Aminopyridinato Complexes as Possible Alternatives for Metallocenes in Ethylene Polymerization

Polyethylene is the most widely used synthetic polymer in the world. Most polyethylene is made with Ziegler-Natta catalysts. Polyethylenes for special applications are made with metallocenes, which are nowadays heavily patented. It is laborious therefore, to develop new metallocenes. The aim of this work was to investigate the feasibility of replacing the cyclopentadienyl ligands of metallocenes by aminopyridinato ligands without losing the good properties of the metallocenes, such as high activity and formation of linear polymer. The subject was approached by studying what kind of catalysts the metallocenes are and how they catalyze polyethylene. The polymerization behavior of metallocenes was examined by synthesizing a piperazino substituted indenyl zirconocene catalyst and comparing its polymerization data with that of the indenyl zirconocene catalyst. On the basis of their isolobality, it was thought that aminopyridinato ligands might replace cyclopentadienyl ligands. It was presumed that the polymerization mechanism and the active center in ethylene polymerization would be similar for aminopyridinato and metallocene catalysts. Titanium aminopyridinato complexes were prepared and their structures determined to clarify the relationship between structure of the catalyst precursor and polymerization results. The ethylene polymerization results for titanium 2-phenylaminopyridinato catalysts and titanocene catalysts were compared.

Mixed ligand complexes in vinyl polymerization. I. [N,N-ethylenebis (salicylideneiminato)](acetylacetonato)cobalt(III) as an initiator

Polymerization of methyl methacrylate in the presence of a mixed ligand complex, [N,N-ethylenebis(salicylideneiminato)](acetylacetonato)cobalt(III) in benzene was studied. The rate of polymerization was proportional to the square root of the concentration of the chelate and the monomer exponent was 1.67 and 1.69 at 60 and 70°C, respectively. The activation energy and the kinetic and transfer constants were evaluated. A free-radical mechanism has been proposed.

Metal chelates in vinyl polymerization. I. Ferric dipivaloylmethide as an initiator

The behavior of the chelate, ferric dipivaloylmethide, Fe(DPM)3, in vinyl polymerization systems was investigated. The polymerization was found to be of free-radical nature. The rate of polymerization was proportional to the square root of the concentration of the chelate. The monomer exponent was close to 1.5 for the Fe(DPM)3-initiated polymerization of styrene and methyl methacrylate. The kinetic and transfer constants and activation energies for these systems have been evaluated. Spectral studies revealed the possibility of a complex formation between the chelate and the monomer. A kinetic scheme for the Fe(DPM)3-initiated polymerization is derived based on this initial complex formation.

Metal chelates in vinyl polymerization. II. Mechanism of initiation by Fe(DPM)3

The nature of the interaction between the unsaturated monomer and the chelate, Fe(DPM)3, is studied in detail. The interaction is found to occur only in solution. The stoichiometry of interaction and the equilibrium constant are evaluated. With the help of spectral evidence, attempts are made to point out the specific sites of interaction.

In situ pump probe optical absorption studies on Sb/As2S3 nanomultilayered film

We report the in situ optical transmission change in the complete visible region of the electromagnetic spectrum to asses the kinetics of photo induced interdiffusion in Sb/As2S3 nanomultilayered film. The interdiffusion of Sb into As2S3 matrix results in the formation of Sb-As2S3 ternary solid solutions which is explained by the change in optical band gap, absorption coefficients and Tauc parameter (B-1/2) with evolution of time. The wavelength dependence of the time constants provides a better description of photo induced effects. The time evolution of the absorption coefficients and optical band gap are significantly faster in this process. (C) 2009 Elsevier B.V. All rights reserved.

In situ cryocrystallization of low melting chloro and bromo substituted anilines

In situ cryocrystallographic Studies of chloro and bromo substituted anilines have been performed to evaluate the role of halogen...halogen interactions and the subsequent formation of supramolecular assemblies in the solid state. Ortho Cl/Br substituted anilines are isostructural and belong to the trigonal P3(1) space group. Halogen...halogen intermolecular contacts along with stronger N-H center dot center dot center dot N hydrogen bonds generate helical motifs along the crystallographic c-axis. (C) 2009 Elsevier B.V. All rights reserved.

Induced higher-order aberrations after laser in situ keratomileusis (LASIK) performed with wavefront-guided IntraLase femtosecond laser in moderate to high astigmatism

Background Wavefront-guided Laser-assisted in situ keratomileusis (LASIK) is a widespread and effective surgical treatment for myopia and astigmatic correction but whether it induces higher-order aberrations remains controversial. The study was designed to evaluate the changes in higher-order aberrations after wavefront-guided ablation with IntraLase femtosecond laser in moderate to high astigmatism. Methods Twenty-three eyes of 15 patients with moderate to high astigmatism (mean cylinder, −3.22 ± 0.59 dioptres) aged between 19 and 35 years (mean age, 25.6 ± 4.9 years) were included in this prospective study. Subjects with cylinder ≥ 1.5 and ≤2.75 D were classified as moderate astigmatism while high astigmatism was ≥3.00 D. All patients underwent a femtosecond laser–enabled (150-kHz IntraLase iFS; Abbott Medical Optics Inc) wavefront-guided ablation. Uncorrected (UDVA), corrected (CDVA) distance visual acuity in logMAR, keratometry, central corneal thickness (CCT) and higher-order aberrations (HOAs) over a 6 mm pupil, were assessed before and 6 months, postoperatively. The relationship between postoperative change in HOA and preoperative mean spherical equivalent refraction, mean astigmatism, and postoperative CCT were tested. Results At the last follow-up, the mean UDVA was increased (P < 0.0001) but CDVA remained unchanged (P = 0.48) and no eyes lost ≥2 lines of CDVA. Mean spherical equivalent refraction was reduced (P < 0.0001) and was within ±0.50 D range in 61 % of eyes. The average corneal curvature was flatter by 4 D and CCT was reduced by 83 μm (P < 0.0001, for all), postoperatively. Coma aberrations remained unchanged (P = 0.07) while the change in trefoil (P = 0.047) postoperatively, was not clinically significant. The 4th order HOAs (spherical aberration and secondary astigmatism) and the HOA root mean square (RMS) increased from −0.18 ± 0.07 μm, 0.04 ± 0.03 μm and 0.47 ± 0.11 μm, preoperatively, to 0.33 ± 0.19 μm (P = 0.004), 0.21 ± 0.09 μm (P < 0.0001) and 0.77 ± 0.27 μm (P < 0.0001), six months postoperatively. The change in spherical aberration after the procedure increased with an increase in the degree of preoperative myopia. Conclusions Wavefront-guided IntraLASIK offers a safe and effective option for vision and visual function improvement in astigmatism. Although, reduction of HOA is possible in a few eyes, spherical-like aberrations are increased in majority of the treated eyes.

In-situ one-step hydrothermal synthesis of a lead germanate-graphene composite as a novel anode material for lithium-ion batteries

Lead germanate-graphene nanosheets (PbGeO3-GNS) composites have been prepared by an efficient one-step, in-situ hydrothermal method and were used as anode materials for Li-ion batteries (LIBs). The PbGeO3 nanowires, around 100–200 nm in diameter, are highly encapsulated in a graphene matrix. The lithiation and de-lithiation reaction mechanisms of the PbGeO3 anode during the charge-discharge processes have been investigated by X-ray diffraction and electrochemical characterization. Compared with pure PbGeO3 anode, dramatic improvements in the electrochemical performance of the composite anodes have been obtained. In the voltage window of 0.01–1.50 V, the composite anode with 20 wt.% GNS delivers a discharge capacity of 607 mAh g−1 at 100 mA g−1 after 50 cycles. Even at a high current density of 1600 mA g−1, a capacity of 406 mAh g−1 can be achieved. Therefore, the PbGeO3-GNS composite can be considered as a potential anode material for lithium ion batteries.

Electrical switching and in situ Raman scattering studies on the set-reset processes in Ge-Te-Si glass

Bulk Ge15Te83Si2 glass has been found to exhibit memory-type switching for 1 mA current with a threshold electric field of 7.3 kV/cm. The electrical set and reset processes have been achieved with triangular and rectangular pulses, respectively, of 1 mA amplitude. In situ Raman scattering studies indicate that the degree of disorder in Ge15Te83Si2 glass is reduced from off to set state. The local structure of the sample under reset condition is similar to that in the off state. The Raman results are consistent with the switching results which indicate that the Ge15Te83Si2 glass can be set and reset easily. (C) 2007 American Institute of Physics.

Visualization of in situ intracellular aggregation of two cataract-associated human gamma-crystallin mutants: Lose a tail, lose transparency

PURPOSE. To understand the molecular features underlying autosomal dominant congenital cataracts caused by the deletion mutations W156X in human gamma D-crystallin and W157X in human gamma C-crystallin. METHODS. Normal and mutant cDNAs (with the enhanced green fluorescent protein [EGFP] tag in the front) were cloned into the pEGFP-C1 vector, transfected into various cell lines, and observed under a confocal microscope for EGFP fluorescence. Normal and W156X gamma D cDNAs were also cloned into the pET21a(+) vector, and the recombinant proteins were overexpressed in the BL-21(DE3) pLysS strain of Escherichia coli, purified, and isolated. The conformational features, structural stability, and solubility in aqueous solution of the mutant protein were compared with those of the wild type using spectroscopic methods. Comparative molecular modeling was performed to provide additional structural information. RESULTS. Transfection of the EGFP-tagged mutant cDNAs into several cell lines led to the visualization of aggregates, whereas that of wild-type cDNAs did not. Turning to the properties of the expressed proteins, the mutant molecules show remarkable reduction in solubility. They also seem to have a greater degree of surface hydrophobicity than the wild-type molecules, most likely accounting for self-aggregation. Molecular modeling studies support these features. CONCLUSIONS. The deletion of C-terminal 18 residues of human gamma C-and gamma D-crystallins exposes the side chains of several hydrophobic residues in the sequence to the solvent, causing the molecule to self-aggregate. This feature appears to be reflected in situ on the introduction of the mutants in human lens epithelial cells.

In situ transmission electron microscope study of single asperity sliding contacts

Direct observation of events taking place at the contacting interfaces is important to understand many tribological phenomena. Transmission electron microscope (TEM) has the ability to look through materials at very high magnifications. Most of the TEM observations are done long after the deforming loads and stresses have been relaxed and the material state is further disturbed during the specimen preparation. We have developed a specimen holder in which two electron transparent surfaces can be brought in contact and moved relative to each other in JEOL 2000FX microscope. This holder enables visualization of not only the contacting surfaces at nanoscale but also the subsurface deformation resulting from the contact interaction. Sliding experimentS have been carried out mimicking a single asperity sliding contact. A sharp tungsten probe is moved laterally against a tip mounted on a cantilever. Magnitude of the contact instability, when the contact is broken is found to be dependent on the local geometry of the contact.(C) 2009 Elsevier Ltd. All rights reserved.

Top Quark Mass Measurement in the lepton+jets Channel Using a Matrix Element Method and in situ Jet Energy Calibration

A precision measurement of the top quark mass m_t is obtained using a sample of ttbar events from ppbar collisions at the Fermilab Tevatron with the CDF II detector. Selected events require an electron or muon, large missing transverse energy, and exactly four high-energy jets, at least one of which is tagged as coming from a b quark. A likelihood is calculated using a matrix element method with quasi-Monte Carlo integration taking into account finite detector resolution and jet mass effects. The event likelihood is a function of m_t and a parameter DJES to calibrate the jet energy scale /in situ/. Using a total of 1087 events, a value of m_t = 173.0 +/- 1.2 GeV/c^2 is measured.

Dual-Drug Delivery System Based on In Situ Gel-Forming Nanosuspension of Forskolin to Enhance Antiglaucoma Efficacy

The present study was designed to improve the bioavailability of forskolin by the influence of precorneal residence time and dissolution characteristics. Nanosizing is an advanced approach to overcome the issue of poor aqueous solubility of active pharmaceutical ingredients. Forskolin nanocrystals have been successfully manufactured and stabilized by poloxamer 407. These nanocrystals have been characterized in terms of particle size by scanning electron microscopy and dynamic light scattering. By formulating Noveon AA-1 polycarbophil/poloxamer 407 platforms, at specific concentrations, it was possible to obtain a pH and thermoreversible gel with a pH(gel)/T-gel close to eye pH/temperature. The addition of forskolin nanocrystals did not alter the gelation properties of Noveon AA-1 polycarbophil/poloxamer 407 and nanocrystal properties of forskolin. The formulation was stable over a period of 6 months at room temperature. In vitro release experiments indicated that the optimized platform was able to prolong and control forskolin release for more than 5 h. The in vivo studies on dexamethasone-induced glaucomatous rabbits indicated that the intraocular pressure lowering efficacy for nanosuspension/hydrogel systems was 31% and lasted for 12 h, which is significantly better than the effect of traditional eye suspension (18%, 4-6 h). Hence, our investigations successfully prove that the pH and thermoreversible polymeric in situ gel-forming nanosuspension with ability of controlled drug release exhibits a greater potential for glaucoma therapy.

In situ surface modification of molybdenum-doped organic-inorganic hybrid TiO2 nanoparticles under hydrothermal conditions and treatment of pharmaceutical effluent

Molybdenum-doped TiO2 organic-inorganic hybrid nanoparticles were synthesized under mild hydrothermal conditions by in situ surface modification using n-butylamine. This was carried out at 150 degrees C at autogeneous pressure over 18 h. n-Butylamine was selected as a surfactant since it produced nanoparticles of the desired size and shape. The products were characterized using powder X-ray diffraction, Fourier transform infrared spectrometry, dynamic light-scattering spectroscopy, UV-Vis spectroscopy and transmission electron microscopy. Chemical oxygen demand was estimated in order to determine the photodegradation efficiency of the molybdenum-doped TiO2 hybrid nanoparticles in the treatment of pharmaceutical effluents. It was found that molybdenum-doped TiO2 hybrid nanoparticles showed higher photocatalytic efficiency than untreated TiO2 nanoparticles.

Measurement of the ttbar production cross section with an in situ calibration of b-jet identification efficiency

A measurement of the top-quark pair-production cross section in ppbar collisions at sqrt{s}=1.96 TeV using data corresponding to an integrated luminosity of 1.12/fb collected with the Collider Detector at Fermilab is presented. Decays of top-quark pairs into the final states e nu + jets and mu nu + jets are selected, and the cross section and the b-jet identification efficiency are determined using a new measurement technique which requires that the measured cross sections with exactly one and multiple identified b-quarks from the top-quark decays agree. Assuming a top-quark mass of 175 GeV/c^2, a cross section of 8.5+/-0.6(stat.)+/-0.7(syst.) pb is measured.