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Extensive Hydrogen Bonding (extensive + hydrogen_bonding)
Selected AbstractsSelf-Assembled Two-Dimensional Water-Soluble Dipicolinate Cu/Na Coordination Polymer: Structural Features and Catalytic Activity for the Mild Peroxidative Oxidation of Cycloalkanes in Acid-Free MediumEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 22 2008Marina V. Kirillova Abstract The new water-soluble 2D Cu/Na coordination polymer [Cu(,-dipic)2{Na2(,-H2O)4}]n·2nH2O (1) has been synthesized by self-assembly in aqueous medium from copper(II) nitrate, dipicolinic acid (H2dipic) and sodium hydroxide in the presence of triethanolamine. It has been characterized by IR spectroscopy, FAB+ -MS, elemental and single-crystal X-ray diffraction analyses, the latter featuring a layered 2D metal,organic structure that is extended to a 3D supramolecular assembly by extensive hydrogen bonding between adjacent layers and involving crystallization water molecules. Compound 1 has been shown to act as a catalyst precursor for the peroxidative oxidation of cyclohexane and cyclopentane to the corresponding cyclic ketones and alcohols by aqueous H2O2 in MeCN solution and in the absence of acid additives.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Crystal structures of CbiL, a methyltransferase involved in anaerobic vitamin B12 biosynthesis, and CbiL in complex with S -adenosylhomocysteine , implications for the reaction mechanismFEBS JOURNAL, Issue 2 2007Kei Wada During anaerobic cobalamin (vitamin B12) biosynthesis, CbiL catalyzes methylation at the C-20 position of a cyclic tetrapyrrole ring using S -adenosylmethionine as a methyl group source. This methylation is a key modification for the ring contraction process, by which a porphyrin-type tetrapyrrole ring is converted to a corrin ring through elimination of the modified C-20 and direct bonding of C-1 to C-19. We have determined the crystal structures of Chlorobium tepidum CbiL and CbiL in complex with S -adenosylhomocysteine (the S -demethyl form of S -adenosylmethionine). CbiL forms a dimer in the crystal, and each subunit consists of N-terminal and C-terminal domains. S -Adenosylhomocysteine binds to a cleft between the two domains, where it is specifically recognized by extensive hydrogen bonding and van der Waals interactions. The orientation of the cobalt-factor II substrate was modeled by simulation, and the predicted model suggests that the hydroxy group of Tyr226 is located in close proximity to the C-20 atom as well as the C-1 and C-19 atoms of the tetrapyrrole ring. These configurations allow us to propose a catalytic mechanism: the conserved Tyr226 residue in CbiL catalyzes the direct transfer of a methyl group from S -adenosylmethionine to the substrate through an SN2-like mechanism. Furthermore, the structural model of CbiL binding to its substrate suggests the axial residue coordinated to the central cobalt of cobalt-factor II. [source] Hydrated metal complexes of N -(6-amino-3,4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl)glycinate: interplay of molecular, molecular,electronic and supramolecular structuresACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2001John N. Low The title anion, (C7H8N5O4),, L,, forms hydrated metal complexes with a range of metal ions M+ and M2+. Lithium and manganese(II) form finite molecular aggregates [Li(L)(H2O)3] (1) and [Mn(L)2(H2O)4].6H2O (4) in which the molecular aggregates are linked into three-dimensional frameworks by extensive hydrogen bonding. The sodium and potassium derivatives, [Na2(L)2(H2O)3] (2) and [K(L)(H2O)] (3) both form organic,inorganic hybrid sheets in which metal,oxygen ribbons are linked by strips containing only organic ligands: these sheets are linked by hydrogen bonds into three-dimensional frameworks. In (2) the metal,oxygen ribbon is built from pairs of edge-shared trigonal bipyramids linked by water molecules, while in (3) it consists of a continuous chain of vertex-sharing octahedra. The nitroso group in the anion acts as an ,1 ligand towards Na+ and as an ,2 ligand towards K+. In all cases the anion L, shows the same unusual pattern of interatomic distances as the neutral parent LH. [source] Two salts of di- p -toluoyltartaric acid with aromatic aminesACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2006Luigi R Nassimbeni The structures of bis[(R)-(+)-1-phenylethylammonium] (2R,3R)-(,)-2,3-di- p -toluoyloxybutanedioate methanol disolvate monohydrate, 2C8H12N+·C20H16O82,·2CH4O·H2O, (I), and bis(benzylammonium) (2R,3R)-(,)-2,3-di- p -toluoyloxybutanedioate dihydrate, 2C7H10N+·C20H16O82,·2H2O, (II), exhibit extensive hydrogen bonding, with (N,)H,O and (O,)H,O distances in the ranges 2.716,(2),2.929,(3) and 2.687,(2),2.767,(2),Ĺ, respectively, in (I), and 2.673,(2),2.888,(2) and 2.785,(2),2.931,(2),Ĺ, respectively, in (II). The amine groups are protonated and the carboxylate groups of the tartrate anions are fully deprotonated. The conformation of the toluoyltartrate anion and its molecular parameters are similar in both structures. [source] (E)- N -[(Benzo[b]thiophen-3-yl)methylene]- N,-(2,5-dichlorophenyl)hydrazineACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2004Vijayakumar N. Sonar The title compound, C15H10Cl2N2S, crystallizes in the centrosymmetric space group P21/c with one molecule in the asymmetric unit. The molecule assumes an approximately planar configuration and has an E geometry about the azomethine C=N double bond. The crystal structure is stabilized by extensive hydrogen bonding. [source] Two polymorphs of a covalent complex between papain and a diazomethylketone inhibitor,CHEMICAL BIOLOGY & DRUG DESIGN, Issue 4 2004R. Janowski Abstract:, The three-dimensional structure of two polymorphs of a ZLFG-CH2,papain covalent complex has been determined by X-ray crystallography. The structures indicate that: (i) the methylene carbon atom of the inhibitor is covalently bound to the S, atom of Cys25 of papain; (ii) the hydrophobic S2 pocket formed by Pro68, Val133, Val157, and Asp158 is occupied by the inhibitor's phenylalanyl P2 side chain; (iii) extensive hydrogen bonding and hydrophobic interactions are responsible for the interaction of the inhibitor with the enzyme. Comparison with similar structures suggests that in covalent complexes preservation of main chain,main chain interactions between the enzyme and the inhibitor may have higher priority than the P,S interactions. [source] Polycyano-Anion-Based Energetic SaltsCHEMISTRY - A EUROPEAN JOURNAL, Issue 4 2008Haixiang Gao Dr. Abstract Energetic salts based on polycyano anions and cations with a high nitrogen content tend to have extensive hydrogen bonding and exhibit heats of formation up to ,Hf=1579.1,kJ,mol,1. Based on theoretical calculations, some of the new salts may be considered to be low-energy monopropellants. One of the salts can be used as a precursor to a carbon nitride. [source] | ||||||||||