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21.
The anodic oxidation of methyl 3-phenyl-2-dimethylsilylpropionate occurs at a potential almost 1 V positive of that required to oxidize other alpha-silyl esters. Semiempirical and ab initio calculations on the model compound 1-phenyl-2-trimethylsilylethane indicate that electron removal from these two compounds is highly stereoelectronically dependent. Both molecules exist almost exclusively in a conformation in which the phenyl group and silicon atom are anti and the side chain is perpendicular to the aromatic ring. This conformation has a higher energy HOMO orbital and lower computed ionization potential than the only other significantly populated conformation of 1-phenyl-2-trimethylsilylethane. Finally, the ab initio calculations show that in the cation radical of this model compound the ipso carbon of the aromatic ring and the side chain carbon bound to silicon draw significantly closer together than in the neutral species; an electrostatic potential map of the cation radical shows that the ipso carbon bears the highest degree of positive charge of any of the benzenoid carbons. We interpret these data, taken together, as an indication that this cation radical is stabilized by overlap of the rear lobe of the carbon-silicon bond with the p-orbital of the ipso carbon. 相似文献
22.
The two new diarylheptanoids, cymodienol (1), and cymodiene (2), obtained from specimens of the sea grass Cymodocea nodosa, collected from the coastal areas of central Greece, are the first members of this class isolated from marine organisms. The chemical structures of the two metabolites were assigned on the basis of their NMR and MS spectroscopic data, including information obtained by 1D- and 2D-NMR experiments. Metabolite 2 possesses an unprecedented skeleton that might be biosynthetically related to metabolite 1. Cymodienol (1) was found to exhibit significant cytotoxic activity against two lung cancer cell lines. 相似文献
23.
Evdoxia Coutouli-Argyropoulou Christos Sideris 《Journal of organometallic chemistry》2006,691(18):3909-3918
Unsymmetrical 1,1′-disubstituted ferrocenes bearing an amino acid moiety and a conjugated electron density controlling substituent were synthesized conveniently starting from 1,1′-ferrocenedicarbaldehyde. The novel ferrocene amino acid derivatives were completely characterized from their MS, 1H NMR and 13C NMR spectra. Their electrochemical behavior was studied by cyclic voltammetry. Their formal redox potentials Ef were slightly influenced by the nature of the amino acid and mainly by the kind of the ethenyl substituent. Furthermore all the (Z)-isomers exhibited a slight anodic shift compared with the corresponding (E)-isomers. 相似文献
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Applied Biochemistry and Biotechnology - 相似文献
25.
Journal of Radioanalytical and Nuclear Chemistry - A medium resolution underwater in-situ gamma-ray spectrometer (GeoMAREA) was deployed in the submarine spring (Kiveri) for continuous monitoring... 相似文献
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Melike Meterelliyoz Christos Alexopoulos David Goldsman 《European Journal of Operational Research》2012
We propose and analyze a new class of estimators for the variance parameter of a steady-state simulation output process. The new estimators are computed by averaging individual estimators from “folded” standardized time series based on overlapping batches composed of consecutive observations. The folding transformation on each batch can be applied more than once to produce an entire set of estimators. We establish the limiting distributions of the proposed estimators as the sample size tends to infinity while the ratio of the sample size to the batch size remains constant. We give analytical and Monte Carlo results showing that, compared to their counterparts computed from nonoverlapping batches, the new estimators have roughly the same bias but smaller variance. In addition, these estimators can be computed with order-of-sample-size work. 相似文献
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An intermolecular trapping of the Pummerer intermediate, generated from 9 with TFAA, by 4 at position 5 under mild Lewis acid conditions gave 5. Sequential treatment of 5 with Ra-Ni, LiAlH4 and again Ra-Ni, afforded 8 in high overall yield. 相似文献
30.
Fabio Cameli Prof. Dr. Joop H. ter Horst Dr. René R. E. Steendam Dr. Ir. Christos Xiouras Prof. Dr. Georgios D. Stefanidis 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(6):1344-1354
Herein, the pivotal role of secondary nucleation in a crystallization-enhanced deracemization process is reported. During this process, complete and rapid deracemization of chiral conglomerate crystals of an isoindolinone is attained through fast microwave-assisted temperature cycling. A parametric study of the main factors that affect the occurrence of secondary nucleation in this process, namely agitation rate, suspension density, and solute supersaturation, confirms that an enhanced stereoselective secondary nucleation rate maximizes the deracemization rate. Analysis of the system during a single temperature cycle showed that, although stereoselective particle production during the crystallization stage leads to enantiomeric enrichment, undesired kinetic dissolution of smaller particles of the preferred enantiomer occurs during the dissolution step. Therefore, secondary nucleation is crucial for the enhancement of deracemization through temperature cycles and as such should be considered in further design and optimization of this process, as well as in other temperature cycling processes commonly applied in particle engineering. 相似文献