Studies on ion association. Calorimetric study of the formation of monoazido complexes of Ni(II), Zn(II) and Cd(II)

From rehydration experiments the hydrates Ba(OH)₂ · 8 H₂O, Ba(OH)₂ · 3 H₂O β-Ba(OH)₂, · 1 H₂O, and γ-Ba(OH)₂ · 1 H₂O have been found in the system Ba(OH)₂-H₂O. Thermoanalytical measurements (DTA, TG, DTG, high temperature X-ray diffraction, high temperature Raman scattering) on these hydrates are reported. Thermal decomposition of Ba(OH)₂ · 8 H₂O and Ba(OH)₂ · 3 H₂O always results in the formation of β-Ba(OH)₂ · 1 H₂O, the stable form of the monohydrates at ambient temperature. Dehydration of β- and γ-Ba(OH)₂ · 1 H₂O, both of which form anhydrous β-Ba(OH)₂ as the first product of decomposition, starts at 105 and 115°C, respectively. Single crystals of Ba(OH)₂ · 3 H₂O and γ-Ba(OH)₂ · 1 H₂O were prepared from Ba(OH)₂ · 8 H₂O meltings and from ethanolic solutions of Ba(OH)₂ , respectively. The crystal data are: Ba(OH)₂ · 3 H₂O (orthorhombic, Pnma): a = 764.0(2), b = 1140,3(5), c = 596.5(1) pm, Z = 4; γ-Ba(OH)₂ · 1 H₂O (monoclinic, P2₁/m or P2₁): a = 704.9(2), b = 418.4(1), c = 633.3(1) pm, β = 111.45(2)°, Z = 2.     

Phase associated with the single-particle density of many-electron systems

In excited states of atoms and molecules, as well as in time-dependent situations, the one-electron density no longer suffices to completely characterize the electronic state; in addition, one now requires information about the electronic phase or the current density. We show that, for a stationary electronic state, the continuity equation of quantum fluid dynamics represents a differential equation for the electronic phase, which must be solved subject to certain periodicity conditions. These periodicity conditions arise from the nodal topology of the wave function and give rise to quantized vortices of current. The consequences of writing an electronic “wave function” for a many-electron system directly in terms of the single-particle density and phase have been investigated. We have shown that such a procedure leads to the appearance of an “internal magnetic vector potential.” We also establish the connection between the electronic phase and the geometrical (“Berry”) phase accompanying the adiabatic transport of a quantal system around a closed loop in parameter space. This leads to a generalization of the current density concept and allows us to discuss the geometrical phase in terms of the circulation of this current in parameter space.     

Synthesis and modeling study of (2S,5R,6R)- and (2S,5R,6S)-6-hydroxy- 8-(1-decynyl)-benzolactam-V8 as protein kinase C modulators

[structures: see text] Both (2S,5R,6R)- and (2S,5R,6S)-6-hydroxy-8-(1-decynyl)benzolactam-V8 were designed and synthesized as PKC modulators. Biological assays reveal the (6R)-ligand to be 20-fold more potent than its (6S)-counterpart in binding to PKC alpha.     

Transferable atom equivalent multicentered multipole expansion method

The transferability of atomic and functional group properties is an implicit concept in chemistry. The work presented here describes the use of Transferable Atom Equivalents (TAE) to represent molecular electrostatic potential fields through the use of integrated atomic multipole moments that are associated with each TAE atom type used in the reconstruction. TAE molecular surface distributions of electrostatic potentials are compared with analytical ab initio and empirical (Gasteiger) partial charge reference models for several conformations of test peptides. Surface electrostatic potential distributions computed using TAE multipole representations were found to converge at the octopole level, with incremental improvement observed when hexadecapoles were included. Molecular electrostatic potential fields that were produced using the TAE method were observed to be responsive to conformational changes and to compare well with ab initio reference distributions. Generation of TAE atom types and their associated multipoles does not involve fitting to sample electrostatic potential fields, but rather utilizes integrated AIM atomic electron density distributions within representative chemical environments. The RECON program was used for TAE reconstruction. RECON is capable of processing 5,000 drug-sized molecules or 25 proteins per minute per 1.7 GHz P4 Linux processor.     

Donor–acceptor complexes in copolymerization. XLIX. Cationic polymerization of donor monomers in presence of polar solvents and acrylic monomers. A revised mechanism for polymerization of comonomer complexes

α-Methylstyrene (MS) and isobutyl vinyl ether (VE) readily polymerize, styrene (S) polymerizes to a small extent, and isobutylene (IB), butadiene (BD), and isoprene (IP) fail to polymerize in the presence of catalytic amounts of AlCl₃ when propionitrile, ethyl propionate, and methyl isobutyrate are used as reaction media. MS polymerizes readily and S polymerizes with difficulty in the presence of AlCl₃ to yield homopolymers when acrylonitrile (AN) is present and copolymers with ethyl acrylate (EA) and methyl methacrylate (MMA). VE readily homopolymerizes, while IB, BD, and IP fail to polymerize in the presence of AlCl₃ and the acrylic monomers. VE readily homopolymerizes, S and MS polymerize to a very small extent, and IB, BD, and IP do not polymerize in the presence of ethylaluminum sesquichloride (EASC) in polar solvents. VE readily homopolymerizes in the presence of EASC and the acrylic monomers. MS polymerizes to a small extent in the presence of EASC and the acrylic monomers to yield equimolar copolymers with EA and MMA and a mixture of cationic homopolymer and equimolar copolymer with AN. S yields equimolar copolymers in low yield in the presence of EASC and the acrylic monomers. IB, BD, and IP in the presence of EASC do not polymerize to any significant extent when EA is present, form AN-rich copolymers and yield poly(methyl methacrylate) in the presence of MMA. A revised mechanism is presented for the formation of cationic, radical, random, and alternating copolymers as well as alternating copolymer graft copolymers in the copolymerization of donor and acceptor monomers.     

Fluorination of polymers by sulfur hexafluoride gas under electric discharge

Fluorination of low-density polyethylene, polyacetylene, and poly(vinyl alcohol) was carried out using SF₆ gas under electric discharge. The polymers were partially fluorinated and the extent of fluorination was more in the case of poly (vinyl alcohol) than the other two polymers. The fluorinated polymers were characterized by elemental analysis (Fluorine), IR, and x-ray diffraction. Optical transparency of the films was also measured. The fluorinated polymers show better solvent resistance and decreased transparency than the virgin polymer. © 1994 John Wiley & Sons, Inc.     

Thermal properties of N-substituted 4-vinylpyridinium ions and their polymers

4-Vinylpyridinium trifluoromethanesulfonate monomers substituted at nitrogen with H, O, CH₃, C₂H₅, C₆H₁₃, and C₁₂H₂₅ were synthesized and characterized spectroscopically. Thermal analyses (DSC and TGA) were carried out on all the compounds. The solid monomers (N? H, N? CH₃, N? C₆H₁₃, and N? C₁₂H₂₅) exhibited endothermic melting followed by exothermic polymerization and exothermic decomposition (>400°C). Liquid N? C₂H₅ monomer revealed only exothermic polymerization and decomposition. The N? O polymer underwent thermal decomposition below 300°C. The N–C₁₂H₂₅ homopolymer, prepared from monomer in the DSC or in bulk, displayed an unusual thermal transition at 250°C, which has been attributed to a polymer backbone reorientation leading to side-chain ordering of the dodecyl groups.     

Density functional theory of born couplings: Consequences for electron flow in Jahn–Teller molecules and superconductors

The dynamics of Jahn–Teller systems has recently been discussed in terms of generalized electronic charge and current densities in nuclear-coordinate space. The introduction of the electronic phase as a function of both electronic and nuclear coordinates, in addition to the electronic density, was a crucial component of this formulation. Here, a densitybased treatment of Born couplings is derived from first-principles quantum mechanics beyond the Born–Oppenheimer approximation. Because of the degenerate electronic configuration of a Jahn–Teller molecule, there are an infinite number of ways in which the charge distribution can be oriented for the same energy, leading to a vanishing bond hardness for the molecule in the symmetric nuclear configuration. Further, the moving nuclear framework serves as the perturbation necessary to define the orientation of the charge density, leading to unhindered rotation of the charge cloud. This leads to the dynamical Jahn–Teller problem, namely, the coupling of electronic and nuclear motions through the Born coupling terms. Applications to superconductivity theory are discussed. © 1995 John Wiley & Sons, Inc.     

Influence of media nutrients on synthesis of lignin peroxidase from Aspergillus sp

The effect of carbon and nitrogen sources, lignocellulosic substrates, and metal ions on lignin peroxidase (LiP) activity of Aspergillus sp., which was isolated from a mangrove area, was studied. Glucose (1%) was found to be the best carbon source. Among the various lignocellulosic substrates used, coir pith at 3% concentration increased LiP activity twofold on the second day of incubation. Peptone and KNO₃ completely inhibited the enzyme synthesis while (NH₄)₂SO₄ at 12.5 mM produced maximum activity. Since seawater contained all the requisite metal ions, any added ions had a negative effect on activity. Cu²⁺ had the most inhibiting effect while K⁺ the least. When all the optimized conditions were provided, in nitrogen- and carbon-sufficient medium, a maximum LiP activity of 345 U/mL was obtained on the second day of incubation.