Oxidation of Sanguinarine and Its Dihydro-Derivative at a Pyrolytic Graphite Electrode Using Ex Situ Voltammetry. Study of the Interactions of the Alkaloids with DNA
This study describes the oxidation of sanguinarine (SG) and its metabolite dihydrosanguinarine (DHSG) on the surface of a basal-plane pyrolytic graphite electrode (PGE). Since both alkaloids strongly adsorb onto the surface of pyrolytic graphite, measurements were performed using ex situ voltammetric methods, adsorptive transfer (AdT) cyclic voltammetry (CV) and square-wave voltammetry (SWV). Oxidation peaks of SG (peak A) and DHSG (peak A*) were observed around the potential of + 0.7 V (vs. Ag/AgCl/3 M KCl), depending on the experimental conditions. The voltammetric peaks A and A* are probably related to the oxidation of N-methylphenanthridine nitrogenous heterocycle of SG and oxidation of DHSG back to SG, respectively. The electrochemical results and optimized AdT SWV were subsequently applied to the study of the interactions of SG and DHSG with DNA in vitro. Analysis of the alkaloid/DNA interactions was based on observing heights of oxidation peaks A and A* after incubation of SG and/or DHSG with supercoiled (sc) DNA [pBSK((-))]. Electrochemical study of the interactions was supported and complemented with measurements using gel electrophoresis (Topoisomerase I scDNA relaxation assay) and steady-state and time-resolved fluorescence spectroscopy. The results suggest that SG intercalates into the double-stranded structure of scDNA (the SG/base pair ratio is max. 1/4) while increased binding affinity was observed for quaternary cation (SG(+)). DHSG which, unlike SG(+), does not possess a strictly planar molecular structure, did not show intercalative DNA binding in any of the three methods applied.