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Taridaporn Bunyapaiboonsri Pornrapee Vongvilai Patchanee Auncharoen Masahiko Isaka 《Helvetica chimica acta》2012,95(6):963-972
Seven new cyclohexadepsipeptides, beauvenniatins F, G1, G2, G3, H1, H2, and H3 ( 1 – 7 , resp.), were isolated from cultures of the fungus Acremonium sp. BCC 2629. Their structures were elucidated by extensive spectroscopic analyses. The absolute configurations were addressed by HPLC analyses of their acid hydrolysates. Their biological activities were evaluated against Mycobacterium tuberculosis H37Ra and Plasmodium falciparum K1; the respective MIC and IC50 values were in the micromolar range. 相似文献
995.
996.
Vanampally Chandrashaker Masahiko Taniguchi Marcin Ptaszek Jonathan S. Lindsey 《Tetrahedron》2012,68(34):6957-6967
A proposed chemical model for the prebiogenesis of tetrapyrrole macrocycles relies on the condensation of a 3-alkyl-substituted 2,4-diketone and an α-aminoketone to form a pyrrole equipped for subsequent self-condensation leading to porphyrinogens. The condensation of acyclic reactants can proceed via competing Knorr (desired) and Fischer–Fink (undesired) pathways. Here, the Knorr and Fischer–Fink pathways are quantitated using (1) analogues of those in the proposed prebiotic route wherein the resulting pyrroles are blocked from subsequent condensation, and (2) a set of internal standards for quantitation of crude reaction mixtures by 1H NMR spectroscopy following extraction into CS2. The reaction of 1-amino-2-butanone and 3-methyl-2,4-pentanedione at 60 °C in aqueous solution at pH 7 for 24 h afforded the Knorr pyrrole and Fischer–Fink pyrrole in yields of 48% and 7%, respectively. The reaction in hot aqueous acid (pH 4.6, reflux, 30 min) afforded the Knorr pyrrole in diminished yield (22%) relative to that of the Fischer–Fink pyrrole (11%). The Knorr pyrrole (4-ethyl-2,3-dimethylpyrrole) is evanescent whereas the Fischer–Fink pyrrole (2,3,4-trimethyl-5-propanoylpyrrole) is quite stable; hence, rapid analysis of the reaction mixture (vs workup and isolation) is essential for accurate analysis. 相似文献
997.
M. N. Ellingham Emily A. Marshall Kenta Ozeki Shoichi Tsuchiya 《Journal of Graph Theory》2019,90(4):459-483
Tutte showed that -connected planar graphs are Hamiltonian, but it is well known that -connected planar graphs need not be Hamiltonian. We show that -minor-free -connected planar graphs are Hamiltonian. This does not extend to -minor-free -connected graphs in general, as shown by the Petersen graph, and does not extend to -minor-free -connected planar graphs, as we show by an infinite family of examples. 相似文献
998.
Prof. Dr. Motonori Watanabe Yuka Ono Prof. Dr. Tatsumi Ishihara Prof. Dr. Yuan Jay Chang Prof. Dr. Masahiko Shibahara 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(43):e202200790
Novel donor–acceptor dyads containing [2.2]- and [3.3]paracyclophane (PCP) as the bridging moiety were synthesized and used to effectively fabricate dye-sensitized hydrogen production systems. All the prepared compounds had a phenothiazine and a cyanoacrylic acid/pyridinyl acrylonitrile moiety acting as an electron donor and acceptor, respectively. Although cyclic voltammetry measurements showed similar electron-donating properties among all the synthesized dyads, the lowest absorption energy of the [2.2]PCP moiety was lower than that of the [3.3]PCP one; this was due to its shorter distance between benzene rings, which could effectively drive the charge transfer between the donor and acceptor chromophores. Under visible light (>395 nm), a dyad-loaded photocatalyst in a 0.5 M aqueous glycerol solution generated detectable hydrogen gases. The optimal turnover number and photocurrent order exhibited the same trend as the hydrogen production rate since the suggested number of excited photons played a critical role in hydrogen production. 相似文献
999.
Masahiko Ito Sana Hraiech Christelle Goutaudier Kheirreddine Lebbou Georges Boulon 《Journal of Crystal Growth》2008,310(1):140-144
Crystal fiber of cubic Yb3+-doped KY3F10 has been grown. Both, mono-doped and concentration gradient fibers were grown by laser-heated pedestal growth (LHPG) method under argon atmosphere. The preparation of feed rod materials under CF4 atmosphere prior to LHPG is efficient to obtain oxygen-free fluorides. Yb3+-doped KY3F10 crystals have excellent spectroscopic properties, weak self-quenching property and can be expected for solid-state laser application. 相似文献
1000.
Michio Yamada Dr. Naomi Mizorogi Dr. Takahiro Tsuchiya Dr. Takeshi Akasaka Prof. Shigeru Nagase Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(37):9486-9493
Herein we show the synthesis and characterization of the second known Ce2@C80 isomer. A 13C NMR spectroscopic study revealed that the structure of the second isomer has D5h symmetry. Paramagnetic NMR spectral analysis and theoretical calculation display that the encapsulated Ce atoms circulate two‐dimensionally along a band of ten contiguous hexagons inside a D5h‐C80 cage, which is in sharp contrast to the three‐dimensional circulation of two Ce atoms in an Ih‐C80 cage. The electronic properties were revealed by means of electrochemical measurements. The D5h isomer of Ce2@C80 has a much smaller HOMO–LUMO gap than cluster fullerenes (M3N@C80, M=Sc, Tm, and Lu) with the same D5h‐C80 cages. The chemical reactivity was investigated by using disilirane as a chemical probe. The high thermal reactivity toward 1,1,2,2‐tetramesityl‐1,2‐disilirane is consistent with the trends of the redox potentials and the lower LUMO level of the D5h isomer of Ce2@C80 compared with that of C60. 相似文献