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Hydrogen Bonding Interactions (hydrogen + bonding_interaction)
Selected AbstractsOrganically Directed Iron Sulfate Chains: Structural Diversity Based on Hydrogen Bonding Interactions.CHEMINFORM, Issue 1 2007Yunlong Fu 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] Hydrogen bonding interaction between 1,4-dioxane and waterINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2010Ajay Chaudhari Abstract This work reports an interaction of 1,4-dioxane with one, two, and three water molecules using the density functional theory method at B3LYP/6-311++G* level. Different conformers were studied and the most stable conformer of 1,4-dioxane-(water)n (n = 1,3) complex has total energies ,384.1964038, ,460.6570694, and ,537.1032381 hartrees with one, two, and three water molecules, respectively. Corresponding binding energy (BE) for these three most stable structures is 6.23, 16.73, and 18.11 kcal/mol. The hydrogen bonding results in red shift in OO stretching and CC stretching modes of 1,4-dioxane for the most stable conformer of 1,4-dioxane with one, two, and three water molecules whereas there was a blue shift in CO symmetric stretching and CO asymmetric stretching modes of 1,4-dioxane. The hydrogen bonding results in large red shift in bending mode of water and large blue shift in symmetric stretching and asymmetric stretching mode of water. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] Spectroscopic rationalization of the separation abilities of decaproline chiral selector in dichloromethane,isopropanol solvent mixtureCHIRALITY, Issue 2 2007Peng Zhang Abstract A chiral column, with decaproline as the chiral selector, has broad chiral selectivity. To understand the separation mechanism of this chiral column, multiple spectroscopic techniques, including optical rotation, electronic circular dichroism, infrared absorption and vibrational circular dichroism, have been used here to study the conformation of the decaproline oligomer in isopropanol(IPA)/dichloromethane(DCM) mixtures. These studies indicate that decaproline oligomer adopts polyproline II conformation in IPA/DCM solvent system (0% IPA , 100% IPA). Hydrogen bonding interactions between CO groups of decaproline and IPA molecules increase as the content of IPA in the solvent mixture increases up to 60% and become less significant from then onwards. These spectroscopic observations are found to have a good correlation with the enantiomeric separation of racemic 2,2,2-trifluoro-1-[10-(2,2,2-trifluoro-1-hydroxy-ethyl-anthracen-9-yl]-ethanol by the decaproline column. Chirality 2006. © 2006 Wiley-Liss, Inc. [source] A Kirkwood-Buff derived force field for amidesJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2006Myungshim Kang Abstract A force field for the computer simulation of aqueous solutions of amides is presented. The force field is designed to reproduce the experimentally observed density and Kirkwood,Buff integrals for N -methylacetamide (NMA), allowing for an accurate description of the NMA activity. Other properties such as the translational diffusion constant and heat of mixing are also well reproduced. The force field is then extended to include N,N,-dimethylacetamide and acetamide with good success. Analysis of the simulations of low concentrations of NMA in water indicates a high degree of solvation with only 15% of the NMA molecules involved in solute,solute hydrogen bonding. There is only a weak angular dependence of the solute,solute hydrogen bonding interaction with a minimum at an angle of 65° for the NH and CO dipole vectors. The models presented here provide a basis for an accurate force field for peptides and proteins. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 1477,1485, 2006 [source] Application of heterogeneous adsorbents in removal of dimethyl phthalate: Equilibrium and heatAICHE JOURNAL, Issue 10 2010Jun Wu Abstract Aminated resin (NDA-101) and oxidized resin (NDA-702) were synthesized to remove Dimethyl phthalate (DMP) from the contaminated water. The equilibrium and heat properties in the course of adsorption process were examined and compared with two commercial heterogeneous adsorbents, namely an acrylic ester resin (Amberlite XAD-7) and a coal-based granular activated carbon (AC-750). The associated equilibrium isotherms can be well fitted by Freundlich equation and the adsorption capacities for DMP followed the order: NDA-702 > NDA-101 > AC-750 > XAD-7. The surface of XAD-7 was demonstrated to be relatively homogeneous through surface energy heterogeneity analysis, offering the sole hydrogen bonding interaction. Contrarily, heterogeneous surface of oxidized resins NDA-702 and the aminated resins NDA-101 exhibited a promising adsorption capacity and affinity toward DMP probably derived by multiple hydrogen bonding, ,,, stacking, and micropore filling interactions. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Microstructure and Molecular Interaction in Glycerol Plasticized Chitosan/Poly(vinyl alcohol) Blending FilmsMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 10 2009Songmiao Liang Abstract Exploring some basic interactions in blending systems is of great significance for designing a blend with controlled structure and properties. This work attempts to analyze microstructure and molecular interaction in glycerol plasticized chitosan/poly(vinyl alcohol) blends by atomic force microscopy, differential scanning calorimetry and ATR-FTIR spectroscopy. Our results show that the blending films are aggregated by spherical chitosan/poly(vinyl alcohol) blending nanoparticles. The size and aggregation behavior of these particles are closely related to glycerol content. The presence of glycerol gives rise to a continuous closing in Tg of poly(vinyl alcohol) and chitosan components, suggesting an improved miscibility of the blend. Strong hydrogen bonding interaction in the blend is observed and further distinguished by peak resolution. Moreover, more interesting evidence on the effect of glycerol in the blends is provided by monitoring the structure evolution of the blend at different blending steps using atomic force microscopy. The formation of strong hydrogen bonding network among glycerol molecules and polymer matrix was considered as the main driving force to result in the changes in the microstructure and miscibility of the blend. [source] Effects of interactions among polyaniline, camphorsulfonic acid and silica on the structure and properties of their conductive hybridsPOLYMER ENGINEERING & SCIENCE, Issue 3 2008Hsun-Tsing Lee In this work, the effects of interactions among polyaniline (PAn), camphorsulfonic acid (CSA), and silica on the structure and properties of their sol-gel hybrids are investigated. These interactions were revealed by FTIR, UV,vis spectra, and XRD patterns. The interaction between PAn and CSA raises conductivities of the CSA-doped PAn/SiO2 (c-PAn/SiO2) hybrids. Moreover, the hydrogen bonding interaction between c-PAn and silicic acid (precursor of SiO2) leads to a less degree of three-dimensional network structure of the SiO2 component in a hybrid with higher PAn content. In addition, because of the interactions among CSA, Pan, and SiO2, the conductive c-PAn-rich phase distributes uniformly in the hybrid and thermal resistance of the hybrid is enhanced consequently. Besides, the c-PAn/SiO2 hybrid with higher SiO2 content exhibits more significant blue-shift of its polaron band, lower conductivity, and higher thermal resistance. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source] Correlation between hydrogen-bonding interaction and mechanical properties of polyimide fibersPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 4 2009Xiangyang Liu Abstract Novel co-polymerization polyimide (PI) fibers based on 4,4,-oxydianiline (ODA)-pyromellitic dianhydride (PMDA) were prepared. 2-(4-Aminophenyl)-5-aminobenzimidazole (PABZ) containing the NH group was introduced into the structure of the fibers as the proton donor. The results of Fourier transform infrared (FTIR) and dynamic mechanical analysis (DMA) showed that hydrogen bonding occured between the NH group and chains, which strongly enhanced interchain interaction. This hydrogen bonding interaction increased the tensile strength and initial modulus of the PI fibers up to 2.5 times and 26 times, respectively, compared to those of homo-PI PMDA-ODA fibers with no hydrogen-bonding interaction because of the absence of proton donors after the imidization process. In the mean time, glass transition temperature (Tg) of the modified PI fibers was found to be 410,440°C, which was higher than that of the homo-PI PMDA-ODA fibers. From the result, a novel access to molecular design and manufacture of high performance PI fibers with good properties could be provided. Copyright © 2009 John Wiley & Sons, Ltd. [source] From 1D Polymeric Chain to Two-fold Parallel Interpenetration of (4,4) Net: Synthesis and Characterization of Two New Copper(II) Complexes Derived from Highly Polydentate Aminopolycarboxylate LigandCHINESE JOURNAL OF CHEMISTRY, Issue 7 2008Ya-Pan WU Abstract Two new copper(II) polymers, {[Cu2(egta)(bpe)(H2O)2]·H2O}n (1) and {[Cu2(egta)(bipy)(H2O)2]·5H2O}n(2), [H4egta=3,12-bis(carboxymethyl)-6,9-dioxa-3,12-diazatetradecanedioic acid, bpe=1,2-bis(4-pyridyl)ethane, bipy4,4,-bipyridyl] have been synthesized and structurally characterized by single-crystal X-ray diffraction, elemental analysis, IR spectra and TG analysis. The structure determination reveals that both 1 and 2 crystallize in a monoclinic system, space group P21/c. Complex 1 exhibits a two-fold parallel interpenetration of (4,4) net framework consisting of 1D zigzag chains interlocked together through hydrogen bonding interaction. However, the meso-helix chains of 2 are packed to form 2D supramolecular structures. Interestingly, in 2, the host frameworks encapsulate a unique pentamer water cluster and are further connected into 1D tapes by water-water hydrogen bonding interaction. Magnetic measurements reveal that there is a weak ferromagnetic interaction between the adjacent Cu(II) ions in 1. [source] New Approaches to 12-Coordination: Structural Consequences of Steric Stress, Lanthanoid Contraction and Hydrogen BondingEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2010Anthony S. R. Chesman Abstract The anionic dinitrile ligand dicyanonitrosomethanide (dcnm), C(CN)2(NO),, and the anion resulting from its addition product with water, carbamoylcyanonitrosomethanide (ccnm), C(CN)(CONH2)(NO),, have been incorporated into lanthanoid complexes and display unusual ,2(N,O) nitroso coordination modes. (Et4N)3[Ln(ccnm)6] (1Ln; 1Ln = 1La, 1Ce, 1Pr, 1Nd, 1Sm) and (Me4N)3[Ln(ccnm)6] (2Ln; 2Ln = 2La, 2Ce, 2Pr, 2Nd) are systems containing 12-coordinate homoleptic trianionic lanthanoidate complexes. The nitroso groups of the ccnm ligands form three-membered ring chelates with the lanthanoid metal centre, with the asymmetry of the nitroso ,2 interactions dependent upon the intramolecular N,H···O=N hydrogen bonding. Additional intermolecular hydrogen bonding interactions exist between adjacent amide and nitrile groups giving rise to 3D ,-Po and 6,8-connected (412.63)(420.68) networks in 1Ln and 2Ln, respectively. The compounds (Me4N)3[Ln(dcnm)6] (3Ln; 3Ln = 3La, 3Ce, 3Nd, 3Sm) also contain a 12-coordinate trianionic lanthanoidate complex with the nitroso group exhibiting a highly symmetrical ,2 interaction. The sterically crowded environments of [Ln(18-crown-6)(dcnm)3] (4Ln; 4Ln = 4La, 4Ce, 4Pr, 4Nd) result in a shift towards a more asymmetric ,2 bonding of the nitroso group with decrease in the Ln3+ radius. There is a corresponding increase of the Ln,O,N angle, and one ligand is ,1(O) binding in 4Nd. The dcnm ligands in the discrete complexes [La(phen)3(dcnm)(3,x)Clx], x , 0.25 (5) (phen = 1,10-phenanthroline), (Et4N)[Ce(phen)2(dcnm)4] (6a/b, 6c) and [Ce(phen)2(dcnm)Cl2H2O] (7) display a variety of coordination modes. Complex 5 has 1D chains formed by ,,, stacking of adjacent phen co-ligands. Complexes 6 contain the monoanionic complex [Ce(phen)2(dcnm)4], with two geometric isomers present in the crystal structure of 6a/b. Complex 7 forms extended 1D chains via hydrogen bonding between coordinated water and chloride atoms and an extensive array of face-to-face , interactions. [source] Reaction of 1,3,5-Triazacyclohexanes with TiCl4: Formation of Cationic ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2005Randolf D. Köhn Abstract N -substituted 1,3,5-triazacyclohexanes [R3TAC; R = cyclohexyl, p -fluorobenzyl or Ph(CH2)n (n = 1, 2, 3)] react with excess TiCl4 to give the corresponding cationic ,3 complexes [(R3TAC)TiCl3][Ti2Cl9]. Attempts to prepare complexes with titanium-free anions at lower Ti:R3TAC ratio or with added Me3SiOTf lead to the same cations with [Ti2Cl10]2, and [Ti2Cl8(OTf)], anions. Five complexes as well as (p -fluorobenzyl)3TAC have been characterised by X-ray crystallography. The ring C,H bonds engage in hydrogen bonding interactions in the crystals and strongly solvent and anion dependent 1H NMR signals are detected in solution. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Crystal structure of human Rad GTPase of the RGK-familyGENES TO CELLS, Issue 8 2006Arry Yanuar Rad (Ras associated with diabetes) is an RGK-family small GTPase that is over-expressed in the skeletal muscle of humans with type II diabetes. Unlike other small GTPases, RGK family members including Rad lack several conserved residues in the GTPase domain. Here, we report the crystal structure of the GTPase domain of human Rad in the GDP-bound form at 1.8 Å resolution. The structure revealed unexpected disordered structures of both switches I and II. We showed that the conformational flexibility of both switches is caused by non-conservative substitutions in the G2 and G3 motifs forming the switch cores together with other substitutions in the structural elements interacting with the switches. Glycine-rich sequences of the switches would also contribute to the flexibility. Switch I lacks the conserved phenylalanine that makes non-polar interactions with the guanine base in H-Ras. Instead, water-mediated hydrogen bonding interactions were observed in Rad. The GDP molecule is located at the same position as in H-Ras and adopts a similar conformation as that bound in H-Ras. This similarity seems to be endowed by the conserved hydrogen bonding interactions with the guanine base-recognition loops and the magnesium ion that has a typical octahedral coordination shell identical to that in H-Ras. [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] Hydrogen bonding characterization of XH2NH2···HNO(X = B, Al, Ga) complexes: A theoretical investigationINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2008Ying Liu Abstract The complexes of XH2NH2···HNO(X = B, Al, Ga) are characterized as head to tail with hydrogen bonding interactions. The structural characteristics can be confirmed by atoms in molecules (AIM) analysis, which also provide comparisons of hydrogen bonds strengths. The calculated interaction energies at G2MP2 level show that stability of complexes decrease as BH2NH2···HNO > AlH2NH2···HNO > GaH2NH2···HNO. On the basis of the vibrational frequencies calculations, there are red-shifts for ,(X1H) and blue-shifts for ,(NH) in the complexes on dihydrogen bonding formations (X1H···HN). On hydrogen bonding formations (NH···O), there are red-shifts for ,(NH) compared to the monomers. Natural bond orbital (NBO) analysis is used to discuss the reasons for the ,(X1H) and ,(NH) stretching vibrational shifts by hyperconjugation, electron density redistribution, and rehybridization. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Understanding selenocysteine through conformational analysis, proton affinities, acidities and bond dissociation energiesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2008Damanjit Kaur Abstract Density functional methods have been employed to characterize the gas phase conformations of selenocysteine. The 33 stable conformers of selenocysteine have been located on the potential energy surface using density functional B3LYP/6-31+G* method. The conformers are analyzed in terms of intramolecular hydrogen bonding interactions. The proton affinity, gas phase acidities, and bond dissociation energies have also been evaluated for different reactive sites of selenocysteine for the five lowest energy conformers at B3LYP/6-311++G*//B3LYP/6-31+G* level. Evaluation of these intrinsic properties reflects the antioxidant activity of selenium in selenocysteine. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Intra and intermolecular hydrogen bonding in formohydroxamic acid,INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 1 2008Damanjit Kaur Abstract The presence of hydrogen bonding interactions in several tautomeric forms of formohydroxamic acid (FHA) and 1:1 association among the tautomeric forms and water-coordinated tautomeric forms of FHA is explored theoretically. Out of the seven equilibrium structures, four tautomeric forms have been selected for aggregation with single water molecule and dimer formation. Fifteen aggregates of FHA with H2O have been optimized at MP2/AUG-cc-PVDZ level and analyzed for intramolecular and intermolecular H-bond interactions. Twenty-seven dimers of the four tautomeric forms have been obtained at MP2/6-31+G* level. The stabilization energies associated with dimerization and adduct formation with water are the result of H-bond interactions and range from very weak to medium. The atomic charges and NBO analysis indicate that the electrostatic and the charge transfer are the important components favoring H-bond formation. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Highly Ordered Interstitial Water Observed in Bone by Nuclear Magnetic Resonance,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 4 2005Erin E Wilson Abstract NMR was used to study the nanostructure of bone tissue. Distance measurements show that the first water layer at the surface of the mineral in cortical bone is structured. This water may serve to couple the mineral to the organic matrix and may play a role in deformation. Introduction: The unique mechanical characteristics of bone tissue have not yet been satisfactorily connected to the exact molecular architecture of this complex composite material. Recently developed solid-state nuclear magnetic resonance (NMR) techniques are applied here to the mineral component to provide new structural distance constraints at the subnanometer scale. Materials and Methods: NMR dipolar couplings between structural protons (OH, and H2O) and phosphorus (PO4) or carbon (CO3) were measured using the 2D Lee-Goldburg Cross-Polarization under Magic-Angle Spinning (2D LG-CPMAS) pulse sequence, which simultaneously suppresses the much stronger proton-proton dipolar interactions. The NMR dipolar couplings measured provide accurate distances between atoms, e.g., OH and PO4 in apatites. Excised and powdered femoral cortical bone was used for these experiments. Synthetic carbonate (,2-4 wt%)-substituted hydroxyapatite was also studied for structural comparison. Results: In synthetic apatite, the hydroxide ions are strongly hydrogen bonded to adjacent carbonate or phosphate ions, with hydrogen bond (O-H) distances of ,1.96 Å observed. The bone tissue sample, in contrast, shows little evidence of ordered hydroxide. Instead, a very ordered (structural) layer of water molecules is identified, which hydrates the small bioapatite crystallites through very close arrangements. Water protons are ,2.3-2.55 Å from surface phosphorus atoms. Conclusions: In synthetic carbonated apatite, strong hydrogen bonds were observed between the hydroxide ions and structural phosphate and carbonate units in the apatite crystal lattice. These hydrogen bonding interactions may contribute to the long-range stability of this mineral structure. The biological apatite in cortical bone tissue shows evidence of hydrogen bonding with an ordered surface water layer at the faces of the mineral particles. This structural water layer has been inferred, but direct spectroscopic evidence of this interstitial water is given here. An ordered structural water layer sandwiched between the mineral and the organic collagen fibers may affect the biomechanical properties of this complex composite material. [source] Interplay between anion-, and hydrogen bonding interactionsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 1 2009Daniel Escudero Abstract The interplay between two important noncovalent interactions involving aromatic rings is studied by means of high level ab initio calculations. They demonstrate that synergistic effects are present in complexes where anion-, and hydrogen bonding interactions coexist. These synergistic effects have been studied using the "atoms-in-molecules" theory and the Molecular Interaction Potential with polarization partition scheme. The present study examines how these two interactions mutually influence each other. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009 [source] How resonance assists hydrogen bonding interactions: An energy decomposition analysisJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 1 2007John Frederick Beck Abstract Block-localized wave function (BLW) method, which is a variant of the ab initio valence bond (VB) theory, was employed to explore the nature of resonance-assisted hydrogen bonds (RAHBs) and to investigate the mechanism of synergistic interplay between , delocalization and hydrogen-bonding interactions. We examined the dimers of formic acid, formamide, 4-pyrimidinone, 2-pyridinone, 2-hydroxpyridine, and 2-hydroxycyclopenta-2,4-dien-1-one. In addition, we studied the interactions in ,-diketone enols with a simplified model, namely the hydrogen bonds of 3-hydroxypropenal with both ethenol and formaldehyde. The intermolecular interaction energies, either with or without the involvement of , resonance, were decomposed into the Hitler-London energy (,EHL), polarization energy (,Epol), charge transfer energy (,ECT), and electron correlation energy (,Ecor) terms. This allows for the examination of the character of hydrogen bonds and the impact of , conjugation on hydrogen bonding interactions. Although it has been proposed that resonance-assisted hydrogen bonds are accompanied with an increasing of covalency character, our analyses showed that the enhanced interactions mostly originate from the classical dipole,dipole (i.e., electrostatic) attraction, as resonance redistributes the electron density and increases the dipole moments in monomers. The covalency of hydrogen bonds, however, changes very little. This disputes the belief that RAHB is primarily covalent in nature. Accordingly, we recommend the term "resonance-assisted binding (RAB)" instead of "resonance-assisted hydrogen bonding (RHAB)" to highlight the electrostatic, which is a long-range effect, rather than the electron transfer nature of the enhanced stabilization in RAHBs. © 2006 Wiley Periodicals, Inc. J Comput Chem 28: 455,466, 2007 [source] Effect of temperature and moisture on the miscibility of amorphous dispersions of felodipine and poly(vinyl pyrrolidone)JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 1 2010Patrick J. Marsac Abstract The physical stability of amorphous molecular level solid dispersions will be influenced by the miscibility of the components. The goal of this work was to understand the effects of temperature and relative humidity on the miscibility of a model amorphous solid dispersion. Infrared spectroscopy was used to evaluate drug,polymer hydrogen bonding interactions in amorphous solid dispersions of felodipine and poly(vinyl pyrrolidone) (PVP). Samples were analyzed under stressed conditions: high temperature and high relative humidity. The glass transition temperature (Tg) of select systems was studied using differential scanning calorimetry (DSC). Atomic force microscopy (AFM) and transmission electron microscopy (TEM) were used to further investigate moisture-induced changes in solid dispersions. Felodipine-PVP solid dispersions showed evidence of adhesive hydrogen bonding interactions at all compositions studied. The drug,polymer intermolecular interactions were weakened and/or less numerous on increasing the temperature, but persisted up to the melting temperature of the drug. Changes in the hydrogen bonding interactions were found to be reversible with changes in temperature. In contrast, the introduction of water into amorphous molecular level solid dispersions at room temperature irreversibly disrupted interactions between the drug and the polymer resulting in amorphous-amorphous phase separation followed by crystallization. DSC, AFM, and TEM results provided further evidence for the occurrence of moisture induced immiscibility. In conclusion, it appears that felodipine-PVP solid dispersions are susceptible to moisture-induced immiscibility when stored at a relative humidity ,75%. In contrast, the solid dispersions remained miscible on heating. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:169,185, 2010 [source] Thermally stable porous supramolecular frameworks based on the metal and ,,, stacking directed self-assembly of 2,6-pyridyldicarboxylic acid bis-4-pyridylamideJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 8 2003Juan C. Noveron Abstract We report the formation of two thermally stable supramolecular structures based on 2,6-pyridyldicarboxylic acid bis-4-pyridylamide (PyI) and bis(hexafluoroacetylacetonato)manganese(II) that exhibits a microporous structure with cavities bearing hydrogen bonding motifs that can enclathrate acetone and methanol molecules via well-positioned hydrogen bonding interactions. Single-crystal x-ray diffraction in combination with thermogravimetric analysis and X-ray powder diffraction (XRPD) studies were utilized to study the structure and thermal behavior of trans -[Mn(hfacac)2(PyI)2]·2(CH3)2CO (1) and trans -[Mn(hfacac)2(PyI)2]·2CH3OH (2). Our studies indicated that 1 and 2 are isostructural with respect to their supramolecular assembly and trap solvent molecules along the crystallographic b direction via the inwardly directed hydrogen bonding motifs of the PyI component. These solvent molecules can be thermally removed to generate a crystalline material with micropores bearing hydrogen bonding rich sites within an overall supramolecular matrix similar to 1 and 2. The removal of the guest solvent molecules is reversible and can be followed with XRPD. Copyright © 2003 John Wiley & Sons, Ltd. [source] Vibrational spectra of bis(L -ornithinium) chloride nitrate sulfateJOURNAL OF RAMAN SPECTROSCOPY, Issue 1 2005S. Ramaswamy Abstract The Raman and infrared absorption spectra of 2(C5H14N2O22+)·Cl,·NO3,·SO42, crystal containing three anions were recorded at room temperature and were interpreted in the light of crystal structure data. The presence of a carbonyl group was identified. The carboxylic group was found to exist as COOH. The formation of OH···O, NH···O and NH···Cl asymmetric hydrogen bonds contributes considerably to the crystal cohesion and is responsible for the changes in the position and intensity of several bands. The vibrational spectra show that the anions were found to coordinate through hydrogen bonding interactions to other ligands in the crystal. The lattice wavenumbers of the halide radical (chlorine anion) were also assigned in terms of hydrogen bond vibrations. Copyright © 2004 John Wiley & Sons, Ltd. [source] Raman and IR spectral studies of D -phenylglycinium perchlorateJOURNAL OF RAMAN SPECTROSCOPY, Issue 9 2002S. Ramaswamy The Raman and infrared spectra of D -phenylglycinium perchlorate were recorded at room temperature. Tentative vibrational assignments of the observed wavenumbers were made by comparison with the vibrational wavenumbers of glycine, phenylalanine and other similar compounds. Anions were found to coordinate through hydrogen bonding interactions to other ligands in the crystal, affecting the Td symmetry and thereby causing the degeneracies of several modes to be removed. The extensive intermolecular hydrogen bonding in the crystal leads to a shift of bands due to the stretching and bending modes of various functional groups. The broadening and appearance of multiple bands for the carbonyl stretching mode due to the resonance interaction is also discussed. Copyright © 2002 John Wiley & Sons, Ltd. [source] Prediction of the Solubility, Activity Coefficient and Liquid/Liquid Partition Coefficient of Organic CompoundsMOLECULAR INFORMATICS, Issue 9 2004H. Hilal Abstract Solvation models, based on fundamental chemical structure theory, were developed in the SPARC mechanistic tool box to predict a large array of physical properties of organic compounds in water and in non-aqueous solvents strictly from molecular structure. The SPARC self-interaction solvation models that describe the intermolecular interaction between like molecules (solute-solute or solvent-solvent) were extended to quantify solute-solvent interaction energy in order to estimate the activity coefficient in almost any solvent. Solvation models that include dispersion, induction, dipole-dipole and hydrogen bonding interactions are used to describe the intermolecular interaction upon placing an organic solute molecule in any single or mixed solvent system. In addition to estimation of the activity coefficient for 2674 organic compounds, these solvation models were validated on solubility and liquid/liquid distribution coefficient in more than 163 solvents including water. The RMS deviations of the calculated versus observed activity coefficients, solubilities and liquid/liquid distribution coefficients were 0.272,log mole fraction, 0.487,log mole fraction and 0.44,log units, respectively. [source] Spectroscopic Properties of Various Quinolone Antibiotics in Aqueous,organic Solvent Mixtures¶PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2004Hyoung-Ryun Park The spectroscopic properties of enoxacin (ENO), oxolinic acid (OXO) and nalidixic acid (NAL) were studied in various H2O-CH3OH and H2O-CH3CN mixed solvents because these solvents were thought to behave as a biological mimetic system. ENO has piperazinyl group, but OXO and NAL do not have this substituent. The fluorescence emission spectra of ENO were very sensitive to the composition of the solvents. In the Lippert-Mataga analysis of the steady-state fluorescence data, clear reverse solvatochromism was exhibited for ENO in both mixed solvents. This observation can be explained using the excited state twisted intramolecular charge transfer (TICT) from the nitrogen of the piperazinyl group to the keto oxygen. Theoretical calculations further support this observation. The nonradiative and radiative rate constants of these molecules were analyzed as a function of dipolarity,polarizability (,*) and hydrogen bond donor acidity (,) of the mixed solvents. These results for ENO were consistent with the suggested mechanism of the TICT very well. The influence of bulk dielectric effect was more significant relative to the specific hydrogen bonding interactions. The emission spectra of OXO and NAL do not exhibit any characteristic responses to the properties of the solvent. [source] Miscibility enhancement of supramolecular polymer blends through complementary multiple hydrogen bonding interactionsPOLYMER INTERNATIONAL, Issue 7 2010Shiao-Wei Kuo Abstract We have investigated the miscibility behavior and specific interactions of supramolecular poly[vinylbenzylthymine- co -(butyl methacrylate)] (T-PBMA) and poly[(2-vinyl-4,6-diamino-1,3,5-triazine)- co -styrene] (VDAT-PS) blends with respect to their vinylbenzylthymine (VBT) and 2-vinyl-4,6-diamino-1,3,5-triazine (VDAT) contents. Fourier transform infrared spectroscopy revealed that multiple hydrogen bonding interactions occurred exclusively between the VDAT and VBT units, which were stronger than adenine and thymine interactions. A miscibility window occurred in the VDAT-PS/T-PBMA blend system when the VBT and VDAT fractions in the copolymers were greater than 7 mol%, as predicted using the Painter,Coleman association model. Copyright © 2010 Society of Chemical Industry [source] Hydrogen bond-mediated self-assembly and supramolecular structures of diblock copolymer mixturesPOLYMER INTERNATIONAL, Issue 5 2009Shiao-Wei Kuo Abstract This review summarizes recent advances in the preparation of hydrogen bonding block copolymer mixtures and the supramolecular structures they form through multiple hydrogen bonding interactions. Hydrogen bonding in block copolymer mixtures that form nanostructures and have unusual electronic, photonic and magnetic properties is a topic of great interest in polymer science. Combining the self-assembly of block copolymers with supramolecular structures offers unique possibilities to create new materials with tunable and responsive properties. The self-assembly of structures from diblock copolymer mixtures in the bulk state is readily controlled by varying the weight fraction of the block copolymer mixture and the copolymer composition; in solution, the morphologies are dependent on the copolymer composition, the copolymer concentration, the nature of the common solvent, the amount of the selective solvent and, most importantly, the hydrogen bonding strength. Copyright © 2008 Society of Chemical Industry [source] Rheology of polyurethane solutions with different solventsPOLYMER INTERNATIONAL, Issue 1 2002L de Vasconcelos Abstract Hard segment hydrogen bonding interactions in a particular polyurethane segmented copolymer have been analysed through a viscometric approach to determine the behaviour of polyurethane solutions with different solvent compositions. Analysis of log,,spversus log c[,] master curves (solely comprising dilute and semidilute regimes) showed that these systems could be differentiated by the slope of the first part of the curve (dilute regime), the characteristic reduced concentration c*[,], and the slope of the second part of the curve (semidilute regime), differences which were related to a possible occurrence of polymer aggregates. Experiments with solutions in the concentrated regime, at different temperatures, were used to relate non-Newtonian behaviour to hydrogen bonding. © 2001 Society of Chemical Industry [source] Mining protein dynamics from sets of crystal structures using "consensus structures"PROTEIN SCIENCE, Issue 4 2010Gerard J. P. van Westen Abstract In this work, we describe two novel approaches to utilize the dynamic structure information implicitly contained in large crystal structure data sets. The first approach visualizes both consistent as well as variable ligand-induced changes in ligand-bound compared with apo protein crystal structures. For this purpose, information was mined from B-factors and ligand-induced residue displacements in multiple crystal structures, minimizing experimental error and noise. With this approach, the mechanism of action of non-nucleoside reverse transcriptase inhibitors (NNRTIs) as an inseparable combination of distortion of protein dynamics and conformational changes of HIV-1 reverse transcriptase was corroborated (a combination of the previously proposed "molecular arthritis" and "distorted site" mechanisms). The second approach presented here uses "consensus structures" to map common binding features that are present in a set of structures of NNRTI-bound HIV-1 reverse transcriptase. Consensus structures are based on different levels of structural overlap of multiple crystal structures and are used to analyze protein,ligand interactions. The structures are shown to yield information about conserved hydrogen bonding interactions as well as binding-pocket flexibility, shape, and volume. From the consensus structures, a common wild type NNRTI binding pocket emerges. Furthermore, we were able to identify a conserved backbone hydrogen bond acceptor at P236 and a novel hydrophobic subpocket, which are not yet utilized by current drugs. Our methods introduced here reinterpret the atom information and make use of the data variability by using multiple structures, complementing classical 3D structural information of single structures. [source] Conformations of Betanova in aqueous trifluoroethanol,BIOPOLYMERS, Issue 10 2010Danny P. Chagolla Abstract Conformations of the designed peptide Betanova in 42% trifluoroethanol/water (v/v) were explored. Circular dichroism (CD) observations provided no evidence for the presence of significant amounts of ,-structures in water, in TFE/water, or in ethanol/water. Nuclear magnetic resonance (NMR) diffusion experiments showed no significant difference in the hydrodynamic radius of the peptide in water and in 42% TFE/water. However, calculations indicated that the hydrodynamic radii of the triple-stranded ,-sheet, originally proposed for Betanova by Kortemme et al. (Science 1998, 281, 253-256), and a variety of partially folded forms of Betanova would be similar and likely could not be convincingly distinguished by diffusion experiments. Temperature coefficients (,,/,T) of the peptide NH chemical shifts are similar in water and 42% TFE/water, implying that most of these protons are highly solvent exposed in both solvents and likely do not participate in intramolecular hydrogen bonding interactions. Possible exceptions to this conclusion are the Lys9 and Lys15 residues, where a more positive coefficient may indicate that these residues are involved to some extent in local turn structures. Peptide proton,solvent fluorine intermolecular nuclear Overhauser effect (NOE)s at 25°C were consistent with the presence of a mixture of conformations, which could include the triple-stranded ,-sheet structure as a minor component. At 0°C, peptide-TFE NOEs indicated that TFE interacts strongly enough with many protons of Betanova that alcohol-peptide interactions persist for times of the order of nanoseconds, appreciably longer than the encounter time characteristic of mutual diffusion of TFE and the solute. © 2010 Wiley Periodicals, Inc. Biopolymers 93: 893,903, 2010. [source] |