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101.
Wolfhart Rüdiger Fritz Thümmler 《Angewandte Chemie (International ed. in English)》1991,30(10):1216-1228
Plants require light for photosynthesis. In order to adapt to the light conditions in their particular habitat, they have developed various photoreceptor systems. Of these, phytochrome allows even two-color vision in the red/far-red region. The photoreceptor phytochrome is of interest not only to botanists, but also to natural product chemists, photochemists, biochemists, photobiologists, and recently molecular biologists. Despite numerous studies, there are still considerable gaps in our knowledge of this photoreceptor. This article first describes the basic structural studies of the tetrapyrrole chromophore and its photochemical cis–trans isomerization, which is the source of the chromoprotein's photochromism. In the section on the protein moiety, beside other topics, the domain structure of phytochrome and the conformational changes during phototransformation are discussed. Finally, the known phytochrome genes are used to derive phylogenetic relationships, and possible structure–function relationships are discussed. 相似文献
102.
Summary The alcoholic portion of avetiver oil (Bourbon), the gas chromatogram of which shows more than 100 components, was analyzed by combined GC-MS with different ionization methods. This enabled us to identify major components. The specificity of the method was improved by using combined gas chromatography-tandem mass spectrometry in the collision-activated-dissociation mode. 相似文献
103.
Fritz Haake Maciej Lewenstein Martin Wilkens 《Zeitschrift für Physik B Condensed Matter》1984,54(4):333-350
We employ high-temperature series to investigate a two-parameter class of renormalization group transformations for the two-dimensional Ising model on the triangular lattice. For the static case we identify an optimal organization of the high-temperature expansion and an optimal transformation matrix and thus find, in second order, =0.96 and the magnetic eigenvaluey=2-/2=1.76.From recursion relations for flip rates we find the dynamic exponent to be the same for all transformations in our two-parameter class,z=2.32.Our fixed-point flip rates do not describe a Markov process even though the corresponding master equation for the single-event probability displays no explicit memory effects. The non-Markovian nature shows up only in a violation of the Markovian detailed balance conditions. 相似文献
104.
Biosensors based on enzyme field-effect transistors for determination of some substrates and inhibitors 总被引:3,自引:0,他引:3
Dzyadevych SV Soldatkin AP Korpan YI Arkhypova VN El'skaya AV Chovelon JM Martelet C Jaffrezic-Renault N 《Analytical and bioanalytical chemistry》2003,377(3):496-506
This paper is a review of the authors' publications concerning the development of biosensors based on enzyme field-effect transistors (ENFETs) for direct substrates or inhibitors analysis. Such biosensors were designed by using immobilised enzymes and ion-selective field-effect transistors (ISFETs). Highly specific, sensitive, simple, fast and cheap determination of different substances renders them as promising tools in medicine, biotechnology, environmental control, agriculture and the food industry.The biosensors based on ENFETs and direct enzyme analysis for determination of concentrations of different substrates (glucose, urea, penicillin, formaldehyde, creatinine, etc.) have been developed and their laboratory prototypes were fabricated. Improvement of the analytical characteristics of such biosensors may be achieved by using a differential mode of measurement, working solutions with different buffer concentrations and specific agents, negatively or positively charged additional membranes, or genetically modified enzymes. These approaches allow one to decrease the effect of the buffer capacity influence on the sensor response in an aim to increase the sensitivity of the biosensors and to extend their dynamic ranges.Biosensors for the determination of concentrations of different toxic substances (organophosphorous pesticides, heavy metal ions, hypochlorite, glycoalkaloids, etc.) were designed on the basis of reversible and/or irreversible enzyme inhibition effect(s). The conception of an enzymatic multibiosensor for the determination of different toxic substances based on the enzyme inhibition effect is also described.We will discuss the respective advantages and disadvantages of biosensors based on the ENFETs developed and also demonstrate their practical application. 相似文献
105.
Michael Leuck Rubina Giare Matthias Paul Nicole Zien Andreas Wolter 《Tetrahedron letters》2004,45(2):317-320
A novel improved controlled pore glass (CPG) support based on the 2-(hydroxymethyl)-6-nitrobenzoyl (HMNB) protecting group was developed for the synthesis of 3′-aminoalkylated oligonucleotides. The release of oligonucleotides with free 3′-amino groups from the support is complete within 2 h at 55 °C in concentrated ammonia. 相似文献
106.
Paul Müller Nicole Pautex Michael P. Doyle Vahid Bagheri 《Helvetica chimica acta》1990,73(5):1233-1241
The thermocatalytic rearrangements of cyclopropenes 1-4 have been investigated in the presence of Rh(IT) perfiuorobutyrate. 1, 2, 3-Triphenylcyclopropene ( 1a ) undergoes rearrangement lo diphenylindene 5a or, with alkoxycyclopropene derivatives, to α, β-unsaturated ketone 6. Furan formation occurs with 2, 3-diphenylcyclo-propenecarboxylate 2, but the diethyl counterpart 3 rearranges to dienoate 8. 2-Alkylcyclopropenecarboxylates 4 afforded (E)-methylidenecyclopentane derivatives 9 as the only isolable product in yields of ca. 35 %. A mechanism involving regio- and stereospecific cyclopropene ring opening to a Rh-complexed vinylcarbene and insertion of the latter into the C? H bond to give 9 is proposed. An analogous mechanism should account for the rearrangement products of 1 to 3 . 相似文献
107.
The low-energy collision-activated dissociation of symmetrical n-butyl-substituted and of allyl-substituted onium cations has been recorded using fast atom bombardment ionization and a tandem mass spectrometry quadrupole mass spectrometer. Structure of the fragments and decomposition pathways have been ascertained using a multi-quadrupole MS/MS/MS triple analyser instrument. Whereas most sulphonium cations exhibit only heterolytic cleavages, fragmentation of ammonium and phosphonium is mainly homolytic. Allylic sulphonium, and to a lesser extent allylic ammonium, easily undergo propene elimination. This reaction, which does not occur in 1-propenyl oniums, might involve a McLafferty type rearrangement. 相似文献
108.
Optimal performance laminar chromatography and automated multiple development chromatography are relatively recent techniques of planar chromatography that can be applied with success in plant material analysis. Therefore, these methods are used to study plant extracts and constituents belonging to different chemical classes of secondary metabolism: heterocyclic oxygen compounds (coumarins, flavonoids, and anthocyanins), alkaloids and quaternary ammonium salts, cannabinoids, essential oils, ginsenosides, and cardiac heterosides. Generally, the results obtained with these methods are good, and in most cases they compare with those of thin-layer chromatography. 相似文献
109.
Based on the lipase-catalysed kinetic resolution of the silyloxyalcohol (1RS,2SR)-5 by transesterification with vinyl acetate in the presence of lipase from Pseudomonas cepacia a synthesis of both enantiomers of the β-amino acid cispentacin (1R,2S)-1 and (1S,2R)-1 using simple functional group interconversions is described. 相似文献
110.
Smaragda Grammenudi Marlene Franke Fritz Vögtle Eberhard Steckhan 《Journal of inclusion phenomena and macrocyclic chemistry》1987,5(6):695-707
The tris-bipyridine ligand3a and its stoichiometric Rh3+ complex have been prepared. Cyclovoltammograms of the complex at pH 7.4 using a glassy carbon disk electrode reveal a strong reduction peak at –620 mV and two weak reduction peaks at more negative voltage. The reduction potential of the new complex is shifted by 300 mV to more positive values as compared to [Rh(bipy)3]3+. There is no reversible reoxidation peak of the Rh(I) complex formed due to the decomplexation of one of the three bipyridine units in the course of the transition Rh(III)Rh(I). The Rh(III) complex of3a was also studied with respect to its function as a possible redox mediator for the electrochemical regeneration of NADH from NAD+. The preparative electrolysis of the Rh3+ complex of3a in the presence of NAD+ yields a selective formation of NADH, whereas NAD dimers were not detected. On the other hand, a significant acceleration of this reaction compared to [Rh(bipy)3]3+ was not observed. 相似文献