Banca de DEFESA: DIÊGO ULYSSES DE MELO

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
DISCENTE : DIÊGO ULYSSES DE MELO
DATA : 14/11/2024
HORA: 13:30
LOCAL: Sala 312-3
TÍTULO:

Combined Experimental-Theoretical Approach for the Elucidation of Mechanisms in Chemiluminescence: 1,2-Dioxetanone Formation with Luciferin-like Analogs and Intramolecular Electron Transfer during Chemiexcitation with in situ Generated 1,2-Dioxetanes

PÁGINAS: 160
RESUMO:

Chemical processes and reactions are often characterized by the macroscopic changes and effects they produce. Chemiluminescence (CL) is typically described as the cold light emitted from specific exothermic reactions, while bioluminescence (BL) refers to these phenomena occurring within living organisms. By applying scientific tools and methodologies, researchers can provide a molecular interpretation of these processes, describing  mechanistic pathways, transition state structures, and thermodynamic changes, among others. In this work, we first provide a brief introduction to basic concepts in the relationship between light and matter in Chapter 1. We then present our findings on the molecular interpretation of two CL systems, combining experimental and theoretical data. Chapter 2 investigates the CL reaction of eight different 2-(4-hydroxyphenyl)-4,5-dihydrothiazole-4-carboxylate esters in the presence of an organic superbase and oxygen, employing both kinetic and computational analyses. These esters are structural analogs of the luciferin substrate involved in the efficient firefly BL. Kinetic data from CL emission and light absorption assays were analyzed through linear free energy relationships (LFER), yielding a Hammett reaction constant of 𝜌 = +1.62 ± 0.09 and a Brønsted constant of 𝛽𝑙𝑔 = -0.39 ± 0.04. These LFER findings, along with activation parameters derived from Arrhenius plots, suggest that the high-energy intermediate (HEI) 1,2-dioxetanone is generated via a concerted mechanism during the rate-determining step. Additionally, density functional theory (DFT) calculations indicate a late transition state for HEI formation, with the reaction pathway characterized by geometric parameters, Wiberg bond indices from natural bond order analysis, and atomic charges obtained from electrostatic potential evaluations. Chapter 3 then discusses the effect of the position of the -O⁻ group in the chemiexcitation efficiency of three isomeric silylperoxides derived from lophines. The experimentally determined singlet excited state formation quantum yield (Φ_𝑆) of the ortho-O⁻ derivative is 100 and 10 times higher than Φ_𝑆 for the meta- and para- ones. By using DFT and time-dependent DFT calculations to address spin states, intrinsic reaction coordinates, and changes in electrostatic charges, for ground and excited states (singlet and triplet), we propose late electron transfer chemiexcitation (LETC) as a novel CL mechanism to rationalize these Φ_𝑆 values. LETC involves the intramolecular electron transfer from the imidazolyl anion moiety to the biradical species initially generated from the homolytic O-O bond cleavage of the 1,2-dioxetane HEI. When the -O⁻ group of the imidazolyl anion is at the ortho position, a field effect pumps LETC, increasing the generation of singlet states and adequately explaining the observed Φ_𝑆 values. Therefore, our combined experimental-theoretical approach to describe CL systems provides significant molecular insights into the findings presented in this work, advancing the current understanding of CL and BL systems.

MEMBROS DA BANCA:
Presidente - Interno ao Programa - 1939561 - FERNANDO HEERING BARTOLONI
Membro Titular - Examinador(a) Interno ao Programa - 1623774 - KARINA PASSALACQUA MORELLI FRIN
Membro Titular - Examinador(a) Interno ao Programa - 1544403 - MAURICIO DOMINGUES COUTINHO NETO
Membro Titular - Examinador(a) Externo à Instituição - JOSEF WILHELM BAADER - USP
Membro Titular - Examinador(a) Externo à Instituição - ATAUALPA ALBERT CARMO BRAGA - USP
Membro Suplente - Examinador(a) Interno ao Programa - 3323134 - LUIZ DUARTE RAMOS
Membro Suplente - Examinador(a) Externo ao Programa - 2605463 - JOSE ANTONIO SOUZA
Membro Suplente - Examinador(a) Externo à Instituição - CASSIUS VINICIUS STEVANI - USP