Silicone-grease-based immobilisation method for the preparation of enzyme electrodes

An approach to the construction of amperometric biosensors based on the incorporation of an enzyme in silicone grease and using the grease to fill micropores on a graphite surface is described. The enzyme-grease electrode concept, illustrated with the enzyme tyrosinase, offers a very simple, rapid and inexpensive approach to the fabrication of enzyme electrodes. The tyrosinase electrode responds very rapidly to dynamic changes in the concentration of phenolic compounds. A response time (t95%) as low as 5 s has been determined. With flow injection, 120 samples per hour can be processed with a relative standard deviation of 2.4%. The electrode remains active for about 12 d. The detection limit for dopamine is 6 x 10(-6) M. This method of biosensor construction should be applicable to other enzyme-substrate systems.     

Electrochemical detection of microcystins, cyanobacterial peptide hepatotoxins, following high-performance liquid chromatography

A novel amperometric HPLC detection method for the cyanobacterial (blue–green algal) peptide toxins microcystin-LR, -YR and -RR was developed. Purified microcystins and cyanobacterial extracts were chromatographed using an internal surface reversed-phase column with acetate- and phosphate-based mobile phase systems. Electrochemical oxidation reactions at 1.20 V vs. Ag/AgCl (glassy carbon working electrode) were shown to originate in arginine and tyrosine residues of microcystins.     

Divergent cyclisations of 2-(5-amino-4-carbamoyl-1H-pyrazol-3-yl)acetic acids with formyl and acetyl electrophiles

The reaction of 2-(5-amino-4-carbamoyl-1-methyl-1H-pyrazol-3-yl)acetic acid and triethylorthoformate did not give the expected dihydropyrazolo[4,3-c]pyridin-4-one product as described in literature, but formed an alternative cyclic imide product, fully characterised by NMR and X-ray crystallography. This mode of reaction was shown to be general to other 1-substituted-2-(5-amino-4-carbamoyl-1H-pyrazol-3-yl)acetic acids. The outcome of the cyclisation was highly sensitive both to the nature of the reagents used and also to the acidity of the reaction medium, such that a number of interesting bicyclic heterocycles could be produced in a controlled fashion from the single starting material. The major tautomeric forms of the bicyclic products in solution were found to vary according to their substitution pattern.     

Information categories

Information systems have been introduced by Dana Scott as a convenient means of presenting a certain class of domains of computation, usually known as Scott domains. Essentially the same idea has been developed, if less systematically, by various authors in connection with other classes of domains. In previous work, the present authors introduced the notion of anI-category as an abstraction and enhancement of this idea, with emphasis on the solution ofdomain equations of the formD F(D), withF a functor. An important feature of the work is that we arenot confined to domains of computation as usually understood; other classes of spaces, more familiar to mathematicians in general, become also accessible. Here we present the idea in terms of what we callinformation categories, which are concrete I-categories in which the objects are structured sets of tokens and morphisms are relations between tokens. This is more in the spirit of information system work, and enables more specific results to be obtained. Following an account of the general theory, several examples are discussed in some detail: Stone spaces (as an ordinary mathematical example), Scott domains, SFP domains, and continuous bounded complete domains.     

Method for the determination of gamma-L-glutamyl-L-dihydroxyphenylalanine and its major metabolites L-dihydroxyphenylalanine, dopamine and 3,4-dihydroxyphenylacetic acid by high-performance liquid chromatography with electrochemical detection

A high-performance liquid chromatographic method for the analysis of gamma-L-glutamyl-L-dihydroxyphenylalanine (gludopa) and its major metabolites L-dihydroxyphenylalanine (L-DOPA), dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) is described. High sensitivity is achieved with a multi-cell coulometric detector utilising the specific electrochemical properties of gludopa (limit of detection 10 pg on-column). The retention time of gludopa was both pH-dependent and sensitive to negatively charged ion-pairing agents. An alumina-based solid-phase sample preparation technique with dihydroxybenzylamine as internal standard is described for plasma and urine (limit of detection 40 pg/ml) and an ultrafiltration technique is described for tissues (limit of detection 1-10 ng/g). After treatment with 50 mg/kg gludopa, in excess of twenty separate catecholic metabolic peaks can be detected in rat urine, whereas in humans after 9 mg/kg the only catechols detected were L-DOPA, dopamine and DOPAC.     

Recent applications of capillary electrophoresis-electrospray ionisation-mass spectrometry in drug analysis

A critical review of applications for the period 2000-2004, taken from the Web of Knowledge database, of the technique capillary electrophoresis-electrospray ionisation-mass spectrometry (CE-ESI-MS) in drug analysis is presented. The review is concerned with molecules of mass less than 500 Da, chosen according to selected structural classes in which they give ESI signals primarily as [M+H](+) ions although other ions, such as [M-H](-), [M+Na](+), and [M+NH(4)](+), are also reported. These structural classes are drugs with amine-containing side chains, drugs with N-containing saturated ring structures, 1,4-benzodiazepines, other heterocyclic hypnotics, carbohydrates, sulphonylureas, anthracyclines, sulphonamides, penicillins, cephalosporins, tetracyclines, nitrocatechols, steroids, flavonoids/polyphenols, cannabinols, and miscellaneous molecules. Details are given on the fragmentations, where available, that these ionic species exhibit in-source and in ion-trap, triple quadrupole, and time of flight-mass spectrometers. The review gives a critical evaluation of these recent CE-ESI-MS analytical methods in drug analysis. Analytical information on, for example, sample concentration techniques, CE separation conditions, recoveries from biological media and limits of detection (LODs) are provided. Potential applications of CE-MS to particular drugs or drug classes are also briefly discussed in the text.     

An O-Xylyl Diol Protecting Group

The use of an o-xylyl group as a bridged diol masking group is described.