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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: In this article, the authors used CT-HNCO to detect small through-H-bond J connectivity (JNC′) in polypeptides and determined the magnitude of these small JNC′ in terms of cross-peak intensity.
Abstract: In macromolecules, the presence of H bonds is indicated by the spatial proximity and relative arrangement of the atoms involved, after the structure has been solved by either crystallography or NMR. A variety of NMR spectroscopic parameters has also been used for characterizing these pivotal interactions. These include the effect of such bonds on isotropic chemical shifts 2 and chemical shift anisotropy, 3 on the quadrupole coupling of 2H involved in a H bond, 4 on protection of exchange of the labile hydrogen with solvent, 5 and1H/2H fractionation. 6 In a recent remarkable report, Dingley and Grzesiek 7 were the first to demonstrate the presence of surprisingly largeJ couplings (6-7 Hz) between the H bond donating and accepting 15N nuclei in a Watson -Crick base pair in double-stranded RNA. This finding was confirmed by Pervushin et al., 8 and these authors additionally discovered the presence of a smaller (2 -4 Hz) J couplings between the imino hydrogen itself and the H bond accepting 15N nucleus. These couplings confirm the interaction between the electronic orbitals of the atoms involved, and most importantly they identify unambiguously the pairs of atoms involved in a given H bond. Although in organic chemistry the possibility of J couplings between atoms separated by less than the sum of the van der Waals radii has long been known, in particular for cases involving 19F,9 Summers et al. were the first to detect such couplings in a protein.10 They observed these interactions, ranging from 0.3 to 4 Hz, between the metal (Cd and Hg) in rubredoxin and backbone amide protons H-bonded to the S atoms ligating the metal. Remarkably, they also found J coupling between an alanyl methyl group, adjacent to such an S atom, and the metals. Here, we demonstrate for the protein ubiquitin that small J couplings can be observed across H bonds between the donating 15N atom and the accepting carbonyl/carboxyl 13C. The scheme used for detecting this through-H-bond J connectivity (JNC′) is essentially the regular CT-HNCO experiment, 11 optimized for the detection of these small 15N-13C′ couplings (Figure 1). The magnitude ofJNC′ is then determined through the principle of quantitative analysis of cross-peak intensity. 12 In brief, the scheme of Figure 1 is executed three times: (A) with the dephasing time, 2T, tuned to 1/(2JNC′), (B) with 2T ) 3/(2JNC′), (C) with 2T ) 4/(2JNC′). Values ofJNC′ in polypeptides are quite homogeneous (15 ( 1 Hz),13 and much larger than the JNC′ which are the focus of this study. The signal intensity observed for a correlation between N and C ′ with couplingJNC′ is proportionate to exp( 4T/T2) sin(2πJNC′T) Πk cos(2πJNkT), where the product extends over all other carbonyl/carboxyl carbons coupled to the 15N of interest with coupling constants JNk, andT2 is the15N transverse relaxation time. The dephasing times, 2 T, used in this study have a maximum duration of 133.2 ms, and cos (2πJNkT) ≈ 1 for JNk e 1 Hz. Hence, a good approximation for T2 is obtained from the ratio between experiments A and B. To a good approximation, therefore, the magnitude of the small J coupling between N and k can be derived from

216 citations

Journal ArticleDOI
TL;DR: Crystal structures of two polymorphs of chitosan, tendon (hydrated) and annealed (anhydrous) polymorphs, have been reported, and chitOSan molecule takes up similar conformation to each other, an extended two-fold helix stabilized by intramolecular O3-O5 hydrogen bond, which is also similar to the conformation of ch itin or cellulose.

216 citations

Journal ArticleDOI
TL;DR: In this article, a model system for a proton-conducting polymer functioning without a liquid phase, but instead using imidazole tethered to the backbone via flexible spacers as proton solvent, is presented and the parameters governing conductivity and its mechanism are discussed.
Abstract: Extensive studies on a model system (imidazole-terminated ethylene oxide oligomers doped with small amounts of strong acids) for a proton-conducting polymer functioning without a liquid phase, but instead using imidazole tethered to the backbone via flexible spacers as a proton solvent, are presented and the parameters governing conductivity and its mechanism are discussed. Temperature-dependent conductivities are well described by free-volume considerations (VTF-behavior). Thus, besides a high density of imidazole moieties, a low Tg is in favor of high proton conductivity, which experimentally is shown to be predominantly due to structure diffusion. The available free volume is suggested to correlate with the rate of hydrogen bond breaking and forming processes within the dynamical hydrogen bond networks, which generally limit the rate of long-range diffusion of protonic defects via structure diffusion. The equilibrium constants for the protonation of imidazole by two different dopants in an oligo(ethyle...

216 citations

Journal ArticleDOI
TL;DR: The results of thermodynamic parameters ΔG, ΔH, and ΔS at different temperatures indicated that the hydrogen bonds and van der Waals interactions played major roles in the reaction, and the effect of ionic strength indicated that electrostatic attraction between the BH and DNA was also a component of the interaction.

216 citations

Journal ArticleDOI
TL;DR: In this paper, the authors compare the hydrogen bonding ability of acetylene and ethylene, and various derivatives, with the analogous properties of alkanes, and find that sp-hybridized acetylene forms the strongest bond, followed by sp2 and then sp3.
Abstract: Ab initio calculations are used to compare the hydrogen bonding ability of acetylene and ethylene, and various derivatives, with the analogous properties of alkanes. Water is used as the universal proton acceptor and paired with HCCH, FCCH, ClCCH, and NCH as well as with ethylene, and its mono-, di-, and trifluorosubstituted derivatives. With regard to the hydrocarbons, sp-hybridized acetylene forms the strongest bond, followed by sp2 and then sp3. Halogenation of the proton donor strengthens each type of hydrogen bond, particularly when the substitution takes place on the C involved in the hydrogen bond. sp3-hybridized systems are most sensitive to this substitution-induced bond strengthening, followed in order by sp2 and sp. For each hybridization type, the length of the hydrogen bond shortens in proportion to the strengthening, with alkanes exhibiting the greatest sensitivity and alkynes the least. Whereas formation of the hydrogen bond causes the sp3 CH bond to contract and undergo a blue shift, the o...

216 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