UV protection and singlet oxygen quenching activity of aloesaponarin I.

The UV protection and singlet oxygen quenching of aloesaponarin I have been studied by means of laser spectroscopy. The excited-state intramolecular proton transfer that provides the UV protection takes place along only one of the molecule's two intramolecular hydrogen bonds, and this can be understood by considering the nodal pattern of the wave function. The functional groups participating in the excited-state intramolecular proton transfer also play important roles in the singlet oxygen quenching. Aloesaponarin I has a quenching rate constant larger than that of vitamin E and has a long duration of action due to its resistance to UV degradation and chemical attacks by singlet oxygen and free radicals.