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排序方式: 共有390条查询结果,搜索用时 15 毫秒
1.
2.
The cucurbit[n]uril (CB[n]) family of macrocycles occupies a prominent role in molecular recognition and self-assembly studies despite the current inability to access specific cucurbit[n]uril homologues, derivatives, and analogues by straightforward tailor-made synthetic procedures. In this paper, we explore an approach that circumvents the challenges posed by the tailor-made synthesis of macrocyclic CB[n] by preparing 1, which functions as an acyclic CB[6] congener. The o-xylylene connections to the glycoluril rings preorganize 1 into the (a,a,a,a)-1 conformation required for binding and reduce its tendency to undergo self-association. We surveyed the binding properties of 1 toward 16 amines (K(a) 相似文献
3.
An efficient synthesis of a low molecular weight, chiral nonracemic and C(2)-symmetric bipyridyl ligand is reported. The ligand was prepared using a catalytic asymmetric dihydroxylation reaction of a pyrindine as a key step. The ligand was evaluated in the asymmetric copper(I)-catalyzed cyclopropanation reactions of a series of alkenes and diazoesters. Very high diastereoselectivities and enantioselectivities were observed (>95:5 dr and up to 99% ee). These are the highest reported stereoselectivities for a chiral bipyridyl ligand. [structure: see text] 相似文献
4.
Paul F. Reigler Jeff Larson Lyle Bowman 《Journal of polymer science. Part A, Polymer chemistry》1981,19(12):3247-3255
The thermal and/or catalytic degradation of chloride-containing polymers causes dehydrohalogenation which produces hydrochloric acid. A nonaqueous method has been developed for the termination of hydrochloric acid. The sample is dissolved in tetrahydrofuran and titrated potentiometrically with a standard tetrabutylammonium hydroxide solution in a 7.5% (V/V) aqueous tetrahydrofuran solution with a combination glass-calomel electrode. The method has a relative precision of ±3.7% at the 95% confidence limit and a sensitivity of 25 ppm HCI. 相似文献
5.
Most tropical fruits for export must be treated with an approved quarantine treatment. Three and a half decades of research have demonstrated the efficacy of irradiation as a quarantine treatment in terms of efficiency, effectiveness, and product quality retention. The USFDA and the USDA-APHIS approved irradiation to disinfest fresh foods/fresh papayas in 1986 and 1989, respectively. In early 1995, the Hawaii Department of Agriculture was granted a special permit from USDA-APHIS allowing untreated Hawaiian fruits to be irradiated on the US mainland. The objectives were to gain experience in commercial irradiation as a quarantine treatment and to gather data on shipping and handling procedures, and on product quality. In April 1995, the first shipment of Hawaiian fruit was irradiated at a minimum quarantine dose of 0.25 kGy in an Isomedix plant near Chicago, and then distributed to supermarkets in Illinois and Ohio. Continuous shipments, irradiation, and marketing of various tropical fruits in the US have shown commercial efficacy, quality retention, and excellent consumer acceptance. A commercial e-beam/converted X-ray facility was installed by Titan Corp. on the Island of Hawaii and was operational by late July 2000. Hawaii has become the first place in the world to use irradiation as a quarantine treatment of fruits. 相似文献
6.
We consider the minimization of a quadratic formzVz+2zq subject to the two-norm constraint z=. The problem received considerable attention in the literature, notably due to its applications to a class of trust region methods in nonlinear optimization. While the previous studies were concerned with just the global minimum of the problem, we investigate the existence of all local minima. The problem is approached via the dual Lagrangian, and the necessary and sufficient conditions for the existence of all local minima are derived. We also examine the suitability of the conventional numerical techniques used to solve the problem to a class of single-instruction multiple-data computers known as processor arrays (in our case, AMT DAP 610). Simultaneously, we introduce certain hardware-oriented multisection algorithms, showing their efficiency in the case of small to medium size problems.This research was partially supported by the National Physical Laboratories of England under Contract RTP2/155/127. 相似文献
7.
ANTIVIRAL ACTIVITY OF MEROCYANINE 540 总被引:1,自引:0,他引:1
Fritz Sieber Jill M. O'Brien Gregory J. Krueger Sheri L. Schober William H. Burns Saul J. Sharkis Lyle L. Sensenbrenner 《Photochemistry and photobiology》1987,46(5):707-711
Abstract Simultaneous exposure to the lipophilic dye merocyanine 540 (MC 540) and white light inactivates several enveloped viruses. The same treatment appears to have little or no effect on pluripotent hematopoietic stem cells, mature red cells, and mature leukocytes. At least some components of the clotting system are spared, too. The molecular basis of the virucidal effect of MC 540 and light is not yet completely understood. Based on what is known about the interactions of MC 540 with cells and artificial membranes, it seems likely that MC 540 binds to and damages the viral envelope. MC 540-mediated photosensitization may have implications for the sterilization of bone marrow and blood products, the preparation of vaccines, and selected areas of antiviral therapy. 相似文献
8.
Reaction of Ph3GeLi with [Et4N][HFe3(CO)11] affords the new carbonylferrate salt [Et4N][Ph3GeFe(CO)4] and the same reaction provides an alternative route to the known silicon and tin analogs. Protonation of [Et4N][Ph3GeFe(CO)4] with HCl in ether-THF forms the air-sensitive, thermally rather unstable cis-Ph3GeFeH(CO)4. The latter protonates chloride ions in dichloromethane. 相似文献
9.
Yoshinori Tominaga Jiann-Kuan Luo Lyle W. Castle Raymond N. Castle 《Journal of heterocyclic chemistry》1993,30(1):267-273
The synthesis of the novel pyrazolo[4′,3′:5,6]pyrido[2,3-d]pyridazine ring system and some of its derivatives has been accomplished such as 4-amino-1-phenyl-5,8-dioxo-, 4-amino-5,8-dioxo-, 1-phenyl-5,8-dioxo-, 5,8-dioxo-, 5,8-dichloro-1-phenyl-, 5-ethoxy-1-phenyl- and 8-ethoxy-1-phenylpyrazolo[4′,3′:5,6]pyrido[2,3-d]pyrid-azines. 相似文献
10.
Yoshinori Tominagaxs Lyle W. Castle Raymond N. Castle 《Journal of heterocyclic chemistry》1996,33(4):1017-1018
Photocyclization of the substituted 2-(naphth-1-yl)-3-(thien-2-yl)propenoic acid ( 3 ) in the presence of iodine and air in a benzene-cyclohexane mixture afforded a separable mixture of three compounds, phenanthro[2,1-b]thiophene-10-carboxylic acid ( 4 ), phenanthro[2,1-b]thiothene ( 5 ), and naphtho[1,8-cde]-thieno[3,2-g][2]benzopyran ( 6 ) 相似文献