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

Recent developments of phosphate glasses for a variety of technological applications, from rare-earth ion hosts for solid state lasers to low temperature sealing glasses, have led to renewed interest in understanding the structures of these unusual materials. In this review, spectroscopic and diffraction studies of simple phosphate glasses, including v-P2O5 and binary phosphate compositions, are described. Special attention is given to the structures of anhydrous ultraphosphate glasses, which have received close attention from the glass community only in the past six years.

Review: the structure of simple phosphate glasses

Jump relaxation in solid electrolytes

http://www.chemie.uni-muenchen.de/ac/kluefers/homepage/L/bac/ca_2004.pdf

Synthetic analogues relevant to the structure and function of zinc enzymes.

Dynamic nuclear polarization (DNP) is a method that permits NMR signal intensities of solids and liquids to be enhanced significantly, and is therefore potentially an important tool in structural and mechanistic studies of biologically relevant molecules. During a DNP experiment, the large polarization of an exogeneous or endogeneous unpaired electron is transferred to the nuclei of interest (I) by microwave (microw) irradiation of the sample. The maximum theoretical enhancement achievable is given by the gyromagnetic ratios (gamma(e)gamma(l)), being approximately 660 for protons. In the early 1950s, the DNP phenomenon was demonstrated experimentally, and intensively investigated in the following four decades, primarily at low magnetic fields. This review focuses on recent developments in the field of DNP with a special emphasis on work done at high magnetic fields (> or =5 T), the regime where contemporary NMR experiments are performed. After a brief historical survey, we present a review of the classical continuous wave (cw) DNP mechanisms-the Overhauser effect, the solid effect, the cross effect, and thermal mixing. A special section is devoted to the theory of coherent polarization transfer mechanisms, since they are potentially more efficient at high fields than classical polarization schemes. The implementation of DNP at high magnetic fields has required the development and improvement of new and existing instrumentation. Therefore, we also review some recent developments in microw and probe technology, followed by an overview of DNP applications in biological solids and liquids. Finally, we outline some possible areas for future developments.

Dynamic nuclear polarization at high magnetic fields

X-ray photoelectron spectroscopy (XPS, ESCA) has been applied to sodium phosphate glasses with compositions between 15 and 50 mol% Na2O and for the purpose of comparison also to crystalline compounds containing oxygen and phosphorus. From the measurements a discrimination between bridging and non-bridging oxygen atoms was possible. The method provides a quantitative technique for structural analysis of phosphate glasses.

X-ray photoelectron spectroscopy of sodium phosphate glasses

Revue des principes et applications de la DNP (aussi appelee double resonance electronique nucleaire ou effet Overhauser nucleaire) en insistant sur les mouvements moleculaires, collisions, couplages intermoleculaires et interactions chimiques

Molecular Motions and Interactions as Studied by Dynamic Nuclear Polarization (DNP) in Free Radical Solutions

The local structure of glasses in the system Na2O−B2O3−Al2O3 is studied by multinuclear magic-angle spinning (MAS) solid-state NMR spectroscopy at 7.0 and 11.7 T. The 23Na isotropic chemical shifts vary linearly with Na2O concentration, indicating that the sodium ions are homogeneously distributed over the network and not clustered. The 11B MAS NMR spectra reveal the presence of trigonal BO3/2 units, tetrahedral BO4/2- sites, and three-coordinate BO2/2O- species containing nonbridging oxygen. The quantitative contributions of these three types of sites are obtained by detailed computer simulations of these spectra. High-resolution 27Al satellite transition spectroscopy indicates that aluminum is predominantly present as AlO4/2- sites. The structure of these glasses is discussed in terms of various melt reaction schemes, in which the network former oxides B2O3 and Al2O3 react with O2- introduced by the network modifier Na2O. While the data suggest that the formation of AlO4/2- units takes priority over bor...

Short-Range Order and Site Connectivities in Sodium Aluminoborate Glasses: I. Quantification of Local Environments by High-Resolution 11B, 23Na, and 27Al Solid-State NMR

Nuclear magnetic resonance and Mössbauer spectroscopy of glasses

1H NMR solid state techniques have been used to study bonding properties, location, and mobility of hydrogen in various phases of the hydrogen bronze HxMoO3. Temperature‐dependent spectra characteristic of different degrees of intercalation have been observed, and furthermore, from measurements of the relaxation rate, dynamic properties have been derived. There is strong evidence of intralayer hydrogen positions on a quasi‐one‐dimensional zig–zag line connecting the vertex‐sharing oxygen atoms of the MoO6 octahedra and these are first occupied if the degree of intercalation x is low. For x>0.85 the hydrogen in excess starts to fill up interlayer positions coordinated with terminal oxygen atoms at the van der Waals gap. Both isolated and paired protons have been detected in the interlayers, whereas clusters or pairs appear along the zig–zag lines. Hydrogen separations within the clusters, bonding with oxygen and charge transfer to the conduction band of the host lattice, are discussed. Hydrogen diffusion c...

Werner Müller-Warmuth

Papers

X-ray photoelectron spectroscopy of sodium phosphate glasses

Molecular Motions and Interactions as Studied by Dynamic Nuclear Polarization (DNP) in Free Radical Solutions

Short-Range Order and Site Connectivities in Sodium Aluminoborate Glasses: I. Quantification of Local Environments by High-Resolution 11B, 23Na, and 27Al Solid-State NMR

Nuclear magnetic resonance and Mössbauer spectroscopy of glasses

Structure and motion of hydrogen in molybdenum bronzes HxMoO3 as studied by nuclear magnetic resonance