1GS3: Contribution of a Low-Barrier Hydrogen Bond to Catalysis by Delta-5-3-Ketosteroid Isomerase is not Extremely High Compared to that of an Ordinary Hydrogen Bond. Low-Barrier Hydrogen Bond of Pi Ksi
TY - JOUR. T1 - Short, strong hydrogen bonds on enzymes. T2 - NMR and mechanistic studies. AU - Mildvan, A. S.. AU - Massiah, M. A.. AU - Harris, T. K.. AU - Marks, G. T.. AU - Harrison, D. H.T.. AU - Viragh, C.. AU - Reddy, P. M.. AU - Kovach, I. M.. PY - 2002/9/26. Y1 - 2002/9/26. N2 - The lengths of short, strong hydrogen bonds (SSHBs) on enzymes have been determined with high precision (±0.05 Å) from the chemical shifts (δ), and independently from the D/H fractionation factors (φ) of the highly deshielded protons involved. These H-bond lengths agree well with each other and with those found by protein X-ray crystallography, within the larger errors of the latter method (±0.2 to ± 0.8 Å) [Proteins 35 (1999) 275]. A model dihydroxynaphthalene compound shows a SSHB of 2.54 ± 0.04 Å based on δ = 17.7 ppm and φ = 0.56 ± 0.04, in agreement with the high resolution X-ray distance of 2.55 ± 0.06 Å. On ketosteroid isomerase, a SSHB is found (2.50 ± 0.02 Å), based on δ = 18.2 ppm and ...
Attempts have been made earlier to determine structures of HIV-1 and simian immunodeficiency virus (SIV) PRs complexed with substrate oligopeptides (10, 12). In these attempts, the crystals of the complex were prepared by using the method of cocrystallization, in the hope that crystal formation preceded product release. However, in the crystals obtained, HIV-1 PR was found to be complexed with only the N-terminal (P) product peptide, whereas SIV PR was found to be complexed with a C-terminal (Q) product peptide. No structures with both products bound simultaneously were obtained (12). Through careful superpositions of the two product complexes, these authors have concluded that unacceptably close separations between scissile carbon and nitrogen atoms (1.3-2.2 Å) preclude the presence of both products in the active site during cocrystallization. In contrast, we have attempted to prepare the complex by the soaking method. Because, as has been shown here, soaking does not result in cleavage of the ...
Introduction] Cooperative binding by proteins to DNA results in higher sequence specificity as well as greater sensitivity to concentration changes. We recently reported cooperative binding of two oligonucleotides at abutting sites by triple helix formation on double helical DNA. However, the enhanced binding observed was modest (a factor of 3.5) and likely due to favorable basestacking interactions between adjacent oligonucleotides and/or induced conformational changes propagated to adjacent binding sites. Thus, the issue arises whether cooperativity in oligonucleotide-directed triple helix formation can be enhanced by the addition of discrete dimerization domains. We report here the binding properties of oligonucleotides that dimerize by Watson-Crick hydrogen bonds and bind neighboring sites on double helical DNA by triple helix formation. ...
hort hydrogen bonds are present in many chemical and biological sys-tems. It is well known that these short hydrogen bonds are found in the active site of enzymes and aid enzyme catalysis. This study aims to system-atically characterize all short hydrogen bonds from a nonredundant dataset of protein structures. The study has revealed that short hydrogen bonds are commonly found in proteins and are widely present in different regions of the protein chain, such as the backbone or side chain, and in different secondary structural regions such as helices, strands and turns. ... ...
It is now well admitted that hydrophobic interactions and hydrogen bonds are the main forces driving protein folding and stability. However, because of the complex structure of a protein, it is still difficult to separate the different energetic contributions and have a reliable estimate of the hydrogen bond part. This energy can be quantified on simpler systems such as surfaces bearing hydrogen-bonding groups. Using the surface force apparatus, we have directly measured the interaction energy between monolayers of lipids whose headgroups can establish hydrogen bonds in water: nitrilotriac-etate, adenosine, thymidine, and methylated thymidine lipids. From the adhesion energy between the surfaces, we have deduced the energy of a single hydrogen bond in water. We found in each case an energy of 0.5 kcal/mol. This result is in good agreement with recent experimental and theoretical studies made on protein systems showing that intramolecular hydrogen bonds make a positive contribution to protein
Those of us who are evaluating hydrogen futures need to become aware of the significant progress in new hydrogen energy research, which could revolutionize our energy picture in short order, once the necessary science and engineering are done. A sophisticated scenario for a hydrogen economy would include at least two eventualities: one is a baseline scenario which includes the tried-and-true hydrogen chemistry of internal combustion and fuel cells, as discussed in this Congress. The second brings into consideration new hydrogen energy and other new energy technologies, which could take the world by storm within a decade or two. As we conceptualize and begin to build solar-hydrogen systems, we would also want to increase our support of new hydrogen energy research which could lead to commercially viable units within years. Why should we do this? We need to keep our options open until such time we can make a more rational decisions about our energy future. On the one hand, we want to move into ...
A hydrogen atom attached to a relatively electronegative atom is a hydrogen bond donor. This electronegative atom is usually fluorine, oxygen, or nitrogen. An electronegative atom such as fluorine, oxygen, or nitrogen is a hydrogen bond acceptor, regardless of whether it is bonded to a hydrogen atom or not. An example of a hydrogen bond donor is ethanol, which has a hydrogen bonded to oxygen; an example of a hydrogen bond acceptor which does not have a hydrogen atom bonded to it is the oxygen atom on diethyl ether. Carbon can also participate in hydrogen bonding, especially when the carbon atom is bound to several electronegative atoms, as is the case in chloroform, CHCl3. The electronegative atom attracts the electron cloud from around the hydrogen nucleus and, by decentralizing the cloud, leaves the atom with a positive partial charge. Because of the small size of hydrogen relative to other atoms and molecules, the resulting charge, though only partial, nevertheless represents a large charge ...
Get this from a library! Planar-Chiral Hydrogen-Bond Donor Catalysts : Synthesis, Application and Structural Analysis.. [Jakob Schneider]
Crystal structure of the title compound is orthorhombic, Pbca, a=7.8689(2)Å, b=9.6519(3)Å, c=31.3579(9)Å. The structure was solved by direct methods and refined by a full-matrix least squares procedure to final R (all)=0.0682 for 2853 unique diffractions merged from 24459 measured at 183(2)K. The molecule is formed by two planar moieties joined through an atom of sulphur. The short intramolecular O...O contact is 2.430(2)Å, the intramolecular hydrogen bond is slightly asymmetric. Theoretical ab initio calculations done at B3LYP/SVP and ONIOM(MP2/SVP:B3LYP/SVP) levels showed that the experimental geometry of pentanedione pseudoring is close to the geometry corresponding to a transition state on the asymmetric potential energy curve. Calculated energy difference between two minima is only 4.72 kJ/mol and the energy barrier 6.02 kJ/mol, which agrees well to ~6.6kJ/mol found in microwave spectroscopic study of malonaldehyde.
Green fluorescent protein (GFP) is a luminescent protein with a central chromophore and is used in biological imaging. By modifying the chromophore itself or the protein environment, the photophysical properties can be fine-tuned, yet until recently this has not been well understood. However, Lars Andersen (Aarhus University) and his group have developed a laser-action spectroscopy technique to enable the chromophore to be studied in a vacuum. This has revealed that a single hydrogen bond initiated a 0.5eV shift in the absorption spectrum of the GFP chromophore and highlights the importance of understanding the biophysics of chromophores and how this can help in the development of new colour chromophores.. ...
H-bond Networks are back! The H-bond Network Objective encourages players to bury satisfied H-bond networks at the interface between symmetric chains. H-bond networks are a great way to introduce polar residues at the interface, but its important that all of the bondable atoms make hydrogen bonds! In this puzzle, there are no limits on the Complex Core, but weve included the Complex Core objective so players can see which residues count as core in the H-bond Networks. There a few other objectives in effect; see the puzzle comments for details. The Baker Lab will run folding predictions on your solutions for this puzzle, and those that perform well will be synthesized in the lab. Remember, you can use the Upload for Scientists button for up to 5 designs that you want us to look at, even if they are not the best-scoring solutions ...
We demonstrate in a combined two-color pump-probe and quantum dynamical study that population of the O-H stretching oscillator of a medium-strong intramolecular hydrogen bond is redistributed along th
The chemistry of acrolein and crotonaldehyde-derived propano-deoxyguanosine (γ-OH-PdG and α-CH3-γ-OH-PdG) adducts was monitored in the 5´-CpG-3´ sequence within a dodecamer duplex by NMR spectroscopy, in situ, using a series of site-specific 13C- and 15N-edited experiments. One striking phenomenon was the formation of an interstrand DNA cross-link, predominantly a carbinolamine. The cross-link existed in equilibrium with the non-crosslinked aldehyde and its geminal diol hydrate. The ratio of aldehyde/diol increased at higher temperatures. The effects of the pH and complementary bases were examined. Molecular modeling suggested that the carbinolamine linkage should be capable of maintaining Watson-Crick hydrogen bonds at both of the tandem C•G base pairs. In contrast, dehydration of the carbinolamine cross-link to an imine (Schiff base) cross-link, or cyclization of the latter to form a pyrimidopurinone cross-link, was predicted to require disruption of Watson-Crick hydrogen bonds at one ...
(15)N and (1)H Solid-State NMR Investigation of a Canonical Low-Barrier Hydrogen-Bond Compound: 1,8-bis(dimethylamino) Naphthalene. (15)N and (1)H
As a means of making chitosan more useful in biotechnological applications, it was hydrolyzed using pepsin, chitosanase and α-amylase. The enzymolysis behavior of these enzymes was further systematically studied for its effectiveness in the production of low-molecular-weight chitosans (LMWCs) and other derivatives. The study showed that these enzymes depend on ion hydronium (H3O+), thus on pH with a pH dependence fitting R2 value of 0.99. In y = 1.484[H^+] + 0.114, the equation of pH dependence, when [H^+] increases by one, y (k_0/k_m) increases by 1.484. From the temperature dependence study, the activation energy (Ea) and pre-exponential factor (A) were almost identical for two of the enzymes, but a considerable difference was observed in comparison with the third enzyme. Chitosanase and pepsin had nearly identical Ea, but α-amylase was significantly lower. This serves as evidence that the hydrolysis reaction of α-amylase relies on low-barrier hydrogen bonds (LBHBs), which explains its low Ea in
Two basic heterocyclic imino structures display a planar backbone with similar features, but differ in the heterocyclic atoms located in the five-membered rings, i.e. N and S. In the pyrrole, centrosymmetric imino-pyrrole dimers are assembled by means of two inverted N-H⋯N hydrogen bonds and two inverted C-H⋯π inter-actions. In the thio-phene, however, mol-ecules are linked by nonclassical C-H⋯N hydrogen bonds in which the mol-ecules play the roles of both hydrogen-bond donors and acceptors, resulting in one-dimensional supra-molecular chains ...
Iron oxyhydroxide (FeOOH) mineral plays an important role in a variety of atmospheric, terrestrial and technological settings. Molecular resolution of reactions involving these minerals is thereby required to develop a fundamental understanding of their contributions in processes taking place in the atmosphere, Earths upper crust as well as the hydrosphere. This study resolves interactions involving four different types of synthetic FeOOH particles with distinct and well-defined surfaces, namely lath- and rod-shaped lepidocrocite (γ), goethite (α) and akaganéite (β). The surface and bulk reactivities of these particles are controlled by their distinct structures. When exposed to ambient atmospheric or aqueous conditions their surfaces are populated with different types of (hydr)oxo functional groups acting as reaction centers. These sites consist of hydroxyl groups that can be singly- (≡FeOH, -OH), doubly- (≡Fe2OH, μ-OH), or triply-coordinated (≡Fe3OH, μ3-OH) with underlying Fe ...
The coupling of hydrogen bonds is central to structures and functions of biological systems. Hydrogen bond coupling in sodium dihydrogen triacetate (SDHTA) is investigated as a model for the hydrogen bonded systems of the type O-H...O. The twodimensional potential energy surface is derived from the full-dimensional one by selecting the relevant vibrational modes of the hydrogen bonds. The potential energy surfaces in terms of normal modes describing the anharmonic motion in the vicinity of the equilibrium geometry of SDHTA are calculated for the different species, namely, HH, HD, DH, and DD isotopomers. The ground state wave functions and their relation to the hydrogen bond structural parameters are discussed. It has been found that the hydrogen bonds in SDHTA are uncoupled, that is elongation of the deuterated hydrogen bond does not affect the non-deuterated one ...
For the first time, a group of scientists from University of California, San Diego in United States has quantitatively measured the strength of hydrogen bonds between two complex molecules. They also observed an abnormal trend regarding the bond strength in the absence and presence of electron transfer. This work contributes to the understanding of how the hydrogen bond strength changes, an important point that reveals the way biological systems function.. Hydrogen bonds are a type of electrostatic attraction between hydrogen atoms and certain highly electronegative atoms including N, O and F. These bonds help to bind individual water molecules together and keep water as liquid at room temperature, a critical condition for the origin of life.. The researchers, led by Prof. Kubiak, picked two ruthenium-based complexes joined by hydrogen bonds as their studying platform. As shown in Figure 1, the two-molecule system has three states depending on whether the ends are charged or not: the neutral ...
Electron-withdrawing trifluoromethyl groups were characterized in combination with hydrogen-bond interactions in three polyols (i.e., CF3CH(OH)CH2CH(OH)CF3, 1; (CF3)2C(OH)C(OH)(CF3)2, 2; ((CF3)2C(OH)CH2)2CHOH, 3) by pKa measurements in DMSO and H2O, negative ion photoelectron spectroscopy and binding constant determinations with Cl-. Their catalytic behavior in several reactions were also examined and compared to a Brønsted acid (HOAc) and a commonly employed thiourea ((3,5-(CF3)2C6H3NH)2CS). The combination of inductive stabilization and hydrogen bonds was found to afford potent acids which are effective catalysts. It also appears that hydrogen bonds can transmit the inductive effect over distance even in an aqueous environment, and this has far reaching implications ...
Hydrogen bonds are crucial factors that stabilize a complex ribonucleic acid (RNA) molecules three-dimensional (3D) structure. Minute conformational changes can result in variations in the hydrogen bond interactions in a particular structure. Furthermore, networks of hydrogen bonds, especially those found in tight clusters, may be important elements in structure stabilization or function and can therefore be regarded as potential tertiary motifs. In this paper, we describe a graph theoretical algorithm implemented as a web server that is able to search for unbroken networks of hydrogen-bonded base interactions and thus provide an accounting of such interactions in RNA 3D structures. This server, COGNAC (COnnection tables Graphs for Nucleic ACids), is also able to compare the hydrogen bond networks between two structures and from such annotations enable the mapping of atomic level differences that may have resulted from conformational changes due to mutations or binding events. The COGNAC server ...
Hydrogen bonds are ubiquitous and play a major role in chemistry. In addition to the classical hydrogen-bond acceptors (namely, N, O, the halogens, S, and P), transition metals have been recognized to also participate in hydrogen bonding toward protonic H‒X fragments. Since the 1990s, such M∙∙∙H-X interactions have garnered great interest (1, 2). Numerous studies have been carried out to better understand this unusual bonding situation, to delineate the influence of M∙∙∙H‒X interactions on the structure and properties of transition metal complexes. It is also of note that M∙∙∙H‒X interactions are relevant to the protonation of transition metals to form metal hydrides (1, 3, 4). M∙∙∙H‒X interactions have been unambiguously authenticated both intra- and intermolecularly with various hydrogen-bond donor moieties (e.g., ammoniums, amides, and water) and electron-rich transition metals (mainly Pt and Co).. The case of gold is very singular and deserves special ...
Translatory and torsional vibrations of the molecules. Using melamine for an example, the elastic properties of the intermolecular hydrogen bonds are demonstrated. Using the thermally induced vibrations at 60 and 300 K it is shown, that they are the mechanical storage means of the specific heat of the melamine crystal.
TY - JOUR. T1 - Structure-reactivity correlation of photochemical reactions in organic crystals. T2 - Intramolecular hydrogen abstraction in an aromatic nitro compound. AU - Padmanabhan, Kaillathe. AU - Venkatesan, Kailasam. AU - Ramamurthy, Vaidyanathan. AU - Schmidt, Rolf. AU - Döpp, Dietrich. PY - 1987. Y1 - 1987. N2 - The molecular structure of 1,4-bis-(2-chloro-1,1-dimethylethyl)-2- nitrobenzene has been determined by X-ray crystallography. The single-crystal X-ray investigation, R = 0.067, showed the compound to be monoclinic, space group P21, a = 6.388(2), b = 13.848(4), c = 8.578(3) Å, β = 94.05(3)°. Structural analysis of 2-nitro-t-butylbenzenes which undergo intramolecular hydrogen abstraction in the solid state upon irradiation by u.v. light was carried out in connection with structure-reactivity correlation studies and X-ray crystallographic investigations. On the basis of intramolecular geometry and molecular packing considerations, it has been possible to identify the hydrogen ...
Herein, the structural path is traced beginning with a pentapeptide ketoamide inhibitor 1. From this starting point, the resulting tripeptides related to 9 are analyzed in detail.. The structure derived from a crystal soaked with 1 shows a covalent complex with the inhibitor which spans subsites S4-S2′. The aliphatic cap of 1 is analogous to IBoc-Val as P4-P3. Si-face attack of Ser139 yields a stable tetrahedral intermediate with a covalent bond from Ser Oγ to the keto C atom and with the keto oxyanion hydrogen bonded to His57. The P1 amide carbonyl O atom is in the oxyanion hole hydrogen bonding to the NH groups of Gly137 and Ser139. Canonical backbone hydrogen bonds are formed: P3CO-Ala157NH, P1NH-Arg155CO, P2′NH-Thr42CO and P2′CO-Thr42NH. P3 lacks an amide NH group so the usual P3NH-Ala157CO hydrogen bond is missing. The inhibitor side chains bind in surface pockets that are primarily hydrophobic, with the S1 pocket being the largest and deepest. For polar protein residues in the ...
In the case of DB32W (Fig. 2b), molecules 1 and 2 interact via a strong N4-H4B⋯N1 hydrogen bond (I) in the asymmetric unit with the stabilization energy of −11.2 kcal mol−1 (57% electrostatic contribution and 43% dispersion contribution). Molecule 2 interacts with the water molecule present in the asymmetric unit via a O1W-H1W⋯N3 hydrogen bond (IV; −6.5 kcal mol−1). Fig. 3b shows the molecular arrangement in the hydrate form down the ab plane. Here, the primary structural motifs involving short and highly directional strong hydrogen bonds generate different types of cyclic tetrameric (R1 and R2) and hexameric (R3 and R4) synthons (Desiraju and co-workers21 have discussed about the tetrameric and hexameric supramolecular synthons associated with a strong N-H⋯O hydrogen bond for aniline-phenol co-crystals). In this case, all the cyclic rings are interconnected with each other. Two symmetry independent molecules (1 and 2) and one water molecule form a molecular chain via the strong ...
TY - JOUR. T1 - Importance of secondary electrostatic interactions in hydrogen-bonding complexes. T2 - An investigation using the self-consistent charge and configuration method for subsystems. AU - Uchimaru, Tadafumi. AU - Korchowiec, Jacek. AU - Tsuzuki, Seiji. AU - Matsumura, Kazunari. AU - Kawahara, Shun Ichi. PY - 2000/2/18. Y1 - 2000/2/18. N2 - We have examined the energy components of hydrogen-bonding interactions by using self-consistent charge and configuration method for subsystems (SCCCMS) and charge sensitivity parameters. Our procedure indicated that the main source of the stabilization for hydrogen-bonding association was the electrostatic contribution. The secondary electrostatic and polarization interactions due to polar functional groups located closely to the hydrogen-bonding sites were shown to significantly alter the magnitude of hydrogen-bonding stabilization. This finding supports Jorgensen and co-workers interpretation toward the hydrogen-bonding energies [e.g., W.L. ...
Hydrogen bonds are much weaker than chemical bonds, but stronger than intermolecular van der Waals interactions ,,. ,, With this study, [AA] have opened up new ways to identify three-dimensional molecules such as nucleic acids or polymers via observation of hydrogen atoms ,,. Hydrogen bonds directly detected for the first time. May 12, 2017 https://m.phys.org/news/2017-05-hydrogen-bonds.html. Shigeki Kawai, Tomohiko Nishiuchi, et al. Direct quantitative measurement of the C═O⋅⋅⋅H-C bond by atomic force microscopy. Science Advances. 12 May 2017:Vol. 3, no. 5, e1603258 DOI: 10.1126/sciadv.1603258. http://advances.sciencemag.org/content/3/5/e1603258. ...
Abstract Various physicochemical factors influence DNA replication fidelity. Since it is now known that Watson-Crick hydrogen bonds are not necessary for efficient and selective replication of a base pair by DNA polymerase enzymes, a number of alternative physical factors have been examined to explain the efficiency of these enzymes. Among these factors are minor groove hydrogen bonding, base stacking, solvation, and steric effects. We discuss the concept of active site tightness in DNA polymerases, and consider how it might influence steric (size and shape) effects of nucleotide selection in synthesis of a base pair. A high level of active site tightness is expected to lead to higher fidelity relative to proteins with looser active sites. We review the current data on what parts and dimensions of active sites are most affected by size and shape, based on data with modified nucleotides that have been examined as polymerase substrates. We also discuss recent data on nucleotide analogs displaying ...
Alstom and Eversholt Rail have unveiled the design of a new hydrogen train for the UK market. The train, codenamed Breeze, will be a conversion of existing Class 321 trains, reengineering some of the UKs most reliable rolling stock. These trains could run across the UK as early as 2022....
Alstom and rolling stock operating company Eversholt Rail have unveiled the design of a new hydrogen train codenamed Breeze for the UK
The report was presented and discussed at the event Delivering the Hydrogen Economy, to showcase several hydrogen projects that position the North West as pioneers in this technology.. Ed Syson, chief safety and strategy officer at Cadent, said: We carried out this study because there is an obvious desire and enthusiasm in the North West to think big and take a lead in finding low-cost ways to cut emissions. Industry and policy makers can now be assured that HyNet can deliver the bulk volume of hydrogen needed in the North West, via a pipeline network. Distributing it this way cuts the costs considerably and means hydrogen can complement electricity and advanced biofuels as an attractive option for future fuel.. At the event INOVYN, a wholly owned subsidiary of INEOS, also announced plans for a study into the potential for grid-scale storage of bulk hydrogen in salt caverns in mid Cheshire. Large-scale, low-cost hydrogen storage is essential to the deployment of hydrogen into the gas grid. A ...
The fact that the oxygen end of a water molecule is negatively charged and the hydrogen end positively charged means that the hydrogens of one water molecule attract the oxygen of its neighbor and vice versa. This is because unlike charges attract. This largely electrostatic attraction is called a hydrogen bond and is important in determining many important properties of water that make it such an important liquid for living things. Water can also form this type of bond with other polar molecules or ions such as hydrogen or sodium ions. Further, hydrogen bonds can occurr within and between other molecules. For instance, the two strands of a DNA molecule are held together by hydrogen bonds. Hygrogen bonding between water molecules and the amino acids of proteins are involved in maintaining the proteins proper shape ...
The Schellman motif is a widely observed helix terminating structural motif in proteins, which is generated when the C-terminus residue adopts a left-handed helical (aL) conformation. The resulting hydrogen-bonding pattern involves the formation of an intramolecular 6 - 1 interaction. This helix terminating motif is readily mimicked in synthetic helical peptides by placing an achiral residue at the penultimate position of the sequence. Thus far, the Schellman motif has been characterized crystallographically only in peptide helices of length 7 residues or greater. The structure of the hexapeptide Boc-Pro-Aib-Gly-Leu-Aib-Leu-OMe in crystals reveal a short helical stretch terminated by a Schellman motif, with the formation of 6 - 1 C-terminus hydrogen bond. The crystals are in the space group P212121 with a = 18.155(3) Å, b = 18.864(8) Å, c 5 11.834(4) Å, and Z = 4 . The final R1 and wR2 values are 7.68 and 14.6%, respectively , for 1524 observed reflections [Fo ,- 3(Fo)]. A 6 - 1 hydrogen bond ...
The donor and acceptor groups found in biological structures which form O - H ··· O bonds are given in Box 6.1. The C - OH ⋯ O hydrogen bonds are the primary intermolecular cohesive force between the...
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The structural features of the compounds presented in the solid state correlate strongly with those found in solution. For example, stereoisomer characterisation [(E)- or (Z)-] and the presence of intramolecular hydrogen bonding are confirmed by both techniques although the X-ray study reveals extended intermolecular hydrogen bonding, which is not observed in solution-based techniques (1H NMR). The predominant motif in the crystal structures is that of intermolecular hydrogen bonding (N-H…O=C) between the 1H-indol-2(3H)-one units. This motif is maintained in the one structure that contains a hydrogen-bonding hydrate molecule. However, one structure, methyl 3-(1-methylethylidene)-2-oxo-2,3-dihydro-1H-indole-1-carboxylate, a carbamate analogue lacking an N-H bond, displays no intermolecular hydrogen bonding.. ...
When an imbalance of electrical charge occurs within a molecule, the molecule is said to be polar or to exhibit polarity - in which case one end has a positive charge and the other has a negative charge (just like a magnet).. A polar molecule acts a little like an atom in need of an electron. Its positively charged end is attracted to negatively charged things around it - most commonly the negatively charged sides of other polar molecules.. The most common example of hydrogen bonding involves water molecules. This figure illustrates how the covalent bond between oxygen and hydrogen creates an electrical imbalance in water molecules and how, as a result, the negative end of one water molecule is attracted to the positive ends of another water molecule forming hydrogen bonds.. Hydrogen bonds are weak compared to covalent and ionic bonds, but these weak bonds play an important role in the environment and in living things. Theyre important in forming DNA chains, and they give liquid water some ...
These results show the dynamical nature of the quenching process; i.e. the quenching is due to the excited state interaction of AC with the amine. The mean value of the quenching constant obtained from Stern-Volmer plots of the steady-state and time-resolved fluorescence data, 5x1010 M-1 s-1, is similar to those of the quenching constants, kq, reported in Table 1 for the AC-DMF and AC-DMA systems. These quenching constants are, on the other hand, of the order of magnitude expected for a difussion controlled process in cyclohexane. Conversely, the changes observed in the absorption and fluorescence spectra of AC in cyclohexane upon the addition of methylethylcetone entirely resemble those produced by the amides.. On the basis of the above results, we conclude that, in the ground state, the pyrrolic NH group of AC interacts preferently with the carbonyl groups of the amides, but, in the excited state, the hydrogen-bonding interactions take place through the lone electron pair of the nitrogen atoms ...
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Design a symmetric protein trimer, with 3 identical chains that assemble together! This puzzle uses the Buried Unsats Objective, with a large penalty for buried polar atoms that cant make H-bonds. The H-bond Network Objective encourages players to build buried, satisfied H-bond networks at the interface between symmetric chains. H-bond networks are a great way to introduce polar residues at the interface, but its important that all of the bondable atoms make hydrogen bonds! In this puzzle, there are no limits on the Complex Core, but weve included the Complex Core objective so players can see the core residues that can be incorporated into H-bond Networks ...
Step by Step Replication The DNA chains unwind and divide at the replication fork. The protein DNA Helicase moves along the DNA breaking the weak hydrogen bonds between the nitrogen bases. DNA Polymerase binds to the separated strands of DNA and assembles new nucleotides in a complimentary chain Covalent bonds hold the phosphates and sugars together. Hydrogen bonds hold the nitrogen bases together.
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There is a predilection amongst chemists for collecting records; one common theme is the length of particular bonds, either the shortest or the longest. A particularly baffling type of bond is that between the very electronegative F atom and an acid hydrogen atom such as that in OH. Thus short C-N…HO hydrogen bonds are extremely common, as are C-O…HO.‡ But F atoms in C-F bonds are largely thought to be inert to hydrogen bonding, as indicated by the use of fluorine in many pharmaceuticals as inert isosteres.[1] Here I do an up-to-date search of the CSD crystal structure database, which is now on the verge of accumulating 1 million entries, to see if any strong C-F…HO hydrogen bonding may have been recently discovered.. (more…). ...
The crystal structure of rivastigmine hydrogen tartrate has been solved and refined using synchrotron X-ray powder diffraction data, and optimized using density functional techniques. Rivastigmine hydrogen tartrate crystallizes in space groupP21(#4) witha= 17.538 34(5),b= 8.326 89(2),c= 7.261 11(2) Å,β= 98.7999(2)°,V= 1047.929(4) Å3, andZ= 2. The un-ionized end of the hydrogen tartrate anions forms a very strong hydrogen bond with the ionized end of another anion to form a chain. The ammonium group of the rivastigmine cation forms a strong discrete hydrogen bond with the carbonyl oxygen atom of the un-ionized end of the tartrate anion. These hydrogen bonds form a corrugated network in thebc-plane. Both hydroxyl groups of the tartrate anion form intramolecular O-H···O hydrogen bonds. Several C-H···O hydrogen bonds appear to contribute to the crystal energy. The powder pattern is included in the Powder Diffraction File™as entry 00-064-1501. ...
TY - JOUR. T1 - Unprecedented four-way-output molecular response system based on biphenyl-2,2′-diyldiacridiniums. T2 - induction of axial chirality through intramolecular hydrogen bonds between chiral amide groups. AU - Suzuki, Takanori. AU - Ohta, Kenji. AU - Nehira, Tatsuo. AU - Higuchi, Hiroki. AU - Ohta, Eisuke. AU - Kawai, Hidetoshi. AU - Fujiwara, Kenshu. PY - 2008/1/28. Y1 - 2008/1/28. N2 - Upon the attachment of N-(R)-2-phenylethylamide moieties to the acridinium units of the title dication, intramolecular hydrogen bonds induce a diastereomeric preference in terms of axial chirality (70% de at -40 °C in CH2Cl2). Thus, external stimuli induce not only UV-vis and fluorescence spectra changes but also changes in the CD and fluorescence-detected CD (FDCD) spectra, realizing unprecedented four-way-output molecular response systems.. AB - Upon the attachment of N-(R)-2-phenylethylamide moieties to the acridinium units of the title dication, intramolecular hydrogen bonds induce a ...
TY - JOUR. T1 - Different intra- and inter-molecular hydrogen-bonding patterns in (3S,4aS,8aS)-2-[(2R,3S)-3-(2,5-X2-benzamido)-2-(2,5-X2-benzo-yloxy)-4-phenyl-butyl]-N-tert-butyldeca-hydro-iso-quinoline-3-carboxamides (X = H or Cl). T2 - compounds with moderate aspartyl protease inhibition activity. AU - Cunico, Wilson. AU - Ferreira, Maria de Lourdes G. AU - Wardell, James L.. AU - Harrison, William T A. N1 - We thank the EPSRC National Crystallography Service (University of Southampton) for the X-ray data collections.. PY - 2017/6/1. Y1 - 2017/6/1. N2 - The crystal structures of (3S,4aS,8aS)-2-[(2R,3S)-3-benzamido-2-benzo-yloxy-4-phenyl-but-yl]-N-tert-butyldeca-hydro-iso-quinoline-3-carboxamide, C38H47N3O4, (I), and (3S,4aS,8aS)-2-[(2R,3S)-3-(2,5-di-chloro-benzamido)-2-(2,5-di-chloro-benzo-yloxy)-4-phenyl-but-yl]-N-tert-butyldeca-hydro-iso-quinoline-3-carboxamide, C38H43Cl4N3O4, (II), are described. Despite their chemical similarity, they adopt different conformations in the solid state: (I) ...
Relevance of weak hydrogen bonds in the conformation of organic compounds and bioconjugates: evidence from recent experimental data and high-level ab initio MO calculations., Relevance of weak hydrogen bonds in the conformation of organic compounds and bioconjugates: evidence from recent experimental data and high-level ab initio MO calculations., 110(10), 6049-6076, ...
Its hard to find anything that is always true in chemistry, but Id bet that within a series of molecules where the only variable is the number of $\ce{OH}$ groups, your statement is generally true, so I basically agree with your position. Your analysis and examples are also good. As you pointed out, it is about intermolecular forces. Specifically, molecules with hydroxyl groups can form intermolecular hydrogen bonds (see first picture below). These hydrogen bonds cause the molecules to stick together and act as if they had a higher molecular weight. Sugars have many hydroxyl groups that give rise to many intermolecular hydrogen bonds and cause sugars to flow in a slow, syrupy manner.. ...
The conversion of cholesterol to pregnenolone is a physiologically essential process which initiates with two sequential hydroxylation processes catalyzed by cytochrome P450 side-chain cleavage enzyme (P450SCC). Extensive efforts have been exerted; however, the mechanistic details remain obscure. In this work, we employed the dispersion-corrected density functional theoretical (DFT-D) calculations to investigate the mechanistic details of such hydroxylation processes. Calculated results reveal that the active intermediate Compound I (CpdI) of P450SCC hydroxylates cholesterol efficiently, which coincides with previous spectrometric observations. The hydrogen bond effect of water molecule within the active site lowers the energy barrier significantly. Intriguingly, the adjacent hydrogen bond (H-bond) between the hydroxyl group of the substrate and the oxo group of CpdI in the second hydroxylation affects the H-abstraction significantly. Such H-bond was weakened during the C-H bond activation ...
An electrochemical test method is proposed for determination of the susceptibility of materials to internal hydrogen embrittlement IHE. The method is based on the assumption that the relative susceptibility of a material depends both on the specific aqueous environment to which the material is exposed and to the dissimilar materials to which it is coupled. Potentiosatic techniques are employed to impress potential on sustained loaded notched round- bar specimens. The result is a plot of impressed potential versus time-to- failure superpositioning of the resultant curves provides a basis for rating the relative susceptibility of various materials to IHE.
Three new hydrogen filling stations opened in California within the span of one week, bringing the total to 39. The new stations are in Palo Alto, at LAX (Los Angeles International Airport), and in the Sacramento area. The Citrus Heights hydrogen station, the 37th retail hydrogen station in California, is...
A hydrogen bond (often informally abbreviated H-bond) is a partial intermolecular bonding interaction between a lone pair on an electron rich donor atom, particularly the second-row elements nitrogen (N), oxygen (O), or fluorine (F), and the antibonding orbital of a bond between hydrogen (H) and a more electronegative atom or group.[4] Such an interacting system is generally denoted Dn-H···Ac, where the solid line denotes a polar covalent bond, and the dotted or dashed line indicates the hydrogen bond. The use of three centered dots for the hydrogen bond is specifically recommended by the IUPAC.[5] While hydrogen bonding has both covalent and electrostatic contributions, and the degrees to which they contribute are currently debated, the present evidence strongly implies that the primary contribution is covalent.[6] Hydrogen bonds can be intermolecular (occurring between separate molecules) or intramolecular (occurring among parts of the same molecule).[7][8][9][10] Depending on the nature of ...
A combination of vapor phase infrared spectroscopy and ab initio calculations has been used to show that sulfur is weaker than, but nearly equivalent to, oxygen as a hydrogen bond acceptor. Enthalpies of hydrogen bond formation were obtained for the hydrogen bonded complexes formed between methanol and eithe
We know what a hydrogen bond is, so now we apply it to the freezing of water. When the molecules of water are still a liquid, they are free-moving and make/break hydrogen bonds very easily and frequently. The molecules can slip in and out at close proximity due to its high energy. But when the temperature drops, the molecules lose energy, slow down, and keep their hydrogen bonds for longer. Soon enough, at 4° C, the hydrogen bonds start altering the layout of the molecules. A single water molecule can only form a maximum of four hydrogen bonds with its neighboring molecules. At 4° C and below, a molecule will keep its bonds and lock into a crystalline lattice with its four neighbors. Then the molecules are at arms length so to speak and there are less molecules in a given space; the density is now lower ...
p,The crystal structure of the title water-soluble analogue of vitamin E, trolox amide, C(14)H(19)NO(3), solved and refined against synchrotron diffraction data, contains two mol-ecules in the asymmetric unit. In both molecules, the heterocyclic ring is in a half-chair conformation. The crystal packing features a herring-bone pattern generated by N-H⋯O hydrogen bonds between the hy-droxy and amide groups. O-H⋯O hydrogen bonds also occur.,/p,. ...
A symmetric hydrogen bond is a special type of hydrogen bond in which the proton is spaced exactly halfway between two identical atoms. The strength of the bond to each of those atoms is equal. It is an example of a 3-center 4-electron bond. This type of bond is much stronger than normal hydrogen bonds, in fact, its strength is comparable to a covalent bond. It is seen in ice at high pressure, and also in the solid phase of many anhydrous acids such as hydrofluoric acid and formic acid at high pressure. It is also seen in the ion [F-H-F]−. Much has been done to explain the symmetric hydrogen bond quantum-mechanically, as it seems to violate the duet rule for the first shell: The proton is effectively surrounded by four electrons. Because of this problem, some consider it to be an ionic bond. ...
In the title compound, C18H22N2O4S2, the 2H-chromene ring system is essentially planar (r.m.s. deviation = 0.012 A ° ). The molecular conformation is stabilized by a C-H� � �O hydrogen bond. In the crystal, N-H� � �S and C-H� � �O hydrogen bonds occur, the former enclosing an R2 2(22) ring motif, and lead to the formation of a two-dimensional slab-like network lying parallel to (101). �-� interactions are observed between inversion-related aromatic rings [shortest centroid-centroid distance = 3.6300 (11) A ° ].. ...
Hydrogen is the simplest element. Each atom of hydrogen has only one proton. Hydrogen is also the most plentiful gas in the universe. Stars like the sun consist primarily of hydrogen.. The sun is essentially a giant ball of hydrogen and helium gases. In the suns core, hydrogen atoms combine to form helium atoms. This process-called fusion-gives off radiant energy.. The radiant energy from the sun gives earth light and helps plants grow. Radiant energy is stored as chemical energy in fossil fuels. Most of the energy that people use today originally came from the suns radiant energy.. Hydrogen as a gas (H2) is not found by itself on earth. Hydrogen gas is found only in compound form with other elements. Hydrogen combined with oxygen is water (H2O). Hydrogen combined with carbon forms different compounds like methane (CH4), coal, and petroleum. Hydrogen is found in all growing things and is an abundant element in the earths crust.. Hydrogen has the highest energy content of any common fuel by ...
terms indicate the distance between atoms A and B, taken from the carbon (C) and oxygen (O) atoms of the C=O group and the nitrogen (N) and hydrogen (H) atoms of the N-H group. Based on this, eight types of secondary structure are assigned. The 310 helix, α helix and π helix have symbols G, H and I and are recognized by having a repetitive sequence of hydrogen bonds in which the residues are three, four, or five residues apart respectively. Two types of beta sheet structures exist; a beta bridge has symbol B while longer sets of hydrogen bonds and beta bulges have symbol E. T is used for turns, featuring hydrogen bonds typical of helices, S is used for regions of high curvature (where the angle between ...
A review of selected literature data related to intramolecular hydrogen bonding in ortho-hydroxyaryl Schiff bases, ortho-hydroxyaryl ketones, ortho-hydroxyaryl amides, proton sponges and ortho-hydroxyaryl Mannich bases is presented. The paper reports on the application of experimental spectroscopic measurements (IR and NMR) and quantum-mechanical calculations for investigations of the proton transfer processes, the potential energy curves, tautomeric equilibrium, aromaticity etc. Finally, the equilibrium between the intra- and inter-molecular hydrogen bonds in amides is discussed.
Reaction of 2-aminomethylpyridine with diphenylborinic acid in a mixture of CHCl3-diethyl ether gives diphenyl-(2-aminomethylpyridine-N,N)borane, a cyclic adduct that in presence of environmental moisture yields the N-8-(diphenyl-hydroxy-2-aminomethylpyridine)borane. The two compounds were characterized by NMR and infrared spectroscopy. The structure of N-8-(diphenyl-hydroxy-2-aminomethylpyridine)borane was confirmed by X-ray diffraction. This adduct crystallizes in monoclinic P21/n space group with unit cell dimensions: a = 13.193(2) (Å), b = 5.913(7) (Å), c = 19.604(2) (Å), = 90.295(3), V = 1529.3(3) Å3, Z = 4. The BN distance is 1.645(3) Å and lies in the range of a dative bond. The NH and OH groups are involved in intermolecular hydrogen bonds formation and they add to the stabilization of the acyclic adduct in the solid state. ...
Two distinct isomers for the binary complex between phenylacetylene and methylamine were observed. The first complex is characterized by the presence of a C-H center dot center dot center dot N hydrogen bond between the acetylenic C-H group and the N atom of methylamine. In the second complex the N-H group of methylamine interacts with the pi electron density of the benzene ring accompanied by a peripheral interaction between the methyl C-H group and the pi electron density of the C C bond. Stabilization energies and Gibbs free energies at the complete basis set (CBS) limit of the coupled cluster theory with single, double, and perturbative triple excitations [CCSD(T)] suggest that while the C-H center dot center dot center dot N hydrogen bonded complex is the global minimum, the N-H center dot center dot center dot pi hydrogen bonded complex is a high energy local minimum. The formation of the N-H center dot center dot center dot pi complex could be related to kinetic trapping or higher ...
Intramolecular hydrogen bonding in alpha-phenylcinnamic acids and their heteroatom-containing derivatives studied by ab initio quantum chemical methods. (deposited 2013. Jan. 25. 11:24) [Ezt látja] ...
Although lamivudine and emtricitabine, two L-deoxycytidine analogs, have been widely used as antiviral drugs for years, it is structrually unknown how they are bound and incoproated by any DNA polymerases or reverse transcriptases. To fill the void, we solved 12 high resolution ternary crystal structures of human DNA polymerase lambda, DNA, and L-dCTP or the triphosphates of lamivudine and emtricitabine. The structures of these 12 ternary complexes reveal that relative to natural D-dCTP in the canonical ternary structure, these L-nucleotides all have their ribose rotated by 180°. Among the four ternary complexes with a specific L-nucleotide in each asymmetric unit, two are similar and show that the L-nucleotide forms three Watson-Crick hydrogen bonds while in the remaining two similar ternary complexes, the L-nucleotide surprisingly interacts with the side chain of a conserved active site residue R517 through one or two hydrogen bonds. Our mutagenic and kinetic studies further demonstrate that ...
Polyethylene glycol (PEG) is a unique polymer material with enormous applicability in many industrial and scientific fields. Here, its use as macromolecular crowder to mimic the cellular environment in vitro is the focus of the present study. We show that femtosecond mid-IR pump-probe spectroscopy using three different IR probes, HDO, HN3, and azido-derivatized crowder, provides complete and stereoscopic information on water structure and dynamics in the cytoplasm-like macromolecular crowding environment. Our experimental results suggest two distinct subpopulations of water molecules: those that interact with other water molecules and those that are part of a hydration shell of crowder on its surface. Interestingly, water dynamics even in highly crowded environment remains bulk-like in spite of significant perturbation to the tetrahedral H-bonding network of water molecules. That is possible because of the formation of water aggregates (pools) even in water-deficient PEGDME-water solutions. In ...
Anion complexation studies on a series of platinum( II) tetrakis( pyrrolylpyridine) salts demonstrate the importance of CH-anion hydrogen bonds in coordinating anionic guests in solution and the solid-state.. Full text not available from this repository.. ...
Gelatin is a protein, made from the hydrolysis of collagen, a protein that makes up about a third of all mammalian tissue. Collagen is what makes up much of the connective tissue, tendons, and the protein part of bones. Hydrolysis in proteins is the process of adding a molecule of water to break the bonds between some of the amino acids, thereby making the protein chains smaller. Collagen forms a triple helix, where three chains of connected amino acids form weak hydrogen bonds between the double bonded oxygen atoms and the hydrogen atoms attached to the adjacent chains nitrogens. The three chains then twist together like three cords in a rope. In gelatin, when the triple helices are heated in water, they open up, and some of the hydrolyzed ends fray out to tangle with other ropes, and water is trapped in the strands. The result is a gel, a wiggly semi-solid mass. ...
The experimental FT-IR and FT-Raman spectra of 9-3-(Dimethylamino)propyl-2-trifluoro-methyl-9H-thioxanthen-9-ol have been recorded. Quantum chemical calculations of geometry and vibrational wavenumbers of 9-3-(Dimethylamino)propyl-2-trifluoro-methyl-9H-thioxanthen-9-ol are carried out theoretically. Four possible stable conformations of the title compound were determined. In terms of the conformational analysis, one of the most interesting structural features of the title compound is the intra molecular OH⋯N hydrogen bond. The barrier of planarity between the most stable and planar form is also predicted. The optimized geometrical parameters obtained by B3LYP method show a good agreement with XRD data. The difference between the observed and theoretical wavenumbers is very small. The complete assignments were performed on the basis of potential energy distribution of the vibrational modes calculated theoretically. The calculated HOMO and LUMO energies allow the calculation of atomic and ...
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A system for producing, dispensing, using and monitoring a hydrogen enriched fuel includes a producing system configured to produce the hydrogen enriched fuel, a vehicle having an engine configured to use the hydrogen enriched fuel, and a dispensing system configured to store and dispense the hydrogen enriched fuel into the vehicle. The system also includes a fuel delivery system on the vehicle configured to deliver the hydrogen enriched fuel to the engine, and a control system configured to control the producing system and to monitor the use of the hydrogen enriched fuel by the vehicle. A method includes the steps of producing hydrogen gas and a hydrocarbon fuel, blending the hydrogen gas and the hydrocarbon fuel into the hydrogen enriched fuel, using the hydrogen enriched fuel in the engine, and tracking emissions during the producing step and during the using step.
DNA is made of the sugar Deoxyribose, and is an acid. The rungs of the molecule are made of a phosphate group linked to a deoxyribose sugar which are linked to one of four nitrogenous bases: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G). A fits with T and C fits with G and vice versa. The bases are linked by weak Hydrogen bonds so it can easily replicate. When it replicates, the molecule unwinds, and an enzyme called DNA Polymerase moves down the bonds and unzips it. Then another strand comes and fits with correct corresponding base. This happens in the Cells nulceus. The molecule replicates when the cell divides. Thats DNA basics for you. Also, to extract DNA, the lower the temp., the better perserved DNA stays when the cell gets dissolved. ...
# 2006 International Union of Crystallography All rights reserved In the crystal structure of the title compound, C16H18N2O2, the indole moiety is nearly planar. The two carbonyl groups are almost perpendicular, with a torsion angle of 105.7 (4) , and the single C-C bond linking the two carbonyl groups is 1.515 (5) Å in length. The molecules are linked together by N-H O intermolecular hydrogen bonds.
Air Products has announced plans to construct a new 180-mile long pipeline connecting its existing Louisiana and Texas hydrogen pipeline systems, creating the worlds largest hydrogen plant and pipeline supply network.
The U.S. Department of Energy has awarded $7 million to projects expected to advance the development of hydrogen fuel cell systems for variously sized vehicles.
Irish drugs and alcohol research, data, policy and sources of evidence on prevention, treatment, rehabilitation, crime and consequences.
hydrogen fuel. This type of hydrogen production method is becoming more popular, as it may represent an efficient way to supply the fuel to those that are m
For the study different datasets were considered i.e the Drugs( taken from drug bank and KEGG drugs),Metabolites(HMDB, HumanCYC, BiGG),Toxic( DSSTox, FDA Carcinogeneticity, ITER, Super Tox icity), Natural Products(ZINC NP database),Leads(BIONET, Maybridge),NCI and CHEMBL.From the compounds duplicates entries ,organic ions, metal ions are removed and also corrupted or missing structure are removed. After all the filtering process the data was clustered in Pipleline pilot Clara program using ECFP_4 or FCFP_4 fingerprints. Physicochemical analysis was done using clutering with respect to the Lipinski properties: molecular weight, the number of hydrogen bond acceptors, AlogP (a hydrophobicity measure) and the number of hydrogen bond donors and other descriptors such as the molecular polar surface area, Molecular solubility, number of rings, number of rotatable bonds. A scaffold analysis was also done and also the results are analysed. ...
The Hydrogen Council, a group made up of the CEOs of … leading energy, transport and industry companies, this week released Path to hydrogen competitiveness: A cost perspective. The report carries some big news. Low-carbon hydrogen can become much more cost-competitive, much more quickly, than is generally appreciated. The gloss from the reports Web page is that the cost of hydrogen is projected to decrease by up to 50% by 2030 for a wide range of applications, making hydrogen competitive with other low-carbon alternatives and, in some cases, even conventional options. The report projects that hydrogen viability will be strongest in long-distance and heavy-duty transportation, industrial heating, and heavy industry feedstocks, in all of which the hydrogen route appears the decarbonisation option of choice.. An April 2017 Ammonia Energy article, The Hydrogen Consensus, suggested that key constituencies were coming together around the vision of hydrogen as a mainstay of the sustainable ...
Researchers from the University of Basels Swiss Nanoscience Institute network have reported the results in the journal Science Advances, phys.org wrote.. Hydrogen is the most common element in the universe and is an integral part of almost all organic compounds.. Molecules and sections of macromolecules are connected to one another via hydrogen atoms, an interaction known as hydrogen bonding.. These interactions play an important role in nature, because they are responsible for specific properties of proteins or nucleic acids and, for example, also ensure that water has a high boiling temperature.. To date, it has not been possible to conduct a spectroscopic or electron microscopic analysis of hydrogen and the hydrogen bonds in single molecules, and investigations using atomic force microscopy have also not yielded any clear results.. Dr. Shigeki Kawai, from Professor Ernst Meyers team at the Swiss Nanoscience Institute and the Department of Physics at the University of Basel, has now ...
We synthesized the new supramolecular host molecules 7 and 13 based on functionalized resorcarenes bearing Kemps triacid. Conformations in solution have been investigated and the influence of intra-and intermolecular hydrogen bonds from the triacid was shown by low temperature and DOSY NMR experiments. The results of host 7 are supported by DFT calculations. The binding behaviour of 7 towards different 2-amino pyridincs in chloroform has been investigated by NMR titrations. The association constants reach from K 207 M-1 for 2-amino-5-cyano pyridine to K=1551 M-1 for 2-amino-4-methyl pyridine. The association constants of the formed complexes of 7 with 2-amino pyridines were compared with those of the simple host systems 14 and 15 in order to evaluate the influence of the attached resorcarene host. (c) 2008 Elsevier Ltd. All rights reserved ...
The U.S. Department of Energy has awarded more than $7 million for hydrogen and fuel cell vehicle and infrastructure projects in four states to speed the development of the technology.
Qorianka Kilcher with her new Honda FCX Clarity hydrogen-powered car. Photo: Honda Qorianka Kilcher Gets a New Honda FCX Clarity Hydrogen Car Green actress Qorianka Kilcher, know for her role of Pocahontas, has been driving a first generation Honda
hydrogen fuel cell. The fuel cell is expected to be developed by Hyundai itself and will be more powerful than the fuel cell used in the current model of th
STM image simultaneously acquired for H2O and D2O dimers (size: 5.5×5.5 nm^2, 2.4×2.0 nm^2). The dimer is characterized by the bi-stable fluctuating image. The dimer consists of hydrogen-bond donor and acceptor molecules. The fluctuating image results from the interchange of the donor and acceptor, in which the roles of their molecules are exchanged. Interestingly, the STM image of the dimer shows drastic change upon substitution with D2O. It suggests that the interchange process involves quantum tunneling. The image was obtained at 24 mV sample bias and 0.5 nA tunneling current at 6 K ...
In the long term the key to the development of a hydrogen economy is a full infrastructure to support it, which includes means for the delivery and storage of hydrogen at the point of use, eg at hydrogen refuelling stations for vehicles. As an interim measure to allow the development of refuelling stations and rapid implementation of hydrogen distribution to them, liquid hydrogen is considered the most efficient and cost effective means for transport and storage.. The Health and Safety Executive (HSE) have commissioned the Health and Safety Laboratory (HSL) to identify and address issues relating to bulk liquid hydrogen transport and storage and update/develop guidance for such facilities. The second phase of the project involved experiments on unignited and ignited releases of liquid hydrogen (HSE RR987) and computational modelling of the unignited releases (HSE RR985). This position paper details the experiments performed to investigate spills of unignited liquid hydrogen at a rate of 60 ...
A cryogenic pressure vessel developed and installed in an experimental hybrid vehicle can hold liquid hydrogen for six days without venting any of the fuel.. Unlike conventional liquid hydrogen (LH2) tanks in prototype cars, the pressure vessel developed by the California-based Lawrence Livermore National Laboratory (LLNL) research team was parked for six days without venting evaporated hydrogen vapour.. LH2 tanks hold super-cold liquid hydrogen at around -420oF. Like water boiling in a tea kettle, pressure builds as heat from the environment warms the hydrogen inside. Current automotive LH2 tanks must vent evaporated hydrogen vapour after being parked three to four days, even when using the best thermal insulation available (200 times less conductive than Styrofoam insulation).. In recent testing of its prototype hydrogen tank onboard a liquid hydrogen powered hybrid, LLNLs tank demonstrated a thermal endurance of six days and the potential for as much as 15 days, helping resolve a key ...
Hydrogen definition. Hydrogen atomic number, Hydrogen atomic weight, Hydrogen symbol, define Hydrogen. Explain Hydrogen. What is Hydrogen? Hydrogen FAQ.