Carbon electrodes biologically active, reactions

Pulsed amperometric detection is used for the direct detection of a variety of polar aliphatic compounds, many of which, like carbohydrates, peptides and sulfur-containing compounds are of biological interest [171,197-200]. Most aliphatic compounds are not amenable to constant potential amperometric detection. Free-radical products from the oxidation of aromatic molecules can be stabilized by it-resonance hence the activation barrier for reaction is decreased. This mechanism is unavailable for stabilizing aliphatic free radicals. The activation barrier for oxidation of aliphatic compounds can be decreased at noble-metal electrodes with partially unsaturated d-orbitals (e.g. gold, platinum) that can adsorb and thereby stabilize free radical oxidation products and intermediates. Carbon electrodes are not electrocatalytic and are unsuitable for pulsed amperometric detection. 

Ideal material should be biologically inert, resistant to degradation over time, and not elicit a marked tissue reaction at the electrode-myocardium interface. Today, materials most often used for electrode building are platinum-iridium, pla-tinized-titanium-coated platinum, iridium oxide, and platinum. Carbon electrodes finally seem to be the least susceptible to corrosion. To increase their surface area, they can be treated with a process called activation, which roughens the lead surface. Carbon electrodes elicit only minimal tissue reac-... 

Hydroxy derivatives or phenolics are frequent target for method development using carbon paste electrodes based either on direct oxidation of hydroxy group on an aromatic ring or on enzyme-based reactions with the final determination of the product of the enzymatic reaction involved. The reason lies both in their usual ease of oxidation and in their relatively frequent occurrence as hydroxy derivatives of aromatic hydrocarbons form the base of various biologically active organic compounds used as disinfectants, pharmaceuticals, herbicides, and pesticides. CPE and CPE modified with humic acids were used for the determination of pentachloro-phenol. With modified electrode lower determination limit was reached due to better accumulatiOTi of the analyte. Formation of a quinone-Uke compound during... 

In biological systems, the enzymes are homogeneons catalysts. For their use in heterogeneons electrochemical reactions, they mnst be immobilized on a carrier suitable for fashioning an electrode. This is most often achieved by adsorption of the enzyme on a carbon material (carbon black, graphite, etc.). This immobilization usually leads to some decrease in activity of the enzymes, bnt on the other hand, raises their stability. 

It has long been established that Pt is the most efficient singlemetal electrode for the catalysis of both reactions (1) and (2). In the case of ddiydrogen activation, no metal electrocatalyst performs better than platinum. However, aside from the fact that platinum is a precious metal, a major drawback is that commercial (fossil-based) hydrogen contains residual amounts of impurities (e g., carbon monoxide) that only serve to poison the catalyst surface." To address this particular problem, present research has focused on the employment of metal additives (e.g., Ru) or of molecular catalysts that mimic the impressive activity of biological materials (e g., hydrogenase enzymes) " the use of molecular catalysts appears to be the more attractive option since such com-... 

---