Tióis de importância biológica - eletroanálise em diferentes superfícies eletródicas e utilização de polímeros molecularmente impressos magnéticos para separação e avaliação de glutationa

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Publication Date	2018-04-06
Authors	Ana Caroline Ferreira Santos

Abstract

Biologically relevant thiols (biothiols), the most important systemic and\nintracellular endogenous antioxidants, play essential roles in the protection against\noxidative damage, cause of several diseases. They include proteins with reduced\ncysteine residues and low-molecular weight (LMW) sulfur compounds. As the result\nof environmental, biochemical, clinical, and pharmacological importance of the thiols\nand disulfides, an accurate determination has gained significant attention within the\nanalytical community. Electrochemical detection offers advantages in terms of\nanalytical methods. The present work aims to develop electroanalytical strategies for\ndetermination of several biothiols, together with a selective approach based on\nmolecular imprinted polymer for the separation and quantification of one of the most\nimportant biothiols, reduced glutathione (GSH). A simple and sensitive\nelectrochemical method for the determination of N-acetyl- cysteine (NAC) and\nreduced glutathione (GSH), on glassy carbon electrode (GCE), using cyclic (CV) and\ndifferential pulse (DPV) voltammetries, was developed, based on the chemical\nreactivity between sulfides and disulfides, especially the lipoic acid (LipS 2 ). The\nresults indicate that lipoic acid (LipS 2 ) can facilitate the electrochemical oxidation of\nthiolates, in a neutral pH, with a substantial increase in the anodic current, for the\noxidation of NAC, GSH, cysteine (Cys) and homocysteine (HCys). LipS 2 plays an\nimportant role as a redox mediator, in solution, being regenerated, at the electrode\nsurface, after oxidation and electron capture from the thiolates. Under optimized\nconditions, by DPV, the analytical parameters for NAC and GSH were obtained in the\nrange of 1 up to 10 μmol L -1 and 1 up to 60 μmol L -1 , respectively. The quantification\nwas performed with high sensitivity, reproducibility and submicro detection limit\n(LOD) of 0.27 and 0.67 μmol L -1 for NAC and GSH, respectively. The standard\naddition method was successfully applied to the determination of NAC and GSH, in\nartificial saliva and human urine samples, with excellent recovery results. The\nsensitivity of the method was also evaluated using a boron doped diamond electrode\n(BDDE) for the determination of NAC. Several analytical parameters were obtained\nfor NAC, in the interval of 1 up to 100 μmol L -1 and nanomolar LOD of 93 nmol L -1 .\nThe method was successfully applied to the quantification of NAC in pharmaceutical\npreparations (capsules, syrup and suspension), without matrix effects. The present\nstudy shows that the redox reaction between the studied thiolates and LipS 2 , in\nBDDE, is a promising analytical tool, which can be used for quantifying NAC in a\nsimple, rapid, convenient, sensitive and low-cost way, for both unmodified electrodes.\nMagnetic Molecularly Imprinted Polymers (MMIP) are efficient analytical tools with\nhigh potential for detecting and separating analytes in complex matrices. In this work,\nthe analyte used was GSH. Thus, the polymer synthesis for GSH identification was\nperformed by thermopolymerization and photopolymerization, by varying the\nfunctional monomer (allylamine and acrylamide). MNIP was similarly synthesized, in\nthe absence of GSH. MMIP was washed for removal of the imprinted molecule\n(GSH). The technique of analysis for the evaluation of MMIPs and MNIPs was UV/Vis\nspectrophotometry. The synthesized materials were physically characterized, with a\nsignificant difference between MMIPs and MNIPs, indicating that in MMIPs, a specific\nbinding occurs, showing this device to be a promising material for GSH detection and\nseparation.

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