bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and characterization of binuclear transition metal complexes incorporating the tridentate chelating ligand dimethyl (N,N-dimethylethanolamino)(1-pyrazolyl)gallate: crystal and molecular structure of bis-μ-pyrazolyl-(N(1),N(2))-bis[dimethyl(N,N-dimethylethanolamino)-(1-pyrazolyl)gallato(N(2),O,N)copper(II)]
Authors: Chong Kenneth S. , Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

Details of the synthesis of the tridentate tris chelating ligand dimethyl(N,N-dimethylethanolamino)(1-pyrazolyl)gallate and the preparation and physical properties of the binuclear transition metal complexes incorporating this ligand are given. Crystals of bis-μ-pyrazolyl(N(1),N(2))-bis[dimethyl(N,N-dimethylethanolamino)(1-pyrazolyl)gallato(N(2),O,N)copper(II)] are monoclinic, a = 12.018(2), b = 10.390(1), c = 13.568(3) Å, β = 100.04(6)°, Z = 2, space group P21/c. The structure was solved by direct methods and was refined by full-matrix least squares procedures to a final R of 0.045 and Rw of 0.058 for 2460 reflections with I ≥ 3σ(I). The centrosymmetric binuclear molecule features copper atoms having distorted square pyramidal co-ordination geometry. Three of the basal positions are occupied by the oxygen, pyrazolyl nitrogen, and amino nitrogen atoms of the tridentate tris-chelating ligand. The two remaining sites are occupied by bridging pyrazolyl groups, which provide a basal nitrogen atom to one copper atom and an apical nitrogen atom to the second copper centre. The gallium atoms have distorted tetrahedral coordination geometry. Important bond lengths (corrected for libration) are: Cu—O, 1.981(3), Cu—N(basal), 1.953(3)–2.143(4), Cu—N(apical), 2.173(3), Ga—O, 1.907(3), Ga—N, 1.991(4), and Ga—C, 1.962(7) and 1.977(7) Å.
L-Proline derivatives of gallium trimethyl and gallium triethyl: crystal and molecular structure of L-prolinatodimethylgallium
Authors: Breakell Kenneth R. , Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

Crystals of L-prolinatodimethylgallium are orthorhombic, a = 10.624(2), b = 10.567(4), c = 8.2268(6) Å, Z = 4, space group P212121. The structure was solved by direct methods and was refined by full-matrix least squares procedures to a final R of 0.029 and Rw of 0.035 for 1109 reflections with I ≥ 3σ(I). Details of the preparation and physical properties of L-prolinatodimethylgallium and L-prolinatodiethylgallium are given. The crystal structure of L-prolinatodimethylgallium consists of molecules each linked to two others by weak Ga—O bonds (2.695(3) Å) and N—H … O hydrogen bonds (N … O = 2.901(4) Å) to form a chain-like polymeric structure extending along the b axis. The gallium atom is five-coordinate and has distorted trigonal bipyramidal geometry. Important bond lengths are: Ga—O (axial), 2.044(3) and 2.695(3); Ga—N, 2.035(3); and Ga—C, 1.942(5) and 1.958(5) Å
Determination of ΔHf2980(C6F5Br, g) from studies of the combustion of bromopentafluorobenzene in oxygen and calculation of D[C6F5 — Br]
Authors: Krech Michael J. , Price Stanley James W. , Sapiano Henry J.
Published: May 2006

The heat of formation of bromopentafluorobenzene has been determined through the use of the direct combustion method which has been applied to hexafluorobenzene, octafluorotoluene, and iodopentafluorobenzene. While a platinum lined bomb is normally used for these types of compounds a steel bomb had to be adopted in this work. The combustion of bromopentafluorobenzene in the steel bomb yields CO2, CF4, F2, Br2, and BrF3. With a ten-fold excess of oxygen, the average CO2 to CF4 molar ratio is 7.29 ± 0.07. A material balance was obtained for carbon, fluorine, and bromine. The value of ΔHf2980(C6F5Br, g) = −711.6 ± 16.7 kJ mol−1 (−170.1 ± 4.0 kcal mol−1) has been combined with ΔHf2980(C6F5, g) = −387.4 kJ mol−1 (−92.6 kcal mol−1) and ΔHf2980(Br, g) = 111.7 kJ mol−1 (26.7 kcal mol−1) to obtain a value for D[C6F5—Br] of 435.9 kJ mol−1 (104.2 kcal mol−1).
Total synthesis of indole and dihydroindole alkaloids. XII. Selective functionalization of various bisindoles. Efficient syntheses of leurosine and related bisindole alkaloid derivatives
Authors: Kutney James P. , Balsevich John , Bokelman Gordon H. , Hibino Toshihiko , Honda Toshio , Itoh Isamu , Ratcliffe Arnold H. , Worth Brian R.
Published: May 2006

Studies involving selective functionalization of the indole unit in a number of bisindole alkaloids and related synthetic derivatives are described. These investigations include such reagents as tert-butyl hydroperoxide, which provides an efficient procedure for epoxidation of olefinic linkages, mercuric acetate, osmium tetroxide, and iodine under basic conditions and oxygenation under acidic conditions. Efficient syntheses of leurosine (8) and various novel vinblastine derivatives are developed.
An aid to the interpretation of electrochemical data measured with spherical and cylindrical electrodes: corrections to the Cottrell equation
Authors: Bansal Narottam P. , Plambeck James A.
Published: May 2006

An analysis of the theoretical correction factors for diffusion toward spherical and cylindrical electrodes has been made. The Cottrell equation is a limiting case for spherical and cylindrical diffusion and is accurate only when both D1/2/r0 and t are small.
Studies of the rhenium–oxygen bond. II. The crystal and molecular structure of µ-oxobis(cis-dichloro-cis-di(pyridine)-trans-oxorhenium(V)), ORe(C5H5N)2Cl2ORe(C5H5N)2Cl2O
Authors: Lock Colin James Lyne , Turner Graham
Published: May 2006

The crystal structure of µ-oxobis(cis-dichloro-cis-di(pyridine)-trans-oxorhenium(V)), ORe(C5H5N)2Cl2•O•Re(C5H5N)2Cl2O bas been studied by single crystal X-ray methods. The crystals were orthorhombic with lattice parameters a = 15.367(2), b = 10.283(2), c = 16.685(2) Å. The space group was Pna21 and there were four formula weights per unit cell. A total of 3339 reflections, of which 2990 were observed, were examined, and the structure refined by full matrix least squares (treating the pyridine rings as groups) to an R2 value of 0.0449. The dimer had a roughly rectilinear O—Re—O—Re—O backbone with pairs of chlorine atoms and pyridine molecules arranged cis in each half of the dimer. The two halves of the dimer were arranged such that the pairs of cis atoms in one half were rotated about the Re(1)–Re(2) axis almost 113 ° when compared to the corresponding pair in the other half. Important bond lengths (Re—O(terminal), 1.715(16), 1.764(16); Re—O(bridging), 1.943(16), 1.903(16); Re—Cl, 2.356(5)–2.390(5); Re—N, 2.116(16)–2.180(16)) were close to previously observed values. The molecule was markedly disturbed from the idealized structure and this was caused by intramolecular non-bonded interactions.
Reactivity of cyclopropylalkenes with p-chlorobenzenesulfenyl chloride
Authors: Cerksus Timothy R. , Csizmadia Valeria M. , Schmid George H. , Tidwell Thomas T.
Published: May 2006

The reactivity of a series of cyclopropylalkenes, as well as norbornene and cyclohexene, with p-chlorobenzenesulfenyl chloride in CH2Cl2 at 25 °C have been measured. Rates of reaction of several of the substrates were also measured in acetic acid and 1,1,2,2,-tetrachloroethane so that factors for converting rates from one solvent to another could be obtained. The rates of the sulfenyl halide additions varied over a total range of 193 from the least reactive alkene, ethylene, to the most reactive, 1,1-dicyclopropylethylene. This relatively small variation is in accord with all of these reactions involving bridged rate-determining transition states. The corresponding range in reactivity for acid-catalyzed hydration, a reaction involving protonation on carbon to give an open carbonium ion, is 1016. These two reactions are proposed as bases for structure–reactivity comparisons to determine whether other reactions involve bridged or open transition states.
Ion–molecule reactions in the binary mixture of acetaldehyde and trioxane. II. Mechanism for the reaction of acetaldehyde molecular ion with trioxane
Authors: Kumakura Minoru , Arakawa Kazuo , Sugiura Toshio
Published: May 2006

The ionic reaction of CH3CHO+with trioxane in acetaldehyde–trioxane mixtures has been studied using a time-of-flight mass spectrometer. The product ions, C3H5O2+, C3H6O2+, and C3H7O2+, were formed by condensation–elimination reactions, which involve the elimination of aformaldehyde molecule. The dissociation of the intermediate-complex, CH3CHO(CH2O)3+*, leads to the formation of the product ions. The structure of the complex is linear with localized positive charge. Rearrangement of hydrogen atoms occurs in the complex but not extensive scrambling. From the distribution of the isotopic product ions in acetaldehyde-d4–trioxane mixtures it was proposed that the origins of the product ions are the acetaldehyde molecule (reactant ion) and fragments from trioxane. The rate constants for the product ions formed in acetaldehyde (or acetaldehyde-d4)–trioxane mixtures were obtained.
The effect of p, d, and f Gaussian polarization functions on the computed one-electron properties of AHn oxygen and sulfur hydrides
Authors: Poirier Raymond , Kari Roy
Published: May 2006

A series of LCAO-MO-SCF calculations, using various basis sets of Gaussian-type functions, has been made in order to study the effects of p, d, and f polarization functions on calculated one-electron properties for a 10-electron isoelectronic series of oxygen hydrides and for an 18-electron series of sulfur hydrides. Conclusions from these results suggest that several one-electron properties have a predictable, although not monotonic convergence pattern. Except for calculated field gradients, f GPF's have only a small effect on the calculated values.
Crystal structure of mercury(II) bromide dithiocarbamate, [HgBr2(S2CNEt2)Hg(S2CNEt2)]n, an inorganic polymer
Authors: Chieh Chung
Published: May 2006

A pale yellow crystal obtained from reaction of HgBr2 and tetraethylthiuram disulfide (TETD) has the composition of HgBr2•Hg[S2CN(C2H5)2]2. TETD was reduced to dithiocarbamate. The molecules are polymeric chains with HgBr2 and Hg2+ alternately bridging to dithiocarbamate ions and vice versa. The crystal is monoclinic: a = 10.421(7), b = 15.244(13), c = 14.649(8) Å, β = 113.3(1)°; space group P21/c. The final R factor for 2085 observed reflections is 0.083. There are two types of coordination geometries for the mercury(II) ions in the crystal: the coordination for one is digonal with two short Hg—S distances of 2.385(11) and 2.365(10) Å. The coordination for the other is tetrahedral with two Hg—S, 2.552(10) and 2.569(10) Å, and two Hg—Br, 2.640(4) and 2.552(7) Å, bonds. The average C=S distance is 1.72(4) Å.
Dielectric relaxation in 2-acetylnaphthalene and related compounds
Authors: Crossley J. , Mazid M. A. , McLellan C. K. , Mountain P. F. , Walker S.
Published: May 2006

The dielectric absorption of 2-acetylnaphthalene and 2- and 3-acetylphenanthrene has been studied in p-xylene solution at several microwave frequencies and in a polystyrene matrix at low frequencies. Acetyl group relaxation has been established from both sets of data. A clear separation of the dielectric absorption of the molecule and the group has been achieved for both 2- and 3-acetylphenanthrene in the matrix. The Eyring activation parameters have been established for acetyl relaxation in these molecules in the matrix. The free energy of activation values for group relaxation increase in the sequence acetophenone < 2-acetylphenanthrene < 3-acetylphenanthrene < 2-acetylnaphthalene. For the p-xylene solution data the weight factor for group relaxation, C2, is appreciably lower than the theoretical value, so that C2 < C1, bearing out the findings of Fong and Smyth for 2-acetylnaphthalene. In polystyrene matrices, the data for 2- and 3-acetylphenanthrene also indicated that C2 < C1. The enthalpy of activation for acetyl relaxation in 2- and 3-acetylphenanthrene is similar to that for acetophenone and 1,4-diacetylbenzene whereas that for 2-acetylnaphthalene would seem somewhat larger.
Pyrrole chemistry. XIX. Reactions of 2-pyrrolecarbonitrile and its 4-substituted derivatives
Authors: Anderson Hugh J. , Riche Cyril R. , Costello Thomas G. , Loader Charles E. , Barnett Graham H.
Published: May 2006

2-Pyrrolecarbonitrile has been acylated to its 4-formyl, trichloroacetyl, ester, and thiolester derivatives. Further reactions gave other 2,4-difunctionalized compounds. These included conversion of the 2-nitriles to the corresponding 2-aldehydes. Subsequent removal of the aldehyde group afforded several 3-substituted pyrroles in good yield.
Analyse des spectres de vibration de la β-alanine, de la taurine et de la ciliatine-β
Authors: Garrigou-Lagrange Chantal
Published: May 2006

Infrared and Raman spectra of solid β-alanine, taurine and ciliatine (β form) are analysed. A normal mode calculation is made. The given valence force fields of the three crystalline molecules are very similar. It shows the N—CαH2—CβH2— radical is electronically equivalent in the three molecules.
Competitive thermal and photochemical processes in cyclopropylketone rearrangements. I. Photolysis of spiro[n.2]alkan-2-ones
Authors: Lee-Ruff Edward , Khazanie Prabhakar Govind
Published: May 2006

The series of cyclopropyl ketones 1–6 was irradiated in methanol. Cyclopentanones 1 and 2 gave mainly products of type I reaction whereas ketones 3, 5, and 6 gave type II products. Formation of type II products can arise by two different mechanisms. One involves the intermediacy of a dienol which can be trapped with methanol-OD. Photochemical degradation of the cyclopentanones was slower than the corresponding cyclohexanones.
The effect of temperature on the optical spectra and the yields of solvated electrons and ion-pairs in amines
Authors: Seddon William Arthur , Fletcher John Wallace , Sopchyshyn Fred Charles
Published: May 2006

Optical absorption spectra for the solvated electron, es−, and ion-pairs, (Na+, es−), have been observed in methylamine (MA), ethylamine (EA), and isopropylamine (IPA), at temperatures ranging from 184 to 338 K. Changes in the (Na+, es−) spectra, relative to es−, are consistent with a gradual transition in the ion-pair structure toward a more 'electron-like' entity with decreasing temperature and increasing solvent polarity. Extinction coefficients, εmax(es−) = 3.3 ± 0.2, 3.2 ± 0.5, and 3.2 ± 0.5 × 104 M−1 cm−1 in MA, EA, and IPA respectively. Corresponding values for the ion-pairs, εmax(Na+, es−) = 2.5 ± 0.2, 2.1 ± 0.2, and 1.9 ± 0.2 × 104 M−1 cm−1.In EA and IPA, the yield [Formula: see text] (molecules/100 eV) shows a marked solute concentration dependence. This is consistent with an empirical scavenging model from which the escaped solvated G(es−)esc and spur G(es−)spur electrons are estimated as G(es−)esc = 0.5 and 0.4, G(es−)spur = 1.8 and 1.4, giving G(es−)total = 2.3 and 1.8 in EA and IPA, respectively. In MA, [Formula: see text] = G(es−)esc = 2.25 ± 0.2, independent of solute concentration.
A Poisson–Boltzmann treatment of the capacitance of a layer of symmetrical spherical dipoles
Authors: Dalrymple-Alford Penny , Oldham Keith B.
Published: May 2006

The capacitance of a layer of spherical orientable dipoles has been determined. The properties attributed to each dipole are those of two point charges on a diameter of the sphere and equidistant from its centre. A one-dimensional potential distribution is assumed to exist normal to the layer and to be coupled to the charge distribution via Poisson's law. The orientation of the dipoles is random in the absence of polarization, but is taken as governed by Boltzmannian statistics when an applied field is present. The treatment predicts that the capacitance will display a pronounced hump at the point of zero charge. Though this study was motivated by a wish to interpret the inner-layer capacitance at a mercury/aqueous electrolyte solution interface, the treatment is shown to be inapplicable quantitatively to such a system.
Crystal structure of dibromotetraethylthiuramdisulfidemercury(II)
Authors: Chieh Chung
Published: May 2006

Dibromotetraethylthiuramdisulfidemercury(II) is one of the products of the reaction between mercury(II) bromide and tetraethylthiuram disulfide (TETD). The crystals are orthorhombic with a = 13.050(5), b = 13.593(7), c = 22.373(12) Å; space group Pbca. The compound is isostructural with the iodo analogue. The final R factor using 1421 observed reflections is 0.10. Mean bond lengths are: Hg—Br = 1.504(6) Å, Hg—S = 2.66(1) Å. The coordination geometry for mercury(II) is tetrahedral.
Ligand exchange reactions of vanadium(III) β diketonate complexes
Authors: Nixon A. J. C. , Eaton D. R.
Published: May 2006

The kinetics of ligand exchange reactions of V(III) β diketonates have been studied. The replacement of acetylacetone by hexafluoroacetylacetone involves a rate law with both first- and second-order terms in the incoming ligand. The replacement of acetylacetone by deuteroacetyl-acetone involves terms zero-order and first-order in the incoming ligand. Both reactions are markedly catalyzed by acids and inhibited by bases. A mechanism involving a dangling ligand intermediate is suggested. The rates of ligand exchange are much less than the rates of isomerization.
7α-Acetoxydihydronomilin: isolation, spectra, and crystal structure
Authors: Ahmed Farid R. , Ng Angs , Fallis Alex G.
Published: May 2006

Methanol extraction of the ground seeds of Uncaria Gambier Roxb. followed by chromatography afforded a crystalline C30H38O10 terpene. This has been shown by X-ray analysis to be 7α-acetoxydihydronomilin. The crystals are orthorhombic, P212121, a = 13.158(2), b = 17.092(2), c = 12.689(2) Å, Z = 4, dx = 1.300, do = 1.300 g cm−3. The structure has been determined by the direct method and Fourier syntheses, and refined by block-diagonal least-squares to R = 0.042 for 2621 observed reflexions. The molecule contains a seven-membered lactone ring A, three six-membered rings B, C, D, a three-membered ring E, a furan ring F, and two acetate groups. A and B are chair, C is twist-boat, D is 1,3-diplanar, while E and F are planar. The A/B, A/C, C/D junctions are trans, D/E is cis, and F is linked to D by an equatorial C—C bond. The two acetate groups are in axial positions on A and B and are cis to each other. The O atom forming the apex of the three-membered ring is wedged between two H atoms and their parent C atoms at short intramolecular distances O … H = 2.28(2) and 2.28(3), and O … C = 2.623(3) and 2.668(4) Å. No intermolecular hydrogen bonding is indicated.
Bifunctionalized resins. Applications to the synthesis of insect sex attractants
Authors: Fyles Thomas M. , Leznoff Clifford C. , Weatherston John
Published: May 2006

A 2% crosslinked divinylbenzene–styrene copolymer, incorporating benzoyl chloride groups, was used to monoprotect the symmetrical diol 1,10-decanediol. The corresponding monotrityl ether and cis-10-tetradecen-1-ol were prepared by this system, the latter by a Wittig reaction of a polymer-bound ylide with an aldehyde in the solution phase. A series of bifunctionalized resins containing proximally located trityl alcohol and benzoic acid groups was prepared in an attempt to prepare diol linked to the polymer via both a trityl ether and a benzoate linkage. It was established that these polymers bound 1,10-decanediol exclusively at one end only. Polymers, containing both trityl alcohol and benzoic acid groups in a random array or polymers containing proximally located trityl alcohol groups, gave mixtures of both monoprotected and doubly protected diol.
The fluoroformate ion, FCO2−. An ion cyclotron resonance study of the gas phase Lewis acidity of carbon dioxide and related isoelectronic species
Authors: McMahon Terrance Brian , Northcott Colleen Joan
Published: May 2006

The gas phase ion molecule reactions of a number of potential fluoride donors with carbon dioxide and carbonyl fluoride have been studied. By determination of preferential directions of fluoride transfer the fluoride affinities of carbon dioxide and carbonyl fluoride have been bracketed and found to be 33 ± 3 kcal/mol and 35 + 3 kcal/mol respectively. In addition, from gas phase acidity studies of acetyl fluoride and 2-fluoropropene the fluoride affinities of ketene and allene have been calculated to be 38 ± 2 kcal/mol and 15 ± 2 kcal/mol respectively. The order of fluoride affinities (Lewis acidities) of carbon dioxide, ketene, and allene have been examined and explained in terms of the electron affinities of the F—C(A)(B) species (A,B=O,CH2) and the C—F bond dissociation energies. These quantities have been estimated and the latter interpreted on the basis of the π bond energies of the three compounds.
Heterogeneous metal-insertion: a novel reaction with porphyrins
Authors: Herrmann Otto , Mehdi S. Husain , Corsini Alfio
Published: May 2006

Metal complexes of water-soluble and other porphyrins have been prepared by a heterogeneous reaction with the metal reactant present in an insoluble form. The oxidation state of the metal is important in the reactions. Metal reactants in the lower oxidation states (0, I, II) react with porphyrins but those in the higher oxidation states (III, IV) do not. Metalloporphyrins of high purity may be conveniently prepared by this method.
Synthesis of 5- and 6-methylene-2-norbornanones
Authors: Werstiuk Nick Henry , Taillefer Roland
Published: May 2006

The syntheses of 4,4,6-trimethyl-5-methylene-2-norbornanone (5a), 6,6-dimethyl-2-methyl- ene-2-norbornanone (5b), 5-methylene-2-norbornanone (5c), and 6-methylene-2-norbornanone (11) are described. An unusual extended Grob-type cleavage of 6-ethylenedioxy-exo-2-methyl-endo-2-norbornanol (13d) to 2-chioroethyl (3-methyl-3-cyclopentenyl)acetate (17) is documented.
Biosynthesis of prodiginines. 13C resonance assignments and enrichment patterns in nonyl-, cyclononyl-, methylcyclodecyl-, and butylcycloheptylprodiginine produced by actinomycete cultures supplemented with 13C-labeled acetate and 15N-labeled nitrate
Authors: Gerber Nancy N. , McInnes A. Gavin , Smith Donald G. , Walter John A. , Wright Jeffrey L. C. , Vining Leo C.
Published: May 2006

Resonances in the 13C nmr spectra of nonylprodiginine, cyclononylprodiginine, methylcyclodecylprodiginine, and butylcycloheptylprodiginine were assigned using information from the literature, from high resolution spectra and double irradiation experiments, and from 13C–15N couplings observed in samples of nonylprodiginine enriched with 15N. Supplementation of cultures with sodium [1-13C]- and [1,2-13C]acetate gave 13C-enriched prodiginines and the labeling patterns were established from 13C nmr spectra. These indicated that rings A and B were formed in a similar manner to rings A and B in prodigiosin and other prodiginine pigments. Ring C and the C2-alkyl substituent were derived in part from acetate units that were condensed in a linear 12- or 14-carbon chain. The same pattern of acetate assembly has been found in ail actinomycete prodiginines examined.
The formation and structure determination of both acyclic and cyclic products in the reaction of sulfene and pyridines
Authors: Grossert J. Stuart , Bharadwaj Madan M. , Langler Richard F. , Cameron T. Stanley , Cordes Ruth E.
Published: May 2006

Sulfene, generated from methanesulfonyl chloride and triethylamine in acetonitrile reacts with itself to form a tetramer which may be isolated as an acyclic crystalline pyridinium sulfonate salt, 1. When sulfene is generated in tetrahydrofuran in the presence of pyridine, the 1,1,3,3-tetraoxide of 4,4a-dihydropyrido[1,2-d][1,5,2]dithiazine, 11, is formed. Structural evidence (including nmr and mass spectra) for these compounds, for homologs of 11, and for a series of acyclic polysulfonyl compounds derived from 1 is presented. An X-ray crystal structure determination was carried out on 9, the 5,7-dimethyl homolog of 11.
Excited state acid–base equilibrium of tyrosine
Authors: Rayner David Michael , Krajcarski Donald Theodore , Szabo Arthur Gustav
Published: May 2006

Fluorescence attributable to the tyrosinate form of the amino acid tyrosine, previously only observed at pH > pK(S0) = 10.3 where tyrosinate exists in the ground state, has been observed at neutral pH in the presence of high buffer base concentrations. This observation is consistent with the large shift in pK(Sl) predicted from absorption measurements and confirms that proton transfer is indeed a mechanism by which carboxylate ions quench tyrosine fluorescence. The dependence of the fluorescence quantum yields of tyrosine and tyrosinate on pH does not fit a simple excited state acid–base equilibrium model but a more complicated system where carboxylate is also capable of simultaneously quenching tyrosine fluorescence by a mechanism not involving proton transfer. Kinetic analysis of the system allows calculation of pK(S1) = 4.2 for tyrosine. The quantum yield of tyrosinate fluorescence can be appreciably higher than that normally measured at alkaline pH where a separate quenching mechanism must operate. These results have significance in the interpretation of the fluorescence properties of proteins.
Aqueous trifluoroacetic acid as a medium for organic reactions. II. The oxidation of hydrocarbons by manganese(VII)
Authors: Stewart Ross , Spitzer Udo A.
Published: May 2006

The oxidation of 11 alkanes, 4 cycloalkanes, and 10 arenes by potassium permanganate in aqueous trifluoroacetic acid has been studied. The reaction rates are approximately first order in hR, the antilogarithm of the acidity function −HR, and the active oxidant is believed to be MnO3+, either free or complexed. The rate of abstraction of primary, secondary, and tertiary hydrogen atoms in the C5H12 isomers is in the ratio 1:60:2100 and the rate per methylene in normal alkanes increases with increasing chain length. Cyclohexane is the least reactive of the cycloalkanes and the isotope effect in the oxidation of cyclo-C6D12 is 4.3 at 25 °C. The mechanism of oxidation of the aliphatic hydrocarbons is believed to be hydrogen-atom abstraction by MnO3+. The oxidation of arenes C6H5Z has a ρ+ value of −5.29 when appropriate σ+ values of Z are used, and there is no isotope effect when the reaction rates of C6H5CH3, C6H5CD3, and C6D5CD3 are compared. The mechanism of oxidation of the aromatic compounds is believed to be electrophilic attack of MnO3+ at the activated positions of the ring followed by rapid degradation of the ring system.
A study of 14N relaxation and nitrogen–proton spin coupling in nucleoside, indole, and ε-caprolactam systems through Fourier transform measurements of NH proton spin–lattice relaxation in the rotating frame
Authors: Moseley Michael Eugene , Stilbs Peter
Published: May 2006

Measurements of nitrogen-14 nuclear spin–lattice relaxation times and direct proton coupling constants are presented for a series of nucleosides and nucleoside bases and indole derivatives in DMSO-d6 and for a series of ε-caprolactam concentrations in CDCl3. The data were obtained through NH proton T1ρ measurements, a potentially useful alternative to direct 14N and 15N nuclear magnetic resonance for the study of e.g. NH hydrogen bonding.
Electron transport via metalloporphyrins
Authors: Johnson Eugene C. , Niem Tony , Doolphin David
Published: May 2006

The controlled potential electrolysis of Ni(II) meso-tetraphenylporphyrin (Ni(II)TPP) gives at room temperature the corresponding metalloporphyrin π-cation radical [Ni(II)TPP]+ •. Upon freezing a solution of the π-cation radical to 77 K an internal electron transfer occurs to give [Ni(III)TPP]+. A discussion of the routes of electron transport in heme proteins is given, and the roles of metalloporphyrin π-cation radicals in electron transport is evaluated.
Synthesis and nuclear magnetic resonance study of the compounds (2-X-1,3-dithiane) (X = H, Me, SiMe3, GeMe3, SnMe3, PbMe3) and their tetracarbonyliron complexes
Authors: Cane David J. , Graham William A. G. , Vancea Liviu
Published: May 2006

A series of (1,3-dithiane)Fe(CO)4 complexes, (2-X-1,3-dithiane)Fe(CO)4, X = H, Me, SiMe3, GeMe3, SnMe3, PbMe3, has been prepared and characterized, and both the complexes and the free ligands studied by 1H and 13C nmr spectroscopy. The energy barrier to ring inversion in (1,3-dithiane)Fe(CO)4, ΔG298†, is 14.7 ± 0.2 kcal mol−1, some 4.4 kcal mol−1 higher than in free 1,3-dithiane.13C nmr spectra showed that within the Fe(CO)4 moiety, rapid averaging of carbonyl groups occurs down to at least −80 °C.
Les fonctions de Hartree–Fock–Slater comme base pour des calculs de perturbation à un électron pour molécules. III. Le calcul de la première hyperpolarisabilité
Authors: Trsic M. , Laidlaw W. G.
Published: May 2006

Uncoupled Hartree–Fock–Slater first hyperpolarizabilities have been calculated for CO, CH4, HCHO, and CN−. Different basis sets have been tested for CH4 and CO.
Enthalpies of formation of crystalline selenium(IV) chloride and bromide
Authors: Westland Alan D. , Makhija Ramesh
Published: May 2006

Standard enthalpies of formation of crystalline selenium(IV) halides were determined by solution calorimetry relative to that of selenium(IV) oxide. The values obtained were: [Formula: see text] SeCl4(c), −42.7 ± 0.4 and [Formula: see text] −17.9 ± 0.5 kcal mol−1.
Etude structurale du fluorure de chloryle en phase solide
Authors: Tantot Georges , Joubert Philippe , Bougon Roland
Published: May 2006

Chloryl fluoride, ClO2F was studied in its solid phase by X-ray and neutron diffraction techniques and by vibrational spectroscopy.The powder diffraction patterns of ClO2F were indexed by comparison with ClF3. At 77 K, the parameters of the monoclinic cell of ClO2F are as follows: a = 8.85 ± 0.02 Å, b = 6.17 ± 0.02 Å, c = 4.62 ± 0.01 Ǻ, β = 95.0 ± 0.1°, Z = 4. This cell, which can be thought as arising from a slight monoclinic deformation of the orthorhombic cell of ClF3, is consistent with the density measurements also performed on ClO2F and ClF3.The space group [Formula: see text] was found to be the best compatible with both the vibrational data and the lines observed in the powder diffraction patterns for ClO2F in the polycrystalline state.
A theoretical study of the energies of solution, association, and migration for univalent substitutional anion impurities in alkali metal chloride crystals
Authors: Corish John , Parker Brenda M. C. , Jacobs Patrick W. M.
Published: May 2006

Theoretical calculations have been made of the energy change accompanying the substitution of a univalent anion, F−, Br−, or I−, into crystals of the alkali metal chlorides LiCl, NaCl, KCl, and RbCl. Association energies for the formation of nearest neighbour (nn) or next nn complexes with a vacancy in the anion sub-lattice and the activation energies for the four basic kinds of single vacancy jumps have also been calculated. The results of these calculations are discussed with respect to ion size and polarization effects and their relation to the activation energy (E′) for the diffusion of a univalent impurity in the host crystals. The availability of experimental values of E′ for some systems permits an assessment of the contribution to E′ from the temperature dependence of the correlation factor and from vacancy pair diffusion.
Oxidation of methyl glycopyranosides by Acetobactersuboxydans
Authors: Schnarr G. Wayne , Szarek Walter A.
Published: May 2006

A synthesis of methyl pentopyranosid-4-uloses bas been achieved by microbiological oxidation by Acetobacter suboxydans of some methyl pentopyranosides. The oxidation products were isolated as their O-methyloxime derivatives, and the assignment of the configuration of the oximes was made on the basis of the carbon-13 magnetic resonance spectra. An analysis of the oxidative specificity of A. suboxydans towards methyl glycopyranosides is presented.
Ligand exchange reactions between ferrocene and 9,10-dimethylanthracene
Authors: Sutherland Ronald G. , Pannekoek W. Jack , Lee Choi Chuck
Published: May 2006

The reaction of 9,10-dimethylanthracene (8) with ferrocene (FcH) in the presence of AlCl3–Al in decalin gave the stereospecifically hydrogenated product, η6-cis-(endo-9,10-dihydro)-9,10-dimethylanthracene-η5-cyclopentadienyliron cation (10a), the hydrogenation at C-9,10 being cis and endo or on the same side as the cyclopentadienyliron (CpFe) moiety. When cis-9,10-dihydro-9,10-dimethylanthracene, generated from 10a by photolysis or pyrolytic sublimation, was used as the arene in the ligand exchange reaction, complexing with the CpFe group could occur from either side of the ring system, giving rise to a mixture of 10a and the η6-cis-(exo-9,10-dihydro)-9,10-dimethylanthracene-η5-cyclopentadienyliron cation (10b). The η6-cis-9,10-dihydro-9,10-dimethylanthracene-trans-bis-η5-cyclopentadienyliron dication, with the two CpFe groups trans, was also prepared either from a stepwise ligand exchange using 10a or directly from reaction of 8 using an excess of FcH. A mechanism is proposed for the hydrogenation that has been found to accompany ligand exchange reactions between polycyclic arenes and FcH and possible applications are pointed out for the synthesis of partially hydrogenated polycyclic aromatic hydrocarbons.
Molecular activation analysis for methylmercury
Authors: Schmit J.-P. , Wiles D. R.
Published: May 2006

The principle of molecular activation analysis is described, as well as its unsuccessful application to the species specific determination of methylmercury in fish. The reasons for the failure of the method were determined and are found to be of significance to hot atom chemistry and to possible future use of this principle. The reasons are: (i) a matrix dilution of the species sought, (ii) a scavenging, probably of methyl groups, by serine or related components of fish powder, and (iii) a methylation by some unidentified component associated with the fish fats.
Chelates of nickel(II) and copper(II) with tridentate Schiff base formed by the condensation of S-benzyldithiocarbazate with benzoin
Authors: Tarafder M. T. H. , Ali M. Akbar
Published: May 2006

New complexes with the Schiff base ligand derived from S-benzyldithiocarbazate (NH2—NH—CSSCH2C6H5) have been prepared and characterized by elemental analyses, magnetic, conductometric, ir, and electronic spectral studies. The tridentate ONS Schiff base S-benzyl-β-N-(phenyl, phenylhydroxymethyl)methylenedithiocarbazate gave mono-ligand complexes with Ni(II) and Cu(II) having the general formula [MligandX] (M = Ni(II) and Cu(II); X = NO3, Cl, Br, NCS). A proposed square-planar structure for the nickel complexes is supported by magnetic and spectral data. A square-planar structure is also suggested for Cu(II) complexes. The ir results give evidence of the different bondings present in the complexes.
Synthesis and vibrational spectra of tin(II) isothiocyanate adducts with some O- and N-donor ligands
Authors: Absi Tewfik B. , Makhija Ramesh C. , Onyszchuk Mario
Published: May 2006

Five new adducts of Sn(NCS)2 have been prepared and characterized: Sn(NCS)2•2L (L = 2,6-dimethyl-y-pyrone and N,N-dimethylacetamide), Sn(NCS)2•LL (LL = 1,10-phenanthroline and 2,2′-bipyridine), and Sn(NCS)(ox) (ox = 8-hydroxyquinolinate). By comparing their infrared and Raman spectra with those of SnX2•L (X = Cl, NCS; L = triphenylphosphine oxide), SnX2•2L (X = Cl, NCS; L = dimethylsulphoxide and pyridine-N-oxide), SnCl2•LL (LL = 1,10-phenanthroline and 2,2′-bipyridine), and SnCl(ox), assignments have been made for v(CN), v(CS), and δ(NCS) vibrations; these suggest the presence of N-bonded and —NCS— bridge-bonded thiocyanate groups. Molecular weight, conductivity, and X-ray powder diffraction data support the conclusion that the adducts with the oxygen donor ligands are molecular with only N-bonded thiocyanate groups. Adducts with the bidentate nitrogen donor ligands are polymeric and have —NCS— bridging and N-bonded thiocyanate.
Metabolites of bird's nest fungi. Part 9. Diterpenoid metabolites of Cyathusafricanus Brodie
Authors: Ayer William A. , Yoshida Takashi , van Schie Dirk M. J.
Published: May 2006

The diterpenoid metabolites produced when the fungus Cyathusafricanus Brodie (Nidulariaceae) is grown in liquid culture have been examined. The known compounds cyathin A3 (1) and allocyathin B3 (2) were isolated along with four new diterpenoids which have been named cyafrin A4, cyafrin B4, allocyafrin B4, and cyafrin A5. The structures of these substances have been determined by chemical and physical methods to be 3a, 10a, 12a, and 15a, respectively. Cyafrin A4 (3a), allocyafrin B4 (12a), and cyafrin A5 (15a) have been correlated with cyathin A3 by chemical transformations. The absolute stereochemistry of cyathin A3 has been confirmed by the exciton chirality method.
Infrared and laser Raman studies of deuterated model membranes: Phase transition in 1,2-perdeuterodipalmitoyl-sn-glycero-3-phosphocholine
Authors: Sunder S. , Cameron D. , Mantsch H. H. , Bernstein H. J.
Published: May 2006

Raman and infrared spectra of multilayer dispersions of 1,2-perdeuterodipalmitoyl-sn-glycero-3-phosphocholine in water are studied as a function of temperature for the CD stretching region. It is found that the bands associated with these vibrations can be used as a sensitive probe to monitor the gel – liquid crystal phase transition which occurs at a lower temperature in the perdeuterated phospholipid than in the corresponding natural (light) lipid.
An internal coordinate model for molecular vibrations: the energy levels of H2O and H2S and related isotopic molecules
Authors: Bron Jan , Wallace R.
Published: May 2006

Refinement of a previously described model for describing the anharmonic vibrations of polyatomic molecules is presented. The nonlinear molecules XY2 (H2O, D2O, H2S, D2S) are used as examples and it is shown that quite good agreement with the observed spectrum can be obtained for the first twenty vibrational excitations with a six parameter potential function. Apart from its relative simplicity, the main improvement over previously reported work is the inclusion of the bending vibration within the formalism and refinement of the form of potential. It is pointed out that the model is readily extendable to the vibrational analysis of larger molecules.
Liquid crystal/glass interface effects on the orientation of lyotropic liquid crystals in magnetic fields
Authors: Fujiwara Fred Y. , Reeves Leonard W.
Published: May 2006

Lyotropic mesophases of both positive (type I) and negative (type II) diamagnetic anisotropy have been prepared. The deuterium magnetic resonance signal from D2O in the sample bas been studied during the process of orientation in a magnetic field. A type II mesophase oriented by a magnetic field in a cylindrical tube perpendicular to the lines of force does not achieve a uniform distribution of directors in a plane perpendicular to the field. The re orientation of a type I mesophase after an initial displacement of the director at an angle to the field has been studied. Previous equations derived for thermotropic liquid crystals are applicable but the velocity of re-orientation was found to be an inverse function of the radius, for nmr tubes of less than 4 mm in diameter, indicating that liquid crystal/glass interface effects are important.
A 19F nuclear magnetic resonance and Raman spectroscopic investigation of the reaction of iodine oxide pentafluoride with the Lewis acids, antimony and arsenic pentafluoride
Authors: Brownstein Morley , Gillespie Ronald J , Krasznai John P.
Published: May 2006

The reactions of IOF5 with SbF5 and with AsF5 have been investigated at low temperature by 19F nmr and Raman spectroscopy. It was found that SbF5 forms labile 1:1 and 2:1 complexes whereas AsF5 forms only a 1:1 complex. The IOF5 is bound through its oxygen atom to the Lewis acids AsF5, SbF5, or (SbF5)2.
The syntheses and properties of C-silylimines and their thermal rearrangements to N-silylenamines
Authors: Brook Adrian G. , Golino Carlo , Matern Eberhard
Published: May 2006

C-Silylimines have been synthesized by silylation of lithioaldimines prepared from isonitriles. Their ultraviolet and C=N infrared absorptions show bathochromic shifts relative to related aldimines or ketimines and the nmr spectra show the presence of syn–anti isomers, probably due to nitrogen inversion. The silylimines undergo intramolecular thermal rearrangements at about 200–235 °C yielding N-silylenamines, which have been characterized.
Concerning the spectra and solvation process of electrons in liquid butanols
Authors: Okazaki Kiyoshi , Freeman Gordon R.
Published: May 2006

The optical absorption spectra of electrons injected into the isomeric butanols settle into that of the equilibrium solvated state at rates that decrease in the order 1-butanol > isobutyl alcohol > 2-butanol at a given temperature. The relative rates reflect the dipolar reorientation times in the liquids. The Arrhenius temperature coefficients of the rates of spectral changes are ∼30 kJ/mol. The distribution of dipolar reorientation times overlaps that of geminate reaction times of the charges in an irradiated alcohol, so a significant fraction of the electrons undergoes geminate reaction before they are able to become fully solvated. At T < 200 K the fraction increases with decreasing temperature. The concurrence of the solvation process and geminate reaction implies that the former involves, at least in part, electron migration from shallower to deeper traps.There is an indication of structure in the absorption band at low temperatures and short times. The infrared peak converts to one with a maximum at ∼780 nm. The latter slides gradually into the shape of the spectrum of the equilibrium solvated state.For the spectra of the equilibrium solvated state, the energies at the absorption maxima are given by Eεmax (eV) = 3.10 − 0.0038T in isobutyl alcohol and 2.93 − 0.00447 in 2-butanol, between 170 and 300 K. The respective band widths at half heights are 1.53 ± 0.04 and 1.59 ± 0.04 eV, independent of temperature within an uncertainty of 1 meV/K.
Cadmium complexation by soil fulvic acid
Authors: Brady Bill , Pagenkopf Gordon K.
Published: May 2006

A soil fulvic acid bas been characterized and the complexation stability constants with cadmium have been evaluated. The average gram formula weight of the fulvic acid is 2775. Three complexes of stoichiometry CdFA, Cd2FA, and Cd3FA have been observed. The respective conditional stability constants at pH 5.7 are 105.3, 109.8, and 1014.0; at pH 6.7 they are 105.6, 1010.6, and 1015.5; and at pH 7.7 they are 106.0, 1010.7, and 1015.4.
Density and temperature effects on electron mobilities in gaseous, critical and liquid n-hexane, cyclohexane, and cyclopentane
Authors: Huang Sam S. -S. , Freeman Gordon R.
Published: May 2006

In the low density vapors the density normalized mobilities μn of thermal electrons decreased in the order n-hexane > cyclopentane > cyclohexane, although the differences were only ∼ 10%. The mobilities began to increase at electric field strengths E/n > 0.4 Td in cyclopentane, > 0.5 Td in cyclohexane and remained independent of field strength up to 1.5 Td in n-hexane. The ratio of the threshold drift velocity for electron heating to the speed of low frequency sound in the gas, υd(threshold)/c0 = 11 in cyclopentane, 14 in cyclohexane, and is > 35 in n-hexane; it increases with decreasing sphericity of the molecules. The electrons are cooled mainly by inelastic collisions with the hydrocarbon molecules. The temperature coefficients of mobilities in the low density gases increase as the molecules become more globular, which could reflect the participation of either low lying transient negative ion states or a Ramsauer–Townsend effect in the scattering processes. The normalized mobilities μn in the saturated vapors began to decrease at n = 4 × 1019 molecules/cm3 in n-hexane, 13 × 1019 in cyclohexane, and 30 × 1019 in cyclopentane. It appears that the minimum size of molecular cluster required for electron quasilocalization is smaller in n-hexane than in cyclohexane, and larger in cyclopentane. Electron localization interactions are weaker for more globular molecules.Mobilities in the critical fluids were 16 cm2/V s in n-hexane, 23 in cyclohexane, and 22 in cyclopentane.Mobilities in the liquids were independent of field up to the highest value used, which was 1.5 Td in the hexanes and 0.9 Td in cyclopentane. The mobilities and their temperature dependences were interpreted in terms of a model.
Heats of vaporization of monoalkylcyclohexanes by the gas chromatography – calorimetry method
Authors: Fuchs Richard , Peacock L. Alan
Published: May 2006

A recently developed empirical method for measuring beats of vaporization (ΔHv25) by a combination of gas chromatography and calorimetric heats of solution in the stationary phase has been applied to a series of 9 monoalkylcyclohexanes having C1–C12 side chains. The uncertainties in the measurements (0.07 – 0.23 kcal/mol) are critically evaluated. Comparison with literature ΔHv measurements indicates good agreement for low boiling compounds, and for high boiling compounds, values substantially more reliable than were previously obtained from vapor pressure measurements.
A revised structure for aubergenone, a sesquiterpenoid related to eudesmane: synthesis of 4-epi-aubergenone
Authors: Kelly Ronald B. , Alward Sandra J. , Murty K. Suryanarayana , Stothers J. B.
Published: May 2006

Syntheses of 4-epi-aubergenone, a sesquiterpenoid related to eudesmane, are described. One synthesis afforded this sesquiterpenoid as a racemate (12) whereas another, utilizing (+)-carissone as starting material, afforded an enantiomer (12a). The fact that naturally occurring aubergenone is the C(4) epimer of the thermodynamically more stable synthetic 12 was revealed by the discovery that it was completely converted into the latter by treatment with base. This epimeric relationship is substantiated by comparison of the nmr spectra of the two isomers. Evidence requiring the reformulation of the structure of aubergenone as 13 is adduced.
15N-Etioporphyrin I and its copper complexes: Proton and electron magnetic resonance characterization
Authors: Momenteau M. , Mispelter J. , Loock B. , Lhoste J. M.
Published: May 2006

15N-Etioporphyrin I was prepared by polycondensation of 5-hydroxymethylpyrrole-2-carboxylic acid, obtained via the Bullock route. This method gives an isomerically pure porphyrin with a high yield. The labelled compound was analyzed by nmr of the free base, of the dicationic form, and of the zinc complex. The spectrum of the free base shows a rapid tautomerism of the NH protons at 34 °C which disappears at low temperature. All spectra reveal several long-range proton—nitrogen-15 interactions. The electron spin resonance spectrum of the paramagnetic complex of this porphyrin with copper-63 is readily analyzed. This analysis was extended to the spectra of the complexes obtained with natural copper and with nitrogen-14 porphyrins.
Phase transformation studies on pure and K-doped Na2SO4
Authors: Murray Ritchie MacLaren , Secco Etalo A.
Published: May 2006

Phase transformation studies on pure Na2SO4 revealed four phases only; phase IV was not observed.Electrical conductivity measurements have been made on polycrystalline undoped and K-doped Na2SO4 and on single crystals of undoped Na2SO4. Kinetic measurements on II → III transformation in undoped Na2SO4 show rate of conversion to be time independent and inversely related to temperature.The presence of K in Na2SO4 effects a lowering of both the transition temperature and the enthalpy of transition along with an alteration from the "athermal" kinetic behavior to first-order kinetics.
Cyclitol analogs of biological interest. Regioselective nucleophilic substitutions of 1,4-cyclohexadiene bisepoxide and bisepisulfide
Authors: Haviv F. , Belleau B.
Published: May 2006

Reaction of cis-1,4-cyclohexadienebisepoxide with aluminium azide afforded the all-equatorial l,3-diazido-4,6-cyclohexanediol (2) through a metal-template mechanism. Hydrogenation of the product gave 2,5-dideoxystreptamine. Synthon 2 underwent normal coupling with 6-deoxy-6-azido-2,3,4-tris(O-benzyl)-α-glucosyl chloride and the resulting product gave the expected glucoside, a precursor of 5-deoxyneamine analogs. The cis- and trans-1,4-cyclohexadienebisepoxides were converted in good yields to the corresponding bisepisulfides and monoepoxide monoepisulfides. Regioselective opening of the cis-bisepisulfide with acetyl chloride and mercuric acetate by a metal-template mechanism led to stereochemically defined dithio analogs of cyclitols.