Aggregation studies of n-alkanoyl-N-methyllactitolamine surfactants.

The micellization processes of n-alkanoyl-N-methyllactitolamines (CnMeLA) were studied by means of isothermal titration calorimetry (ITC) and compared with those of decanoyl-N-methyl glucamide (MEGA-10). The critical micelle concentrations (cmc), the enthalpies (deltaH(m)) and the entropies (deltaS(m)0) of micellization as well as the contributions of the head groups to the Gibbs free energies (deltaG(m)0 (hy)) were calculated. The molecular modeling studies including the conformational analysis and calculations of some molecular descriptors related to hydrophilic and hydrophobic interactions were done to elucidate the experimental results at the atomic level. Despite the significantly bigger size of the headgroup of CnMeLA, the value of deltaG(m)0 (hy) for this compound is close to those for the MEGA-n and CnGluc. The introduction of gluco ring to polyoxyethylene chain of MEGA-10 decreases its hydrophobicity to a similar extent as shortening of the alkyl chain by one methylene group. Molecular modeling studies suggest that these effects came from conformational properties of the gluco ring and polyoxyethylene chain, which are different when they constitute CnMeLA headgroup and when they constitute head groups of CnGluc and MEGA-10, respectively.