Photochemical and photophysical properties of dibenzoylmethane derivatives within protein

In the present work, three dibenzoylmethane derivatives in their β-diketo form have been selected to investigate their photophysical and photochemical behavior upon interaction with human serum albumin (HSA). In organic solvents, absorption and phosphorescence emission spectra of the α-bromo derivative of avobenzone (BrAB) were similar to those of the α-methylated and α-propyl analogs (MeAB and PrAB). However, laser flash photolysis experiments revealed a different transient species centered at 350 nm, assigned to the radical obtained from a singlet excited state dehalogenation process. Interestingly, the transient absorption spectrum of BrAB within HSA showed the typical features of the β-diketone triplet excited state. In the case of MeAB and PrAB derivatives, binding to HSA was associated with a significant increase of their triplet lifetimes as compared to acetonitrile. Finally, the Norrish type II process has been considered as a model to evaluate the influence of the protein microenvironment on the photoreactivity. In this context, photodegradation of PrAB in aerated solutions, to give avobenzone (AB), has been monitored by UV spectroscopy. Interestingly, the quantum yields of AB formation were markedly dependent on the reaction medium (1.4 × 10(-2) in acetonitrile and 3.9 × 10(-2) within albumin medium); by contrast, chemical yields of ca. 50% were obtained in both cases.