bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonadiabatic coupling in the Li2-Li2+ system
Authors: Vojtík Jan , Krtková Alena , Polák Rudolf
Published: September 2010

Nonadiabatic coupling between the lowest two doublet potential energy surfaces of the Li2-Li2+ system is calculated using the semiempirical VB technique of diatomics-in-molecules (DIM). Location of nonadiabatic region in the configuration space and basic characteristics of the system in nonadiabatic and asymptotic regions are used to discuss the influence of the nonadiabatic effects on the behaviour of the Li2-Li2+ system under chemical conditions.
Syntheses of 1, 2, and 9-methyl derivatives of 4,9-dihydro-3-methyl-4-oxo-1H(2H)-pyrazolo[3,4-b]quinoline and their antiviral activity
Authors: Rádl Stanislav , Zikán Viktor , Šmejkal František
Published: September 2010

The paper describes syntheses of 4,9-dihydro-3-methyl-4-oxo-1H(2H)-pyrazolo[3,4-b]quinoline (Ia), its 1-methyl derivative (Ib), 2-methyl derivative (IIa), 9-methyl derivative (Ic), 1,9-dimethyl derivative (Id) and 2,9-dimethyl derivative (IIb). Sodium salts of compounds Ia, Ib, Ic and IIa were methylated with methyl iodide in dimethylformamide at room temperature, compounds Id and IIb were demethylated with pyridine hydrochloride. The compounds prepared were tested for antiviral activity in vivo in mice against influenza virus A2-Hongkong and the Encephalomyocarditis virus.
Synthesis of 7-chloro-5-(4-chlorophenyl)-1-methyl-1,3-dihydro-1,4-benzodiazepin-2-one
Authors: Vejdělek Zdeněk , Polívka Zdeněk , Protiva Miroslav
Published: September 2010

The synthesis of the title compound II was carried out from 5-chloro-3-(4-chlorophenyl)-2,1-benzisoxazole (III) by two methods proceeding via new intermediates V and VI. 5-(2-Fluorophenyl)-1,3-dihydro-1,4-benzodiazepin-2-one (VII) was synthesized from 2-amino-2'-fluorobenzophenone via VIII.
Synthesis of the semi-rigid analogues of prothiadene and dithiadene as potential antidepressant and antihistamine agents: 11-[2-(Dimethylaminomethyl)cyclohexylidene]-6,11-dihydrodibenzo[b,e]thiepins and 4-[2-(dimethylaminomethyl)cyclohexylidene]-4,9-dihydrothieno-[2,3-c]-2-benzothiepins
Authors: Polívka Zdeněk , Holubek Jiří , Svátek Emil , Metyš Jan , Protiva Miroslav
Published: September 2010

Reaction of dibenzo[b,e]thiepin-11(6H)-one with 2-(dimethylaminomethyl)cyclohexylmagnesium chloride gave a mixture of stereoisomeric amino alcohols IX from which four homogeneous bases (IXa to IXd) were separated by chromatography. Dehydration of these compounds with boiling dilute hydrochloric acid afforded mixtures of racemic geometric isomers of the title compound VII, which were separated by crystallization. To the prevailing less polar base VIIa (E)-configuration was assigned on the basis of the IR spectrum. Using a similar procedure, thieno[2,3-c]-2-benzothiepin-4(9H)-one gave mixture of amino alcohols X from which three homogeneous stereoisomers X-A to X-C were isolated. Their dehydration resulted in both expected racemic geometric isomers VIII-A and VIII-B. Pharmacological testing proved the character of an antidepressant for the semi-rigid analogue of dithiadene VIII.
A simple method of digitalization of polarographic curves. Description of the apparatus
Authors: Jermář Zdeněk , Vítek Antonín , Krupička Josef , Šerák Lubomír
Published: September 2010

The paper deals with the construction of a simple electronic equipment made from commercially available components, suitable for recording alternately the potential and the current data for a polarographic curve on a five-track perforated tape. The apparatus can operate in three modes making it possible either to record the polarographic curve or the current as a function of the time at constant polarization potential or the current-time curves on individual drops.
Crystal symmetry of the chlorate anion in host structures
Authors: Hájek Bohumil , Muck Alexander , Smrčková Olga
Published: September 2010

The infrared spectra were studied for the pyramidal ClO3- anion (C3v) embedded in host structures of various symmetries. Small amounts of NaClO3 or KClO3 were incorporated in NaBrO3 (T4), NaIO3 (D162h), KBrO3 (C3v5), and KIO3 (C11) structures. The ClO3- anion was found to assume the site symmetry of the host structure anion, i.e. C3, Cs, C3v, and C1, respectively, in accordance with the results of group analysis.
Hydroboration of 1-allyl-1,2,3,4-tetrahydroquinoline
Authors: Kafka Stanislav , Ferles Miloslav , Richter Miloslav
Published: September 2010

Hydroboration of 1-allyl-1,2,3,4-tetrahydroquinoline (I) with triethylamine-borane in the molar ratio 1 : 1 afforded a product from which 6,7-benzo-5-aza-1-boraspiro[4,5]decane (II) was isolated. Ethanolysis of II gave diethyl 3-(1,2,3,4-tetrahydro-1-quinolyl)propylboronate (III). Acid hydrolysis of the crude hydroboration product and subsequent oxidation with alkaline hydrogen peroxide led to a mixture of 3-(1,2,3,4-tetrahydro-1-quinolyl)-1-propanol (IV), 1,2,3,4-tetrahydroquinoline (V) and 1-propyl-1,2,3,4-tetrahydroquinoline (VI). Hydroboration of I with triethylamine-borane in the molar ratio 3 : 1, followed by oxidation, gave a mixture of IV, V, VI and 1-(1,2,3,4-tetrahydro-1-quinolyl)-2-propanol (VIII). Hydroboration of I with diborane in situ in diethylene glycol dimethyl ether at 20 °C and subsequent acid hydrolysis and oxidation with alkaline hydrogen peroxide afforded a mixture of IV, V and VIII when the hydroboration product was first heated to 150 °C and then subjected to the above-mentioned processing, only compounds IVand V were formed.
Alkaloids from Papaver bracteatum LINDL.
Authors: Slavík Jiří , Slavíková Leonora
Published: September 2010

N-Methylthebainium (as iodide) and corytuberine were isolated from the roots and green aerial parts of Papaver bracteatum LINDL., thebaine race Halle III, as significant alkaloids in addition to the predominant alkaloid thebaine (0.61 and 0.23% respectively), as well as the minor alkaloids isothebaine, scoulerine, protopine, epialpinine (O-methylalpinigenine), N-methylisothebainium (as iodide), isoboldine, corydine, rhoeadine, magnoflorine, a mixture of coptisine and palmatine and a new alkaloid PB 1 C18H19NO4. Bracteoline and papaverrubines G, E, D and C were detected chromatographically. From the ripe capsules of the race Halle III N-methylthebainium (as perchlorate), corytuberine and a mixture of coptisine and palmatine were isolated in addition to thebaine (0.67%). From the ripe capsules of P. bracteatum, population Demavend (Iran), thebaine (0.56%), epialpinine, alpinigenine, corytuberine, N-methylthebainium (as iodide) and a mixture of coptisine and palmatine were isolated and the presence of papaverrubines G, D and C was detected. In the latex of flowering plants salutaridine was also detected. Fourteen of the mentioned alkaloids were detected in the species P. bracteatum for the first time.
Homogeneous hydrogenolysis of the C-I bond; Preparation of [5-2H]uracil
Authors: Roček Josef , Sváta Vladimír , Lešetický Ladislav
Published: September 2010

Reductive dehalogenation of 5-iodouracil by deuterium, catalysed by coordination compounds of transition metals, has been studied. Conditions were found under which the deuteration product contained 80% of [5-2H]uracil and less than 2% of [5,6-2H2]uracil.
Adsorption of nitrogen oxide on a V2O5/Al2O3 catalyst
Authors: Sobalík Zdeněk , Pour Vladimír , Sokolova Ludmila A. , Nevskaya Olga V. , Popova Nina M.
Published: September 2010

The adsorption and desorption of nitrogen oxide on oxidized and reduced V2O5/Al2O3 catalysts (14.7% (m/m) V2O5) were studied by gravimetry, infrared spectroscopy, and temperature programmed desorption measurements. On the reduced catalyst, NO is adsorbed giving rise to mono- and dinitrosyls which exhibit infrared bands at 1 690, 1 760, 1 820, and 1 895 cm-1. A band also appears at 1 220 cm-1 corresponding to nitrite structures. The ratio between the nitrosyl and nitrite structures is approximately 4 : 1. Desorption at elevated temperatures is associated with the evolution of NO and N2O in a volume ratio of 10 : 1. On the oxidized catalyst the adsorption occurs to an extent at least two order of magnitude lower and no nitrosyls are formed.
Quantum-chemical study of photochemical E-Z isomerization of methanimine and its fluoro derivatives
Authors: Ertl Peter , Leška Jaroslav
Published: September 2010

The CNDO/2 CI method has been used for full optimization of geometry of methanimine and its fluoro derivatives in the first excited singlet state (S1). The reaction paths of the photochemical E-Z isomerization of these molecules in the S1 state by inversion and rotation mechanisms have been studied by the method of reaction coordinate with full optimization of all other coordinates. Each of the two mechanisms mentioned goes through an energy minimum, the rotation minimum being deeper. The non-radiative transition from the rotation minimum in the S1 state to the corresponding Franck-Condon ground state enables the isomerization of the molecule. The reaction paths obtained are similar to, and the energy differences of the corresponding Franck-Condon states are close to or identical with results of the model ab initio calculations published by other authors.
Synthesis of polyenylidenemalonaldehydes
Authors: Yanovskaya Ludmila A. , Kryshtal Galya V. , Dvořák Dalimil , Král Vladimír , Arnold Zdeněk
Published: September 2010

Condensation of polyenals I, where substituents R1 and R2 are CH3, H, C2H5OCO, Cl or CN, with 1,3-bis(dimethylamino)trimethinium perchlorate (II), followed by hydrolysis of the intermediate III, afforded polyenylidenemalonaldehydes IV. Properties and spatial arrangement of these products are briefly discussed.
The wavenumbers of C=O stretching vibrations of maleinimides
Authors: Perjéssy Alexander , Augustin Manfred , Köhler Manfred
Published: September 2010

The infrared spectra in the region of fundamental C=O stretching vibrations in tetrachloromethane and chloroform were measured for 59 maleinimide derivatives. A linear correlation between the wavenumbers of symmetric and antisymmetric C=O stretching vibrations was found for a series of 102 experimental data obtained in both solvents. The slope of the νs(C=O) vs νas(C=O) dependence as well as the degree of the vibrational coupling in imide system were discussed and compared with those for analogical five-membered cyclic 1,3-diketones.
Condensation of supersaturated vapours. Homogeneous nucleation of naphthalene and phthalic anhydride
Authors: Smolík Jiří , Vítovec Jaroslav
Published: September 2010

The critical supersaturation required for the homogeneous nucleation of naphthalene and phthalic anhydride from their vapours has been measured using upward thermal diffusion cloud chamber. The results obtained are compared with the predictions of the classical theory of homogeneous nucleation (Volmer-Becker-Doring-Zeldovich) and the corresponding states correlation of homogeneous nucleation. The classical theory is found to be in excellent agreement with the experimental results on naphthalene but overpredicts the critical supersaturation of phthalic anhydride vapours by about 30%. In order to fit the experiment and theory, the new values of surface tension of phthalic anhydride were recalculated from the theory. Critical supersaturation of naphthalene plotted versus temperature reveals the same regular departure from single fluid behaviour as found for alkylbenzenes. The experimental results on phthalic anhydride were found to be in very good agreement with the corresponding states correlation.
How to measure information obtained from biased quantitative analyses
Authors: Eckschlager Karel , Štěpánek Vladimír
Published: September 2010

It is shown that the use of the divergence measure for expressing the information content of the results of a quantitative analysis is justified only then if we need not to expect the rise of a systematic, i.e., statistically significant mean error. However, unless we can exclude the rise of a systematic error we have to adopt the information measure I(r, p, p0) proposed earlier; then of course every even statistically insignificant mean error has effect upon the information content. It is studied the relationship of this measure to another information measure used in a specific case for expressing the information content of biased results of a quantitative analysis.
Preparation and solubility of sodium hydrogenselenites. Thermoanalytical properties, infrared spectra and crystal data of NaH7(SeO3)4
Authors: Mička Zdeněk , Kratochvíl Bohumil , Podlahová Jana , Niinistö Lauri
Published: September 2010

The solubility diagram was studied at 25 °C for the Na2SeO3-H2SeO3-H2O system. On the basis of the solubility study, the conditions for the preparation of the hydrogenselenites, NaHSeO3, NaH3(SeO3)2 and NaH7(SeO3)4, were refined. For the compound, NaH7(SeO3)4, the infrared spectrum was measured, the crystal data were determined and a mechanism of thermal decomposition was proposed on the basis of the results of the study of the thermoanalytical properties of the compound.
A study of the mechanism of decay of alkyl macroradicals in isotactic polypropylene
Authors: Bartoš Josef , Tiňo Jozef
Published: September 2010

The kinetic data of decay of alkyl macroradicals in two temperature regions in isotactic polypropylene exposed to gamma radiation at 77 K were interpreted in terms of the model of diffusion-limited reactions at the activation energy level. The potential molecular mechanisms of transfer of the radical centres were tested from the point of view of their physical and/or chemical migration. Two mechanisms are suggested for the mutual approach of the centres in macroradical decay regions I and II in the amorphous zones of the matrix. Both of them involve the contribution of segmental conformational motions, the mobility of the terminal segments being of importance in region I whereas in region II the mutual nearing of the reactants proceeds in a relay way via intermolecular H-abstraction in conjunction with crank and crankshaft motions of the end and inner segments of the chain.
13C NMR spectra and substituent effects of meta and para substituted benzoyl isothiocyanates
Authors: Danihel Ivan , Imrich Ján , Košťík Dušan , Kristian Pavol , Barančíková Gabriela
Published: September 2010

13C NMR spectra have been studied of 20 meta and para substituted benzoyl isothiocyanates and corresponding benzoyl chlorides. The 13C SCS values of the carbon atom in NCS group have been found to correlate linearly with the Hammet σm,p constants of the substituents as well as with the corresponding π electron charges. The 13C SCS (substituent chemical shift) values of the carbonyl carbon atom of the compounds investigated are little sensitive to substituent effects and are analyzed on the basis of the dual-substituent-parameter approach. Also discussed are the intercorrelation relations of the 13C SCS values of benzoyl isothiocyanates and phenyl isothiocyanates and substituent effects on chemical shifts of carbon atoms of the benzene nucleus. For the benzoyl isothiocyanates the 13C NMR increments of chemical shifts and σm,p substituent constants of CONCS group have been determined.
Wavenumbers of C=O valence vibrations of endo-bicyclo[2.2.1]hept-5-ene-2,3-dicarboximides
Authors: Perjéssy Alexander , Sidóová Eva
Published: September 2010

Wavenumbers of symmetrical and antisymmetrical C=O valence vibrations of 50 derivatives of endo-bicyclo[2.2.1]hept-5-ene-2,3-dicarboximide have been measured in tetrachloromethane and chloroform. A satisfactory linear correlation between νs(C=O) and νas(C=O) has been found for 98 experimental points obtained in the two solvents. The anomalous low slope value ρ = 0.43 of this dependence can be used as evidence for endo configuration of the bicyclic 2,3-dicarboximides. The results are discussed in comparison with analogous relations found for other five-membered cyclic dicarboximides.
Reduced double-minimum potential curves for XY3 pyramidal molecules
Authors: Špirko Vladimír , Civiš Svatopluk , Beran Stanislav , Čársky Petr , Fabian Jürgen
Published: September 2010

The reduced potential curve (RPC) method used by Jenc and Pliva for studying the diatomic potentials is adapted for three-parameter studies of the inversional double-minimum potential functions of XY3 pyramidal molecules. Reduced double-minimum potential curves (RDMPC's) of the first, second and third row hydrides (CH3-, NH3, OH3+; SiH3-, PH3, SH3+; GeH3-, AsH3, SeH3+) are constructed using CNDO/2 and ab initio MBPT(2) theoretical potentials. The theoretical RDMPC's corresponding to a group of isoelectronic hydrides coincide to a high degree of approximation, so that they can be represented by a single curve. Furthermore, there is a nearly perfect coincidence between the theoretical RDMPC's of the first row hydrides and the ammonia experimental RDMPC (the only curve known experimentally). To illustrate a practical use of the proposed RPC approach, several approximants to the genuine phosphine potential are constructed (over a wide range of values for the inversion motion coordinate) by combining the available experimental data and the calculated RDMPC's. The resulting potentials exhibit a very close coincidence.
On the characterization of CO2 laser photosensitized reactions
Authors: Kubát Pavel , Pola Josef
Published: September 2010

The study of the effect of some variable parameters of the cw CO2 laser photosensitized reactions as concentration of inert gas and sensitizer, and laser output upon the temperature distribution inside the reactor is presented together with the application of two kinetic approaches to the laser photosensitized (SF6) dehydrochlorination of 1,1,1-trichloroethane.
cw CO2 laser powered pyrolysis of methane
Authors: Pola Josef , Chvalovský Václav
Published: September 2010

The cw CO2 laser-photosensitized (SF6) pyrolysis of methane with high content of the sensitizer affords ethylene and acetylene the yields of those are shown to depend upon the laser output and the foccusing conditions of the laser radiation.
Synthesis of 2-amino-8-benzylidene-4-phenyl-3,4,5,6,7,8-hexahydro- and -5,6,7,8-tetrahydroquinazoline derivatives
Authors: Deli József , Lóránd Tamás , Szabó Dezsö , Földesi András , Zschunke Adolf
Published: September 2010

Base-catalyzed reaction of 2,6-dibenzylidenecyclohexanone and alkylguanidines gave 2-alkylamino-8-benzylidene-4-phenyl-3,4,5,6,7,8-hexahydroquinazolines IVa-c, which were oxidized to 2-alkylamino-8-benzylidene-4-phenyl-5,6,7,8-tetrahydroquinazolines Va-c. The acylamino (VIa-c, VIIa-d, IXa,b) and diacylamino derivatives (VIIIa,b) of the 2-amino-8-benzylidene-4-pheny]-3,4,5,6,7,8-hexahydroquinazoline (II), 2-amino-8-benzylidene-4-phenyl-5,6,7,8-tetrahydroquinazoline (III) and compounds Va-c have also been prepared. These compounds having the E-configuration were converted into the Z isomers XIIa-e by photoisomerization. The structures were confirmed by spectroscopic methods (IR, 1H NMR, 13C NMR).
Physico-chemical properties of the ternary system urea-ammonium nitrate-water. Surface tension
Authors: Šišková Marie , Hejtmánková Jiřina , Bartovská Lidmila
Published: September 2010

Surface tension of two binary systems ammonium nitrate-water and urea-water and of the ternary system ammonium nitrate-urea-water was measured as a function of concentration at 20 and 40 °C. The experimental values were compared with those calculated from the relations which were proposed for calculating surface tensions of ternary systems from measured surface tensions of both binary systems.
The reaction of nickel(II) bis(diethyldithiocarbamate) with N,N,N',N'-tetraethyl thiuramdisulphide
Authors: Beinrohr Ernest , Staško Andrej , Garaj Ján
Published: September 2010

The oxidation of nickel(II) bis(diethyldithiocarbamate) (NiL2) by N,N,N',N'-tetraethyl thiuramdisulphide (tds) can be described by the equation 2 NiL2 + tds ⇄ 2 NiL3 (NiL3 = tris(diethyldithiocarbamate) nickel(III)). The equilibrium constant of the reaction depends on the polarity of the solvent (4.4 . 10-3 in toluene, 1.3 . 10-3 in chloroform, and 8 . 10-4 in acetone and methanol). The rate constants k1 and k-2 and the ratio k2/k-1 were found for the reaction steps NiL2 + tds ⇄ NiL3 + L. and NiL2 + L. ⇄ NiL3, where L. is the (C2H5)2NCS2. radical.
Optimization of the spectrophotometric determination of mercury using copper(II) diethanoldithiocarbamate
Authors: Beinrohr Ernest , Blazseková Katarina , Garaj Ján
Published: September 2010

The work deals with the optimization of the conditions for the spectrophotometric determination of mercury using copper(II) diethanoldithiocarbamate [Cu((HOCH2CH2)2NCS2)2] (I). The determination is based on replacement of Cu2+ ions by Hg2+ ions in complex I in acidic aqueous acetone medium and measuring the decrease in the absorbance at the absorption maximum of complex I (λ = 440 nm). The statistical importance of the factors affecting the analytical signal (absorbance) was found by the analysis of variance. The analytical signal is affected most by the pH value, the concentration of Cu2+ ions, and the acetone content. The best results were obtained at pH ~ 2 and an acetone content of 15% (v/v). The analytical calibration curve is nonlinear. The determination limit is 50 μg Hg in 1 dm3. The method is useful for the rapid determination of mercury with a precision of ± 5% in colourless solutions not containing Cu2+ or Ag+ ions or strong oxidants.
Mass transfer accompanied by chemical reaction in a liquid dispersion
Authors: Ptáček Jan , Rod Vladimír , Hančil Vladislav
Published: September 2010

An experimental procedure has been worked out to measure mass transfer rates in the presence of a chemical reaction in a liquid dispersion in a batch mixed vessel by a dynamic method. Transfer rates have been observed of iodine between decalin and water phase containing potassium iodide. The transfer was described by the pseudohomogeneous model. Transport parameters of this model have been evaluated from the response of the system to a step concentration change in the continuous phase. The model of the experiment described distortion of the information in the sampling device for the continuous phase. Dependences have been measured of the iodine transfer coefficients in both phases on the intensity of mixing and volume hold-up of the dispersed liquid. By a suitable choice of the concentration in the continuous phase the ratio could be adjusted of the resistance against the transfer in both phases and the sensitivity could be affected of the objective function to the evaluated model parameters.
On alkaloids of three Papaver species from the section Scapiflora REICHB.
Authors: Věžník František , Israilov Irgash A. , Táborská Eva , Slavík Jiří
Published: September 2010

The main alkaloid of the aerial part of P. croceum LEDEB. was nudaurine (I), isolated for the first time. In addition to amurine, known to be present in this species, oxysanguinarine (II) and corydine (IIIa) were also newly isolated and the presence of papaverrubine D demonstrated. In the fraction of tertiary bases from P.kerneri HAYEK allocryptopine and epialpinine (IV) were isolated as further alkaloids in addition to the already known alkaloids amurensine (the main alkaloid), amurensinine, amurine, alpinigenine, muramine, protopine, mecambridine, nudaurine, cryptopine and papaverrubines B, D, and G. In the fraction of quaternary bases the presence of traces of coptisine was detected, and in addition to alborine (alkaloid PO-5) cis-N-methyltetrahydropalmatinium hydroxide (V) was isolated for the first time in the form of iodide from P. kerneri. In P. tatricum (NYÁR.) EHREND. allocryptopine, epialpinine, and amurensinine were identified as the dominant alkaloids, while among the minor components protopine, amurensine, muramine, palmatine, coptisine, corytuberine (IIIb), N-methyltetrahydropalmatinium hydroxide, and N-methylamurensinium hydroxide could be demonstrated. Corydine (IIIa) and corytuberine (IIIb) represent the first two aporphine alkaloids found in the Scapiflora section.
Fluorescence behaviour of some 4-substituted halobenzenes
Authors: Koutek Bohumír , Musil Lubomír , Velek Jiří , Souček Milan
Published: September 2010

The fluorescence characteristics of 4-substituted chloro and fluorobenzenes I and II were studied in isooctane and acetonitrile solutions. It was found that all compounds exhibit a weak (substituent and solvent dependent) fluorescence in the range 305-370 nm with quantum yields 1.2 . 10-2-2.3 . 10-1. The relation between the substituent nature and fluorescence band position may be quantified by log νf~ = ρσp + log νf~0, the magnitude of the shift paralleling the donor strength of the substituent. Fluorescence quantum yields are increased approximately by a factor 2 on going from isooctane to acetonitrile and solvent-induced shifts are proportional to the static dipole moment change Δμ which occurs upon excitation. Radiative decay rate varies only slightly around a mean value of 5 . 107 s-1 and shows no substantial difference between chloro (I) and fluoro (II) derivatives. The non-radiative decay rate (of the order ~ 109 s-1) was found to be about 5 times higher in the case of chloro compounds due to the more efficient S1 - Tn intersystem crossing.
Conformational study on ribonucleoside O-phosphonylmethyl derivatives by 1H NMR spectroscopy
Authors: Masojídková Milena , Zajíček Jaroslav , Buděšínský Miloš , Rosenberg Ivan , Holý Antonín
Published: September 2010

Conformational properties of ribonucleoside 5'-O-phosphonylmethyl derivatives have been determined by 1H NMR spectroscopy and compared with those of natural nucleosides and 5'-nucleotides.
Metachors and dissociation of salts of oxo acids of group VI heavy metals in aqueous solutions
Authors: Škramovský Stanislav , Čeleda Jiří
Published: September 2010

The backround of the previously introduced concept of the metachor is outlined. This concept is applied to aqueous solutions of Se, Te, Mo, and W oxo acids and their sodium and potassium salts for which the metachors, calculated from the experimental surface tension values, are used to gain insight into their dissociation state in solution. The normal salts with mononuclear and binuclear anions (Me2XO3, Me2XO4, and Me2X2O7 types) in aqueous solutions at concentrations of 0.1-0.5 mol dm-3 are completely dissociated in the 2nd step and their metachors are about 10 cm3 mol-1, whereas KHSeO4 and Na2W3O10 with its bulky trinuclear anion are dissociated in the 1st step only and their metachors at the above concentrations lie in the 4.5 to 5.5 cm3 mol-1 range (at concentrations as low as 0.025 mol dm-3 for the latter). The metachor of the free acid H2SeO4 is as low as 2.5-1.5 cm3 mol-1, corresponding to an appreciable association in the 1st dissociation step. The metachor only reflects the "chemical" association due to short-range forces, whereas it is indifferent to physical outer-sphere ion pairing.
Molecular structure of para-substituted 3-aryl-2-arylmethylene-3-oxopropanenitriles in solution phase
Authors: Marchalín Štefan , Jehlička Václav , Böhm Stanislav , Trška Petr , Kuthan Josef
Published: September 2010

The conformational structure of the title compounds has been investigated by application of EHT calculations, 1H and 13C NMR spectral measurements, and calculated/found electrical dipole moments. It has been proved that compounds Ia-Ie and IIa-IIf obtained by thermodynamically-controlled Knoevenagel condensation are all E isomers. The dipole moment of compound Ia indicates a partially dipolar structure.
Alkylating activity of polyphosphate ester in the course of the synthesis of benzimidazoles
Authors: Bistocchi Giovanni Allunni , De Meo Giovanni , Pedini Mauro , Ricci Adolfo , Jacquignon Pierre
Published: September 2010

5-Fluoro-2-(5-nitrofuryl)benzimidazole (I) was synthesized from 4-fluoro-1,2-diaminobenzene and 5-nitro-2-furoic acid using ethyl polyphosphate as cyclization reagent. N-Ethyl derivative was isolated as by-product in substantial amount.
Solvent and substituent effects on rearrangement of 4-(4-X-phenyl)-2,7-dioxa-3-azabicyclo[3,3,0]oct-3-enes
Authors: Fišera Lubor , Konopíková Marta , Štibrányi Ladislav , Timpe Hans-Joachim
Published: September 2010

Preparation of the title compounds V is described. They give, on irradiation, the 2,3-dihydro-6H-1,3-oxazine derivatives VI as the main products besides the tetrahydrofuro[3,4-d]oxazoline derivatives VII. The VI to VII product ratio depends on the substituent bound to the aromatic residue. Polar solvents favour formation of the VI derivatives in the order Cl >H > CH3. In non-polar solvents the proportion of VII is increased. The quantum yields of the photoreaction vary within the limits from 0.006 to 0.04 (H >F > Cl > CH3 > OCH3).
Isopropylidenation of L-arabinose N,N-dimethylhydrazone
Authors: Koóš Miroslav , Mosher Harry S.
Published: September 2010

Direct isopropylidenation of L-arabinose N,N-dimethylhydrazone (I) was studied. Four major products whose structures were proven were produced in varying ratios depending upon the conditions. 2,2-Dimethoxypropane and sulfuric acid at 20 °C gave a 36% yield of 2,3:4,5-di-O-isopropylidene-L-arabinose N,N-dimethylhydrazone (II). Attempted aldol condensations directly on this hydrazone with paraformaldehyde were unsuccessful. This hydrazone was readily hydrolyzed to the corresponding protected aldehyde VI which underwent an aldol-Cannizzaro reaction to give the branched chain pentitol VII in high yield.
Syntheses of some N-carboxymethyl derivatives of 4,9-dihydro-3-methyl-4-oxo-1H-(2H)-pyrazolo[3,4-b]quinoline with antiviral effects
Authors: Rádl Stanislav , Zikán Viktor , Šmejkal František
Published: September 2010

The paper describes the syntheses of 4,9-dihydro-9-carboxymethyl-1,3-dimethyl-4-oxo-1H-pyrazolo[3,4-b]quinoline (Ic), 4,9-dihydro-9-carboxymethyl-2,3-dimethyl-4-oxo-2H-pyrazolo[3,4-b]quinoline (IIc), 4,9-dihydro-1-carboxymethyl-3-methyl-4-oxo-1H-pyrazolo[3,4-b]quinoline (Id), 4,9-dihydro-1-carboxymethyl-3,9-dimethyl-4-oxo-1H-pyrazolo[3,4-b]quinoline (If) and 4,9-dihydro-2-carboxymethyl-3,9-dimethyl-4-oxo-2H-pyrazolo[3,4-b]quinoline (IIf). The compounds were tested in vivo in mice for their efficacy against the virus A2-Hongkong and the encephalomyocarditis virus.
Contribution to the knowledge of the role of SH-groups in the molecule of pea alcohol dehydrogenase
Authors: Čeřovská Noemi , Leblová Sylva
Published: September 2010

p-Chloromercuribenzoate irreversibly inactivates alcohol dehydrogenase (ADH) isolated from germinating pea seeds. The reaction follows the first order kinetics. The inactivation of pea ADH is pH-dependent and is maximal at pH 9.0. NAD protects the enzyme from inactivation by p-chloromercuribenzoate; the higher the concentration of the coenzyme and the longer the period of incubation of NAD with the enzyme, the lower the degree of inactivation. Ethanol does not prevent the enzyme from inactivation. o-Phenanthroline in a concentration of 1 . 10-3 mol l-1 decreases the degree of inactivation of the enzyme by p-chloromercuribenzoate by 20%; imidazole is without effect on the reaction. Zn2+-ions in concentration of 1 . 10-5 mol l-1 also partly protect the enzyme from inactivation by p-chloromercuribenzoate. The results obtained show that the SH-groups sensitive to labeling with p-chloromercuribenzoate are localized in the active center of the enzyme, probably in the coenzyme-binding site. The protective action of Zn2+-ions and of o-phenanthroline against this inactivation confirms the assumption that the SH-group acts as a zinc ligand in the active center of the enzyme.
Immobilization of pectin esterase from tomatoes and Aspergillus foetidus on various supports
Authors: Markovič Oskar , Machová Eva
Published: September 2010

The pectin esterases from tomatoes and Aspergillus foetidus were immobilized by covalent attachment to CNBr-activated Sepharose 4B and by adsorption to polyethylene terephthalate and the properties of the immobilized enzymes were compared. The relative activity of tomato pectin esterase after the immobilization to both supports was almost 7%, whereas the activity of A. foetidus pectin esterase covalently immobilized on CNBr-activated Sepharose 4B was close to 11.5% and a value of almost 23% was measured with the enzyme immobilized by adsorption to polyethylene terephthalate. The pH-optima of both pectin esterases were unchanged after their immobilization, their temperature stability and temperature optimum of activity, however, significantly increased. The differences in the action of free and immobilized pectin esterases were also observed when the final esterification degree of the substrate was compared: the immobilized enzymes, unlike the free pectin esterases, did not act on pectin showing a higher esterification degree. An increase in Km.app which was 5-fold for the tomato pectin esterase and 4-7-fold for the A. foetidus pectin esterase was observed after the immobilization. The immobilization of both pectin esterases on Enzacryl AA which had been activated by diazotization resulted in complete loss of activity; this indicates the role of the residues of tyrosine (and histidine, resp.) in the catalytic action of these enzymes, which has been observed in earlier experiments.
Monte Carlo quasiclassical trajectory study of a 2D model of chemisorption of H2 on a metallic cluster surface
Authors: Vojtík Jan , Šavrda Jiří , Fišer Jiří
Published: September 2010

Dynamics of a 2-dimensional model of chemisorption of H2 on a metallic surface is studied by quasiclassical trajectory Monte Carlo approach. The process is governed by a H2-cluster potential energy surface based on the diatomics-in-molecules potential for H2 on a planar Li8 cluster. The probabilities of dissociative adsorption of H2 on the surface and some additional characteristics of the collision process for a selected set of initial vibrational and translational conditions are presented. The effect of the initial vibrational and translational energy on the outcome of the H2-surface collision events is discussed.
Assignment techniques for 29Si NMR spectra of pertrimethylsilylated products. 29Si satellites in 13C NMR spectra measured with selective 29Si decoupling
Authors: Past Jaan , Puskar Jüri , Schraml Jan , Lippmaa Endel
Published: September 2010

It is shown that measurement of 29Si satellites in proton decoupled 13C NMR spectra with selective 29Si decoupling allows correct assignment of lines in 29Si NMR spectra of pertrimethylsilylated products. The experimental scheme, where selective decoupling and FID phase alternation are used (difference spectroscopy), has sufficient sensitivity and selectivity, provided the 29Si lines are well separated. The main advantage of the method is that it can be applied to compounds with unresolved 1H NMR spectra or with no protons in γ position to the silicon atom.
Vapour-liquid equilibrium in strongly associated systems. The propionic acid-n-heptane system
Authors: Malijevská Ivona , Vlčková Dagmar
Published: September 2010

Vapour-liquid equilibrium in the propionic acid-n-heptane system was measured at normal pressure. When treating the data, emphasis was laid on the correct expression of volumetric behaviour in the vapour phase and the analysis of the data obtained.
Theory of the equilibrium in a microapparatus for the isolation and concentration of organic substances from water by continuous steam distillation-extraction
Authors: Janda Václav , Doležal Bohuslav
Published: September 2010

The phase equilibrium establishing in a microapparatus designed for the isolation and concentration of organic substances from water by continuous steam distillation-extraction is treated. This technique, used for the preconcentration of water pollutants followed by the gas chromatographic analysis of the extract, is suitable for organic substances with boiling temperatures higher than that of water which form azeotropic mixtures with water, the boiling temperatures of which are lower than those of water and the organic substances themselves. The organic solvent used for the extraction must have a very low boiling temperature. The recovery from the whole procedure and the concentration factor depend on the volumes of the water sample and the organic solvent as well as on the volume of the space where the extraction of the organic substance from the aqueous condensate takes place.
Non-stationary experiments on thiophene and tetrahydrothiophene hydrodesulphurization
Authors: Morávek Vladimír , Kraus Miloš
Published: September 2010

The reactions of tetrahydrothiophene and thiophene in hydrogen on sulphided Mo/Al2O3, Co-Mo/Al2O3, and Ni-W/Al2O3 catalysts have been studied using pulse-flow, stopped flow, and started flow techniques. The composition of the effluent from the reactor was analyzed after a perturbation and the observed response curves have been interpreted from the point of view of the reaction mechanism and influence of the promotor (Co) in the Co-Mo/Al2O3 catalyst. The results confirm that at least partial saturation of the thiophene ring is necessary for hydrodesulphurization and that at least one C-S bond is splitted by hydrogenolysis, the second one either by hydrogenolysis or by elimination. Cobalt increases the hydrogenolytic activity of molybdenum, in its absence the predominant reaction of tetrahydrothiophene is dehydrogenation to thiophene.
Reactions of vinylene diisothiocyanate with aniline, N-benzylidenemethylamine and N,N'-dicyclohexylcarbodiimide
Authors: Hritzová Oľga
Published: September 2010

Reaction of vinylene diisothiocyanate with aniline, N-benzylidenemethylamine and N,N'-dicyclohexylcarbodiimide affords the stable 1-(anilinothiocarbonyl)-4-imidazoline-2-thione and 1,3,5-thiadiazine derivatives, respectively.
A simple method of isomerization of the terminal double bond in a terpene chain
Authors: Streinz Ludvík , Wimmer Zdeněk , Roshka Georgii K. , Ishchenko Raisa I. , Romaňuk Miroslav , Kovalev Boris G.
Published: September 2010

The utilisability of the isomerization of the terminal double bond in terpenic compounds with trifluoroacetic acid was investigated. The results obtained were used in the synthesis of the main part of the pheromone of Quadraspidiotus perniciosus COMSTOCK, i.e. (2E)-3,7-dimethyl-2,7-octadien-1-yl propionate.
A general form of an equation of state
Authors: Chen Chone Naing , Fried Vojtech , Hirsch Waren
Published: September 2010

It is shown that all the equations of state are simplified version of the general equation of state, PΩ(V - μ) = RT.Ω, the term responsible for the attractive forces, is a function of volume and temperature. μ, the term responsible for the repulsive forces, is also a function of volume and temperature. A detailed analysis of a large number of experimental P-V-T data reveals that the Ω vs P function and the μ vs P function, at a constant temperature, go through a maximum. These maxima must be predicted by all physically consistent equations of state.
A contribution to the description of the retention mechanism of metal chelates during their reversed-phase chromatography
Authors: Vláčil František , Hamplová Věra
Published: September 2010

Mercury(II) diethyldithiocarbamate was chromatographed on silica gel with chemically bonded octadecyl groups using aqueous mixtures with methanol, acetonitrile, dioxane, and tetrahydrofuran, respectively, as the mobile phase, and the dependence of logarithm of the capacity ratio (k) on the volume fraction of water in the binary mobile phase was examined. Also, the dependence of k on the liquid-liquid extraction distribution ratio in an aqueous methanol-n-alkane extraction system was investigated for Cu, Co, Ni, Pb, and Hg diethyldithiocarbamates. Both kinds of dependence are linear, which suggests that the retention of the electroneutral metal chelates during the reversed-phase liquid chromatography on a nonpolar chemically bonded phase is due to the solvophobic effect.
Substituted methylenemalonaldehydes: Condensation of dialdehydes with 1,3-bis(dimethylamino)trimethinium perchlorate
Authors: Yanovskaya Ludmila A. , Kryshtal Galya V. , Dvořák Dalimil , Král Vladimír , Arnold Zdeněk
Published: September 2010

Selected unsaturated, aromatic, and heterocyclic dialdehydes reacted with 1,3-bis(dimethylamino)trimethinium perchlorate in acetic anhydride in the presence of acid. One of the aldehyde group participated in the condensation, whereas the other was transformed into the diacetate. The obtained substituted methylenemalonaldehydes were characterized by their 1H NMR, IR, and mass spectra.
Applicability of glutaminyl-tRNA cyclotransferase in the peptide synthesis
Authors: Čeřovský Václav , Jošt Karel
Published: September 2010

Peptides with amino-terminal glutamine and their derivatives on treatment with crude papain preparation, containing glutaminyl-tRNA cyclotransferase (E.C. 2.3.2.5.), are converted into the corresponding compounds with pyroglutamic acid. This enzymic cyclization does not take place with glutamic acid or its γ-derivatives. The reaction has been optimized for the preparation of pyroglutamic acid phenylhydrazide. Glutaminyl-leucine phenylhydrazide and glutaminyl-histidyl-proline amide reacted to give pyroglutamyl-leucine phenylhydrazide and TRH, respectively. Treatment of crude papain with iodoacetamide completely inhibited its activity without affecting the glutaminyl-cyclotransferase activity.
Simple explicit model of liquid mean flow in region above axial impeller
Authors: Hošťálek Miloslav , Fořt Ivan
Published: September 2010

The study describes a method of modelling axial-radial circulation in a tank with an axial impeller and radial baffles. The proposed model is based on the analytical solution of the equation for vortex transport in the mean flow of turbulent liquid. The obtained vortex flow model is tested by the results of experiments carried out in a tank of diameter 1 m and with the bottom in the shape of truncated cone as well as by the data published for the vessel of diameter 0.29 m with flat bottom. Though the model equations are expressed in a simple form, good qualitative and even quantitative agreement of the model with reality is stated. Apart from its simplicity, the model has other advantages: minimum number of experimental data necessary for the completion of boundary conditions and integral nature of these data.
A study of the MgCl2-tetrahydrofurane system
Authors: Handlíř Karel , Holeček Jaroslav , Beneš Ludvík
Published: September 2010

The solid phase-solution equilibrium has been studied in the MgCl2-tetrahydrofurane system. Below 28 °C the saturated solution of magnesium chloride is in equilibrium with the solid phase composed of MgCl2.4C4H8O, whereas at higher temperatures the equilibrium solvate has the composition of MgCl2.2C4H8O. The solvate MgCl2.4C4H8O forms tetragonal crystals composed of molecules of trans-dichloro-tetrakis(tetrahydrofurane)magnesium(II) complex. The solvate MgCl2.2C4H8O most probably represents a polymeric catena-di-μ-dichloro-trans-bis(tetrahydrofurane)magnesium(II) complex.
Preparation of carbamate derivatives of 2-(4-hydroxybenzyl)-1-cyclohexanone with a juvenoid activity
Authors: Wimmer Zdeněk , Streinz Ludvík , Romaňuk Miroslav
Published: September 2010

The synthesis of four carbamate derivatives of 2-(4-hydroxybenzyl)-1-cyclohexanone displaying a juvenilizing effect in insects is described. The substances prepared have a greater stability and activity than their carba-analogues prepared earlier.
The bubble method for measuring surface tension of liquids
Authors: Novotný Ladislav
Published: September 2010

The principle of the bubble method for measuring surface tension of solutions and its changes is described. It is based on the determination of the volume or of the changes of the volume of a gas bubble at the orifice of a capillary in the moment of its detachment. One version of the bubble tensiometer is described.
Gas holdup and interfacial mass transfer in gas-liquid tower contactors with ejector-type gas distributors
Authors: Zahradník Jindřich , Kratochvíl Jan , Rylek Milan
Published: September 2010

The effect of decisive construction parameters of ejectors on gas holdup and on the rate of interfacial mass transport (characterized by kLa values) was studied in a gas-liquid tower reactor (I.D. 0.3 m) with an ejector (Venturi-tube type) gas distributor. The selected ejector characteristics included diffuser length and angle of diffuser walls inclination as well as nozzle type and geometry. Experimental data confirmed validity of our previously published conclusions on the relation between the rate of energy dissipation in the place of dispersion formation (i.e. in the ejector) and gas holdup and kLa values. The efficiency of dissipated energy utilization was however significantly influenced by the diffuser geometry. According to our experimental evidence the increase of ejector energy effectiveness with increasing diffuser length can be ascribed solely to its favourable effect on the gas suction rate while the mechanism of phases mixing (dispersion formation) in ejector was apparently independent of diffuser geometry within the whole range of experimental conditions.
Smoothing of stationary random signal in continuous flow mixer with gamma-distribution of residence times
Authors: Hasal Pavel , Kudrna Vladimír , Vyhlídková Jitka
Published: September 2010

The paper is focused on a theoretical analysis of the function of continuous flow mixer with the so-called gamma-distribution of fluid residence times, used as a linear filter smoothing undesirable fluctuations of input properties. A relation is derived expressing the degree of smoothing of the signal passing through the system, as a function of statistical parameters of this signal and of gamma-distribution of fluid-residence times in the mixer. The analysis of this relation leads to conclusions concerning the prediction of the operation of smoothing mixers or the design of their basic parameters.
Precipitation fractionation of block copolymers
Authors: Tuzar Zdeněk , Sikora Antonín , Straková Dagmar , Podešva Jiří , Stejskal Jaroslav , Kratochvíl Pavel
Published: September 2010

Possibilities offered by classical precipitation fractionation in the preparative separation of polymer admixtures from block copolymers and in an estimate of the polydispersity in molar mass and of the heterogeneity in chemical composition of block copolymers have been examined. A mixture of a two-block copolymer, polystyrene-block-polyisoprene, with polystyrene was separated in the systems cyclohexane/1-propanol and 1,4-dioxan/1-propanol, and a mixture of three two-block styrene-isoprene copolymers having different chemical composition was fractionated in the system benzene/methanol. In the cyclohexane/1-propanol system, two commercial samples of three-block copolymers polystyrene-block-poly(ethene-co-butene)-block-polystyrene and their mixture were fractionated. The results showed that the polydispersity and chemical heterogeneity thus estimated are much lower than the real ones, especially due to the colloid properties of block copolymers.
Topological aspects of chemical reactivity. Simple alternative method for determining parity of Kékule structures
Authors: Ponec Robert
Published: September 2010

A simple alternative procedure for determining the parity of Kékule structures is presented. The procedure is based on the formalism of overlap determinant method.
Effect of reaction conditions on the activity of the WCl6 + (CH3)4Sn catalytic system in the metathesis of methyl 10-undecenoate
Authors: Balcar Hynek , Dosedlová Alena , Petrusová Lidmila , Matyska Bohumír
Published: September 2010

In contrast to published data, metathesis of methyl 10-undecenoate is found to proceed with a good yield even if the ester is present in a high excess with respect to the catalyst, if the former is first reacted with WCl6 to form a complex (owing to which the reaction mixture acquires red colour), and only then the metathesis is started by adding (CH3)4Sn. Moreover, satisfactory degrees of conversion are only attained if the catalyst concentration is low enough so that the deactivation of the active centres is slowed down.