Hydrogen-Deuterium Isotope Effects and Chiral Solvation in Polymer Solutions

1.氘取代的旋光聚异氰酸己酯在稀溶液中的螺旋构象研究了氘取代的聚异氰酸己酯在稀溶液中的旋光度随分子量和温度的变化。Lifson et al.的统计热力学理论，其中每个单体在多异氰酸酯链被假定采取三种状态之一，左手螺旋，右手螺旋，和螺旋反转。根据拟合，每个单体的左手螺旋和右手螺旋之间的自由能差DELTAG_h估计为几个cal/mol，而螺旋反转的自由能大于3000 cal/mol。前者的值表明一个非常小的氢氘同位素的单体构象的影响。然而，后一个值证明了螺旋逆转发生的困难。这个难度积累了小DELTAG-- 关于我们 2.多异氰酸酯在液晶溶液中的螺旋构象旋光不活泼的聚异氰酸正己酯（PHIC）以外消旋混合物的形式存在，其浓溶液形成手性相。当向PHIC向列相溶液中加入一些光学活性低摩尔质量物质或由一些光学活性和非光学活性异氰酸酯单体组成的共聚物时，溶液由向列相转变为胆甾相。这种转变表明PHIC链中由于与旋光活性物质的累积手性相互作用而导致左右手螺旋状态的不成比例。尽管上述共聚物在稀溶液中的旋光度依赖于单体组成，但诱导的螺旋结构的螺距不依赖于单体组成。这种独立性可以通过在液晶溶液中从共聚物链中排除螺旋反转状态来解释。少

1.Helical conformation of deuterium-substituted optically-active poly(hexyl isocyanate)s in dilute solutionThe optical rotation of poly(hexyl isocyanate)s with deuterium substituted on the alpha- or beta-carbon in the hexyl side chain was measured in dilute solution as a function of the molecular weight and temperature. The results were fitted by Lifson et al.'s statistical thermodynamic theory, where each monomer in the polyisocyanate chain was assumed to take one of three states, the left-handed helix, right-handed helix, and helix reversal. From the fitting, the free energy difference DELTAG_h between left- and right-handed helices per monomer was estimated to be a few cal/mol, while the free energy of the helix reversal more than 3000 cal/mol. The former value indicates a very small hydrogen-deuterium isotope effect on the monomer conformation. However the latter value demonstrates the difficulty in the occurrence of the helix reversal. This difficulty accumulates the small DELTAG_ … More h to provide a large disproportion of the left- and right-handed helical monomers in the chain.2.Helical conformation of polyisocyanates in liquid crystalline solutionOptically inactive poly(n-hexyl isocyanate)(PHIC) exists as a racemic mixture, and it's concentrated solution forms a nematic phase. When some optically active low-molar-mass substances or copolymers consisting of some optically active and inactive isocyanate monomers were added to the nematic solution of PHIC, the solution transformed from the nematic to cholesteric. This transformation indicates the disproportion of the left- and right-handed helical states in the PHIC chain due to an accumulated chiral interaction with the optically active substances.Although the optical rotation of the above copolymer in dilute solution depended on the monomer composition, the pitch of the induced cholesteric structure did not. This independence can be explained by the exclusion of the helix reversal state from the copolymer chain in the liquid crystalline solution. Less