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The electrochemical behaviour of novel nicotinic α4β2 subtype receptor partial agonist varenicline (VAR) which is used for smoking cessation, was investigated in Britton-Robinson buffers (pH 2.0-12.0) by cyclic, differential pulse and square wave voltammetry at a hanging mercury drop elctrode. The influence of pH, scan rate, concentration, accumulation potential and time on peak current and potential suggested that in alkaline media the redox process was adsorption controlled. Also, the experimental value of surface coverage, G = 1.03´10-10 mol cm-2, was used to determine the conditions when VAR was fully adsorbed at the electrode surface. Having in mind potential high toxicity of VAR due to the presence of quinoxaline structure, its interaction with DNA was postulated, and studied when both compounds were in the adsorbed state at modified HMDE. Using adsorptive transfer technique, the changes in potential and decrease in normalized peak currents were observed. The estimated value of the ratio of surface-binding constants indicated that the reduced form of VAR interacted with dsDNA more strongly than the oxidized form. Subtle DNA damage under conditions of direct DNA-VAR interaction at room temperature was observed. The proposed type of interaction was an intercalation. This study used simple electroanalytical methodology and showed the potential of DNA/HMDE biosensor for investigation of genotoxic effects.

An extensive electrochemical study of brimonidine at boron doped diamond electrode (BDDE) was done by applying cyclic voltammetry (CV) and square-wave voltammetry (SWV) in sulfuric acid of different concentrations (pH ranged from 0.6 to 1.6), and in BR buffer (pH ranged from 2.0 to 9.0). It was found that the reduction of brimonidine occurred in a one-step quasi-reversible mechanism, involving the transfer of two electrons and two protons. The reduction process took place at the quinoxaline ring and the corresponding mechanism of reduction was confirmed to be the same as for the other quinoxaline derivatives. The nature of the electrode process was found to be diffusion controlled in acid medium, while in a more alkaline medium a certain degree of adsorption was noticed. Based on this study, two sensitive voltammetric methods, differential pulse (DPV) and square wave (SWV) were developed, fully validated and suggested for rapid electroanalytical determination of low concentrations of brimonidine. The linearity was achieved within the concentration range from 2×10−6 M to 3×10−5 M for DPV ( LOD=6.31×10−7 M, LOQ=2.1×10−6 M) and from 5×10−7 M to 1.5×10−5 M for SWV ( LOD=1.28×10−7 M, LOQ=4.28×10−7 M). The methods were applied for brimonidine determination in pharmaceutical dosage form, eye drops. The obtained good recoveries suggested these simple and accurate methods for quality control of brimonidine in dosage form. Due to its high sensitivity, the SWV method could be a good alternative for determination of low concentrations of brimonidine, even in biological samples. [ABSTRACT FROM AUTHOR]