Pyrene functional poly(vinyl alcohol) by “click” chemistry

Side‐chain pyrene functional poly(vinyl alcohol) (PVA) was synthesized by using “click chemistry” strategy. First, partial tosylation of PVA with p‐toluene sulfonyl chloride were performed. The resulting PVA‐Ts polymer was then quantitatively converted into poly(vinyl alcohol)‐azide (PVA‐N₃) in the presence of NaN₃/DMF at 60 °C. Propargyl pyrene was prepared independently as a photoactive click component. Finally, azido functionalized PVA was coupled to propargyl pyrene with high efficiency by click chemistry. Incorporation of pyrene functionality in the resulting polymer was confirmed by spectral analysis. It is also shown that pyrene functionalized PVA (PVA‐Py) exhibited characteristic fluorescence properties and improved solubility in highly polar solvents such as water, DMSO, and DMF as well as less polar solvent such as THF compared with pristine PVA. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1317–1326, 2009     

Approximate analysis of load-dependent generally distributed queuing networks with low service time variability

In this paper, we present an approximate method for solution of load-dependent, closed queuing networks having general service time distributions with low variability. The proposed technique is an extension of Marie’s (1980) method. In the methodology, conditional throughputs are obtained by an iterative procedure. The iterations are repeated until an invalid result is detected or no improvements are found. We demonstrate the performance of the technique with 10 different examples. On average, the solutions have 5% or lower deviations when compared to simulation results.     

Catechol oxidase activity of dinuclear copper(II) complexes of Robson type macrocyclic ligands: Syntheses, X-ray crystal structure, spectroscopic characterization of the adducts and kinetic studies

Five dinuclear copper(II) complexes, [Cu₂L¹(N₃)₂·2H₂O] (1), [Cu₂L²(N₃)₂·2H₂O] (2), [Cu₂L³(N₃)₂·2H₂O] (3), [Cu₂L⁴(N₃)₂·2H₂O] (4) and [Cu₂L⁵(N₃)₂·2H₂O] (5) of Robson type macrocyclic Schiff-base ligands derived from [2 + 2] condensation of 4-methyl-2,6-diformylphenol with 1,3-diaminopropane (H₂L¹), 1,2-diaminoethane (H₂L²), 1,2-diaminopropane (H₂L³), 1,2-diamino-2-methylpropane (H₂L⁴) and 1,2-diaminocyclohexane (H₂L⁵), respectively have been synthesized and characterized. Catecholase activity of those complexes using 3,5-di-tert-butylcatechol as substrate has been investigated in two solvents, methanol and acetonitrile. The role of the solvent and of the steric properties of the macrocyclic ligand of these complexes on their catecholase activity has been examined thoroughly. Acetonitrile is observed to be a better solvent than methanol as far as their catalytic activity is concerned. However, methanol reveals to be a better choice to identify the enzyme–substrate adduct. The investigation also prompted that chelate ring size does affect on the catalytic efficiency: 6-membered ring (as in H₂L¹) exhibits better activity than its 5-membered counterpart (as in H₂L²). The activity of the 5-membered counter parts also depend upon the steric factor. Moreover, the catalytic activity of the complexes is enhanced to a significant extent by increasing the bulkiness of the substituents on the backbone of macrocyclic H₂L² ligands.     

Relativistic coulomb excitation of neutron-rich 54,56,58Cr

The first excited 2⁺ states in neutron-rich ^54,56,58Cr were populated by relativistic Coulomb excitation and B (E2, 2 ₁ ⁺ → 0⁺) values were determined for ⁵⁶Cr and ⁵⁸Cr. The B(E2) values show a minimum for ⁵⁶Cr providing evidence for a subshell closure at N=32.     

Exclusive measurement of the nonmesonic weak decay of the lambda(5)He hypernucleus

We performed a coincidence measurement of two nucleons emitted from the nonmesonic weak decay of lambda(5)He formed via the 6Li(pi+, K+) reaction. The energies of the two nucleons and the pair number distributions in the opening angle between them were measured. In both np and nn pairs, we observed a clean back-to-back correlation coming from the two-body weak reactions of lambda p --> np and lambda n --> nn, respectively. The ratio of the nucleon pair numbers was N(nn)/N(np) = 0.45 +/- 0.11(stat) +/- 0.03(syst) in the kinematic region of cos theta(NN) < -0.8. Since each decay mode was exclusively detected, the measured ratio should be close to the ratio of gamma(lambda p --> np)/gamma(lambda n --> nn). The ratio is consistent with recent theoretical calculations based on the heavy meson and/or direct-quark exchange picture.     

Hypernuclear fine structure in (16)(Lambda)O and the LambdaN tensor interaction

We have observed two gamma-ray transitions in (16)(Lambda)O from the 6.6 MeV excited 1(-)(2) state to both ground-state spin-doublet members (1(-)(1),0(-)) by the (K-,pi(-)gamma) reaction. We have obtained the ground-state doublet spacing to be 26.4+/-1.6(stat)+/-0.5(syst) keV and the excitation energy of the 1(-)(2) state to be 6561.7+/-1.1(stat)+/-1.7(syst) keV. The ground-state doublet spacing provides a small but nonzero strength of the tensor interaction between a Lambda and a nucleon. This is the first experimental result on the LambdaN tensor interaction.     

Controlled aggregation of ME8(n-) binary anions (M = Cr,Mo; E = As,Sb) into one-dimensional arrays: structures,magnetism and spectroscopy

The [ME(8)](n)()(-) ions where M = Cr, Mo; E = As, Sb; n = 2, 3 have been prepared from the corresponding E(7)(3)(-) Zintl ions and M(naphthalene)(2) precursors. The complexes and their [A(crypt)](+) salts (A = Na, K) are formed in 20-45% crystalline yields and have been characterized by UV-vis spectroscopy, EPR, cyclic voltammetry, magnetic susceptibility, electrospray mass spectrometry (ESI-MS) and single-crystal X-ray diffraction. The structures are defined by crown-like cyclo-E(8) rings that are centered by transition metals. MoAs(8)(2)(-) (2) is a 16 e(-) diamagnetic complex whereas MoSb(8)(3)(-) (5) and the CrAs(8)(3)(-) salts (3 and 4) are 17 e(-) paramagnetic complexes. The ESI-MS spectra show free and alkali-complexed ME(8)(n)()(-) ions. The K(+) salt of CrAs(8)(3)(-) (4) crystallizes in a one-dimensional chain structure of [KCrAs(8)](2)(-) repeat units whereas the Na(+) salt (3) as well as 2 and 5 crystallize in "free ion" structures. The Cr atoms in 3 and 4 are formally d(1) Cr(5+) centers that show EPR signals at g = 2.001 with small As hyperfine interactions of 3.6 G. The susceptibility of the [KCrAs(8)](2)(-) salt 4 was modeled as a 1D Heisenberg antiferromagnet with a small -J/k(B) of 3K arising from antiferromagnetic couplings of the d(1) centers whereas 3 shows Curie-Weiss behavior. The electrochemical studies show metal-based oxidations for 3-5 but a ligand based oxidation for 2. The electronic spectra are interpreted in terms of the molecular orbital analysis of Li and Wu. The differences in formal oxidation states of the metals is described in terms of a Zintl-Klemm formalism involving E(8)(8)(-) rings that are isoelectronic to S(8). The factors governing the formation of 1D chains versus free ions are presented.     

Selective detection and recovery of gold at tannin-immobilized non-conducting electrode

A tannin-immobilized glassy carbon electrode (TIGC) was prepared via electrochemical oxidation of the naturally occurring polyphenolic mimosa tannin, which generated a non-conducting polymeric film (NCPF) on the electrode surface. The fouling of the electrode surface by the electropolymerized film was evaluated by monitoring the electrode response of ferricyanide ions as a redox marker. The NCPF was permselective to HAuCl₄, and the electrochemical reduction of HAuCl₄ to metallic gold at the TIGC electrode was evaluated by recording the reduction current during cyclic voltammetry measurement. In the mixed electrolyte containing HAuCl₄ along with FeCl₃ and/or CuCl₂, the NCPF remained selective toward the electrochemical reduction of HAuCl₄ into the metallic state. The chemical reduction of HAuCl₄ into metallic gold was also observed when the NCPF was inserted into an acidic gold solution overnight. The adsorption capacity of Au(III) on tannin-immobilized carbon fiber was 29 ± 1.45 mg g⁻¹ at 60 °C. In the presence of excess Cu(II) and Fe(III), tannin-immobilized NCPF proved to be an excellent candidate for the selective detection and recovery of gold through both electrochemical and chemical processes.