bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tungsten: Organometallic ChemistryBased in part on the article Tungsten: Organometallic Chemistry by Andreas Mayr which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Pamplin Craig B. , Hayton Trevor W. , Legzdins Peter 
Published: December 2011

AbstractThis article surveys the organometallic chemistry of tungsten in a systematic manner according to the various types of complexes known to contain tungsten–carbon bonds. The first section deals with complexes having the inorganic ligands CO (carbonyl), CNR (isocyanide), and CN (cyanide) in the metal's coordination sphere. The second and by far the largest section considers tungsten complexes containing organic ligands. This section is divided into subsections dealing with compounds having η1‐hydrocarbyl ligands (i.e. alkyl and aryl complexes, vinyl and alkynyl complexes, carbene complexes, and carbyne complexes), η2‐hydrocarbon ligands (i.e. alkene complexes and alkyne complexes), η3‐hydrocarbon ligands (i.e. allyl complexes), η4‐hydrocarbon ligands (i.e. diene complexes), η5‐hydrocarbon ligands (i.e. cyclopentadienyl complexes), and η6‐hydrocarbon ligands (i.e. arene complexes). Within each category of complex, the material is generally presented in the following order: common methods of synthesis of these complexes, their characteristic physical properties, and their representative chemical properties. The latter are usually illustrated by examples taken from the literature published since 1992, the final year of coverage by the first edition of the Encyclopedia of Inorganic Chemistry. Other articles in the current encyclopedia also cover some aspects of this chemistry, most notably, alkene and alkyne metathesis reactions mediated by organotungsten complexes, the organometallic chemistry of di‐ and polynuclear tungsten complexes, and tungsten compounds containing main group element ligands. Consequently, these topics are not specifically discussed in this article.
Vanadium in Biology
Authors: Wever Ron , Renirie Rokus , Hasan Zulfiqar 
Published: December 2011

AbstractIn this article, the role of vanadium in a number of biological systems will be discussed. The metal oxide (vanadate) is present as the prosthetic group in the haloperoxidases, enzymes that are able to oxidize halides in the presence of hydrogen peroxide to hypohalous acids. The bromoperoxidases seem to be involved in the production of the huge amounts of brominated compounds formed by several seaweeds. The enzymes have unusual properties in terms of stability and structural organization. X‐ray structures at high resolution are available now for four vanadium haloperoxidases and details of the events occurring at the active site during catalysis are known. The metal oxide binds peroxide in a side‐on fashion and seems to acts as a Lewis acid in polarizing the bound peroxide for further nucleophilic attack by an incoming halide. These enzymes are also able to mediate in the presence of hydrogen peroxide, the enantioselective sulfoxidation of organic sulfides yielding chiral sulfoxides with high enantiomeric excess. The active site of the haloperoxidases is very similar to that found in acid phosphatases that hydrolyze phosphate monoesters and there is some evidence that the haloperoxidases have evolved from the phosphatases. Vanadium is found in the vanadiumIIIstate in certain blood cells of tunicates (Ascidians) under very acidic conditions. Despite many studies, there is no clue as to the physiological role of the metal and there are many questions regarding the mechanism of accumulation and reduction of the metal in these organisms. The metal also seems to be used as an electron sink by certain bacteria under anaerobic conditions. Furthermore, vanadium is accumulated in Amanita species. These toadstools contain up to 10 mM of a vanadiumIVcompound with very special structure in which the vanadiumIVis eightfold coordinated in an unusual geometry. Although the compound has been reported to carry out redox reactions, the physiological function is elusive.
Zinc:DNA‐Binding Proteins
Authors: Pennella Mario A. , Giedroc David P. 
Published: December 2011

AbstractZinc‐containing nucleic acid‐binding proteins are ubiquitous in nature and interact with all types of nucleic acids, including ssDNA, duplex DNA, and RNA. The primary role played by these Zn(II) coordination complexes is to provide local or global stability to these proteins that function in transcriptional regulation, DNA metabolism, and nucleic acid packaging. These proteins are now broadly designated as zinc finger (zf) proteins. Six structural classes of zf proteins are discussed here that are distinguished from one another on the basis of the secondary and tertiary structure of the zf domain, the nature of the ligating side chains (Cys and/or His), and the linear spacing of amino acid ligands in the primary structure. These structural zinc sites are compared with metalloregulatory zinc coordination complexes found in metal‐sensing transcriptional regulatory proteins that control zinc homeostasis in bacteria (e.g.E. coliZurR and ZntR;S. aureusCzrA;SynechococcusSmtB), lower eukaryotes (S. cerevisiaeZap1), and mammalian cells (MTF‐1). Structural and functional comparisons of the bacterial zinc sensors with homologous sensors specific for other transition metal ions (e.g. Cu, Ni, Mn) and xenobiotics (e.g. Cd, Pb, and Hg) suggest that coordination number and therefore geometry are primary determinants of metal selectivity of metal sensor proteins in vivo.
Zinc: Inorganic & Coordination ChemistryBased in part on the article Zinc: Inorganic & Coordination Chemistry by Reg H. Prince which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Burgess John , Prince Reg H. 
Published: December 2011

AbstractAlloys and salts of zinc have been known for many centuries; commercial production of the metal dates from early in the eighteenth century. Of the several million tons now produced annually, by electrolytic and smelting processes, much is used in alloys, in batteries, in corrosion prevention, and in the manufacture of a range of compounds with various uses. In particular, zinc oxide and zinc chloride have a large number of uses, detailed in this article. Zinc sulfide is both one of the main zinc ores and the archetype for the two main structural forms of 4:4‐coordinated structures (zinc blende and wurtzite). Many zinc compounds and complexes have interesting structural, spectroscopic, optical, magnetic, and conductivity properties, some of which are of actual or potential value in technical and industrial applications. Zinc‐containing species have also proved valuable in synthesis and self‐assembly of a range of supramolecular structures. Both in the solid state and in solution zinc exhibits a range of coordination numbers, though tetrahedral and, especially in solution, octahedral stereochemistries dominate. Zinc forms a variety of complexes, especially with nitrogen, oxygen, sulfur, and halide donor ligands. Many of these complexes show high stability, but they are generally labile in solution. Zinc plays an essential role in biology, being a key constituent of at least 200 metalloproteins. It is an essential element in human nutrition, but toxic in large quantities. Many zinc complexes have been synthesized as biochemical models; a few zinc salts are used in dietary supplements.
Zinc: Organometallic ChemistryBased in part on the article Zinc: Organometallic Chemistry by Gerard Parkin which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Grévy Jean‐Michel 
Published: December 2011

AbstractSince the discovery of the first organozinc compounds by Sir Edward Frankland in 1849, the organometallic chemistry of zinc made remarkable advances and organozinc species have become essential tools for organic chemists. During the past decade, numerous new and modified procedures for the preparation of the title compounds have been published, rendering their synthesis easier, faster, and less expensive and giving higher yields. The coordination chemistry of organozinc derivatives has been subject of further interest and various intra‐ and intermolecular complexes with different donor ligands have been structurally characterized by X‐ray crystallography and spectroscopic methods. The accumulation of molecular structures, physicochemical studies, and computational calculations has led to a better understanding of the organozinc chemistry, and consequently to the design of new derivatives for specific applications. Even if the development of areas like the chemistry of organozinc anions and cations is still in its early stage, these compounds, which exhibit properties different than those of the parent organometallic species, appear to have promising applications in synthesis and catalytic reactions. During the past ten years, the chemistry of organo‐gem‐dizincio derivatives has also been the subject of much interest and progress. These reagents can form two carbon–carbon bonds in a one‐pot reaction and with high stereoselectivity. They became key reagents for organic chemists who want to combine multiple transformations in one operation. The importance of organometallic compounds of zinc can be seen in the growing number of their applications in synthesis. They are used in many reactions such as substitutions, additions to carbonyl compounds and unsaturated systems, cyclopropanations, and polymerizations. Furthermore, as a result of their low reactivity, they tolerate a wide variety of functionalities and perform most of the transformations with high regio‐ and enantioselectivity. After spending more than half a century in the shade of Grignard and organolithium reagents, organozinc reagents are becoming more and more important in modern chemistry.
Zirconium & Hafnium: Inorganic & Coordination ChemistryBased in part on the article Zirconium & Hafnium: Inorganic & Coordination Chemistry by Grigorii L. Soloveichik which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Kozak Christopher M. , Mountford Philip 
Published: December 2011

AbstractThe inorganic and coordination chemistry of zirconium and hafnium is described. The physical properties of the metals, as well as their isolation, purification, and commercial and industrial uses are discussed. A section on the binary compounds of zirconium and hafnium containing hydride and main group elements follows. Oxoacid salts of the two metals are described, as well as aqueous chemistry. Examples of zirconium and hafnium coordination chemistry are presented according to ligand type: molecular and silica‐supported hydride complexes; ionic and neutral halide complexes; complexes with oxygen donor ligands; complexes with nitrogen donor ligands; dinitrogen complexes; complexes with phosphorus and sulphur donors ligands; complexes with mixed‐donor ligands. Lastly, lower oxidation state inorganic, coordination, and cluster compounds are discussed.
Zirconium & Hafnium: Organometallic ChemistryBased in part on the article Zirconium & Hafnium: Organometallic Chemistry by Bernard Gautheron, Roland Broussier, & Philippe Meunierk which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Meunier Philippe , Pirio Nadine 
Published: December 2011

Abstract
This review considers the main aspects of organometallic chemistry of zirconium and hafnium during the last 10 years. It is complementary to the first edition of Encyclopedia of Inorganic Chemistry. The material is presented in two major parts divided in five and three sections respectively. The first part is devoted to syntheses: the first section, by far the largest, covers in a systematic manner bis and mono cyclopentadienyl complexes with +4, +3, and +2 oxidation states and more especially constrained‐geometry (CG) complexes, cationic complexes, and anionic or zwitterionic 18‐electron complexes; unusual coordination geometries at carbon stabilized by group 4 metallocenes are presented in the second section; other anionic π‐ligands complexes and also lacking π‐ligands complexes are considered in two different sections and bimetallics are developed in the last section. Applications in metal‐mediated organic synthesis and catalysis are reviewed in the second part: neutral organozirconium complexes in organic and organometallic syntheses (hydrozirconation and carbozirconation), cationic zirconocenes in organic synthesis and catalysis, and organozirconium complexes in asymmetric catalysis.
Bond Lengths in Inorganic Solids & Liquids
Authors: Brown I. David 
Published: December 2011

Abstract
The length of a chemical bond is determined by the number of valence electron pairs associated with it. In a simple electrostatic picture, this number is equal to the electrostatic flux linking the bonded atoms. The flux obeys a number of chemically useful theorems, and since it is independent of the ionic or covalent character of the bond, any bond can be transformed to the ionic limit where the flux can be calculated using Coulomb's law. Alternatively, by recognizing that a network of ionically bonded atoms is a capacitive electric circuit, the flux can be determined using the Kirchhoff equations. The correlation between the bond length and bond flux (or bond valence) allows the bond geometry to be predicted even for unknown compounds. A comparison of the observed bond lengths with those expected is useful in validating and analyzing an observed structure. Atomic radii can also be used to predict bond lengths in regular coordination spheres, but they are unable to predict the distortions from regularity typically found in low symmetry structures.
Metal‐Related Diseases of Genetic Origin
Authors: Sarkar Bibudhendra 
Published: December 2011

AbstractIn humans, there are several genetic disorders of metal metabolism. Wilson and Menkes diseases are genetic disorders of copper transport. The genes from these two diseases encode copper‐transporting ATPases. Mutations in Wilson disease gene cause toxic accumulation of copper in the cells whereas mutations in Menkes disease gene cause copper deficiency and lack of its incorporation in important copper enzymes. Wilson disease is treated by chelating agents such asD‐penicillamine and trientine and zinc, which inhibits absorption of copper from the intestine. Current treatment for Menkes disease is subcutaneous injection of copper‐histidine. Hereditary hemochromatosis, thalassemia, and aceruloplasminemia are major disorders of iron metabolism. The gene responsible for hereditary hemochromatosis encodes a protein, which is very similar to major histocompatibility complex on chromosome 6, that has been proposed to down‐regulate iron absorption. The disease is treated by weekly venesection of approximately 0.5 L of blood. Thalassemia causes severe iron accumulation as a result of disturbances in the synthesis of one or more of the globin chains of hemoglobin. The chelating agent used for the treatment is deferoxamine administered subcutaneously. The search for an orally administered iron chelator has been intensified in recent years leading to chemical trials of chelator such as deferiprone (L1). Aceruloplasminemia is caused by mutations in the ceruloplasmin gene resulting in iron accumulation in various tissues. Deferoxamine has been used to treat this disease. Acrodermatitis enteropathica is a genetic disorder of zinc metabolism. Mutations in the gene responsible for zinc transport result in insufficient absorption of zinc in this disease, which can be ameliorated by zinc supplementation. Several less common genetic disorders of metal metabolism are discussed briefly.
Hard & Soft Acids and Bases
Authors: Martin R. Bruce 
Published: December 2011

AbstractPractical metal ion hardness–softness scales applicable to aqueous solutions and corresponding to what most chemists probably imply when they use the terms hardness and softness are presented. The scales are derived from experimentally determined log stability constant differences for substitution reactions of one ligand for another on a metal ion. Correlations between scales for different ligand systems are high but not perfect. In an analogous ligand scale, all oxygen donors are hard and all nitrogen donors borderline. The principle of hard and soft acids and bases finds its most consistent application, not in direct stability constant comparisons, but rather in log stability constant differences of appropriate substitution reactions.
Metal‐Based Drugs
Authors: Shaw C. Frank 
Published: December 2011

AbstractMetallopharmaceuticals have a long history in the development of chemotherapy. The more recent success of cisplatin and six related Pt‐based antitumor drugs, and longer histories of chrysotherapy (gold treatments) for arthritis, bismuth antiulcer agents, and silver‐, antimony‐ and arsenic‐based antimicrobial agents demonstrate that the periodic table represents a potential wealth of medicinal agents to be explored and developed in the future. This article reviews the use of twelve elements (Ag, As, Au, Bi, Ga, Li, Pt, Ru, Sb, Sn, Ti, V) for a wide variety of diseases and disorders. The current state of research on particular applications varies widely – from promising treatments that have not yet reached the clinic to those that are well established empirically despite uncertain mechanisms of action. The array of antitumor agents licensed or in clinical trials includes compounds of As, Ga, Ru, and Ti, in addition to platinum. There are also exciting efforts to apply known treatments or biological properties to new diseases by taking advantage of extensive databases, for example, developing antitumor agents from organotin complexes that have long been used as fungicides and antifouling agents, and antimicrobial agents from gold complexes. The ability to modulate the properties of metal complexes by choice of the oxidation state (AuIvs AuIII; PtIIvs PtIV; VIII, VIV& VV, etc.) and design of the medical carrier ligands (e.g. 1,2‐diaminocyclohexane vs two ammine ligands for Pt antitumor agents) allows targeting of particular tissues or cells and balancing of lipophilicity, solubility, and reactivity to balance therapeutic activity against toxicity. Many, if not most, metallopharmaceuticals are prodrugs that undergo redox changes and/or ligand exchange reactions in vivo to generate the active species. Hence, research on metallodrug metabolism and pharmacology is as important as the initial medicinal screening of the agents.
Metal‐Based Imaging Agents
Authors: Francesconi Lynn C. , Cantorias Melchor V. , Howell Robertha C. 
Published: December 2011

Abstract

Radiopharmaceuticals are drugs that contain a radionuclide and are routinely used for diagnosis and treatment of disease. This review discusses imaging agents that are useful for diagnosis using Single Photon Emission Computed Tomography (SPECT) and Positron Emission Tomography (PET). Moreover, this entry focuses on the growing class of metal‐based imaging agents, wherein the radionuclide is a transition metal or posttransition metal. The most widely used radionuclide for radiopharmaceuticals is technetium‐99m,
99m
Tc, owing its widespread availability from the parent–daughter generator and its excellent physical properties for imaging. The radionuclides
67
Ga,
111
In,
210
Tl,
57
Co, and
51
Cr are used in the clinic as well. There are a number of radioisotopes, including
64
Cu,
67
Cu,
68
Ga, that show promise for diagnostic purposes. An increased understanding of the coordination chemistry of
99m
Tc and other radiometals resulted in first‐generation metal‐essential imaging agents. This understanding of coordination chemistry is responsible for the introduction and development of targeted receptor‐specific agents, many of which are in clinical trials and some of which are on the market.
Metallocenter Biosynthesis & Assembly
Authors: Mulrooney Scott B. , Hausinger Robert P. 
Published: December 2011

AbstractMetalloproteins have been characterized intensively for decades, yet only recently has progress been made in characterizing the mechanisms of biological metallocenter biosynthesis and assembly. Here, we describe how cellular synthesis of metal sites makes use of several recurring themes, often with multiple themes combined into a single pathway. In the simplest situation, binding of a metal ion to a biological ligand occurs by reversible thermodynamic control. However, the prevalence of metallocenters deeply buried within macromolecules, the exceedingly low concentrations of free metal ions within cells, and the sophisticated structures of many metal‐containing active sites and cofactors provide evidence that alternative and more complex approaches also must exist. In some cases, metallochaperones are used to deliver the metal of interest to an apoprotein. In other cases the target protein undergoes posttranslational modification at the metal‐binding site, either prior to or after the metal is bound. Many metallocenters contain additional components that are added along with the metal ion or used to form a preassembled metal‐containing cofactor. Scaffolding proteins may be used to provide a framework for construction of the cofactor. Electron transfer reactions involving the metal, an added compound, or the protein ligand can participate in activation. Finally, molecular chaperones that bind to and alter the conformation of the target apoprotein may be utilized. In many cases, the function of the molecular chaperone is coupled to nucleotide triphosphate hydrolysis.
Metalloprotein Design & Engineering
Authors: Lu Yi 
Published: December 2011

AbstractThis review covers recent advances in metalloprotein design, with focus on different approaches to the design. Impressive progress has been made in designing metal‐binding sites in peptides, de novo designed proteins, and native protein scaffolds. The approach can be rational or combinatorial. Under rational design, redesigning an existing metal‐binding site to a new site with dramatically different structure and function complements well the design of new metal‐binding sites by revealing the role of specific residues responsible for a particular structural or functional feature of the metal‐binding site of interest. To create a new metal‐binding site, several approaches have been used, including design based on structural homology, by inspection, using automated computer search algorithms, or combination of the above approaches. In addition, modular approach by transplanting a conserved structural unit from one protein into another has also been shown to be effective. Design through combinatorial and evolution methods has also been successful as it requires little prior knowledge of the protein structure. Finally, introducing unnatural amino acids or nonnative metal ions/prosthetic groups to expand the repertoires of metalloproteins have been demonstrated. Successful examples of each of the approaches are given; advantages and disadvantages of the approaches are discussed; the outlook for future research is also presented.