Tyrosyl radicals complexes

The CC and CO vibrations are also sensitive to the molecular environment by virtue of electrostatic and hydrogen bonding interactions. The frequencies of phenoxyl and tyrosyl radicals complexed by macrocyclic hgands and generated in wVo were measured by resonance Raman and FTIR techniques. Thus a selective enhancement of the vibrational CC and CO stretch modes of the phenoxyl chromophores in metal-coordinated radical... 

The continuous development of phenoxyl radical complexes started with an aim of modeling primarily the enzyme GO. The number of papers cited testily to the uninterrupted interest in this chemistry. Thus a small selection of more recent references from the literature including reviews (224), theoretical (225) and model studies (226), and characterization of tyrosyl radicals in biological systems (227) will close this chapter. 

There are numerous reports on the chemical synthesis of models for the active site of galactose oxidase both in the reduced Cu(l) and the oxidized Cu(II) form. We mention only a selection in which EPR is at least used to characterize the complex either on the phenoxy radical or on the copper part, typically in conjunction with X-ray data.48,49 50 A review on structural, spectroscopic and redox aspects of galactose oxidase models is available.51 More important with respect to EPR is the report on the 3-tensor calculation of the thioether substituted tyrosyl radical by ab initio methods but this is borderline to the aspects treated in this review since the copper ion is not involved.52... 

The generation, stability, and function of tyrosyl radicals in ribonucleotide reductase, PGH synthase, and galactose oxidase continue to be active areas of research. The difficulties encountered in preparing and handling these proteins, as well as in probing the physical properties and reactivity of their metal-phenoxyl radical active sites, make the preparation and investigation of stable phenoxyl radical metal model complexes an attractive goal. 

Transition metal ions with organic radicals exist in the active sites of metalloproteins. The best understood example is galactose oxidase, which features a single Cu(II) ion coordinated to a modified tyrosyl radical. Many combined experimental and theoretical studies have focused on electronic properties of metal complexes with redox active ligands, yet reactivity beyond characterization has been limited. We will demonstrate the influence of the metal complex redox state on H2 activation by anilino-phenolate noninnocent ligands. 

The demanded electron transfer in E. coli RNR could present a real enigma As estimated from the docked complex of the two separately solved three-dimensional structures of R1 and R2 (Figure 4), the site of the stable tyrosyl radical in protein R2 is at a distance of approximately 30n 40 from the active site in protein R1 (Eklund et al 1997 Uhlin and Eklund, 1994). According to theoretical as well as experimental considerations of electron transfer reactions in proteins (Gray and Winkler, 1996 Beratan et al., 1992 Moser et al 1992 Marcus and Sutin, 1985), the electron transfer rate over such a distance would be on the order of InO.OOl s ... 

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