Novel Redox Systems

The authors gratefully acknowledge the support of the UK Medical Research Council, Cancer Research UK, the Biotechnology and Biological Sciences Research Council, the Wellcome Trust, the Lister Institute of Preventative Medicine, and the Emopean Union, EPSRC (Engineering and Physical Sciences Research Council) and the Royal Society. 

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K. S. Estes, M. E. Brewster, J. W. Simpkins, and N. Bodor, A novel redox system for CNS-directed delivery of estradiol causes sustained LH suppression in castrate rats, Life Sci. 40 1327 (1987). 

P450s from Thermophilic Microbes and Novel Redox Systems for Sulfolobus P450s... 

Some of the materials highlighted in this review offer novel redox-active cavities, which are candidates for studies on chemistry within cavities, especially processes which involve molecular recognition by donor-acceptor ii-Jt interactions, or by electron transfer mechanisms, e.g. coordination of a lone pair to a metal center, or formation of radical cation/radical anion pairs by charge transfer. The attachment of redox-active dendrimers to electrode surfaces (by chemical bonding, physical deposition, or screen printing) to form modified electrodes should provide interesting novel electron relay systems. 

Nevertheless, the mid-peak potentials determined by cyclic voltammetry and other characteristic potentials obtained by different electroanalytical techniques (such as pulse, alternating current, or square wave voltammetries) supply valuable information on the behavior of the redox systems. In fact, for the majority of redox reactions, especially for the novel systems, we have only these values. (The cyclic voltammetry almost entirely replaced the polarography which has been used for six decades from 1920. However, the abundant data, especially the half-wave potentials, 1/2, are still very useful sources for providing information on the redox properties of different systems.)... 

Another example of a photoredox molecular switch is based on a ferrocene-ruthenium trisbipyridyl conjugate, in which the luminescent form 4 switches to the non-luminescent form 5 upon electrochemical oxidation (Figure 2/bottom)171. Biological systems exploit the interplay of redox and molecular recognition to regulate a wide variety of processes and transformations. In an attempt to mimic such redox systems, Deans et al. have reported a three-component, two-pole molecular switch, in which noncovalent molecular recognition can be controlled electrochemically. x Willner et al. have reported on their research activities in developing novel means to achieve reversible photostimulation of the activities of biomaterials (see Chapter 6).[91 Recently, we have shown that it is possible to switch the luminescence in benzodi-furan quinone 6 electrochemically. 101 The reduction in THF of the quinone moiety... 

A novel light-reversible redox system has been discovered381 with glycylglycine it is summarized in Scheme 7. Preparations of mixed cobalt(m) complexes of macrocycles and amino-acids, trans-[Co [ 14]aneN4 (amino-acid)2]3 + and trans-[Co Me4-[14]tetraeneN4](amino-acid)2]3+, have been reported using glycine, S-alanine, S-phenylalanine, and S-leucine.382... 

The mechanism of particle formation at submicellar surfactant concentrations was established several years ago. New insight was gained into how the structure of surfactants influences the outcome of the reaction. The gap between suspension and emulsion polymerization was bridged. The mode of popularly used redox catalysts was clarified, and completely novel catalyst systems were developed. For non-styrene-like monomers, such as vinyl chloride and vinyl acetate, the kinetic picture was elucidated. Advances were made in determining the mechanism of copolymerization, in particular the effects of water-soluble monomers and of difunctional monomers. The reaction mechanism in flow-through reactors became as well understood as in batch reactors. Computer techniques clarified complex mechanisms. The study of emulsion polymerization in nonaqueous media opened new vistas. 

By further evaluation of the redox system SeBr4/SeBr2/Se/Br in aprotic solvents (Section III,A), the first examples of bromoselenates-(II,IV) containing selenium in both oxidation states +2 and +4 were prepared. Three dinuclear, trinuclear, and tetranuclear types of anions are reported in this novel class of mixed-valence compounds Se2Brg, SeaBrio , and Se4Bri2 . They are shown in Fig. 31. Similar to the bromoselenates(II), they were obtained by nucleophilic addition reactions of bromide ions within the complex reaction mixtures of selenium bromides. Evidently, the formation of Bra" is important for the stabilization of Se(II) in addition to Se(IV), shifting the equilibrium... 

NADPH. In a number of examples it has been demonstrated that cyclic sesquiter-penoids result from 2-trans-FFP by dephosphorylation and conversion into 2-cis-farnesol (and hence presumably 2-c/5-FPP) via a redox system. However, in the present case farnesol was not a substrate and no tracer could be demonstrated to be associated with the farnesals. The fact that the added hydrogen came from the opposite face of NADPH to that utilized in common redox systems e.g. liver alcohol dehydrogenase) may indicate that a totally different type of mechanism occurs from that previously proposed for the trans to cis conversion, and the occurrence of a novel cyclopropyl intermediate was suggested (Scheme 12). 

Lacking GSH-dependent peroxidases, Plasmodium spp. rely on a Prx-linked detoxification for hydroperoxides and reduced GSH acts primarily as the principal redox buffer. It is also important in detoxification reactions as a co-factor for GST and glyoxalase and has been shown to be involved in the breakdown of free ferriprotoporphyrin IX. The lack of two major antioxidants present in other cells (catalase and GSH peroxidase) suggests that malaria parasites would be vulnerable to disturbances in their anti-oxidant systems. As a consequence, pro-oxidant drugs such as the artemisinins, which increase the oxidative stress, are efficient antimalarials. It has been proposed that a novel approach to malaria chemotherapy would be to develop drugs that disrupt the anti-oxidant and redox system of Plasmodium (Muller, 2004 Nickel et al., 2006 Rahlfs and Becker, 2005). 

The literature concerned with the polarographic reduction of metal ions on mercury in non-aqueous solvents is vast and has been reviewed by Mann and Barnes. Much less effort has been expended in the equally important field of the anodic behaviour of metal ions in such solvents. Redox couples, which may have very different standard potentials in non-aqueous media from those observed in aqueous solutions (e.g. Fe lFe ref. Q62), might form the basis of novel oxidative systems. 

The hybrid complexes composed of transition metals and redox-active 7C-conjugat-ed polymers (synthetic metals) or molecules provide novel multi-redox systems, with much potential. The structural control in the complexation leads to structurally defined hybrid systems. These systems are promising for the development of efficient catalysts and functionalized materials. 

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