Banca de QUALIFICAÇÃO: MAYRA SILVA COUTINHO
Uma banca de QUALIFICAÇÃO de MESTRADO foi cadastrada pelo programa.DISCENTE : MAYRA SILVA COUTINHO
DATA : 14/05/2019
HORA: 14:30
LOCAL: Sala de aula do Química I
TÍTULO:
Development of chromogenic sensors based in enzymatic reactions and silver nanoparticles for analysis of ascorbic acid and iron (III) in aqueous medium.
PALAVRAS-CHAVES:
Sensors; Enzymatic reactions; Nanoparticles; Ascorbic acid; Iron (III)
PÁGINAS: 80
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Química
SUBÁREA: Química Orgânica
ESPECIALIDADE: Polímeros e Colóides
RESUMO:
The development of chemical systems aiming detection of specific analytes in solution has attracted great attention due the possibility of fast, low cost and practical implementation. In this context, methods based on enzymatic reactions and nanostructured systems play a relevant role. This work consist in two main parts. Firstly, a new method for detection of ascorbic acid (AA, vitamin C) based on its interfering effect in the quantification of glucose by the enzymatic colorimetric method is presented. This method is based in the inhibition of chromophore quinoneimine, generated by sequential enzymatic processes, which its concentration is proportional to concentration of glucose in the medium. UV-vis analysis showed a linear correlation between decreasing of quinoneimine concentration concomitantly to increasing of AA concentration. The method was validated by quantification of AA from commercial effervescent tablets, with satisfactory errors, from 0.01 to 1.25 %, and limits of detection and quantification of 0.045 and 0.138 mg.L-1, respectively. In the second part of the work, silver nanoparticles functionalized with the natural product rutin (RU-AgNPs) were employed in the detection of Fe3+ ions in solution, in the presence of AA. In the best experimental condition (AgNO3, 0,2mM; AA, 0,1 mM; NaOH, 0,1 M e AA, 1mM), according to UV-vis analysis, small but polydisperse nanoparticles (4.1 nm), as verified by transmission electronic microscopy. In the presence of Fe3+, these nanoparticles increase in size (14.7 nm average) and undergo aggregation, as verified by TEM. These effects are not verified in the presence of Cu2+, Zn2+, Hg2+, Ni2+, Pb2+, Mg2+, Cr3+, Sr2+, Ba2+, Cu+ e Al3+. Although Co2+ ions also affects the RU-AgNPs, this effect is not pronounced enough for interfering in the detection of Fe3+ ions. Mechanistically, adsorption of anionic RU to silver surface via 3-hydroxychromen-4-one moiety, since it is the main site to coordinate to metal, while addition of Fe3+ induces to the formation of a coordination complex through anionic catechol group, in which at least 2:1 ligand-Fe3+ stoichiometry is required for aggregative effect. In this process, AA has a crucial role for selective detection and two possible explanation include avoid of previous oxidation of RU by silver and/or coordination of ascorbate do other cations. UV-vis analysis showed a linear correlation between concentration of Fe3+ ions in solution (1-10 μM) and the decreasing in the surface plasmon resonance band (396 nm) associated to RU-AgNPs. Limits of detection and quantification for quantification of Fe3+ were found to be 0.031 e 0.103 µmol.L-1, respectively.
MEMBROS DA BANCA:
Presidente - 1803692 - FABRICIO GAVA MENEZES
Interno - 1198847 - JOSE LUIS CARDOZO FONSECA
Interno - 2087667 - TIAGO PINHEIRO BRAGA