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排序方式: 共有145条查询结果,搜索用时 93 毫秒
1.
Grażyna Janowska Teresa Mikołajczyk Dorota Wołowska-Czapnik M. Boguń 《Journal of Thermal Analysis and Calorimetry》2005,82(1):129-135
The paper discusses the thermal properties of alginate fibres made from alginic acid or sodium alginate and from alginates
substituted with divalent metal ions during the fibre-forming stage. Alginate fibres with an addition of silica nanoparticles
have also been examined. The selection of fibre-forming parameters was intended to obtain the best either sorption or strength
properties depending on the specific fibre application. Thermal curves of the fibres under investigations obtained by under
air atmosphere and differential scanning calorimetry (DSC) under neutral gas atmosphere have been interpreted from the view
of physical and chemical changes in the fibre-forming material. Based on thermogravimetric curves, the fibre thermal stability
indices have been determined. It has been found that the addition of silica nanoparticles exerts a positive influence on the
thermal properties of the examined fibres. 相似文献
2.
3-(Dimethoxyphosphorylmethyl)cyclopent-2-enone was converted into (+/-)-prostaglandin B1 methyl ester in two steps involving regioselective alkylation at C(2) with methyl 7-iodoheptanoate and subsequent Horner-Wittig reaction with dimer of 2-hydroxyheptanal (42% overall yield). The use of (R)- and (S)-2-(tert-butyldimethylsilyloxy)heptanal for the Horner olefination reaction gave, after deprotection of the hydroxy group, the enantiopure forms of the title compound in 28% overall yield. 相似文献
3.
M. Mikoŀajczyk J. Michalski A. Halpern R. Sochaxcka 《Monatshefte für Chemie / Chemical Monthly》1969,100(4):1266-1273
Zusammenfassung An den Modellverbindungen Dialkylchlorthiophosphat (RO)2P(S)Cl (R=Me, Et, n-Pr) und Diphenylchlorthiophosphat (PhO)2P(S)Cl wurde der Austausch Chlorid—Radiochlorid am Thiophosphorylzentrum untersucht. Die bimolekularen Geschwindigkeitskonstanten, die Aktivierungsenergien und Aktivierungsentropien wurden berechnet. Der Einfluß von Substituenten auf bimolekulare Substitutionsreaktionen am vierfach koordinierten Phosphoratom wurde diskutiert.
Mit 3 Abbildungen 相似文献
Chlorine isotopic exchange at phosphorus atoms, I.: Chloridothiophosphates
The chloride—radiochloride ion exchange at the thiophosphoryl centre has been studied using dialkylchloridothiophosphates (RO)2P(S)Cl (R=Me, Et, n-Pr) and diphenylphosphorochloridothionate, (PhO)2P(S)Cl, as model compounds. The bimolecular rate constants, energies and entropies of activation have been calculated. Effects of the substituents in the bimolecular displacement reaction on four-coordinated phosphorus atom have been discussed.
Mit 3 Abbildungen 相似文献
4.
Maj-Urawska M Ziemianek D Mikołajczuk A Mieczkowski J Lewenstam A Hulanicki A Sokalski T 《Analytical and bioanalytical chemistry》2003,376(4):524-526
The properties of the carbonate neutral carrier 4-( n-hexadecyl)-3-nitro-1-trifluoroacetylbenzene were compared with those of a similar carrier, without a nitro group, studied previously. In spite of differences in the Hammett constant of the carbonyl group responsible for interaction with the analyte, the analytical characteristics of both carriers, measured under the same conditions, were comparable. Special care was taken to avoid the presence of an excessive carbon dioxide level in the diffusion layer at the membrane-solution interface. The internal reference solution was prepared without carbonate components; the external solution was protected from contact with atmospheric carbon dioxide. Under such conditions the detection limit of both electrodes was extended to 10(-11 )mol L(-1), and the selectivity towards salicylate, chloride, and acetate was significantly improved. 相似文献
5.
cis- and trans-2-Chloro-2-oxo-4-methyl-1,3,2-dioxaphosphorinans have been obtained by stereospecific reactions of diastereomerically pure 2-methoxy-4-methyl-1,3,2-dioxaphosphorinans or 2-hydrogen-2-oxo-4-methyl-1,3,2-dioxaphosphorinans with chlorine and sulphuryl chloride, respectively. Similarly, the action of the corresponding brominating agents on isomeric phosphites and phosphonates afforded pure cis- and trans-2-bromo-2-oxo-4-methyl-1,3,2-dioxaphosphorinans. It has been shown that halogenolysis proceeds with retention of configuration at the P atom. On the basis of the 1H- and 31P-NMR spectra conformation of the halogenoanhydrides obtained has been discussed briefly.It has been also found that model nucleophilic substitution reactions occur with inversion of configuration at the P atom in the cyclic halogenoanhydrides. 相似文献
6.
Marian Miko?ajczyk Jerzy A. Krysiak Wanda H. Midura Micha?W. Wieczorek Jaros?aw B?aszczyk 《Tetrahedron: Asymmetry》1996,7(12):3513-3520
A general and efficient synthesis of enantiomeric α-chlorovinyl p-tolyl sulfoxides 1 using (+)-(S)C(S)S-α-chloro-α-dimethoxyphosphorylmethyl p-tolyl sulfoxide as a key substrate for the Horner-Wittig reaction with carbonyl compounds is described. The ratio of geometrical isomers of 1 was determined and briefly investigated. The X-ray diffraction structures of (Z)-1-chloro-1-p-tolylsulfinyl-2-phenyl-ethene and (Z)-1-chloro-1-p-tolylsulfinyl-2-(2-thienyl)-ethene are reported. 相似文献
7.
Racemic phosphocarnitine 3 has been synthesized starting from diethyl 3-chloro-2-oxopropanephosphonate 4 in three steps involving reduction of 4 to the corresponding 2-hydroxyphosphonate 5, conversion of the latter to phosphonic acid 6, and final reaction with trimethylamine, affording the trimethylammonium salt of 3. Baker's yeast reduction of 4 and enzymatic kinetic resolution of (+/-)-5 afforded the enantiomerically pure precursors of phosphocarnitine, (R)-(+)-5 and (S)-(-)-5, which were converted to (S)-(-)- and (R)-(+)-phosphocarnitine 3, respectively. 相似文献
8.
Vitamin B12 Phosphate Conjugation and Its Effect on Binding to the Human B12‐Binding Proteins Intrinsic Factor and Haptocorrin 下载免费PDF全文
Keith Ó Proinsias Michał Ociepa Katarzyna Pluta Mikołaj Chromiński Prof. Ebba Nexo Prof. Dorota Gryko 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(24):8282-8289
The binding of vitamin B12 derivatives to human B12 transporter proteins is strongly influenced by the type and site of modification of the cobalamin original structure. We have prepared the first cobalamin derivative modified at the phosphate moiety. The reaction conditions were fully optimized and its limitations examined. The resulting derivatives, particularly those bearing terminal alkyne and azide groups, were isolated and used in copper‐catalyzed alkyne–azide cycloaddition reactions (CuAAC). Their sensitivity towards light revealed their potential as photocleavable molecules. The binding abilities of selected derivatives were examined and compared with cyanocobalamin. The interaction of the alkylated derivatives with haptocorrin was less affected than the interaction with intrinsic factor. Furthermore, the configuration of the phosphate moiety was irrelevant to the binding process. 相似文献
9.
M. Mikołajczyk S. Grzejszczak W. Midura A. Zatorski 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-3):175-178
Abstract The use of organic phosphorus and sulfur compounds in the general synthesis of biologically active functionalized cyclopentenones is presented. 相似文献
10.
Józef Drabowicz Piotr Łyżwa Jan Omelańczuk Marian Mikołajczyk 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1)
Abstract The title compound optically active t-butylphenylphosphine oxide 1 is widely used as a key substrat for the synthesis of other optically active derivatives such as α-hydroxyphosphine oxides, vinylphosphine oxides Till now, it has been obtained by a few rather laborious procedures1 相似文献