Coordination cluster

The definitions of the cluster ligands of the [3Fe-4S] cluster and of the related structural features are quite useful to predict cluster types in other Fds of known sequence, as well as to determine the nature of the cluster coordinating atoms (and variability) and their control on the type and performances of the metal sites, in particular in terms of cluster stability, cluster interconversion capability, and acceptance of other metals at the cluster. 

Noodleman, L., C. Y. Peng, D. A. Case, and J. M. Muesca. 1995. Orbital Interactions, Electron Delocalization and Spin Coupling in Iron-Sulfur Clusters. Coordination Chemistry Reviews 144, 199. 

The native iron-sulfur clusters of many enzymes can be directly observed by EPR spectroscopy (Beinert, 1978). In several cases, appearance of the DNIC signal from nitrogen oxide-treated enzyme (Salerno et al., 1976 Dervartanian et al., 1973 Hyman et al., 1992) or cells (Reddy et al., 1983 Payne et al., 1990) results in the disappearance of these native signals, indicating conversion of the iron from the native cluster coordination to DNIC complexes. However, loss of EPR signal from native clusters does not necessarily correlate with appearance of the DNIC signal (Hyman et al., 1992). 

While many compounds of the type X As(ER3)3 (n =0-2 X = any other group, e.g. H, Hal, R etc. R = H, alkyl, aryl E = Ge,263 Sn, 64 Pb265) have been produced, they are mainly of interest to theoreticians and synthesists. They have the expected pyramidal geometry of AsX3 compounds, and their interest to coordination chemists lies in their behaviour as ligands, which is dealt with elsewhere (Chapter 12.2) there is some special interest in cluster coordination compounds involving As—Ge bonding,... 

An activation barrier is associated with the cluster transformation. If the dissolved gas is methane, the barrier for transforming the cluster coordination number from 20 (for the 512) to 24 (for the 51262) is high, both because the guest cannot lend much stability to the larger cavity (see Section 2.1.3.2) and because the 51262 cavities outnumber the 512 in si by a factor of 3. Transformation of methane-water clusters from... 

Enzymes are large protein molecules (apoenzymes), which act as catalysts for almost all the chemical reactions that occur in living organisms. The structures of a number of enzymes contains groups of metal ions, known as metal clusters, coordinated to the peptide chain. These enzymes are often referred to as metalloenzymes. Many enzymes require the presence of organic compounds (co-enzymes) and/or metal ions and inorganic compounds (co-factors) in order to function. These composite active enzyme systems are known as holoenzymes. 

Two classes of DNA repair enzymes contain [4Fe-4S] + clusters that are not involved in catalysis and appear to have purely structural roles. Several members of the superfamily of helix-hairpin-helix DNA repair enzymes contain a redox-inert [4Fe-4S] + cluster coordinated by a C-X6-C-X2-C-X5-C cysteine motif, for example, endonuclease in 50,5i,263 52,79,264,265 thymine-DNA... 

As in mononuclear nitrosyl complexes, it is convenient to separate the reactivity into two sections (1) reactions directly involving change at the NO, and (2) reactions of the metals that are enhanced by the presence of the nitrosyl ligand. The reaction of overwhelming importance that occurs with cluster coordinated nitric oxide is deoxygenation. Depending on the conditions this can ultimately sdeld NH, NH2, NCO, or simply N atoms coordinated to the cluster. 

F . 3 Changes in ionicity of oxygen ion with local sites in Si04 and SizO - clusters coordinating metal ions. 

For the Si04 cluster coordinating Na", the contour map of the charge difference, Ap (p (Si04Na )—p (Si04 )), was calculated, in order to obtain better understanding of a decrease in the bond order... 

Figure 1 Four examples of cluster structures (a) Na2[Pt3(CO)6] ( = 2,3,5) inset TEM picture of Pt nanoparticles from [Pt3(CO)e]fo precursor (b) unit cell of Pt2Ru4(CO)is cluster. Coordination distances in a cluster are i pt Ru = 2.70 A, = 2.66 A, and Rru.ru = 2.16 A (c) unit cell of Ru4Se2(CO)n cluster. Coordination distances in a cluster are Rru-ru = 2.79 2.77 A, i Ru-se = 2.56 2.60 A. Inset TEM picture of Ru Se, colloidal nanoparticles from Ru3(CO)i2 and Se, via the Ru4Se2(CO)n chemical precursor (the stabilizer was octade-canthiol) (d) Chevrel cluster phase MoeScg. Coordination distances in a cluster are Rmo-mo = 2.68 2.83 a, and RMo-se = 2.598 A. For a pseudo-ternary compound Mo4Ru2Ses. Coordination distances in a cluster are 7 Me-Me = 2.659, 2.71 A i Me-se = 2.623 A.

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