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941.
A new aurone, 4,6-dihydroxy-2-[alpha,alpha-(4-hydroxyphenyl)hydroxy]methylene-3(2H)-benzofuranone (2) and two rare metabolites viz. selin-4(15)-en-1beta,11-diol (5) and 5,7-dihydroxy-3-O-beta-D-glucopyranosyl-l' --> 6'glucopyranoside-2-{4-hydroxyphenyl}-4H-benzopyran-4-one (6) in addition to the known protocatechuic acid methyl ester (1), quercitin (3) and gallic acid (4) were isolated from the methanol extract of Diospyros melanoxylon leaves. The structures were elucidated by a combination of chemical and spectroscopic analysis. Interestingly, compound 2 was found to exist in both E- and Z-isomeric forms in a 15:85 ratio. The present isolation of compounds 2 and 5 assumes taxonomic significance as aurones and sesquiterpenes have not yet been reported from the Diospyros genus, consisting of more than 350 identified species. 相似文献
942.
The known cholinesterase inhibitory capability of the Amarylidaceae alkaloid galanthamine prompted preparation of analogs in which the position of the nitrogen within the azepine ring is altered. The analogs 6H-benzofuro[3a,3,2-e,f][1]benzazepine and 6H-benzofuro[3a,3,2-e,f][3]benzazepine were prepared in 19 and 2.5%, respectively, following Kametani and Shimizu approaches, respectively. The aniline derivative 6H-benzofuro[3a,3,2-e,f][1]benzazepine failed to undergo most of the reactions typical for galanthamine. Thus, it neither oxidized to the analogous narwedine, nor epimerized to the analogous epigalanthamine, nor reduced to the lycoramine analog, under the conditions used for galanthamine. 相似文献
943.
Room temperature ionic liquids are found to catalyze efficiently the three component-coupling reactions of aldehydes, amines and homophthalic anhydride under mild and convenient conditions to afford the corresponding cis-isoquinolonic acids in excellent yields with high cis-selectivity. 相似文献
944.
Ritu Bala Raj Pal Sharma Upendra Sharma Valeria Ferretti 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(12):m628-m631
In the title complex salt, tetrakis[hexaamminecobalt(III)] hexachlorocadmate(II) bis[aquatetrachlorothiocyanatocadmate(II)] dichloride dihydrate, the discrete ions, i.e. [Co(NH3)6]3+, Cl−, [CdCl6]4− (located on an inversion centre) and [CdCl4(SCN)(H2O)]3−, together with cocrystallized water molecules, are assembled by means of a network of hydrogen‐bonding interactions. This is the first X‐ray structure determination of a hexaamminecobalt(III) salt with two different complex chlorocadmium anions. 相似文献
945.
Nirmala Ramanujam Michele Follen Mitchell Anita Mahadevan-Jansen Sharon L. Thomson Gregg Staerkel Anais Malpica Thomas Wright Neely Atkinson Rebecca Richards-Kortum 《Photochemistry and photobiology》1996,64(4):720-735
Abstract— A portable fluorimeter was developed and utilized to acquire fluorescence spectra from 381 cervical sites in 95 patients at 337, 380 and 460 nm excitation immediately prior to colposcopy. A multivariate statistical algorithm was used to extract clinically useful information from tissue spectra acquired in vivo. Two full-parameter algorithms were developed using tissue fluorescence emission spectra at all three excitation wavelengths (161 excitation-emission wavelength pairs) for cervical precancer (squamous intraepithelial lesion [SIL]) detection: a screening algorithm that discriminates between SIL and non-SIL with a sensitivity of 82 ± 1.4% and specificity of 68 ± 0.0%, and a diagnostic algorithm that differentiates high-grade SIL from non-high-grade SIL with a sensitivity and specificity of 79 ± 2% and 78 ± 6%, respectively. Multivariate statistical analysis was also employed to reduce the number of fluorescence excitation-emission wavelength pairs needed to redevelop algorithms that demonstrate a minimum decrease in classification accuracy. Two reduced-parameter algorithms that employ fluorescence intensities at only 15 excitation-emission wavelength pairs were developed: the screening algorithm differentiates SIL from non-SIL with a sensitivity of 84 ± 1.5% and specificity of 65 ± 2% and the diagnostic algorithm discriminates high-grade SIL from non-high-grade SIL with a sensitivity and specificity of 78 ± 0.7% and 74 ± 2%, respectively. Both the full-parameter and reduced-parameter screening algorithms discriminate between SIL and non-SIL with a similar specificity (±5%) and a substantially improved sensitivity relative to Pap smear screening. A comparison of the full-parameter and reduced-parameter diagnostic algorithms to colposcopy in expert hands indicates that all three have a very similar sensitivity and specificity for differentiating high-grade SIL from non-high-grade SIL. 相似文献
946.
Anita Fossdal 《Journal of solid state chemistry》2004,177(8):2933-2942
The phase relations in the pseudo-binary system SrO-Fe2O3 have been investigated in air up to 1150°C by means of powder X-ray diffraction and thermal analysis. Sr3Fe2O7−δ, SrFeO3−δ and SrFe12O19 are stable phases in the entire investigated temperature region, whereas Sr2FeO4−δ and Sr4Fe3O10−δ decompose above 930±10°C and 850±25°C, respectively. Sr4Fe6O13±δ is entropy-stabilized relative to SrFeO3−δ and SrFe12O19 above 775±25°C. Extended solid-solution Sr1±xFeO3−δ was demonstrated. On the Fe-deficient side, the extent of solid solubility appeared to decrease gradually with temperature, whereas an abrupt decrease due to formation of Sr4Fe6O13±δ was observed above 775°C on the Sr-deficient side. 相似文献
947.
The stopped-flow measurements on the disappearance of alkaline osmium(VIII) at 402 nm indicated a first-order dependence each in [Os(VIII)] and [HCHO]. The pseudo first-order rate constant kobs ([HCHO] ? [Os(VIII)]) decreased with increasing [OH?]. The ionic strength, however, had no effect on kobs. The rapid scan spectra of the reaction mixture indicated the formation of an inert complex which absorbs at 319 nm. Therefore the rate determining step is considered to involve the bimolecular collision between OsO4(OH) and hydrated formaldehyde. The values of the rate limiting constant k and the equilibrium constant Kha for the formation of the alkoxide ion from the reaction of hydrated formaldehyde with OH? are evaluated. The equilibrium constant Kha, within the experimental limits, is independent of temperature. The pKa value, calculated from Kha, is 13.62 ± 0.05 which is in good agreement with the pKa value 13.27 for formaldehyde. The activation parameters, ΔH? = 40 ± 2 kJ mol?1 and ΔS? = ?51 ± 6 JK?1 mol?1, for the rate limiting constant k are determined. 相似文献
948.
The transmetalation reaction between a sacrificial nanoparticle and more noble metal ions in solution has emerged as a novel method for creating unique hollow and bimetallic nanostructures. In this report, we investigate the possibility of carrying out the transmetalation reaction between hydrophobic silver nanoparticles assembled and constrained at the air-water interface and subphase gold ions. We observe that facile reduction of the subphase gold ions by the sacrificial silver nanoparticles occurs resulting in the formation of elongated gold nanostructures that appear to cross-link the sacrificial silver particles. This transmetalation reaction may be modulated by the insertion of an electrostatic barrier in the form of an ionizable lipid monolayer between the silver nanoparticles and the aqueous gold ions that impacts the gold nanoparticle assembly. Transmetalation reactions between nanoparticles constrained into a close-packed structure and appropriate metal ions could lead to a new strategy for metallic cross-linking of nanoparticles and generation of coatings with promising optoelectonic behavior. 相似文献
949.
John A. Montgomery Sarah D. Clayton Anita T. Shortnacv 《Journal of heterocyclic chemistry》1979,16(1):157-160
An improved procedure for the preparation of 9-β-D -arabinofuranosyl-2-fluoroadenitie (11) utilizing the readily available 2,4,5,6-tetraaminopyrimidine (1) is described; the overall yield based on the arabinosugar was quadrupled. 相似文献
950.
W. U. Malik S. K. Srivastava Raj Pal Singh Satish Kumar 《Journal of Radioanalytical and Nuclear Chemistry》1977,36(2):469-477
The sorption of univalent, bivalent and trivalent ions has been studied on chromium ferrocyanide gel. The studies reveal a
high sorption capacity for Cs+, Tl+, Ag+, Cu2+, Zn2+, Cd2+, Fe3+ and Th4+. The sorption of monovalent cations show purely ion-exchange mechanism while the uptake of bivalent and trivalent cations
is non-equivalent in nature. Single elution of Rb+, Cs+ and Tl+ has been performed from the columns of this exchanger and the recovery is almost complete in all the cases. Cu2+ and Ag+ get completely adsorbed on the gel column and their elution is not possible probably due to the formation of some new solid
phases. Depending on the Kd values of the metal ions, a large number of separations of radiochemical as well as analytical importance can be performed
on the columns of this exchanger material. 相似文献