bluuebunny/crossref_metadata_2025_split huggingface dataset:
Iridium: Organometallic Chemistry
Authors: Merola Joseph S. 
Published: March 2006

AbstractThe organometallic chemistry of iridium is reviewed. The general classes of complexes of iridium containing iridium to carbon bonds are surveyed. The preparations of iridium olefin complexes, iridium arene complexes, iridium carbonyl complexes, iridium cyclopentadienyl complexes, and other types of complexes are covered along with the use of those classes of compounds in preparing other organometallic iridium species. In addition, three areas in which organoiridium compounds find particular application are specifically reviewed: catalysis utilizing organometallic compounds of iridium, carbon–hydrogen (CH) bond activation chemistry with iridium, and hydrodesulfurization (HDS) studies using iridium. References to other reviews, to monographs, and to the primary literature are provided in all cases.
Iron: Heme Proteins & Dioxygen Transport & StorageBased in part on the article Iron: Heme Proteins & Dioxygen Transport by Harold M. Goff which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Hayashi Takashi 
Published: March 2006

AbstractMost organisms require dioxygen (O2) to survive; however, simple O2diffusion in blood does not supply a sufficient amount of oxygen for respiration. Thus, in all mammals, O2is carried and stored by O2‐binding heme proteins, myoglobin, and hemoglobin. Myoglobin is a single‐chain globular protein with heme as a prosthetic group, while hemoglobin consists of four heme‐containing subunits. O2binds to ferrous pentacoordinated heme‐iron and is stabilized by distal and proximal amino acid residues in the heme pocket. The O2pathway in the protein matrix and the binding mechanisms are discussed in detail by O2‐binding kinetic data for a series of myoglobin and hemoglobin mutants. Particularly, several residues, B10, E7, E10, E11, F7, and F8, mainly regulate the O2binding in the vertebrate heme proteins. In contrast, invertebrate and plant hemoglobins with unusually high O2affinities have been found in nature. InAscarishemoglobin, O2dissociation is very slow, whereas leghemoglobin shows a large O2association rate constant. In the case of trematode hemoglobin fromParamphistonum epiclitum, both kinetic parameters are improved. Artificial molecular design to modify O2affinity is another way to understand the O2binding mechanisms of the heme proteins. The strategy of heme protein modification can be divided into at least two approaches: One is a point mutation at distal or proximal amino acid residues, and the other is reconstitution by replacement of the native heme with an artificial heme. The physiological function of vertebrate hemoglobins is O2transport from the lungs or gills to the tissues; thus, they are required to exhibit cooperative interactions in binding O2to heme‐iron in the protein matrix. Although it is well known that a Hill coefficient of approximately 3.0 has been observed for tetrameric human hemoglobin, the mechanism of allosteric interaction is still discussed based on theoretical and experimental data. At present, an a two‐state (MWC) model proposed by Monod, Wyman, and Changeux for cooperative ligand binding is preferred to a sequential model. In addition, a study on the allosteric effectors for hemoglobins seems to be attractive from physiological aspects. The conventional effectors such as organic polyphosphate for human hemoglobin reduce the O2affinity of the T‐state, while it has been found that bezafibrate (BZF) or inositol hexaphosphate (IHP) can regulate O2binding not only for the T‐state but also for the R‐state. Finally, the interaction of NO with the heme proteins and modification of myoglobin for conversion into a new oxidase are briefly described.
Iron: Heme Proteins & Electron Transport
Authors: Durham Bill , Millett Francis S. 
Published: March 2006

AbstractThis chapter discusses the structure and function of cytochromes, which are a class of iron‐containing heme proteins primarily involved in biological electron‐transfer reactions. Subcellular organelles called mitochondria are responsible for carrying out oxidative phosphorylation, the major energy‐transduction process in eukaryotic cells. Enormous progress has been made in our understanding of the molecular mechanism of the mitochondrial electron‐transport chain over the past decade. X‐ray crystal structures have been determined for three of the four electron‐transfer complexes: succinate–ubiquinone reductase, cytochromebc1, and cytochromecoxidase (CcO). Cytochromec(Cc) is a small heme protein with a molecular weight of 12 500 Da that transports electrons from cytochromebc1to CcO. It is a very positively charged protein, and is known to bind to both cytochromebc1and CcO by means of electrostatic interactions. Extensive chemical modification studies have demonstrated that the binding domain on Cc for both proteins involves lysines immediately surrounding the heme crevice, and Cc functions as a mobile shuttle during electron transport. The reactions of Cc with its redox partners are too fast to resolve by conventional techniques such as stopped‐flow spectroscopy. A new method to study biological electron transfer has been introduced that utilizes a photoactive tris(bipyridine)ruthenium complex, Ru(II), which is covalently attached to a protein such as Cc. Photoexcitation of Ru(II) to the metal‐to‐ligand charge‐transfer state, Ru(II*), a strong reductant, leads to rapid electron transfer to the ferric heme group in Cc. Subsequent electron transfer from photoreduced heme c to redox center(s) in another protein can be measured on a timescale as short as 50 ns. This technique has been used to measure intracomplex electron transfer between Cc and its physiological partners, CcO, cytochromebc1, cytochromecperoxidase (CcP), and cytochromeb5. The ruthenium technique was used to characterize sequential electron transfer in cytochromebc1from ubiquinol to the Rieske iron–sulfur protein (2Fe2S), cytochromec1, and finally to Cc. Cytochrome oxidase contains four redox centers, CuA, heme a, heme a3, and CuB. A ruthenium Cc derivative was used to demonstrate that the initial site of electron entry into CcO is CuA, followed by electron transfer to heme a, and then heme a3.
Iron: Inorganic & Coordination ChemistryBased in part on the article Iron: Inorganic & Coordination Chemistry by Pelham N. Hawker & Martyn V. Twigg which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Burgess John , Twigg Martyn V. 
Published: March 2006

Abstract

Iron, the most abundant transition element in the biosphere, is essential in higher forms of life and its compounds have numerous industrial applications. The element has catalytic properties. Several simple iron compounds are industrially important, for example, large amounts of iron oxides are produced for pigment and magnetic recording media applications. Oxidation states ranging from −2 to +6 are known, the most familiar are +2 (ferrous iron) and +3 (ferric iron). Most common complexes are octahedral, although examples of higher (e.g. seven coordinate) and lower (e.g. tetrahedral and square planar) geometries are well known, as are a variety of mixed oxidation state compounds. Depending on ligands involved high‐ and low‐spin complexes can be formed, and temperature‐dependent spin‐state crossover complexes are well documented. The thermodynamics and kinetics of reactions of low‐spin iron(II) complexes with ligands such as 1,4‐diimines and CN
−
have been extensively studied. While low‐spin iron(II) is present in biological systems such as oxygenated heme centered oxygen carriers and thiolate clusters, iron(III) is more common. Thiolate‐containing iron clusters form readily, and here mixed oxidation states are a prominent feature that is exploited in some important electron transfer proteins. Microorganism iron uptake is facilitated by tris‐catecholate and tris‐hydroxamate ligands like enterobactin that have an extraordinarily high affinity for iron(III) that results in a dramatic enhancement of the 3+ relative to the 2+ state in terms of redox potential.
Iron: Organometallic ChemistryBased in part on the article Iron: Organometallic Chemistry by James R. Green which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Paley Robert S. 
Published: March 2006

Abstract
Studies involving the preparation, reactivity, and properties of the organometallic complexes of iron (compounds possessing a FeC bond) have played a central role in the growth of organometallics as a major subdiscipline with chemistry. From the discovery of ferrocene in the 1950s to the present day, interest and research activity remain high. This entry provides a survey of this large and diverse area of organometallic chemistry, and is arranged by increasing hapticity of the organic ligand of interest that is bound to iron. Included are discussions of the chemistry of iron σ‐alkyl, acyl, alkynyl, and vinyl complexes, iron carbenes, η1‐ and η3‐allyl iron complexes, η2‐alkene and η4‐diene iron complexes, trimethylenemethane and cyclobutadiene complexes of iron, cationic iron pentadienyl, cyclohexadienyl, and arene complexes, and ferrocenes and heteroferrocenes.
Iron Porphyrin Chemistry
Authors: Walker F. Ann , Simonis Ursula 
Published: March 2006

AbstractThis article reviews most aspects of the chemistry of iron porphyrins, from Fe(0) to Fe(V), including occurrence and roles of natural iron porphyrins (hemes) and their synthetic analogs, structures and electron configurations of iron porphyrins of all oxidation and spin states, π electron configuration of the porphyrin ring, synthesis of metal‐free porphyrins and other related macrocycles, insertion of iron into free‐base porphyrins and related macrocycles, the properties, reactions, uses and biological relevance of iron(0), ‐(I), ‐(II) porphyrins (the latter withS = 0, 1, and 2 spin state possibilities), of iron(II) porphyrin π‐cation radicals, of iron(III) porphyrins (withS = 1/2, 3/2, and 5/2 spin state possibilities), of iron(III) porphyrin and corrole π‐cation radicals, of iron(IV) porphyrins (including five‐ and six‐coordinate ferryl (FeO)2+, iron(IV) phenyl, carbene and hydrazine complexes, and the bis‐methoxide complex) and a comparison of iron(IV) porphyrins to iron(III) porphyrin π‐cation radicals, of iron(IV) porphyrin π‐cation radicals, and of the possible existence of iron(V) porphyrins. Included in the Fe(II) part are sections on addition of ligands to four‐coordinate iron(II) porphyrins, including equilibrium binding constants, photodissociation of ligands from PFeL2complexes, binding of small molecules (O2, CO, NO, HNO) to 5‐coordinate iron(II) porphyrins and design of porphyrin ligands that will mimic the active sites of heme proteins such as myoglobin and hemoglobin, the cytochromes P450 and nitric oxide synthases, and the nitrophorins and guanylyl cyclases. Included in the iron(III) part are sections on both 5‐ and 6‐coordinate high‐spin complexes and their similarities and differences, bridged or through‐space magnetically coupled complexes of high‐spin iron(III) porphyrins with other metal complexes as possible models for cytochrome oxidase and the assimilatory sulfite reductases, coupled oxidation of hemes by hydrogen peroxide or its equivalent, and the relationship of this reactivity to the reactions of heme oxygenase, iron(III) porphyrins as reduction catalysts, and photochemistry of iron(III) porphyrins, possible electron configurations of low‐spin iron(III) porphyrins, the phenomenon and possible electronic consequences of ruffling of the porphinato core in iron(III) porphyrins, the preferred orientation of planar axial ligands bound to low‐spin iron(III) porphyrins, NO complexes of iron(III) porphyrins, reduction potentials, equilibrium constants and rates of axial‐ligand addition and exchange, kinetics of axial‐ligand rotation and porphyrin ring inversion, kinetics of reduction and autoreduction of iron(III) porphyrins, electron self‐exchange between low‐spin iron(III) and iron(II) porphyrins, synthetic ferriheme proteins, and synthesis of five‐coordinate low‐spin iron(III) porphyrins having σ‐alkyl or σ‐aryl groups as axial ligands. The iron(IV) and iron(IV) cation radical sections discuss the high‐valent states of cytochromes P450 and related enzymes.
Iron Proteins with Dinuclear Active Sites
Authors: Kurtz Donald M. 
Published: March 2006

AbstractIron proteins with dinuclear active sites include those containing stable nonheme, non‐sulfur diiron sites. Though still dwarfed by the numbers of heme or iron‐sulfur proteins, the list of proteins known to contain nonheme, non‐sulfur diiron sites has steadily expanded over the past thirty years. These proteins share the following active site properties: (1) two iron atoms separated by 4 Å or less; (2) stable high spin ferrous and ferric oxidation states; (3) terminal histidinyl imidazole, carboxylate and solvent ligands; (4) at least one ligand that bridges the two irons; and (5) magnetic superexchange coupling of the unpaired spins on the two irons mediated by the bridging ligand atom(s). With one possible exception, the bridging ligands are either known or are strongly suspected to include one or two carboxylates. Two distinct subclasses, the purple acid phosphatases and the flavo‐diiron enzymes, seem to have no structural or functional relationships to each other or to any of the other diiron enzymes. The oxygen‐carrying protein, hemerythrin, for many years served as the prototype for nonheme, non‐sulfur diiron proteins. However, its structure and function have turned out to be distinct from those of the O2‐activating enzymes, which now form the largest subclass of these diiron‐containing proteins, with at least seven distinct types known; the most numerous of these are the alkane (including methane) monooxygenases and fatty acyl desaturases. Evidence for catalytically competent high‐valent diiron intermediates resulting from reaction of the diferrous sites with dioxygen have been obtained for at least two of the O2‐activating enzymes. Among the most intriguing and mysterious of the O2‐activating enzymes are the membrane‐bound ‘eight‐His’ diiron desaturases and monooxygenases.
Iron Proteins with Mononuclear Active Sites
Authors: Emerson Joseph P. , Mehn Mark P. , Que Lawrence 
Published: March 2006

AbstractMetalloenzymes containing a mononuclear nonheme iron center are often involved in dioxygen metabolism. We have divided this superfamily of enzymes into seven subcategories: iron superoxide dismutase and superoxide reductase, lipoxygenase, catechol dioxygenases, α‐keto acid‐dependent enzymes, isopenicillinNsynthase, pterin‐dependent hydroxylases, and Rieske dioxygenases. The degree of catalytic versatility and coordination flexibility encompassed by these enzymes is unsurpassed by any other known metalloenzyme superfamily. Herein we discuss the present state of knowledge regarding their active site structures and the critical role the metal center plays in their respective catalytic mechanisms.
Iron Proteins for Storage & Transport & Their Synthetic Analogs
Authors: Lewin Allison , Le Brun Nick E. , Moore Geoffrey R. 
Published: March 2006

AbstractThis article reviews proteins involved in iron metabolism. Brief descriptions are given of the biological contexts for the proteins discussed but the main emphasis is on chemical and structural aspects of them.Iron is essential to almost all forms of life, but its low bioavailability and toxicity mean that they require sophisticated mechanisms to transport it. Mammals acquire heme and nonheme iron via proteins in the gut wall, and transport it around the body using serum transferrin, for ferric iron, and hemopexin, for heme. Microbes have an active iron uptake mechanism involving small iron chelators called siderophores, for example, ferrichrome inEscherichia coli. Ferrichrome enters the cell via FhuA, a β‐barrel in the outer membrane. The periplasmic protein FhuD then transfers it to the FhuBC complex in the cytoplasmic membrane. FhuB forms a channel through which the ferric siderophore passes using energy supplied by FhuC. Once inside the cytoplasm the iron is removed from the ligand, possibly via reduction by FhuF. Some pathogenic bacteria have a similar system for heme uptake, secreting hemophores such as HasA, which can remove heme from hemoglobin. Other pathogens have outer membrane receptors that remove ferric iron from transferrin and transport it into the periplasm, where it is bound by ferric binding proteins that closely resemble a single lobe of transferrin.Following its acquisition, iron needs to be stored safely. The most widespread form of iron storage is the ferritin superfamily, which includes ferritin, bacterioferritin, and Dps. Ferritin is found in bacteria, plants, and animals and is a large shell made up of 24 subunits within which up to 4,500 ferric ions can be stored as a ferrihydrite mineral core. Bacterioferritin is found in bacteria and is closely related to ferritin, but contains up to 12 heme groups bound between pairs of subunits, which may play a role in iron release or electron storage. The bacterial protein Dps is smaller than ferritin, with 12 subunits forming the protein shell, and can hold up to 500 ferric ions. All of these proteins contain dinuclear iron sites that catalyze the oxidation of ferrous iron. An alternative form of iron storage is frataxin, found in mitochondria. Although not related to ferritin, this protein has the ability to form large aggregates that can store up to 50 ferric ions per monomer in a mineral core resembling those of ferritins.
Iron–Sulfur Models of Protein Active SitesBased in part on the article Iron–Sulfur Models of Protein Active Sites by Akira Nakamura & Norikazu Ueyama which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Collins David J. , Zhou Hong‐Cai 
Published: March 2006

Abstract

In pervasiveness of occurrence and multiplicity of function, iron–sulfur clusters rival biological prosthetic groups such as hemes and flavins. The development of iron–sulfur cluster chemistry paralleled the founding and maturation of the field of bioinorganic chemistry. Starting from the first spontaneous self‐assembly of the [Fe
4
S
4
(SR)
4
]
2−
cluster in 1972, and the identification of the protein‐bound Fe
4
S
4
in the same year, the study of iron–sulfur models of protein active sites has evolved into a unique field in which synthetic inorganic chemistry now resembles the total synthesis of natural products in organic chemistry. Some of the models had been built before the crystal structure of the protein was determined. Almost all the models successfully replicated the topology and the electronic properties of the protein active sites. In this article, the models will be discussed in the order of their complexity, from single iron rubredoxin models to Fe
2
S
2
, Fe
3
S
4
, Fe
4
S
4
, and Fe
8
S
7
model compounds. In each section, the chemical synthesis of the model compound will be discussed first, followed by structure comparison and contrast, electrochemical properties, and biochemical activities. Since the major function of iron–sulfur proteins is electron transfer, and the oxidation state of the iron atom determines its reactivity, electrochemical and Mössbauer data will be tabulated in detail. Some of the recent developments in site‐differentiated, peptide, and all‐ferrous Fe
4
S
4
clusters will be reviewed. Recent studies in modeling the topology of the P‐cluster of nitrogenase will also be covered. The challenge posed by iron–sulfur proteins has inspired new iron–sulfur cluster chemistry. No other metal–nonmetal combination has produced more structural types than the iron–sulfur system; the majority of them have yet to be found in biological systems. However, the modeling of the P‐cluster and the FeMoco center of nitrogenase have posed a daunting challenge to the analog chemists.
Magnetism of Extended Arrays in Inorganic Solids
Authors: Landee Christopher P. , Turnbull Mark M. 
Published: March 2006

Abstract
The dominant magnetic interaction in insulators is magnetic exchange. This quantum mechanical effect arises from the overlap of wavefunctions of two different paramagnetic centers, either directly (direct exchange) or through an intervening ligand (superexchange). The associated exchange energy is electrostatic in origin but formally equivalent to the difference between the single and triplet states for the two interacting electrons. Magnetic exchange, plus other effects arising from the orientation of an electronic moment to the lattice through spin‐orbit coupling, leads to a wide variety of magnetic behavior, as illustrated with examples of magnetically one‐dimensional lattices.
Manganese: Inorganic & Coordination ChemistryBased in part on the article Manganese: Inorganic & Coordination Chemistry by Charles A. McAuliffe, Stephen M. Godfrey, & Michael Watkinson which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Collomb Marie‐Noëlle , Deronzier Alain 
Published: March 2006

Abstract
This article covers the last 10 years of the inorganic and coordination chemistry of manganese at oxidation states (II), (III), (IV), (V), (VI), and (VII), as well as multinuclear compounds having oxidation states (II)–(IV) with both unitary and mixed valencies. The common ligands for manganese compounds involve the donor atoms nitrogen, oxygen, and the halogens while only few are known with other group V and group VI donors. One of the major areas of expansion has been the multinuclear complexes that are relevant to such diverse fields as metalloenzymes and single‐molecule magnets. Besides the small clusters, comprising two to four metal ions synthesized to model the structures and functions of manganese metalloenzymes, a lot of interest has been invested in larger clusters, not only for their biological relevance, but also for the development of materials with novel magnetic properties. Significant advances have been also been made in the chemistry of higher oxidation state manganese complexes (V), (VI), and (VII).
Manganese Proteins with Mono‐ & Dinuclear Sites
Authors: Penner‐Hahn James E. 
Published: March 2006

AbstractAlthough manganese is not as widely recognized as iron and copper, it nevertheless plays an essential role in several key biological processes. Consequently, manganese concentrations are tightly regulated in most cells. Several Mn‐specific transporters have been identified and a novel Mn‐regulatory protein has been characterized. Manganese‐activated enzymes are proteins that have relatively weak affinities for Mn; in many cases these are isolated without any metal bound. Manganese‐activated enzymes are especially important in hydrolytic reactions, and appear, in at least some cases, to have physiologically significant changes in activity that respond to changes in Mn concentration. The best characterized Mn proteins are redox‐active enzymes, where Mn typically cycles between the MnIIand MnIIIoxidation states, although some MnIV‐containing species are known.
Metal Vapor Synthesis of Transition Metal Compounds
Authors: Schmidt Eckhardt , Klabunde Kenneth J. , Ponce Aldo , Smetana Alexander , Heroux David 
Published: March 2006

Abstract
The title topic is reviewed with special reference to the reactivity of metal atoms, their energetics of vaporization, vaporization techniques, and some detailed examples of reaction products. Recent advances in nanoparticle work are also discussed.