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The conformational behavior of amylose and the formation of helical inclusion complexesof amylose with a substrate, N-ethyl-4-hexadecyloxycarbonyl pyridinium iodide (1) -- asolvent-polarity probe, have been investigated in the DMSO--H_2O mixed-solvent system bymeans of surface tension, viscosity, UV, electrical conductance and ORD measurements. Thedecrease of the volume-fraction of DMSO, Φ_(DMSO) of the mixed-solvent system inducesconformational changes of the amylose from tight helices to loose and extended helicesinterrupted by short disordered regions. Such a transition is accompanied by abrupt changesof the viscosity and ORD curves. The mechanism of interaction between amylose and the substrate 1 also depends on thesolvent composition. When Φ_(DMSO) is larger than 0.70, the interaction of amylose with 1is apparently similar to those cases in which superhelices are formed between a macromo-lecule and some azo dyes; the latter are known to be bound exteriorly around the macro-molecular helices by oriented association. However, when Φ_(DMSO) begins to drop below0.70, the substrate molecules start to be bound in the helical cavities of the host and thussupramolecular inclusion complexes are formed. At Φ_(DMSO)<0.70, ORD shows a new nega-tive Cotton peak at a wavelength which coincides with the λ_(max) of 1 (276 nm). This implicatesinduced asymmetry for the achiral substrate 1 in a chiral microenvironment. Intrinsicdissociation constants (K_(d~*)) for the inclusion complexes can be obtained from the surface ten-sion- substrate concentration (σ-[1]) curves and the largest number of binding sites isfound to be below 30. The K_(d~*) values decrease with decreasing Φ_(DMSO), apparently inagreement with the results from conductance measurements. Presumably, the driving forcefor the transfer of the substrate molecules from the solvent-mixture bulk phase to the non-polar cavities of the host molecules comes from hydrophobic-lipophilic interactions. 相似文献
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疏水-亲脂作用对反应性的影响III:环糊精对碳氟表面活性剂的熵驱动包结以及亲脂作用对形成糖淀粉型包结物的贡献 总被引:3,自引:0,他引:3
用表面张力-浓度曲线法系统地研究了环糊精(CD)和羧甲基糖淀粉钠(Na-CMA)与H(CF2)12CO2K(1),Cl(CF2)nCH2CH2N^+(CH3)3I^-[n=8(3),10(5)]和相应的碳氢表面活性剂(2,4和6)的相互作用.由于几何尺寸的限制,碳氟表面活性剂不能与α-CD形成包结络合物,但3与β-CD形成的包结络合物的稳定性远大于相应的碳氢受物4、3与β-CD的相互作用是熵驱动过程,而C12H25N^+(CH3)3I^-(6)则是焓有利的.与具有"预组织化"内穴的CD不同,糖淀粉的包结是与大分子从线团到螺旋构象变化的协同过程,由于缺乏宿主-受物间的亲脂相互作用,Na-CMA不能与所有的碳氟受物形成包结络合物. 相似文献