Redox induced structural changes

Although the redox reactions in Sch. 12 have not been achieved electrochemically, they illustrate another type of redox-induced structural change in a dimolybdenum compound with a sulfur-rich coordination sphere. In this case, Mo2(/r-S)2 ring opening in 18 (cleavage of Mo—Mo and Mo—S bonds) is associated with the exposure of vacant coordination sites, and the uptake of two carbonyl ligands in 17 [7, 53]. 

Kochi s book from 1978 [la] helped to establish electron-transfer and radical reactions as a crucial part of mainstream organometallic chemistry. The importance of such reactions is evident from Astruc s book [lb], still the most comprehensive and authoritative book in the area, and from several reviews and review collections [2] on aspects of organometallic electron-transfer reactivity. This chapter will be fully devoted to the use of electrochemical techniques to obtain bond-energy data for organometallic complexes, a topic that has not been previously reviewed. Aspects of the energetics of redox-induced structural changes and isomerizations, a thoroughly pursued topic, has been reviewed [2o] and will not be included here. 

Because this is an oxidation, and E , < E , the trans cation stays in its oxidized form during the positive-going part of the scan but is reoxidized to the neutral trans compound when the scan is reversed (Fig. 5). Cyclic voltammetry is a way to study redox-induced structure changes like these. 

Square Schemes and Redox-Induced Structural Changes 302... 

Square schemes related to those discussed in the previous sections have been applied to investigate kinetic, thermodynamic, and mechanistic aspects of redox-induced structural changes in organometallic complexes. The... 

High concentrations of heavy metals that affect, directly or indirectly, the redox potential in the reducing intracellular milieu, particularly copper, induce the formation of reactive oxygen species. These, in turn, can trigger the chain reaction causing lipid peroxidation, which affects membrane integrity and induces structural changes to proteins and nucleic acids that can result in cell death. 

Whereas in many metalloprotein redox systems the oxidation states +2, +3, and +4 are involved, horseradish peroxidase catalysis appears to involve five oxidation states. The interest to coordination chemists of this study goes well beyond bioinorganic systems, for here, as in several cases reported earlier, the X-rays used to obtain the high-resolution structures induced chemical changes during structure determination. The X-rays liberate electrons, which may change the oxidation state of the metal. ... 

Nmr methods are also valuable in other areas of protein structure. For example, information about the role and extent of induced conformational changes (caused, for example, by inhibitor-substrate binding, by ionization of side chains, or by redox changes) can be obtained. 

In the X-ray structure of bovine heart cytochrome c oxidase in the fully oxidized state at 2.8 resolution, two hydrogen bond networks connecting the molecular surface on the matrix side to that on the intermembrane surface were identified (Tsukihara et ah, 1996). Both networks contain possible hydrogen bond structures, as defined by the criteria stated above, but do not include elements of structure comprising the O2 reduction site. However, small conformational changes induced by changes in the redox... 

In a general sense, metal clusters have been regarded as electron reservoirs which can gain or lose electrons at will without molecular disruption. However, few real species possess this property, and the addition or subtraction of more than one electron usually leads to structural changes, and a concomitant increase in reactivity. Detailed studies are being made, therefore, of redox-induced changes in structure and reactivity, studies which promise to provide rational routes to new polymetallic complexes and information about electronic structure. 

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