Thermodynamics of micellization of nonionic saccharide-based N-acyl-N-alkylaldosylamine and N-acyl-N-alkylamino-1-deoxyalditol surfactants

Eight homologous series of nonionic carbohydrate-derived surfactants in whi ch the alkyl chains are linked through N-acylated amine bonds were synthesi zed, and their critical micelle concentrations (cmc's) and standard enthalp ies of micellization were determined using titration microcalorimetry. Gibb s energies of micellization (Delta(mic)G degrees) were calculated from the critical micelle concentrations. N-Acyl-N-alkylaldosylamines (acyl = acetyl /propionyl, aldosyl = glucosyl/lactosyl) and N-acyl-N-alkylamino-1-deoxyald itols (acyl = acetyl/propionyl, alditol = glucitol/lactitol) with alkyl cha in lengths of 8, 10, and 12 carbon atoms show a 1.0-fold decrease in cmc wh en the length of the chain is increased by two methylene groups. The enthal pograms for the C-8 analogs are more complicated than those for the C-10 an d C-12 analogs. Therefore, the enthalpograms were modeled using a computer- based program which takes account of the nonideal properties of the solutio ns, yielding enthalpies of micelle formation. Increments in the thermodynam ic parameters show satisfactory self-consistency. Each CH2 group Contribute s -2.4 kJ mol(-1) to Delta(mic)H degrees, Delta(mic)G degrees- (CH2) is -3. 0 kJ mol(-1) for each series, and T Delta(mic)S degrees(CH2) is 0.7 kJ mol( -1) at 40 degrees C. Although the change in entropy is the main driving for ce for micellization, the enthalpy of micellization may also contribute sig nificantly to the Gibbs energy of micellization, particularly for longer al kyl chains.