Surfactant Synthesis via Lipase Esterification of Methyl alpha-D-Glucopyranoside with Selected Aliphatic Carboxylic Acids

Lipase-catalyzed esterification and properties of synthesized carbohydrate esters were investigated. Methyl alpha-D-glucopyranoside was the acyl group acceptor and different carbon atom chain lengths of aliphatic carboxylic acids (C12, C14 and C16) as the acyl group donors were applied in the esterification. Physico-chemical studies on the synthesized carbohydrate esters were carried out. It was found that melting point for the methyl 6-O-hexadecanoyl-alpha-D-glucopyranoside was the highest consecutively followed by methyl 6-O-tetradecanoyl-alpha-D-glucopyranoside and methyl 6-O-dodecanoyl-alpha-D-glucopyranoside. Liquid crystal properties of the synthesized carbohydrate ester synthesized were evaluated via optical polarized microscopy. It was found that the liquid crystal textures for mono-substituted carbohydrate esters were of the smectic phase. In a quaternary system (carbohydrate ester/n-butanol/n-hexadecane/water), a maximum 34 % of water (by mass) was contained in the monophasic region of methyl 6-O-tetradecanoyl-alpha-D-glucopyranoside and a maximum of 52 % water (by mass) was contained in a monophasic methyl 6-O-dodecanoyl-alpha-D-glucopyranoside. For methyl-6-O-dodecanoyl-alpha-D-glucopyranoside, its concentration at aggregation was 5.2 x 10(-4) mM, with minimum air/water surface tension of 26 mN m(-1). The Gibbs energy of micellization was calculated at -50 kJ mol(-1). The maximum adsorption density of methyl 6-O-dodecanoyl-alpha-D-glucopyranoside was determined at 4 x 10(-6) mol m(-2) while its minimum area per surfactant molecule at the air/water surface was 47 angstrom(2).