidic conditions exhibited thermo-reversible gel-sol transitions under appropriate conditions of mixing ratio and PEG content in the mixing process. The transitions were induced by supramolecular association and dissociation. These supramolecular hydrogels were found to have phase-separated structures that consist of hydrophobic crystalline PIC domains, which were formed by the host-guest interaction between alpha-CD and PEG, and hydrated chitosan matrices below the pK(a).The formation of inclusion complexes between alpha-cyclodextrin and PEG-modified chitosan leads to the formation of hydrogels that can undergo thermo-reversible supramolecular dissociation. 相似文献
We have previously prepared a stimuli-responsive inclusion complex between PEG–b-PEI–g-dextran graft copolymer (PEG–PEI–dex) and γ-cyclodextrin (γ-CD) in order to investigate unique inclusion phenomena, double-axle
inclusion. For further study, a γ-CD derivative, mono-6-O-(2-sulfonato-6-naphthyl)-γ-CD (SN-γ-CD) was additionally synthesized for 1H NMR titration study, which is expected to induce the competition of pendant naphthyl group with external polymer guests.
Consequently, 1H NMR titration results of the inclusion complex of PEG–PEI–dex with SN-γ-CD showed stoichiometric changes, temperature-dependence,
and reversibly pH-responsive properties of the inclusion complexes in terms of chemical shift variation. 相似文献
This article is concerned with describing novel structural features of the water vapor coagulated Poly-p-phenylenebenzobisoxazole fiber in comparison with other PBO fibers made with hot liquid water and non-aqueous coagulation. Micro-focus X-ray diffraction was adopted to see the skin-core difference of molecular orientation and crystal size along the fiber-radius direction. Low temperature differential scanning calorimetry (DSC) was performed to elucidate the structural features of never-dried fibers made with the different coagulation techniques. Comparison of micro-focus X-ray diffraction profiles from the different positions on the fiber suggests less anisotropy of preferential orientation for the water vapor coagulated fiber. The fiber made through water vapor coagulation showed a large skin-core difference in molecular orientation with structural inhomogeneity along the fiber axis. 相似文献
A functional polyrotaxane of a PEI-b-PEG-b-PEI copolymer is synthesized in aqueous solution in a one-pot sequence. To obtain a polyrotaxane with PEG-block-selective inclusion complexes, the solution pH of the polypseudorotaxane is lowered to 4.4 in the presence of 9-anthraldehyde (AN), which triggers the expulsion of the alpha-cyclodextrins (alpha-CDs) from the flank PEI chains. Synthetic strategy of a block-selective polyrotaxane between a PEI-b-PEG-b-PEI copolymer and alpha-cyclodextrins. 相似文献
Poly(ethylene glycol) (PEG)‐interlocked hydrogels were prepared by linking the PEG with α‐cyclodextrins (α‐CDs) threaded onto a PEG chain having ester linkages at the terminals (hydrolyzable polyrotaxane). These hydrogels were examined to clarify the effect of ionic strength of phosphate buffers, pH, and the addition of ethanol on erosion time in relation to inclusion states of α‐CDs with the ester linkages. The most characteristic phenomenon of the hydrogel erosion was observed in an ethanol/PBS cosolvent system: the time to reach the complete erosion time was shortened with decreasing water content. NMR analysis revealed that the ester linkages were exposed to the aqueous environment due to the aggregation of α‐CDs. These results suggest that the movement of α‐CDs in the polyrotaxanes from the terminal ester region to the another region gives the ester linkages a chance to interact with water.