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排序方式: 共有464条查询结果,搜索用时 15 毫秒
91.
Masafumi Yano Yutaka Ishida Kazunobu Sato Munetaka Oyama 《Journal of Physics and Chemistry of Solids》2004,65(4):733-736
A series of N,N,N′,N′-tetraaryl-1,3-phenylenediamines with various substituents at the para-position of peripheral rings were designed and synthesized. Electrochemical and novel electron transfer stopped-flow methods were invoked for characterizing the absorption spectra of the corresponding short-lived mono- and dicationic states. Both thermodynamic and kinetic stabilization are required to extend the lifetime of the dicationic states. Useful molecular design rules for stabilizing the dicationic states of N,N,N′,N′-tetraaryl-1,3-phenylenediamines as precursors for positively charged high-spin systems were elucidated. 相似文献
92.
T. Oyama 《European Journal of Operational Research》1985,20(2):273-274
93.
Hirata KS Inoue K Ishida T Kajita T Kihara K Nakahata M Nakamura K Ohara S Sato N Suzuki Y Totsuka Y Yaginuma Y Mori M Oyama Y Suzuki A Takahashi K Yamada M Koshiba M Nishijima K Suda T Tajima T Miyano K Miyata H Takei H Fukuda Y Kodera E Nagashima Y Takita M Kaneyuki K Tanimori T Beier EW Feldscher LR Frank ED Frati W Kim SB Mann AK Newcomer FM Van Berg R Zhang W 《Physical review D: Particles and fields》1991,44(8):2241-2260
94.
95.
Hitoshi Kamauchi Masahiro Noji Kaoru Kinoshita Toshikatsu Takanami Kiyotaka Koyama 《Tetrahedron》2018,74(23):2846-2856
The unprecedented tetracyclic coumarin derivatives 1 and 2 and the coumarin dimers 3–5 were isolated from chemically engineered extracts (coumarin dimerization of natural extract) of the marine-derived fungus Eurotium rubrum. The structures of these compounds were established using NMR, MS and IR methods. The absolute configuration of 1 was determined by ECD calculations. The unprecedented tetracyclic coumarin skeleton was generated by domino-Knoevenagel-Diels-Alder reactions. Compounds 1–5 showed tyrosinase inhibitory activity (IC50?=?1.7, 1.2, 4.9, 1.8 and 2.9?μM, respectively). The isolated coumarin derivatives 1–5 were not observed by HPLC analysis in crude extracts of E. rubrum, suggesting that chemically engineered extract generated these new coumarin derivatives with tyrosinase inhibitory activity. 相似文献
96.
Investigation of the cyclization efficiency of N-methyl linear tetrapeptides using a molecular modeling study and chemical synthesis is described. The linear peptide with two N-methyl groups, MeAla-Leu-MePhe-Gly, forms γ-turn like conformation with the amine at N-terminus and the carbonyl at C-terminus in closer proximity to give the desired cyclic tetrapeptide, dihydrotentoxin. In addition, synthesis of tentoxin B by the combination of Fmoc solid-phase peptide synthesis and cyclization in solution phase has been reported. An unusual amino acid, an L-N-methyl-β-hydroxyphenylalanine derivative, which was assembled on solid support, was prepared from ethyl cinnamate. Cyclic tetrapeptide formation and cleavage of benzyl ether were optimized with DIPCI/HOBt/DIPEA and Et3SiH/Pd(OH)2, respectively. 相似文献
97.
Aerobic Oxidation of 5‐(Hydroxymethyl)furfural Cyclic Acetal Enables Selective Furan‐2,5‐dicarboxylic Acid Formation with CeO2‐Supported Gold Catalyst
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Dr. Minjune Kim Yaqiong Su Prof. Atsushi Fukuoka Prof. Dr. Emiel J. M. Hensen Dr. Kiyotaka Nakajima 《Angewandte Chemie (International ed. in English)》2018,57(27):8235-8239
The utilization of 5‐(hydroxymethyl)furfural (HMF) for the large‐scale production of essential chemicals has been largely limited by the formation of solid humin as a byproduct, which prevents the operation of stepwise batch‐type and continuous flow‐type processes. The reaction of HMF with 1,3‐propanediol produces an HMF acetal derivative that exhibits excellent thermal stability. Aerobic oxidation of the HMF acetal with a CeO2‐supported Au catalyst and Na2CO3 in water gives a 90–95 % yield of furan 2,5‐dicarboxylic acid, an increasingly important commodity chemical for the biorenewables industry, from concentrated solutions (10–20 wt %) without humin formation. The six‐membered acetal ring suppresses thermal decomposition and self‐polymerization of HMF in concentrated solutions. Kinetic studies supported by DFT calculations identify two crucial steps in the reaction mechanism, that is, the partial hydrolysis of the acetal into 5‐formyl‐2‐furan carboxylic acid involving OH? and Lewis acid sites on CeO2, and subsequent oxidative dehydrogenation of the in situ generated hemiacetal involving Au nanoparticles. These results represent a significant advance over the current state of the art, overcoming an inherent limitation of the oxidation of HMF to an important monomer for biopolymer production. 相似文献
98.
T. Yamazaki R. S. Hayano K. Itahashi K. Oyama A. Gillitzer H. Gilg M. Knülle M. Münch P. Kienle W. Schott H. Geissel N. Iwasa G. Münzenberg 《Zeitschrift für Physik A Hadrons and Nuclei》1996,355(1):219-221
Narrow lines were observed around 133 MeV excitation energy in the208Pb(d,3He) reaction atT d=300 MeV/u using the Fragment Separator System at GSI. They are assigned to the deeply boundπ ??207Pb states with configurations of $\left( {2p} \right)_{\pi ^ - } $ (3p1/2, 3p3/2) n ?1 . 相似文献
99.
Using the properties of the Jordan curve, the following theorem on the heteroclinic tangency in orientation-preserving two-dimensional maps is proved: LetT
:R
2 R
2 be a one-parameter family ofC
1 diffeomorphisms andJ=DetDT
be such that 0<J1 or 1J<. LetW
u
n
be the unstable manifold of a hyperbolicn-cycle andW
s
m
the stable manifold of a hyperbolicm-cycle. Suppose that for<
c
,W
u
n
andW
s
m
have no common points, and that for>
c
,W
u
n
andW
s/m have a transversal heteroclinic point. Then at=
c
,W
u
n
andW
s
m
are in the first asymptotic heteroclinic tangency except for the following three cases: (1)n=m; both cycles are without reflection. (2)m=2n; then- andm-cycles are with and without reflection, respectively; (3)n=2m; then- andm-cycles are without and with reflection, respectively. 相似文献
100.
Takushi Nagata Kiyoaki D. Sugi Kiyotaka Yorozu Tohru Yamada Teruaki Mukaiyama 《Catalysis Surveys from Japan》1998,2(1):47-57
Optically active aldiminato cobalt(II) complexes have been found to catalyze the enantioselective reduction of ketones with sodium borohydride affording the corresponding optically active secondary alcohols in high chemical yields with high enantioselectivities. The enantioselective borohydride reduction is also applicable to not only C=O bonds in aromatic ketones but also to C=N bonds in aromatic imines. 相似文献