Investigation of the physicochemical and biological properties of proline-based surfactants in single and mixed surfactant systems

A series of surfactants derived from l-Proline, the free amine esters, the ester hydrochlorides and the quaternary ammonium compounds with varying chain lengths (C₈–C₁₄) were synthesised. The physicochemical and biological properties were determined in both single and sodium dodecyl sulphate (SDS) mixed systems with a view of enhancing the properties of the individual surfactants as potential ingredients in detergent formulations. The mode of action of the proline surfactants were investigated by their ability to form mixed micelles with the phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC). The presence of a quaternary ammonium moiety and an increase in alkyl chain length were found to enhance the antibacterial activity of the proline QUAT derivatives. The SDS-C₁₄ QUAT mixed system displayed good antibacterial activity with optimum activity at mole fractions α_QUAT: 0.4 and 0.6. The antibacterial activity of the mixed system was found to be governed by the monomers rather than the micelles. The SDS-C₁₄ QUAT mixed system also showed moderate irritancy which makes them potential candidates as detergents.