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171.
Craig S. Truebenbach D. M. Hercules Marwan Houalla 《Analytical and bioanalytical chemistry》2001,369(3-4):335-341
Electrospray time-of-flight (TOF) mass spectrometry has been carried out on aqueous solutions of isopoly tungstate. A number of factors affecting the speciation of tungstate were studied, including concentration, and pH. The concentrations of the solutions ranged from 10–2 to 10–5 M. At all concentrations studied, the pH range was sufficient to investigate all major species expected to be in aqueous solution. In all cases, the results obtained by electrospray showed changes in speciation which were limited to protonation and solvation effects; the tungstate core remained intact. 相似文献
172.
173.
174.
Red-Coloured Abietanoids from Leaf-Glands of Plectranthus strigosus BENTH . Chromatographic examination of the red-coloured diterpenoids from the South-African title plant yielded the following compounds: parviflorone A(1) , parviflorone B (2) , parviflorone C(3) , parviflorone E (4) parviflorone D (5) , parviflorone F (6) , parviflorone G (7) , and parviflorone H (8) . Compounds 7 and 8 represent new variants of these quinone methides. 相似文献
175.
Abstract— Sporulation of starving plasmodia of Physarum polycephalum was found to be induced by far-red light, blue light or heat shock, each of which is perceived by a different input receptor system. The branched signal transduction pathway was mapped and the time-dependent formation of some of its components analyzed. 相似文献
176.
Summary In vitro selection, or SELEX, has been used both to characterize the interaction of natural nucleic acids with proteins and to generate novel nucleic acid-binding species, or aptamers. Although numerous reports have demonstrated the power of the technique, they have not expanded on the methodologies that can be used for selection. This review focuses on the considerations and problems involved in selecting protein-binding aptamers from a random-sequence RNA pool. As an illustration, we describe two approaches to selecting aptamers to a particular target, the HTLV-I Rex protein. In the first, complete randomization is used to find an artificial, high-affinity RNA binding site. In the second, the contributions of individual nucleotides and/or base pairs to the natural Rex-binding element are determined by mutating the wild-type sequence and selecting active binding variants. 相似文献
177.
178.
Alfredo Carlos Alder Peter Rüedi Roland Prewo Jost H. Bieri Conrad Hans Eugster 《Helvetica chimica acta》1986,69(6):1395-1417
Novel Diterpenoids from Leaf-Glands of a Plectranthus sp. from Rwanda More than 20 highly modified abietanoid compounds belonging to 6,7-dioxocoleons, serveral kinds of royleanones, spirocoleons, extended quinones, quinone methides, and 1,4-phenanthraquinones have been isolated from a Plectranthus sp. from the borders of Lake Kiwu (Rwanda). The structure of plectranthon A ( 1 ), a 5,7,8-trimethyl-1,4-phenanthraquinone, has been confirmed by an X-ray analysis of its p-bromobenzoate. It is twisted around the C(4)–C(5) moiety; this fact renders the molecule chiral. Notable features of the hydroxylation pattern in all of the isolated compounds are: (a) a predominant hydroxylation at C(16) (abietan numbering) leading to the (15S)-configuration of the 2-hydroxy-l-methylethyl side-chain and to the (13S, 15R)-configuration of the derived spirocyclopropanes and to the derived (S)-2-hydroxypropyl side-chain; (b) the 6β,7α-dihydroxylation which, together with further hydroxylations at C(3) and/or C(2), are considered as a prerequisite for the formation of the conjugated system extending over rings A, B and C (e.g. in the coleons E and F), hence allowing a complete aromatization of the basic ring skeleton. The reasons for these extensive dehydrogenation and oxygenation reactions that cost the plant a great many of oxidation equivalents are not clear. Presumably, these modifying reactions preceed the degradation of the ring system. 相似文献
179.
K. Nünighoff Ch. Pohl V. Bollini A. Bubak H. Conrad D. Filges H. Glückler F. Goldenbaum G. Hansen B. Lensing R. -D. Neef N. Paul D. Prasuhn K. Pysz H. Schaal H. Soltner H. Stelzer H. Tietze-Jaensch W. Bernnat J. Keinert M. Mattes W. Ninaus S. Koulikov A. Smirnov M. Wohlmuther 《The European Physical Journal A - Hadrons and Nuclei》2004,22(3):519-528
180.
Takeshi Matsumoto Akitami Ichihara Mitsutoshi Yanagiya Tamio Yuzawa Akiyoshi Sannai Hideaki Oikawa Sadao Sakamura Conrad Hans Eugster 《Helvetica chimica acta》1985,68(8):2324-2331
By a simple process, 3-methoxyjuglone (= 8-hydroxy-2-methoxy-1,4-naphthoquinone; 9 ) has been synthesized from 1,2,4-trimethoxybenzene ( 5 ) and converted, after prenylation, to α-caryopterone ( 1 ; Scheme 1), a pyranojuglone pigment from Caryopteris clandonensis. On the other hand, juglone (= 5-hydroxy-1,4-naphthoquinone; 12 ) was regioselectively prenylated at C(2) via its 1-methoxy-cyclohexa-1,3-diene adduct 15 (Scheme 2). The 2-prenyljuglone ( 4 ) thus formed led to 1 after oxidation and other reactions. 相似文献