Banca de DEFESA: NATHALIA LOPES DE QUEIROZ

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : NATHALIA LOPES DE QUEIROZ
DATE: 23/02/2023
TIME: 09:00
LOCAL: VIRTUAL
TITLE:

VOLTAMETRIC STUDY OF THE OXIDATION MECHANISM OF THE PROTEIN DENATURATING AGENTS DITHIOBUTYLAMINE AND DITHIOTHREITOL, OF THE ANTINEOPLASTIC ALEMTUZUMAB AND OF THE INHIBITORS 1-METHYLTRIPTOPHANE AND 680C91 AND DEVELOPMENT OF ELECTROANALYTICAL METHODS FOR THEIR QUANTIFICATIONS

KEY WORDS:

Electrochemistry, Glassy Carbon Electrode, Proteins, Amino Acids, Alemtuzumab, Protein Reducing Agents, IDO and DOT Inhibitors.

PAGES: 116
BIG AREA: Ciências Exatas e da Terra
AREA: Química
SUBÁREA: Química Analítica
SPECIALTY: Eletroanalítica
SUMMARY:

A study of the redox and thermodynamic properties of the protein denaturing agents dithiobutylamine (DTBA) and dithiothreitol (DTT), the monoclonal antibody alemtuzumab (ATZ) and the inhibitors 1-methyl-tryptophan (1-mTrp) and 680C91 in aqueous electrolytes, with different pH values, and under different experimental conditions, were performed on the glassy carbon electrode (GCE) and using cyclic voltammetry (CV) and pulse techniques, differential pulse voltammetry (DPV) and square wave voltammetry (SWV).

The voltammetric study demonstrated that DTBA as well as DTT are both susceptible to direct electro-oxidation at GCE. It has been established that the oxidation of DTBA takes place in three subsequent steps, the first two steps occurring on the thiol groups forming a cyclic intermediate. This intermediate is electro-oxidized in the third step at a high potential value, close to the electro-oxidation of water. A DTBA oxidation mechanism has been postulated and proposed. Using DPV and anodically pre-treated GCE, an analytical method was developed to quantify DTBA in aqueous electrolyte with pH = 7, with a limit of detection (LOD) of 0.54 μmol L^-1 and quantification (LOQ) of 1.79 µmol L^-1.

An oxidation mechanism of ATZ has been proposed. The results using the DPV and SWV pulse techniques clearly demonstrated the spontaneous adsorption of ATZ on the hydrophobic surface of the GCE and that it undergoes electro-oxidation on its Tyr and Trp amino acids residues, superficially exposed on the three-dimensional structure of the protein and on the surface of the GCE.

The oxidation of 1-mTrp was associated with an electrochemical-chemical (EC) mechanism: one electron and one proton were removed from C2 to form an intermediate radical, 1-mTrp⋅. This was followed by a two-way reaction producing a 1-mTrp dimer and/or reaction with water to form a hydroxylated product. The Trp oxidation mechanism was also revisited and compared to the proposed 1-mTrp mechanism. The diffusion coefficients of Trp and 1-mTrp were also determined in phosphate buffer electrolyte, pH = 7.0, D_Trp = 8.13 x 10^-5 cm² s^-1 and D_1-mTrp = 4.43 x 10^-5 cm² s^-1. DPV was explored to quantify Trp and 1-mTrp in drug samples. In phosphate buffer (pH = 7.0) in an anodically pretreated GCE for Trp the LOD was 0.04 μmol L⁻¹ and the LOQ 0.12 μmol L^-1; and for 1-mTrp it reached a LOD of 0.33 μmol L⁻¹ and LOQ of 1.12 μmol L⁻¹.

The voltammetric study of the 680C91 inhibitor demonstrated that it undergoes oxidation in aqueous electrolytes in four subsequent steps; the first two with the withdrawal of two electrons and two protons possibly in the indole at the C2' position of the pyrrole ring, while the third and fourth possibly occur in the pyridine ring with the withdrawal of two electrons and two protons.

COMMITTEE MEMBERS:
Presidente - SEVERINO CARLOS BEZERRA DE OLIVEIRA
Interno - JANDYSON MACHADO SANTOS
Interno - MARCILIO MARTINS DE MORAES
Externa à Instituição - KÁTIA MESSIAS BICHINHO - UFPB
Externo à Instituição - VAGNER BEZERRA DOS SANTOS - UFPE