For present purposes, a protein-bound metal site consists of one or more metal ions and all protein side chain and exogenous bridging and terminal ligands that define the first coordination sphere of each metal ion. Such sites can be classified into five basic types with the indicated functions: (1) structural -- configuration (in part) of protein tertiary and/or quaternary structure; (2) storage -- uptake, binding, and release of metals in soluble form: (3) electron transfer -- uptake, release, and storage of electrons; (4) dioxygen binding -- metal-O{sub 2} coordination and decoordination; and (5) catalytic -- substrate binding, activation, and turnover. The authors present here a classification and structure/function analysis of native metal sites based on these functions, where 5 is an extensive class subdivided by the type of reaction catalyzed. Within this purview, coverage of the various site types is extensive, but not exhaustive. The purpose of this exposition is to present examples of all types of sites and to relate, insofar as is currently feasible, the structure and function of selected types. The authors largely confine their considerations to the sites themselves, with due recognition that these site features are coupled to protein structure at all levels. In themore » next section, the coordination chemistry of metalloprotein sites and the unique properties of a protein as a ligand are briefly summarized. Structure/function relationships are systematically explored and tabulations of structurally defined sites presented. Finally, future directions in bioinorganic research in the context of metal site chemistry are considered. 620 refs.« less

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Structural and Functional Aspects of Metal Sites in Biology

Synthetic Analogues and Reaction Systems Relevant to the Molybdenum and Tungsten Oxotransferases

The biologically relevant oxygen atom transfer chemistry of molybdenum: from synthetic analogue systems to enzymes

Publisher Summary This chapter discusses some of the most significant recent findings and unusual properties of native and synthetic Fe4S4 clusters. Certain properties lead to newer types of clusters, viz., the cuboidal and heterometal cubane-type species. These afford new structural and reactivity themes in both inorganic chemistry and biology. This contention is well supported by consideration of just four of the major discoveries in the field in the last decade. With the former clusters, structural definition has advanced to the point where the relative stabilities of oxidation states of conventional Fd versus HP proteins may be sensibly interpreted in terms of the influence of the immediate protein environment, viz., the different numbers of protein-cluster N–H . . . S hydrogen bonds. Equilibrium and kinetic data may be derived with just trace amounts of protein and verified by preparation of appropriate spectroscopic samples.

Trinuclear Cuboidal and Heterometallic Cubane-Type Iron–Sulfur Clusters: New Structural and Reactivity Themes in Chemistry and Biology

Publisher Summary This chapter presents a discussion on the bioinorganic chemistry of pterin-containing molybdenum and tungsten enzymes. The chapter focuses on the current results and the interplay of model and enzyme chemistry. Attention is directed to sulfite oxidase and xanthine oxidase, the archetypal examples of molybdenum enzymes, containing, respectively, dioxo-Mo(VI) and oxo-thio-Mo(VI) oxidized centers. Biochemical and model studies of molybdopterin, Mo-co, and related species are described in this chapter. A brief survey on the physical and spectroscopic techniques employed in the study of the enzymes is presented and their impact on the current understanding of the coordination about the molybdenum atom in sulfite oxidase and xanthine oxidase is discussed. Structural and spectroscopic models are also presented in the chapter. The chapter also explains the xanthine oxidase cycle and facets of intramolecular electron transfer in molybdenum enzymes. The pterin-containing tungsten enzymes and the evolving model chemistry are discussed. Current descriptions of the coordination environment of the molybdenum centers of the enzymes rest primarily upon the comparisons of the spectra of the enzymes with the spectra of well-characterized molybdenum complexes. The unexpected discovery that several hyperthermophilic organisms possess pterin-containing tungsten enzymes promises to stimulate the development of oxo-thio-tungsten chemistry.

Bioinorganic chemistry of pterin-containing molybdenum and tungsten enzymes

A series of dioxo-Mo(VI) Schiff base complexes of the type MoO 2 (R-L)(solv) has been prepared: L=2-(salicylideneamino)-phenolate(2-) (sap) or 2-(salicylideneamino)benzenethiolato(2-) (ssp); solv=solvent. Salicylidene ring substituents R were selected to promote solubility and crystallinity. The unsubstituted complexes MoO 2 (sap)(solv) and MoO 2 (ssp)(solv) have been previously reported. The structures of two members of the series were determined

Oxomolybdenum(IV,V,VI) Complexes: Structures, Reactivities, and Criteria of Detection of Binuclear (μ-oxo)molybdenum(V) Products in Oxygen Atom Transfer Systems

Anaerobic reaction of equimolar FeX/sub 2/ and RS/sup -/ in acetonitrile affords the trinuclear complexes (Fe/sub 3/(SR)/sub 3/X/sub 6/)/sup 3 -/ (with X = Cl and R = Ph (4a), p-tolyl (4b), 2,6-Me/sub 2/C/sub 6/H/sub 3/ (4d), and X = Br, R = Ph (4c)) isolated as Et/sub 4/N/sup +/ salts. These species constitute the fourth known type of discrete Fe(II) thiolates, the others being (Fe(SR)/sub 4/)/sup 2 -/, (Fe/sub 2/(SR)/sub 6/)/sup 2 -/, and (Fe/sub 4/(SR)/sub 10/)/sup 2 -/. The following crystallographic results were obtained (crystal system; space group; cell parameters; Z; unique data (I > 3sigma(I)); R (%)). (Et/sub 4/N)/sub 3/ (4a): monoclinic; C2/c; a = 24.500 (6) A, b = 13.488 (3) A, c = 18.217 (5) A, ..beta.. = 110.68 (2)/sup 0/; 4; 2679; 4.9. (Et/sub 4/N)/sub 3/ (4d) x 3MeCN: monoclinic: P2/sub 1//n; a = 15.07 (1) A, b = 22.38 (3) A, c = 20.46 (3) A, ..beta.. = 91.5 (1)/sup 0/; 4, 3311; 9.7. (Et/sub 4/N)/sub 3/ (4c) x MeCN: hexagonal, P/sup -/62c; a = b = 13.970 (4) A, c = 18.274 (3) A; 2; 890; 5.7. The reaction system FeBr/sub 2/ + NaSCH/sub 2/Ph in acetonitrile yields a different type ofmore » compound with the composition (Et/sub 4/N)/sub 2/(Fe/sub 4/(SCH/sub 2/Ph)/sub 6/Br/sub 4/) (5): triclinic; P/sup -/1; a = 12.874 (2) A, b = 13.949 (3) A, c = 43.272 (8) A, ..cap alpha.. = 94.85 (2)/sup 0/, ..beta.. = 94.07 (2)/sup 0/, ..gamma.. = 114.98 (1)/sup 0/; 4; 7402; 6.7. Anions of type 4 contain a new type of inorganic ring system, Fe/sub 3/(..mu..-SR)/sub 3/, distinguished by its nearly or exactly planar conformation and unusually large Fe-S-Fe angles of approx. 140/sup 0/, the largest values observed for this angle type.« less

New inorganic ring system: planar Fe/sub 3/(. mu. /sub 2/-SR)/sub 3/ in (Fe/sub 3/(SR)/sub 3/X/sub 6/)/sup 3 -/ - synthesis, structures, and solution conformation and equilibrium

The macrocyclic polyether trithiol (c-L(SH) 3 ) was synthesized in five steps from resorcinol. The cyclic structures of the tris (1,3-phenylene) crown ether and protected trithiol intermediates were demonstrated by X-ray methods. Compound (C 26 H 28 O 6 ) crystallizes in the monoclinic space group P2 1 /c

Subsite-Differentiated Analogues of Biological [4Fe-4S] Clusters Effected by Binding of a Macrocyclic Polyether Trithiol

Oxomolybdenum(IV,V,VI) Complexes: Structures, Reactivities, and Criteria of Detection of Binuclear (μ-Oxo)molybdenum(V) Products in Oxygen Atom Transfer Systems.

M. A. Whitener

Papers

Oxomolybdenum(IV,V,VI) Complexes: Structures, Reactivities, and Criteria of Detection of Binuclear (μ-oxo)molybdenum(V) Products in Oxygen Atom Transfer Systems

New inorganic ring system: planar Fe/sub 3/(. mu. /sub 2/-SR)/sub 3/ in (Fe/sub 3/(SR)/sub 3/X/sub 6/)/sup 3 -/ - synthesis, structures, and solution conformation and equilibrium

Subsite-Differentiated Analogues of Biological [4Fe-4S] Clusters Effected by Binding of a Macrocyclic Polyether Trithiol

Oxomolybdenum(IV,V,VI) Complexes: Structures, Reactivities, and Criteria of Detection of Binuclear (μ-Oxo)molybdenum(V) Products in Oxygen Atom Transfer Systems.

A New Inorganic Ring System: Planar Fe3(μ2-SR)3 in (Fe3(SR)3X6)3- - Synthesis, Structures, and Solution Conformation and Equilibrium.