Theoretical Treatment of Environmental Effects on Spectra and Chemical Reactivity

本研究由美国国家科学基金会理论与计算化学项目资助。反应场模型将用于预测溶剂对大分子体系的结构、反应性和光谱性质的影响。该理论的初步测试将采用半经验分子电子结构方法。随后的测试将使用从头算对小分子系统进行计算。要研究的反应场模型的具体方面包括溶质腔的形状和产生反应场的电子分布的性质。该理论模型将用于计算：(a)染料的溶剂化变色效应，(b)溶剂化对反应速率和平衡的影响，以及(c)从非极性到两性离子到离子的各种溶质的绝对溶剂化能。近年来，在从第一性原理（通过近似求解电子薛定谔方程）理解和预测气相分子的性质方面取得了显著的成功，但在溶解于液体溶液中的分子方面取得的成功要少得多。众所周知，将一个分子（溶质）溶解在溶剂中可以极大地改变它的颜色、其他光谱特性和化学反应性。反应场模型试图描述造成这些观察到的效应的溶质-溶剂力。已经提出了许多这样的反应场模型，但仍然需要进行大量的测试来确定许多数学近似的有效性，如果该模型实际用于大分子（如染料或各种光敏药理学剂），则必须引入这些近似。

This research is supported by the NSF theoretical and computational chemistry program. Reaction field models will be developed for the prediction of solvent effects on structure, reactivity and spectroscopic properties of large molecular systems. Initial tests of the theory will employ semi-empirical molecular electronic structure methods. Subsequent tests will be carried out using ab initio calculations for small molecular systems. Specific aspects of the reaction field model to be studied include the shape of the solute cavity and the nature of the electronic distribution that generates the reaction field. The theoretical model will be applied to the calculation of: (a) solvatochromic effects in dyestuffs, (b) solvation effects on reaction rates and equilibria, and (c) absolute solvation energies for various solutes ranging from nonpolar to zwitterionic to ionic. Remarkable success has been achieved in recent years in understanding and predicting the properties of gas phase molecules from first principles (by approximately solving the electronic Schroedinger equation), but far less success had been achieved for molecules dissolved in liquid solution. It is well known that dissolving a molecule (the solute) in a solvent can dramatically change its color, its other spectroscopic properties, and its chemical reactivity. Reaction field models attempt to describe the solute-solvent forces responsible these observed effects. A number of such reaction field models have been proposed, but considerable testing is still required to determine the validity of the many mathematical approximations which must be introduced if the model is to be of practical use for large molecules such as dyes or various light-sensitive pharmacological agents.