STRUCTURE AND INTERACTION BETWEEN THE [BMIM][Ala] ALANINE ANION AND THE 1-BUTYL-3-METHYLIMIDAZOLIUM CATION IN ION PAIRS
Z. W. Li1, W. S. Wu1, Z. Y. Du2, X. Y. Hao1
1Zhaoqing University, Zhaoqing 526061, China
2Technical University of Guangdong, Guangzhou 510006, P. R. China
Keywords: amino acid ionic liquids (AAILs), density functional theory (DFT), natural bond orbital (NBO), second order interaction energy
Abstract
The equilibrium geometries and vibrational frequencies of the ionic liquid 1-butyl-3-methylimidazolium cation and the alanine anion [BMIM][Ala] are studied using density functional theory (DFT) at the B3PW91/6-311+G(d,p) leve1. The most stable structures of the anion, the cation, and the ion pairs are obtained and characterized, and the geometry parameters of the ion pairs confirm the presence of a hydrogen bonding interaction between the anion and the cation. Natural bond orbital (NBO) analysis is also performed to analyze the atomic charge distribution and charge transfer in the [BMIM]+ cation and [BMIM][Ala] ionic liquids. The results show that there are the electrostatic interaction and multiple hydrogen bond interactions between the cation and the anion of the ionic liquids, and the stability of the ground state of the ion pairs mostly results from the hydrogen bonding between the lone pairs of O atoms in the anion and H in the imidazole cycle of the cation. There are some changes in microstructures and the charge distribution during the formation of the ion pairs.
|
