Estudos bioeletroquímicos e eletroanalíticos da diospirina : agente leishmanicida e antitumoral

Abstract

Analysis of molecular constituents based on natural products has acquired an important perspective in view of the renewed interest in the consumption of herbal prescriptions all over the world. Natural quinonoid compounds possess significant pharmacological properties and are responsible for the bioactivities of several plants. They showed several bioactivities, mainly microbicidal, trypanocidal, virucidal and antitumoral, being also inhibitors of repair systems in cells. Among the quinones, diospyrin is relevant; it is extracted from the stem-bark of Diospyros montana Roxb. It is a bisnaphtoquinone that has significant leishmanicidal activity and in the cancer cells inhibition, by interaction with topoisomerases, enzymes responsible for DNA replication. Due to its importance, it is also necessary to develop simple and accurate methods for its detection, beyond analysis of probable DNA interaction through the use of biosensors. This work shows the electrochemical study of diospyrin in mixed (DMSO/acetate buffer solution, 1:1 v/v, pH* 5.4), using Cyclic Voltammetry (CV) and Square Wave Voltammetry (SWV). We also show the development of a diospyrin sensor in nanomolar concentrations using a chemically modified electrode with cobalt tetrasulphonate phthalocyanine (CoTSPc) and poly-L-lysine (PLL). The diospyrin quantification in plant crude extract was performed, using the described CME, through addition and recovery methods by using Differential Pulse Voltammetry (DPV), technique also used for the DNA interaction study. The diospyrin voltammograms have showed two redox wave couples and, in its quantification, the glassy carbon electrode was modified with CoTSPc immobilized in PLL film. A significant increase was observed in the reduction current of diospyrin, in CoTSPc modified electrode, in a potential of 0.16 V, in comparison with GC bare electrode. The high-observed activity with modified GC electrode can be associated with the catalytic effect of CoTSPc over the reduction reaction of the diospyrin. These results allowed the diospyrin detection in nanomolar concentrations after parameters optimization like CoTSPc (0.6 mmol L-1), PLL (0.5 mmol L-1) and acetate buffer concentrations (0.15 mol L-1), the scan rate (0.035 V s-1) and amplitude (0.09 V) studies. The limits of detection and quantification were 0.3 nmol L-1 and 1.0 nmol L-1, respectively. The developed sensor was used for diospyrin determination in a chloroformic crude extract of stem-bark of D. montana Roxb. and the recovery average for the samples was 101.9 (± 3.1)%. It was observed the diospyrin-DNA interaction through the use of a dsDNA biosensor and the observation of diagnostic oxidation peaks in potentials relative to the oxidation of guanine and adenine nucleobases, after incubation with the analyte.