Oxidation of hydrogen peroxide

For this type of sensor, a catalase-free glucose oxidase must be used. In such a case, the hydrogen peroxide produced by the reaction with oxygen remains in the selective layer and can be detected by oxidation according to the reaction 

This sensor uses cylindrical microelectrode geometry (Fig. 7.14) for which the diffusion-reaction reaction is written in spherical coordinates, similar to (2.24). 

The sign in front of the reaction term is positive only for hydrogen peroxide. Also, the function 3Ipn can be made constant by operating the sensor in a medium of high buffer capacity. This is clearly a distinct advantage compared to the potentiometric sensors in which the buffer capacity represented a major interference. 

The initial and boundary conditions depend again on the model and on the operating conditions. Initially (at t = 0) there is no glucose (G) or hydrogen peroxide 

Oxygen, which is consumed by the primary glucose oxidation, is regenerated by the oxidation of hydrogen peroxide at the surface of the electrode. Moreover, because the operating potential is positive, oxygen is not consumed at the electrode. Therefore, the reaction is not limited by the concentration of oxygen for which the boundary conditions are 

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Oxygen can be produced by certain reactions in solution, for example the oxidation of hydrogen peroxide by potassium manganate(VII) acidified with sulphuric acid ... 

A preliminary account of the kinetics of the oxidation of hydrogen peroxide by Ag(II) nitrate in 3 M HNO3 has appeared the rate law being... 

The Co(III) perchlorate oxidation of hydrogen peroxide affords a rate law... 

Other solutions to dealing with interferences in the detection of H O have included the use of a copperfll) diethyldithiocarbamate precolumn to oxidize the sample before it reaches the immobilized enzyme, as well as the use of a palladium/gold sputtered electrode which catalyzes the oxidation of hydrogen peroxide In addition, peroxidase has been used to catalyze the reaction between hydrogen peroxide and iodide ferrocyanide and organo-fluorine compounds Am-... 

HTAC cationic micelles also markedly enhance the CL intensity of fluorescein (FL) in the oxidation of hydrogen peroxide catalyzed by horseradish peroxidase (HRP) [39], However, no CL enhancement was observed when anionic micelles of sodium dodecyl sulphate (SDS) or nonionic micelles of polyoxyethylene (23) dodecanol (Brij-35) were used (Fig. 9). CL enhancement is attributed to the electrostatic interaction of the anionic fluorescein with the HTAC micelles. The local concentration of fluorescein on the surface of the micelle increases the efficiency of the energy transferred from the singlet oxygen (which is produced in the peroxidation catalyzed by the HRP) to fluorescein. This chemiluminescent enhancement was applied to the determination of traces of hydrogen peroxide. The detection limit was three times smaller than that obtained in aqueous solution. 

At the same time the interaction of superoxide with MPO may affect a total superoxide production by phagocytes. Thus, the superoxide adduct of MPO (Compound III) is probably quantitatively formed in PMA-stimulated human neutrophils [223]. Edwards and Swan [224] proposed that superoxide production regulate the respiratory burst of stimulated human neutrophils. It has also been suggested that the interaction of superoxide with HRP, MPO, and LPO resulted in the formation of Compound III by a two-step reaction [225]. Superoxide is able to react relatively rapidly with peroxidases and their catalytic intermediates. For example, the rate constant for reaction of superoxide with Fe(III)MPO is equal to 1.1-2.1 x 1061 mol 1 s 1 [226], and the rate constants for the reactions of Oi and HOO with HRP Compound I are equal to 1.6 x 106 and 2.2 x 1081 mol-1 s-1, respectively [227]. Thus, peroxidases may change their functions, from acting as prooxidant enzymes and the catalysts of free radical processes, and acquire antioxidant catalase properties as shown for HRP [228] and MPO [229]. In this case catalase activity depends on the two-electron oxidation of hydrogen peroxide by Compound I. 

The kinetics of the oxidation of hydrogen peroxide by Ag(bipy)i+ were investigated in aqueous nitric acid medium.529 The reactive species was found to be Ag(bipy),2+ present in equilibrium with Ag(bipy)2+. It was claimed that this was not necessarily due to the freeing of coordination sites but may be due to the difference in redox reactivity. 

There are several species in this reaction that can be used for electrochemical sensing. Detection of proton released from the gluconic acid was used in the poten-tiometric glucose electrode (Section 6.2.1). The amperometric sensor can be based on oxidation of hydrogen peroxide, on reduction of oxygen, or on the oxidation of the reduced form of glucose oxidase itself. 

Current-potential curves of the oxidation of hydrogen peroxide with a vitreous-carbon electrode in an alkaline environment with a hydrogen peroxide concentration of (a) 0.15 mol I-1 and pH = 12.04 and (c) 0.44mol I-1 and pH = 12.80, and their corresponding table graphs with (b) an inclination of 0.50 and (d) an inclination of 0.48. 

Table 4.1 Possible species in solution and adsorbed at the surface of a glassy-carbon electrode that can occur and take part in the oxidation of hydrogen peroxide in alkaline solution...

Hecht SM, Long EC, van Atta RB, De Vroom E, Carter BJ (1990) On the mechanism of bleomycin activation and polynucleotide strand scission. In Bleasdale C, Golding BT (eds) Mol. Mech. Bioorg. Processes, Conference Proceedings. Royal. Soc. Chem., London, pp 100-114 Held AM, Halko DJ, Hurst JK (1978) Mechanisms of chlorine oxidation of hydrogen peroxide. J Am Chem Soc 100 5732-5740... 

M.A.T. Gilmartin, R.J. Ewen, J.P. Hart and C.L. Honeybourne, Volt-ammetric and photoelectron spectral elucidation of the electrocatalytic oxidation of hydrogen-peroxide at screen-printed carbon electrodes chemically-modified with cobalt phthalocyanine, Electroanalysis, 7 (1995) 547-555. 

The oxidation of hydrogen peroxide is actually quite complicated and depends upon the formation of a metal oxide on the electrode surface 42-44 Consequently, there is no... 

Zhang Y, Wilson GS. Electrochemical oxidation of hydrogen peroxide on platinum and platinum/iridium electrodes in physiological buffer and its applicability to hydrogen peroxide-based biosensors. Journal of Electroanalytical Chemistry 1993, 345, 253-271. 

Hall SB, Khudaish EA, Hart AL. Electrochemical oxidation of hydrogen peroxide at platinum electrodes. Part I. An adsorption-controlled mechanism. Electrochimica Acta 1998, 43, 579-588. 

Thin-layer Studies. The thin-layer electrochemical system was developed to address the lack of sensitivity of a preliminary bulk amperometric activity assay (77). The first set of thin-layer studies was taken to characterize the thin-layer cells in soluble enzyme solutions and to determine if there were any interferences to the detection of hydrogen peroxide. Preliminary thin-layer studies (23) indicated that the oxidation of hydrogen peroxide could be detected at approximately 1080 mV with only minimal interference from the oxidation of glucose by gold. The addition of chloride ion to the solution further suppressed the glucose electrooxidation interference. 

The multilayer membrane coverage (of Fig. 6.6) improves the relative surface availability of oxygen and excludes potential interferences (common at the potentials used for detecting the peroxide product). Electrocatalytic transducers based on Prussian Blue layers (15) or metallized carbons (16), which preferentially accelerate the oxidation of hydrogen peroxide, are also useful for minimizing potential interferences. The enzymatic reaction can also be followed by monitoring the consumption of the oxygen cofactor. 

Yamaguchi, K., Mizugaki,T., Ebitani, K. and Kaneda, K. (1999). Heterogeneous N-oxidation of pyridines using a combined oxidant of hydrogen peroxide and nitriles catalysed by basic hydrotalcites. New J. Chem. 23, 799. 

Ground-state dioxygen ( 2) can be activated by photolytic energy transfer to the singlet state ( 2) (eqnation 129) and this may be dnplicated at the snrface of biomembranes by solar radiation. In the laboratory, singlet dioxygen is conveniently prodnced by the stoichiometric oxidation of hydrogen peroxide by hypochlorous acid (eqnation 130). 

The Auto-Oxidation of Hydrogen Peroxide. When hydrogen peroxide decomposes, by the reaction... 

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