Banca de QUALIFICAÇÃO: ALANE PRISCILLA AMÉRICO DOS SANTOS

Uma banca de QUALIFICAÇÃO de MESTRADO foi cadastrada pelo programa.
STUDENT : ALANE PRISCILLA AMÉRICO DOS SANTOS
DATE: 06/11/2020
TIME: 08:00
LOCAL: Remotamente pelo google meet
TITLE:

Synthesis of N,N-dialkylated bisbenzimidazole derivatives as potential liquid crystals and computational studies of L-cysteine sensing by the chemodosimeter 2,3-dichloro-6,7-dinitroquinoxaline and fluoride bu the (quercetin)₂Al³⁺ complex

KEY WORDS:

benzimidazole; quinoxaline; quercetin; liquid crystals; sensor; organic synthesis; computational chemistry

PAGES: 80
BIG AREA: Ciências Exatas e da Terra
AREA: Química
SUBÁREA: Química Orgânica
SPECIALTY: Físico-Química Orgânica
SUMMARY:

Heterocycles comprise a variety of compounds classes with particular structural features and applications in many areas. Heterocycles are relevant in technological field as, for example, advanced materials such as liquid crystals, which are popularly known due to their use in the screens of TV and computers. The are also relevant to biological field due to several pharmacological activities, and have been sussccefully applied as signaling unities in chemosensors.  The present dissertation is divided in three parts, each one exploring a differrent class of heterocycle. Firstly, a series of six N,N-dialkyl benzimidazole derivatives is proposed as potential liquid crystals. The methodology is based on the synthesis of methyleno-bisbenzimidazole (MtBBI) from reaction of 1,2-diaminobenzene and diethyl malonate, followed by its direct alkylation (C₈, C₁₀ and C₁₂). These products were obtained in good yeilds and properly characterized by IR and NMR (¹H and ¹³C). At this moment, the oxidation of MtBBI to the respective ketone as weel as its alkylation is aimed. All target molecules will be investigated based on their optical (UV-Vis and fluorescence) as well as termal properties searching for a liquid crystallined behaviour. The second parto f this work aims to provide theoretical support to the results obtainted in our research group for the L-cysteine (Cys) sensing ability of the chemodosimeter 2,3—dichloro-6,7-dinitroquinoxaline (DCDNQX). The method M06-2X with 6-311+G (2d,p) basis set was applied for all calculations. They were evaluated several mechanistic proposals taken into account the versatility of Cys as nucleophiles, including: mono-substitution by chloro via N- or S-attack, double substitution of chlorines via N- or S-attack, and initial S-attack followed by intramolecular cyclization. Geometric parameters, inclding transition states for all molecules and reactions were optimized searching for thermodynamics and kinetics information. The resuklts indicated the preference for the S- over N-attack, and the cyclized product being the most stable. The last part of this dissertation was devoted to a computational understanding of fluoride sensing ability by the (quercetin)₂Al³⁺ complex in aqueous médium, in attemp to provide additional evidence for current work in progress at our lab. It was confirmed the substituion of a quercetin ligand by three fluoride anions, resulting in lost of color and fluorescence quenching. This computational study was based on costomized spectific method APDF (functional Austin-Frisch-Petersson) and 6-311+G (2d,p) basis set. Optimization of all chemical species involved in the reaction was performed searching to thermodynamics information about the whole process. Also, UV-Vis spectra were simulated in attempt to support optical evidences associated to the initital/experimental findings. The proposed ligands exchange was found to be thermodynamically favored, and a interesting correlation between simulated and experimental UV-Vis spectra was obtained.

BANKING MEMBERS:
Presidente - 1803692 - FABRICIO GAVA MENEZES
Interno - 1859346 - MIGUEL ANGELO FONSECA DE SOUZA
Externa à Instituição - ANA CAROLINA DE OLIVEIRA NEVES MENEZES