Influences of several factors on the photolysis of glabridin under UV irradiation

Abstract

Abstract In order to design more stable formulations for glabridin and to assess the degradation of glabridin as a pollutant in the environment, the photodegradation of glabridin by UV irradiation was investigated. The influences of initial concentrations, solvents, pH values, H 2 O 2 , metal ions and UV absorbers on the photolysis of glabridin were all taken into account. It was found that the photodegradation rate constant increased when decreasing the initial glabridin concentrations, and the degradation of glabridin followed pseudo first-order reaction kinetics. Glabridin in pure methanol exhibited the highest stability with lowest rate constant of 0.357 ± 0.054 h −1 , compared to other saturated monohydric alcohols, and degradation seemed to be affected by the polarity of the solvent. From the experiments to test the effect of pH values on the photolysis of glabridin, we found that glabridin was unstable in both acidic and alkaline solutions. In the UV/H 2 O 2 process, the photodegradation increased with increasing the initial H 2 O 2 concentration. Addition of metal ions such as Fe 2+ , Fe 3+ and Cu 2+ to the glabridin solutions also induced faster degradation compared to negative control, and the degradation processes were dependent on the UV irradiation. In order to stabilize glabridin in the UV process, UV absorbers were added to the solutions. The results suggested that cinnamate and phenyl salicylate could protect glabridin against UV irradiation effectively. More interestingly, we demonstrated that photodegradation products of glabridin would be a valuable source for discovering new tyrosinase inhibitors with higher activity and better stability.