bluuebunny/crossref_metadata_2025 huggingface dataset:
Infrared intensities of liquids. IX. The Kramers–Kronig transform, and its approximation by the finite Hilbert transform via fast Fourier transforms
Authors: Bertie John E. , Zhang Shuliang L.
Published: May 2006

It is well known that the infinite Kramers–Kronig transform is equivalent to the infinite Hilbert transform, which is equivalent to the allied Fourier integrals. The Hilbert transform can thus be implemented using fast Fourier transform routines. Such implementation is usually some 60 times faster than the Kramers–Kronig transform for a data file containing about 7 points. This paper reports that, for transformations between the real and imaginary refractive indices, [Formula: see text] and [Formula: see text] in [Formula: see text], the FFT-based Hilbert transform can be much less accurate than, or as accurate as, the Kramers–Kronig transform, depending on the algorithm used. The Kramers–Kronig transform, incorporating Mclaurin's formula for finding the principal value of the integral, transforms [Formula: see text] spectra into [Formula: see text] spectra that are accurate to about 0.05%. Some Hilbert transform algorithms in the literature yield only about 4% accuracy. The BZ algorithm for the Hilbert transform is presented, for use on a laboratory computer running under DOS, that yields [Formula: see text] spectra accurate to 0.05%. For the transform from [Formula: see text] to [Formula: see text], the BZ algorithm gives [Formula: see text] accurate to about −0.2% of the largest k value in the spectrum. This compares with an accuracy of 0.5% for the Kramers–Kronig transform. In cases where the [Formula: see text] spectrum is truncated at low wavenumbers, a simple method is presented that improves by a factor of ~10 the accuracy at low wavenumber of the [Formula: see text] spectrum obtained by Hilbert or Kramers–Kronig transforms of the [Formula: see text] spectrum. Keywords: infrared intensities, complex refractive indices, Kramers–Kronig transform, Hilbert transform, optical constants.
Low-energy conformational domains of polypeptides, characterized by a random-search and minimization procedure
Authors: Michel André G. , Ameziane-Hassani Chakib , Bredin Nathalie
Published: May 2006

In the framework of molecular mechanics conformational energy calculations, a random-search and minimization procedure is presented to characterize low-energy domains of polypeptidic structures. Rather than striving for global minima, populations of conformers are randomly generated, and their energy is minimized in order to study their intrinsic properties. The application to the opioid peptide Met-Enkephalin allowed the identification of low-energy domains that are compared with previous results of conformational studies on this molecule. Our method gives a complete overview of the conformational behaviour of the polypeptide under study, including previously reported structures as determined from experimental and theoretical studies. To illustrate the usefulness of this method to determine bioactive peptidic structures and their active conformers, the application to geometrically constrained chemotactic tripeptides is presented. Keywords: peptides, conformation, theoretical prediction.
Structure cristalline et moléculaire d'un composé tricyclique contenant le cycle à dix chaînons dioxo diaza diphosphécine
Authors: Duthu Brigitte , Abed Karim El , Houalla Douraid , Wolf Robert , Jaud Joël
Published: May 2006

The sulfuration of the tricyclic organophosphorous dimer 2 leads easily to the dithiotricyclic derivative 3, which has been characterized by 31P, 1H, and 13C NMR, elemental analysis, and mass spectroscopy. Its crystal and molecular structure has been established by X-ray diffraction and compared to that of 2, which was previously determined. The comparative analysis of X-ray diffraction and NMR parameters gives accurate information about the molecular structure of both compounds. A numerical value of the anistropy cone of the P=S double bond is proposed. Keywords: phosphecine, NMR, X-ray, tricycle.
Crystal and molecular structures of 1,4-dibromo- and 1,4-diiodocubane
Authors: Kawai N. T. , Gilson D. F. R. , Britten J. F. , Butler I. S. , Farrell P. G.
Published: May 2006

The crystal structure of 1,4-dibromocubane has been determined by X-ray diffraction. The crystal is monoclinic, P21/n, a = 6.878(1), b = 6.960(7), c = 8.793(2) Å, β = 113.08(2)°, Z = 2, R = 0.055. The C—Br bond length, at 1.926 Å, is shorter than usual and the carbon framework is probably distorted by longer bonds along the edges. The direct dipole coupling constants between protons, obtained from the partially oriented NMR spectrum, show that a distortion of the proton positions from the ideal cube occurs in the bromo compound but not in diiodocubane, presumably because of the higher strain energy in the former. Keywords: halocubanes, crystal structures, NMR spectroscopy, molecular modelling calculations.
Preparation and structure of silver complexes with 4-nitroimidazole
Authors: Ségalas Isabelle , Beauchamp André L.
Published: May 2006

The reaction of 4-nitroimidazole (NO2ImH) with AgNO3 and AgBF4 in neutral or weakly acidic aqueous media yielded the insoluble [Ag(NO2Im)] compound, whose infrared and 13C NMR spectra are consistent with a polymeric chain of deprotonated ligands bridging silver atoms via the endocyclic nitrogen atoms. In strongly acidic solution, [Ag(NO2ImH)2]X salts (X = NO3, BF4) were obtained and their crystal structures were determined. [Ag(NO2ImH)2]NO3: monoclinic, P2/n, a = 14.214(1), b = 12.571(2), c = 14.222(1) Å, β = 111.38(7)°, Z = 8, R = 0.021, 3443 observed reflections; [Ag(NO2ImH)2]BF4; monoclinic, P21/c, a = 9.543(4), b = 6.478(2), c = 20.869(9) Å, β = 90.84(3)°, Z = 4, R = 0.027, 1646 observed reflections. In both compounds, the two-coordinated metal forms roughly collinear bonds to two neutral ligands via the endocyclic nitrogen atom adjacent to the nitro group. One oxygen of each nitro group makes a secondary Ag—O bond near the equatorial plane. The anions are hydrogen bonded to the ligand N—H groups and do not directly interact with the metal. Solution 1H and 13C NMR spectra show that the cationic complexes dissociate in DMSO. The infrared and CP-MAS 13C NMR spectra are discussed in connection with the coordination patterns observed. Keywords: silver, imidazole, crystal structure, infrared spectroscopy, nuclear magnetic resonance.
Formation of 14-membered carbocycles by intramolecular Michael addition on ynones and enones
Authors: Girard Suzanne , Deslongchamps Pierre
Published: May 2006

The base-catalyzed intramolecular Michael addition of substituted malonates on ynones or enones proceeds efficiently to give the 14-membered carbocycles.
π-Facial diastereoselectivity in the Diels–Alder reactions of cis-cyclohexa-3,5-diene-1,2-diol and derivatives with N-phenylmaleimide
Authors: Gillard James R. , Burnell D. Jean
Published: May 2006

N-Phenylmaleimide undergoes Diels–Alder cycloaddition predominantly to the face of cis-cyclohexa-3,5-diene-1,2-diol (3) syn to the oxygen functions. Derivatization can be used to alter the π-facial diastereoselectivity in a synthetically useful manner. The best cases are the exclusive, high yield, production of the syn-addition product with the trimethylsilyl ether derivative (8), and the exo-benzylidine derivative (26) gave a 96:4 anti/syn ratio of adducts.
An alternative synthesis of temafloxacin, a potent antibacterial agent
Authors: Chu Daniel T. W. , Lico Isabella M. , Claiborne Akiyo K. , Faubl Hermann
Published: May 2006

An alternative synthesis of (±)-7-(3-methylpiperazin-1-yl)-6-fluoro-1-(2,4-difluorophenyl)-1,4-dihydro-4-oxoquinoline-3-carboxylic acid hydrochloride 4, a potent antibacterial agent, was developed. The method was characterized by regiospecific displacement of the 4-fluoro of the 2,4,5-trifluoroacetophenone by 2-methylpiperazine to produce the key intermediate, 2,5-difluoro-4-(3-methylpiperazin-1-yl)acetophenone 12, which was subsequently converted to 4 via an intramolecular nucleophilic displacement cyclization reaction.
The anomeric and reverse anomeric effect. A simple energy decomposition model for acetals and protonated acetals
Authors: Grein F. , Deslongchamps P.
Published: May 2006

Geometry optimizations at the 6-31G** level were performed on various conformers of XHmCH2YHn and XHmCH2YHn+I+ (protonated), with X, Y = N, O. The resulting anomeric stabilization energies were decomposed into steric, electrostatic (lone pair – lone pair, lone pair – hydrogen), and electronic contributions. Using approximate values for steric and electrostatic terms, the electronic energy was determined to be about −2 kcal/mol for the anomeric effect to arise from O, and −2.5 kcal/mol if it arises from N. For protonated systems, an additional energy term for the reverse anomeric effect had to be added, having a value of −4 kcal/mol for O in OH-CH2-NH3+ and −5 kcal/mol for N in NH2C-H2-NH3+. The anomeric effect due to N drives NH2-CH2-OH2+ to a charge-dipole complex of the type NH2=CH2+… OH2. The energy parameters obtained have been applied to predict relative stabilities of various conformers of methanetriol, aminomethanediol, and protonated methanetriol, with good success.
NMR kinetic study of ethyl silicate hydrolysis by ammonia in alcoholic solvents
Authors: Bakali Idriss El , Rhess Essaïd El , Rousselot Christophe , Mercier René , Mercier Marie-France
Published: May 2006

Hydrolysis of Si(OC2H5)4 by ammonia has been investigated using 1H and 13C NMR measurements in alcoholic media. Use of deuterated CD3CD2OD and CD3OD solvents proves the absence of transesterification by alkoxy exchange between silicate and alcohols. The rate constant increases when CD3OD replaces CD3CD2OD as the solvent (k = 2.8 × 10−3 L mol−1 min−1 in CD3CD2OD; 7.5 × 10−3 L mol−1 min−1 in CD3OD for similar experiments).
A model of nonelectrolytic behaviour: activity coefficients
Authors: Singh Prem p. , Maken Sanjeev
Published: May 2006

A model is presented for binary mixtures of nonelectrolytes that reproduces successfully the activity coefficient (γi, γj, xi) data for even those (I + j) mixtures that are known to be characterized by the presence of 1:1 or 1:1 and 1:2 molecular complexes or have components that differ appreciably in their molar volumes when only limited [Formula: see text] or [Formula: see text] or [Formula: see text] data are available).
A variable-temperature 13C NMR study of (η5-C5H5)2Mo2(CO)4 complexes of chiral alkynes derived from a terpene or a hormonal steroid: interconversion of diastereomers via exchange of terminal and semi-bridging carbonyls
Authors: Tondu Sylvie , Jaouen Gérard , D'Agostino Michael F. , Malisza Krisztina L. , McGlinchey Michael J.
Published: May 2006

The reaction of (C5H5)2Mo2(CO)4 with the steroidal hormone 11β-(4-dimethylaminophenyl)-17β-hydroxy-17α-(1-propynyl)-estra-4,9-dien-3-one (RU 38486) or with propynylborneol yields in each case a chiral cluster that exhibits two cyclopentadienyl resonances in both the 1H and 13C NMR regimes. At low temperature the interconversion of diastereomers arising from the different orientations of the semi-bridging carbonyl ligand can be slowed on the NMR time scale. The barrier to diastereomer interchange has been determined for the terpenoid cluster and the mechanism of this process is discussed.
Structural studies of organoboron compounds. LV. N,N′-Di-tert-butyl-N,N′- dihydroxypropane-1,3-diamine(O-B)ethoxydiphenylborane and N1,N2-di-tert-butyl-N1,N2-dihydroxy-1-phenylpropane-1,3-diamine(N2-O-B)hydroxydiphenylborane
Authors: Kliegel Wolfgang , Lubkowitz Gottfried , Rettig Steven J. , Trotter James
Published: May 2006

The 1,3-propanediamine derivatives N,N′-di-tert-butyl-N,N′-dihydroxy-1,3-propanediamine and N,N′-di-tert-butyl-N,N′-dihydroxy-1-phenyl-1,3-propanediamine have been prepared and reacted with oxybis(diphenylborane) to yield, respectively, the crystalline organoboron compounds N,N′-di-tert-butyl-N,N′-dihydroxypropane-1,3-diamine(O-B)-ethoxydiphenylborane, 5a, and N1,N2-di-tert-butyl-N1,N2-dihydroxy-1-phenylpropane-1,3-diamine(N2-O-B)-hydroxydiphenylborane, 5b. Crystals of 5a are monoclinic, C2/c, a = 35.402(1), b = 9.212(2), c = 18.101(2) Å, β = 116.688(3)°, Z = 8, ρc = 1.079 g cm−3, and crystals of 5b are monoclinic, P21/c, a = 12.899(4), b = 12.571(4), c = 17.412(3) Å, β = 90.02(2)°, Z = 4, ρc = 1.121 g cm−3. The structures were solved by direct methods and were refined by full-matrix least-squares procedures to final R values of 0.047 and 0.041 for 2492 and 3334 reflections with I ≥ 3σ(I), respectively. Compounds 5a and 5b are open-chain hydroxylamine adducts of diphenylborinic acid and ethyl diphenylborinate, respectively. Both of these compounds are stabilized by a system of three intramolecular hydrogen bonds [Formula: see text]. Bond lengths involving the tetrahedrally coordinated boron atoms are: (C)O—B = 1.457(3), (N)O—B = 1.558(3), and C—B = 1.613(4) and 1.615(4) Å for 5a; (H)O—B = 1.475(3), (N)O—B = 1.562(2), and C—B = 1.618(3) and 1.619(3) Å for 5b.
Electrochemical behavior of C-methoxy, amino, cyano, and mercapto nitrones
Authors: Acken Bruce J. , Gallis David E. , Warshaw James A. , Crist DeLanson R.
Published: May 2006

The redox behavior of various C-substituted nitrones was investigated by cyclic voltammetry in acetonitrile. These included C-methoxynitrones (MeO)CR = N(O)t-Bu with R = C6H5(1a), p-MeOC6H4 (1b), p-NO2C6H4 (1c), and H (1d) and nitrones YCH = N(O)t-Bu with Y = n-BuS (2a), CN (2b), and C6H5NH (2c). All gave anodic peaks which can be identified as oxidations of the nitrone function. Controlled potential electrolysis of 1a at 1.05 V (SCE) showed that its oxidation was a one-electron process. Reduction of 1a occurs stepwise at −2.08 and at −2.47 V, the same potential for reduction of methyl N-tert-butylbenzimidate (MeO)CPh = Nt-Bu. With electrochemical windows of ca. 3 V, all of the nitrones studied appear suitable for spin-trapping experiments.
Ascorbate: antioxidant activity determined in a hydrocarbon phase using quaternary ammonium salts as phase-transfer agents
Authors: Barclay L. Ross C. , Dakin Kelly A. , Zahalka Hayder A.
Published: May 2006

By shaking sodium ascorbate with tetra-n-butyl ammonium bromide in a two-phase system consisting of water and organic phases, such as 1,1,2,2-tetrachloroethane (TCE) or chlorobenzene, sufficient concentrations of the quaternary ammonium-ascorbate (quat-ascorbate) are transferred into the organic phase to be useful for antioxidant studies in non-polar solvents. The antioxidant activity of the quat-ascorbate was determined by measurement of the (inhibition) rate constant, kinh, for the inhibition of autoxidation of styrene initiated thermally by azobisisobutyrylnitrile (AIBN) at 30 °C. The kinh of ascorbate in styrene, found to be (9.63 ± 2.0) × 104 M−1 s−1, is very much lower than that found for ascor-byl-6-palmitate, kinh = (110 ± 11) × 104 M−1 s−1 under these conditions. The differences are discussed in terms of the relative effectiveness of hydrogen-atom transfer from the enolic hydroxyl at position 2 of the ascorbate ion compared with the more facile such transfer from position 3 of ascorbyl 6-palmitate in a nonpolar medium.
Catalysis of the deprotonation of β-diketones during formation of the 1:1 metal complexes
Authors: Blanco Carlos A. , Hynes Michael J.
Published: May 2006

Catalytic effects on the deprotonation rate constants of β-diketones were observed during kinetic studies of the formation reactions of the 1:1 complexes of these ligands. When vanadium(IV), chromium(III), iron(III), cobalt(II), nickel(II), copper(II), and uranium(VI) react with pentane-2,4-dione, heptane-3,5-dione, 1,1,1-trifluoropentane-2,4-dione, 4,4,4-trifluoro-1-(2-thienyl)-butane-1,3-dione, 1-phenylbutane-1,3-dione, and 2-acetylcyclohexanone a significant catalytic effect on the rate of ionization of the keto tautomer of the ligand was observed. A considerable enhancement of the rate of ionization of the enol tautomers of these ligands was observed during the complex formation reactions with Cu2+. A mechanism is proposed that accounts for these catalytic effects. In the case of Cu2+ the increased rate of proton removal from the ligands may be rationalized in terms of the relatively large reduction potential of this metal ion.
Stereocontrolled chiral synthesis of a trans-anti-trans tricycle by a transannular Diels–Alder reaction
Authors: Marinier Anne , Deslongchamps Pierre
Published: May 2006

The racemic and chiral synthesis of trans-cis-cis macrocyclic triene 5 is described. Heating this compound at 262 °C leads via a transannular Diels–Alder reaction to the tricyclic structure 6, which can be further transformed into tricyclic compound 7. This work constitutes a preliminary study for the synthesis of corticoids.
Thermal and photochemical reactions of steroidal α-azido ketones
Authors: Edwards O. E. , Douglas J. L. , Horwell D. C. , Rank W. , Sano T.
Published: May 2006

Photolysis of 9α-azido-3β,20β-diacetoxy-5α-pregnan-11-one in methanol gave the N-acyl imine 11-aza-3β,20β-diacetoxy-C-homo-5α-pregn-9,11-en-12-one 4 and the aminoketone 9a-aza-3β,20β-diacetoxy-9-methoxy-B-homo-5α-pregnan-11-one 7. In dichloromethane containing triethylamine the irradiation of this azide gave the N-acyl imine 4 and the α,β-unsaturated amino ketone 9a-aza-3β,20β-diacetoxy-B-homo-5α-pregn-8-en-11-one 8. Thermolysis or photolysis of 12α-azido-3α,20β-diacetoxy-5β-pregnan-11-one gave the N-acyl imine 12-aza-3α,20β-diacetoxy-C-homo-5β-pregn-12-en-11-one 10 as major product. Photolysis of 20β-acetoxy-12α-azido-3α-hydroxy-5β-pregnan-11-one gave the 3-hydroxy analogue of 10. Transformation products of the N-acyl imines are described.
Cyano-bridged heterodinuclear complexes of nickel(II) and palladium(II). A disordered structure for the linkage isomer [LPd-CN-NiL](ClO4)
Authors: Paul Parimal , Das Ramprasad , Nag Kamalaksha , Gabe Eric J. , Charland Jean-Pierre
Published: May 2006

The homodinuclear [M2L2μ(CN)](ClO4) complexes and the heterodinuclear [LPd-CN-NiL](ClO4) and [LNi-CN-PdL](ClO4) complexes of nickel(II) and palladium(II) have been synthesized with a tridentate ligand HL (methyl 2-[(2′-aminoethyl)amino]cyclopent-1-enedithiocarboxylate). In solution both the isomers dissociate, [LNi-CN-PdL]+ much more rapidly than [LPd-CN-NiL]+, and a steady state equilibrium between the [LPd-CN-NiL]+, [Pd2L2μ-(CN)]+, and [Ni2L2μ-(CN)]+ species is established. The isomer [LPd-CN-NiL]+ exhibits a band at 555 nm that is absent in the other isomer and homodinuclear complexes. The X-ray structure of [LPd-CN-NiL](ClO4) has been studied. Crystals of the compound are monoclinic, a = 8.964(2), b = 23.852(2), c = 14.096(2) Å, β = 105.92(1)°, Z = 4, space group P21/a. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.054 and Rw = 0.034 for 4426 reflections with I ≥ 2.5σ(I). The two metal centres are in a square-planar environment provided by the N2S donor set of the ligand and cyanide bridge, but the metal atoms as well as C and N atoms of μ-CN could not be distinguished due to disorder. An alternate stacking of Pd-CN-Ni and Ni-NC-Pd units has been proposed to explain the 1:1 occupancy of the atoms concerned.
A kinetic study of the thermal dehydration of calcium sulphite hemihydrate
Authors: Anderson Carl , Galwey Andrew K.
Published: May 2006

An isothermal kinetic study of the dehydration of orthorhombic calcium sulphite hemihydrate is reported:[Formula: see text]Fractional reaction (α)–time curves exhibit the sigmoid shape characteristic of nucleation and growth reactions proceeding in the solid state. Yield–time data exhibit a very satisfactory obedience to the Avrami–Erofe'ev (n = 2) equation[Formula: see text]Rate studies were concerned with the temperature interval 573–673 K and the calculated activation energy was 173 ± 8 kJ mol−1, showing the hydrate to be thermally relatively stable. The mechanism of dehydration is discussed and reference is made to the dehydration of calcium hydroxide with which it shows close similarities.
The synthesis and structural characterization of a series of triphenyltin(IV) esters of N-arylidene-ω-amino acids
Authors: Toong Y. C. , Tai S. P. , Pun M. C. , Hynes Rosemary C. , Khoo L. E. , Smith F. E.
Published: May 2006

Methods of synthesis, elemental analyses, and IR and NMR spectroscopic data are reported for a series of triphenyltin esters of N-salicylidene-ω amino acids of the general formula: Ph3SnOCO(CH2)nN=CHAr (Ar = 2-HOC6H4− and 2-HOC10H6−; n = 1, 2, 3, and 5). The crystal structure of triphenyltin N-salicylidene-6-aminohexanoate was determined. The crystals are monoclinic, space group P21/a, with a = 16.3493(8) Å, b = 9.0675(7) Å, c = 18.8562(14) Å, β = 100.493(5)°, V = 2748.6(3) Å3, Z = 4, and Dcalc = 1.427 Mg m−3. The final discrepancy factors are RF = 0.033, and RW = 0.036 for 2339 significant reflections. This compound, believed typical of the series described, adopts a polymeric trans-O2SnC3 trigonal bipyramidal geometry with the axial positions occupied by a carboxylate oxygen and the phenolic oxygen of an adjacent molecule. These compounds appear to be the first reported triphenyltin(IV) carboxylates with phenolic oxygen bridges.
Competitive Diels–Alder and ene addition of N-arylmaleimides to 7-dehydrocholesteryl acetate
Authors: Leigh William J. , Hughes Donald W. , Mitchell D. Scott
Published: May 2006

Thermolysis of N-phenyl, N-para-biphenyl, and N-para, para′-terphenylmaleimide with 7-dehydrocholesteryl acetate in benzene solution at 200 °C yields mixtures of four cycloadducts in relative yields that are essentially independent of the maleimide substituent. The three major products are those of ene addition to C7 of the steroid with abstraction of the proton at C9 or C14. The α-endo-Diels-Alder adduct is formed as a minor product. The structures of the adducts have been elucidated on the basis of one- and two-dimensional 1H and 13C NMR spectroscopic techniques, including homonuclear 1H decoupling, NOE, 1H–1H COSY, heteronuclear 1H–13C shift correlation, and TOCSY 2-D experiments, and the results of molecular mechanics (MMX) calculations. The combination of these techniques has made it possible to almost completely assign the 1H and 13C NMR spectra for two of the ene adducts and the Diels–Alder adduct from reaction of 7-dehydrocholesteryl acetate with N-phenyl maleimide.
CP-MAS 13C NMR investigation of phase structure in mixtures of poly(ethyl acrylate) ionomers with sodium palmitate
Authors: Natansohn A. , Bazuin C. G. , Tong X.
Published: May 2006

A solid-state NMR study of mixtures of poly(ethyl acrylate) (PEA) or poly(ethyl acrylate-co-sodium acrylate) (PEA-i) with sodium palmitate (SP) shows that (1) there is a change in the electron density of the carboxylate carbons of SP in the mixtures compared to pure SP; (2) the T1ρH value for SP in the mixtures with PEA or PEA-i is depressed in comparison with pure SP for mixtures containing over 4 mol% SP. This can be interpreted as a result of interfacial magnetization transfer from the protons of PEA or PEA-i to the protons of SP; (3) deuterated SP (D-SP) shows a similar growth in magnetization as a function of contact time when pure or when mixed with PEA. The growth is significantly slower in its mixtures with PEA-i. All these findings can be explained by a PEA-i:SP mixture morphology involving bilayers of carboxylate ions at the interface; the same tendency exists in the PEA:SP mixtures, only in this case the ester groups of PEA are preferentially located at the interface.
An ion-exchange/atomic absorption method for the measurement of ionized calcium and magnesium at micromolar concentrations
Authors: Hewavitharana Amitha K. , Kratochvil Byron
Published: May 2006

A quantitative ion-exchange/atomic absorption method is described for measuring the concentration of free (hydrated) calcium and magnesium in solution at micromolar levels. Sample solutions are pumped through a micro-column of strong acid-type cation-exchange resin until equilibrium has been achieved between resin and solution. After removal of interstitial solution by first air, then water, the sorbed metal ion is eluted from the resin with nitric acid directly into an atomic absorption spectrophotometer. In a 0.1 M 1:1 electrolyte, here KNO3, the amount of metal ion sorbed on the resin is directly proportional to the free metal ion concentration in solution over a concentration range of 1.25 to 5 × 10−5 mol/L (12–50 μmol/L). Selectivities for free calcium and magnesium in the presence of complexing ligands such as citrate and phosphate compare well with calculated values.
Estérification de l'acide stéarique catalysée par les titanates greffés
Authors: Blandy Claudine , Pellegatta Jean-Louis , Choukroun Robert , Gilot Bernard , Guiraud Roland
Published: May 2006

The esterification of stearic acid using titanates fixed on alumina or silica as catalysts has been studied. The anchoring of titanium, obtained by action of CH3Ti(OR)3 with the acid sites of the support, has been studied using different contact times and different concentrations. The heterogeneized catalyst leads to a better efficacity than the homogeneous system. The activity of the catalyst is strongly increased by using crushed solid instead of balls. The catalyst has been recovered and recycled. The stability of the (M)–Ti(OR)3 bond (with M = Al2O3 or SiO2) has been shown by kinetic measures and exchange reactions of the alcoxy groups fixed on titanium with heavy alcohol.
Studies of the synthesis, structure, and reduction of trans-dichloro bis(2,3-dihydro-4- and 7-methylbenzo[b]thiophene)palladium(II) complexes
Authors: Clark Peter D. , Kirk Martin J. , Parvez Massood
Published: May 2006

trans-Dichlorobis(2,3-dihydro-4- and -7-methylbenzo[b]thiophene)palladium(II), 1b and 1c, have been prepared by reaction of 2,3-dihydro-4- and -7-methylbenzo[b]thiophenes with palladium(II) chloride. Both 1b and 1c exhibit complex 1H and 13C NMR spectra as a result of inversion of the sulfur-containing ligands. Their structures were confirmed by single crystal X-ray studies. 1b crystallized in the triclinic space group [Formula: see text] (a = 7.219(2), b = 8.441(5), c = 8.494(7) Å, α = 61.47(5)°, β = 88.85(4)°, γ = 84.40(3)°, and R = 0.067 for 1372 observed of 1760 unique reflections). 1c also crystallized in the triclinic space group [Formula: see text] (a = 7.730(3), b = 8.056(3), c = 8.516(4) Å, α = 62.87(3)°, β = 82.31(3)°, γ = 88.82(3)°, and R = 0,040 for 1425 observed of 1825 unique reflections), 1b and 1c and the complex 1a (prepared from 2,3-dihydrobenzo[b]thiophene) were unstable in the presence of molecular hydrogen at ambient conditions, liberating the parent dihydrobenzothiophenes and forming elemental palladium. 1a was also unstable to the organic hydrogen donor tetrahydronaphthalene, again forming Pd and 2,3-dihydrobenzothiophene. Complexes 1a–c were shown to promote the shift of CO/H2O to hydrogen and CO2 although most of the hydrogen was consumed by the reduction of Pd(II) to Pd0.
Reactions of SO2X mono-substituted arenes with SO3 in nitromethane: electronic and steric directing effects of the sulfonic acid group and some model substituents
Authors: Ansink Harold R. W. , Graaf Erik J. De , Zelvelder Erwin , Cerfontain Hans
Published: May 2006

The sulfonation of benzene-SO2X (X = CH3, OCH3, OH, and Cl) and of 1- and 2-naphthalene-SO2X (X = CH3, OCH3, and Cl) with sulfur trioxide in nitromethane as solvent has been studied. In the benzene series, substitution only occurs at the 3-position irrespective of X; the reaction rates, which are all within the same order of magnitude, are low. Upon sulfonation of the 1-SO2X-substituted naphthalenes, the main sulfonation product (58–80%) is the 5-sulfonic acid (5-S); in addition, 6-S and small amounts of 3-S and 7-S are formed. Also, the formation of the intermolecular sulfonic anhydride of 1-(methylsulfonyl)naphthalene-5-S is observed. The 2-SO2X-substituted naphthalenes all yield the 5-S and 8-S in a ratio of [Formula: see text] For both the benzene and naphthalene series, insertion of SO3 between the SO2 and X moieties of the chlorosulfonyl and methoxysulfonyl substituents proper takes place. In the benzene series these reactions are fast as compared with the actual ring sulfonation, whereas in the naphthalene series they are, in general, relatively slow. In the naphthalene series the mesomeric directing effect of the SO2X groups is less important than in the benzene series; the "naphthalene α-effect" also plays an important role.
The acidity constant of fluorene-9-carboxylic acid in aqueous solution. Determination of the pKa of a sparingly soluble substance
Authors: Kresge A. J. , Pojarlieff I. G. , Rubinstein E. M.
Published: May 2006

The acid ionization constant of the carboxylic acid group of fluorene-9-carboxylic acid in aqueous solution at 25 °C was determined to be pKa = 3.61, using a method based upon the increase in solubility of this sparingly soluble substance brought about by its ionization. This corrects an earlier considerably different value of this quantity determined by equating pKa with the pH measured at half-neutralization. The hazard inherent in the latter method when applied to sparingly soluble substances is discussed.
Bifunctional conjunctive reagents: 5-chloro-2-lithio-1-pentene and related substances. A methylenecyclohexane annulation method
Authors: Piers Edward , Yeung Bik Wah Anissa , Fleming Fraser F.
Published: May 2006

The development of a new, synthetically useful methylenecyclohexane annulation method is described. Transmetallation (MeLi, tetrahydrofuran, −78 °C) of 5-chloro-2-trimethylstannyl-1-pentene (8) affords the novel bifunctional reagent 5-chloro-2-lithio-1-pentene (9), which, at temperatures higher than approximately −50 °C, self-destructs to give methylenecyclobutane (14). Reagent 9 can be converted into the Grignard reagent 10 and the organocopper(I) species 15. Conjugate addition of 10 and 15 to a number of cyclic enones (16–22), followed by intramolecular alkylation of the resultant adducts (23–29), produces the corresponding methylenecyclohexane annulation products (30–40).
Diatomic centrifugal distortion constants for large orders at any level: application to the state
Authors: Korek Mahmoud , Kobeissi Hafez
Published: May 2006

The determination of the centrifugal distortion constants (CDC) of a diatomic molecule is sought for high orders. When the vibrational energy e0 = Ev is known for a vibrational level v, the use of Rayleigh–Schrödinger perturbation theory gives the rotational constant [Formula: see text] and the CDC,[Formula: see text] [Formula: see text] [Formula: see text] where Φn(r) is the solution of the nth rotational Schrödinger equation. The problem of the determination of a function Φn is solved by deriving exact analytical expressions for the initial values Φn(r0) and [Formula: see text] at an arbitrary "origin" r0, the determination of any Φn(r) becoming as easy as that of Φn(r) when e0 is known; that of en becomes as easy as that of [Formula: see text] The application of the present formulation to the model Lennard–Jones potential function allows the numerical computation of Dv, Hv, Lv, Mv, Nv, Ov, Pv, Qv for low and high v; the CDC beyond Mv are given for the first time; higher order CDC may be reached. The results for the four lowest order constants are in good agreement with those from previously confirmed methods. Appropriate tests for all orders show that the present method provides an elegant and competitive solution to the diatomic CDC problem even for large orders and high levels (near dissociation). Similar good results are obtained for an RKR potential of the [Formula: see text] state bounded by 109 levels.
Preparation and reactions of bromo-2-nitro- and bromo-2-aminoimidazoles
Authors: Farah Salim F. , McClelland Robert A.
Published: May 2006

Treatment of 1-methyl-2-nitroimidazole with bromine in water resulted in rapid dibromination to give 4,5-dibromo-1-methyl-2-nitroimidazole. In dioxane, the bromination was slower, and could be controlled to give 4-bromo-1-methyl-2-nitroimidazole 5 and 5-bromo-1-methyl-2-nitroimidazole 6 in a 4:1 ratio. In an attempt to displace the bromine, the monobromo compounds were treated with cysteamine hydrochloride. In each case the nitro group was displaced instead, the 4-bromo 5 resulting in 2-[(2-aminoethyl)thio]-4-bromo-1-methylimidazole 9 as sole product, and the 5-bromo 6 giving two products identified as the monosubstituted 2-[(2-aminoethyl)thio]-5-bromo-1-methylimidazole 13 and the disubstituted 2,5-bis[2-(aminoethyl)thio]-1-methylimidazole 12. The latter product forms by further reaction of the former and was the sole material observed at long reaction times. A fraction of 12 may also originate from an initial displacement of bromine giving 5-[(2-aminoethyl)thio]-1-methyl-2-nitroimidazole 14, although this cannot be observed due to a rapid further displacement of its nitro group. The bromonitroimidazoles 5 and 6 were reduced to 4-bromo-2-amino-1-methylimidazole 25 and 5-bromo-2-amino-1-methylimidazole 26 with Zn/HCl. On reflux in water, in the presence or absence of cysteamine hydrochloride, these undergo a protodebromination resulting in the same product, 2-amino-1-methylimidazole 17. In D2O the 4-bromo isomer was demonstrated to react specifically to give 2-amino-4-deuterio-1-methylimidazole 27. Attempted preparation of the bromoaminoimidazoles 25 and 26 by bromination of 2-amino-1-methylimidazole in water resulted in the clean formation of cis and trans 2-amino-4,5-dihydro-4,5-di-hydroxyimidazolium ions 18.
Carbon-13 nuclear magnetic resonance study of phenyl derivatives of B, Si, Sn, P, and Te fluorides
Authors: Wang Chengrui , Mo Yuxiang , Jang Meehae , Janzen Alexander F.
Published: May 2006

13C nuclear magnetic resonance data for a variety of phenyl derivatives of boron, silicon, tin, phosphorus, and tellurium fluorides are presented. Neutral, anionic, and cationic complexes are included and the coordination number of the central element varies from 3 to 6. Empirical equations of the 13C chemical shifts of the benzene ring have been deduced by taking into consideration the charge density, dipole moment, and binding energy, and the 13C chemical shifts calculated from these equations deviate from the experimental values by up to 1.4 ppm, but mostly less than 0.7 ppm.
Reactions of 5-cyano-1,4-diphenylpyridazino[4,5-a]indolizines with dimethyl acetylenedicarboxylate: regioselective formation of 1:2 Michael type adducts
Authors: Matsumoto Kiyoshi , Ikemi Yukio , Shiro Motoo , Uchida Takane , Lown James William
Published: May 2006

Reactions of 5-cyano-1,4-diphenylpyridazino[4,5-a]indolizines with dimethyl acetylenedicarboxylate afforded the 1:2 adducts regioselectively and, unexpectedly, in a Michael fashion rather than in a 1,3-dipolar manner. The structure of the products was established by X-ray crystallography. Regiospecific formation of the observed product 3 can be explained by the higher nucleophilicity of the nitrogen at the 2 position than at the 3 position of the 5-cyano-1,4-diphenylpyridazino[4,5-a]indolizine 1 owing to the contribution of a resonance structure 5 to the hybrid. This favors two successive Michael additions to two equivalents of dimethyl acetylenedicarboxylate affording the observed 1:2 adducts 3.
Preparation, characterization, and biologic evaluation of copper(II) – Schiff base complexes derived from anthranilic acid and aldoses
Authors: Iqbal Mohammad S. , Khurshid Syed J. , Iqbal Mohammad Z.
Published: May 2006

Cu(II) – Schiff base complexes containing anthranilic acid and aldoses (sugars) as part of the base were prepared and characterized by microanalytical, thermogravimetric, magnetic, and spectroscopic data. The complexes are four-coordinate, anhydrous, and ML2 type. The electron paramagnetic resonance spectral lines exhibited rhombic distortion from axial symmetry in the square-planar Cu(II) complexes with [Formula: see text] The complexes were found to be active against kaolin paw oedema and standard strains of Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa.
Chemical and electrochemical oxidation of phenothiazine
Authors: Pankratov Alexei N. , Uchaeva Inna M. , Stepanov Alexander N.
Published: May 2006

The oxidation of phenothiazine in dilute solutions of sulphuric acid leads to the corresponding cation radical. Using a potentiometric technique, a pKa value of 5.72 ± 0.05 was determined for phenothiazine. The kinetics has been studied and participation of both protonated and unprotonated oxidant in the oxidation reaction has been confirmed. Using a voltammetric technique with a rotating disk electrode, the anodic oxidation of phenothiazine was shown to be a one-electron diffusion-controlled process. A quantum chemical explanation was found for the direction of phenothiazine protonation and the absence of a dimerization stage of oxidation.
Solution speciation in the aqueous Na(I)–EDTA and K(I)–EDTA systems
Authors: Chen Min , Reid R. Stephen
Published: May 2006

Speciation in the aqueous sodium(I) – ethylenediaminetetraacetic acid and potassium(I) – ethylenediaminetetraacetic acid equilibrium systems was investigated by automated gravimetric potentiometric titration. It was found that in both cases, particularly below neutral pH values, speciation includes a previously uncharacterized diprotonated complex. All formation and acid dissociation constants were measured for the full systems. The validity of previous literature equilibrium constants, which are based on incomplete equilibrium models, is discussed.
Acid and oxidative dissolution of coprecipitated iron–chromium oxides
Authors: Rodenas Luis García , Morando Pedro J. , Blesa Miguel A. , Duhalde Stella , Saragovi Celia
Published: May 2006

A mixed Fe,Cr oxide formed of maghemite and chromium hydrous oxide was prepared by oxidative precipitation at 90 °C. Mineral acids dissolve the chromium phase very quickly, whereas iron dissolves slowly and independently; there is little mutual influence in the dissolution behaviour. Calcination of this oxide at 600 °C yields a mixture of α-Fe2O3 and Cr1.3Fe0.7O3 that leaches iron slowly upon acid attack. The reactivity of the oxide towards H+ is largely determined by the degree of crosslinking of the Cr-containing phase. Oxidative attack (by KBrO3) increases the rate of dissolution of both Cr and Fe, against simple expectations that Fe dissolution rates might be reduced. This effect is of importance in chemical cleaning and decontamination of stainless steels. This influence of acidity and [BrO3−] are interpreted in terms of the formation of surface ≡Cr(III)-O-Br(V) species that evolve to produce Cr(VI)aq. These surface complexes form more readily than analogous solution species, making surface Cr(III) more readily oxidizable than aqueous (Cr(III).
A new and simple spectrophotometric method for the determination of selenium in the presence of copper and tellurium
Authors: Somer Güler , Kutay Nuray
Published: May 2006

Selenium in anodic slime is determined by using an indirect method. Selenite is reduced by ferrous iron, the ferric iron formed is complexed with KSCN, and the absorbance at 480 nm is measured. In this way selenium (10−3–10−2 M) can be determined in the presence of copper and tellurium without any separation.
The photocycloaddition of dibenzoylmethanatoboron difluoride (DBMBF2) with conjugated enones and en-esters
Authors: Chow Yuan L. , Wang Shi-Sen , Cheng Xian-En
Published: May 2006

Dibenzoylmethanatoboron difluoride (DBMBF2), the BF2 complex of dibenzoylmethane, reacted from its singlet excited state with α,β-unsaturated ketones and esters to give 1,5-diketones by a [2+2] cycloaddition and ring-opening sequence in an analogous pathway to that observed in the photocycloaddition to olefins and dienes. The present photoreaction is unexpected since conjugated enones and en-esters are poor electron donors to comply with the previously proposed charge transfer requirement in DBMBF2 photoreactions. The photocycloaddition to these substrates was highly regioselective and stereoselective, giving the head-to-head orientation, which could be enhanced by α-methyl substitution; β-methyl substitution increased the alternate head-to-tail orientation. The photolysis of a mixture of DBMBF2 and a cyclic enone also caused the latter to dimerize to give head-to-head and head-to-tail dimers in significant yields. These photodimerizations were apparently caused by DBMBF2 sensitization. The mechanism of the sensitization is discussed.
Reactions of catecholborane with iridium complexes: molecular structure of trans-IrHCl(CO)(Bcat)(PPh3)2
Authors: Westcott Stephen A. , Marder Todd B. , Baker R. Thomas , Calabrese Joseph C.
Published: May 2006

Reactions of certain iridium complexes with catecholborane (HBcat) gave boron-substituent redistribution products ([Bcat2]−, B2cat3) with concomitant formation of a complex mixture of iridium hydrides. While "IrCl(PPh3)(COE)n" generated in situ from [Ir(μ-Cl)(COE)2]2 (COE = cyclooctene) (2) plus 2 equivalents of PPh3 also promoted HBcat degradation, this catalyst system was extremely active and selective for alkene hydroborations. Oxidative addition of HBcat to the metal centre can be the sole reaction pathway, however, with iridium complexes containing electron-rich phosphines. The unsaturated boryl complex IrHCl(Bcat)(PPri3)2 was prepared and isolated in high yield from reaction of HBcat with 2 in the presence of four equivalents of PPri3. Ancillary carbonyl ligands also appear to facilitate oxidative addition of HBcat to an iridium centre. Addition of HBcat to trans-IrCl(CO)(PPh3)2 gives the first structurally characterized metal-carbonyl boryl complex trans-IrHCl(CO)(Bcat)(PPh3)2 (7). Colourless crystals of 7 are triclinic, [Formula: see text] (No.2) with two molecules per unit cell of dimensions a = 12.223(2) Å, b = 12.684(2) Å, c = 14.652(1) Å, α = 70.81(1)°, β = 72.47(1)°, and γ = 71.92(1)°.
Calorimetric investigation of complex formation in the aqueous Fe (III)–citrate system
Authors: Chen Qiyuan , Zhang Xin , Wu Ching-Hsien , Hepler Loren G.
Published: May 2006

We have made calorimetric measurements of thermal effects associated with adding NaOH(aq) or HCl(aq) to aqueous solutions (pH = 1.623) of ferric chloride + sodium citrate. Combination of these measured heats with concentrations of various species calculated from stoichiometric compositions and previously known K and ΔH values leads to ΔH values for four aqueous Fe(III)–citrate complexes. Further combination of ΔG0 values from equilibrium constants with our ΔH values leads to ΔS0 values, which are discussed in relation to conventional ideas about relationships between entropy and solute–water interactions.
cis-Cyclohexano-9-crown-3 ether. Solid state and low-temperature solution stereochemistry as determined by X-ray crystallography and nuclear magnetic resonance spectroscopy
Authors: Buchanan G.W. , Driega A.B. , Moghimi A. , Bensimon C. , Bourque K.
Published: May 2006

The X-ray crystal structure of the title material has been determined at −130 °C. Low-temperature 1H1H COSY, 13C1H HETCOR, and DEPT 13C NMR spectra have been recorded, which permit unambiguous assignments of all carbon resonances when ring inversion is slow on the NMR timescale. The limiting low-temperature solution phase 13C spectrum has many common features with the solid phase 13C CPMAS spectrum recorded at 300 K. Spectra for the 7,10-tetra-deuterio derivative have also been obtained and substituent influences on 13C shieldings are discussed in detail.
Solution and solid state studies of mixed ligand binuclear complexes containing one binucleating ligand
Authors: Patel Pushpa , Bhattacharya P.K.
Published: May 2006

Stability constants of homobinuclear binary Cu(II) complexes of the dinucleating ligands, having equivalent coordination sites, 5,5′-methylene-bis-salicylaldehyde (H2A1), 5,5′-methylene-bis-(3-bromosalicylaldehyde) (H2A2), and 5,5′-methylene-bis-(3-nitrosalicylaldehyde) (H2A3), and mixed ligand Cu(II) complexes with one of the above ligands and bipyridyl (L1) or 1,10-phenanthroline (L2) as second ligand, have been determined potentiometrically in water:dioxane medium (50:50 and 30:70,v/v using a computer programme. The values of [Formula: see text] and [Formula: see text] have been compared within the series of complexes having different H2A and L. Probable explanations for the stability order have been extended. The complexes (Cu2AL2)(ClO4)2 have been isolated and characterized by elemental analysis, electronic and ESR spectral, and magnetic studies.
Oligometallic cobalt 3,5-dimethylpyrazolate complexes: synthesis, structural and magnetic studies
Authors: Ehlert Martin K. , Rettig Steven J. , Storr Alan , Thompson Robert C. , Trotter James
Published: May 2006

Three oligometallic 3,5-dimethylpyrazolate (dmpz) bridged Co(II) compounds have been synthesized and characterized spectroscopically: dimeric [Co(dmpz)2(Hdmpz)]2, the related oligometallic compound, Co(dmpz)2•0.344(Hdmpz), and the trimetallic [Co(dmpz)2Cl(Hdmpz)]2Co. The first and last of these compounds have been studied magnetically and by single crystal X-ray diffraction. Crystals of [Co(dmpz)2(Hdmpz)]2 are orthorhombic, a = 17.022(1), b = 29.224(2), c = 13.576(3) Å, Z = 8, space group Fddd; and those of [Co(dmpz)2Cl(Hdmpz)]2Co are triclinic, a = 11.742(3), b = 18.604(4), c = 8.950(2) Å, α = 99.76(2)°, β = 102.32(2)°, γ = 93.36(2)°, Z = 2, space group [Formula: see text] The structures were solved by the Patterson method and were refined by full-matrix least-squares procedures to R = 0.035 and 0.042 (Rw = 0.034, 0.047) for 938 and 3853 reflections with I ≥ 3σ(F2), respectively. Magnetic susceptibility studies on the dimeric and trimetallic complex show them to exhibit antiferromagnetic behaviour. Analysis of the magnetic data (2– 300 K) for the trimetallic complexes reveals antiferromagnetic coupling between the terminal and central Co(II) ions with J (Heisenberg) ≈ −3 cm−1. Either intramolecular next-nearest neighbour or intermolecular antiferromagnetic exchange is also present in this compound. The dimeric complex shows significant antiferromagnetic exchange between cobalt centres. Susceptibility data over the range 12–300 K are adequately modelled with the Ising S = 1/2 dimer model (J ≈ −23 cm−1).
Electronic energies, dipole moment matrix elements, and static polarizabilities and hyperpolarizabilities for some diphenyl molecules
Authors: Nilar Shahul H. , Thakkar Ajit J. , Kondo Anne E. , Meath William J.
Published: May 2006

The "giant dipole" molecules, NR1R2—C6H4—(C≡C)n—C6H4—NO2n = 0, 1, 2, are studied theoretically for three sets of substituents: R1 = R2 = H, R1 = H, R2 = CH3, and R1 = R2 = CH3. For each of these nine molecules, the energies, and permanent and transition dipole moments for the 20 lowest electronic states are calculated using the intermediate neglect of differential overlap (INDO) approximation at the configuration interaction with single excitations (CIS) level. Static polarizabilities and hyperpolarizabilities for the ground states are reported for these "push–pull" molecules. The changes in the physical properties of interest due to increase in conjugation length and the inductive effect of substituents on the donor group attached to the rings are discussed. The energies and permanent and transition dipole moments for the ten lowest electronic states are tabulated for use in future studies of the spectral and dynamical effects of permanent dipoie moments on laser-induced one- and multi-photon electronic transitions in realistic models for many-level giant dipole molecules.