pH调控的两性多肽表面活性剂自组装

In this paper, the pH-responsive self-assembly of a zwitterionic peptide surfactant, I3CGK-OH, was studied using a combination of techniques including circular dichroism, transmission electron microscopy, atomic force microscopy, and zeta potential measurements. I3CGK-OH has three pH-responsive groups, which are a carboxyl group, a hydrosulfide group, and a primary amine group. The molecule can bear different charges with changing of pH value. At pH 2.5, 7.0, and 12.0 the molecule is charged as +0.5, 0, and -1.9, respectively. Such a difference in charge affected the self-assembly process as well as the molecular conformation in the assembly. At pH 7.0, I3CGK-OH is nearly zero charged, and low inter-molecular charge repulsion was the case. Hence it could fufill the self-assembly process at relatively lower concentration. The molecule took a compact conformation during assembly and the formed primary fibers gave smaller diameters. These primary fibers were also lower-charged on their surface and they exhibited high propensity for lateral association and formed sheet-like higher-order structures by parallel aligning. While at pH 2.5 and 12.0, I3CGK-OH is relatively higher-charged, and reasonably higher inter-molecular charge repulsion resulted in increased concentration to reach equilibrium of self-assembly. The molecule took relatively extended conformations during assembly and the formed primary fibers gave larger diameters. These fibers were higher-charged on the surface, and they can existed separately or fromed higher-order fibrils through twisting of two or more primary fibers. This study clears the effect of pH on the self-assembly of zwitterionic peptide surfactants, and is helpful in developing methods in controlled fabrication of the self-assembled structures.