Hydrogen bond

About: Hydrogen bond is a research topic. Over the lifetime, 57701 publications have been published within this topic receiving 1306326 citations.

Hydrogen Bonding of Water to Phosphatidylcholine in the Membrane As Studied by a Molecular Dynamics Simulation: Location, Geometry, and Lipid-Lipid Bridging via Hydrogen-Bonded Water

Abstract: Hydrogen (H-) bonding between water and phosphatidylcholine was studied using a molecular dynamics simulation of a hydrated phosphatidylcholine bilayer membrane in the liquid crystalline phase. A membrane in the liquid-crystalline phase composed of 72 L-R-dimyristoylphosphatidylcholine (DMPC) and 1622 water molecules was generated, starting from the crystal structure of DMPC. At the beginning of the equilibration process, the temperature of the system was raised to 550 K for 20 ps, which was effective in breaking the initial crystalline structure. The thermodynamic and structural parameters became stable after the equilibration period of 1100 ps, and the trajectory of the system obtained during the following 500 ps agreed well with most of the published experimental data. Each DMPC molecule forms 5.3 H-bonds with water, while only 4.5 water molecules are H-bonded to DMPC. The primary targets of water for the formation of H-bonds are the non-ester phosphate oxygens (4.0 H-bonds) and the carbonyl oxygens (1.0 H-bonds). Of DMPC’s H-bonds, 1.7 are formed with water molecules that are simultaneously H-bonded to two different DMPC oxygens (bridging water). In effect, approximately 70% of the DMPC molecules are linked by water molecules and form clusters of two to seven DMPC molecules. Approximately 70% of the intermolecular water bridges are formed between non-ester phosphate oxygens. The rest are formed between non-ester phosphate and carbonyl oxygens. About half of the intermolecular water bridges are involved in formation of multiple bridges, where two DMPC molecules are linked by more than one parallel bridge. These results suggest a possibility that water bridges are involved in reducing head group mobility and in stabilizing the membrane structure. Non-ester phosphate oxygen of DMPC makes one, two, or three H-bonds with water, but two H-bonds are formed most often (60%). In the case where two H-bonds are formed on non-ester phosphate or carbonyl oxygens, the average geometry of H-bonding is planar trigonal (in the case of water oxygen with two H-bonds, geometry is steric tetragonal). When oxygen atoms form three H-bonds, the geometry of H-bonding is steric tetragonal both for non-ester phosphate and water oxygens. On average, H-bonds make nearly right angles with each other when two or three water molecules are bound to the same DMPC oxygen, but the distribution of the angle is broad.

Different surface chemistries of water on Ru[0001]: from monomer adsorption to partially dissociated bilayers.

Abstract: Density functional theory has been used to perform a comparative theoretical study of the adsorption and dissociation of H2O monomers and icelike bilayers on Ru{0001}. H2O monomers bind preferentially at atop sites with an adsorption energy of ∼0.4 eV/H2O. The main bonding interaction is through the H2O 1b1 molecular orbital which mixes with Ru dz2 states. The lower-lying set of H2O molecules in an intact H2O bilayer bond in a similar fashion; the high-lying H2O molecules, however, do not bond directly with the surface, rather they are held in place through H bonding. The H2O adsorption energy in intact bilayers is ∼0.6 eV/H2O and we estimate that H bonding accounts for ∼70% of this. In agreement with Feibelman (Science 2002, 295, 99) we find that a partially dissociated OH + H2O overlayer is energetically favored over pure intact H2O bilayers on the surface. The barrier for the dissociation of a chemisorbed H2O monomer is 0.8 eV, whereas the barrier to dissociate a H2O incorporated in a bilayer is just 0...

Quantum hydrogen-bond symmetrization in the superconducting hydrogen sulfide system

Abstract: The quantum nature of the proton can crucially affect the structural and physical properties of hydrogen compounds. For example, in the high-pressure phases of H2O, quantum proton fluctuations lead to symmetrization of the hydrogen bond and reduce the boundary between asymmetric and symmetric structures in the phase diagram by 30 gigapascals (ref. 3). Here we show that an analogous quantum symmetrization occurs in the recently discovered sulfur hydride superconductor with a superconducting transition temperature Tc of 203 kelvin at 155 gigapascals--the highest Tc reported for any superconductor so far. Superconductivity occurs via the formation of a compound with chemical formula H3S (sulfur trihydride) with sulfur atoms arranged on a body-centred cubic lattice. If the hydrogen atoms are treated as classical particles, then for pressures greater than about 175 gigapascals they are predicted to sit exactly halfway between two sulfur atoms in a structure with Im3m symmetry. At lower pressures, the hydrogen atoms move to an off-centre position, forming a short H-S covalent bond and a longer H···S hydrogen bond in a structure with R3m symmetry. X-ray diffraction experiments confirm the H3S stoichiometry and the sulfur lattice sites, but were unable to discriminate between the two phases. Ab initio density-functional-theory calculations show that quantum nuclear motion lowers the symmetrization pressure by 72 gigapascals for H3S and by 60 gigapascals for D3S. Consequently, we predict that the Im3m phase dominates the pressure range within which the high Tc was measured. The observed pressure dependence of Tc is accurately reproduced in our calculations for the phase, but not for the R3m phase. Therefore, the quantum nature of the proton fundamentally changes the superconducting phase diagram of H3S.

Hydrogen-bonded Liquid crystalline materials : Supramolecular polymeric assembly and the induction of dynamic function

Abstract: Liquid crystals are molecular materials that combine anisotropy with dynamic nature. Recently, the use of hydrogen bonding for the design of functional liquid crystalline materials has been shown to be a versatile approach toward the control of simple molecularly assembled structures and the induction of dynamic function. A variety of hydrogen-bonded liquid crystals has been prepared by molecular self-assembly processes via hydrogen bond formation. Rod-like and disk-like low-molecular weight complexes and polymers with side-chain, main-chain, network, and guest-host structures have been built by the complexation of complimentary and identical hydrogen-bonded molecules. These materials consist of closed-type hydrogen bondings. Another type of hydrogen-bonded liquid crystals consists of open-type hydrogen bonding. In this case, the introduction of hydrogen bonding moieties, such as hydroxyl groups, induces microphase segregation leading to liquid crystalline molecular order. Moreover, liquid crystalline physical gels have been prepared by the molecular aggregation of hydrogen-bonded molecules in non-hydrogen-bonded liquid crystals. They show significant electrooptical properties. An anisotropic gel is a new type of anisotropic materials forming heterogeneous structures.

Sio-...hosi hydrogen bonds in as-synthesized high-silica zeolites

Abstract: The positive charge of quaternary ammonium cations used in structure-directing agents in high-silica zeolites is balanced by a nonprotonated defect site (siloxy group). This siloxy group functions as hydrogen bond acceptor in SiO{sup -}...HOSi hydrogen bonds. This paper presents the {sup 1}H MAS NMR spectra of a variety of as-synthesized, high-silica zeolites prepared with different quaternary ammonium cations as structure-directing agents. The NMR results obtained are used to construct a model for the structure of the defect sites in as-synthesized, high-silica zeolites. 37 refs., 10 figs., 2 tabs.