摘要
Ab initio calculations were performed using the Gaussian 03 software package to obtain the optimized structure,interaction energy and infrared spectrum of ionic liquids(ILs)containing a tetraalkylphosphonium cation and an amino acid anion.In order to investigate the effect of the presence of nitrogen in the cation,the tetraalkylphosphonium cation was replaced by a tetraalkylammonium cation,while amino acids were retained as anions in the ionic liquid.The amino acids studied here included glycine,alanine,serine,lysine,and glutamine.Optimized structures of several ILs in the gas phase were determined at the levels of Hartree-Fock(HF/6-3+G(d))and 1density functional theory(B3LYP/6-31++G(d,p)).At high-level estimations,MP2/6-31+G(d)and MP2/6-31++G(d,p),the interaction energies between the cations and anions of the ILs were determined.In order to investigate the effect of alkyl-chain length on interaction energy,the alkyl groups were varied from methyl to ethyl and propyl in the tetraalkylphosphonium functional groups.This procedure revealed that there is a considerably stronger interaction between the alkylphosphonium cations and amino acids than between alkylammonium cations and amino acids.Vibrational spectroscopy of ILs shows that a significant-OH vibration peak occurs at 4124 cmt in serine-containing ILs,and a prominent C=O vending peak occurs at 1626 cm^-1 in amino acids.
