Hydrolase Models of Bis-Quaternary Ammonium Salts

Abstract

In this study, amphiphiles possessing two equivalent ammonium groups substituted with one methyl and two dodecyls, and a connecting chain were synthesized; the connecting chain consisting of such hydrophilic group that hydroxyl group and ether linkage were introduced on and into the alkanediyl chain. This paper reports the structural effects of a segment connecting two quaternary ammonium salts on the recognition of amino acids in the hydrolysis of amino acid esters using bis-quaternary ammonium salts as catalysts. The hydrophilic nature of the connecting chain was found to have effect on substrate recognition. A connecting chain with high HLB (Hydrophile-Lipophile Balance) increased the hydrolyzing rate of a hydrophilic substrate but decreased that of a hydrophobic substrate. From the relationship between the rate constant k2 and Michaelis constant Km in the hydrolysis of amino acid esters, clearly shows that the uptake process of substrate is a rate-determining step, that is, a substrate is recognized by connecting chain in the uptake step. The connecting chain may thus be considered to form a pocket capable of discerning the hydrophilic nature of a substrate.