Voltammetric Studies of Spinach Ferredoxin on a Glassy Carbon Electrode Modified with Cobalt(II) Tetrasulfophthalocyanine

Synthesis, spectral and electrochemical properties of a new family of pyrrole substituted cobalt, iron, manganese, nickel and zinc phthalocyanine complexes

A new family of pyrrole substituted metallophthalocyanine complexes, namely cobalt(II), iron(II), manganese(III), nickel(II) and zinc(II) tetrakis-4-(pyrrol-1-yl)phenoxy phthalocyanines (noted as M ( TPhPyrPc ), where M is the metallic cation) have been synthesized and fully characterized. In particular, the UV-visible spectra of the iron and nickel complexes showed extensive aggregation even at low concentrations. The cyclic voltammetry of the cobalt, iron and manganese complexes showed three to four redox couples assigned to metal and ring based processes. Spectroelectrochemistry of the manganese derivative confirmed that the synthesized complex is Mn III( TPhPyrPc -2) and that the reduction of Mn II( TPhPyrPc -2) to be centred on the ring and rather than on the metal, forming the Mn II( TPhPyrPc -4) species. Also, the electrochemical polymerization of these newly synthesized pyrrole-substituted phthalocyanines has been demonstrated in the case of the cobalt complex and the electrocatalytic activity of the obtained film has been tested towards the oxidation of L-cysteine.

Electrocatalytic determination of reduced glutathione in human erythrocytes

The determination of reduced glutathione (GSH) in human erythrocytes using a simple, fast and sensitive method employing a glassy carbon electrode modified with cobalt tetrasulfonated phthalocyanine (CoTSPc) immobilized in poly(L: -lysine) (PLL) film was investigated. This modified electrode showed very efficient electrocatalytic activity for anodic oxidation of GSH, decreasing substantially the anodic overpotentials for 0.2 V versus Ag/AgCl. The modified electrode presented better performance in 0.1 mol l(-1) piperazine-N,N'-bis(2-ethanesulfonic acid) buffer at pH 7.4. The other experimental parameters, such as the concentration of CoTSPc and PLL in the membrane preparation, pH, type of buffer solution and applied potential, were optimized. Under optimized operational conditions, a linear response from 50 to 2,160 nmol l(-1) was obtained with a high sensitivity of 1.5 nA l nmol(-1) cm(-2). The detection limit for GSH determination was 15 nmol l(-1). The proposed sensor presented good repeatability, evaluated in terms of the relative standard deviation (1.5%) for n = 10. The modified electrode was applied for determination of GSH in erythrocyte samples and the results were in agreement with those obtained by a comparative method described in the literature The average recovery for these fortified samples was 100 +/- 1)%. Applying a paired Student's-t test to compare these methods, we could observe that, at the 95% confidence level, there was no statistical difference between the reference and the proposed methods.

Cobalt tetrasulphonated phthalocyanine immobilized on poly-l-lysine film onto glassy carbon electrode as amperometric sensor for cysteine

The present work describes the development of a simple and efficient method for the amperometric determination of cysteine (CySH) in wild medium at an applied potential of 0.150 V versus Ag/AgCl. In this sense, the electrocatalytic oxidation of cysteine (CySH) was carried out on a glassy carbon electrode modified with cobalt tetrasulphonated phthalocyanine (CoTSPc) and poly-L-lysine (PLL) film. The immobilization of CoTSPc in PLL film was performed by a simple evaporation of the solvent. The CoTSPc/PLL film, formed on the GC electrode showed an electrocatalytic activity to the CySH oxidation. The sensor presented its best performance in 0.1 mol l(-1) Pipes at pH 7.5. Under optimized operational conditions, the sensor provided a wide linear response range for CySH from 0.50 up to 216.0 micromol l(-1) with a sensitivity and detection limit of 157 nA cm(-2) l micromol(-1) and 150 nmol l(-1), respectively. The proposed sensor presented higher sensitivity when compared to the other modified electrodes described in the literature and showed a stable response for at least 200 successive determinations. The repeatability of the measurements with the same sensor and different sensors, evaluated in term of relative standard deviation, were 4.1 and 5.2%, respectively, for n=10. The developed sensor was applied for the CySH determination in food supplement samples and the results were statistically the same to those obtained by a comparative method described in the literature at a confidence level of 95%.