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41.
Distribution ratios of 15 ethers were determined with various ammonium sulfate eluents and were used to determine the conditions necessary for the separation of five-and seven-component mixtures by salting-out chromatography. The application of this technique was found to be less successful than ion-exchange chromatography for the separation of carboxylic acids. 相似文献
42.
Darwish AD Avent AG Abdul-Sada AK Taylor R 《Chemical communications (Cambridge, England)》2003,(12):1374-1375
Trifluoromethylation of [60]- and [70]fullerenes occurs across both 6:6- and 5:6-bonds giving unsymmetrical tetramethyl adducts having four contiguous CF3 groups; both fullerenes give bis adducts which do not involve 6:6-addition, and unsymmetrical hexa-adducts (with contiguous CF3 groups) are also obtained from [60]fullerene. 相似文献
43.
Kim C. Pich Roger Bishop Donald C. Craig Ian G. Dance A. David Rae Marcia L. Scudder 《Structural chemistry》1993,4(1):41-51
In a further exploration of the structural factors causing alicyclic diols such asexo-2,exo-6-dihydroxy-2,6-dimethylbicyclo[3.3.1]nonane (1) to adopt the helical tubuland inclusion host structure, the title compound (8) has been synthesized and its crystal structure determined. This 9-oxa analogue of (1) has a totally different structure [C10H18O3; orthorhombic;P21212;a 18.989(4),b 19.064(3),c 14.256(3) Å;Z 20; with finalR 0.065] due to involvement of the ether oxygen atom in the hydrogen bonding network. The structure of the diol (8) approximatesP¯421
c symmetry, and 16 of the 20 molecules per cell create a hostlike structure of this symmetry, which consists of tightly bound hydrogen bonded pillars parallel toc. The remaining guestlike molecules occupy inequivalent pseudo ¯4 sites separated byc/2 to form weakly bound columns parallel toc. Hydrogen bonds also occur between the pillars and columns. An ordered structure with sensible intermolecular contacts can be formed inP212121 with thec axis doubled. A difference betweena andb axial lengths correlates with a difference in occupancies of pseudo-¯4-related sites for the guest-like component of the structure. 相似文献
44.
De Jonghe S Lamote I Venkataraman K Boldin SA Hillaert U Rozenski J Hendrix C Busson R De Keukeleire D Van Calenbergh S Futerman AH Herdewijn P 《The Journal of organic chemistry》2002,67(3):988-996
The synthesis of a new series of D-erythro-homoceramide analogues is described. Several synthetic approaches were investigated. Homoceramides can be successfully synthesized from L-homoserine as chiral building block and a protected Weinreb-amide as a key intermediate. The synthesis of short-chain analogues with a heptyl side chain, as well as with a phenyl residue in the sphingoid part (instead of the naturally occurring tridecyl side chain), was effected. The homoceramides 15-17 and 24 were investigated for their potential to reverse the inhibitory effect of fumonisin B(1) on axonal growth. Unfortunately, none of the tested compounds showed any biological activity due to their lack of metabolism to glucosylhomoceramide. 相似文献
45.
Alison T. Ung Roger Bishop Donald C. Craig Ian G. Dance A. David Rae Marcia L. Scudder 《Journal of inclusion phenomena and macrocyclic chemistry》1993,15(4):385-398
The inclusion compounds of 2,8-dimethyltricyclo[5.3.1.13,9]dodecane-syn-2,syn-8-diol,3, with ferrocene and with squalene have been prepared. The crystal structures of these helical tubulate compounds: (3)3·(ferrocene)0.75 [P3121,a=b=13.7480(6),c=7.0312(5) Å,Z=1,R=0.038] and (3)3·(squalene)0.23 [P3121,a=b=13.677(1),c=7.0533(9) Å,Z=1,R=0.042] are described.
Supplementary Data relating to this article are deposited with the British Library as supplementary publication No. SUP 82151 (16 pages). 相似文献
46.
Roger J. Greathead Rod S. Mason Keith R. Jennings Janet A. Page Robert J. Pryce 《Journal of mass spectrometry : JMS》1985,20(2):110-114
The behaviour of gibberellic acid (GA3) under electron impact and chemical ionization conditions has been examined. The tendency of GA3 to undergo pyrolysis by the loss of the elements of water and carbon dioxide has been identified. Two methods of sample introduction can be used to minimize the occurrence of this pyrolysis. Accurate mass measurement allows the composition of the pyrolysis product to be determined and metastable techniques confirm the structure of this product to be epi-allogibberic acid rather than its isomer allogibberic acid. This result corrects a misconception in the literature and illustrates the advantage of metastable methods compared with accurate mass measurements, for the determination of small structural differences within a molecule. 相似文献
47.
Solvent effects on the electrochemistry and spectroscopic properties of alkyl- and aryl-substituted corroles in nonaqueous media are reported. The oxidation and reduction of six compounds containing zero to seven phenyl or substituted phenyl groups on the macrocycle were studied in four different nonaqueous solvents (CH(2)Cl(2), PhCN, THF, and pyridine) containing 0.1 M tetra-n-butylammonium perchlorate. Dimers were formed upon oxidation of all corroles in CH(2)Cl(2), but this was not the case in the other three solvents, where either monomers or dimers were formed upon oxidation depending upon the solvent Gutmann donor number and the number or location of aryl substituents on the macrocycle. The half-wave potentials were analyzed as a function of the number of aryl substituents on the macrocycle as well as the concentration of added pyridine to PhCN solutions of the compound, and these data were combined with data from the spectroelectrochemistry experiments to determine the stoichiometry of the species actually in solution after the first oxidation or first reduction of each compound. The results of these experiments indicate that reduction of the bispyridine adduct (Cor)Co(III)(py)(2) proceeds via the monopyridine complex (Cor)Co(III)(py) to give in each case the unligated cobalt(II) corrole [(Cor)Co(II)](-). In contrast, pyridine remains coordinated after electrooxidation, and the final product was characterized as [(Cor)Co(III)(py)(2)](+). 相似文献
48.
PHOTOSENSITIZATION OF MELANINS: A COMPARATIVE STUDY 总被引:3,自引:0,他引:3
Abstract— Measurements of photosensitized free-radical production and oxygen consumption have been made in several melanin systems. The melanins studied were cysteinyldopa melanin (a model for pheomelanin), natural pheomelanins extracted from red hair and from red chicken feathers, and eumelanin extracted from bovine eyes. Rose Bengal was used as photosensitizer. A significant enhancement in the rates of free radical production and oxygen consumption was found in all systems when sensitizer was present. The largest effects were found with cysteinyldopa melanin and effects on pheomelanins were shown to be greater (by factors of4–6) than on eumelanins. 相似文献
49.
We prove that the-optimal solutions of convex optimization problems are Lipschitz continuous with respect to data perturbations when these are measured in terms of the epi-distance. A similar property is obtained for the distance between the level sets of extended real valued functions. We also show that these properties imply that the-subgradient mapping is Lipschitz continuous.Research supported in part by the National Science Foundation and the Air Force Office of Scientific Research. 相似文献
50.
Photodegradation of Polychlorinated Dibenzo-p-dioxins in Liquid Samples by Near UV Light Irradiation
Photodegradation of 1,2,3,4-tetrachlorodibenzo-p-dioxin (1,2,3,4-TCDD) in hexane solution was studied under controlled near-UV light exposure in the spectral region from 325 to 269 nm. GC-MS was used to detect the amount of unreacted dioxin and to characterize the relevant degradation products. Irradiation experiments carried out at a constant light energy (700 mJ) showed that the percentage of 1,2,3,4-TCDD left in the solution after irradiation changed from about 55 to 75%, with a minimum of 55% at 310 nm. Further irradiation experiments carried out at two wavelengths, namely 310 and 269 nm, and light energy ranging from 0 to 4000 mJ, showed that the photodegradation reaction of the TCDD always followed a pseudo-first-order kinetic, with a rate constant of 8 × 10−4and 5 × 10−4mJ−1, respectively. These experiments also showed that trichloro- and dichloro-dibenzo-p-dioxins were produced with less than 15% of the initial quantity of TCDD, leading to the conclusion that the dechlorination process is a minor photolysis pathway. 相似文献