Structural and Functional Models

In terms of precedent, copper(I) is well known to bind CO and such adducts typically exhibit high values of v o. which suggest susceptibility to attack by nucleophiles. Nucleophilic attack at Cu-CO by this enzyme, however, is proposed to lead to an O-bound thiocarbonate, which entails scission of an initially formed Cu-CO bond. Precedent for this reactivity is provided by the reaction of Pd(ll) complexes of CNMe with W-SH species (Eq. 12.14) [142]. 

Models for monodithiolene molybdenum species related to xanthine oxidase and aerobic CODH have been described, e.g. [Mo(S2CgH4)02(SR)] [143]. The synthesis of related species with terminal sulfido ligands would enable assembly of the indicated (dithiolene)Mo02S-CuSR ensembles. The interaction of M0S4 and Cu has received considerable study, motivated by interest in the ability of dietary Mo to inhibit copper uptake in ruminants [144]. Bi-, tri-, tetra-, or higher nuclearity Cu-Mo clusters result from the reaction of MoS and Cu in the presence of tertiary phosphines, amines, or cyanide [144]. 

---

The value of the tris(pyrazolyl)hydroborato complexes [TpRR ]ZnOH is that they are rare examples of monomeric four-coordinate zinc complexes with a terminal hydroxide funtionality. Indeed, [TpBut]ZnOH is the first structurally characterized monomeric terminal hydroxide complex of zinc (149). As such, the monomeric zinc hydroxide complexes [TpRR ]ZnOH may be expected to play valuable roles as both structural and functional models for the active site of carbonic anhydrase. Although a limitation of the [TpRR ]ZnOH system resides with their poor solubility in water, studies on these complexes in organic solvents... 

Professor M. R. Maurya is currently heading the Department of Chemistry, IIT Roorkee. He has more than 26 years of teaching and research experience. He had worked in Loyola University of Chicago, USA, Iowa State University, Ames, Iowa, USA, National Chemical Laboratory, Pune, and Pune University Pune, before joining department of Chemistry at IIT Roorkee in 1996 and became full professor in 2008. His current area of research interests include structural and functional models of vanadate-dependent haloperoxidases, coordination polymers and their catalytic study, metal complexes encapsulated in zeolite cages and their catalytic study, polymer-anchored metal complexes and their catalytic study, and medicinal aspects of coordination compounds. So far, he has guided 21 doctoral and 7 Master s theses, co-authored more than 140 research papers in the international refereed journals. 

Figure 7.10 Structural and functional model of the NAD-reducing hydrogenase of R. eutropha, showing the positions of residues modified by mutagenesis. 

Bauwman E, Reedijk J (2005) Structural and functional models related to the nickel hydrogenases. Coord Chem Rev 249 1555-1581... 

Fukuzumi and co-workers described spectroscopic evidence for a ix-rf- ] -peroxo-(Cu )2 species stabilized with a fcidentate nitrogen ligand, but no (catalytic) oxidation behavior towards catechol was noted (a related trinu-clear copper species converted 2,4-di-ferf-butylphenol stoichiometrically towards the biphenol derivative) [224], Stack et al. have described a similar ] -peroxo-(Cu )2 species (28, vide supra) that could be considered a structural and functional model for tyrosinase-activity, as it efficiently reacted with catechol, benzyl alcohol and benzylamine to yield quinone (95%), benzaldehyde (80%) and benzonitrile (70%) [172,173]. This dinuclear per-0X0 species is generated by association of two monomeric copper centers, in contrast to the systems based on dinucleating Ugand scaffolds described above. 

Several manganese complexes have recently been proposed as structural and functional models of SOD. 

III. STRUCTURAL AND FUNCTIONAL MODELS A. Urea Binding to Metal Ions General Aspects... 

The sequential electron transfer path in nitrogenase is followed first models of the Fe4S4 cluster of the iron-protein are discussed, then mimics of the P-cluster in the molybdenum-iron protein, and finally structural and functional models of the FeMo-cofactor are summarized. 

This complex has been shown to be an excellent structural and functional model for the zinc hydrolytic enzymes, particularly carbonic anhydrase but also carboxypeptidase and the zinc phosphate esterases (24-26). The same complex also catalyzes the hydration of acetaldehyde and hydrolysis of carboxylic esters. These reactions appear to progress via a mechanism similar to that proposed for carbonic anhydrase. The rates are slower for [Zn([12]aneN3)OH] than for the enzyme but an order of magnitude faster than for existing model systems such as [(NH3)5Co(OH)]2+ (26). 

Structural and Functional Models of the Native Enzymes, Including Applications in Organic Synthesis... 

Lee-Huang S, Maiorov V, Huang PL et al (2005) Structural and functional modeling of human lysozyme reveals a unique nonapeptide, HL9, with anti-HIV activity. Biochemistry 44 4648-4655... 

The Mo (VI) and Mo (IV) complexes above are excellent structural and functional models for the oxidized and reduced states of DMSO reductase. They also reproduce absorptions at similar wavelengths to those observed for the enzyme from R sphaeroides. The desoxo-Mo(IV) complexes are reduced only at very negative potentials, a fact likely to account for the absence of Mo (III) enzyme states. 

Copper(I) complexes supported by certain capping ligands react with molecular oxygen in a 2 1 ratio to afford dinuclear copper dioxygen (CU2/O2) complexes. Such complexes can be regarded as structural and functional models of the reactive intermediates of tyrosinase and catechol oxidase. Numerous review articles on the subject have been published so far. ... 

COORDINATION COMPLEXES AS STRUCTURAL AND FUNCTIONAL MODELS OF THE Mn4 CLUSTER... 

---