多两性构象理论
Theory of polyzwitterion conformations
摘要：
用变分法研究了两性离子分子在水溶液中的构象特征。解析关系推导出一个单一的聚两性离子链的回转半径的链长，静电相互作用强度，添加的盐浓度，偶极矩和两性离子单体的电离度的函数。在没有小离子（抗衡离子和共离子）附近的聚两性离子链，有吸引力的偶极-偶极相互作用被证明是诱导崩溃的聚两性离子链。然而，在小离子的存在下，的回转半径被证明是一个相互作用的静电相互作用和两性离子网站上的反吸附的屏蔽。除了众所周知的电荷-电荷相互作用的Debye-Huckel屏蔽之外，电荷-偶极和偶极-偶极相互作用的屏蔽被发现在确定链的大小中起重要作用。屏蔽电荷偶极和偶极-偶极相互作用势的函数形式。此外，两性离子单体上的抗衡吸附预计是不对称的，这取决于添加的盐和两性离子基团的性质。关于这些分子在水溶液中的溶解度以及经典的“抗氧化”效果（增加在水中的溶解度与添加盐）的定性评论。
英文摘要：
Conformational characteristics of polyzwitterionic molecules in aqueous solutions are investigated using the variational method. Analytical relations are derived for the radius of gyration of a single polyzwitterionic chain as a function of the chain length, electrostatic interaction strength, added salt concentration, dipole moment and degree of ionization of the zwitterionic monomers. In the absence of the small ions (counterions and coions) near the polyzwitterionic chain, attractive dipole-dipole interactions are shown to induce a collapse of the polyzwitterionic chain. However, in the presence of the small ions, the radius of gyration is shown to be an interplay of the screening of the electrostatic interactions and the counterion adsorption on the zwitterionic sites. In addition to the well-known Debye-Huckel screening of the charge-charge interactions, screening of the charge-dipole and dipole-dipole interactions are found to play important roles in determining the size of the chain. Functional forms for the screened charge-dipole and dipole-dipole interaction potentials are presented. Furthermore, counterion adsorption on the zwitterionic monomers is predicted to be asymmetric depending on the nature of the added salt and the zwitterionic groups. Qualitative remarks regarding the solubility of these molecules in aqueous solutions along with the classical "anti-polyelectrolyte" effect (increase in the solubility in water with the addition of salt) are presented.
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