Oxidation detection, early

Surprisingly, the bromoperoxidases do not (like other peroxidases) oxidize organic electron donors il9,31) such as o-dianisidine or guaia-col, which are normally used to detect peroxidase activity, and thus enzymic activity easily escapes detection. When bromide or iodide are present in the assay medium HOBr and HOI are formed these reactive species will oxidize, brominate, or iodinate the organic dyes, thus allowing detection. Early in this century similar organic dyes were used to detect peroxidase activity in seaweed tissues and extracts. However, the results were not clearly reproducible. This is understandable since in seaweed variable amounts of iodide and bromide are present. On purification of the bromoperoxidase the halides are removed, resulting in an apparent decrease in or lack of activity. 

Improvements in instrumentation have led to increased spectral sensitivity and to more reliable methods for data integration. These improvements coupled with larger, more efficient and faster computers have given quantitative 13c NMR applications the boost required for broad useage. A sensitivity of at least one structural unit per 10,000 carbon atoms is required for useful molecular weight and branching measurements and to allow species produced by oxidation and irradiation (12)(13) to be detected early in the process. 

In conlcusion, the rates of ethanol metabolism and the activity of hepatic alcohol dehydrogenase are both reduced in fetal life and in the newborn when compared with values obtained in the adult. Significant microsomal ethanol oxidizing system and catalase activities are detected early in fetal life and do not increase during further fetal development However, the contribution of these two enzymes to the m vivo metabolism of ethanol during development remains to be evaluated. 

Moseley P, Williams DE (1989) Gas sensors based on oxides of early transition meteds. Polyhedron 8 1615-1618 Mosley PT, Norris J, Williams DE (eds) (1991) Techniques and mechanisms in gas sensing. Adam Hilger, New York Moulson AJ, Herbert JM (1990) Electroceramics materieils, properties, applications. Chapman and Hall, London Mukundan R, Brosha E, Brown D, Garzon F (1999) Ceria-electrolyte-based mixed potential sensors for the detection of hydrocarbons and carbon monoxide. Electrochem Soc Lett 2(8) 412-414 MuUa IS, Ramgir NS, Hwang YK, Chang J-S (2004) Semiconductor tin oxide gas sensors from bulk to thin films. J Ind Eng Chem 10(7) 1242-1256... 

Dielectric analysis has also been applied to study polymer thermal ageing [894], e.g. of adhesive bonded structures [895]. Dielectric loss is a means for detecting early steps in polymer degradation by oxidation, although nowadays CL is a strong competitor. The dielectric behaviour of post-irradiation oxidised PP/HALS was also reported [796]. Dielectric analysis has not been extended to many elastomer applications. Dissociation and mobility of salt complexes as heat stabilisers in PA4.6 have been investigated by means of DIES the technique was also used to study thiourea-doped PVAL [903]. 

There have been many instances of examination of the effect of additive product on the initiation of nucleation and growth processes. In early work on the dehydration of crystalline hydrates, reaction was initiated on all surfaces by rubbing with the anhydrous material [400]. An interesting application of the opposite effect was used by Franklin and Flanagan [62] to inhibit reaction at selected crystal faces of uranyl nitrate hexa-hydrate by coating with an impermeable material. In other reactions, the product does not so readily interact with reactant surfaces, e.g. nickel metal (having oxidized boundaries) does not detectably catalyze the decomposition of nickel formate [222],... 

ANDERSEN M L and SKIBSTED L H (2002) Detection of early events in lipid oxidation by electron spin resonance spectroscopy, Eur J Lipid Sci Technol, 104, 65-8. 

Multiple electrodes have been used to obtain selectivity in electrochemical detection. An early example involved the separation of catecholamines from human plasma using a Vydac (The Separation Group Hesperia, CA) SCX cation exchange column eluted with phosphate-EDTA.61 A sensor array using metal oxide-modified surfaces was used with flow injection to analyze multicomponent mixtures of amino acids and sugars.62 An example of the selectivity provided by a multi-electrode system is shown in Figure 2.63... 

The formation and role of hydroperoxide groups, particularly in the early stages of polymer oxidation is well discussed in the introduction to the next chapter and also features in many of the references cited in this chapter. Their detection and quantification is therefore important. Although this can be done directly or implicitly through many of the instrumentation techniques discussed in this chapter, there are several tests that have been developed, some of which are still widely used, that are based more on chemical methods, titration or staining. The majority have been applied to polyolefins, especially polyethylene. 

Exceeding the limitation of molecular dynamics, the steric requirement of trimethylsilyl groups can cause drastic changes both in structure and of molecular properties of organosilicon compounds. For illustration, the so-called "Wurster s-Blue11 radical ions are selected On one-electron oxidation of tetramethyl-p-phenylenediamine, its dark-blue radical cation, detected as early as 1879 [11a], is gene-... 

Later work by several research workers, and most particularly Greef (1969), showed that the very early stages of oxide film formation could be detected using more sensitive instrumentation and the changes in A, 4 and the light intensity correlated very well with the charge passed both in the anodic and cathodic sweeps (see Figure 3.13). 

Korotchenko and coworkers detected PG-like compounds in five starfish from the Sea of Japan Asterias amurensis, Distolasterias nippon, Evasterias r. tabulata, Lysastrosoma anthosticta, and Patina pectinifera [189]. Perry and Epel showed that Pisaster ochraceous homogenates were able to oxidize AA [190]. Early studies on oocyte maturation in starfish suggested that HETE s might play a role [195]. Two compounds, 12- and 15-HETE, were able to induce oocyte maturation. Subsequent work showed that the activity was actually due to 8-HETE (33), which was a minor contaminant of both HETE preparations [196]. The 8R enantiomer of this compound (33) and 8R-HEPE (32) were also isolated from the aqueous extracts of Patiria miniata from the Gulf of California [197],... 

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