Detailed Electrochemical Probing of a Biologically Active Isoquinoline

Abstract

The detailed electrochemistry of a biologically active isoquinoline, 2-benzoyl-7-methoxy-2,3-dihydroisoquinoline-4(1H)-one (IQN) was carried out in different pH media with the objective of elucidating its redox mechanism. Cyclic voltammetry was used to determine pka, diffusion coefficient and heterogeneous electron transfer rate constant. The involvement of protons in redox mechanism was confirmed from a shift in peak potential as a function of pH. Differential pulse voltammetry was used to verify the number of electrons involved in the redox process. The reversibility of the redox process was decided on the basis of the results obtained from square wave voltammetry. The existence of IQN in keto and enol forms was evidenced by UV-Vis spectroscopy. The redox mechanism proposed on the basis of voltammetric and electronic absorption spectroscopic investigations was supported by theoretical calculations. These mechanistic pathways are expected to present a key in understanding the hidden routes by which isoquinolines exert their biochemical action.Isoquinoline is a structural isomer of quinoline. A number of isoquinoline derivatives bestowed with remarkable biological activities have been identified. Andreas et al. have reported the inhibitory properties of some isoquinolines against gastric acid secretion. 1 Literature survey reveals the cytotoxicity of isoquinolines against cancer cells. Won et al. reported indeno [1,2-c]isoquinoline to have strong potency against tumor cells. 2 The same group further investigated that such compounds exert their cytotoxic effect by inhibiting topoisomerase I. Berberine, a medicinally important isoquinoline derivative was found to have strong antidiarrheal activity 3 and ability of preventing the adherence of E coli to the host cells without producing any harm in the intestinal layer. 4 The role of isoquinoline is not only limited to medicines but have significantly important role in agricultural as well. 2-dodecylisoquinolinium bromide has been reported to have pesticidal and insecticidal activities. 5 Some quaternary isoquinolinium salts are used as disinfectants or micellar catalysts of wide industrial applications. 6 A few isoquinoline derivatives are used as additives in metal plating for improving the brightness of metal surfaces. 5 Isoquinolinium quaternary salts are industrially used as demulsifiers and flocculating agents in petroleum industry. 7-10 Similarly isoquinoline methobisulphate play active role in photographic improvement. 5 Other unique and special uses of some isoquinoline derivatives are their utilization as organic semiconductors 11,12 and catalysts in the ring opening or polymerization reaction of epoxides. 13 Isoquinolines have also been found useful in environmental monitoring activities. One of its derivative, bis(isoquinoline N-oxide) has been identified as fluorosensor with significant sensitivity toward Li +1 , Ca +2 and Mg +2 ions. 14 As most of the isoquinolines applications like their role as semiconductors and catalysts involve electron transfer rea...

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