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61.
C. Mioskowski A. Solladie-Cavallo G. Solladie 《Journal of organometallic chemistry》1978,149(3):C63-C65
Attachment of a Cr(CO)3 moiety to one of the aromatic rings in rigid diaryl ketones of very low prochirality followed by addition of a chiral and optically pure reagent leads to satisfactory asymmetric induction ~40%. Asymmetric induction is smaller in the case of acyclic systems. 相似文献
62.
Heinz Haschke 《Monatshefte für Chemie / Chemical Monthly》2003,134(1):81-105
Summary. A biokinetic model has been developed to describe the mathematical consequences of inhibition, respectively stimulation of proofreading. According
to data reported in the literature, a first approximative calibration of the model has been carried out in an attempt to make
it both: practically applicable and comparable with experimental data and clinical facts. The model is open for further improvements
and adjustable according to results of further researches via the parameters chosen. In a first test of the model it is shown
that it does well reflect the results described in the literature upon proof-reading-inhibition and its consequences, i.e., the reduction of replication-fidelity (→ exponential increase of malignant cells with time). As a further result it is
shown that the model also does well describe in its kinetic approach opposite effects as, e.g., a reduction of wrong genetic information by classical cancer-therapies like chemotherapy and surgergy.
The system is orientated towards known biochemical relations and chemical similarities together with a discussion of the potential chance which offer special combinations of chemically identifyable substances
(like nucleotides’ precursors or effector-molecules contained in low-molecular-human-placenta-extracts as an alternative to
umbilical cords’-blood/cells) as stimulators of the enzymatic proof-reading- and -repair-machinery.
E-mail: Haschke.H@isovolta.com
Received January 20, 2002; accepted (revised) June 26, 2002 相似文献
63.
Raquel F. P. Nogueira Ronaldo A. Pilli Nelson durÁn 《Applied biochemistry and biotechnology》1992,33(3):169-176
Growth of the ascomyceteChrysonilia sitophila during degradation of lignin model dimers and monomers was compared to a glucose control. An inhibition of growth by Cα-carbonyl
monomers and stimulation by β-O-4 lignin model and vanillyl alcohol were observed. A comparison of the degradation by this
ascomycete with the basidiomycetePhanerochaete chrysosoporium showed similarities in relation to the type of degradation caused. 相似文献
64.
Langlet J. Claverie P. Pullman B. Piazzola D. Daudey J. P. 《Theoretical chemistry accounts》1977,46(2):105-116
The effect of water on the conformational preferences of acetylcholine has been studied within the discrete, the continuum and the combined discrete-continuum models described in parts I and II of this series. All the models lead to the conclusion that the trans-gauche form which is, following refined quantum-mechanical computations, the intrinsically preferred one and the one observed in the crystal of acetylcholine and of a number of analogues should remain also the preferred conformation in water. This result agrees with NMR studies. The results of the empirical discrete model used here compare favorably to those obtained by an ab initio super-molecule treatment. The continuum model utilized here represents a net improvement above such models utilized in other works. 相似文献
65.
The number of products and the H2/CH4 ratio obtained from the flow pyrolyses of (CH3)3GeH and (CH3)3SiH were very different. The (CH3)3GeH decomposition is consistent with the following mechanism:
The pyrolysis of (CH3)3SiH was found to be much more complex, presumably due to the formation of silicon-carbon double bonded intermediates and the (CH3)2Si(H)CH2 radical. We also present data which supports the presence of a H atom chain sequence during this pyrolysis. 相似文献
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66.
The degradation of acenaphthylene, acenaphthene, 2-methylnaphthalene, 2-methylindene, 3-methylindene and indene in water solutions was studied. These compounds at the 25-150 mug/l. level were almost totally degraded at ambient temperature within three days. The microbial population responsible for the degradation occurs naturally in ground-water taken from an aquifer in Ames, Iowa, which is contaminated with coal-tar products. These unidentified micro-organisms adapt readily to other waters when used as an inoculant for the degradation of aromatic compounds. The preservation of water to prevent such degradation was also investigated. Filtration through a 0.45-mum filter was found the most effective procedure for preserving the hydrocarbons in these waters. 相似文献
67.
The cis fused bicyclic sulfones 1a, 1c and 3a are lithiated in benzene with n-butyllithium under concomitant cis/trans isomerization of the ring fusion, involving intramolecular proton transfer. H/D exchange of the three α-hydrogens in protic solvents proceeds with retention of configuration. The lithiated sulfones are chlorinated with hexachloroethane (HCE) and show a strong preference for introduction of halogen at an equatorial α-position. 相似文献
68.
The Cr(CO)3(CH3CN)3 complex is found to catalyze the 1,4-addition of hydrogen to 1,3-dienes such as 2-methyl-1,3-butadiene, trans-1,3-pentadiene, and trans, trans-2,4-hexadiene at low temperature (40°) and low H2 pressure (20 psi). For trans, trans-2,4-hexadiene the only product obtained when D2 is used is 2,5-dideuterio-cis-3-hexene. The catalytic 1,4-hydrogenation can be carried out in neat dienes, and turnover numbers for the catalyst of greater than 3000 have been observed. 相似文献
69.
The phenylseleno group (PhSe) has evolved in recent years as a very useful and versatile functionality. Its facile introduction into organic molecules and its subsequent oxidative or reductive removal, has allowed many important synthetic transformations.1–7 Due to the fact that, similarly to halogens, it can exist either as an electrophilic species (PhSe+) or as a nucleophilic one (PhSe-), this group can be introduced either via nucleophilic substrates (e.g. carbanions, olefins), or via electrophilic ones (e.g. epoxides, halides), as illustrated in Scheme 1. Another valuable aspect of the phenylseleno group is that it can be readily oxidized to the corresponding selenoxide(PhSe(O)—), which undergoes β-hydrogen abstraction and syn-elimination to form olefins, under relatively mild conditions (Scheme 2(a)). Furthermore, this group can be substituted with hydrogen, upon the action of an appropriate reducing agent (Scheme 2(b)).The great synthetic utility of the phenylseleno group is apparent from its extensive utilization in numerous natural products syntheses,1 as well as many other synthetic studies.2–7 相似文献
70.
An important goal in single molecule fluorescence correlation spectroscopy is the theoretical simulation of the fluorescence signal stemming from individual molecules and its autocorrelation function. The simulation approaches developed up to now are based exclusively on continuous-wave (cw) illumination and consequently on cw-excitation. However, this approximation is no longer valid in the case of two-photon excitation, for which pulsed illumination is usually employed. We present a novel theoretical model for the simulation of the fluorescence signal of single molecules and its autocorrelation function with consideration of the time dependence of the excitation flux and thus of all illumination-dependent photoprocesses: two-photon excitation, induced emission and photobleaching. Further important characteristics of our approach are the consideration of the dependence of the photobleaching rate on illumination and the low intersystem-crossing rates of the studied coumarins. Moreover, using our approach, we can predict quantitatively the effect of the laser pulse width on the fluorescence signal of a molecule, that is, the contributions of the photobleaching and saturation effects, and thus we can calculate the optimal laser pulse width. The theoretical autocorrelation functions were fitted to the experimental data, and we could ascertain a good agreement between the resulting and the expected parameters. The most important parameter is the photobleaching constant sigma, the cross section of the transition Sn<--S1, which characterises the photostability of the molecules independent of the experimental conditions. Its value is 1.7 x 10(-23) cm2 for coumarin 153 and 5 x 10(-23) cm2 for coumarin 314. 相似文献