bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of halides on kinetics of copper dissolution in sodium hydroxide
Authors: Miadoková Milica , Sušinka Peter , Korintušová Alena
Published: August 2011

The influence of F-, Cl-, Br-, and I- ions on the kinetics of dissolution of (100) and (111) faces of a copper single crystal in a sodium hydroxide solution in the presence of oxygen was investigated. The results are interpreted in terms of adsorbability of the anions. Differences between the crystal faces are attributed both to the potentials of zero charge and to the different kinetic behaviour of these faces in pure sodium hydroxide solutions.
Acid-base properties of modified aluminas
Authors: Paukshtis E. A. , Soltanov P. I. , Yurchenko E. N. , Jirátová Květa
Published: August 2011

Acid-base properties of the pure alumina and aluminas modified by addition of various ions were determined by IR spectroscopic and Benesi method. The quality and concentration of OH groups of alumina samples containing SO42-, F-, Cl-, Na+, Zn2+ and Mg2+ ions were determined by IR spectroscopy, Pyridine, benzonitrile and carbon monoxide were used to determine the concentration and strength of aprotic centres and deuteriochloroform was used to determine the concentration and strength of basic centres. The results allowed to evaluate changes in the above properties caused by changes in the concentration of ions in alumina. It was found that the total acidity of modified aluminas determined by Benesi method correlates well with the relative proportion of acidic OH groups in the total spectrum of OH groups.
Kinetics and thermodynamics of the reaction between thyroxine and antithyroxine antiserum under the conditions of radioimmunoanalysis
Authors: Talán Peter , Mucha Juraj
Published: August 2011

Thermodynamics and kinetics of the reaction between thyroxine and antithyroxine antiserum has been studied using the concentration and temperature conditions usual in the radioimmunoanalysis. The reaction is assumed to be homogeneous and of the second order. Because of the initial concentrations of thyroxine and of the free bonds of the heterogeneous population of antibodies present in the used antiserum the rate constant equation for second-order reaction has been used in the integrated form. The relative rate constants have been obtained and the activation energy of the reaction in absence of the serum proteins in the reaction mixture or, respectively, in the presence of the euthyroidic serum has been calculated. The nature of the effect of so-called deblockators (J) (8-anilino-1-naphthalene sulphonic acid and tiomersal) on the reaction rate and on the change of the reaction enthalpy (or entropy) has also been investigated. The association constant of this reaction has been evaluated from the radioimmunoanalytical data transformed by the Scatchard relation, modified for the conditions of thyroxine radioimmunoanalysis.
Complex-formation reactions of 7-(o-carboxyphenylazo)-8-hydroxyquinoline-5-sulphonic acid with copper(II) ions: An application in EDTA photometric microtitrations
Authors: Chýlková Jaromíra , Říha Václav , Kotrlý Stanislav
Published: August 2011

Colour reactions of 7-(o-carboxyphenylazo)-8-hydroxyquinoline-5-sulphonic acid (OKFAZOX) with various metal ions are described. The formation of copper(II) complexes has been studied spectrophotometrically within a wide pH range by molar ratio method using computer-assisted regression matrix analysis of the absorbance sets. The following complexes have been identified, in agreement with the results of non-linear regression of continuous variation plots, as predominating species: CuLH2 within pH 1.3-2.9; CuLH within pH 3-7. Then, between pH 7 and 10, the complexes CuL and CuL2 take part in a stepwise equilibrium. Relevant conditional stability constants have been determined. A new photometric EDTA microtitration of copper(II) using OKFAZOX as indicator is proposed with the following optimum arrangement: pH about 5 (acetate buffer) and ionic strength 0.01; indicator concentration approx. 5 μmol l-1 or slightly higher; absorbance followed at 510 nm. End-point extrapolation gives precise results even within micromolar range:e.g. 2 μmol l-1 Cu2+ can be determined with a relative error less than 2%.
3-Ethoxy-2-hydroxybenzaldehyde as a starting compound for synthesis of isoquinoline alkaloids
Authors: Šmidrkal Jan
Published: August 2011

3-Ethoxy-2-hydroxybenzaldehyde (I) was used to prepare 6-bromo-2,3-dihydroxybenzaldehyde (V), 6-bromo-2,3-methylenedioxybenzaldehyde (VIa), 6-bromo-2,3-methylenedioxybenzoic acid (VIIa), and for new synthesis of compounds II, IIIa, IIIb, IV, VIb, VIIb, VIIIa, VIIIb, IXa and IXb.
Kinetic study of cyclization of 1-acyl-1'-alkenoylferrocenes. The effect of substitution on the donor and acceptor of Michael addition upon activation parameters of the reaction
Authors: Toma Štefan , Gáplovský Anton
Published: August 2011

Two series of disubstituted ferrocenes, 1-acyl-1'-cinnamoylferrocenes and 1-acyl-1'-alkenoylferrocenes, were prepared and kinetics of their cyclization to [5]ferrocenophane-1,5-dione derivatives has been studied. It was found that substitution on the double bond of the acceptor affects the activation parameters of the reaction less than substitution on the donor of Michael addition. Bulky substituents increase markedly ΔH##f up to 116 kJ mol-1 and ΔS##f up to +44 J mol-1 K-1.
Circular dichroism of alkaloids of colchicine type and their derivatives
Authors: Hrbek Jaromír , Hruban Ladislav , Šimánek Vilím , Šantavý František , Snatzke Günther , Yemul Srishalam S.
Published: August 2011

The CD spectra of 48 colchicine alkaloids and of some of their derivatives were given. The effects of the substituents and of the basic skeleton on the chiroptical properties of the measured compounds were discussed.
Cyclopropyl→cyclobutyl rearrangement in intramolecular cyclization of 3,5-bridged B-secoandrostane-6,7(or 5,7)-diols and mass spectra of products
Authors: Velgová Helena , Smolíková Jorga , Trka Antonín , Vítek Antonín
Published: August 2011

Acid-catalyzed intramolecular cyclization of 6,7-dihydroxy-3α,5-cyclo-6,7-seco-5α-androstan-17-one (VII), 5,7-dihydroxy-3,5-methylene-5,7-secoandrostan-17-one and 5,7-dihydroxy-3β,5-cyclo-5,7-seco-A-homo-5β-androstan-17-one (XIII) in benzene and dioxane was investigated. The main cyclization products were 3,5-methylene-6-oxaandrostan-17-one (I) and/or 3β,5-cyclo-6-oxa-A-homo-5β-androstan-17-one (VIII). In the case of VI and VII the ratio of I and VIII was solvent-dependent: in benzene more VIII was formed than in dioxane. The mass spectra of I and VIII were almost identical and corresponded to the structure VIII.
The influence of temperature and structure of palladium surfaces on the adsorption of ethylene and hydrogenation of adsorption complexes by molecular and atomic hydrogen
Authors: Kopešťanský Josef
Published: August 2011

A measurement of the work-function change, combined with the volumetric method and gas product analysis were used for investigation of the influence of temperature and palladium surface structure on the adsorption of ethylene and hydrogenation of its adsorption complexes by molecular and atomic hydrogen. It was verified that on palladium the highest activity for the C-H bond splitting of hydrocarbons is found on the adsorption sites corresponding to low-coordination surface atoms. The activation energy of the C-H bond dissociation is very low (ED ##i 2 kJ/mol); as a result, in the early stages of surface coverage, hydrogen appears on the surface - together with the formation of surface adsorption complexes. The presence of hydrogen is the main reason for the non-linearity of the work-function changes, observed for ethylene adsorption in the low-coverage region. Stable dehydrogenated surface particles are formed also by self-hydrogenation of ethylene in the higher-coverage region. With increasing temperature, the extent of dehydrogenation of the adsorbed complexes also increases - while the influence of molecular hydrogen on the work-function of the surface with pre-adsorbed ethylene becomes less significant. The interaction of atomic hydrogen with ethylene adsorption-complexes caused in all cases irreversible changes of the surface work-function.
Molecular-mechanical calculation of torsion potential in hexane
Authors: Gajdoš Ján , Bleha Tomáš
Published: August 2011

The report gives molecular-mechanical calculations of potential V(φ) of internal rotation around the central C-C bond in n-hexane with full geometry optimization. Basides the conformational dependence of the potential energy (strain energy), also torsion dependence of vibration entropy, zero point energy (E0) and heat of formation have been calculated for hexane. Limitations of bond-drive technique in application to quantitative static and dynamic characterization of internal rotation are pointed out. Effect of the condensed phase on V(φ) has been assessed on the basis of a simplified model of medium as continuum.
Statistical model of dehydrochlorination of polyvinyl chloride in inert atmosphere
Authors: Šimon Peter , Valko Ladislav
Published: August 2011

A statistical model of dehydrochlorination of PVC in inert atmosphere based on zip mechanism has been suggested. A good agreement has been found between experimental and theoretical curves of the dehydrochlorination carried out to high conversion degrees. Mathematical evaluation gives the activation energy and the frequency factor of the random splitting off of HCl from PVC: Ea = 170 kJ mol-1, log (A/s-1) = 12.9 (independent of the PVC type).
A study of porosity and impregnation of whetlerites
Authors: Kloubek Jan
Published: August 2011

The apparent and actual densities were measured for a set of seven porous samples with an identical carbon skeleton but differing in the content of inorganic salts. The corresponding values of porosity and density both of the active carbon skeleton and the impregnant of the whetlerites were calculated. In addition, the extractability of inorganic components from the samples was studied. On this basis, the chemical composition of the impregnant and a mechanism of the impregnant decomposition (occurring during its heat treatment) was proposed.
The calculation of ternary liquid-liquid (L-L) equilibrium data using a ternary correction to the excess gibbs free energy
Authors: Surový Július , Dojčanský Ján , Bafrncová Soňa
Published: August 2011

A universal form is proposed for the ternary correction to GE, which is based on the MacLaurin fourth-order expansion, With data on four ternary equilibrium liquid systems of the hydrocarbon-hydrocarbon-polar solvent type, it is demonstrated that a very good reproducibility of equilibrium L-L concentrations can be achieved by using this ternary correction. The ternary correction was applied to the NRTL, modified Wilson and Redlich-Kister equations. The correction parameters were determined from ternary L-L data, binary parameters were found from vapour-liquid (V-L) equlibrium data. For the determination of correction parameters with the help of the activity objective function, it is desirable to use weights from the law of the error propagation. For the determination of correction parameters with the help of the concentration objective function, an approximate expression was derived for calculating the probable value of the mole fraction of the solute in one of the equilibrium phases.
Effect of water vapour on the determination of trace substances trapped on activated carbon
Authors: Kaláb Pavel
Published: August 2011

The effect is studied of the activated carbon moisture on the recovery (R) of some organic substances, viz. benzene, acetone, tetrahydrofuran, ethanol, 2-methyl-1-propanol, and 1-butanol, trapped from air of different humidity and desorbed with carbon disulphide to equilibrium. If the weight fraction of water in the activated carbon is w = 0.02, the variations of R lie within the limits of error (for 0.3 g of activated carbon and 5 ml of CS2), whereas if w = 0.15, the variations of R, if disregarded, can result in errors as high as -45% for ethanol and -6 to -12% for butanol and acetone. In the case of benzene and tetrahydrofuran, the increase in the water content in the carbon does not affect the R value. The error increases as the activated carbon-to-carbon disulphide weight ratio is raised. For the standard addition method, the relative error was in average 18% (largely negative) for ethanol and -4.5 to -13% for the remaining substances.
Antioxidant action of 1,4-phenylenediamine antidegradants in selected liquid hydrocarbons
Authors: Rotschová Jitka , Pospíšil Jan
Published: August 2011

The antioxidant action of six N,N'-disubstituted derivatives of 1,4-phenylenediamine in the oxidation of tetralin, cyclohexene, squalane and squalene initiated with 2,2'-azobis(isobutyronitrile) at 60 °C was investigated. The amines under investigation acted as very strong antioxidants. The effect of substitution in positions N,N' on effectiveness is not very essential; it depends on the type of the substrate and does not make possible an unambiguous formulation of the relation between structure and effectiveness. It has been proved unequivocally that retardation of oxidation after completion of the induction period is a result of the formation of derivatives of benzoquinone diimine. The retardative action also is affected by the type of the oxidized hydrocarbon.
Acid catalysed opening of 4,4-dimethyl-4a,5-epoxy-A-homocholestane derivatives
Authors: Velgová Helena
Published: August 2011

The acid catalysed cleavage of 4,4-dimethyl-4a,5-epoxy-A-homocholestane derivatives bearing an oxygen-containing substituent (OH, OCOCH3, OCH3) in the position 3 with hydrobromic acid or aqueous perchloric acid was investigated. It was found that 4a,5-epoxides of 4,4-dimethyl-A-homocholestane series are opened on the side of the more substituted carbon atom C(5), where a normal cleavage leads to the formation of 4a-hydroxy-5,6-unsaturated derivatives, while the participation of the substituent in the position 3 leads to 3,5-epoxides. In none of the investigated epoxides was an attack of an external nucleophile observed. The effect of the nature of the substituent in the position 3 on the ratio of the products of a normal cleavage and the participation of the 3-substituent is discussed from the point of view of conformational effects. The dependence of the products ratio on the nucleophilicity of the acid used is also discussed.
The crystal structure of tris(diallyldithiocarbamato) iron(III)
Authors: Lokaj Jan , Kettmann Viktor , Pavelčík František , Vrábel Viktor , Garaj Ján
Published: August 2011

The crystal and molecular structure of [Fe(S2CN(C3H5)2)3] was solved by X-ray structural analysis and refined by the least squares method to give R = 0.09 for 1 834 observed reflections. The compound crystallizes in the C2/c space group and the monoclinic unit cell has dimensions of a = 18.709(6), b = 10.217(3), c = 15.546(6) . 10-10 m, β = 106.03(3)°. The experimentally observed density is 1.35 Mg m-3 and the calculated value for Z = 4 is 1.33 Mg m-3. In the structure the iron atom occupies a special position on the two-fold axis and is coordinated by six sulfur atoms in a trigonally deformed octahedron: Fe-S1 2.340(6), Fe-S2 2.367(7), Fe-S3 2.323(6) . 10-10 m. The S2CNC2 ligands are approximately planar.
Heat capacities of monomer models of some hydrophilic polymers in an aqueous solution from 20° to 60 °C
Authors: Biroš Ján , Sikora Antonín , Živný Antonín , Pouchlý Julius
Published: August 2011

The apparent molar heat capacities of propionic and isobutyric acids and of 2-hydroxyethyl pivalate and 2-(2'-hydroxyethoxy)ethyl pivalate in a dilute aqueous solution were determined with a DASM-1 m calorimeter. Moreover, the apparent specific volumes of these compounds in the aqueous solution and their molar heat capacities in the bulk liquid state were also determined. In the range 20° - 60 °C the apparent heat capacity in the aqueous solution is temperature-independent, or (in the case of propionic acid) increases slightly with temperature. The apparent heat capacities measured at 25 °C were compared with values estimated using various reported additivity schemes. Good agreement was observed for both acids; the other two compounds with more complicated molecules showed significant deviations from additivity.
Endo-D-galacturonanase immobilized by adsorption on porous polyethyleneterephthalate
Authors: Rexová-Benková Lubomíra , Omelková Jiřina , Kubánek Vladimír
Published: August 2011

Endo-D-galacturonanase of Aspergillus sp. was irreversibly adsorbed on polyethyleneterephthalate in an acetate 0.1 mol l-1 buffer solution of pH 4.2. Immobilization of the enzyme resulted in lowering of its activity, the measure of which depended on the amount of the enzyme fixed on the carrier. The highest relative activity (42.4%) had the preparation containing 5.25 mg of the enzyme per 1 g of the carrier. The velocity and intensity of the sorption of the enzyme depended on the ionic strength of the medium, whilst pH, on the other hand, was of no influence. Endo-D-galacturonanase immobilized in a 0.1 mol l-1 buffer was characteristic a) of its fixation strength in salt solutions of various ionic strength and pH, in a 3 mol l-1 guanidine solution, and also in sodium pectate and pectin solutions, b) of its high stability during a long-lasting storage at 4 °C, c) of its operational stability. The immobilization led to a partial change of the action pattern onto the high-molecular substrate, manifested in lowering the decrease of viscosity to degradation degree ratio.
ab initio MO-SCF study of prototropic transformations of non-substituted dihydropyridines
Authors: Böhm Stanislav , Kuthan Josef
Published: August 2011

The equilibrium systems formed by ionization of all the isomeric dihydropyridines I, II, III, IV and V with the particles H3O+, H2O and OH- have been characterized on the basis of the total energy changes calculated with the use of the STO-3G and 4-31G basis sets. Relative thermodynamic stabilities of the corresponding dihydropyridine forms are discussed.
Diethylamine addition to natural sesquiterpenic α-exomethylene-γ-lactones and its use for chemical transformations of these compounds
Authors: Harmatha Juraj , Samek Zdeněk
Published: August 2011

Addition of diethylamine to exomethylene double bond in natural sesquiterpenic α-methylene-γ-lactones is more advantageous in structural studies than the addition of other amines used so far. In some instances a simultaneous solvolysis of the ester groups also takes place. This fact was made use of for selective deacylation. The possibility of solvolysis impairs the potential use of diethylamine and other amines for the isolations of α-methylene-γ-lactone fractions directly from the extract of natural material.
Synthesis and biological activity of N-substituted 5-fluorouracil-1-acetamides
Authors: Pischel Helmut , Holý Antonín , Veselý Jiří , Wagner Günther , Cech Dieter
Published: August 2011

Reaction of 5-fluorouracil (I) with sodium chloroacetate in the presence of sodium hydride afforded a mixture of 5-fluorouracil-1-acetic acid (II) and 5-fluorouracil-3-acetic acid (III). p-Nitrophenyl 5-fluorouracil-1-acetate (IV) reacted with amines in methanol or dimethylformamide to give N-substituted 5-fluorouracil-1-acetamides V. The following amides were prepared: diethylamide Vc, n-hexylamide Vd, cyclohexylamide Ve, adamantylamide Vf, anilide Vg, benzylamide Vh, benzhydrylamide Vi, pyrrolidide Vj, piperidide Vk, morpholide Vl, 3-dimethylaminopropylamide Vm, 3-aminopropylamide Vn, 2-hydroxyethylamide Vo, bis(2-hydroxyethyl)amide Vp and tris(hydroxymethyl)methylamide Vq. Compounds Vc-Vq do not inhibit the growth of Escherichia coli in concentrations up to 1 mg/ml. Compounds Vf and Vh have a weak, compound Vq a significant, inhibition effect on the growth of L-1210 mouse leukemic cells in vitro in concentrations 1.5 . 10-5 mol l-1.
Sensitivity of some arabinosylcytosine derivatives to enzymatic deamination by cytidine deaminase from mouse kidney
Authors: Kára Jindřich , Bártová Markyta , Ryba Miloš , Hřebabecký Hubert , Brokeš Josef , Novotný Ladislav , Beránek Jiří
Published: August 2011

Enzymatic deamination of derivatives of arabinosylcytosine by partially purified cytidine deaminase isolated from mouse kidney is studied. The rate of deamination of 5'-chloroarabinosylcytosine (Ia), 5'-bromoarabinosylcytosine (Ib), 5'-chlorocyclocytidine (II), and 2',5'-anhydroarabinosylcytosine (III) is compared with that of arabinosylcytosine, of its N4-acetyl-, tri-O-acetyl-, tetraacetyl derivatives and of cyclocytidine. The deamination of the anhydro derivative III to the corresponding uracil derivative IV proceeds significantly slower than that of arabinosylcytosine, and comparably to that of cyclocytidine. The deamination of the 5'-halogeno derivatives Ia, Ib and II proceeds via the anhydro derivative III to IV. Some of the known arabinosylcytosine derivatives, cyclocytidine, N4-acetyl-, tetraacetyl- and tri-O-acetyl derivatives, show a resistance to enzymatic deamination. Different nucleoside analogs are tested as inhibitors of deaminase; only 2-β-D-ribofuranosyl-1,2,4-triazol-3-one possesses some activity.
Kinetics of oxidation of α-ketoglutaric acid with Ce(IV) ions in relation to Belousov-Zhabotinskii reaction
Authors: Treindl Ľudovít , Dorovský Vasil
Published: August 2011

Oxidation of α-ketoglutaric acid with Ce(IV) ions in a solution of sulphuric acid is a reaction of the first order with respect to both Ce(IV) ions and substrate, is acid catalysed, and its rate is proportional to the reciprocal square of the equilibrium HSO4- concentration. From the temperature dependence of the rate constant in 1.5M-H2SO4, the activation parameters were determined as ΔH##f = 57 kJ/mol and ΔS##f = -45 J mol-1 K-1. The redox reaction proper consists apparently of two steps: in the first one, the enol form of α-ketoglutaric acid reacts with Ce(IV) ions with the formation of the corresponding radical; in the second one, the latter is oxidized further with Ce(IV) to give malonic and succinic acids. Conditions are indicated under which α-ketoglutaric acid serves as substrate for the Belousov-Zhabotinskii oscillation reaction in the presence of Ce(IV)-Ce(III) redox catalyst. Oscillations of Ce(IV) and Br2 concentrations, shifted in phase, can be recorded polarographically with a rotating platinum electrode.
Distinguishing some types of one-electron reversible processes according to different polarographic wave forms
Authors: Vítek Antonín , Krupička Josef
Published: August 2011

Based on different shapes of polarographic one-electron waves influenced by preceding or follow-up dimerization reactions, a computational diagnostic method for distinguishing various types of the corresponding reaction mechanisms was elaborated, based on approximate relations between current and applied voltage. It enables one to evaluate statistically the distinguishing of a simple reversible reduction from a reduction accompanied by a rapid dimerization either in the adsorbed state on the electrode or in its vicinity. Factors influencing the selectivity of the method are discussed.
Electrochemical behaviour of some olefins and products of their chlorohydroxylation on platinum and graphite electrodes
Authors: Kazarinov Vladimir , Tedoradze Gurami , Gorokhova Liya , Bairamov Damat
Published: August 2011

The electrochemical behaviour on platinum and graphite electrodes of propylene, 1,3-butadiene and products of their chlorohydroxylation by electrochemically generated chlorine has been studied. It has been demonstrated by two methods: the potential sweep method with the use of a rotating disc electrode and the galvanostatic method. On graphite electrodes (unlike on platinum) redox reactions occur at a very low rate.
Extraction of dithiocarbamic acids from solutions of their salts
Authors: Oktavec Drahomír , Síleš Bohumil , Remeň Ján , Konečný Václav , Garaj Ján
Published: August 2011

The extraction of dithiocarbamic acids with chloroform from aqueous phase containing their alkali salts has been investigated with regard to the fact that absorbing strongly in the 200-310 nm range, the acids interfere with the spectrophotometric determination of metals whose dithiocarbamate ligands exhibit their analytical absorption bands in that region. The amount of the dithiocarbamic acids formed depends on the kinetics of their formation and decomposition reactions and on the pH of the aqueous phase. The stability of the acids in chloroform extracts is highly time dependent. The maximum extraction of the acids (R2NCS2H) is attained at the following pH (R, pH): CH3 5.0, C2H5 5.9, C3H8 6.3, C4H9 6.8, C5H11 6.9, C6H13 6.9, iso-C3H7 7.2, iso-C4H9 6.9; for (CH3, iso-C3H7)NCS2H 7.3, C5H10NCS2H 7.2, C4H8ONCS2H 5.2.
Acid-base properties of 1,3-diphenyl-5-(1H-tetrazol-2-yl)formazan and 1,3-diphenyl-5-(2H-1,2,4-triazol-3-yl)formazan
Authors: Likhareva Nadezhda , Šůcha Ladislav , Suchánek Miloslav
Published: August 2011

Two new compounds from the formazan series, viz. 1,3-diphenyl-5-(1H-tetrazol-2-yl)formazan and 1,3-diphenyl-5-(2H-1,2,4-triazol-3-yl)formazan, were prepared, and the dissociation constants and molar absorptivities of all of their acid-base species were determined spectrophotometrically employing the SPEKTFOT computer program.
Study of reactions in two-phase systems hydrolysis of triphenylmethyl chloride in water-organic solvent systems
Authors: Šilhánek Jaroslav , Konrádová Lenka , Šimečková Olga , Horák Josef
Published: August 2011

The rate of hydrolysis was studied for triphenylmethyl chloride in water-organic solvent systems with an unstirred interface of a known area. The hydrolytic reaction was found to take place at the interface only. The temperature dependence of the reaction rate indicates that at lower temperatures (up to 60 °C) the rate-determining step is the chemical reaction, whereas at higher temperatures a deviation from the Arrhenius type dependence is observed, which along with the low activation energy value points to the diffusion as the governing phenomenon. The effect of salts added to the aqueous phase is consistent with the expected behaviour for the SN1 mechanism, but suprising is the inhibiting effect od some quaternary ammonium salts. In the study of the effect of the organic solvent, the reaction rate was found to correlate satisfactorily with the solubility of the organic solvent in water, but no correlation was established with the solubility of water in the solvent. From the results obtained it can be inferred that the reaction site is the laminary layer adjacent to the interface from the aqueous phase side.
Alkaloids of Rauvolfia salicifolia GRISEB species
Authors: Sierra Patricia , Novotný Ladislav , Samek Zdeněk , Buděšínský Miloš , Dolejš Ladislav , Bláha Karel
Published: August 2011

From the endemic Cuban species Rauvolfia salicifolia GRISEB nine alkaloids were isolated of which the following seven had been already described: (+)-ajmalidine (I), (-)-reserpiline (II), (-)-isoreserpiline (III), (-)-isocarapanaubine (IV), (-)-ajmalicine (V), (+)-vellosimine (VI), and (+)-yohimbine (VII). The structure of (-)-raucubaine (VIII) had been previously determined by X-ray diffraction and the structure of the alkaloid (-)-raucubainine (IX) was suggested on the basis of its conversion to (-)-raucubaine (VIII). The absolute configuration of (-)-raucubaine and (-)-raucubainine was elucidated by CD spectroscopy.
Synthesis of eight stereoisomeric 5-(adenin-9-yl)-2,3,4-trihydroxypentanoic acids
Authors: Holý Antonín
Published: August 2011

Condensation of 5-O-p-toluenesulfonyl-2,3-O-isopropylidene-D-ribonolactone (XIIIb) with sodium salt of adenine afforded compound XIV which on alkaline, followed by acid, hydrolysis gave the (2R,3R,4R)-isomer V. The (2S,3S,4S)-isomer VIII was prepared analogously from the L-ribonolactone derivative XVb via the adenine derivative XVI. Compound XVIIc was transformed by reaction with adenine into 6-(adenin-9-yl)-6-deoxy-D-glucose (XIX); similarly, 6-(adenin-9-yl)-6-deoxy-D-mannose (XXI) was prepared from the protected D-mannofuranoside XX. Oxidation of compounds XIX and XXI in alkaline medium afforded the (2S,3R,4R)-isomer VI, 1,2:3,4-di-O-isopropylidene-D-galactopyranose (XXIIa) was transformed into 6-(adenin-9-yl)-6-deoxy-D-galactose (XXIIIb) which was oxidatively cleaved to give the (2S,3S,4R)-isomer VII. Methyl 5,6-di-O-methanesulfonyl-2,3-O-isopropylidene-D-mannofuranoside (XXVIb) was transformed into the reactive L-gulofuranoside derivative XXVIIe which on condensation with adenine and oxidative cleavage gave the (2S,3R,4S)-isomer IX. The (2R,3S,4R)-isomer XI was prepared analogously from the D-gulofuranose derivative XXXIb. Starting from L-mannose, the (2R,3S,4S)-derivative X was prepared via the 6-(adenin-9-yl)-6-deoxy-L-mannofuranoside derivative XXXc. Methyl 5-O-p-toluenesulfonyl-2,3-O-isopropylidene-L-lyxofuranoside XXXVb was transformed into 5-(adenin-9-yl)-5-deoxy-2,3-O-isopropylidene-L-lyxofuranose (XXXVII) which was oxidized to the lactone XXXVIII; this compound on successive alkaline and acid hydrolysis afforded the (2R,3R,4S)-isomer XII.
Work function studies of propylene, acetylene, hydrogen and nitrogen chemisorption on molybdenum
Authors: Bastl Zdeněk
Published: August 2011

The work function changes of vacuum deposited molybdenum films caused by the chemisorption of propylene, acetylene, hydrogen and nitrogen were measured using the Kelvin vibrating capacitor method. During the hydrocarbon chemisorption, the work function increased in a low surface coverage region but decreased at the higher surface coverages. The saturation values of the work function changes corresponding to complete coverage of the surface by chemisorbed propylene and acetylene equal -0.08 eV and -0.42 eV, respectively. The observed dependences of the work function change on surface coverage are interpreted by the dissociative chemisorption of hydrocarbons on a limited number of surface sites which are simultaneously the sites of preferred adsorption. The extent of dissociation decreases in the adsorption with the increasing surface coverage. The results of the study of the work function changes induced by the hydrogen and nitrogen chemisorption enabled to draw several conclusions on the surface topography of the used films.
Calculation of stabilization energy of parallel hexane molecules
Authors: Gajdoš Ján , Bleha Tomáš
Published: August 2011

Molecular-mechanics method has been used for calculation od stable configurations of n-hexane pairs and triads in extended all-trans conformations with full translational and rotational freedom of the molecules during optimization. The calculated stabilization energies and equilibrium distances have been compared with the experimental data obtained for molecular crystals of paraffins. The comparison enables to distinguish the effects characteristical of the collective packing forces in the crystal. The optimum configurations of some hexane pairs have also been calculated by the quantum-chemical PCILO method. The results indicate superiority of MMC to the quantum-chemical methods and other empirical calculation procedures for the purposes of the stabilization energy determination.
Mass transfer in heterogeneous system enzyme-substrate; Approximate analytical model for the case of liquid substrate-immobilized enzyme
Authors: Kaštánek František , Zahradník Jindřich , Ocampo Germanico
Published: August 2011

Calculation procedure is suggested for flow intensity of substrate toward reaction interface of immobilized enzyme at simultaneous effect of enzymatic reaction and internal diffusion. The approximate model is presented in an analytical form for the basic type of Michaelis-Menten kinetics and for the case of inhibition in excess of substrate.
Mass transfer in heterogeneous system enzyme-substrate; Kinetic model of enzymatic reaction in system of two immiscible liquids
Authors: Kaštánek František , Zahradník Jindřich , Ocampo Germanico
Published: August 2011

Mathematical model is proposed enabling calculation of enzymatic reaction rates occuring in one phase of a system of two immiscible liquids under conditions of substrate and product transfer over the interphase boundary.
Scale-up of stirred crystallisers. Batch precipitation of aluminium potassium sulphate
Authors: Karpiński Piotr , Žáček Stanislav , Nývlt Jaroslav , Budz Jerzy
Published: August 2011

Aluminium potassium sulphate has been precipitated batchwise by mixing equal volumes of 0.6 mol/l solutions of potassium sulphate and aluminium sulphate with eventual addition of water in advance. The experiments were performed at 20 and 25 °C in the volume 100 to 200 cm3 and in the volume 0.021 m3. From the size distribution of product crystals, the mean size of crystals has been evaluated and calculated the system kinetic constant of crystallization BN. The system constant is different in both series of experiments and can be correlated with the size of the crystallizer or with mixing intensity. Its value and the value of relative kinetic exponent g/n is comparable with the values obtained in experiments with cooling of solutions.
An-Additions to 2,5-dimethoxy-2,5-dihydrofurans, containing electron-accepting substituents in position 3
Authors: Stibor Ivan , Šrogl Jan , Janda Miroslav , Piričová Naděžda , Vlažný Karel
Published: August 2011

3-Acetyl-2,5-dimethoxy-2,5-dihydrofuran (V) was alkylated in position 4 with lithium dimethylcuprate and lithium dibutylcuprate. The reaction, proceeding with loss of methanol, afforded 4-acetyl-3-methyl-2-methoxy-2,3-dihydrofuran (X) and 4-acetyl-3-n-butyl-2-methoxy-2,3-dihydrofuran (XI), respectively. Addition of sodium salt of diethyl malonate gave 3-acetyl-4-bis(ethoxycarbonyl)methyl-2,5-dimethoxytetrahydrofuran (XVII) in 69% yield. Addition of methanol, n-butanol and tert-butyl alcohol to methyl 2,5-dimethoxy-2,5-dihydro-3-furoate (VI) in the presence of the corresponding alkoxides afforded the 4-alkoxy derivatives in 95%, 62% and 56% yield, respectively. Reaction of the compound VI with ethyl lithioacetate led to 3-ethoxycarbonylmethyl-4-methoxycarbonyl-2-methoxy-2,3-dihydrofuran (XVI) arising from the addition product by loss of methanol.
Tricyclic psychotropic agents containing two chalcogen atoms in the central ring: 8-Substituted 6-(4-piperidyl)-6H-dibenz[b,e]-1,4-oxathiepins
Authors: Šindelář Karel , Metyšová Jiřina , Holubek Jiří , Svátek Emil , Protiva Jiří , Protiva Miroslav
Published: August 2011

2-(2-Fluorophenylthio)benzaldehydes IXa-c and 5-chloro-2-(2-fluorophenylthio)acetophenone were treated with 1-methyl-4-piperidylmagnesium chloride and 3-dimethylaminopropylmagnesium chloride, respectively, and the resulting amino alcohols VIa-c, XVII and XVIII were cyclized with sodium hydride in dimethylformamide. In addition to the title compounds Ia-c, XIX and XX, several types of by-products were obtained. Demethylation of compound Ib by the chloroformate method afforded the secondary amine IIb which was transformed to the amino alcohols IIIb and Vb. Compounds Ia-c are very potent neuroleptics with a high degree of central depressant and cataleptic activity. The amino alcohol Vb exhibits a very strong antiapomorphine effect in rats.
Reactions of 11-chloro-11-phenyl-6,11-dihydrodibenzo[b,e]-thiepin with piperidine and some further nucleophiles
Authors: Protiva Miroslav , Šindelář Karel , Valenta Vladimír , Holubek Jiří , Svátek Emil , Ryska Miroslav , Schlanger Jiří , Urban Jiří , Hrubantová Marta
Published: August 2011

The title compound Vb affords with piperidine normal nucleophilic substitution product and the isomeric 3-piperidino derivative XXXII. The structure of XXXII was proven by (1) the 1H NMR and 13C NMR spectra, (2) an independent synthesis via the intermediates XXXV, XXXVI, XXX, IV and VIIIa, and (3) with the help of model reactions of the 2-methyl derivative VIb and the 3-methyl derivative VIIb with piperidine. The rearranged cation XXXVII is considered a precursor of the product XXXII. Similar mixtures are apparently formed in reactions of the chloro derivative Vb with a series of further amines where, however, mostly the normal substitution products (XV-XXI) were isolated and only in two cases the formation of the 3-substituted compounds (XXXIII, XXXIV) was noted. The 11-amino derivatives of the type XIII are unstable in ethanol in the presence of hydrogen chloride; the product of their acid catalyzed solvolysis is the ethoxy derivative XIV. Potassium phthalimide reacts with the compound Vb under the formation of the normal product XXII accompanied by 9-phenylanthracene (XXXVIII). Reaction of Vb with 3-dimethylaminopropylmagnesium chloride affords on the one hand the normal product XXIV, and the isomer on the other, to which the structure XXXIX is ascribed. The biological screening of the amines prepared showed with some compounds a rather significant antimicrobial activity in vitro (e.g. XXXIII) and some structurally less specific neurotropic effects, especially the spasmolytic (XXII, XXXIX) and the central depressant one (XX, XXXIII).
Constituents of the liverwort Lophocolea heterophylla
Authors: Konečný Karel , Ubik Karel , Vašíčková Soňa , Streibl Milan , Herout Vlastimil
Published: August 2011

From Lophocolea heterophylla sesquiterpene hydrocarbons β-barbatene, ent-β-selinene, cuparene, calacorene, calamenene and cadalene were obtained; α-barbatene is probably an artifact. ent-Isoalantolactone is the main sesquiterpenoid component. The characteristic smell of the plant is due to the presence of a minute quantity of the alcohol C12H20O, not characterized in details. Nonacosan-10-one and esterified nonacosan-10-ol are present in the lipid part of extract, in addition to „normal" components (n-alkanes, cerides).
Representation of binary excess enthalpy data
Authors: Prchal Miloslav , Dohnal Vladimír , Veselý František
Published: August 2011

An extensive test of five correlation relations for the concentration dependence of excess enthalpy of non-electrolyte solutions was carried out. The Redlich-Kister, root and reciprocal expansions, the SSF and Wilson equations were used to represent experimental data of 54 systems of different character. For the representation of data of symmetric and slightly asymmetric systems, we recommend the Redlich-Kister polynomial, more asymmetric systems are described excellently by the SSF equation.
MNDO conformations of chloromethyloxirane and solvent effect
Authors: Tvaroška Igor
Published: August 2011

Structure of chloromethyloxirane during rotation around the C-C single bond connecting oxirane ring and chloromethyl group has been studied theoretically in twelve solvents. Molecular characteristics and energy of the isolated molecule have been calculated by the semi-empirical MNDO method of molecular orbitals. The MNDO calculation predicts the existence of only two synclinal conformers G-1 and G-2, more stable being the less polar G-2, μ = 2.39 . 10-30 mC. However, the calculation carried out for dilute solutions including the solvation energy by the method of continuum reveals the presence of the third, antiperiplanar conformer T, μ = 9.26 . 10-30 mC. Populations of the individual conformers depend considerably on solvent, the most stable in ethanol being G-1, μ = 11.06 . 10-30 mC. The results obtained are compared with experimental data and also discussed from the point of view of the gauche effect.
Hydrophobic hydrogen anode with a nickel catalyst
Authors: Marholová Olga , Smrček Karel
Published: August 2011

A hydrophobic porous hydrogen anode was prepared whose electrochemical parameters are comparable with anodes containing a platinum catalyst. For its successful preparation, oxidation of the Raney nickel catalyst with air oxygen or with fluorine from Teflon must be prevented. The electrodes of a geometric surface area up to 450 cm2 were tested in cells and modules filled with 7M-KOH.
4-(Aminoacylamido)-s-hydrindacenes and related compounds: Synthesis and pharmacological screening
Authors: Vejdělek Zdeněk , Holubek Jiří , Bartošová Marie , Protiva Miroslav
Published: August 2011

Chloracylamido derivatives IIIa-Va were obtained by acylation of 4-amino-s-hydrindacene with chloroacetyl chloride, 2-chloropropionyl chloride and 3-chloropropionyl chloride; their reactions with excessive diethylamine, pyrrolidine, piperidine and morpholine afforded the title compounds IIIbcde-Vbcde. A reaction of 4-amino-s-hydrindacene with benzoyl isothiocyanate gave 1-benzoyl-3-(s-hydrindacen-4-yl)thiourea (VI) whose mild alkaline hydrolysis resulted in N-(s-hydrindacen-4-yl)thiourea (VII). The following treatment with methyl iodide and then with ethylenediamine afforded the imidazoline derivative VIII in a low yield. N-(s-Hydrindacen-4-yl)-2-piperidinoacetamide (IIId) in the form of the hydrochloride revealed a high degree of local anaesthetic and antiarrhythmic activity.
Synthesis of optically active 4,4- and 5,5-disubstituted 4,5-dihydro-6H-canthin-6-ones and their CD spectra
Authors: Hájíček Josef , Trojánek Jan
Published: August 2011

Synthesis of several optically active 4,4- and 5,5-disubstituted 4,5-dihydro-6H-canthin-6-ones ((R)-(+)-VII, (S)-(-)-XII and (R)-(+)-XVIII) and 5,5-disubstituted 4,5-dihydro-6H-canthin-4,6-diones ((S)-(-)-XIX and (R)-(+)-XX) is described and CD spectra of these compounds are discussed.
Non-cyclol (lactame) ergot alkaloids
Authors: Stuchlík Josef , Krajíček Alois , Cvak Ladislav , Spáčil Jiří , Sedmera Petr , Flieger Miroslav , Vokoun Jindřich , Řeháček Zdeněk
Published: August 2011

Two new alkaloids were isolated from the field ergot. Their structures, N-(D-lysergyl-L-valyl)cyclo(L-valyl-D-prolyl) (IV) and N-(D-lysergyl-L-valyl)cyclo(L-leucyl-D-prolyl) (V), were assigned by mass, 1H and 13C NMR spectroscopy.
Mass spectra of 4,4-dimethyl-A-homocholestane-3,5- and 3,4a diols and their derivatives
Authors: Trka Antonín , Velgová Helena
Published: August 2011

Partial mass spectra of the following 4,4-dimethyl-A-homocholestane derivatives are given: 3,5-epoxides I and II, 3,5-diols III-VI, 3-methoxy-5-ols VII-IX, 3-acetoxy-5-ol X, 3,4a-diols XI-XIV, 3-acetoxy-4a-ols XV-XVIII and 4,4-[2H6]-dimethyl-3,4a-diol XIX, and their electron impact fragmentation investigated. The mass spectra of epoxides I and II, diols III-VI and acetate X are very similar. Considerable differences in mass spectra of methoxy derivatives VII-IX are explained by two mechanisms of elimination of CH3OH from M+. The same similarity of the fragmentation processes and the mass spectra is also observed in diols XI-XIV and acetates XV-XVIII. For the formation of the characteristic ion m/z 288 a fragmentation scheme containing an usual cleavage of the rings A, B, and C is proposed. On the basis of comparison with the mass spectrum of the 4,4-[2H6]dimethyl analogue XIX it was shown that the ion m/z 361 in the mass spectra of diols XI-XIV is formed by elimination of the neutral fragment C6H13 from A-ring of the molecular ion, the last process being accompanied by the 3-hydroxyl transfer from A-ring to the rest of the molecular ion.
Analysis of one enzyme recyclization system with low enzyme concentration
Authors: Kovář Jan , Kučera Igor
Published: August 2011

One enzyme recyclization reactions in the presence of two substrates and a small amount of a coenzyme are characterized by a long prestationary phase, in the course of which the distribution of coenzyme forms varies. The kinetics of the coenzyme prestationary phase was analyzed theoretically and some equations characterizing mainly the start and the end of this phase were derived. To verify experimentally the derived equations two recyclization systems with horse liver alcohol dehydrogenase, NAD or NADH, and corresponding substrate pairs (p-nitrosodimethylaniline and 1-butanol, or furyl alcohol and acetaldehyde) were investigated. Consequences for the analytical practice and utilization of these reactions for the determination of small coenzyme and enzyme concentrations are discussed.
Precipitation and filtration of zinc, magnesium, copper and aluminium hydroxides
Authors: Söhnel Otakar , Matějčková Eva
Published: August 2011

Filtration properties of batchwise precipitated suspensions of Zn(OH)2, Mg(OH)2 and Cu(OH)2 and continuously precipitated Al(OH)3 were studied. For batchwise precipitated suspensions was verified the theoretically predicted dependence of specific filtration resistance on initial supersaturation and for the continuously precipitated Al(OH)3 the relation between the specific filtration resistance and the mean residence time of suspension in the reactor. Dependences were also recorded between the bed porosity and concentration of precipitated solutions, specific filtration resistance and used filtration pressure and the effect of aging of the batchwise precipitated suspension of Mg(OH)2on its filtration properties. The used CST method for determination of filtration characteristics of Zn(OH)2 suspension was also studied.
Oxidation of (1-hydroxybenzyl)ferrocene and its derivatives substituted in phenyl ring with bis(triphenylsilyl) chromate
Authors: Holeček Jaroslav , Handlíř Karel , Nádvorník Milan , Vlček Milan
Published: August 2011

Kinetics have been studied of oxidation of (1-hydroxybenzyl)ferrocenes substituted in phenyl ring with bis(triphenylsilyl) chromate in benzene solutions as well as protonation of these alcohols in sulphuric acid medium. Logarithms of the oxidation rate constants (kobs, 20-40 °C) and those of the protonation equilibrium constants (KR+, 25 °C) show linear dependence on the Hammett σ constants, the ρ constant values being -0.86 to -0.40 and -2.50, respectively. These negative values suggest that the both processes are influenced by the same effects and confirm the mechanism proposed earlier for oxidation of alcohols with ferrocenyl substituent by action of bis(triphenylsilyl) chromate in aprotic solvents.
Reaction of chromocene with acetylacetone
Authors: Beneš Ludvík , Votinský Jiří , Kalousová Jaroslava , Nádvorník Milan , Klikorka Jiří
Published: August 2011

Crystalline chromocene reacts with excess liquid acetylacetone to give chromium(III) acetylacetonate, cyclopentadiene and hydrogen. The reaction is exothermic and fast as low as at 25 °C. The reaction of solid chromocene with acetylacetone vapours is substantially slower, transient formation of chromium(II) acetylacetonate being observed.
Determination of crystallization kinetics from batch experiments
Authors: Nývlt Jaroslav
Published: August 2011

Three types of batch crystallization model experiments are considered: a) crystallization in which a constant supersaturation is maintained throughout the experiment (e.g. by programmed cooling); b) crystallization during which supersaturation is produced at a constant rate; c) crystallization (e.g. by precipitation) in which an initial supersaturation produced at the beginning gradually decreases during the run. The kinetic data obtained in the first case are of the same kind as those obtained in a continuous MSMPR (mixed suspension - mixed product removal) crystallizer. The two remaining types of experiment, on the other hand, can only provide relative kinetic data with respect to a reference run.
Stereochemistry of some substituted 2-furyl- and 2-thienyl ethylene derivatives. 1H NMR study
Authors: Dandárová Miloslava , Kováč Jaroslav , Végh Daniel , Žvak Vladimír
Published: August 2011

Stereochemistry of (E)- and (Z)-1-(5-nitro-2-furyl)-2-Y-ethylenes and 1-(5-nitro-2-thienyl)-2-Y-ethylenes (where Y = CH3O, 4-CH3C6H4O, N3 and Br) and of E and Z isomers of methyl 2-methyl-3-(2-furyl)propenoate and methyl 2-methyl-3-(2-thienyl)propenoate was studied by 1H NMR spectroscopy. With 1-(5-nitro-2-furyl)-2-Y-ethylenes, it was found that the preferred conformation of the furyl substituent relative to the side chain double bond is s-trans in the E isomers and s-cis in the Z isomers. The s-cis conformation is prevailing in both isomers of methyl 2-methyl-3-(2-furyl)propenoate. The E and Z isomers of all studied thiophene derivatives exist in the s-trans conformation.