Bidirectional role of synthetic musk tonalide as photosensitizer and activator on amino acids: Formation of sensitizer imine at aqueous chemistry interface of skin

Abstract

Personal care products (PCPs) inevitably come into contact with the skin in people’s daily life, potentially causing adverse effects on human health. The adverse effects can be exacerbated under UV irradiation but are rarely studied. In this study, to clearly understand the damage of representative PCPs to human skin and their photochemical transformation behaviors, fragrance tonalide (AHTN) was measured in the presence of amino acids as a basic building block of human tissue. The results showed that amino acids could decelerate the photochemical transformation rate of AHTN, increasing the likelihood of AHNT persisting on the skin surface and the health risk to the human being. Further, the interaction between amino acids and AHTN was investigated. AHTN could play bidirectional roles in damaging amino acids: the photosensitizer and reactive activator. As a photosensitizer, the ¹O₂ generated from the AHTN photosensitization was partly employed to oxidative damage amino acids. Furthermore, by combining experiments with quantum chemical computation, the carbonyl group of the activator AHTN was found to be the active site to activate the N-containing group of amino acids. The activation mechanism was the electron transfer between AHTN and amino acids. Imines formed during the photochemical transformation of AHTN with histidine/glycine were the molecular initiating event for potential skin sensitization. This study reported for the first time that skin photosensitizer formation threatens human health during the photochemical transformation of AHTN.