Portugaliae
Electrochimica Acta

The coordination chemistry of cyanamide (N=CNH-2 ) or derived compounds remains virtually unexplored and, within our interest on the activation of such species by transition metal centres [1], we have prepared some complexes of Pd(II) or Pt(II) of the following types: irara^MC^L^] ( 1, M = Pd or Pt; L = NCNMe2 or NCNEt2 ), trans-[Pt(CF3)L(PPh3)2][BF4] [2, L = NCNMe2, NCNEt2 or NCNC(NH2)2 (cyanoguanidine)], trans- or cw-[PtClL(PPh3)2][BPh4] [3, L = NCNH2, NCNMe2, NCNEt2 or NCNC(NH2)2]-. Although their syntheses and spectroscopic properties are reported separately, we now present their electrochemical behaviour, as well as that of the free cyanamides, as investigated by cyclic voltammetry (CV) and controlled potential electrolysis ( CPE ) in 0.2 M [NBU4KBF4] / NCMe at a Pt-disc or -gauze electrode, respectively.

The electrochemical behaviour, in aprotic medium, of the 18-electron octahedral-type nitrile complexes fr

In the present work we have studied the behaviour of sodium nitroprusside in the presence of Cu(II) using differential pulse voltammetry. For a nitroprusside solution at pH 7.7 three polarographic waves were observed. The cathodic stripping peak observed at - 0.60 V vs. Ag/AgCl for the nitroprusside-copper species, which was formed after accumulation at 0.00 V, can be used for a quantitative determination of copper in the concentration range of 10-7 - 10-6 mol/dm3.

Batch injection analysis in conjunction with preconcentration by anodic stripping voltammetry and adsorptive stripping voltammetry has been investigated and optimised. Mercury films are pre-formed in situ within the cell on glassy carbon substrates by injection of l00 µl electrolyte containing mercury ions. Increased electrolysis efficiency in the stripping experiment is obtained by continuing preconcentration after injection of <100 µl of the metal-ion-containing analyte. Detection limits are in the nanomolar range. This procedure should find widespread application to all types of stripping voltammetry.

The electrochemical reduction of the pentacyanonitrosylferrate(II) ion ([Fe(CN)5NO]2", nitroprusside ion) has been studied in aqueous solutions of low pH by polarography and cyclic voltammetry. There are consistent evidences for the existence of the protonated ion, [Fe(CN)5NOH]2-, electrochemically generated at the potential of the first reduction of the nitroprusside ion. Moreover, a fast regeneration of the reactant(s) of the second reduction process must be assumed, which, at high nitroprusside concentration, can be viewed as a comproportionation reaction between nitroprusside and the product of the second reduction in acidic media. The reduction products adsorb at the mercury electrode.

The influence of anions on the electro-oxidation of D-sorbitol, at a platinum polycrystalline electrode, was studied in HCIO4 and H2SO4 solutions. Results show that Pt has a higher activity in perchloric than in sulfuric medium for the oxidation of D-sorbitol. Based on the rates of oxidation of D-sorbitol, the following sequence has been found for D-sorbitol oxidation in presence of adsorbed anions: Cl04- ~ F- > HS04- (S042-) » CI- » Br-.

Rubredoxin (Rd), desulforedoxin (Dx), rubrerythrin (Rr) and desulfoferrodoxin (Dfx) are bacterial proteins containing the simplest iron-sulfur cluster found in biology: a mononuclear iron center coordinated by four cysteinyl sulfur atoms (FeCys4 or Rd type centers). Although believed to be involved in electron transfer, their function in anaerobic bacteria is still unknown. The reversibility of redox reactions of these metalloproteins systems was studied by cyclic voltammetry, differential pulse voltammetry and square-wave voltammetry. Rd and Dx have been found to exhibit quasireversibility with E°'s in the range -50 to +20 mV versus S.H.E.

Electrochemical studies on Desulfovibrio desulfuricans ATCC 27774 Aldehyde Oxido-Reductase (AOR) were carried out in order to optimize the conditions for the development of an enzymatic sensor for aldehydes. In presence of both aliphatic and aromatic aldehydes, AOR develops a catalytic activity with a characteristic Michaelis-Menten type behavior.

Studies concerning to adsorption and oxidation of amino acids have been the subject of some publication [1, 2]. In the present work, irreversible adsorption of alanine, serine and glycine has been carried out on Pt(lll) electrodes in 0.1M HC104 solution.

It is demonstrated that the electrochemical oxidation of zerovalent palladium complexes involves a two electron process at low scan rates, affording cationic palladium(II) complexes, but at high scan rates, one electron oxidation affords palladium(I) complexes. This may be interpreted by a geometrical rearrangement induced by the solvent.

The present work is a voltammetric study on the behavior followed by gold and platinum electrodes covered by copper or oxide monolayers, in aqueous 0.5 M sulphuric acid solution, and in the presence of organic adsorbates containing a sulphur heteroatom The adsorbates employed were 2-Mercaptopyridine (2-MP) and 4-Mercaptopyridine (4¬MP). All experiments were made with both electrodes.

The electropolymerization of acrylamide in the presence of NaN03 in aqueous solution has been investigated on platinum electrodes. The polymer (polyacrylamide) is obtained in the bosom of the solution. The dependence of yields and molecular weights on parameters such as current density, monomer concentration, electrolyte concentration and temperature was determined.

Conducting polymer composite, polypyrrole/polyvinylsulphonate film prepared on a Pt electrode was degradated by applying anodic potentials at which the irreversible oxidation occurs. The effect of the "overoxidation" potential and polarization time on the electroactivity degradation was determined through the percentage of loss of stored charge. The degradation kinetic promoted by anodic polarization was obtained.

Swelling process related to electrochemical switching of conducting polymers between their reduced and oxidized states has been modelled, by using a thermodynamic treatment based on polymer gels swelling theories. A free energy function is assigned to both reduced and oxidized states, depending upon chemical and physical features of the polymer. The model is able to explain the changes in polymer volume observed when oxidation charge or electrolyte concentration are varied.

A sulphate-reducing bacteria (SRB) that is able to use nitrate as a final electron acceptor (Desulfovibrio desulfuricans ATCC 27774) was grown in lactate-nitrate medium. Weight loss and open circuit potential measurements, cyclic voltammetry and unidirectional polarisation were performed, both in sterile media as well as in the culture, using a mild steel electrode. These results were compared with previous ones obtained with the same bacteria grown in lactate-sulphate medium, thus allowing testing biocorrosion mechanism where either sulphide acumulates and cathodic depolarisation occurs or when only the last mechanism occurs.