Biomolecules oxygen reduction

Although many polyphenolic compounds can quench DPPH215 218 and scavenge radicals in competition with spin traps,225 232,278 consideration must also be given to the fate of the resultant phenoxyl radicals, which can include their direct reaction with important biomolecules, further oxidation to cytotoxic quinones and, in the case of semiquinones, their reduction of oxygen to superoxide. Thus,... 

This composite satellite image displays areas on the surface of the Earth where chlorophyll-bearing plants are located. Chlorophyll, which is one of nature s most important biomolecules, is a member of a class of compounds called porphyrins. This Glass also includes hemoglobin and cytochrome c, which is discussed in Feature 19-1. Many analytical techniques have been used to measure the chemical and physical properties of chlorophyll to explore Its role in photosynthesis. The redox titration of chlorophyll with other standard redox couples reveals the oxidation/ reduction properties of the molecule that help explain the photophysics of the complex process that green plants use to oxidize water to molecular oxygen. 

Oxidation of nutrients to provide energy for an organism cannot take place without reduction of some electron acceptor. The ultimate electron acceptor in aerobic oxidation is oxygen we shall encounter intermediate electron accep)-tors as we discuss metabolic processes. Reduction of metabolites plays a significant role in living organisms in anabolic processes. Important biomolecules are synthesized in organisms by many reactions in which a metabolite is reduced while the reduced form of a coenzyme is oxidized. 

Lead appears to be able to interact with complex small biomolecules as well, such as flavins for example, bis(lO-methylisoalloxazine) perchlorate tetrahy-drate (223). IsoaUoxazine is a planar three-ringed heterocychc amino cofactor associated with riboflavin and is active in oxidation-reduction reactions with metals such as Mo and Fe. Lead binds to bis(lO-methylisoalloxazine) in a 1 1 metal-ligand complex, with two additional waters bound resulting in a four coordinate molecule with a total of four oxygen donors. An active lone pair results in a distorted square-pyramidal structure. As is the case for citrate, extensive hydrogen bonding was observed in the crystal lattice. 

At the same time, toxic forms of oxygen, free radicals and covalent compounds, form as byproducts (through one, two and three-electron reduction), which oxidise lipids of biological membranes, then subsequently DNA, proteins and other biomolecules (Figure 3.77). Fortunately, organisms are also equipped with detoxifying mechanisms, which include ... 

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