Physical properties and processing conditions correlations of the ldpe/lldpe tubular blown films

Experiments are carried out to verify a theory developed to correlate the strain history of the polymer during film blowing to the ultimate physical properties of the film. The theory predicts that the amount of strain put into the film once it starts to freeze, defined as strain in the amorphous region and the plastic strain, has a dominant effect on the film properties. Two grades of low and linear low density polyethylene, experimental resins supplied by Mobil chemical company, were used to produce the blown film yielding a 1.25 mil film at the for all experimental runs. Film surface and bulk temperatures, along the machine direction and around the bubble, were measured using the infra-red techniques to identify the points where film starts to crystallize. A video digitization technique was used to measure the bubble kinematics. Film properties were measured using standard ASTM methods. The results indicate a correlation between the amount of strain and a measure of stress with ultimate physical properties of the blown film. This principle leads to the correlation of both the machine and transverse film properties on the same surface. The results obtained can potentially be exploited by designing the blown-film equipment and processing conditions such that optimal bubble stretching produces desired film properties.     

New Explanation for Ligand Bending in Transition Metal Tris(dithiolate) Complexes

The results of Fenske-Hall molecular orbital calculations are reported for the trigonal prismatic complexes Mo(S(2)C(2)H(2))(3) and Mo(S(2)C(6)H(4))(3). Both complexes exhibit a bend of the S-C-C-S ligand plane away from the S-Mo-S plane. A series of calculations which systematically follow the changes in electronic structure as the bend angle alpha is varied between 0 and 30 degrees indicates that the bend can be attributed to a second order Jahn-Teller distortion. The driving force for this distortion, which allows mixing between a set of ligand pi orbitals and the metal d(z)()()2 orbital, should be greatest for d(0) systems. In these systems the bent geometry leads to the stabilization of the doubly occupied HOMO. The driving force for ligand bending should be lower in systems having more or fewer electrons (e.g. Re(S(2)C(2)Ph(2))(3) or V(S(2)C(2)Ph(2))(3), respectively). While the steric bulk of the dithiolate ligands in the latter complexes may also influence the degree of ligand bending, this is probably a secondary effect.     

Catalytic cycles for the reduction of [UO2]2+ by cytochrome c7 proteins proposed from DFT calculations

The mechanism of the reduction of the hydrated uranyl cation, [UO2](2+), by the cytochromes G. sulfurreducens and D. acetoxidans has been studied using density functional theory calculations. We propose that the initial electron transfer step from the heme is to a cation-cation complex in the case of D. acetoxidans, but for G. sulfurreducens, it is to a single uranyl cation, which then forms a U(V)-U(VI) complex with a second uranyl cation. For both enzymes, the subsequent catalytic pathways are very similar. A U(V)-U(V) complex is formed, which then undergoes disproportionation via two successive protonation steps of one uranyl group, to give a U(VI)-U(IV) complex which dissociates to individual U(VI) and U(IV) species, the former being bound at the enzyme active site. Intermediate structures along the catalytic pathway are consistent with EXAFS data.     

Tandem multi-step synthesis of C-carboxyazlactones promoted by N-heterocyclic carbenes

Cascade reaction sequences incorporating N-heterocyclic carbene-based organocatalysis have been developed that allow the direct preparation of a range of (+/-)-4-phenoxycarbonylazlactones in good isolated yields (66-84%) from the corresponding N-p-anisoyl amino acids.     

Win X-ray: a new Monte Carlo program that computes X-ray spectra obtained with a scanning electron microscope.

A new Monte Carlo program, Win X-ray, is presented that predicts X-ray spectra measured with an energy dispersive spectrometer (EDS) attached to a scanning electron microscope (SEM) operating between 10 and 40 keV. All the underlying equations of the Monte Carlo simulation model are included. By simulating X-ray spectra, it is possible to establish the optimum conditions to perform a specific analysis as well as establish detection limits or explore possible peak overlaps. Examples of simulations are also presented to demonstrate the utility of this new program. Although this article concentrates on the simulation of spectra obtained from what are considered conventional thick samples routinely explored by conventional microanalysis techniques, its real power will be in future refinements to address the analysis of sample classifications that include rough surfaces, fine structures, thin films, and inclined surfaces because many of these can be best characterized by Monte Carlo methods. The first step, however, is to develop, refine, and validate a viable Monte Carlo program for simulating spectra from conventional samples.     

Determination of monensin, narasin, and salinomycin in mineral premixes, supplements, and animal feeds by liquid chromatography and post-column derivatization: collaborative study

A liquid chromatographic (LC) method for the analysis of monensin, narasin, and salinomycin in mineral premixes, supplements, and complete animal feeds at medicating and trace levels was collaboratively studied. The method uses methanol-water (90 + 10) extraction with mechanical shaking for 1 h, filtration, and dilution if necessary. Determination of the 3 ionophores is by reversed-phase LC using post-column derivatization with vanillin and detection at 520 nm. Suspect positive trace-level products and medicated feeds containing unexpected ionophores are confirmed by hexane extraction or post-column derivatization with dimethylaminobenzaldehyde (DMAB). Twenty-five test samples of medicated feeds, supplements, and mineral and drug premixes, and 9 test samples for trace-level analysis were sent to 11 collaborators in Bulgaria, Czech Republic, Portugal, France, The Netherlands, United States, and Canada. Acceptable results were received from 10 laboratories. For the medicated complete feeds, supplements, and mineral premixes, RSDr values (within-laboratory repeatability) ranged from 2.5 to 5.2%, RSDR values (among-laboratory reproducibility) ranged from 2.7 to 6.8%, and HorRat values ranged from 0.31 to 1.30. For the drug premixes, the result variability was excessive and HorRat values ranged from 2.27 to 14.1. For the trace-level test samples, all laboratories correctly identified the analytes and did not report any false positives. RSDr values ranged from 1.3 to 9.5%, RSDR values ranged from 5.2 to 13.1%, and HorRat values ranged from 0.4 to 0.97.     

Conjugated microporous poly(phenylene butadiynylene)s

High surface area porous poly(phenylene butadiynylene) networks were obtained (BET surface area up to 842 m(2) g(-1)) by the palladium-catalyzed homocoupling of 1,3,5-triethynylbenzene and 1,4-diethynylbenzene.     

Total synthesis of lucilactaene, a cell cycle inhibitor active in p53-inactive cells

Hetero-bis-metalated 1,3-butadiene is employed in the lynchpin coupling of synthetic fragments of the side chain of the antitumor agent, lucilactaene. Sequential Stille and Suzuki-Miyaura couplings interpolate this unique boron/tin diene into the pentaene chain. The total synthesis of lucilactaene was accomplished efficiently, in just eight linear steps.     

Assessing the exchange coupling in binuclear lanthanide(iii) complexes and the slow relaxation of the magnetization in the antiferromagnetically coupled Dy2 derivative

We report here the synthesis and the investigation of the magnetic properties of a series of binuclear lanthanide complexes belonging to the metallacrown family. The isostructural complexes have a core structure with the general formula [Ga₄Ln₂(shi^3–)₄(Hshi^2–)₂(H₂shi^–)₂(C₅H₅N)₄(CH₃OH)_x(H₂O)_x]·xC₅H₅N·xCH₃OH·xH₂O (where H₃shi = salicylhydroxamic acid and Ln = Gd^III1; Tb^III2; Dy^III3; Er^III4; Y^III5; Y^III_0.9Dy^III_0.16). Apart from the Er-containing complex, all complexes exhibit an antiferromagnetic exchange coupling leading to a diamagnetic ground state. Magnetic studies, below 2 K, on a single crystal of 3 using a micro-squid array reveal an opening of the magnetic hysteresis cycle at zero field. The dynamic susceptibility studies of 3 and of the diluted DyY 6 complexes reveal the presence of two relaxation processes for 3 that are due to the excited ferromagnetic state and to the uncoupled Dy^III ions. The antiferromagnetic coupling in 3 was shown to be mainly due to an exchange mechanism, which accounts for about 2/3 of the energy gap between the antiferro- and the ferromagnetic states. The overlap integrals between the Natural Spin Orbitals (NSOs) of the mononuclear fragments, which are related to the magnitude of the antiferromagnetic exchange, are one order of magnitude larger for the Dy₂ than for the Er₂ complex.