bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermodynamics of aqueous EDTA systems: Apparent and partial molar heat capacities and volumes of aqueous EDTA4−, HEDTA3−, H2EDTA2−, NaEDTA3−, and KEDTA3− at 25 °C. Relaxation effects in mixed aqueous electrolyte solutions and calculations of temperature dependent equilibrium constants
Authors: Hovey Jamey K. , Hepler Loren G. , Tremaine Peter R.
Published: May 2006

Calorimetric and densimetric measurements have led to apparent molar heat capacities and volumes for aqueous solutions of the mixed electrolytes [(CH3)4N]4EDTA + (CH3)4NOH, Na4EDTA + NaOH, and K4EDTA + KOH, and single electrolytes Na2H2EDTA and [(CH3)4N]3[HEDTA] at 25 °C. We have analyzed these results in terms of Young's rule and Pitzer's ion interaction model to obtain standard state partial molar heat capacities and volumes of EDTA4−(aq), HEDTA3−(aq), H2EDTA2−(aq), NaEDTA3−(aq), and KEDTA3−(aq) at 25 °C. For these calculations it was also necessary to evaluate the "relaxation" contribution to the measured heat capacities of some solutions. The partial molar heat capacities obtained here have been used with enthalpies from previous investigations for calculations of several equilibrium constants over wide ranges of temperature; volumes can be used for similar calculations of the effects of pressure.
Calorimetric determination of the deviation between the International Practical Temperature Scale 1968 and the Thermodynamic Temperature Scale
Authors: Ernst Günter , Bräuning Günter , Lai Joon-Fen
Published: May 2006

A flow calorimeter was constructed to measure the isobaric heat capacity cp for dilute fluids for pressure [Formula: see text] and for temperature [Formula: see text]. The special design features of the calorimeter facilitate measurements at extremely high accuracy. In this paper the measurements have been used to explore the metrology of the temperature. Measured values of cp were compared with corresponding theoretical values calculated via statistical mechanics. From the comparison, the deviation between the International Practical Temperature Scale of 1968 and the (theoretical) Thermodynamic Temperature Scale has been obtained. The results of this metrology are in good agreement with those obtained with the PVT gas thermometer and those obtained by radiometry. The comparison establishes the accuracy of the calorimeter and, more important, the feasibility of cp metrology, especially for probing local stretching or contraction of the International Practical Temperature Scale. The integration of this distortion, starting from the triple point of water, yields the deviation between the scales. It is, e.g., between 30 mK and 40 mK at the boiling point of water, according to our results.
Synthesis and structural characterization of two triclinic modifications of diethylammonium trans-tetrachlorobis(dimethylsulfoxide-S)rhodate(III): an example of hydrogen-bond acceptor structural isomerism
Authors: Gamage Sujatha N. , James Brian R. , Rettig Steven J. , Trotter James
Published: May 2006

Two crystalline modifications (I and II) of diethylammonium trans-tetrachlorobis(dimethylsulfoxide-S)rhodate(III) have been isolated from the same reaction mixture. The compound is formed by hydrolysis, in the presence of hydrochloric acid, of an η1-ylidic enamine complex of rhodium(III), which is made via dehydrogenation of triethylamine in the presence of mer-trichlorotris(dimethylsulfoxide)rhodium(III). Crystals of form I are triclinic, a = 8.1787(7), b = 10.761(1), c = 10.927(1) Å, α. = 86.681(6), β = 84.879(7), γ = 71.814(8)°, Z = 2, space group [Formula: see text], and those of form II are triclinic, a = 7.931(2), b = 9.489(2), c = 13.302(2) Å, α = 102.03(1), β = 97.40(1), γ = 107.49(1)°, Z = 2, space group [Formula: see text].Both structures were solved by Patterson and Fourier methods and were refined by full-matrix least-squares procedures to R = 0.024 and 0.060 for 4959 and 4320 reflections with I ≥ 3σ(I), respectively. Both crystal structures consist of centrosymmetric [RhCl4(Me2SO)2]− anions and (NEt2H2)+ cations, linked by hydrogen bonds to form infinite chains. In form I the hydrogen bonds are all of the type [Formula: see text], while in form II they are all of the type [Formula: see text].
2,6-Di-tert-butylpyridine: an unusually weak base in dimethylsulfoxide
Authors: Benoit Robert L. , Fréchette Monique , Lefebvre Diane
Published: May 2006

The ionization constants of the conjugate acids BH+ of pyridine, 2-picoline, 2,6-lutidine, and 2,6-di-tert-butylpyridine (DTBP) have been determined in Me2SO. The partition coefficients of the bases B between Me2SO and water, and the enthalpies of solution and protonation of B in Me2SO have also been obtained. In contrast to its high basicity in the gas phase, DTBP is an abnormally weak base in Me2SO (pK = 0.81). The factors responsible for this very low basicity are analyzed by considering correlations between the gas-phase, Me2SO, and aqueous basicities of B and by comparing the transfer parameters for B and BH+. The solvation of DTBP and DTBPH+ in Me2SO and in water differs. While the solvation of DTBP in Me2SO is normal, the enthalpy of solution of DTBPH+ in Me2SO is abnormally low and close to that of a cation whose solvation is nonspecific. This suggests a much reduced H-bonding between sterically hindered DTBPH+ and the large Me2SO solvent molecule.
Enzyme catalysed hydrolysis of chlorophenoxypropionates
Authors: Chênevert Robert , D'astous Linda
Published: May 2006

We report on the enzymatic hydrolysis of methyl 2-phenoxypropionate and of the following chlorinated derivatives: methyl o-chloro-, m-chloro-, p-chloro-, and o,p-dichloro-2-phenoxypropionates. α-Chymotrypsin, lipase, and pig liver esterase have an R enantioselectivity whereas subtilisin has an S enantioselectivity. Enantiomeric excesses (e.e.) cover a wide range (from 5 to 100%).
Excess molar enthalpies of binary mixtures containing esters of fatty acids
Authors: Otin Santos , Senar Ignacio , Soriano Ma José , Losa Celso Gutierrez
Published: May 2006

Excess molar enthalpies [Formula: see text] at 310.15 K and 101.32 kPa, have been determined for the binary mixtures: lauric acid ethyl ester +, stearic acid ethyl ester +, oleic acid ethyl ester +, linoleic acid ethyl ester + n-hexadecane, + toluene, or + ethyl alcohol, and elaidic acid ethyl ester + n-hexadecane or + toluene.The results show that HE of ester + n-hexadecane mixtures increases with decreasing chain length and with increasing unsaturation of the ester molecule. Ester + toluene mixtures are slightly exothermic and ester + alcohol are strongly endothermic, with [Formula: see text] values ranging from 1535 to 1740 J mol−1 at the maximum.
Conductimetric studies of ionic association of tetraalkylammonium halides in iso-propanol + water mixtures at 25 °C. Part II.
Authors: Ansari Auaz Ahmad , Islam M. R.
Published: May 2006

Electrical conductivities of Me4NBr, Et4NBr, Pr4NBr, Bu4NBr, and Bu4PBr have been measured in isopropanol + water (2-PrOH + H2O) mixtures covering the approximate range of dielectric constant (71.40 ≥ D ≥ 19.40) at 25 °C. The conductance data have been analysed by using the Fuoss-1978 (F78) conductance equation and the results compared with those obtained from the Fuoss–Onsager–Skinner (FOS) equation. The values of the limiting equivalent conductance, Λ0, the association constant, KA, and the distance of ion-size parameter [Formula: see text] are computed from these data. A better fit of the conductance data was provided by the F78 equation. Ion–solvent interactions and effective sizes of tetraalkylammonium ions are also discussed in order to understand the magnitude of the ionic association. The overall association behaviour of these salts has been found to increase with decrease in dielectric constant of the medium.
Molecular emission and electronic structure of associated chlorophyll a
Authors: Binnie N. E. , Haley L. V. , Mattioli T. A. , Thibodeau D. L. , Wang W. , Koningstein J. A.
Published: May 2006

We report the wavelength-selective Raman and fluorescence spectra of monomeric and aggregate species of chlorophyll a in solution. The excitation profile for the molecular emission of the various chlorophyll complexes permit the construction of part of the electronic energy level diagram. For a T-shaped dimeric chlorophyll a, pseudo-exciton splittings of 667 cm−1 in the Soret and 397 cm−1 in the Qy bands are obtained.
Orientation of some disk-shaped solutes in nematic liquid crystals
Authors: Yim C. T. , Gilson D. F. R.
Published: May 2006

The solute orientation parameters for benzene, trichloro-, and tribromobenzene have been measured, as functions of temperature, in the nematic solvents EBBA and ZLI-1132. The potential functions for orientation were derived for the model based on short and long-range contributions to the potential, with the former dependent on either a function of molecular shape or of molecular volume. There is reasonable agreement between calculated and experimental solute order parameters in both cases, and the difference in solute order parameter in the two solvents arises mainly from the difference in solvent electric field gradient.
Long-range formyl proton coupling constants of 4-X-phenyl formats (X = H, F, CH3, NO2) and 2,6-dichlorophenyl formate. Conformations in solution
Authors: Schaefer Ted , Sebastian Rudy , Penner Glenn H.
Published: May 2006

The signs and magnitudes of the long-range coupling constants between the formyl and ring protons over five, six, seven, and eight bonds in phenyl formate and its 4-fluoro, 4-methyl, and 4-nitro derivatives are reported. These numbers are combined with CNDO/2 and INDO MO FPT computations of their conformational dependence and with STO-3G MO populational distributions to provide a description of the conformational behaviour of these molecules. The Z conformers, predominantly nonplanar and having the carbonyl group pointing towards the ring, appear to account for more than 95% of the molecules in CS2 solution at 300 K. In polar solvents, significant populations of the E conformers are indicated by the long-range coupling constants. The long-range coupling constants for the formyl proton in 2,6-dichlorophenyl formate are consistent with geometry-optimized STO-3G MO computations, which imply that the Z conformation, with the aldehyde group lying near the plane perpendicular to the benzene plane, is again at least 95% abundant at 300 K. The proton chemical shifts are also consistent with these conclusions.
Main group (IIIA or 13) complexes of benzohydroxamic acid and the crystal structure of tris(benzohydroxamato)indium(III)
Authors: Matsuba Carey A. , Rettig Steven J. , Orvig Chris
Published: May 2006

A series of tris(benzohydroxamato)metal(III) complexes has been prepared and characterized wherein the metals are aluminum, gallium, and indium. The complexes are synthesized in high yield from aqueous solution. The indium complex, as its ethanol solvate In(C7H6NO2)3•C2H5OH, has been studied by single crystal X-ray diffraction. The crystals are monoclinic with a = 11.091(2), b = 18.065(3), c = 12.861(2) Å, β = 105.55(1)°, Z = 4, and space group P21/n. The structure was solved by Patterson and Fourier methods and was refined by full-matrix least-squares procedures to R = 0.038 and Rw = 0.037 for 2579 reflections with I ≥ 3σ(I). Bond lengths and angles in the compound were normal, although there is a strong In—O(C) interaction; the arrangement of the three ligands is mer. There is extensive hydrogen bonding involving all possible donors. All three complexes have been studied by mass spectrometry, and by infrared and nuclear magnetic resonance (1H, 27Al) spectroscopies. Parallel studies have been attempted with acetohydroxamic acid.
Synthesis and structural characterization of N,N′-diarylpiperazine N,N′-dioxide tetrahydrates (aryl = o-tolyl, p-tolyl, p-chlorophenyl)
Authors: Kwok Chun-Kiu , Mak Thomas C. W.
Published: May 2006

The synthesis and X-ray structure determination of N,N′-di(o-tolyl)piperazine N,N′-dioxide tetrahydrate, I, N,N′-di(p-tolyl)piperazine N,N′-dioxide tetrahydrate, II, and N,N′-di(p-chlorophenyl)piperazine N,N′-dioxide tetrahydrate, III, are described. Compound I crystallizes in space group [Formula: see text] with a = 7.778(1), b = 7.915(2), c = 8.919(2) Å, α = 106.25(2), β = 99.56(1), γ = 108.80(2)°, and Z = 1. Compound II crystallizes in space group [Formula: see text] with a = 6.558(1), b = 7.134(2), c = 11.610(3) Å; α = 73.23(2), β = 78.08(2), γ = 72.67(2)°, and Z = 1. Compound III crystallizes in space group P21/c with a = 9.159(3), b = 12.390(4), c = 8.339(4) Å, β = 97.38(3)°, and Z = 2. The structures of I–III were solved by the direct method and refined to R = 0.049 (1749 observed MoKα reflections), 0.055 (2651 observed reflections), and 0.035 (1827 observed reflections), respectively. In each case, the N,N′-dioxide molecule occupies a site of symmetry [Formula: see text]. The piperazine ring takes the chair form, with two N—O bonds oriented axially in a trans configuration. The structures are characterized by strong hydrogen bonding between the water molecules, as well as between the N-oxide groups and water molecules, giving rise to puckered layers composed of various combinations of edge-sharing four-membered, six-membered, ten-membered, and twelve-membered rings. The aryl rings, which protrude on both sides of each puckered layer, constitute hydrophobic regions separating the hydrophilic layers in the crystal packing.
The core binding energies of some gaseous aromatic carboxylic acids and their relationship to profon affinities and gas phase acidities
Authors: McQuaide B. H. , Banna M. S.
Published: May 2006

The C 1s and O 1s core binding energies of gaseous benzoic, phthalic, isophthalic, and terephthalic acids have been measured by X-ray photoelectron spectroscopy. The π-donor relaxation energies associated with the carbonyl oxygen ionization in these systems have been found to be around 2 eV, close to the value for acetic acid. Comparison of the O 1s binding energies in phenol and benzoic acid with the gas phase acidities shows that the increased acidity of benzoic acid is attributable mostly to initial-state inductive effects. A number of O 1s – proton affinity correlations have been used to predict proton affinities for these acids. It is found that benzoic acid is the strongest base and the weakest acid.
Conjugate symmetry of molecular systems and determination of their conformations
Authors: Maruani Jean , Toro-Labbé Alejandro
Published: May 2006

In nonrigid molecules and molecular aggregates, the dependence of a property on conformation may be expressed in the form of a limited expansion in terms of appropriate harmonics. The use of the conjugate symmetry of the molecular groups to reduce such an expansion may have several advantages: (i) it helps decrease, sometimes drastically, the time required to calculate the conformational dependence of the considered property; (ii) it provides a parameterized functional form that can be used by experimentalists to rationalize their results. The symmetry rules that define the distinct non-zero harmonics are determined by a set of indices that depend on both the form and type of the property (scalar, polar, axial, tensorial; aggregate, mononuclear, binuclear) and the nature of the isodynamic operations characterizing the system. We have applied Altmann's isodynamic groups to the analysis of Wigner's harmonic expansions of dynamical, electric, and magnetic properties of various molecular structures: binary molecular associations, quasi-atoms in molecular fields, rigid molecules in crystal lattices, and non-rigid molecules involving one to three rotors. A few examples are given to illustrate these considerations.
Dérivés hydrosilylés des complexes (η-arène) tricarbonylchrome, de type (η C6R6)(CO)2Cr(H)SiHPh2; liaison à 2 électrons/3 centres, Cr—H—Si
Authors: Matarasso-Tchiroukhine Elisabeth , Jaouen Gérard
Published: May 2006

Diphenylsilane reacts photochemically, at low temperature, on the η(tricarbonylchromium) arenes, to give unstables hydrosilylcomplexes, (η-C6R6)(CO)2Cr(H)SiHPh2 with a three-center two-electron bond, Cr—H—Si; according to 29Si NMR data, the degree of this bond is higher than both the degree of the Mn—H—Si bond in isoelectronic manganese compounds, (η-C5R5)L2Mn(H)SiHPh2, and the degree of the three-center Cr—H—Si bond in the permethylated complex, (η-C6Me6)(CO)2Cr(H)SiHPh2, of chromium. The variation of [Formula: see text] depending on the electron density of the metal is discussed.
Effect of residual linear orientation on the optical properties of cholesteric films
Authors: Ritcey Anna M. , Charlet Gérard , Gray Derek G.
Published: May 2006

The apparent circular dichroism arising from the selective reflection of circularly polarized light by cholesteric films of (hydroxypropyl)cellulose is extremely sensitive to residual linear orientation. The introduction of a uniaxially oriented film in the spectropolarimeter beam in front of a liquid crystalline sample may change both the intensity and the sign of the observed mesophase reflection band. The results can be understood by a simple consideration of the way in which the polarization state of light is altered as it traverses the birefringent film. These observations emphasize a potential problem in the use of circular reflectivity as a method to characterize the reflection properties of polymeric cholesteric liquid crystals. The presence of linear orientation in such samples can give rise to artifacts.
Vanadium(V) oxyanions. The dependence of vanadate alkyl ester formation on the pKa of the parent alcohols
Authors: Tracey Alan S. , Galeffi Bruno , Mahjour Soroush
Published: May 2006

The interaction of vanadate (VO4H21−) with a variety of alkyl alcohol's (ROH) covering about seven pKa units of acidity have been studied in aqueous solution by 51V nuclear magnetic resonance spectroscopy. A linear free energy relationship between the equilibrium constant for the formation of the vanadate monoester (HOVO3R1−) and the acidity of the alcohol was established at 23 °C. The correlation was found to be [Formula: see text] where K = [HOVO3R1−]/[VO4H21−][ROH]. This correlation was shown not to extend to ligands with π-bonding capability such as phenols or phosphates, where the products are highly favoured relative to the alkyl esters. An interesting correlation between pKa values of the product esters and the pKa of the parent alcohols was also observed. It was found that below a [Formula: see text] of about 15 the pKa values of the esters were essentially constant. However, above this value of 15 the pKa of the ester was found to increase rapidly with an increase in pKa of the alcohol. This result may indicate that the electron accepting ability of the metal is exhausted with the higher pKa alcohols, and the extra electron density is transferred to the oxygens, thus causing an increase in pKa of the ester.
The kinetics of gas phase reactions studied in a "homogeneous reactor"
Authors: Roscoe John M.
Published: May 2006

The use of a "well-stirred" or "homogeneous" reactor in kinetic studies of gas phase reactions has been examined to assess the sensitivity of the method to the criteria upon which its use is based. The effects of heterogeneous and homogeneous secondary reactions are considered and the validity of the assumption of homogeneity has been examined experimentally for conditions similar to those which have been used elsewhere. The atom sink presented by the excess reagent under pseudo first order conditions results in failure of the homogeneity assumption. However, it is found that homogeneity is not required for successful use of the method provided the analytical measurements have good spatial resolution and the reaction volume is well-defined. The method is illustrated by using it to study some reactions of O(3P).
Determination of the dissociation constant of D2O2 in D2O by a conventional method and via muonium kinetics
Authors: Brodovitch Jean-Claude , Percival Paul W. , Poteryko Derek
Published: May 2006

The dissociation constant of deuterium peroxide has been determined from measurements of the pH of mixtures of D2O2/NaODinD2O. At 25 °C, pKa = 12.35 (5), confirming the value previously deduced from a kinetic study of the reactions of muonium with H2O2 and D2O2. The enthalpy and entropy of dissociation of D2O2 are estimated to be 34.7 (8.8) kJ mol−1 and −120 (30) J K−1 respectively.
A 6-31G* chemistry of isoelectronic tetrahedral XL4ε and YL4ε (X = Li to F; Y = Na to Cl; L = H, F, Cl) species. Part 2. Energies, bond lengths, and critical radii
Authors: Choi S. C. , Boyd Russell J. , Knop Osvald
Published: May 2006

The 6-31G* ab initio treatment of isoelectronic tetrahedral species now covers the complete XL4ε and YL4ε series (X = Li to F; Y = Na to Cl; L = H, F, Cl). The optimized equilibrium molecular parameters comprise the total electronic energy E, bond lengths, critical radii rc, MO energy levels, net charges, and electron densities at the bond critical points; only the first four are discussed in this part. The stability in terms of E, of the tetrahedral species relative to some competing systems, is examined. The energy requirements associated with the transfer of electronic charge from L to the central atom are reflected in the variation of the critical radii with the oxidation state m of X and Y, with important differences between the first- and the second-row elements. In an appendix it is shown that the E~HF limit energies of isoelectronic He-core (Li+ ff.), Ne-core (Na+ ff.), and Ar-core (K+ ff.) series of ions can be represented analytically by quadratic polynomials in m to an accuracy of ~0.0023% of the E~HF limit range or better, and that these approximations for the three series are qualitatively of the type E = −a(Z − b)2.
Equilibria between Bi2O3 and Bi5O7I in aqueous solutions at 10–60 °C, and in oxygen atmospheres at 550–800 °C
Authors: Taylor Peter , Lopata Vincent J.
Published: May 2006

Equilibria between Bi5O7I and Bi2O3 have been measured with the solids in contact with aqueous solutions at 10–60 °C, and with low-pressure oxygen (0.2–100kPa) at 550–800 °C. In the aqueous systems, iodide activities were measured as functions of pH and temperature. In the dry system, iodine partial pressures were measured spectrophotometrically while varying the temperature and oxygen partial pressure. The standard enthalpy of formation and entropy of α-Bi5O7I were derived from these measurements, and values for BiOI were also estimated. The results combine to give a self-consistent account of phase relations between Bi5O7I and Bi2O3 up to 800 °C. Some equilibria involving BiOI are discussed briefly.
The preparation of SeI3SbF6 and TeI3SbF6; the X-ray crystal structures of SBr3AsF6, SeI3AsF6, SeI3SbF6, and TeI3SbF6; some considerations of the energetics of the formation of SBr3AsF6 and SeI3AsF6.
Authors: Johnson James P. , Murchie Michael , Passmore Jack , Tajik Mahmoud , White Peter S. , Wong. Chi-Ming
Published: May 2006

not available
Glycosides from Muscari armeniacum and Muscari botryoides. Isolation and structure of Muscarosides G–N
Authors: Adinolfi Matteo , Barone Gaspare , Corsaro Maria Michela , Mangoni Lorenzo , Lanzetta Rosa , Parrilli Michelangelo
Published: May 2006

Eight novel oligoglycosides, Muscarosides G–N 3–10, have been isolated from the bulbs of Muscari armeniacum and Muscari botryoides, in addition to known Muscarosides A–C 12–14 and scillascilloside D–1 11. Their structure was elucidated mainly by spectral analysis (FAB–MS and 1D- and 2D-nmr spectroscopy) and, in some cases, degradative chemical study. The aglycone of 3–10 is the spirocyclic nortriterpenoid 1 or 2. The monose units of their di-, tri-, tetra-, or hexasaccharide chain are β-D-glucopyranose, α-L-arabinopyranose, α-L-rhamnopyranose, β-D-galactopyranose, α-L-arabinofuranose, and β-D-apio-D-furanose.
Structure and reactivity in highly halogenated ketazines
Authors: Lai Ellen C.K. , Mackay Donald , Taylor Nicholas J. , Watson Kenneth N.
Published: May 2006

The azines of acetophenone and its mono- and di-chlorinated derivatives show a bathochronic shift in the yellow region, but the azine of trichloroacetophenone is colorless. Similar trends are observed in the brominated analogs and in the chlorinated propiophenone azines. The colorless tétrachloropropiophénone azine (13) is shown by X-ray analysis to be nonplanar at the azine atoms (N—N torsion angle, 126.7°). Hexachloroacetophenone azine (9) undergoes displacement of all its chlorines with NaOMe to give the hexamethoxy compound 16, also colorless. With acid, 16 gives the yellow planar (X-ray) ketazine diester 20. These reactions appear to be general for the trichloromethyl group in azines, but not for the α,α-dichloroalkyl group, attempts at the sequence 13 to 28 proving unsuccessful.
A further view on the calculation of the enthalpy of cavity formation in liquids. The influence of the cavity size and shape
Authors: Moura-Ramos Joaquim J. , Dionísio Madalena S. , Gonçalves Raquel C. , Diogo Hermínio P.
Published: May 2006

A reformulation of the Sinanoglu–Reisse semi-empirical approach to describe the cavity formation process in liquids is proposed. The energy of cavity formation is regarded as a strictly potential energy corrected for short range order effects in the liquid state. Deviations from the Corresponding States Principle quantified by the Pitzer acentric factor are considered to describe these short range order effects.The influence of the cavity shape on the calculation of its energetics is emphasized as well as the need for a realistic description of the dependence of the microscopic surface tension on the size and shape of the cavities. The proposed method is successfully applied to binary mixtures of n-alkanes at infinite dilution.
Hydrolysis of p-nitrophenyl alkanoates in aqueous organic solvent mixtures. The dispersal of aggregates and the uncoiling of n-alkyl chains
Authors: Tee Oswald S. , Enos John A.
Published: May 2006

Rate constants have been measured for the hydrolysis of six p-nitrophenyl alkanoates (C2, C4, C6, C8, C10, and C12) in basic aqueous media containing up to 80% (v/v) of the cosolvents: ethylene glycol (EG), 2-methoxyethanol (2ME), 1,2-dimethoxyethane (DME, glyme), bis(2-methoxyethyl) ether (diglyme), or DMSO. Addition of these cosolvents reduces and ultimately removes hydrophobic aggregation and coiling of the longer chain alkanoates, with the ether-type solvents (2ME, DME, and diglyme) being more efficient than EG or DMSO. Once the rate-lowering effects of aggregation and coiling have been removed by addition of a cosolvent, the rates of hydrolysis of the C4–C12 esters are all virtually the same, in a given medium. Thus, the apparent "steric size" of the C4–C12 (and even C16) acyl chains does not differ significantly in basic p-nitrophenyl ester hydrolysis. Addition of DMSO brings about rate increases that are greater in a carbonate buffer (pH 10.48) than those in 0.05 M NaOH solution, and these increases are larger than those observed for ethyl acetate in 0.05 M NaOH solution. None of the rate increases rise as quickly as the enhanced basicity of aqueous DMSO media.
LEED and AES studies of chemisorption resulting from low exposures of C2H4, CO, and PH3 to the (0001) surface of zirconium
Authors: Lou J. R. , Wong P. C. , Mitchell K. A. R.
Published: May 2006

Low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES) have been used to study for the first time the chemisorption systems formed on the (0001) surface of zirconium by exposing to C2H4, CO, and PH3 in the one to ten Langmuir regime. The adsorptions are done at room temperature, but there is subsequent heating to optimize the surface ordering. The main observations are as follows: (i) after heating C2H4-covered surfaces to effect hydrogen desorption, the remaining carbon can form two different ordered (1 × 1)-C structures; (ii) CO forms both (2 × 2)- and (1 × 1)-type structures; (iii) the temperature at which the bulk diffusion of oxygen becomes significant, as determined by AES, is about 40 °C greater on a CO-treated surface than for an O2-treated Zr(0001) surface; and (iv) heating a PH3-covered surface can yield a weakly-ordered (3 × 3)-P structure. The observation (iv) contrasts with that for the analogous surface prepared previously with H2S; the poorly developed (3 × 3)-P surface structure results from the fact that the temperatures required for surface ordering overlap with those which yield a loss of phosphorus from the surface region.
The ion-pair mechanism and bimolecular displacement at saturated carbon. VII. Racemization of substituted 1-phenylbromoethanes; ionic strength effects
Authors: Stein Allan R.
Published: May 2006

No, or at most very small, salt effects have been detected for second-order racemizations of various 1-phenylbromoethanes, confirming that the "mixed kinetics", previously reported for 4-methyl- and 3,4-dimethylphenylbromoethanes with tetrabutylammonium bromide in acetonitrile and nitromethane, did not reflect a salt effect on a unimolecular reaction. Thus the uni- and bimolecular rate components can be evaluated using the equation:[Formula: see text]where k1 = first-order or unimolecular rate constant, the intercept, and [Formula: see text], the latter being the rate constant for the bimolecular substitution. A "special salt effect" was found for the unimolecular component; it was especially pronounced for 3,4-dimethyl substrate in acetonitrile with Bu4NClO4 as the electrolyte. In acetone, where no unimolecular reaction component was detected even with those substrates giving the most stable carbocations, the only salt effect was a common ion, Bu4N+, effect on the incomplete dissociation of Bu4NBr. From an iterative best fit for plots of observed rate versus calculated bromide ion activity for unsubstituted, 4-methyl, and 3,4-dimethyl substrates, Kassoc ~ 15 ± 1 at 40 °C. The results are interpreted as additional support for a progression of mechanism with nucleophilic attack possible at any stage of the series of equilibria: substrate [Formula: see text] contact ion pair [Formula: see text] various solvated ion pairs [Formula: see text] dissociated ions. Keywords: special salt effects, ionic strength effects, racemization of 1-phenylbromoethanes, mechanism of nucleophilic substitution, ion pair mechanism.
Coprinolone and Δ6-coprinolone: new sesquiterpenes from Coprinus psychromorbidus
Authors: Starratt Alvin N. , Ward Edmund W. B. , Stothers J. B.
Published: May 2006

The structure of coprinolone (1), an oxygen-bridged protoilludane from the W2 isolate of the fungus Coprinuspsychromorbidus, has been elucidated by chemical transformations and detailed 1H and 13C magnetic resonance studies, including homo- and heteronuclear correlation spectra. The 1H–1H coupling data and nuclear Overhauser difference spectra for 1 and derived isomers led to the establishment of its stereochemistry. A second metabolite was identified as Δ6-coprinolone (20) by spectroscopic results. Confirmatory evidence in support of the structures was obtained from the labelling patterns of the compounds from cultures supplemented with sodium [1,2-13C2]acetate. Keywords: coprinolone, Δ6-coprinolone, protoilludane, sesquiterpenes, NMR.
The structure of μ4-oxo-hexa-μ-chloro-tetrakis{(dimethyl sulfoxide)copper(II)}. dimethyl sulfide
Authors: Brownstein Sydney , Han Nam Fong , Gabe Eric , Lee Florence
Published: May 2006

μ4-Oxo-hexa-μ-chloro-tetrakis{(dimethyl sulfoxide)copper(II)}•dimethyl sulfide, from the reaction of copper metal, dimethyl sulfoxide, and carbon tetrachloride crystallizes as orange crystals in the orthorhombic noncentrosymmetric space group P212121 with a = 10.5820(20), b = 10.5710(20), and c = 28.255(5) Å and Z = 4. The chirality of the individual molecules is attributed to twists of the planes of the sulfur and carbon atoms of the dimethyl sulfoxide ligands relative to the oxygen–copper–oxygen axes. Keywords: crystal structure, copper cluster complex.
Diels–Alder addition of the fumarate and acrylate of S-methyl lactate to α-hydroxy orthoquinodimethanes
Authors: Charlton James L. , Plourde Guy L. , Koh Kevin , Secco Anthony S.
Published: May 2006

The cycloaddition of α-hydroxy orthoquinodimethane, generated photochemically from 2-methylbenzaldehyde, to the fumarate and acrylate of S-methyl lactate has been found to give a single diastereomer with high asymmetric induction (>95% de). This reaction provides a new and versatile synthetic route to substituted tetralins of high optical purity. A trans stereochemistry between the vicinal hydroxyl and carboxylactyl groups has been established for these cycloadducts. This is in contrast to previous work where cis stereochemistry has always been found for major cycloadducts of α-hydroxy o-QDMs. The high asymmetric induction, unusual diastereoselectivity, and the potential use of these reactions in asymmetric synthesis are discussed. Keywords: o-quinodimethanes, Diels–Alder, asymmetric, cycloaddition, induction, diastereoselective.
The binding of bilirubin by immobilized oligopeptides containing lysine
Authors: Bouvier M. , Brown G. R. , St-Pierre L. E.
Published: May 2006

Peptides consisting of portions of the sequence Arg-(Lys)2-(Ser)2-Lys-(Ala)3 have been immobilized onto a polyacrylamide support by solid phase peptide synthesis. Isotherms at 0 °C for the adsorption of bilirubin from phosphate buffer by these peptide resins are highly dependent on pH, in the range 7.80–11.00, demonstrating the importance of ionic interactions. The adsorption behaviour of bilirubin-related tetrapyrroles shows that structural factors also influence the process. Peptide resins containing two or more residues of lysine have two binding sites on each pendant and are characterized by positive cooperativity, to a degree that is highly dependent on the number of residues. It is proposed that bilirubin molecules bound by lysine-containing pendants are stacked, the dimer state being stabilized by π-π electron interactions, hydrogen bonds, and hydrophobic interactions. Site binding constants show that arginine-containing pendants manifest a stronger affinity for bilirubin. Keywords: bilirubin, adsorption, lysine, oligopeptides, cooperativity.
Structure of the lipopolysaccharide O-antigen of Actinobacillus (Haemophilus) pleuropneumoniae serotype 6 (ATCC 33590)
Authors: Altman Eleonora , Brisson Jean-Robert , Perry Malcolm B.
Published: May 2006

One- and two-dimensional high resolution 1H and 13C nuclear magnetic resonance spectroscopy at 500 MHz and 125 MHz together with methylation and partial hydrolytic degradation methods were used to determine the structure of the antigenic O-polysaccharide produced by Actinobacillus (Haemophilus) pleuropneumoniae serotype 6 (ATCC 33590). The O-polysaccharide was shown to be a high molecular weight unbranched linear polymer of repeating pentasaccharide units having the structure:[Formula: see text].Keywords: Actinobacilluspleuropneumoniae, lipopolysaccharide, O-antigen, nuclear magnetic resonance.
Étude cinétique de la N-chloration de la diméthylamine et de la diéthylamine en phase aqueuse
Authors: Matte Denise , Solastiouk Bernard , Merlin André , Deglise Xavier
Published: May 2006

A complete kinetic study of the N-chlorination, in aqueous medium, of dimethylamine and diethylamine by a stopflow spectrophotometric method is presented. In neutral or basic medium our experimental results can be interpreted by two kinetically indistinguishable mechanisms; the reactions between protonated amine (R2NH2+) and hypochlorite ion (ClO−) and the reaction between R2NH and hypochlorous acid (ClOH) are equivalent because of the fast equilibrium of proton exchange existing between the two groups of possible reactants [Formula: see text]. In acid medium, in the presence of chloride ions, we observed a reaction by aqueous chlorine (Cl2) on the amine (Cl2 + R2NH → chloramine).Keywords: kinetics, N-chlorination, amines, aqueous medium.
Dielectric relaxation of acetyl- and benzoyl-acetones
Authors: Khanna R. K. , Bhatnagar Abha
Published: May 2006

Dielectric absorption measurements are reported at radio and microwave frequencies (at six different wavelengths) for acetylacetone and benzoylacetone solutions in benzene, in a temperature range 25–60 °C. Analysis of dielectric data in terms of Cole–Cole arc plots and multiple relaxation processes reveals that, at higher temperatures, overall molecular relaxation is the dominant relaxation mechanism in these β-diketones. The observed relaxation times, distribution parameters, and dipole moments are in reasonable agreement with the few data reported for some temperatures, in the literature. The activation energy parameters are also evaluated assuming dielectric relaxation to be a rate process. Molar polarization vs. weight fraction (concentration) plots show anomalous behaviour for acetylacetone. Keywords: dielectric properties, dielectric losses, relaxation times, dipole moment, dielectric absorption and dispersion, microwave measurements.
Protium–deuterium exchange of benzo-substituted heterocycles in neutral D2O at elevated temperatures
Authors: Werstiuk Nick Henry , Ju Chen
Published: May 2006

H–D exchange of 2-methylbenzofuran (1), 2-methylindole (2), 2-methylbenzimidazole (3), 2-methylbenzothiazole (4), and 2-methylbenzoxazole (5) has been studied in neutral D2O at elevated temperatures. While 1, 2, 3, and 4 can be specifically labelled and 4 can be perlabelled at 255 °C, 5 undergoes facile hydrolysis in D2O at 115 °C to 2-acetamidophenol (8) with the incorporation of deuterium into the methyl group. Keywords: H–D exchange, heterocycles, D2O, elevated temperatures.
Structural studies of organoboron compounds. XXXIII. 4,4-Dimethyl-2,2-diphenyl-1,3-dioxa-4-azonia-2-boratacyclohexaneand 3,3-dimethyl-2-phenoxy-2-phenyl-1-oxa-3-azonia-2-boratacyclopentane
Authors: Ebeling Eckardt , Kliegel Wolfgang , Rettig Steven J. , Trotter James
Published: May 2006

Details of the syntheses, physical properties, and crystal structures of the title compounds are reported. Crystals of 4,4-dimethyl-2,2-diphenyl-1,3-dioxa-4-azonia-2-boratacyclohexane, 3, are monoclinic, a = 6.512(1), b = 15.765(2), c = 14.342(4) Å, β = 93.170(7)°, Z = 4, space group Pn, and those of 3,3-dimethyl-2-phenoxy-2-phenyl-1-oxa-3-azonia-2-boratacyclopentane, 4, are orthorhombic, a = 13.5829(8), b = 16.940(1), c = 6.3181(4) Å, Z = 4, space group P21212. Both structures were solved by direct methods and were refined by full-matrix least-squares procedures to R = 0.034 and 0.034 for 1974 and 1478 reflections with I ≥ 3σ(I), respectively. The molecular structures are discussed in terms of the thermally-induced 1,2-migration of B-substituents by which 3 is converted to 4. Keywords: crystal structures, boron compounds, organoboron compounds.
Examination of the inert solvent assumption in the ideal associated solution model. Enthalpy of chloroform–triethylamine complex dissociation
Authors: Smith John F. , Hepler Loren G.
Published: May 2006

We have made new measurements of the enthalpies of adding cyclohexane to mixtures of chloroform + triethylamine + cyclohexane at 25 °C. The results of these measurements have been analysed in terms of the ideal associated solution model to obtain ΔHθ for the dissociation of the chloroform-triethylamine complex. Our value of ΔHθ is in excellent agreement with a published value that was obtained from results of measurements on binary mixtures of chloroform + triethylamine. This agreement indicates that it is usefully accurate to treat mixtures of chloroform + triethylamine + cyclohexane as ideal mixtures of chloroform, triethylamine, cyclohexane, and chloroform-triethylamine complex. This result has important implications for studies of associated systems dissolved in "inert" solvents and helps to provide a connection between complex formation in dilute solutions and in binary systems (A + B, no solvent). Keywords: ideal associated solution model, chloroform, triethylamine, inert solvent, hydrogen bonded complex.
An analysis of the pathways for magnesium ion in the field of a macrocyclic ligand
Authors: Hannongbua Supot V. , Kokpol Sirirat U. , Limtrakul Jumras P.
Published: May 2006

An abinitio MO-SCF calculations have been performed with a minimal Gaussian lobe basis set for numerous Mg(II) 1,4,7,10-tetraazacyclododecane (cyclen) configurations. Mg(II) shows a strong interaction with all functional groups of cyclen. The strongest interaction occurs when magnesium points to the cavity and perpendicular to the ligand plane. However, in the complex formation processes, the ion does not prefer to move along this direction because of the repulsive interaction with the NH functional groups. The favourable path for entering the cavity of the ligand encloses an angle of 30° with the z axis and lies in the plane between the opposite NH groups. Keywords: cyclen, macrocyclic effect, complex formation, favourable path, abinitio calculations.
Metabolites of the fairy ring fungus, Marasmiusoreades. Part 2. Norsesquiterpenes, further sesquiterpenes, and agrocybin
Authors: Ayer William A. , Craw Peter
Published: May 2006

The fungus Marasmiusoreades has previously been reported to produce the sesquiterpenes marasmone (1), anhydromarasmone (2), isomarasmone (3), and dihydromarasmone (4) when grown in liquid culture. We report herein several other sesquiterpene metabolites of the same skeleton but with differing oxidation patterns. The norsesquiterpenes O-formyloreadone (15a), 3α-hydroxyoreadone (15c), and dehydrooreadone (17b) are also reported. It is suggested that the formyl group in 15a is derived biogenetically from C-15 of a precursor sesquiterpene. Oxidation of 1α, 15-dihydroxymarasmene (13a), one of the new sesquiterpenes reported, with one equivalent of pyridinium dichromate gives O-formyloreadone (15a) as one of the products. Agrocybin (5), a polyacetylene amide previously isolated from the fungus Agrocybedura, has also been isolated from the cultures of M. oreades. It is suggested that agrocybin (5) is the phytotoxic compound responsible for the killing of grass caused by the fairy ring mushroom fungus. Keywords: sesquiterpenes, fungal metabolites, drimanes, fairy ring mushroom, agrocybin.
ortho-Specific alkylation of phenols via 1,3,2-benzodioxaborins
Authors: Lau Cheuk K. , Williams Haydn W.R. , Tardiff Sylvie , Dufresne Claude , Scheigetz John , Bélanger Patrice C.
Published: May 2006

Reaction of a phenol with an aldehyde in the presence of phenylboronic acid gives a 1,3,2-benzodioxaborin. The latter could be reduced to the corresponding ortho-alkylphenol with tert-butylamine borane in the presence of aluminum chloride. Alternatively, the dioxaborin, when reacted with an alkylthiol or an alcohol in the presence of an acid, gave the corresponding ortho-alkylthiomethyl- or ortho-alkoxymethylphenol. Keywords: phenol, alkylation, ortho-specific, 1,3,2-benzodioxaborin.
Ultraviolet spectrum of domoic acid
Authors: Falk Michael , Walter John A. , Wiseman Paul W.
Published: May 2006

The ultraviolet spectrum of aqueous domoic acid solutions has an intense absorption band, whose λmax shifts from 240.0 ± 0.3 nm at pH 1.3 to 244.7 ± 0.3 nm at pH 12.3. At the same time, its εmax increases from 24250 to 26700 L mol−1 cm−1. At pH 7 λmax is 242.8 ± 0.3 nm and εmax is 26035 ± 200 L mol−1 cm−1 Analysis of the variation of λmax and εmax with pH allowed us to estimate the values of these quantities for each of the five stages of protonation of domoic acid and to verify the pK values reported by Takemoto and Daigo. Keywords: ultraviolet spectrum, pK values, protonation, domoic acid.
Diphosphido bridged early/late heterobimetallic complexes: synthesis and molecular structure of Cp2Zr(μ-PPh2)2ReH(CO)3
Authors: Zheng Pei Yao , Stephan Douglas W.
Published: May 2006

The reaction of the metal–metal bonded complex Re2(CO)10 with Cp2Zr(PPh2)2 results in formation of the diphosphido bridged heterobimetallic species, Cp2Zr(μ-PPh2)2ReH(CO)3, 1. Complex 1 crystallizes in the space group P21/c with a = 17.393(3) Å, b = 14.348(7) Å, c = 13.036(3) Å, β = 92.35(2)°, Z = 4, and V = 3250(2) Å3. The crystallographic study confirmed that complex 1 contains two phosphido bridges between the Zr and Re centres. The Zr—P bond distances are 2.629(3) and 2.615(3) Å, while the Re—P bonds are 2.498(3) and 2.474(3) Å. The Zr—Re separation is 3.274(1) Å. The details of the geometry of the ZrP2Re core are discussed in relation to that of other diphosphido bridged early/late heterobimetallics. The possibility of dative bonding between the electron-rich, late metal and the electron-deficient early metal centre is discussed. The data indicate that if such dative bond is present in the d0–d6 complex 1, it is very weak. Keywords: rhenium, zirconium, heterobimetallic, crystal structure.
The conversion of a divinyldi-μ-methylene-dirhodium complex into a (μ-ethylidene-(μ-methylene-dirhodium complex
Authors: Martinez Jesus , Gill John B. , Adams Harry , Bailey Neil A. , Saez Isabel M. , Maitlis Peter M.
Published: May 2006

The dichloro-μ-ethylidene-μ-methylene-dirhodium complex, [(C5Me5Rh)2(μ-CHMe)(μ-CH2)Cl2] (2) was the main product of the reaction of the divinyl-di-μ-methylene-dirhodium complex [(C5Me5Rh-μ-CH2)2(CH=CH2)2] (1), with HCl in toluene at −78 °C. It was identified by an X-ray crystal structure determination and spectroscopically. Keywords: vinyl, μ-methylene, μ-ethylidene, rhodium, X-ray.
One-pot synthesis of N-substituted-3-hydroxy-4-pyridinone chelate complexes of aluminum, gallium, and indium
Authors: Zhang Zaihui , Hui T. L. Thomas , Orvig Chris
Published: May 2006

A series of tris(3-hydroxy-2-methyl-4-pyridinonato)metal(III) and tris(3-hydroxy-6-hydroxymethyl-4-pyridinonato)metal(III) complexes have been prepared in water by one-pot synthesis directly from maltol and kojic acid, respectively, and the metal ion (M = Al, Ga, In) with an appropriate amine. The pyridinones have substituents at the ring nitrogen atom (CH3, C2H5). The tris(3-hydroxy-4-pyronato)metal(III) complexes are formed insitu and these undergo nucleophilic attack by the primary amine; the appropriate tris(3-hydroxy-4-pyridinonato)metal(III) complexes are obtained. This method bypasses the sequential syntheses of ligand and metal complex, and has improved the yields of the tris(ligand)metal complexes, in particular by making them much more easily accessible. The electronic effects of binding the pyrone to the metal ions and of the substituents on the pyrone ring on the reactivity are discussed. Keywords: 3-hydroxy-4 pyridinone complexes, group 13 metal ions, one-pot synthesis.
Superacid-induced ring-opening reactions of fluorinated heterocycles
Authors: Kotun Stefan P. , DesMarteau Darryl D.
Published: May 2006

HF/AsF5 and HF/SbF5 superacid mixtures react with fluorinated small-ring heterocycles such as 1,2-oxazetidines and oxetanes with consequent addition of HF to give alcohol and amine ring-opened products in high yield. Excess HF serves as solvent and reactant. Ring compounds containing both nitrogen and oxygen as heteroatoms protonate predominantly on nitrogen; a case with competing O-protonation arises in the case of a chloro-substituted oxazetidine. In general, rings containing two heteroatoms retain the heteroatom–heteroatom bond and it is a carbon–heteroatom bond that opens. The resulting OH and NH functional groups are not protonated and lost in the superacid medium due to the instability of the highly fluorinated cations that would be left behind. Most of the heterocycles react at or below room temperature, although the very weakly basic 2,2-bis(trifluoromethyl)-3,3,4,4-tetrafluorooxetane requires the stronger HF/SbF5 superacid system and more severe conditions. Keywords: superacids, hydrogen fluoride, ring opening, fluorinated oxazetidines, fluorinated oxetanes.
Synthesis of fluorinated phosphonic, sulfonic, and mixed phosphonic/sulfonic acids
Authors: Su Debao , Cen Wenbiao , Kirchmeier Robert L. , Shreeve Jean'ne M.
Published: May 2006

The acids (HO)2P(O)CFHSO3H, (HO)2P(O)(CF2)4O(CF2)2SO3H, H(CF2)2O(CF2)2P(O)(OH)2, H(CF2)2O(CF2)4P(O)(OH)2, (HO)2P(O)(CF2)2O(CF2)4H, and the acid precursor (C2H5O)2P(O)CF(SO3Na)2 have been synthesized. Elemental analysis, 19F, 1H, and 31P NMR, and mass spectroscopy were used for characterization of these materials. They are very strong acids, and exhibit a high degree of stability in aqueous solution at elevated temperature, which makes them attractive candidates for use as electrolytes in fuel cells. Keywords: fluorinated phosphonic acids; fluorinated sulfonic acids; 1H, 19F, 31P NMR.