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141.
An electrochemical method for the determination of the ionophores monensin and lasalocid was developed, based on the polarization of an agar gel/nitrobenzene electrolyte interface. The measured current corresponding to the facilitated ion transfer across this interface is directly proportional to the concentration of an ionophore dissolved in the organic phase. Using cyclic voltammetry in a three-electrode system the detection limit for both ionophores is about 3 × 10?5 M. 相似文献
142.
D. M. Petrović-Djakov J. M. Filipović Lj. P. Vrhovac J. S. Veličković 《Journal of Thermal Analysis and Calorimetry》1996,46(6):1681-1686
The kinetics of the AIBN-initiated free radical bulk polymerization of fiveo-alkylphenyl methacrylates was studied by means of DSC in the temperature range 353–373 K, and the enthalpy of polymerization, the overall reaction rate constant and the activation energy were determined. The results were compared with those published recently on correspondingp-alkylaryl methacrylates. All measured reaction rate constants were found to increase with increasing temperature and to decrease with increasingo-alkyl substituent mass and size. It was shown thato-substituents influence the rates of polymerization to a greater extent thanp-substituents. At about 373 K, all differences in rate, most probably resulting from steric hindrance caused by the alkyl groups, disappear in both series, a phenomenon earlier observed for dimethyl phenyl methacrylates.This work was supported by the Ministry of Science of the Republic of Serbia. 相似文献
143.
Zusammenfassung Die Reaktion von 1-Nitroso-2-naphthol mit 1-und 2-Naphthol sowie die Reaktion von 2-Nitroso-1-naphthol mit 2-Naphthol in Äthanol und in Äther bei Anwesenheit von HNO3 gibt 5H-Dibenzo[a,j]phenoxazon-(5) (I), 5H-Dibenzo[a,j]phenoxazon-(5)-14-oxid (II), 5H-Dibenzo[a,h]phenoxazon-(5) (III) sowie 5H-Dibenzo[a,h]phenoxazon-(5)-14-oxid (IV). Es wurde ein Reaktionsmechanismus vorgeschlagen und die Konstitution der hergestellten Verbindungen spektrophotometrisch und potentiometrisch bestimmt.
Mit 4 Abbildungen 相似文献
The reaction of 1-nitroso-2-naphthol with 2-and 2-naphthol and the reaction of 2-nitroso-1-naphthol with 2-naphthol in ethanol or ether in the presence of nitric acid have been studied. The main reaction products isolated were the dibenzophenoxazones I–IV. The reaction mechanism for their formation is proposed.
Mit 4 Abbildungen 相似文献
144.
P. Baláž K. Tkáčová E. G. Avvakumov 《Journal of Thermal Analysis and Calorimetry》1989,35(5):1325-1330
Experimental results on the influence of preliminary mechanical activation on the thermal decomposition of chalcopyrite are presented and discussed. The following experimental facts were found:
The intensive grinding of chalcopyrite leads to a shift in temperature of the endothermic DTA peak and brings about a decrease in the activation energy of the thermal decomposition of CuFeS2. These results can be attributed to the mechanically produced alterations in structure and surface properties of the mineral. 相似文献
1. | a decrease in the temperature of the endothermic DTA peak of-CuFeS2 from 821 K for a non-activated sample to 763 K for an optimally activated one; |
2. | a decrease in the apparent activation energy of the thermal decomposition of CuFeS2 from 238 kJ mol–1 for a non-activated sample to 72 kJ mol–1 for an optimally activated sample. |
145.
I. Belič T. Kastelic-Suhadolc R. Kavčič J. Marsel V. Kramer B. Kralj 《Tetrahedron》1976,32(24):3045-3049
The oxidation of higher aliphatic ethers with oxygen at 50° yields two peroxides as the main oxidation products for each ether, namely a dihydroperoxy-dialkyl ether and a dihydroperoxy-dialkyl peroxide. The mass spectra of these compounds are recorded and the main fragmentation pattern is discussed. 相似文献
146.
The perfect matching vector and forcing and the Kekulé-vector of cata-benzenoids are defined. Two theorems are given which
set the sufficient and necessary conditions for HKZ-vector (Harary et al. J Math Chem 6:295, 1991) and Kekulé-vector in cata-benzenoids.
Additional two theorems are obtained which give sharp bounds for the modules of HKZ- and Kekulé vectors.
Dedicated to Professor Tadeusz Marek Krygowski on the happy occasion of his 70th birthday. 相似文献
147.
Vanadium determination in rat tissues and biological reference materials by neutron activation analysis 总被引:2,自引:0,他引:2
J. Kučera M. Šimková J. Lener A. Mravcová L. Kinova I. Penev 《Journal of Radioanalytical and Nuclear Chemistry》1990,141(1):49-59
Vanadium was determined in adrenal gland, brain, ileum, kidney, liver, lung, muscle, myocard, skin, spleen, gonads, thyroid, and tibia of rats fed with normal diet and exposed to high vanadium doses in drinking water. Both radiochemical neutron activation analysis (RNAA) and instrumental neutron activation analysis (INAA) were employed. The RNAA procedure consisted in dry ashing samples prior to irradiation and vanadium separation from the irradiated samples by extraction with N-benzoyl-N-phenylhydroxylamine (BPHA) in toluene from 5 mol·l–1 HCl. Vanadium accumulation as a function of a type of the tissue, exposure time, sex of rats, and administration of V(IV) or V(V) was studied. For quality assurance purposes, the biological (standard) reference materials NBS SRM 1571 Orchard Leaves, NBS SRM 1577a Bovine Liver, IAEA H-4 Animal muscle, and Bowen's Kale were analyzed.Presented at the 2nd Balkan Conference on Activation Analysis and Nuclear-Related Analytical Techniques, Bled, 4–6 October, 1989. 相似文献
148.
V. Spěváček 《Tetrahedron》1973,29(15):2285-2291
Reaction mechanism of halogen exchange between arylhalogenide and halogenide anion is studied in a case when the aromatic core is inactivated with respect to the SNAr substitution by other substituents. The exchange of iodine between o-iodobenzoic acid and 131I labelled NaI serves as a modelling reaction. The reaction was found to proceed heterogeneously on a glass surface. In the case of a rapid course of the surface reaction the reaction mechanism is more complicated and the equation derived by McKay cannot be applied for expressing the time dependence of the degree of isotopic exchange. Reaction mechanism was proposed for this reaction and compared with experimental data. 相似文献
149.
Organophosphorus pesticides parathion, chlorpyrifos, and malathion inhibit the enzyme acetylcholinesterase (AChE; EC 3.1.1.7)
via phosphorylation of its active site. AChE reactivators and anticholinergics are compounds used as antidotes in the case of
intoxication by these AChE inhibitors. In this work, chlorpyrifos, a representative member of this pesticide family, was used
to inhibit the AChE activity of rat brain. The effect of twenty-one structurally different AChE reactivators was tested in vitro and subsequently, the relationship between their chemical structure and biological activity was outlined. 相似文献
150.
P. Šimon Marta Fratričová P. Schwarzer H.-W. Wilde 《Journal of Thermal Analysis and Calorimetry》2006,84(3):679-692
Degradation
of poly(ester-urethanes), poly(ether-urethanes) and poly(acrylic-urethanes),
as a base for automotive paintings in interior applications, has been studied
by DSC. The samples were clearcoat and black-pigmented paints, unstabilized
and stabilized with HALS Tinuvin 292, UV absorber Tinuvin 1130 and antioxidant
Hostanox O3, exposed to weathering in Xenotest and in Arizona desert. From
the dependences of oxidation onset temperature on the heating rate, the kinetic
parameters enabling to calculate the oxidation induction time for a chosen
temperature have been obtained. From the values of oxidation induction time,
the protection factors of the additives and the residual stability of the
polymer after an ageing stress has been evaluated. It has been shown that
the equivalence between the two methods of weathering depends on the polymer
composition. A new criterion for the evaluation of synergism/antagonism of
additives in the stabilizing mixture has been proposed. 相似文献