Ionic Liquid Based on α-Amino
Acid Anion and N7,N9-Dimethylguaninium Cation ([dMG][AA]): Theoretical
Study on the Structure and Electronic Properties
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Abstract
The interactions between five amino acid based anions
([AA]<sup>−</sup> (AA = Gly, Phe, His, Try, and Tyr)) and N7,N9-dimethylguaninium
cation ([dMG]<sup>+</sup>) have been investigated by the hybrid density
functional theory method B3LYP together with the basis set 6-311++G(d,p).
The calculated interaction energy was found to decrease in magnitude
with increasing side-chain length in the amino acid anion. The interaction
between the [dMG]<sup>+</sup> cation and [AA]<sup>−</sup> anion
in the most stable configurations of ion pairs is a hydrogen bonding
interaction. These hydrogen bonds (H bonds) were analyzed by the quantum
theory of atoms in molecules (QTAIM) and natural bond orbital
(NBO) analysis. Finally, several correlations between electron densities in
bond critical points of hydrogen bonds and interaction energy as well
as vibrational frequencies in the most stable configurations of ion
pairs have been checked