Time-Resolved Electron Paramagnetic Resonance Investigation on the Quenching Reaction of Photo-Induced Excited Triplet Vitamin K3 by Antioxidant Vitamin C in Homogeneous and Micelle Solutions

Abstract

The reaction mechanism and dynamics of the quenching of the excited triplet of vitamin by vitamin C was studied in both homogenous ethylene glycol-H2O plus hexadecyltrimethylammonium bromide, aerosol OT, sodium dodecyl sulfate, and Triton X-100 micelle solutions by time-resolved electronic paramagnetic resonance. The photolysis of vitamin K3 in EG-H2O solution led to the chemically induced dynamic electron polarization (CIDEP) of the vitamin K3 neutral radical VK3H• and ethylene glycol ketyl radical, which showed that a hydrogen atom abstraction reaction of with the solvent ethylene glycol occurred. The triplet mechanism was the primary mechanism underlying the generation of CIDEP, suggesting that quickly reacted with ethylene glycol before spin-lattice relaxation. During the photolysis of vitamin K3 and vitamin C in ethylene glycol-H2O solution, abstracted hydrogen atoms not only from the solvent ethylene glycol but also from a vitamin C monoanion. The stronger CIDEP signal of the vitamin C monoanion radical indicated that can be rapidly quenched by vitamin C. In hexadecyltrimethylammonium bromide (aerosol OT, sodium dodecyl sulfate)/ethylene glycol-H2O micelle solutions, lipid-soluble needed to diffuse around the micelle surface to react with the water-soluble vitamin C. The spin-lattice relaxation of the parent resulted in weaker CIDEP of the reaction-generated radicals. Furthermore, the attraction between the positive charge layer of the hexadecyltrimethylammonium bromide micelle and vitamin C monoanion made the quenching reaction of by vitamin C rapid, whereas the repulsion between the negative charge layer of aerosol OT (sodium dodecyl sulfate) micelle and vitamin C monoanion made the quenching reaction slow. For Triton X-100 micelle, the coexistence of vitamin K3 and vitamin C in the same polyethylene glycol shell resulted in the fastest quenching reaction and strong CIDEP of the monoanion radical.