bluuebunny/crossref_metadata_2025 huggingface dataset:
The influence of water on the spectroscopic properties of a liposoluble magnesium porphyrin
Authors: Chapados Camille , Girard Denis , Ringuet Michel
Published: May 2006

Complexation of water by chlorophyll molecules in natural photosynthetic processes is a matter of great interest. In the present work the influence of water on a model porphyrin, magnesium 2,7,12,17-tetrahexyl-3,8,13,18-tetramethyl porphin (MgTHTMP) has been studied by infrared spectroscopy. A CCl4 (spectroscopic grade) solution of MgTHTMP showed two small bands in the 3600 cm−1 infrared region. These bands are assigned to ν3 and ν1 vibrations of water coordinated to the Mg atom. For MgTHTMP in the solid state, either deposited on an infrared plate or suspended in a Nujol film, none of the OH bands is observed. An elemental analysis confirmed that the solid porphyrin was anhydrous. This evidence indicates that while no water is complexed with MgTHTMP in the solid state, this porphyrin is highly hygroscopic in a CCl4 solution and will easily complex with the few water molecules (less than 0.01%) present in the spectro grade solvent by forming a coordinate bond between the central magnesium atom and the oxygen of water. Several other metallic porphyrins in CCl4 solutions have been studied for comparison with the Mg porphyrin. The spectra of these substances did not show any complexed water. A model of the H2O–MgTHTMP interaction is given and the implication of this model on the aggregation states of chlorophyll will be discussed.
Temperature dependance of adiabatic compressibility, sound velocity, and specific acoustic impedance of water–cyclohexanone mixture
Authors: Ramanjappa T. , Rajagopal E.
Published: May 2006

The temperature dependance of adiabatic compressibility minimum (TACM), sound velocity maximum (TSVM), and specific acoustic impedance (TSAIM) of water–cyclohexanone mixture has been studied by experimentally determining the sound velocity in and density of aqueous solution at different concentrations over a temperature range 36–77 °C. The structural contribution to the shift in TACM, TSVM, and TSAIM has been evaluated. The shifts are negative and increase with concentration. The results indicate that cyclohexanone behaves as a structure breaker at higher temperature.
Pyrazolo[3,4-b]pyridines: Syntheses, reactions, and nuclear magnetic resonance spectra
Authors: Lynch Brian Maurice , Khan Misbahul Ain , Teo Huk Chia , Pedrotti Francisco
Published: May 2006

Efficient syntheses of approximately 70 simple substituted representatives of pyrazolo[3,4-b]pyridine 1 are reported from the following: (a) suitably substituted pyridines onto which a pyrazole ring is annelated, and (b) appropriately substituted pyrazoles onto which a pyridine ring is annelated. Selected examples of electrophilic, nucleophilic, and homolytic substitution reactions and group transformations are described, providing regiosynthetic paths to useful intermediate species. Some systematic aspects of substituent chemical shift influences in the 1H and 13C nuclear magnetic resonance spectra, aiding in structural assignments, are illustrated.
Brillouin scattering near the α–β phase transitions of N2 and CO
Authors: Askarpour V. , Klefte H. , Clouter M. J.
Published: May 2006

The technique of high resolution Brillouin spectroscopy has been used to determine the adiabatic elastic constants of single crystals of β-N2 and β-CO as a function of temperature, in an effort to study the α–β phase transition. For all elastic constants, there is an increase of approximately 1%/K on cooling and there is no evidence of further mode softening, even within 0.5 K of the phase transition. Three large single crystals of α-CO were grown. The orientations were determined, by Laue X-ray diffraction, and correlated to the orientations of the parent β-crystals. The β-phase hexagonal basal planes appear to transform to planes of the form {110} in the α-phase cubic structure.
The infrared multiphoton dissociation of hexafluoroethane
Authors: Brown Carl E. , Smith Donald R.
Published: May 2006

The infrared multiphoton dissociation (IRMPD) of "neat" hexafluoroethane has been investigated for the first time. The stable products of photolysis are CF4, C2F4, C3F8, and C4F10. Product analysis involved tunable diode laser (TDL) and fourier transform infrared spectroscopy, as well as gas chromatography where applicable. The high sensitivity and resolution of the TDL allows for measurement of the stable products CF4 and C2F4 after irradiation by a single infrared laser pulse. The yield of CF3 radicals produced by the IRMPD of C2F6 as a function of fluence was measured via the TDL high frequency modulation technique. The role of added H2, leading to elimination of CF4 and increase of C2F4 as products, is clarified.
Rotational excitations of A-CH4 II in the meV range studied by inelastic neutron scattering
Authors: Press W. , Heidemann A. , Lauter H. , Morrison J. A. , Neumaier K.
Published: May 2006

The excitation spectrum of solid methane (CH4) with all molecules converted to the nuclear spin state with A symmetry has been measured with incoherent inelastic neutron scattering. For energies [Formula: see text], there are no dramatic differences with samples consisting of a mixture of all three spin states A, T, and E. A qualitative understanding of the measurements is achieved by comparison with calculations of Ozaki et al.
Adsorbate spectra of rare-gas atoms on metal surfaces
Authors: Mavroyannis Constantine
Published: May 2006

The optical excitation spectra of neutral rare-gas atoms physisorbed on metal surfaces have been considered. Emphasis has been given to the dynamic effects of the surface plasmons on the lifetimes of the adsorbed atoms. At low coverage and when the damping of the surface plasmons is much greater than the effective radiative damping, the spectral functions of the symmetric and antisymmetric modes consist of asymmetric Lorentzian lines, whose asymmetry depends on the strength of the surface plasmons. At this limit the relative intensities of the symmetric and antisymmetric modes take positive and negative values describing the physical processes of absorption (attenuation) and stimulated emission (amplification), respectively. Hence, the occasional disappearance of the spectral lines of the optical absorption is due to a cancellation process, which takes place between the frequency profiles arising from two nearby excited states of the adsorbed atom. The red shifted peak of the symmetric mode of the higher excited state and the blue shifted peak of the antisymmetric mode of the lower excited state of the atom cancel each other out provided that their frequency profiles nearly coincide. This may be a possible explanation of the persistence-extinction phenomenon that has been observed for a number of rare-gas substrate systems in the low coverage limit, where it has been proposed that a charge-transfer instability exists. Numerical results indicate that the peaks of excited Xe on Al and excited Kr on Au vanish in the low coverage limit.
The low temperature structure of ethylene monolayers physisorbed on the graphite basal plane
Authors: Moller Michael A. , Klein Michael L.
Published: May 2006

The low temperature structure of low density ethylene monolayers physisorbed on the graphite basal plane has been examined by molecular dynamics calculations with an intermolecular potential based on atom–atom interactions. The simulations predict that the ethylene molecules are arranged in a herringbone with a centered rectangular unit cell of dimensions 4.95 Å × 7.05 Å. In this structure, the molecular C=C axes are parallel to the surface, and are oriented at 60° angles from each other, while the molecular planes are tilted some 55° from the plane of the surface. The structure was found to be essentially independent of the assumed corrugation of the graphite surface.
Static and dynamic properties of hydrogen sulphide in hydroquinone clathrates
Authors: Ukegawa Harutoshi , Matsuo Takasuke , Suga Hiroshi , Leadbetter Alan J. , Ward Richard C. , Clark Jon W.
Published: May 2006

A variety of investigations has been undertaken on hydrogen sulphide hydroquinone clathrates, with the aim of achieving a better understanding of the motions of the guest molecules and of the phase transition near 8 K, Measurements have been made, over a wide temperature range including the phase transition, of heat capacities on H2S, D2S, and HDS clathrates, dielectric constants perpendicular and parallel to the trigonal axis of single crystal specimens, incoherent quasi-elastic neutron scattering, and neutron diffraction. All of the data are consistent with the H2S molecular dipole being able to rotate rather easily about an axis parallel to the trigonal crystal c axis. Rotations about the other axes are much more difficult. The rotation about the trigonal axis is almost free at high temperatures but there is evidence for three preferred orientations at temperatures just above the phase transition. No discrete energy states are observed at any temperature due to strong guest–cage and guest–guest interactions. The experiments provide direct evidence that the phase transition is associated with a cooperative freezing out of the dipole reorientations.
Mononuclear Rh, Ir, Pd, and Pt complexes of the tripod ligand (Ph2P)3CH.The molecular structure of bis[1,1,1-tris(diphenylphosphino)methane]platinum(II) tetrafluoroborate
Authors: Beckett Kenneth J. , Loeb Stephen J.
Published: May 2006

The mononuclear complexes [Rh(η2-(Ph2P)3CH)2]X, [Ir(CO)(η2-(Ph2P)3CH)2]X, [Pd(η2-(Ph2P)3CH)2]X2, and [Pt(η2-(Ph2P)3CH)2]X2[Formula: see text],are synthesized and fully characterized by 31P{1H} nmr and infrared spectroscopy. The complex [Pt(η2-(Ph2P)3CH)2][BF4]2 was further characterized by a single crystal X-ray diffraction study. Crystals are triclinic, a = 12.514(6) Å, b = 13.289(7) Å, c = 12.609(9) Å, α = 120.63(4)°, β = 104.51(5)°, γ = 99.45(4)°, Z = 1, space group [Formula: see text]. The structure was solved by conventional heavy atom methods and refined by full-matrix least-squares procedures to R(%) = 6.87 and Rw(%) = 7.28 for 2995 reflections with [Formula: see text]. The Rh, Pd, and Pt complexes are square planar and shown by 31P{1H} nmr to exist in solution as a mixture of syn and anti isomers. The structure of [Pt(η2-(Ph2P)3CH)2][BF4]2 shows the anti isomer exists in the solid state for this complex. Both the syn and anti isomers of the complex [Rh(η2-(Ph2P)3CH)2][BF4] react with HX (X = Cl, Br) to give a single octahedral Rh(III) product trans-[RhX(H)(η2-(Ph2P)3CH)2)][BF4] characterized by 31P{1H} and 1H nmr.
Excess partial molar enthalpies of tert-butanol in water–tert-butanol mixtures
Authors: Koga Yoshikata
Published: May 2006

Excess partial molar enthalpies of tert-butanol (TBA) in water–tert-butanol mixtures were measured at 20.00, 26.90, 45.17, and 59.49 °C in the water-rich region, and at 30.00 °C for the entire range. The results together with those of the previous work, (Y. Koga. Can. J. Chem. 64, 206 (1986)), appear to support the following views: At XTBA ≈ 0, TBA molecules form hydrogen bonds with H2O molecules, and they enhance the structure of the hydrogen bond network of H2O. The latter effect is of very long range; the enthalpic repulsion between solutes is already operative via enhancement of hydrogen bond network when two TBA molecules are separated by 12 H2O molecules. This enthalpic repulsion becomes stronger as the concentration of TBA increases. At a certain threshold, XTBA ≈ 0.03 at 30.00 °C for example, the new scheme in which solutes tend to associate sets in, and for XTBA > 0.06 this scheme becomes predominant. The effect of higher temperature is to shift this threshold to the lower values of XTBA. Therefore, it is probable that a lower critical solution temperature may exist at a temperature higher than the boiling points of the solution. It was also shown that if species of TBA(H2O)k type persist, they exhibit a hard-sphere nature in terms of enthalpic interaction among themselves.
Metal ion catalysis of the decomposition of transient 2-carboxy-2,5-cyclohexadienones in aqueous solution
Authors: Tee Oswald S. , Iyengar N. Rani
Published: May 2006

Bromide ion induced debromination of the anion of 4-bromo-4-methyl-2,5-cyclohexadienone-2-carboxylic acid (1) is catalyzed by cupric ions and ferric ions. Similarly, the enolization of the anion of the benzocyclohexadienone 3, which is formed during the bromination of 1-naphthol-2-carboxylic acid, is catalyzed by some metal ions. The origin of the catalysis in these reactions is strong metal ion binding to the incipient dianion products that are of the salicylate type. Evidence for this is that the efficiency of the metal (and hydrogen) ion catalysis parallels the stability of the analogous complexes with the salicylate dianion.
Thin-layer steady-state voltammetry under control by diffusion and migration
Authors: Colyer Christa L. , Connelly Paul J. J. , Gordon Heather L. , Oldham Keith B.
Published: May 2006

Measurements of steady-state currents in thin-layer cells provide an opportunity to apply a stringent test of theories of electrochemical transport by simultaneous diffusion and migration. We have applied such a test and find the theory to be vindicated.
The preparation and fungicidal activity of a series of thiazolyl- and isothiazoiyl-diarylcarbinols
Authors: Katritzky Alan R. , Laurenzo Kathleen S. , Relyea Douglas I.
Published: May 2006

(Isothiazol-5-yl)diarylcarbinols were prepared from 5-lithioisothiazole. (Thiazol-5-yl)diarylcarbinols were obtained via 5-lithio-2-bromothiazole or 5-lithio-2-trimethylsilylthiazole with subsequent removal of the 2-substituent. Corresponding 2-aminothiazol-5-ylcarbinols were made by protecting 2-aminothiazole as its bis(trimethylsilyl) derivative. Biological activities were compared to the calculated electron densities at the heterocyclic N-atoms.
Ab initio studies on 1,2-oxathietane, Z and E 3,4-dimethyl-1,2-oxathietane, and their products of formal [σ2s + σ2a] cycloreversion
Authors: Naghipur Ali , Lown J. William , Jain Duli C. , Sapse Anne-Marie
Published: May 2006

Ab initio calculations at the level of 3-21G* SCF and MP3/3-21G* have been performed on the novel heterocycle 1,2-oxathietane and the formal [σ2s + σ2a] cycloreversion products. Hartree–Fock calculations have been performed for the E and Z 3,4-dimethyl-1,2-oxathietanes and their corresponding cycloreversion products. The calculations afford fully geometry optimized conformations, energies, net atomic charges, and HOMO values for the heterocycles. 1,2-Oxathietane is found to be close in energy to the sum of energies of either pair of its cycloreversion products. The most plausible mechanism of cycloreversion features the formation of ground state formaldehyde and thioformaldehyde via a biradical intermediate. This result is in accord with the lack of detection of chemiluminescence with the 1,2-oxathietanes, in contrast to the 1,2-dioxetanes.
Residence-time of muonium at micelles: Effect of added micelles on the reactivity of muonium towards ionic solutes in water
Authors: Venkateswaran Krishnan , Barnabas Mary V. , Ng Bill W. , Walker David C.
Published: May 2006

The effective rate constant for the reaction of muonium with NO3−, S2O32−, and Tl+ ions in water is altered by the addition of micelles. There is a decrease when the charge on the micelle is the same as that of the solute and an increase when their charges are opposite. From the magnitude of the effect a mean residence-time for muonium of 2 ns has been deduced for dodecyl sulphate micelles. This suggests there is barely any preferred localization, because 2 ns is smaller, even, than the expected diffusion time if the micelle core is as viscous as reported. This use of muonium atoms to probe the dynamics of micelles seems to support the view that there are regions of low microviscosity and considerable water penetration within the micellar structure.
Photolysis of, and the reactions of H-atoms with, isopropanethiol
Authors: Lam W. W. , Yokota T. , Safarik I. , Strausz O. P.
Published: May 2006

Detailed investigation of the photolysis of i-C3H7SH has been carried out in the absence and presence of the inert gas, n-C4H10. A mechanism consisting of three primary photochemical steps: [Formula: see text], [Formula: see text]; [Formula: see text], [Formula: see text]; [Formula: see text],[Formula: see text]; six hot reaction steps and seven thermal reaction steps adequately explains all the experimental observations. As in the case of hot H* atoms both the H-atom abstraction, [Formula: see text], and the SH-displacement, [Formula: see text], reactions occur with thermalized H-atoms, with the rate constant ratio k7/k8 = 19.2 ± 4.3 at 25 °C. The Arrhenius expressions have been determined over the temperature range 25–145 °C, to be: k7 = (4.0 ± 0.7) × 1012 exp [(−1066 ± 43)/RT] and k8 = (2.8 ± 0.6) × 1012 exp[(−2597 ± 114)/RT] cm3 mol−1 s−1. It was found that the overall mechanism for the photolytic decomposition of i-C3H7SH is analogous to that established for C2H5SH in previous investigations.
Durene-capped porphyrins: synthesis and characterization
Authors: Wijesekera Tilak P. , David Shantha , Paine III John B. , James Brian R. , Dolphin David
Published: May 2006

The synthesis of porphyrins having a fully hydrophobic cavity capped by a durene moiety is described. The size of the cavity is adjusted by varying the number of methylene -(CH2)n- groups linking the tetramethylphenylene cap with the diametrically opposite β-positions of the porphyrin. Bis(chloromethyl)durene (1) was first converted to durene-bisalkanoic acids 11 (n = 4), 13 (n = 5), and 18 (n = 7) using standard chain extension methods. The diacid chlorides were then used to acylate two equivalents of a β-unsubstituted pyrrole to give a chain-linked bispyrrole. Each pyrrole, following appropriate manipulation of the α substituents, was condensed with an α-unsubstituted pyrrole and the resulting chain-linked dipyrromethane dimer was cyclized intramolecularly under high dilution to give the capped porphyrin 34 (n = 4, 5, or 7).
The σ* molecular orbitals of perfluoroalkanes as studied by inner-shell electron energy loss and electron transmission spectroscopies
Authors: Ishii I. , McLaren R. , Hitchcock A. P. , Jordan K. D. , Choi Y. , Robin M. B.
Published: May 2006

Absolute oscillator strength spectra in the C 1s (280–340 eV) and F 1s (680–740 eV) regions of the perfluoro-n-alkanes from C2 to C6 and perfluorocycloalkanes from C3 to C6 have been determined from inner-shell electron energy loss spectra recorded under electric-dipole scattering conditions. The spectral features are interpreted in terms of spatially localized transitions terminating at orbitals of predominantly σ*(C—F) and σ*(C—C) character. When compared to the spectra of the perfluoro-n-alkanes, both the C 1s and F 1s spectra of the perfluorocycloalkanes exhibit additional low-lying bands which are assigned to transitions terminating at σ*(C—C) orbitals which are shifted to low energy by the combination of the strain of cyclization and the inductive effect of the fluorination. The electron transmission spectra of selected perfluorocycloalkanes (which provide information on their anion states) show as well that the electron affinities of the cyclic systems are substantially lower than those of the corresponding perfluoro-n-alkanes, again as a result of a low-lying σ* orbital in the cyclic species. Quantum chemical calculations of the alkane and perfluoroalkane ground-state orbital structures support the experimental results. The localized character of the inner-shell excitations, indicated by the constancy of both term values and oscillator strengths with increasing chain length, contrasts with the more delocalized character of the states accessed in ultraviolet excitation or negative ion formation.
A comparative study on the dynamics of epimeric 1-hydroxymethyl quinolizidines: II. The solvent and concentration dependence of the association properties
Authors: Kulińska K. , Wiewiórowski M.
Published: May 2006

The homo and heteroassociation patterns of lupinine and epilupinine in different solvents and at various concentrations have been studied. In n-hexane, n-heptane, CCl4, and C2H4Cl2 solvents, lupinine monomers with an intramolecular OH … N hydrogen bond dominate over homoassociates with an OH … O′ intermolecular hydrogen bond even in concentrated solutions. Homoassociation of lupinine by intermolecular OH … N′ hydrogen bonding is observed only in saturated solutions. In chloroform solution any intermolecular homoassociation is effectively blocked because of significant affinity of chloroform molecules acting as a weak acid toward the free electron pairs of the oxygen atom from the hydroxyl group that would be otherwise engaged in intramolecular OH … N hydrogen bonding. Epilupinine in n-hexane, n-heptane, CCl4, C2H4Cl2, and chloroform solutions forms possible homoassociates both by OH … N′ and OH … O′ intermolecular hydrogen bonding. In dioxane-d8, DMSO, and D2O solvents both lupinine and epilupinine form heteroassociates with solvent molecules.
Ion chemistry of transition metals in hydrocarbon flames. I. Cations of Fe, Co, Ni, Cu, and Zn
Authors: Tran Quang , Karellas Nicholas S. , Goodings John M.
Published: May 2006

A fuel-rich, premixed, conical, methane–oxygen flame at 2200 K and atmospheric pressure is doped with approximately 1 ppm of the transition metals Fe, Co, Ni, Cu, and Zn. Metallic ions of these metals and their compounds formed by chemical ionization reactions with H3O+ are observed by sampling the flame through a nozzle into a quadrupole mass spectrometer. Concentration profiles of individual and total cations are measured as a function of distance along the flame axis, and also mass spectra at a fixed point in the burnt gas. For a given metal A, the mass spectra are dominated by the atomic ion A+ with smaller amounts of the molecular ions AH+, AOH+, A(OH)H+, A(OH)2H+, and ACO+ and their hydrates. The spectra for Fe, Co, Ni, and Cu are very similar, but no ions are observed for Zn. The ion chemistry is dominated by proton transfer reactions from H3O+ to A and to the metallic compounds AO, AOH, and A(OH)2 which exist in the flame. In addition, A+ can be formed from the reaction of H3O+ with A by a charge transfer process. Also, some ions are formed by three-body association and free radical stripping reactions. The chemistry is discussed in detail to explain the relative magnitudes of the ion signals observed. In particular, when the atomic A+ ion is dominant, its concentration can reach a superequilibrium level early in the burnt-gas region before it slowly decays downstream; the phenomenon is similar to the free radical overshoot which occurs in hydrogen flames.
Fungal biotransformation of 1,3-oxathiolanes
Authors: Holland Herbert L. , Munoz Benito
Published: May 2006

A series of 2,2-disubstituted 1,3-oxathiolanes has been incubated with fungi known to be capable of efficient asymmetric oxidation of sulfides to sulfoxides. In three cases (2-phenyl-1,3-oxathiolane, 2-methyl-2-phenyl-1,3-oxathiolane, and 2-tert-butyl-2-phenyl-1,3-oxathiolane), sulfoxidation occurred to give a single diastereomer of sulfoxide, whose relative stereochemistry has been assigned by 1H nuclear magnetic resonance analysis. The sulfoxides were obtained as racemates or had low enantiomeric enrichment. In some cases ketones, assumed to be formed by spontaneous hydrolysis of oxathiolane sulfoxides, were obtained, together with their reduction products, secondary alcohols.
The effects of aggregation, counterion binding, and added NaCl on diffusion of aqueous methylene blue
Authors: Leaist Derek G.
Published: May 2006

A simplified version of the Hamed conductimetric technique is used to measure binary diffusion of the self-associating dye methylene blue chloride in water at 25 °C. As the dye concentration is increased from 0.0006 to 0.02 mol dm−3, aggregation of the dye monomers and binding of the chloride counterions cause the dye's binary diffusion coefficient to drop from 0.83 × 10−9 to 0.63 × 10−9 m2 s−1. Ternary diffusion coefficients for aqueous methylene blue chloride +NaCl solutions are also reported. These results show that small amounts of added NaCl (0.005 or 0.01 mol dm−3) sharply reduce the diffusivity of the dye component, and that each mole of diffusing dye cotransports 0.2–0.7 mol NaCl. Diffusion of trace amounts of the dye in the presence of a large excess of an inert supporting electrolyte is discussed briefly.
Complexes of 15-crown-5 and cyclohexano-15-crown-5 with lithium, sodium, and potassium phenoxide having macrocycle: salt ratios of 1:1 and 1:2. The crystal structures of two polymorphs of 15-crown-5•2LiOPh
Authors: Murchie Michael P. , Bovenkamp John W. , Rodrigue André , Watson Kimberley A. , Fortier Suzanne
Published: May 2006

The syntheses, in ethereal solvents, of the complexes of 15-crown-5 and cyclohexano-15-crown-5 with lithium, sodium, and potassium phenoxide are described. The two macrocycles form complexes with lithium and sodium phenoxide with host:guest ratios of 1:2. Potassium phenoxide, however, was complexed by the two macrocycles to give products with macrocycle:salt ratios of 1:1. Crystals of 15-crown-5•2LiOPh were obtained for X-ray diffraction structure determinations. In fact, the crystal structures of two co-crystallizing polymorphs of this complex (1a and 1b) have been determined. Polymorph 1a crystallizes in space group [Formula: see text] with a = 11.386(4), b = 11.901(4), c = 10.654(4) Å, α = 106.53(3), β = 112.60(3), γ = 106.52(3)°, and Z = 2. Polymorph 1b crystallizes in space group P21/n with a = 15.355(4), b = 11.642(2), c = 13.595(6) Å, β = 104.56(3)°, and Z = 4. Both structures were solved by direct methods, and refined by full-matrix least-squares calculations to residuals, R, of 0.053 and 0.055 for polymorphs 1a and 1b, respectively. The structures of the two polymorphs differ only in the orientation of the phenoxides. The structures show a dimer, (15-crown-5•2LiOPh)2, which consists of an aggregate of four lithium phenoxide molecules complexed by two 15-crown-5 macrocycles. The two lithiums of each monomeric unit of this dimer have different crystallographic and chemical environments. One lithium is coordinated to all five oxygens of the macrocycle and to one of the phenoxide oxygens while the other lithium is coordinated to only one oxygen of the macrocycle and to three phenoxide oxygens.
Anodic oxidation of lead in aqueous carbonate solutions. I. Film formation and dissolution at pH = 12
Authors: Shoesmith D. W. , Bailey M. G.
Published: May 2006

The anodic oxidation of lead has been studied using rotating disk electrodes, under voltammetric and potentiostatic conditions, in aqueous carbonate solutions at pH = 12. The solid films formed on the electrode surface have been identified by X-ray diffractometry. Two distinct surface layers are formed: a compact layer composed of two separate phases, plumbonacrite (Pb10O(OH)6(CO3)6) and hydrocerussite (Pb3(OH)2(CO3)2); and a more dispersed layer of hydrocerussite. The plumbonacrite in the compact layer is formed directly on the electrode surface by a solid-state growth process. The hydrocerussite component of this compact layer appears to form by conversion of the outer layers of plumbonacrite. The dispersed layer is formed by deposition from solution. The extent of deposition is controlled by the rate of transport of soluble Pb2+ species to the bulk of solution.
Pressure effects on the rate of electron transfer between tris(1,10-phenanthroline)iron(II) and -(III) in aqueous solution and in acetonitrile
Authors: Doine Hideo , Swaddle Thomas Wilson
Published: May 2006

Proton nmr line-broadening experiments at ambient and elevated (to 215 MPa) pressures show that the rate of electron transfer between Fe(phen)32+ and Fe(phen)33+ as bisulfates in D2O/D2SO4 is represented by the activation parameters (at ionic strength I ~ 0.4 mol kg−1) ΔH≠ = 1.6 ± 0.5 kJ mol−1, ΔS≠ = −102.2 ± 1.6 JK−1mol−1, k(276 K) = 1.31 × 107 kg mol−1s−1, and (at I ~ 0.3 mol kg−1 and a mean pressure of 100 MPa) ΔV≠ = −2.2 ± 0.1 cm3mol−1. For the same reaction of the perchlorate salts (total [Fe] 0.046–0.065 mol kg−1) in CD3CN, ΔH≠ = 11.0 ± 1.0 kJ mol−1, ΔS≠ = −72.5 ± 3.6 J K−1 mol−1, k(277 K) = 8.0 × 106 kgmol−1s−1, and ΔV≠ = −5.9 ± 0.5 cm3 mol−1. For water as solvent, ΔV≠ is satisfactorily accounted for by a classical theory of the Stranks–Hush–Marcus type. Volumes of activation for electron self-exchange are shown to provide criteria for non-adiabaticity and for dominance of (non-aqueous) solvent reorganization dynamics; on this basis, it is seen that neither of these factors is important in the title reactions.
The multiphoton spectra of the 1,3-trans-butadiene molecule from AB-initio and configuration interaction calculations
Authors: Nascimento Marco Antonio Chaer
Published: May 2006

The multiphoton spectra of the 1,3-trans-butadiene is investigated using highly correlated wave-functions. On the basis of computed transitions energies, intensities and polarization ratios, assignments are made to the first members of five Rydberg series and to a valence (π → π*) state. The results are in good agreement with the experimental results.
On the calculation of atomization energies of organic molecules in the Xα local spin density approximation
Authors: Fliszàr S. , Rioux S. , Andzelm J. , Minichino C. , Vauthier E. C.
Published: May 2006

The atomization energies of selected alkanes, alkyl radicals, and amines are deduced from Xα local spin density calculations of E, the total energy of a molecule in its potential minimum. Both the exchange-correlation energy, [Formula: see text], and [Formula: see text] itself obey, in a first approximation, simple atom-by-atom additivity rules. The appropriate α's for use in Xα(LSD) calculations of organic molecules thus appear as weighted averages and depend on the particular composition of each molecule. The at least approximate validity of this averaging procedure is illustrated by the accuracy of calculated atomization energies.
Mobility of thermal cations in liquids of n-alkanes, n-pentane to n-tetradecane: effect of viscosity and comparison to neutral molecule diffusion
Authors: Gee Norman , Freeman Gordon R.
Published: May 2006

The cation mobility μ+ was measured in n-pentane at 295 K and in n-C6 to C11 and n-C14 alkanes from ~295 K to their normal boiling points. The dependence on viscosity [Formula: see text] was reexamined and the best fit occurred with p = 1.0. The ratio of diffusion coefficients of neutral molecules to analogous cations was ~3 because of the stronger interaction of ions with the fluid molecules (electrostriction). The dependence of μ+ on free volume is illustrated. Keywords: thermal cation mobility, n-alkane solvents, viscosity effects
Reduction processes in the fast atom bombardment mass spectra of pyridinium salts. The effect of reduction potential and concentration
Authors: Kazakoff Clement W. , Rye Robin T. B. , Tee Oswald S.
Published: May 2006

The enhancement of the (C + 1)/C ratio in the fast atom bombardment mass spectra of seven pyridinium cations has been measured. No dependence of the enhancement on the cation reduction potential could be identified. The N-methyl pyridinium cation, which showed no enchancement under matrix-free conditions, exhibited an increase in the (C + 1)/C ratio with decreasing concentration. This concentration dependence was eliminated when the bombardment energy was reduced from 9 to 5 keV. Possible mechanisms for the concentration dependence and the variation with bombardment energy are proposed. Keywords: fast atom bombardment, reduction, pyridinium salts.
Limonoids from the Fijian medicinal plant Dysoxylumrichii
Authors: Jogia Madhu K. , Andersen Raymond J.
Published: May 2006

Three new limonoids have been isolated from the Fijian medicinal plant Dysoxylumrichii. Dried D. richii leaves collected at Suva yielded the known limonoid dysoxylin (1) as well as the previously unreported dysoxylone (2). A Taveuni collection of leaves contained the two new metabolites tigloyldysoxylin (3) and 6α-acetoxyobacunol acetate (4). The structures of all three new compounds were determined by spectroscopic analysis. Keywords: Dysoxylumrichii, limonoid, dysoxylone, tigloyldysoxylin, 6α-acetoxyobacunol acetate.
Nouveaux alcaloïdes bisbenzylisoquinoléiques biphényliques de Crematosperma sp.
Authors: Saez Jairo , Fernandez Estella , Jossang Akino , Cavé André , Cavé Adrien
Published: May 2006

Four new alkaloids, (−)-cordobine 1, (−)-monterine 2, (−)-granjine 3, and (−)-cordobimine 4 have been isolated from a Colombian Annonaceous plant, Crematosperma sp. Structures were elucidated from spectral data and chemical reactions. These alkaloids are the first 1R, 1′S bisbenzyltetrahydroisoquinolines including 8,7′ ether and 11,11′ biphenyl linkages. Keywords: Annonaceae, Crematosperma, alkaloids, biphenylbisbenzylisoquinolines.
Thermodynamic aspects in the adsorption of polynuclear aromatic hydrocarbons on chrysotile and silica – possible relation to synergistic effects in lung toxicity
Authors: Fournier Jeanine , Fubini Bice , Bolis Vera , Pezerat Henri
Published: May 2006

This study is to compare the adsorption of phenanthrene — a polynuclear aromatic hydrocarbon — (apolar molecule) and water (polar molecule) on chrysotile, a mainly ionic solid and on one silica (Aerosil), a covalent solid. The adsorption of water shows that the adsorption capacity and the interaction energies are much higher for chrysotile than for silica. With phenanthrene, the adsorption mechanism on these two materials is very different: on chrysotile — a solid with a surface having a basic character — there is a multilayer adsorption, with lateral interactions between PAH molecules vertically oriented with regard to solid surface, whereas on silica (acidic solid), the PAH molecules are adsorbed flat and form only one layer. Chrysotile turns out to be a much more powerful adsorbent than silica towards both polar molecules and apolar molecules. The calorimetric data concerning the adsorption of phenanthrene on chrysotile in xylene reveal three thermal stages, showing the influence of preadsorbed water and solvent and permit to propose a model of adsorption mechanism. The formation of multilayers of phenanthrene on chrysotile converts its marked hydrophilic surface into a hydrophobic one which may act as a carrier of organic molecules and slowly release them into the biological medium. These phenomena may provide a possible interpretation for some synergistic effects concerning lung cancers observed after asbestos and cigarette-smoke exposure. Keywords: adsorption, phenanthrene, chrysotile, silica, water.
On the shape of spherically averaged Fermi-hole correlation functions in density functional theory. 1. Atomic systems
Authors: Tschinke Vincenzo , Ziegler Tom
Published: May 2006

We have compared, for atomic systems, the spherically averaged Fermi-hole correlation function [Formula: see text] in the Hartree–Fock theory with the corresponding function [Formula: see text] employed in local density functional theory. It is shown that, in contrast to [Formula: see text], the function [Formula: see text] behaves qualitatively incorrectly at positions r1 of the reference electron far from the nucleus. Furthermore, we have shown that the qualitatively incorrect behaviour of [Formula: see text] can be remedied by an approximate expansion of [Formula: see text] in powers of s, where s is the inter-electronic distance. However, such an expansion must be conducted in two regions due to the discontinuity of [Formula: see text] as a function of s at the atomic nucleus. Based on the two-region expansion of [Formula: see text] we have developed an alternative approximate density functional expansion [Formula: see text] for the spherically averaged Fermi-hole correlation function. The corresponding exchange energy density functional yields values for the exchange energies of atoms in good agreement with Hartree–Fock results. Keywords: atomic exchange energy, density functional theory, Fermi hole.
A structural reinvestigation of 4,6-dinitrobenzofuroxan by 1H, 13C, and 15N nuclear magnetic resonance
Authors: Terrier F. , Halle J. C. , MacCormack P. , Pouet M. J.
Published: May 2006

A detailed nuclear magnetic resonance study of 4,6-dinitro-2,1,3-benzoxadiazole N-oxide (DNBF), which includes a 2D INADEQUATE analysis and experiments with samples 15N-labelled at the NO2 groups, is described. The results lead to an unambiguous assignment of the carbon and proton chemical shifts in various solvents. Some 1H and 13C data pertaining to 4,6-dinitro-2,1,3-benzoxadiazole (DNBZ), the deoxygenated analog of DNBF, are also reported, allowing the influence of the N-oxide group on the proton and carbon chemical shifts to be discussed. It is shown that all of the 1H nmr evidence so far reported for the characterization of DNBF σ adducts as arising from nucleophilic addition to the 7-position, i.e., as structure 2a, has no significance. That complexation actually occurs at this position is, however, convincingly demonstrated by 15N data. These also allow us to establish that this process is both kinetically and thermodynamically favored. Keywords: nitrobenzofuroxans, Meisenheimer complexes, 13C nmr of benzofuroxans, 2,1,3-benzoxadiazole N-oxides, nitrobenzofuroxan σ-adducts.
The vibrational spectra (100–1600 cm−1) and scaled 3-21G abinitio harmonic force fields for 7-oxanorbornane and 7-thianorbornane
Authors: Shaw R. A. , Ibrahim N. , Wieser H.
Published: May 2006

The vibrational spectra in the region of 1600–100 cm−1 are reported for 7-oxa- and 7-thianorbornane. Abinitio 3-21G harmonic force fields based on optimized structures determined previously at the same level of theory were calculated for both molecules. The vibrational spectra were assigned unambiguously and almost completely with the aid of the 3-21G force fields, scaled using ten factors previously optimized in an overlay refinement to fit assigned frequencies of norbornane, norbornene, and norbomadiene, and including two others, where appropriate, from dimethyl ether and thietane. Reoptimization of 12 scaling factors reproduced 60 assigned frequencies out of a total of 70 in the specified region with average errors of 7.4 and 4.9 cm−1, respectively, for the two molecules. The final refinement changed the scaling factors transferred from norbornane generally by less than 1%. Keywords: 7-oxanorborane, 7-thianorborane, vibrational spectra, abinitio harmonic force field.
Kadsulignan A and B, two novel lignans from Kadsuracoccinea
Authors: Liu Jia-Sen , Li Liang , Yu Han-Gang
Published: May 2006

Two novel lignans, kadsulignan A (1) and B (2), were isolated from the seeds of Kadsuracoccinea. Their structures were elucidated by 2D1H–13C COSY, 2D1H–13C long-range COSY experiments, and chemical transformation to a known compound (5) using AlCl2H. Keywords: isolation and structures, kadsulignan A, kadsulignan B, Kadsuracoccinea.
Kinetics of oxidation of Cu(I) complexes of cysteine and penicillamine: nature of intermediates and reactants at pH 10.0
Authors: Mezyk Stephen P. , Armstrong David A.
Published: May 2006

The Cu(I)•L2 complex with cysteine ligands at total Cu(I) concentrations of 10–30 μM was shown to be oxidised by cysteinyl radicals (RS•) with a diffusion-controlled rate constant k11a = 1.8 × 109 M−1 s−1. The corresponding reaction with the cysteine disulphide anion (RS•—SR−) proceeded at a slower rate, k11b = 2.7 × 108 M−1s−1. At higher Cu(I) concentrations, a slow and a fast component of absorption growth was observed. The slow component rate was independent of Cu(I) concentration, but it became more intense as the Cu(I) concentration rose. The yields and kinetic data were shown to be consistent with the presence of an equilibrium between the Cu(I)•L2 species and a second Cu(I) complex, Cu(I)2•L3, with an equilibrium constant of K1 = 162.[Formula: see text]This finding is consistent with the earlier work of Bagiyan etal. The rate constant of the oxidation of Cu(I)2•L3 by the cysteinyl radical was k12 = 1.0 × 109 M−1 s−1. Similar results were obtained with penicillamine, except the rate constants and equilibrium constant were smaller, (k11a = 4.5 × 108 M−1 s−1, k11b < 2 × 108 M−1 s−1, k12 = 5.5 × 108 M−1 s−1 and K1 = 113). This was attributed to the presence of the β-methyl groups in penicillamine, which exert a large steric effect.The ultraviolet spectra of the long-lived products, which are stable on a millisecond timescale, was consistent with a Cu(II)•L2 structure with a square planar geometry. The oxidation of the Cu(I)2.L3 species proceeded via intermediates, which relaxed to the final product spectra with rate constants of k13b = 2.6 and 1.1 × 104 s−1 for cysteine and penicillamine, respectively. Comparison of the spectra of the intermediates with published data showed that they were consistent with the presence of a bridging thiolate ligand between Cu(I) and Cu(II). Keywords: oxidation, copper, mixed valence, cysteine, penicillamine, complexation.
Effect of precipitation inhibitors on calcium phosphate scale formation
Authors: Amjad Zahid
Published: May 2006

The highly reproducible pH-stat technique was used to study the influence of various types of inhibitors on the precipitation of calcium phosphate from solution. Three types of inhibitors were evaluated: (1) homo- and copolymers of acrylic acid, (2) polyphosphate and phosphonates, and (3) polycarboxylic acids. Experimental variables studied included pH, temperature, and inhibitor dosage all of which were found to greatly affect the precipitation of calcium phosphate. The role of polyacrylic acid molecular weight is addressed. Comparative data for the various types of inhibitors is discussed. Keywords: precipitation inhibitors, calcium phosphate scale formation.
Surface electrochemistry of the oxidation of glycine at Pt
Authors: Marangoni Daniel G. , Smith Richard S. , Roscoe Sharon G.
Published: May 2006

The electrochemical oxidation of glycine at a Pt electrode was investigated in aqueous solutions at pH 1 and 13 using steady-state current–potential measurements, cyclic voltammetry, and open circuit potential decay. The capacitance behaviour and the high Tafel slopes suggest the production of free radicals at the surface of the electrode accompanied by a second reaction involving loss of CO2 which is the rate determining step. In the electro-oxidation of glycine, it appears that the adsorbed intermediate species is either hydrolyzed anodically to formaldehyde and ammonia, or is oxidized to a carbonium ion which is subsequently hydrolyzed to formaldehyde and ammonia in solution. This behaviour differs from the dimerization process typical of the radical reactions associated with the Kolbe mechanism. Keywords: glycine, amino acid, electrochemical oxidation, surface electrochemistry, Kolbe mechanism.
Internal motion in benzylidene diacetate and its 2,6-dibromo derivative by DNMR and the J method
Authors: Schaefer Ted , Takeguchi Craig S.
Published: May 2006

The 1H nuclear magnetic resonance spectral parameters are reported for benzylidene diacetate in CS2 and acetone-d6 solutions. The long-range spin–spin coupling constant over six formal bonds, 6J, is used to derive apparent twofold barriers to rotation about the exocyclic C(1)—C bond in the two solutions. The conformation of lowest energy has the α. C—H bond in the benzene plane. The barrier is higher in CS2 than in acetone-d6 solution, in contrast to a molecule like benzyl chloride. In the 2,6-dibromo derivative, the free energy of activation for reorientation about the bond in question is 36 kJ/mol at 165 K in dimethyl ether solution. Such a high barrier implies a very small six-bond proton–proton coupling constant for this derivative because 6J is proportional to the expectation value of sin2θ. The angle θ is zero when the α C—H bond lies in the benzene plane. 6J is −0.051 Hz in acetone-d6 solutions; its sign is determined by double resonance experiments. The question of an angle-independent component of 6J, that is, whether 6J is finite at θ = 0°, is addressed. A maximum magnitude of 0.02 Hz may be present at θ = 0° for the 2,6-dibromo derivative, although a zero magnitude is also compatible with the experimental data. In a compound with a higher internal barrier, α,α,2,6-tetrachlorotoluene, the experimental results are best in accord with a negligibly small 6J at θ = 0°. Keywords: 1H NMR of benzylidene diacetate, spin–spin coupling constants for benzylidene diacetate, DNMR, 2,6-dibromobenzylidene diacetate.
Bis(imidazol-2-yl)phosphinic acid hemihydrate, [(C3H3N2)(C3H4N2)PO2].(1/2)H2O
Authors: Howard-Lock Helen E. , Lock Colin J.L. , Penny Sarah , Turner Mary A.
Published: May 2006

The title compound was obtained as the major product of our handling of the literature preparation of tris(imidazol-2-yl)phosphine. The compound was characterized by 1H NMR, mass and vibrational spectroscopy. The structure was determined by single crystal X-ray diffraction. Crystals were triclinic, [Formula: see text], a = 7.677(1), b = 12.658(2), c = 10.072(2) Å, α = 91.18(1),β = 114.44(1),γ = 99.49(1)°, Z = 4. Intensities were measured on a Syntex P21 diffractometer with MoKα radiation and 3088 reflections were used to determine the structure. R = 0.0698, Rw = 0.0534. The phosphinic acid exists in the solid as the zwitterionic form and bond lengths and angles are normal. Keywords: tris(imidazol-2-yl)phosphine, X-ray structure, bis(imidazol-2-yl)phosphinic acid hemihydrate.
Remarks on the barrier to rotation about the Csp2—O bond in anisole
Authors: Schaefer Ted , Sebastian Rudy
Published: May 2006

Molecular orbital computations with the basis set 6-31G are reported for seven values of θ, the torsion angle about the [Formula: see text] bond in anisole. All bond angles and lengths are optimized but the atoms of the phenyl group are constrained to a plane. The relative energies are fit by V(θ)/kJ mol−1 = 7.78(5) sin2θ + 2.41(5) sin2 2θ − 0.54(5) sin2 3θ, where θ is zero when the heavy-atom skeleton is planar. Computations with the basis set 6-31G*(5D) for three values of θ can be reproduced by V(θ)/kJ mol−1 = 6.07 sin2θ + 2.68 sin2 2θ. These results are compared with experimental gas phase data from the literature. The analysis of the 1H nuclear magnetic resonance spectrum of anisole-α-13C in aCS2/C6D12/TMS solvent mixture yields a value of 6J(1H, 13C), the long-range spin-spin coupling constant between the 13C nucleus in the methyl group and thepara proton. Because this coupling constant is proportional to sin2 θ, it is shown, together with previous dynamic nmr measurements, that the barrier to rotation about the [Formula: see text] bond in solution cannot be purely twofold. The internal potential must also contain a fourfold term of the same sign as that of the twofold component. If the V2/V4 ratio given by the various molecular orbital computations holds in solution, then V2 is 15.0 ± 2.0 kJ/mol and V4 is 5.6 ± 2.2 kj/mol. The apparent doubling of the internal barrier in solution is perhaps unprecedented for such a simple molecule. Keywords: anisole, internal barrier in solution, anisole-α-13C, 1H NMR, conformational behaviour, MO computations.
The photolysis of ethylene at 193 nm
Authors: Giroux L. , Back M. H. , Back R. A.
Published: May 2006

The photolysis of ethylene has been studied at pressures from 50 to 3000 Torr using a pulsed ArF excimer laser at 193.3 nm. Major products were acetylene, n-butane, 1-butene, ethane, and 1,3-butadiene, with smaller amounts of propane, propene, methane, and allene. Quantum yields varied with pressure and reaction time; the latter dependence is ascribed to secondary photolysis of butene and butadiene. The reaction products are accounted for by three primary processes:[Formula: see text]followed by reactions of H, [Formula: see text] and C2H5 radicals. The vibrationally excited C2H3radical can decompose to H + C2H2 or can be stabilized by collision. The pressure dependence of the quantum yields of the primary processes [1]–[3] is complex, and a photodissociation mechanism involving several intermediates and excited states of ethylene is presented to account for the present results and previous measurements at 185 nm. Keywords: ethylene, uv photolysis.