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171.
Cyclic peptidic RGD models were efficiently synthesized by Pd(P(t-Bu)3)2-catalyzed carbonylative macrolactamization in the presence of 4 A molecular sieves under 10 atm of carbon monoxide. 相似文献
172.
We report the synthesis and the photochromic behavior of a newly designed, photochromic, radical diffusion-inhibited hexaarylbiimidazole (HABI) derivative with markedly improved photochromic performance in coloration and decoloration rates as well as greater optical density in the colored state. The thermal bleaching rate (tau1/2 = 260 ms at 295 K) is the fastest among the reported ones for HABI derivatives. 相似文献
173.
Activation parameters were determined for the recombination of radical pairs arising from newly designed, photochromic, radical diffusion-restricted hexaarylbiimidazole (HABI) derivative. We have developed a new type of radical diffusion-inhibited HABI derivative, which contains two equivalent HABI units and yields a tetraradical with four equivalent 2,4,5-triphenylimidazolyl radical (TPIR) units by photoirradiation. This radical dimerization proceeds by a successive first-order reaction from the tetraradical to the parent molecule via a diradical. The rate constants of each reaction were determined from the decay profile of EPR signal intensities. The entropies of activation (DeltaS(double dagger)) for the first and the successive dimerization steps were estimated to be -178.5 and -205.5 J K(-1) mol(-1), respectively. Within the experimental temperature range, the radical dimerizations are entropy-controlled (-TDeltaS(double dagger) > DeltaH(double dagger)). The large negative DeltaS(double dagger) values imply a highly ordered transition state, indicating that the radical dimerizations occur when the TPIR units interact at a specific orientation. The present study demonstrates the availability of radical diffusion-inhibited HABI for the kinetic study of radical-radical reaction. 相似文献
174.
On the Ramsey Number of Sparse 3-Graphs 总被引:1,自引:0,他引:1
Brendan Nagle Sayaka Olsen Vojtěch Rödl Mathias Schacht 《Graphs and Combinatorics》2008,24(3):205-228
We consider a hypergraph generalization of a conjecture of Burr and Erd?s concerning the Ramsey number of graphs with bounded degree. It was shown by Chvátal, Rödl, Trotter, and Szemerédi [The Ramsey number of a graph with bounded maximum degree, J. Combin. Theory Ser. B 34 (1983), no. 3, 239–243] that the Ramsey number R(G) of a graph G of bounded maximum degree is linear in |V(G)|. We derive the analogous result for 3-uniform hypergraphs. 相似文献
175.
176.
Hamase K Takagi S Morikawa A Konno R Niwa A Zaitsu K 《Analytical and bioanalytical chemistry》2006,386(3):705-711
Using a column-switching HPLC system combining a micro-ODS column and a chiral column, the amounts of d-proline (d-Pro) have been determined in 18 tissues, plasma and urine of mice. To avoid the enzymatic degradation of d-amino acids in vivo, a mutant mouse strain lacking d-amino acid oxidase activity (ddY/DAO− mouse) was used. In the brain, relatively large amounts of d-Pro were observed in the anterior pituitary, posterior pituitary and pineal glands. In the peripheral tissues, the amounts
of d-Pro were high in the pancreas and kidney. Above all, it is surprising that the ddY/DAO− mice excreted large amounts of d-Pro in their urine (433 nmol/mL, 20 times that of l-Pro). The origin of d-Pro has also been investigated. By comparing germ-free mice and gnotobiotic mice, intestinal bacteria were shown to have
no effect on the urinary d-Pro amount. Concerning the dietary origin, a notable amount of d-Pro was still excreted in the urine after starvation for 4 days, suggesting that some of the d-Pro is produced in the mice. Age-dependent changes in the urinary d-Pro amount have also been investigated from the postnatal 1st month up to 12 months, and ddY/DAO− mice were found to excrete large amounts of d-Pro in the urine constantly throughout their lives.
Kenji Hamase is Associate Professor in the Department of Bioanalytical Chemistry, Graduate School of Pharmaceutical Sciences at Kyushu
University. His current research interests focus on the development of analytical methods for d-amino acids and the study of their physiological functions and diagnostic values. He received the Japanese Society for Analytical
Chemistry Award for Young Scientists in 2003, and the PSJ Award for Young Scientists in 2006. 相似文献
177.
Ishida Y Amano S Iwahashi N Saigo K 《Journal of the American Chemical Society》2006,128(40):13068-13069
A cross-linked polymer, prepared by the in situ polymerization of a thermotropic columnar liquid crystal, was found to work as a host with a flexible framework, which was reminiscent of intercalation hosts, such as clays, graphites, and coordination polymers. The structural order of the cross-linked polymer was reversibly switched by changing the amount or shape of a guest incorporated in the polymer. 相似文献
178.
Ono M Takara Y Egami M Uranaka K Yoshimitsu H Matsushita S Fujiwara Y Ikeda T Nohara T 《Chemical & pharmaceutical bulletin》2006,54(2):237-239
Two new steroidal alkaloid glycosides, esculeosides C and D, have been isolated from the ripe fruit of Cherry tomato [Lycopersicon esculentum var. cerasiforme (DUNAL) ALEF.], along with three known steroidal alkaloid glycosides, esculeoside A, esculeoiside B, and lycoperoside G. Their chemical structures were determined on the basis of spectroscopic data. 相似文献
179.