Synthesis of imido analogs of the uranyl ion

Here we describe the synthesis of two imido analogs of the uranyl ion, UO(2+)2, in which the oxygens are replaced by divalent alkyl or aryl nitrogen groups: U(NtBu)2I2(THF)2 (1) and U(NPh)2I2(THF)3 (2) (where tBu is tert-butyl and THF is tetrahydrofuran). Both compounds have been fully characterized by standard analytical techniques, including x-ray crystallography, and the chemical bonding between the metal center and the nitrogen ligands was quantified by using hybrid density functional theory calculations. As expected for a uranyl analog, these complexes exhibit linear N-U-N linkages and very short U-N bonds. In addition, the theoretical calculations show strong involvement of the 5f and 6d electrons in the U-N bonding.     

Crystal structure of the extracellular segment of integrin alpha Vbeta3

Integrins are alphabeta heterodimeric receptors that mediate divalent cation-dependent cell-cell and cell-matrix adhesion through tightly regulated interactions with ligands. We have solved the crystal structure of the extracellular portion of integrin alphaVbeta3 at 3.1 A resolution. Its 12 domains assemble into an ovoid "head" and two "tails." In the crystal, alphaVbeta3 is severely bent at a defined region in its tails, reflecting an unusual flexibility that may be linked to integrin regulation. The main inter-subunit interface lies within the head, between a seven-bladed beta-propeller from alphaV and an A domain from beta3, and bears a striking resemblance to the Galpha/Gbeta interface in G proteins. A metal ion-dependent adhesion site (MIDAS) in the betaA domain is positioned to participate in a ligand-binding interface formed of loops from the propeller and betaA domains. MIDAS lies adjacent to a calcium-binding site with a potential regulatory function.     

alpha-Hydroxy and alpha-amino acids under possible Hadean, volcanic origin-of-life conditions

To test the theory of a chemoautotrophic origin of life in a volcanic, hydrothermal setting, we explored mechanisms for the buildup of bio-organic compounds by carbon fixation on catalytic transition metal precipitates. We report the carbon monoxide-dependent formation of carbon-fixation products, including an ordered series of alpha-hydroxy and alpha-amino acids of the general formula R-CHA-COOH (where R is H, CH3,C2H5,orHOCH2 and A is OH or NH2) by carbon fixation at 80 degrees to 120 degrees C, catalyzed by nickel or nickel,iron precipitates with carbonyl, cyano, and methylthio ligands as carbon sources, with or without sulfido ligands. Calcium or magnesium hydroxide was added as a pH buffer. The results narrow the gap between biochemistry and volcanic geochemistry and open a new gateway for the exploration of a volcanic, hydrothermal origin of life.     

Theoretical organometallic chemistry

Organometallic chemists have synthesized a remarkable variety of new structural types. In these structures ligands, which are organic or inorganic molecules of variable independent stability, bind to one or more transition metal atoms. An approach to an understanding of the electronic structure, geometrical preferences, and reactivity of these complexes may be made if the molecule is "decomposed" conceptually into a metal fragment, ML(n), and a ligand. A library of the molecular orbitals of these fragments is becoming available. One then "reconstructs" the molecule by examining the interaction of the orbitals of the ligand, typically an organic molecule, with the orbitals of the ML(n), fragment.     

Concentration of dissolved amino acids from saline waters by ligand-exchange chromatography

Amino acids dissolved in salt solutions may be concentrated and removed from the solution by ligand exchange on copper-Chelex 100 resin. Competing inorganic ligands do not interfere, and ion exchange with cations does not occur; thus loss of metal ion from this column is avoided. To test the potentiality of ligand exchange for chromatography, the type and nature of the dissolved amino compounds in sea water were investigated. The data revealed that the bulk of the dissolved amino compounds is present in a combined rather than a free state.     

Three-dimensional structure of favin: saccharide binding-cyclic permutation in leguminous lectins

The three-dimensional structure of favin, the glucose- and mannose-binding lectin of Vicia faba (vetch, broad bean), has been determined at a resolution of 2.8 angstroms by molecular replacement. The crystals contain specifically bound glucose and provide the first high-resolution view of specific saccharide binding in a leguminous lectin. The structure is similar to those of concanavalin A (Con A) and green pea lectin; differences from Con A show that minimal changes are needed to accommodate the cyclic permutation in amino acid sequence between the two molecules. The molecule is an ellipsoidal dimer dominated by extensive beta structures. Each protomer contains binding sites for two divalent metal ions (Mn2+ and Ca2+) and a specific saccharide. Glucose is bound by favin in a cleft in the molecular surface and has noncovalent contacts primarily with two peptide loops, one of which contains several metal ion ligands. The specific carbohydrate-binding site is similar to that of Con A in location and general peptide folding, despite several differences in specific amino acid residues.     

Molecular recognition and metal ion template synthesis

Methods for the design and synthesis of ligands intended to be specific for a metal ion have been a recent chemical development. This article describes how this process can be inverted so that the specifics of the coordination environment around the metal ion can be used as a template in large-scale ligand synthesis. The synthesis of macrobicyclic ligands for ferric ion has been accomplished by using active esters of catechol ligands in which catecholate coordination to iron is a prelude to the organic chemical reactions that link the coordination subunits together into one ligand system surrounding a central metal ion coordination site. The lanthanide(III) ions, which are among the most labile metal ions known, have coordination numbers of 8 or higher, and thus their encapsulation into a macrobicyclic structure is a challenging problem. Lanthanide amine complexes have been used as metal templates in the synthesis of such macrobicyclic lanthanide complexes. There is evidence that such a complex is inert to exchange in aqueous solution.     

A simple, multidimensional approach to high-throughput discovery of catalytic reactions

Transition metal complexes catalyze many important reactions that are employed in medicine, materials science, and energy production. Although high-throughput methods for the discovery of catalysts that would mirror related approaches for the discovery of medicinally active compounds have been the focus of much attention, these methods have not been sufficiently general or accessible to typical synthetic laboratories to be adopted widely. We report a method to evaluate a broad range of catalysts for potential coupling reactions with the use of simple laboratory equipment. Specifically, we screen an array of catalysts and ligands with a diverse mixture of substrates and then use mass spectrometry to identify reaction products that, by design, exceed the mass of any single substrate. With this method, we discovered a copper-catalyzed alkyne hydroamination and two nickel-catalyzed hydroarylation reactions, each of which displays excellent functional-group tolerance.     

Open Framework Structures Based on Sex2- Fragments: Synthesis of (Ph4P)[M(Se6)2] (M = Ga, In, TI) in Molten (Ph4P)2Sex

Polychalcogenide compounds with open polymeric frameworks are rare, and they represent a class of compounds in which microporosity might be achieved. Microporous frameworks that are not oxide-based are now attracting interest because of the combination of catalytic and electronic properties they may simultaneously possess. Three new compounds that may be forerunners to such materials have been discovered and are reported here. The reaction of gallium (Ga), indium (In), and thallium (TI) metal with (Ph(4)P)(2)Se(5) (Ph, phenyl) and an excess of elemental selenium (Se) in a sealed, evacuated Pyrex tube at 200 degrees C yielded small red crystals of (Ph(4)P)[Ga(Se(6))(2)] (I), (Ph(4)P)[In(Se(6))(2)] (II), and (Ph(4)P)[TI(Se(6))(2)] (III), respectively. The [M(Se(6))(2)](-) (M = Ga, In, TI) ions form a two-dimensional, open framework filled with Ph(4)P(+) ions. The [M(Se(6))(2)](n)(n-) structure consists of tetrahedral M(3+) centers and bridging Se(6)(2-) ligands, leading to an extended structure in two dimensions. These layers stack perfectly one on top of the other giving rise to one-dimensional channels running down the c axis that are filled with Ph(4)P(+) cations. These cations are situated in the layers, as opposed to between the layers, and the whole structure can be viewed as a template. Compound II shows remarkable thermal stability and melts congruently at 242 degrees C. Upon cooling to room temperature it gives a glassy phase that recrystallizes upon subsequent heating to 160 degrees C.     

Oxygen-carrying iridium complexes: kinetics, mechanism, and thermodynamics

The rates of oxygenation and deoxygenation of a series of iridium complexes increase and decrease, respectively, with increasing electron-releasing tendency of the anionic ligands (A) attached to the metal atom in the oxygencarrying compounds, [IrA(CO)(Ph(3)P)(2)]. Calculated heats of oxygenation (-DeltaH(2)(0)), related to Ir-O(2) bond energies, are proportional to the previously reported O-O bond lengths in the oxygen adducts, [O(2)IrA(CO)(Ph(3)P)(2)].     

Monodisperse metal clusters 10 angstroms in diameter in a polymeric host: the "monomer as solvent' approach

A general methodology is presented for the dispersion of an inorganic compound within an organic polymer host through the use of solubilizing and polymerizable ligands. The dispersion of metal cluster cations 10 angstroms in diameter within a polymer host is achieved by free-radical polymerization of the hexafunctional metal cluster [Mo(6)Cl(8)(NVI)(6)](triflate)(4) with bound polymerizable ligands in N-vinylimidazole (NVI) solutions. Copolymerization of the activated cluster-bound ligands with the surrounding medium probably plays a key role in preventing aggregation and produces near monodisperse molecular clusters within the polymer matrix.     

Stable magnesium(I) compounds with Mg-Mg bonds

The chemistry of the group 2 metals (beryllium, magnesium, calcium, strontium, and barium) is dominated by the +2 oxidation state. Here, we report the reductions of two magnesium(II) iodide complexes with potassium metal in toluene, leading to thermally stable magnesium(I) compounds, (L)MgMg(L) (where L is [(Ar)NC(NPri2)N(Ar)]- or {[(Ar)NC(Me)]2CH}-, Ar is 2,6-diisopropylphenyl, Me is methyl, and Pri is isopropyl) in moderate yields. The results of x-ray crystallographic and theoretical studies are consistent with central Mg2+(2) units that have single, covalent magnesium-magnesium bonding interactions with 2.8508 +/- 0.0012 (standard deviation) and 2.8457 +/- 0.0008 angstrom bond lengths, respectively, and predominantly ionic interactions with the anionic ligands (L).     

荧光性质可调控的π-共轭寡聚吡啶配体

主要介绍含寡聚吡啶配体基元的共轭寡聚物的结构、光物理性质及其与金属离子的络合行为,尤其是芳香基团取代的联二吡啶、1,10-邻菲罗啉和2,2′:6,′2′′-联三吡啶。在溶液中,这类配体对可见光表现出较强的吸收,同时具有较强的荧光发射能力,并且可通过加入外来物如质子或金属离子来调控其光物理性能。扼要讨论配体质子化以及与金属离子配位对其光物理性质的影响。     

Stable high-order molecular sandwiches: hydrocarbon polyanion pairs with multiple lithium ions inside and out

Stable ten-component sandwich compounds have been characterized in which four lithium ions reside between two tetraanions derived from corannulene or its alkyl-substituted derivatives and four additional lithium ions decorate the exterior. In tetrahydrofuran solution, the four lithium ions inside the sandwich can exchange environments with the four external lithium atoms, but the two tetraanion decks of the sandwich never separate from one another on the time scale of nuclear magnetic resonance. Theoretical calculations point to a "stacked bowl" conformation and a low energy barrier for synchronous double inversion of the tetraanion bowls in the solvated sandwich compounds.     

A late-transition metal oxo complex: K7Na9[O=PtIV(H2O)L2], L = [PW9O34]9-

Terminal mono-oxo complexes of the late transition metal elements have long been considered too unstable to synthesize because of repulsion between the oxygen electrons and the mostly filled metal d orbitals. A platinum(IV)-oxo compound flanked by two polytungstate ligands, K7Na9[O=Pt(H2O)L2], L = [PW9O34(9-)], has now been prepared and isolated at room temperature as air-stable brown crystals. X-ray and neutron diffraction at 30 kelvin revealed a very short [1.720(18) angstrom] Pt-O bond and no evidence of a hydrogen atom at the terminal oxygen, ruling out a better precedented Pt-OH complex. Density functional theory and spectroscopic data account for the stability of the Pt(IV)-oxo unit by electron withdrawal into delocalized orbitals of the polytungstates.     

天然有机质和金属离子在矿物表面的共吸附

天然有机质(NOM)在土壤、沉积物和水体等环境中无处不在,其中富里酸和胡敏酸是主要形态。富里酸及胡敏酸活性高,易与天然矿物颗粒和金属离子发生相互作用,影响矿物的表面化学特性以及金属离子的形态与迁移性,进而在控制环境中金属离子的生物有效性和毒性等方面起重要作用。本文主要综述了富里酸和胡敏酸等NOM和金属离子在矿物表面共吸附特性与主要影响因素,归纳了表面络合模型和现代光谱技术在上述三元体系研究中的应用及其反应机制研究进展。NOM在较大程度上改变了金属离子在矿物表面的吸附特性和反应机制,并受体系pH、金属离子类型和浓度、NOM浓度、NOM和金属离子的添加顺序、矿物类型等因素的影响。低pH时,NOM通常促进矿物对金属离子的吸附。NOM和金属离子在矿物表面的共吸附机制包括:NOM和金属离子竞争吸附表面活性吸附位点;在溶液中形成NOM-金属离子络合物;形成金属离子桥接矿物表面位点与NOM的A型三元络合物(矿物-金属离子-NOM)或NOM联接矿物表面与金属离子的B型三元表面络合物(矿物-NOM-金属离子);静电作用改变表面电荷特征。最后展望了天然有机质等配体与金属离子在矿物表面共吸附有关的研究热点和方向。     

Cu、Pb、Zn及复合重金属对油菜种子萌发的抑制性研究

本文通过种子萌发试验,探讨了2种油菜种子对重金属耐性的大小.研究发现,2种油菜种子萌发率在不同重金属及其不同浓度下存在差异,重金属Zn和Pb低浓度时促进油菜种子的萌发,高浓度时抑制其种子的萌发.重金属Cu和复合重金属对2个不同油菜品种的萌发率都存在显著的抑制作用,其萌发率随浓度的增高而降低.来自矿区的油菜种子在低浓度时萌发率低于正常油菜种子,在较高的浓度中,其萌发率较高,表现较强的耐性.结果表明,油菜对Cu耐性较弱,而对Pb、Zn的耐性较强,污染地区铜尾矿的油菜种子对高浓度的重金属具有比正常油菜种子较好的耐性.     

Plastic and moldable metals by self-assembly of sticky nanoparticle aggregates

Deformable, spherical aggregates of metal nanoparticles connected by long-chain dithiol ligands self-assemble into nanostructured materials of macroscopic dimensions. These materials are plastic and moldable against arbitrarily shaped masters and can be thermally hardened into polycrystalline metal structures of controllable porosity. In addition, in both plastic and hardened states, the assemblies are electrically conductive and exhibit Ohmic characteristics down to approximately 20 volts per meter. The self-assembly method leading to such materials is applicable both to pure metals and to bimetallic structures of various elemental compositions.     

Zinc mediation of the binding of human growth hormone to the human prolactin receptor

Human growth hormone (hGH) elicits a diverse set of biological activities including lactation that derives from binding to the prolactin (PRL) receptor. The binding affinity of hGH for the extracellular binding domain of the hPRL receptor (hPRLbp) was increased about 8000-fold by addition of 50 micromolar ZnCl2. Zinc was not required for binding of hGH to the hGH binding protein (hGHbp) or for binding of hPRL to the hPRLbp. Other divalent metal ions (Ca2+, Mg2+, Cu2+, Mn2+, and Co2+) at physiological concentrations did not support such strong binding. Scatchard analysis indicated a stoichiometry of one Zn2+ per hGH.hPRLbp complex. Mutational analysis showed that a cluster of three residues (His18, His21, and Glu174) in hGH and His188 from the hPRLbp (conserved in all PRL receptors but not GH receptors) are probable Zn2+ ligands. This polypeptide hormone.receptor "zinc sandwich" provides a molecular mechanism to explain why nonprimate GHs are not lactogenic and offers a molecular link between zinc deficiency and its association with altered functions of hGH.     

Crystal structure of Cd,Zn metallothionein

The anomalous scattering data from five Cd in the native protein were used to determine the crystal structure of cadmium, zinc (Cd,Zn) metallothionein isoform II from rat liver. The structure of a 4-Cd cluster was solved by direct methods. A 2.3 A resolution electron density map was calculated by iterative single-wavelength anomalous scattering. The structure is folded into two domains. The amino terminal domain (beta) of residues 1 to 29 enfolds a three-metal cluster of one Cd and two Zn atoms coordinated by six terminal cysteine thiolate ligands and three bridging cysteine thiolates. The carboxyl terminal domain (alpha) of residues 30 to 61 enfolds a 4-Cd cluster coordinated by six terminal and five bridging cysteine thiolates. All seven metal sites have tetrahedral coordination geometry. The domains are roughly spherical, and the diameter is 15 to 20 A; there is limited contact between domains. The folding of alpha and beta is topologically similar but with opposite chirality. Redundant, short cysteine-containing sequences have similar roles in cluster formation in both alpha and beta.