N-lauroylglutamates with two and four carboxylate head groups: Their interactions with bovine serum albumin

Abstract

N-lauroyl derivatives of amino acids have widely been reported as environmentally benign surfactants. Although N-lauroyl-l-glutamate is reported in the literature, the effect of the two carboxylate groups in it has not been specifically addressed. In this study, we report the interactions of bovine serum albumin (BSA) with N-lauroylglutamate (S1) and an N-lauroyl derivative of a tripeptide of glutamic acid (S2), respectively. The surfactant S1 has two and S2 has four carboxylic acid groups making them different from other N-lauroyl amino acids, which have just one carboxylic acid group. The aim of this study is to understand the role of the number of carboxylate groups present in these amino acid-based anionic surfactants while interacting with biomolecules such as BSA. The critical micelle concentration (CMC) of the surfactants were measured both in the presence and absence of BSA using fluorescence spectroscopy. The fluorescence of BSA was quenched on addition of the surfactants. The mechanisms of fluorescence quenching were established by studying the fluorescence at three different temperatures. CD studies were performed to calculate the temperature at which BSA unfolds completely in the presence and absence of the surfactants. Conformational changes in the secondary structure of BSA were also observed on the addition of S1 and S2. The results of these studies are compared with those previously reported for the interactions between BSA and N-lauroylglycinate. We find that S1 has a lower CMC than S2 and lauroylglycinate. The surfactant S1 stabilized the secondary structure of BSA better at higher temperatures.