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131.
Monomeres [(CH3)3Si]2NBeN[Si(CH3)3]2 (I) entsteht in 68% Ausb. bei der Reaktion von BeCl2-Ätherat mit NaN[Si(CH3)3]2. Eigenschaften, IR-, Raman- und1H-NMR-Spektren sprechen für einen NBeN-Winkel von 180°. Die SiN- und BeN-Valenzkraftkonstanten werden zu 3,40 bzw. 2,96 mdyn/Å errechnet.Monomeric I has been prepared (yield 68%) by the reaction of BeCl2 with NaN[Si(CH3)3]2 in ether. Properties, infrared, raman and1H-NMR-spectra support a NBeN angle of 180°. SiN and BeN force constants were calculated to be 3,40 and 2,96 mdyn/Å, respectively.
9. Mitt. über silylsubstituierte Metallamide; 8. Mitt.:H. Bürger, W. Sawodny undU. Wannagat, J. Organometall. Chem.2, 113, (1965). 相似文献
9. Mitt. über silylsubstituierte Metallamide; 8. Mitt.:H. Bürger, W. Sawodny undU. Wannagat, J. Organometall. Chem.2, 113, (1965). 相似文献
132.
Simple and sensitive spectrophotometric methods for the assay of retinol have been presented. The first method was based on the reaction of retinol with iodine to give a molecular charge-transfer complex, the retinol acting as n-donor and iodine as -electron acceptor. The second method depends on the formation of a highly coloured stable radical anion between retinol and 7,7,8,8-tetracyanoquinodimethane (TCNQ as a -electron acceptor. The molecular ratios of the reactants in the complexes have been established and the experimental conditions leading to maximum charge-transfer bands were also studied. Beer's law is obeyed over the retinol concentration range 2.5–26 µg/ml. The proposed procedures have been applied successfully to the analysis of drug formulation. The average recovery and average standard deviation was 99.99 ±1.13% with retinol-iodine and 100.001 ± 1.31% with retinol-TCNQ. A kinetic study was performed by heating retinol at 50°C for different periods of time, the result obtained by plotting log c against time indicates that thermal decomposition of retinol is of first order. The results obtained by both methods were in good agreement with those obtained by the official method. The developed procedures were found to be simple, accurate and precise and can be used for the determination of retinol in presence of its degradation products. 相似文献
133.
M. M. Ibrahim M. M. Wakkad E. Kh. Shokr H. A. Abd-El-Ghani 《Journal of Thermal Analysis and Calorimetry》1991,37(4):813-827
The thermal diffusivities, specific heats and thermal conductivities of the binary compositions Sb40Te60 and Sb40Se60 and the ternary composition Sb40Te30Se30 were measured in the range 320 to 500 K. It was found that the environmental temperature, the content of Se in the composition and the conditions of measurements are decisive factors greatly influencing both the values and the behaviour ot the thermal parameters, and the mechanisms of thermal transport. Although the tested compositions exhibit semiconducting behaviour, the free charge carrier component of the thermal conductivity was so small as to be negligible. Thus, it could be concluded that the observed thermal conductivity is attributable to both photon and phonon mechanisms.
Zusammenfassung Im Temperaturbereich 320–500 K wurde das Temperaturleitvermögen, die spezifische Wärme und die Wärmeleitfähigkeit der binären Kompositionen Sb40Te60 bzw. Sb40Se60 und der ternären Komposition Sb40Te30Se30 untersucht. Man fand, daß die Umgebungstemperatur, der Se-Gehalt der Kompositionen und die Meßbedingungen entscheidende Faktoren sind, welche sowohl Wert als auch Verhalten der thermischen Parameter, weiterhin den Mechanismus des Wärmetransportes beeinflussen. Obwohl die untersuchten Kompositionen Halbleiterverhalten zeigten, war die freie Ladungsträgerkomponente der Wärmeleitfähigkeit so gering, daß sie vernachlässigt werden konnte. Somit konnte darauf geschlossen werden, daß die beobachtete Wärmeleitfähigkeit sowohl Photonen- als auch Phononenmechanismen zugeschrieben werden kann.相似文献
134.
Thierry Boulanger Christine Evrard Daniel P. Vercauteren Guy Evrard François Durant 《Journal of chemical crystallography》1991,21(3):287-295
The crystal structures ofp-methoxyphenyl-3-triazolo [4,3-a] isoquinoline (SR95926),p-methoxyphenyl-3-triazolophtalazine (CMW1842), andp-methoxyphenyl-3-N-dimethoxyethylamino-6-triazolophtalazine (L16317) have been solved by direct methods from single-crystal X-ray diffraction data, and refined by full-matrix least squares. SR95926: monoclinic,P21/n,a=20.950(3),b=6.769(1),c=9.465(2) Å,=100.90(1)°. CMW1842: triclinic,P¯1,a=8.784(1),b=9.160(4),c=8.555(1) Å,=99.10(2),=93.90(1), =106.77(1)°. L16317: monoclinic,P21/n,a=20.124(3),b=9.586(1),c=10.788(1) Å,=91.91(1)°. FinalR factors are 0.034, 0.037, and 0.053, respectively. Experimental geometries were used to perform STO-3Gab initio molecular-orbital calculations. A relationship between the electronic pattern within the molecules and the affinity of the benzodiazepine receptor sites is pointed out. 相似文献
135.
The problem of computing the dimension of spaces of splines whose elements are piecewise polynomials of degreed withr continuous derivatives globally has attracted a great deal of attention recently. We contribute to this theory by obtaining dimension formulae for certain spaces of super splines, including the case where varying amounts of additional smoothness is enforced at each vertex. We also explicitly construct minimally supported bases for the spaces. The main tool is the Bernstein-Bézier method.Communicated by Klaus Höllig. 相似文献
136.
Hesham Ibrahim Saleh 《中国化学会会志》2002,49(3):341-348
The reactions between strontium and iron nitrates have been studied in an open atmosphere system using three different molar ratios, 1:1 (I), 1:2 (II) and 2:1 (III) at different temperatures as pointed out from the DTA data. The reaction mechanism was discussed based on the chemical composition characterized by means of thermal analysis, X‐ray diffraction patterns, infrared spectra and magnetic susceptibility. It was found that the reaction products depend on both temperature of reaction and the ratio between reactants. The reaction products were found to be composed of a variety of iron compounds that possess different valences: SrFeO2.86, SrFeO2.97, SrFe2O4, SrFe12O19, Sr2Fe2O5 and Sr7Fe10O22 in addition to some accessory reaction products namely α‐Fe2O3 and FeO(OH). 相似文献
137.
Yousry M. Issa Hosny Ibrahim Adel F. Shoukry Sabry K. Mohamed 《Mikrochimica acta》1995,118(3-4):257-263
Ion-association complexes of antazoline HCl [I], hydralazine HCl [II], amiloride HCl [III] and quinine sulphate [IV] with [Co(SCN)4]2– and [Co(NO2)6]3– were precipitated and the excess unreacted cobalt complex was determined. A new method using atomic emission and atomic absorption spectrometry for the determination of the above drugs in pure solutions and pharmaceutical preparations is given. The drugs can be determined in the ranges 0.3–3.0, 0.19–1.96, 0.3–3.0, and 0.78–7.82 mg/25 ml solutions of I, II, III, and IV, respectively, with mean relative standard deviations of 0.65–2.03 % and recovery values of 95.76–101.2% indicating high precision and accuracy. 相似文献
138.
Thamyongkit P Speckbacher M Diers JR Kee HL Kirmaier C Holten D Bocian DF Lindsey JS 《The Journal of organic chemistry》2004,69(11):3700-3710
The incorporation of symmetrically branched tridecyl ("swallowtail") substituents at the meso positions of porphyrins results in highly soluble building blocks. Synthetic routes have been investigated to obtain porphyrin building blocks bearing 1-4 swallowtail groups. Porphyrin dyads have been synthesized in which the zinc or free base (Fb) porphyrins are joined by a 4,4'-diphenylethyne linker and bear swallowtail (or n-pentyl) groups at the nonlinking meso positions. The swallowtail-substituted Zn(2)- and ZnFb-dyads are readily soluble in common organic solvents. Static absorption and fluorescence spectra and electrochemical data show that the presence of the swallowtail groups slightly raises the energy level of the filled a(2u)(pi) HOMO. EPR studies of the pi-cation radicals of the swallowtail porphyrins indicate that the torsional angle between the proton on the alkyl carbon and p-orbital on the meso carbon of the porphyrin is different from that of a porphyrin bearing linear pentyl groups. Regardless, the swallowtail substituents do not significantly affect the photophysical properties of the porphyrins or the electronic interactions between the porphyrins in the dyads. In particular, time-resolved spectroscopic studies indicate that facile excited-state energy transfer occurs in the ZnFb dyad, and EPR studies of the monocation radical of the Zn(2)-dyad show that interporphyrin ground-state hole transfer is rapid. 相似文献
139.
Todd B. Vinzant Christine I. Ehrman William S. Adney Steven R. Thomas Michael E. Himmel 《Applied biochemistry and biotechnology》1997,62(1):99-104
A series of correlations was made between the performance of 15 wood species in simultaneous saccharification and fermentation (SSF) and their respective chemical compositions. A compelling inverse trend (p < 0.001) was demonstrated between the percent conversion of glucan to ethanol during SSF and the Klason lignin content of the wood samples before dilute acid pretreatment. No significant relationships were found between the glucan, xylan, and ash compositions of the native wood samples and ethanol yield. This observation is unique and provides a convenient predictor of biomass conversion efficiency. 相似文献
140.
Glasses of the composition XNa2O · 4Al2O3 (96-X) B2O3 (mole%) where X = 10, 20, 30 to which 0.03 g V2O5 per 100 g glass was added, were prepared by normal melting. Their absorption characteristics together with the corresponding V-free base glasses were determined before and after gamma irradiation. The characteristic spectra of the unirradiated glasses show absorption bands at 315, 470, 560–580, 610–650, 700–870, and 860–1000 nm, indicating the presence of vanadium ions in more than one oxidation state, viz, V5+, V4+, and V3+. Gamma irradation of V-containing glasses causes the formation of color centers in the glass matrices, with absorption bands at 330, 500, and 610 nm, and photoreduced [V3+] and [V2+] ions with absorption bands at 350–355 and 530–570 and 520 nm, respectively. Photoreduced [V4+] may also be formed, giving rise to absorptions at 690–700 and 750–800 nm. The induced vanadium ions are found to absorb at shorter wavelengths than the intrinsic ones. An explanation based on the difference in the field energy of the two states is given. 相似文献