Ruthenium compounds 2 phen

During recent years, interest in the bipy (and phen) compounds has been renewed because of their interesting redox and photoredox properties, with particular attention being given to the ruthenium compounds (see also Chapter 45). In the case of Cu compounds of these ligands, many systems have been shown to have strong antimicrobial effects. ... 

Early reports on interactions between redox enzymes and ruthenium or osmium compounds prior to the biosensor burst are hidden in a bulk of chemical and biochemical literature. This does not apply to the ruthenium biochemistry of cytochromes where complexes [Ru(NH3)5L] " , [Ru(bpy)2L2], and structurally related ruthenium compounds, which have been widely used in studies of intramolecular (long-range) electron transfer in proteins (124,156-158) and biomimetic models for the photosynthetic reaction centers (159). Applications of these compounds in biosensors are rather limited. The complex [Ru(NHg)6] has the correct redox potential but its reactivity toward oxidoreductases is low reflecting a low self-exchange rate constant (see Tables I and VII). The redox potentials of complexes [Ru(bpy)3] " and [Ru(phen)3] are way too much anodic (1.25 V vs. NHE) ruling out applications in MET. The complex [Ru(bpy)3] is such a powerful oxidant that it oxidizes HRP into Compounds II and I (160). The electron-transfer from the resting state of HRP at pH <10 when the hemin iron(III) is five-coordinate generates a 7i-cation radical intermediate with the rate constant 2.5 x 10 s" (pH 10.3)... 

Ruthenium(iv).—Several novel Ru compounds have been isolated from the reaction sequence shown in Scheme 9. These diamagnetic complexes are assumed to be mononuclear with two trans oxide groups. In addition, the dinuclear complex [Ru(0H)3(phen)]20 was reported to be formed by evaporating a methanolic solution of [Ru03(phen)]20. A study of the mechanism... 

Most photosensitizers, however, are reasonably photostable compounds, and their optical properties have been studied in depth. In particular, there has been much interest in ruthenium-based photosensitizers such as [Ru(bpy)3]2+ and [Ru(phen)3]2+, due to their stability and absorption of visible light. Detailed information on their optical properties, including ground and excited state information in relation to photosensitization, has been reviewed by Creutz et al. [16]. Similarly, the photochemistry and photophysics of rhenium complexes, as discussed here, have been reviewed in detail by Kirgan et al. [7]. 

The intense red-colored diamagnetic tris-bipyridyl and tris-phen-anthroline iron(II) complex cations are perhaps the most widely studied compounds of these ligands. It is now accepted that the absorption responsible for their characteristic deep color results from a Laporte-allowed transition of the t., tt type (7). This is supported by the fact that the intensity increases in cooling [578) and by measurement of the circular dichroism of the complexes [372). The corresponding complexes of ruthenium(II) (5 3) and osmium(II) [252) have very similar charge transfer spectra. 

The emission lifetimes of the bipy and phen complexes of ruthenlum(II) at 77°K are generally in the range t = 0.5-10 ps. (Table 7). Since these values are intermediate to those generally observed for the fluorescence and phosphorescence of organic compounds, the radiative transition in the ruthenium complexes was suggested to be a heavy-atom perturbed spin-forbidden process (168,169). From a determination of the absolute quantum yields as well as lifetimes of a series of ruthenium(II) and osmium(II) complexes, the associated radiative lifetimes were calculated (170). The variations in these inherent lifetimes within the series could be rationalized with a semi-emipirical spin-orbit coupling model thus affording further evidence that the radiative transitions are formally spin forbidden in these systems. 

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