bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of the temperature curves in non-isothermal adsorption on compacted zeolites
Authors: Kočiřík Milan , Bezus Arkadii G. , Zikánová Arlette , Erashko Irina T. , Dubinin Michail M. , Volushchuk Albert M.
Published: February 2011

An analytical description is presented of the temperature curves describing adsorption on thin zeolite plates. The solution, based on the model of simultaneous mass and heat transport was obtained by linearization of the kinetic equations. A method is proposed for verification of the plausibility of the model and for evaluation of the kinetic data by numerical simulation of the temperature curves.
A theoretical scheme of annulenes aromaticity
Authors: Leška Jaroslav , Loos Dušan
Published: February 2011

An aromaticity scheme for annulenes is developed and applied on set of [6] to [18]annulenes. The dependence of annulenes aromaticity on the ring size, noncoplanarity and strain is considered which factors are in the aromaticity indices HOMAW and HOMAM implicitely included. The decrease in aromaticity index with increasing ring size was modelled for [4n+2] and [4n] annulenes by the functions Δ4n+2(N) and Δ4n(N). Two quantities, κd and νs, as the average measures of noncoplanarity and strain have been defined. Significant correlations of the differences Δx(N) - HOMAW and Δx(N) - HOMAM, which represent the decrease in aromaticity index by noncoplanarity and strain, with a function of the parameters κd and νs, have been obtained. The quantitative results show that not only the [4n]annulenes, but also the large part of the [4n+2]annulenes are antiaromatic, even for the presence of noncoplanarity and strain in the molecules.
Investigation of the products of carbothermal reduction of yttrium oxide by the hydrolysis method
Authors: Hájek Bohumil , Karen Pavel , Brožek Vlastimil
Published: February 2011

For the investigation of the products of reaction of yttrium oxide with carbon mixed in various proportions, the chemical and X-ray diffraction methods of analysis were combined with the gas chromatographic analysis of the mixture of hydrocarbons and hydrogen formed on the sample decomposition with water. The carboreduction of Y2O3 was examined at relatively low temperatures, convenient for obtaining the reaction intermediates in higher yields. At

1 600 °C and pressures of 10-3 Pa the reduction of a mixture of Y2O3 with carbon in a stoichiometric ratio of 1 : 7 yields YC2 in equilibrium with 20% of Y2OC phase. At lower carbon contents (down to the Y2O3 : C ratio of 1 : 2) tha fraction of the Y2OC phase increases up to approximately 30%. In addition to Y2O3, the reaction mixture contains also Y2C, Y2OC and a phase giving propyne on hydrolysis. The presence of traces of C3 hydrocarbons and small amounts of methane in the product of hydrolysis of the carbide sample prepared by the carbothermal reduction of the oxide can be explained in terms of the occurrence of the Y15C19 phase, probably substituted in part by oxygen, and of the Y2OC phase. The results are compared with those obtained previously for the Sc2O3 + C system.
Investigation of the products of reaction of (Sc, Y)2O3 and (Sc, Dy)2O3 mixed crystals with carbon in proportions corresponding to the formation of M15C19 phase
Authors: Hájek Bohumil , Karen Pavel , Brožek Vlastimil
Published: February 2011

Scandium, yttrium, and dysprosium formates were subjected to reaction with carbon in a stoichiometric ratio of M2O3 : C = 1 : (83/15) at 1 650 °C and 1 Pa for 40 h to give products containing typical phases of Sc2OC and Sc15C19, Y2OC and YC2, and Dy2OC and DyC2, respectively (Y2OC and Dy2OC Fm3m, a = 494.7 ± 0.2 and 495.0 ± 0.2 pm, respectively). The mixed scandium-yttrium or scandium-dysprosium carbides prepared under the same conditions did not exhibit diffraction patterns of the M15C19 carbides, and were constituted by mixed dicarbide and mixed oxide-carbide crystals. Yttrium and, to a greater extent, dysprosium are preferentially located in the dicarbide structure, whereas scandium occupies more the oxide-carbide structure. The mixed scandium-dysprosium carbide (Sc0,94Dy0,06)15C19 (P421c, a = 753 ± 1 pm, c = 1 506 ± 3 pm) starts to form at temperatures above the melting temperature of the mixture (1750-1800 °C). The composition of the gaseous products of hydrolysis is consistent with the phase composition of the samples. The method of quantitative phase analysis based on the GLC analysis of the gases evolved on the hydrolysis is employed for the analysis of complex phase systems. In addition to chemical and X-ray diffraction analysis, the hydrolysis method is also applied to the determination of additional products.
Synthesis and properties of some derivatives of 3,4-dihydro-3-oxo-2-quinoalinylacetic acid
Authors: Toman Jaromír , Klicnar Jiří
Published: February 2011

The paper describes opening of isoxazole ring with 1,2-diaminobenzene leading to 2-cyanomethylene-3-oxo-1,2,3,4-tetrahydroquinoxaline and preparation of its derivatives. Synthesis have been studied of substituted 3,4-dihydro-3-oxo-quinoxaline-oxides, and tautomers of 1-oxides of 2-ethoxycarbonylmethylquinoxalines have been obtained.
Reaction of 2-cyano-3-(4,5-dibromo-2-furyl)-2-propenenitrile and methyl 2-cyano-3-(4,5-dibromo-2-furyl)-2-propenoate with nucleophiles
Authors: Kada Rudolf , Knoppová Viera , Kováč Jaroslav , Čepec Pavel
Published: February 2011

Methyl 2-cyano-3-(4-bromo-5-R-X-2-furyl)-2-propenenitriles and 2-propenoates were prepared from 2-cyano-3-(4,5-dibromo-2-furyl)-2-propenenitrile and methyl 2-cyano-3-(4,5-dibromo-2-furyl)-2-propenoate and the respective nucleophiles R-XNa (X = S, R = C6H5, 2-benzimidazolyl, 2-benzothiazolyl, 2-pyrimidinyl, and X = SO2, R = C6H5). The same products also originate by condensation of 4-bromo-5-R-X-2-furaldehydes with malononitrile or methyl cyano acetate under catalysis of alcoholates. Bis(3-bromo-5-formyl-2,2'-furyl) sulfide and bis(5-formyl-2,2'-furyl) sulfide were prepared from 4-X-5-bromo-2-furaldehydes (X = H, Br) with sodium sulfide. 4-Bromo-5-X-2-furaldehydes (X = H, Br) react with sodium hydrogen selenide to give bis-(3-bromo-5-formyl-2,2'-furyl)- or bis(5-formyl-2,2'-furyl) selenides. 2-Cyano-3-(4-bromo-5-amino-2-furyl)-2-propenenitrile and methyl 2-cyano-3-(4-bromo-5-amino-2-furyl)-2-propenoate were synthesized from the corresponding 4,5-dibromo derivatives, sodium azide and malononitrile. All compounds are characterized by UV spectral data; kinetics of nucleophilic substitution reactions with piperidine is presented, as well.
Potential noncataleptic neuroleptic agents: 2,3-Dichloro-10-[4-(2-hydroxyethyl)piperazino]-10,11-dihydrobenzo[b,f]thiepin
Authors: Urban Jiří , Dlabač Antonín , Valchář Martin , Protiva Miroslav
Published: February 2011

The 6-nitro derivative V, obtained by nitration of 3,4-dichlorobrombenzene, was transformed via the amine VI and nitrileVII to 2-bromo-4,5-dichlorobenzoic acid (IX). Its reaction with thiophenol in 3-methyl-1-butanol in the presence of potassium carbonate and catalytic amounts of copper and cuprous iodide afforded 4,5-dichloro-2-(phenylthio)benzoic acid (Xa) which was reduced to the alcohol XIa. The transformation to the homologous acid XIVa proceeded via noncharacterized intermediates XIIa and XIIIa. The cyclization with polyphosphoric acid at 150 °C resulted in 2,3-dichlorodibenzo[b,f]thiepin-10(11H)-one (XV) which was reduced to the alcohol XVI. Treatment with hydrogen chloride gave the unstable chloro derivative XVII whose substitution reaction with 1-(2-hydroxyethyl)piperazine led to the title compound II. Its dimethanesulfonate showed properties of a little toxic and noncataleptic tranquillizer. Because it does not influence the dopamine metabolism in rat brain in a rather high dose, it cannot be considered a neuroleptic.
Classification scheme of chemical reactions
Authors: Kvasnička Vladimír
Published: February 2011

The main concept of the suggested classification scheme of chemical reactions is the so-called reaction core. The reaction core is determined as an ordered triple, R = (R, G, φ, where R is a reaction graph, G is an intact molecular subgraph containing the edges and loops that are common for both substrate and product molecular graphs mutually related by the above reaction graph, and finally, φ is an evaluation of vertices from G by appropriate atomic symbols. An arbitrary chemical reaction, independently of its mechanistic stepwise realization, may be unambiguously characterized by this concept of reaction core.
Increasing the accuracy of calculation of the velocity field in a rotating electrolyser with axial electrolyte inlet
Authors: Šimek Michal , Roušar Ivo
Published: February 2011

A higher precision in the calculation of the velocity field has been achieved by determining functions of the fifth order in the expansions for velocities. Since the solution was carried out in a new way and quite generally, it turned out that functions of higher orders could also be found by the proposed method if necessary. The assumption that the functions of higher order may influence the individual velocity courses, especially in the inlet region, was substantiated.
The determination of trace amounts of heavy metals in foodstaffs by anodic stripping voltammetry: Optimization of chemical factors
Authors: Aliakbar Alireza , Popl Milan
Published: February 2011

A study was made of the use of differential pulse anodic stripping voltammetry (DPASV) for the determination of heavy metals (Cd, Pb, Cu) in foodstaffs. A thin-film mercury electrode was used for preconcentration from solution and dissolution. After prior optimization of the instrumental parameters, the effect of the following chemical factors was studied: concentration of mercury(II) ions, electrolysis (enrichment) time and the pH of the background electrolyte. It was found that all three factors affect the sensitivity of the determination of Cd and Pb, while only the electrolysis time and electrolyte pH are important for Cu. All three factors were optimized by the simplex method. The dependence between the concentration and the peak dissolution current was measured for all three metals and the detection and determination limits were found.
Reduction of fluorographite with lithium tetrahydridoaluminate
Authors: Klouda Karel , Pošta Antonín , Dědek Václav
Published: February 2011

Fluorographite (CF0.9)n was reduced with LiAlH4 in the diethyl ether, tetrahydrofuran, and dioxane, and the reduction is suggested involving intercalation of the reagent within the interlayer space of fluorocarbide, and also formation of an intercalate intermediate. The product of the reduction is carbon possessing a lamelar structure.
Substituent effect on solvolysis of 3-acetyl-1,3-diphenyltriazenes
Authors: Pytela Oldřich , Pilný Miroslav , Večeřa Miroslav
Published: February 2011

Eleven symmetrically disubstituted 3-acetyl-1,3-diphenyltriazenes have been synthetized by anew method. The solvolysis kinetics of the title compounds has been measured in 20% aqueous ethanol at several temperatures. The results are discussed from the point of view of temperature and substituent effects on the solvolysis rate constant of the 3-acetyl-1,3-diphenyltriazenes and conclusions are drawn about the reaction mechanism.
Dissociation of substituted benzenesulphonamides in water, methanol and ethanol
Authors: Ludwig Miroslav , Pytela Oldřich , Kalfus Karel , Večeřa Miroslav
Published: February 2011

Thirteen monosubstituted arylsulphonamides (XC6H4SO2NH2) and two 3,4-disubstituted arylsulphonamides (X2C6H3SO2NH2) have been synthetized and their dissociation constants have been measured by potentiometric titration in water, methanol, and ethanol. The Hammett substitution dependences have been calculated for all the media, and changes in the reaction constants due to transition from water to alcohols are discussed in confrontation with analogous dependences of benzoic acids. The reaction constant ρ found in methanol is lower than that in water. The dissociation constants have been treated mathematically by the method of the principal components and by multiple linear regression.
Calculation of thermodynamic functions of halogen derivatives of silane and germane
Authors: Bureš Michal , Černý Čestmír
Published: February 2011

Molar heat capacity, absolute entropy, relative enthalpy and relative Gibbs energy were calculated for all halogen derivatives of silane and germane. The calculation was performed for the ideal gas state at atmospheric pressure in the temperature range 100 to 1 500 K in the usual rigid rotator - harmonic oscillator approximation. In the case of molecules where the necessary experimental values of fundamental vibrational frequencies were missing, the calculation was performed using the predicted frequencies. On the basis of the values of molar heat capacities obtained in both these ways, a critical examination of the influence of the inaccuracy of the predicted vibration frequencies on the accuracy of calculated ideal gas thermodynamic functions was made.
Sharpening of metal sheets during electrochemical polishing. Theory and experiments
Authors: Novák Petr , Roušar Ivo
Published: February 2011

The electrochemical polishing with simultaneous shape changes of anodes was studied. A theory was derived based on the knowledge of basic electrochemical parameters and the solution of the Laplace equation. To this purpose, the finite element method and the finite difference method with a double transformation of the inter-electrode region were employed. Only the former method proved well and can therefore be recommended for different geometries.
Transient convective diffusion on a convex electrode in the presence of anomalous wall effects
Authors: Wein Ondřej , Kovalevskaya N. D.
Published: February 2011

The effect of the shape of an electrode on the course of electrochemically driven transient mass transfer at potentiostatic conditions is investigated for the case of a nonlinear velocity profile in the region of the concentration boundary layer. Particular results for circular electrodes are given.
Structure of istanbulin A and istanbulin B - two sesquiterpenic lactones from Smyrnium olusatrum L.
Authors: Buděšínský Miloš , Holub Miroslav , Šaman David , Smítalová Zdenka , Ulubelen Ayhan , Öksüz Sevil
Published: February 2011

The structures of istanbulin A (I) and istanbulin B (III), including absolute configurations, have been derived on the basis of spectral methods, primarily a detailed analysis of 1H NMR spectra and circular dichroism measurements. Both substances belong to the type of (4R, 5S,10R)-eremophilan-8,12-olides.
5-Methyl-1,3,4-thiadiazolylazo-resorcinol as a new metallochromic indicator for complexometric titration of lead
Authors: Cacho Juan , Nerin Cristina , Romero José
Published: February 2011

The synthesis, characteristics and analytical reactions of 5-methyl-1,3,4-thiadiazolylazo-resorcinol (MTDAR) are described. Their dissociation constants of OH groups in ortho and para position are respectively pK1 = 8.09 ± 0.01 and pK2 = 5.72 ± 0.02. For the Pb-MTDAR complex, the molar absorptivity is 2.0 . 104 l mol-1 cm-1 at 525 nm and pH = 8.0. The complex of ML type is formed. Beer`s law is obeyed between 0 and 9 ppm of Pb. The formation constant is 7.9 . 105. The studied reagent can be employed as a metallchromic indicator in chelometric titrations with visual and photometric indication. The interferences and their elimination are studied, too. The triestimul coordinates to chromatic transition are determined. This transition is increased by adding indigo carmine as an inert dyestuff.
Preparation of a partially hydrogenated dibenzo[c,h][1,2,6,7]tetrazecine and its pyridine analogue
Authors: Palát Karel , Vontor Tomáš , Čeladník Milan , Hanuš Vladimír
Published: February 2011

Heating of hydrazides of salicylic acid and/or 3-hydroxyisonicotinic acid gave rise to a partially hydrogenated dibenzo[c,h][1,2,6,7]tetrazecine and its pyridine analogue.
Synthesis of sanguinarine, chelerythrine, and oxysanguinarine
Authors: Šmidrkal Jan
Published: February 2011

Benzo[c]phenanthridines Va and Vb have been prepared by photocyclization of amines IVa and IVb and transformed into the alkaloids sanguinarine (VIa) and chelerythrine (VIb). Oxysanguinarine (XIV) has been prepared from diazoketone XVIII.
Acetylene chemisorption at palladium: Effect of temperature and structure of the surface
Authors: Kopešťanský Josef
Published: February 2011

The effect of temperature and structure of the palladium surfaces on acetylene chemisorption was studied along with the interaction of the adsorbed layers with molecular and atomic hydrogen. The work function changes were measured and combined with the volumetric measurements and analysis of the products. At temperature below 100 °C, acetylene is adsorbed almost without dissociation and forms at least two different types of thermally stable adsorption complexes. Acetylene adsorbed at 200 °C is partly decomposed, especially in the low coverage region. Besides the above mentioned effects, the template effect of adsorbed acetylene was studied in the temperature range from -80° to 25 °C. It has been shown that this effect is a typical phenomenon of the palladium-acetylene system which is not due to surface impurities.
Polarography of 3,4,5-trihydroxybenzoic acid
Authors: Pospíšil František
Published: February 2011

Polarographic oxidation of 3,4,5-trihydroxybenzoic acid on mercury and platinum electrodes is described. The electrode process is influenced by dissociation of the acid and adsorption of the oxidation products on the electrodes. The anodic peak height in differential pulse polarography is not a linear function of the concentration, which limits the determination of the acid concentration. A linear dependence of the anodic current on the concentration was found on a rotating platinum disc electrode at pH 6.5 or 2.0, which is of advantage determining the acid in physiological solutions and eluates from chromatographic columns.
Photometric determination of microgramme quantities of 1,3,5-trinitro-1,3,5-triazacyclohexane in air
Authors: Eminger Stanislav , Vejrostková Marie
Published: February 2011

A method is suggested for the determination of 1,3,5-trinitro-1,3,5-triazacyclohexane in workroom atmosphere. The substance is trapped in a sampling tube containing glass microfibres and activated silica gel, decomposed with sulphuric acid to give formaldehyde, the latter is reacted with 1,8-dihydroxynaphthalene-3,6-disulphonic acid, and the derivative of dibenzoxanthiliumtetrasulphonic acid formed is determined protometrically at 580 nm.
Photometric determination of aluminium and zinc with salicylaldehyde semicarbazone
Authors: Holzbecher Záviš , Lipská Dagmar
Published: February 2011

The effect of some tensides on the absorption, excitation, and fluorescence spectra of Al and Zn complexes of salicylaldehyde semicarbazone in aqueous-alcoholic solutions and on their extractability into ethyl acetate has been studied. The shape of the absorption spectra is unaffected by the presence of the tensides while the time of the complex formation is shorter. The complexes are extractable into ethyl acetate in the presence of the anionactive tenside tested, sodium lauryl sulphate. The optimum conditions for the spectrophotometric and fluorometric determination of Al and Zn have been established. The limit of determination is 2 ng ml-1 (pH 3.8-4.8) for Al and 50 ng ml-1 (pH 8.4-8.6) for Zn. Using thiosulphate or fluoride as masking agents, Zn can be determined in a concentration of 2 μg ml-1 in the presence of the same quantity of Al or Cu, or in the presence of a tenfold excess of Fe, with a relative standard deviation of 1.5%.
Semisynthetic cephalosporines. The synthesis of some substituted tetrazolylacetic acids
Authors: Janda Ľubomír , Votický Zdeno , Světlík Jan , Grimová Jaroslava , Maturová Eva
Published: February 2011

5-[5-(Substituted phenyl)-2-furyl]-1-tetrazolylacetic acids were synthesized from ethyl 5-(substituted phenyl)-2-furylcarbamidoacetates and phosphorus pentachloride via the corresponding imidoyl chlorides, which gave with sodium azide the respective ethyl 5-[5-(substituted phenyl)-2-furyl]-1-tetrazolyl acetates. A positive antiinflammatory effect was found when testing the acids obtained by hydrolysis of the acetates prepared.
Substituent effects on hydrolytic stability and herbicidal activity of 3-arylimidazolidine-2,4-diones
Authors: Čegan Alexandr , Večeřa Miroslav
Published: February 2011

Twenty-one derivatives of imidazolidine-2,4-dione have been prepared by reactions of substituted amino acids with aryl isocyanates in aqueous medium. Pre- and post-emergent herbicidal activities of all the compounds have been tested, and stability of five derivatives has been followed in aqueous medium within the pH range from 7.6 to 13.0. The highest pre-emergent herbicidal activity has been found with the derivatives XI-XVI which inhibit the growth of most indicator plants at the doses of 1.6 kg/ha. The derivatives studied are relatively stable in aqueous medium, the hydrolysis half-life of the compound XI being 9 days at pH 8.
Effect of the hydrophilicity of the polymer matrix on immobilized α-chymotrypsin
Authors: Kumakura Minoru , Kaetsu Isso
Published: February 2011

α-Chymotrypsin was immobilized by radiation polymerization at low temperatures and the effect of the hydrophilicity of the polymer matrix on the enzyme activity and thermal stability was studied. The activity and thermal stability of immobilized chymotrypsin increased with the increasing hydrophilicity of the polymer matrix or monomer. The thermal stability was affected by the form and pore size of the polymer matrix; chymotrypsin immobilized on a soft-gel polymer matrix exhibited an enhanced thermal stability.
A convenient preparation of 1-CB11H12- and its C-amino derivatives
Authors: Plešek Jaromír , Jelínek Tomáš , Drdáková Eva , Heřmánek Stanislav , Štíbr Bohumil
Published: February 2011

Treatment of 7-(CH3)3N-7-CB10H12 with triethylamineborane(3) at 180-200 °C proceeds under splitting off one methyl group and inserting one boron vertex to obtain 1-(CH3)2NH-1-CB11H11. Methylation of the latter compound produces 1-(CH3)3N-1-CB11H11 which can be reduced to the parent 1-CB11H12- anion with sodium in liquid ammonia. The constitution of all compounds was established by NMR and mass spectroscopy.
A polymeric analog of dimethyl sulfoxide: Synthesis of crosslinked polymers with bound sulfoxide groups
Authors: Janout Václav , Hrudková Hana , Čefelín Pavel
Published: February 2011

By using a sequence of functionalization reactions, a series of crosslinked polymers with pendant sulfoxide units of the P-(CH2SOCH2)nR type with n = 1, 2, 3 and R = H, CH3, where P is poly(styrene-co-divinylbenzene) (content of the crosslinking component 1%, 2%) were prepared. The high reactivity of the crosslinked polymeric thiol P-CH2SH in alkylation reactions was used in the preparation. Conditions for the selective oxidation of polymeric sulfides to sulfoxides were checked.
Synthesis of ten-vertex closo-metallacarbaboranes from 4-CB8H14
Authors: Štíbr Bohumil , Janoušek Zbyněk , Baše Karel , Plešek Jaromír , Solntsev Konstantin A. , Butman Lev A. , Kuznetsov Igor I. , Kuznetsov Nikolai T.
Published: February 2011

Nickelocene and 4-CB8H13-Na+ react in diglyme at 130-140 °C to produce an unstable [6-η5-C5H5Ni-η5-1-CB8H9] complex which rearranges to the isomeric [10-η5-C5H5Ni-η4-1-CB8H9] species. Modification of the synthesis led to the isolation of a bimetallic [(6,7-η5-C5H5Ni)2-η6-1-CB7H8] compound. The [2-η5-C5H5Co-η5-1-CB8H9]- anion was prepared by treatment of 4-CB8H14 with cyclopentadiene and CoCl2.6H2O in ethanolic potassium hydroxide. Structures of the complexes were determined by their spectra and X-ray diffraction studies.
Hydroformylation of propene catalyzed with carbonylchlorobis(triphenylphosphine)rhodium(I)
Authors: Polievka Milan , Jegorov Alexandr , Uhlár Ladislav , Macho Vendelín
Published: February 2011

Influence of some amines, amino acids, nitrogen heterocyclic compounds and urea derivatives (as ligands of carbonylchlorbis(triphenylphosphine)rhodium(I) on velocity of the catalyzed hydroformylation of propene has been investigated. A positive effect on the catalytic activity has been found with the modifying ligands of very low basicity.
1,3-vs- 1,5-dipolar reactivity of 1-phenylmethyl-4N-acetylimino-1H-1,2,4-triazolium betain toward aromatic isothiocyanates
Authors: Zálupský Peter , Martvoň Augustin
Published: February 2011

The title betain was found to display both 1,3 and 1,5-dipolar reactivity, depending on reaction conditions. Whereas the reaction with aromatic isothiocyanates in nonpolar solvents produced cycloadducts in concerted manner stewise addition in dimethylformamide led to a single product, presumably with sevenmembered ring. An open-chain intermediate could be isolated and characterized.
Plastic capillary for dropping mercury electrode
Authors: Tenygl Jiří
Published: February 2011

Described is a polarographic capillary easily realizable from a commercially available plastic tubing and its performance characteristics are demonstrated.
Heats of immersion and heat of H+/Cu2+ exchange for amorphous zirconium phosphate
Authors: Ilić Petar V. , Tolić Alexander , Pekárek Vladimír , Ruvarac Alexander
Published: February 2011

Heats of Immersion of amorphous and crystalline zirconium phosphates in water were determined, and heat of H+/Cu2+ exchange on amorphous zirconium phosphate at 298.15 K was obtained by direct calorimetric measurement.
Partial hydrolysis of acyl 1,6-anhydro-β-D-glucopyranose
Authors: Kučár Štefan , Zámocký Juraj , Zemek Juraj , Anderle Dušan , Matulová Mária
Published: February 2011

Partial hydrolysis of per-O-acetyl- and per-O-benzoyl derivatives of 1,6-anhydro-β-D-glucopyranose with methanolic hydrogen chloride and hydrazine hydrate was investigated. The acyl group at C(3) is of substantial influence on the course of hydrolysis. The esterified hydroxyl group at C(3) was found to be most stable on acid hydrolysis with methanolic hydrogen chloride when compared with that at C(2), or C(4); on the other hand, this ester group is the most labile upon hydrolysis with hydrazine hydrate. Selectivity of the respective ester groups towards hydrolysis made it possible to prepare all variations of acetyl and benzoyl derivatives of 1,6-anhydro-β-D-glucopyranose.
Amidinoyl isothiocyanates in the synthesis of condensed quinazolines. Preparation of S-triazolo[4,3-c]quinazolines
Authors: Stankovský Štefan , Sokyrová Mária
Published: February 2011

The s-triazolo[4,3-c]quinazolines were obtained from 4-hydrazinoquinazolines by condensation with ethyl orthoformate. 4-Hydrazinoquinazoline were prepared by hydrazinolysis of corresponding quinazoline-4-thiones which in turn were obtained by isomerization of amidinoyl isothiocyanates. The infrared and 1H NMR spectra of the final products are interpreted.
A physico-chemical study of the interaction between human hemoglobin and benzene
Authors: Sedláček Pavel , Pavlíček Zdeněk , Kalous Vítěz
Published: February 2011

The interaction between human hemoglobin and benzene produced difference spectra (in the visible region) changing with time. In addition to these changes we studied the dependence of the interaction on temperature and on concentration of the two components. The interaction of hemoglobin and benzene was also followed by means of CD spectra. These spectra in the region 200-260 nm demonstrate that the secondary structure of hemoglobin was not affected by the interaction. By contrast, in the region 270-300 nm the CD spectra show a change in the quaternary structure of hemoglobin, which goes from the R state to the T state, and after a period it returns to the original state.
Monte Carlo calculations of solvent effect in the reaction F- + CH3F = F...CH3....F-
Authors: Černušák Ivan , Urban Miroslav
Published: February 2011

A new approach is suggested and tested to calculation of solvent effect on chemical reactivity based on the statistical-thermodynamic Monte Carlo simulation of models of aqueous solutions devised by Metropolis. The results of computer experiments are presented for the following systems: F-.26H2O, CH3F.26H2O, FCH3F-.52H2O, 26 H2O, 52 H2O at a temperature of 300 K at the conditions of canonical ensemble. The pair potentials MCY-CI (for water-water interactions) and 4-31G (for solute-water interactions) have been used. The 4-31G potentials have been derived from the SCF calculations of the interaction energies of the systems: F-.H2O, CH3F.H2O, and FCH3F-.H2O. Internal energies, radial distribution functions, and snapshots of the configurations have been calculated. The calculated partial molar internal energies depend strongly on quality of the solute-water pair potentials and are overestimated with respect to experiment. On the basis of the results obtained, further possibilities of the suggested approach are discussed.
Derivatives of 6-amino-6-N,N-bis(carboxymethyl)-6-deoxy-D-galactose
Authors: Čapek Karel , Čapková Jindra , Jarý Jiří , Trška Petr
Published: February 2011

On reaction of 6-amino-6-deoxy-1,2;3,4-di-O-isopropylidene-α-D-galactopyranose (II) with sodium chloracetate 6-amino-6-N,N-bis(carboxymethyl)-6-deoxy-1,2;3,4-di-O-isopropylidene-α-D-galactopyranose (III) was obtained. Melting of compound III with urea or its heating with a mixture of formamide and urea causes cyclocondensation of the N,N-bis(carboxymethyl)group under formation of 6-deoxy-1,2;3,4-di-O-isopropylidene-6-C(3,5-dioxopiperazin-1-yl)-α-D-galactopyranose (IX). Some derivatives of compound III are also described in the paper; the structures of all the products have been confirmed by NMR spectra.
Synthesis and properties of [2-[3,5-3H2]-tyrosine,4-glutamic acid]deamino-1-carba-oxytocin
Authors: Lebl Michal , Barth Tomislav , Crankshaw Denis J. , Černý Bohuslav , Daniel Edwin E. , Grover A. K. , Jošt Karel
Published: February 2011

The title compound (specific activity 11.1-32.7 Ci (0.41-1.22 TBq)/mmol) was prepared by iodination and subsequent catalytic replacement of iodine by tritium. The analogue which was unstable in the form of a lyophilizate was purified by reversed phase liquid chromatography. Using the N,N'-dicyclohexylcarbodiimide method, the pure analogue was converted into N-hydroxybenzotriazolyl ester, an irreversible oxytocin inhibitor. However, attempts to label specifically the uterotonic receptor, present in the enriched rat myometrium fraction, were hithero unsuccessful
Binding of calcium ions to 2,3-dicarboxy derivatives of starch and amylose
Authors: Kohn Rudolf , Tihlárik Karol
Published: February 2011

A series of 2,3-dicarboxy derivatives of oxidation degree DO(d.c.) 0.13 to 0.90 was prepared by a two-stage oxidation of corn starch and amylose. The activity coefficient γCa2+ of calcium counterions was estimated in solutions of calcium salts of these carboxy derivatives in a 3.00 mmol (COOCa0.5)l-1 concentration by a metallchromic indicator (tetramethylmurexide) method. A loss of electrostatic free enthalpy, Δ(Gel/N)KCa, due to the exchange of Ca2+ → 2K+ cations was determined by potentiometric titrations of the investigated polyacids and pectinic acids of various linear charge density of the macromolecule employing potassium and calcium hydroxides. 2,3-Dicarboxy derivatives of starch and amylose show a considerably strong binding of calcium ions even at low oxidation degree of the starting polysaccharides in contrast to solutions of the corresponding pectinates and carboxymethyl derivatives of cellulose and amylose. The strong bond of calcium ions to 2,3-dicarboxy derivatives of starch and amylose is ascribed to a favourable spatial arrangement of two neighbouring carboxyl groups at C(2) and C(3) of the oxidized D-glucose units due to a flexibility of the macromolecule chain at sites of the pyrane ring cleavage.
Reactions of 1-cyano-1-R-2-(5-X-2-furyl)ethylenes with nucleophilic reagents
Authors: Kada Rudolf , Knoppová Viera , Kováč Jaroslav , Mäčková Naděžda
Published: February 2011

The Knoevenagel condensation of phenylsulphonylacetonitrile and benzoylacetonitrile with 5-X-furane-2-carbaldehydes ( X = Br, NO2, C6H5S, C6H5SO2) has been used for preparation of the respective condensation products 1-cyano-1-fenylsulphonyl-2-(5-X-2-furyl)- and 1-cyano-1-benzoyl-2-(5-X-2-furyl)ethylenes. These condensation products react with nucleophilic reagents which replace the group X at the 5 position of the furane nucleus. These nucleophilic substitutions have been also studied kinetically.
Thermal desorption under conditions of freely occurring readsorption: A method for evaluation of the experimental data
Authors: Pavlíček Jan
Published: February 2011

A method is proposed which permits to determine the differential enthalpy, differential entropy and kinetic order of desorption from the thermal desorption experiments carried out under close-to-equilibrium conditions. The main preference of the proposed method can be seen in the possibility to use for evaluation the entire range of the desorption curve, as well as, in the unified description of the most frequently used types of heating. The approximations enabling such a unified description lead to deviations which are, in major, mutually eliminated and the resulting error is therefore negligible if compared with the accuracy of the experimental data.
Coadsorption of bulky ions by surfactants. Monomolecular layers of tris(2,2'-bipyridyl)ruthenium(II) complex with sodium lauryl sulphate on glassy carbon, platinium, n-SnO2, and n-Si electrodes
Authors: Lasovský Jan , Grambal František , Rypka Miroslav
Published: February 2011

The electrochemical and photochemical behaviour of tris(2,2'-bipyridyl)ruthenium(II) complex (I) on glassy carbon, platinium, n-SnO2, and n-Si electrodes in the presence of sodium lauryl sulphate (II) was investigated. The surfactant in low concentrations induces self-association of the complex cation and its accumulation in the electrode-solution interface. At the optimum concentrations of sodium lauryl sulphate (cII ~0.6 mmol l-1) and of the complex (cI < 0.1 mmol l-1), monomolecular layers composed of I, II counterions are formed on the electrodes. The formation of the surface films does not depend on the kind of the electrode and improves the sensitivity of the voltammetric determination of I by as much as an order of magnitude. For the semiconductor electrodes, the surface films enhance the efficiency of conversion of radiant energy into electric energy. The effect under study may participate in the photosynthesis of green plants.
Reliability of the linear effective calibration method in gel permeation chromatography
Authors: Kubín Miroslav
Published: February 2011

The validity of the effective linear calibration (ELC) method in gel permeation chromatography of polymers has been checked by means of computer generated chromatograms. The ratio Mw/Mn calculated using ELC form an uncorrected chromatogram is always smaller than that determined by means of the true calibration dependence, but the extent of this correction for longitudinal spreading depends on the polydispersity of both the original calibration standard and the analyzed polymer, and also on the separation efficiency of the given column. If the respective molecular weight averages of the analyzed sample and of the calibration standard differ considerably, the effective linear calibration method leads to serious systematic errors in the calculated average molar mass values.
Decomposition of hydrogen peroxide on nickel-silver two-component catalyst
Authors: Múčka Viliam , Silber Rostislav
Published: February 2011

The catalytic and physico-chemical properties of low-temperature nickel-silver catalysts with nickel oxide concentrations up to 43.8% (m/m) are examined via decomposition of hydrogen peroxide in aqueous solution. The mixed catalysts prepared at 250°C are composed of partly decomposed silver carbonate or oxide and nickel carbonate or hydroxide decomposed to a low degree only and exhibiting a very defective crystal structure. The activity of these catalysts is determined by the surface concentration of silver ions, which is affected by the nickel component present. The latter also contributes to the thermal stability of the catalytic centres of the silver component, viz. the Ag+ ions. The concentration of these ions varies with the temperature of the catalyst treatment, the activity varies qualitatively in the same manner, and the system approaches the Ag-NiO composition. The catalytic centres are very susceptible to poisoning by chloride ions. A previous exposition of the catalyst to a gamma dose of 10 kGy from a 60Co source has no measurable effect on the physico-chemical properties of the system.
Decomposition of hydrogen peroxide on nickel oxide-cerium dioxide catalysts and the effect of ionizing radiation on them
Authors: Múčka Viliam
Published: February 2011

Physical characteristics of nickel oxide-cerium dioxide catalysts and their catalytic activity in the decomposition of hydrogen peroxide were studied over the entire region of catalyst composition. The systems under study, prepared from cerium(III) nitrate, were compared with those prepared previously from cerium(IV) ammonium nitrate, and the properties of the catalysts were found to be affected considerably by the nature of the precursor used. Nevertheless, in spite of the differences the catalytic reaction on the catalysts of the two series seems to proceed on catalytic centres of the same kind, the extent to which the centres operate being dependent on the catalyst composition. The changes in the catalyst activity brought about by sample ageing, heat treatment, or previous exposition to gamma or beta rays or fast neutrons can be accounted for, in terms of the bivalent catalytic centres concept, by interaction of the catalytic centres with oxygen or the radiation applied.
The kinetics of reduction of nickel oxide-cerium dioxide mixed systems with hydrogen and the effect of ionizing radiation on it
Authors: Pospíšil Milan , Petrecký Igor
Published: February 2011

The reduction with hydrogen is studied thermogravimetrically over the temperature region of 260-500 °C for nickel oxide-cerium dioxide mixed systems of various composition. The overall rate of reduction increases and the maximum rate of reduction of nickel oxide decreases with increasing cerium dioxide content as a result of two counteracting processes occurring on the reaction interface and conditioned by the presence of the finely dispersed unreducible component. The dependence of the degree of reduction α on time t obeys the relation (α + 0.3)/(1 - α) = Aekt over the entire system composition region. Previous exposition of the samples to gamma does of 100 and 500 kGy from a 60Co source or to a fast neutron dose of 400 Gy from a 252Cf source results in a decrease in the rate of reduction for region with excess nickel oxide, but as the concentration of cerium dioxide is increased, inversion of the radiation-induced effect takes place and the rate of reduction becomes higher than for the initial, unexposed samples. The effect of temperature and system composition on the phenomena under study is examined and discussed.
Thioxanthene derivatives of pharmacological interest: 1,2,4-Trichloro and 2,4,5,6-tetrachloro derivatives of 9-(3-dimethylaminopropylidene)thioxanthene
Authors: Bártl Václav , Kmoníček Vojtěch , Šedivý Zdeněk , Svátek Emil , Protiva Jiří , Protiva Miroslav
Published: February 2011

Reactions of 2,4,5-trichlorothiophenol (II) with 2-iodobenzoic acid and 2,3-dichlorothiopheno with 3,5-dichloro-2-iodobenzoic acid gave the acids III and IX which were cyclized to thioxanthones VI and XV. Reactions of these ketones with 3-dimethylaminopropylmagnesium chloride afforded the amino alcohols VII and XVI which were transformed by the acid catalyzed dehydration to the title compounds I and VIII. 2-Chloro-9-[1-(2-hydroxyethyl)-4-piperidylidene]thioxanthene (XVII) was obtained by a modified synthesis. Compound I is inactive in the line of the CNS effects but it has high inhibitory activity in the in vitro tests towards gram-positive microorganisms. Compound XVII has properties of a mild tranquillizer.
A new approach to 5H-pyrano[2,3-d]pyrimidine derivatives
Authors: Marchalín Štefan , Kuthan Josef
Published: February 2011

Reaction of 2-amino-3,5-dicyano-4H-pyran derivative I with triethoxymethane gives the corresponding 2-ethoxymethyleneamino derivative II which reacts with amines RNH2 to give 5H-pyrano[2,3-d]pyrimidines of general formula III. Spectral characteristics of compounds IIIa - IIIg are discussed.
Use of currentless potential-time curves for determining the rate constants of diazotation reactions
Authors: Dlask Vladimír
Published: February 2011

The kinetics and the rate constants for the diazotation of nine aromatic amines at various conditions (temperature, medium) were determined by the method of currentless potential-time curves. A comparison with an independent method and with literature data is presented.
Crystal and molecular structure of carbonylcyanide-4-chlorophenylhydrazone(4-chlorophenylhydrazonopropanedinitrile)
Authors: Vrábel Viktor , Šturdík Ernest , Dunaj-Jurčo Michal , Lokaj Jan , Garaj Ján
Published: February 2011

The crystal structure of carbonylcyanide-4-chlorophenylhydrazone was solved by the single crystal X-ray diffraction method and interpreted by the heavy atom method. The compound crystallizes in the P21/c monoclinic group with 4 molecules per unit cell and with lattice parameters: a = 1.1843(3), b = 0.5944(1), c = 1.4922(3) nm and β = 117.92(2)°. The structure was refined by the least squares method for 1 078 observed reflections to a final value of R = 4.9%. The crystal structure consists of monomeric units, where hydrogen bonds were observed between atoms N3...H5 0.2193 nm and N3...H3 0.2404 nm between two molecules transformable through centre of symmetry -x, -y, -z. The name 4-chlorophenylhydrazonopropanedinitrile is recommended for the studied compound on the basis of this X-ray structural analysis.
The effect of changes in hydrodynamic conditions on the response of calcium-selective membrane electrodes with a macrocyclic carrier
Authors: Ryba Olen , Petránek Jaromír
Published: February 2011

Shifts of the potentials of a calcium ion-selective electrode based on the complex of 7,19-dibenzyl-2,2,3,3-tetramethyl-7,19-diaza-1,4,10,13,16-pentaoxacycloheneicosane-6,20-dione with calcium tetra(4-chlorophenyl)borate in various membrane solvents caused by changes in hydrodynamic conditions in the measured solution were examined. The use of 2-fluoro-2'-nitrodiphenyl ether as a membrane solvent combined with substitution of benzyl groups with octyl ones in the neutral carrier eliminates this unfavourable phenomenon while preserving the selectivity parameters of the electrode.
Investigation of the mechanism of thiophene hydrodesulphurization by isotopic method
Authors: Gudkov Boris S. , Gayday Nataliya A. , Beránek Ludvík , Kiperman Savelii L.
Published: February 2011

The reaction of thiophene with deuterium on aluminia supported Ni-, Mo- and Ni-Mo-catalysts (laboratory samples) and Ni-W-, Ni-Mo- and Co-Mo-catalysts (commercial samples) was investigated at 150-455°C and different D2/C4H4S ratio in a closed system with internal circulation (total reactant pressure 3 kPa) and in a gradientless flow system (atmospheric pressure). Analysis of the deuterium distribution in thiophene and hydrogen sulphide and of its change in dependence on the extent of reaction revealed that thiophene hydrodesulphurization proceeds with participation of external hydrogen and not intramolecularly with participation of the β-hydrogen atoms of thiophene. This conclusion was checked also by the reaction of deuterothiophene with light hydrogen. In the analysis of the results, the fast H2 - D2 exchange with thiophene was taken into account; exchange reaction of deuterium with hydrogen sulphide was not significant.
A dual equilibrium diffusion model for epitaxial growth of gallium arsenide layers from the gas phase and an a priori computation of growth rates
Authors: Erdös Emerich , Voňka Petr , Stejskal Josef , Klíma Přemysl
Published: February 2011

A model is proposed and quantitatively treated of epitaxial growth of gallium arsenide layers, where the rate controlling step consists in the diffusion of reactants through a stagnant gas film adhering to the substrate, and where chemical equilibria are established between the reactants in the main gas stream and at the surface of substrate. The boundary layer theory is applied to the hydrodynamic part of the model which is simplified by introducing a mean effective film thickness, and the system of Ga-As-Cl-H is reduced to six molecular species and to three chemical reactions. With this basis and using estimated values of diffusion coefficients, the growth rates of epitaxial gallium arsenide layers have been a priori computed in dependence of the feed rate, its composition and on temperature. The predicted three dependences are discussed from the view-point of their courses and of the significance of computed results.
The possibility of using chronopotentiometry in studies of ionic association or complexation at the interface between two immiscible electrolyte solutions
Authors: Makrlík Emanuel
Published: February 2011

Theoretical potential-time curves were derived in the form Δαβφ = f(t) (Δαβφ denotes Galvani potential difference between phases β and α), expressing mathematically a reversible transfer of a cation across the interface between two immiscible electrolyte solutions under galvanostatic conditions. The formation of ion pairs or complexes was taken into account, and the influence of certain components of two-phase systems on the form of potential-time curves is discussed.
Excess volumes and excess enthalpies of the mixtures tetrachloromethane + cycloalkane and trichloromethane + cycloalkane: Calculation in terms of equations of state of the van der Waals type
Authors: Cibulka Ivan , Holub Robert
Published: February 2011

The excess volumes and excess enthalpies for equimolar compositions and a temperature of 298.15 K for the binary liquid mixture of tetrachloromethane and trichloromethane with cyclopentane, cyclohexane and cyclooctane were calculated in terms of equations of state of the van der Waals type, the Redlich-Kwong equation of state and an equation following from the Flory theory. The pure-component parameters were evaluated in three different ways. The equations of state with pure-component parameters determined from gas-liquid critical constants yielded poor agreement with experiment. The best agreement with experiment was yielded by the Snider-Herrington equation with the pure-component parameters evaluated from molar volumes and thermal pressure coefficients and by the Flory equation. The Frisch equation extended to mixtures by using the van der Waals one-fluid approximation gave a good agreement with experiment in case of mixtures of molecules of approximately the same size. The excess entropies and the values of temperature derivatives of excess functions were as well calculated and compared with available experimental data.
Spectrophotometric determination of trivalent cerium with feriin in the presence of tetravalent cerium
Authors: Novák Josef , Vyhlídka Pavel , Kohout Vladimír , Hájek Bohumil
Published: February 2011

A method is suggested for the indirect determination of cerium(III) ions in the presence of a high excess of tetravalent cerium. Ce(III) is oxidized to Ce(IV) by tris(1,10-phenanthroline)iron(III) complex (ferriin) in the presence of sodium diphosphate, and the purple-red iron(II) complex (ferroin) formed is determined photometrically at 530 nm. Trivalent cerium can be so determined in quantities of 0-400 μg/50 ml with a relative error of ±3.5%. Cerium(III) was determined in commercial cerium(IV) sulphate and cerium dioxide preparations.