Conformers influence on UV-absorbance of avobenzone

Abstract

Avobenzone is most commonly used FDA approved chemical UV-A filter in many sunscreen formulations. An important drawback of avobenzone is its photounstability and undergoes chemical transformation upon exposure to UV-radiation/sunlight. Eventhough single bond rotations are implicated in the radiation induced chemical modification of avobenzone, the conformers role of avobenzone on UV absorbance is yet to be addressed. Using the In silico platform working on Density Functional Theory (DFT), the communication evaluates the role of conformers on UV absorbance spectra of enol/keto forms of avobenzone. The results indicate that the conformers of enolic-form of avobenzone have broad range of absorbance from 273-389 nm and the keto-form has relatively narrow range of absorbance from 266-288 nm. The chelated conformers of enolic-avobenzone with intramolecular hydrogen bond are swingy in nature yet possessing strong bond contributing to its broad-spectrum UVA filtering activity. Among the conformers of keto-form of avobenzone, the planar conformer with the torsional angle 180° undergo facile Norrish Type-I cleavage. Mapping of the data with previous experimental results has allowed identifying 3D structures involved in the key steps of photoketonization process of avobenzone. The reported results may help to understand the molecular basis of enol-to-keto photochemical transformation of avobenzone and to develop photostabilizer to endure long-lasting photoprotection to avobenzone.