Banca de DEFESA: LEILA SANTANA VIANA BARBOSA

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
DISCENTE : LEILA SANTANA VIANA BARBOSA
DATA : 28/06/2019
HORA: 08:30
LOCAL: Instituto de Química
TÍTULO:

Evaliation of amino acids and glutathione coated CdTe quantum dots interaction to urine and dietary supplements analysis

PALAVRAS-CHAVES:

Quantum dots. Luminescent methods. Amino acids. Urine. Dietary Supplement

PÁGINAS: 72
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Química
SUBÁREA: Química Analítica
ESPECIALIDADE: Métodos Óticos de Análise
RESUMO:

Amino acids (AA) are the main constituents of proteins, and their deficiency or accumulation leads to health damage. Different methods were developed using quantum dots (QD), as photoluminescent probes for indirect AA determination in different matrices.These methods were based on the turn-off-turn-on strategy, which consists in quencher removal (usually metal species) from QD surface by interaction with analytes.Thereby, the present work aims to evaluate AA-QD for the direct analytical methods and its application in urine and supplements samples. Sensitization assays of glutathione-coated CdTe QD (GSH-CdTe) with different sizes were performed against 7 amino acids alone and they were divided according to the properties of their side chain. Experiments with different temperatures and ionic strength were performed to evaluate the quenching mechanism and AA-QD interaction type. Chemical parameters of the probe, such as pH (5 to 10), buffer concentration (0.1 to 0.8 mol L^-1), QD size (2.2 to 3.0 nm) and concentration (2.5 to 35 μmol L^-1) were evaluated to ensure greater method sensitivity. It was observed that AA with positive charge or neutral polar chains, namely L-histidine (His) and L-threonine (Thr), have reduced 90% of nanocrystal fluorescence. Reaction parameters assesment has shonw that in ammoniacal buffer (0.25 mol L^-1) at pH 8.0 GSH-CdTe (2.2 nm) responded only to His, indicating specificity of luminescent probe to the analyte. Studies on the His-QD mechanism suppression and interaction indicated the occurrence of static quenching with complex association constant (k_a) ranging from 2.81x10^-5 to 9.7x10^-6 L mol^-1 from 20 °C to 35 °C. In addition, no variation of k_a (Δk_a <11%) was observed changing ionic strength suggesting preferently His-QD interations of Van der Waals force and/or hydrogen bonding.The thermodynamic parameters of His-QD interaction were determined using the Van 'Hoff equations, obtaining values of ΔH = -160.5 kJ mol^-1 K, ΔS = -0.858 J mol^-1 and ΔG of -411.931 to -424.803 kJ mol^-1 K (T = 20 to 35 °C). Parallelism was observed between the calibration curves in aqueous solvent and sample indicating the absence of matrix effect. Under optimal conditions the developed method presented a linear range of 2.5 to 35 mmol L^-1 (R = 0.9970, n = 7). The detection limit was 1.1x10^-3 mol L^-1 (0.170 mg mL ^-1), showing good precision with RSD <2.5% (for 2.5 and 20 mmol L^-1; n = 6). The accuracy method was evaluated by addition and recovery assays for two to three concentration levels in real triplicate in urine and supplement samples, presenting adequate recovery values for both samples demonstrating good accuracy.The method was applied to urine and dietary supplement samples. Histidine was not detected in urine samples. However, in supplement samples, His was determined in amounts equal to 135±5 and 417.2±0.2 mg per tablet.

MEMBROS DA BANCA:
Presidente - 1190574 - RODOLFO DE MELO MAGALHAES SANTANA
Interno - 1698441 - RENNAN GEOVANNY OLIVEIRA ARAUJO
Interno - 282814 - MARIA DAS GRACAS ANDRADE KORN
Externo à Instituição - MAURO KORN - UNEB
Externo à Instituição - JOSUE CARINHANHA CALDAS SANTOS - UFAL