985 resultados para hydrogen atom


Relevância:

20.00% 20.00%

Publicador:

Resumo:

Legal Context In the wake of the Copenhagen Accord 2009 and the Cancun Agreements 2010, a number of patent offices have introduced fast-track mechanisms to encourage patent applications in relation to clean technologies - such as those pertaining to hydrogen. However, patent offices will be under increasing pressure to ensure that the granted patents satisfy the requisite patent thresholds, as well as to identify and reject cases of fraud, hoaxes, scams, and swindles. Key Points This article examines the BlackLight litigation in the United States, the United Kingdom, and the European Patent Office, and considers how patent offices and courts deal with patent applications in respect of clean energy and perpetual motion machines. Practical Significance The capacity of patent offices to grant sound and reliable patents is critical to the credibility of the patent system, particularly in the context of the current focus upon promoting clean technologies.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

In the structure of the title complex [[Na(H2O)3]+ (C6H2Cl3N2O2)-^ . 3(H2O)]n, the Na salt of the herbicide picloram, the cation is a polymeric chain structure, based on doubly water-bridged NaO5 trigonal bipyramidal complex units which have in addition, a singly-bonded monodentate water molecule. Each of the bridges within the chain which lies along the a cell direction is centrosymmetric with Na...Na separations of 3.4807(16) and 3.5109(16)Ang. In the crystal, there are three water molecules of solvation and these, as well as the coordinated water molecules and the amino group of the 4-amino-3,5,6-trichloropicolinate anion are involved in extensive inter-species hydrogen-bonding interactions with carboxyl and water O-atoms as well as the pyridine N-atom. Among these association is a centrosymmetric cyclic tetra-water R4/4(8) ring , resulting in an overall three-dimensional structure.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

This paper presents the fabrication and study of a Schottky diode based on Pt/WO3 nanoplatelet/SiC for H2 gas sensing applications. The nanostructured WO3 films were synthesized from tungsten (sputtered on SiC) via an acidetching method using a 1.5 M HNO3 solution. Scanning electron microscopy of the developed films revealed platelet crystals with thicknesses in the order of 20-60 nm and lengths between 100-700 nm. The current-voltage characteristic and dynamic response of the diodes were measured in the presence of air and 1% H2 gas balanced in air from 25 to 300°C. Upon exposure to 1% H2, voltage shifts of 0.64, 0.93 and 1.14 V were recorded at temperatures of 120, 200 and 300°C, respectively at a constant forward bias current of 500 μA.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

In the structure of the title hydrated salt, NH4+·C8H5Cl2O3-·0.5H2O, where the anion derives from (3,5-di­chloro­phen­oxy)acetic acid, the ammonium cation is involved in extensive N-H...O hydrogen bonding with both carboxyl­ate and ether O-atom acceptors giving sheet structures lying parallel to (100). The water mol­ecule of solvation lies on a crystallographic twofold rotation axis and is involved in intra-sheet O-H...Ocarboxyl­ate hydrogen-bonding inter­actions. In the anion, the oxoacetate side chain assumes an antiperiplanar conformation with the defining C-O-C-C torsion angle = -171.33 (15)°.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

The two-dimensional coordination polymeric structures of the hydrated potassium and rubidium salts of (3,5-dichlorophenoxy)acetic acid, (3,5-D) namely, poly[mu-aqua-bis[mu3-2-(3,5-dichlorophenoxy)acetato]potassium, [K2(C8H5Cl2O3)2 (H2O)]n (I) and poly[mu-aqua-bis[mu3-2-(3,5-dichlorophenoxy)acetato]dirubidium] [Rb2(C8H5Cl2O3)2 (H2O)]n (II), respectively have been determined and are described. The two compounds are isotypic and the polymer is based on centrosymmetric dinuclear bridged complex units. The irregular six-coordination about the metal centres comprises a bridging water molecule lying on a twofold rotation axis, the phenoxy O-atom donor and and a triple bridging carboxylate O-atom of the oxoacetate side chain of the 3,5-D ligand in a bidentate chelate mode, the second carboxy O-donor, also bridging. The K-O and Rb-O bond-length ranges are 2.7238(15)--2.9459(14) and 2.832(2)--3.050(2) \%A respectively and the K...K and Rb...Rb separations in the dinuclear unit are 4.0214(7) and 4.1289(6) \%A, respectively. Within the two-dimensional layers which lie parallel to (100), the coordinated water molecule forms an O---H...O hydrogen bond to the single bridging carboxylate O atom.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

In plants and nematodes, RNAi can spread from cells from which it is initiated to other cells in the organism. The underlying mechanism controlling the mobility of RNAi signals is not known, especially in the case of plants. A genetic screen designed to recover plants impaired in the movement but not the production or effectiveness of the RNAi signal identified RCI3, which encodes a hydrogen peroxide (H2O2)-producing type III peroxidase, as a key regulator of silencing mobility in Arabidopsis thaliana. Silencing initiated in the roots of rci3 plants failed to spread into leaf tissue or floral tissue. Application of exogenous H2O2 reinstated the spread in rci3 plants and accelerated it in wild-type plants. The addition of catalase or MnO2, which breaks down H2O2, slowed the spread of silencing in wild-type plants. We propose that endogenous H2O2, under the control of peroxidases, regulates the spread of gene silencing by altering plasmodesmata permeability through remodelling of local cell wall structure, and may play a role in regulating systemic viral defence.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Pt/TiO2 sensitized by the cheap and organic ortho-dihydroxyl-9,10-anthraquinone dyes, such as Alizarin and Alizarin Red, achieved a TON of approximately 10 000 (TOF > 250 h−1 for the first ten hours) during >80 hours of visible light irradiation (>420 nm) for photocatalytic hydrogen evolution when triethanolamine was used as the sacrificial donor. The stability and activity enhancements can be attributed to the two highly serviceable redox reactions involving the 9,10-dicarbonyl and ortho-dihydroxyl groups of the anthracene ring, respectively

Relevância:

20.00% 20.00%

Publicador:

Resumo:

By increasing the density of exposed active edges, the perpendicularly oriented structure of MoSe2 nanosheets facilitates ion/electrolyte transport at the electrode interface and minimizes the restacking of nanosheets, while the graphene improves the electrical contact between the catalyst and the electrode. This makes the MoSe2/graphene hybrid perfect as a catalyst in the hydrogen evolution reaction (HER). It shows a greatly improved catalytic activity compared with bare MoSe2 nanosheets.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

In an attempt to generate supramolecular assemblies able to function as self-healing hydrogels, a novel ureido-pyrimidinone (UPy) monomer, 2-(N ′-methacryloyloxyethylureido)-6-(1-adamantyl)-4[1H]-pyrimidinone, was synthesized and then copolymerized with N,N-dimethylacrylamide at four different feed compositions, using a solution of lithium chloride in N,N-dimethylacetamide as the polymerization medium. The assembling process in the resulting copolymers is based on crosslinking through the reversible quadruple hydrogen bonding between side-chain UPy modules. The adamantyl substituent was introduced in order to create a “hydrophobic pocket” that may protect the hydrogen bonds against the disruptive effect of water molecules. Upon hydration to equilibrium, all copolymers generated typical hydrogels when their concentration in the hydrated system was at least 15%. The small-deformation rheometry showed that all hydrated copolymers were hydrogels that maintained a solid-like behavior, and that their extrusion through a syringe needle did not affect significantly this behavior, suggesting a self-healing capacity in these materials. An application as injectable substitutes for the eye's vitreous humor was proposed

Relevância:

20.00% 20.00%

Publicador:

Resumo:

The two-dimensional polymeric structures of the caesium complexes with the phenoxyacetic acid analogues (4-fluorophenoxy)acetic acid, (3-chloro-2-methylphenoxy)acetic acid and the herbicidally active (2,4-dichlorophen­oxy)acetic acid (2,4-D), namely poly[[5-(4-fluorophenoxy)acetato][4-(4-fluorophenoxy)acetato]dicaesium], [Cs2(C8H6FO3)2]n, (I), poly[aqua[5-(3-chloro-2-methylphenoxy)acetato]caesium], [Cs(C9H8ClO3)(H2O)]n, (II), and poly[[7-(2,4-di­chlorophenoxy)acetato][(2,4-dichlorphenoxy)acetic acid]caesium], [Cs(C8H5Cl2O3)(C8H6Cl2O3)]n, (III), are described. In (I), the Cs+ cations of the two individual irregular coordination polyhedra in the asymmetric unit (one CsO7 and the other CsO8) are linked by bridging carboxylate O-atom donors from the two ligand molecules, both of which are involved in bidentate chelate Ocarboxy,Ophenoxy interactions, while only one has a bidentate carboxylate O,O'-chelate inter­action. Polymeric extension is achieved through a number of carboxylate O-atom bridges, with a minimum CsCs separation of 4.3231 (9) Å, giving layers which lie parallel to (001). In hydrated complex (II), the irregular nine-coordination about the Cs+ cation comprises a single monodentate water molecule, a bidentate Ocarboxy,Ophenoxy chelate interaction and six bridging carboxylate O-atom bonding interactions, giving a CsCs separation of 4.2473 (3) Å. The water mol­ecule forms intralayer hydrogen bonds within the two-dimensional layers, which lie parallel to (100). In complex (III), the irregular centrosymmetric CsO6Cl2 coordination environment comprises two O-atom donors and two ring-substituted Cl-atom donors from two hydrogen bis[(2,4-dichlorophenoxy)acetate] ligand species in a bidentate chelate mode, and four O-atom donors from bridging carboxyl groups. The duplex ligand species lie across crystallographic inversion centres, linked through a short O-HO hydrogen bond involving the single acid H atom. Structure extension gives layers which lie parallel to (001). The present set of structures of Cs salts of phenoxyacetic acids show previously demonstrated trends among the alkali metal salts of simple benzoic acids with no stereochemically favourable interactive substituent groups for formation of two-dimensional coordination polymers.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Gelonin is a single chain ribosome inactivating protein (RIP) with potential application in the treatment of cancer and AIDS. Diffraction quality crystals grown using PEG3350, belong to the space group P2(1), with it a = 49.4 Angstrom b = 44.9 Angstrom, c = 137.4 Angstrom and beta = 98.4 degrees, and contain two molecules in the asymmetric unit. Diffraction data collected to 1.8 Angstrom resolution has a R(m) value of 7.3%. Structure of gelonin has been solved by the molecular replacement method, using ricin A chain as the search model. Crystallographic refinement using X-PLOR resulted in a model for which the r.m.s deviations from ideal bond lengths and bond angles are 0.012 Angstrom and 2.7 degrees, respectively The final R-factor is 18.4% for 39,806 reflections for which I > 1.0 sigma(I).The C-alpha atoms of the two molecules in the asymmetric unit superpose to within 0.38 Angstrom for 247 atom pairs. The overall fold of gelonin is similar to that of other RIPs such as ricin A chain and alpha-momorcharin, the r.m.s.d. for C-alpha superpositions being 1.3 and 1.4 Angstrom, respectively The-catalytic residues (Glu166, Arg169 and Tyr113) in the active site form a hydrogen bond scheme similar to that observed in other RIPs. The conformation of Tyr74 in the active site, however, is significantly different from that in alpha-momorcharin. Three well defined water molecules are located in the active site cavity and one of them, X319, superposes to within 0.2 Angstrom of a corresponding water molecule in the structure of alpha-momorcharin. Any of the three could be the substrate water molecule in the hydrolysis reaction catalysed by gelonin.Difference electron density for a N-linked sugar moiety has been observed near only one of the two potential glycosylation sites in the sequence. The amino acid at position 239 has been established as Lys by calculation of omit electron density maps.The two cysteine residues in the sequence, Cys44 and Cys50, form a disulphide bond, and are therefore not available for disulphide conjugation with antibodies. Based on the structure, the region of the molecule that is involved in intradimer interactions is suggested to be suitable for introducing a Cys residue for purposes of conjugation with an antibody to produce useful immunotoxins.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

In the anhydrous salt formed from the reaction of morpholine with cinnamic acid, C4H10NO+ C9H7O2-, the acid side chain in the trans-cinnamate anion is significantly rotated out of the benzene plane [C-C-C-C torsion angle = 158.54(17)deg. In the crystal, one of the the aminium H atoms is involved in a asymmetric three-centre cation-anion N-H...(O,O') R2/1(4) hydrogen-bonding interaction with the two carboxyl O-atom acceptors of the anion. The second aminium H atom forms an inter-species N-H...O(carboxyl) hydrogen bond, generating a one-dimensional chain structure extending along [100]. Chains are linked by C-H...O interactions forming a supramolecular layer parallel to (01-1).

Relevância:

20.00% 20.00%

Publicador:

Resumo:

The nature of amorphous carbon has been explored by molecular mechanics by examining the structures of species such as C84Hx and C150Hx, wherein the percentage of sp(3) carbons is progressively increased in a graphitic network. The nature of diamond-like carbon has been similarly investigated by examining the structures of C84Hx and C102Hx where the percentage of sp(2) carbons is varied in an sp(3) network. The dependence of the average coordination number as well as the sp(3)/sp(2) atom ratio on the atom fraction of hydrogen has been investigated in light of the random covalent network model.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

The crystal structure determination of the heptapeptide Boc-Val-Ala-Leu-Aib-Val-Ala-Phe-OMe reveals two peptide helices in the asymmetric unit, Crystal parameters are: space group P2(1), a = 10.356(2) Angstrom, b = 19.488(5) Angstrom, c = 23.756(6) Angstrom, beta = 102.25(2)degrees), V = 4685.4 Angstrom(3), Z = 4 and R = 5.7% for 7615 reflections [I>3 sigma(I)]. Both molecules adopt largely alpha-helical conformations with variations at the C-terminus, Helix type Is determined by analysing both 4-->1 and 5-->1 hydrogen-bond interactions and comparison with the results of analysis of protein structures. The presence of two 4-->1 hydrogen-bond interactions, besides four 5-->1 interact ions in both the conformations provides an opportunity to characterize bifurcated hydrogen bonds at high resolution, Comparison of the two helical conformations with related peptide structures suggests that distortions at the C-terminus are more facile than at the N-terminus.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Several mechanisms have been proposed to explain the action of enzymes at the atomic level. Among them, the recent proposals involving short hydrogen bonds as a step in catalysis by Gerlt and Gassman [1] and proton transfer through low barrier hydrogen bonds (LBHBs) [2, 3] have attracted attention. There are several limitations to experimentally testing such hypotheses, Recent developments in computational methods facilitate the study of active site-ligand complexes to high levels of accuracy, Our previous studies, which involved the docking of the dinucleotide substrate UpA to the active site of RNase A [4, 5], enabled us to obtain a realistic model of the ligand-bound active site of RNase A. From these studies, based on empirical potential functions, we were able to obtain the molecular dynamics averaged coordinates of RNase A, bound to the ligand UpA. A quantum mechanical study is required to investigate the catalytic process which involves the cleavage and formation of covalent bonds. In the present study, we have investigated the strengths of some of the hydrogen bonds between the active site residues of RNase A and UpA at the ab initio quantum chemical level using the molecular dynamics averaged coordinates as the starting point. The 49 atom system and other model systems were optimized at the 3-21G level and the energies of the optimized systems were obtained at the 6-31G* level. The results clearly indicate the strengthening of hydrogen bonds between neutral residues due to the presence of charged species at appropriate positions. Such a strengthening manifests itself in the form of short hydrogen bonds and a low barrier for proton transfer. In the present study, the proton transfer between the 2'-OH of ribose (from the substrate) and the imidazole group from the H12 of RNase A is influenced by K41, which plays a crucial role in strengthening the neutral hydrogen bond, reducing the barrier for proton transfer.