bluuebunny/crossref_metadata_2025 huggingface dataset:
A carbon-13 nuclear magnetic resonance study of solid tetracyclines
Authors: Mooibroek Sandra , Wasylishen Roderick E.
Published: May 2006

Magic angle sample spinning and proton/carbon-13 cross-polarization techniques have been used to obtain high resolution solid state 13C nuclear magnetic resonance spectra of several tetracycline antibiotics. Carbon-13 resonances in the solid state are assigned by measuring the extent of dipolar broadening due to neighbouring quadrupolar nuclei and by using a pulse sequence that suppresses non-quaternary carbon resonances. The observed 13C chemical shifts are discussed in light of the known solid state structures derived from X-ray diffraction, and are compared with those in solution. It is shown that the solid state nuclear magnetic reosnance technique is capable of clearly distinguishing between the neutral and zwitterionic forms of the tetracycline free bases.
Hydrodésazotation de l'indole sur catalyseur fer supporté sur amiante
Authors: Zalma Roger , Bonneau Lionel , Fournier Jeanine , Guignard Joëlle , Borg Françoise , Pezerat Henri
Published: May 2006

The aim of this study is to examine hydrodenitrogenation (HDN) of indole on asbestos catalysts (chrysotile and crocidolite) under hydrogen pressure. HDN is carried out according to two competitive pathways, either via ortho-ethylaniline or via ortho-toluidine. This reaction is assisted by increase of temperature and pressure and by pre-reduction of the asbestos. Particles of Fe0on the fibre surface are formed from the original material. Their presence plays a role in the initial breaking of the C—N bond and in the hydrogenation reaction.
Réduction électrochimique de dérivés carbonylés en milieu non aqueux en présence de EuCl3•6H2O
Authors: Douch Jamaâ , Mousset Guy
Published: May 2006

The electrochemical reduction of aromatic or α,β ethylenic aromatic ketones in nonaqueous solvent (DMF) has been performed in the presence of EuCl3•6H2O. Ligand exchange between DMF and water molecules of the europium salt was first studied. A voltammetric study shows that complexation involving electrogenerated Eu(II) and ketone may occur at the electrode interface or in solution, leading respectively to [Formula: see text] and [Formula: see text] stoichiometries. The stereochemistry of hydrodimerization products is studied.
Raman and far-infrared spectra of triphenyltin isochalcocyanates and their adducts with O- and N-donor ligands: the crystal and molecular structure of isocyanato-triphenyl (pyridine-N-oxide) tin
Authors: Wharf Ivor , Piehler Lars , Sailofsky Bruce M. , Onyszchuk Mario , Simard Michel G.
Published: May 2006

Solid state infrared and Raman data (350–100 cm−1) are reported for Ph3SnNCY (Y = O, S, Se) and their 1:1 adducts with hexamethylphosphoramide (HMPA), pyridine-N-oxide (pyO), 4-picoline-N-oxide (4-picO), triphenylphosphine oxide (Ph3PO), and pyridine (py), as well as for Ph3SnNCSe•L where L = β-pic (β-picoline) or γ-pic (γ-picoline), and assignments are given. The crystal structure of Ph3SnNCO•pyO was determined by single crystal X-ray analysis. The compound crystallizes in space group Pbca with a = 14.443(3), b = 16.676(4), c = 17.523(6) Å (−110 °C); Z = 8. The structure was solved by the direct method and refined by full-matrix least-squares methods to R = 0.024 for 2086 observed reflections. The tin atom has distorted trigonal bipyramidal coordination with the isocyanate group and pyridine-N-oxide at the apices of the bipyramid and phenyl rings in the equatorial positions. Changes in v(Sn—NCY) on adduct formation are correlated with either increased coordination at tin (Y = O) or breaking of strong chalcocyanate bridges with tin remaining five-coordinate (Y = S, Se).
The direct electrochemical synthesis of dialkyldithiocarbamate and diethyldithiophosphate complexes of main group and transition metals
Authors: Geloso Corrado , Kumar Rajesh , Lopez-Grado Jaime Romero , Tuck Dennis G.
Published: May 2006

Dialkyldithiocarbamate derivatives (R2NCS2)nM of a number of metals (M = Fe, Co, Ni, Cu, Ag, Zn, Cd, In, Tl) have been synthesised in good yield by electrochemical oxidation of appropriate sacrificial anodes in non-aqueous solutions of either the corresponding tetraalkylthiuram disulphide (R2NCS2)2 (R = Me, Et) or a mixture of carbon disulphide plus the secondary amine R2NH (R = Et, i-Pr; R2NH = piperidine). Similar experiments with solutions of (EtO)2P(S)SH (= HL) gave MLn•derivatives (M = Fe, Co, Ni, Cu, Ag, Au, Zn, Cd, Hg, Ga, In, Tl) while in the presence of HL + 1,10-phenanthroline, MLn•phen derivatives were obtained for M = V, Mn, Fe, Co, Zn, and Ga.
First rotational analysis of the A2Π-X2Π system of the P35Cl+ cation
Authors: Coxon John A. , Naxakis Stavros , Roychowdhury Utpal K.
Published: May 2006

The visible A2Π → X2Π band system of PCl+ has been recorded photoelectrically with a resolution of 0.006 nm. Fourteen 2Π1/2–2Π1/2 and six 2Π3/2–2Π3/2 sub-bands of P35Cl+ in the ν′ = 0 and 1 progressions with 10 ≤ ν″ ≤ 20 have been rotationally analysed. The measured positions of 1214 lines have been fitted directly by least squares to obtain a set of reliable constants for the two states that reproduce the entire data. These constants include the first estimated spin–orbit coupling constants for both states. The reliability of these estimates is discussed. The equilibrium internuclear separations are re(X) = 0.1900 and re(A) = 0.2334 nm.
63Ni β range and backscattering in confined geometries
Authors: Siu K. W. Michael , Aue Walter A.
Published: May 2006

To know the spatial distribution of ion pairs resulting from 63Ni β radiation in the gas phase is important for a variety of theoretical and practical reasons, in particular those concerning the electron capture detector. Literature estimates of this distribution vary by about one order of magnitude, yet this parameter is necessary for the modelling of this detector. The 63Ni-induced, initial ion pair distribution was therefore measured in a variety of gases with two techniques: a conventional one based on the electrical saturation current at variable interelectrode distances, and an unconventional one based on luminescence from a plastic scintillator. The data are analyzed in terms of two ranges, d50 and d95, that describe the distances from a planar radioactive foil within which 50% and 95% of the total gas-phase ionization occur. The data from the electrical measurement show unexpected evidence of strong β backscattering and secondary electron emission from the counter-electrode. Under these (non-exponential) conditions, d50 values in the common detector gases nitrogen and argon/methane vary from 0.5 to 1.0 mm, depending on the nature of the counter-electrode. Calculations based on the quasi-exponential range found at longer distances in electrical measurements yield values of about 2.5 mm (which are low because of geometric measurement bias). In contrast, the data from the luminescence measurement are almost completely exponential and d50 values for argon (+5% methane) and nitrogen are 2.8 and 3.8 mm, respectively. The d95 values vary from 12 to 16 mm for the luminescence, to 6 and 9 mm for the (less reliable) electrical measurement; all at ambient conditions. The luminescence data are considered closer to the "true" (unimpeded) charge distribution, while the ionization data may be closer to the initial charge topography inside an electron capture detector of confining geometry. All range data, however, are short enough to advise modelling the detector as a system with strongly heterogeneous charge distribution. No evidence was found for some of the very large range estimates found in the literature.
Binding of isocyanides to five-coordinate, durene-capped hemes
Authors: David Shantha , James Brian R. , Dolphin David
Published: May 2006

Solution data at 20 °C are presented for the binding of t-butylisocyanide and tosylmethylisocyanide (TMIC) to the five-coordinate hemes Fe(porp)(Cy2Im), where Cy2Im = 1,5-dicyclohexylimidazole and porp = the dianion of some durene-capped porphyrins with variable length linking methylene straps on either side of the durene moiety (4/4, 5/5, or 7/7 methylenes). The tBuNC and TMIC ligands are used to probe the steric nature of the distal binding site under the cap, in particular the respective "central" and "peripheral" effects as defined by Traylor etal. The binding constants range from 1.1 × 109 M−1 for the 7/7—TMIC system to immeasurably small for the 4/4—tBuNC system, this range spanning data reported in the literature for related anthracene- and adamantane-capped systems.
Identification of the photolysis products of nitrofurazone irradiated with laboratory illumination
Authors: Quilliam Michael A. , McCarry Brian E. , Hoo Ken H. , McCalla Dennis R. , Vaitekunas Susan
Published: May 2006

Illumination of aqueous or organic solutions of nitrofurazone, 1, with fluorescent or tungsten light caused the appearance of two new compounds, 2 and 3. Compound 2, which eluted just before nitrofurazone on a reverse phase hplc column, had a mass spectrum identical to that of 1 and converted back to 1 at a rate proportional to the temperature and the polarity of the solvent when allowed to sit in the dark. High resolution proton nmr spectroscopy provided conclusive evidence that compound 2 is the syn isomer of 1. Compound 3 had a retention time, ultraviolet spectrum, and mass spectrum that were indistinguishable from those of synthetic 5-nitrofuraldehyde azine. The toxicity of 3 to E. coli was determined to be the same as 1 while its mutagenicity was over 10-fold lower. No detectable cross-links were formed in the DNA of E. coli in the presence of compound 3. Thus, it is unlikely that the relatively small amounts of the azine 3 formed have much influence on the antibacterial potency or mutagenicity of nitrofurazone solutions. However, these results do confirm the desirability of conducting experiments with these agents in the dark or under yellow light. Photochemical formation of syn isomers was also observed with two other Schiff 's base nitrofuran derivatives, nitrofurantoin and furazolidone.
The preferred rotamer about the C5—C6 bond of D-galactopyranoses and the stereochemistry of dehydrogenation by D-galactose oxidase
Authors: Ohrui Hiroshi , Nishida Yoshihiro , Higuchi Hiroko , Hori Hiroshi , Meguro Hiroshi
Published: May 2006

1H nuclear magnetic resonance studies on D-galactopyranoses with chirally deuterated hydroxymethyl groups revealed that the preferred rotamer about the C5—C6 bond of the D-galactopyranoses was not tg but gt. Studies on the stereochemistry of dehydrogenation of D-galactose oxidase from Dactyliumdendroides with chirally pure deuterated methyl β-D-galactopyranosides showed that there were two mechanisms for the enzymatic reaction: an efficient pro-S hydrogen atom specific oxidation and a far less efficient non-specific or pro-R specific oxidation.
The sonolysis of cytosine and thymine
Authors: Yu Tain-Jen , Sutherland Ronald G. , Verrall Ronald E.
Published: May 2006

Sonolysis of cytosine has been studied at 630 kHz in the presence of air and nitrogen. The degradation products were identified by gas chromatographic – mass spectral analysis. Under aerated conditions the following products were found: urea, formyl urea, parabanic acid, isobarbituric acid, oxaluric acid, alloxan monohydrate, alloxantin, dialuric acid, and uracil glycols. Under nitrogen the degradation products were isobarbituric acid, alloxan monohydrate, and uracil glycols. The observed products have been used to develop a possible mechanism for the sonolytic degradation. There appears to be some similarity with the products reported from radiolysis studies of this compound. Sonolysis of thymine in the presence of air was reinvestigated and the gc–ms analysis shows that a previously reported, unidentified, product may be 5-hydroxy-5-methylbarbituric acid.
17O nuclear magnetic resonance spectroscopic study of substituted phthalic anhydrides and phthalides
Authors: Boykin David W. , Baumstark Alfons L. , Kayser Margaret M. , Soucy Chantal M.
Published: May 2006

17O chemical shift data (natural abundance) for 3-substituted phthalic anhydrides and 4- and 7-substituted phthalides in acetonitrile at 75 °C are reported. Steric interactions of substituents ortho to the carbonyl groups result in deshielding effects (9–22 ppm) relative to parent compounds regardless of the electronic character of the substituents. Factors contributing to the deshielding effects are discussed. The relationship between 17O chemical shifts and regiochemistry of the phthalic anhydrides is discussed.
Determination of substituent effects by factor analysis and multiple linear regression for the carbon-13 nuclear magnetic resonance chemical shifts in 4-substituted phenols and 2-nitrophenols
Authors: Hutton Harold M. , Kunz Kenneth R. , Bozek John D. , Blackburn Barry J.
Published: May 2006

Carbon-13 nuclear magnetic resonance chemical shifts are reported for a series of 4-substituted phenols and 2-nitrophenols in dimethyl sulfoxide solution. For chemical shift correlations, it was found by factor analysis and iterative multiple linear regression that the para chemical shifts require two substituent factors whereas the ipso, ortho, and meta chemical shifts require three factors. Regression analyses were performed using the field and resonance parameters (σF, σR0) and the appropriate ipso, ortho, and meta parameters (I, O, M) determined by Reynolds. Good correlations were obtained except for the three meta carbon analyses, where the correlation coefficients range from 0.877 to 0.963.
The 59Co nuclear magnetic resonance spectra of polycrystalline complexes
Authors: Eaton Donald R. , Buist Richard J. , Sayer Brian G.
Published: May 2006

The solid state 59Co nmr spectra of a number of octahedral complexes are reported. In the case of sodium hexanitrocobaltate(III) the spectra have been obtained at several different field strengths and the results are analysed to give a quadrupole coupling constant of 9.4 MHz, an asymmetry parameter of zero and an axial chemical shift tensor with an anisotropy of 180 ppm. Several other complexes have been examined at high field (11.8 T) to minimize the effects of quadrupole coupling and maximize the influence of chemical shift anisotropy. The results are, where possible, compared with single crystal X-ray and low field nmr data. It is concluded that high fields are necessary to obtain reliable chemical shift anisotropy values. The conditions necessary for obtaining reasonable quality spectra from polycrystalline samples containing quadrupolar nuclei are discussed.
Acidity level in concentrated mineral acid mixtures. Iso-acidic media
Authors: Louis C. , Bebba A. , Bessiere J.
Published: May 2006

Assuming the relationship between the R0(H) acidity function and the water activity in mineral acid concentrated solutions, iso-acidic solutions are prepared by mixing in all proportion two or three of the acids: H3PO4, HCl, HClO4, H2SO4, H2SiF6. These solutions are characterized by an equal R0(H) acidity level and different redox and complexing properties. Their R0(H) acidity level is determined from potential measurements involving o-chloranil as an H+ indicating system and ferricinium/ferrocene as a comparison system.
Electroionization study of ethane: ionization and appearance energies, ion-pair formations and negative ions
Authors: Plessis Pierre , Marmet Paul
Published: May 2006

Threshold region ionization efficiency curves of ethane, of all singly charged fragments consisting of at least one carbon atom, and of [Formula: see text] and [Formula: see text] are presented and analysed. An energy filtered monoenergetic electron beam apparatus capable of producing very high signal-to-noise ratio data was used to study these ions. The C2H6 ionization energy is evaluated to be 11.57 ± 0.02 eV and structures due to competition with [Formula: see text] fragment production are observed at higher energy in the [Formula: see text] curve. As a result of the high apparatus sensitivity several of the measured appearance energies are lower (some by several eV) than previously reported. [Formula: see text], [Formula: see text], and [Formula: see text] ion pair formations are observed. The [Formula: see text] ion pair formation, previously reported by several studies, is shown to be obscured by the isotopic [Formula: see text] fragment signal.
Binuclear metal chelate complexes of anthraquinones having a MO4 chromophore. Part 1. Quinizarin
Authors: Bakola-Christianopoulou M. N. , Akrivos P. D. , Baumgarten M.
Published: May 2006

Homobinuclear metal chelate complexes having 1,4-dihydroxy-9,10-anthracenedione (quinizarin) as a bridging unit have been prepared with four bivalent first row transition elements, namely cobalt, nickel, copper, and zinc. The coordination spheres of the metal ions consist of two nearly equivalent six-membered rings with oxygen donor atoms derived from the quinizarin and the terminal ligands which are either β-diketones or salicylic aldehyde. TG, spectroscopic (ir, uv–vis, epr), and magnetic measurements have been applied to an investigation of the geometry adopted by the MO4 chromophores. The results are consistent with varying degrees of distortion from the ideal square planar toward a tetrahedral arrangement around the metal ions, closely related to the specific metal center involved.
Mécanisme de réaction de mélanges méthane–chlore à haute température et faible taux de chlore
Authors: Chambon Marc , Marquaire Paul-Marie , Côme Guy-Marie
Published: May 2006

A patent of Benson (1980) states that a methane/chlorine flame produces some ethane and some ethylene. A fundamental study of the reaction has been carried out using an isothermal, continuous, stirred reactor operated at temperatures varying from 800 to 1000 °C, at subatmospheric pressures, at low concentrations of chlorine (about 1% by volume), and with reaction times of about 1 s. Under these conditions, the reaction leads mainly to the formation of the following carbon compounds: CH3Cl, C2H4, C2H6, and C3H6. The percentage of methane that is transformed into non-chlorinated hydrocarbons rises with the temperature and reaches a level of 77% at 1000 °C. A radical mechanism which takes into account all the data is proposed and analysed. [Journal translation]
Crystal chemistry of complex indium(III) and other M(III) halides, with a discussion of M—Cl bond lengths in complex M(III) chlorides and of the structures of and hydrogen bonding in (NH4)2[InCl5(H2O)], K3InCl6•nH2O, (MeNH3)4[InCl6]Cl, and (Me2NH2)4[InCl6]Cl
Authors: Knop Osvald , Cameron T. Stanley , Adhikesavalu D. , Vincent Beverly R. , Jenkins James A.
Published: May 2006

The crystal chemistry of complex In(III) halides is discussed and compared with that of other Group III elements and Fe(III), with critical comments and analysis of the available information. The cation/anion packing types occurring among A+[M3+X4] halides are classified according to volume per formula unit and the relative ionic sizes of M, X, and A, and the structural trends in this class of compounds are identified. The effect of systematic factors responsible for variation in M(III)—Cl bond lengths is examined in detail. It is shown that the mean M(III)—Cl bond lengths in [MClnLm]ε(M = Al, Ga, Fe, In, Tl; L = Cl or a neutral ligand) complexes can be approximated, to within about 0.02 Ă, by a linear function of the coordination number CN = n + m and the charge ε over the range 3 ≤ CN ≤ 6 and.−3 ≤ ε ≤2. This analytical expression provides a norm for comparing M(III)—Cl bond lengths and demonstrates that the CN is always a more important factor than ε in determining the variation in the mean bond length and that it becomes dominant when M is small. The crystal structure of (Me2NH2)4[InCl6]Cl (P21212, a = 10.156(4) Å, b = 13.007(4) Å, c = 8.751(3) Å, Z = 2) has been determined and those of (NH4)2InCl5(H2O)] (Pnma, a = 13.953(4) Å, b = 10.086(5) Å, c = 7.152(3) Å, Z = 4), K3InCl6•nH2O (I4mm, a = 15.659(8) Å, c = 18.106(5) Å, Z = 14) and (MeNH3)4[InCl6]Cl (P2/n, a = 16.113(3) Å, b = 7.446(2) Å, c = 16.163(4) Å, β = 103.75(2)°, Z = 4) redetermined. The water in K3InCl6•nH2O appears to be in part zeolitic; the hydrate examined contained more water than the monohydrate reported previously. Hydrogen bonding in these and related structures is described and discussed in detail; descriptions of the hydrogen-bonding schemes in (NH4)2[InCl5(H2O)] and (MeNH3)4[InCl6]Cl constitute the main improvement over earlier structure determinations.
Thermodynamics of ionization of aqueous alkanolamines
Authors: Kim Jin-Ho , Dobrogowska Celina , Hepler Loren G.
Published: May 2006

We have made electrochemical measurements with a glass electrode that have yielded pK values at T = 298.15 K for monothanolamine (MEA), triethanolamine (TEA), diisopropanolamine (DIPA), and methyldiethanolamine (MDEA) relative to the already well-known pK for diethanolamine (DEA), with all pK values referring to equilibria of the type AmH+(aq) = Am(aq) + H+(aq) in which Am(aq) represents an alkanolamine in aqueous solution and AmH+(aq) represents the corresponding protonated alkanolamine. We have also made calorimetric measurements leading to ΔH0 values for dissociation of the protonated species of all five of these alkanolamines in aqueous solution at T = 298.15 K. These pK and ΔH0 values have led to ΔG0 and ΔS0 values for the corresponding dissociation reactions of all five AmH+(aq) species.
Rate constant for hydroxylation of a primary alkyl radical by induced decomposition of an alpha hydroperoxyalkyl diazene
Authors: Lakhani Chandra , Mathew Lukose , Warkentin John
Published: May 2006

Rate constants for induced decomposition of 5-hexenyl(1-hydroperoxy-1-methylethyl) diazene ((CH3)2C(OOH)N=N(CH2)4CH=CH2, 2) have been estimated. Thermolysis of 2 at 50 °C affords 5-hexenyl radicals which abstract the hydroxyl group from 2 in competition with cyclization of 5-hexenyl to cyclopentylmethyl radicals. The known rate constant (kc) for that cyclization was used to clock the bimolecular hydroxyl abstraction process. For reaction in hexafluorobenzene at 50 °C, the rate constant for abstraction of hydroxyl from 2 (kOH) was found to be dependent on the concentration of 2. For example, at [2] = 0.4 M, kOH = 3.2 × 106 M−1 s−1 whereas, at [2] = 0.10 M, kOH = 1.8 × 107 M−1 s−1. The concentration dependence of kOH is attributed to the effects of intermolecular hydrogen bonding and the large absolute values of kOH are ascribed to concerted induced decomposition, the O—O bond being broken in concert with scission of the nearest C—N bond of the azo function. The relevance of the results, to synthetic application of α-hydroperoxyalkyl diazenes in hydroxyalkylation reactions, is discussed.
A study of chiral induction in some diene additions catalyzed by chiral alkoxyaluminum dichlorides
Authors: Northcott Colleen J. , Valenta Zdenek
Published: May 2006

A reliable procedure for the preparation of the chiral Lewis acid catalysts, (−)-menthoxy- ((−)-1) and (−)-bornyloxy-aluminum dichloride ((−)-2), has been established for the study of diene additions. The geometry of conformationally mobile α,β-unsaturated carbonyl compounds complexed with these catalysts has been probed using the α-methylene ketones 3 and 4 and 2,6-dimethyl-1,4-benzoquinone 5 as dienophiles of fixed geometry. The addition of the first two to cyclopentadiene and (−)-1 yields exo and endo adducts that exhibit a range of 28–54% enantiomeric excess (ee); with 5, only the endo isomer, showing 8% ee, is formed. In the corresponding additions catalyzed by (−)-2, adducts displaying ee in the range of 3–18% are formed.
The binding energies of trialkylgermanium cations to water molecules studied by high pressure mass spectrometry
Authors: Stone John Alfred , Wytenburg Wilhelmus Johannes
Published: May 2006

The binding energies of H2O to R3Ge+ have been measured using pulsed electron beam, high pressure mass spectrometry. van't Hoff plots have yielded thermodynamic data (ΔH0, ΔS0) for the reactions, [5], [Formula: see text]and [7], [Formula: see text]. [Formula: see text] decreases with increasing size of R (CH3 28.6 ± 0.5 kcal mol−1, C4H9 20.6 ± 1.2 kcal mol−1) while [Formula: see text] shows much less change (34.4 ± 0.9 to 30.3 ± 2.8 cal K−1 mol−1). Comparison with data for (CH3)3M+ (M = Si, Sn) shows that binding energy decreases with increasing size of M.
The crystal structure of Sn6O2(CF3CO2)8•CF3CO2H
Authors: Batchelor R. J. , Birchall T. , Johnson J. P.
Published: May 2006

The X-ray crystal structure of Sn6O2(CF3CO2)8•CF3CO2H has been determined: R1 = 0.0519. The crystals were orthorhombic, space group Pna21, a = 18.327(4) Å, b = 12.209(3) Å, c = 19.218(3) Å, fw = 1762.29, and Z = 4. The structure consists of two sets of three tin(II) atoms, each set linked by a μ3-oxo bridge. The tin atoms are further linked by trifluoroacetate groups to form an extended structure in which the tin atoms can be described as having either SnX4E or SnX5E coordination.
Solubility of non-polar gases in cyclohexanone between 273.15 and 303.15 K at 101.32 kPa partial pressure of gas
Authors: Gallardo María Asunción , Melendo José María , Urieta José Santiago , Losa Celso Gutierrez
Published: May 2006

Solubility measurements of several non-polar gases (He, Ne, Ar, Kr, Xe, H2, D2, N2, O2, C2H4, C2H6, CF4, SF6, andCO2) in cyclohexanone at 273.15 to 303.15 K and a partial pressure of gas of 101.32 kPa, are reported. Gibbs energy, enthalpy, and entropy of solution at 298.15 K and 101.32 kPa partial pressure of gas were evaluated. Effective hard-sphere diameter temperature dependence has been studied and its effect on the calculated SPT (Scaled Particle Theory) solubilities, and enthalpies and entropies of solution was also examined.
Autoxidation of model membranes. The kinetics and mechanism of autoxidation of mixed phospholipid bilayers
Authors: Barclay Lawrence Ross Coates , Baskin Kimberly Ann , Kong David , Locke Steven Jeffrey
Published: May 2006

Kinetics of autoxidation of bilayer mixtures of oxidizable dilinoleoylphosphatidylcholine (DLPC) with saturated phospholipids as solvents (dimyristoyl-, DMPC, and dipalmitoyl-phosphatidylcholine, DPPC) follow the classical rate law of autoxidation: −d[O2]/dt = kp/2kt1/2[RH]Ri1/2. The kinetic order in substrate [RH] was found to be unity for peroxidation initiated by a lipid-soluble initiator, azobis-2,4-dimethylvaleronitrile (ADVN), and by the water-soluble azobis(2-amidinopropane•HCl) (ABAP). The kinetic order in rate of chain initiation, Ri, was found to be one-half for both initiation by ADVN, photochemically decomposed, and by ABAP. The oxidizability of unilamellar DLPC liposomes (kp/2kt1/2 = 0.232 M−1/2 s−2) is twice that of multilamellar DLPC (kp/2kt1/2 = 0.116 M−2 s−2). Analysis of the hydroperoxides formed during ABAP-initiated autoxidations of mixed DLPC + DPPC liposomes showed a linear trend between the ratio of cis,trans to trans,trans geometrical isomeric hydroperoxides and [DLPC], consistent with the peroxidation mechanism proposed for homogeneous systems.31P nmr spectra of mixed bilayers were used to distinguish between heterogeneous and homogeneous mixtures of DLPC + DPPC. Such spectra taken at various stages of oxidation indicate that the bilayer structure of DLPC is preserved at least to the 10% extent of oxidation used in kinetic studies. At much higher oxidative conversion, the spectra indicate changes in lamellar structures.
Enthalpies of interaction of nonpolar solutes with nonpolar solvents. The role of solute polarizability and molar volume in solvation
Authors: Fuchs Richard , Chambers Eric J. , Stephenson W. Kirk
Published: May 2006

Heats of solution of 10 nonpolar solutes (carbon tetrachloride, perfluoroheptane, diiodomethane, benzene, hexane, decane, hexadecane, cyclohexane, toluene, and mesitylene) in 11 nonpolar solvents (heptane, cyclohexane, carbon tetrachloride, benzene, carbon disulfide, diiodomethane, toluene, mesitylene, tetrachloroethylene, 1,1,2-trichlorotrifluoroethane, and hexadecane) have been combined with solute heats of vaporization to give enthalpies of transfer from vapor to solvent (ΔH(v → S)). The heat of vaporization of diiodomethane has been measured (11.70 ± 0.01 kcal/mol). Correlations of the form ΔH(v → S) = a + bMMR + cMV describe the solvent–solute interaction enthalpies with high precision (correlation coefficients 0.991–0.999). Earlier correlations with only the molar refraction are limited to solutes of similar refractive index. In each solvent ΔH(v → S) becomes more exothermic with an increase in the solute molar refraction term, and less exothermic with an increase in the solute molar volume term. These terms represent solvent–solute dispersion interaction enthalpies, and solvent cavity formation enthalpies, respectively.
Synthesis of 31P nmr spectroscopic study of [Ag(μ-R2PCH2PR2)3Ag]2+ (R = Me or Ph). Observation of an intramolecular "end-over-end" exchange of bridging R2PCH2PR2
Authors: Dean Philip A. W. , Vittal Jagadese J. , Srivastava Radhey S.
Published: May 2006

Reaction of AgAsF6 with R2PCH2PR2 (R = Ph or Me) in a 2:3 ratio in MeNO2 or Me2CO produces the new compounds [Ag2(R2PCH2PR2)3](AsF6)2, which have been isolated in good yield. The analogous 107Ag-enriched compounds are produced using 107AgAsF6. The 2:3 compounds have interesting variable temperature 31P nmr spectra which have been studied in detail using the 107Ag-enriched compounds. The 31P nmr spectra of [107Ag2(Ph2PCH2PPh2)3](AsF6)2:[107Ag2(Me2PCH2PMe2)3](AsF6)2 mixtures at ambient probe temperature show the formation of the mixed ligand binuclear cations [107Ag2(Ph2PCH2PPh2)3−x(Me2PCH2PMe2)x]2+ (x = 1 or 2). By analogy, the two parent complexes also contain binuclear cations, and the limiting low temperature 31P nmr spectra of these can be interpreted in terms of the manxane structure, [107Ag(μ-R2PCH2PR2)3107Ag]2+. With increase in temperature, the 31P nmr spectra of the parents provide evidence for an intramolecular exchange process which is faster for R = Ph than for R = Me and which is shown to involve "end-over-end" exchange of bridging R2PCH2PR2. This type of exchange has not been observed previously for these ligands. With Me2CO as solvent, an approximate value of the enthalpy of activation for exchange is 59 kJ mol−1 for [107Ag((μ-Ph2PCH2PPh2)3107Ag]2+ and 50 kJ mol−1 for [107Ag(μ.-Me2PCH2PMe2)3107Ag]2+.
The effect of electron-pair donor solvents on methylene reactivity
Authors: Moreno Miquel , Lluch José M. , Oliva Antonio , Bertrán Juan
Published: May 2006

The effect of electron pair donor solvents on methylene reactivity has been theoretically studied by means of abinitio methods, using the split valence 3-21G basis set. The calculations have been done on the well-known methylene addition to ethylene, taking one water molecule in order to represent the donor solvent. We have shown that the process takes place via the formation of a reversible complex between water and methylene, the formation of this complex permitting to explain the experimentally observed decrease of methylene's electrophilicity. The analysis of the variation of the electronic charge density and of the solvation parameters along the reaction coordinate have also allowed to interpret the reaction in terms of the transfer of an electrophile (methylene) from a nucleophile (water) to another nucleophile (ethylene).
Copper (II) complexes of a macrocyclic binucleating ligand which exhibit two-electron oxidation and two-electron reduction. Structure of [Cu2(C24H34N4O2)(CH3OH)2](ClO4)2, a macrocyclic dicopper(II) complex involving coordinated methanol
Authors: Mandal Sanat K. , Thompson Laurence K. , Nag Kamalaksha , Charland Jean-Pierre , Gabe Eric J.
Published: May 2006

The saturated ligand H2L1, derived by template condensation of 4-methyl-2,6-diformylphenol and 1,3-diaminopropane, followed by borohydride reduction, generates binuclear, antiferromagnetically coupled, copper(II) complexes which exhibit cyclic voltammetry involving two one-electron oxidation steps (E1/2 = 1.1 to 1.2 V, 1.3 to 1.4 V; Pt/CH3CN/SCE) and two one-electron reduction steps (E1/2 = −0.75 to −0.76 V, −0.89 to −0.90 V (GC/DMSO/SCE) with the formation of Cu(III)–Cu(III) and Cu(I)–Cu(I) and mixed oxidation state species. A trinuclear derivative, [Cu2(L1)(CuCl4)], appears to contain a spin-coupled binuclear species bound to a magnetically isolated tetrachlorocuprate(II) entity. The complex [Cu2(L1)(CH3OH)2](ClO4)2 forms brown crystals with a = 8.6516(7), b = 11.6832(9), c = 16.7205(6) Å, β = 92.596(5)°, P21/n, Z = 2, Rf = 0.037 and has a copper–copper separation of 3.088(1) Å and two weakly bound trans-axial methanol molecules (Cu—O, 2.413(4) Å). Variable temperature magnetic studies on [Cu2(L1)(ClO4)2] and [Cu2(L1)](ClO4)2 indicate strong antiferromagnetic exchange (−2J = 824 ± 5cm−1, 827 ± 7cm−1, respectively) in both cases.
Some phase relationships between basic bismuth chlorides in aqueous solutions at 25 °C
Authors: Taylor Peter , Lopata Vincent J.
Published: May 2006

Observations are reported on the interconversion of solid α-Bi2O3, Bi12O17Cl2, BiOCl, and a daubréeite-like phase tentatively identified as Bi2O2(OH)Cl, in aqueous chloride solutions at 25 °C. Equilibrium constants, K, for these interconversions are expressed as anion activity ratios, {Cl−}/{OH−}. Experimental values of K for equilibrium between Bi2O3 and each of the chlorides are 100.56 ± 0.20 for Bi12O17Cl2, 101.5 ± 0.4 for Bi2O2(OH)Cl, and 103.13 ± 0.04 for BiOCl; the fatter two represent metastable equilibria. These equilibrium constants yielded the following estimates of Gibbs energies of formation: Bi12O17Cl2, −3141 ± 6 kJ mol−1;"Bi2O2(OH)Cl", −696 ± 4 kJ mol−1; BiOCl, −321.5 ± 1.3 kJ mol−1. Phase relationships among these solids are discussed, with reference to natural occurrence, other bismuth oxychlorides, and the stability of other basic salts of bismuth.
Controlled formation of dipyranoside derivatives through C6 and O4. Pyranosidic homologation. VII
Authors: Molino Bruce Francis , Fraser-Reid Bert
Published: May 2006

A procedure has been developed for pyranosidic homologation of methyl α-D-glucopyranoside via C4 and C6. Reaction of the aldehydo group of compound 2 with the Wittig–Bestmann reagent, Ph3P=CHCH(OEt)2, gave an E/Z mixture of acetals, 4, which cyclizes under the specific catalysis of pyridinium p-toluenesulfonate and in the presence of alcohols to give anomerically pure olefinic bipyranosides, 6a–d. A general procedure for epoxidation of the latter involves osmium tetroxide hydroxylation, followed by reaction with phosgene iminium chloride (Viehe's salt) to give chlorocarbamates 12 and 13, which are then subjected to the action of sodium methoxide. This allows for the formation of a single series of diastereomeric epoxides, 7, and controlled cleavage of the latter with nucleophiles then follows well-established precedents. Selective access to the "ends" of the bipyranosides 7c and d can be obtained by oxidative removal of the activated benzyl glycosides with DDQ.
Thujin, a novel lactone isolated from the discolored heartwood of Thuja plicata Donn.
Authors: Jin Lehong , Wilson Jack W. , Swan Eric P.
Published: May 2006

The chemical structure of a novel lactone isolated from the discolored heartwood of living western red cedar (WRC) (Thuja plicata Donn.) trees has been determined as 3,3,4,7,7,8-hexamethyl-2,6-dioxa-1,5-anthracene-dione, and given the trivial name thujin (1). The isolation, purification, and determination of the structure were carried out by a combination of chemical, chromatographic, and spectroscopic methods.
The electrochemical behavior of flavin adenine dinucleotide in neutral solutions
Authors: Birss V. I. , Elzanowska H. , Turner R. A.
Published: May 2006

A detailed investigation of the electrochemical behavior of flavin adenine dinucleotide (FAD) in neutral solutions has been carried out at Hg and glassy carbon electrodes. At FAD concentrations of about 10−4 M, cyclic voltammetry (CV) shows a pair of anodic and cathodic peaks having a peak separation at low sweep rates indicative of a two-electron transfer process and yielding a formal redox potential for FAD of −0.206 ± 0.003 V vs. NHE at pH 7. Evidence for FAD adsorption was obtained in experiments at high sweep rates, from the effect of time of exposure of the electrode surface to FAD in solution and from the effect of the potential limits on the cyclic voltammetric response. The process of FAD adsorption was studied in detail in dilute FAD solutions (ca 10−6 M) using a hanging mercury drop electrode and the techniques of CV and ac voltammetry. Three distinct stages of FAD adsorption were observed and a model of the orientation of FAD on the electrode surface as a function of time and potential is presented. In addition, the kinetics of oxidation and reduction of adsorbed FAD was studied for each of the stages of FAD deposition, and a surface standard rate constant of ca. 40 s−1 was obtained for Stages II and III of FAD adsorption.
Dosage du Sr-90 dans l'eau des lacs et des rivières du Québec par précipitation avec l'oxine et comptage β
Authors: Haddad E. , Zikovsky L.
Published: May 2006

A new method for the determination of Sr-90 dissolved in surface waters has been developed. It is based on the precipitation of Sr with 8-hydroxyquinoline at pH 11.3 and counting of β particles with energy above 150 keV. The detection limit obtained is 0.5 mBq/L and the mean yield is 28%. The decontamination factors from other β emitters achieved are better than 10 000. This method has been used to measure the Sr-90 in 5 lakes and 5 rivers in Québec and activities ranging from 3 to 15 mBq/L were obtained. This new method is as efficient and reliable as conventional techniques while being less tedious.
Synthesis and biological activity of (S)-2′-fluorodaunorubicin
Authors: Baer Hans H. , Siemsen Lisa
Published: May 2006

Methyl 3-amino-2,3,6-trideoxy-2-fluoro-β-L-galactopyranoside was hydrolyzed to the free sugar, (S)-2-fluorodaunosamine hydrochloride, which was converted into the α,β-1,4-di-O-acetyl-N-trifluoroacetyl derivative and thence into the corresponding glycosyl bromide. The latter was condensed with daunomycinone, and the product was deprotected to give the title compound. The fluoroanthracycline displayed significant cytotoxicity against a number of tumor cell lines in vitro. Antitumor activity against L1210 murine leukemia in vivo was lower than that of the parent daunorubicin, but toxicity appeared to be reduced.
Étude des complexes fluorés et chlorés du cadmium dans les mélanges eau–HF
Authors: Beaudoin Réjean , Ménard Hugues
Published: May 2006

The formation of fluoride and chloride complexes in water – hydrogen fluoride mixtures has been studied using polarography. The reduction of the complexation by the fluoride ions from CdF3−down to CdF+ is in good agreement with the reduction of the fluoride ion activity, R0(F) with increasing HF concentration. At higher HF concentration than 60%, the half-wave potential for the reduction of cadmium is shifted in a pattern that cannot be explained by fluoride in complexation. The formation of CdCl3− and CdCl42− has been observed in H2O–HF–KCl mixtures when the HF concentration was increased to 60%.
Crystal and molecular structure of [dimethyl(1-pyrazolyl)(2-pyridyl-methoxy)gallato-N2,O,N3](η3-allyl)dicarbonylinolybdenum(II)
Authors: Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

Crystals of [dimethyl(1-pyrazolyl)(2-pyridylmethoxy)gallato-N2,O,N3](η3-allyl)dicarbonylmolybdenum(II) are triclinic, a = 9.632(2), b = 9.798(2), c = 10.255(2) Å, α = 80.16(1), β = 87.38(1), γ = 81.75(1)°, Z = 2, space group [Formula: see text]. The structure was solved by conventional heavy-atom methods and was refined by full-matrix least-squares procedures to R = 0.033 and Rw = 0.037 for 3000 reflections with I ≥ 3σ(I). The molecule has pseudo-octahedral coordination geometry with the tridentate [Me2Ga(N2C3H3)(OCH2(C5H4N))]− ligand facially coordinated and the η3-allyl ligand occupying one coordination site trans to the pyridyl nitrogen atom. Important bond lengths are Mo—O = 2.219(2), Mo—N(py) = 2.212(3), Mo—N(pz) = 2.232(2), Mo—C(allyl) = 2.290(4), 2.189(4), 2.341(4), Mo—CO (trans to O) = 1.928(4), and Mo—CO (trans to N) = 1.952(4) Å.
Ion–ion–solvent interactions in aqueous ionic cosolvent systems. IV. Transfer energetics of water, p-nitroaniline, and benzoic acid from emf/solubility measurements at different temperatures in aqueous sodium nitrate solvent system
Authors: Rudra Sibaprasad , Talukdar Himansu , Kundu Kiron K.
Published: May 2006

Autoionization constants (Ks) of aqueous mixtures of 1, 2, and 4 m sodium nitrate used as an ionic cosolvent system have been determined from emf measurements of the cell: Pt, H2 (g, 1 atm)/KOH (m1) KCl (m2), solvent/AgCl–Ag at five equidistant temperatures ranging from 15–35 °C. The standard free energies (ΔG0) and entropies (ΔS0) of autoionisation of the solvents were then evaluated from these data. Relative free energies (ΔG0) and entropies of (ΔS0)of autoionization of the solvents when coupled with the previously determined transfer free energies [Formula: see text] and entropies [Formula: see text] of H+ yielded [Formula: see text][Formula: see text],[Formula: see text] and [Formula: see text]. Values of [Formula: see text] and [Formula: see text] obtained after correcting for [Formula: see text], as well as [Formula: see text] and [Formula: see text]obtained after correcting the "cavity effect" and Born-type electrostatic effect suggests that while the "basicity" of the aqueous NaNO3 solutions decreases, the "acidity" more or less increases with NaNO3 concentration. The observed [Formula: see text]– and [Formula: see text]–composition profiles were also examined in the light of Kundu et al.'s four-step transfer process and the involved order–disorder phenomena, respectively, as proposed earlier.Standard free energies [Formula: see text] and entropies [Formula: see text] of transfer of p-nitroaniline (pNA) and benzoic acid (HBz) for the solvent system have also been determined from solubility measurements at different temperatures. The observed [Formula: see text]–and [Formula: see text]–composition profiles appear to reflect the salting-out effect of the salt and the [Formula: see text]–and [Formula: see text]–composition profiles confirm the applicability of either of these quantities rather than [Formula: see text], as a better structural probe both for aquo-ionic and aquo-organic solvents.
Ground and excited-state interactions of coumarin and nucleotide base
Authors: Wenska Grażyna , Paszyc Stefan
Published: May 2006

Steady-state and time-resolved fluorescence measurements for a series of bichromophoric compounds containing 7-methoxy-coumarin and nucleotide base residues have been performed in water and in organic solvents. The data from these studies have been used to calculate the relative proportion of folded and extended conformations of bichromophores. Ground-state stacking interactions of coumarin and nucleotide base have been found to be limited to aqueous solution. The contribution of the dynamic quenching mechanism to the total fluorescence quenching in water has been estimated. The absence of dynamic quenching in organic solvents is.explained on the basis of the very short lifetime of the fluorophore in methanol.
Synthesis and conformational analysis of 2-amino-1,2,3,4-tetrahydro-1-naphthalenols
Authors: Delgado Antonio , Garcia José Miguel , Mauleon David , Minguillon Cristina , Subirats Joan Ramon , Feliz Miguel , Lopez Francisco , Velasco Dolores
Published: May 2006

Synthesis and conformational analysis of several cis- and (or) trans-2-amino-1,2,3,4-tetrahydro-1-naphthalenols are described. Introduction of the nitrogen atom at the C(2) position of the starting tetralones 3 has been carried out through nitrosation followed by reduction of the intermediate hydroxyimino tetralone and (or) Neber rearrangement of the tosyloxy derivatives 7a–e. Stereoselective reduction of the C(1) carbonyl group of acetamidotetralones 5a–e or aminotetralones 8a–e afforded the corresponding acetamido or aminotetralols, respectively, of OH/N trans stereochemistry whereas an opposite stereoselectivity was observed in reduction of C(8)-OCH3 derivatives 5f and 8f under the same experimental conditions. Finally, acid hydrolysis of trans-acetamidotetralols led to cis-aminoalcohols in high yields. Conformational analysis has been carried out by 1H nuclear magnetic resonance techniques and MM2 theoretical calculations. All cis derivatives showed a major conformation in which the C(1)-OH group adopts a pseudoaxial disposition. On the other hand, trans-aminoalcohols in CDCl3 showed a major or exclusive OH/N trans-dipseudoequatorial conformation in which stabilization by intramolecular OH/N hydrogen bonding is possible. The only exception was found in C(8)-OCH3trans-aminoalcohols in DMSO-d6 solution, which showed a major OH/N trans-diaxial conformation.
Reactions of α-carbon- and nitrogen-centered radicals of piperazine with lumiflavin and paranitroacetophenone at pH 7
Authors: Surdhar Parminder S. , Armstrong David A.
Published: May 2006

Analysis of data from radiation chemical and photochemical studies shows that the reactions of hydroxyl radicals and flavin triplets (Fl3) with amines produce aminyl as well as α-amino radicals. This must be taken into account, since the former tend to oxidise •FlH and FlH−, while the latter are inherently reducing. In the reaction of •OH with piperazine the ratio of aminyl to α-amino radicals at pH 7 is about 60:40. The former undergo complexation to form a [Formula: see text] bonded species, which possess a broad absorption peaking at 520 nm and are inert to lumiflavin (Fl) and paranitroacetophenone on a 30 µs time scale. However, they oxidise dihydrolumifiavin anion (FlH−) to flavin semiquinone radical (•FlH). The α-amino radicals of piperazine reduced lumiflavin to •FlH with a rate constant of 3.3 ± 0.3 × 109 M−1 s−1. This rate constant is similar to that observed for the CH3S(ĊH2)2HNH2 radical formed from methionine.The 40:60 mixture of α-amino and [Formula: see text] radicals produced in N2O-saturated piperazine solutions decayed by a second order process with a rate constant of 7.2 × 108 M−1s−1. Similar mixtures of •FlH and the [Formula: see text] species also underwent second order decay (k = 2.7 × 109 M−1 s−1) with reoxidation of •FlH to Fl as the major process.
The evolution of membranes
Authors: Bloom Myer , Mouritsen Ole G.
Published: May 2006

Consideration of the influence of cholesterol on the physical properties of biological membranes leads to the conclusion that cholesterol increases the thickness of fluid membrane bilayers without appreciably increasing the microviscosity component of membrane fluidity. At sufficiently high cholesterol concentrations, the gel–liquid crystalline phase transition is completely eliminated in phospholipids–cholesterol mixtures and the system has the properties of a two-dimensional liquid over a wide range of temperatures. It is proposed that with the evolution of cholesterol and related sterols in an oxygen-rich atmosphere, the resulting modification of physical constraints on membrane properties made it possible for new evolutionary driving forces to manifest themselves leading to the peculiar properties of plasma membranes of eucaryotic cells.
Models of picosecond-scale mobilities in glassy and polycrystalline quinoline
Authors: Rothschild Walter G.
Published: May 2006

The observed inhomogeneous band broadening of the 1033-cm−1 ir C—H in-plane deformation fundamental of quinoline in a glassy state and a polycrystal at 115 K was related to the theoretical concepts of the underlying vibrational T2 processes. The motional narrowing model that fits best the spectral data and reflects the particular physical nature of the locally-ordered glass is the recently introduced stretched ("extended", "fractional") exponential exp [−(t/τ)α]. Extension of the model to shorter time regimes is discussed. The modulation model which simulates the corresponding spectral data and describes the longer-range order of the polycrystal is the damped oscillator exp (−tγ/2) [cos θt + (γ/2θ) sin θt], previously proposed for oscillator – lattice mode coupling.