Research on solubility and bio-solubility of amino acids ionic liquids

Abstract

Herein, the synthesis of l-(+)-α-(positive butyl)-leucine ethyl ester ionic liquids with anions based on bromide (Br−), terafluoroborate (BF4−) and hexafluorophosphate (PF6−) were presented. The structures and purities of these amino acids ionic liquids (AAILs) were characterized by 1H NMR and the determinations of water content. The interaction energies of AAILs-solvents/amino acids and dipole moment of AAILs were obtained through ab initio at MP2/6-311G++(2d, p). The relationships between the solubility of AAILs and common solvents, molecular structure and the interaction energies of AAILs-solvents along with the influences of temperature and molecular structure on the bio-solubility of AAILs were discussed systematically. The results revealed that the solubility of the title AAILs increased firstly and then decreased with decreasing dielectric constant of solvent. With the dipole moment of AAILs and hydrogen bond interaction increasing, the solubility in polar solvents had an increasing trend. With the interaction energies of AAILs-solvents becoming bigger, AAILs can be easily dissolved in the solvents. The dissolution of amino acids in AAILs was largened with temperature increasing. Additional, the ease or difficulty of dissolution for amino acids in AAILs can be predicted by theoretical calculation. This prediction is consistent with the dissolution behavior of AAILs.