Search results for "bond"
showing 10 items of 3527 documents
NMR spectral and X-ray structural investigation of 1,3-bis(2-quinolyl)-2-(p-chlorophenyl)-2-propanol
2000
Abstract 1,3-Bis(2-quinolyl)-2-(p-chlorophenyl)-2-propanol (BQCP) has been prepared and characterised by 1H, 13C, 15N NMR spectral and X-ray structural parameters. The methylene protons of BQCP are diastereotopic in solution (CDCl3) as revealed by 1H NMR. In crystalline state there exists an intramolecular hydrogen bond O–H⋯N with one of two nitrogen atoms in BQCP. Variable temperature 1H NMR and PFG 1H, 15N HMBC runs show that in solution BQCP shows C2v-symmetry (both CH2-2-quinolyl fragments are equivalent) in NMR-time scale due to a fast exchange of the hydrogen bond from one nitrogen to the other even at 223 K.
Reversible hydrogen bond network dynamics: molecular dynamics simulations of calix[4]arene-catenanes.
2011
We present detailed molecular dynamics (MD) simulations of mechanically interlocked calix[4]arene-catenanes under external force. Single-molecule force spectroscopy experiments revealed that the separation of dimers with two aliphatic loops results in reversible hydrogen bond breakage through an intermediate in a triple-well potential, while the tetra-loop species separates in a one-step manner (Janke, M.; et al. Nat. Nanotechnol. 2009, 4, 225). MD simulations show that calix[4]arenes interlocked by four loops (1) display a complete restructuring of the hydrogen bond network under mechanical force. All hydrogen bonds of the closed structure open, and new ones are formed in the extended stru…
Metal complex-DNA binding: Insights from molecular dynamics and DFT/MM calculations.
2012
Molecular dynamics (MD) simulations, followed by density functional theory/molecular mechanics (DFT/MM) calculations, provided a detailed structure of the binding site between the cationic metallointercalator (dipyrido [3,2-a:2',3'-c]phenazine)(glycinato)copper(II), [Cu(gly)(dppz)](+), and the two dodeca-deoxynucleotide duplexes [dodeca(dG-dC)]2 and [dodeca(dA-dT)]2. Three simultaneous DNA binding types were detected in the fully optimized DFT/MM structures: 1) metal coordination through exocyclic oxygen atoms of nitrogen bases; 2) intercalation of the dppz chromophore between stacked Watson-Crick AT-AT and GC-GC bases; and 3) hydrogen bonding between the glycinato ligand and amine groups o…
Ionic liquids as solvents for the Knoevenagel condensation: understanding the role of solvent–solute interactions
2015
The Knoevenagel condensation in ionic liquids has been demonstrated as a strongly solvent-dependent process. The objective of this study was to establish a simple and descriptive trend of solvent–solute interactions that favour the Knoevenagel condensation in ionic liquid media. The reaction between 4-(dimethylamino)benzaldehyde and ethyl cyanoacetate in several imidazolium- and pyrrolidinium-based ionic liquids and one ionic liquid mixture was studied. The rate constants were rationalised by studying the change in the 1H NMR chemical shift of representative starting materials in the ionic liquids and the measurement and consideration of the Kamlet–Taft descriptors for each solvent. The hyd…
Bis(N,N′-diphenylbenzamidinium) fumarate
2010
The crystal structure of the title compound, 2C(19)H(17)N(2) (+)·C(4)H(2)O(4) (2-), consists of centrosymmetric trimers built up of two crystallographically independent N,N'-diphenyl-benzamid-in-ium cations and one fumarate dianion, which is located on a centre of inversion. The components of the trimers are linked by N-H⋯O hydrogen bonding. In the cation, the outer rings make dihedral angles of 53.66 (5) and 78.38 (5)° with the central ring. The two outer rings make a dihdral angle of 81.49 (5)°.
On the Formation and Desolvation Mechanism of Organic Molecule Solvates: A Structural Study of Methyl Cholate Solvates
2017
Solvate formation and the desolvation mechanism of 25 obtained methyl cholate solvates were rationalized using crystal structure analysis and study of the phase transformations. The facile solvate formation was determined to be associated with the possibility for more efficient packing in structures containing solvent molecules. Most of the obtained solvates crystallized in one of the six isostructural solvate groups, with solvent selection based on the solvent capability to provide particular intermolecular interactions along with appropriate size and shape. In crystal structures several different methyl cholate conformers were observed, as apparently more efficient packing could be achiev…
Hydrogen bond studies on n-pentanol and 2-methyl-2-butanol by Raman spectroscopy
1986
Polarized Raman spectra of n-pentanol and its isomer 2-methyl-2-butanol are obtained in the liquid phase near the melting points and at superheated temperatures. The measurements are performed in the intramolecular O-H stretching region. Our analysis of the Raman data provides an interpretation of the spectral features in terms of symmetric O-H bands, originated by various degrees of intermolecular coupling, for which mechanism is different for the two isomers. Temperature dependence of the spectra is also discussed in terms of available structural and dynamical models for these H-bonded liquids.
Equilibrium and kinetic studies on complex formation and decomposition and the movement of Cu2+metal ions within polytopic receptors
2013
Potentiometric studies carried out on the interaction of two tritopic double-scorpiand receptors in which two equivalent 5-(2-aminoethyl)-2,5,8-triaza[9]-(2,6)-pyridinophane moieties are linked with 2,9-dimethylphenanthroline (L1) and 2,6-dimethylpyridine (L2) establish the formation of mono-, bi- and trinuclear Cu(2+) complexes. The values of the stability constants and paramagnetic (1)H NMR studies permit one to infer the most likely coordination modes of the various complexes formed. Kinetic studies on complex formation and decomposition have also been carried out. Complex formation occurs with polyphasic kinetics for both receptors, although a significant difference is found between bot…
Resorcarenes in the Boat Conformation as Building Blocks for Hydrogen-Bonded Assemblies Including Two Ammonium Cations
2001
Crystal structures are reported for various co-crystals of rccc-resorcarenes with triethylammonium chloride. Usually, two molecules of a C2v-symmetric tetraester 2 in the boat conformation are linked through four hydrogen-bonded chloride anions to give dimeric assemblies. Two of the chloride anions may be replaced by four hydrogen-bonded ethanol molecules in an otherwise similar structure. These assemblies, which consist of six or eight components, posses voluminous, negatively charged chambers in which two triethylammionium cations, 3+, are included as guests by strong electrostatic and hydrogen-bonding interactions. The host-guest N-H...Cl hydrogen bonds were clearly detected at 173 K. Th…
Structural characterization of β-2′-pyridylaminocrotonoyl-2-pyridylamide by ESI-MS, NMR, single crystal X-ray analysis and ab initio methods
2003
Abstract In contradiction with earlier reports 1H, 13C and 15N NMR spectra show that β-2′-pyridylaminocrotonoyl-2-pyridylamide is the only form present in chloroform solution. According to the X-ray data the same tautomer exists also in the crystal state. The studied amide has a dimeric form where the monomer molecules are held together by two intermolecular hydrogen bonds. The NMR spectral data show that there is also an intramolecular hydrogen bond in each monomer subunit. The dilution experiments and variable-temperature 1H NMR runs show that β-2′-pyridylaminocrotonoyl-2-pyridylamide tends to form the dimers also in chloroform solution at higher concentrations. The ESI-TOF MS measurement…