Catechol oxidase mimetic activity of cadmium sulfide nanoparticles for the oxidation of L- 3,4 -dihydroxyphenylalanine

In the present work we have investigated the oxidation of L-3,4 -dihydroxyphenylalanine (L-Dopa) using colloidal cadmium sulfide nanoparticles (CdS NPs) as a photocatalyst. The CdS NPs were synthesized and characterized using UV-visible absorption spectroscopy, transmission electron microscopy (TEM) and powder x-ray diffraction (XRD). It was observed that the CdS NPs oxidized L-Dopa within 30 min of irradiation using a 200 W Hg(Xe) arc lamp. The oxidation product was identified using high performance liquid chromatography (HPLC). The HPLC analyses were carried out on a reverse-phase C18 column under isocratic conditions using methanol/water (10/90) as the mobile phase. The retention time of the product matched with that of dopachrome. The mechanistic studies indicated the participation of hydroxyl radicals ( OH) in the photocatalytic oxidation of L-Dopa. The kinetic analysis was carried out using the Michaelis-Menten equation. The results demonstrated that the as-prepared CdS NPs mimicked the activity of the catechol oxidase enzyme. To the best of our knowledge, this is the first report on the oxidation of L-Dopa using semiconductor NPs.