Bonding Interactions (bonding + interaction)

Distribution by Scientific Domains
Distribution within Chemistry

Kinds of Bonding Interactions

  • hydrogen bonding interaction

  • Selected Abstracts

    Structure-Directing Effects in the Supramolecular Intercluster Compound [Au9(PPh3)8]2 [V10O28H3]2: Long-Range versus Short-Range Bonding Interactions.

    CHEMINFORM, Issue 33 2007
    Martin Schulz-Dobrick
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]

    Organically Directed Iron Sulfate Chains: Structural Diversity Based on Hydrogen Bonding Interactions.

    CHEMINFORM, Issue 1 2007
    Yunlong Fu
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]

    Complexes of the Bicyclic Multifunctional Sulfur-Nitrogen Ligand F3CCN5S3 with Co2+, Zn2+, Cu2+, and Cd,

    Carsten Knapp
    Abstract The ability of the sulfur-nitrogen-carbon bicycle F3CCN5S3 to act as a donor towards transition metal cations has been investigated. F3CCN5S3 forms complexes with [M(SO2)2](AsF6)2 [M = Co, Cu, Zn, Cd] in the ratio 2:1 of the composition [M(F3CCN5S3)2(OSO)2(FAsF5)2] [M = Co (1), Zn (3)], [Cu(F3CCN5S3)2(,-F)(,-F2AsF4)]2 (4), and [Cd(F3CCN5S3)(,-F3CCN5S3)(,2 -F2AsF4)2]2 (5) in liquid sulfur dioxide. In the octahedral Co and Zn complexes F3CCN5S3 coordinates as a monodentate ligand through the bridging nitrogen atom N5, which carries the highest negative charge according to theoretical calculations. With Cu2+ a dinuclear structure with a central planar, four-membered Cu2F2 ring is formed, which has the shortest CuCu distance of all structurally characterized Cu2F2 units. Similar to the Co and Zn complexes, F3CCN5S3 acts as a terminal monodentate ligand in the Cu compound. The reaction with the larger and softer Cd2+ cation results in a dinuclear complex that contains terminal and bridging F3CCN5S3 ligands. The bridging ligands coordinate through N5 and a nitrogen atom neighboring the carbon atom. In addition, a third weak bonding interaction between one fluorine atom of the trifluoromethyl substituent and the Cd2+ center is observed. The formation of the different structures and the versatile coordination modes of the F3CCN5S3 ligand are discussed. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

    Use of Molecular Scaffolding for the Stabilization of an Intramolecular Dative PIII -PV System

    Petr Kilian
    Abstract The reaction of NapP2S4 (1; Nap = naphthalene-1,8-diyl) with chlorine gas gave [Nap(PCl2)(PCl4)] (2), displaying a rare ,4P-,6P bonding interaction. An X-ray structure analysis confirmed the PCl5 -like, P,P bond containing phosphonium-phosphoride structure of 2 in the crystal, which was also found in solution at low temperature. At ambient and higher temperatures, dynamic behaviour on the NMR time-scale was observed, which was assigned to interchange of the ionic phosphonium-phosphoride form 2 and the molecular bis(phosphorane) Nap(PCl3)2 form 3, rather than to the ionic phosphonium salt-phosphorane form [Nap(PCl3)(PCl2)][Cl] 4. Electronic structure calculations were performed at the B3LYP/6,31G(d,p) level of theory on structures 2 and 3; structure 3 was located as a local minimum on the potential energy surface, 15 kcalmol,1 higher in energy than structure 2. The crystal structure and calculated P,P distances are 2.34 and 2.31 for 2 and 3, respectively. An activation energy of 19.7 kcalmol,1 was found for the transition state structure by coordinate driving calculations; the line-shape analysis of variable temperature 31P{1H} NMR spectra gave an activation energy of 14.4 kcalmol,1. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

    Hydrogen bonding interaction between 1,4-dioxane and water

    Ajay Chaudhari
    Abstract This work reports an interaction of 1,4-dioxane with one, two, and three water molecules using the density functional theory method at B3LYP/6-311++G* level. Different conformers were studied and the most stable conformer of 1,4-dioxane-(water)n (n = 1,3) complex has total energies ,384.1964038, ,460.6570694, and ,537.1032381 hartrees with one, two, and three water molecules, respectively. Corresponding binding energy (BE) for these three most stable structures is 6.23, 16.73, and 18.11 kcal/mol. The hydrogen bonding results in red shift in OO stretching and CC stretching modes of 1,4-dioxane for the most stable conformer of 1,4-dioxane with one, two, and three water molecules whereas there was a blue shift in CO symmetric stretching and CO asymmetric stretching modes of 1,4-dioxane. The hydrogen bonding results in large red shift in bending mode of water and large blue shift in symmetric stretching and asymmetric stretching mode of water. 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source]

    A Kirkwood-Buff derived force field for amides

    Myungshim Kang
    Abstract A force field for the computer simulation of aqueous solutions of amides is presented. The force field is designed to reproduce the experimentally observed density and Kirkwood,Buff integrals for N -methylacetamide (NMA), allowing for an accurate description of the NMA activity. Other properties such as the translational diffusion constant and heat of mixing are also well reproduced. The force field is then extended to include N,N,-dimethylacetamide and acetamide with good success. Analysis of the simulations of low concentrations of NMA in water indicates a high degree of solvation with only 15% of the NMA molecules involved in solute,solute hydrogen bonding. There is only a weak angular dependence of the solute,solute hydrogen bonding interaction with a minimum at an angle of 65 for the NH and CO dipole vectors. The models presented here provide a basis for an accurate force field for peptides and proteins. 2006 Wiley Periodicals, Inc. J Comput Chem 27: 1477,1485, 2006 [source]

    Application of heterogeneous adsorbents in removal of dimethyl phthalate: Equilibrium and heat

    AICHE JOURNAL, Issue 10 2010
    Jun Wu
    Abstract Aminated resin (NDA-101) and oxidized resin (NDA-702) were synthesized to remove Dimethyl phthalate (DMP) from the contaminated water. The equilibrium and heat properties in the course of adsorption process were examined and compared with two commercial heterogeneous adsorbents, namely an acrylic ester resin (Amberlite XAD-7) and a coal-based granular activated carbon (AC-750). The associated equilibrium isotherms can be well fitted by Freundlich equation and the adsorption capacities for DMP followed the order: NDA-702 > NDA-101 > AC-750 > XAD-7. The surface of XAD-7 was demonstrated to be relatively homogeneous through surface energy heterogeneity analysis, offering the sole hydrogen bonding interaction. Contrarily, heterogeneous surface of oxidized resins NDA-702 and the aminated resins NDA-101 exhibited a promising adsorption capacity and affinity toward DMP probably derived by multiple hydrogen bonding, ,,, stacking, and micropore filling interactions. 2010 American Institute of Chemical Engineers AIChE J, 2010 [source]

    Microstructure and Molecular Interaction in Glycerol Plasticized Chitosan/Poly(vinyl alcohol) Blending Films

    Songmiao Liang
    Abstract Exploring some basic interactions in blending systems is of great significance for designing a blend with controlled structure and properties. This work attempts to analyze microstructure and molecular interaction in glycerol plasticized chitosan/poly(vinyl alcohol) blends by atomic force microscopy, differential scanning calorimetry and ATR-FTIR spectroscopy. Our results show that the blending films are aggregated by spherical chitosan/poly(vinyl alcohol) blending nanoparticles. The size and aggregation behavior of these particles are closely related to glycerol content. The presence of glycerol gives rise to a continuous closing in Tg of poly(vinyl alcohol) and chitosan components, suggesting an improved miscibility of the blend. Strong hydrogen bonding interaction in the blend is observed and further distinguished by peak resolution. Moreover, more interesting evidence on the effect of glycerol in the blends is provided by monitoring the structure evolution of the blend at different blending steps using atomic force microscopy. The formation of strong hydrogen bonding network among glycerol molecules and polymer matrix was considered as the main driving force to result in the changes in the microstructure and miscibility of the blend. [source]

    Effects of interactions among polyaniline, camphorsulfonic acid and silica on the structure and properties of their conductive hybrids

    Hsun-Tsing Lee
    In this work, the effects of interactions among polyaniline (PAn), camphorsulfonic acid (CSA), and silica on the structure and properties of their sol-gel hybrids are investigated. These interactions were revealed by FTIR, UV,vis spectra, and XRD patterns. The interaction between PAn and CSA raises conductivities of the CSA-doped PAn/SiO2 (c-PAn/SiO2) hybrids. Moreover, the hydrogen bonding interaction between c-PAn and silicic acid (precursor of SiO2) leads to a less degree of three-dimensional network structure of the SiO2 component in a hybrid with higher PAn content. In addition, because of the interactions among CSA, Pan, and SiO2, the conductive c-PAn-rich phase distributes uniformly in the hybrid and thermal resistance of the hybrid is enhanced consequently. Besides, the c-PAn/SiO2 hybrid with higher SiO2 content exhibits more significant blue-shift of its polaron band, lower conductivity, and higher thermal resistance. POLYM. ENG. SCI., 2008. 2008 Society of Plastics Engineers [source]

    Correlation between hydrogen-bonding interaction and mechanical properties of polyimide fibers

    Xiangyang Liu
    Abstract Novel co-polymerization polyimide (PI) fibers based on 4,4,-oxydianiline (ODA)-pyromellitic dianhydride (PMDA) were prepared. 2-(4-Aminophenyl)-5-aminobenzimidazole (PABZ) containing the NH group was introduced into the structure of the fibers as the proton donor. The results of Fourier transform infrared (FTIR) and dynamic mechanical analysis (DMA) showed that hydrogen bonding occured between the NH group and chains, which strongly enhanced interchain interaction. This hydrogen bonding interaction increased the tensile strength and initial modulus of the PI fibers up to 2.5 times and 26 times, respectively, compared to those of homo-PI PMDA-ODA fibers with no hydrogen-bonding interaction because of the absence of proton donors after the imidization process. In the mean time, glass transition temperature (Tg) of the modified PI fibers was found to be 410,440C, which was higher than that of the homo-PI PMDA-ODA fibers. From the result, a novel access to molecular design and manufacture of high performance PI fibers with good properties could be provided. Copyright 2009 John Wiley & Sons, Ltd. [source]

    Analytic Models of Domain-Averaged Fermi Holes: A New Tool for the Study of the Nature of Chemical Bonds

    Robert Ponec Prof.
    Abstract Simple analytical models are introduced that significantly enhance the ability to understand and rationalise the nature of bonding interactions depicted by domain-averaged Fermi hole (DAFH) analysis. The examples presented show that besides shedding new light on the role of electron-sharing in ordinary two-centre two-electron (2c,2e) chemical bonds that are well represented by the classical Lewis model, the proposed approach also provides interesting new insights into the nature of bonding interactions that go beyond the traditional Lewis paradigm. This is, for example, the case of 3c,2e multicentre bonding, but a straightforward extension of the approach also reveals for direct metal,metal bonding the existence of a completely new type of bonding interaction that involves the mutual exchange of electrons between the lone pairs on adjacent metal atoms. [source]

    From 1D Polymeric Chain to Two-fold Parallel Interpenetration of (4,4) Net: Synthesis and Characterization of Two New Copper(II) Complexes Derived from Highly Polydentate Aminopolycarboxylate Ligand

    Ya-Pan WU
    Abstract Two new copper(II) polymers, {[Cu2(egta)(bpe)(H2O)2]H2O}n (1) and {[Cu2(egta)(bipy)(H2O)2]5H2O}n(2), [H4egta=3,12-bis(carboxymethyl)-6,9-dioxa-3,12-diazatetradecanedioic acid, bpe=1,2-bis(4-pyridyl)ethane, bipy4,4,-bipyridyl] have been synthesized and structurally characterized by single-crystal X-ray diffraction, elemental analysis, IR spectra and TG analysis. The structure determination reveals that both 1 and 2 crystallize in a monoclinic system, space group P21/c. Complex 1 exhibits a two-fold parallel interpenetration of (4,4) net framework consisting of 1D zigzag chains interlocked together through hydrogen bonding interaction. However, the meso-helix chains of 2 are packed to form 2D supramolecular structures. Interestingly, in 2, the host frameworks encapsulate a unique pentamer water cluster and are further connected into 1D tapes by water-water hydrogen bonding interaction. Magnetic measurements reveal that there is a weak ferromagnetic interaction between the adjacent Cu(II) ions in 1. [source]

    Eight-Coordinate Endohedral Rhenium, Osmium and Iridium Atoms in Rare-Earth Halide Cluster Complexes

    Sina Zimmermann
    Abstract Endohedral (interstitial) atoms are essential for almost all of the rare-earth halide cluster complexes. Most of these contain octahedral clusters, some are isolated, but the majority exhibits condensation by common edges to structures of higher dimensionality. Higher coordination numbers of the endohedral atoms are rare. Four examples of extended cluster complexes with eight-coordinate endohedral atoms of sixth-period elements (Re, Os, Ir) are presented. In the quasi-isostructural, non-isotypic halides {ReGd4}Br4 and {OsSc4}Cl4, square antiprisms of gadolinium and scandium atoms, respectively, are connected by two common faces to chains, surrounded and loosely connected by halogenido ligands. The Re and Os atoms build a slightly bent chain with only little bonding interactions. Chemical bonding is dominated by endohedral atom,cluster atom and cluster atom,halide interactions. The same is true for the two scandium bromides {Ir3Sc12}Br16 and {Os3Sc12}Br16Sc, which contain chains of face-sharing square antiprisms and cubes in a ratio of 2:1. Metal,metal bonding is attested by short distances between those endohedral Ir and Os atoms, respectively, which center the square antiprisms (283 pm and 290 pm, respectively). Magnetic and conductivity measurements on {Ir3Sc12}Br16 reveal paramagnetism and a small-band-gap semiconductor. This is in accord with electronic structure calculations. [source]

    New Approaches to 12-Coordination: Structural Consequences of Steric Stress, Lanthanoid Contraction and Hydrogen Bonding

    Anthony S. R. Chesman
    Abstract The anionic dinitrile ligand dicyanonitrosomethanide (dcnm), C(CN)2(NO),, and the anion resulting from its addition product with water, carbamoylcyanonitrosomethanide (ccnm), C(CN)(CONH2)(NO),, have been incorporated into lanthanoid complexes and display unusual ,2(N,O) nitroso coordination modes. (Et4N)3[Ln(ccnm)6] (1Ln; 1Ln = 1La, 1Ce, 1Pr, 1Nd, 1Sm) and (Me4N)3[Ln(ccnm)6] (2Ln; 2Ln = 2La, 2Ce, 2Pr, 2Nd) are systems containing 12-coordinate homoleptic trianionic lanthanoidate complexes. The nitroso groups of the ccnm ligands form three-membered ring chelates with the lanthanoid metal centre, with the asymmetry of the nitroso ,2 interactions dependent upon the intramolecular N,HO=N hydrogen bonding. Additional intermolecular hydrogen bonding interactions exist between adjacent amide and nitrile groups giving rise to 3D ,-Po and 6,8-connected (412.63)(420.68) networks in 1Ln and 2Ln, respectively. The compounds (Me4N)3[Ln(dcnm)6] (3Ln; 3Ln = 3La, 3Ce, 3Nd, 3Sm) also contain a 12-coordinate trianionic lanthanoidate complex with the nitroso group exhibiting a highly symmetrical ,2 interaction. The sterically crowded environments of [Ln(18-crown-6)(dcnm)3] (4Ln; 4Ln = 4La, 4Ce, 4Pr, 4Nd) result in a shift towards a more asymmetric ,2 bonding of the nitroso group with decrease in the Ln3+ radius. There is a corresponding increase of the Ln,O,N angle, and one ligand is ,1(O) binding in 4Nd. The dcnm ligands in the discrete complexes [La(phen)3(dcnm)(3,x)Clx], x , 0.25 (5) (phen = 1,10-phenanthroline), (Et4N)[Ce(phen)2(dcnm)4] (6a/b, 6c) and [Ce(phen)2(dcnm)Cl2H2O] (7) display a variety of coordination modes. Complex 5 has 1D chains formed by ,,, stacking of adjacent phen co-ligands. Complexes 6 contain the monoanionic complex [Ce(phen)2(dcnm)4], with two geometric isomers present in the crystal structure of 6a/b. Complex 7 forms extended 1D chains via hydrogen bonding between coordinated water and chloride atoms and an extensive array of face-to-face , interactions. [source]

    Reaction of 1,3,5-Triazacyclohexanes with TiCl4: Formation of Cationic Complexes

    Randolf D. Khn
    Abstract N -substituted 1,3,5-triazacyclohexanes [R3TAC; R = cyclohexyl, p -fluorobenzyl or Ph(CH2)n (n = 1, 2, 3)] react with excess TiCl4 to give the corresponding cationic ,3 complexes [(R3TAC)TiCl3][Ti2Cl9]. Attempts to prepare complexes with titanium-free anions at lower Ti:R3TAC ratio or with added Me3SiOTf lead to the same cations with [Ti2Cl10]2, and [Ti2Cl8(OTf)], anions. Five complexes as well as (p -fluorobenzyl)3TAC have been characterised by X-ray crystallography. The ring C,H bonds engage in hydrogen bonding interactions in the crystals and strongly solvent and anion dependent 1H NMR signals are detected in solution. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

    Structural Studies of Lithium Telluro- and Seleno-Phosphorus Compounds

    Robert P. Davies
    Abstract Lithium tellurophosphinite [Ph2PTe][Li(TMEDA)1.33(THF)1.33] (4), ditellurophosphinate, [Ph2PTe2][Li(THF)3.5(TMEDA)0.25] (5), and selenotellurophosphinate [Ph2P(Se)Te][Li(THF)2(TMEDA)] (6) complexes have been prepared from the insertion/oxidation reactions of lithiated secondary phosphanes with elemental chalcogens and characterised by X-ray crystallography. Compounds 4,6 contain no tellurium,lithium bonding interactions in the solid state, instead existing as ion-separated species with THF/TMEDA-solvated lithium cations. Reaction of dilithiated primary phosphanes with more than three equivalents of elemental selenium gives [{(c -C6H11)P(Se)(SeLi)}22TMEDA] (7) via a phosphorus-phosphorus coupling reaction. Solid state characterisation of 7 reveals the organo groups in the tetradentate tetraselenohypodisphosphinate ligand to be in an anti conformation to one another and each lithium atom to be coordinated by two selenium atoms, one from each of the diselenophosphinate groups. Multinuclear NMR spectroscopic data are consistent with retention of the solid-state structures of 4,7 in solution. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

    Crystal structure of human Rad GTPase of the RGK-family

    GENES TO CELLS, Issue 8 2006
    Arry Yanuar
    Rad (Ras associated with diabetes) is an RGK-family small GTPase that is over-expressed in the skeletal muscle of humans with type II diabetes. Unlike other small GTPases, RGK family members including Rad lack several conserved residues in the GTPase domain. Here, we report the crystal structure of the GTPase domain of human Rad in the GDP-bound form at 1.8 resolution. The structure revealed unexpected disordered structures of both switches I and II. We showed that the conformational flexibility of both switches is caused by non-conservative substitutions in the G2 and G3 motifs forming the switch cores together with other substitutions in the structural elements interacting with the switches. Glycine-rich sequences of the switches would also contribute to the flexibility. Switch I lacks the conserved phenylalanine that makes non-polar interactions with the guanine base in H-Ras. Instead, water-mediated hydrogen bonding interactions were observed in Rad. The GDP molecule is located at the same position as in H-Ras and adopts a similar conformation as that bound in H-Ras. This similarity seems to be endowed by the conserved hydrogen bonding interactions with the guanine base-recognition loops and the magnesium ion that has a typical octahedral coordination shell identical to that in H-Ras. [source]

    Development and Testing of Energetic Materials: The Concept of High Densities Based on the Trinitroethyl Functionality

    Michael Gbel
    Abstract The development of new energetic materials is an emerging area of materials chemistry facilitated by a worldwide need to replace materials used at present, due to environmental considerations and safety requirements, while at the same time securing high performance. The development of such materials is complex, owing to the fact that several different and apparently mutually exclusive material properties have to be met in order for a new material to become widely accepted. In turn, understanding the basic principles of structure property relationships is highly desirable, as such an understanding would allow for a more rational design process to yield the desired properties. This article covers the trinitroethyl functionality and its potential for the design of next generation energetic materials, and describes relevant aspects of energetic materials chemistry including theoretical calculations capable of reliably predicting material properties. The synthesis, characterization, energetic properties, and structure property relationships of several new promising compounds displaying excellent material properties are reported with respect to different kinds of applications and compared to standard explosives currently used. Based on a review of trinitroethyl-containing compounds available in the literature, as well as this new contribution, it is observed that high density can generally be obtained in a more targeted manner in energetic materials taking advantage of noncovalent bonding interactions, a prerequisite for the design of next generation energetic materials. [source]

    Hydrogen bond of radicals: Interaction of HNO with HCO, HNO, and HOO

    Yong Yang
    Abstract Ab initio quantum mechanics methods are employed to investigate hydrogen bonding interactions between HNO and HCO, HOO radicals, and closed-shell HNO. The systems were calculated at MP2/6-311++G (2d, 2p) level and G2MP2 level. The topological and NBO analysis were investigated the origin of hydrogen bonds red- or blue-shifts. In addition, the comparisons were performed between HNO-opened-shell radical (HCO, HOO) complexes and HNO-corresponding closed-shell molecule (H2CO, HOOH) complexes. It is found that the stabilities of complexes increase from HNO-HCO to HNO-HOO. There are blue-shifts of NH, CH stretching vibrational frequencies and a red-shift of OH stretching vibrational frequency in the complexes. Rehybridization and electron density redistribution contribute to the blue-shifts of CH and NH stretching vibrational frequencies. Compared with the closed-shell H2CO, HCO is weaker proton donor and weaker proton acceptor. For the HOO, it is stronger proton donor and weaker proton acceptor than the HOOH is. 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source]

    Hydrogen bonding characterization of XH2NH2HNO(X = B, Al, Ga) complexes: A theoretical investigation

    Ying Liu
    Abstract The complexes of XH2NH2HNO(X = B, Al, Ga) are characterized as head to tail with hydrogen bonding interactions. The structural characteristics can be confirmed by atoms in molecules (AIM) analysis, which also provide comparisons of hydrogen bonds strengths. The calculated interaction energies at G2MP2 level show that stability of complexes decrease as BH2NH2HNO > AlH2NH2HNO > GaH2NH2HNO. On the basis of the vibrational frequencies calculations, there are red-shifts for ,(X1H) and blue-shifts for ,(NH) in the complexes on dihydrogen bonding formations (X1HHN). On hydrogen bonding formations (NHO), there are red-shifts for ,(NH) compared to the monomers. Natural bond orbital (NBO) analysis is used to discuss the reasons for the ,(X1H) and ,(NH) stretching vibrational shifts by hyperconjugation, electron density redistribution, and rehybridization. 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source]

    Understanding selenocysteine through conformational analysis, proton affinities, acidities and bond dissociation energies

    Damanjit Kaur
    Abstract Density functional methods have been employed to characterize the gas phase conformations of selenocysteine. The 33 stable conformers of selenocysteine have been located on the potential energy surface using density functional B3LYP/6-31+G* method. The conformers are analyzed in terms of intramolecular hydrogen bonding interactions. The proton affinity, gas phase acidities, and bond dissociation energies have also been evaluated for different reactive sites of selenocysteine for the five lowest energy conformers at B3LYP/6-311++G*//B3LYP/6-31+G* level. Evaluation of these intrinsic properties reflects the antioxidant activity of selenium in selenocysteine. 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source]

    Intra and intermolecular hydrogen bonding in formohydroxamic acid,

    Damanjit Kaur
    Abstract The presence of hydrogen bonding interactions in several tautomeric forms of formohydroxamic acid (FHA) and 1:1 association among the tautomeric forms and water-coordinated tautomeric forms of FHA is explored theoretically. Out of the seven equilibrium structures, four tautomeric forms have been selected for aggregation with single water molecule and dimer formation. Fifteen aggregates of FHA with H2O have been optimized at MP2/AUG-cc-PVDZ level and analyzed for intramolecular and intermolecular H-bond interactions. Twenty-seven dimers of the four tautomeric forms have been obtained at MP2/6-31+G* level. The stabilization energies associated with dimerization and adduct formation with water are the result of H-bond interactions and range from very weak to medium. The atomic charges and NBO analysis indicate that the electrostatic and the charge transfer are the important components favoring H-bond formation. 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source]

    Highly Ordered Interstitial Water Observed in Bone by Nuclear Magnetic Resonance,

    Erin E Wilson
    Abstract NMR was used to study the nanostructure of bone tissue. Distance measurements show that the first water layer at the surface of the mineral in cortical bone is structured. This water may serve to couple the mineral to the organic matrix and may play a role in deformation. Introduction: The unique mechanical characteristics of bone tissue have not yet been satisfactorily connected to the exact molecular architecture of this complex composite material. Recently developed solid-state nuclear magnetic resonance (NMR) techniques are applied here to the mineral component to provide new structural distance constraints at the subnanometer scale. Materials and Methods: NMR dipolar couplings between structural protons (OH, and H2O) and phosphorus (PO4) or carbon (CO3) were measured using the 2D Lee-Goldburg Cross-Polarization under Magic-Angle Spinning (2D LG-CPMAS) pulse sequence, which simultaneously suppresses the much stronger proton-proton dipolar interactions. The NMR dipolar couplings measured provide accurate distances between atoms, e.g., OH and PO4 in apatites. Excised and powdered femoral cortical bone was used for these experiments. Synthetic carbonate (,2-4 wt%)-substituted hydroxyapatite was also studied for structural comparison. Results: In synthetic apatite, the hydroxide ions are strongly hydrogen bonded to adjacent carbonate or phosphate ions, with hydrogen bond (O-H) distances of ,1.96 observed. The bone tissue sample, in contrast, shows little evidence of ordered hydroxide. Instead, a very ordered (structural) layer of water molecules is identified, which hydrates the small bioapatite crystallites through very close arrangements. Water protons are ,2.3-2.55 from surface phosphorus atoms. Conclusions: In synthetic carbonated apatite, strong hydrogen bonds were observed between the hydroxide ions and structural phosphate and carbonate units in the apatite crystal lattice. These hydrogen bonding interactions may contribute to the long-range stability of this mineral structure. The biological apatite in cortical bone tissue shows evidence of hydrogen bonding with an ordered surface water layer at the faces of the mineral particles. This structural water layer has been inferred, but direct spectroscopic evidence of this interstitial water is given here. An ordered structural water layer sandwiched between the mineral and the organic collagen fibers may affect the biomechanical properties of this complex composite material. [source]

    Interplay between anion-, and hydrogen bonding interactions

    Daniel Escudero
    Abstract The interplay between two important noncovalent interactions involving aromatic rings is studied by means of high level ab initio calculations. They demonstrate that synergistic effects are present in complexes where anion-, and hydrogen bonding interactions coexist. These synergistic effects have been studied using the "atoms-in-molecules" theory and the Molecular Interaction Potential with polarization partition scheme. The present study examines how these two interactions mutually influence each other. 2008 Wiley Periodicals, Inc. J Comput Chem, 2009 [source]

    How resonance assists hydrogen bonding interactions: An energy decomposition analysis

    John Frederick Beck
    Abstract Block-localized wave function (BLW) method, which is a variant of the ab initio valence bond (VB) theory, was employed to explore the nature of resonance-assisted hydrogen bonds (RAHBs) and to investigate the mechanism of synergistic interplay between , delocalization and hydrogen-bonding interactions. We examined the dimers of formic acid, formamide, 4-pyrimidinone, 2-pyridinone, 2-hydroxpyridine, and 2-hydroxycyclopenta-2,4-dien-1-one. In addition, we studied the interactions in ,-diketone enols with a simplified model, namely the hydrogen bonds of 3-hydroxypropenal with both ethenol and formaldehyde. The intermolecular interaction energies, either with or without the involvement of , resonance, were decomposed into the Hitler-London energy (,EHL), polarization energy (,Epol), charge transfer energy (,ECT), and electron correlation energy (,Ecor) terms. This allows for the examination of the character of hydrogen bonds and the impact of , conjugation on hydrogen bonding interactions. Although it has been proposed that resonance-assisted hydrogen bonds are accompanied with an increasing of covalency character, our analyses showed that the enhanced interactions mostly originate from the classical dipole,dipole (i.e., electrostatic) attraction, as resonance redistributes the electron density and increases the dipole moments in monomers. The covalency of hydrogen bonds, however, changes very little. This disputes the belief that RAHB is primarily covalent in nature. Accordingly, we recommend the term "resonance-assisted binding (RAB)" instead of "resonance-assisted hydrogen bonding (RHAB)" to highlight the electrostatic, which is a long-range effect, rather than the electron transfer nature of the enhanced stabilization in RAHBs. 2006 Wiley Periodicals, Inc. J Comput Chem 28: 455,466, 2007 [source]

    Effect of temperature and moisture on the miscibility of amorphous dispersions of felodipine and poly(vinyl pyrrolidone)

    Patrick J. Marsac
    Abstract The physical stability of amorphous molecular level solid dispersions will be influenced by the miscibility of the components. The goal of this work was to understand the effects of temperature and relative humidity on the miscibility of a model amorphous solid dispersion. Infrared spectroscopy was used to evaluate drug,polymer hydrogen bonding interactions in amorphous solid dispersions of felodipine and poly(vinyl pyrrolidone) (PVP). Samples were analyzed under stressed conditions: high temperature and high relative humidity. The glass transition temperature (Tg) of select systems was studied using differential scanning calorimetry (DSC). Atomic force microscopy (AFM) and transmission electron microscopy (TEM) were used to further investigate moisture-induced changes in solid dispersions. Felodipine-PVP solid dispersions showed evidence of adhesive hydrogen bonding interactions at all compositions studied. The drug,polymer intermolecular interactions were weakened and/or less numerous on increasing the temperature, but persisted up to the melting temperature of the drug. Changes in the hydrogen bonding interactions were found to be reversible with changes in temperature. In contrast, the introduction of water into amorphous molecular level solid dispersions at room temperature irreversibly disrupted interactions between the drug and the polymer resulting in amorphous-amorphous phase separation followed by crystallization. DSC, AFM, and TEM results provided further evidence for the occurrence of moisture induced immiscibility. In conclusion, it appears that felodipine-PVP solid dispersions are susceptible to moisture-induced immiscibility when stored at a relative humidity ,75%. In contrast, the solid dispersions remained miscible on heating. 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:169,185, 2010 [source]

    Thermally stable porous supramolecular frameworks based on the metal and ,,, stacking directed self-assembly of 2,6-pyridyldicarboxylic acid bis-4-pyridylamide

    Juan C. Noveron
    Abstract We report the formation of two thermally stable supramolecular structures based on 2,6-pyridyldicarboxylic acid bis-4-pyridylamide (PyI) and bis(hexafluoroacetylacetonato)manganese(II) that exhibits a microporous structure with cavities bearing hydrogen bonding motifs that can enclathrate acetone and methanol molecules via well-positioned hydrogen bonding interactions. Single-crystal x-ray diffraction in combination with thermogravimetric analysis and X-ray powder diffraction (XRPD) studies were utilized to study the structure and thermal behavior of trans -[Mn(hfacac)2(PyI)2]2(CH3)2CO (1) and trans -[Mn(hfacac)2(PyI)2]2CH3OH (2). Our studies indicated that 1 and 2 are isostructural with respect to their supramolecular assembly and trap solvent molecules along the crystallographic b direction via the inwardly directed hydrogen bonding motifs of the PyI component. These solvent molecules can be thermally removed to generate a crystalline material with micropores bearing hydrogen bonding rich sites within an overall supramolecular matrix similar to 1 and 2. The removal of the guest solvent molecules is reversible and can be followed with XRPD. Copyright 2003 John Wiley & Sons, Ltd. [source]

    Nonclassical forces: Seemingly insignificant but a powerful tool to control macromolecular structures

    Michiya Fujiki
    Abstract Strong chemical forces such as covalent and ionic bonds are responsible for building discrete molecules, nature dwells on noncovalent forces weaker by three orders in magnitude, like the hydrophobic effect, hydrogen bonding, and van der Waals forces. Despite being weak, they possess the potential to drive spontaneous folding or unfolding of proteins and nucleic acids and the recognition between complimentary molecular surfaces. The power of these forces lies in the cooperativity with which they act, thereby generating a cumulative effect of many bonding interactions occurring together. Many ongoing research aims to translate the potential of these forces to the synthetic world to create desired structures with specific chemical functions. Achieving this offers unlimited opportunities for designing and synthesizing the most complex structures with specific applications. This highlight aims to reflect the critical role these noncovalent forces play in controlling macromolecular structures, which hold immense untapped potential for applications defying conventions, and briefly touches on the concept of homochirality in nature based on chiral and weak noncovalent interactions in synthetic nonpolar Si-catenated polymers. It sheds some light on the discovery and characterization of Si/F-C interactions in fluoroalkylated polysilanes in chemosensing of fluoride ions and nitroaromatics with a great sensitivity and selectivity. 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4637,4650, 2008 [source]

    Vibrational spectra of bis(L -ornithinium) chloride nitrate sulfate

    S. Ramaswamy
    Abstract The Raman and infrared absorption spectra of 2(C5H14N2O22+)Cl,NO3,SO42, crystal containing three anions were recorded at room temperature and were interpreted in the light of crystal structure data. The presence of a carbonyl group was identified. The carboxylic group was found to exist as COOH. The formation of OHO, NHO and NHCl asymmetric hydrogen bonds contributes considerably to the crystal cohesion and is responsible for the changes in the position and intensity of several bands. The vibrational spectra show that the anions were found to coordinate through hydrogen bonding interactions to other ligands in the crystal. The lattice wavenumbers of the halide radical (chlorine anion) were also assigned in terms of hydrogen bond vibrations. Copyright 2004 John Wiley & Sons, Ltd. [source]

    Raman and IR spectral studies of D -phenylglycinium perchlorate

    S. Ramaswamy
    The Raman and infrared spectra of D -phenylglycinium perchlorate were recorded at room temperature. Tentative vibrational assignments of the observed wavenumbers were made by comparison with the vibrational wavenumbers of glycine, phenylalanine and other similar compounds. Anions were found to coordinate through hydrogen bonding interactions to other ligands in the crystal, affecting the Td symmetry and thereby causing the degeneracies of several modes to be removed. The extensive intermolecular hydrogen bonding in the crystal leads to a shift of bands due to the stretching and bending modes of various functional groups. The broadening and appearance of multiple bands for the carbonyl stretching mode due to the resonance interaction is also discussed. Copyright 2002 John Wiley & Sons, Ltd. [source]