Hydrogen-Deuterium Isotope Effects and Chiral Solvation in Polymer Solutions

1.稀溶液中氘取代光活性聚（异氰酸己基酯）s的螺旋构象稀溶液中测量了氘取代在己基侧链α -碳或β -碳上的聚（异氰酸己基酯）s的旋光度作为分子量和温度的函数。结果与Lifson等人的统计热力学理论相吻合，其中假定多异氰酸酯链中的每个单体具有三种状态中的一种，即左旋螺旋、右旋螺旋和螺旋反转。通过拟合，估计单体左、右手螺旋的自由能差DELTAG_h约为几cal/mol，而螺旋反转的自由能大于3000 cal/mol。前者的值表明氢氘同位素对单体构象的影响很小。然而，后者的值表明了螺旋反转发生的困难。这个困难积累了小的DELTAG_…More h，从而在链中提供了很大比例的左旋和右旋螺旋单体。多异氰酸酯在液晶溶液中的螺旋构象光非活性聚（正己基异氰酸酯）以外消旋混合物的形式存在，其浓溶液形成向列相。当向列相溶液中加入一些具有光学活性的低摩尔质量物质或由一些具有光学活性和不具有光学活性的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。这一转变表明，由于与旋光性物质的手性相互作用积累，在旋光性链中出现了左旋和右旋螺旋态的不平衡。虽然上述共聚物在稀溶液中的旋光度与单体组成有关，但诱导胆甾结构的节距与此无关。这种独立性可以通过在液晶溶液中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