排序方式: 共有65条查询结果,搜索用时 234 毫秒
41.
Patrick L. Holland Kenton R. Rodgers William B. Tolman 《Angewandte Chemie (International ed. in English)》1999,38(8):1139-1142
Direct attack of the bis(μ-oxo)dicopper core on an arene appears feasible in tyrosinase and model complexes on the basis of studies of new [CuIII2(μ-O)2]2+ compounds supported by bidentate imine/amine ligands. In the first demonstration of such reactivity for a bis(μ-oxo)dicopper core, decomposition of these intermediates caused hydroxylation of a pendant phenyl ring [Eq. (a)] in a reaction analogous to that catalyzed by tyrosinase. 相似文献
42.
43.
44.
John N. Scholz Paul S. Engel Christopher Glidewell Kenton H. Whitmire 《Tetrahedron》1989,45(24):7695-7708
The X-ray crystal structures of the four stable phenylhydroxylamines PhSO2NHOH, (PhSO2)2NOH,PhSO2NHOSO2Ph, (PhSO2)2NOSO2Ph), and of PhSO3−+H3NHNS02Ph are presented. The last of these is a by-product obtained during the isolation of PhSO2NHOH (Piloty's Acid). The formation of and the bonding in these molecules are discussed. 相似文献
45.
We argue that the epistemic theory of vagueness cannot adequately justify its key tenet-that vague predicates have precisely
bounded extensions, of which we are necessarily ignorant. Nor can the theory adequately account for our ignorance of the truth
values of borderline cases. Furthermore, we argue that Williamson’s promising attempt to explicate our understanding of vague
language on the model of a certain sort of “inexact knowledge” is at best incomplete, since certain forms of vagueness do
not fit Williamson’s model, and in fact fit an alternative model. Finally, we point out that a certain kind of irremediable
inexactitude postulated by physics need not be-and is not commonly-interpreted as epistemic. Thus, there are aspects of contemporary
science that do not accord well with the epistemicist outlook. 相似文献
46.
47.
Hina Chaudhry Mary Lynch Kevin Schomacker Reginald Birngruber Kenton Gregory Irene Kochevar 《Photochemistry and photobiology》1993,58(5):661-669
The relaxation of rabbit aorta rings induced by low-power laser radiation was investigated in vitro to determine the location of the chromophore(s) responsible for this response and evaluate possible mechanisms. An action spectrum for relaxation was measured on rabbit thoracic aorta rings precontracted with norepinephrine. The decrease in isometric tension was measured during exposure to laser light (351–625 nm) delivered via a fiber optic to a small spot on the adventitial surface. The shortest UV wavelength (351 nm) was 35-fold more effective than 390 nm and 1700-fold more effective than 460 nm. Ultraviolet wavelengths also produced greater maximum relaxation (0.40–0.45) than visible wavelengths (0.20–0.25), suggesting that photovasorelaxation involves more than one chromophore.
The adventitial layer was not necessary for photovasorelaxation, indicating that the light is absorbed by a chromophore in the medial layer. The same degree of relaxation was obtained on rings without adventitia when either one-half of the ring, or a small spot was irradiated indicating that communication between smooth muscle cells spreads a signal from the area illuminated to the entire ring.
The mechanism for photovasorelaxation was investigated using potential inhibitors. N -monomethyl-l-arginine and N -amino-L-arginine, inhibitors of nitric oxide synthase, did not alter photovasorelaxation nor did indomethacin, an inhibitor of cyclooxygenase, and zinc protoporphyrin, an inhibitor of heme oxygenase. 相似文献
The adventitial layer was not necessary for photovasorelaxation, indicating that the light is absorbed by a chromophore in the medial layer. The same degree of relaxation was obtained on rings without adventitia when either one-half of the ring, or a small spot was irradiated indicating that communication between smooth muscle cells spreads a signal from the area illuminated to the entire ring.
The mechanism for photovasorelaxation was investigated using potential inhibitors. N -monomethyl-l-arginine and N -amino-L-arginine, inhibitors of nitric oxide synthase, did not alter photovasorelaxation nor did indomethacin, an inhibitor of cyclooxygenase, and zinc protoporphyrin, an inhibitor of heme oxygenase. 相似文献
48.
Shine HJ Zhao B Qian DQ Marx JN Guzman-Jimenez IY Thurston JH Ould-Ely T Whitmire KH 《The Journal of organic chemistry》2003,68(23):8910-8917
Phenoxathiin cation radical perchlorate (PO.+ClO4(-)) added stereospecifically to cyclopentene, cyclohexene, cycloheptene, and 1,5-cyclooctadiene to give 1,2-bis(5-phenoxathiiniumyl)cycloalkane diperchlorates (4-7) in good yield. The diaxial configuration of the PO+ groups was confirmed with X-ray crystallography. Unlike additions of thianthrene cation radical perchlorate (Th.+ClO4(-)) to these cycloalkenes, no evidence for formation of monoadducts was found in the reactions of PO.+ClO4(-). This difference is discussed. Addition of Th.+ClO4(-) to five trans alkenes (2-butene, 2-pentene, 4-methyl-2-pentene, 3-octene, 5-decene) and four cis alkenes (2-pentene, 2-hexene, 2-heptene, 5-decene) gave in each case a mixture of mono- and bisadducts in which the configuration of the alkene was retained. Thus, cis alkenes gave erythro monoadducts and threo bisadducts, whereas trans alkenes gave threo monoadducts and erythro bisadducts. In these additions to alkenes, cis alkenes gave predominantly bisadducts, while trans alkenes (except for trans-2-butene) gave predominantly monoadducts. This difference is explained. 1,2-Bis(5-phenoxathiiniumyl)cycloalkanes (4-7) and 1,2-bis(5-thianthreniumyl)cycloalkanes underwent fast elimination reactions on activated alumina forming, respectively, 1-(5-phenoxathiiniumyl)cycloalkenes (8-11) and 1-(5-thianthreniumyl)cycloalkenes (12-16). Among adducts of Th.+ClO4(-) and alkenes, monoadducts underwent fast ring opening on alumina to give (5-thianthreniumyl)alkenes, while bisadducts underwent fast eliminations of H+ and thianthrene (Th) to give (5-thianthreniumyl)alkenes also. Ring opening of monoadducts was a stereospecific reaction in which the configuration of the original alkene was retained. Thus, erythro monoadducts (from cis alkenes) gave (E)-(5-thianthreniumyl)alkenes and threo monoadducts (from trans alkenes) gave (Z)-(5-thianthreniumyl)alkenes. Among bisadducts, elimination of a proton and Th occurred and was more complex, giving both (E)- and (Z)-(5-thianthreniumyl)alkenes. These results are explained. Configurations of adducts and (5-thianthreniumyl)alkenes were deduced with the aid of X-ray crystallography and (1)H and (13)C NMR spectroscopy. In the NMR spectra of (E)- and (Z)-(5-thianthreniumyl)alkenes, the alkenyl proton of Z isomers always appeared at a lower field (0.8-1.0 ppm) than that of E isomers. 相似文献
49.
Bismuth(III) salicylate, [Bi(Hsal)(3)](n), reacts readily with the trivalent metal beta-diketonate compounds M(acac)(3) (acac = acetylacetonate; M = Al, V, Cr, Fe, Co) to produce trinuclear coordination complexes of the general formula Bi(2)(Hsal)(6).M(acac)(3) (M = Al, V, Cr, Fe, Co) in 60-90% yields. Spectroscopic and single crystal X-ray diffraction experiments indicate that these complexes possess an unusual asymmetric nested structure in both solution and solid state. Upon standing in dichloromethane solution, Bi(2)(Hsal)(6).Co(acac)(3) eliminates Bi(Hsal)(3) to give the 1:1 adduct Bi(Hsal)(3).Co(acac)(3). The 2:1 heterobimetallic molecular compounds undergo facile thermal decomposition on heating in air to 475 degrees C to produce heterometallic oxide materials, which upon annealing for 2 h at 700 degrees C form crystalline oxide materials. The synthetic approach detailed here represents a unique, general approach to the formation of heterobimetallic bismuth-based coordination complexes via the coordination of M(acac)(3) complexes to bismuth(III) salicylate. 相似文献
50.