Monika J. Green

[1] Chemistry of dioxygen

Publisher Summary The chemistry of molecular oxygen, or dioxygen as it is increasingly coming to be called, is dominated by the relative reluctance with which the element reacts with most, but not all, compounds. This quality is rarely thermodynamic in origin; rather the slow rate of reaction is associated with either the strong oxygen–oxygen bond or the character of the ground state of dioxygen or both. If a reaction is to take place with dioxygen in its ground state, there must be a change of spin at some stage during the reaction. This is forbidden, within the limitations of the descriptions used; at the very least, the reactions are improbable. For dioxygen to react rapidly, this spin restriction should be removed or the oxygen–oxygen bond should be partially weakened or both of these should occur simultaneously. It is not surprising that much of the chemistry of dioxygen is concerned with reactions with paramagnetic species, with electron-donating species, with light, or with various combinations of these three factors. This chapter discusses the chemistry of the reduction products of dioxygen, but one should be aware of the marked influence of all of these factors on most reactions of dioxygen. They are often, if not always, responsible for the promotion or catalysis of oxidation reactions.

Ferricinium ion as an electron acceptor for oxido-reductases

Abstract The ability of ferrocene monocarboxylic acid to act as a mediator to some oxido-reductases was investigated. Dc cyclic voltammetry was used to study the coupling of the electrode reaction, associated with the oxidation of ferrocene to ferricinium ion, to an enzymatic oxidation reaction. The reactions catalysed by pyruvate oxidase, xanthine oxidase, sarcosine oxidase, lipoamide dehydrogenase, glutathione reductase and alcohol dehydrogenase were investigated. The rates of reaction between the ferricinium ion and the reduced form of each of the enzymes, in the presence of their substrates, were measured.

Amperometric enzyme electrodes

The design of a new type of amperometric enzyme electrode, exploiting ferrocene as mediator between enzyme and electrode, is described. Its use is illustrated by application to the determination of glucose through the use of glucose oxidase. Other flavoproteins accept ferrocene as a mediator, as do peroxidases. The synthesis of ferrocene analogues of drugs, e.g. lidocaine and theophylline, permits the development of analytical methods employing components of the immune system.

Measurement of alkaline phosphatase activity by electrochemical detection of phosphate esters: Application to amperometric enzyme immunoassay

Abstract Dc cyclic voltammetry and chronoamperometry have been used to examine the electrochemistry of a series of phosphate esters that are substrates for calf intestinal alkaline phosphatase. p-Aminophenyl phosphate was selected as the most suitable substrate for the electrochemical measurement of alkaline phosphatase activity. Picomolar levels of enzyme can be detected, which enables the design of electrochemical immunoassays using this system. Theophylline and phenytoin have been used as model analytes in competition and displacement assay formats.

Disposable electrochemical biosensors.

The market for decentralized clinical testing is undergoing expansion. Electrochemical biosensors represent one approach to the different demands of this market. A range of sensing systems are described which use electrochemical techniques for the measurement of various analytes and which have been demonstrated to be applicable to the manufacturing methods required for single-use disposable tests.

Amperometric biosensor for the rapid determination of salicylate in whole blood

Abstract A method for the determination of salicylate in whole blood is described. The assay uses salicylate hydroxylase to convert salicylate to catechol in the presence of NADH and molecular oxygen. The formation of catechol is monitored amperometrically by oxidation at +300 mV vs.Ag/AgCl and the size of the oxidation current is related to the concentration of salicylate in the sample. The reagents are incorporated into the working electrode of a disposable strip, allowing measurements to be made on a drop of blood within 1 min. The functional range of the assay can be extended to the equivalent of 7.2 mM plasma salicylate by incorporating benzoate as a component of the reaction system. The method has the advantages of simplicity and speed compared with standard procedures, and should prove especially useful in suspected overdose situations.

Detection of ATP and creatine kinase using an enzyme electrode

Abstract An electrochemical method for the detection of ATP and creatine kinase (ATP:creatine N -phosphotransferase, EC 2.7.3.2) coupled through hexokinase to an amperometric glucose enzyme electrode is described. The assay can be used to monitor creatine kinase activity over the range 0.01–10 U ml −1 and forms the basis for the development of a single-use biosensor.

Method for determining paracetamol in whole blood by chronoamperometry following enzymatic hydrolysis.

A method is proposed for the determination of paracetamol in whole undiluted blood, based on the enzymatic hydrolysis of the drug to p-aminophenol, which is then measured by chronoamperometry at a glassy carbon electrode. Hydrolysis of the paracetamol prior to electro-oxidation is shown to alleviate problems that arise from high background currents in the whole blood and so ensures a good linear correlation (r greater than 0.99) between the current and the paracetamol concentration. Recovery experiments and comparison with a reference method based on spectrophotometry suggest that the electrochemical assay only measures that proportion of paracetamol that is not bound to serum albumin.

Rapid electrochemical assay for theophylline in whole blood based on the inhibition of bovine liver alkaline phosphatase

Abstract A disposable electrochemical test strip for determining clinically relevant concentrations of theophylline (0–300 μM) in whole blood is described, based on the generation of p-aminophenol from p-aminophenyl phosphate by the action of bovine liver alkaline phosphatase. Theophylline is an uncompetitive inhibitor of alkaline phosphatase and thus inhibits this process. The test strip consists of a screen-printed, carbon-based electrode system containing the enzyme and substrate in separate layers. Application of a 20-μl blood sample to the strip initiates the enzymic reaction, which will proceed to an extent that is inversely dependent on the amount of theophylline in the sample. After a 2-min incubation, the p-aminophenol generated is quantified by its electrochemical oxidation at + 150 mV (vs. Ag/AgCl) on the underlying carbon electrode. Caffeine and theobromine (0–1 mM), phenylalanine (

An opsonised electrode. The direct electrochemical detection of superoxide generated by human neutrophils.

A pyrolytic graphite electrode was surface modified with human IgG and used as a stimulus to elicit a respiratory burst from human neutrophils. The oxidation current observed was shown to be due to re‐oxidation of superoxide produced by the neutrophils. Both superoxide dismutase and N‐ethylmaleimide were effective inhibitors of the oxidation current.