Hydrogen Bond Interactions (hydrogen + bond_interaction)

Distribution by Scientific Domains

Selected Abstracts

Control of Intramolecular Ether-Oxygen Coordination in the Crystal Structure of Copper(II) Complexes With Dipicolylamine-Based Ligands

Yuji Mikata
Abstract Thirteen crystal structures of copper(II) complexes with a series of dipicolylamine (DPA)-derived ligands, N -(2-methoxyethyl)- N,N -bis(2-pyridylmethyl)amine (L1), N -[2-(2-hydroxyethyloxy)ethyl]- N,N -bis(2-pyridylmethyl)amine (L2) and N -(3-methoxypropyl)- N,N -bis(2-pyridylmethyl)amine (L3), have been determined and the factors that control the coordination of the ether-oxygen atom of these ligands to the copper centre are discussed. Complexes that have +1 or +2 charges exhibit coordination of the ether-oxygen atom, whereas neutral complexes in which two anions are bound to the copper(II) centre tend to lose the oxygen coordination. Upon chelation of the oxygen atom, L3 forms a six-membered chelate ring with respect to the 3-aminopropyl ether moiety whereas L1 and L2 form a five-membered chelate. This difference, especially in the nitrate and bromide complexes, determines whether the ether-oxygen atom chelates to the metal centre to give a monocationic complex, or the second anion coordinates to the metal centre to form the ether-free, neutral complex. The terminal anchor hydroxy group of L2 facilitates the ether-oxygen coordination via a hydrogen bond interaction to the donor atom located trans to the aliphatic nitrogen atom in the basal plane. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

Theoretical study of CH,O hydrogen bond in proton transfer reaction of glycine

P. Selvarengan
Abstract Density functional theory (DFT) calculations are used to study the strength of the CH,O H-bond in the proton transfer reaction of glycine. Comparison has been made between four proton transfer reactions (ZW1, ZW2, ZW3, SCRFZW) in glycine. The structural parameters of the zwitterionic, transition, and neutral states of glycine are strongly perturbed when the proton transfer takes place. It has been found that the interaction of water molecule at the side chain of glycine is high in the transition state, whereas it is low in the zwitterionic and neutral states. This strongest multiple hydrogen bond interaction in the transition state reduces the barrier for the proton transfer reaction. The natural bond orbital analysis have also been carried out for the ZW2 reaction path, it has been concluded that the amount of charge transfer between the neighboring atoms will decide the strength of H-bond. 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source]

Polymers or Supramolecules Generated From a New V-Shaped Bis-monodentate Ligand and the Effect of Steric Hindrance on Coordination Modes of the Ligand

Caihua Zhou
Abstract A new V-shaped bis-monodentate ligand L (L = 2,3,-dipyridylamine) (1) has been designed and synthesized by alkylation reaction of pyridylamine. An investigation of the charge distributions of the coordination atoms and single-point energy calculations of four conformers of ligand L based on the geometry of conformers optimized by the DFT (density functional theory) method was carried out. The results show that the four conformers of ligand L take on two stable and two less stable configurations. Theory forecasts that two relatively stable configurations present in complexes as probable coordination motifs of the ligand, and that steric hindrance of pyridine nitrogen atoms in isomers will affect its coordination ability together with the electronic factor. This forecast has been demonstrated by the coordination chemistry of ligand L, that is, configuration (a) and (b) of the ligand occur in the following reported complexes, which combines with AgI or CuII through two coordination modes (bidentate bridging or a monodentate mode) resulting in coordination polymers {[Ag (L)2]NO3}n (2), [Cu2(L)2(maa)4]n (maa = methacrylic acid) (3), and the mononuclear molecule [Cu(L)4](ClO4)22CH3CH2OH (4). The ligand assumes different coordination modes in the three complexes because of different levels of steric hindrance of the pyridine nitrogen atoms in the conformers. Interestingly, polymers 2 and 3 assume a 1D helical structure and a linear framework, respectively, and 4 has a 2D supramolecular architecture induced from hydrogen bond interactions. In addition, the magnetic properties of 3 have been explored, which shows a strong antiferromagnetic interaction.( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

Dye,fiber interactions in PET fibers: Hydrogen bonding studied by IR-spectroscopy

Karen De Clerck
Abstract Dye,fiber interactions are studied in poly (ethylene terephthalate) fibers by FT-IR spectroscopy. It is shown for the first time that DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) serves as an easy applicable and accurate technique for the study of fibrous structures. This article focuses on the possible hydrogen bond interactions in the dye,fiber system, where the PET fibers are dyed with anthraquinone-based disperse dyes. The dyes and related anthraquinone structures are studied in both the dilute solution state, the solid state, and as present in the PET fibers. It is proven that 1-amino anthraquinones show strong "chelate-type" intramolecular hydrogen bonding in all three states. In the fibers an important supplementary intermolecular hydrogen bonding with the CO groups in the PET fiber is observed. The extend of hydrogen bonding seems to be prone to dye concentration variations. Further analysis by modulated differential scanning calorimetry links the hydrogen bonding to an intrinsic plasticizing effect of the dyes affecting the dye diffusion process. This thus offers a tool for the fundamental understanding of the dyeing process and possible observed differences in dyeing behavior in dye,fiber systems. 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source]

Advancing beyond charge analysis using the electronic localization function: Chemically intuitive distribution of electrostatic moments

Julien Pilm
Abstract We propose here an evaluation of chemically intuitive distributed electrostatic moments using the topological analysis of the electron localization function (ELF). As this partition of the total charge density provides an accurate representation of the molecular dipole, the distributed electrostatic moments based on the ELF partition (DEMEP) allows computing of local moments located at non atomic centers such as lone pairs, , bonds and , systems. As the local dipole contribution can be decomposed in polarization and charge transfer components, our results indicate that local dipolar polarization of the lone pairs and chemical reactivity are closely related whereas the charge transfer contribution is the key factor driving the local bond dipole. Results on relevant molecules show that local dipole contributions can be used to rationalize inductive polarization effects in alcohols derivatives and typical hydrogen bond interactions. Moreover, bond quadrupole polarization moments being related to a , character enable to discuss bond multiplicities, and to sort families of molecules according to their bond order. That way, the nature of the CO bond has been revisited for several typical systems by means of the DEMEP analysis which appears also helpful to discuss aromaticity. Special attention has been given to the carbon monoxide molecule, to the CuCO complex and to a weak intramolecular N|---CO interaction involved in several biological systems. In this latter case, it is confirmed that the bond formation is mainly linked to the CO bond polarization. Transferability tests show that the approach is suitable for the design of advanced force fields. 2008 Wiley Periodicals, Inc. J Comput Chem 2008 [source]

Solvent dependent study of carbonyl vibrations of 3-phenoxybenzaldehyde and 4-ethoxybenzaldehyde by Raman spectroscopy and ab initio calculations

Veerabahu Ramakrishnan
Abstract A Raman spectroscopy investigation of the carbonyl stretching vibrations of 3-phenoxybenzaldehye (3Phbz) and 4-ethoxybenzaldeheyde (4Etob) was carried out in binary mixtures with different polar and nonpolar solvents. The purpose of this study was twofold: firstly, to describe the interaction of the carbonyl groups of two solute molecules in terms of a splitting in the isotropic and anisotropic components and secondly, to analyze their spectroscopic signatures in a binary mixture. Changes in wavenumber position, variation in the anisotropic shift and full width half maximum were investigated for binary mixtures with different mole fractions of the reference systems. In binary mixtures, the observed increase in wavenumber with solvent concentration does not show linearity, indicating the significant role of molecular interactions on the occurrence of breaking of the self-association of the solute. In all the solvents, a gradual decrease in the anisotropic shift reflects the progressive separation of the coupled oscillators with dilution. ,i(,c), 3Phbz,solvent mixtures, exhibit a gradual decrease with decrease in the concentration of the solute which is an evidence on the influence of micro viscosity on linewidth. For 4Etob, the carbonyl stretching vibration shows two well-resolved components in the Raman spectra, attributed to the presence of two distinct carbonyl groups: hydrogen-bonded and free carbonyl groups. The intensity ratio of the carbonyl stretching vibration of these two types of carbonyl groups is studied to understand the dynamics of solute/solvent molecules owing to hydrogen bond interactions. Ab initio calculations were employed for predicting relevant molecular structures in the binary mixtures arising from intermolecular interactions, and are related to the experimental results. Copyright 2009 John Wiley & Sons, Ltd. [source]

Spontaneous Resolution of Chiral Polyoxometalate-Based Compounds Consisting of 3D Chiral Inorganic Skeletons Assembled from Different Helical Units

Ya-Qian Lan Dr.
Abstract Four enantiomerically pure 3D chiral POM-based compounds, [Ni2(bbi)2(H2O)4V4O12],2,H2O (1,a and 1,b) and [Co(bbi)(H2O)V2O6] (2,a and 2,b) (bbi=1,1,-(1,4-butanediyl)bisimidazole) based on the achiral ligand, different vanadate chains, and different metal centers have been synthesized by hydrothermal methods. Single-crystal X-ray diffraction analyses revealed that 1,a and 1,b, and 2,a and 2,b, respectively, are enantiomers. In 1,a and 1,b two kinds of vanadate chains with different screw axes link Ni cations to generate 3D chiral inorganic skeletons, which are connected by the achiral bbi ligands to form complicated 3D 3,4-connected chiral self-penetrating frameworks with (72,8)(72,82,92)(73,82,10) topology. They represent the first examples of chiral self-penetrating frameworks known for polyoxometalate (POM) systems. Contrary to 1,a and 1,b, in 2,a and 2,b the vanadate chains link CoII cations to generate 3D chiral inorganic skeletons, which are assembled from two kinds of heterometallic helical units of opposite chirality along the c axes. The chiral inorganic skeletons are connected by bbi to form 3D 3,4-connected chiral POM-based frameworks with (62,8)2(62,82,102) topology. It is believed that the asymmetrical coordination modes of the metal cations in 1,a,2,b generate the initial chiral centers, and that the formation of the various helical units and the hydrogen bond interactions are responsible for preservation of the chirality and spontaneous resolution when the chirality is extended into the homochiral 3D-networks. This is the first known report of chiral POM-based compounds consisting of 3D chiral inorganic skeletons being obtained by spontaneous resolution upon crystallization in the absence of any chiral source, which may provide a rational strategy for synthesis of chiral POM-based compounds by using achiral ligands and POM helical units. [source]

Self-assembly of Two Novel Supramolecular Frameworks Based on Flexible Oligo- , -Pyridylamino Ligands and Copper(II) Maleate

Cai-Hua Zhou
Abstract Two novel supramolecular complexes, [Cu(bpapa)(mal)]H2OCH3OH (1) and {[Cu(bpapap)](Hmal)2}2H2O (2) [bpapa=bis-[6-(2-pyridylamino)pyrid-2-yl]amine, bpapap=2,6-bis-[6-(pyrid-2-ylamino)pyrid-2-ylamino]-pyridine, mal=maleate dianion] were rationally designed and synthesized based on flexible multidentate ligands and copper(II) maleate. Complexes 1 and 2 were all characterized by elemental analysis, spectroscopic techniques, thermal analysis and single crystal X-ray diffraction analysis. Complex 1 is of an infinite 3-D supramolecular framework constructed by 2-D sheets to contain 1-D helical chains formed by intermolecular hydrogen bond interactions between the non-coordinated oxygen atoms from maleate and nitrogen atoms from amino groups of bpapa. Complex 2 also takes a 3-D supramolecular structure, which is built from 2-D rhombic sheets produced by sequential dimer units. Interestingly, three pairs of symmetrical hydrogen bonds generate these dimer units. [source]

Synthesis and structure of the first protonated zincoborophosphate: (H3O)Zn(H2O)2BP2O8H2O

Heng-Zhen Shi
Abstract The solid acid of the first protonated zincoborophosphate, (H3O) Zn (H2O)2BP2O8H2O (1), was soventothermally synthesized by the reaction of Zn(NO3)2 6H2O and H3BO3 with H3PO4 in a mixed solvent, and structurally characterized by single-crystal X-ray diffraction analysis. It crystallizes in the hexagonal P6122, a = 0.9604(4) nm, c = 1.5297(6) nm, V = 1.2218(8) nm3, Dc = 2.921 g/cm3, Z = 6, F (000) = 1080, , =3.495 mm,1. The structure features that the tetrahedra-tetrahedra helices interconnected by octahedra and strong hydrogen bond interactions form a three-dimensional framework. The protonated water molecules are located at unique positions. Other characterizations by IR and thermal analysis are also described. [source]

Study on the Gas Phase Stability of Heme-binding Pocket in Cytochrome Tb5 and Its Mutants by Electrospray Mass Spectrometry

Chong-Tian Yu
Abstract To elucidate the effect of various amino add residues on the heme-binding pocket in cytochrome Tb5, several residues were chosen for replacement by means of site-directed mutagenesis. Comparison of the mass spectrum between the F35Y mutant and the wild type shows that the relative abundance of holoprotein ion of F35Y is lower than that of the wild type in gas phase. It is concluded that mutation from Phe35 residue to tyrosine decreases the hydrophobic character of cytochrome Tb5 heme pocket, which decreases the stability of heme-binding pocket. ESI-MS spectra of the mutants V61E, V61K, V61H and V61Y show various contribution of amino acid to the stability of heme-binding pocket. The small and non-polar residue Val61 was replaced with large or polar residues, resulting in enhancing the trend of heme leaving from the pocket. In addition, comparison of the mass relative abundance of holo-proteins among all the Vakil-mutants, shows mat their stability in gas phase appropriately submit the following order: wild type > V61H > V61E > V61K , V61Y. The extra great stability of quadruple sites mutant E44/48/56A/D60A shows that reduction of electrostatic or hydrogen bond interactions among the residues locating in the outside region of the heme edge remarkably affect the stability of heme. The results of analyzing the oxidation states of heme iron in Tb5 and its mutants by insource-CAD experiment suggest that the charge states of heme iron Maintain inflexible in mutation process. [source]