A mechanistic study of the oxidation of natural antioxidants at the oil/water interface using scanning electrochemical microscopy

Abstract Scanning electrochemical microscopy (SECM) was used to study the reaction mechanism of the oxidation of natural antioxidants (ascorbic acid and chlorogenic acid) at oil/water (O/W) interfaces. The apparent first-order rate constants ( k f ) were determined for the electron transfer (ET) between the antioxidant in the W phase and the radical cation of 5,10,15,20-tetraphenylporphirinato zinc(II), which was generated on an ultramicroelectrode immersed in the O phase. For both the antioxidants, the values of k f showed a linear dependence on the square root of the antioxidant concentration in the W phase. The kinetic analysis based on the reaction layer theory suggested a new type of ion transfer (IT) mechanism, in which the ET reaction occurs homogeneously in the O phase (not in the W phase as in the previous IT mechanism).