Platinum electrodes amino acids

Several alkyl aryl sulfides were electrochemically oxidized into the corresponding chiral sulfoxides using poly(amino acid)-coated electrodes448. Although the levels of enan-tioselection were quite variable, the best result involved t-butyl phenyl sulfoxide which was formed in 93% e.e. on a platinum electrode doubly coated with polypyrrole and poly(L-valine). Cyclodextrin-mediated m-chloroperbenzoic acid oxidation of sulfides proceeds with modest enantioselectivity44b. 

Fortier [6] found that AQ polymer from Eastman was not deleterious for the activity of a variety of enzymes such as L-amino acid oxidase, choline oxidase, galactose oxidase, and GOD. Following mixing of the enzyme with the AQ polymer, the mixture was cast and dried onto the surface of a platinum electrode. The film was then coated with a thin layer of Nafion to avoid dissolution of the AQ polymer film in the aqueous solution when the electrode was used as a biosensor. These easy-to-make amperometric biosensors, which were based on the amperometric detection of H202, showed high catalytic activity. 

A study was made of RP-HPLC with constant-potential (1.2 V vs SCE) and pulsed-potential amperometric detection using platinum or gold electrodes, of the derivatives of the common amino acids, obtained from phenyl and methyl isothiocyanates. All the thiohydantoins (98) were oxidized at both electrodes LOD was less than 0.2 pM for lysine and glycine, for 50 pL injection268. 

Cys is an amino acid of great interest and its redox behavior is influenced by the electrode materials, and buffer and electrolyte conditions. S-Based oxidation results in the formation of sulfinic or sulfonic acids. The electrochemical oxidation takes place in two irreversible steps at gold and platinum rotating disc electrodes at peak... 

Other metals, such as copper, nickel, or silver, have been used as electrode materials in connection with specific applications, such as the detection of amino acids or carbohydrates in alkaline media (copper and nickel) and cyanide or sulfur compounds (silver). Unlike platinum or gold electrodes, these electrodes offer a stable response for carbohydrates at constant potentials, through the formation of high-valence oxyhydroxide species formed in situ on the surface and believed to act as redox mediators (40,41). Bismuth film electrodes (preplated or in situ plated ones) have been shown to be an attractive alternative to mercury films used for stripping voltammetry of trace metals (42,43). Alloy electrodes (e.g., platinum-ruthenium, nickel-titanium) are also being used for addressing adsorption or corrosion effects of one of their components. The bifunctional catalytic mechanism of alloy electrodes (such as Pt-Ru or Pt-Sn ones) has been particularly useful for fuel cell applications (44). 

Kinetic measurements of H2O2 formation result in fast electrode responses (less than 12 s) using chemically bound L-amino acid oxidase (LAAO) covering a platinum electrode (170) to assay for cysteine, leucine, tyrosine, phenylalanine, tryptophane, and methionine. Potentiometric-selective electrodes for amino acids are Constructed by immobilizing LAAO on chemically modified graphite... 

Immobilized L-amino acid oxidase catalyzes the oxidation of L-amino acids to 2-oxo acids. Detection of the hydrogen peroxide product is accomplished using a fluorometric or chemiluminescent assay subsequent to the reaction in the packed bed. L-Amino acids can also be quantified amperometrically using a platinum electrode Ag/AgCl on which the enzyme is... 

Yao and Wasa (1988a) assembled modified electrodes for amino acids by crosslinking L- or D-amino acid oxidase with glutaraldehyde on silanized platinum probes. The sensors were employed as detectors in high pressure liquid chromatography. Whereas the L-amino acid oxidase electrode responded to L-tyrosine, L-leucine, L-methionine, and L-phenylalanine in amounts as low as 2 pmoles, the D-amino acid electrode measured only D-methionine and D-tyrosine. The response time in steady state measurements was only 5-10 s. 

The three monocyclic heteroaromatic 1,2,3,5-triazines 1-3 can be isolated when cyanamide is oxidized electrochemically at a platinum electrode in 2 M potassium hydroxide followed by neutralization with hydrochloric acid or carbon dioxide. The structures of 4-ainino-6-cyanamino-, 4-amino-6-cyanoguanidino- and 4-ureido-6-cyanoguanidino-l,2,3,5-tetrazine (1), (2) and (3), respectively, were confirmed by elemental analysis, IR spectral data and by further transformations.3... 

First tissue-based biosensor antennules from blue crabs mounted in a chamber with a platinum electrode to detect amino acids [18]... 

J. A. Polta and D. C. Johnson, The Direct Electrochemical Detection of Amino Acids at a Platinum Electrode in an Alkaline Chromatographic Effluent. J. Liq. Chromatogr.y 6 (1983) 1729. 

Individual amino acids in proteins undergo oxidation reactions at potentials on the positive side of ca. 0.7 V. Tryptophan and tyrosine residues are oxidizable at carbon, " platinum, and gold electrodes while histidine is oxidizable at carbon. The sulfur-containing amino acids cysteine, cystine, and methionine have been shown to be oxidized at carbon. Adsorption processes are important in these reactions. 

Pulsed amperometric detection (PAD) Amino acids are not generally considered to be electrochemically active because products of the oxidation accumulate on the electrode surface and prevent it from participating in any further electrochemical processes. This problem can be overcome if PAD is employed. Amino acids are generally detected using a platinum electrode under alkaline conditions (0.25 mol 1 NaOH) using a triple-pulse waveform with Ei, E2, and E3 at 0.50, — 0.89, and 0.70 V, respectively. Due to the basic conditions required for the detection of amino acids, a base-stable anion-exchange column must be employed. Detection limits of 50 pmol have been obtained for phenylalanine and methionine using this technique. 

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