MACROMOLECULAR STEREOCHEMISTRY OF POLY(PARA-BIPHENYLMETHYL L-GLUTAMATE) - LINKAGE BETWEEN BIPHENYL TWIST SENSE AND POLYPEPTIDE CONFORMATION AND OBSERVATION OF MICROAGGREGATION-DRIVEN, SUDDEN, TEMPERATURE-DEPENDENT CHIRAL OPTICAL-CHANGES
MACROMOLECULAR STEREOCHEMISTRY OF POLY(PARA-BIPHENYLMETHYL L-GLUTAMATE) - LINKAGE BETWEEN BIPHENYL TWIST SENSE AND POLYPEPTIDE CONFORMATION AND OBSERVATION OF MICROAGGREGATION-DRIVEN, SUDDEN, TEMPERATURE-DEPENDENT CHIRAL OPTICAL-CHANGES
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DOI：
10.1021/ma00221a008
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发表时间：
1990-09-17
期刊：
影响因子：
5.5
通讯作者：
GREEN, MM
中科院分区：
文献类型：
--
作者：
REIDY, MP;GREEN, MM
在预期中，联苯部分的通常相等分布的左旋（M）和右旋（P）扭转义在多肽的侧链中将被主链的螺旋构象扰乱，因此可能揭示侧链构象的特征，我们合成了邻位和对位取代的聚（L-谷氨酸）和聚（L-天冬氨酸）的联苯甲酯。在天冬氨酸系列中，适当的N-羧基氰基生成邻位和对位取代的联苯甲基酯的聚合物。帕拉异构体不溶于适合紫外圆二色性测量的溶剂中，而邻位异构体表明不存在α-螺旋构象。在谷氨酸盐系列中，虽然我们不能从邻位异构体获得结晶N-羧基酸酐，但在帕拉异构体中，我们能够获得高聚合物，其在各种溶剂中均采用α-螺旋构象并显示与联苯发色团相关的强正圆二色谱带。这种手性光学特性在多肽的邻苯二甲酸变性时几乎完全丧失。令人惊奇的是，聚（L-谷氨酸对联苯甲酯）在几种旋光溶剂中的稀溶液，除了氯仿外，在低于0 ℃的温度下，其旋光性质出现突然的、大的、几乎与浓度无关的可逆变化。特性粘度和光散射测量点聚集与此相关的变化，而紫外线，红外线，和excimerfluorescence测量提供没有证据的多肽链或联苯基团之间的关系的显着构象变化。
In the expectation that the normally equally populated left-(M) and right-handed (P) twist senses of a biphenyl moiety would, in the side chain of a polypeptide, be perturbed by the helical conformation of the mainchain and therefore potentially reveal characteristics of theside-chain conformation, we have carried out the syntheses of the ortho-and para-substituted biphenylmethyl esters of poly (L-glutamic acid) and poly (L-aspartic acid). In theaspartate series the appropriate N-carboxyanhydrides yielded polymer for both the ortho-and para-substitutedbiphenylmethyl esters. The para isomer was not soluble in solvents appropriate to ultraviolet circular dichroism measurements while the ortho isomer indicated the absence of the a-helical conformation. In the glutamate series although we could not obtain a crystalline iV-carboxy-anhydride from the ortho isomer, in the para isomer we were able to obtain a high polymer, which, in a variety of solvents, both adopts the a-helical conformation and displays a strong positive circular dichroism band associated with the biphenyl chromophore. This chiral optical characteristic is almost entirely lost on dichlo-roacetic acid denaturation of the polypeptide. As a complete surprise, dilute solutions of poly (p-biphenylmethyl L-glutamate) in several helicogenic solvents, with the notable exception of chloroform, exhibit a sudden, large, almost concentration-independent, reversible change intheir optical activity properties just below 0 C. Intrinsic viscosity and light-scattering measurements point to aggregation associated with this change while ultraviolet, infrared, and excimerfluorescence measurements offer no evidence for significant conformational changes of the polypeptide chain or of the relationships among the biphenyl groups.