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Intermolecular Hydrogen Bonds (intermolecular + hydrogen_bond)
Kinds of Intermolecular Hydrogen Bonds Selected AbstractsAsymmetry 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] Synthesis and X-ray study of the 6-(N -pyrrolyl)purine and thymine derivatives of 1-aminocyclopropane-1-carboxylic acidCHEMICAL BIOLOGY & DRUG DESIGN, Issue 5 2004M. Cetina Abstract:, The novel purine and pyrimidine derivatives of 1-aminocyclopropane-1-carboxylic acid 1 and 2 were obtained by alkylation of 6-(N -pyrrolyl)purine and thymine with methyl 1-benzamido-2-chloromethylcyclopropanecarboxylate. X-ray crystal structure analysis shows that the cyclopropane rings in 1 and 2 posses Z -configuration. The cyclopropane ring atoms and attached atoms of the benzamido and methoxycarbonyl moiety of both molecules are disposed perpendicularly to each other. The carbonyl oxygen of the methoxycarbonyl moiety adopts in both compounds a synperiplanar conformation with respect to the midpoint of the distal bond of the cyclopropane ring. The torsion angles , and , for the 1-aminocyclopropane-1-carboxylic acid residue in 1 and 2 correspond to a folded conformation, while the torsion angles , define antiperiplanar conformation. Intermolecular hydrogen bonds connect the molecules of 1 into dimers. Each dimer is hydrogen-bonded with four ethanol molecules, thus forming discrete unit. On the contrary, intermolecular hydrogen bonds link the molecules of 2 generating three-dimensional network. [source] Electrochemical Oxidation of QuercetinELECTROANALYSIS, Issue 22 2003Maria, Oliveira Brett Abstract The mechanism of electrochemical oxidation of quercetin on a glassy carbon electrode has been studied using cyclic, differential pulse and square-wave voltammetry at different pH. It proceeds in a cascade mechanism, related with the two catechol hydroxyl groups and the other three hydroxyl groups which all present electroactivity, and the oxidation is pH dependent. Quercetin also adsorbs strongly on the electrode surface; and the final oxidation product is not electroactive and blocks the electrode surface. The oxidation of the catechol 3,,4,-dihydroxyl electron-donating groups, occurs first, at very low positive potentials, and is a two electron two proton reversible reaction. The hydroxyl group oxidized next was shown to undergo an irreversible oxidation reaction, and this hydroxyl group can form a intermolecular hydrogen bond with the neighboring oxygen. The other two hydroxyl groups also have an electron donating effect and their oxidation is reversible. [source] Effect of water on zinc (II), cadmium (II) complexes with pyridylimidazole: Theoretical study of stability and electronic spectrumINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2006Yi Liao Abstract The geometry structures of complexes such as [Zn(PIm)2(H2O)] and [Cd(PIm)2(H2O)2] [PIm = (2-(2,-pyridyl) imidazole)] are optimized by density functional theory (DFT) B3LYP methods. On the basis of their stable structures, the stability of the coordinated water existing in the complexes is analyzed quantitatively in terms of the interaction between the central metal and the coordinated water. The interaction energy of the Zn pyridylimidazole complex increased obviously by considering the intermolecular hydrogen bond (OH,N). The theoretical calculation well explained penta- and hexa-coordinated conformation, respectively, in Zn and Cd pyridylimidazole complexes. The spectral properties of the Zn Cd complexes have been studied by time-dependent density functional theory (TD-DFT). The calculation results show that the coordinated waters in Cd complexes have little effect on their spectral properties. While the axially coordinated waters in Zn pyridylimidazole cause a red shift in the absorption wavelength and change the pattern of charge transfer as a result of the effect of polarization from intermolecular hydrogen bond. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source] Time-dependent density functional theory study on the electronic excited-state geometric structure, infrared spectra, and hydrogen bonding of a doubly hydrogen-bonded complexJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 16 2009Yufang Liu Abstract The geometric structures and infrared (IR) spectra in the electronically excited state of a novel doubly hydrogen-bonded complex formed by fluorenone and alcohols, which has been observed by IR spectra in experimental study, are investigated by the time-dependent density functional theory (TDDFT) method. The geometric structures and IR spectra in both ground state and the S1 state of this doubly hydrogen-bonded FN-2MeOH complex are calculated using the DFT and TDDFT methods, respectively. Two intermolecular hydrogen bonds are formed between FN and methanol molecules in the doubly hydrogen-bonded FN-2MeOH complex. Moreover, the formation of the second intermolecular hydrogen bond can make the first intermolecular hydrogen bond become slightly weak. Furthermore, it is confirmed that the spectral shoulder at around 1700 cm,1 observed in the IR spectra should be assigned as the doubly hydrogen-bonded FN-2MeOH complex from our calculated results. The electronic excited-state hydrogen bonding dynamics is also studied by monitoring some vibraitonal modes related to the formation of hydrogen bonds in different electronic states. As a result, both the two intermolecular hydrogen bonds are significantly strengthened in the S1 state of the doubly hydrogen-bonded FN-2MeOH complex. The hydrogen bond strengthening in the electronically excited state is similar to the previous study on the singly hydrogen-bonded FN-MeOH complex and play important role on the photophysics of fluorenone in solutions. © 2009 Wiley Periodicals, Inc. J Comput Chem 2009 [source] Chitosan(chitin)/cellulose composite biosorbents prepared using ionic liquid for heavy metal ions adsorptionAICHE JOURNAL, Issue 8 2009Xiaoqi Sun Abstract Chitosan(chitin)/cellulose composites as biodegradable biosorbents were prepared under an environment-friendly preparation processes using ionic liquids. Infrared and X-ray photoelectron spectra indicated the stronger intermolecular hydrogen bond between chitosan and cellulose, and the hydroxyl and amine groups were believed to be the metal ion binding sites. Among the prepared biosorbents, freeze-dried composite had higher adsorption capacity and better stability. The capacity of adsorption was found to be Cu(II) (0.417 mmol/g) > Zn(II) (0.303 mmol/g) > Cr(VI) (0.251 mmol/g) > Ni(II) (0.225 mmol/g) > Pb(II) (0.127 mmol/g) at the same initial concentration 5 mmol L,1. In contrast to some other chitosan-type biosorbenrts, preparation and component of the biosorbent were obviously more environment friendly. Moreover, adsorption capacity of chitosan in the blending biosorbent could be fully shown. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Role of hydrogen bonding in the oxidation potential of enolsJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 7 2003Mukul Lal Abstract Three stable ,,,-dimesityl enols with heteroaromatic rings in the ,-position were synthesized to study the effect of OH···N hydrogen bonding on the oxidation potentials of enols. In contrast to its solid-state structure, enol E1 exists predominantly as intramolecularly hydrogen-bonded species in solution. For enol E2 an intermolecular hydrogen bond and for E3 a partial proton transfer were established based on NMR, dilution experiments, solvent dependence and UV,visible spectroscopic studies. Cyclic voltammetric investigations revealed that OH···N hydrogen bonding may shift the oxidation potentials of enols by up to 510,mV cathodically. Copyright © 2003 John Wiley & Sons, Ltd. [source] Crystal packing in vicinal diols CnHm(OH)2ACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2002Carolyn Pratt Brock The O,H,O bonds in vic -diols CnHm(OH)2 have been studied using data retrieved from the Cambridge Structural Database. About half of these diols form complete, or almost complete, sets of intermolecular O,H,O bonds (i.e. two satisfied donors per molecule). For this half of the structures the frequencies of high-symmetry space groups and of structures with Z,,>,1 (more than one molecule in the asymmetric unit) are substantially elevated. The most common motif among fully bonded structures is an dimer, which can be linked in a variety of ways to form one-, two- or even three-dimensional patterns. Most of the other half of the vic -diols form simple O,H,O chains in which each OH group participates in only one intermolecular hydrogen bond. The space-group frequencies for this second group of structures are unexceptional. The most important factor determining the extent of O,H,O bond formation is the degree of substitution of the vic -diol. The spatial segregation of OH groups that is necessary for the formation of O,H,O bonds is found to make the dense filling of space more difficult because the intermolecular spacings that are appropriate for the O,H,O bonds may be inappropriate for the rest of the molecule. [source] Ferrocene compounds: methyl 1,-aminoferrocene-1-carboxylateACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2010Christoph Förster The title compund, [Fe(C5H6N)(C7H7O2)], features one strong intermolecular hydrogen bond of the type N,H...O=C [N...O = 3.028,(2),Å] between the amine group and the carbonyl group of a neighbouring molecule, and vice versa, to form a centrosymmetric dimer. Furthermore, the carbonyl group acts as a double H-atom acceptor in the formation of a second, weaker, hydrogen bond of the type C,H...O=C [C...O = 3.283,(2),Å] with the methyl group of the ester group of a second neighbouring molecule at (x, ,y , , z , ). The methyl group also acts as a weak hydrogen-bond donor, symmetry-related to the latter described C,H...O=C interaction, to a third molecule at (x, ,y , , z + ) to form a two-dimensional network. The cyclopentadienyl rings of the ferrocene unit are parallel to each other within 0.33,(3)° and show an almost eclipsed 1,1,-conformation, with a relative twist angle of 9.32,(12)°. The ester group is twisted slightly [11.33,(8)°] relative to the cylopentadienyl plane due to the above-mentioned intermolecular hydrogen bonds of the carbonyl group. The N atom shows pyramidal coordination geometry, with the sum of the X,N,Y angles being 340,(3)°. [source] Monothioindigo, determined by microcrystal structure analysisACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2010Jürgen Brüning Indigo and thioindigo pigments are used for a wide range of applications. The crystal structure of the mixed compound monothioindigo [systematic name: (E)-2-(3-oxo-2,3-dihydro-1-benzothiophen-2-ylidene)-2,3-dihydro-1H -indol-3-one], C16H9NO2S, has been determined by microcrystal structure analysis from a crystal with a size of just 1 × 2 × 10,µm. The crystal structure of monothioindigo resembles those of indigo and thioindigo. The molecules show orientational disorder, with site-occupation factors of 0.962,(2) and 0.038,(2) for the major and minor disorder components, respectively. The indigo fragment donates an intermolecular hydrogen bond, leading to a criss-cross arrangement of molecules similar to that in indigo, whereas the thioindigo fragment exhibits only van der Waals interactions and molecular stacking, similar to that in thioindigo. [source] 5-(3,4-Dimethoxybenzyl)-7-isopropyl-1,3,5-triazepane-2,6-dione acetonitrile solvate refined using a multipolar atom modelACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2010Krzysztof Ejsmont The crystal structure of the title compound, C16H23N3O4·CH3CN, was refined using a multipolar atom model transferred from an experimental electron-density database. The refinement showed some improvement in crystallographic statistical indices compared with the independent atom model. The triazepane ring adopts a twist-boat conformation. In the crystal structure, the molecule forms intermolecular contacts with 14 different neighbours. There are two N,H...O and one C,H...O intermolecular hydrogen bond. [source] Methyl 4- O -,- d -galactopyranosyl ,- d -mannopyranoside methanol 0.375-solvateACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2010Xiaosong Hu Methyl ,- d -galactopyranosyl-(1,4)-,- d -mannopyranoside methanol 0.375-solvate, C13H24O11·0.375CH3OH, (I), was crystallized from a methanol,ethanol solvent system in a glycosidic linkage conformation, with ,, (O5Gal,C1Gal,O1Gal,C4Man) = ,68.2,(3)° and ,, (C1Gal,O1Gal,C4Man,C5Man) = ,123.9,(2)°, where the ring is defined by atoms O5/C1,C5 (monosaccharide numbering); C1 denotes the anomeric C atom and C6 the exocyclic hydroxymethyl C atom in the ,Galp and ,Manp residues, respectively. The linkage conformation in (I) differs from that in crystalline methyl ,-lactoside [methyl ,- d -galactopyranosyl-(1,4)-,- d -glucopyranoside], (II) [Pan, Noll & Serianni (2005). Acta Cryst. C61, o674,o677], where ,, is ,93.6° and ,, is ,144.8°. An intermolecular hydrogen bond exists between O3Man and O5Gal in (I), similar to that between O3Glc and O5Gal in (II). The structures of (I) and (II) are also compared with those of their constituent residues, viz. methyl ,- d -mannopyranoside, methyl ,- d -glucopyranoside and methyl ,- d -galactopyranoside, revealing significant differences in the Cremer,Pople puckering parameters, exocyclic hydroxymethyl group conformations and intermolecular hydrogen-bonding patterns. [source] 4,6-Dinitro- N,N,-di- n -octylbenzene-1,3-diamine, 4,6-dinitro- N,N,-di- n -undecylbenzene-1,3-diamine and N,N,-bis(2,4-dinitrophenyl)octane-1,8-diamineACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2009Gary Teng 4,6-Dinitro- N,N,-di- n -octylbenzene-1,3-diamine, C22H38N4O4, (I), 4,6-dinitro- N,N,-di- n -undecylbenzene-1,3-diamine, C28H50N4O4, (II), and N,N,-bis(2,4-dinitrophenyl)octane-1,8-diamine, C20H24N6O8, (III), are the first synthetic meta -dinitroarenes functionalized with long-chain aliphatic amine groups to be structurally characterized. The intra- and intermolecular interactions in these model compounds provide information that can be used to help understand the physical properties of corresponding polymers with similar functionalities. Compounds (I) and (II) possess near-mirror symmetry, with the octyl and undecyl chains adopting fully extended anti conformations in the same direction with respect to the ring. Compound (III) rests on a center of inversion that occupies the mid-point of the central C,C bond of the octyl chain. The middle six C atoms of the chain form an anti arrangement, while the remaining two C atoms take hard turns almost perpendicular to the rest of the chain. All three molecules display intramolecular N,H...O hydrogen bonds between the amine and nitro groups, with the same NH group forming a bifurcated intermolecular hydrogen bond to the nitro O atom of an adjacent molecule. In each case, these interactions link the molecules into one-dimensional molecular chains. In (I) and (II), these chains pack so that the pendant alkyl groups are interleaved parallel to one another, maximizing nonbonded C,H contacts. In (III), the alkyl groups are more isolated within the molecular chains and the primary nonbonded contacts between the chains appear to involve the nitro groups not involved in the hydrogen bonding. [source] (Z)-2-(1H -Indol-3-ylmethylene)-1-azabicyclo[2.2.2]octan-3-oneACTA CRYSTALLOGRAPHICA SECTION C, Issue 1 2004Vijayakumar N. Sonar The title compound, C16H16N2O, which contains a double bond connecting an azabicyclic ring system to an indol-3-ylmethylene group, crystallizes from a solution in ethyl acetate. The geometries of the two crystallographically independent molecules are nearly identical. The crystal packing of the title compound involves two types of intermolecular hydrogen bond. [source] Bis(2-aminopyridine- N)bis(benzoato- O)zincACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2000S. Shanmuga Sundara Raj The crystal structure of the title compound, [Zn-(C7H5O2)2(C5H6N2)2], is built of monomeric [Zn(2-apy)2(OBz)2] molecules (apy is aminopyridine and OBz is benzoate). The Zn atom lies on a twofold symmetry axis and adopts a slightly distorted tetrahedral coordination. The Zn,O distances to the non-coordinated O atoms are long at 2.872,(3),Å. Each non-ligating carbonyl O atom of the benzoate anion accepts one intramolecular and one intermolecular hydrogen bond from the amino group. The molecules form a chain along the c axis through intermolecular N,H,O hydrogen bonds between the amino and carboxyl groups. [source] Ultrafast Relaxation Dynamics of the Excited States of 1-Amino- and 1-(N,N -Dimethylamino)-fluoren-9-onesCHEMPHYSCHEM, Issue 17 2009Mahendra Varne Abstract The dynamics of the excited states of 1-aminofluoren-9-one (1AF) and 1-(N,N -dimethylamino)-fluoren-9-one (1DMAF) are investigated by using steady-state absorption and fluorescence as well as subpicosecond time-resolved absorption spectroscopic techniques. Following photoexcitation of 1AF, which exists in the intramolecular hydrogen-bonded form in aprotic solvents, the excited-state intramolecular proton-transfer reaction is the only relaxation process observed in the excited singlet (S1) state. However, in protic solvents, the intramolecular hydrogen bond is disrupted in the excited state and an intermolecular hydrogen bond is formed with the solvent leading to reorganization of the hydrogen-bond network structure of the solvent. The latter takes place in the timescale of the process of solvation dynamics. In the case of 1DMAF, the main relaxation pathway for the locally excited singlet, S1(LE), or S1(ICT) state is the configurational relaxation, via nearly barrierless twisting of the dimethylamino group to form the twisted intramolecular charge-transfer, S1(TICT), state. A crossing between the excited-state and ground-state potential energy curves is responsible for the fast, radiationless deactivation and nonemissive character of the S1(TICT) state in polar solvents, both aprotic and protic. However, in viscous but strong hydrogen-bond-donating solvents, such as ethylene glycol and glycerol, crossing between the potential energy surfaces for the ground electronic state and the hydrogen-bonded complex formed between the S1(TICT) state and the solvent is possibly avoided and the hydrogen-bonded complex is weakly emissive. [source] Structures of N - (2,3,4,6-Tetra- O -acetyl-,- D -glycosyl) thiocarbamic Benzoyl HydrazineCHINESE JOURNAL OF CHEMISTRY, Issue 2 2002Shu-Sheng Zhang Abstract The crystal structure of N - (2,3,4,6-Tetra- O -acetyl-,- D -glycosyl)-thiocarbamic benzoyl hydrazine (C22H27N3O9S) was determined by X-ray diffraction method. The hexopyranosyl ring adopts a chair conformation. All the ring substituents are in the equatorial positions. The acetoxyl-methyl group is in synclinal conformation. The S atom is in synperiplanar conformation while the benzoyl hydrazine moiety is anti -periplanar. The thiocarbamic moiety is almost coplanar with the benzoyl hydrazine group. There are two intramolecular hydrogen bonds and one intermolecular hydrogen bond for each molecule in the crystal structure. The molecules form a network structure through intermolecular hydrogen bonds. [source] Hydrogen bonding of modified bases involving Watson-Crick sites: Crystal structure and conformation of Benzyl 6-aminopurine-7-carboxylateCRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2006J. M. Ohrt Abstract Crystals of benzyl 6-aminopurine-7-carboxylate (C13H11N5O2) are monoclinic, space group C2/c, Z = 8, with a = 25.448 (9), b = 6.052 (1), c = 16.975 (6)Å, , = 112.05 (5)°, M = 269.27, Dm= 1.49, Dx= 1.48 g/cm3. The structure was determined from three-dimensional diffractometric data by the multisolution technique and refined to a final reliability factor of 0.068. The molecule is planar with an intramolecular hydrogen bond from one of the amino hydrogens, Ha(N6) to the keto oxygen O(10) of the acyl group. The molecules are hydrogen bonded across the center of inversion by a pair of intermolecular hydrogen bonds using the Watson-Crick sites. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spectroscopic and crystal structure analysis of diamminebis(2,4,6-triiodophenolato-O) copper(II)CRYSTAL RESEARCH AND TECHNOLOGY, Issue 5 2006Gülsün Göka Abstract The crystal structure of [Cu(C6H2I3O)2(NH3)2] (CCDC 238896) has been determined by x-ray diffraction. This monomeric centrosymmetric Cu(II) complex crystallizes in the monoclinic system. The CuO2N2 coordination sphere is trans -planar, [Cu,O: 1.943(5) Å and Cu-N: 1.972(7)] with the fifth and sixth coordination sites occupied by I atoms from the phenoxide ions [Cu,I1: 3.3552(8) Å] to form a tetragonally elongated octahedral structure for CuO2N2I2 coordination. The complex molecules hold together in a one dimensional chain true [100] direction by intermolecular hydrogen bonds. Differantial scanning calorimeter, FTIR and magnetic susceptibility measurements were also performed in order to identify the title complex. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Crystal structure of a tetrazole derivativeCRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2006H. S. Yathirajan Abstract 5-(4'-Methyl-1,1'-biphenyl-2-yl)-1H-tetrazole(MBT), C28H24N8, CCDC: 223082, F.W.=472.55, triclinic, P1, a=4.99(1)Å, b=14.25(4)Å, c=16.63(5)Å, , = 90.27(5)°, , = 91.19(5)°, , = 90.64(5)°, V = 1182(6)Å3, Z = 4, Dcal = 1.327 Mgm -3, , = 0.084mm -1, F000 = 496, , (MoK,) = 0.71073Å, final R1 and wR2 are 0.0924 and 0.2309, respectively. There are two crystallographically independent molecules in the asymmetric unit. The dihedral angles between the two phenyl rings of the biphenyl ring system are 44.2(2)° and 44.3(2)° for the two molecules respectively. The molecules are stabilized by N-H,N and C-H,N types of intermolecular hydrogen bonds in the unit cell in addition to van der Waals forces. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim [source] Synthesis and structural conformation of N-substituted 1,4-dihyropyridine derivativesCRYSTAL RESEARCH AND TECHNOLOGY, Issue 1 2006M. Mahendra Abstract N-(Phenyl)-3,5-dicarbethoxy-2,6-dimethyl-4-(phenyl)-1,4-dihydropyridine (A) and N-(4-methoxy phenyl)--3,5 dicarbethoxy-2,6 dimethyl-4-(3-nitro phenyl)-1,4-dihydropyridine (B) has been synthesized as per scheme and characterized by the X-ray diffraction method. The compound A crystallizes in monoclinic space group P21/c with cell parameters a = 9.2770(11)Å, b = 8.6410(5)Å, c = 27.601(3)Å, , = 97.724(3)°, Z = 4. The compound B crystallizes in monoclinic space group P21/c with cell parameters a = 11.229(6), b = 12.746(7)Å, c =17.606(6)Å, , = 104.531(3)°, Z = 4. The structures exhibit both intra and intermolecular hydrogen bonds. Dihydropyridine ring of both the compounds adopt a flat boat conformation. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Crystal structures and spectroscopic characterization of chiral and racemic 4-phenyl-1,3-oxazolidin-2-oneCRYSTAL RESEARCH AND TECHNOLOGY, Issue 4 2004S. Kitoh Abstract Crystal structures of (R)- and (rac)-4-phenyl-1,3-oxazolidin-2-one (4-POO) have been determined by X-ray diffraction and characterized by the solid state 13C NMR and IR spectra. Molecular geometries and intermolecular interactions in (R)- and (rac)-4-POO crystals are very similar to each other; 4-POO molecules are linked via the N-H,O intermolecular hydrogen bonds to form the chained structure. Chemical shifts of the solid state 13C NMR spectra are very similar to each other, whereas the 1H spin-lattice relaxation times (T1H) value for (R)-4-POO is five times as large as that for (rac)-4-POO, reflecting the more restricted mobility of the (R)-4-POO chain. Although both crystals contain an unique molecule in the asymmetric unit, a doublet feature is observed for the C=O stretching mode in the IR spectra of (R)- and (rac)-4-POO crystals. The frequency gap of the C=O bands are correlated with the strength of the dipole-dipole interactions between the neighboring C=O groups. © 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim [source] Three Novel Functional CdII Dicarboxylates with Nanometer Channels: Hydrothermal Synthesis, Crystal Structures, and Luminescence PropertiesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2007Yu-Peng Tian Abstract Three novel functional transition-metal complexes with H2A (H2A = 9-ethylcarbazole-3,6-dicarboxylic acid), Cd(HA)2(H2O)2 (1), [Cd(A)(phen)]·1.5H2O (2) (phen = 1,10-phenanthroline), and Cd(HA)2(bipy) (3) (bipy = 4,4,-bipyridine), have been successfully synthesized by a hydrothermal synthetic method and characterized by single-crystal X-ray diffraction, infrared spectroscopy, elemental analysis, thermogravimetric analysis, and photoluminescence. The results show that all of the complexes contain nanometer channels, while the coordination modes were changed by the addition of the mixed ligands. The 2D supramolecular open-framework 1 is constructed through hydrogen-bond and aromatic ,,, interactions. 2D coordination polymer 2 is constructed by ,,, interactions between adjacent metal-organic polymeric coordination chains. Interestingly, the 3D supramolecular architecture of 3 first formed 2D grid layers from 1D chains by intermolecular hydrogen bonds and then extended into a 3D structure through aromatic ,,, interactions. Furthermore, strong emissions from these complexes were also changed by the coordination modes in the solid state. However, complexes 1,3 show high thermal stability.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Synthesis and structural studies of N -(p -toluenesulfonyl)-amino acid 3,5-di- tert -butyl-2-phenolamidesHETEROATOM CHEMISTRY, Issue 2 2004Margarita Tlahuextl This paper describes the synthesis and structural studies of N -(p -toluenesulfonyl)-amino acid 3,5-di- tert -butyl-2-phenolamides by 1H, 13C, and 15N. The presence of intra - and intermolecular hydrogen bonds were studied by variable temperature NMR spectroscopy. The molecular structure of two amides in the solid state was determined by X-ray diffraction experiments. The results show that tert -butyl substituents in the phenolic ring have important effects in the nature of hydrogen bonds and conformation of these amides. © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:114,120, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10223 [source] Quantum chemical studies on molecular structural conformations and hydrated forms of salicylamide and O-hydroxybenzoyl cyanideINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 3 2005K. Anandan Abstract Ab initio and density functional theory (DFT) methods have been employed to study the molecular structural conformations and hydrated forms of both salicylamide (SAM) and O-hydroxybenzoyl cyanide (OHBC). Molecular geometries and energetics have been obtained in the gaseous phase by employing the Møller,Plesset type 2 MP2/6-311G(2d,2p) and B3LYP/6-311G(2d,2p) levels of theory. The presence of an electron-releasing group (SAM) leads to an increase in the energy of the molecular system, while the presence of an electron-withdrawing group (OHBC) drastically decreases the energy. Chemical reactivity parameters (, and ,) have been calculated using the energy values of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) obtained at the Hartree,Fock (HF)/6-311G(2d,2p) level of theory for all the conformers and the principle of maximum hardness (MHP) has been tested. The condensed Fukui functions have been calculated using the atomic charges obtained through the natural bond orbital (NBO) analysis scheme for all the optimized structures at the B3LYP/6-311G(2d,2p) level of theory, and the most reactive sites of the molecules have been identified. Nuclear magnetic resonance (NMR) studies have been carried out at the B3LYP/6-311G(2d,2p) level of theory for all the conformers in the gaseous phase on the basis of the method of Cheeseman and coworkers. The calculated chemical shift values have been used to discuss the delocalization activity of the electron clouds. The dimeric structures of the most stable conformers of both SAM and OHBC in the gaseous phase have been optimized at the B3LYP/6-311G(2d,2p) level of theory, and the interaction energies have been calculated. The most stable conformers of both compounds bear an intramolecular hydrogen bond, which gives rise to the formation of a pseudo-aromatic ring. These conformers have been allowed to interact with the water molecule. Special emphasis has been given to analysis of the intermolecular hydrogen bonds of the hydrated conformers. Self-consistent reaction field (SCRF) theory has been employed to optimize all the conformers in the aqueous phase (, = 78.39) at the B3LYP/6-311G(2d,2p) level of theory, and the solvent effect has been studied. Vibrational frequency analysis has been performed for all the optimized structures at MP2/6-311G(2d,2p) level of theory, and the stationary points corresponding to local minima without imaginary frequencies have been obtained for all the molecular structures. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source] Unexpected fluorescence emission of poly(,,,- L -malic acid) in aqueous mediumJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2007Yaofeng Fan Abstract Unexpected fluorescence of poly(,,,- L -malic acid) (,,,-PMA) without traditional fluorophore was observed firstly. This fluorescent polymer was synthesized via melt polycondensation of L -malic acid. The polymer was characterized by gel permeation chromatography (GPC), nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), thermogravimetry (TG), Fourier transform infrared spectroscopy (IR), Fourier transform Raman spectroscopy (Raman), and X-ray powder diffractometry (XRD). The high molecular weight ,,,-PMA was synthesized by the optimum polycondensation at 130°C for 15 h, followed by fractional precipitation with diethyl ether and petroleum ether. The degree of branching of ,,,-PMA was from 10% to 20% according to the reaction condition. Terminal group of ,,,-PMA was mainly hydroxycarboxylic group companied with a few CHCHCOOH groups owing to dehydration of a normal terminal during the melt polycondensation. A fluorescence emission maximum of ,,,-PMA in water appeared at 420 nm when it was excited at 340 nm. Further study indicated that the fluorescence intensity was concentration-dependent, pH-dependent, and molecular-weight-dependent. The fluorescence formation may result from multichain aggregations, which was formed readily in aqueous solution due to intermolecular hydrogen bonds between branched ,,,-PMA. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 [source] Time-dependent density functional theory study on the electronic excited-state geometric structure, infrared spectra, and hydrogen bonding of a doubly hydrogen-bonded complexJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 16 2009Yufang Liu Abstract The geometric structures and infrared (IR) spectra in the electronically excited state of a novel doubly hydrogen-bonded complex formed by fluorenone and alcohols, which has been observed by IR spectra in experimental study, are investigated by the time-dependent density functional theory (TDDFT) method. The geometric structures and IR spectra in both ground state and the S1 state of this doubly hydrogen-bonded FN-2MeOH complex are calculated using the DFT and TDDFT methods, respectively. Two intermolecular hydrogen bonds are formed between FN and methanol molecules in the doubly hydrogen-bonded FN-2MeOH complex. Moreover, the formation of the second intermolecular hydrogen bond can make the first intermolecular hydrogen bond become slightly weak. Furthermore, it is confirmed that the spectral shoulder at around 1700 cm,1 observed in the IR spectra should be assigned as the doubly hydrogen-bonded FN-2MeOH complex from our calculated results. The electronic excited-state hydrogen bonding dynamics is also studied by monitoring some vibraitonal modes related to the formation of hydrogen bonds in different electronic states. As a result, both the two intermolecular hydrogen bonds are significantly strengthened in the S1 state of the doubly hydrogen-bonded FN-2MeOH complex. The hydrogen bond strengthening in the electronically excited state is similar to the previous study on the singly hydrogen-bonded FN-MeOH complex and play important role on the photophysics of fluorenone in solutions. © 2009 Wiley Periodicals, Inc. J Comput Chem 2009 [source] Enhancing Physical Properties and Antimicrobial Activity of Konjac Glucomannan Edible Films by Incorporating Chitosan and NisinJOURNAL OF FOOD SCIENCE, Issue 3 2006Bin Li ABSTRACT: The antimicrobial effect of konjac glucomannan (KGM) edible ûlm incorporating chitosan (CHI) and nisin at various ratios or concentrations was studied. This activity was tested against pathogenic bacteria, namely, Escherichia coli, Staphylococcus aureus, Listeria monocytogenes, and Bacillus cereus. Mechanical and physical properties were determined, and the results indicated that the blend film KC2 (mixing ratio KGM 80/ CHI 20) showed the maximum tensile strength (102.8 ± 3.8 MPa) and good transparency, water solubility, and water vapor transmission ratio. Differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy were used to characterize the structural change of the blend films; and the results showed that strong intermolecular hydrogen bonds occurred between CHI and KGM. Incorporation of nisin at 463IU per disk of film for the selected KC2 was found to have antimicrobial activity against S. aureus, L. monocytogenes, and B. cereus. The mean value of inhibition zone diameter of the CHI-N series and the KC2-N series were higher than the KGM-N series at each corresponding concentration and with significant difference (P < 0.05), however, there was no significant difference in the antimicrobial effect between CHI and KC2 incorporating nisin. At all these levels, the blend ûlm KC2-nisin had a satisfactory appearance, mechanical and physical properties, and antimicrobial activity. Therefore, it could be considered as a potential "active" packaging material. [source] 1,6- and 1,7-naphthyridines III.JOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 2 200213C-NMR analysis of some hydroxy derivatives The 13C-NMR spectra of some 1,6-naphthyridines 2 and 1,7-naphthyridines 3, as well as those of N -methyl derivatives 4 and 5, were recorded and analyzed. Results in dimethyl- d6 sulfoxide and deuteriochlo-roform provide useful data on intra and intermolecular hydrogen bonds. [source] Solution, solid phase and computational structures of apicidin and its backbone-reduced analogsJOURNAL OF PEPTIDE SCIENCE, Issue 6 2006Michael Kranz Abstract The recently isolated broad-spectrum antiparasitic apicidin (1) is one of the few naturally occurring cyclic tetrapeptides (CTP). Depending on the solvent, the backbone of 1 exhibits two ,-turns (in CH2Cl2) or a ,-turn (in DMSO), differing solely in the rotation of the plane of one of the amide bonds. In the X-ray crystal structure, the peptidic COs and NHs are on opposite sides of the backbone plane, giving rise to infinite stacks of cyclotetrapeptides connected by three intermolecular hydrogen bonds between the backbones. Conformational searches (Amber force field) on a truncated model system of 1 confirm all three backbone conformations to be low-energy states. The previously synthesized analogs of 1 containing a reduced amide bond exhibit the same backbone conformation as 1 in DMSO, which is confirmed further by the X-ray crystal structure of a model system of the desoxy analogs of 1. This similarity helps in explaining why the desoxy analogs retain some of the antiprotozoal activities of apicidin. The backbone-reduction approach designed to facilitate the cyclization step of the acyclic precursors of the CTPs seems to retain the conformational preferences of the parent peptide backbone. Copyright © 2005 European Peptide Society and John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||||||||||||||