Contribution of multicentered short hydrogen bond arrays to potency of active site-directed serine protease inhibitors

We describe and compare the pH dependencies of the potencies and of the bound structures of two inhibitor isosteres that form multicentered short hydrogen bond arrays at the active sites of trypsin, thrombin, and urokinase type plasminogen activator (urokinase or uPA) over certain ranges of pH. Depending on the pH, short hydrogen bond arrays at the active site are mediated by two waters, one in the oxyanion hole (H(2)O(oxy)) and one on the other (S2) side of the inhibitor (H(2)O(S2)), by one water (H(2)O(oxy)), or by no water. The dramatic variation in the length of the active site hydrogen bonds as a function of pH, of inhibitor, and of enzyme, along with the involvement or absence of ordered water, produces a large structural manifold of active site hydrogen bond motifs. Diverse examples of multicentered and two-centered short hydrogen bond arrays, both at and away from the active site, recently discovered in several protein crystal systems, suggest that short hydrogen bonds in proteins may be more common than has been recognized. The short hydrogen bond arrays resemble one another with respect to ionic nature, highly polar environment, multitude of associated ordinary hydrogen bonds, and disparate pK(a) values of participating groups. Comparison of structures and K(i) values of trypsin complexes at pH values where the multicentered short hydrogen bond arrays mediating inhibitor binding are present or absent indicate that these arrays have a minor effect on inhibitor potency. These features suggest little covalent nature within the short hydrogen bonds, despite their extraordinary shortness (as short as 2.0 A).     

含Co或Ni的双金属及三金属纳米颗粒制备方法及其催化制氢性能

常见的氢气储存方法有液态储氢、高压气态储氢、有机化合物储氢、金属氢化物储氢、吸附储氢及液相化学储氢材料储氢等,其中液相化学储氢材料由于具有含氢量高、且可按时即需释放氢气的优点,引起了研究人员的广泛关注;选择合适的催化剂催化液相储氢材料制氢已成为一个研究热点。含有Co或Ni的双金属或三金属纳米颗粒是一种极具应用前景的催化剂,具有价格低廉、储量丰富和催化性能优异等众多优点。本文综述了含Co或Ni的双金属或三金属纳米颗粒的制备方法及其催化制氢性能,并提出了其目前研究中存在的问题和未来潜在的发展方向。     

Pathways of diffusion mixed with subsequent reactions with examples of hydrogen extraction from hydride-forming electrode and oxygen reduction at gas diffusion electrode

This paper covers the role of the rate-determining step (RDS) in anodic hydrogen extraction from hydride-forming electrode. In general, hydrogen extraction from the electrode proceeds through the following steps: (1) hydrogen diffusion within the electrode, (2) hydrogen transfer from absorbed state to adsorbed state, (3) electrochemical oxidation of hydrogen to hydrogen ion involving charge transfer, and (4) hydrogen ion conduction through the electrolyte. In most theoretical and experimental investigations, it has been assumed that the RDS of anodic hydrogen extraction is hydrogen diffusion through the electrode. In real situation, however, the overall rate of hydrogen extraction is simultaneously determined by the rates of two or more reaction steps including hydrogen diffusion. The present work provides the overview of anodic hydrogen extraction in case that diffusion is coupled with interfacial charge transfer, interfacial hydrogen transfer, and hydrogen ion conduction through the electrolyte as well as the purely diffusion-controlled hydrogen extraction. In addition, the mixed controlled diffusion model was also exemplified with oxygen reduction at gas diffusion electrode of fuel cell system.     

Pathways of diffusion mixed with subsequent reactions with examples of hydrogen extraction from hydride-forming electrode and oxygen reduction at gas diffusion electrode

This paper covers the role of the rate-determining step (RDS) in anodic hydrogen extraction from hydride-forming electrode. In general, hydrogen extraction from the electrode proceeds through the following steps: (1) hydrogen diffusion within the electrode, (2) hydrogen transfer from absorbed state to adsorbed state, (3) electrochemical oxidation of hydrogen to hydrogen ion involving charge transfer, and (4) hydrogen ion conduction through the electrolyte. In most theoretical and experimental investigations, it has been assumed that the RDS of anodic hydrogen extraction is hydrogen diffusion through the electrode. In real situation, however, the overall rate of hydrogen extraction is simultaneously determined by the rates of two or more reaction steps including hydrogen diffusion. The present work provides the overview of anodic hydrogen extraction in case that diffusion is coupled with interfacial charge transfer, interfacial hydrogen transfer, and hydrogen ion conduction through the electrolyte as well as the purely diffusion-controlled hydrogen extraction. In addition, the mixed controlled diffusion model was also exemplified with oxygen reduction at gas diffusion electrode of fuel cell system.

     

Hydrogen desorption exceeding ten weight percent from the new quaternary hydride Li3BN2H8

Mobile applications of hydrogen power have long demanded new solid hydride materials with large hydrogen storage capacities. We report synthesis of a new quaternary hydride having the approximate composition Li(3)BN(2)H(8) with 11.9 wt % theoretical hydrogen capacity. It forms by reacting LiNH(2) and LiBH(4) powders in a 2:1 molar ratio either by ball milling or by heating the mixed powders above 95 degrees C. This new quaternary hydride melts at approximately 190 degrees C and releases > or =10 wt % hydrogen above approximately 250 degrees C. A small amount of ammonia (2-3 mol % of the generated gas) is released simultaneously. Preliminary calorimetric measurements suggest that hydrogen release is exothermic and, hence, not easily reversible.     

Tantalum(V) or niobium(V) catalyzed oxidation of sulfides with 30% hydrogen peroxide

Tantalum(V) and niobium(V) are effective catalysts for the oxidation of sulfides with 30% hydrogen peroxide. The reaction of sulfides with 30% hydrogen peroxide catalyzed by tantalum(V) chloride or niobium(V) chloride in acetonitrile, i-propanol or t-butanol selectively provided the corresponding sulfoxides in high yields. The corresponding sulfones are efficiently obtained from the reaction of sulfides with 30% hydrogen peroxide in methanol catalyzed by tantalum(V) or niobium(V).     

Molecular complexes of the hydrogen halides studied by matrix isolation infrared spectroscopy

Spectroscopic studies of base—hydrogen halide complexes are reviewed, including previously unpublished data for complexes of hydrogen chloride and hydrogen bromide with a variety of bases in argon matrices. The variation of the HX stretching relative frequency shift with the hydrogen halide and with the medium (gas phase, argon matrix or nitrogen matrix) and correlations of the HX stretching and hydrogen bond bending frequencies with the proton affinity of the base and with the hydrogen bond stretching force constant or dissociation energy of the complex are discussed.     

Kinetics of hydrogen production upon reduction of aqueous TiO2 nanoparticles catalyzed by Pd(0), Pt(0), or Au(0) coatings and an unusual hydrogen abstraction; steady state and pulse radiolysis study

Reduction of H(+) by TiO(2) electrons (e(TiO)(2)(-)) in aqueous colloidal solution takes place in the presence of surface metal catalysts. The catalytic reduction gives rise to adsorbed hydrogen atoms. In the presence of Pd(0) or Pt(0), material balance shows that most of the adsorbed H atoms combine to molecular hydrogen. When the TiO(2) nanoparticles are partially coated with Au(0) instead of Pd(0) or Pt(0), a higher than expected molecular hydrogen level is observed, attributed to a short chain reaction involving hydrogen abstraction from 2-propanol. This unusual hydrogen abstraction reaction has not been reported before. The mechanism and energy balance are discussed. The surface modification of TiO(2) nanoparticles was carried out by reduction of K(2)PdCl(4), H(2)PtCl(6), or HAuCl(4) with e(TiO)(2)(-). The latter had been generated through electron injection from hydrated electrons, hydrogen atoms, or 2-propanol radicals, produced by gamma or pulse radiolysis prior to the addition of the metal compounds. Upon addition of the metal compounds, immediate reactions take place producing metals clusters (M(0)) by multistep reductions reactions on the TiO(2) surface. The chemical kinetics involving the different metals and the reaction rate constant of e(aq)(-) and e(TiO)(2)(-) with AuCl(4)(-) is also reported.     

Structures and energetics of hydrated oxygen anion clusters

Hydration of the atomic oxygen radical anion is studied with computational electronic structure methods, considering (O(-))(H(2)O)(n) clusters and related proton-transferred (OH(-))(OH)(H(2)O)(n)(-)(1) clusters having n = 1-5. A total of 67 distinct local-minimum structures having various interesting hydrogen bonding motifs are obtained and analyzed. On the basis of the most stable form of each type, (O(-))(H(2)O)(n)) clusters are energetically favored, although for n > or = 3, there is considerable overlap in energy between other members of the (O(-))(H(2)O)(n) family and various members of the (OH(-))(OH)(H(2)O)(n)(-)(1) family. In the lower-energy (O(-))(H(2)O)(n) clusters, the hydrogen bonding arrangement about the oxygen anion center tends to be planar, leaving the oxygen anion p-like orbital containing the unpaired electron uninvolved in hydrogen bonding with any water molecule. In (OH(-))(OH)(H(2)O)(n)(-)(1) clusters, on the other hand, nonplanar arrangements are the rule about the anionic oxygen center that accepts hydrogen bonds. No instances are found of OH(-) acting as a hydrogen bond donor. Those OH bonds that form hydrogen bonds to an anionic O(-) or OH(-) center are significantly stretched from their equilibrium value in isolated water or hydroxyl. A quantitative inverse correlation is established for all hydrogen bonds between the amount of the OH bond stretch and the distance to the other oxygen involved in the hydrogen bond.     

Mechanistic aspects of transition metal-catalyzed hydrogen transfer reactions

In this tutorial review recent mechanistic studies on transition metal-catalyzed hydrogen transfer reactions are discussed. A common feature of these reactions is that they involve metal hydrides, which may be monohydrides or dihydrides. An important question is whether the substrate coordinates to the metal (inner-sphere hydrogen transfer) or if there is a direct concerted transfer of hydrogen from the metal to substrate (outer-sphere hydrogen transfer). Both experimental and theoretical studies are reviewed.     

多壁碳纳米管储氢的物理吸附特性

The physisorption of hydrogen stored in armchair multi-walled carbon nanotubes (MWCNTs) is simulated by the grand canonical Monte Carlo (GCMC) method on the condition of 10 MPa at normalt emperature. Hydrogen-hydrogen and hydrogen-carbon interactions are both modeled with Lennard-Jones potential. The hydrogen storage in double-walled carbon-nanotubes (DWCNTs) has been investigated on the condition that the internal or external radius is changed while the other radius remains constant. The results show that hydrogen molecules are mostly absorbed near the tube walls, and the hydrogens to rage capacityisim proved effectively when the difference between the internal radius and the external radius increases from 0.34 to 0.61 or 0.88 nm. Its simple theoretic explanation also is given. Further more, the capacity of hydrogen physisorbed in there-walled carbon nanotubes (TWCNTs) is calculated when the wall-wall distance is 0.34, 0.61 and 0.88 nm respectively. Then its hydrogen storage capacity is compared with that of single-walled carbon nanotubes (SWCNTs) and DWCNTs, and it is discovered that the capacity of hydrogen physisorbed in MWCNTs decreases as the number of wall increases.     

Multidimensional infrared spectroscopy of water. II. Hydrogen bond switching dynamics

We use multidimensional infrared spectroscopy of the OH stretch of HOD in D2O to measure the interconversion of different hydrogen bonding environments. The OH stretching frequency distinguishes hydrogen bonded (HB) and non-hydrogen-bonded (NHB) configurations by their absorption on the low (red) and high (blue) sides of the line shape. Measured asymmetries in the two dimensional infrared OH line shapes are manifestations of the fundamentally different spectral relaxations of HB and NHB. HB oscillators exhibit coherent oscillations within the hydrogen-bonded free energy well before undergoing activated barrier crossing, resulting in the exchange of hydrogen bonded partners. Conversely, NHB oscillators rapidly return to HB frequencies within 150 fs. These results support a picture where NHB configurations are only visited transiently during large fluctuations about a hydrogen bond or during the switching of hydrogen bonding partners. The results are not consistent with the presence of entropically stabilized dangling hydrogen bonds or a conceptual picture of water as a mixture of environments with varying hydrogen bond strength separated by barriers >kT.     

化学制氢技术研究进展

本文综述了化学制氢技术的新近研究进展.氢能作为一种很有应用前景的载能体,已得到越来越广泛的研究和应用.在化学制氢、电解水制氢、生物制氢这三种制氢模式中,化学制氢仍是近期主要的制氢方式,其中催化重整制氢仍然是大规模制氢的主流.随着燃料电池这一环境友好的发电方式在技术上的不断突破,诸如生物质制氢、金属置换制氢、太阳能制氢、金属氢化物制氢等许多其他的化学制氢技术得到了迅速的发展,并将伴随着燃料电池、氢燃料发动机等技术的发展和应用,一同步入氢能时代.     

Supramolecular Assembly: A Comparative Structural Study of the Incorporation of Bis(2-guanidinobenzimidazolo)nickel(II) into Supramolecular Arrays

The structural effects of incorporating a non-planar neutral metal complex, bis(2-guanidinobenzimidazolo)nickel(II), into three supramolecular arrays are described. The complex has a donor-acceptor-donor (DAD) hydrogen bonding motif on each ligand and this motif is used to link it to bis(biureto)nickelate(II) ions, or to 1,8-naphthalimide or phthalimide molecules, all of which incorporate a complementary acceptor-donor-acceptor (ADA) hydrogen bonding motif. The geometry about the metal ion as well as the nature of the network of hydrogen bonds formed have significant influences on the supramolecular structure adopted. An interesting combination of intramolecular hydrogen bonding and close ~ -stacking interactions also occur in each species.     

Hydrogen bonding interactions in α-substituted cinnamic acid ester derivatives studied by FT–IR spectroscopy and calculations

Intermolecular hydrogen bonding interactions in stereoisomeric α-substituted cinnamic acid methyl esters (methyl 2,3-diphenylpropenoate, methyl 2-phenyl-3-(2′-methoxyphenyl)-propenoate, methyl 2-(2′-methoxyphenyl)-3-phenylpropenoate and methyl-2,3-bis(2′-methoxyphenyl)-propenoate) were studied by FT–IR spectroscopy and model calculations at the semi-empirical quantum chemical level of theory. Intermolecular hydrogen bonds of C–H…O types were found to be general in the solid state, but rare in solution. In this hydrogen bond the carbon may be part of either aromatic ring or the olefinic bond. The hydrogen bond acceptor may be the carbonyl oxygen or the oxygen in the methoxy substituent. Modeling helped in determining probable hydrogen bonding sites and their positions and provided with approximate geometric parameters (bond lengths and angles). Pointing out differences between the stereoisomers was also possible.     

L'hydrogene pour le transport sur route : réalisations et développements

Hydrogen for road transportation : achievements and developments. At the beginning of this millenium, hydrogen appears as a potential energy carrier for the future. Thus, it could serve as a storage medium for renewable energy forms, which should play an increasing part in the world energy supply. In a closer future, hydrogen could also become a fuel for prospective fuel-cell and internal-combustion vehicles. We present here an inventory of the various technologies related to the use of hydrogen in road transportation : propulsion type (fuel cell and electric motor, or internal combustion engine), hydrogen production, on-board storage, infrastructure. Safety, standardization and regulation aspects will also be addressed. Presently, the majority of hydrogen buses are equipped with polymer membrane fuel cells (PEMFC), directly supplied with hydrogen from pressurized vessels (300 bars). On the other hand, car manufacturers are developing various types of experimental vehicles : internal-combustion engine cars with liquid hydrogen storage, fuel cell (PEMFC) cars with storage of hydrogen (liquid, gaseous, hydride) or of methanol. The type of required infrastructured will depend on the type of fuel chosen by the car makers and on the requirements of the oil companies. Several hydrogen supply stations, of different technologies, have already been set up. They deliver gaseous or liquid hydrogen produced by reforming of natural gas or by electrolysis. The building of a hydrogen-based fueling system requires the development of specific means of production, transportation, storage and delivery. Public acceptance will have to be won by guaranteeing safety, reliability, performance and competitivity. Presently, research and development work is mainly carried out on : on-board storage of hydrogen ; on-board systems for the production of hydrogen from methanol and petrol ; standardization and regulation.     

Catalysis by heteropolyacid—VII. catalytic oxidation of cyclohexanol by dodecamolybdate

In the oxidation of cyclohexanol to cyclohexanone and the further oxidation to adipic acid, a dodecamolybdo-heteropolyanion (HPA) functions catalytically in the presence of aqueous hydrogen peroxide, whereas the HPA without hydrogen peroxide reacts only stoichiometrically. Air- or oxygen-passing through the refluxing system of cyclohexanone and the HPA in the presence of active charcoal, without hydrogen peroxide, has also promoted the oxidation catalytically. Since both hydrogen peroxide and aeration in the presence of active charcoal convert the reduced-form (blue) of the HPA produced by the oxidation of substrate to the oxidized-form (yellow), they play a role as a promoter or a reoxidizing reagent for the oxidation by the HPA. The reoxidizing effect of the aqueous hydrogen peroxide is much the more effective.     

A counter-intuitive approach to calculating non-exchangeable 2H isotopic composition of hair: treating the molar exchange fraction fE as a process-related rather than compound-specific variable

Hair is a keratinous tissue that incorporates hydrogen from material that an animal consumes but it is metabolically inert following synthesis. The stable hydrogen isotope composition of hair has been used in ecological studies to track migrations of mammals as well as for forensic and archaeological purposes to determine the provenance of human remains or the recent geographic life trajectory of living people. Measurement of the total hydrogen isotopic composition of a hair sample yields a composite value comprised of both metabolically informative, non-exchangeable hydrogen and exchangeable hydrogen, with the latter reflecting ambient or sample preparation conditions. Neither of these attributes is directly measurable, and the non-exchangeable hydrogen composition is obtained by estimation using a commonly applied mathematical expression incorporating sample measurements obtained from two distinct equilibration procedures. This commonly used approach treats the fraction of exchangeable hydrogen as a mixing ratio, with a minimal procedural fractionation factor assumed to be close or equal to 1. Instead, we propose to use full molar ratios to derive an expression for the non-exchangeable hydrogen composition explicitly as a function of both the procedural fractionation factor α and the molar hydrogen exchange fraction f(E). We apply these derivations in a longitudinal study of a hair sample and demonstrate that the molar hydrogen exchange fraction f(E) should, like the procedural fractionation factor α, be treated as a process-dependent parameter, i.e. a reaction-specific constant. This is a counter-intuitive notion given that maximum theoretical values for the molar hydrogen exchange fraction f(E) can be calculated that are arguably protein-type specific and, as such, f(E) could be regarded as a compound-specific constant. We also make some additional suggestions for future approaches to determine the non-exchangeable hydrogen composition of hair and the use of standards.     

Separation behaviors of xylenol isomers by gas chromatography with helps of hydrogen bonding

Summary Xylenol isomers can be resolved on most polyols (sugars or sugar alcohols) and polyethers (polyethylene glycol or polypropylene glycol) with hydrogen-bonding interaction. They are separated on vinical polyols which have more hydroxy hydrogen than tetrol, and even on vicinal triol when its hydroxy hydrogen is acidic (stronger proton donor). The stronger is the hydrogen bonding interaction between xylenols and the liquid phase, the better is the separation of 2,4- and 2,5-xylenol, and the poorer the separation of 2,4-and 2,3-xylenol.     

多壁碳纳米管的改性及其储氢性能研究

考察了空气处理、混酸处理、H₂O₂处理和等离子体活化等化学改性和多种活性金属修饰对碳纳米管储氢性能的影响,采用TPD-H₂评价装置测试了不同样品吸附的氢气在程序升温后的脱附情况,用峰面积和氢气的校正因子计算出样品吸附氢气的体积,从而计算出碳纳米管的储氢容量.实验结果表明,化学改性和金属修饰均能明显提高碳纳米管的储氢性能,其中经过混合酸和H₂O₂化学处理并负载质量分数为20%Ni的碳纳米管,在常温常压下的氢气储存的质量分数达到2.55%,比未做任何处理的碳纳米管的储氢容量提高了7倍.