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Hydrogen Bonds (hydrogen + bond)
Kinds of Hydrogen Bonds Terms modified by Hydrogen Bonds Selected Abstracts9-Fluoro-18-hydroxy-[3.3]metacyclophane: Synthesis and Estimation of a C,F···H,O Hydrogen BondEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 9 2004Hiroyuki Takemura Abstract A cyclophane composed of fluorobenzene and phenol units was synthesized in order to observe the C,F···H,O hydrogen bond. In the crystal structure, 20% of the molecule clearly shows the intramolecular hydrogen bond and the other 80% is free from hydrogen bonding. On the other hand, a distinct low-field shift of the phenolic OH proton was observed in the 1H NMR spectrum compared to that of the F-free analog. Furthermore, O,H···F through-space coupling was observed. From the results of the crystallographic analysis, IR, and NMR spectra, the C,F···H,O hydrogen bond energy of this system was estimated to be 0.84,3.7 kJ·mol,1. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] A Theoretical Study of Correlation between Hydrogen-Bond Stability and J -Coupling through a Hydrogen BondHELVETICA CHIMICA ACTA, Issue 10 2003Shun-ichi Kawahara trans -Hydrogen-bond hyperfine splitting via magnetic interaction, which is observed as J -coupling in NMR experiments, was theoretically studied. trans -Hydrogen-bond hyperfine splitting should be closely related to the orbital interaction between the lone-pair orbital of the H-bond acceptor and the antibond orbital of the H-bond donor. A linear relationship was observed between magnetic interaction hyperfine splitting through a H-bond and the H-bond strength. The relationship was dependent on the type of the nucleus forming the H-bond; linear correlation was observed in NH,,,O/N type or OH,,,N type H-bonded complexes, but not in OH,,,O type H-bonded complexes. [source] Photosensitization of Hypomycin B,A Novel Perylenequinonoid Pigment with Only One Intramolecular Hydrogen Bond,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2001Hong-Yu Zhang ABSTRACT Electron spin resonance technique and spin-trapping methods were used to determine the photoproduction of 1O2 and O2·, by hypomycin B (HMB), a novel perylenequinonoid pigment (PQP) possessing only one hydroxyl group. It was found that the yields of 1O2 and O2·, for HMB were comparable to those for hypocrellin A, a typical natural PQP with good photosensitivity. In addition, the absorption and fluorescence spectra for HMB were investigated. The pKa values in the ground and excited states of HMB were determined to be 8.94 and 5.54, respectively. Thus, the photodynamic mechanisms of HMB may involve not only the photogeneration of 1O2 and O2·, but also the light-induced acidification. Consequently, HMB is proposed to be a good photodynamic therapeutic agent. [source] Dispersion-Driven Hydrogen Bonding: Predicted Hydrogen Bond between Water and Platinum(II) Identified by Neutron Diffraction,ANGEWANDTE CHEMIE, Issue 41 2010Dr. Silvia Rizzato Klassisch oder nicht? Die Metallionen quadratisch-planar koordinierter d8 -Komplexe können als Lewis-Säuren oder -Basen mit H2O-Molekülen in axialen Positionen wechselwirken. Ab-initio-Rechnungen zufolge bilden neutrale PtII -Komplexe Wasserstoffbrücken mit H2O, in denen PtII als Lewis-Base auftritt. Solche nichtklassischen OH,,,Pt-Brücken wurden nun in Kristallen von trans -[PtCl2(NH3)(N -Glycin)],H2O mithilfe von Neutronenbeugung identifiziert. [source] Structure and Function Converge To Identify a Hydrogen Bond in a Group,I Ribozyme Active Site,ANGEWANDTE CHEMIE, Issue 39 2009Marcello Forconi Dr. Enzyme nutzen ein ausgefeiltes Netzwerk aus Wechselwirkungen, um Reaktionen zu katalysieren, und die Röntgenbeugung ist eine große Hilfe, um solche Netzwerke sichtbar zu machen. Doch was passiert, wenn unterschiedliche Strukturmodelle (siehe Bild) für denselben Rest unterschiedliche Wechselwirkungen vorschlagen? Funktionsdaten aus Doppelmutantenzyklen können eine Antwort liefern, wie für das Tetrahymena -Gruppe-I-Ribozym gezeigt wurde. [source] A Single ,-Helical Turn Stabilized by Replacement of an Internal Hydrogen Bond with a Covalent Ethylene Bridge,ANGEWANDTE CHEMIE, Issue 31 2009Andrea Durch eine Kohlenstoffbrücke stabilisiert: ,-Helix-Mimetika wurden hergestellt, in denen eine Ethylenbrücke die (i,i+4)-Wasserstoffbrücke ersetzt (siehe Struktur). Das kleinste denkbare Beispiel, ein modifiziertes Pentapeptid, zeigt die Charakteristika einer Helix (siehe CD-Spektrum). Der Einbau der Kohlenstoffbrücke stellt den ersten Austausch einer internen Wasserstoffbrücke in einem Peptidrückgrat dar. [source] ChemInform Abstract: In situ Formation of N,O-Bidentate Ligand via the Hydrogen Bond for Highly Efficient Suzuki Reaction of Aryl Chlorides.CHEMINFORM, Issue 35 2010Weibo Yang Abstract An efficient protocol is elaborated for the phosphine-free Suzuki reaction mediated by hydrogen bond complexes between EtOH and DMA. [source] Hydrogen Bond in Layered Materials: Structural and Vibrational Properties of Kaolinite by a Periodic B3LYP Approach.CHEMINFORM, Issue 27 2006Sergio Tosoni Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Electron Donation in the Water,Water Hydrogen BondCHEMISTRY - A EUROPEAN JOURNAL, Issue 4 2009Rustam Donation is not from an sp3orbital: Decomposition analysis, based on absolutely localized molecular orbitals, provides an alternative and somewhat unconventional view of hydrogen bonding in the water dimer. A new description of the electron-donating orbital is uncovered:,unlike sp3 lone pairs, a single donor,acceptor orbital pair forms, in which the donating orbital changes its orientation according to the relative positions of the two molecules. [source] Hydrogen-Bonding Cooperativity: Using an Intramolecular Hydrogen Bond To Design a Carbohydrate Derivative with a Cooperative Hydrogen-Bond Donor CentreCHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2004Virginie Vicente Dr. Abstract Neighbouring groups can be strategically located to polarise HO,,,OH intramolecular hydrogen bonds in an intended direction. A group with a unique hydrogen-bond donor or acceptor character, located at hydrogen-bonding distance to a particular OH group, has been used to initiate the hydrogen-bond network and to polarise a HO,,,OH hydrogen bond in a predicted direction. This enhanced the donor character of a particular OH group and made it a cooperative hydrogen-bond centre. We have proved that a five-membered-ring intramolecular hydrogen bond established between an amide NH group and a hydroxy group (1,2-e,a), which is additionally located in a 1,3 -cis- diaxial relationship to a second hydroxy group, can be used to select a unique direction on the six-membered-ring intramolecular hydrogen bond between the two axial OH groups, so that one of them behaves as an efficient cooperative donor. Talose derivative 3 was designed and synthesised to prove this hydrogen-bonding network by NMR spectroscopy, and the mannopyranoside derivatives 1 and 2 were used as models to demonstrate the presence in solution of the 1,2-(e,a)/five-membered-ring intramolecular hydrogen bond. Once a well-defined hydrogen-bond is formed between the OH and the amido groups of a pyranose ring, these hydrogen-bonding groups no longer act as independent hydrogen-bonding centres, but as hydrogen-bonding arrays. This introduces a new perspective on the properties of carbohydrate OH groups and it is important for the de novo design of molecular recognition processes, at least in nonpolar media. Carbohydrates 1,3 have shown to be efficient phosphate binders in nonpolar solvents owing to the presence of cooperative hydroxy centres in the molecule. [source] Entrapment of a Hexamer of Nitrobenzene Molecules between the Layers of (4,4)-Coordination Networks Containing Intra-,-Sheet Hydrogen BondsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 3 2006Madhushree Sarkar Abstract Two exo -bidentate pyridyl ligands containing diamides as spacers were shown to form non-interpenetrated 2D-coordination networks of (4,4)-geometry upon treatment with Cu(NO3)2 and NaSCN. The crystal structures reveal that both structures contain intralayer ,-sheet hydrogen bonds. In one of these structures nitrobenzene occupies 60,% of the crystal volume included between the coordination networks. The nitrobenzene molecules form a layer which has the hexameric C,H···O hydrogen bonded aggregate as a basic building block. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Smart Hydrogels Co-switched by Hydrogen Bonds and ,,, Stacking for Continuously Regulated Controlled-Release SystemADVANCED FUNCTIONAL MATERIALS, Issue 4 2010Fang Li Abstract A series of hydrogels with continuously regulatable release behavior can be achieved by incorporating hydrogen bonding and ,,, stacking co-switches in polymers. A poly(nitrophenyl methacrylate- co -methacrylic acid) hydrogel (NPMAAHG) for control over drug release is fabricated by copolymerizing 4-nitrophenyl methacrylate and methacrylic acid using ethylene glycol dimethacrylate as a crosslinker. The carboxylic acid groups and nitrylphenyl groups form hydrogen bonds and ,,, stacking interactions, respectively, which act as switches to control the release of guest molecules from the polymers. As revealed by the simulated gastrointestinal tract drug release experiments, the as-synthesized NPMAAHG hydrogels can be regulated to release only 4.7% of drugs after 3,h in a simulated stomach and nearly 92.6% within 43,h in the whole digestive tract. The relation between the release kinetics and structures and the mechanism of the smart release control are analyzed in terms of diffusion exponent, swelling interface number, drug diffusion coefficient, and velocity of the swelling interface in detail. The results reveal that the release of guest molecules from the hydrogels can be continuously regulated for systemic administration by controlling the ratio of the hydrophilic hydrogen bonds and the hydrophobic ,,, stacking switches. [source] Tuning the cis/trans Conformer Ratio of Xaa,Pro Amide Bonds by Intramolecular Hydrogen Bonds: The Effect on PPII Helix Stability,ANGEWANDTE CHEMIE, Issue 36 2010Michael Kuemin Dr. Attraktive H-Brücken: Prolinderivate mit einem C4- endo -Ringpucker und einer Präferenz für trans -Amidbindungen werden als Bausteine eingesetzt, um das cis/trans -Verhältnis der Amidbindung in Xaa-Pro-Einheiten von Peptiden einzustellen. Nichtkovalente Wechselwirkungen wie H-Brücken zwischen dem Substituenten am Prolinring-C4 und dem Amidrückgrat sind ausschlaggebend für die Begünstigung oder Benachteiligung des trans -Konformers (siehe Bild). [source] ChemInform Abstract: Copper-Catalyzed Cyanation of Heterocycle Carbon,Hydrogen Bonds.CHEMINFORM, Issue 41 2010Hien-Quang Do Abstract Two procedures are presented which allow the regioselective sequential iodination/cyanation of heterocycles and azulene. [source] Hydrogen Bonds in the Crystal Structure of Strontium Hydroxide Octahydrate Sr(OH)2×8H2O.CHEMINFORM, Issue 19 2007Hans Reuter Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Blue Shifting and Red Shifting Hydrogen Bonds: A Study of the HArF×××N2 and HArF×××P2 ComplexesCHEMINFORM, Issue 21 2003Sean A. C. McDowell Abstract For Abstract see ChemInform Abstract in Full Text. [source] Reinforced Self-Assembly of Hexa- peri -hexabenzocoronenes by Hydrogen Bonds: From Microscopic Aggregates to Macroscopic Fluorescent OrganogelsCHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2008Xi Dou Abstract Hexa- peri -hexabenzocoronene derivatives (HBCs) that have hydrogen-bonding functionalities (either amido or ureido groups) adjacent to the aromatic cores have been synthesized to study the effects of intracolumnar hydrogen bonds on the self-assembly behavior of HBCs. The hydrogen bonds effectively increased the aggregation tendency of these compounds in solution. In the bulk state, the typical columnar supramolecular arrangement of HBCs was either stabilized substantially (1,a, 1,b, 2,a, and 2,b), or suppressed by dominant hydrogen-bonding interactions (3). For some of the compounds (1,a, 2,a, and 2,b), the supramolecular arrangement adopted in the liquid-crystalline state was even retained after annealing, presumably owing to the reinforcement of the ,-stacking interactions by the hydrogen bonds. Additionally, the combined effect of the hydrogen bonds and ,-stacking of the aromatic moieties led to the formation of fluorescent organogels, whereby some derivatives were further investigated as novel low molecular-mass organic gelators (LMOGs). [source] Ionic Hydrogen Bonds Controlling Two-Dimensional Supramolecular Systems at a Metal SurfaceCHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2007Dietmar Payer Abstract Hydrogen-bond formation between ionic adsorbates on an Ag(111) surface under ultrahigh vacuum was studied by scanning tunneling microscopy/spectroscopy (STM/STS), X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS), and molecular dynamics calculations. The adsorbate, 1,3,5-benzenetricarboxylic acid (trimesic acid, TMA), self-assembles at low temperatures (250,300,K) into the known open honeycomb motif through neutral hydrogen bonds formed between carboxyl groups, whereas annealing at 420,K leads to a densely packed quartet structure consisting of flat-lying molecules with one deprotonated carboxyl group per molecule. The resulting charged carboxylate groups form intermolecular ionic hydrogen bonds with enhanced strength compared to the neutral hydrogen bonds; this represents an alternative supramolecular bonding motif in 2D supramolecular organization. [source] NMR Parameters and Geometries of OHN and ODN Hydrogen Bonds of Pyridine,Acid ComplexesCHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2004Hans-Heinrich Limbach Prof. Abstract In this paper, equations are proposed which relate various NMR parameters of OHN hydrogen-bonded pyridine,acid complexes to their bond valences which are in turn correlated with their hydrogen-bond geometries. As the valence bond model is strictly valid only for weak hydrogen bonds appropriate empirical correction factors are proposed which take into account anharmonic zero-point energy vibrations. The correction factors are different for OHN and ODN hydrogen bonds and depend on whether a double or a single well potential is realized in the strong hydrogen-bond regime. One correction factor was determined from the known experimental structure of a very strong OHN hydrogen bond between pentachlorophenol and 4-methylpyridine, determined by the neutron diffraction method. The remaining correction factors which allow one also to describe H/D isotope effects on the NMR parameters and geometries of OHN hydrogen bond were determined by analysing the NMR parameters of the series of protonated and deuterated pyridine- and collidine,acid complexes. The method may be used in the future to establish hydrogen-bond geometries in biologically relevant functional OHN hydrogen bonds. [source] Geometric H/D Isotope Effects and Cooperativity of the Hydrogen Bonds in PorphyceneCHEMPHYSCHEM, Issue 2 2007Mohamed F. Shibl Dr. Abstract We investigate the primary, secondary, and vicinal hydrogen/deuterium (H/D) isotope effects on the geometry of the two intramolecular hydrogen bonds in porphycene. Multidimensional potential energy surfaces describing the anharmonic motion in the vicinity of the trans isomer are calculated for the different symmetric (HH/DD) and asymmetric (HD) isotopomers. From the solution of the nuclear Schrödinger equation the ground-state wavefunction is obtained, which is further used to determine the quantum corrections to the classical equilibrium geometries of the hydrogen bonds and thus the geometric isotope effects. In particular, it is found that the hydrogen bonds are cooperative, that is, both expand simultaneously even in the case of an asymmetric isotopic substitution. The theoretical predictions compare favorably with NMR chemical-shift data. [source] Asymmetry Induction by Cooperative Intermolecular Hydrogen Bonds in Surface-Anchored Layers of Achiral Molecules,CHEMPHYSCHEM, Issue 10 2006Alexandre Dmitriev Dr. Abstract The mesoscale induction of two-dimensional supramolecular chirality (formation of 2D organic domains with a single handedness) was achieved by self-assembly of 1,2,4-benzenetricarboxylic (trimellitic) acid on a Cu(100) surface at elevated temperatures. The combination of spectroscopic [X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS)], real-space-probe [scanning tunneling microscopy (STM)], and computational [density functional theory (DFT)] methods allows a comprehensive characterization of the obtained organic adlayers, where details of molecular adsorption geometry, intermolecular coupling, and surface chemical bonding are elucidated. The trimellitic acid species, comprising three functional carboxylic groups, form distinct stable mirror-symmetric hydrogen-bonded domains. The chiral ordering is associated with conformational restriction in the domains: molecules anchor to the substrate with an ortho carboxylate group, providing two para carboxylic acid moieties for collective lateral interweaving through H bonding, which induces a specific tilt of the molecular plane. The ease of molecular symmetry switching in domain formation makes homochiral-signature propagation solely limited by the terrace width. The molecular layer modifies the morphology of the underlying copper substrate and induces ,m-sized strictly homochiral terraces. [source] Luminescent Property of a Supramolecular Silver(I)-Thiolate Complex Based on Secondary Ag-S Interactions and Hydrogen BondsCHINESE JOURNAL OF CHEMISTRY, Issue 9 2001Wei-Ping Su Abstract The supramolecular silver(I)-thiolate complex [Ag(,2 -SC4N2H4)2(SCN)]n has been prepared from the reaction of AgSCN and pyrimidine-2-thiol in DMF. X-ray diffraction analysis shows that the supramolecular structure exhibits one-dimensional chain through the secondary Ag-S interactions and the chains are further linked by strong hydrogen bonds to form a three dimensional network. The luminescence effect from the silver-centered state of S,Ag LMCT in solid state is different from that in solution due to the secondary Ag-S interactions. [source] Hydrogen bond of radicals: Interaction of HNO with HCO, HNO, and HOOINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2010Yong Yang Abstract Ab initio quantum mechanics methods are employed to investigate hydrogen bonding interactions between HNO and HCO, HOO radicals, and closed-shell HNO. The systems were calculated at MP2/6-311++G (2d, 2p) level and G2MP2 level. The topological and NBO analysis were investigated the origin of hydrogen bonds red- or blue-shifts. In addition, the comparisons were performed between HNO-opened-shell radical (HCO, HOO) complexes and HNO-corresponding closed-shell molecule (H2CO, HOOH) complexes. It is found that the stabilities of complexes increase from HNO-HCO to HNO-HOO. There are blue-shifts of NH, CH stretching vibrational frequencies and a red-shift of OH stretching vibrational frequency in the complexes. Rehybridization and electron density redistribution contribute to the blue-shifts of CH and NH stretching vibrational frequencies. Compared with the closed-shell H2CO, HCO is weaker proton donor and weaker proton acceptor. For the HOO, it is stronger proton donor and weaker proton acceptor than the HOOH is. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] Formation of 2,4,D complexes on montmorillonites , an ab initio molecular dynamics studyEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2007D. Tunega Summary Sorption of the anionic form of the pesticide 2,4,D (2,4,dichlorophenoxyacetic acid) on the surface of the clay mineral montmorillonite was investigated using a short-time ab initio molecular dynamics (MD) simulation at room temperature. Three different situations were modelled: sorption on a dry surface, on a hydrated surface and an intercalation between montmorillonite layers. In all three cases, the calcium cation compensates the excess negative charge of the montmorillonite layer and the negative charge of the 2,4,D anion. It was found that in all models with direct contact of the Ca2+ cation with the montmorillonite layer, the most stable position of Ca2+ is above the ditrigonal hole of the mineral layer. While in the case of a dry surface very stable bidentate binding is created between the 2,4,D anion and the Ca2+ cation, the formation of the monodentate complexes is preferred in all models that include water molecules. Hydrogen bonds formed between water molecules and the 2,4,D anion make a considerable contribution to the formation of the monodentate complexes. Tetrahedral substitutions in the montmorillonite layer have a significant effect on the formation of the complexes of any type. However, the MD simulations did not support the role of Ca2+ as a cation bridge in the adsorption mechanism. Calculations showed that hydrated 2,4,D···Ca2+ complexes are thermodynamically more stable than complexes in which the Ca2+ cation acts as a bridge to the surface. On the other hand, it is possible that phyllosilicates with a greater concentration of isomorphic substitutions (e.g. mica) will be able to form stable surface complexes with a cation bridge mechanism. [source] Hydrogen bonds assisted by ,-electron delocalization , the influence of external intermolecular interactions on dimer of formic acidJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 7-8 2008awomir J. Grabowski Abstract MP2 and DFT calculations with the use of 6-311++G(d,p) basis set were carried out to study formic acid dimer as well as this species interacting with additional Lewis acids such as HF, Li+ and Na+. These Lewis acids were positioned near carbonyl or hydroxyl oxygen atoms and their influence on geometrical and other parameters of formic acid dimer was analysed. Additionally the ,quantum theory of atoms in molecules' (QTAIM) was applied as well as the ,natural bond orbitals' (NBO) method. Numerous correlations between geometrical, QTAIM and energetic parameters were found. It was found that ,-electron delocalization is not always connected with the enhancement of H-bond strength. Copyright © 2008 John Wiley & Sons, Ltd. [source] Thermo-Responsive Organic/Inorganic Hybrid Hydrogels based on Poly(N -vinylcaprolactam)MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 1 2003Wouter Loos Abstract A new type of ,intelligent' hydrogels has been developed in the form of organic/inorganic hybrid materials by making use of the sol-gel technology. Poly(N -vinylcaprolactam) (PVCL) has been incorporated in these materials for its thermo-responsive properties. The synthesis of the hybrid hydrogels was achieved by the in situ formation of an inorganic silica phase in the presence of an aqueous solution of high molecular weight PVCL. This methodology results in the preparation of micro-heterogeneous systems in which silica particles of nanometer dimensions act as physical cross-links for the PVCL molecules. Hydrogen bonds between the remaining non-condensed silanol groups and the PVCL carbonyl functions, together with physical entanglements, are responsible for the strong interactions between the organic and inorganic phases. Stress-strain tests on highly swollen materials demonstrated that the unique structure of these thermo-responsive hybrid hydrogels improves the mechanical stability to a great extent as compared to conventional hydrogels. Transmission measurements demonstrate that the presence of the inorganic phase does not influence the cloud point temperatures of PVCL significantly. On the other hand, the response of the reinforced hybrid hydrogels to temperature becomes less pronounced for increasing silica fractions. The reversibility of the swelling/deswelling process has been demonstrated by swelling experiments as a function of temperature. PVCL/SiO2 hybrid hydrogels. [source] Hydrogen bonds and local symmetry in the crystal structure of gibbsiteMAGNETIC RESONANCE IN CHEMISTRY, Issue 11 2010Anastasia Vyalikh Abstract First-principles quantum mechanical calculations of NMR chemical shifts and quadrupolar parameters have been carried out to assign the 27Al MAS NMR resonances in gibbsite. The 27Al NMR spectrum shows two signals for octahedral aluminum revealing two aluminum sites coordinated by six hydroxyl groups each, although the crystallographic positions of the two Al sites show little difference. The presence of two distinguished 27Al NMR resonances characterized by rather similar chemical shifts but quadrupolar coupling constants differing by roughly a factor of two is explained by different character of the hydrogen bonds, in which the hydroxyls forming the corresponding octahedron around each aluminum site, are involved. The Al-I site characterized by a CQ = 4.6 MHz is surrounded by OHgroups participating in four intralayer and two interlayer hydrogen bonds, while the Al-II site with the smaller quadrupolar constant (2.2 MHz) is coordinated by hydroxides, of which two point toward the intralayer cavities and four OH-bonds are aligned toward the interlayer gallery. In high-resolution solid-state 1H CRAMPS (combination of rotation and multiple-pulse spectroscopy) four signals with an intensity ratio of 1:2:2:1 are resolved which allow to distinguish six nonequivalent hydrogen sites reported in the gibbsite crystal structure and to ascribe them to two types of structural OH groups associated with intralayer and interlayer hydrogen bonds. This study can be applied to characterize the gibbsite-like layer,intergallery interactions associated with hydrogen bonding in the more complex systems, such as synthetic aluminum layered double hydroxides. Copyright © 2010 John Wiley & Sons, Ltd. [source] Dry Grinding of Mefenamic Acid Particles for Enhancement of its Water Dissolution RatePARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 3 2007Tomohiro Iwasaki Abstract This paper details an investigation into the enhancement of the water dissolution rate of mefenamic acid (MA) by means of a dry grinding treatment. The physico-chemical properties of the ground MA particles were analyzed by measurements of specific surface area, powder X-ray diffraction patterns, differential scanning calorimetry thermograms and infrared spectra, and the effects of the change in the physico-chemical properties (especially, crystalline structure) on the dissolution rate were studied. The polymorphic transition from Form I (original) to II and the change of the molecular structure of MA did not occur in the grinding treatments. However, the specific surface area of the MA particles increased, and the crystallinity decreased (i.e., the amorphization level increased) as the grinding progressed. Hydrogen bonds formed between the carboxyl groups of the opposed asymmetric MA molecules were broken gradually after the grinding limit was attained in the grinding system, resulting in an effective improvement of the initial dissolution rate. [source] New organically templated vanadium tellurites: (H2pn)[V2TeO8] (pn is propane-1,3-diamine)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2009Xihe Huang The title compound, poly[propane-1,3-diaminium hexa-,-oxido-dioxidotellurium(IV)divanadium(V)], (C3H12N2)[V2O8Te] or (H2pn)[V2TeO8] (pn is propane-1,3-diamine), contains a two-dimensional anionic layer and the diprotonated pn cation for charge compensation. The anionic layer consists of pyrovanadates and [TeO3] pyramids, which are linked alternately through corner-sharing to form a one-dimensional chain. These one-dimensional chains are crosslinked through two weak Te,O bonds, constructing an anionic layer. Hydrogen bonds are observed involving the diprotonated pn cation and the O atoms of the anionic framework. [source] Poly[diaqua[,-1,4-bis(imidazol-1-ylmethyl)benzene-,2N3:N3,](,- trans -cyclohexane-1,4-carboxylato-,2O1:O4)manganese(II)]: a three-dimensional hydrogen-bonding ,-polonium netACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2009Qing-Wei Wang In the title coordination compound, [Mn(C8H10O4)(C14H14N4)(H2O)2]n, each MnII centre occupies an inversion centre. The 1,4-bis(imidazol-1-ylmethyl)benzene (1,4-bix) ligand and the trans -cyclohexane-1,4-dicarboxylate dianion (chdc) both function in bridging modes, linking adjacent MnII centres into a two-dimensional four-connected (4,4) network. These two-dimensional layers are stacked in a parallel mode. Hydrogen bonds between water molecules and carboxylate O atoms link neighbouring (4,4) networks, yielding a three-dimensional ,-polonium net. [source] | ||||||||||||||||||||||||||||||||||||||||