中文摘要：

同时考虑亮氨酸可能的水分子络合方式及亮氨酸分子的所有内轴转动，对亮氨酸与1—3个水分子的复合结构Leu-（H2O）n进行了系统寻找．分别用BHandHLYP／6—31＋G^＊[IBHandHLYP／6—311＋＋G^＊＊方法对结构进行了优化和单点能计算．发现亮氨酸水合结构与孤立亮氨酸有着很好的对应关系，且亮氨酸的水合结构可以可靠地通过对亮氨酸的结构直接加水得到,对中性、双电性亮氨酸水合结构的红外计算光谱与溶液中亮氨酸实验光谱进行了比较与分析，发现双电性Leu-（H2O）3的红外光谱与实验符合得最好，表明溶质在气相中与适量的水分子络合便能较好地模拟溶质在溶液中的红外光谱．

英文摘要：

The conformations for leucine （Leu） hydrated with one to three water molecules, Leu-（H2O）n （n=1-3）, were carefully searched by considering the trial structures generated by all possible combinations of rotamers of Leu combined with all likely hydration modes. The structures were optimized at the BHandHLYP/6-31＋G^＊ level and the single point energies were calculated at the BHandHLYP/6-311＋＋G^＊＊ level. Good correspondence between the conformations of Leu-（H2O）n and bare Leu is found, showing that the conformations of Leu-（H2O）n may be efficiently and reliably determined by the hydration of Leu conformers. The simulated IR spectra of canonical and zwitterionic conformers of Leu-（H2O）n are compared with the experimental result of Leu in aqueous solution. The IR spectrum of zwitterionic Leu- （H2O）3 provides the best description of the experiment. The result demonstrates that the IR spectrum of solute in solution may be simulated by the solute hydrated with an adequate number of water molecules in the gas phase.