bluuebunny/crossref_metadata_2025 huggingface dataset:
Article
Authors: Barclay L Ross C , Grandy Jennifer K , MacKinnon Heather D , Nichol Heather C , Vinqvist Melinda R
Published: April 2011

3,5-Di-tert-butyl-ortho-quinone, 6, and 1-(3,4-dimethoxyphenyl-2-(2-methoxyphenoxy)-1-propanone, 7, models for oxidized lignin and for lignin, were used as sensitizers of photo-oxidation. Product studies by HPLC from oxidation of methyl linoleate in solution sensitized by 6 or 7, and in sodium dodecyl sulfate (SDS) sensitized by 6, showed a product distribution of six hydroperoxides, the four conjugated 9- and 13-hydroperoxides of the geometrical isomers: trans-10, cis-12 (2), cis-9, trans-11 (3), trans-10, trans-12 (4), and trans-9, trans-11 (5)-octadecadienoates plus two nonconjugated hydroperoxides. The higher cis/trans to trans/trans (ct/tt) of geometrical isomers (2 + 3//4 + 5) compared to ct/tt from known thermal free-radical peroxidations (Type 1) indicate that singlet oxygen (Type 2) oxidation occurs in reactions sensitized by 6 or 7. Kinetic studies by oxygen uptake are reported on oxidations of hydrocarbons 1-phenyl-2-methylpropene,8, and trans-stilbene,9, sensitized by the quinone, 6, or by a dye, Rose Bengal. Quenching studies imply singlet oxygen reactions. Milled wood lignin undergoes self-initiated photo-oxidation in water, and oxygen uptake was quenched by sodium azide. Cellobiose, a cellulose model, undergoes sensitized photo-oxidation using model quinone, 6, in a mixture of tert-butyl alcohol and water or using the sensitizers benzophenone or the lignin model, 7, delivered on a solid support, silica gel, and these oxidations were quenched with sodium azide. These results implicate singlet oxygen in the photo-yellowing of high lignin content wood pulps.Key words: lignin models, ortho-quinone, photo-oxidation, singlet oxygen, lignin, cellobiose.
Kinetics and mechanism of the reduction of CrVI to CrIII by D-ribose and 2-deoxy-D-ribose
Authors: Daier Verónica , Signorella Sandra , Rizzotto Marcela , Frascaroli María Inés , Palopoli Claudia , Brondino Carlos , Salas-Peregrin Juan Manuel , Sala Luis F
Published: April 2011

The oxidation of D-ribose and 2-deoxy-D-ribose by CrVI yields the aldonic acid and Cr3+ as final products when an excess of sugar over CrVI is used. The redox reaction occurs through CrVI–>CrIII and CrVI–>CrV–>CrIII paths. The complete rate laws for the CrVI oxidation reactions are expressed by -d[CrVI]/dt = kH[H+]2 [ribose][CrVI], where kH = (5.9 ± 0.1) × 10-2 mol-3 dm9 s-1, and -d[CrVI]/dt = (k0 + kH'[H+]2) [2-deoxyribose][CrVI], where k0 = (1.3 ± 0.5) × 10-3 mol-1 dm3 s-1 and kH' = (4.2 ± 0.1) × 10-2 mol-3 dm9 s-1, at 33°C. An intermediate sugar alkoxide radical could be trapped with DMPO and observed by EPR as a multiline signal at g = 2.003. CrV is formed in a rapid step by reaction of the sugar radical with CrVI. CrV reacts with the substrate faster than CrVI does. The EPR spectra show that five- and six-coordinate oxochromate(V) intermediates are formed, and the distribution of these CrV species in the reaction mixture essentially depends on the solution acidity.Key words: ribose, 2-deoxyribose, chromium, redox, mechanism, kinetics.
Heterocyclic aromatic amide protecting groups for aryl and phthalocyaninesulfonic acids
Authors: Li Zhaopeng , Lier Johan van , Leznoff Clifford C
Published: April 2011

Pyrroles, indole, imidazole, and a pyrazole were treated with 3,4-dibromobenzenesulfonyl chloride to form 3,4-dibromobenzenesulfonamides. The 1-(3,4-dibromophenylsulfonyl)pyrrole and 1-(3,4-dibromophenylsulfonyl)indole were stable to CuCN in DMF to produce 1-(3,4-dicyanophenylsulfonyl)pyrrole and 1-(3,4-dicyanophenylsulfonyl)indole, which upon treatment with ammonia in 2-N,N-dimethylaminoethanol gave the protected phthalocyanine-2,9,16,23- tetrasulfonamides. Base cleavage of these sulfonamides yielded the free acids. A mixed condensation of 4,5-diheptylphthalonitrile and 1-(3,4-dicyanophenylsulfonyl)pyrrole gave 9,10,16,17,23,24-hexakis(1-heptyl)-2-(1- pyrrolylsulfonyl)phthalocyanine. Cleavage of the latter yielded the lithium salt of the monosulfonic acid.Key words: sulfonic acid blocking groups, phthalocyanine sulfonic acids, 1-(3,4-dicyanophenylsulfonyl)pyrrole, 1-(3,4-dicyanophenylsulfonyl)indole.
The total synthesis of a technetium chelate - tamoxifen complex
Authors: Bell Russell A , Dickson Kieran C , Valliant John F
Published: April 2011

A potential agent for imaging breast cancer has been synthesized by derivatization of the anti-estrogen tamoxifen. A multistep synthesis was required to conjugate a technetium chelate to tamoxifen in such a fashion that the biodistribution of the complex should mimic that of the parent compound.Key words: tamoxifen, radioimaging, technetium, synthesis.
Remarkable kinetic stability of α-thiocarbamoyl substituted 4-methoxybenzylcations
Authors: McClelland Robert A , Licence Victoria E , Richard John P , Williams Kathleen B , Lin Shrong-Shi
Published: April 2011

4-Methoxybenzyl cations bearing α-(N,N-dimethylcarbamoyl) and α-(N,N-dimethylthiocarbamoyl) substituents have been generated photochemically upon irradiation of precursors with pentafluorobenzoate or 4-methoxybenzoate leaving groups. The ions have been observed with flash photolysis in 40:60 acetonitrile:water and in 50:50 methanol:water, and rate constants were measured for their decay in solvent alone and for their capture by azide ion. The cations so studied and their lifetimes in 40% acetonitrile are 6, ArC+H-CONMe2, 0.6 μs; 2, ArC+H-CSNMe2, 7 ms; and 4, ArC+(CH3)-CSMe2, 6 ms, where Ar = 4-MeOC6H4. The cation 4 reacts with solvent by elimination of a proton from the α-methyl group, and the rate constant for solvent addition must be less than 1 s-1. The CSNMe2 substituted cations are 105-107-fold longer lived than analogs where the thioamide group has been replaced with an α-methyl. The UV-visible absorption spectra of these two cations also show significant differences from those of typical 4-methoxybenzyl cations. Thus, both the lifetimes and spectra point to a strong interaction of the benzylic centre with the thioamide group. Key words: flash photolysis, thiocarbamoyl stabilized carbocation, photosolvolysis.
Reactions of (η5-C9H7)Rh(η2-C2H4)2 with quinones: molecular structure of [(η5-C9H7)Rh(2,3,5,6-C6O2(CH3)4)]
Authors: Westcott Stephen A , Taylor Nicholas J , Marder Todd B
Published: April 2011

Reactions of (η5-C9H7)Rh(η2-C2H4)2 (1) with quinones were investigated. Substitution of the labile ethylene ligands was observed upon addition of either duroquinone (2,3,5,6-tetramethyl-1,4-benzoquinone) or 1,4-benzoquinone to complex 1. The molecular structure of neutral (η5-C9H7)Rh(2,3,5,6-C6O2(CH3)4) (3), determined by X-ray diffraction, shows that the duroquinone ligand lies in a plane nearly parallel to the indenyl group. The carbonyl moieties of duroquinone lie in a plane incorporating Rh, C2, and the midpoint between C3a and C7a of the indenyl ring. The slip parameter (Δ= d(average Rh-C3a,7a) -d(average Rh-C1,3)) was calculated to be 0.112(2) Å; whereas a value of ca. 0.05 Å had been obtained previously from film data. Values for the hinge angle (HA = angle between normals to the least-squares planes defined by C1, C2, C3 and C1, C7a, C3a, C3) and fold angle (FA = angle between normals to the least-squares planes defined by C1, C2, C3 and C3a, C4, C5, C7, C7a) are 7.2° and 4.0°, respectively.Key words: indenyl, rhodium, quinones, ring-slippage, ground-state distortion.
A computational study on the sources of deuterium secondary kinetic isotope effects in carbocation-forming reactions
Authors: Muchall Heidi M , Werstiuk Nick H
Published: April 2011

Calculations at the HF-DFT hybrid Becke3LYP level of theory have been undertaken on protonated 2-exo- and 2-endo-norbornanols as model substrates for 2-exo- and 2-endo-norbornyl brosylates to explore the source of the experimentally determined deuterium secondary kinetic isotope effects (KIEs). Calculations on protonated alcohols as models reproduce the "normal" behaviour of 2-endo substrate 5. The observed endo γ-KIE in the 7-unsubstituted 2-exo system 4 is shown to arise from internal return, while those in the 7-chloro substituted 2-exo substrates 1 and 2 can be explained with competing 1,3 (6,2)-elimination.Key words: deuterium secondary kinetic isotope effects, 2-norbornyl cation, Becke3LYP.
Complete determination of the solid (RI)-liquid equilibria of four consecutive n-alkane ternary systems in the range C14H30-C21H44 using only binary data
Authors: Metivaud Valérie , Rajabalee Fazil , Oonk Harry AJ , Mondieig Denise , Haget Yvette
Published: April 2011

The liquidus surfaces and thermal windows of four ternary systems implying consecutive n-alkanes (for n between 14 and 21 carbon atoms) have been studied combining Differential Scanning Calorimetry (DSC), X-ray experiments, and calculation using the program Txy-CALC. From the DSC measurements, the transition temperatures as well as the melting enthalpies have been determined. X-ray experiments performed at temperatures just below melting have shown that there is almost complete syncrystallization in the rotator form RI. The calculation of the RI –> L liquidus surfaces has been made with temperature-independent as well as temperature-dependent excess Gibbs energies. In both cases, the agreement between experimental and calculated data is very good, the average temperature difference being within the uncertainty of the former.Key words: n-alkanes, ternary mixtures, liquidus and solidus surfaces, rotator phase, thermodynamic analysis.
Synthesis, characterization, and Cu(II) solution chemistry of dioxotetraazamacrocycles
Authors: Motekaitis Ramunas J , Sun Yizhen , Martell Arthur E , Welch Michael J
Published: April 2011

The synthesis and characterization of four new dioxotetraazamacrocycles: 1,4,8,11-tetraazacyclotetradecane-3,9-dione; 1,4,7,10-tetraazacyclotridecane-2,9-dione; 1,4,7,10-tetraazacyclotridecane-3,8-dione; and 1,4,7,10-tetraazacyclododecane-2,9-dione are described. Two related, previously prepared macrocycles, are included in this study: 1,4,8,11-tetraazacyclotetradecane-5,7-dione and 1,4,7,10-tetraazacyclotridecane-11,13-dione. The protonation constants, stability constants with Cu2+ ions, as well as electronic spectra of the di-deprotonated copper(II) complexes are also reported. These results are discussed in terms of the suitability of this new class of 62Cu, 64Cu, 67Cu complexes in PET imaging or radiotherapeutic applications. The synthetic schemes outlined provide a study of the relative Cu2+ behavior with a family of positional isomers of unsubstituted dioxotetraazamacrocycles.Key words: multidentate ligand, tetraazamacrocyclic compound, dioxopolyaza macrocycles, cyclic amides, copper(II) complexes.
Classical variational rate theory portraits of the dynamical stereochemistry of the F + H2> FH + H reaction
Authors: Rutenburg Irina , Koeppl Gerald W
Published: April 2011

A general classical variational theory of reaction rates is applied to the F + H2→> FH + H reaction. The variational theory gives the rate as the equilibrium flux of phase points through a trial surface which divides reactants from products and is varied to obtain a least upper bound for the rate. This dividing surface (DS) is defined by a power-series expansion of the H-H internuclear separation (r) in internal coordinates R and θ, i.e., r = F(R, θ) where R is the approach coordinate and θ is the orientation angle. The downhill simplex algorithm is used to search the space of 6 and 10 variational parameters of second- and third-order expansions of the DS and obtain minimum values for the canonical rate constant or, in the microcanonical formulation of the theory, the energy-dependent mean reaction cross section. The presence of angle-dependent terms in the DS makes it possible to describe the dynamical stereochemistry of atom-diatom reactions in a new and useful manner. Portraits of the dynamical stereochemistry are obtained by plotting contours of the density of reaction systems on the DS; such plots are reactivity relief maps of the DS. Reactivity relief maps show how the field of reactivity which surrounds the diatomic reactant molecule expands with increasing temperature and energy. Results are presented here for a new power series formulation of the DS which obeys a condition: δF(R, θ)/δθ = 0 at θ = π/2 which is appropriate for reaction of a homonuclear diatomic molecule. The relationship between reactivity relief maps obtained using quadratic and cubic formulations of the new DS and the locations of angle-dependent energy barriers for reaction is described. Variational and classical mechanical trajectory results are used to show how energy-dependent factors, which correct the variational mean reaction cross section for trajectories which cross and recross the DS, depend on the orientation angle. Key words: variational, transition, rate, dividing, surface.
The effect of metal ions on the reaction of hydrogen peroxide with Kraft lignin model compounds
Authors: Sun Yujun , Fenster Michael , Yu Annie , Berry Richard M , Argyropoulos Dimitris S
Published: April 2011

Peroxide bleaching is significantly affected by transition and alkaline earth metals. Isolating the effects of different transition and alkaline earth metals on the reactions of peroxide with different representative lignin structures allows the separation of the positive from the negative contributions of these metal ions. In this work, five monomeric or dimeric phenolic lignin model compounds were treated with alkaline hydrogen peroxide in the absence or presence of Mn2+, Cu2+, Fe3+, and Mg2+. We followed the disappearance of the starting material and the progress of demethylation, radical coupling and oxalic acid formation were followed. Transition metals increased the reactivities of all the lignin model compounds with hydrogen peroxide in the order Mn2+> Cu2+> Fe3+, which is the same as the order of activity toward peroxide decomposition while Mg2+stabilized the system. Demethylation, radical coupling, and oxalic acid formation were all increased by the presence of transition metals in the system and decreased by the addition of Mg2+. The acceleration of the total degree of reaction and of the demethoxylation reactions improves peroxide bleaching, but the increase in the radical coupling reactions can affect the further bleachability of pulp while the increase in the formation of oxalic acid could lead to a greater probability of scaling.Key words: lignins, hydrogen peroxide, peroxide bleaching, reactivity, chemical pulps, metal compounds, alkali treatment, transition metals, delignification.
Acid-catalyzed decomposition of diazodiphenylmethane in dimethylsulfoxide
Authors: Eliason Robert
Published: April 2011

Acid-catalyzed decomposition of diazodiphenylmethane (DDM) has been studied in DMSO containing varying amounts of water. The reaction was found to be first-order in DDM and first-order in acid. The Brønsted plot for a series of carboxylic acids is curved with the H+ point falling below the curve defined by the carboxylic acids. In near-anhydrous DMSO, kinetic hydrogen isotope effects (KIEs) are 1.7 and 1.6 for acetic acid and chloroacetic acid, respectively. The chloroacetic acid KIE increases with increasing water concentration, rising to 2.9 at 3.6 M water. As a function of [H2O], kHA for chloroacetic acid shows a sharply defined minimum occurring at 1 M water. This behavior and the water effect on KIE suggest that the carboxylic acid-catalyzed reactions in near-anhydrous DMSO do not use the ASE-2 mechanism attributed to the reaction of DDM in hydroxylic solvents. A mechanism, leading to an azoalkane, is suggested. Either directly or indirectly, this may lead to diphenylcarbene, which would account for the observed products: benzophenone, benzhydrol, and benzhydryl esters. For the H+ catalyzed decomposition of DDM in near-anhydrous DMSO, benzophenone is not found among the products, and we suggest that this reaction does not undergo a change in mechanism and continues to use the ASE-2 mechanism.Key words: decomposition mechanism, kinetics, solvent effect, reaction with carboxylic acids.
Estimation of hydrocarbon types in light gas oils and diesel fuels by ultraviolet absorption spectroscopy and multivariate calibration
Authors: Wentzell Peter D , Andrews Darren T , Walsh Jennifer M , Cooley Jean M , Spencer Paige
Published: April 2011

Ultraviolet absorption spectra are used in conjunction with multivariate calibration methods to predict the percent content of saturates (61-99%), monoaromatics (1-34%), diaromatics (0-5%), and polyaromatics (0-1%) in light gas oil and diesel fuel samples. A total of 114 samples taken from three pilot plant studies between 1992 and 1994 were used to develop the calibration models. Supercritical fluid chromatography with flame ionization detection was employed as the reference method for quantifying hydrocarbon types. Several multivariate calibration methods (classical least squares, multiple linear regression, principal components regression (PCR), and partial least squares (PLS)) were examined. PCR and PLS gave the best overall performance, with root-mean-squared errors of prediction (absolute) of 0.9% (saturates), 0.8% (monoaromatics), 0.2% (diaromatics), and 0.05% (polyaromatics) based on 44 prediction samples. Relative errors (absolute × 100/range) for these same species were 2.4%, 2.4%, 3.2%, and 5.3%.Key words: light gas oil, diesel, hydrocarbon content, UV spectroscopy, multivariate calibration, aromatics, petroleum.
Ketonization equilibria of phenol in aqueous solution
Authors: Capponi Marco , Gut Ivo G , Hellrung Bruno , Persy Gaby , Wirz Jakob
Published: April 2011

The two keto tautomers of phenol (1), cyclohexa-2,4-dienone (2) and cyclohexa-2,5-dienone (3), were generated by flash photolysis of appropriate precursors in aqueous solution, and the pH-rate profiles of their enolization reactions, 2 –> 1 and 3 –> 1, were measured. The rates of the reverse reactions, 1 –> 2 and 1 –> 3, were determined from the rates of acid-catalyzed hydron exchange at the ortho- and para-positions of 1; the magnitude of the kinetic isotope effect was assessed by comparing the rates of hydrogenation of phenol-2t and -2d. The ratios of the enolization and ketonization rate constants provide the equilibrium constants of enolization, pKE(2, aq, 25°C) = -12.73 ± 0.12 and pKE(3, aq, 25°C) = -10.98 ± 0.15. Combination with the acidity constant of phenol also defines the acidity constants of 2 and 3 through a thermodynamic cycle. These ketones are remarkably strong carbon acids: pKa(2) = -2.89 ± 0.12 and pKa(3) = -1.14 ± 0.15. They disappear by proton transfer to the solvent with lifetimes, τ(2) = 260 μs and τ(3) = 13 ms, that are insensitive to pH in the range from 3-10.Key words: proton transfer, tautomers, flash photolysis, kinetic isotope effect, pH-rate profiles.
An ab initio study on the magnetic susceptibility and magnetically induced current density distribution of the bicyclo[3.2.1]octa-3,6-dien-2-yl anion
Authors: Werstiuk Nick Henry , Ma Jiangong
Published: April 2011

The molecular susceptibility and the atomic contributions including the basin and surface components calculated at the RHF/6-31+G(d)//6-31+G(d) level of theory along with vector current densities obtained at the 6-31++G(d,p)//6-31+G(d) and 6-31+G(d)//6-31+G(d) levels are reported for benzene (1) and correlated - the agreement is excellent - with the results obtained by Keith and Bader with the 6-311++G(2d,2p) basis. This validates our similar studies on the bicyclo[3.2.1]octa-3,6-dien-2-yl anion (2) - initially considered to be a bishomoaromatic species - its parent hydrocarbon bicyclo[3.2.1]octa-2,5-diene (3), the bicyclo[3.2.1]oct-3-ene-2-yl anion (4), and 5, the lithium complex of 2. While a magnetic susceptibility exhalation is found in going from 4 to 2, the increase in atomic surface contribution to Δχ arises predominately (42.6%) from the ethenyl bridge carbons C6 and C7, with C2 + C4 and C3 exhibiting substantially smaller increases (27.4 and 8.3%, respectively). This result, in conjunction with the nature of the vector current density maps of 2 and 4, provides further evidence that 2 does not possess a ring current as depicted in 2-bh, the usual representation of "bishomoaromatic" 2.Key words: ab initio calculations, IGAIM, CSGT, magnetic susceptibility, induced current density distributions, bicyclo[3.2.1]octa-3,6-dien-2-yl anion.
Electrochemistry of 1,2,5-thiadiazole 1,1-dioxide derivatives with 3,4 substituents presenting separated, connected, and fused Pi-systems
Authors: Svartman Esther Lea , Caram José Alberto , Mirífico María Virginia , Vasini Enrique Julio
Published: April 2011

The voltammetric electroreduction properties of 1,2,5-thiadiazole 1,1-dioxide derivatives with different 3,4 substituents have been investigated in aprotic (mainly acetonitrile) solvent solution. The 3,4 substituents, selected according to the characteristics of their π-system, were phenanthro-9,10 (connected π-system) and acenaphtho-1,2 (fused π-system). New measurements are also presented for 3,4-diphenyl (separated π-systems). The basic properties of the substrates were investigated through voltammetry in acidic acetonitrile solutions. The substrates were more easily electroreduced (between -0.6 and -1.0 V vs. Ag/Ag+, acetonitrile solvent) than the parent (non-1,1-dioxide) heterocycles (which are electroreduced at ca. -2.5 V). They were also more easily electroreduced (by ca. 0.4 V) than the corresponding diketones (benzil, 9,10-phenanthrenequinone, and acenaphthenequinone). The influence on voltammetric behavior of the electron-withdrawing properties of the 1,2,5-thiadiazole 1,1-dioxide ring and that of the structure of the molecules was analyzed in light of previous structural studies by X-ray crystallography and theoretical chemistry calculations. Bulk electrolysis experiments in acidic acetonitrile solutions of the phenanthro[9,10-c] derivative produced its previously unreported dihydrogenated derivative (thiadiazoline), which oxidizes easily. Infrared spectroscopy data suggested that the structure of this compound differs from that of 3,4-diphenyl-1,2,5-thiadiazoline 1,1-dioxide.Key words: organic electrochemistry, 1,2,5- thiadiazoles, structure-reactivity relations.
Reactions of aryl sulfides and phosphorus(V) esters of thiols with acidic hydrogen peroxide
Authors: Bunton Clifford A , Foroudian Houshang J , Gillitt Nicholas D , Kumar Anurag
Published: April 2011

Oxidations of sulfides and phosphorus(V) esters of thiols by H2O2 are catalyzed by H2SO4 and HClO4. Sulfides are 4-ZC6H4SMe, 1a-1e, respectively, Z = MeO, Me, H, Cl, NO2; PhSCH2CH2Cl, 2, Ph2S, 3, and the esters are Ph(R)PO·SEt, 4a, 4b, R = Ph, EtO. Electron donation by Z moderately accelerates reaction, but the sulfides are much more reactive than the esters. Reactions are first order in H2O2 and substrate, and second-order rate constants, k2, in H2SO4 are related to excess acidity, X. Plots of log k2 against X have slopes in the range 0.61-0.85. Rate constants are similar for given concentrations of H2SO4 and HClO4, except that with greater than 50 wt.% H2SO4 peroxymonosulfuric acid is formed and the observed rate constants then increase. Methanesulfonic acid is a less effective catalyst than the mineral acids. Oxidations of the sulfides are also catalyzed by strongly acidic ion-exchange resins.Key words: sulfide oxidation, hydrogen peroxide, acid catalysis, excess acidity.
Oxidative dealkylation of aromatic amines by "bare" FeO+ in the gas phase
Authors: Brönstrup Mark , Schröder Detlef , Schwarz Helmut
Published: April 2011

The gas-phase oxidations of aniline, N-methylaniline, and N,N-dimethylaniline by FeO+ cation are examined by using mass spectrometric techniques. Although bare FeO+ is capable of hydroxylating aromatic CH bonds, the fate of the oxidation of arylamines is determined by docking of the FeO+ unit at nitrogen. The major reactions of the metastable aniline/FeO+ complex are losses of molecular hydrogen, ammonia, and water, all involving at least one N-H proton. N-alkylation results in a complete shift of the course of the reaction. The unimolecular processes observed can be regarded as initial steps of an oxidative dealkylation of the amines mediated by FeO+. More detailed mechanistic insight is obtained by examining the CH(D) bond activation of N-methyl-N-([D3]-methyl)aniline by bare and ligated FeO+ species. The gas-phase reactions of FeO+ with methylanilines show some similarities to the enzymatic dealkylation of amines by cytochrome P-450. The kinetic isotope effects observed experimentally suggest an electron transfer mechanism for the gas-phase reaction.Key words: mass spectrometry, gas-phase chemistry, iron, dealkylation, N,N-dimethylaniline.
Biotransformation of organic sulfides. Part 12. Conversion of heterocyclic sulfides to chiral sulfoxides by Helminthosporium sp. NRRL 4671 and Mortierella isabellina ATCC 42613
Authors: Holland Herbert L , Turner Carl D , Andreana Peter R , Nguyen Doan
Published: April 2011

The enantioselective oxidation of a series of heterocyclic prochiral sulfides to chiral sulfoxides has been examined using the fungal biocatalysts Helminthosporium species NRRL 4671 and Mortierella isabellina ATCC 42613. Methylthiofuranyl and -thiophenyl substrates gave (S)-configuration products in low to moderate enantiomeric purity on biotransformation with H. species, but pyridyl sulfides with the nitrogen atom located at an optimal distance of 8-10 Å from the sulfur centre gave (S) sulfoxides of high enantiomeric purity. The biotransformation of appropriately substituted benzothiane substrates by M. isabellina also gave products of high enantiomeric purity, but with (R) configuration at sulfur. The acceptability of the substrate and the configuration of sulfur oxidation by both H. species and M. isabellina for the range of substrates examined were found to be consistent with predictions based on cubic space models for these oxidations.Key words: bioconversion, biotransformation, Helminthosporium, Mortierella isabellina, sulfide, sulfoxide.
How does organic structure determine organic reactivity? The effect of ortho-dimethyl groups on the nucleophilic substitution and alkene-forming elimination reactions of ring-substituted cumyl derivatives
Authors: Amyes Tina L , Mizerski Tadeusz , Richard John P
Published: April 2011

The addition of a pair of ortho-methyl groups to ring-substituted cumyl derivatives to give the corresponding 2,6-dimethylcumyl derivatives X-1-Y leads to modest (<5-fold) changes in the observed rate constant for reaction in 50:50 (v:v) trifluoroethanol-water (I = 0.50, NaClO4). The reactions of X-1-Y proceed by a stepwise mechanism through the liberated 2,6-dimethylcumyl carbocations X-2 that partition between nucleophilic addition of solvent and deprotonation to give good yields ([Formula: see text] 67%) of the corresponding 2-(2,6-dimethylaryl)propenes X-3. The carbocations X-2 are also trapped by nucleophilic addition of azide ion to give good yields ([Formula: see text] 68% at [N3-] = 0.50 M) of the corresponding 2,6-dimethylcumyl azides X-1-N3. In the presence of high concentrations of azide ion there are constant limiting yields of the alkenes X-3, which shows that X-2 also undergo significant reactions with azide ion as a Brønsted base. The product rate constant ratios for partitioning of the 2,4,6-trimethylcumyl carbocation Me-2 between reaction with azide ion as a Lewis and a Brønsted base, kaz/kB, the nucleophilic addition of azide ion and solvent, kaz/ks (M-1), and deprotonation by solvent, kaz/ke (M-1), were combined with (kaz + kB) = 5 × 109 M-1 s-1 for the diffusion-limited reaction of azide ion to give absolute rate constants for the reactions of Me-2. The data show that the addition of a pair of ortho-methyl groups to the 4-methylcumyl carbocation to give the sterically hindered Me-2 results in a 70-fold decrease in the rate constant for nucleophilic addition of solvent to the benzylic carbon, but a 60-fold increase in the rate constant for deprotonation of the carbocation by solvent.Key words: carbocation, ortho-substituent effects, steric effects, solvolysis, elimination.
Solubility of diphenyl sulfone in organic nonelectrolyte solvents. Comparison of observed versus predicted values based upon the general solvation model
Authors: Fletcher Kristin A , Hernández Carmen E , Roy Lindsay E , Coym Karen S , Acree, Jr. William E
Published: April 2011

Experimental solubilities are reported for diphenyl sulfone dissolved in 8 alkane, 10 alcohol, and in aqueous solvent media at 25°C. Results of these measurements are used to test the predictive ability of the general solvation model log CA,orgsat/CA,aqsat = c + rR2 + sπ2H + aΣα2H + bΣβ2H + vVxwhere CA,orgsat and CA,aqsat refer to the solute solubility in the organic solvent and in water, respectively, R2 is the solute's excess molar refraction, Vx is the McGowan characteristic volume of the solute, π2H denotes the solute's dipolarity/ polarizability, and Σα2H and Σβ2H are the overall hydrogen-bond acidity and basicity descriptors for the solute. The remaining symbols in the above expression are known solvent coefficients, which have been determined previously through regressional analysis of published organic solvent - water partition coefficient and vapor-liquid equilibrium data. Computations show that the general solvation model predicts the solubility behavior of diphenyl sulfone in the 11 organic solvents for which predictions could be made to within an overall average absolute deviation of about ±20%. Key words: diphenyl sulfone solubilities, organic solvents, solubility predictions, general solvation model.
Electrocatalytic hydrogenation of 4-phenoxyphenol on active powders highly dispersed in a reticulated vitreous carbon electrode
Authors: Dabo Pierre , Cyr André , Lessard Jean , Brossard Louis , Ménard Hugues
Published: April 2011

Electrodes consisting of particles of a transition metal entrapped and dispersed in a reticulated vitreous carbon (RVC) matrix were prepared in situ by stirring the particles in the presence of an RVC cathode. Such electrodes were used for the electrocatalytic hydrogenolysis (ECHsis) of 4-phenoxyphenol, a compound representative of the 4-O-5 type linkage in lignins. The electrolyses were carried out under galvanostatic control in aqueous 1 M NaOH. Raney nickel, nickel boride, and transition metals supported on activated charcoal or alumina were used as catalytic powders. The extent and efficiency of the ECHsis of 4-phenoxyphenol was found to depend on the catalyst and on the temperature.Key words: electrocatalytic hydrogenation, electrocatalytic hydrogenolysis, 4-phenoxyphenol, Raney nickel, palladium on charcoal, palladium on alumina.
Stereospecific thionation of 2-ethoxy-1,2-oxaphosphorinane 2-oxide and its derivatives with Lawesson's reagent
Authors: Polozov Alexandre M , Cremer Sheldon E , Fanwick Phillip E
Published: April 2011

The parent phostone, 2-ethoxy-1,2-oxaphosphorinane 2-oxide 1, and derivatives with substituents at the 3-position (methyl, phenyl, and benzyl; compounds 2-4) were converted with Lawesson's reagent to provide the corresponding sulfide analogues 5-8 in moderate yields. The conversion of 2-4 occurred with retention of configuration at the phosphorus center. This was implied from the relative Rfvalues and13C and31P NMR chemical shifts of the individual isomers and confirmed for the transformation of 3b to 7b by X-ray structures of each of these. Oxidation of 7b, 8a, and 8b with m-chloroperoxybenzoic acid alone led to the corresponding oxides 3b, 4a, and 4b with retention. The presence of trifluoroacetic acid during this oxidation process led to varying degrees of epimerization about phosphorus and was dependent on the relative molar equivalents of this acid.Key words: 2-ethoxy-1,2-oxaphosphorinane 2-oxide, 2-ethoxy-1,2-oxaphosphorinane 2-sulfide, phostone, thiophostone, Lawesson's reagent, stereoselective synthesis, X-ray diffraction.
Mechanism of silylene extrusion reaction in cyclic polysilane via triplet energy surface: a direct MO dynamics study
Authors: Tachikawa Hiroto , Yamada Yoshihisa , Iyama Tetsuji
Published: April 2011

Dynamics of photoreaction of permethylcycloheptasilane (Me2Si)7 on the triplet state surface, (Me2Si)7 (T1) →> (Me2Si)6 + Me2Si (T1), has been investigated by means of the direct MO dynamics method in order to elucidate mechanism of silylene extrusion from the Si-ring following the triplet energy transfer from a carbonyl compound. Full dimensional potential energy surface calculated at the PM3 method was employed in the dynamics calculation: the total energy and energy gradient on each atom were calculated at each time step during the reaction. The calculations showed that the seven-membered Si-ring is spontaneously changed to the six-membered ring without activation barrier on T1 surface. The photoreaction of (Me2Si)7 is significantly fast (reaction is completed within 1.0 ps), although heavy molecule (silylene radical) is dissociated. This is due to the fact that the T1 surface is strongly repulsive for the coordinate between the silylene and the Si-ring. The mechanism of the silylene extraction from the Si-ring was discussed on the basis of theoretical results.Key words: direct MO dynamics, polysilane, photoreaction, permethylcycloheptasilane, silylene.
Étude du système U-Sr-O par diffraction X à haute température
Authors: Pialoux André , Touzelin Bernard
Published: April 2011

High-temperature X-ray diffraction (293 [Formula: see text] T(K) [Formula: see text] 1773) is used to investigate the reaction between strontium monoxide and uranium dioxide under controlled atmosphere (105 [Formula: see text] [Formula: see text] (Pa) [Formula: see text] 10-24), with lattice parameter measurements and composition estimates of the different uranates obtained. Thus, with a Sr/U = 1 sample, we successively observe the phases: (a) orthorhombic α-"SrUO4", whose reduction (3.67 [Formula: see text] O/U [Formula: see text] 3.62) is shown by a constant volume of the cell (V = 0.367 nm3) between 1173 et 1373 K; (b) rhombohedral β-"SrUO4", which shows a large composition variation between the metastable oxidized form (β-SrUO3.60) below 1108 K and the stable conjugate reduced form (β'-SrUO3.11) at whatever temperature; (c) "SrUO3" of constant composition (O/U [Formula: see text] 3) between 293 and 1533 K, then variable (O/U < 3) above 1533 K, with a probable second-order transformation (α-Pnma, β-Imma) for this distorted perovskite near 1073 K; (d) fluorite type U1-δSrδO2-δ solid solution for which a maximal account in SrO (δ [Formula: see text] 0.25) induces a 0.5 % thermal expansion parameter in comparison with UO2.00. A pseudo-binary "SrUO3"-"SrUO4" phase diagram is propounded. With a sample compound of Sr/U = 3, the monoclinic "Sr3UO6" perovskite is stable under [Formula: see text] [Formula: see text] 105 Pa up to 1373 K. On the other hand, in reducing atmosphere ([Formula: see text] [Formula: see text] 10-19 Pa), it becomes orthorhombic "Sr3UO5" with much greater lattice constants at every temperature.Key words: high-temperature X-ray diffraction, reactivity in metallic oxides, U-Sr-O system, nuclear fuels.
Kinetic and equilibrium studies of the acid dissociation of the cobalt(II) complexes of N,N'-dialkyl- 1,10-phenanthroline-2,9-dimathanamine ligands
Authors: Sun Hongwei , Zhou Zhifen , Lin Huakuan , Zhao Guanghua , Zhu Shourong , Su Xuncheng , Chen Yunti
Published: April 2011

The complexation property and the acid dissociation kinetics of four N,N'-dialkyl-1,10-phenanthroline-2,9-dimathanamine complexes with cobalt(II) were studied using a pH meter and a stopped-flow spectrophotometer. In 6.6 × 10-3~0.5 mol dm-3 HCl (I = 0.5 mol dm-3 HCl + NaCl), the dissociation rate follows the law kobs = kK2[H+]/(1 + K2[H+]). The acid dissociation can be rationalized in terms of a four-step kinetic process involving two rapid pre-equilibrium protonations and rate-determining cleavage of the Co(II)-N(phenanthroline) bond. The temperature dependence of the rate was determined, and the appropriate thermodynamic parameters were obtained. The linear relationship between ΔH not equal and ΔS not equal suggests that an isokinetic temperature, Tiso of 282 ± 2 K exists. Key words: N,N'-dialkyl-1,10-phenanthroline-2,9-dimathanamine, complexation property, acid dissociation kinetics, mechanism, cobalt(II) complex.
Determination of trace silicon in zirconium matrices and steels by inductively coupled plasma – atomic emission spectrometry
Authors: Choi Kwang-Soon , Joe Kih-Soo , Mitchell Steven L , Everall Candace J , Betty Keith R
Published: April 2011

The determination of trace silicon by inductively coupled plasma - atomic emission spectrometry in samples containing HF is inhibited by the high blank caused by attack of the quartz torch. Use of a proprietary commercial amine to neutralize the HF and increase the pH to between 7 and 7.5 allows the simultaneous determination of silicon and other impurities in zirconium or zircaloy samples. The determination of silicon in steels requires the addition of an auxiliary complexing agent to the amine solution to prevent precipitation of iron(III). The analytical results obtained for several Standard Reference Materials (SRMs) with and without the amine reagent agree well with one another, and also with the certified values.Key words: silicon, zirconium, zirconium alloys, steel, amine neutralization.
Tris{(diphenylphosphino)dimethylsilyl}methane: a sterically hindered tripod
Authors: Friesen Dawn M , McDonald Robert , Rosenberg Lisa
Published: April 2011

The synthesis and characterization of a new tripodal tris(phosphine) molecule, HC(Me2SiPPh2)3(3) is described. The impact of dimethylsilyl "elbows" on the conformational preferences of this tris(dimethylsilyl)methane core in solution and in the solid state was assessed for 3 and its precursor HC(Me2SiBr)3(2). Hindered rotation around the "arms" of 3, evident from its solid state structure, has been probed in solution by variable temperature,1H{31P} NMR spectroscopy, and molecular modelling studies based on the solid state structure of 2 also indicate significant barriers to rotation in this molecule. The susceptibility of 3 to cleavage of the P-Si bonds by protic reagents is described.Key words: tripodal tris(phosphine), polyphosphine, trisilylmethane, C3-symmetry.
1999 Pure or Applied Inorganic Chemistry Award Lecture Curves in chemistry: supramolecular materials taking shape
Authors: Ozin Geoffrey A
Published: April 2011

A large part of the development of mathematics was driven by the desire to understand why objects in nature are found in a myriad of shapes and sizes and why certain forms are preferred over others. The area of mathematics called the calculus of variations has been utilized to handle the optimal forms in geometry and nature. It has been used to comprehend morphogenesis and the similarity, yet variety, of forms in the natural world. The mathematical underpinnings of natural form are beginning to influence the inorganic materials world, especially the unusual morphologies that arise in the field of self-assembly. These morphologies often exhibit curved shapes resembling those of minimal surfaces rather than familiar Platonic, polyhedral crystal habits. The curved shapes of mesostructured inorganic materials synthesized by supramolecular templating are striking examples of minimal surface area and energy principles at work in their growth and form.Key words: mesoporous materials, morphosynthesis, silica, supramolecular.
Fluctuations in aqueous methanol, ethanol, and propan-1-ol: amplitude and wavelength of fluctuation
Authors: Koga Y
Published: April 2011

Density, heat capacity, and isentropic compressibility data for aqueous methanol, ethanol, and propan-1-ol by Benson's group were used to evaluate two kinds of fluctuations; mean-square fluctuation densities; and (mean-square) normalized fluctuations, respectively, in volume, entropy, and cross (entropy/volume) effect. The mean-square fluctuation densitiesprovide measures for the amplitude (intensity) of the fluctuation, while the normalized fluctuations contain information regarding the wavelength (extensity) of the fluctuation. Furthermore, their composition derivatives, the partial molar fluctuationsof alcohols were calculated. These quantities signify the effect of additional solute on the respective fluctuations. These data were interpreted in terms of mixing schemes learned earlier in this laboratory by using the data of excess partial molar enthalpy, entropy, and volume, and the respective alcohol-alcohol interaction functions, i.e., the composition derivatives of partial molar quantities.

Key words: aqueous methanol, ethanol, and propan-1-ol;fluctuation density; normalized fluctuation; partial molar fluctuations of alcohol.
New abietane diterpenoids from the cones of Larix kaempferi
Authors: Ohtsu Hironori , Tanaka Reiko , In Yasuko , Matsunaga Shunyo , Tokuda Harukuni , Nishino Hoyoku
Published: April 2011

A new podocarpane diterpene, 7α,15-dihydroxypodocarp-8(14)-en-13-one (1) and eight new abietane diterpenes, abiet-8(14)-en-7α,13β,15,18-tetraol (2), 7α,13β,15-trihydroxyabiet-8(14)-en-18-oic acid (3), 13β,18-dihydroxyabiet-8(14)-en-7-one (4), 13β,15,18-trihydroxyabiet-8(14)-en-7-one (5), 7-oxo-13β-methoxyabiet-8(14)- en-18-oic acid (7), abiet-8(14)-en-7α,12α,13β,18-tetraol (8), 7α,12α,13β-trihydroxyabiet-8(14)-en-18-oic acid (9), and abiet-8(14)-en-7α,12α,13β,15,18-pentaol (10) were isolated from the CHCl3 extract of the cones of Larix kaempferi. Their structures were determined on the basis of chemical and spectral evidence. The inhibitory effects of compounds 1-4 and 7-9 on Epstein-Barr virus early antigen (EBV-EA) activation induced by the tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA), were examined for a primary screening for anti-tumor promotors.

Key words: Larix kaempferi, Pinaceae, cones, abietane, EBV-EA.
Dehydrocoupling reactions of hydrosilanes with group 4 metallocenes Cp2MY2 (M = Ti, Zr, Hf; Y = F, OPh, NMe2)
Authors: Wang Qingzheng , Corey Joyce Y
Published: April 2011

Dehydrocoupling polymerization of phenylsilane with group 4 metallocene precatalysts Cp2MY2 (M = Ti, Zr, Hf; Y = F, OPh, NMe2) under comparable conditions has been examined. All nine title metallocenes produced polysilane products which ranged in molecular weight from 1100 to 4400 and exhibited ratios of linear to cyclic products from ~2 to 30. The highest molecular weight polysilanes observed for each metal were obtained from Cp2M(NMe2)2 and the highest percentage of linear polysilane was found with Cp2Hf(NMe2)2. The near stoichiometric reactions of Cp2MY2 with PhSiH3, PhMeSiH2, and Ph2MeSiH were monitored by 1H, 19F and 29Si NMR spectroscopy and in all cases exchange products containing Si-Y were identified. Metal hydride species could be observed only with Cp2TiY2.Key words: metallocene, dehydrocoupling, polymerization, hydrosilanes, polysilane.
Mineralization of [14C]octadecane by Acinetobacter calcoaceticus S19
Authors: Bajpai Urmi , Kuhad R C , Khanna Sunil
Published: April 2011

Uptake of octadecane by Acinetobacter calcoaceticus S19 was found to be 70% during growth (doubling time of 4 h), of which 60% was incorporated into the cells and 40% was oxidized to 14CO2. The ratio of [14C]octadecane uptake to its mineralization by whole cells was similar to that found during the growth of A. calcoaceticus S19. After 4 h of incubation of cells with [14C]octadecane, 44% was mineralized to 14CO2, while the rest remained associated with the cells. Octadecane uptake was not observed under anaerobic conditions, indicating an absolute requirement for oxygen. Acinetobacter calcoaceticus S19 converted octadecane to the corresponding octadecanol and octadecanoic acid; the corresponding aldehyde was not detected, however. Octadecanoic acid was partially degraded through β-oxidation to CO2 and partly assimilated as cell biomass.Key words: Acinetobacter calcoaceticus, octadecane uptake, mineralization.
Characteristics of phenanthrene-degrading bacteria isolated from soils contaminated with polycyclic aromatic hydrocarbons
Authors: Aitken Michael D , Stringfellow William T , Nagel Robert D , Kazunga Chikoma , Chen Shu-Hwa
Published: April 2011

Ten bacterial strains were isolated from seven contaminated soils by enrichment with phenanthrene as the sole carbon source. These isolates and another phenanthrene-degrading strain were examined for various characteristics related to phenanthrene degradation and their ability to metabolize 12 other polycyclic aromatic hydrocarbons (PAH), ranging in size from two to five rings, after growth in the presence of phenanthrene. Fatty acid methyl ester analysis indicated that at least five genera (Agrobacterium, Bacillus, Burkholderia, Pseudomonas, and Sphingomonas) and at least three species of Pseudomonas were represented in this collection. All of the strains oxidized phenanthrene according to Michaelis-Menten kinetics, with half-saturation coefficients well below the aqueous solubility of phenanthrene in all cases. All but one of the strains oxidized 1-hydroxy-2-naphthoate following growth on phenanthrene, and all oxidized at least one downstream intermediate from either or both of the known phenanthrene degradation pathways. All of the isolates could metabolize (oxidize, mineralize, or remove from solution) a broad range of PAH, although the exact range and extent of metabolism for a given substrate were unique to the particular isolate. Benz[a]anthracene, chrysene, and benzo[a]pyrene were each mineralized by eight of the strains, while pyrene was not mineralized by any. Pyrene was, however, removed from solution by all of the isolates, and the presence of at least one significant metabolite from pyrene was observed by radiochromatography for the five strains in which such metabolites were sought. Our results support earlier indications that the mineralization of pyrene by bacteria may require unique metabolic capabilities that do not appear to overlap with the determinants for mineralization of phenanthrene or other high molecular weight PAH.Key words: kinetics, polycyclic aromatic hydrocarbons, phenanthrene, mineralization, benzo[a]pyrene.
Natural attenuation of aqueous metal contamination by an algal mat
Authors: Lawrence J R , Swerhone GDW , Kwong YTJ
Published: April 2011

Naturally occurring mechanisms of attenuation for metals in the environment are important for understanding and remediating acid rock drainage. A filamentous green algae was found forming an extensive mat below an outflow of acidic, metal-laden groundwater, at Macintosh Creek, MacMillan Pass, Yukon Territory, Canada. Emerging waters had a pH of 3.3 and the following dissolved metal concentrations in milligrams per litre: Al = 156, Fe = 298, Mn = 1.1, Cd = 0.13, Ni = 2.52, Cu = 0.69, and Zn = 5.0. In contrast, waters that had coursed over the algal mat had the following concentrations in milligrams per litre: Al = 26.4, Fe = 29.3, Mn = 0.18, Cd = 0.03, Ni = 0.4, Cu = 0.2, Zn = 0.88. In addition, the concentration of dissolved As declined from 32.9 to 9.3 µg·L-1. Thus, the concentrations of potentially deleterious elements were typically reduced by between 5- and 10-fold. Scanning electron microscopy (SEM) indicated that individual filaments of the algae were encrusted with mineral precipitate. Microprobe analyses indicated that the coatings were predominantly composed of Fe with other metals, in the presence of S and P, the latter possibly associated with the algal biomass. While culturing methods indicated the presence of 104-106 Thiobacillus ferrooxidans·mL-1 in the water, epifluorescence microscopy observations using DAPI and SYTO 9 nucleic acid stains did not reveal bacteria in association with the algal filaments. Hydrated samples were also observed using confocal scanning laser microscopy (CSLM) with FITC-conjugated lectin staining, autofluorescence, and reflection imaging. These observations indicated that the algal filaments had an extensive exopolysaccharide surrounding the filaments and that mineralization occurred within the matrix. This suggested that factors such as the Eh and pH proximal to the algae may be playing an important role in mineral production.Key words: heavy metals, exopolymers, acid drainage, confocal microscopy.