Search

This work presents the results obtained for a thioether derivative of bipyridine, (E,Z)-1-(4′-methyl-[2,2′-bipyridine]-4-yl)-N-(4(methylthio)phenyl)methanimine (4-mbpy-Bz-SMe), and its copper complex [CuII(4-mbpy-Bz-SMe)2]2+. Electronic spectra acquired at 183 K of the cuprous complex [CuI(4-mbpy-Bz-SMe)2]+ generated in situ indicated the formation of the peroxodicopper compound {[CuII(4-mbpy-Bz-SMe)2]2(μ-O22−)}2+. A gold electrode modified with [CuII(4-mbpy-Bz-SMe)2]2+ (Au/[Cu]) was fully characterized by SERS spectroscopy, electrochemistry and impedance spectroscopy thus showing adsorption occurs through the sulfur atom of the 4-mbpy-Bz-SMe moieties. DNA cleavage assays showed the copper complex, in solution and adsorbed on gold, degrades DNA if reducing conditions are maintained, i.e. ascorbic acid (H2AA) in solution or applied potentials more negative than 0.12 V vs. Ag/AgCl (CuI form). The electron paramagnetic resonance (EPR) spectra obtained for the electrolyzed solution (Eapl = −0.2 V, no H2O2) and for the solution containing [CuII(4-mbpy-Bz-SMe)2]2+ and H2O2 showed hydroxyl radical, HO˙, generation had occurred. The cyclic voltammograms obtained with H2AA in solution at Au/[CuII(4-mbpy-Bz-SMe)2]2+ as the working electrode showed a one-electron reaction leading to the ascorbyl radical (HA˙), which was detected by EPR. The current assigned to the electrode oxidation of HA˙ to AA decreased with the addition of catalase, a scavenger of H2O2, meaning peroxide is involved in the mechanism. [ABSTRACT FROM AUTHOR]

The increase in anthropogenic pollution raises serious concerns regarding contamination of water bodies and aquatic species with potential implications on human health. Pharmaceutical compounds are a type of contaminants of emerging concern that are increasingly consumed and, thus, being frequently found in the aquatic environment. In this sense, an electrochemical sensor based on an unmodified and untreated carbon fiber paper (CPS—carbon paper sensor) was simply employed for the analysis of trimethoprim antibiotic in fish samples. First, the analytical conditions were thoroughly optimized in order for the CPS to achieve maximum performance in trimethoprim determination. Therefore, an electrolyte (0.1 M Britton–Robinson buffer) pH of 7 was selected and for square wave voltammetry parameters, optimum values of amplitude, frequency and step potential corresponded to 0.02 V, 50 Hz, and 0.015 V, respectively, whereas the deposition of analyte occurred at +0.7 V for 60 s. In these optimum conditions, the obtained liner range (0.05 to 2 µM), sensitivity (48.8 µA µM−1 cm−2), and LOD (0.065 µM) competes favorably with the commonly used GCE-based sensors or BDD electrodes that employ nanostructuration or are more expensive. The CPS was then applied for trimethoprim determination in fish samples after employing a solid phase extraction procedure based on QuEChERS salts, resulting in recoveries of 105.9 ± 1.8% by the standard addition method. [ABSTRACT FROM AUTHOR]