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71.
As part of a fundamental study of the behaviour of mixed plastics during reprocessing and in service, blends of low density polyethylene (LDPE) and polyvinyl chloride (PVC) have been investigated. It was found that Young's modulus increased steadily from pure LDPE to pure PVC whereas both tensile strength at break and elongation at break passed through a minimum at about 5% PVC. Optical and scanning electron microscope studies have related this mechanical behaviour to morphological changes in the two phase system under stress. 相似文献
72.
Binoy K. Bordoloi Eli M. Pearce L. Blight B. R. Currell R. Merrall R. A. M. Scott C. Stillo 《Journal of polymer science. Part A, Polymer chemistry》1980,18(2):383-406
Liquid sulfur–olefinic reactions at 140°C forming crosslinked polysulfide polymers have been investigated. A systematic approach to the characterization and some structure–property studies on these new polymeric materials has been presented. The olefinic systems of interest are endo-and exo-dicyclopentadiene and an oligomeric alkenyl polysulfide. Equimolar S8–olefinic system copolymers are amorphous and they show no tendency for sulfur crystallization. A correlation has been drawn between chemical structure and glass transition temperature of the copolymers and terpolymers. Mechanical properties and, in particular, chemical stress relaxation of the crosslinked polysulfide polymers have been investigated. 相似文献
73.
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. 相似文献
74.
Sternfeld T Thilgen C Hoffman RE Del Rosario Colorado Heras M Diederich F Wudl F Scott LT Mack J Rabinovitz M 《Journal of the American Chemical Society》2002,124(20):5734-5738
Reduction of the two "closed" [6,6] methanofullerenes, [6,6]C(61)H(2) (1) and [6,6]C(71)H(2) (5), to the corresponding hexaanions with lithium metal causes the bridgehead-bridgehead bonds to open, at least partially, and this change gives rise to diamagnetic ring currents in the resulting homoconjugated six-membered rings (6-MRs). These new ring currents shield the overlying hydrogen atoms on the methylene bridge and induce upfield shifts of 1.60 and 0.11 ppm in their (1)H NMR resonances, respectively. Analogous reduction of the already "open" [5,6]methanofullerenes, [5,6]C(61)H(2) (2) and [5,6]C(71)H(2) (3 and 4), only slightly enhances the shielding of the hydrogen atoms over the homoconjugated 6-MRs (upfield shifts of 0.13, 0.68, and 0.14 ppm, respectively) but leads to exceptionally strong diamagnetic ring currents in the homoconjugated five- membered rings (5-MRs), as evidenced by dramatic shielding of the hydrogen atoms situated over them (upfield shift of 5.01, 6.78, and 1.63 ppm, respectively). The strongest shielding is seen for the hydrogen atom sitting over the 5-MR at the pole of C(71)H(2)(6)(-) (delta = -0.255 ppm) indicating that the excess charge density is concentrated at the poles. 相似文献
75.
Protein phosphorylation is a major mechanism of post-translational protein modification used to control cellular signaling. A challenge in phosphoproteomics is to identify the direct substrates of each protein kinase. Herein, we describe a chemical strategy for delivery of a bio-orthogonal affinity tag to the substrates of an individual protein kinase. The kinase of interest is engineered to transfer a phosphorothioate moiety to phosphoacceptor hydroxyl groups on direct substrates. In a second nonenzymatic step, the introduced phosphorothioate is alkylated with p-nitrobenzylmesylate (PNBM). Antibodies directed against the alkylated phosphorothioate epitope recognize these labeled substrates, but not alkylation products of other cellular nucleophiles. This strategy is demonstrated with Cdk1/cyclinB substrates using ELISA, western blotting, and immunoprecipitation in the context of whole cell lysates. 相似文献
76.
Chester M. Mikulski Scott Grossman Chung Ja Lee Nicholas M. Karayannis 《Transition Metal Chemistry》1987,12(1):21-25
Summary Complexes of the general types Pd(L)(LH)Cl (LH=hxH, xnH, or tbH) and Pt(L)(LH)Cl3 (LH=hxH, or xnH) are formed by boiling under reflux 21 molar mixtures of hypoxanthine (hxH), xanthine (xnH) or theobromine (tbH) and PdCl2 or PtCl4 in ethanol-triethyl orthoformate. These complexes appear to be linear chain polymeric species, characterized by single monoanionic L– ligands bridging between adjacent Pd2+ or Pt4+ ions. Inclusion of one terminal neutral LH and one terminal chloro-ligand completes the coordination sphere in the square-planar Pd2+ complexes, while the Pt4+ complexes aretrans-octahedral, involving three terminal chloro and one terminal LH ligand per platinum. The possible binding sites of the bidentate bridging L– and the unidentate terminal LH are discussed. 相似文献
77.
Emtenäs H Ahlin K Pinkner JS Hultgren SJ Almqvist F 《Journal of combinatorial chemistry》2002,4(6):630-639
A new method for the solid-phase synthesis of enantiomerically enriched highly substituted ring-fused 2-pyridinones 13 has been developed. The synthesis mediates introduction of substituents at two positions in the 2-pyridinone ring in a diverse manner and is suitable for parallel synthesis. (19)F NMR spectroscopy was used as a tool to monitor each of the five steps in the reaction sequence. The optimized conditions thus obtained were then used to prepare a library of 20 2-pyridinones with high yields. The library members were chosen from a statistical multivariate design to ensure diversity and reliable data for structure-activity relationships. Screening of the library against the bacterial periplasmic chaperone PapD was performed using surface plasmon resonance. Three new 2-pyridinones with a higher affinity for the chaperone PapD than the previous best 13[10,1] were found, and important structural features could be deduced. 相似文献
78.
Warren J. Oldham Brian L. Scott Kent D. Abney Wayne H. Smith David A. Costa 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(3):m139-m140
In the title complex, [UCl(C2H6OS)7]Cl3, the uranium metal center is coordinated in a distorted bicapped trigonal prism geometry by seven O atoms from dimethyl sulfoxide ligands and by a terminal chloride ligand. Charge balance is maintained by three outer‐sphere chloride ions per uranium(IV) metal center. Principle bond lengths include U—O 2.391 (2)–2.315 (2) Å, U—Cl 2.7207 (9) Å, and average S—O 1.540 (5) Å. 相似文献
79.
Silver (Ag+) salts adsorbed on amorphous silica or mesoporous SBA-15 extract dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-Me2DBT) from simulated, hydrotreated petroleum feedstocks. 相似文献
80.
Scott L. Gibson My Lien Nguyen Thomas H. Foster Geoffrey White Russell Hilf 《Photochemistry and photobiology》1995,61(2):196-199
Abstract— Photodynamic therapy has demonstrated efficacy toward primary, metastatic and recurrent human tumors. Here, we investigated the ability of photodynamic therapy, using Photofrin, to inhibit growth of R3230AC mammary adenocarcinomas when tumors were treated as original implants and again as lesions recurring at the initial treatment site. The results demonstrate that both initial implants and lesions recurring after the first photodynamic treatment respond similarly to the same photodynamic therapy protocol, with mean tumor volume doubling times of ˜ 11 days in both cases. Cells cultured from original tumor implants or tumors that recurred after photodynamic treatment accumulate equivalent amounts of [14 C]polyhematoporphyrin. Single cell suspensions prepared from either original or recurrent tumors from animals administered 5 mg/kg Photofrin and exposed to light in vitro displayed comparable phototoxicity. Additionally, examination of tumors by light microscopy revealed no morphological differences between the original tumor implants and the recurrent lesions. Taken together, these data indicate that lesions which recurred at the site of the initial photodynamic treatment were not resistant to a second identical course of photodynamic therapy. 相似文献