Satoh M, Fujiwara T, Komiyama J
Department of Polymer Science, Tokyo Institute of Technology, Japan.
Biophys Chem. 1995 Feb;53(3):207-12. doi: 10.1016/0301-4622(94)00101-o.
Effects of divalent counterions (Mg2+, Ca2+, Sr2+, Ba2+) on the helix formation of poly(L-glutamic acid) are investigated in aqueous alcohol (MeOH, EtOH, 2PrOH, tBuOH) solutions. To observe helix formation inherent to the divalent counterions, the chlorides were added to a poly(L-glutamate) having an inert monovalent counterion, tetrabutylammonium cation. Marked counterion- and alcohol-specificities were observed for the dependence of helix content, theta, on the alcohol content. The theta values for most Mg2+ and Ca2+ systems decreased with increasing alcohol content in a higher alcohol region, while those for Sr2+ and Ba2+ systems were almost constant. A specific helix stabilization was observed for mixed divalent counterion systems. These results are self-consistently interpreted by taking into account contact ion-pair formation between the counterions and the polymer charges on the coil conformation.
研究了二价抗衡离子（Mg2+、Ca2+、Sr2+、Ba2+）对聚（L-谷氨酸）在水醇（甲醇、乙醇、2-丙醇、叔丁醇）溶液中螺旋形成的影响。为了观察二价抗衡离子固有的螺旋形成，将氯化物添加到具有惰性一价抗衡离子四丁铵阳离子的聚（L-谷氨酸盐）中。观察到螺旋含量θ对醇含量的依赖性存在明显的抗衡离子和醇特异性。在较高醇区域，大多数Mg2+和Ca2+体系的θ值随醇含量增加而降低，而Sr2+和Ba2+体系的θ值几乎恒定。对于混合二价抗衡离子体系，观察到了特定的螺旋稳定作用。通过考虑抗衡离子与线圈构象上聚合物电荷之间形成的接触离子对，对这些结果进行了自洽解释。
