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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: The protein dynamical transition and its connection with the liquid-glass transition (GT) of hydration water and aqueous solvents are reviewed in this paper, where the protein solvation shell exhibits a regular glass transition, characterized by steps in the specific heat and the thermal expansion coefficient at the calorimetric glass temperature T(G) approximately 170 K.

174 citations

Journal ArticleDOI
TL;DR: The crystal structure of the ternary complex formed between carbon monoxide, camphor, and ferrous cytochrome P-450CAM has been refined to an R value of 17.9% at 1.9-A resolution, and CO appears to be bent from the heme normal, as it is in various CO-globin complexes, due to steric interactions with active site groups.
Abstract: The crystal structure of the ternary complex formed between carbon monoxide (CO), camphor, and ferrous cytochrome P-450CAM has been refined to an R value of 17.9% at 1.9-A resolution. To accommodate the CO molecule, the substrate, camphor, moves about 0.8 A while at the same time remaining in nonbonded contact with CO. The average temperature factor of the camphor atoms is about 50% higher in the CO complex, suggesting that the camphor is more loosely bound in this ternary complex. The Fe-C-O angle is about 166 degrees, and thus, CO appears to be bent from the heme normal, as it is in various CO-globin complexes, due to steric interactions with active site groups. The oxygen atom of the CO molecule is nestled into a groove formed by an unusual helical hydrogen bond in the distal helix between the highly conserved Thr 252 and Gly 248 residues. In the transition from the ferric camphor-bound binary complex to the ferrous CO-camphor-bound ternary complex, the heme iron atom moves into the plane defined by the pyrrole nitrogens by about 0.41 A. Although the axial Cys ligand also moves toward the heme, the S-Fe bond stretches from about 2.20 A in the absence of CO to about 2.41 A once CO has bound.

173 citations

Journal ArticleDOI
TL;DR: In this paper, the binding energies of van der Waals (vdW) molecules are derived from a superposition of pairwise atom-atom potentials, the R-carbon atom pair potentials being taken from the heats of adsorption of rare-gas atoms on graphite, while the Rhydrogen atom pair pair potential is estimated by using empirical combination rules.
Abstract: In this paper we report the results of model calculations of the nuclear potential surfaces of van der Waals complexes consisting of large aromatic molecules and rare-gas (R) atoms. These potentials were constructed as a superposition of pairwise atom-atom potentials, the R-carbon atom pair potentials being taken from heats of adsorption of rare-gas atoms on graphite, while the R-hydrogen atom pair potentials are estimated by using empirical combination rules. The binding energies of the tetracene (T) complexes TRI are 0.7 kcal mol-' for Ne, 1.5 kcal mol-' for Ar, 1.8 kcal mol-' for Kr, and 2.2 kcal mol-' for Xe, while the equilibrium distance between R and the molecular plane of tetracene is 3.0 A for Ne, 3.45 A for Ar, 3.5 A for Kr, and 3.7 A for Xe. Low-frequency, large-amplitude motion of the R atoms parallel to the molecular plane along the long molecular axis is predicted for TR, and TR2 complexes. The potential for TRI along the long molecular axis has a symmetric double-well form, giving rise to a "tunneling-type'' motion of the R atom. For the TR2 complexes, the configuration with two R atoms located on the same side of the aromatic molecule is energetically favored over that with the two R atoms on opposite sides. No chemical isomers are expected to exist for the TRI and TR2 complexes, while for TR,, complexes with n 1 3 the possibility of the existence of two or more nearly isoenergetic isomers is indicated. The applications and implications of these data for the elucidation of some features of excited-state energetics and dynamics of such van der Waals complexes are considered. van der Waals (vdW) molecules'" are weakly bound molecular complexes held together by attractive (eg, dispersive, electrostatic, charge transfer, hydrogen bonding) interactions between closed- shell atoms or molecules. The primary characteristics of vdW molecules'd are their low (10-1000 cm-I) dissociation energies, the large length of the vdW bond, and the retention of many of the individual properties of the molecular constituents within the vdW complex. During the last few years remarkable progress was achieved in the understanding of the many facets of these interesting systems. These advances were initiated by the utili- zation of supersonic free expansion^^.^ to prepare a variety of fascinating vdW molecules, whose structure, energetics, and dy- namics were explored. The elucidation of the structure, the mapping of the potential surface, and the determination of the energetics of vdW molecules pertain to the basic understanding of intermolecular interactions in chemistry. In this context the ground-state properties of a variety of molecules, e.g., (HF)2,7 ArHF: ArHC1,9 ArHBr,l0 KrHCI," XeHC1,I2 ArCIF," ArOC- S," and the benzene dimer3 were investigated. Studies of in- tramolecular dynamics of vdW molecules in vibrationally excited or electronically vibrationally excited states provided central in- formation on reactive vibrational predissocation processes,57 this being relevant for establishing the general features of intramo- lecular vibrational energy flow in weakly coupled molecular systems. Intramolecular dynamical processes in a variety of vdW molecules, e.g., RIz (R = He, Ne, and Ar),'>'' (C12)2,18 (N2O)2,I9 (NH3)r20 and the ethylene dimer2' were recently explored both experimentally'52' and theoretically.6 The understanding of the reactive and nonreactive dynamics in vdW complexes requires detailed information on potential surfaces. The general conceptual framework advanced for the elucidation of the structural and energetic features of all these small and medium-sized vdW complexes mentioned above rests on a microscopic approach, taking advantage of the advanced techniques of molecular spec- tro~copy~~~~-" to probe the molecular equilibrium configuration, the details of nuclear motion, and the binding energies. This general approach may require some gross modifications when the structure, energies, and dynamics of very large vdW complexes will be considered. Recently, there have been experimental st~dies~~-~~ of very large vdW complexes consisting of aromatic molecules, such as anthracene, tetracene, pentacene, and ovalene

173 citations

Journal ArticleDOI
TL;DR: In this article, crystal structures and circular dichroism (CD) spectra of two oligomers of optically active trans-2-aminocyclohexanecarboxylic acid are reported.
Abstract: The preparation, crystal structures, and circular dichroism (CD) spectra of two oligomers of optically active trans-2-aminocyclohexanecarboxylic acid are reported. In the solid state, both the tetramer and the hexamer of this β-amino acid display a helical conformation that involves 14-membered-ring hydrogen bonds between a carbonyl oxygen and the amide proton of the second residue toward the N-terminus. (For comparison, the familiar α-helix observed in conventional peptides is associated with a 13-membered-ring hydrogen bond between a carbonyl oxygen and the amide proton of the fourth residue toward the C-terminus.) These crystallographic data, along with CD data obtained in methanol, suggest that the 14-helix constitutes a stable secondary structure for β-amino acid oligomers (“β-peptides”). In addition, the crystal packing pattern observed for the hexamer offers a blueprint for the design of β-peptides that might adopt a helical bundle tertiary structure.

173 citations

Journal ArticleDOI
TL;DR: In this article, the Bader theory was also applied to characterise different hydrogen bonds, typical as O-H⋯O and O-N, weak like C-Hππ, dihydrogen bonds, etc.

173 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20232,352
20224,647
20211,701
20201,599
20191,598
20181,668