Search

Boron functional groups are often introduced in place of aromatic carbon-hydrogen bonds to expedite small-molecule diversification through coupling of molecular fragments.sup.1-3. Current approaches based on transition-metal-catalysed activation of carbon-hydrogen bonds are effective for the borylation of many (hetero)aromatic derivatives.sup.4,5 but show narrow applicability to azines (nitrogen-containing aromatic heterocycles), which are key components of many pharmaceutical and agrochemical products.sup.6. Here we report an azine borylation strategy using stable and inexpensive amine-borane.sup.7 reagents. Photocatalysis converts these low-molecular-weight materials into highly reactive boryl radicals.sup.8 that undergo efficient addition to azine building blocks. This reactivity provides a mechanistically alternative tactic for sp.sup.2 carbon-boron bond assembly, where the elementary steps of transition-metal-mediated carbon-hydrogen bond activation and reductive elimination from azine-organometallic intermediates are replaced by a direct, Minisci.sup.9-style, radical addition. The strongly nucleophilic character of the amine-boryl radicals enables predictable and site-selective carbon-boron bond formation by targeting the azine's most activated position, including the challenging sites adjacent to the basic nitrogen atom. This approach enables access to aromatic sites that elude current strategies based on carbon-hydrogen bond activation, and has led to borylated materials that would otherwise be difficult to prepare. We have applied this process to the introduction of amine-borane functionalities to complex and industrially relevant products. The diversification of the borylated azine products by mainstream cross-coupling technologies establishes aromatic amino-boranes as a powerful class of building blocks for chemical synthesis. Selective borylation of azines--nitrogen-containing aromatic heterocycles used in the synthesis of many pharmaceuticals--is made possible by forming a radical from an aminoborane using a photocatalyst., Author(s): Ji Hye Kim [sup.1] , Timothée Constantin [sup.1] , Marco Simonetti [sup.1] , Josep Llaveria [sup.2] , Nadeem S. Sheikh [sup.3] , Daniele Leonori [sup.1] Author Affiliations: (1) Department [...]

We recorded the Raman spectra of NodaxTM (PHBHx-copolymer of hydroxybutyrate) biopolymer class with varying amounts of comonomer hydroxyhexanoate (Hx). The properties of Nodax is controlled by the amount of Hx added. Engineering the polymer for specific applications requires understanding the effects of Hx on the physical and chemical properties, and vibrational spectra provide a window on this information. Inspection of the structure of PHBHx indicates that the addition of Hx only replaces the methyl group with a propyl group on the hydroxyhexanoate segments of the polymer chains. To utilize the vibrational spectra to aid in the prediction of properties, the bands associated with these extra groups should be identified. The spectra shown here were acquired from polymers dissolved in deuterated chloroform; the carbon--hydrogen band of the solvent that would normally overlap with the spectrum of the polymer is replaced by a carbon-deuterium (CD) stretch in a region in which nothing else occurs. In solution, the spectra of the polymers exhibit the noncrystalline disordered phase and can be used to evaluate the contributions of the various functional groups., The polymers discussed here were originally engineered by Professor Isao Noda during his career at Proctor & Gamble (P&G). The goal was to engineer a class of polymers that would [...]

Author(s): Valentin V. Karasiev [sup.1] , Joshua Hinz [sup.1] , S. X. Hu [sup.1] , S. B. Trickey [sup.2] Author Affiliations: (1) Laboratory for Laser Energetics, University of Rochester, Rochester, [...]

Direct C-H functionalization can quickly increase useful structural and functional molecular complexity.sup.1-3. Site selectivity can sometimes be achieved through appropriate directing groups or substitution patterns.sup.1-4--in the absence of such functionality, most aromatic C-H functionalization reactions provide more than one product isomer for most substrates.sup.1,4,5. Development of a C-H functionalization reaction that proceeds with high positional selectivity and installs a functional group that can serve as a synthetic linchpin for further functionalization would provide access to a large variety of well-defined arene derivatives. Here we report a highly selective aromatic C-H functionalization reaction that does not require a particular directing group or substitution pattern to achieve selectivity, and provides functionalized arenes that can participate in various transformations. We introduce a persistent sulfur-based radical to functionalize complex arenes with high selectivity and obtain thianthrenium salts that are ready to engage in different transformations, via both transition-metal and photoredox catalysis. This transformation differs fundamentally from all previous aromatic C-H functionalization reactions in that it provides direct access to a large number of derivatives of complex small molecules, quickly generating functional diversity with selectivity that is not achievable by other methods. A highly site-selective aromatic C-H functionalization reaction that does not require a particular directing group or arene substitution pattern provides functionalized arenes that can participate in various transformations., Author(s): Florian Berger [sup.1] , Matthew B. Plutschack [sup.1] , Julian Riegger [sup.1] , Wanwan Yu [sup.1] , Samira Speicher [sup.1] , Matthew Ho [sup.1] , Nils Frank [sup.1] , [...]

In 1906, Theodore Lyman discovered his eponymous series of transitions in the extreme-ultraviolet region of the atomic hydrogen spectrum.sup.1,2. The patterns in the hydrogen spectrum helped to establish the emerging theory of quantum mechanics, which we now know governs the world at the atomic scale. Since then, studies involving the Lyman-[alpha] line--the 1S-2P transition at a wavelength of 121.6 nanometres--have played an important part in physics and astronomy, as one of the most fundamental atomic transitions in the Universe. For example, this transition has long been used by astronomers studying the intergalactic medium and testing cosmological models via the so-called 'Lyman-[alpha] forest'.sup.3 of absorption lines at different redshifts. Here we report the observation of the Lyman-[alpha] transition in the antihydrogen atom, the antimatter counterpart of hydrogen. Using narrow-line-width, nanosecond-pulsed laser radiation, the 1S-2P transition was excited in magnetically trapped antihydrogen. The transition frequency at a field of 1.033 tesla was determined to be 2,466,051.7 [plus or minus] 0.12 gigahertz (1[sigma] uncertainty) and agrees with the prediction for hydrogen to a precision of 5 × 10.sup.-8. Comparisons of the properties of antihydrogen with those of its well-studied matter equivalent allow precision tests of fundamental symmetries between matter and antimatter. Alongside the ground-state hyperfine.sup.4,5 and 1S-2S transitions.sup.6,7 recently observed in antihydrogen, the Lyman-[alpha] transition will permit laser cooling of antihydrogen.sup.8,9, thus providing a cold and dense sample of anti-atoms for precision spectroscopy and gravity measurements.sup.10. In addition to the observation of this fundamental transition, this work represents both a decisive technological step towards laser cooling of antihydrogen, and the extension of antimatter spectroscopy to quantum states possessing orbital angular momentum.The observation of the 1S-2P Lyman-[alpha] transition in the antihydrogen atom, the antimatter counterpart of hydrogen, is reported., Author(s): M. Ahmadi [sup.1] , B. X. R. Alves [sup.2] , C. J. Baker [sup.3] , W. Bertsche [sup.4] [sup.5] , A. Capra [sup.6] , C. Carruth [sup.7] , C. [...]

Author(s): Kumiko Yamamoto [1, 2]; Jiakun Li [1]; Jeffrey A. O. Garber [1, 2]; Julian D. Rolfes [1, 2]; Gregory B. Boursalian [1, 2]; Jannik C. Borghs [2]; Christophe Genicot [...]

In the problem of the production silver nanoparticles, mass spectrometry allows one to identify nanoclusters as nuclei or intermediates in the synthesis of nanoparticles and to understand the mechanisms of their formation. Using low-temperature secondary emission mass spectrometry, we determined the cluster composition of a system formed in the microwave treatment of a solution of AgN[O.sub.3] in ethylene glycol (M). Along with silver ion-ethylene glycol associates [M.sub.m] x [Ag.sup.+] (m = 1-5) and small silver clusters [Ag.sup.+.sub.n] (n = 1-9), unusual silver clusters with one hydrogen atom [[[Ag.sub.n] H].sup.+] (n = 2, 4) were observed. Possible pathways for the formation of silver nanoparticles taking into account hydrogen-containing cluster intermediates are discussed. Keywords: low-temperature secondary emission mass spectrometry, silver nanoclusters, ethylene glycol DOI:10.1134/S1061934817130032, INTRODUCTION The development and improvement of methods for the synthesis of silver nanoparticles as a material useful for various engineering, pharmacological, biomedical, and environmental applications [1-7] remain to be one [...]

The effect of hydrogen on the electrooxidation current of a palladium--hydrogen precipitate is studied. It is shown that the UV irradiation of the solution changes the mechanism of the formation of molecular hydrogen in the electrochemical deposition of palladium. A procedure is developed for determining palladium in platinum metal preconcentrates by stripping voltammetry. Keywords: electrooxidation, hydrogen absorption, palladium--hydrogen binary precipitate, Stripping voltammetry has long been used to determine palladium in mineral raw materials and products of its processing [1]. When palladium is determined by stripping voltammetry, palladium is electrochemically preconcentrated [...]

Author(s): Jin Liu [1]; Qingyang Hu [1, 2]; Duck Young Kim [2]; Zhongqing Wu [3]; Wenzhong Wang [3]; Yuming Xiao [4]; Paul Chow [4]; Yue Meng [4]; Vitali B. Prakapenka [...]

Author(s): Waiz Karim [1, 2, 3]; Clelia Spreafico [4]; Armin Kleibert [5]; Jens Gobrecht [2]; Joost VandeVondele [4]; Yasin Ekinci (corresponding author) [2]; Jeroen A. van Bokhoven (corresponding author) [1, [...]

Abstract: The non-monotonic behavior of the electron repulsion energy and the inter-electronic distance, as a function of the internuclear separation, in the [.sup.3[product].sub.u] excited state of the hydrogen molecule has [...]

Abstract: To improve the certainty that a specific small organic molecule has been detected in a given sample by high-resolution mass spectrometry, other techniques that give conclusive evidence about the [...]

Switching of static friction and adhesion of a liquid drop on a corrugated solid boron nitride surface is linked to the intercalation of hydrogen, which changes the electric field of in-plane dipole rings and thus reduces the adsorption energy. Stiction versus adhesion in a single liquid drop Stiction, or static friction, is the force required to persuade an object to start sliding across a surface. It is technologically important in devices with moving parts in contact, but is not well understood. Stijn Mertens et al. describe an inorganic model system for the study of the relationships between surface wetting, stiction, adhesion and lubrication. The system is a hexagonal boron nitride monolayer that can be electrochemically switched by intercalation of hydrogen between a corrugated and a flat morphology. The change in the surface structure of the boron nitride alters the adhesion and its balance with stiction of an aqueous drop sliding across the monolayer. The work of adhesion increases in going from the flat to the corrugated surface, whereas the stiction threshold does not change significantly. Thus the authors make a quantitative connection between the macroscopic properties of stiction and adhesion as a result of structural control at the atomic scale. When a gecko moves on a ceiling it makes use of adhesion and stiction. Stiction--static friction--is experienced on microscopic and macroscopic scales and is related to adhesion and sliding friction.sup.1. Although important for most locomotive processes, the concepts of adhesion, stiction and sliding friction are often only empirically correlated. A more detailed understanding of these concepts will, for example, help to improve the design of increasingly smaller devices such as micro- and nanoelectromechanical switches.sup.2. Here we show how stiction and adhesion are related for a liquid drop on a hexagonal boron nitride monolayer on rhodium.sup.3, by measuring dynamic contact angles in two distinct states of the solid-liquid interface: a corrugated state in the absence of hydrogen intercalation and an intercalation-induced flat state. Stiction and adhesion can be reversibly switched by applying different electrochemical potentials to the sample, causing atomic hydrogen to be intercalated or not. We ascribe the change in adhesion to a change in lateral electric field of in-plane two-nanometre dipole rings.sup.4, because it cannot be explained by the change in surface roughness known from the Wenzel model.sup.5. Although the change in adhesion can be calculated for the system we study.sup.6, it is not yet possible to determine the stiction at such a solid-liquid interface using ab initio methods. The inorganic hybrid of hexagonal boron nitride and rhodium is very stable and represents a new class of switchable surfaces with the potential for application in the study of adhesion, friction and lubrication., Author(s): Stijn F. L. Mertens [sup.1] [sup.2] , Adrian Hemmi [sup.3] , Stefan Muff [sup.3] , Oliver Gröning [sup.4] , Steven De Feyter [sup.1] , Jürg Osterwalder [sup.3] , Thomas [...]

Phthaloyl peroxide functions as a selective oxidant of C-H bonds in the transformation of arenes to phenols under mild conditions, in a reaction that is compatible with a wide array of functional groups. Phenol synthesis without the fuss The selective oxidation of the C-H bond is central to synthetic organic chemistry, both by producing the target functional molecule and in 'build-up' molecules on more complex syntheses. Here Dionicio Siegel and colleagues use computational analysis to develop a new method of transforming arenes to phenols that requires much milder conditions than most established routes. They use phthaloyl peroxide as a selective oxidant in a reaction that does not require a metal catalyst, is entropically favourable and has high tolerance for a variety of different functional groups. Methods for carbon-hydrogen (C-H) bond oxidation have a fundamental role in synthetic organic chemistry, providing functionality that is required in the final target molecule or facilitating subsequent chemical transformations. Several approaches to oxidizing aliphatic C-H bonds have been described, drastically simplifying the synthesis of complex molecules.sup.1,2,3,4,5,6. However, the selective oxidation of aromatic C-H bonds under mild conditions, especially in the context of substituted arenes with diverse functional groups, remains a challenge. The direct hydroxylation of arenes was initially achieved through the use of strong Brønsted or Lewis acids to mediate electrophilic aromatic substitution reactions with super-stoichiometric equivalents of oxidants, significantly limiting the scope of the reaction.sup.7. Because the products of these reactions are more reactive than the starting materials, over-oxidation is frequently a competitive process. Transition-metal-catalysed C-H oxidation of arenes with or without directing groups has been developed, improving on the acid-mediated process; however, precious metals are required.sup.8,9,10,11,12,13. Here we demonstrate that phthaloyl peroxide functions as a selective oxidant for the transformation of arenes to phenols under mild conditions. Although the reaction proceeds through a radical mechanism, aromatic C-H bonds are selectively oxidized in preference to activated [Formula omitted]-H bonds. Notably, a wide array of functional groups are compatible with this reaction, and this method is therefore well suited for late-stage transformations of advanced synthetic intermediates. Quantum mechanical calculations indicate that this transformation proceeds through a novel addition-abstraction mechanism, a kind of 'reverse-rebound' mechanism as distinct from the common oxygen-rebound mechanism observed for metal-oxo oxidants. These calculations also identify the origins of the experimentally observed aryl selectivity., Author(s): Changxia Yuan [sup.1] , Yong Liang [sup.2] , Taylor Hernandez [sup.1] , Adrian Berriochoa [sup.1] , Kendall N. Houk [sup.2] , Dionicio Siegel [sup.1] Author Affiliations: (1) Department of [...]

Density functional theory (DFT) calculations have been performed to investigate Ti adsorption on B[C.sub.2]N nanotubes and the hydrogen adsorption capacity of Ti-coated structures. Different adsorption sites have been examined for the Ti adatom, and it is found that the most stable structure has a configuration with alternating columns of carbon and boron-nitrogen hexagons. The DFT calculations indicate that an adsorbed Ti atom on a carbon hexagon can bind four hydrogen molecules in molecular form, while Ti atoms on boron-nitride hexagons can adsorb three hydrogen molecules and two hydrogen atoms. Based on the calculations, the gravimetric efficiency corresponding to decoration of 67% of six carbon rings with Ti adatoms is estimated to be 8 wt %. Computation of the charge transfer reveals that the Ti atom on B[C.sub.2]N is in a cationic state. In addition, Ti adsorption has a significant influence on the electronic structure of the nanotubes and allows for the conversion of nanotubes from semiconductors in the pristine state to conductors upon doping. The interactions between the nanotubes, the Ti atom and hydrogen molecules have also been analyzed using Dewar coordination and Kubas interactions. Key words: hydrogen storage, metal-nanotube interaction, B[C.sub.2]N nanotube, density of states, Dewar coordination, Kubas interaction. Resume : On a fait appel a des calculs selon la theorie de la fonctionnelle de la densite (TFD) pour etudier l'adsorption du Ti sur des nanotubes de B[C.sub.2]N et la capacite d'adsorption de l'hydrogene par les structures recouvertes de Ti. On a examine les divers sites d'adsorption pour l'adatome de Ti et on a trouve que la structure la plus stable possede une configuration comportant des colonnes alternantes de carbones et d'hexagones de bore-azote. Les calculs selon la TFD indiquent qu'un atome de Ti adsorbe sur un hexagone de carbone peut se lier a quatre molecules d'hydrogenes pour donner une forme moleculaire alors que les atomes de Ti sur les hexagones de bore-azoture peuvent absorber trois molecules d'hydrogene et deux atomes d'hydrogene. Sur la base de ces calculs, on a evalue que l'efficacite gravimetrique correspondant a la decoration de 67% des six cycles carbones avec des adatomes de Ti est egale a 8% en poids. Des calculs de transfert de charge revelent que l'atome de Ti du B[C.sub.2]N est dans un etat cationique. De plus l'adsorption du Ti a une influence significative sur la structure electronique des nanotubes et elle permet la conversion de nanotubes de semiconducteurs a l'etat pur a conducteur apres dopage. Les interactions entre les nanotubes, l'atome de Ti et les molecules d'hydrogene ont aussi ete analysees a l'aide de la coordination de Dewar et des interactions de Kubas. [Traduit par la Redaction] Mots-cles : emmagasinage de l'hydrogene, interaction metal-nanotube, nanotube de B[C.sub.2]N, etats de densite, coordination de Dewar, interaction de Kubas., Introduction Recent advances in materials science have led to a rapid expansion of research and development in the discovery of novel materials for a sustainable and affordable energy future. Since [...]

In today's automotive industry, the goal to lower C[O.sub.2] emissions is the driving force in material development in a wide range of applications. This ecological stimulus is also influencing the [...]

The application of electron-transfer dissociation (ETD) to obtain single-residue resolution in hydrogen exchange-mass spectrometry (HX-MS) experiments has recently been demonstrated. For such measurements, it is critical to ensure that the level of gas-phase hydrogen scrambling is negligible. Here we utilize the abundant loss of ammonia upon ETD of peptide ions as a universal reporter of positional randomization of the exchangeable hydrogens (hydrogen scrambling) during HX-ETD experiments. We show that the loss of ammonia from peptide ions proceeds without depletion of deuterium when employing optimized mild electrospray ion source settings for the HX-ETD analysis of a selectively labeled model peptide and peptides derived from fully labeled [beta]-microglobulin. Hydrogen scrambling, as induced by excessive vibrational excitation of peptide ions during harsh declustering conditions, is easily detected by a depletion of deuterium when deuterated ammonia is lost from peptides during ETD. This straightforward method requires no modifications to the experimental workflow and has the great advantage that the occurrence of hydrogen scrambling can be directly detected in the actual peptides analyzed in the HX-ETD experiment. 10.1021/ac101889b

Theoretical study of the stereo-dynamics of the reaction, H + [HeH.sup.+] (v = 0, j = 0) → [H.sup.+.sub.2] + He, have been performed with quasi-classical trajectory (QCT) method at different collision energies on a new ab initio potential energy surface. The distributions of P([θ.sub.r]), P([θ.sub.r]) and four generalized polarization-dependent differential cross-sections have been calculated. The results indicate that both the orientation and alignment of the rotational angular momentum are impacted by collision energies. With the collision energy increases, the rotation of the product molecule has a preference of changing from the 'in-plane' reaction mechanism to the 'out-of-plane' mechanism. Although the reaction is mainly dominated by the direct reaction mechanism, the indirect mechanism plays a role while the collision energy is very low. PACS No: 34.10.+X Nous avons fait une etude de la dynamique tridimensionnelle de la reaction H + [HeH.sup.+] (v = 0, j = 0) → [H.sup.+.sub.2] + He, a l'aide de la meethode des quasi-trajectoires (QCT) a diffeerentes energies de collision sur une nouvelle surface d'energie obtenue ab initio. Nous avons calcule; les distributions P([θ.sub.r]), P([φ.sub.r]) et quatre sections efficaces diffeerentielles geeneralisees dependant de la polarisation. Les resultats indiquent que les deux orientations et l'alignement du moment angulaire de rotation sont affectes par l'energie des collisions. Lorsque l'energie de la collision augmente, la rotation de la molecule produite a le choix de passer du mecanisme dans le plan au mecanisme hors plan. Meme si la reaction est majoritairement dominee par le mecanisme de reaction directe, le mecanisme indirect joue un role lorsque l'energie est tres basse. [Traduit par la Redaction], 1. Introduction In recent decades, the reaction of He + [H.sup.+.sub.2] has received considerable attention for its importance in the studies of ion-molecule reaction dynamics [1-11]. In 2000, Aquilanti et [...]

Swirling flows are widely used in industrial burners and gas turbine combustors for flame stabilization. Several prior studies have shown that these flames exhibit complex dynamics under near blowoff conditions, associated with local flamelet extinction and alteration in the vortex breakdown flow structure. These extinction events are apparently due to the local strain rate irregularly oscillating above and below the extinction strain rate values near the attachment point. In this work, global temporally resolved and detailed spatial measurements were obtained of hydrogen/methane flames. Supporting calculations of extinction strain rates were also performed using detailed kinetics. It is shown that flames become unsteady (or local extinctions happen) at a nearly constant extinction strain rate for different hydrogen/methane mixtures. Based upon analysis of these results, it is suggested that classic Damkohler number correlations of blowoff are, in fact, correlations for the onset of local extinction events, not blowoff itself Corresponding Mie scattering imaging of near blowoff flames also was used to characterize the spatio-temporal dynamics of holes along the flame that are associated with local extinction. [DOI: 10.1115/1.4000601] Keywords: swirling, hydrogen, lean blowout

Amide hydrogen/deuterium exchange (HDX) rate constants of bovine ubiquitin in an ammonium acetate solution containing 1% of the electrospray ionization (ES1) 'supercharging' reagent m-nitrobenzyl alcohol (m-NBA) were obtained using top-down, electron transfer dissociation (ETD) tandem mass spectrometry (MS). The supercharging reagent replaces the acid and temperature 'quench' step in the conventional MS approach to HDX experiments by causing rapid protein denaturation to occur in the ESI droplet. The higher charge state ions that are produced with m-NBA are more unfolded, as measured by ion mobility, and result in higher fragmentation efficiency and higher sequence coverage with ETD. Single amino acid resolution was obtained for 44 of 72 exchangeable amide sites, and summed kinetic data were obtained for regions of the protein where adjacent fragment ions were not observed, resulting in an overall spatial resolution of 1.3 residues. Comparison of these results with previous values from NMR indicates that the supercharging reagent does not cause significant structural changes to the protein in the initial ESI solution and that scrambling or back-exchange is minimal. This new method for top-down HDX-MS enables real-time kinetic data measurements under physiological conditions, similar to those obtained using NMR, with comparable spatial resolution and significantly better sensitivity. 10.1021/ac101957x

In this article, we show how neutron reflectometry (NR) can provide deep insight into the absorption and desorption properties of commercially promising hydrogen storage materials. NR benefits from the large negative scattering length of hydrogen atoms, which changes the reflectivity curve substantially, so that NR can determine not only the total amount of stored hydrogen but also the hydrogen distribution along the film normal, with nanometer resolution. To use NR, the samples must have smooth surfaces, and the film thickness should range between 10 and 200 nm. We performed a systematic study on thin [Mg.sub.1-x][Al.sub.x] alloy films (x = 0.2, 0.3, 0.4, 0.67) capped with a Pd catalyst layer. Our NR experiments showed that [Mg.sub.0.7][Al.sub.0.3] is the optimum alloy composition with the highest amount of stored hydrogen and the lowest desorption temperature. All the thin films expand by about 20% because of hydrogen absorption, and the hydrogen is stored only in the MgAl layer with no hydrogen content in the Pd layer. PACS Nos: 61.05.fj, 82.40 Nous montrons ici comment la Reflectomeetrie Neutronique (NR) peut permettre une etude plus approfondie des proprietes d'absorption et de desorption de mateeriaux de stockage d'hydrogene commercialement prometteurs. NR utilise la grande longueur de diffusion negative des atomes d'hydrogene qui change substantiellement la courbe de reflectivite de telle sorte que NR peut determiner non seulement la quantite totale d'hydrogene stockee, mais egalement la distribution de l'hydrogene selon la normale au film, avec une precision du nanometre. Pour pouvoir utiliser NR, les films doivent avoir une surface lisse et leur eepaisseur doit se trouver entre 10 et 200 nm. Nous avons etudie systematiquement des films minces d'alliage [Mg.sub.1-x][Al.sub.x] (x = 0,2, 0,3, 0,4, 0,67) recouverts d'une couche de Pd comme catalyseur. Nos mesures montrent que [Mg.sub.0.7][Al.sub.0,3] est l'alliage optimum qui permet le plus haut stockage d'hydrogene et la plus basse temperature de desorption. Tous les films minces gonflent d'environ 20 % suivant l'absorption d'hydrogene qui est stocke; uniquement dans la couche de MgAl, sans hydrogene dans le Pd. [Traduit par la Redaction], Introduction A modern vehicle would need about 5 kg of hydrogen in combination with a fuel cell to achieve a travel range of about 500 km. Intense research efforts have [...]

The causes of past changes in the global methane cycle and especially the role of marine methane hydrate (clathrate) destabilization events are a matter of debate. Here we present evidence from the North Greenland Ice Core Project ice core based on the hydrogen isotopic composition of methane [[delta]D(C[H.sub.4])] that clathrates did not cause atmospheric methane concentration to rise at the onset of Dansgaard-Oeschger (DO) events 7 and 8. Box modeling supports boreal wetland emissions as the most likely explanation for the interstadial increase. Moreover, our data show that [delta]D(C[H.sub.4]) dropped 500 years before the onset of DO 8, with C[H.sub.4] concentration rising only slightly. This can be explained by an early climate response of boreal wetlands, which carry the strongly depleted isotopic signature of high-latitude precipitation at that time. 10.1126/science.1187651

Solution-phase hydrogen/deuterium exchange (HDX) monitored by mass spectrometry is an excellent tool to study protein--protein interactions and conformational changes in biological systems, especially when traditional methods such as X-ray crystallography or nuclear magnetic resonance are not feasible. Peak overlap among the dozens of proteolytic fragments (including those from autolysis of the protease) can be severe, due to high protein molecular weight(s) and the broad isotopic distributions due to multiple deuterations of many peptides. In addition, different subunits of a protein complex can yield isomeric proteolytic fragments. Here, we show that depletion of [sup.13]C and/or [sup.15]N for one or more protein subunits of a complex can greatly simplify the mass spectra, increase the signal-to-noise ratio of the depleted fragment ions, and remove ambiguity in assign. ment of the m/z values to the correct isomeric peptides. Specifically, it becomes possible to monitor the exchange progress for two isobaric fragments originating from two or more different subunits within the complex, without having to resort to tandem mass spectrometry techniques that can lead to deuterium scrambling in the gas phase. Finally, because the isotopic distribution for a small to medium-size peptide is essentially just the monoisotopic species ([sup.12][C.sub.c][sup.1][H.sub.h][sup.14][N.sub.n] [sup.16][O.sub.o][sup.32][S.sub.s]), it is not necessary to deconvolve the natural abundance distribution for each partially deuterated peptide during HDX data reduction. 10.1021/ac100079z

Electrochemical methods proved useful as simple and inexpensive tools for the analysis of natural as well as chemically modified nucleic acids. In particular, covalently attached metal-containing groups usually render the DNA well-pronounced electrochemical activity related to redox processes of the metal moieties, which can in some cases be coupled to catalytic hydrogen evolution at mercury or some types of amalgam electrodes. In this paper we used voltammetry at the mercury-based electrodes for the monitoring of DNA modification with cis-diamminedichloroplatinum (cisplatin), a representative of metallodrugs used in the treatment of various types of cancer or being developed for such purpose. In cyclic voltammetry at the mercury electrode, the cisplatin-modified DNA yielded catalytic currents the intensity of which reflected DNA modification extent. In square-wave voltammetry, during anodic polarization after prereduction of the cisplatinated DNA, a well-developed, symmetrical signal (peak P) was obtained. Intensity of the peak P linearly responded to the extent of DNA modification at levels relevant for biochemical studies (rb = 0.01-0.10, where rb is the number of platinum atoms bound per DNA nucleotide). We demonstrate a correlation between the peak P intensity and a loss of sequence-specific DNA binding by tumor suppressor protein p53, as well as blockage of DNA digestion by a restriction endonuclease Msp I (both caused by the DNA cisplatination). Application of the electrochemical technique in studies of DNA reactivity with various anticancer platinum compounds, as well as for an easy determination of the extent of DNA platination in studies of its biochemical effects, is discussed. 10.1021/ac902987x

The concept of the cyclic periodical mixing combustion process (Kalb, and Sattelmayer, 2004, 'Lean Blowout Limit and N[O.sub.x]-Production of a Premixed Sub-ppm-N[O.sub.x] Burner With Periodic Flue Gas Recirculation,' Proceedings of the ASME Turbo Expo 2004, Paper No. GT2004-53410; Kalb, and Sattelmayer, 2006, 'Lean Blowout Limit and N[O.sub.x]-Production of a Premixed Sub-ppm-N[O.sub.x] Burner With Periodic Recirculation of Combustion Products,' ASME J. Eng. Gas Turbines Power, 128(2), pp. 247-254) for the extension of the lean blowout limit had been implemented in an atmospheric experimental combustor for testing with both external perfect (Bruckner-Kalb, Hirsch, and Sattelmayer, 2006, 'Operation Characteristics of a Premixed Sub-ppm N[O.sub.x] Burner With Periodical Recirculation of Combustion Products,' Proceedings of the ASME Turbo Expo 2006, Paper No. GT2006-90072) and technical (Bruckner-Kalb, Napravnik, Hirsch, and Sattelmayer, 2007, 'Development of a Fuel-Air Premixer for a Sub-ppm N[O.sub.x] Burner,' Proceedings of the ASME Turbo Expo 2007, Paper No. GT2007-27779) premixing of reactants. It had been tested with natural gas and has now been tested with a mixture of [70%.sub.vol] of hydrogen and [30%.sub.vol] of natural gas (98% C[H.sub.4]) as fuel. With natural gas the N[O.sub.x] emissions are unaffected by the limited technical premixing quality, as long as the air preheat is in the design range of the premixers (Bruckner-Kalb, Napravnik, Hirsch, and Sattelmayer, 2007, 'Development of a Fuel-Air Premixer for a Sub-ppm N[O.sub.x] Burner,' Proceedings of the ASME Turbo Expo 2007, Paper No. GT2007-27779). Then, for adiabatic flame temperatures of up to 1630 KN[O.sub.x] emissions are below 1 ppm(v) with CO emissions below 8 ppm(v) in the whole operation range of the test combustor (15% [O.sub.2], dry). With the '[70%.sub.vol][H.sub.2]-[30%.sub.vol]C[H.sub.4]' mixture the N[O.sub.x] emissions increase by nearly one order of magnitude. Then, N[O.sub.x] emissions below 7 ppm(v) (15% [O.sub.2], dry) are achieved for adiabatic flame temperatures of up to 1600 K. They approach the 1 ppm(v) level only for flame temperatures below 1450 K. CO emissions are below 4 ppm(v). The reason for the increase in the N[O.sub.x] emissions is the higher reactivity of the mixture, which leads to earlier ignition in zones of still elevated unmixedness of reactants near the premixer-injector exits. This effect was investigated by chemical reactor network simulations analyzing a pressure effect and an additional chemical effect of hydrogen combustion on N[O.sub.x] formation. [DOI: 10.1115/1.3124789]

The rapid and complete digestion of preteins is important when protein characterization by hydrogen-deuterium exchange (HDX) is coupled with mass spectrometry. We developed a single-pump, online, high-pressure digestion system that relies on UPLC technology to aid in the digestion of proteins. Two model proteins, amyloid [beta]-peptide 1-42 (A[beta] 1-42) and an HIV-1 capsid mutant protein (NBSA), were used to demonstrate the efficacy of the high-pressure system. Both model proteins readily aggregate and are difficult to digest under normal conditions. Our high-pressure system successfully digests these proteins into small, overlapping peptides. The extra information afforded by overlapping peptides allows us to pinpoint HDX protection to protein segments smaller than the digested peptide. The calculated average segment length (ASL) for both model proteins decreased by 2-fold for high-pressure digestion compared to digestion at ambient pressure. 10.1021/ac902477u

To examine the molecular details of ligand activation of G-protein coupled receptors (GPCRs), emphasis has been placed on structure determination of these receptors with stabilizing ligands. Here we present the methodology for receptor dynamics characterization of the GPCR human [[beta].sub.2] adrenergic receptor bound to the inverse agonist carazolol using the technique of amide hydrogen/ deuterium exchange coupled with mass spectrometry (HDX MS). The HDX MS profile of receptor bound to carazolol is consistent with thermal parameter observations in the crystal structure and provides additional information in highly dynamic regions of the receptor and chemical modifications demonstrating the highly complementary nature of the techniques. After optimization of HDX experimental conditions for this membrane protein, better than 89% sequence coverage was obtained for the receptor. The methodology presented paves the way for future analysis of [[beta].sub.2]AR bound to pharmacologically distinct ligands as well as analysis of other GPCR family members. 10.1021/ac902484p

The knock and combustion characteristics of CO, [H.sub.2], C[H.sub.4], and their mixtures were determined experimentally in a variable compression ratio spark ignition (SI) cooperative fuel research (CFR) engine. The significant effects of gaseous fuel mixtures containing [H.sub.2] in enhancing the combustion and oxidation process of C[H.sub.4] were examined. The unique combustion characteristics of CO in dry air and its distinct performance in mixtures with H-containing fuels were investigated. The addition of a simulated synthesis gas (2[H.sub.2] + CO) to C[H.sub.4] was found to enhance the combustion process of the resulting mixture and lowers its knock resistance. The effectiveness of such an addition is slightly weaker than that of a comparable [H.sub.2] addition but much stronger than that with CO addition only. A predictive model with detailed kinetic chemistry was used successfully to simulate SI engine operation fuelled with C[H.sub.4], [H.sub.2], CO, and their mixtures. The predicted engine performance and knock limits of C[H.sub.4], [H.sub.2], CO, and their mixtures agree well with experimental data with the exception around pure CO operation in dry air with the presence of small amounts of C[H.sub.4] or [H.sub.2]. A remedial approach to improve the prediction of the knock limits of fuel mixtures containing mainly CO with a small amount of H-containing fuels such as [H.sub.2] and C[H.sub.4] was proposed and discussed. [DOI: 10.1115/1.3155795]

A turbulence model that calculates the turbulent Prandtl and Schmidt numbers as part of the solution is presented. This model also accounts for compressibility effects, and addresses turbulence/chemistry interaction. Its predictions are compared with two experiments: an axisymmetric case involving mixing, hydrogen combustion, and ethylene combustion; and a three-dimensional ethylene mixing experiment. Fair to good agreement is indicated in the cases where data is available. Chemical mechanisms are found to have an influence on autoignition for hydrogen combustion cases, and on ignition location and flame size for hydrogen/ethylene combustion cases using reduced mechanisms. DOI: 10.2514/1.43213

We report on the simultaneous and two-dimensional measurement of laser-induced fluorescence (LIF) and Raman scattering (Ramanography) applied inside a hydrogen internal combustion (IC) engine. Two different LIF tracer molecules, triethylamine (TEA) and trimethylamine (TMA), were used for the LIF experiments. The LIF and Raman results were found to be in very good agreement. The simultaneous application of Ramanography and LIF imaging indicated that TMA is the more suitable LIF tracer molecule, compared to TEA. OCIS codes: 260.2510, 280.1740, 280.2490, 300.2530, 110.0115, 290.5860.

A solar reactor consisting of a cavity-receiver containing an array of tubular absorbers is considered for performing the ZnO-dissociation as part of a two-step [H.sub.2]O-splitting thermochemical cycle using concentrated solar energy. The continuity, momentum, and energy governing equations that couple the rate of heat transfer to the Arrhenius-type reaction kinetics are formulated for an absorbing-emitting-scattering particulate media and numerically solved using a computational fluid dynamics code. Parametric simulations were carried out to examine the influence of the solar flux concentration ratio (3000-6000 suns), number of tubes (110), ZnO mass flow rate (2-20 g/min per tube), and ZnO particle size (0.06-1 [micro]m) on the reactor's performance. The reaction extent reaches completion within 1 s residence time at above 2000 K, yielding a solar-to-chemical energy conversion efficiency of up to 29%. [DOI: 10.1115/1.3097280]

Currently there are a number of Generation IV supercritical water-cooled nuclear reactor (SCWR) concepts under development worldwide. The main objectives for developing and utilizing SCWRs are (1) to increase the gross thermal efficiency of current nuclear power plants (NPPs) from 33-35% to approximately 45-50% and (2) to decrease the capital and operational costs and, in doing so, decrease electrical-energy costs (approximately US$ 1000/kW or even less). SCW NPPs will have much higher operating parameters compared to current NPPs (i.e., pressures of about 25 MPa and outlet temperatures of up to 625[degrees]C). Additionally, SCWRs will have a simplified flow circuit in which steam generators, steam dryers, steam separators, etc. will be eliminated. Furthermore, SCWRs operating at higher temperatures can facilitate an economical cogeneration of hydrogen through thermochemical cycles (particularly, the copper-chlorine cycle) or direct high-temperature electrolysis. To decrease significantly the development costs of a SCW NPP and to increase its reliability, it should be determined whether SCW NPPs can be designed with a steam-cycle arrangement that closely matches that of mature supercritical (SC) fossil power plants (including their SC turbine technology). On this basis, several conceptual steam-cycle arrangements of pressure-channel SCWRs, their corresponding T-s diagrams and steam-cycle thermal efficiencies are presented in this paper together with major parameters of the copper-chlorine cycle for the cogeneration of hydrogen. Also, bulk-fluid temperature and thermophysical properties profiles were calculated for a nonuniform cosine axial heat-flux distribution along a generic SCWR fuel channel for reference purposes. [DOI: 10.1115/1.2983016]

In recent decades, fuel cell technology has been undergoing revolutionary developments, with fundamental progress being the replacement of electrolyte solutions with polymer electrolytes, making the device more compact in size and higher in power density. Nowadays, acidic polymer electrolytes, typically Nafion, are widely used. Despite great success, fuel cells based on acidic polyelectrolyte still depend heavily on noble metal catalysts, predominantly platinum (Pt), thus increasing the cost and hampering the widespread application of fuel cells. Here, we report a type of polymer electrolyte fuel cells (PEFC) employing a hydroxide ion-conductive polymer, quaternary ammonium polysulphone, as alkaline electrolyte and nonprecious metals, chromium-decorated nickel and silver, as the catalyst for the negative and positive electrodes, respectively. In addition to the development of a high-performance alkaline polymer electrolyte particularly suitable for fuel cells, key progress has been achieved in catalyst tailoring: The surface electronic structure of nickel has been tuned to suppress selectively the surface oxidative passivation with retained activity toward hydrogen oxidation. This report of a [H.sub.2]-[O.sub.2] PEFC completely free from noble metal catalysts in both the positive and negative electrodes represents an important advancement in the research and development of fuel cells. nonprecious metals | hydrogen oxidation | oxygen reduction