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One Water Molecule (one + water_molecule)
Selected AbstractsDinuclear Complexes of MII Thiocyanate (M = Ni and Cu) Containing a Tridentate Schiff-Base Ligand: Synthesis, Structural Diversity and Magnetic PropertiesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2005Suparna Banerjee Abstract A dinuclear NiII complex, [Ni2(L)2(H2O)(NCS)2]·3H2O (1) in which the metal atoms are bridged by one water molecule and two ,2 -phenolate ions, and a thiocyanato-bridged dimeric CuII complex, [Cu(L)NCS]2 (2) [L = tridentate Schiff-base ligand, N -(3-aminopropyl)salicylaldimine, derived from 1:1 condensation of salicylaldehyde and 1,3-diaminopropane], have been synthesized and characterized by IR and UV/Vis spectroscopy, cyclic voltammetry and single-crystal X-ray diffraction studies. The structure of 1 consists of dinuclear units with crystallographic C2 symmetry in which each NiII atom is in a distorted octahedral environment. The Ni,O distance and the Ni,O,Ni angle, through the bridged water molecule, are 2.240(11) Å and 82.5(5)°, respectively. The structure of 2 consists of dinuclear units bridged asymmetrically by di-,1,3 -NCS ions; each CuII ion is in a square-pyramidal environment with , = 0.25. Variable-temperature magnetic susceptibility studies indicate the presence of dominant ferromagnetic exchange coupling in complex 1 with J = 3.1 cm,1, whereas complex 2 exhibits weak antiferromagnetic coupling between the CuII centers with J = ,1.7 cm,1. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Modeling the three-dimensional structure of H+ -ATPase of Neurospora crassaFEBS JOURNAL, Issue 21 2002Proposal for a proton pathway from the analysis of internal cavities Homology modeling in combination with transmembrane topology predictions are used to build the atomic model of Neurospora crassa plasma membrane H+ -ATPase, using as template the 2.6 Å crystal structure of rabbit sarcoplasmic reticulum Ca2+ -ATPase [Toyoshima, C., Nakasako, M., Nomura, H. & Ogawa, H. (2000) Nature 405, 647,655]. Comparison of the two calcium-binding sites in the crystal structure of Ca2+ -ATPase with the equivalent region in the H+ -ATPase model shows that the latter is devoid of most of the negatively charged groups required to bind the cations, suggesting a different role for this region. Using the built model, a pathway for proton transport is then proposed from computed locations of internal polar cavities, large enough to contain at least one water molecule. As a control, the same approach is applied to the high-resolution crystal structure of halorhodopsin and the proton pump bacteriorhodopsin. This revealed a striking correspondence between the positions of internal polar cavities, those of crystallographic water molecules and, in the case of bacteriorhodopsin, the residues mediating proton translocation. In our H+ -ATPase model, most of these cavities are in contact with residues previously shown to affect coupling of proton translocation to ATP hydrolysis. A string of six polar cavities identified in the cytoplasmic domain, the most accurate part of the model, suggests a proton entry path starting close to the phosphorylation site. Strikingly, members of the haloacid dehalogenase superfamily, which are close structural homologs of this domain but do not share the same function, display only one polar cavity in the vicinity of the conserved catalytic Asp residue. [source] Adsorption of water in mordenite,An ab initio studyINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 1 2001Th. Demuth Abstract The adsorption of water in mordenite has been investigated using density functional theory using gradient corrections to the exchange,correlation functional. In the neutral complex water is strongly physisorbed through two different hydrogen bonds, the stronger between the acid site and the water oxygen atom, the weaker between a hydrogen atom of the adsorbed molecule and a framework oxygen atom. Strong polarizations and structural distortions of both the acid site and the molecule have been observed. To elucidate the question if a chemisorbed complex (creation of a hydroxonium ion) is possible, ab initio molecular dynamics have been performed, indicating that a protonation of water occurs even for the low coverage of one water molecule per unit cell. However, this ionic configuration cannot be stabilized by the electrostatic field of the zeolite framework and is therefore not a minimum of the potential energy surface. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 84: 110,116, 2001 [source] Identification and fragmentation of hydrolyzed aluminum species by electrospray ionization tandem mass spectrometryJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 10 2004Arja Sarpola Abstract Earlier characterization of some hydrolysis products of AlCl3·6H2O was confirmed by electrospray ionization tandem mass spectrometry with increasing collision energy of projectile ions. At lower collision energies, the aqua ligands were stripped off. At higher energies, two hydroxo groups formed a bridging oxo group with loss of one water molecule. Aluminum complexes could also capture aqua ligands in the collision chamber so long as the parent ion did not fragment, and the fragment ion spectra broadened toward higher m/z values. The chloro ligands were eliminated as hydrochloric acid. The aluminum cores remained highly intact. Copyright © 2004 John Wiley & Sons, Ltd. [source] Water and urea interactions with the native and unfolded forms of a ,-barrel proteinPROTEIN SCIENCE, Issue 12 2003Kristofer Modig CD, circular dichroism; I-FABP, intestinal fatty acid-binding protein; MRD, magnetic relaxation dispersion; NOE, nuclear Overhauser effect Abstract A fundamental understanding of protein stability and the mechanism of denaturant action must ultimately rest on detailed knowledge about the structure, solvation, and energetics of the denatured state. Here, we use 17O and 2H magnetic relaxation dispersion (MRD) to study urea-induced denaturation of intestinal fatty acid-binding protein (I-FABP). MRD is among the few methods that can provide molecular-level information about protein solvation in native as well as denatured states, and it is used here to simultaneously monitor the interactions of urea and water with the unfolding protein. Whereas CD shows an apparently two-state transition, MRD reveals a more complex process involving at least two intermediates. At least one water molecule binds persistently (with residence time >10 nsec) to the protein even in 7.5 M urea, where the large internal binding cavity is disrupted and CD indicates a fully denatured protein. This may be the water molecule buried near the small hydrophobic folding core at the D,E turn in the native protein. The MRD data also provide insights about transient (residence time <1 nsec) interactions of urea and water with the native and denatured protein. In the denatured state, both water and urea rotation is much more retarded than for a fully solvated polypeptide. The MRD results support a picture of the denatured state where solvent penetrates relatively compact clusters of polypeptide segments. [source] Tris(1,10-phenanthroline-,2N,N,)cadmium(II) bis(perchlorate) 3.5-hydrate: a water chain stabilized by perchlorate anionsACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2010Yu-Hui Sun The title compound, [Cd(C12H8N2)3](ClO4)2·3.5H2O, contains a cross-shaped one-dimensional channel along the c axis which encapsulates an ordered water chain. This water chain features a centrosymmetric cyclic water hexamer unit with a chair-like conformation. Neighbouring hexamers are linked by bridging water molecules. The host perchlorate anions recognize and stabilize the guest water chain via three kinds of hydrogen-bond patterns, leading to the formation of a complex one-dimensional {[(H2O)7(ClO4)4]4,}n anionic chain. One perchlorate acts as a single hydrogen-bond acceptor dangling on the chain, the second perchlorate on the chain serves as a double hydrogen-bond acceptor for only one water molecule to form an R22(6) ring, where both entities lie on a twofold axis, while the third perchlorate, which also lies on a twofold axis, accepts two hydrogen bonds from two equivalent water molecules and is involved in the construction of an R65(14) ring. [source] An ice-like water hexamer with symmetry in the hydrogen-bonded structure of 2,3,5,6-tetrafluoro-1,4-bis(imidazol-1-ylmethyl)benzene dihydrateACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2010Huan Xu An ice-like hexameric water cluster, stabilized by the flexible bis-imidazolyl compound 2,3,5,6-tetrafluoro-1,4-bis(imidazol-1-ylmethyl)benzene (Fbix), is found in the trigonal R crystal structure of the title compound, C14H10F4N4·2H2O or Fbix·2H2O. The Fbix molecule lies about an inversion centre with one water molecule in the asymmetric unit in a general position. A cyclic chair-like hexameric water cluster with symmetry is generated with a hydrogen-bonded O...O distance within the hexamer of 2.786,(3),Å. The Fbix molecule adopts a trans conformation, where the imidazole ring makes a dihedral angle of 70.24,(11)° with the central tetrafluorinated aromatic ring. Each water hexamer is connected by six Fbix molecules through intermolecular O,H...N hydrogen bonds [N...O = 2.868,(3),Å] to yield a three-dimensional supramolecular network with primitive cubic (pcu) topology. Large voids in each single pcu network lead to fourfold interpenetrated aggregates of Fbix·2H2O. [source] Unexpected conformational consequences of weak hydrogen bonds on 1,3,7,9,13,15,19,21-octaazapentacyclo[19.3.1.13,7.19,13.115,19]octacosane monohydrateACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2010Augusto Rivera In the title compound, C20H40N8·H2O, the organic molecule crystallizes with one water molecule located within the molecular cavity of the octaaza macrocycle. The two molecules are linked via two weak O,H...N hydrogen bonds. The assembly has noncrystallographic C2 axial symmetry. [source] A three-dimensional homochiral metal,organic framework constructed from manganese(II) with S -carboxymethyl- N -(p -tosyl)- l -cysteine and 4,4,-bipyridineACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2009Wei Xiong In the chiral polymeric title compound, poly[aqua(4,4,-bipyridine)[,3 - S -carboxylatomethyl- N -(p -tosyl)- l -cysteinato]manganese(II)], [Mn(C12H13NO6S2)(C10H8N2)(H2O)]n, the MnII ion is coordinated in a distorted octahedral geometry by one water molecule, three carboxylate O atoms from three S -carboxyatomethyl- N -(p -tosyl)- l -cysteinate (Ts-cmc) ligands and two N atoms from two 4,4,-bipyridine molecules. Each Ts-cmc ligand behaves as a chiral ,3 -linker connecting three MnII ions. The two-dimensional frameworks thus formed are further connected by 4,4,-bipyridine ligands into a three-dimensional homochiral metal,organic framework. This is a rare case of a homochiral metal,organic framework with a flexible chiral ligand as linker, and this result demonstrates the important role of noncovalent interactions in stabilizing such assemblies. [source] The crystallographic structure of the aldose reductase,IDD552 complex shows direct proton donation from tyrosine 48ACTA CRYSTALLOGRAPHICA SECTION D, Issue 8 2004Federico Ruiz The X-ray crystal structure of human aldose reductase (ALR2) in complex with the inhibitor IDD552 was determined using crystals obtained from two crystallization conditions with different pH values (pH 5 and 8). In both structures the charged carboxylic head of the inhibitor binds to the active site, making hydrogen-bond interactions with His110 and Tyr48 and electrostatic interactions with NADP+. There is an important difference between the two structures: the observation of a double conformation of the carboxylic acid moiety of the inhibitor at pH 8, with one water molecule interacting with the main configuration. This is the first time that a water molecule has been observed deep inside the ALR2 active site. Furthermore, in the configuration with the lower occupancy factor the difference electron-density map shows a clear peak (2.5,) for the H atom in the hydrogen bond between the inhibitor's carboxylic acid and the Tyr48 side-chain O atom. The position of this peak implies that this H atom is shared between both O atoms, indicating possible direct proton transfer from this residue to the inhibitor. This fact agrees with the model of the catalytic mechanism, in which the proton is donated by the Tyr48 hydroxyl to the substrate. These observations are useful both in drug design and in understanding the ALR2 mechanism. [source] Two Nucleophilic Mutants of the Micromonospora viridifaciens Sialidase Operate with Retention of Configuration by Two Different MechanismsCHEMBIOCHEM, Issue 11 2005Jacqueline N. Watson Dr. Abstract Mutants of the Micromonospora viridifaciens sialidase, Y370E and Y370F, are catalytically active retaining enzymes that operate by different mechanisms. Previous substitutions with smaller amino acids, including Y370D, yielded inverting sialidases. At least one water molecule can fit into the active-site cavity of this mutant and act as a nucleophile from the face opposite the leaving group (Biochemistry 2003, 42, 12,682). Thus, addition of a CH2 unit (Asp versus Glu) changes the mechanism from inversion back to retention of configuration. Based on Brønsted ,lgvalues, it is proposed that the Y370E mutant reacts by a double-displacement mechanism (,lgon kcat/Km,0.36±0.04) with Glu370 acting as the nucleophile. However, the Y370F mutant (,lgon kcat/Km,0.79±0.12) reacts via a dissociative transition state. The crystal structure of the Y370F mutant complexed with 2-deoxy-2,3-dehydro- N -acetylneuraminic acid shows no significant active-site perturbation relative to the wild-type enzyme. [source] Organocatalyzed Highly Enantioselective Direct Aldol Reactions of Aldehydes with Hydroxyacetone and Fluoroacetone in Aqueous Media: The Use of Water To Control RegioselectivityCHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2007Xiao-Hua Chen Abstract An organocatalyst prepared from (2R,3R)-diethyl 2-amino-3-hydroxysuccinate and L -proline exhibited high regio- and enantioselectivities for the direct aldol reactions of hydroxyacetone and fluoroacetone with aldehydes in aqueous media. It was found that water could be used to control the regioselectivity. The presence of 20,30 mol,% of the catalyst afforded the direct aldol reactions of a wide range of aldehydes with hydroxyacetone to give the otherwise disfavored products with excellent enantioselectivities, ranging from 91 to 99,%,ee, and high regioselectivities. Aldolizations of fluoroacetone with aldehydes mediated by 30 mol,% of the organocatalyst in aqueous media preferentially occurred at the methyl group, yielding products with high enantioselectivities (up to 91,%,ee); however, these additions took place dominantly at the fluoromethyl group in THF. Optically active 3,5-disubstituted tetrahydrofurans and (2S,4R)-dihydroxy-4-biphenylbutyric acid were prepared by starting from the aldol reaction of hydroxyacetone. Theoretical studies on the role of water in controlling the regioselectivity revealed that the hydrogen bonds formed between the amide oxygen of proline amide, the hydroxy of hydroxyacetone, and water are responsible for the regioselectivity by microsolvation with explicit one water molecule as a hydrogen-bond donor and/or an acceptor. [source] | ||||||||||