STRUCTURE-FUNCTION RELATIONSHIP OF ACYL AMINO-ACID SURFACTANTS - SURFACE-ACTIVITY AND ANTIMICROBIAL PROPERTIES

Amino acid surfactants (AAS), having the general structure alpha-amino-(N-acyl)-beta-alkoxypropionate, were synthesized chemically. Surface activity and antimicrobial properties of the AAS were evaluated. Increases in acyl chain length (i.e., C-10-C-14) resulted in a linear reduction in surface tension (i.e., 43-36 mN . m(-1)), as well as dramatic decreases in critical micelle concentrations (cmc) (i.e., 17.9-0.43 mM). Strong correlations existed between the cmc of AAS and their minimal inhibitory concentrations (mic) against Escherichia coli, Pseudomonas aeruginosa, Aspergillus niger, and Saccharomyces cerevisiae. Sensitivity of the microorganisms to the various AAS followed the order Staphylococcus aureus > A. niger = S. cerevisiae > E. coli > P. aeruginosa. In comparison with methyl p-hydroxybenzoate, AAS (MN14) showed 2-8, 64, and 4-8 times the activity against Gram-negative bacteria, Gram-positive bacteria, and fungi, respectively. Surface adsorption and/or bifunctional binding to the cell membrane may account for AAS action on microorganisms.