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981.
A formal total synthesis of cephalotaxine (CET), the parent structure of antileukemia Cephalotaxus alkaloids, was achieved through a novel synthesis of the pentacyclic amino enone 4 by a rapid annulation of readily available beta-(3,4-methylenedioxy)phenethylamine (2), delta-valerolactone, and bromoacetone. 相似文献
982.
Differential thermal analysis and thermogravimetry were used to evaluate the effect of some additives, such as CaSO4, CaCl2 and silica fume amorphous silica from ferrosilicon synthesis on the mechanism and kinetics of reactions occurring in fly
ash-Ca(OH)2 system. The accelerating role of these additives was demonstrated from the data relating to Ca(OH)2 consumption in hydrated pastes, determined by TG measurements.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
983.
Solid-state synthesis of a conducting polythiophene via an unprecedented heterocyclic coupling reaction 总被引:2,自引:0,他引:2
Meng H Perepichka DF Bendikov M Wudl F Pan GZ Yu W Dong W Brown S 《Journal of the American Chemical Society》2003,125(49):15151-15162
Prolonged storage ( approximately 2 years) or gentle heating (50-80 degrees C) of crystalline 2,5-dibromo-3,4-ethylenedioxythiophene (DBEDOT) affords a highly conducting, bromine-doped poly(3,4-ethylenedioxythiophene) (PEDOT), as confirmed by solid-state NMR, FTIR, CV, and vis-NIR spectroscopies. The novel solid-state polymerization (SSP) does not occur for 2,5-dichloro-3,4-ethylenedioxythiophene (DCEDOT), and requires a much higher temperature (>130 degrees C) for 2,5-diiodo-3,4-ethylenedioxythiophene (DIEDOT). X-ray structural analysis of the above dihalothiophenes reveals short Hal.Hal distances between adjacent molecules in DBEDOT and DIEDOT, but not in DCEDOT. The polymerization may also occur in the melt but is significantly slower and leads to poorly conductive material. Detailed studies of the reaction were performed using ESR, DSC, microscopy, and gravimetric analyses. SSP starts on crystal defect sites; it is exothermic by 14 kcal/mol and requires activation energy of approximately 26 kcal/mol (for DBEDOT). The temperature dependence of the conductivity of SSP-PEDOT (sigma(rt) = 20-80 S/cm) reveals a slight thermal activation. It can be further increased by a factor of 2 by doping with iodine. Using this approach, thin films of PEDOT with conductivity as high as 20 S/cm were fabricated on insulating flexible plastic surfaces. 相似文献
984.
This study presented results on reduction of alumina
supported chromium and platinum–chromium catalysts using temperature
programmed reduction method (TPR). It has been shown that catalysts after
earlier oxidation step but without calcinations one undergo reduction in lower
temperature in comparison to calcined only catalysts. Moreover, addition platinum
to Cr/Al2O3 catalysts also caused
decrease of reduction temperature. It has been observed that over the examined
catalysts oxidation CO to CO2 and reduction CO to CH4
occurs. However, on Pt–Cr catalysts both reactions proceed at lower
temperature compare to Cr catalysts. 相似文献
985.
Summary The optimization of the heating conditions, absorbance profiles, the influence of different matrix composition and the effect of delivering different volumes of urine samples were examined in order to evaluate the use of simple aqueous standards for the determination of cadmium in urine samples, using atomic absorption spectrometry with electrothermal atomization and the L'vov platform. Three reference materials were analysed for cadmium by the proposed method. The results indicate that a direct and accurate determination of urine cadmium is possible by using simple aqueous calibration standards, independently of the composition of the urine matrix. 相似文献
986.
E. Kuzmann Z. Homonnay A. Vértes I. Halász J. Bánkuti I. Kirschner 《Journal of Radioanalytical and Nuclear Chemistry》1989,135(5):373-380
151Eu,119Sn and57Fe Mössbauer spectroscopy was used to study high Tc superconductors. Mössbauer spectra of Sn substituted EuBa2Cu3O7–y, YBa2Cu3O7–y and TlBaCaCuO4.5+y as well as of Fe Substituted TlBaCaCuO4.5+y were compared. The Sn and Fe ions replace the regular Cu positions in the YBa2Cu3O7–y and in TlBaCaCuO4.5+y materials, fespectively, while the localization of tin atoms in both the119Sn doped EuBa2Cu3O7–y and TlBaCaCuO4.5+y superconductors is different from that of previous cases. Up to our knowledge, this is the first publication on a Mössbauer study of a Tl-containing superconductor. 相似文献
987.
The strong affinity of natural ionic polysaccharides for certain metal ions is exploited in the design of a new class of voltammetric sensing devices. In particular, carbon-paste electrodes containing pectic and alginic acids are used for the nonelectrolytic collection and subsequent voltammetric determination of copper and lead, respectively. Cyclic and differential pulse voltammetry are used to quantify the accumulated ions. The response is characterized with respect to modifier loading, preconcentration period, metal concentration, reproducibility, possible interferences and other variables. Titrimetric experiments illustrate the potential of polysaccharide electrodes for speciation work. Preliminary data are also given for analogous measurements of copper at heparin-modified electrodes. Detection limits are 1 mug/ml and the relative standard deviation is 4.8%. 相似文献
988.
Z. I. Pavlenko L. A. Badovskaya V. G. Kul'nevich 《Chemistry of Heterocyclic Compounds》1977,13(12):1283-1285
A product of addition of diazomethane to the double bond of crotonolactone — 1-pyrazolinolactone — was obtained, and its isomerization to 2-pyrazolino-lactone in dry chloroform in the presence of triethylamine was studied. The structures of the compounds were confirmed by elementary analysis and the IR, UV, and PMR spectra.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1610–1612, December, 1977. 相似文献
989.
A new photoionization detector for gas chromatography 总被引:1,自引:0,他引:1
Summary A new photoionization detector for gas chromatography is discribed. The source of vacuum ultra-violet (VUV) radiation is separated from the ionization chamber by a window and thus the ionization chamber may be run at atmospheric pressure using an intense source of ionizing radiation. The operation consequently is improved and considerably simplified. Except for a ten times reduction in linearity, the performance characteristics of the detector are comparable to those of the flame ionization detector. Filtration of the VUV radiation allows the selectivity to be varied without affecting the dynamic properties of the detector.Z. ternberg, N. Ostoji, Yug. Pat. Appl. 相似文献
990.
Survila A. Mockus Z. Kanapeckaitė S. Jasulaitienė V. 《Russian Journal of Electrochemistry》2004,40(8):855-859
Voltammetry and x-ray photoelectron spectroscopy data show micromolar amounts of halides to noticeably affect co-deposition of copper and tin from acidic sulfate solutions containing polyether Laprol 2402C as the surface-active substance. The reduction of Cu(II) slows down and that of Sn(II) accelerates in the series Cl– < Br– < I–. Compounds on the surface of bronze coatings are oxides of Cu(I) and Sn(II) and halides of Cu(I). 相似文献