Abstract
Bay-region containing polyaromatic hydrocarbons (PAHs) like Benzo(a)pyrene (BaP), which comprise several strained benzenoid rings, are representative organic compounds for the carcinogenic and mutagenic activities in physiological system. In general, cytochrome c, peroxidase and certain soil-bacteria oxidize these compounds to respective hydroxylated metabolites like BaP-7,8-diol (BaP–2OH), that can interact with DNA, RNA and protein, and in turn makes the cellular system dysfunctional. The structure - activity relationship of these compounds is still unclear and therefore, it is necessary for a new analytical approach to delineate the intricate mechanism behind the oxidation of the PAHs. Herein, we report, a simple electrochemical approach of surface-confined oxidation of BaP on multiwalled carbon nanotube (MWCNT) modified glassy carbon electrode (GCE/MWCNT) in physiological condition (pH 7 phosphate buffer solution). It has been found that MWCNT-surface adsorbed BaP (electro-inactive compound) gets electro-oxidized to highly redox active BaP–2OH compound at high positive potential, 1.2 V vs Ag/AgCl, in which, the water molecule was oxidized to molecular oxygen via hydroxyl radical intermediate. From the collective electrochemical and physicochemical studies using Raman, FTIR, GC-MS and 1,2-dihydroxy redox active probe, cysteine (CySH), it has been observed that the hydroxyl radical species produced on the surface has assisted the BaP oxidation to BaP-7,8-diol product, which is similar to the biocatalyzed oxidation of BaP observed in the physiological system. The BaP-7,8-diol surface confined MWCNT modified GCE showed a well-defined and stable redox peak at an apparent standard electrode potential, Eo’ = 0 V vs Ag/AgCl. The redox process is found to be proton-coupled electron-transfer in nature. As an independent study, selective electrocatalytic oxidation of CySH has been demonstrated as an application.
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