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101.
A new pyrenemethylamine substituted l-Boc-tyrosine derivative was synthesized and characterized. UV-vis, FL, CD, and light scattering experiments proved that the chiral molecules were able to self-assemble for formation of new aggregate structure. The SEM and AFM images indicated that the helical wires could be fabricated by π-π stacking interaction between adjacent pyrene molecules. 相似文献
102.
Ab initio molecular orbital theory and density functional theory have been used to study nine isomers of N7 ionic clusters with low spin at the HF/6-31G*, MP2/6-31G*, B3LYP/6-31G*, and B3LYP/6-311(+)G* levels of theory. All stationary
points are examined with harmonic vibrational frequency analyses. Four N7
+ isomers and five N7
− isomers are determined to be local minima or very close to the minima on their potential-energy hypersurfaces, respectively.
For N7
+ and N7
−, the energetically low lying isomers are open-chain structures (C
2
v
and C
2
v
or C2). The results are very similar to those of other known odd-number nitrogen ions, such as N5
+, N9
+, and N9
−, for which the open-chain structures are also the global minima. This research suggests that the N7 ionic clusters are likely to be stable and to be potential high-energy-density materials if they could be synthesized.
Received: 16 July 2001 / Accepted: 8 October 2001 / Published online: 21 January 2002 相似文献
103.
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
104.
105.
Two- or three-component aza Diels-Alder reactions of Danishefsky's diene with imines or aldehydes and amines in water took place smoothly under neutral conditions in the presence of a catalytic amount of an alkaline salt such as sodium triflate to afford dihydro-4-pyridones in high yields. 相似文献
106.
Masao Nohara Masaki Hasegawa Hatsuhiko Harashina Yoichi Iitaka 《Journal of polymer science. Part A, Polymer chemistry》1988,26(10):2695-2704
Photoreactive polyamides having m- or 1 -type cyclobutane moiety were prepared via a topochemical photodimerization of 4-(3-oxo-3-phenyl-1-propenyl)benzoic derivatives,4 followed by polycondensation of cyclobutane dicarboxylate derivatives with diamines. From the spectral studies of resulted polyamides compared with the corresponding reference diamides, it was concluded that both types of polyamides were depolymerized photochemically to give the same type of amide derivative having chalcone moiety with a small amount of undefined side reaction. The cyclobutane ring of the m-dimer from 4-(3-oxo-3-phenyl-1-propenyl)benzoic acid in crystal is severely twisted presumably because of the enhanced steric repulsions between two pairs of adjacent substituents. The higher quantum yield of the m-dimer for the photocleavege, compared with that of the 1 -dimer, has been interpreted in terms of such steric repulsions by the strained structure of the m-dimer. 相似文献
107.
The cerium‐containing MCM‐41 (Ce‐MCM‐41) has been synthesized by direct hydrothermal method. The low‐angle XRD patterns revealed the typical five major peaks of MCM‐41 type hexagonal structures. The interplanar spacing d100 = 38.4 Å was obtained that can be indexed on a hexagonal unit cell parameter with ao = 44.3 Å which was larger than that of pure siliceous MCM‐41 (Si‐MCM‐41). Transmission electron micrograph shows the regular hexagonal array of uniform channel characteristics of MCM‐41. The BET surface area of Ce‐MCM‐41 was 840 m2/g, which is much reduced as compared to that of Si‐MCM‐41, with the pore size of 26.9 Å and mesopore volume of 0.78 cm3/g were measured by nitrogen adsorption‐desorption isotherm at 77 K. Along with the results, the synthesized Ce‐MCM‐41 exhibited a well‐ordered MCM‐41‐type mesoporous structure with the incorporation of cerium. Using Ce‐MCM‐41 as a support, the Rh (0.5 wt%) catalyst exhibited very high activity for the NO/CO reactions. 相似文献
108.
Sheng‐Xiong Huang Xun Liao Quan‐Jiang Nie Li‐Sheng Ding Shu‐Lin Peng 《Helvetica chimica acta》2004,87(3):598-604
Three new phenyl glycosides, scrophenoside A ( 1 ), B ( 2 ), and C ( 3 ), and two new phenylethyl glycosides, scroside D ( 4 ) and scroside E ( 5 ), were isolated from the stem of Picrorhiza scrophulariiflora Pennell (Scrophularlaceae), besides five known compounds. On the basis of spectroscopic evidence, the structures of the new compounds were elucidated as 4‐acetyl‐2‐methoxyphenyl 6‐O‐[4‐(β‐D ‐glucopyranosyloxy)vanilloyl]‐β‐D ‐glucopyranoside ( 1 ), 4‐acetylphenyl 6‐O‐[(E)‐p‐coumaroyl]‐β‐D ‐glucopyranoside ( 2 ), 4‐[(1R)‐ and (1S)‐1‐hydroxyethyl]‐2‐methoxyphenyl β‐D ‐glucopyranoside ( 3a and 3b , resp.), 2‐(3,4‐dihydroxyphenyl)ethyl O‐β‐D ‐glucopyranosyl‐(1→3)‐4‐O‐[(E)‐feruloyl]‐β‐D ‐glucopyranoside ( 4 ), and 2‐(3,4‐dihydroxyphenyl)ethyl O‐β‐D ‐glucopyranosyl‐(1→3)‐6‐O‐[(E)‐feruloyl]‐β‐D ‐glucopyranoside ( 5 ). 相似文献
109.
Zhen‐Yu Li Ping Chen Hong‐Gui Xu Shu‐Ying Peng Yi‐Ming Yang Zhong‐Zhen Zhao Yue‐Wei Guo 《Helvetica chimica acta》2007,90(7):1353-1359
Five new polycyclic Daphniphyllum alkaloids, macropodumines F ( 1 ) and G ( 2 ), 17‐oxoyuzurimine ( 3 ), and macropodumines H ( 4 ) and I ( 5 ), were isolated from the leaves of D. macropodum Miq ., collected in Sichuan Province, China. The structures and relative configurations of the new compounds – as well as of four known, related alkaloids – were elucidated on the basis of in‐depth spectroscopic and mass‐spectrometric analyses, by chemical derivatization, and by comparison of spectroscopic data with those of known compounds. 相似文献
110.
Tohru Takabatake Yumiko Hasegawa Minoru Hasegawa 《Journal of heterocyclic chemistry》1993,30(6):1477-1479
The cyclocondensations of benzofuroxan 1a with carbonyl compounds were smoothly and efficiently carried out by the adsorption of the components on the surface of silica gel or a molecular sieve to form a 2,3-disubstituted quinoxaline 1,4-dioxide. When the reactions using a molecular sieve 3A (powder) were carried out at 90°, the actual reaction times were reduced to 0.5-2 hours. Although Duerckheimer has reported the isolation of only the 7-substituted quinoxaline 1,4-dioxide when 5-methoxybenzofuroxan 1e was allowed to react with ethyl acetoacetate 2j , it produced only the 6-methoxy isomer as the reaction product by our method. 5-Carboxybenzofuroxan 1f did not react with the carbonyl compound. 相似文献