bluuebunny/crossref_metadata_2025 huggingface dataset:
Solvolysis kinetics of ethyl 3-ethoxy-3-iminopropanoate
Authors: Kaválek Jaromír , Panchartek Josef , Potěšil Tomáš , Štěrba Vojeslav
Published: September 2010

Kinetics have been studied of hydrolysis and methanolysis of ethyl 3-ethoxy-3-iminopropanoate. The methanolysis rate constant is lower than the hydrolysis rate constant by about 3 orders of magnitude. The rate-limiting step of the hydrolysis consists in the nucleophilic attack of the protonated substrate by a water molecule, whereas that of the methanolysis consists in the decomposition of tetrahedral intermediate which is several orders of magnitude slower than the decomposition of the intermediate formed in the hydrolysis.
Poly(ethylene terephthalate) immobilized exo-D-galacturonanase
Authors: Heinrichová Kveta , Zliechovcová Dagmar
Published: September 2010

Exo-D-galacturonanase (E.C. 3.2.1.67) isolated from carrot was irreversibly adsorbed on poly(ethylene terephthalate) in a 0.1 mol l-1 acetate buffer solution of pH 5.1. Activity of the immobilized enzyme depended on the amount of the enzyme bound to the support, on the ionic strength, and, to a very little extent, also on the pH of the reaction medium during immobilization. Activity of the immobilized enzyme dropped; the greatest relative activity (51.8%) had the preparation composed of 9.12 mg of the enzyme per 1g of the support. The pH optimum for catalytical activity of the immobilized enzyme was identical with that of the dissolved enzyme (5.1). Immobilization of the enzyme did not change its thermal optimum, and its thermal stability did not improve, either. The substrate specificity did not alter by immobilization, no differences were found in the mode of action on the polymeric substrate; digalacturonic acid was degraded by the immobilized enzyme like by the dissolved one. Differences in the kinetics of polymeric substrate degradation by the bonded exo-D-galacturonanase were manifested by a lower V' app value and by an increased K'm value. Exo-D-galacturonanase preparation obtained by adsorption on poly(ethylene terephthalate) was extraordinarily stable during storage at 4 °C, and towards action of salts and pH changes; its operation stability was high.
A quantum-chemical study of structure of H3O+ in electronically excited states
Authors: Ertl Peter , Leška Jaroslav
Published: September 2010

The CNDO/2-Cl method has been used for full optimization of geometry of the H3O+ ion in all its electronically excited singlet states and for calculation of electron distribution. The electronic structure shows that H3O+ in almost all states exhibits lower tendency to split off the proton than it does in the ground state. For the first excited state the geometries and electron distributions of the isoelectronic set H3O+, NH3, CH-3 have been calculated by the INDO-Cl method in the triplet state, too. The particles only have slightly different geometry and electronic distribution from those of the first singlet state.
Kinetics of individual steps in reaction network ethanol-diethyl ether-ethylene-water on alumina
Authors: Morávek Vladimír , Kraus Miloš
Published: September 2010

The rates of single reactions have been measured at 250 °C in the complex reaction of ethanol dehydration to ethylene and to diethyl ether involving also hydrolysis of the ether, its disproportionation to ethanol and ethylene and its dehydration to ethylene. The found dependences of the initial reaction rates on partial pressures of the reactants were correlated by semiempirical Langmuir-Hinshelwood type rate equations.
Kinetics of individual reactions in reaction network 1-butanol-di-(1-butyl) ether-butenes-water on alumina
Authors: Krampera František , Beránek Ludvík
Published: September 2010

The complex system of six reactions occurring when 1-butanol is dehydrated on alumina at 260 °C was investigated. Initial kinetics of 1-butanol, di-(1-butyl) ether and 1-butene transformations were analyzed and best fitting rate equations for all reactions were selected. The inhibiting effects of water on initial rates was quantitatively expressed. Very low conversion data provided additional evidence for the validity of the parallel-consecutive reaction network of alcohol dehydration. In all the alkene-forming reactions, 1-butene was the primary product which was then isomerized into a mixture of cis- and trans-2-butenes.
The optimization of the current sampling time in pulse polarography
Authors: Bolzan Jorge Alfredo
Published: September 2010

A method for computing the approximate value of the non-faradayic component of the total decay current in a pulse polarographic experiment is described. Undesirable effects of such component are discussed. The method employed is simpler than computing the non-faradayic current from RC measurements and has the advantage of being applied under actual polarographic working conditions.
Polydisperse model of the VPE extractor hydrodynamics
Authors: Sovová Helena
Published: September 2010

A computer simulation model of the dispersed phase holdup in the vibrating-plate extractor was developed. Drop transport, breakage and coalescence equation were solved simultaneously, the stage being divided in the internal part and in the dense-packed layer of dispersion at the plate. The verified simulator can be used to predict and to analyse both steady state holdup and its dynamics and it can help to design a VPE extractor or a pulsed sieve-plate extractor. Holdup measured in a VPE column with toluene dispersed in water without mass transfer was simulated by the model with a standard deviation 6% rel. in the whole range from the mixer-settler region to the emulsion region.
Reaction of α-Fe2O3 (hematite) with potassium carbonate at elevated temperatures
Authors: Vinš Jaroslav , Urbanová Markéta , Šubrt Jan , Zapletal Vladimír , Zakharov Aleksander A. , Shaplygin Igor S.
Published: September 2010

The kinetics of the reaction between α-Fe2O3 and K2CO3 have been investigated over the temperature range 600 to 800 °C, and the phase composition of the products has been determined. The reaction follows the rate law α = 1 - exp (-kτn). At molar ratios K : Fe 1, KFeO2 is the only product. At K : Fe 1, initially formed KFeO2 reacts with hematite to yield K2Fe4O7. The latter phase has been assigned a cubic structure with a = 1.681 ± 0.003 nm. based on X-ray powder diffraction patterns and Mossbauer spectra, the structure of K2Fe4O7 is proposed to be a cubic close-packed array of oxygen atoms, part of these being replaced by potassium atoms, with Fe atoms occupying the octahedral interstices.
Silica supported cationic rhodium(I) complexes as hydrogenation catalysts
Authors: Zbirovský Vladimír , Čapka Martin
Published: September 2010

Cationic silica-supported Rh(I) complexes prepared from Rh(COD) (acac) and phosphines of the type (C2H5O)3Si(CH2)nP(C6H5)2 (n = 1,3) in the presence of p-toluenesulphonic acid were found to be efficient catalysts for hydrogenation of alkenes, alkadienes, and Z-α-acetamidocinnamic acid at 40 °C and normal hydrogen pressure. Kinetic measurements showed that the most efficient catalysts are obtained at the P : Rh mol. ratio = 2. When this ratio was ensured for each molecule of the immobilized complex, such catalysts were three to four times more active than their homogeneous analogues.
Catalysed liquid phase oxidation of acetals by molecular oxygen
Authors: Včelák Jaroslav , Klímová Miroslava , Chvalovský Václav
Published: September 2010

Nine different acetals have been oxidized in the presence of Co(OOCCH3)2.4 H2O under isobaric conditions (0.1 - 0.2 MPa O2 while following the uptake of molecular oxygen. The reactivity of acetals was expressed by the rate constants of the autocatalytic model of oxidation. The main products of the oxidation are alcohols, esters and acids. The distribution of products and the total reactivity of acetals are controlled by the structure of both parts of acetal molecule. The dominant effect on the course of the reaction exerts the type of carbon atoms on which radicals are formed. The oxidation is accompanied by consecutive and co-oxidation reactions, by deactivation of the catalyst and by decarbonylation of intermediate products. The effect of oxygen pressure is reported and the more detailed radical mechanism of the oxidation is proposed.
Lipidic compounds from the extract of the springtail Tetrodontophora bielanensis (WAGA)
Authors: Stránský Karel , Trka Antonín , Buděšínský Miloš , Streibl Milan
Published: September 2010

Surface and internal lipidic compounds from the springtail Tetrodontophora bielanensis (WAGA) were investigated. Using chromatographic and spectroscopic methods the following compounds were detected: n-alkanes (C15 - C35), lycopane (C40H82), olefin C40H80, seven groups of esters (including sterol esters), secondary alcohol C40H82O, triacyl glycerols, free saturated and unsaturated fatty acids (C12 - C22) and free sterols (cholesterol and desmosterol).
Photolysis of hydrogen peroxide, photocatalytic effects of Cu(II) and reaction kinetics
Authors: Luňák Stanislav , Sedlák Petr , Vepřek-Šiška Josef
Published: September 2010

The quantum yield of hydrogen peroxide photolysis has been measured as a function of the concentration of photocatalytically active Cu2+ ions, intensity of photolytic radiation, temperature, and hydrogen peroxide concentration. The results obtained are consistent with the concept that high quantum yields of hydrogen peroxide photolysis (Φ >> 1) are due to thermal decomposition of hydrogen peroxide catalyzed by photochemically generated copper ions in oxidation states which are catalytically active.
Kinetics of oxidation of bis(ethylenediamine)mercaptoacetatocobalt(III) and cysteinatobis(ethylenediamine)cobalt(III) ions by peroxodisulphate in aqueous-nonaqueous mixed solvents
Authors: Vollárová Oľga , Benko Ján , Matejeková Ivana
Published: September 2010

The kinetics of oxidation in the first step was studied for coordination-bonded sulphur in the cysteinatobis(ethylenediamine)cobalt(III) and bis(ethylenediamine)mercaptoacetatocobalt(III) ions using peroxodisulphate as oxidant. The effect of the acid-base equilibria of the reactants was established based on the dependences of the rate constant and the thermodynamic activation parameters ΔH and ΔS on perchloric acid concentration. The effect of ionic strength at various perchloric acid concentrations, was examined for the two complex ions. The combined effect of perchloric acid and sodium perchlorate was investigated in water-tert-butyl alcohol and water-ethylene glycol solutions. The transfer functions were calculated from the changes in the solubility of the reactants on passing from aqueous to the mixed aqueous-nonaqueous solutions, and the role of solvation during the oxidation of the complexes by peroxodisulphate was assessed based on the dependences of the transfer functions on the nonaqueous component content of the solvent system.
New organic luminophores on the basis of cyano- and dicyanopyridines
Authors: Marchalín Štefan , Fähnrich Jan , Popl Milan , Kuthan Josef
Published: September 2010

Absorption and fluorescence spectra of solutions of cyanopyridine derivatives of polyphenylene type, II-VIII, were investigated. The spectral characteristics determined are interpreted in relation to the probable conformational structure of the investigated substances in the states S0 and S1. The relationship between the Stokes shift and the solvent effect on the fluorescence spectra is discussed.
The Diels-Alder reaction of butadiene with hexacyclic olefins in the synthesis of triamantane
Authors: Kafka Zdeněk , Vodička Luděk
Published: September 2010

The paper describes the composition of products arising from the Diels-Alder reaction of butadiene with hexacyclic olefins (hexacyclo[8,4,0,02,7,03,14,04,8,09,13]tetradec-5-ene and hexacyclo[6,6,0,02,6,05,14,07,12,09,13]tetradec-3-ene) under different conditions. The reaction afforded a mixture of heptacyclic olefins (heptacyclo[8,8,0,02,17,03,11,04,9,012,16,013,18]octadec-6-ene and heptacyclo[8,8,0,02,13,03,11,04,9,012,17,014,18]octadec-6-ene), which is an important intermediate in the synthesis of triamantane.
Preparation and Z-E isomerization of substituted nitrostyrenes
Authors: Bláha Ivo , Lešetický Ladislav
Published: September 2010

This study concerns the synthesis of β-sustituted β-nitrostyrenes by two procedures: addition of nitryl halogenides to double bonds, connected with the elimination of hydrogen halide, and condensation of aldehydes with substituted nitromethanes, and it compares the utilizability of the two procedures. Two of the substances prepared, methyl (Z)-nitro-3-phenylpropenoate and (Z)-4-phenyl-β-nitro-β-buten-2-one, were submitted to Z-E isomerization at various temperatures, and thermodynamic isomerization parameters were estimated from the dependence of the equilibrium constants on temperature.
5-Nitro-2-thienylvinylation. Preparation of 2-substituted 1-(5-nitro-2-thienyl)ethylenes
Authors: Hrabovský Ján , Kováč Jaroslav , Kaprinayová Mária
Published: September 2010

The preparation of 2-substituted 1-(5-nitro-2-thienyl)-ethylenes based on the reaction of (Z)-2-bromo-1-(5-nitro-2-thienyl)ethylene with aromatic or heteroaromatic compounds in the presence of aluminum chloride is described. The structure of the derivatives prepared was investigated by means of 1H NMR and UV spectra and dipole moments measurement.
Hydrogenation of methyl ester of Z-α-acetamidocinnamic acid catalysed by rhodium-phosphine carboxylates
Authors: Zikanová Zuzana , Vaisarová Věra , Hetflejš Jiří
Published: September 2010

The title reaction has been studied using the in situ catalysts prepared from [Rh(COD)Cl]2, [Rh(COD)OOCCH3]2 or Rh(COD) (acac) and a series of mono- and diphosphines. The use of (+)-N-acetylphenylalanine as a chiral carboxylato ligand gave catalytic systems with low asymmetric efficiency ( optical yields from 5 to 10%). Kinetics of the hydrogenation catalysed by [Rh(COD)OOCCH3]2 + (C6H5)2P(CH2)4P(C6H5)2 or P(n-C4H9)3 (Rh : P mol.ratio = 1 : 2) is reported.
Synthesis of pressinoic acid by enzymatically catalyzed formation of peptide bonds
Authors: Čeřovský Václav
Published: September 2010

Three fully enzymatic syntheses of the 1-6 vasopressin hexapeptide were investigated using papain, α-chymotrypsin and thermolysin. Best results were obtained with thermolysin in the 2 + 4 fragment condensation. The α-chymotrypsin-catalyzed 3 + 3 condensation is less advantageous and the 4 + 2 condensation with papain gave only low yield. Using the mentioned enzymes, further fragments of vasopressin molecule were prepared. Amino groups were protected with benzoylcarbonyl or tert-butyloxycarbonyl groups, carboxyl groups as phenylhydrazides or methyl esters, and the cysteine sulfhydryl group as the benzyl derivate. The tyrosine hydroxyl was not protected.
Contamination by oxygen and nitrogen during the high-temperature synthesis of rare earth element carbides and the hydrocarbon contents of their hydrolysis products
Authors: Karen Pavel , Hájek Bohumil
Published: September 2010

Contamination of reaction mixtures of rare earth elements and carbon by air oxygen and nitrogen at high temperatures results in changes in the phase composition of the products, which in turn lead to changes in the composition of the hydrolysis gas. La, Ce, Pr, and Nd give carbide-oxides Ln2O2C2 of acetylide nature, in concentrations increasing with increasing extent of contamination. For the smaller rare earth elements from Dy, Ho to Lu, the contamination leads to methanide-type carbide-oxides (or nitrides) M(C, N, O, ). A slight contamination of mixtures of the metals with carbon which are somewhat carbon-deficient with respect to the 1 : 2 composition gives rise to a phase which evolves a gas containing C3 hydrocarbons in a high concentration (nearly 50%), while its methane content is very low. The stability of this allylenide phase, which is not the M15C19 carbide, increases in the direction towards Lu to an extent such that the phase forms even besides higher amounts of the carbide-oxide-nitride, i.e., also on extensive contamination.
Facile coupling of alkyl or aryl halogenides with organolithium compounds in the presence of alkoxides of heavier alkali metals
Authors: Lochmann Lubomír , Trekoval Jiří
Published: September 2010

Nonactivated alkyl or aryl halogenides readily react with organolithium compounds in the presence of alkoxides of heavy alkaline metals. In the case of organic bromides and iodides, coupling products in the sense of the Wurtz reaction are mainly formed.
Dipole moments and conformation of some aromatic benzamidoximes
Authors: Exner Otto , Motekov Nedelko
Published: September 2010

Dipole moments of aromatic benzamidoximes I - VI were measured in benzene solution. Assuming the Z configuration as established previously on another set of similar derivatives, some details of conformation could be determined, e.g. the position of an unsymmetrically substituted aromatic ring or mutual position of several methoxy groups.
5-Tricyanovinyl-2-furylation of aromatic derivatives
Authors: Berkeš Dušan , Kováč Jaroslav
Published: September 2010

A new method for heteroarylation of aromatic derivatives has been developed. The highly reactive 2-bromo-5-tricyanovinylfuran acts in the presence of AlCl3 under conditions of Friedel-Crafts reaction as an electrophilic furylation reagent to give 5-aryl-2-tricyanovinylfurans with selected benzene and naphthalene derivatives.
Solvolysis of Westphalen-type compounds
Authors: Kasal Alexander , Zajíček Jaroslav
Published: September 2010

Action of some nucleophilic reagents (CH3COOAg, CH3COOK, LiAlH4) on 6β-chloro- and 6β-methanesulfonyloxy-5-methyl-19-nor-5β-cholest-9-enes VIII - XII affords predominantly A-homo-B,19-dinor-5β-cholest-9-ene derivatives, arising by rearrangement and substitution (XIII, XXIV) or rearrangement and elimination (e.g. XX). Hydrogenolysis of compounds of the type VIII with lithium aluminium hydride gives, in addition, a product of rearrangement, fragmentation and further reduction (XXVI), and 5-methyl-6α,10-cyclo-19-nor-5β,9β,10α-cholestan-3β-ol (XXX).
4-Phenylalanine analogues of vasopressin: Synthesis, pharmacological and chiroptical properties
Authors: Brtník František , Barth Tomislav , Maloň Petr , Frič Ivo , Kluša Vija E. , Jošt Karel
Published: September 2010

Synthesis, some pharmacological properties and CD spectra of [4-phenylalanine, 8-arginine]vasopressin and [4-phenylalanine, 8-lysine]vasopressin are described.
Nucleation in supersaturated vapours of solid and liquid naphthalene and phthalic anhydride
Authors: Smolík Jiří , Vítovec Jaroslav , Vašáková Jana
Published: September 2010

The critical supersaturations of vapours of solid naphthalene and phthalic anhydride have been measured by using downward thermal diffusion cloud chamber. The experimental data have been fitted by an empirical fitting formula to allow predictions of behaviour of vapour-noncondensable gas mixtures of both compounds in condensation processes. Including the previously published data on critical supersaturations of vapours, measured above the triple point, the P-T diagrams have been drawn for both compounds.
Effect of the ionizing radiation on the catalytic activity of the BASF K-3-10 catalyst in the low-temperature conversion of carbon monoxide by water vapour. Stability of the radiation catalytic effects
Authors: Motl Alois
Published: September 2010

The radiation catalytic properties of the BASF K-3-10 catalyst were studied, namely the dependence of these effects on the time interval between the catalyst irradiation and the reaction itself and also on the length of the catalyst use. The catalytic effects decrease exponentially with the interval between the irradiation and the reaction if the catalyst is kept in the presence of air. The stability of effects induced by various types of radiations increases in the sequence beta radiation - gamma radiation - fast neutrons. The radiation catalytic effect stability in the reaction increases in the same sequence.
Particles segregation in fluidized bed binary systems
Authors: Čársky Milan , Veselý Václav , Pata Jaroslav
Published: September 2010

Binary systems have been divided into six groups according to their minimum fluidization velocities, densities, and size of particles. A concentration profile of fluidized bed has been studied. Experimental results have indicated that interval (45 - 90 sec.) is necessary for concentration profile generation. The profile appears to be uninfluenced by original arrangement of system components, the composition of bulk and grid region being in mutual equilibrium. Superficial velocity strongly affects system equilibrium, especially at higher jetsam concentrations. The best segregation of the system was achieved at velocities close to the minimum fluidization velocity of the binary system. The binary systems of the 3rd and 6th types change from segregated to mixed fluidized bed if gas velocity increases. The binary system of the 1st type was difficult to mix up since flotsam entrained partially if velocity of air was increased. The equilibrium concentration profile was uninfluenced by the size of the equipment - provided fluidized bed height was above a critical limit.
Synthesis of N-hydroxymethylacrylamide in an aqueous solution
Authors: Matějíček Alois , Černý Jaroslav
Published: September 2010

The paper deals with a reaction between acrylamide and formaldehyde leading to the synthesis of N-hydroxymethylacrylamide. The reaction was carried out in the temperature range 303.2 to 333.2 K, pH 9.2-10.35, at the methanol concentration 0-6.5239 mol l-1 at the constant molar ratio of acrylamide to formaldehyde 1 : 1. The time dependence of the loss of formaldehyde in the reaction mixture was approximated by an empirical relation (cF)0 - cF = t/(A + Bt), which was used in the determination of the rate constants for a reaction leading to the synthesis of N-hydroxymethylacrylamide and for the reversible reaction, and of the equilibrium constant of the reaction. The measurements and calculations showed that the optimal conditions for the synthesis of N-hydroxymethylacrylamide were 313.2 K, methanol concentration 1.5 mol l-1 and pH 9.8-10.1.
Photoreaction of 3,4-dimethoxy-1-nitrobenzene with butylamine. A pH dependence of regioselectivity
Authors: Kuzmič Petr , Pavlíčková Libuše , Velek Jiří , Souček Milan
Published: September 2010

Irradiation of 3,4-dimethoxy-1-nitrobenzene in the presence of butylamine leads to the formation of both possible photosubstitution products, i.e., 2-methoxy-4-nitro-N-butylaniline and 2-methoxy-5-nitro-N-butylaniline with the predominance of the latter. Regioselectivity of the reaction as measured by molar ratio of the two isomeric products varies with pH of the solution, ranging from 3 : 1 at pH 10 to 12. The results are discussed in view of possible use of 3,4-dimethoxy-1-nitrobenzene moiety as a lysine-directed photoaffinity probe.
Methyl esthers of methyl 2-deoxy-α- and β-D-threo-pentopyranoside
Authors: Medonos Ivan , Kocíková Věroslava , Staněk Jan , Zobáčová Alena , Jarý Jiří
Published: September 2010

Methyl 2-deoxy-α- and β-D-threo-pentopyaranosides (Ia, IIa) were prepared. Various conditions for partial methylation of the β-anomer IIa were tried out, leading to methyl 2-deoxy-3-O-methyl-β-D-threo-pentopyranoside (IIc), methyl 2-deoxy-4-O-methyl-β-D-threo-pentopyranoside (IId) and methyl 2-deoxy-3,4-di-O-methyl-β-D-threo-pentopyranoside (IIe). The structures of the products were determined by means of 1H NMR.
Preparation and reactions of thieno[3,2-b]furan derivatives
Authors: Kraľovičová Eva , Krutošíková Alžbeta , Kováč Jaroslav
Published: September 2010

Reactions of 3-(5-aryl-2-furyl)propenoic, 3-(2-benzo[b]furyl)propenoic and 3-(5-ethoxycarbonyl-4H-furo[3,2-b]-2-pyrrolyl)propenoic acids with thionyl chloride in the presence of triethylbenzylammonium chloride were investigated. The obtained 2-arylthieno[3,2-b]-furan-5-carboxylic acid chlorides Ia - Ic and 3-chlorothieno[3,2-b]benzo[b]furan-2-carboxylic acid chloride afforded in substitution nucleophilic reactions the corresponding esters V and carboxylic acids VI which were decarboxylated to VII. 3-Chlorothieno[3,2-b]benzo[b]furan-2-carboxylic acid chloride (Id), 6-ethoxycarbonyl-3-chlorothieno[2',3':4,5]furo[3,2-b]pyrrole-2-carboxylic acid chloride (IV), and ethyl 3-chlorothieno[2',3':4,5]furo[3,2-b]indole-2-carboxylate (VIII), synthesized under conditions of triethylphosphite reduction from ethyl 6-chloro-2-(2-nitrophenyl)thieno[3,2-b]furan-5-carboxylate (Va), are new heterocyclic systems.
Sesquiterpene lactones of Urospermum dalechampii SCHMIDT
Authors: Rychłewska Urszula , Hodgson Derek J. , Grabarczyk Halina , Drożdż Bohdan , Daniewski Włodzimierz M. , Kroszczyṅski Wojciech , Buděšínský Miloš , Holub Miroslav
Published: September 2010

In the species Urospermum dalechampii SCHMIDT urospermal A (I) and 11βH,13-dihydrourospermal A (II) were detected. The latter compound was also detected in U. picroides SCHMIDT. The spectral characteristics of both lactones were completed by 13C NMR data. The structure of 11βH,13-dihydrourospermal A (II) was also confirmed by X-ray analysis.
Isolation of (23R) 3α, 7α,23-trihydroxy-5β-cholan-24-oic (β-phocaecholic) acid from duck bile. 1H NMR spectra of its derivatives
Authors: Klinot Jiří , Jirsa Milan , Klinotová Eva , Ubik Karel , Protiva Jiří
Published: September 2010

(23R) 3α, 7α,23-Trihydroxy-5β-cholan-24-oic acid (IV) - a bile acid typical of some marine mammals - was now isolated from duck bile. Acid IV was characterized as derivatives V - VIII, XI and XII and oxidatively degraded to derivatives of 24-nor-5β-cholan-23-oic acid, XIII - XVIII. The 1H NMR spectra of these compounds and (23S) methyl ester X are discussed and the effect of substitution in position 23 on the chemical shifts of the methyl groups is summarized.
Synthesis of anomeric 5-cyclopropyl-2'-deoxyuridines and 1H NMR spectroscopic study of their conformation
Authors: Bašnák Ivan , Farkaš Jiří , Zajíček Jaroslav , Havlas Zdeněk
Published: September 2010

The title compounds Ia,b were prepared by ammonolysis of the corresponding p-tolyl nucleosides IIa,b obtained by the silylation method in the yields of 26% and 53% respectively. Conformation of the furanose ring in the free (Ia,b) as well as blocked (IIa,b) nucleosides was investigated by 1H NMR spectroscopy.
Formation of the poly(Lys-Ala-Ala) complex with pectin of various esterification degree
Authors: Bystrický Slavomír , Kohn Rudolf , Sticzay Tibor , Bláha Karel
Published: September 2010

The helix-forming interaction of poly(Lys-Ala-Ala) with potassium pectinates of various esterification degree (E 0-87%) was quantitatively investigated by circular dichroism spectra. The helix-forming effect of pectinates is significant even at a low density of carboxyl anions in the molecule at a high esterification degree. The mutual complementarity of linear charge density of both interacting polyions plays a decisive role. The charge densities of unesterified pectate and helical poly(Lys-Ala-Ala) are very close. Orientation of the potassium pectate macromolecule (E0%) in the proposed spatial model is parallel to the axis of poly(Lys-Ala-Ala) α-helix. Saturation of the polypeptide charge with pectinates of an esterification degree E > 0% is achieved through formation of a superhelical structure of the pectinate with a turn density corresponding to the equivalence of charge densities of both interacting components in the complex.
Interaction of human hemoglobin with haptoglobin studied by the method of oxygen saturation curves
Authors: Hájková Hana , Pavlíček Zdeněk , Kalous Vítěz
Published: September 2010

Two types of hemoglobin-haptoglobin complexes were studied which had been prepared by mixing together the two components in a different order. The oxygen saturation curves have shown that hemoglobin was bound in these complexes either in the form of tetramers or in the form of noncooperative dimers. The investigation of the interaction of deoxyhemoglobin with haptoglobin demonstrated that these two proteins do not bind to one another; the corresponding oxygen saturation curve was the same as the curve obtained with hemoglobin alone. In contrast, haptoglobin interfered with the saturation curves of deoxyhemoglobin containing an allosteric effector
Interaction of human hemoglobin with oxygen in the presence of benzene and use of computer for construction of saturation curves
Authors: Hájková Hana , Pavlíček Zdeněk , Kalous Vítěz
Published: September 2010

The time profile of changes in the oxygen saturation curves of human hemoglobin in the presence of benzene was investigated. The partial oxygen pressure p50, necessary for a half saturation, decreases during the first 3.5 h of interaction of hemoglobin with benzene and did not change afterwards. The character of changes in Hill's coefficient was similar. The oxygen saturation was modeled both for hemoglobin alone and, using MWC as a model of allosteric interaction, also for hemoglobin and benzene in a computer.
A quantum-chemical study of dehydration of ortho forms of formaldehyde and formic acid
Authors: Leška Jaroslav , Németh Eugen , Loos Dušan
Published: September 2010

Gas-phase dehydration of methanediol (I) and methanetriol (II) has been studied by the MINDO/3 method with full optimization of the reaction paths. The intramolecular dehydration goes via high barriers (I 257.4, II 193.3 kJ mol-1). The acid-catalyzed dehydration involving protonation at oxygen atom of I goes via a considerably lower barrier (63.3 kJ mol-1), whereas protonation at oxygen atom of II results in practically spontaneous dehydration (0.4 kJ mol-1), which is the reason for the formic acid not being hydrated in water. Deprotonation of the protonated formaldehyde (II) and protonated formic acid (IV) is connected with high barriers (429.1 and 523.0 kJ mol-1, resp.). The deprotonation by a water molecule added to III and IV involves substantially lower barriers (53.9 and 96.3 kJ mol-1, resp.).
Topological aspects of chemical reactivity. Correlation diagrams and overlap determinant method
Authors: Ponec Robert
Published: September 2010

The recently proposed overlap determinant method is applied as an alternative means of construction of correlation diagrams. In comparison with existing techniques the main advantage of the proposed formalism lies above all in its universality allowing the unified classification of all types of chemical reactions.
Kinetic properties of the chelating derivatives of spheric cellulose
Authors: Tokarová Věnceslava , Tokar Oldřich , Kareš Jaromír
Published: September 2010

The steric effect of the functional groups on the kinetic properties of the chelating cellulose ion exchanger OSTSORB SALICYL is demonstrated. The exponential dependence was found between the diffusion coefficient and the concentration of the ion-exchanging functional groups and, together with its total mass capacity and its content of water, it has been used for the estimation of the sorbent kinetic properties. Moreover, the results obtained show that the attempt to achieve the highest possible capacity of the ion exchanger can lead to a substantial decrease of the sorption rate.
A probability form of the diffusion equation and its use to describe the distribution of the solid phase particle concentrations in a mechanically agitated charge
Authors: Kudrna Vladimír , Sýsová Marie , Fořt Ivan
Published: September 2010

An attempt is made in this paper to describe the solid particle motion in a flowing (agitated) incompressible liquid on the assumption that this motion may be considered as a diffusion Markov process. It is shown that such a procedure leads to a relation which differs from the diffusion equation commonly used in chemical engineering by the form of diffusion term. The expression proposed, unlike the relation usually used, makes it possible to describe the local concentration extremes of solid phase in the charge mixed.
A study of photocyclization of O-alkyl N-(3-chloro-2-benzo[b]thienocarbonyl)monothiocarbamates
Authors: Kutschy Peter , Imrich Ján , Bernát Juraj , Kristian Pavol , Fedoriková Iveta
Published: September 2010

The O-alkyl N-(3-chloro-2-benzo[b]thienocarbonyl)monothiocarbamates prepared by the reaction of 2-isothiocyanatocarbonyl-3-chlorobenzo[b]thiophene with methanol, ethanol, 1-propanol, and 2-propanol are cyclized on irradiation with light of the wavelength above 300 nm to give high yields (80-90%) of 2-alkoxy-4H-benzo[b]thieno[2,3-e]-1,3-thiazin-4-one derivatives. From the absorption and emission spectra of the starting compounds as well as from a study of model compounds and influence of the reaction conditions it is presumed that the investigated intramolecular photosubstitution of chlorine by sulphur proceeds from the first singlet excited state (π, π*) by a radical mechanism through the phase of radical complex formation.
Mechanism of alkenylation of aromatic substrates with 5-nitro-2-furylvinyl bromide
Authors: Hrabovský Ján , Kováč Jaroslav , Považanec František
Published: September 2010

Mechanism has been studied of electrophilic aromatic substitution with (Z)- and (E)-5-nitro-2-furylvinyl bromide in the presence of aluminium(III) chloride. From chemical findings and 1H NMR study it follows that the mechanism can be interpreted as an electrophilic addition-elimination pathway (AdE-E) from the point of view of the vinyl substitution.
Reduction of triterpenoid ketones by chloroiridic acid and trimethyl phosphite
Authors: Protiva Jiří , Klinotová Eva , Klinot Jiří , Kušiak Miroslav , Vystrčil Alois
Published: September 2010

Selective reduction of keto groups on triterpenoid pentacyclic skeleton by chloroiridic acid and trimethyl phosphite (Henbest method) was studied. The 2-oxo group is stereospecifically reduced to give axial 2β-hydroxy group whereas oxo groups in positions 1,3,11,12,16,20,21,22, and 28 do not react. An analogous reduction was observed with a 2-oxo steroid.
A study of the medium effect of mixed solvents; The benzene-acetonitrile system
Authors: Nevěčná Taťjana , Vymětalová Jitka , Bekárek Vojtěch
Published: September 2010

Rate constants of the reaction of triethylamine with ethyl iodide (at 293.15, 313.15, 323.15, and 333.15 K) and wave numbers of the longest wavelength band maxima of 4-nitroso-N,N-dimethylaniline, 3-nitro-N,N-dimethylaniline, and 2,6-diphenyl-4-(2,4,6-triphenyl-1-pyridinio)phenoxide were measured in benzene, acetonitrile, and their eleven mixtures. Activation characteristics of the reaction of triethylamine with ethyl iodide in these media were calculated, and the correlations of rate constants and spectral data with the functions of relative permittivity and refractive index of the media used and mutually with each other were carried out.
Protection, efficiency, and some practical aspects of use of CGC columns in high performance liquid chromatography
Authors: Kehr Ján , Chavko Mikuláš
Published: September 2010

Some practical adaptations of compact glass cartridge (CGC) columns and design of related components of the high-performance liquid chromatographic system are suggested; included are the design of a Teflon guard column and its filling procedure, an intra-column sample injector for on-column sample delivery or for injection into the precolumn, replacement of a contaminated packing or replenishment of packing at the top of the CGC column, a procedure for shortening the column to a desired length, and the possibility of thermostatting the column by means of a water jacket. These adaptations make it possible to increase the lifetime of the CGC column as much as five times without loss of efficiency, and to use partly damaged or imperfectly packed columns.
Photoinduced rearrangement of hydroxymethylisoxazolines, a route to enaminoaldehydes
Authors: Fišera Lubor , Kozhina Nadezhda D. , Oravec Peter , Timpe Hans-Joachim , Štibrányi Ladislav , Badovskaya Larisa A.
Published: September 2010

3-Aryl-4-R-carbamoyl-5-hydroxymethylisoxazolines (IV) were synthesized by allowing R-NH2 amines with R = H, CH3, C3H7, C6H5C2H5, and NH2 to act on 3-(X-phenyl)-4-oxo-3a,4,6,6a-tetrahydrofuro[3,4-d]isoxazoles (III) with X = H, 4-CH3, 4-OCH3, 2-OCH3, 4-Cl, 2-Cl, 4-F, 2-F, 4-Br, 4-NO2, and 3-NO2. Exposed to radiation, the substances IV give Z-2-hydroxymethylamino-2-aryl-1-formylacrylamides (V) in good yields. The 4-Cl and 4-F substituted Z-derivatives V isomerize irreversibly to the E-derivatives VI if allowed to stand in solvent; the remaining derivatives V are stable. The quantum yields of the photoreaction are from 0.012 to 0.106 in dependence on the substituent X. In all cases where the compounds IV were used for the preparation of condensed heterocycles in conditions of acid-catalyzed reactions, lactones III were preferentially formed; the action of thionyl chloride on IV results in the formation of chloromethyl derivatives VIII, which do not undergo further cyclization.
Synthesis of some new pyrazolo[1,5-a]pyrimidine and pyrazolo[1,5-c]-as-triazine derivatives
Authors: Elagamey Abdel Ghani A. , El-Taweel Fathy M. A. , Amer F. A.
Published: September 2010

Several new pyrazolo[1,5-a]pyrimidine and pyrazolo[1,5-c]-as-triazine derivatives were synthesized via the reaction of 3-antipyrinyl-5-aminopyrazole or its diazonium salt with enaminonitriles, enaminoesters and active methylene reagents. The action of hydrazine hydrate on the obtained polyfunctional products was also studied.
Distribution pattern of uronic acid units in 4-O-methyl-D-glucurono-D-xylan of beech (Fagus sylvatica L.)
Authors: Kohn Rudolf , Hromádková Zdena , Ebringerová Anna , Toman Rudolf
Published: September 2010

4-O-Methyl-D-glucurono-D-xylan isolated from beech sawdust was characterized: its main chain consists of D-xylopyranose units linked by a glycosidic β(1 → 4) bond; uronic acid units are bound to C(2) of D-xylose units of the main chain as monomeric side units by a glycosidic α(1 → 2) bond. The distribution pattern of uronic acid units along the macromolecule chain was investigated in the water-soluble polysaccharide fraction of the D-xylose to uronic acid 6.1 to 1 molar ratio. The method based on interpretation of the activity coefficient of calcium counterions γCa2+ as determined with the calcium salt of glucuronoxylan was applied. The activity coefficient is a function of the linear charge density of the acid polysaccharide. It has been evidenced that the 4-O-methyl-D-glucurono-D-xylan under investigation is irregularly branched; it consists of longer segments of the macromolecule, each second D-xylose unit of which binds a uronic acid unit as a monomeric side terminal; these segments alternate with those composed of only D-xylan units.
Theoretical interpretation of the decrease of activity of enzyme during its chemical modification
Authors: Kéry Vladimír
Published: September 2010

A mathematical description of the decrease of the activity of enzyme during its chemical modification, based on probability theory as well as on chemical kinetics and considering both stochastically independent as well as stochastically dependent chemical modifications of any number of essential amino acid residues of the enzyme is proposed. Two types of the stochastically dependent chemical modifications, i.e. with negative cooperative effects and with positive cooperative effects were studied. A direct correlation was found to exist between the relative decrease of enzyme activity on the one hand and the number of essential amino acid residues as well as their role and relative mutual positions on the other. The procedure derived can be used for computer simulation of curves representing the decrease of the activity of enzyme during its chemical modification or for the nonlinear regression analysis of such curves.
Immobilization of exo-D-galacturonanase by coupling to a polyacrylamide type support
Authors: Heinrichová Kveta , Lehoczki Mária , Zliechovcová Dagmar
Published: September 2010

Exo-D-galacturonanase (E.C. 3.2.1.67) from carrot was immobilized by covalent bonding to a polyacrylamide type support (with free carboxyl groups) activated by water-soluble carbodiimides. The activity of the immobilized enzyme (under optimal reaction conditions of the immobilization) was around 43% of the activity of the free enzyme. The pH-optimum of activity was shifted from 5.1 to 5.3. The immobilization of the enzyme did not change its temperature optimum and the thermal stability of the enzyme was slightly increased after its immobilization. No change in the mode of action of the immobilized enzyme on a polymeric substrate or digalacturonic acid was observed. When sodium pectate was digested with the immobilized enzyme the value of Kmapp was substantially increased and the Vapp-value dropped to 40% of that observed with the free enzyme.
Electrocatalytic oxidation of benzyl alcohol on a platinum electrode modified by underpotential-deposited heavy metal adatoms
Authors: Sazou Dimitra , Xonoglou Nicolaos , Kokkinidis Georgios
Published: September 2010

The oxidation of benzyl alcohol on platinum surfaces modified by foreign metal adatoms (Pb, Tl, Bi) deposited at an underpotential region was studied in both acid and alkaline media; it was found that Pb, Tl, and Bi submonolayers intensively catalyse the benzyl alcohol oxidation. The enhancement of the electrocatalytic activity of Pt for the benzyl alcohol oxidation in acid solutions has been explained through the mechanism of ăthird body" effect in electrocatalysis. On the other hand, the enhanced catalytic activity in alkaline media, which in the case of Bi adatoms yields current densities close to the diffusion-limited values, has been interpreted in terms of the bifunctional theory in electrocatalysis.
A study of the sorption of strontium ions on α-FeOOH
Authors: Vaněk Karel , Jedináková Věra
Published: September 2010

The sorption of strontium ions on the solid liquid interface of the α-FeOOH-0.1M-NaNO3 system was studied over a wide concentration region of strontium ions and a constant concentration of sorbent so that crel = csorbent/csorbate was 101-104. The ΔG value of the sorption varies with crel and pH; it is as low as -32 kJ mol-1 at crel = 10 000 and pH 11 and increases to -18 kJ mol-1 at crel = 10 and pH 7.5. None of the conventional sorption equations can be applied to the studied system over the entire concentration region, but an equation of a different form is suggested for the description of this system.
Crystallization kinetics for the system CuSO4-ZnSO4-H2O forming solid solutions
Authors: Nývlt Jaroslav , Šnoblová Věra , Karel Miloslav
Published: September 2010

The three-component system CuSO4-ZnSO4-H2O forms three types of solid solution. Metastable zone widths measured for selected solution compositions at two cooling rates were used to calculate the kinetic parameters of nucleation. The rate of crystal growth was measured by the fluidized bed method. The results show that the addition of Zn2+ to a solution of CuSO4 increases both the nucleation and crystal growth rates, whereas Cu2+ added to a solution of ZnSO4 retards the nucleation rate and slightly increases the rate of crystal growth. The nucleation rate (the metastable zone width) is substantially more sensitive to the addition of a second component than is the rate of crystal growth. The crystal growth rate is controlled by a diffusion mechanism.
Mathematical modelling of salt purification by recrystallization. A cross-current flow model and its comparison with the countercurrent arrangement
Authors: Mayrhofer Benitto , Mayrhoferová Jana , Neužil Lubomír , Nývlt Jaroslav
Published: September 2010

A model is derived for a multi-stage crystallization with cross-current flows of the solution and the crystals being purified. The purity of the product is compared with that achieved in the countercurrent arrangement. A suitable function has been set up which allows the cross-current and countercurrent flow models to be compared and reduces substantially the labour of computation for the countercurrent arrangement. Using the recrystallization of KAl(SO4)2.12 H2O as an example, it is shown that, when the cross-current and countercurrent processes are operated at the same output, the countercurrent arrangement is more advantageous because its solvent consumption is lower.
Activity and selectivity of non-uniform bifunctional catalysts. Analysis of the fixed-bed reactor performance
Authors: Ardiles Darío R.
Published: September 2010

This paper reports a study about the effect of activity distributions of a bifunctional catalyst on the conversion and product distribution in a fixed-bed reactor. Uniform as well as increasing and decreasing activity profiles of both catalytic functions are considered. The analysis is performed assuming three different reaction schemes. Results show that reactor performance is greatly affected by the use of catalysts with non-uniform activity distributions.
Oxidation of 1,2,3,4-tetrahydronaphthalene by dioxygen. Effects of 3 transition metal 2,4-pentanedionates on the thermal and photoinitiated reactions
Authors: Luňák Stanislav , Vašková Marie , Vepřek-Šiška Josef
Published: September 2010

The effects of MnIII, CoII, CoIII, FeIII, and CrIII 2,4-pentanedionates on the thermal and photoinitiated reactions of 1,2,3,4-tetrahydronaphthalene by dioxygen have been investigated. CoII and MnIII, which are highly efficient catalysts for the thermal reaction, do not increase the rate of the photoinitiated reaction. FeIII and CoIII, which are poorly active in catalyzing the thermal reaction, have profound photocatalytic effects. The catalytic effect of CrIII is critically dependent on the presence of 1,2,3,4-tetrahydro-1-naphthyl hydroperoxide. An increase in the reaction temperature increases the rate of the photoinitiated reaction and enhances the catalytic and photocatalytic effects.
Selektivität der heptan-spaltung bei scharfen pyrolysebedingungen
Authors: Králíková Ulrika , Bajus Martin , Baxa Jozef
Published: September 2010

Unter Bedingungen der scharfen Pyrolyse wurde bei der Umwandlung von Heptan die Abhangigkeit der Hauptzerfallprodukte und der Koksmenge von der Temperatur und der Verweilzeit untersucht. Die Zersetzung des Heptans erfolgte in einem Stahlrohrreaktor in Gegenwart von inerten Verdunnungsmitteln bei einem Druck von 0.1 MPa, im Temperaturbereich 700 bis 820 °C und bei Verweilzeiten 0.02-0.70 s. Bei steigender Temperatur nimmt die Bildung von Methan, Wasserstoff und Koks zu, wobei die Bildung von Athan nicht beeinflusst wird. Bis zu einer bestimmten Verweilzeit wird die Bildung der Alkene unterstuzt. Ihre Uberschreitung fuhrt dann zu einer Abnahme der gebildeten Alkene. Ahnlich wie die Temperatur wirkt sich auch die Verlangerung der Verweilzeit auf die Bildung der angefuhrten Kohlenwasserstoffe aus.
Liquid phase oxidation of mesitylene to 3,5-dimethylbenzaldehyde
Authors: Valehrachová Gabriela , Hronec Milan , Veselý Václav
Published: September 2010

Liquid phase oxidation of mesitylene to 3,5-dimethylbenzaldehyde has been studied in the presence of cobalt bromide catalysts activated with triethanolamine or pyridine. The selectivity for the aldehyde is affected by the presence of the amine, by solvent, and only little by concentration of the catalyst and its components. The lower value of rate constant of the subsequent oxidation of the aldehyde, k2 = (7.66 ± 0.39) . 10-5 s-1, as compared with that of the oxidation of mesitylene, k1 = (1.66 ± 0.13) . 10-4 s-1 at 60 °C, indicates an important role of the cooxidation reactions in the process of oxidation of mesitylene, which affects the reaction selectivity.
Structure and stereochemistry of some neothiobinupharidine methiodides
Authors: Wróbel Jerzy T. , Scholl-Aleksandrowicz Anna , Wojtasiewicz Krystyna
Published: September 2010

Quaternization of neothiobinupharidine was examinated. The structure and stereochemistry of three methiodides were proposed on the basis of 13C NMR and 1H NMR spectroscopy and Hofmann degradation.