Effect of Headgroup Chirality in Nanoassemblies. 2. Thermal Behavior of Vitamin C-Based Surfactants

L-ascorbic and D-isoascorbic acids are epimers and their alkanoyl-esters are surfactant-like in water. These ascorbic acid derivatives retain the same stereogenic configurations of the parent molecules. That circumstance strongly affects their physico-chemical properties, both in the solid and in the dispersed states. The thermal behavior of 6-O-L-ascorbyl-dodecanoate (L-ASC12), of 6-O-D-isoascorbyl-dodecanoate (D-ASC12) and of their mixtures was investigated through DSC, XRD and FTIR experiments. The results indicate that the mixtures of the two epimers produce two eutectics and a 1:1 molecular compound, both in the pure phase and in the coagel state. From the phase diagram data, the activity coefficients of the different species and the main excess thermodynamic functions can be calculated. The results provide insight into the effects of stereochemistry on their intermolecular interactions.