Assignment of 15N-NMR resonances of vitamin B12 analogues by 2D-[15N, 1H] long-range correlation: Fully [15N]-labelled Co-β-cyano-5-hydroxybenzimidazoylcobamide (factor III) and derivatives

The ¹⁵N-NMR spectra of vitamin B₁₂ analogues obtained in fully ¹⁵N-labelled form have been measured by direct and inverse (¹⁵N, ¹H) correlated spectroscopy. All resonances, except those of the NH₂ groups, have been assigned to individual N-atoms. The influences on δ (N) are analyzed and discussed which are caused by changing the α-face ligand from CN to H₂O or CH₃ and by switching the β-face ligand from the base-on to the base-off state. An implication of the correct resonance assignment on biosynthetic pathways is demonstrated.     

Shear flow experiments in an assembly of gel beads and modelling of bingham behavior

In this paper, we present a rheological study of a compact layer of highly swollen gel beads. The flow regimes of these systems are modelled by an elastic sinusoid moving in a Newtonian fluid. This model predicts a yield stress varying with the square root of the elastic modulus of the gel bead. The slope at the origin (at zero velocity) of the flow curve is expected to depend only on geometrical parameters and on the solvent viscosity. The experimental data are in qualitative agreement with the theoretical predictions.     

Analysis of polyaddition levels in i-Sc3NC80

Using the density functional method, the stabilities of highly hydrogenated and fluorinated [80]fullerenes, both empty and containing the Sc3N molecule, have been calculated. Addition of 44 atoms to i-Sc3NC80 is predicted to be most favorable due to the formation of six octahedrally located benzenoid rings, while addition of up to 52 atoms (consistent with preliminary fluorination data) gives a structure stabilized by the presence of four benzenoid rings. The most stable isomers at this addition level have been determined and the relative stabilities of a number of C80H52, C80F52, and i-Sc3NC80H52 species calculated. The hydrogenation of the i-Sc3NC80 has been computed to be more difficult than the corresponding partner, C80. From the geometrical point of view, the Sc3N molecule is planar in the parent [80]fullerene but is calculated to be pyramidal in some of the hydrogenated/fluorinated derivatives. Moreover, in these it has fixed locations due to orbital interactions arising from deformation of the cage and the presence of localized double bonds.     

Préparation,configuration et réduction électrochimique d'α-cyano β-nitrostyrènes. Synthèse d'amino-5 isoxazoles

Z α-Cyano-β-nitrostyrenes were prepared by nitration with dinitrogentetroxide of the corresponding α-cyanostyrenes. Elsomers were obtained by photoirradiation of Z isomers. The electrochemical reduction of these cyanonitro compounds generates the α-cyanooximes which lead, according to the experimental conditions(ring closure or hydrolysis), either to 5-aminoisoxazoles or to β-ketonitriles.     

Reactions of NO3-naphthalene adducts with O2 and NO2

The kinetics of the gas-phase reaction of the NO₃ radical with naphthalene have been investigated at 150 torr O₂ + 590 torr N₂ and 600 torr O₂ + 140 torr N₂ at 298 ± 2 K. Relative rate measurements were carried out in reacting NO₃? N₂O₅-naphthalene-propene-O₂? N₂ mixtures by longpath Fourier transform infrared absorption spectroscopy. A rate constant ratio for the reactions of O₂ and NO₂ with the NO₃-naphthalene adduct of k/k < 4 × 10^?7 was obtained from the competition between O₂ and NO₂ for reaction with the NO₃-naphthalene adduct and thermal decomposition of the adduct back to reactants. Atmospheric pressure ionization MS/MS measurements of the nitronaphthalene products of the NO₃ radical-initiated reaction of naphthalene are consistent with the proposed reaction mechanism, and the atmospheric implications of the data are discussed. © 1994 John Wiley & Sons, Inc.     

Osmotic and activity coefficients at 25°C for tetraalkylammonium bromides in deuterium oxide

Earlier work by Lindenbaum and Boyd has demonstrated the important role of hydrophobic interactions involving the water solvent in determining the osmotic coefficients and properties of aqueous solutions of the tetraalkylammonium halides. Osmotic coefficients of solutions of tetramethyl-, tetraethyl-, tetrapropyl-, and tetrabutylammonium bromides in the more highly structured solvent D₂O have now been determined by the gravimetric isopiestic method, using reference solutions of NaCl in D₂O. The data were fitted to the Rush-Johnson and Pitzer equations. Satisfactory agreement with the results for aqueous solutions at comparable concentrations indicates that the solution chemistry of these quaternary ammonium bromides is not highly dependent on the degree of structure of the pure solvents. Supplementary data for mixtures of Me₄NBr with Et₄NBr, Pr₄NBr, or Bu₄NBr in both H₂O and D₂O are consistent with this conclusion.On leave 1980–82 from Banaras Hindu University, India     

Complexes of polyacids with poly(vinylbenzocrown ether)s and polyvinylbenzoglymes in water

Insoluble complexes are formed in acidic aqueous media when poly(acrylic acid) (PAA) and poly-(vinylbenzo-18-crown-6) (P18C6) or polyvinylbenzoglymes are mixed. Complex formation results from hydrogen bonding between carboxyl groups and crown ether- or glyme–oxygen atoms as well as from hydrophobic interactions. The precipitation is pH dependent and was determined as a function of the ratio PAA to P18C6 or to polyglyme at different HCl concentrations in 10^?4M solutions of polycrown or polyglyme. Precipitation is nearly quantitative in 0.01N HCl. The compositions of PAA/P18C6 precipitates were determined as a function of the initial PAA/P18C6 ratio in solution. The complexes with P18C6 can be solubilized in acidic media when crown-complexable cations (K⁺, Cs⁺, Ba²⁺) are added, but the charged P18C6 reprecipitates in basic solution as a polysalt complex with the PAA–polyanion. More stable PAA–P18C6 complexes in the form of fibers can be obtained by interfacial complex formation. Poly(methacrylic acid) is less effective as a complex former.     

Metal ion complexes of 2-picolinamineN-oxide

Summary A series of cobalt(II), nickel(II) and copper(II) complexes of 2-picolinamineN-oxide, HA, has been prepared. Solids of formula [M(HA)₃](BF₄)₂ (M=cobalt(II) or nickel(II); [Cu(HA)₂]X₂ (X=BF ₄ ^– , NO ₃ ^– ); [Co(HA)₂X₂] (X=Cl^– or Br^–); [Ni(HA)₂Cl₂] and [Cu(HA)X₂] (X=Cl^– or Br^–] have been isolated and characterized by partial elemental analyses, molar conductivities, magnetic susceptibilities, DSC-TGA, and spectral methods. All complexes were found to be monomeric, and their spectral parameters are compared with those of the metal ion complexes ofN-alkyl-2-picolinamineN-oxides, 2-dialkylaminopyridineN-oxides and 2-picolinamine. The cobalt(II) and nickel(II) halide complexes spectrally show a mixture of octahedral and tetrahedral centres.     

Synthesis and spectroscopic studies of metal(II) complexes prepared withN-2-(5-picolyl)-N′-phenylthiourea

Summary The chlorides and bromides of cobalt(II), nickel(II) and copper(II) along with the acetates of the latter two metal ions and copper(II) tetrafluoroborate were used to prepare complexes ofN-2-(5-picolyl)-N-phenylthiourea (5MTUH). 5MTUH coordinates as a bidentate ligand via the pyridyl nitrogen and the sulphur atoms in the cobalt(II) complexes and the compounds isolated with Cu(BF₄)₂ and CuCl₂. Complexes of stoichiometry [Cu(5MTU)X] (X=Br or C₂H₃O₂) appear to have the deprotonated ligand coordinated via the pyridyl andN thioamide nitrogens and the sulphur atom. The nickel(II) complexes involve monodentate 5MTUH with sulphur being the donor atom. A violet, octahedral [Co(5MTUH)₂Cl₂] complex and a blue, tetrahedral [Co(5MTUH)Cl₂] complex have been isolated, but with CoBr₂ only an octahedral complex could be prepared.