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181.
The Michael-additions of aliphatic, alicyclic, and arylsubstituted nitroolefins and enamines lead to γ-nitroketones 3 in good chemical and excellent (> 90%) diastereomeric yields (see Table 1). The known threo-configuration of one type of adducts 3 (entries 8, 10, and 11 of Table 1) can be arrived at by assuming the approach 8 of the Michael-acceptor and -donor; the reaction follows a topological rule, which is formulated and which is applicable to such diverse reactions as the diene synthesis, cyclopropanations, carbonyl olefinations and methylenations, aldol- and nitroaldol-type additions, as well as additions of lithium, boron, and chromium derivatives to aldehydes (see 9 , 10 , 11 , and Table 2). 相似文献
182.
The lipidic cubic phase can be characterized as a curved bilayer forming a three-dimensional, crystallographical, well-ordered structure that is interwoven by aqueous channels. It provides a stable, well-organized environment in which diffusion of both water-soluble and lipid-soluble compounds can take place. Cubic phases based on monoacylglycerols form readily and attract our interest due to their ability to incorporate and stabilize proteins. Their lyotropic and thermotropic phase behaviour has been thoroughly investigated. At hydration over 20%, lipidic cubic phases Ia3d and Pn3m are formed. The latter is stable in the presence of excess water, which is important when the cubic phase is considered as an electrode-modifying material. Due to high viscosity, the cubic phases can be simply smeared over solid substrates such as electrodes and used to host enzymes and synthetic catalysts, leading to new types of catalytically active modified electrodes as shown for the determination of cholesterol, CO(2), or oxygen. The efficiency of transport of small hydrophilic molecules within the film can be determined by voltametry using two types of electrodes: a normal-size electrode working in the linear diffusion regime, and an ultramicroelectrode working under spherical diffusion conditions. This allows determining both the concentration and diffusion coefficient of the electrochemically active probe in the cubic phase. The monoolein-based cubic phase matrices are useful for immobilizing enzymes on the electrode surface (e.g., laccases from Trametes sp. and Rhus vernicifera were employed for monitoring dioxygen). The electronic contact between the electrode and the enzyme was maintained using suitable electroactive probes. 相似文献
183.
An extraction-AAS method of determination of Co, Ni, and Mn in metallurgical copper materials containing considerable amounts ofCu, Fe, Pb, Zn, and Al has been developed. Good selectivity of group separation of Co, Ni, and Mn has been achieved by (a) the use of tetrabutylammonium bromide to improve extractability of HTTA complexes by ion-pair formation, and (b) the masking of major elements with sodium thiosulphate and sulphosalicylic acid. The extracts are stable for at least 3 weeks. 相似文献
184.
In neutral medium, picric acid (PA) reacts with chlorpromazine (CPM) hydrochloride with the formation of an orange compound, sparingly soluble in water, of molar ratio PA:CPM = 1:1. The compound is thermally stable up to a temperature of about 200 degrees C. The m.p. (178 degrees C) can be used for identification of picric acid as well as of chlorpromazine hydrochloride. Chlorpromazine picrate is extracted quantitatively with benzene, and the extract can be used for colorimetric determination of chlorpromazine hydrochloride. Beer's law is obeyed in the CPM concentration range 10-60 mug/ml. 相似文献
185.
The fragmentation patterns of the thioacyl derivatives of 2-aminothiazole and 2-aminobenzothiazole and of their ‘fixed structure’ imino and amino tautomeric forms give evidence of the predominance of the imino tautomer in the molecular ions of the trifluorothioacetyl compounds. On the other hand, the M+˙ ions of the thioacetyl and thiobenzoyl derivatives are mainly the amino tautomers. A rearrangement with elimination of RCN and formation of the 2-thiazolothione (2-benzothiazolothione) ion is characteristic for ail the compounds investigated. Additional evidence for the interpretation of the main fragmentation paths is provided by the mass spectra of the N-trideuteromethyl and N-deuterated derivatives, high-resolution mass spectrometry being used to determine the elemental composition of some selected peaks. 相似文献
186.
Biliński B 《Journal of colloid and interface science》2000,226(1):105-111
A model for the steady laminar flow of an incompressible fluid through a deformable gel-coated channel with slowly varying tapered shape is presented. Previous work has shown that the flow rate through such a channel is less than that which would be expected from the Hagen-Poiseuille equation (1973, J. Lahav, N. Eliezer, and A. Silberberg, Biorheology 10, 595; 1979, P. Krindel and A. Silberberg, J. Colloid Interface Sci. 71, 39). Krindel and Silberberg also observed the onset of turbulent flow at lower rates than would normally be expected; they attributed these phenomena to a turbulent boundary layer near the channel walls. Our analysis shows that the rate reduction is in fact due to kinetic energy effects related to the converging flowlines. A model to describe this rate reduction is presented and is shown to agree well with experimental results, successfully predicting the observed flow rate reduction over Reynolds numbers ranging from 1 to 1000. Copyright 2000 Academic Press. 相似文献
187.
Ali Jabalameli Andrzej Nowek Richard H. Sullivan Jerzy Leszczyński 《Structural chemistry》1997,8(4):245-256
Ab initio studies (LCAO-MO method) on conformers of three seleno derivatives of the biuret molecules diselenobiuret [I], selenobiuret [II], and selenothiobiuret [III] were carried out at the Hartree-Fock (HF) and MP2 levels. The molecular geometries of these species were fully optimized at the HF level and characterized by analysis of the harmonic vibrational frequencies using a split-valence triple-zeta basis set augmented by a set ofd polarization functions on heavy atoms andp polarization functions on hydrogen atoms [TZP(d, p)]. The total energies of the HF-optimized structures were calculated at the MP2 (frozen core) level using a larger TZP (2df, 2pd) basis set. The potential energy searches revealed a total of 11 minimum-energy conformers (assigned astrans-trans, trans-cis, cis-trans, andcis-cis) and seven transition-state species for the title molecules. The two predicted conformers for diselenobiuret (Ia=trans-trans andIc=cis-cis) are characterized byC
2 and the third byC
s symmetry. For selenothiobiuret two forms (IIIa=trans-trans andIIId=cis-cis) possessC
1 and two (IIIb=trans-cis andIIIc=cis-trans) possessC
s symmetries, respectively. For selenobiuret, four formsIIa=trans-trans (C1),IIb=trans-cis (C
s),IIc=cis-trans (C
1), andIId=cis-cis (C1), were obtained as a result of gradient optimization. Comparison of the relative energies for the considered species indicated that thecis-trans forms are the most stable conformations for all three systems at both the HF and MP2 levels of theory. 相似文献
188.
The measurement of the isotope-exchange reaction between U/IV/ in the organic phase and U/III/ in the aqueous phase in the extraction systems: 7-8M HCl—5–40% TBP /aromatic diluent or CCL4/ were made. The high rate of exchange with the rate constant >102M–1min–1 was observed. 相似文献
189.
Lewiński J Dranka M Kraszewska I Sliwiński W Justyniak I 《Chemical communications (Cambridge, England)》2005,(39):4935-4937
The first magnesium and zinc alkyls derived from N-(iso-propyl)-pyrrolylaldimine have been synthesised and structurally characterised: both tBuM(N,N')-type compounds exist as three-coordinate monomers in benzene solution, but in the solid state the magnesium complex is a centrosymmetric dimer with Mg2(mu-N)2 bridges, whereas the zinc complex is a Zn...pi bonded dimer with a pi-coordinated pyrrole unit. 相似文献
190.
Microcalorimetry and measurement of culture turbidity using a Bioscreen C Analyzer System were applied to study the toxic effect of phenanthrene on Cunninghamella elegans IM 1785/21Gp spore germination. The results of C. elegans spore incubation in Bioscreen C microbiology reader showed the inhibition of spore germination by 70% (with 25 mg l−1 of phenanthrene) and total inhibition of the fungus growth with a higher content of the xenobiotic (50-100 mg l−1). The microcalorimetric technique showed to be useful for the estimation of metabolic activity of C. elegans spores in growth medium up to xenobiotic concentrations of 90 mg l−1. These data corresponded with the microscopic observations. The obtained results showed that the microcalorimetry method could be a valuable supplement in the study on the mechanism of PAHs detoxification by fungi. 相似文献