bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of chloro(2-methylimidazole) ruthenium(III) complexes and their aqueous solution chemistry, and the crystal structure of [2-MeImH]2[RuCl52-MeIm]
Authors: Anderson Craig
Published: April 2011

2-Methylimidazole (2-MeIm) reacts with RuCl3 in aqueous acidic ethanolic medium to give (2-MeImH)2[RuCl5(2-MeIm)] (1) and (2-MeImH)[RuCl4(2-MeIm)2] (2) (2-MeImH = protonated 2-methylimidazole), the ratio depending on reaction conditions used. Molecule 1 crystallizes in the space group Pnma: a = 14.046(2), b = 17.294(2), and c = 8.2778(12) Å. The 1H NMR spectra of these ruthenium(III) complexes have been measured and show peaks with large isotropic shifts and large line broadening characteristic of such paramagnetic complexes. The aquation of complexes 1 and 2 were followed by proton NMR spectroscopy. 1,2-Dimethyl imidazole (1,2-diMeIm) reacts with RuCl3 in methanolic solution to give [RuCl3(1,2-diMeIm)(H2O)S] (S=H2O (3a) or CH3OH (3b)). The aquation reactions of complexes 3a and 3b were followed by 1H NMR.Key words: ruthenium, paramagnetic, antitumour, NMR.
Effect of the molecular weight on the lower critical solution temperature of poly(N,N-diethylacrylamide) in aqueous solutions
Authors: Lessard D G , Ousalem M , Zhu X X
Published: April 2011

The molecular weight dependence of the lower critical solution temperature of poly(N,N-diethylacrylamide) was studied with 11 samples of the polymer with a number-average molecular weight (Mn) ranging from 9.6 × 103 to 1.3 × 106 g mol1 and relatively narrow polydispersity indices from 1.19 and 2.60. These samples were obtained by fractional precipitation of the polymer. LCST values of polymers were measured by turbidimetry and microcalorimetry. An inverse dependence of LCST on the molar mass was found and the LCST of the samples remained more or less a constant above a critical molecular weight of ca. 2 × 105 g mol1. The enthalpy and the entropy changes as well as the LCST of the polymer depend strongly on the molar mass of the polymer, especially in low molecular weight range.Key words: poly(N,N-diethylacrylamide), LCST, thermosensitive, phase diagram, effect of molecular weight.
Stereoselective syntheses of α-amino acid and peptide derivatives by the U-4CR of 5-desoxy-5-thio-D-xylopyranosylamine
Authors: Ross Günther , Ugi Ivar
Published: April 2011

Since 1961, the synthesis of α-amino acids derivatives by the four-component reaction of isocyanides (U-4CR) as a one-pot reaction has been developed. Only recently it was found that a variety of these α-amino acids compounds can be formed stereoselectively by the U-4CR using 1-amino-5-deoxy-5-thio-2,3,4-tri-O-isobutanoyl-β-D-xylopyranose as the amine component. The stereoselectivity inducing auxiliary 5-desoxy-5-thio-D-xylopyranosyl group of the so-formed products can be replaced selectively by hydrogen.Key words: stereoselective U-4CR, chiral amine component, amino carbohydrate, α-amino acid derivatives.
Synthesis, characterization, and crystal structures of novel oligomeric Zn(II) and Cd(II) complexes withN,N′-dimethyl-2,2′-biimidazole
Authors: Gruia Letitia M , Rochon Fernande D , Beauchamp André L
Published: April 2011

Zn(II) and Cd(II) complexes with N,N′-dimethyl-2,2′-biimidazole (Me2biim) were synthesized and characterized by IR spectroscopy and by X-ray crystallographic methods. The reaction of zinc perchlorate with Me2biim produced the dinuclear compound [(Me2biim)Zn(µ-Me2biim)3Zn(Me2biim)](ClO4)4, containing two monodentate and three bridging Me2biim ligands bonded to Zn atoms in a distorted tetrahedral environment. A related neutral (NO3)2Cd(µ-Me2biim)3Cd(NO3)2complex, containing only bridging Me2biim ligands, was also synthesized, in which the distorted octahedral coordination of each Cd atom is completed by one monodentate and one bidentate nitrato ligand. Two ionic trinuclear Cd compounds were also obtained, which include two sets of three bridging Me2biim ligands connecting a central Cd atom to two terminal Cd centers. An extra Me2biim ligand is chelated to each terminal metal, and the sixth coordination site is occupied by water molecules in the symmetric [(Me2biim)(H2O)Cd(µ-Me2biim)3Cd(µ-Me2biim)3Cd(H2O)(Me2biim)](ClO4)6complex, whereas the aqua ligand is replaced by methanol at one of the terminal units in the non-symmetric [(Me2biim)(H2O)Cd(µ-Me2biim)3Cd(µ-Me2biim)3Cd(CH3OH)(Me2biim)](ClO4)6compound. In the chelating ligands, dihedral angles of ~38° between the two imidazole rings reduce repulsion between the N-methyl groups, but considerable strain remains, as evidenced from one of the Cd–N bonds being much longer than the other. In the various compounds, dihedral angles of 60–80° are found between the imidazole rings in the bridging ligands, and intramolecular inter-ligand π–π stacking contributes to stabilization.Key words: zinc, cadmium, dimethylbiimidazole, crystal structure, dinuclear, trinuclear.
Cleavage reactions of 4′-dimethylamino-2,2,2-tris-(p-dimethyl-aminophenyl)-acetophenone and a related compound
Authors: Sandin R. B. , Elofson R. M. , Schulz K. F.
Published: April 2011

Ultraviolet irradiation of benzene solutions of 4′-dimethylamino-2,2,2-tris-(p-dimethyl-aminophenyl)-acetophenone (I) and 2,2-bis-(p-dimethylaminophenyl)-2-phenylacetophenone (II) and iodine gave crystal violet triiodide and malachite green triiodide, respectively. Irradiation of I in hexane and in the presence of air gave a brilliant blue solid III. Analytical and spectral data support a proposed structure which is a tetraoxide, or its ion-pair equivalent, of the homolytic cleavage products of I.
The isolation of 11-oxotetrahydrorhombifoline from Ormosia coutinhoi and a study of its mass spectrum
Authors: McLean Stewart , Harrison A. G. , Murray D. G.
Published: April 2011

11-Oxotetrahydrorhombifoline (I) has been isolated from the alkaloidal extract of the bark of Ormosia coutinhoi, and its dihydro derivative II has been prepared. An examination of the mass spectra of these compounds and of their 3,3-d2 derivatives has led to the elucidation of the course of the major electron impact induced fragmentations undergone by the molecules. The main fragmentation of I leads to loss of C3H5 from the side chain to form an ion of m/e 221, with a minor path involving a central fission of the molecular ion to form an ion of m/e 150. The mass spectrum of II shows that the loss of C3H7 to form the ion of m/e 221 is a minor process, the main fragmentation reaction involving a central fission to form an ion of m/e 152 analogous to the ion of m/e 150 from I. This change in the spectrum is shown to be consistent with predictions based on the quasi-equilibrium theory of mass spectra.
Conformation of the C15 lupine alkaloids
Authors: Wiewiorowski M , Edwards O E , Bratek-Wiewiorowska M D
Published: April 2011

Methods have been developed for preparing 17α-deuterio-, 17β-deuterio-, and l7-dideuteriolupanines. The nuclear magnetic resonance and infrared spectra of these provided strong evidence that ring C in the alkaloid is in a boat conformation in solution. Reduction of these compounds to the deuterated sparteines confirmed the same geometry for sparteine. In contrast, moilodeuteration of aphylline at C-17 showed that i t had an all-chair conformation in solution. 13β-Hydroxylupanine was shown to have the same conformation as lupanine in solution, but to adopt an all-chair conformation in the solid state. Interpretation of the nuclear magnetic resonance spectra enabled the conformation of ring C of 15-oxosparteine to be assigned. The oxidation and reductions involving C-17 of lupanine have been shown to be highly stereospecific, and an interpretation is given of the difference betmeen the dehydrogenation of lupanine by mercuric acetate and those by Nbromosuccinimide or by the mercuric acetate - ethylenediatninetetraacetic acid complex. It has now been found that the C—H stretching “trans bands” in the infrared are evident when only one hydrogen is alpha to the basic nitrogen and in an antiparallel relation to the lone pair of electrons.
Reaction of 3-O-p-bromophenylsulfonyl-1,2:5,6-di-O-isopropylidene-α-D-glucofuranose with dimethylamine
Authors: Horton Derek , Jewell Jon S. , Prihar H. S.
Published: April 2011

The p-bromobenzenesulfonate (3) of 1,2:5,6-di-O-isopropylidene-α-D-glucofuranose (4) reacts with dimethylamine by aromatic nucleophilic substitution to give the p-dimethylaminobenzenesulfonate (5) of (4), rather than by attack at C-3 of the sugar moiety.
Chalkogenides of the transition elements. VI. X-Ray, neutron, and magnetic investigation of the spinels Co3O4, NiCo2O4, Co3S4, and NiCo2S4
Authors: Knop Osvald , Reid K. I. G. , Sutarno  , Nakagawa Yasuaki
Published: April 2011

The crystal structures of the spinels Co3O4, NiCo2O4, Co3S4, and NiCo2S4 were refined from X-ray and neutron powder data. Their lattice parameters at room temperature and the positional parameters of the oxygen and sulfur atoms were: Co3O4, 8.0835 ± 6 Å, 0.2640 ± 8; NiCo2O4, 8.114 ± 14 Å, 0.2583 ± 34; Co3S4, 9.4055 ± 12 Å, 0.2591 ± 5; NiCo2S4, 9.3872 ± 7 Å, 0.2591 ± 3. The thermal stabilities of the two oxides in air and in oxygen at 1 atm were investigated by thermogravimetric analysis and differential thermal analysis, and the magnetization of NiCo2O4 was measured down to 4.2 °K in fields up to 11.70 kOe. From neutron diffraction NiCo2O4. was found to be inverse, while NiCo2S4 was shown to be normal. The results of the magnetization measurements and the neutron-diffraction patterns at 111 and 393 °K were found to be equally consistent with the magnetic structure proposed for NiCo2O4 by Blasse, Co2+[Ni3+Co3+]O4 (Co2+ in a high-spin and Ni3+ andCo3+ in low-spin states), and with Co3+[Ni2+Co3+]O4 (Co3+ in 8(a) in a high-spin and Co3+ in 16(d) in a low-spin state). The sublattice magnetizations were not completely aligned even at 4.2 °K; the net magnetic moment derived from the magnetization measurements was only 1.25 μB, which is lower than the value of 2 μB expected from either model. At 111 °K the moments of the ions in the tetrahedral and octahedral sites were estimated to be 1.9 ± 0.2 and −0.5 ± 0.1 bohr magnetons respectively.
Cycloalkylation d'aryloléfines par le trifluorure de bore. Synthèse d'hydrocarbures aromatiques polyméthylés
Authors: Canonne P. , Regnault A.
Published: April 2011

A survey of the results obtained by us in the course of cyclizations of 4-arylolefins indicates that boron trifluoride is the most satisfactory catalyst in the case of otherwise non-functionalized substrates. Its use is illustrated by the synthesis of the heretofore unknown 1,3,6,8-tetramethyltriphenylene and by an improved preparation of 1,5-dimethylnaphthalene.
From early spin-trapping experiments to acyl nitroxide chemistry: synthesis of and spin trapping with a water-soluble nitrosopyrazole derivative
Authors: Perkins M John , Kaur Harparkash
Published: April 2011

A personal view of early experiments which led to the use of C-nitroso-compounds as spin traps is presented, and it is shown how these experiments resulted in the first isolation, and subsequent investigation, of acyl nitroxide radicals: the use of 1-methyl-4-nitroso-3,5-diphenylpyrazole as a spin trap, and the preparation and preliminary investigation of its water-soluble analogue (1) are described.
Trans to cis photoisomerization of N,N′-disubstituted indigo dyes via excited singlet states; a laser flash photolysis and steady state irradiation study
Authors: Görner Helmut , Pouliquen Joseph , Kossanyi Jean
Published: April 2011

The relaxation pathways of excited trans-N,N′-diacylindigo dyes (trans-1–trans-4) and of the rigid trans (5) and cis (6) indigo analogues have been studied by nanosecond flash photolysis and steady state measurements. In fluid solution the trans to cis photoisomerization of 1–4 occurs via a singlet excited state mechanism on direct excitation, and the triplet state appears to be reached only by sensitized reaction. The lower quantum yield for trans → cis isomerization of 2–4 at room temperature, as compared to 1, is due to a thermally activated internal conversion step leading to the trans ground state. This pathway competes with fluorescence and twisting of the molecule around the central double bond in the excited singlet state. Increasing the viscosity of the medium decreases the twisting of the flexible molecules and, as a consequence, increases the population of the lowest triplet state. A triplet transient, the intensity of which increases with the viscosity of the medium, could be characterized at low temperature under direct excitation. A transient species, which can be assigned to a triplet state on the basis of quenching experiments and on the fact that the same transient could be found under sensitized conditions, also has been observed at room temperature for the rigid 5 and 6 molecules. Quenching measurements of triplet sensitizers by 5, trans-1, and trans-2 enables the localization of the triplet energy at around 40 kcal/mol.
Metabolites produced by the Scleroderris canker fungus, Gremmeniellaabietina. Part 4. Biosynthetic studies
Authors: Ayer William A. , Pedras M. Soledade , Ward Dale E.
Published: April 2011

The biosynthetic origin of the carbon atoms of the most highly oxidized, polyketide derived, ring (carbons 1–3) of the Gremmeniellaabietina metabolites sclerodione (3), scleroderolide (4), sclerodin (5), and Scleroderris green (6) has been studied. It is shown that both C-1 and C-3 of 3 and 4 are derived from C-1 of acetate, and that C-2 of scleroderolide (4) is derived from C-2 of acetate while C-3 is derived from C-1 of acetate. As expected, C-1 and C-3 of Scleroderris green (6) originate from the carboxyl carbon of acetate, while C-2 originates from the methyl carbon of acetate. Complete 13C and 1H nuclear magnetic resonance spectra of these metabolites are reported. It has also been shown that ent-atrovenetin (ent-7a) is a metabolite of G. abietina.
Kinetic study of the reaction between cystine and sulfide in alkaline solutions
Authors: Liu David K. , Chang S. G.
Published: April 2011

The reaction between cystine (CySSCy) and hydrogen sulfide ion (HS−) in alkaline solutions has been studied by amino acid analysis and uv–visible spectroscopy. The reaction occurs in two reversible steps to form cysteine (CySH), S-thiocysteine (CySS−), and disulfide (S22−), as represented by the reactions [Formula: see text] and [Formula: see text]. The equilibrium and rate constants were pH dependent due to the presence of various charge types of reactants and products. The rate constants at 25 °C, pH 10.0, and μ = 0.17 M were determined to be: k1 = 3.7 ± 0.4 M−1 min−1, k−1 = 5.5 ± 0.6 M−1 min−1, k2 = 6.1 ± 0.5 M−1 min−1, and k−2 = 122 ± 20 M−1 min−1. When the rate constant k1 is expressed as k1 = A exp (−Ea/RT), values of A = (4.7 ± 0.3) × 1011 M−1 min−1 and Ea = 15.8 ± 0.9 kcal mol−1 were obtained. The ionic strength and pH dependence of k1 were also studied.
Stereochemical assignment of 2-amino-1,2,3,4-tetrahydro-1-naphthalenols via oxazolidin-2-one derivatives
Authors: Delgado Antonio , Mauleon David , Minguillon Cristina , Feliz Miguel , Pericas Miquel A. , Riera Antoni
Published: April 2011

The stereochemical assignment of cis- and trans-2-amino-1,2,3,4-tetrahydro-1-naphthalenols (1) can be performed by means of their conformationally restrained tricyclic tetrahydronaphtho[2,1-d]oxazol-2-one derivatives 2–6. Thus, 1H and 13C nuclear magnetic resonance data of compounds 2–6 reveal differences between the cis and trans stereoisomers that are independent of the nature and number of the aromatic substituents. Conformational analysis of compounds 2–6 has been performed from the LAOCOON/3 analysis of their nuclear magnetic resonance spectra and MNDO theoretical results, through the use of the Karplus–Altona equation. Whereas the trans compounds exist in a rigid half-chair conformation, a 1:1 equilibrium of two interconverting half-chair conformers is found for the cis derivatives.
Formation of oxy radicals by oxygen reduction arising from the surface activity of asbestos
Authors: Zalma Roger , Bonneau Lionel , Guignard Joëlle , Pezerat Henri , Jaurand Marie-Claude
Published: April 2011

Formation of hydroxyl radicals, in relatively large quantities, by oxygen reduction due to the surface activity of asbestos in a cell-free system is demonstrated, using electron spin resonance and a spin trapping agent. The quantity of OH• produced (in general, above 1014 mg−1 for a Canadian chrysotile) is a function of activation or passivation of the electron donor surface sites of the minerals. The role of these radicals in oxidative stress in relation to the toxic properties of these minerals is discussed.
The preparation of esters of formic acid using boron oxide
Authors: Carlson Charles G. , Hall Judith E. , Huang Yan. Y. , Kotila Sirpa , Rauk Arvi , Tavares Donald F.
Published: April 2011

Boron oxide has been found to act as an efficient reagent in the preparation of a number of formate esters by the direct esterification of formic acid with the alcohol. The reaction is most appropriate for primary and secondary alcohols, including unsaturated alcohols. The formate ester so produced is free of contamination by unreacted alcohol.
Variational transition state calculation: collision energy dependence of the M + RX → MX + R (M = alkali, X = halogen, R = radical) reaction family
Authors: Alonso J. , Banares L. , Menéndez M. , Ureña A. González
Published: April 2011

A variational transition state theory has been developed to account for the kinetic energy dependence of the reaction cross-section which is valid for the case where experiments are carried out at different, but fixed, collision energies. One of the main aspects of the present work is the inclusion of non-collinear configurations for the transition state.Analytical expressions for σR(ET) averaged over the angle of attack are presented and several model calculations where carried out for the M + RX → MX + R reaction family with an orientational dependence of the energy barrier. The relative success of the present model calculations has been rationalized considering the possibility that long range interactions, via alignment forces, would favour the collinear approach regardless of the initial angle of attack.
Absorption and photoacoustic spectroscopies of lutein and zeaxanthin Langmuir–Blodgett films in connection with the Haidinger's brushes
Authors: N'soukpoé-Kossi C. N. , Leblanc R. M.
Published: April 2011

The molecular state of a single monolayer of lutein, zeaxanthin, and of a mixture of lutein and L-α-phosphatidylcholine-β-oleoyl-γ-stearoyl has been investigated using absorption and photoacoustic spectroscopies. Both methods, confirmatively, reveal that the two carotenoids are mostly in a monomer state coexisting with carotenoid crystals. We observe that the absorption as well as the photoacoustic bands are red-shifted relative to the bands in solution. The absorption bands are found to peak at mean values of 440.0, 464.8, and 503.8 ± 0.5 nm for lutein, and at 452.7, 475.9, and 513.7 ± 0.5 nm for zeaxanthin. The photoacoustic peaks are situated at 444.0, 467.2, and 502.4 ± 0.5 nm for lutein, and 455.4, 473.8, and 509.0 ± 0.5 nm for zeaxanthin. Diluting lutein monolayer with the phospholipid results into a blue-shift of the absorption bands compared with those of the pure carotenoid monolayer and the macular pigment spectra. The results are discussed in connection with the Haidinger's brushes. It is concluded that lutein molecules might not be mixed with membrane lipids in the macular tissue, but form a monolayer protruding from the Henle fiber membranes to form the Haidinger's brushes in the macula.
The crystal and molecular structure of the coordinatively unsaturated Ni(0) species Ni(PPh3)3
Authors: Dick David G. , Stephan Douglas W. , Campana Charles F.
Published: April 2011

The disproportionation of the complex (Et2N)3Ti(μ-PCy2)Ni(PPh3) affords the coordinatively unsaturated species Ni(PPh3)3, 1. This compound crystallizes in the triclinic space group [Formula: see text], with a = 18.483(4) Å, b = 16.203(3) Å, c = 17.783(4) Å, α = 105.85(2)°, β = 117.33(3)°, γ = 92.33(3)°, Z = 4, and V = 4464(2) Å3. Full-matrix least-squares refinement of 1042 variables using 6484 data (Fo2 > 3σFo2) gave R = 0.0441 and Rw = 0.0438. The two crystallographically independent molecules are essentially identical, each exhibiting a trigonal planar coordination sphere at Ni. The most interesting feature of the structure is the close approach (2.744–3.094 Å) of three ortho hydrogens of the PPh3 groups to the Ni centres. The implications of the structural data regarding ortho metallation and the known instability of 1 are discussed. Keywords: coordinatively unsaturated, nickel phosphine complex.
Oxidative radical cyclization to pyrroles under reducing conditions. Reductive desulfonylation of α-sulfonylpyrroles with tri-n-butyltin hydride
Authors: Antonio Yulia , De La Cruz Ma. Elizabeth , Galeazzi Edvige , Guzman Angel , Bray Brian L. , Greenhouse Robert , Kurz Lilia J. , Lustig David A. , Maddox Michael L. , Muchowski Joseph M.
Published: April 2011

1-(2-Bromobenzyl)-2-alkanesulfonylpyrroles (1c, 1d) and 1-(4-bromobutyl)-2-methylsulfonfylpyrrols (8) undergo oxidative radical cyclization with partial or complete reductive desulfonylation to the pyrrolizidine derivatives 5 and 9 by an AIBN initiated reaction with tri-n-butyltin hydride. These cyclizations are suggested to proceed via a pseudo SRN1 process involving radical addition to the α position of the pyrrole nucleus not bearing the sulfonyl group. Reductive removal of the alkylsulfonyl moiety is proposed to occur in a second process after completion of the oxidative radical cyclization. The site of the radical addition is supported by deuterium labelling studies. Consistent with the timing of the loss of the sulonyl group is that 2-alkysulfonylpyrroles 11 are reductively desulfonylated under the same conditions that effect the oxidative radical cyclizations.
Diastereoselectivity in the synthesis of D-glycero-D-aldoheptoses by 2-trimethylsilylthiazole homologation from hexodialdo-1,5-pyranose derivatives
Authors: Khare Naveen K. , Sood Ramesh K. , Aspinall Gerald O.
Published: April 2011

An exploration of the synthesis of D-glycero-D-altro-heptose, a constitutent of O antigen chains in lipopolysaccharides from Campylobacter jejuni serotypes O:23 and O:36 led to a study of the 2-trimethylsilylthiazole homologation procedure for heptose synthesis. In contrast to the diastereoselective formation of a 1,2:3,4-di-O-isopropylidene-D-glycero-α-D-galacto-heptopyranose derivative from 1,2:3,4-di-O-isopropylidene-α-D-galacto-hexodialdo-1,5-pyranose, methyl 2,3,4-tri-O-benzyl-D-hexodialdo-1,5-pyranosides with the gluco and manno configurations showed no preference for the formation of compounds with the D-glycero configuration. Attempts to achieve high diastereoselectivity in the conversion of L-glycero into the D-glycero isomers by oxidation at C-6 followed by reduction with L-selectride were unsuccessful with the thiazole adducts, but the desired products were formed in similar reactions of methyl 2,3,4-tri-O-benzyl-7-O-tert-butyldimethylsilyl-D-heptopyranosides. The approach to homologation in the altro series was thwarted by epimerization at C-5 in the attempted formation of methyl 2,3,4-tri-O-benzyl-α-D-altro-hexodialdo-1,5-pyranoside. The successful synthesis of methyl D-glycero-α-D-altro-heptopyranoside from methyl α-D-glucopyranoside was achieved by homologation followed by configurational alteration from the D-gluco to the D-altro series.
Synthesis of cis-p-dioxano-12-crown-4 and X-ray crystallography of the (1:1) complex with lithium thiocyanate
Authors: Driega Alex B , Buchanan Gerald W , Bensimon Corinne
Published: April 2011

The synthesis of a novel 12-crown-4 analogue (cis-p-dioxano-12-crown-4 or cis-3,6,9,13,15- pentaoxabicyclo[9.3.1]pentadecane) is described. The (1:1) LiNCS complex crystallizes in the monoclinic Cc space group; a = 8.4973(2) Å, b = 18.0659(4) Å, c = 8.9168(1) Å, and β = 90.713(1)° with Z = 4. The crown adopts C1 symmetry to which the Li+ is coordinated in a rectangular pyramid with an apical -NCS.Key words: crown ethers, structure, complexation.
Article
Authors: Drennan Catherine E , Hughes Rachelle J , Reinsborough Vincent C , Soriyan Oladega O
Published: April 2011

Kinetic studies through stopped-flow spectroscopy were undertaken in the dilute solution range of anionic surfactants where pronounced rate enhancement or inhibition of Ni2+-ligand complexations is often observed at surfactant concentrations much below the critical micelle concentration (CMC). The results are interpreted in terms of Ni-surfactant micelles as the agents responsible for the rate changes in dilute surfactant solution. At higher surfactant concentrations these micelles are transformed into mixed micelles (counterion and size changes), eventually becoming normal surfactant micelles close to the CMC. Surface tension, dye solubility, conductivity, and fluorescent probe investigations support this interpretation.Key words: micellar catalysis, sodium dodecyl sulfate, micelles, critical micelle concentration, premicelles, Ni2+-ligand complexations.
Article
Authors: Cordes A Wallace , Haddon Robert C , Hicks Robin G , Oakley Richard T , Vajda Kristen E
Published: April 2011

Electroreduction of the 2,5-thiophene-bridged bis(1,2,3,5-diselenadiazolylium) salt [T-2,5-Se][SbF6]2in acetonitrile, at a Pt wire and in the presence of iodine, affords a highly conductive ( sigma = 102S cm-1at 293 K) 1:1 charge-transfer (CT) salt [T-2,5-Se][I], the crystal structure of which has been determined by single-crystal X-ray diffraction. The crystals belong to the orthorhombic space group Fm2m, a = 3.544(2), b = 10.9808(16), c = 31.464(5) Å , V = 1224.5(7) Å3. The structure consists of perfectly superimposed pi -stacks of molecular units bridged by columns of disordered iodines. This packing motif is similar to that of the related 1,3-benzene-bridged derivative [1,3-Se][I], but the lateral intermolecular Se···Se interactions linking adjacent pi -stacks are considerably shorter, indicative of a more isotropic electronic structure for [T-2,5-Se][I]. Magnetic susceptibility measurements on [T-2,5-Se][I] nonetheless indicate a phase transition to a diamagnetic state near 200 K, behaviour similar to that observed for [1,3-Se][I]. The electronic structures and transport properties of the two compounds are discussed in the light of extended Hückel band-structure calculations.Key words: diselenadiazolyl, diradical, charge-transfer salt, magnetic susceptibility, crystal structure.
Interdeterminancy of basin and surface properties of an open system
Authors: Bader RFW , Martín F J
Published: April 2011

This paper delineates and illustrates an important physical consequence of the Heisenberg equation of motion governing the expectation value of an observable for a proper open system, one whose basin is bounded by a surface of zero flux in the gradient vector field of the electron density. For a system in a stationary state, this theorem derives from the variation of Schrödinger's energy functional over an open system. The variation demonstrates that the surface of the open system, as well as the wave function and energy of the total system, are simultaneously stationary with respect to any and all variations δ ψ , corresponding to a stationarity with respect to any and all physical perturbations -(i ε/ Planck's constant) G caret ψ caused by a generator G caret. Thus the properties of a proper open system are dependent upon its surface and vice versa, the theorem equating the expectation value of the commutator of the Hamiltonian and a generator G caret for the open system to the flux in the current density for G caret through its surface. The criticisms of the interdependence of the basin and surface properties of a proper open system that appeared recently in this journal are refuted, including the argument that mutiplication of an electron density by a constant factor yields a density for a different system. The consequences of this interdependence in the construction of a polypeptide through the use of amino acid residues defined as proper open systems is discussed and illustrated through the explicit calculation of the properties of the C|N interatomic surfaces of the amidic bonds. It is demonstrated that the the degree of transferability of a residue is determined by the degree of similarity in the properties of its two bounding amidic surfaces.Key words: electron density, ransferability of density, atoms in molecules, zero flux surface.
Pyridinium N-phenoxide betaines and their application to the determination of solvent polarities, XXIV. Syntheses and UV-vis spectroscopic properties of new lipophilic tert-butyl- and 1-adamantyl substituted, negatively solvatochromic pyridinium N-phenolate betaine dyes
Authors: Reichardt Christian , Löbbecke Stefan , Mehranpour Abdol Mohammed , Schäfer Gerhard
Published: April 2011

Syntheses and negative solvatochromism of two new lipophilic pentaphenyl pyridinium N-phenolate betaine dyes, substituted with seven tert-butyl groups (9) or with three tert-butyl and two 1-adamantyl groups (13) in the peripheral phenyl rings, are described in order to get zwitterionic dyes that are more soluble in nonpolar solvents such as the standard betaine dye, 1, which has been used for the construction of an empirical scale of solvent polarity, called the ET(30) scale.Key words: betaine dyes, ET(30) values, lipophilic dyes, pyridinium N-phenolate betaine dyes, solvatochromism, solvent polarity.
On the formation of diphenylmethane structures in lignin under kraft, EMCC®, and soda pulping conditions
Authors: Ahvazi Behzad C , Pageau Gerry , Argyropoulos Dimitris S
Published: April 2011

This paper describes our efforts focused at defining the formation of diphenylmethane moieties in lignin during conventional kraft and soda pulping conditions. This objective was realized by confirming, initially, the assignment of a31P NMR signal as being due exclusively to the presence of phosphitylated diphenylmethane (DPM) phenolic hydroxyl groups. More specifically, softwood milled wood lignin (Picea mariana) was subjected to kraft pulping conditions in the presence and absence of varying amounts of formaldehyde. After quantitative recovery of the lignin, the31P NMR spectra were recorded and the spectra revealed selective signal growth in the region confined between 142.8 and 144.3 ppm, in accordance with previous model compound work and detailed calculations based on the Hammett principles. To further substantiate our conclusions we also carried out two series of isothermal (120°C) kraft and soda pulping experiments followed by quantitative determinations of the DPM moieties, and correlated our findings with the differences in chemistry known to occur between the two processes. Finally, diphenylmethane phenolic moieties were determined in isolated residual lignins from two western hemlock kraft pulp samples produced via an EMCC®mill protocol and a laboratory batch digester, respectively. These structures prevailed amongst the condensed phenolic units of the conventional pulp, providing additional evidence to support the fact that modern modified pulping technologies beneficially alter the structure of residual kraft lignin.Key words: phenyl groups, kraft pulping, modified kraft process, nuclear magnetic resonance (NMR), phosphorus spectroscopy.
1997 McBryde Medal Award Lecture Radio frequency quadrupole ion guides in modern mass spectrometry
Authors: Thomson Bruce A
Published: April 2011

The role of RF quadrupoles in modern mass spectrometer and tandem mass spectrometer systems is described. A good deal of the success in the application of tandem quadrupole mass spectrometers and atmospheric pressure ionization mass spectrometers is due to new applications of the RF quadrupole ion guide. Developments that led from the use of very open, "transparent" electrodes in a cryopumped system to the opposite extreme of well-confined RF quadrupoles that operate advantageously at pressures of several mTorr are described. The ion containment properties of RF quadrupoles are remarkably insensitive to the accuracy of the electrode positions. This has allowed the use of novel quadrupole designs in order to provide unique solutions to instrumentational and physical-chemical problems.Key words: quadrupole, focusing, mass spectrometer.
Reactions of benzyl methyl substituted-benzyl phosphites with tert-butyl hypochlorite: "balanced TS" validating reactivity/selectivity principle
Authors: Kim Sung Soo , Zhu Yu , Oh In Seok , Lim Chang Gyeong
Published: April 2011

Reactions of a series of several benzyl methyl substituted-benzyl phosphites with tert-butyl hypochlorite were investigated. The reactions produced phosphates, isobutene, alkyl chlorides, and benzyl chlorides via phosphonium chlorides as intermediates. Furthermore, the phosphates bearing a tert-butyl group underwent fragmentation to yield isobutene and another phosphates. Relative rates of formations of substituted benzyl and benzyl chloride (kY/kH) were measured at the temperatures (-20, 0, 20, 40°C). Logarithms of the rates (log kY/kH) were plotted against sigma + and 1/T, respectively. The former gave Hammett correlations to suggest a polar transition state (TS). The latter yielded differential activation parameters (ΔΔ Hdouble daggerY-H and ΔΔ Sdouble daggerY-H ), which indicate isokinetic relations and enthalpy control of rates. The selectivities (kY/kH) decrease with higher temperatures and thereby follow the reactivity/selectivity principle.Key words: phosphites, tert-butyl hypochlorite, Hammett correlations, differential activation terms, reactivity/selectivity principle.
The preparation, X-ray crystal structure, and spectroscopic characterization of pentafluorophenyl-bis(pentafluorophenylthio)sulfonium hexafluoroarsenate, [(C6F5S)2SC6F5][AsF6]
Authors: Brownridge Scott , Cameron T Stanley , Passmore Jack , Schatte Gabriele , Sutherland George W
Published: April 2011

Pentafluorophenyl-bis(pentafluorophenylthio)sulfonium hexafluoroarsenate, [(C6F5S)2SC6F5][AsF6], was prepared by the reaction of (C6F5)2S2 and AsF5 in liquid SO2 at room temperature. The compound has been characterized by single-crystal X-ray and powder diffraction, and IR and FT-Raman spectroscopy. Crystals of [(C6F5S)2SC6F5][AsF6] are orthorhombic, space group P212121 (cell dimensions measured at room temperature in brackets): a = 13.132(3) [13.157(2)] Å, b = 21.477(4) [21.575(3)] Å, c = 8.770(2) [8.775(1)] Å, α = ß = γ = 90.00°; V = 2473.3(9) Å3, Z = 4, temperature = 181 ± 1 K. The structure consists of [AsF6]- anions and [(C6F5S)2SC6F5]+ cations that have a different structure than the related [X2MMMX]+ cations (M = S, Se; X = Cl, Br), which contain a trichalcogen chain with a pronounced chalcogen-chalcogen bond alternation. Ab initio calculations suggest the observed [(C6F5S)2SC6F5]+ geometry is due to steric and solid state effects. Comparison of the Raman spectra of [(C6F5)S2SC6F5][AsF6], [Cl2SSSCl][AsF6], and [(CH3)2ClS3]+ implies that [(CH3)2ClS3]+ has a structure with equal sulfur-sulfur distances, and therefore the structure is likely [(CH3S)2SCl]+ and probably not the previously reported [(CH3)2SSSCl]+.Key words: [R3X3]+ cations, X-ray crystal structure, FT-Raman spectroscopy, [(C6F5S)2SC6F5]+, pentafluorophenyl-bis(pentafluorophenylthio)sulfonium cation, hexafluoroarsenate.
1997 Polanyi Award Lecture Why are there atoms in chemistry?
Authors: Bader RFW
Published: April 2011

Dalton made a bold assumption in his atomic hypothesis by stating that atoms retained their mass and their identity in chemical combination. Its vindication had to await Rutherford's nuclear model of the atom. The continuing evolution of chemistry led to the realization that atoms exhibit not only a unique mass but also characteristic additive properties, thereby making it possible to recognize their presence in a molecule and to predict the molecule's static and reactive properties. The theoretical vindication of the model of a functional group as the carrier of chemical information had to await the work of Feynman and Schwinger. Their generalization of physics leads to a unique definition of an atom as an open quantum system and makes possible the renormalization that is required to account for the short-range nature of the forces that enable one to identify a given group in any environment. The lecture will demonstrate that the proper open systems predicted by the quantum action principle define the atom and that this definition accounts for the retention of an atom's chemical identity by enabling one to replace the quantum mechanical observables for force and energy with dressed, real space density distributions whose forms parallel the transferable topology of the electron density distribution.Key words: atom, action principle, atoms in molecules, functional groups.
Noble gas catalysed 1,2-migrations in N2H+ and N2CH3+
Authors: Cunje Alwin , Rodriquez Christopher F , Bohme Diethard K , Hopkinson Alan C
Published: April 2011

Molecular orbital calculations are reported for N2H+ and N2CH3+ and for the transition structures for the rearrangement of these ions by 1,2-shifts of H and CH3. All reaction profiles were also calculated with one atom of noble gas, M, present (M = Ne, Ar, Kr). Structure optimizations were performed at B3LYP/6-311++G(d,p) and, in the case of N2H+···M, single point calculations were also performed at QCISD(T)(full)/6-311++G(2df,p). For N2H+, inclusion of one noble gas atom reduces the barrier to rearrangement from 46.6 kcal mol-1 for the uncatalysed reaction to 42.6 kcal mol-1 (by Ne), to 21.4 kcal mol-1 (by Ar), and to 11.0 kcal mol-1 (by Kr). For N2CH3+, the barrier of 36.4 kcal mol-1 is reduced to 35.1 kcal mol-1 by Ne, to 27.4 kcal mol-1 by Ar, and to 18.4 kcal mol-1 by Kr.Key words: catalysis, molecular orbital theory, argon, krypton.
A study of the vacuum pyrolysis of para-substituted diazoacetophenones with He(I) ultraviolet photoelectron spectroscopy
Authors: Werstiuk Nick H , Muchall Heidi M , Ma Jiagong , Liu Michael TH
Published: April 2011

An ultraviolet photoelectron (PE) spectrometer apparatus that utilizes a tuneable 50 W CW CO2 laser as a directed heat source was used to study the vacuum pyrolysis of diazoacetophenone (1a) and its p-methyl, p-methoxy, p-chloro, and p-nitro analogues 1b, 1c, 1d, and 1e. Analysis of the pyrolysate with He(I) ultraviolet PE spectroscopy shows that at a laser power level of 26 W (500 ± 50°C) 1a, 1b, 1c, and 1d, cleanly yield the corresponding phenylketenes 2a, 2b, 2c, and 2d, respectively, the products of the Wolff rearrangement of the incipient ketocarbenes. Of this group of highly reactive ketenes, which cannot be isolated in the condensed phase at ambient temperature, only 2a has been the subject of a previous PE spectroscopic study. But our work indicates that the sample of 2a prepared in the earlier study was impure. The low volatility of p-nitrodiazoacetophenone (1e) thwarted our attempts to generate 2e and obtain its spectrum. Calculations at semiempirical (AM1) and ab inito (HF/6-31G(d)) levels of theory established that the diazoacetophenones prefer to adopt twisted syn conformations. That the calculated ionization potentials (HAM/3 and Becke3LYP/6-31+G(d)//HF/6-31G(d)) of 1a-1d and the synthesized PE spectra of 1a, 1b, and 1c correlate well with the PE spectroscopic data supports this finding. Shifts observed in the three low-energy ionizations of ketenes 2b, 2c, and 2d induced by the para-substitution can be related to the character of the corresponding occupied molecular orbitals of phenylketene (2a).Key words: diazoacetophenones, phenylketenes, He(I) photoelectron spectroscopy, thermolysis, quantum chemical calculations.
Article
Authors: Hore Dennis , Natansohn Almeria , Rochon Paul
Published: April 2011

This paper concerns itself with photoinduced anisotropy in two azobenzene-functionalized polymers. A simple physical model of the process that considers only three possible states of azo chromophores is proposed. This model predicts an equilibrium level of anisotropy that depends on the pump irradiance and temperature. Each of these influences is examined in turn, with experimental illustrations from the two polymers poly[4-[2-(methacryloxy)-ethyl-ethyl]azobenzene] (pMEA) and poly[4prime-[[2-(methacryloxy)ethyl]-ethyl]amino-4-nitroazobenzene] (pDR1M).Key words: azobenzene polymers, photoinduced orientation, irradiance, temperature.
Solubilité de la beta-cyclodextrine dans les mélanges eau - nitrate d'éthylammonium à 25°C
Authors: Duvivier Stéphane , Turmine Mirielle , Letellier Pierre
Published: April 2011

β-Cyclodextrin solubilities were determined in water - ethylammonium nitrate (EAN) mixtures at 25°C. EAN is a molten salt at room temperature (θ f = 14°C). It is miscible with water in the whole range of mixtures. Unlike molecular solvents, addition of EAN to water involves a decrease of β-cyclodextrin solubility. In mixtures rich in salt, this solubility increases anew. β-Cyclodextrin solubility in pure salt is about 20 times the value in pure water. β-Cyclodextrin behavior in water-EAN mixtures can be easily described by assuming the presence in solution of a complex ion linking two molecules of β-cyclodextrin to one ethylammonium ion, which precipitates with nitrate ion.Key words: ethylammonium nitrate, β-cyclodextrin, solubility, solubility product, inclusion compounds.
Ternary cobalt germanium pnictides CoGexPn1-x (Pn = P, As, Sb) and the structure of Co3Ge2Sb, an intermetallic compound with stuffed Sb2 pairs
Authors: Mills Allison M , Lam Robert , Mar Arthur
Published: April 2011

The ternary cobalt germanium pnictide systems CoGexPn1-x (Pn = P, As, Sb; 0 <x <1) were investigated. The ternary phosphides CoGexP1-x and arsenides CoGexAs1-x adopt the MnP structure (Pnma) in the range 0 <x <0.8, with Ge and Pn (Pn = P, As) disordering over the anion sites. Reactions in the antimonide system CoGexSb1-x result in a mixture of ternary phases, one with the NiAs structure (P63/mmm) in which Ge and Sb disorder over the anion sites, and another that is a new intermetallic compound, Co3Ge2Sb. Single-crystal X-ray diffraction reveals that Co3Ge2Sb crystallizes in the hexagonal space group P6/mmm with a = 8.9128(13) Å, c = 7.6312(8) Å, and Z = 6 (T = 22°C). The structure of Co3Ge2Sb comprises alternating kagomé nets of Co atoms and 63 nets of Ge atoms, with Sb2 pairs stuffed along the centres of the concentric hexagons of these nets. Co3Ge2Sb may be regarded as an intermediate structure that is distorted from the limiting CoSn and CaCu5 structures. Key words: cobalt, germanium, antimony, pnictide, crystal structure
Article
Authors: Yam Chi Ming , Dickie Adam , Malkhasian Aramice , Kakkar Ashok K , Whitehead M A
Published: April 2011

The hydrolysis of surface-bound basic tin-amide moieties with acidic protons of alkynyl chromophores leads to molecular self-assembly of a variety of rigid-rod alkynes on inorganic oxide surfaces such as glass, quartz, and single crystal silicon. Characterization of these newly developed thin films was achieved by contact-angle goniometry, FTIR-ATR, ellipsometry, and X-ray photoelectron spectroscopy, which indicate that these thin films are densely packed. Comparative molecular mechanics modeling studies on unbound and chemisorbed -Sn-Ctriple bondC-H monomer, dimer, trimer, and a 12 × 12 (144 molecule) model substrate, suggest that surface anchoring of Sn-alkynyl units is essential for highly ordered thin-film structures that can effect topochemical polymerization. Preliminary MO calculations on a 4 × 4 model show conjugated molecular orbitals through the system.Key words: molecular self-assembly, rigid-rod alkynes, acid-base hydrolysis, tin-alkynyl thin films, molecular mechanics modeling studies, topochemical polymerization, molecular orbitals.
Regular polyhedral molecules. P20 and its inclusion compounds
Authors: Rulísek Lubomír , Havlas Zdenek , Hermánek Stanislav , Plesek Jaromír
Published: April 2011

Based upon the geometrical properties of regular polyhedrons, the possibility of the existence of certain polyhedral molecules composed of only one element is investigated. A very promising candidate - the regular dodecahedron - is selected as the convenient polyhedral structural pattern and phosphorus as the appropriate element. A series of high-level ab initio calculations is performed on the dodecahedral P20 molecule, including predictions of its thermodynamic and kinetic stability, natural bond orbital analysis, vibrational analysis, and inclusion of some elements into the molecular skeleton. Due to the potential stabilizing agents that may eventually form stable inclusion compounds and the estimated high kinetic stability, the question of the possible existence of P20 is answered in the positive.Key words: ab initio calculations, inclusion compounds, P20, phosphorus clusters, polyhedra.
Surface studies of nano-dimensional particle size iron-manganese spinel mixed oxides
Authors: Uzunova Ellie L , Klissurski Dimitar G , Nemska Stella D
Published: April 2011

Monophase binary iron-manganese spinel oxides of high dispersity are prepared by thermal decomposition of carbonate precursors in the limits 0.33 < Fe/Mn < 2, at temperatures 570-770 K. Interparticle meso- and macropores contribute to the surface morphology of the spinel oxides, composed from spherical-shaped particles with diameters in the range 7-12 nm. The cation distribution of manganese ferrite corresponds to Mn0.85Fe0.15[Mn0.14Fe1.86]O4+δ. Surface analysis by ESCA reveals high concentration of nonstoichiometric oxygen and presence of Mn(III) and Mn(IV) is indicated in the X-ray photoelectron spectra. Reduction with hydrogen proceeds in two steps and is shifted to higher temperatures with increasing the iron content.Key words: ferrite, spinel, Fe, Mn.
Coordination complexes derived from 3,6-di(2-pyridyl)-1,4-dihydro-1,2,4,5-tetrazine (DPDHT). Synthesis and molecular structure of [(DPT)(GaMe2)2]
Authors: Preston Peter N , Rettig Steven J , Storr Alan , Trotter James
Published: April 2011

The facile reaction of 3,6-di(2-pyridyl)-1,4-dihydro-1,2,4,5-tetrazine (DPDHT) (1) with trimethylgallium has resulted in the formation of the purple crystalline product, [(DPT)(GaMe2)2] (2), via methane elimination. Crystals of [(DPT)(GaMe2)2] are orthorhombic, Pbca, a = 15.380(2), b = 21.642(4), c = 11.355(2) Å, Z = 8. The structure was solved by heavy-atom Patterson methods and refined by full-matrix least-squares procedures to R = 0.035 for 1570 reflections with I >= 3σ(I) (Rw = 0.063 for all 4342 reflections). The [(DPT)(GaMe2)2] molecule is roughly planar (apart from the four methyl groups), in contrast to the folded structure of the DPDHT molecule; molecular dimensions are normal.Key words: methylgallium, crystal structure, dipyridyldihydrotetrazine.