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21.
Atiya MS Chiang IH Frank JS Haggerty JS Ito MM Kycia TF Li KK Littenberg LS Sambamurti A Stevens A Strand RC Louis WC Akerib DS Marlow DR Meyers PD Selen MA Shoemaker FC Smith AJ Blackmore EW Bryman DA Felawka L Kitching P Konaka A Kuno Y Macdonald JA Numao T Padley P Poutissou JM Poutissou R Roy J Soluk R Turcot AS 《Physical review letters》1993,70(17):2521-2524
22.
23.
Versatile procedures for the preparation of the title compounds are described. Representatives of ketones ( 12 and 27 ), hydrocarbons ( 19 and 28 ), acids ( 13 ), esters ( 15 . and 20 ), ethers ( 22 ) and nitriles ( 18 ) possess wide-range nematic phases, provided their terminal chains R2 and R3 contain at least three methylene units. 相似文献
24.
Koji Konomi He-Sheng Li† Norihito Kuno Masaki Furuya‡ 《Photochemistry and photobiology》1993,58(6):852-857
Abstract Treatment of imbibed embryonic axes taken from seeds of Pisum sativum with N-phenylimide S-23142, a herbicide that has been suggested to inhibit protoporphyrin synthesis, or with N -methyl mesoporphyrin IX, an inhibitor of the iron chelatase for heme, resulted in a significant decrease in the amount of spectrophotometrically detectable phytochromc in the axes in both cases. However, the amount of immunochemically detectable phytochrome was not affected by either treatment. If S-23142 inhibits the synthesis of protoporphyrin IX in pea, it appears that the conversion of protoporphyrinogen IX to protoporphyrin IX is involved in the biosynthesis of the phytochrome chromophore. The conversion of protoporphyrin IX to heme (Fe-protoporpbyrin) also appears to be a step in the biosynthesis of the chromophore, since N -methyl mesoporphyrin IX prevented the synthesis of spectrophotometrically detectable phytochrome but did not affect the magnesium chelatase activity required for the synthesis of chlorophyll in pea embryonic axes. The results suggest that protoporphyrinogen IX, protoporphyrin IX and heme are intermediates in the biogenesis of the phytochromc chromophore. The pathway to phytochromobilin might become fixed after protoporphyrin IX, being directed toward the Fe branch for heme rather than to the Mg branch for chlorophyll. 相似文献
25.
Furusho Y Oku T Hasegawa T Tsuboi A Kihara N Takata T 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(12):2895-2903
A dynamic covalent approach to disulfide-containing [2]- and [3]rotaxanes is described. Symmetrical dumbbell-shaped compounds with two secondary ammonium centers and a central located disulfide bond were synthesized as components of rotaxanes. The rotaxanes were synthesized from the dumbbell-shaped compounds and dibenzo-[24]crown-8 (DB24C8) with catalysis by benzenethiol. The yields of isolated rotaxanes reached about 90 % under optimized conditions. A kinetic study on the reaction forming [2]rotaxane 2 a and [3]rotaxane 3 a suggested a plausible reaction mechanism comprising several steps, including 1) initiation, 2) [2]rotaxane formation, and 3) [3]rotaxane formation. The whole reaction was found to be reversible in the presence of thiols, and thermodynamic control over product distribution was thus possible by varying the temperature, solvent, initial ratio of substrates, and concentration. The steric bulk of the end-capping groups had almost no influence on rotaxane yields, but the structure of the thiol was crucial for reaction rates. Amines and phosphines were also effective as catalysts. The structural characterization of the rotaxanes included an X-ray crystallographic study on [3]rotaxane 3 a. 相似文献
26.
[reaction: see text] On treatment of 5-siloxyhexa-1,2,5-trienes with a catalytic amount of W(CO)(6) under photoirradiation, formal Cope rearrangement proceeded to give 2-siloxyhex-1-en-5-ynes in good yield. The electrophilic activation of the allenyl moiety by W(CO)(5) triggers the intramolecular attack of the silyl enol ether in a 6-endo manner to produce a cyclohexenyl tungsten species. Carbon-carbon bond cleavage occurs by electron donation from the anionic W(CO)(5) into the silyloxonium moiety to afford the products with regeneration of the W(CO)(5)(L). 相似文献
27.
Katsuhiko Tomooka Nobuyuki Komine Tomoya Sasaki Hideo Shimizu Takeshi Nakai 《Tetrahedron letters》1998,39(52):2362-9718
Treatment of (E)-6-phenyl-5-hexenyl carbamates with s-BuLi/(−)-sparteine is shown to afford the trans-1,2-disubstituted cyclopentane derivatives in high % ee, along with the bicyclo[3.1.0]hexanes (bicyclization products). 相似文献
28.
Tomoya Kitazume Zaiju Jiang Kana Kasai Yuma Mihara Mamie Suzuki 《Journal of fluorine chemistry》2003,121(2):205-212
The utility of reusable ionic liquid-proline (or aldolase antibody 38C2) reaction system, proceeding the aldol reactions, is described. Further, obtained α-chloro-β-hydroxy compounds were transformed to the optically active α,β-epoxy carbonyl compounds. The aldolase antibody 38C2-ionic liquid system was able to reuse in Michael additions and the reaction of fluoromethylated imines. 相似文献
29.
Yoshida N Ishizuka T Yofu K Murakami M Miyasaki H Okada T Nagata Y Itaya A Cho HS Kim D 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(12):2854-2866
A series of zinc(II) porphyrin-imide dyads (ZP-Im), in which an electron donating ZP moiety is directly connected to an electron accepting imide moiety in the meso position, have been prepared for the examination of energy gap dependence of intramolecular electron transfer reactions with large electronic coupling. The nearly perpendicular conformation of the imide moiety towards the porphyrin plane has been revealed by Xray crystal structures. The energy gap for charge separation, 1ZP* - Im --> ZP+ - Im-, is varied by changing the electron accepting imide moiety to cover a range of about 0.8 eV in DMF. Definitive evidence for electron transfer has been obtained in three solvents (toluene, THF, and DMF) through picosecond-femtosecond transient absorption studies, which have allowed us to determine the rates of photoinduced charge separation, 1ZP* - Im --> ZP+ - Im-, and subsequent thermal charge recombination ZP+ - Im- --> ZP - Im. The free-energy gap dependence (energy gap law) has been probed from the normal to the nearly top region for the charge separation rate alone, and only the inverted region for the charge recombination rate. Although both of the energy gap dependencies can be approximately reproduced by means of the simplified semiclassical equation, when we take into consideration the effect of the high frequency vibrations replaced by one mode of averaged frequency, many features, including the effects of solvent polarity and the electron tunneling matrix element on the energy gap law, differ considerably from those of the previously studied porphyrin-quinone systems, which have weaker interchromophore electronic interactions. 相似文献
30.