Extraction of Amino Acid Esters Using a Pillar[6]arene Carboxylic Acid Derivative as a Novel Acidic Macrocyclic Compound

Abstract

Pillararenes are a series of novel macrocyclic compounds discovered in the 2000s. However, solvent extraction based on ion exchange using pillararene derivatives is currently limited. Recently, a pillar[6]arene hexaacetic acid derivative (OctP[6]CH₂COOH) has been developed as a new acidic extractant. In this study, the extraction of amino acid esters using OctP[6]CH₂COOH was investigated. The extraction of tryptophan methyl ester using OctP[6]CH₂COOH was much greater than that using the 6-fold equivalent monomer analog. The extraction of more hydrophobic cationic guests was relatively high. This process is based on a proton exchange reaction. The results of slope analysis and Job plot analysis confirmed the formation of a 1:1 complex between OctP[6]CH₂COOH and the guest cation.