Photoprotective properties of natural antioxidant flavonoids: A DFT and TD-DFT study on acridone derivatives

Abstract

Antioxidant and photoprotective properties of two natural acridone derivatives namely Paratrimerin C (1) and Citrusinine-I (2) have been studied by DFT and TD-DFT at the M05-2X/6-311 HG(3df. 3p)//M05-2X/6-31+G(d) level of theory. Three common mechanisms characterized for the antioxidant properties including H-atom transfer (HAT) and proton transfer (PT) towards HOO• /HO• radicals and single electron transfer (SET) were investigated in the gas phase, water and pentyle thanoate. The DFT results revealed that both compounds can efficiently scavenge HOO• and HO• radicals Via HAT mechanism in all media. Particularly, the HAT reactions of 2 with HO• radical in water are the most favored reaction (∆H -37.7 kcal/mol). In addition, the efficient UV-absorption ability of the studied compound was elucidated by TD-DFT. All compounds can absorb UV radiations in the range of 200-335 nm, for which the easiest excitations are at 334-332 nm and the strongest absorptions were found at 234-227 nm, for 1 and 2, respectively. The HOMO to LUMO and HOMO-3 to LUMO (π-π*) transitions are assigned for the corresponding UV-absorption.