Understanding electrooxidation mechanism of anticancer drugs utilizing ultrafast pump probe spectroscopy

Abstract

In an attempt to gain deeper insight on the charge transfer mechanism of anticancer drugs and their electrochemically oxidized products, steady state absorption, fluorescence and ultrafast time resolved spectroscopy measurements were performed. All selected compounds exhibit the charge transfer fluorescence in methanol solution. Fluorescence intensity of the studied compounds is significantly quenched in 0.1M H2SO4 solution due to the increasing of intramolecular charge transfer. Ultrafast charge transfer (under 100 fs) mechanism is observed between the singlet exited states and charge transfer states. Femtosecond time resolved spectroscopy results indicate that, the charge transfer rates are faster in methanol:0.1M H2SO4 (20:80;v/v) mixture than that of methanol and the lifetime of the charge transfer states increases in methanol as compared to methanol: 0.1 M H2SO4 (20:80;v/v) mixture. It is also found that the lifetime and rates of the charge transfer state can be altered by electrochemically oxidation of the drugs. Our results reveal that, the structure of compounds transforms to form of semiquinone structure in the studied solution medium. Using the combination of electrochemical and ultrafast pump probe spectroscopy measurements, the determination of in vitro electrochemical oxidation mechanisms of the drugs, mimicking in the body, via intramolecular charge transfer can be easily suggested.