Comportamento eletroquimico de alguns compostos organicos eletroativos imobilizados em suportes inorganicos visando o desenvolvimento de sensores para NADH

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

Inorganic matrices modified with niobium oxide or niobium phosphate, obtained for gel and sol-gel processes, which were denominated as: (SN, SNP, SNsol-gel e SNPsol-gel), were employed in this work. The SN and SNsol-gel materials presented 1400 and 1600 mmol Nb/g of material, respectively; while 1100 and 780 mmol P/g of material for SNP and SNPsol-geI. These matrices (SN, SNP, SNsoI-gel e SNPsol-gel) were used as support to riboflavin (RF) immobilization, which adsorbed, respectively, 27, 31, 36 and 44 mmol/g of material. These matrices were employed in the preparation of the modified carbon paste electrodes. Investigations of the electrochemical behavior of RF, evaluating the acidity effect, surface area and porosity of the materials were carried out with these electrodes, as well as the kinetics of electron transfer between immobilized RF and the electrode. The capacity of the immobilized RF in the electrocatalytic NADH oxidation was also estimated. In these studies was observed that the formal potential of adsorbed RF on different matrices kept constant in the pH range between 3 and 8. The studies to estimate the kinetics of electron transfer between immobilized RF and the electrode showed that these electrodes are excellent devices for NADH detection. However, the electrocatalytical activity of the systems employing the immobilized RF presented low efficiency, and it was attributed to a probable matrix effect, making difficult the interaction between RF and NADH. Another important aspects were verified through the development of the EPC/SNFDA sensor. This device allowed to carry out more than 300 NADH determinations with a relative standard deviation (sdr) lower than 3 %. This sensor containing o-phenylenediamine presented a linear response range from 0.4 10 up to 8.0 10 mol L with a sensitivity of 24.2 mA L mol cm, with an applied potential of -50 mV vs. SCE. The kinetic of electron transfer between the adsorbed mediator and NADH, employing rotation disk electrode was also verified. These studies indicated that the NADH oxidation reaction should occurs through of the formation of a charge transfer complex between the mediator and NADH. The increase of the rate constant of the reaction, kobs, with the increase of the solution pH was assigned to the increase in the difference of the redox potential between NADH and the mediator.

ASSUNTO(S)

eletrodos eletroquimica silica gel compostos organicos

ACESSO AO ARTIGO

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