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931.
Leopoldo Suescun Alvaro W. Mombrú Raúl A. Mariezcurrena Helena Pardo Silvia Russi Carlos Kremer Mario Rivero Eduardo Kremer 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(8):930-931
Trichlorooxo[1,3‐propanediylbis(diphenylphosphine)‐P,P′]rhenium(V), [ReCl3O(C27H26P2)], crystallizes with four formula units per unit cell. The crystal structure consists of neutral complexes of [ReOCl3(dppp)] [dppp is 1,3‐bis(diphenylphosphino)propane] packed by H?π‐ring interactions. The Re atom is octahedrally coordinated to the oxo anion, three Cl atoms and two P atoms from the dppp ligand. The six‐membered ring formed by the bidentate dppp ligand and the rhenium metal centre is in a chair conformation. The title compound is an intermediate in the synthesis of bis(dppp) complexes of rhenium. 相似文献
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938.
Spirolactams as conformationally restricted pseudopeptides: synthesis and conformational analysis 总被引:1,自引:0,他引:1
Fernández MM Diez A Rubiralta M Montenegro E Casamitjana N Kogan MJ Giralt E 《The Journal of organic chemistry》2002,67(22):7587-7599
The synthesis of 1-(tert-butoxycarbonyl)-7-[1-(tert-butoxycarbonyl)-3-methylbutyl]-6-oxo-1,7-diazaspiro[4.5]decanes (S,S)-1a and (S,R)-1b is described. Derivatives 17a,b and 19a are prepared for use in peptide synthesis as constrained surrogates of the Pro-Leu and Gly-Leu dipeptides. The Ac-[Gly-Leu]-Met-NH(2) derivatives (S,S,S)-2a and (S,R,S)-2b, with the tripeptidic C-terminal region present in tachykinins, are also synthesized. Conformational analyses of these tripetide analogues by NMR experiments and molecular modeling calculations show that both (S,S,S)-2a and (S,R,S)-2b epimers are gamma-turn/distorted type II beta-turn mimetics. 相似文献
939.
Kinetic modeling of the thermal degradation of polyethylene and polystyrene mixtures 总被引:5,自引:0,他引:5
Tiziano Faravelli Giulia Bozzano Mauro Colombo Eliseo Ranzi Mario Dente 《Journal of Analytical and Applied Pyrolysis》2003,70(2):1193-777
One possible process for recovering valuable chemical and petrochemical products from plastic waste is the stepwise thermal degradation of polymer mixtures. This potentially allows the step by step simultaneous separation of the different product fractions generated by the polymers of the blend. The aim of this paper is to investigate the effect of the mixing scale of the polymers and their interactions in the melt. Several thermogravimetric analyses were performed on small samples of polyethylene (PE) and polystyrene (PS) mixtures. Two types of operating conditions were adopted: the first one is a dynamic analysis with a linear increase of the temperature over time, the latter consists of two sequential isothermal steps. The experimental results confirm that if the mixing scale is poor, the decomposition of each polymer behaves independently of the presence of the other one. Conversely, when the mixing of the two polymers reaches the molecular scale, a co-pyrolysis takes place with partial interactions. A two phase system is assumed: one phase characterized by a larger PS fraction, the other one by a prevailing PE amount. In order to properly predict the kinetic interactions typical of the mixed phases, it was necessary to extend the detailed kinetic model already developed and validated for the single polymers. The resulting two phase model gives a satisfactory explanation of several experimental data from the thermal degradation of PE–PS mixtures. 相似文献
940.
Elaine C. Cabral Mario F. Mirabelli Consuelo J. Perez Demian R. Ifa 《Journal of the American Society for Mass Spectrometry》2013,24(6):956-965
Imprints of potato sprout (Solanum tuberosum L.), gingko leaves (Gingko biloba L.) and strawberries (Fragaria x ananassa Duch.) were successfully imaged by desorption electrospray ionization mass spectrometry (DESI-MS) on TLC plates through blotting assisted by heating and/or solvent extraction. Ion images showing the distribution of significant compounds such as glycoalkaloid toxins in potato sprout, ginkgolic acids and flavonoids in ginkgo leaves, and sugars and anthocyanidin in strawberry were obtained. Practical implications of this work include analysis of a wide range of irregular or soft materials by different imprinting conditions without requiring the addition of matrices or use of specific kinds of surfaces. Figure
DESI-MS Imaging analysis of gingko leaves imprinted onto TLC plates. The ion image shows the spatial distribution of quinic acid ion (m/z 191). 相似文献