Abstract:

We investigated the effect of ascorbic acid (AA) cosolubilized with vitamin E (VE) on reverse hexagonal (HII) mesophase. The HII phase comprises monoolein (GMO)/D-$\alpha$-tocopherol (VE) in a ratio of 90/10 by wt. and 12.5 wt% water. The macrostructural characteristics of this system were detd. by polarized light microscopy and small-angle X-ray scattering measurements. We used differential scanning calorimetry and attenuated total reflectance Fourier transform IR to characterize the microstructure, the vibration of the functional groups, and the location of the AA guest mol. AA was incorporated to the system in two steps: 1-4 wt% AA and 5-6 wt% AA. We compared this system to one contg. tricaprylin as the oil phase, as previously reported. These measurements revealed that AA is localized first in the water rich-core and in the interface, and acts as a chaotropic mol. that decreases the water m.p. When a larger quantity of AA (5-6 wt%) is added, the system is satd., and the AA is located in the inner cylinder and manifested by more moderate distortion. The addn. of AA also causes alteration in the behavior of the GMO hydrocarbon chains and makes them more flexible. Further addn. of AA caused the GMO hydrocarbon chain to be more solvated by the VE hydrocarbon chain and enabled addnl. migration of VE; hence a decrease in the hydrophobic melting temp. occurred (similar to tricaprylin). Increasing the amt. of AA weakened the bonding between the GMO and water and created new bonds between AA and GMO and AA with water. [on SciFinder(R)]