Measurement of antiphotooxidative properties of isoquinoline alkaloids using transient thermal lens spectroscopy

The antiphotooxidative properties of boldine and chloride berberine were studied by time-resolved thermal lensing technique. These compounds belong to isoquinoline alkaloids possessing interesting biological activity (e.g. antibacterial, antimalarial, antitumor). Antiphotooxidative properties of the alkaloids were studied by mechanism of energy transference between powerful oxidizing agents such as singlet oxygen. Singlet oxygen was produced by energy transfer from chlorophyll-sensitized photooxidation of oil by exposure of high light intensities like laser. The lifetimes of singlet oxygen in dimethylsulfoxide, methanol and water were determined to confirm the assignment of the singlet molecular oxygen O 2 ( 1 Δ g ) in the experiments. In order to understand the effect of the alkaloids on active oxygen species, we carried out in detail an analysis of the thermal lensing signal. It was shown that the alkaloids can act as quenchers of singlet oxygen. To demonstrate the ability of the alkaloids to act efficient singlet oxygen acceptors, we have measured the fluorescence spectra of the studied alkaloids in the presence and in the absence of singlet oxygen. The antiphotooxidative activity of boldine and chloride berberine can be explained by the ability to quench singlet oxygen.