bluuebunny/crossref_metadata_2025 huggingface dataset:
Novel, air-stable, lanthanide catalysts for the hetero Diels–Alder reaction
Authors: Spino Claude , Clouston Laurel , Berg David
Published: May 2006

Novel, air-stable, yttrium and ytterbium complexes were found effective in the catalysis of the typical hetero Diels–Alder reaction of crotonaldehyde and ethylvinyl ether. They represent an attractive solution to the problem of ligand lability in the realm of lanthanide catalysts. Key words: lanthanide, catalyst, hetero Diels–Alder, yttrium, ytterbium.
Conformational behaviour of highly hindered ethanes:meso- and racemic-2,2,2′,2′-tetramethyl-1,1′-biindanyl
Authors: Grindley T. Bruce , MacLeod Paula J. , Pincock James A. , Cameron T. Stanley
Published: May 2006

MM3(94), AM1, and STO-3G calculations on racemic 2,2,2′,2′-tetramethyl-1,1′-biindanyl (1) show that seven minima are present on its conformational potential energy surface. 1 crystallizes in the space group Pbcn (no. 60) with cell parameters a = 11.190(7), b = 11.679(7), c = 13.19(1) Å, V = 1724(3) Å3, Z = 4, R = 0.0357, Rw = 0.0362 in the conformation predicted to be the global minimum by STO-3G and AM1, but not by MM3(94). Application of the Karplus equation and observation of a deshielded proton signal indicate that the same conformation is the major species present in solution, perhaps along with another conformation. The meso isomer 2 shows evidence of slow exchange between conformers in its room temperature NMR spectra. Barriers to exchange were obtained from13C NMR coalescence experiments and from1H NMR line shape analysis of the exchanging AB pattern. The potential energy surface for 2 was calculated as for 1 and used to determine the nature of the process observed. The slow exchange was calculated to be between two enantiomeric conformers. The populated conformers for both 1 and 2 had the benzene rings from the two halves of the dimer stacked in an offset manner and the favourable interactions associated with this stacking may be a factor in the relative stabilities of these conformations. Key words: MM3, molecular mechanics, hindered rotation, dialkyldiphenylethanes, X-ray crystal structure.
1995 Alcan Award Lecture New intermediates in the homolytic and heterolytic splitting of dihydrogen
Authors: Morris Robert H.
Published: May 2006

Some of the research of the author and his research group into the structure and reactions of dihydrogen complexes of transition metals is reviewed. The characterization of osmium complexes that can be regarded as having intermediate structures on the way to the homolytic splitting and to the heterolytic splitting of dihydrogen is described. The properties of an iridium complex with novel short proton–hydride contacts is also reviewed. Key words: transition metal, dihydrogen, hydride, complexes, NMR, neutron diffraction, osmium, iridium.
A facile synthesis of metalla- octafluorocyclopentane complexes of ruthenium and nickel
Authors: Gasafi-Martin Waltraud , Oberendfellner Gabriele , Werner Konrad Von
Published: May 2006

Reduction of the dihalogeno complexes RuCl2(PPh3)4 and NiBr2L2 (L = tertiary phosphine) with sodium hydride in MeCN in the presence of tetrafluoroethylene gives complexes containing five-membered MC4F8 rings. 1,2-Dihydrotetrafluoroethane is a by-product of these syntheses, especially when hydrogen is added. The M—C bonds of the metalla-perfluorocyclopentane complexes are remarkably stable against hydrogenolysis. Key words: metalla-octafluorocyclopentanes of ruthenium(II) and nickel(II).
Synthesis of the complexes [PdCIR(cod)] (R = benzyl, ethyl; cod = 1,5-cyclooctadiene). β-Elimination from [PdCIEt(cod)] to give the η1,η2 and η3 isomers of [Pd2(μ-Cl)2(C8H13)2]
Authors: Stockland Jr. Robert A. , Anderson Gordon K. , Rath Nigam P. , Braddock-Wilking Janet , Ellegood J. Christopher
Published: May 2006

Treatment of [PdCl2(cod)] with tetrabenzyltin gives the benzylpalladium complex [PdCl(CH2Ph)(cod)] (cod = 1,5-cyclooctadiene), 1a, whose structure has been determined by X-ray crystallography. It adopts approximate square-planar geometry, with the double bonds perpendicular to the square plane. The corresponding ethylpalladium derivative 1b has been prepared by a similar method, but it is considerably less stable. It decomposes by (β-elimination to produce ethene and a transient hydride complex, which either undergoes migratory insertion to give [Pd2(μ-Cl)2(η1,η2-C8H13)2], 2a, or dinuclear reductive elimination with a second molecule of 1b to produce ethane, [PdCl2(cod)], free cyclooctadiene, and palladium metal. Complex 2a has also been prepared by reaction of [PdCl2(cod)] with NaBH4. At higher temperatures 2a converts to an equilibrium mixture with its η3-allyl isomer, 2b. Reactions of [PdCl2(cod)] or K2PdCl4 in the presence of cyclooctadiene in aqueous solution to produce 2a or 2b have also been investigated. Key words: palladium, diene complexes, allyl complexes, isomerization, β-elimination.
Study of formation and fragmentation of ionic complexes of polydentate ligands with Al(III) and glycerol by fast atom bombardment mass spectrometry. Part 1: Polydentate ligands
Authors: Saraswathi Mandapati , Miller Jack M.
Published: May 2006

The complexation reactions of aluminum ions with polydentate ligands such as 12-crown-4,15-crown-5,18-crown-6, 1,10-dithia-18-crown-6, dicyclohexyl-18-crown-6, dibenzo-18-crown-6, and dibenzo-24-crown-8 and acyclic analogs mono-, di-, tri-, tetra-, penta-, and hexaethylene glycols were studied using FAB mass spectrometry. These cyclic ligands form (M + 117)+, (M + 157)+, (M + 231)+, and (M + 253)+ ions with different aluminum-containing species. Collisionally activated dissociations of these adduct ions gave fragment ions, initially due to the loss of ligands directly attached to aluminum, followed by insertion of aluminum into the remaining ligand skeleton. Further fragmentation of the metal-containing species gave ions corresponding to consecutive losses of C2H4O units. Fragmentations of deuterium-labelled ions were used to help in establishing fragmentation pathways. Selectivity towards metal chelation is observed in this order: 12-crown-4 < 15-crown-5 < 18-crown-6. The elemental compositions of adduct ions were confirmed by high-resolution measurements. The formation of (M + Al − 2H)+ ion, obtained by the displacement of two hydroxy protons, is more favored for tetra- and pentaethylene glycols. Key words: crown ethers, polyethylene glycols, aluminum(III)–glycerol, ionic complexes and ion dissociations.
The metal-mediated conversion of octachlorocycloheptatriene into dodecachloroheptafulvalene: a synthetic, structural, and EHMO study
Authors: Dunn James A. , Gupta Hari K. , Bain Alex D. , McGlinchey Michael J.
Published: May 2006

Octachlorocycloheptatriene, C7Cl8, 3, reacts with a variety of organometallic precursors, e.g., Fe2(CO)9, Co2(CO)8, [(C5H5)Fe(CO)2]−, to give dodecachloroheptafulvalene, C14C12,12, in yields ranging from 54 to 68%. There is no evidence to support the intermediacy of carbene complexes of the type C7Cl6=MLn, and it is suggested that the reaction proceeds by the dechlorination of C7Cl8 to give hexachlorotropylidene, which dimerizes to the observed product. Extended Hückel molecular orbital calculations are used to show that the chlorinated carbene, C7Cl6, should be more stable than the corresponding parent system, C7Cl6. The EHMO calculations also reveal that planar heptafulvalenes are electronically disfavored and should exist preferentially in the S-anti conformation, as is the case for C14H12. The molecule C14Cl12,12, is shown by X-ray crystallography to be formed only as the syn conformer, which isomerizes to the anti structure only at high temperature. The conformations of the two seven-membered rings in 12 closely resemble that found in octachlorocycloheptatriene itself. C7Cl8, 3, crystallizes in the orthorhombic space group Pnma with a = 7.140(1) Å, b = 13.329(3) Å, c = 12.595(3) Å, and V = 1198.7(4) Å3 for Z = 4.3 adopts a severely bent boat structure in which the planes C(1)-C(7)-C(6) and C(2)-C(3)-C(4)-C(5) make angles of 51.8° and 32.4°, respectively, with the C(1)-C(2)-C(5)-C(6) plane. Key words: octachlorocycloheptatriene, heptafulvalenes, metal-mediated dimerization.
A density functional study of the bonding in tertiary phosphine chalcogenides and related molecules
Authors: Sandblom Nicole , Ziegler Tom , Chivers Tristram
Published: May 2006

The nature of the phosphorus–tellurium bond in tertiary phosphine tellurides is not well understood. There is also controversy over the nature of multiple bonding in the lighter chalcogenides and the related ylides and imides. Density functional theory (DFT) was used to investigate the interactions in the molecule, Me3PE (E = O, S, Se, Te, BH3, CH2, NH). The calculated PE bond energies and orbital populations reveal contributions from both σ donation from the phosphine and π back-donation to the phosphine in all of the above cases. Down the group from oxygen to tellurium, the PE bond weakens from 544 kJ mol−1 to 184 kJ mol−1, but multiple bonding becomes more significant with respect to the single bond. For E = BH3, the PB bond energy is 166 kJ mol−1. Trimethylphosphine ylide was found to have a π-bond order of 0.5, while that of trimethylphosphine imine is 0.6. For comparison, the oxides of trimethylamine and trimethylarsine were also calculated to examine the pnictogen–oxygen bond; Me3N does not participate in multiple bonding with oxygen, while the π-bond orders for Me3PO and Me3AsO were calculated as 0.7 and 0.6, respectively. Key words: phosphine chalcogenides, phosphine ylides, phosphine imides, DFT calculations
Dihydrofurans from α-diazoketones due to facile ring opening – cyclization of donor–acceptor cyclopropane intermediates
Authors: Lund Elizabeth A. , Kennedy Isaac A. , Fallis Alex G.
Published: May 2006

A series of α-diazoketones, 8, 25, 28, 31, and 34, have been synthesized and their reaction with ethyl vinyl ether examined under various reaction conditions. In the presence of metal salts (Rh2(OAc)4, Pd(OAc)2, CuCl) the ethoxy-dihydrofurans 12, 37, 39, 41, and 43 are produced. Sensitized irradiation of the α-diazoketone 8 afforded the dihydrofuran 12 plus cyclobutanone 7, while direct photolysis of α-diazoketones 8, 25, 28, 31, and 34 gave the cyclobutanones 7, 38,40,42, and 44, respectively. A sample of the cyclopropylketone 45 was isolated from the rhodium(II) acetate mediated reaction of 34 and its facile rearrangement to dihydrofuran 43 demonstrated. Collectively, these results indicate that the initial product from the reaction of an α-diazoketone with an electron-rich alkene such as ethyl vinyl ether is a cyclopropylketone. The donnor–acceptor substitution pattern of this intermediate results in spontaneous rearrangement to a dihydrofuran. Thus a direct dipolar cycloaddition mechanism is not involved when α-diazoketones react with enol ethers under metal-mediated conditions. Instead, these reactions follow a cyclopropanation rearrangement or, more accurately, cyclopropanation – ring opening – cyciization pathway. Key words: diazoketone, rhodium acetate, dihydrofuran, cyclopropylketone, vinyl ether.
Ryanoids and related compounds. Identification of five new ryanoids from the plantRyaniaspeciosaVahl. Formal total syntheses of 3-deoxyryanodol (cinnzeylanol), 10-O-acetyl-3-deoxyryanodol (cinnzeylanine), 2-deoxyryanodol, 2-deoxy-2-epiryanodol, 2,3-dideoxy-2,3-dihydroryanodol, 2-deoxy-3-epiryanodol, and 2-deoxy-3-epiryanodine
Authors: Ruest Luc , Dodier Marco
Published: May 2006

In the course of a preliminary investigation on the relationships between the chemical structure of ryanoids and their affinity to the ryanodine binding site, we have isolated, from the plant Ryania speciosa Vahl, four new members of this family of natural insecticidal compounds (ryanoids 3,4,5, and 6) and corrected the reported structure of a fifth one (ryanoid 7). In addition, we have synthesized, from anhydroryanodol (10), new members of this family having fewer hydroxyl groups in ring A: cinnzeylanol (14) and cinnzeylanine (15), 2,3-dideoxy-2,3-dihydroryanodol (16), 2-deoxy-3-epiryanodol (18), and 2-deoxy-3-epiryanodine (19), 2-deoxyryanodol (20), and 2-deoxy-2-epiryanodol (21). Key words: ryanoids synthesis, cinnzeylanine, 2-deoxyryanodols, 2-deoxy-3-epiryanodine.
Synthesis of β-hydroxypiperidine alkaloids by anodic oxidation of carbamates and hydroboration
Authors: Plehiers Mark , Hootelé Claude
Published: May 2006

The β-hydroxypiperidine alkaloids (±)-pseudoconhydrine, (±)-N-methylpseudoconhydrine, (−)-5-hydroxysedamine, and (+)-sedacryptine were synthesized. Successive functionalization of the piperidine ring via anodic methoxylation allowed the regio- and stereoselective introduction of the substituents. The α and α′ substituents were introduced by application of the sequence elimination–nucleophilic addition from 2- or 2,5-substituted 6-methoxycarbamates. Hydroboration – oxidation of enecarbamates, obtained by elimination of methanol from α-methoxycarbamates, allowed the introduction of the β-hydroxy function. Key words: alkaloid, Sedum, N-acyliminium, enecarbamate.
Rhenium(V) complexes with benzimidazole (BzimH) and crystal structure of the hemiprotonated compound [ReO2(BzimH)4][ReO(OH)(BzimH)4](ReO4)3
Authors: Bélanger Suzanne , Fortin Sébastien , Beauchamp André L.
Published: May 2006

trans-[ReO2(BzimH)4]I is generated by reacting ReO2I(PPh3)2 with excess BzimH in methanol, but free ligand is difficult to eliminate from the product. Pure samples of the trans-[ReO2(BzimH)4]BPh4 salt and of the protonated oxo-hydroxo form [ReO(OH)(BzimH)4](BF4)2 are isolated. Recrystallization of the dioxo complex in acetone–ether yields a pink solid. Red crystals suitable for X-ray diffraction are obtained by recrystallization of this solid in ethanol. The crystallographic study reveals a hemiprotonated [ReO2(BzimH)4][ReO(OH)(BzimH)4](ReO4)3 phase (Acam, a = 10.794, b = 21.520, c = 27.196 Å, R = 0.049). The O=Re=O fragments are parallel to one another along the unit cell c axis, forming layers of dimeric units consisting of one dioxo and one oxo-hydroxo species connected by a very short [Formula: see text] hydrogen bond of 2.44 Å. The ReO4− anions form hydrogen bonds with ligand N-H groups. The complexes are characterized by solution (1H and 13C) and solid-state (13C CP-MAS) NMR, UV–VIS, and IR spectroscopies. 1H NMR reveals that the benzimidazole protons in close proximity to the rhenium–oxo multiple bond or adjacent benzimidazole ligands are very sensitive to nonbonded magnetic effects. Keywords: rhenium, oxo complexes, benzimidazole, X-ray diffraction.
Synthesis, structure, and properties of oligo-tridentate ligands; covalently assembled precursors of coordination arrays
Authors: Hanan Garry S. , Schubert Ulrich S. , Volkmer Dirk , Rivière Emmanuel , Lehn Jean-Marie , Kyritsakas Nathalie , Fischer Jean
Published: May 2006

Oligo-tridentate ligands based on alternating pyridines and pyrimidines were synthesised by Stille-type carbon–carbon bond-forming reactions. The terpyridine-like sites are designed to coalign upon metal complexation, giving rise to organized and rigidly spaced metal ions. Peripheral functionalization of the basic bis-tridentate framework was explored. The heterocycles in the ligands are in an all-trans conformation about the interannular bonds as indicated by comparison of their 1H NMR spectra. An X-ray crystal structure analysis of the nonchiral tris-tridentate ligand 2a reveals a helical structure in the solid state. The seven heterocycles form a helical structure with resulting overlap of the terminal pyridines. Their centroid-to-centroid distance is 4.523 Å with 38.8° between the planes. NMR investigations support a helical conformation in solution as well. Electrochemical and UV absorption measurements indicate that the LUMO resides on the pyrimidine moiety of the ligands. Keywords: nitrogen-containing ligands, Stille coupling, helical structure, supramolecular chemistry.
Excess molar volumes and isothermal vapor-liquid equilibria in the tetrahydrofuran with propan-1-ol and propan-2-ol systems at 298.15 K
Authors: Salas Julio A. , Arancibia Eleuterio L. , Katz Miguel
Published: May 2006

Densities and vapor-liquid equilibria were determined for tetrahydrofuran with propan-1-ol and propan-2-ol systems at 298.15 K. From the experimental results, excess molar volumes and excess Gibbs free energies were calculated. Information could be obtained from the possible interaction between both chemical species in the two systems. The Prigogine–Flory–Patterson method was applied to calculate excess molar volumes. Liquid activity coefficients were calculated and correlated with different expressions existing in the literature. Keywords: excess molar volumes, vapor–liquid equilibria, activity coefficients, excess Gibbs free energies, tetrahydrofuran, propan-1-ol, propan-2-ol.
Weak interactions observed in ruthenium and iridium complexes containing hydride, amine, and bulky phospyhine ligands
Authors: Xu Wei , Lough Alan J. , Morris Robert H.
Published: May 2006

New amineruthenium and amineiridium hydride derivatives have been synthesized and characterized with the objective of observing intramolecular [Formula: see text] or [Formula: see text] interactions. These include RuHCl(CO)(L)(PPri3)2 (1a, L = NH2NH2; 1b, L = NH3) and IrCl2(L)(H)(PCy3)2 (2a, L = SC(NH2)2; 2b, L = NH3; 2c, L = NH2NH2; 2d, L = NH2(CH2)3NH2; 2e, L = NH2OH). Instead, weak [Formula: see text] van der Waals contacts have been detected in the solid state by X-ray analysis and in solution by NMR T1 measurements and nOe techniques. Both X-ray crystal structure analysis and minimum T1 measurements indicate that the [Formula: see text] distances in the [Formula: see text] interactions are ca•2.0–2.2 Å. The weak interactions might influence the course of deuteration of these complexes under D2 gas. The crystal and molecular structure of IrCl2(NH3)(H)(PCy3)22a has been determined by X-ray diffraction at 173 K: monoclinic, space group P21/n, a = 14.859(2) Å, b = 18.579(3) Å, c = 18.548(3) Å, β = 97.29(1)°, V = 5079.1(13) Å3, Z = 4, full-matrix least-squares refinement on F2 for 10 953 independent reflections; R[F2 > 4σ(F2)] = 0.0283, wR(F2) = 0.0704. Keywords: ruthenium, iridium, hydride, dihydrogen, complexes, hydrogen bond, NMR, X-ray.
An annulene TCNQ derivative with rather weak acceptor properties
Authors: Mitchell Reginald H. , Jin Xin , Otsubo Tetsuo , Takimiya Kazuo
Published: May 2006

Reaction of the bridged [14]annulenequinone, trans-10b,10c-dimethyl-10b,10c-dihydropyrene-2,7-quinone (12), with malononitrile in the presence of pyridine and TiCl4 gave 68% of the deep-purple extended TCNQ derivative, α,α,α′,α′-tetracyano-trans-10b, 10c-dimethyl-10b, 10c-dihydropyrene-2,7-quinodimethide (13). In solution, quinodimethide 13 appears to form a complex with diethylamine, but is too weak an electron acceptor to form complexes with tetrathiafulvalene, TTF, and related donors. The reduction potential of 13 was substantially lower than that found for TCNQ itself, and in properties 13 behaves more like a benzannelated TCNQ derivative, e.g., α,α,α′,α′-tetracyanopentacene-7,14-quinodimethide (11), than a pyrene derivative, e.g., α,α,α′,α′-tetracyanopyrene-2,7-quinodimethide (6). This is in agreement with molecular orbital calculations, which indicate that the LUMOs of 13 and 11 are approximately 0.6 eV higher in energy than those for 6 and TCNQ. Keywords: TCNQ — extended, TCNQ-pyrene derivative, reduction potential, annulene-quinodimethide, electron acceptor — weak.
Four new hydrolyzable tannins and an acylated flavonol glycoside from Euphorbiamaculata
Authors: Amakura Yoshiaki , Kawada Keita , Hatano Tsutomu , Okuda Takuo , Yoshida Takashi , Agata Isao , Sugaya Takeshi , Nishibe Sansei
Published: May 2006

The structure of a new acylated flavonol glycoside from the leaf extract of Euphorbiamaculata was characterized as quercetin 3-O-(2″,3″-di-O-galloyl)-β-D-glucopyranoside. Four new hydrolyzable tannins together with twelve known tannins were also isolated and their structures were established by spectral and chemical means as 1,2,6-tri-O-galloyl-α-D-glucose, 1-O-galloyl-2,4;3,6-di-O-chebuloyl-β-D-glucose (eumaculin E), and dimers (eumaculins B and D) having a tergalloyl and a macaranoyl group as the linking unit of monomers, respectively. Keywords: Euphorbiamaculata, Euphorbiaceae, tannin, eumaculin B, eumaculin E.
Diversity in crystal production by some bird's nest fungi (Nidulariaceae) in culture
Authors: Shinners Tracy C. , Tewari Jalpa P.
Published: May 2006

Hyphae of many species of bird's nest fungi (Nidulariaceae) were examined for the presence of crystals. Scanning electron microscopy revealed crystals typical of calcium oxalate associated with hyphae. Crystal depositions included complete hyphal encrustation, organized druses, randomly arranged groups, single crystals, and relatively "clean" hyphae. The majority of crystals could be morphologically classified as styloid, raphide, or bipyramidal type. Energy-dispersive X-ray microanalyses confirmed that all crystal types were rich in calcium, and X-ray diffraction identified both the dihydrate (weddellite) and monohydrate (whewellite) forms of calcium oxalate. Morphological variation of crystals was species and medium specific, with generally more crystals being produced on relatively calcium-rich V8 juice agar than on PDA. No association was found between crystal types and geographic and habitat distribution of species. Keywords: wood rotting fungus, decomposition, calcium oxalate.
Benzenoid hydrocarbon aromaticity in terms of charge density descriptors
Authors: Howard S.T. , Krygowski T.M.
Published: May 2006

Hartree–Fock/6-31G** calculations on the benzenoid hydrocarbons benzene, naphthalene, phenanthrene, anthracene, pyrene, tetracene, triphenylene, chrysene, perylene, and coronene are used to investigate the link between aromaticity and the electron distribution. Topological charge density analysis is used, concentrating on the electron distribution ρ (and its Hessian) at bond and ring critical points. With regard to the bond critical point data, it is shown that ρc, [Formula: see text]ρc, and the bond "ellipticity" ε are closely correlated with the bond lengths so, as aromaticity indicators, they have little to add over and above existing indices based on structure. However, the same properties evaluated at the ring critical points in the total density, and also at the equivalent stationary points in the π and σ densities, correlate closely with two different aromaticity indices (one based on structure, the other on magnetic properties), the curvature of ρ perpendicular to the ring plane giving (marginally) the best results. Hence a ring critical point (RCP) index is proposed as a way of quantifying aromaticity, based directly on the electron distribution. Keywords: quantum chemistry, electron density, aromaticity, aromaticity index, HOMA, NICS.
Naphthalene-based poly(aryl ether)s. II. Synthesis and characterization of poly(ether ketone)s containing two 1,4-naphthylene moieties in the repeat unit
Authors: Wang Zhi Yuan , Broughton Peter W.
Published: May 2006

Two new monomers, 4-chloro-1-(4′-fluoro-1-naphthoyl)naphthalene and 1,4-bis(4′-fluoro-1′-naphthoyl)benzene, have been synthesized and polymerized with four different bisphenols to give two series of the naphthalene-based poly(ether ketone)s that are analogous to commercial PEEK and PEEKK. The effect of the introduction of one or two 1,4-naphthylene moieties, in the backbone of the repeat unit, on the glass transition temperatures has been studied. The glass transition temperatures usually increased by 20–45 °C upon replacing one 1,4-phenylene with one 1,4-naphthylene moiety. All new poly (ether ketone)s prepared in tetramethylene sulfone were amorphous, with the glass transition temperatures in a range of 212–273 °C. The polymer produced from 1,4-bis(4′-fluoro-1′-naphthoyl)benzene and 1,4-hydroquinone in phenyl sulfone as a solvent at 300 °C showed semicrystalline properties with a melting temperature of 310 °C. Keywords: naphthalene, poly(ether ketone)s, synthesis, characterization, glass transition temperature.
Structural studies and redox reactivity of platinum complexes of 14-membered tetraaza macrocyclic ligands
Authors: Chandrasekhar S. , Waltz W.L. , Quail J.W. , Prasad L.
Published: May 2006

Pt(II) monomeric complexes of N-containing macrocycles have been synthesized and characterized in solution by 1H NMR, 13C NMR, and electrospray mass spectroscopy (ESMS) and in the solid state by X-ray crystallography. Crystals of [Pt(cyclam)](ClO4)2 (cyclam = 1,4,8,11-tetraazacyclotetradecane) are orthorhombic, space group P21cn, a = 9.596 (3), b = 14.595 (21), c = 24.8782 (20) Å, Z = 8. The structure was solved by direct methods and was refined by the full-matrix least-squares method to R = 0.073 and Rw = 0.093 for 2976 reflections with I ≥ 2.5σ(I). Crystals of [Pt(N-methylcyclam)]-(ClO4)2•CH3CN (N-methylcyclam = 1,4,8,11 tetramethyl-1,4,8,11-tetraazacyclotetradecane = NMe4cyclam = tmc) are orthorhombic, space group Pmcn, a = 9.574 (8), b = 14.116 (5), c = 17.5456 (15) Å, Z = 4. The structure was solved by direct methods and was refined by the full-matrix least-squares method to R = 0.067 and Rw = 0.091 for 2216 reflections with I ≥ 2.5σ(I). Cyclic voltammetry and EPR spectroscopy have been used to study the redox reactivity of the Pt(II)and Pt(IV) complex ions. The solution chemistry of Pt(IV) complexes based on cyclam and N-methylcyclam was investigated by electrospray mass spectrometry. Electrospray mass spectral evidence has been obtained for the formation of [Pt(III)(cyclam)Cl2]+ and [Pt(III)(N-methylcyclam)Cl2]+ ions. Keywords: Pt macrocycles, crystallography, electrospray mass spectroscopy, cyclic voltammetry, Pt(III) complex ions, tetraaza macrocycles.
Morphological, chemical, and electrochemical properties of Ti/(TiO2 + IrO2) electrodes
Authors: Silva L.A. da , Alves V.A. , Silva M.A.P. da , Trasatti S. , Boodts J.F.C.
Published: May 2006

Electrodes of general composition IrxTi(1−x)O2 with 0.2 ≤ x ≤ 1.0 were prepared on a Ti support by calcination of the chlorides at 450 °C. Ex situ and in situ characterization included the use of techniques such as scanning electron microscope (SEM), energy dispersive X-ray analysis (EDX), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). EDX showed a surface enrichment with Ti. The voltammetric charge was found to go through a maximum at 60% IrO2. O2 evolution was studied in 1.0 mol dm−3 HClO4 by determining Tafel slopes and impedance parameters. Tafel slopes were found to vary between 40 and 60 mV depending on the overpotential range and the oxide composition. Solution and film resistance, film and double layer capacitance, and charge transfer resistance were determined as a function of potential and oxide composition. A reaction mechanism has been proposed. Separation of geometric and electronic effects has been attempted. Keywords: oxygen evolution, oxide electrode, electrocatalysis, electrochemical impedance spectroscopy, iridium dioxide.
The mean spherical approximation and medium effects in the kinetics of solution reactions involving ions
Authors: Fawcett W. Ronald , Tikanen Alex C. , Henderson Douglas J.
Published: May 2006

The mean spherical approximation has been applied to describe medium effects in the kinetics of reactions between ions in water. When the ionic strength of the medium is altered by the addition of an inert electrolyte, the rate of reaction can be accurately predicted with the inert electrolyte concentration up to 1 M. The theoretical rate constant at the limit of infinite dilution kr0, has been estimated for five earlier kinetics studies for which data are available in the literature. Keywords: kinetic medium effects, mean spherical approximation, activity coefficients.
Anodic oxidation of Au(111)
Authors: Schneeweiss Marie Anne , Kolb Dieter M. , Liu Dezhong , Mandler Daniel
Published: May 2006

The initial stages of the anodic oxidation of Au(111) were investigated by means of cyclic voltammetry as well as in situ scanning tunneling microscopy (STM). The results suggest that the place exchange process, which initiates the oxide formation, starts at step edges. The oxide phase was imaged in situ by scanning tunneling and atomic force microscopy (AFM). The topographic information acquired by the two techniques is compared. Keywords: gold, gold oxide, corrosion, scanning tunneling microscopy (STM), atomic force microscopy (AFM).
Interlamellar amino functionalization of kaolinite
Authors: Tunney James J. , Detellier Christian
Published: May 2006

The interlamellar surface of kaolinite has been modified with molecules possessing amino functionalities. Either the dimethyl sulfoxide intercalate of kaolinite (Kao/DMSO) or the N-methylformamide intercalate of kaolinite (Kao/NMF) were used as starting materials. One of the products, an ethanolamine functionalized kaolinite (Kao–EOA) was resistant to thermal decomposition in both air and N2 atmospheres up to temperatures greater than 150 °C. Based on results from thermal analysis, IR analysis, 13CCP/MAS NMR spectroscopy, and elemental analysis, a structural model is proposed in which every third interlayer surface hydroxyl group on the aluminol (Al-OH) surface of kaolinite is either replaced with an interlayer Al-OCH2CH2NH2 group or is strongly H-bonded to an aminoalcohol molecule. A mixture of both types of linkages could coexist. The amino groups that point away from this surface are each keyed into the -(SiO−)6 macro-rings of the adjacent silicate surface, resulting in an amino-functionalized ordered two-dimensional organo-mineral assembly. Keywords: kaolinite, halloysite, organo-mineral nanocomposites, clay functionalization, supramolecular assemblies.
X+ transfer from the halonium ions of adamantylideneadamantane to acceptor olefins. The possibility of chiral induction in the transfer process
Authors: Neverov Alexei A. , Muise Theresa L. , Brown R.S.
Published: May 2006

The bromonium ion of adamantylideneadamantane (Ad=Ad-Br+) has been used to induce the bromocyclization of a 4-pentenyl glycoside (10) and a 5-hexenyl glycoside (11) in dichloroethane. The kinetics of these processes have been studied at 25 °C in the presence of varying [Ad=Ad] and, in the case of the transfer to 10, in the presence of pentanol. The second-order rate constants for bromocyclization of these two alkenes are (1.04 ± 0.06) × 10−1 M−1 s−1 and (5.34 ± 0.2) × 10−1 M−1 s−1, respectively, and in no case does added Ad=Ad or pentanol alter the reaction rate. The kinetic behavior is interpreted in terms of cyclization occurring directly from a 1:1 complex of Ad=Ad-Br+ and 10 or 11. The chiral induction for the bromocyclization of 10 promoted by AdAd-Br+ was measured at 20% e.e., the (−)-(S)-tetrahydrofurfuryl bromide being the dominant stereoisomer. Ad=Ad molecules substituted at one of the homoallylic carbons by an axial methyl group (12), or by two methyl groups (axial and equatorial), were synthesized and the 1H NMR spectra of their bromonium ions is given. These materials are not stable for prolonged times at room temperature. A limited kinetic study of the reaction of 12-Br+ and 4-pentenol indicated that the Br+ transfer is 500 times faster than the comparable transfer from Ad=Ad-Br+ to 4-pentenol. The possibility of using these materials to induce chiral bromocyclization is discussed. Keywords: bromonium ion, halonium, transfer, chiral, adamantylideneadamantane.
THE ROLE OF THE BASAL GANGLIA IN EXPLORATION IN A NEURAL MODEL BASED ON REINFORCEMENT LEARNING
Authors: SRIDHARAN D. , PRASHANTH P. S. , CHAKRAVARTHY V. S.
Published: May 2006

We present a computational model of basal ganglia as a key player in exploratory behavior. The model describes exploration of a virtual rat in a simulated water pool experiment. The virtual rat is trained using a reward-based or reinforcement learning paradigm which requires units with stochastic behavior for exploration of the system's state space. We model the Subthalamic Nucleus-Globus Pallidus externa (STN-GPe) segment of the basal ganglia as a pair of neuronal layers with oscillatory dynamics, exhibiting a variety of dynamic regimes such as chaos, traveling waves and clustering. Invoking the property of chaotic systems to explore state-space, we suggest that the complex exploratory dynamics of STN-GPe system in conjunction with dopamine-based reward signaling from the Substantia Nigra pars compacta (SNc) present the two key ingredients of a reinforcement learning system.
DYNAMICAL ANALYSIS OF A ALLELOPATHIC PHYTOPLANKTON MODEL
Authors: BANDYOPADHYAY MALAY
Published: May 2006

In this paper we have considered a two-species competitive phytoplankton system with one toxin producing phytoplankton. Local asymptotic stability of various equilibrium points are considered to understand the effect of toxic substance on the dynamics of the model system. By using a suitable Lyapunov function we have observed that the toxic substance has some stabilizing effect on the dynamics of model system.
IL-17A acts via p38 MAPK to increase stability of TNF-α-induced IL-8 mRNA in human ASM
Authors: Henness Sheridan , van Thoor Eveline , Ge Qi , Armour Carol L. , Hughes J. Margaret , Ammit Alaina J.
Published: May 2006

Human airway smooth muscle (ASM) plays an immunomodulatory role in asthma. Recently, IL-17A has become of increasing interest in asthma, being found at elevated levels in asthmatic airways and emerging as playing an important role in airway neutrophilia. IL-17A predominantly exerts its neutrophil orchestrating role indirectly via the induction of cytokines by resident airway structural cells. Here, we perform an in vitro study to show that although IL-17A did not induce secretion of the CXC chemokine IL-8 from ASM cells, IL-17A significantly potentiates TNF-α-induced IL-8 protein secretion and gene expression in a concentration- and time-dependent manner ( P < 0.05). Levels of IL-8 protein produced after 24 h of incubation with TNF-α were enhanced 2.7-fold in the presence of IL-17A, and conditioned media significantly enhanced neutrophil chemotaxis in vitro. As IL-17A had no effect on the activity of NF-κB, a key transcriptional regulator of IL-8 gene expression, we then examined whether IL-17A acts at the posttranscriptional level. We found that IL-17A significantly augmented TNF-α-induced IL-8 mRNA stability. Interestingly, this enhanced stability occurred via a p38 MAPK-dependent pathway. The decay of IL-8 mRNA transcripts proceeded at a significantly faster rate when cells were pretreated with the p38 MAPK inhibitor SB-203580 (−0.05763 ± 0.01964, t1/2= 12.0 h), compared with vehicle (−0.01030 ± 0.007963, t1/2= 67.3 h) [results are expressed as decay constant (means ± SE) and half-life ( t1/2in h): P < 0.05]. Collectively, these results demonstrate that IL-17A amplifies the synthetic function of ASM cells, acting via a p38 MAPK-dependent posttranscriptional pathway to augment TNF-α-induced secretion of the potent neutrophil chemoattractant IL-8 from ASM cells.
Glucose-evoked alterations in connexin43-mediated cell-to-cell communication in human collecting duct: a possible role in diabetic nephropathy
Authors: Hills Claire E. , Bland Rosemary , Wheelans Dianne C. , Bennett Jeanette , Ronco Pierre M. , Squires Paul E.
Published: May 2006

Aberrant sodium absorption has been linked to the development of hypertension in both renal disease and diabetes. Efficient absorption depends on coordination of cellular activity across the entire epithelium via cell-to-cell coupling. In the current study we have utilized a model human collecting duct cell line (HCD) to assess the role of connexin43 (Cx43)-mediated gap junctions in the transfer of intracellular Ca2+ transients within coupled cell clusters. HCD cells express Cx43 mRNA and protein, as well as that for the mechanosensitive transient receptor potential receptor (TRPV4). Mechanical stimulation of individual cells within a cluster evoked a transient rise in cytosolic Ca2+ concentration ([Ca2+]i) that propagated between cells via a heptanol-sensitive mechanism. The rise in [Ca2+]i was dependent on both store release and Ca2+-influx pathways. Lucifer yellow dye transfer and Cx43 knockdown experiments confirmed direct cell-to-cell communication. Application of the Ca2+ ionophore ionomycin, or an increase in glucose (5 to 25 mM), produced a time-dependent (48 h) increase in Cx43 protein expression. The transmission rate of touch-evoked Ca2+ transients between coupled cells was accelerated after exposure to high glucose, providing a functional correlate to increased Cx43 expression. These data suggest a pivotal role for Cx43-mediated gap junctions in the synchronization of activity between HCD cells in response to stimuli that mimic osmotic and physical changes. Cx43 expression and cell-to-cell communication increased in response to high glucose and may protect the collecting duct from renal damage associated with more established diabetic nephropathy.
Platelet Expression Profiling and Clinical Validation of Myeloid-Related Protein-14 as a Novel Determinant of Cardiovascular Events
Authors: Healy Aileen M. , Pickard Michael D. , Pradhan Aruna D. , Wang Yunmei , Chen Zhiping , Croce Kevin , Sakuma Masashi , Shi Can , Zago Alexandre C. , Garasic Joseph , Damokosh Andrew I. , Dowie Tracy L. , Poisson Louis , Lillie James , Libby Peter , Ridker Paul M , Simon Daniel I.
Published: May 2006

Background—

Platelets participate in events that immediately precede acute myocardial infarction. Because platelets lack nuclear DNA but retain megakaryocyte-derived mRNAs, the platelet transcriptome provides a novel window on gene expression preceding acute coronary events.

Methods and Results—

We profiled platelet mRNA from patients with acute ST-segment–elevation myocardial infarction (STEMI, n=16) or stable coronary artery disease (n=44). The platelet transcriptomes were analyzed and single-gene models constructed to identify candidate genes with differential expression. We validated 1 candidate gene product by performing a prospective, nested case-control study (n=255 case-control pairs) among apparently healthy women to assess the risk of future cardiovascular events (nonfatal myocardial infarction, nonfatal stroke, and cardiovascular death) associated with baseline plasma levels of the candidate protein. Platelets isolated from STEMI and coronary artery disease patients contained 54 differentially expressed transcripts. The strongest discriminators of STEMI in the microarrays were CD69 (odds ratio 6.2,
P
<0.001) and myeloid-related protein-14 (MRP-14; odds ratio 3.3,
P
=0.002). Plasma levels of MRP-8/14 heterodimer were higher in STEMI patients (17.0 versus 8.0 μg/mL,
P
<0.001). In the validation study, the risk of a first cardiovascular event increased with each increasing quartile of MRP-8/14 (
P
trend
<0.001) such that women with the highest levels had a 3.8-fold increase in risk of any vascular event (
P
<0.001). Risks were independent of standard risk factors and C-reactive protein.

Conclusions—

The platelet transcriptome reveals quantitative differences between acute and stable coronary artery disease. MRP-14 expression increases before STEMI, and increasing plasma concentrations of MRP-8/14 among healthy individuals predict the risk of future cardiovascular events.
A Real-Time Hurricane Surface Wind Forecasting Model: Formulation and Verification
Authors: Xie Lian , Bao Shaowu , Pietrafesa Leonard J. , Foley Kristen , Fuentes Montserrat
Published: May 2006

A real-time hurricane wind forecast model is developed by 1) incorporating an asymmetric effect into the Holland hurricane wind model; 2) using the National Oceanic and Atmospheric Administration (NOAA)/National Hurricane Center’s (NHC) hurricane forecast guidance for prognostic modeling; and 3) assimilating the National Data Buoy Center (NDBC) real-time buoy data into the model’s initial wind field. The method is validated using all 2003 and 2004 Atlantic and Gulf of Mexico hurricanes. The results show that 6- and 12-h forecast winds using the asymmetric hurricane wind model are statistically more accurate than using a symmetric wind model. Detailed case studies were conducted for four historical hurricanes, namely, Floyd (1999), Gordon (2000), Lily (2002), and Isabel (2003). Although the asymmetric model performed generally better than the symmetric model, the improvement in hurricane wind forecasts produced by the asymmetric model varied significantly for different storms. In some cases, optimizing the symmetric model using observations available at initial time and forecast mean radius of maximum wind can produce comparable wind accuracy measured in terms of rms error of wind speed. However, in order to describe the asymmetric structure of hurricane winds, an asymmetric model is needed.
The ITCZ in the Central and Eastern Pacific on Synoptic Time Scales
Authors: Wang Chia-chi , Magnusdottir Gudrun
Published: May 2006

The ITCZ in the central and eastern Pacific on synoptic time scales is highly dynamic. The active season extends roughly from May through October. During the active season, the ITCZ continuously breaks down and re-forms, and produces a series of tropical disturbances. The life span of the ITCZ varies from several days to 3 weeks.

Sixty-five cases of ITCZ breakdown have been visually identified over five active seasons (1999–2003) in three independent datasets. ITCZ breakdown can be triggered by two mechanisms: 1) interaction with westward-propagating disturbances (WPDs) and 2) the vortex rollup (VR) mechanism. Results show that the frequency of occurrence of ITCZ breakdown from these two mechanisms is the same. The VR mechanism may have been neglected because the produced disturbances are rather weak and they may dissipate quickly. The ITCZ shows a strong tendency to re-form within 1–2 days in the same location. The ITCZ may break down via the VR mechanism without any other support, and thus it may continuously generate numerous tropical disturbances throughout the season.

There are two main differences between the two mechanisms: 1) The WPDs-induced ITCZ breakdown tends to create one or two vortices that may be of tropical depression strength. The VR-induced ITCZ breakdown generates several nearly equal-sized weak disturbances. 2) The WPDs tend to disturb the ITCZ in the eastern Pacific only. Disturbances generally move along the Mexican coast after shedding off from the ITCZ and do not further disturb the ITCZ in the central Pacific. Therefore, the VR mechanism is observed more clearly and is the dominating mechanism for ITCZ breakdown in the central Pacific.
Beyond Binaries
Authors: Patel Sujata
Published: May 2006

This article examines the evolution of sociological traditions within India in the context of colonization and assesses their continuation in its contemporary practices. It evaluates two new perspectives, indigenization and postcolonial studies, that have emerged to reorganize these traditions. The author argues that the divisions of knowledge and power represented within the disciplines of sociology and anthropology structure the ways in which distinct traditions of sociology have evolved and continue to play a major role in defining theories, perspectives and methods of doing sociologies in the world. How can these perspectives take the challenge of globalization that is reorganizing the distribution of world power, its knowledge and that of its institutions in new and seminal ways? The globalization of knowledge can have two possible effects. It can reconstruct earlier binaries in new ways, refashioning them to maintain the structure connecting knowledge with power. Alternatively, global processes can distil and uncouple these binaries, thereby allowing for the play of plural perspectives, so that all traditions of doing sociology are placed at equal levels and given equal significance. We have to decide the path that we travel.
Sociology and the South
Authors: Elizaga Raquel Sosa
Published: May 2006

Latin American sociology has gone through critical revisions since the mid-20th century. However, the latest view proposes one of the more radical changes ever thought of: to stop seeing the region as ‘opposed to’ the US empire, and begin working on the idea of the belonging to a greater region, known globally as the South. Redefinition of time and space, territory, history, knowledge and social subjects, as well of other important categories, play a crucial part in this shift. A new horizon has been opened for social sciences, and it seems that new sources for creativity have emerged.
A Procedure for Estimating Intrasubject Behavior Consistency
Authors: Hernández José M. , Rubio Víctor J. , Revuelta Javier , Santacreu José
Published: May 2006

Trait psychology implicitly assumes consistency of the personal traits. Mischel, however, argued against the idea of a general consistency of human beings. The present article aims to design a statistical procedure based on an adaptation of the π* statistic to measure the degree of intraindividual consistency independently of the measure used. Three studies were carried out for testing the suitability of the π* statistic and the proportion of subjects who act consistently. Results have shown the appropriateness of the statistic proposed and that the percentage of consistent individuals depends on whether test items can be assumed as equivalents and the number of response alternatives they contained. The results suggest that the percentage of consistent subjects is far from 100%, and this percentage decreases when items are equivalent. Moreover, the greater the number of response options, the lesser the percentage of consistent individuals.
An Investigation Into the Factors Influencing Extreme-Response Style
Authors: Arce-Ferrer Alvaro J.
Published: May 2006

Translation and cultural adaptation of rating scales are two critical components in testing culturally and/or linguistically heterogeneous populations. Despite the proper use of these scales, challenges typically arise from respondents’ language, culture, ratiocination, and characteristics of measurement processes. This study investigated factors affecting the rates of extreme response using direct measures and Spanish-speaking respondents from rural and urban settings. Issues of respondents’ familiarity with rating scales, respondents’ subjective categories, and scale characteristics were investigated and their relation to extreme response documented. The tendency to choose extreme portions of a rating scale seems to be rooted in the mismatch between scale characteristics and respondents’ subjective categories, respondents’ familiarity with rating scales, and communication norms. This article discusses implications of findings for validity of translated and adapted rating scales.
Suppression Situations in Multiple Linear Regression
Authors: Shieh Gwowen
Published: May 2006

This article proposes alternative expressions for the two most prevailing definitions of suppression without resorting to the standardized regression modeling. The formulation provides a simple basis for the examination of their relationship. For the two-predictor regression, the author demonstrates that the previous results in the literature are incomplete and oversimplified. The proposed approach also allows a natural extension for multiple regression with more than two predictor variables. It is shown that the conditions under which both types of suppression can occur are not fully congruent with the significance of the partial F test. This implies that all the standard variable selection techniques—backward elimination, forward selection, and stepwise regression procedures—can fail to detect suppression situations. This also explains the controversial findings in the redundancy or importance of correlated variables in applied settings. Furthermore, informative visual representations of various aspects of these phenomena are provided.