Gas‐Phase Olefin Polymerization in the Presence of Supported and Self‐Supported Ziegler‐Natta Catalysts

The RPPFM is employed to describe the gas‐phase catalytic polymerization of ethylene in the presence of supported or self‐supported Z‐N catalysts. Numerical simulations are carried out to analyze the effect of the catalyst type on the polymerization rate, particle overheating and the average molecular polymer properties of the polyolefin. It is shown that non‐porous, self‐supported Ziegler‐Natta catalysts exhibit higher particle growth rates and lower particle overheating. The average molecular weight of polyethylene produced by both catalysts is almost identical. Depending on particle size and polymer crystallinity, the average monomer solubility and the effective monomer diffusivity can significantly vary.

     

Reconciling semiclassical and Bohmian mechanics. V. Wavepacket dynamics

In previous articles [B. Poirier J. Chem. Phys. 121, 4501 (2004); C. Trahan and B. Poirier, ibid. 124, 034115 (2006); 124, 034116 (2006); B. Poirier and G. Parlant, J. Phys. Chem. A 111, 10400 (2007)] a bipolar counterpropagating wave decomposition, psi = psi(+) + psi(-), was presented for stationary states psi of the one-dimensional Schrodinger equation, such that the components psi(+/-) approach their semiclassical Wentzel-Kramers-Brillouin analogs in the large action limit. The corresponding bipolar quantum trajectories are classical-like and well behaved, even when psi has many nodes, or is wildly oscillatory. In this paper, the method is generalized for time-dependent wavepacket dynamics applications and applied to several benchmark problems, including multisurface systems with nonadiabatic coupling.     

Antibody-gold quantum dot-PAMAM dendrimer complex as an immunoglobulin immunoassay

Gold quantum dots (AuQDs) were synthesized and electrostatically conjugated to goat-derived anti-human IgG for the purpose of detecting human IgG in solution over a broad range of concentrations. The system is able to detect human IgG by linear fluorescence quenching over a micromolar to nanomolar concentration range. We have demonstrated the specificity and a wide dynamic range of the proposed immunoassay. The quenching is a result of competitive surface quenching of the AuQDs. Characterization, details of the immunoassay, and the quenching mechanism, are discussed.     

A bridging hexazene (RNNNNNNR) ligand from reductive coupling of azides

This communication reports the first examples of transition metal complexes containing an RNNNNNNR 2- ligand. Addition of 1-azidoadamantane to the diiron(I) synthon LRFeNNFeL R (L R = HC[C(R)N(2,6- iPr 2C 6H 3)] 2; R = methyl, tert-butyl) leads to the diiron complexes L RFe(mu-eta2:eta2-AdN6Ad)FeLR, which are surprisingly thermally stable. Magnetic, M?ssbauer, and crystallographic data are consistent with pairs of high-spin iron(II) ions antiferromagnetically coupled through a dianionic AdN6Ad 2- bridge.     

Secondary bonding interactions in biomimetic [2Fe-2S] clusters

A series of synthetic [2Fe-2S] complexes with terminal thiophenolate ligands and tethered ether or thioether moieties has been prepared and investigated in order to provide models for the potential interaction of additional donor atoms with the Fe atoms in biological [2Fe-2S] clusters. X-ray crystal structures have been determined for six new complexes that feature appended Et (1(C)), OMe (1(O)), or SMe (1(S)) groups, or with a methylene group (2(C) ), an ether-O (2(O)), or an thioether-S (2(S)) linking two aryl groups. The latter two systems provide a constrained chelate arrangement that induces secondary bonding interactions with the ether-O and thioether-S, which is confirmed by density functional theory (DFT) calculations that also reveal significant spin density on those fifth donor atoms. Structural consequences of the secondary bonding interactions are analyzed in detail, and effects on the spectroscopic and electronic properties are probed by UV-vis, M?ssbauer, and (1)H NMR spectroscopy, as well by SQUID measurements and cyclic voltammetry. The potential relevance of the findings for biological [2Fe-2S] sites is considered.     

Normal number constructions for Cantor series with slowly growing bases

Let Q = (q_n)_n=1^∞ be a sequence of bases with q_i ≥ 2. In the case when the q_i are slowly growing and satisfy some additional weak conditions, we provide a construction of a number whose Q-Cantor series expansion is both Q-normal and Q-distribution normal. Moreover, this construction will result in a computable number provided we have some additional conditions on the computability of Q, and from this construction we can provide computable constructions of numbers with atypical normality properties.     

Neutral-ligand complexes of bis(imino)pyridine iron: synthesis, structure, and spectroscopy

A family of bis(imino)pyridine iron neutral-ligand derivatives, ((iPr)PDI)FeL(n) ((iPr)PDI = 2,6-(2,6-iPr2-C6H3N=CMe)2C6H3N), has been synthesized from the corresponding bis(dinitrogen) complex, ((iPr)PDI)Fe(N2)2. When L is a strong-field ligand such as tBuNC or a chelating alkyl diphosphine such as DEPE (DEPE = 1,2-bis(diethylphosphino)ethane), a five-coordinate, diamagnetic compound results with no spectroscopic evidence for mixing of paramagnetic states. Reducing the field strength of the neutral donor to principally sigma-type ligands such as tBuNH2 or THT (THT = tetrahydrothiophene) also yielded diamagnetic compounds. However, the 1H NMR chemical shifts of the in-plane bis(imino)pyridine hydrogens exhibit a large chemical shift dispersion indicative of temperature-independent paramagnetism (TIP) arising from mixing of an S = 1 excited state via spin-orbit coupling. Metrical data from X-ray diffraction establish bis(imino)pyridine chelate reduction for each structural type, while M?ssbauer parameters and NMR spectroscopic data differentiate the spin states of the iron and identify contributions from paramagnetic excited states.     

Iron complexes of new pentadentate ligands containing the 1,4,7-triazacyclononane-1,4-diacetate motif. spectroscopic, electro-, and photochemical studies

Three new pentadentate, pendent arm macrocycles containing the 1,4,7-triazacyclononane-1,4-diacetate motif have been synthesized, and their coordination chemistry with Fe(III) has been investigated. Eight new octahedral Fe(III) complexes containing chloro, azido, or mu-oxo ligands have been synthesized, five of which have been characterized by X-ray crystallography. Spectroscopic characterization of these octahedral Fe(III) complexes by UV-vis, IR, electrochemistry, EPR, magnetic susceptibility, and zero-field M?ssbauer measurements firmly establishes the high-spin state of the iron in all complexes. Electrochemistry studies of the azido-Fe(III) complexes show that they can be reversibly oxidized to the corresponding Fe(IV) species at -20 degrees C, and Fe(II), Fe(III), and Fe(IV) species show characteristic IR and UV-vis profiles. Photolysis of one of the azido complexes was studied as a function of temperature (room temperature vs 77 K) and wavelength (480, 419, and 330 nm). Photoreduction to a high-spin Fe(II) species occurs under all conditions, which is proposed to be the dominant photochemical pathway generally available to high-spin ferric azido complexes.