Biological systems transformations

The hydroxyl radical plays two essentially different roles (a) as a reactant mediating the transformations of xenobiotics and (b) as a toxicant that damages DNA. They are important in a number of environments (1) in aquatic systems under irradiation, (2) in the troposphere, which is discussed later, and (3) in biological systems in the context of superoxide dismutase and the role of iron. Hydroxyl radicals in aqueous media can be generated by several mechanisms ... 

After effects of nuclear transformations in solids Biological systems Minerals... 

Harry B. Gray and Walther Ellis,13 writing in Chapter 6 of reference 13, describe three types of oxidation-reduction centers found in biological systems. The first of these, protein side chains, may undergo oxidation-reduction reactions such as the transformation of two cysteine residues to form the cystine dimer as shown in equation 1.28 ... 

Enzymes are remarkable molecular devices that determine the pattern of chemical transformations in biological systems. The most striking characteristics of enzymes are their catalytic power and specificity. As a class of macromolecules, they are highly effective in catalyzing diverse chemical reactions because of their ability to specifically bind to a substrate and their ability to accelerate reactions by several orders of magnitude. Applying enzymes or organisms in... 

In proteomics, quantitation is typically a comparison of two biological systems, for example, cells in a normal state versus cells in a transformed state. MS-based quantitation utilizes analyses of digested extracted proteins (Fig. 7.1a). The comparison... 

It is well known that pyrimidine bases convert to photodimers upon irradiation to UV light near the X max( > 270 nm). This photochemical reaction has a lethal effect in biological systems due to the photochemical transformation of pyrimidine bases of nucleic acids. However the photodimerization is a reversible reaction and the photodimers split to afford the original monomers very efficiently upon irradiation at a shorter wavelengths as shown in Scheme 1(1). 

Metabolism. Although no information was located regarding mechanisms of chlorine dioxide and chlorite metabolism, ultimate transformation to chloride ions is likely achieved via redox reactions with a variety of substances in biological systems that are readily oxidized. 

X-ray absorption spectroscopy is an exciting new tool, ideally suited to probing the immediate environment of a specific atom type in a physical, chemical or biological system. The advent of synchrotron radiation has transformed this technique from a topic of relatively minor interest to one of major scientific importance and activity " . A major attraction of the technique is the possibility it provides of probing a reaction centre in a wide range of materials ranging from an industrial catalyst to an enzyme the technique is not limited by the physical state of the sample. In this review, suitability of this technique for biochemical systems is discussed. 

The roles of carbocations in commercially important hydrocarbon transformations are still not perfectly understood. The same can be said for carbocations in biological systems. Significant questions concerning reactivity still need to be explained. Why do so many reactions of carbocations show constant selectivity, in violation of the reactivity-selectivity principle Is it possible to develop a unified scale of elec-trophilicity-nucleophilicity, in particular one that incorporates these parameters into the general framework of Lewis acidity and basicity. Finally, quite sophisticated synthetic transformations are being developed that employ carbocations, based upon insights revealed by the mechanistic studies. 

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