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Hydrogen bond
About: Hydrogen bond is a research topic. Over the lifetime, 57701 publications have been published within this topic receiving 1306326 citations.
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TL;DR: Spectroscopic properties of chymotrypsin and model compounds indicate that a low-barrier hydrogen bond participates in the mechanism of serine protease action, supported by the chemical shift of this proton, the deuterium isotope effect on thechemical shift, and the properties of hydrogen-bonded model compounds in organic solvents.
Abstract: Spectroscopic properties of chymotrypsin and model compounds indicate that a low-barrier hydrogen bond participates in the mechanism of serine protease action. A low-barrier hydrogen bond between N delta 1 of His57 and the beta-carboxyl group of Asp102 in chymotrypsin can facilitate the formation of the tetrahedral adduct, and the nuclear magnetic resonance properties of this proton indicate that it is a low-barrier hydrogen bond. These conclusions are supported by the chemical shift of this proton, the deuterium isotope effect on the chemical shift, and the properties of hydrogen-bonded model compounds in organic solvents, including the hydrogen bond in cis-urocanic acid, in which the imidazole ring is internally hydrogen-bonded to the carboxyl group.
663 citations
TL;DR: The relative influence of thermal and quantum fluctuations on the proton transfer properties of the charged water complexes H5O2+ and H3O2− was investigated with the use of ab initio techniques and found that quantum zero-point motion played a crucial role even at room temperature.
Abstract: The relative influence of thermal and quantum fluctuations on the proton transfer properties of the charged water complexes H5O2+ and H3O2− was investigated with the use of ab initio techniques. These small systems can be considered as prototypical representatives of strong and intermediate-strength hydrogen bonds. The shared proton in the strongly hydrogen bonded H5O2+ behaved in an essentially classical manner, whereas in the H3O2− low-barrier hydrogen bond, quantum zero-point motion played a crucial role even at room temperature. This behavior can be traced back to a small difference in the oxygen-oxygen separation and hence to the strength of the hydrogen bond.
663 citations
TL;DR: It is of interest that the aromatic hydrogen bond arises from small partial charges centred on the ring carbon and hydrogen atoms: there is no need to consider delocalized electrons.
651 citations
TL;DR: Fully rotationally resolved spectra of three isotopic species of 1:1 clusters of benzene with water were fit to yield moments of inertia that demonstrate unambiguously that water is positioned above the benzene plane in nearly free internal rotation with both hydrogen atoms pointing toward the π cloud.
Abstract: Fully rotationally resolved spectra of three isotopic species of 1:1 clusters of benzene with water (H_2O, D_2O, and HDO) were fit to yield moments of inertia that demonstrate unambiguously that water is positioned above the benzene plane in nearly free internal rotation with both hydrogen atoms pointing toward the π cloud. Ab initio calculations (MP2 level of electron correlation and 6-31 G** basis set with basis set superposition error corrections) predict a binding energy D_e ≳ 1.78 kilocalories per mole. In both the experimental and theoretical structures, water is situated nearly 1 angstrom within the van der Waals contacts of the monomers, a clear manifestation of hydrogen bond formation in this simple model of aqueous-π electron interactions.
651 citations
TL;DR: H-H bonding is shown to be distinct from "dihydrogen bonding", a form of hydrogen bonding with a hydridic hydrogen in the role of the base atom.
Abstract: Bond paths linking two bonded hydrogen atoms that bear identical or similar charges are found between the ortho-hydrogen atoms in planar biphenyl, between the hydrogen atoms bonded to the C1–C4 carbon atoms in phenanthrene and other angular polybenzenoids, and between the methyl hydrogen atoms in the cyclobutadiene, tetrahedrane and indacene molecules corseted with tertiary-tetra-butyl groups. It is shown that each such H–H interaction, rather than denoting the presence of “nonbonded steric repulsions”, makes a stabilizing contribution of up to 10 kcal mol−1 to the energy of the molecule in which it occurs. The quantum theory of atoms in molecules—the physics of an open system—demonstrates that while the approach of two bonded hydrogen atoms to a separation less than the sum of their van der Waals radii does result in an increase in the repulsive contributions to their energies, these changes are dominated by an increase in the magnitude of the attractive interaction of the protons with the electron density distribution, and the net result is a stabilizing change in the energy. The surface virial that determines the contribution to the total energy decrease resulting from the formation of the H–H interatomic surface is shown to account for the resulting stability. It is pointed out that H–H interactions must be ubiquitous, their stabilization energies contributing to the sublimation energies of hydrocarbon molecular crystals, as well as solid hydrogen. H–H bonding is shown to be distinct from “dihydrogen bonding”, a form of hydrogen bonding with a hydridic hydrogen in the role of the base atom.
646 citations