Antioxidative properties of vitamins C and E in micellar systems and in microemulsions

In this contribution the results of atmospheric oxidation of vitamin C in the SDS and CTAB micellar solutions and vitamins C and E in the microemulsions stabilized by these surfactants are presented. The hydrophilic vitamin C readily dissolves in water and O/W microemulsions as well as easily undergoes the two-electron oxidation reaction under aerobic conditions. It was found that the atmospheric oxidation of vitamin C is accelerated by the SDS up to the CMC and, then, inhibited in the concentrated SDS solutions. Similar behaviour is observed in CTAB micelles. In the SDS microemulsions the rate of atmospheric oxidation of vitamin C increases with the increasing pentanol content. In the microemulsions stabilized by CTAB the initial oxidation rate is lower than that in the pure water and reaches minimum in the bicontinuous systems. When two vitamins C and E are present in the SDS microemulsion system, the antioxidant capability of their mixture increases. For the vitamin C to vitamin E weight ratio 0.13, vitamin C stimulates vitamin E decomposition as long, as it is present in the non-oxidized form. As follows from the analysis of absorption spectra obtained during titration of vitamin C by vitamin E these antioxidants form 1:1 associates in the SDS microemulsions. The association constants can be calculated from the absorption data using the non-linear fitting procedure.