Dinuclear structural motifs

The general dinuclear structural motifs are of the weakly linked, 1, or covalently-bridged, 2, types shown in which... 

Pt(en)(N03)2] and [Pt(OTf)2L2] (L = mono- or 1/2 bidentate tertiary phosphine) or dinuclear complexes of the type [Pt2(OTf)2(/i-monodentate tertiary phosphine cr-aryl = 4, -biphenyl, / -terphenyL 4,4 -benzophenone, etc.) other structural motifs employing platinum(II) have also been reported.2 0 The addition of bridging, multidentate N-donor ligands of various shapes and sizes to the labile complexes in a suitable solvent system has afforded several classes of discrete, plat-inum(II)-containing polygons, polyhedra, and catenanes. 

Fig. 7.1 Structural motifs for the dinuclear complex [(CjEOPtCfiF, proposed by Pfeiffer in 1927 (I) and Kharasch and Ashford in 1936 (II)...

The iron ligands in the dinuclear sites of these proteins are very similar — the structures of the (p-carboxylato) di-iron cores found for MMOH, ToMOH, RNR-R2, rubreythrin, stearoyl-acyl carrier protein A desaturases, bacterioferritin, and methaemerythrin are presented in Figure 13.26. They all have the same three-amino-acid structural motif on one side of the di-iron site, made up of a bridging Glu and two His residues, coordinated in... 

Type 1 copper proteins are the class of proteins for which cupredoxins were originally named. Type 1 copper proteins include both proteins with known electron transfer function (e.g., plastocyanin and rusticyanin), and proteins whose biological functions have not been determined conclusively (e.g., stellacyanin and plantacyanin). Although these proteins with unknown function cannot be called cupredoxins by the strict functional definition, they have been classified as cupredoxins because they share the same overall structural fold and metal-binding sites as cupredoxins. In addition, many multidomain proteins, such as laccase, ascorbate oxidase, and ceruloplasmin, contain multiple metal centers, one of which is a type 1 copper. Those cupredoxin centers are also included here. Finally, both the Cua center in cytochrome c oxidase (CcO) and nitrous oxide reductase (N2OR), and the red copper center in nitrocyanin will be discussed in this chapter because their metal centers are structurally related to the type 1 copper center and the protein domain that contains both centers share the same overall structural motif as those of cupredoxins. The Cua center also functions as an electron transfer agent. Like ferredoxins, which contain either dinuclear or tetranuclear iron-sulfur centers, cupredoxins may include either the mononuclear or the dinuclear copper center in their metal-binding sites. 

A connection between the manganese catalyzed formation of benzyl radicals and tyrosyl radicals can be formally established. It is known that Mn can replace Fe in some ribonucleotide reductases (RR) with retention of activity. Also, a dinuclear Mn active site has been proposed for authentic manganese ribonucleotide reductases (MnRR).l Both RR s share the X-oxo bridged dinuclear manganese motif with 1, except that, as discussed above, 1 comprises two such structural units. 

Using a copper(I) source such as CuBr-SMej and reacting it with Mes-34 revealed another dinuclear, yet rarely observed structural motif, which hkely is formed driven by steric effects. We presume that by going from the JV-methyl NHCP Me-34 to the more bulky Af-mesityl ligand favors the formation of cluster Mes-54, since the ligands are then at a greater distance from each other. A further increase of steric bulk to the NHCP tBu-34 prevented the formation of a bis-ligated species. Instead, the mono nuclear complex fBu-55 [56] was formed. Extraordinarily, the bromide does not coordinate to the copper center, which has never been observed previously. The only other known complex of the type... 

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