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11.
Julia E. Barker 《Tetrahedron letters》2005,46(40):6805-6808
Mononuclear (Me3TACN)MnX3 compounds, where X is Cl−, Br−, or N3−, and Me3TACN is 1,4,7-N,N′,N″-trimethyl-1,4,7-triazacyclononane, have been tested for catalyzing both sulfide oxygenation and styrene epoxidation by tert-butyl hydroperoxide (TBHP) and display turnover frequencies (TOF) up to 200 h−1 at room temperature. Sulfoxides or sulfones may be produced selectively by varying reaction conditions. Product distribution from the oxygenation reactions of ethyl phenyl sulfide, 2-chloroethyl phenyl sulfide, and styrene is consistent with a mechanism involving an early single-electron transfer (SET) step. 相似文献
12.
Luesch H Hoffmann D Hevel JM Becker JE Golakoti T Moore RE 《The Journal of organic chemistry》2003,68(1):83-91
The biosynthesis of the unusual amino acid 4-methylproline in the Nostoc genus of cyanobacteria was investigated on the genetic and enzymatic level. Two genes involved in the biosynthesis were cloned and the corresponding enzymes, a zinc-dependent long-chain dehydrogenase and a Delta(1)-pyrroline-5-carboxylic acid (P5C) reductase homologue, were overexpressed in Escherichia coli and biochemically characterized. Putative substrates were synthesized to test enzyme substrate specificities, and deuterium labeling studies were carried out to reveal the stereospecificities of the enzymatic reactions with respect to the substrates as well as to the coenzymes. 相似文献
13.
Martin Christlieb Hannah J. Claughton Andrew R. Cowley Julia M. Heslop Jonathan R. Dilworth 《Transition Metal Chemistry》2006,31(1):88-92
During the condensation of 4-methyl-4-phenyl-3-thiosemicarbazide (3) with 2,3-butanedione an unexpected by-product, 8a-methyl-6,8a-dihydro-8-methyl-2-[N-methyl-N-phenylamino]-5H-1,3,4-thiadiazolo[3,2-d][1,2,4]triazine-5-thione, (5) was obtained in addition to the desired bis(thiosemicarbazone) (4). An X-ray crystal structure was obtained and is presented together with a proposed mechanism for its formation. A brief investigation
of the coordination chemistry of bicycle (5) was carried out. The formation of cyclic compounds during the synthesis of analogues with extended backbones is also described. 相似文献
14.
Jan F. Rabek Gran Canbck Julia Lucky Bengt Rnby 《Journal of polymer science. Part A, Polymer chemistry》1976,14(6):1447-1462
The photolysis of virgin PVC powder suspended in water, methanol, n-hexane, aqueous NH4OH (30 wt-%), and 0.1 wt-% iodine in methanol and also as dry powder was studied. The mechanism of photolysis of PVC powder has been investigated by using ESR spectroscopy, conductivity titration, gel-permeation chromatography (GPC), and absorption spectroscopy. Photolysis of PVC has been found to occur by a free-radical mechanism. ESR spectroscopy permits a partial identification of several different types of free radicals in PVC such as alkyl, polyenyl, and peroxy radicals. An interpretation is proposed of the mechanism of formation of conjugated polyene structures, and also a new explanation of the crosslinking mechanism, in which transfer of unpaired electrons to double bonds occurs, is suggested. It has also been found that conjugated double bonds can photosensitize free-radical formation as a result of increased ultraviolet absorption due to polyene structures. 相似文献
15.
16.
[structure: see text] Thioxo peptide analogues of the alpha-helical peptide GCN4-p1 were synthesized and evaluated for helicity and oligomeric state. Sedimentation equilibrium and CD measurements indicate that the thioxo peptides fold into parallel alpha-helical coiled coil structures essentially identical to the native structure. This work marks the first incorporation of a thioamide linkage into the backbone of an alpha-helix and demonstrates that a thioamide linkage is compatible with positions within the helix as well as near the C-terminus. 相似文献
17.
Sergei D. Kirik Julia N. Zaitseva Igor S. Yakimov Nikolay N. Golovnev 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(11):i159-i160
Lithium sodium aluminium fluoride was obtained as a white powder by melting a stoichiometric mixture of AlF3, NaF and LiF at 1223 K, and then cooling to 923 K and sintering at this temperature for 4 h. The ab initio crystal structure determination was carried out using X‐ray powder diffraction techniques. The monoclinic structure of LiNa2AlF6 can be related to cubic elpasolite. The Li and Al atoms lie on inversion centres. The main octahedral AlF6 structural elements are not deformed, but are rotated slightly with respect to the unit‐cell axes. The Li atoms have octahedral coordinations, whereas the Na atoms have cubo‐octahedral coordinations. The Na coordination polyhedron is distorted in comparison with that of elpasolite. 相似文献
18.
Julia Lucki 《Polymer Degradation and Stability》1985,11(1):75-97
The new thiooligomers of hydroxyphenylene and hydroxymethoxyphenylene sulphides have been used as photo-stabilizers for cis-1,4-polybutadiene. The photo-stabilizing properties of these thiooligomers were compared with commercial sulphur-containing compounds such as bis(4-hydroxyphenylene)sulphide, 2,2′-thiobis(4-methyl-6-tert.butylphenol) (Irganox 1081), bis((beta-(3,5-di-tert,butyl-4-hydroxybenzyl)-methylcarboxyethyl))sulphide (Irganox 1035) and dilaurylthiodipropionate (Irganox PS800). The photo-stabilizing mechanisms of these compounds have been discussed in detail. 相似文献
19.
Determination of triclosan in foodstuffs 总被引:1,自引:0,他引:1
Sanches-Silva A Sendón-García R López-Hernández J Paseiro-Losada P 《Journal of separation science》2005,28(1):65-72
A reverse-phase high-performance liquid chromatographic (RP-HPLC) method coupled with an ultraviolet detector was developed to determine triclosan which had migrated into foodstuffs from packaging materials. The method includes extraction with hexane, followed by evaporation to dryness and residue re-dissolution in ACN 90%. Chromatographic separation was performed with a Kromasil 100 C18 column (15 cm x 0.4 cm ID, 5 microm particle size) at 30 degrees C and using ACN and water as mobile phases. Regarding recoveries, good results (higher than 83% and lower than 112%) were obtained for the three representative food matrixes selected (orange juice, chicken breast meat, and Gouda cheese). 相似文献
20.
Stasko DJ Perzynski KJ Wasil MA Brodbeck JK Kirschbaum K Kim YW Lind C 《Inorganic chemistry》2004,43(13):3786-3788
The acid H(2)B(12)(OH)(12) can be isolated as a crystalline solid by protonation of the hydroxylated borane anion, B(12)(OH)(12)(2)(-). This acidic compound has low solubility in water, conducts protons in the solid state, and has thermal stability to a temperature of 400 degrees C. The conductivity mechanism is a Grotthuss mechanism with a low activation enthalpy (9-13 kcal/mol). This new acid represents an addition to the class of oxoacids, of which sulfuric and phosphoric acid are the most prominent examples. 相似文献