An interesting and surprising rearrangement was observed during the reaction of 4-N-benzyl piperazinone derivatives with Lawesson’s reagent as a thionating agent. Investigation into the possible mechanism responsible for these results is reported herein. 相似文献
The effect of crystal polymorphism on barrier and mechanical properties of PLLA is detailed in this contribution. PLLA films containing different amounts of α and α′ crystal forms were prepared by annealing quenched PLLA at different temperatures. The polymorphic structure of the films was analyzed by X-ray diffraction. Mechanical properties and permeability to water vapor were investigated as a function of degree of crystallinity (wC) and related to crystal polymorphism developed during annealing. The polymorphic structure of PLLA significantly affects mechanical and barrier properties. The α crystal modification provides a better barrier to water vapor and a higher Young’s modulus, compared to films containing the α′ modification, but a lower elongation at break. The varied barrier and mechanical properties were correlated to the different packing of PLLA chains in the two analyzed polymorphs. The conformational disorder of the α′ form makes this structure a mesophase (condis crystal), with remarkable effects on material properties. 相似文献
The amyloid β-peptide (Aβ) and aluminum are found, among other components, in the senile plaques of patients with Alzheimer’s
disease. Aggregated Aβ and aluminum are toxic to neurons but the mechanism of accumulation and toxicity remains poorly understood.
It has been proposed that Aβ and aluminum toxicity results from Aβ– and aluminum–membrane interactions. It was therefore of
interest to study the effect that Aβ and aluminum could have on cell membranes. Thus, the interactions of Aβ(1-40), Aβ(1-42),
and Al(III) with the human erythrocyte membrane and a molecular model of the erythrocyte membrane were examined by electron
microscopy and X-ray diffraction, respectively. The molecular model consisted of bilayers built up of dimyristoylphosphatidylcholine
and dimyristoylphosphatidylethanolamine, phospholipid classes located in the outer and inner monolayers of most cell membranes,
respectively. Aβ(1-40) and Aβ(1-42) in the presence of Al(III) altered the erythrocyte membrane morphology and the structure
of dimyristoylphosphatidylcholine bilayers, effects that were different and stronger than those induced by Aβ and Al(III)
separately. 相似文献
Bio‐derived polysaccharide aerogels are of interest for a broad range of applications. To date, these aerogels have been obtained through the time‐ and solvent‐intensive procedure of hydrogel fomation, solvent exchange, and scCO2 drying, which offers little control over meso/macropore distribution. A simpler and more versatile route is developed, using freeze drying to produce highly mesoporous polysaccharide aerogels with various degrees of macroporosity. The hierarchical pore distribution is controlled by addition of different quantities of t‐butanol (TBA) to hydrogels before drying. Through a systematic study an interesting relationship between the mesoporosity and t‐butanol/water phase diagram is found, linking mesoporosity maxima with eutectic points for all polysaccharides studied (pectin, starch, and alginic acid). Moreover, direct gelation of polysaccharides in aqueous TBA offers additional time savings and the potential for solvent reuse. This finding is a doorway to more accessible polysaccharide aerogels for research and industrial scale production, due to the widespread accessibility of the freeze drying technology and the simplicity of the method.
