Investigation of uranyl nitrate ion pairs complexed with amide ligands using electrospray ionization ion trap mass spectrometry and density functional theory

Ion populations formed from electrospray of uranyl nitrate solutions containing different amides vary depending on ligand nucleophilicity and steric crowding at the metal center. The most abundant species were ion pair complexes having the general formula [UO(2)(NO(3))(amide)(n=2,3)](+); however, singly charged complexes containing the amide conjugate base and reduced uranyl UO(2)(+) were also formed as were several doubly charged species. The formamide experiment produced the greatest diversity of species resulting from weaker amide binding, leading to dissociation and subsequent solvent coordination or metal reduction. Experiments using methyl formamide, dimethyl formamide, acetamide, and methyl acetamide produced ion pair and doubly charged complexes that were more abundant and less abundant complexes containing solvent or reduced uranyl. This pattern is reversed in the dimethylacetamide experiment, which displayed lower abundance doubly charged complexes, but augmented reduced uranyl complexes. DFT investigations of the tris-amide ion pair complexes showed that interligand repulsion distorts the amide ligands out of the uranyl equatorial plane and that complex stabilities do not increase with increasing amide nucleophilicity. Elimination of an amide ligand largely relieves the interligand repulsion, and the remaining amide ligands become closely aligned with the equatorial plane in the structures of the bis-amide ligands. The studies show that the phenomenological distribution of coordination complexes in a metal-ligand electrospray experiment is a function of both ligand nucleophilicity and interligand repulsion and that the latter factor begins exerting influence even in the case of relatively small ligands like the substituted methyl-formamide and methyl-acetamide ligands.     

Steric, electronic, and secondary effects on the coordination chemistry of ionic phosphine ligands and the catalytic behavior of their metal complexes

The effects of introducing ionic functionalities in phosphine ligands on the coordination chemistry of these ligands and the catalytic behavior of the corresponding metal complexes are reviewed. The steric and electronic consequences of such functionalizations are discussed. Apart from these steric and electronic effects, the presence of charged groups often leads to additional, supramolecular interactions that occur in the second coordination sphere of the metal complex, such as intramolecular, interligand hydrogen bonding and Coulombic repulsion. These interactions can significantly alter the behavior of the phosphine ligand in question. Such effects have been observed in phosphine-metal association/dissociation equilibria, ligand substitution reactions, and stereoisomerism in phosphine-metal complexes. By drawing general conclusions, this review offers an insight into the coordination and catalytic behavior of phosphine ligands containing ionic functionalities and their corresponding metal complexes.     

Parallel Water/Aromatic Interactions of Non‐Coordinated and Coordinated Water

The parallel interactions of non‐coordinated and coordinated water molecules with an aromatic ring were studied by analyzing data in the Cambridge structural database (CSD) and by using quantum chemical calculations. The CSD data show that water/aromatic contacts prefer parallel to OH/π interactions, which indicates the importance of parallel interactions. The results reveal the influence of water coordination to a metal ion; the interactions of aqua complexes are stronger. Coordinated water molecules prefer a parallel‐down orientation in which one O?H bond is parallel to the aromatic ring, whereas the other O?H bond points to the plane of the ring. The interactions of aqua complexes with parallel‐down water/benzene orientation are as strong as the much better known OH/π orientations. The strongest calculated interaction energy is ?14.89 kcal mol^?1. The large number of parallel contacts in crystal structures and the quite strong interactions indicate the importance of parallel orientation in water/benzene interactions.     

A comparative study of aluminum(III), gallium(III), indium(III), and thallium(III) binding to human serum transferrin

Group 13 cations exhibit an essentially similar chemical behavior in aqueous solution. Under physiological conditions these cations exist as metal complexes. They are known to bind tightly to human serum transferrin in the blood. Here, the numerous published studies on the interactions of Group 13 metals with transferrin are reviewed, particular attention being given to the comparative analysis of the binding constants and to the kinetics and mechanisms of metal ion uptake and release. The structural and functional information obtained on these metallotransferrins by advanced physicochemical methods, such as NMR spectroscopy, is presented in light of the recent crystal structures of ferric- and apotransferrin. The biological consequences of binding of aluminum(III), gallium(III) and indium(III) to transferrin are discussed in relation to the relevant roles played by these metal ions in pharmacology and toxicology.     

Metal ion selectivity of oligopeptides

Metal binding affinity and selectivity of peptides are reviewed with a special emphasis on the high structural variety of peptide complexes. The most common structural type of these complexes is built up by the deprotonation and metal ion coordination of subsequent amide groups in the form of fused five-membered chelate rings. The metal ion selectivity of this process and the role of various anchoring groups are discussed in detail. The highest metal binding affinity of peptides is connected to the presence of two anchoring groups in appropriate location (the "double anchor"): e.g. the NH2-Xaa-Xaa-His/Cys/Asp/Met-Xaa sequence. Among the side chain donor functions, the imidazole of histidyl and thiolate of cysteinyl residues are the most effective ligating groups and their involvement in metal binding results in a great variety of different macrochelate or loop structures and/or formation of various polynuclear complexes. Examples of these structural motifs and their possible applications have been thoroughly discussed.     

The Hydrophobic and Metal-Ion Coordinating Properties of α-Lipoic Acid—An Example of Intramolecular Equilibria in Metal-Ion Complexes

Hydrophobic interactions as structure determining factors for macromolecules are well-known in biochemistry. Considerably less recognized is the fact that these law-energy interactions may also determine the structure of low-molecular species. The same applies for weak ligand-metal ion interactions. That both these factors may lead to intramolecular, contraction-independent equilibria between isomeric metal-ion complexes is demostrated with α-lipoic acid as ligand. This cofactor affers metal ions two different binding sites: the carboxylate group and the disulfide linkage. The carboxylate group dominates the coordinating properties of this ligand towards the biologically important metal ions, but a disulfide-metal ion interaction is still possible and under sterically favourable conditions may becomevery important; this could also be true under enzymic conditions here the carboxyl group is no longer free but amide-liked to the protein. Furthermore, due to the valeric acid side chain, the lipoyl moiety is ideally suited to undergo hydrophobic ligand-ligand interactions in mixed-ligand complexes. Such hydrophobic interactions seem to be ideal to allwe migration, e.g., of the 14 Å long lipoyllysyl moiety, and also to caciliutate the correct ‘fixation’ at the surface of the enzyme.     

Structure and Reactivity of Late Transition Metal η3‐Benzyl Complexes

The coordination of transition metals to organic fragments can yield complexes with fascinating and unexpected binding patterns. The study of metal‐benzyl complexes has demonstrated the feasibility of η³‐coordination, which results in a dearomatized ring. These complexes also offer insight into reaction mechanisms as proposed intermediates in catalytic cycles. In this Review we discuss the synthesis and characterization of these complexes with late transition metals and the subsequent development of catalytic benzylic functionalization methods, including asymmetric variants.     

Metal-assembled anion receptors

This review describes the self-assembly of anion receptors from organic ligands and transition metal ions. These metal-assembled anion receptors can be synthesised from a number of different species; bidentate ligands with metals that prefer octahedral coordination geometries and monodentate ligands with metals that prefer square planar geometries are common. Anion binding transition metal helicates and systems where the coordination of metal ions results in the formation of an anion receptor by conformational locking are also reported. The effect of anion binding on the different properties of these complexes is discussed.     

Azidoacetone as a complexing agent of transition metals Ni2+/Co2+ promoted dissociation of the C-C bond in azidoacetone

The relevance of metal interactions with azides has led us to the study of the complexation of some transition metals, nickel and cobalt, by azidoacetone by means of electrospray ionization mass spectrometry (ESI-MS). Complexes were obtained from solutions of NiCl(2) and CoCl(2) , in methanol/water. Nickel was electrosprayed with other counter ion, bromide (Br), as well as other solvent (ethanol/water). For nickel and cobalt, the complexes detected were single positively charged, with various stoichiometries, some resulted from the fragmentation of the ligand, the loss of N(2) being quite common. The most abundant species were [Ni(II)Az(2)X](+) where X = Cl, Br and Az = azidoacetone. Some of the complexes showed solvation with the solvent components. Metal reduction was observed in complexes where a radical was lost, resulting from the homolytic cleavage of a metal coordination bond. Collision-induced dissociation (CID) experiments followed by tandem mass spectrometry (MS-MS) analysis were not absolutely conclusive about the coordination site. However, terminal ions of the fragmentation routes were explained by a gas-phase mechanism proposed where a C-C bond was activated and the metal inserted subsequently. Density functional theory calculations provided structures for some complexes. In [Ni(II)Az(2)X](+) species, one azidoacetone ligand is monodentate and the dominant binding location is the alkylated nitrogen and not the carbonyl group. The other azidoacetone ligand is bidentate showing coordination through alkylated nitrogen and the carbonyl group. These are also the preferential binding sites for the most stable isomer of [Ni(II)AzX](+) species.     

超高真空条件下碱基与金属在Au(111)表面的相互作用

碱基是生命体中核酸的重要组成部分,用以携带遗传信息。碱基之间的互补配对行为在DNA和RNA的高保真复制过程中起到重要作用。除了碱基间的特异性识别,碱基分子与金属,盐类和一些小分子也可发生相互作用,特别是与某些金属原子或离子的相互作用会造成核酸的损伤,并可能进一步导致基因突变甚至诱发细胞的癌变。同时,基于DNA金属化形成的纳米器件逐渐成为纳米科技领域的研究热点。因此研究碱基与金属作用的现象和机制对于生物化学和纳米科学都十分重要。扫描隧道显微镜可以在实空间原子尺度下揭示纳米结构,密度泛函理论计算可以帮助确定反应机理。本文对近年来报道的利用以上两种方法在超高真空环境下碱基及其衍生物与碱金属、碱土金属和过渡金属的相互作用进行了介绍,总结了碱基与金属的作用位点及反应发生的机理,并进一步提出单原子尺度下的结构模型、可能的反应路径,进而揭示相互作用的本质。     

Nucleoside 5'-triphosphates: self-association, acid-base, and metal ion-binding properties in solution

Adenosine 5'-triphosphate (ATP(4-)) and related nucleoside 5'-triphosphates (NTP(4-)) serve as substrates in the form of metal ion complexes in enzymic reactions taking part thus in central metabolic processes. With this in mind, the coordination chemistry of NTPs is critically reviewed and the conditions are defined for studies aiming to describe the properties of monomeric complexes because at higher concentrations (>1 mM) self-stacking may take place. The metal ion (M(2+)) complexes of purine-NTPs are more stable than those of pyrimidine-NTPs; this stability enhancement is attributed, in accord with NMR studies, to macrochelate formation of the phosphate-coordinated M(2+) with N7 of the purine residue and the formation degrees of the resulting isomeric complexes are listed. Furthermore, the formation of mixed-ligand complexes (including also those with buffer molecules), the effect of a reduced solvent polarity on complex stability and structure (giving rise to selectivity), the use of nucleotide analogues as antiviral agents, and the effect of metal ions on group transfer reactions are summarized.     

Dissociation of polyether-transition metal ion dimer complexes in a quadrupole ion trap

The formation and dissociation of dimer complexes consisting of a transition metal ion and two polyether ligands is examined in a quadrupole ion trap mass spectrometer. Reactions of three transition metals (Ni, Cu, Co) with three crown ethers and four acyclic ethers (glymes) are studied. Singly charged species are created from ion-molecule reactions between laser-desorbed monopositive metal ions and the neutral polyethers. Doubly charged complexes are generated from electrospray ionization of solutions containing metal salts and polyethers. For the singly charged complexes, the capability for dimer formation by the ethers is dependent on the number of available coordination sites on the ligand and its ability to fully coordinate the metal ion. For example, 18-crown-6 never forms dimer complexes, but 12-crown-4 readily forms dimers. For the more flexible acyclic ethers, the ligands that have four or more oxygen atoms do not form dimer complexes because the acyclic ligands have sufficient flexibility to wrap around the metal ion and prevent attachment of a second ligand. For the doubly charged complexes, dimers are observed for all of the crown ethers and glymes, thus showing no dependence on the flexibility or number of coordination sites of the polyether. The nonselectivity of dimer formation is attributed to the higher charge density of the doubly charged metal center, resulting in stronger coordination abilities. Collisionally activated dissociation is used to evaluate the structures of the metal-polyether dimer complexes. Radical fragmentation processes are observed for some of the singly charged dimer complexes because these pathways allow the monopositive metal ion to attain a more favorable 2 + oxidation state. These radical losses are observed for the dimer complexes but not for the monomer complexes because the dimer structures have two independent ligands, a feature that enhances the coordination geometry of the complex and allows more flexibility for the rearrangements necessary for loss of radical species. Dissociation of the doubly charged complexes generated by electrospray ionization does not result in losses of radical neutrals because the metal ions already exist in favorable 2+ oxidation states.     

Heteroligand Metal Complexes with Extended Redox Properties Based on Redox-Active Chelating Ligands of o-Quinone Type and Ferrocene

A combination of different types of redox-active systems in one molecule makes it possible to create coordination compounds with extended redox abilities, combining molecular and electronic structures determined by the features of intra- and intermolecular interactions between such redox-active centres. This review summarizes and analyses information from the literature, published mainly from 2000 to the present, on the methods of preparation, the molecular and electronic structure of mixed-ligand coordination compounds based on redox-active ligands of the o-benzoquinone type and ferrocenes, ferrocene-containing ligands, the features of their redox properties, and some chemical behaviour.     

A simple thermodynamic model for quantitatively addressing cooperativity in multicomponent self-assembly processes--Part 2: Extension to multimetallic helicates possessing different binding sites

The extended site-binding model, which explicitly separates intramolecular interactions (i.e., intermetallic and interligand) from the successive binding of metal ions to polytopic receptors, is used for unravelling the self-assembly of trimetallic double-stranded Cu(I) and triple-stranded Eu(III) helicates. A thorough analysis of the available stability constants systematically shows that negatively cooperative processes operate, in strong contrast with previous reports invoking either statistical behaviours or positive cooperativity. Our results also highlight the need for combining successive generations of complexes with common binding units, but with increasing metallic nuclearities, for rationalizing and programming multicomponent supramolecular assemblies.     

On the Conformation and Structure of Organometal Complexes in the Solid State: Two Studies Relevant to Chemical Synthesis

Conformational preferences of two classes of organometal complexes have been surveyed by inspecting the Cambridge Structural Database (CSD). Lewis acid carbonyl complexes demonstrate a variety of coordination geometries, depending on the electronic and steric requirements of the carbonyl ligands and the nature of the Lewis acid. Similarly, the solid-state conformation of various π-bonding ligands in metal acyl, metal nitrosyl, metal acetylene, and metal imido complexes is revealed. These insights have stimulated the development of a conformational model that is based on considerations of π-bond hybridization and frontier molecular orbital theory. The analyses are relevant to the mechanism and transition structures of many synthetically important transformations. A deeper understanding of the conformational properties of organometal complexes, based on accurate structural information, will likely expedite the design and improvement of metal-mediated processes.     

Keys for unlocking photolabile metal-containing cages

Photolabile metal-containing cages are metal complexes that undergo a change in coordination environment upon exposure to light of an appropriate wavelength. The light-responsive functionality can either be a component of the encapsulating ligand or a property of the metal complex itself. The altered coordination properties of light-responsive complexes can result in release of the coordinated metal ion into its surroundings, a differential reactivity of the metal center, or the liberation of a reactive molecule that had been passivated by binding to the metal center. These triggerable agents can be useful tools for manipulating the bioavailability of metals or their coordinating ligands in order to study biological pathways or for potential therapeutic purposes.     

Nanosized polymetallic resorcinarene-based host assemblies that strongly bind fullerenes

Polymetallic nanodimensional assemblies have been prepared via metal directed assembly of dithiocarbamate functionalized cavitand structural frameworks with late transition metals (Ni, Pd, Cu, Au, Zn, and Cd). The coordination geometry about the metal centers is shown to dictate the architecture adopted. X-ray crystallographic studies confirm that square planar coordination geometries result in "cagelike" octanuclear complexes, whereas square-based pyramidal metal geometries favor hexanuclear "molecular loop" structures. Both classes of complex are sterically and electronically complementary to the fullerenes (C(60) and C(70)). The strong binding of these guests occurred via favorable interactions with the sulfur atoms of multiple dithiocarbamate moieties of the hosts. In the case of the tetrameric copper(II) complexes, the lability of the copper(II)-dithiocarbamate bond enabled the fullerene guests to be encapsulated in the electron-rich cavity of the host, over time. The examination of the binding of fullerenes has been undertaken using spectroscopic and electrochemical methods, electrospray mass spectrometry, and molecular modeling.     

螯合物离子色谱

螯合物离子色谱是一种利用螯合物进行不同方式分离和检测的离子色谱模式，目前已经被痕量金属分析广泛采用，本文对一些螯合物阳离子交换色谱、螯合物色谱、阴离子交换色谱和离子对色谱最新进展进行了综述，并采用基本螯合物化学理论（金属螯合物稳定性、金属原子有效电荷、螯合剂能力等）对保留和分离机理进行了讨论。     

Preparation, thermoanalytical and IR study of mixed-ligand complexes formed in water-1,2-ethanediol-cobalt(II)sulfate systems

Parent and mixed-ligand cobalt(II) complexes of different compositions were prepared with water, sulfate ion and 1,2-ethanediol as ligands. The magnetic susceptibility data, the IR spectra and the thermoanalytical curves of the complexes were recorded. Oxygen atoms bound by one or two coordinate bonds to the metal ion, or by hydrogen-bonds were observed in the crystals pace. An erratum to this article is available at .     

Dissociation of doubly charged transition metal/polyether/pyridyl ligand complexes in a quadrupole ion trap mass spectrometer

The dissociation of a series of doubly charged pyridyl ligand/polyether/transition metal complexes is studied using electrospray ionization and collision activation methods. Both doubly charged mixed-ligand dimer and trimers are observed by electrospray ionization. The mixed-ligand trimer complexes always dissociate by cleavage of one entire ligand, whereas the mixed-ligand dimers show a more diverse array of fragmentation pathways, including charge reduction processes. The fragmentation pathways of these mixed-ligand dimers are influenced by the second ionization energy and electron configuration of the metal and relative coordination strength of the ligands.