Abstract

During this investigation, NMR spectroscopy was used to study the biosurfactant undecyl-LL-Alanine-Phenylalaninate (und-Ala-Phe). This surfactant has a hydrocarbon tail and an Alanine-Phenylalaninate dipeptide headgroup. Bio-based surfactants like und-Ala-Phe are of interest because they are more biodegradable and biocompatible than many other commercial surfactants. The binding of positively-charged counterions, such as Lysine, Arginine, 1,4-diaminobutane, and 1,6-diaminohexane, to the surface of und-Ala-Phe micelles in solution was studied as a function of pH. Linear correlations with an r-squared value greater than 0.9 were observed between free energy of counterion binding and counterion charge. Molecular modeling experiments showed that the surfactant isomers undecyl-LL-Alanine-Phenylalaninate (und-Ala-Phe) and undecyl-LL-Phenylalanine-Alaninate (und-Phe-Ala) had different shapes, with the und-Ala-Phe surfactant shaped as a cone but the und-Phe-Ala surfactant shaped as a cylinder. This result may explain why und-Ala-Phe is water-soluble while und-Phe-Ala is not. Finally critical micelle concentration (CMC) measurements of und-Ala-Phe in solution with 1,6-diaminohexane counterions will be presented.