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C Atoms (c + atom)
Selected AbstractsChemInform Abstract: Ruthenium-Catalyzed Regioselective ,-Alkylation of Ketones: The First Alkyl-Group Transfer from Trialkylamines to the ,-C Atom of Ketones.CHEMINFORM, Issue 24 2001Chan Sik Cho Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Six-Membered N-Heterocyclic Carbenes with a 1,1,-Ferrocenediyl Backbone: Bulky Ligands with Strong Electron-Donor Capacity and Unusual Non-Innocent CharacterEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 31 2009Ulrich Siemeling Abstract The stable, crystalline N-heterocyclic diaminocarbene fc[N(CH2tBu)-C-N(CH2tBu)] (2d, fc = 1,1,-ferrocenediyl) was prepared by deprotonation of its formamidinium precursor fc[N(CH2tBu)-CH-N(CH2tBu)][BF4] (1d) and used for the preparation of the 16 valence electron complexes [Mo(2d)(CO)4], [RhCl(2d)(cod)] (cod = 1,5-cyclooctadiene) and [RhCl(2d)(CO)2]. 1d, 2d and [RhCl(2d)(cod)] were structurally characterised by single-crystal X-ray diffraction studies. The electrochemical properties of 2d, its 2-adamantyl analogue 2c, its complex [RhCl(2d)(CO)2] and of the precursors 1d and 1,1,-bis(neopentylamino)ferrocene were investigated by electrochemistry. The carbenes are easily oxidised to the corresponding radical cation, whose persistent nature is unprecedented in the chemistry of N-heterocyclic carbenes. The spin density is located at the Fe atom and the carbene C atom according to the results of EPR spectroscopic studies and DFT calculations.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Tuning the Energy Level and Photophysical and Electroluminescent Properties of Heavy Metal Complexes by Controlling the Ligation of the Metal with the Carbon of the Carbazole Unit,ADVANCED FUNCTIONAL MATERIALS, Issue 4 2007L. Yang Abstract Four novel IrIII and PtII complexes with cyclometalated ligands bearing a carbazole framework are prepared and characterized by elemental analysis, NMR spectroscopy, and mass spectrometry. Single-crystal X-ray diffraction studies of complexes 1, 3, and 4 reveal that the 3- or 2-position C atom of the carbazole unit coordinates to the metal center. The difference in the ligation position results in significant shifts in the emission spectra with the changes in wavelength being 84,nm for the Ir complexes and 63,nm for the Pt complexes. The electrochemical behavior and photophysical properties of the complexes are investigated, and correlate well with the results of density functional theory (DFT) calculations. Electroluminescent devices with a configuration of ITO/NPB/CBP:dopant/BCP/AlQ3/LiF/Al can attain very high efficiencies. [source] Quantum chemical metabolism-based simulation of carcinogenic potency of benzene derivativesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 7 2010Pavel N. D'Yachkov Abstract Using an oxenoid model, we investigated dependences of carcinogenic potency of the benzenes C6H5 -X on a nature of substituents X. According to the model, a P450 enzyme breaks a dioxygen molecule and generates the oxens, which readily react with substrates. We suggest that a stability of the intermediate OC6H6 -X with tetrahedrally coordinated C atom relative to the molecule C6H5 -X determines a rate of substrate biotransformation. Using MO LCAO MNDO approach, we calculated the total energies of molecules C6H6 -X and arene oxides OC6H6 -X. A difference ,Emin of these values determines activation energy of oxidation reaction. The compounds with the low ,Emin values are noncarcinogenic. Benzene derivatives with high ,Emin values belong to carcinogenic compounds series. The carcinogenicity of amino- and nitro-substituted benzenes is also determined by N-oxidation of amino and reduction of the nitro group. As the phenylhydroxylamines XC6H4NHOH and nitrenium ions XC6OH4NH+ are the common metabolites of the nitro- and amino-substituted benzenes and nitrenium ions XC6H4NH+ are the ultimate carcinogens, we use the differences ,EN = E(XC6H4NH+) , E(XC6H4NHOH) as the second parameter characterizing the carcinogenic activity of amino- and nitro-substituted benzenes. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] Prediction of octanol,water partition coefficients of organic compounds by multiple linear regression, partial least squares, and artificial neural networkJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 15 2009Hassan Golmohammadi Abstract A quantitative structure,property relationship (QSPR) study was performed to develop models those relate the structure of 141 organic compounds to their octanol,water partition coefficients (log Po/w). A genetic algorithm was applied as a variable selection tool. Modeling of log Po/w of these compounds as a function of theoretically derived descriptors was established by multiple linear regression (MLR), partial least squares (PLS), and artificial neural network (ANN). The best selected descriptors that appear in the models are: atomic charge weighted partial positively charged surface area (PPSA-3), fractional atomic charge weighted partial positive surface area (FPSA-3), minimum atomic partial charge (Qmin), molecular volume (MV), total dipole moment of molecule (,), maximum antibonding contribution of a molecule orbital in the molecule (MAC), and maximum free valency of a C atom in the molecule (MFV). The result obtained showed the ability of developed artificial neural network to prediction of partition coefficients of organic compounds. Also, the results revealed the superiority of ANN over the MLR and PLS models. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009 [source] Methyl ,- d -galactopyranosyl-(1,4)-,- d -allopyranoside tetrahydrateACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2010Wenhui Zhang The title compound, C13H24O11·4H2O, (I), crystallized from water, has an internal glycosidic linkage conformation having ,, (O5Gal,C1Gal,O1Gal,C4All) = ,96.40,(12)° and ,, (C1Gal,O1Gal,C4All,C5All) = ,160.93,(10)°, where ring-atom numbering conforms to the convention in which C1 denotes the anomeric C atom, C5 the ring atom bearing the exocyclic hydroxymethyl group, and C6 the exocyclic hydroxymethyl (CH2OH) C atom in the ,Galp and ,Allp residues. Internal linkage conformations in the crystal structures of the structurally related disaccharides methyl ,-lactoside [methyl ,- d -galactopyranosyl-(1,4)-,- d -glucopyranoside] methanol solvate [Stenutz, Shang & Serianni (1999). Acta Cryst. C55, 1719,1721], (II), and methyl ,-cellobioside [methyl ,- d -glucopyranosyl-(1,4)-,- d -glucopyranoside] methanol solvate [Ham & Williams (1970). Acta Cryst. B26, 1373,1383], (III), are characterized by ,, = ,88.4,(2)° and ,, = ,161.3,(2)°, and ,, = ,91.1° and ,, = ,160.7°, respectively. Inter-residue hydrogen bonding is observed between O3Glc and O5Gal/Glc in the crystal structures of (II) and (III), suggesting a role in determining their preferred linkage conformations. An analogous inter-residue hydrogen bond does not exist in (I) due to the axial orientation of O3All, yet its internal linkage conformation is very similar to those of (II) and (III). [source] Ethyl[tris(3- tert -butyl-5-methylpyrazol-1-yl)hydridoborato]zinc(II)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2010Mukesh Kumar The X-ray crystal structure of the title compound, [Zn(C2H5)(C24H40BN6)], or TptBu,MeZnEt [TptBu,Me is tris(3- tert -butyl-5-methylpyrazolyl)hydridoborate], reveals a distorted tetrahedral geometry around the Zn atom. The Zn center is coordinated by three N atoms of the borate ligand and by one C atom of the ethyl group. The present structure and other tetrahedral Tp zinc alkyl complexes are compared with similar Ttz ligands (Ttz is 1,2,4-triazolylborate), but no major differences in the structures are noted, and it can be assumed that variation of the substitution pattern of Tp or Ttz ligands has little or no influence on the geometry of alkylzinc complexes. Refinement of the structure is complicated by a combination of metric pseudosymmetry and twinning. The metrics of the structure could also be represented in a double-volume C -centered orthorhombic unit cell, and the structure is twinned by one of the orthorhombic symmetry operators not present in the actual structure. The twinning lies on the borderline between pseudomerohedral and nonmerohedral. The data were refined as being nonmerohedrally twinned, pseudomerohedrally twinned and untwinned. None of the approaches yielded results that were unambiguously better than any of the others: the best fit between structural model and data was observed using the nonmerohedral approach which also yielded the best structure quality indicators, but the data set is less than 80% complete due to rejected data. The pseudomerohedral and the untwinned structures are complete, but relatively large residual electron densities that are not close to the metal center are found with values up to three times higher than in the nonmerohedral approach. [source] Hydrogen-bonded supramolecular networks of N,N,-bis(4-pyridylmethyl)oxalamide and 4,4,-{[oxalylbis(azanediyl)]dimethylene}dipyridinium dinitrateACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2010Gene-Hsiang Lee The molecule of N,N,-bis(4-pyridylmethyl)oxalamide, C14H14N4O2, (I) or 4py-ox, has an inversion center in the middle of the oxalamide group. Adjacent molecules are then linked through intermolecular N,H...N and C,H...O hydrogen bonds, forming an extended supramolecular network. 4,4,-{[Oxalylbis(azanediyl)]dimethylene}dipyridinium dinitrate, C14H16N4O22+·2NO3,, (II), contains a diprotonated 4py-ox cation and two nitrate counter-anions. Each nitrate ion is hydrogen bonded to four 4py-ox cations via intermolecular N,H...O and C,H...O interactions. Adjacent 4py-ox cations are linked through weak C,H...O hydrogen bonding between an ,-pyridinium C atom and an oxalamide O atom, forming a two-dimensional extended supramolecular network. [source] 2-Amino-5-(3,4-dimethoxybenzylidene)-1-methylimidazol-4(5H)-one N,N -dimethylformamide monosolvateACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2010Laura M. Tvedte The crystal structure of the title compound, C13H15N3O3·C3H7NO, was determined as part of a larger project focusing on creatinine derivatives as potential pharmaceuticals. The molecule is essentially planar, in part because of intramolecular hydrogen bonding. Inversion-related pairs of molecules result from intermolecular hydrogen bonding. The , systems of 2-amino-5-(3,4-dimethoxybenzylidene)-1-methylimidazol-4(5H)-one and an inversion-related molecule overlap slightly, indicating a small amount of ,,, stacking. Bond lengths, angles and torsion angles are consistent with similar structures, except in the imidazolone ring near the doubly bonded C atom, where significant differences occur. [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-(9,10-Dihydroacridin-9-ylidene)thiosemicarbazide and its five-membered thiazole and six-membered thiazine derivativesACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2010Ivan Poto Two methyl derivatives, five-membered methyl 2-{2-[2-(9,10-dihydroacridin-9-ylidene)-1-methylhydrazinyl]-4-oxo-4,5-dihydro-1,3-thiazol-5-ylidene}acetate, C20H16N4O3S, (I), and six-membered 2-[2-(9,10-dihydroacridin-9-ylidene)-1-methylhydrazinyl]-4H -1,3-thiazin-4-one, C18H14N4OS, (II), were prepared by the reaction of the N -methyl derivative of 4-(9,10-dihydroacridin-9-ylidene)thiosemicarbazide, C14H12N4S, (III), with dimethyl acetylenedicarboxylate and methyl propiolate, respectively. The crystal structures of (I), (II) and (III) are molecular and can be considered in two parts: (i) the nearly planar acridine moiety and (ii) the singular heterocyclic ring portion [thiazolidine for (I) and thiazine for (II)] including the linking amine and imine N atoms and the methyl C atom, or the full side chain in the case of (III). The structures of (I) and (II) are stabilized by N,H...O hydrogen bonds and different ,,, interactions between acridine moieties and thiazolidine and thiazine rings, respectively. [source] A monomeric gold(I) carbanion complex with an uncoordinated thioether: [2-(methylsulfanyl)phenyl](triphenylphosphine)gold(I)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2009Doris Y. Melgarejo The title compound, [Au(C7H7S)(C18H15P)], is conformationally chiral and crystallizes from benzene,hexane as individually enantiopure crystals. This mononuclear compound has the AuI atom linearly bound to a triphenylphosphine P atom and to a phenyl C atom of a 2-(methylsulfanyl)phenyl group. The angle at the AuI atom is 175.9,(2)°. The linear ligand coordination about the AuI atom has geometric parameters inside the remarkably narrow range found for gold complexes bound by a phosphine ligand and by the ortho -C atom of a substituted phenyl group. This is the first example of gold(I) attached to a methylsulfanyl aromatic carbanion. [source] 2-Oxo-2-phenyl- N -[(R)-1-phenylethyl]acetamide and N,N -dimethyl-2-(1-naphthyl)-2-oxoacetamide: possibility of Yang photocyclization in a crystalACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2009Julia B, kowicz The crystal structures of 2-oxo-2-phenyl- N -[(R)-1-phenylethyl]acetamide, C16H15NO2, (I), and N,N -dimethyl-2-(1-naphthyl)-2-oxoacetamide, C14H13NO2, (II), were determined in an attempt to understand the reason for the lack of Yang photocyclization in their respective crystals. In the case of (I), the long distance between the O atom of the carbonyl group and the ,-H atom, and between the C atom of the carbonyl group and the ,-C atom, preclude Yang photocyclization. For (II), the deviation of the ,-H atom from the plane of the carbonyl group and interactions between the naphthalene rings are regarded as possible reasons for the chemical inertia. The two independent molecules of (I) differ in their conformation. N,H...O hydrogen bonds link molecules of (I) into chains extended along the b axis. [source] Bromido(,5 -carboxycyclopentadienyl)dinitrosylchromium(0) and (,5 -benzoylcyclopentadienyl)bromidodinitrosylchromium(0)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2009Yu-Pin Wang In the structures of each of the title compounds, [CrBr(C6H5O2)(NO)2], (I), and [CrBr(C12H9O)(NO)2], (II), one of the nitrosyl groups is located at a site away from the exocyclic carbonyl C atom of the cyclopentadienyl (Cp) ring, with twist angles of 174.5,(3) and 172.5,(1)°. The observed orientation is surprising, since the NO group is expected to be situated trans to an electron-rich C atom in the ring. The organic carbonyl plane is turned away from the Cp ring plane by 5.6,(8) and 15.2,(3)°in (I) and (II), respectively. The exocyclic C,C bond in (I) is bent out of the Cp ring plane towards the Cr atom by 2.8,(3)°, but is coplanar with the Cp ring in (II); the angle is 0.1,(1)°. [source] A commonly used spin label: S -(2,2,5,5-tetramethyl-1-oxyl-,3 -pyrrolin-3-ylmethyl) methanethiosulfonateACTA CRYSTALLOGRAPHICA SECTION C, Issue 11 2008Vitali Zielke The title compound, C10H18NO3S2, which finds application as a spin label, has triclinic (P) symmetry at 100,(2),K with two independent molecules in the asymmetric unit. Both molecules are very similar with respect to bond lengths and angles, but molecule 2 shows disordering of its side chain. The pyrroline rings differ slightly with respect to the position of the NO group, which in both cases are sterically shielded by the surrounding methyl groups. The crystal structure of the title compound represents the first example of a 2,2,5,5-tetramethyl-1-oxyl-,3 -pyrroline derivative with a side chain at the double bond which is linked to it through an sp3 -hybridized C atom. In the solid state, the side chain adopts a conformation with the methyl group above/below the pyrroline ring and a H atom directed towards a C atom of the double bond. The disordered side chain of molecule 2 represents a second conformation with low potential energy. Both molecules exhibit planar chirality, but in the solid state both pairs of stereoisomers are present. These four stereoisomers are stacked one behind the other in four different columns, denoted A, A,, B and B,, the angle between the vectors of the N,O bonds in columns A and B being 80.38,(8)°. [source] 3,5-Bis{3-[4-(dimethylamino)phenyl]prop-2-enylidene}-1-methyl-4-piperidone and 3,5-bis[3-(4-methoxyphenyl)prop-2-enylidene]-1-methyl-4-piperidone: potential biophotonic materialsACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2008Vladimir N. Nesterov The structures of the title compounds, C28H33N3O, (I), and C26H27NO3, (II), together with their two-photon absorption properties and fluorescence activities are reported. Molecules of (II) reside on crystallographic mirror planes containing the piperidone C=O group and N -methyl H atoms. Because of the conjugation between the donor and acceptor parts, the central heterocycle in both (I) and (II) exhibits a flattened boat conformation, with deviations of the N atom and the opposite C atom from the planar fragment. The dihedral angles between the coplanar heterocyclic atoms and terminal C6 rings are less than 20° in both (I) and (II). In (I), the N -methyl group of the ring occupies an equatorial position, but in (II) it is positioned in an axial site. In the crystal structure of (I), weak intermolecular C,H...,(arene) and C,H...O steric contacts link the molecules along the a axis. In the crystal structure of (II), molecules form stacks along the b axis. [source] Hydrogen-bonded networks in 1-(4-methoxyphenyl)-2,2-dimethylpropan-1-olACTA CRYSTALLOGRAPHICA SECTION C, Issue 12 2007Marek Gli The asymmetric unit of the title compound, C12H18O2, contains two independent molecules. They differ only slightly in conformation but form completely different intermolecular hydrogen-bonded arrays. One molecule exhibits disorder in the hydroxy group region, but this does not influence the formation of hydrogen bonds. The bulky tert -butyl group on one side of the carbinol C atom and the benzene ring on the other side promote the formation of discrete dimeric motifs via hydrogen-bridged hydroxy groups. Dimers are further joined by strong hydroxy,methoxy O,H...O bonds to form chains with dangling alcohol groups. Weaker intermolecular C,H...O interactions mediate the formation of a two-dimensional network. [source] catena -Poly[[(trifluoromethanesulfonato-,O)silver(I)]-,-di-2-pyridylamine-,2N2:N2,], a chain polymer with short Ag,C contactsACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2006Peter G. Jones The title compound, [Ag(CF3O3S)(C10H9N3)]n, is a chain polymer in which neighbouring monomeric units are related by a glide plane. The silver centre is four-coordinate; the donor atoms are one trifluoromethanesulfonate O atom and one pyridine N atom from each of two symmetry-related dipyridylamines, and an additional and unexpected Ag,C contact [2.6464,(16),Å] is observed to a pyridine C atom. The chains are reinforced by one classical N,H,O and two `weak' C,H,O hydrogen bonds. [source] Three substituted (Z)-5-benzylidene-2-thioxothiazolidin-4-ones: hydrogen-bonded dimers that can be effectively isolated or linked into chains either by aromatic ,,, stacking interactions or by dipolar carbonyl,carbonyl interactionsACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2006Paula Delgado In each of the isomeric compounds (Z)-5-(2-fluorobenzylidene)-2-thioxothiazolidin-4-one, C10H6FNOS2, (I), and (Z)-5-(4-fluorobenzylidene)-2-thioxothiazolidin-4-one, C10H6FNOS2, (II), there is a very wide C,C,C angle (ca 130°) at the methine C atom linking the two rings. In each isomer, paired N,H,O hydrogen bonds link the molecules into centrosymmetric R22(8) dimers; the hydrogen-bonded dimers are linked into chains by an aromatic ,,, stacking interaction in isomer (I) and by an antiparallel dipolar carbonyl,carbonyl interaction in isomer (II). (Z)-5-(3,4,5-Trimethoxybenzylidene)-2-thioxothiazolidin-4-one, C13H13NO4S2, (III), which crystallizes with Z, = 2 in the space group P, shows the same very wide angle at the bridging methine C atom; the two independent molecules are linked into an isolated dimer having no crystallographic symmetry. [source] Isoamylcobalamin,acetone,water (1/0.385/12.650)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2004Christopher B. Perry The title compound, [Co(C5H11)(C62H88N13O14P)]·0.385C3H6O·12.650H2O, contains the isoamyl (3-methylbutyl) anion bonded to the CoIII ion through a C atom. The compound is thus a structural analog of the two biologically important vitamin B12 coenzymes adenosylcobalamin and methylcobalamin. The lower axial Co,N bond length [2.277,(2),Å] is one of the longest ever reported for a cobalamin and reflects the strong ,-donor ability of the isoamyl group. [source] Dibothrioclinin I and II, epimers from Gerbera piloselloides (L.) CassACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2003Cheng Wang Dibothrioclinin I and II, namely (+)-(11R,12S,25R,27S)- and (±)-(11RS,12RS,25RS,27SR)-3,3,7,17,21-pentamethyl-4,12,18,26-tetraoxaheptacyclo[15.11.1.02,15.05,14.06,11.019,28.020,25]nonacosa-5(14),6,8,10,19(28),20,22,24-octaene-13,27-dione, respectively, are C30H28O6 epimers which are derived from two bothrioclinin moieties joined so as to create an additional six-membered ring. Structurally, the epimers differ only by inversion at one C atom of a central ring junction and the corresponding six-membered rings have similar conformations in each molecule, except for one ring adjacent to this inversion site. [source] 1,1-Bis(phenylsulfonyl)-1-(pyridinio)methanideACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2003Kenneth W. Muir The title disulfonyl-stabilized pyridinium ylide, C5H5N+,C,(SO2C6H5)2 or C18H15NO4S2, contains a near planar NCS2 core. The structure suggests that the formal negative charge of the ylide C atom is delocalized to the S atoms rather than the N atom. Structural features of pyridinium ylides are briefly discussed. [source] 6-(2-Hydroxybenzoyl)-5-(pyrrol-2-yl)-3H -pyrrolizineACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2003Sankar Prasad Dey The title compound, 2-hydroxyphenyl 5-(pyrrol-2-yl)-3H -pyrrolizin-6-yl ketone, C18H14N2O2, was isolated from the base-catalyzed 1:2 condensation of 2-hydroxyacetophenone with pyrrole-2-carbaldehyde. The pyrrole N,H and hydroxybenzoyl O,H groups are hydrogen bonded to the benzoyl O atom. The allylic C=C double bond of the 3H -pyrrolizine system is located between ring positions 1 and 2, the C atom at position 3 (adjacent to the N atom) being single bonded. [source] 2,3-Dihydro-3,3-dimethylspiro[1H -4-oxanthracene-5,2,-oxiran]-10(5H)-oneACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2002Vitor F. Ferreira The central six-membered ring in the title compound, C16H16O3, is almost planar (and almost coplanar with the aromatic ring), despite one of its C atoms being formally sp3 hybridized. The planarity is a consequence of the C atom at the centre of the spirocyclic system also being part of the three-membered epoxide ring. The molecules are linked by ,,, and C,H,, interactions. [source] Chemical surface passivation of 3C-SiC nanocrystals: A first-principle studyINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 13 2010A. Trejo Abstract The effect of the chemical surface passivation, with hydrogen atoms, on the energy band gap of porous cubic silicon carbide (PSiC) was investigated. The pores are modeled by means of the supercell technique, in which columns of Si and/or C atoms are removed along the [001] direction. Within this supercell model, morphology effects can be analyzed in detail. The electronic band structure is performed using the density functional theory based on the generalized gradient approximation. Two types of pores are studied: C-rich and Si-rich pores surface. The enlargement of energy band gap is greater in the C-rich than Si-rich pores surface. This supercell model emphasizes the interconnection between 3C-SiC nanocrystals, delocalizing the electronic states. However, the results show a clear quantum confinement signature, which is contrasted with that of nanowire systems. The calculation shows a significant response to changes in surface passivation with hydrogen. The chemical tuning of the band gap opens the possibility plenty applications in nanotechnology. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem 110:2455,2461, 2010 [source] A Density Functional Theory Study of the Stille Cross-Coupling via Associative Transmetalation.ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2007Coordinating Solvents, The Role of Ligands Abstract An associative mechanism has been computationally characterized for the Stille cross-coupling of vinyl bromide and trimethylvinylstannane catalyzed by PdL2 (L=PMe3, AsMe3) with or without dimethylformamide as coordinating ligand. All the species along the catalytic cycles that start from both the cis - and the trans -PdL(Y)(vinyl)Br complexes (Y=L or S; L=PMe3, AsMe3 or PH3; S=DMF) have been located in the gas phase and in the presence of polar solvents. Computations support the central role of species trans -PdL(DMF)(vinyl)Br which react by ligand dissociation and stannane coordination in the rate-limiting transmetalation step via a puckered four-coordinate (at palladium) transition state comprised of Pd, Br, Sn and sp2 C atoms. A donating solvent may enter the catalytic cycle assisting isomerization of cis -PdL2(vinyl)Br to trans -PdL(DMF)(vinyl)Br complexes via a pentacoordinate square pyramidal Pd intermediate. In keeping with experimental observations, the activation energies of the catalytic cycles with arsines as Pd ligands are lower than those with phosphines. Polytopal rearrangements from the three-coordinate T-shaped Pd complexes resulting from transmetalation account for the isomerization and the CC bond formation on the reductive elimination step. [source] Hierarchical structures formed by partially crystalline polymers in solution: from fundamentals to applications , a combined conventional, focusing and ultra-small-angle neutron scattering studyJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2007Dietmar Schwahn Multilevel aggregates with characteristic sizes covering four orders of magnitude, from 1,nm to 10,µm, are formed upon cooling decane solutions of poly(ethylene-butene) random copolymers (designated as PEB- n, where n is the number of ethyl side branches per 100 backbone C atoms) and wax-containing mixed solutions. The partially crystalline PEB-7.5 copolymers form two distinct morphologies that evolve on a range of length scales. When these polymers are mixed with wax molecules having a crystallization point lower than the polymer aggregation temperature, a hierarchy of morphologies evolves on decreasing the temperature. The multilevel structures were elucidated by combining conventional small-angle neutron scattering, focusing small-angle neutron scattering and ultra-small-angle neutron scattering investigations with microscopy. Contrast-matching analysis of the wax and copolymer components within the common morphologies revealed the wax-crystal modification capacity of the PEB-7.5 copolymers. Since the copolymers limit the growth of wax crystals, they are potential pour-point depressants for the fuel industry. [source] Relevant activities of extracts and constituents of animals used in traditional Chinese medicine for central nervous system effects associated with Alzheimer's diseaseJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 7 2006Yuhao Ren The centipede Scolopendra subspinipes mutilans L. Koch (,Wugong'), the beetle Mylabris phalerata Pallas (,Ban mao') and the earthworm Pheretima aspergillum Chen (,DiLong') have a reputation in traditional Chinese medicine for reducing symptoms of central nervous system decline, including memory loss. A series of extracts of all three organisms was tested for acetylcholinesterase (AChE) inhibition and copper ion binding effects, the latter likely to reduce oxidative damage caused by excess copper. The beetle and centipede chloroform extracts showed the strongest AChE inhibitory effects (30.6% inhibition at 105 ,g mL,1 and 32.3% inhibition at 167 ,g mL,1, respectively) and, in the case of the centipede, this was traced to the unsaturated fatty acids present using bioassay-guided fractionation. Cantharidin from the beetle was shown to have AChE activity (31% inhibition at 1 ,M, 0.196,g mL,1), making it a major contributor to the activity of the beetle extract. The earthworm showed no AChE inhibitory activity. Since unsaturated fatty acids have not been previously reported to have AChE inhibitory activity, a series of related compounds was tested to determine structure-activity relationships. It was found that activity existed where there was a chain length of more than 16 C atoms with at least one unsaturated bond in the chain. The carboxylic acid group was also necessary for activity. The fatty acids present in the centipede also showed the ability to bind copper ions when tested using a novel thin layer chromatography method designed to detect copper-binding compounds. The activities reported give some support to the use of the beetle and centipede in traditional Chinese medicine for improving cognitive function. [source] X-ray absorption spectroscopic studies on model compounds for biological iodine and bromineJOURNAL OF SYNCHROTRON RADIATION, Issue 1 2005Martin C. Feiters X-ray absorption spectra of a number of organic iodine and bromine compounds of biological relevance, as well as of a series of iodine compounds with different oxidation states, have been measured. The iodine K -edge spectra (XANES) are found to be relatively featureless but the position of the edge is found to be sensitive to formal valence (among other factors), and the edge shape to the number of bound O atoms. EXAFS spectra of organohalogen compounds (both iodine and bromine) can be used to discriminate between aliphatic and aromatic compounds. There are differences both in the distances from the halogens to the first shell of C atoms, which are shorter for aromatic compounds, and in the patterns of shells in the Fourier transforms. This result is expected to be relevant to studies at these edges in biological systems. [source] XAFS study on a pressure-induced superconductor Cs3C60 under high pressureJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2001Satoshi Fujiki Cs K-edge XAFS of Cs3C60 which is a pressure-induced superconductor were measured at 21 and 34 kbar by using a diamond anvil cell (DAC) in order to obtain the structural information under high pressure, and to clarify the origin of the pressure-induced superconductivity. The distances and the mean square displacements between the Cs and C atoms are consistent with those determined by X-ray powder diffraction. Consequently, the high-pressure XAFS can give the reliable structural-information on a fullerene superconductor under high pressure. We also show the procedure of the analysis of high-pressure XAFS with DAC in detail. [source] | |||||||||||||||||||||||||||||||