Structure transfer from a polymeric melt to the solid state. Part II: Dependence on molecular weight

Melt spinning experiments of polyethylene, using a high quenching rate have been carried out. Molecular weight has been varied. From measurements of the mechanical properties of the monofilaments produced it is concluded that melt history influences the solid state behavior. This is reflected in the hypothesis of a transference of knots, preexisting in the melt into the solid state. Measurements of the elastic recovery allow to offer an interpretation, in which this network of knots does not percolate, until a critical value of the molecular weightM _{c knot}10⁵ is surpassed. The possible influence of these knots on the mobile entanglements is discussed.On leave from the Institut für Technische und Makromolekulare Chemie, Universität Hamburg, Hamburg, Germany.     

Thermal analysis of some metal n-benzoyl-n-phenylhydroxylamine chelates

The preparation and thermal analysis of the metal chelates of N-benzoyl-N-phenylhydroxylamine (BPHA) with Al(III), Cd(II), Co(II), Cr(III), Cu(II), Fe(III), Mn(II), Ni(II) and Zn(II) is discussed. The differential thermal analysis apparatus is described in detail. DTA and TGA curves of BPHA arid the chelates from 25 to 700° in oxygen and in nitrogen are presented.     

Aspects of the mechanism of catalysis of glucose oxidase: A docking, molecular mechanics and quantum chemical study

The complex structure of glucose oxidase (GOX) with the substrate glucose was determined using a docking algorithm and subsequent molecular dynamics simulations. Semiempirical quantum chemical calculations were used to investigate the role of the enzyme and FAD co-enzyme in the catalytic oxidation of glucose. On the basis of a small active site model, substrate binding residues were determined and heats of formation were computed for the enzyme substrate complex and different potential products of the reductive half reaction. The influence of the protein environment on the active site model was estimated with a point charge model using a mixed QM/MM method. Solvent effects were estimated with a continuum model. Possible modes of action are presented in relation to experimental data and discussed with respect to related enzymes. The calculations indicate that the redox reaction of GOX differs from the corresponding reaction of free flavins as a consequence of the protein environment. One of the active site histidines is involved in substrate binding and stabilization of potential intermediates, whereas the second histidine is a proton acceptor. The former one, being conserved in a series of oxidoreductases, is also involved in the stabilization of a C4a-hydroperoxy dihydroflavin in the course of the oxidative half reaction.     

Separation of positional isomers of oxidation catalyst precursors

A series of polypyridyl ruthenium complexes of the general formula [Ru(tpy)(bpy')Cl]+ where tpy is 2,2':6',2"-terpyridine and bpy' is 4-carboxy-4'-methyl-2,2'-bipyridine (4-CO2H-4'-Mebpy), a proline derviative (4-CO-Pra-(Boc)(OMe)-4'-Mebpy), or 4-((diethoxyphosphinyl)methyl)-4'-methyl-2,2'-bipyridine (4-CH2PO3Et2-4'-Mebpy) are prepared. For each complex, two isomers exist, and these are separated chromatographically. The structure of the hexafluorophosphate salt of cis-[Ru(tpy)(4-CO2H-4'-Mebpy)Cl]+, cis-1, is determined by X-ray crystallography. The salt crystallizes in the monoclinic space group Cc with a = 12.4778(6) A, b = 12.6086(6) A, c = 20.1215(9) A, beta = 107.08200(1) degrees, Z = 4, R = 0.058, and Rw = 0.072. The structures of the remaining complexes are assigned by 1H NMR comparisons with cis-1. The complexes are potentially important precursors for the incorporation of RuIV=O2+ oxidants into polymers or peptides or for their adsorption onto oxide surfaces. Preliminary electrochemical results for the isomers of [Ru(tpy)(4-CH2PO3H2-4'-Mebpy)(H2O)]2+, 4, adsorbed on ITO (In2O3:Sn) surfaces add support to a recently proposed electron-transfer mechanism involving cross-surface proton-coupled electron transfer.     

Crystal Structure,Electronic Structure,and Luminescence of Cs2KYF6:Pr3+

The crystal structure, electronic states and VUV spectroscopic behaviour of Cs₂KYF₆ doped with Pr³⁺ ions have been investigated both by experimental and theoretical methods. Cs₂KYF₆ ( , Z = 4, a = 945.5(3) pm, R1_all = 0.0297) crystallizes with the cubic elpasolite type of structure. The local relaxation of the activator ions in the host lattices has been calculated by the projector augmented wave method (computer code VASP). The electronic states have been calculated using a spin density functional procedure based on the atomic sphere approximation (computer code ASW). VUV spectroscopic measurements show fast 4f¹5d¹ → 4f² emission of nanosecond duration as well as slow 4f² → 4f² emission depending on the excitation energy which indicates the occupation of different sites in the host lattice. This assumption was verified by a recently developed quantum mechanical method. The combination of the experimental and the theoretical results show that the Pr³⁺ ions are occupying three different sites, namely the Y³⁺ and the Cs⁺ site as well as the K⁺ site.     

Efficient photodissociation of O2 from synthetic heme and heme/M (M = Fe, Cu) complexes

Single wavelength excitation (lambdaex = 355 or 532 nm) of low-temperature stabilized (198 K) synthetic heme-dioxygen and heme-dioxygen/M complexes, where M = copper or iron in a non-heme environment, results in the dissociation of dioxygen as indicated by the generation of the ferrous heme (Soret band, 427 nm) and the bleaching of the ferric-superoxide (FeIII(O2-)) 410-nm Soret band in the transient absorption difference spectrum. Dioxygen rebinds to the four heme complexes studied with comparable rate constants ( approximately 6-9 x 105 M-1 s-1). However, the quantum yield for complete dissociation of O2 from our simplest heme-O2 complex (F8)FeIII(O2-) (phi = 0.60) is higher than the other complexes measured (phi = approximately 0.2-0.3) as well as that for oxy-myoglobin (phi = 0.3).     

The coherent K L 0 C → K S 0 C regeneration at high energies

New experimental results on the coherentK _L ⁰ C K _S ⁰ C regeneration in the momentum range 10p30 GeV/c are presented. For the quantity (f ₀–¯f ₀/k (where f₀ and¯f ₀ are theKC and¯K ⁰C forward scattering amplitudes andk is the wave number) we have obtained: arg (f ₀–¯f ₀)/k=–126±14 and ¦(f ₀–¯f ₀/k¦ p ^{–0.62±0.14} These results are well described by a simple Regge pole model including only the (-trajectory exchange in thet-channel with the intercept (0) close to 0.4.Presented at the IV International Symposium on High Energy and Elementary Particle Physics, Warszaw, September 1975.