Banca de DEFESA: JOSÉ AILTON MOTA NASCIMENTO

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : JOSÉ AILTON MOTA NASCIMENTO
DATE: 30/08/2024
TIME: 14:00
LOCAL: VIRTUAL
TITLE:

REDOX MECHANISMS AND ANALYTIC APPLICATIONS OF TRYPTOPHAN METABOLITES KYNURENINE AND KYNURENIC ACID 

KEY WORDS:

Biomarkers, Kynurenines, voltammetry, impedance, redox mechanism, glassy carbon electrode, screen-printed carbon electrode.

PAGES: 104
BIG AREA: Ciências Exatas e da Terra
AREA: Química
SUBÁREA: Química Analítica
SPECIALTY: Eletroanalítica
SUMMARY:

Tryptophan (TRP) can be metabolized by two distinct pathways: the serotonin pathway and the kynurenine pathway, where a large part of TRP is consumed by the latter. Studies report that the imbalance between these two pathways is associated with several types of diseases. The kynurenine pathway in which most of the TRP is consumed produces several intermediate metabolites such as kynurenine (KYN) and kynurenic acid (KYNA), that are considered biomarkers of human diseases. Therefore, this work aimed to investigate for the first time in the literature the redox properties of KYN and KYNA in aqueous electrolytes on functionalized carbon electrodes, the glassy carbon electrode (GCE) and the screen-printed carbon electrode (SPCE) pretreated anodically, using electrochemical techniques, cyclic voltammetry (CV), differential pulse voltammetry (DPV), square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS). The redox properties of similar molecules, aniline and tyrosine, were also investigated and compared in relation to the biomarkers investigated here. The results clearly indicated that KYN and KYNA were electroactive molecules and both were oxidized from complex and multistep mechanisms. The oxidation mechanism of KYN was proposed and occurs at the 2- aminobenzoyl group from a main step with the withdrawal of one electron and formation of an intermediate radical cation (KYN+•). KYN+• follows a dimerization and finally polymerization pathway (polyKYN), forming different electroactive products that are strongly adsorbed on the surfaces of carbon electrodes. The electrochemical data also indicated that the adsorbed polyKYN films on carbon electrodes in a strongly acidic medium are conductive and in a physiological medium they are resistive, hindering new subsequent reactions. All redox reactions identified were dependent on an acid-base equilibrium, since they were strongly influenced by the pH of the medium, occurring more easily in alkaline media. The oxidation mechanism of KYNA was also proposed, occurring from a main irreversible step, in the electroactive hydroxyl group, with the removal of one electron and one proton, with the formation of a radical (KYN• ). The radical, due to its high reactivity, followed two reaction routes, with water to form a para-quinone derivative and the polymerization pathway. These pathways were strongly influenced by the pH of the medium, since quinone derivatives were not detected in physiological medium. The voltammetric responses of DP and SW were also explored here for the development of sensitive electroanalytical methods for detection and quantification of these biomarkers. For the development of the proposed methods for quantification of KYN and KYNA, different analytical parameters were explored, such as working concentration range, linearity, detection and quantification limits, selectivity in relation to possible interferents, analytical frequency, accuracy and precision. A method using DPV and GCE was developed for determination of KYN in acidic medium (pH = 0.30), with a working range of 2.00 to 8.62 μmol L-1 (r = 0.997), limit of detection (LOD) of 0.54 μmol L-1 and limit of quantification (LOQ) of 1.81 μmol L-1 . For KYNA, a method was developed using SWV and SPCE, with a working range of 4.65–12.86 μmol L-1 , r = 0.996, LOD of 0.78 μmol L-1 and LOQ of 2.61 μmol L-1 . The spectrometric properties of KYN were also explored here for the development of a sensitive and selective analytical method, based on digital fluorescence imaging (FDIB), for the detection and determination of KYN in biological samples.

COMMITTEE MEMBERS:
Presidente - SEVERINO CARLOS BEZERRA DE OLIVEIRA
Interno - ANDRE FERNANDO LAVORANTE
Interno - MARCILIO MARTINS DE MORAES
Externo à Instituição - WILLIAN TOITO SUAREZ - UFV
Externo à Instituição - José Licarion Pinto Segundo Neto - UERJ