水合甘氨酸体系水桥式质子迁移的理论研究

Theoretical Studies on the Proton Transfer through Water Bridges in Hydrated Glycine Cluster

水分子与甘氨酸作用会导致甘氨酸羧基上的质子迁移到氨基上,质子可以通过水分子链进行迁移.采用密度泛函理论的B3LYP/6-31++g**方法研究了水分子链的逐渐增长(1～5个水分子)对质子迁移的影响,发现水分子数少于5时,质子迁移一步完成;水分子数为5时,质子迁移经由一个中间体,需两步完成;水分子链的增长使质子迁移反应的自由能改变值越来越低,但是反应的能垒越来越高,即在热力学上有利于质子迁移反应,在动力学上不利于质子迁移反应.

Density function theory（DFT） at the level of B3LYP/6-31＋＋g＊＊ was employed to theoreti-cally investigate the intramolecular proton transfer through water bridge chain from carboxyl to amino in glycine cluster.The number of water molecules plays an important role in the proton transfer through water bridge chain.When the number of water molecules in water bridge chain is less than 5,the proton transfer through water bridge chain will complete cooperatively in one step,otherwise the proton transfer will com-plete in two steps via an intermediate.With the increase of water molecule chain increasing the activation energy but reducing the free energy of the reaction,so,the increase of water molecule chain is not in favor of the proton transfer dynamically,but is in favor of proton transfer thermally.