Hybrid Biosurfactant: Syntheses of Hybrid Corynomycolic Acid and its Monolayer Formation

Abstract

Abstract Corynomycolic acids have two hydrophilic heads (OH and COOH) and two hydrophobic tails on adjacent carbon atoms. In this work, hybrid type corynomycolic acids (syn- and anti-isomers) were synthesized via the following three steps: 1) crossed Claisen condensation of t-butyl tridecanoate with ethyl per fluorooctanoate, 2) reduction of C = O to OH, and 3) conversion of COO-t-Bu to COOH using CF3COOH. Both hydrophilic groups (OH and COOH) of hybrid corynomycolic acid would dissociate to –O– and –COO– at alkaline condition (pH = 12) while they remain unchanged at acidic condition (pH < 3). The effect of hybrid structure on the surfactant properties was investigated by the surface tension and surface pressure-area (π-A) measurements. Hybrid type corynomycolic acid gave smaller cmc and γcmc than dialkyl type one due to fluoroalkyl chain. With respect to the stereochemistry, the anti-isomer attained a smaller γcmc value than the syn-isomer. In π-A measurements, the monolayer of the syn-isomer showed a lower collapsing pressure (∼15 mN m– 1) than that of the anti-isomer.