bluuebunny/crossref_metadata_2025 huggingface dataset:
Peptide synthesis catalyzed by native proteinase K in water-miscible organic solvents with low water content
Authors: Čeřovský Václav , Martinek Karel
Published: May 2010

Reaction of Ac-Tyr-OEt with HBr.Gly-NH2, catalyzed by free proteinase K in various water-miscible organic solvents in the presence of triethylamine and 5 vol.% of water, was studied. Some aliphatic alcohols and acetonitrile proved to be suitable solvents. The effect of water content (2%-20%) on the synthesis of Ac-Tyr-Gly-NH2 was studied using acetonitrile as solvent. Lowering of the water content to 5% or 2% led to almost 100% yield of the desired dipeptide; higher water content accelerated the reaction, reducing at the same time the yield of Ac-Tyr-Gly-NH2 due to the concurrent hydrolysis of the ester Ac-Tyr-OEt. No reaction was observed in the absence of base (triethylamine), whereas an excess of base only retarded the reaction. The enzyme is capable of catalyzing the peptide bond synthesis with N-acylamino acids or N-acyl peptides as acylating components, which may contain all types of L-amino acid residues (except Pro) in the P1 position. However, the peptide bond synthesis depends strongly on the amino component composition, particularly on the amino acid residue in the P'1 position. Only amides of glycine and of hydrophilic amino acids were acylated with Ac-Tyr-OEt; amides of hydrophobic amino acids enter the reaction only reluctantly or not at all. The presence of Leu or Phe in position P'2 and Leu in position P'3 has not so negative effect on acylation of the amino component as has its presence in the P'1 position. The choice of protecting groups for the α-carboxyl of the amino component is restricted only to amide and in some cases its undesired enzymatic removal was observed. Unprotected peptides seem to be suitable amino components.
A vibrational study of tautomerism and associations of 2-mercaptoimidazole and 2-mercaptothiazole
Authors: Perez-Peña Jesús , Gonzalez-Davila Melchor , Suarez-Tangil Miguel , Hernandez-Brito Joaquin
Published: May 2010

Infrared and Raman spectra of 2-mercaptoimidazole and 2-mercaptothiazole in solid state as well as i.r. spectra of 2-mercaptothiazole in HCCl3 and CS2 0.05M solutions have been investigated. A general assignment of all the observed bands is proposed for both fundamental vibrations and for overtone and combination bands. For 2-mercaptothiazole, the thiocarbonyl-form, intermolecularly hydrogen-bonded dimers in solid state, and unassociated molecules in dilute solutions of inert solvents have been established. Finally, based on this data, thermodynamic functions have been computed.
Hydrodesulphurization of thiophene over zirconia and alumina supported Co-Mo catalysts
Authors: Sedláček Jiří , Vít Zdeněk
Published: May 2010

The zirconia supported CoMo catalysts and the commercial sample CoMo/Al2O3 were characterized by XPS measurements and by testing of activity in the HDS of thiophene at 280 °C and 1 MPa of total pressure. The XPS measurements revealed the better reducibility of molybdenum, higher sulphidability of cobalt and the absence of surface sulphur oxidation in the presence of zirconia support. The surface atomic concentration ratios S/Mo were 1.2 and 2.2 for zirconia and alumina supported catalysts, respectively. The activity of the zirconia supported CoMo catalyst normalized to the overal amounts of active metals was lower than that of the commercial CoMo/Al2O3 catalyst.
Chemisorption of oxygen and hydrogenation of ethylene on sulphided Co-Mo/Al2O3 catalyst. Effect of activation process
Authors: Zahradníková Hana , Beránek Ludvík
Published: May 2010

Oxygen chemisorption by pulse dynamic method at room temperature and the activity for ethylene hydrogenation at 300 °C in a flow regime were determined for Co-Mo/Al2O3 catalyst CHEROX 36-01 sulphided by a H2S/H2 (1:10) mixture at 400 °C. The measurements were carried out either immediately after sulphidation or after subsequent reduction of the sulphided catalyst by hydrogen. The chemisorption of oxygen was measured both prior to and after the catalytic reaction. In addition, the reactivation of the catalyst was examined after its passivation by oxygen chemisorption. The reactivation was effected either by resulphidation or by reduction with hydrogen at 400 °C, on repeated reactivation also by combination of both procedures, variables being the time of activation and reactivation steps. The results are discussed from the standpoint of the structure and interrelation between active sites for oxygen chemisorption and catalytic, especially hydrogenation reactions. Formation of coordinately unsaturated sites and SH groups is emphasized. The reasons of possible failures in correlations between chemisorption capacity for oxygen and catalytic activity are mentioned.
Effect of radionuclide 32P incorporation on the catalytical activity of the BASF K-3-10 catalyst for the low-temperature conversion of carbon monoxide by water vapour
Authors: Motl Alois
Published: May 2010

The catalytical activity of the BASF K-3-10 catalyst for the low-temperature conversion of carbon monoxide by water vapour has been studied in dependence on the activity of incorporated radionuclide 32P. Radioactivity of the catalytical bed ranged from 0 to 630 MBq of incorporated 32P. It has been observed that at first the catalytical activity increases with the increasing activity of 32P and finally it reaches a limit value that is by about 50 per cent higher than that of the same non-radioactive catalyst. The comparison of these results with those obtained in the studies of the catalytical activity of the same catalyst pre-irradiated by β radiation of the 90Sr-90Y source revealed that in the case of radioactive beds the observed positive radiation-catalytical effect can be ascribed to the pre-irradiation of the catalyst (during the period between the preparation of the radioactive catalytical bed and the catalytical reduction itself) and to the interactions of the ionizing radiation with the catalyst during the subsequent operations. The radiation-catalytical effects induced by the two processes mentioned above differ substantially by their time stability. The probable explanation of the nature of these two effects is proposed using the published mechanism of this reaction.
Some views about the relation between the rate constants of retarded electrode reactions requiring reactant adsorption and the corresponding inhibitor concentrations at high coverages
Authors: Anastopoulos Anastos
Published: May 2010

By the combination of some well known equations, an attempt is made to develop a relation between the logarithms of the rate constant, k, of inhibited reactions, requiring reactant adsorption and the corresponding inhibitor concentration ci which can assign a definite physical meaning to the slope of any type of the ln k vs ln ci plots.
Kinetics of esterification of diisopropylphenols with phosphoryl trichloride
Authors: Magura Miroslav , Vojtko Ján , Ilavský Ján
Published: May 2010

The title liquid-phase isothermal esterification kinetics have been measured in the temperature intervals of 110-125 and 110-160 °C for 2,4- and 2,6-diisopropylphenols, resp. The values measured have been used to calculate the rate constants of the respective three steps and to determine the activation energies. 2,6-Diisopropylphenol has been found to react only to the first degree, and the rate constants of the other two reaction steps (k2, k3) were only calculated from the differential equations given by means of a computer.
The polarographic and voltammetric determination of 5-(3-phenoxysulphenylazo)-6-hydroxy-3-cyano-1,4-dimethyl-2-pyridone
Authors: Barek Jiří , Švagrová-Hauserová Ivana , Zima Jiří
Published: May 2010

The polarographic reduction of the title azodye has been studied, a mechanism was proposed and optimal conditions were found for the determination of this substance by TAST polarography in the range 5.10-5-2.10-6 mol l-1 and differential pulse polarography at a dropping mercury electrode in the range 5.10-5-2.10-8 mol l-1. The sensitivity was further increased by adsorptive accumulation of the determined substance on the surface of a hanging mercury drop electrode with linear scan voltammetry (determination limit 5.10-10 mol l-1). The selectivity was increased by prior separation of the determined azodye using thin layer chromatography and by transferring the substance adsorbed on the surface of the hanging mercury drop to a new base electrolyte solution.
A study of the separation of Mo(VI) and W(VI) by reversed phase HPLC
Authors: Vrchlabský Milan , Pollaková Naděžda , Hrdlička Aleš
Published: May 2010

The RP HPLC separation of Mo(VI) and W(VI) in the form of their oxoanions or anionic chelates with 2,3-dihydroxynaphthalene (DHN) was studied using a 100 x 4 mm i.d. column packed with Silasorb C18 (10μm). The two elements were separated with a resolution of Rij = 1.8 in 10 min after injection of the DHN-derivatized anions into the stream (flow rate 1 ml min-1) of the mobile phase containing phosphate buffer (50 mmol l-1), DHN (0.5 mmol l-1) and tetrabutylammonium cations (1 mmol l-1) in 60% (v/v) methanol at pH 7.
Description of the equilibrium single-stage extraction from a flowing raffinate into a batch of extraction solvent
Authors: Doležal Bohuslav , Ledvinka Karel
Published: May 2010

Relations are derived for calculating the trace concentration of investigated component contained in a real fluid extracted in a flow set-up with one stirred batch of extraction solvent dosaged. The presented method of derivation stems from the assumptions of sufficient stirring and the rapid establishment of thermodynamic equilibrium in the defined system of constant volume, containing one batch of extraction solvent through which flows continuously the raffinate containing the constant trace concentration of extracted component. The relations derived describe both the mutual limited miscibility of the liquids involved and the excess mixing effects.
Path and walk matrices of trees
Authors: Kunz Milan
Published: May 2010

The relation between the Rouse matrix R and the Zimm matrix Z, defined for polymer chains, is generalized for all trees. The path matrix Wu of an unoriented tree and the walk matrix Wo of an oriented tree are defined and their relations with the corresponding incidence matrices G and S of trees: (GGT) = n(WuTWu)-1 and (SST) = n(WoTWo)-1 are proved. The elements of the quadratical forms WTW are the number of path (selfavoiding walks) in which the edge (arc) i is present together with the edge (arc) j. The traces of WTW are the Wiener path number.
An efficient photochemical formation of phenoxazine and phenothiazine from their respective cyclopentadienyliron complexes
Authors: Maciejewski Andrzej , Jaworska-Augustyniak Anna , Radocki Dariusz , Sutherland Ronald G. , Piórko Adam
Published: May 2010

The photochemical liberation of phenoxazine and phenothiazine from their cyclopentadienyliron complexes was studied in THF, methanol and dimethylsulfoxide. Quantum yields of decay of the complexes and the formation of free heterocycles have been determined to be about 1.0, independent of solvent, concentration and wavelength of light used. The ease of isolation of free heterocycles after photolysis show that this efficient way of heterocycle recovery is superior to the previously utilized pyrolytic sublimation.
Light-catalyzed bromination of 3,4-dimethyl-1,2,5-thiadiazole with N-bromosuccinimide
Authors: Desvard Osvaldo E. , Rozas Maria F. , Mirífico Maria V.
Published: May 2010

1H NMR study of light-catalyzed bromination of 3,4-dimethyl-1,2,5-thiadiazole with N-bromosuccinimide has been carried out in order to reach conclusions on synthetic possibilities and relative reactivities of several products formed.
The effect of non-coded amino acids on the degradation of oxytocin analogs with α-chymotrypsin
Authors: Hlaváček Jan , Frič Ivo
Published: May 2010

Oxytocin and a series of its analogs, containing a non-coded amino acid in the carboxy-terminal linear part, were incubated with α-chymotrypsin and their degradation was monitored using high performance liquid chromatography (HPLC). Degradation of the analogs was markedly slower than that of oxytocin, its rate depending on the structure of the amino acid in position 8. Whereas in oxytocin the cleavage takes place at the leucine-glycine peptide bond in its carboxy-terminal moiety, no cleavage at this position was observed in the analogs; these were cleaved only at the tyrosine-isoleucine bond in the cyclic part. The same type of cleavage was observed in analog with a disulfide bond in the C-terminal oxytocin tripeptide. The degradation sites in oxytocin and its analogs were determined using the amino acid and sequentional analysis of the products isolated from the incubation mixture by preparative HPLC.
Crystal structure of N-(2,6-dimethylphenyl)chloromaleinimide
Authors: Vrábel Viktor , Kellö Eleonóra , Lokaj Jan , Konečný Václav
Published: May 2010

The crystal structure of N-(2,6-dimethylphenyl)chloromaleinimide solved by the heavy atom method was refined by the 9 x 9 block-diagonal matrix least-squares method to a final R value 0.08 for 1 147 observed diffractions. The compound crystallizes in the orthorhombic system with Pbca group and lattice parameters a = 13.622(4), b = 13.483(7), c = 12.768(6) Å, Z = 8. Monomeric units, between which interactions of type Cl···H-C and O···H-C occured, formed the crystal structure. Both moieties of the molecule, i.e. the phenyl and the five-membered maleinimide rings were found to be virtually planar and the central planes intersecting these rings form an angle 78.3°.
p-Substituted benzamidinium carboxylates
Authors: Krechl Jiří , Smrčková Svatava , Pavlíková Františka , Kuthan Josef
Published: May 2010

Various p-substituted benzamidinium formates (I), acetates (II), trifluoroacetates (III) and pyruvates (IV) were prepared and the nature of the amidinium-carboxylate interactions were examined by 1H and 13C NMR spectra. The spectroscopic data are consistent with the presumption that the carboxylic part is only slightly influenced by the diverse substitution of the aromatic benzamidinium ring.
Reactions of 2-furfurylidenemalonaldehyde with aromatic amines and Meldrum's acid
Authors: Šafář Peter , Kováč Jaroslav
Published: May 2010

2-Furfurylidenemalonaldehyde (II) reacts with primary aromatic amines as an organic Lewis acid, affording 1,3-di-(N-4-X-phenylamino)-3-(2-furyl)-2-formyl-1-propenes (IIIa-IIIj). Condensation of these compounds with 2,2-dimethyl-1,3-dioxane-4,6-dione (I) gives the products IVa-IVj.
Effect of soybean extract on nitrosamines formation. In vitro study
Authors: Zakhary Nadia I. , El-Aaser Abdelbaset A. , Abdel-Malak Camelia A.
Published: May 2010

Soybean (SB) extracts markedly inhibit formation of diphenylnitrosamine (DPNA) from the precursors diphenylamine (DPA) and nitrite (NO2-). SB extracts interact with nitrite, as shown by the decrease in the nitrite level. The rate of interaction between SB extracts and nitrite was lower than the rate of inhibition of DPNA formation. Thus the reduction of DPNA yield by SB extracts is not caused mainly through their competition for the available nitrite, but it might be due to the adsorption of the DPNA formed to the SB proteins, internitrosation between SB constituents and DPNA formed, or through the breakdown of the DPNA.
Characterization of alcohol dehydrogenase isolated from germinating bean Vicia faba seeds
Authors: Leblová Sylva , El Ahmad Mustafa
Published: May 2010

We have isolated alcohol dehydrogenase (ADH, E.C. 1.1.1.1) from beans germinating 3 days by ammonium sulfate precipitation of the sodium phosphate extract of the homogenate of seeds, followed by chromatography on DEAE-cellulose and gel chromatography on Sephadex G-200 and G-100; both chromatographic operations were repeated twice. The activity of ADH increased 960 times after these procedures. The enzyme whose Mr is 60 000 consists of two identical subunits of Mr = 30 000. Allyl alcohol is oxidized and acetaldehyde reduced at the highest rate of all the alcohols and aldehydes tested. The reaction rate decreases with the increasing length of the carbon chain of the substrate. In contrast, the rate of oxidation of alcohols with a double bond in their molecules increased. The pH-optimum of substrate oxidation (pH 8.5) is different from the pH-optimum of substrate reduction (pH 7.5). From kinetic studies of the effect of pH on Vmax and Km the pK-value of amino acids participating on substrate oxidation is 9.2 and 8.5 whereas amino acids with pK 8.3 and 6.8 participate on substrate reduction. We have verified the participation of the SH-groups in experiments with the inactivation of ADH by iodoacetate: the inactivation was weaker after the enzyme had been preincubated with NAD or AMP, adenosine or nicotinamide. Likewise pyridoxal phosphate inactivates bean ADH by modifying its ε-amino group of lysine. The degree of inactivation depends also on the pH and the ionic strength of the medium. The protective effect of NAD or its analogs shows that lysine is present in the active center of the enzyme in the coenzyme-binding site.
Immobilization of ribonucleotide reductase from Streptomyces aureofaciens
Authors: Halický Peter , Kollárová Marta , Kois Pavol , Zelinka Ján
Published: May 2010

Ribonucleotide reductase from Streptomyces aureofaciens (E.C.1.17.4.) has been isolated. The effects of concentration of substrate, effector, coenzyme, reductant, pH, and ionic strength upon the activity of this enzyme have been studied and the data obtained by research have been completed. Based on some properties of this enzyme, we have chosen a proper hydrophobic carrier-Trityl-agarose for immobilization. It has been found out that the properties of the immobilized enzyme are significantly different from those of the free enzyme. Principal differences are in the loss of the effector dependence of the immobilized enzyme and in a significant increase of its stability.
Electroreduction of Cr(VI) from solutions of bifunctional alcohols
Authors: Balanchivadze David I. , Chelidze Tamara R. , Japaridze Jondo J.
Published: May 2010

The effect of bifunctional alcohols ethylene glycol (EG) and 1,2-propylene glycol (1,2 PG) on the kinetic parameters for the irreversible chromate ion reduction were investigated by polarographic and coulometric methods of analysis. The electroreduction of chromate ion in neutral bifunctional alcohol solutions proceeds according to the scheme: Cr(VI)–Cr(III)–Cr(II) and the values of the standard rate constant k*0 decrease in the order H2O > EG > 1,2 PG. The values of real activation energy, Q, activation energy of diffusion, QD, and frequency factor log A° have been calculated. The obtained values of QD as well as Q proved the diffusion nature of limiting current. The values of the frequency factor log A° decrease in the order H2O > EG > 1,2 PG, which points to a less favourable orientation of the electroactive ions at the electrode surface in glycols.
The determination of copper by flow injection analysis with flame AAS detection after preconcentration by solvent extraction
Authors: Kubáň Vlastimil , Komárek Josef , Čajková Dagmar
Published: May 2010

Trace amounts of copper (QCu = 2 to 900 mg ml-1)) were determined by FIA-FAAS after extraction of the Cu chelate with ammonium pyrrolidine dithiocarboxylate (APDC), present in a concentration of QAPDC = 1 mg ml-1, from 0.2M acetate buffer at pH 5.05 into 4-methyl-2-pentanone. The limit of determination was LQ = 2 ng ml-1 for the injection of 150 μl of the organic phase into a continuous stream of air as the carrier medium. The maximum throughput was about 40 samples per hour. The method was applied to the determination of copper in water samples from power station cooling circuits.
Reactivity of nucleophiles in dimethyl sulfoxide and its comparison with nucleophilic reactivity in protic medium
Authors: Zima Vítězslav , Pytela Oldřich , Kaválek Jaromír , Večeřa Miroslav
Published: May 2010

Reactions of 2,4-dinitrophenyl acetate and 2,4-dinitrofluorobenzene as model substrates with 12 nucleophiles have been studied in dimethyl sulfoxide. The rate constants obtained have been discussed with regard to the nucleophilic reactivity differences in dimethyl sulfoxide and protic solvents inclusive of the different manifestation of the charge of nucleophiles. The applicability of an earlier-suggested correlation equation to the data obtained has been verified. The reaction medium markedly affects the reactivity of nucleophiles, the effect of charge being substantially greater in aprotic solvents (electrostatic interaction) than in protic ones (solvation). In spite of these differences the correlation with application of an empirical nucleophilicity scale suggested earlier is satisfactory, the regression coefficients obtained reflect changes in the nature of medium.
Preparation and synthetic utilization of diarylmethylenemalonaldehydes
Authors: Král Vladimír , Jelínek Ladislav , Šaman David
Published: May 2010

A general synthetic approach to disubstituted methylenemalonaldehydes consisting in reaction of geminal dihalogeno derivatives with 1,3-bis(dimethylamino)trimethinium perchlorate is described. Solution of the prepared compounds has been determinated by NMR spectroscopy. The prepared compounds were utilized as suitable synthons of pyrazole (XII), 4H-1,2,6-oxadiazine (XIV) and diazepine (XV) derivatives.
Synthesis and biological activity of some derivatives related to 2-methylenebutanedioic acid
Authors: Veverka Miroslav , Kraľovičová Eva
Published: May 2010

Nucleophilic reactions of methyl 3-chloroformyl-3-butenoate with N-substituted anilines and substituted phenols, and also preparation of 2-methylenebutanedioic acid monoanilides and their dehydration to the corresponding N-arylimides are described.
Evolution thermique de derives des hexahydrobenzazocines-2 et des hexahydro-1H-benzazonines-2 N-quaternarises (ammoniums, N-oxydes)
Authors: Elmasmodi Abdellatif , Barbry Didier , Hasiak Bruno , Couturier Daniel
Published: May 2010

La thermolyse des hydroxydes d’ammonium derives des hexahydrobenzazocines-2 et de la methyl-2-hexahydro-1H benzazonine-2 conduit a un melange de composes ethyleniques [butenyl-3 (ou pentenyl-4) N,N-dimethylbenzylamine et dimethylamino-1 orthotolyl-4 butene-3 (ou pentene-4)]. Les N-oxydes de N-methyl hexahydrobenzazocines-2 se decomposent thermiquement en derives de l’oxa-2 hexahydro-1H-benzazonines-3 souilles de la benzazocine de depart.
An alternative synthesis of O-(2-acetamido-2-deoxy-β-D-glucopyranosyl)-(1→4)-N-acetylnormuramoyl-L-α-aminobutanoyl-D-isoglutamine
Authors: Ledvina Miroslav , Farkaš Jiří , Zajíček Jaroslav , Ježek Jan , Zaoral Milan
Published: May 2010

Silver triflate-promoted condensation of 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-β-D-glucopyranosyl bromide (VIII) with benzyl 2-acetamido-6-O-benzoyl-2-deoxy-3-O-(methoxycarbonyl)-methyl-α-D-glucopyranoside (IV) afforded benzyl 2-acetamido-4-O-(3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-β-D-glucopyranosyl)-6-O-benzoyl-2-deoxy-3-O-(methoxycarbonyl)methyl-α-D-glucopyranoside (IX) which, after deprotection, was converted into the acid XI. Condensation of acid XI with L-α-aminobutanoyl-D-isoglutamine benzyl ester and subsequent hydrogenolysis of the product XIII furnished compound XIV. Benzyl 2-acetamido-6-O-benzoyl-2-deoxy-3-O-(methoxycarbonyl)methyl-α-D-glucopyranoside (IV) was prepared by partial benzoylation of benzyl 2-acetamido-2-deoxy-3-O-(methoxycarbonyl)methyl-α-D-glucopyranoside (III) with benzoyl cyanide.
Hydrolysis of olive oil by pancreatic lipase in biphasic organic-aqueous system
Authors: Kéry Vladimír , Trančíková Jana , Schmidt Štefan
Published: May 2010

Six ethylene oxide-based surfactants were tested for their suitability to mediate lipase action on olive oil in a water-organic biphasic system. In Slovasol EL only it was possible by lipase to catalyze hydrolysis of the substrate over a wide range of isooctane and water content in the system. The Michaelis-Menten parameters of lipase measured for this system are comparable with those measured in a reversed emulsion of water and oil-isooctane solution. The hydrolysis rate was not increased, however, in the presence of isooctane.
Application of the maximum likelihood method to the parameter evaluation in heterogenous systems
Authors: Voňka Petr , Novák Josef P. , Matouš Jaroslav
Published: May 2010

The maximum likelihood method was applied to the calculation of parameters of a thermodynamic model in a heterogenous binary system. The calculation program was tested on using the tetrahydrofuran-water system.
Isobaric vapour-liquid equilibrium data of the 1,2-dichloroethane-water system at 101.3 kPa
Authors: Bobok Daniel , Kossaczký Elemír , Surový Július
Published: May 2010

Isobaric vapour-liquid equilibrium data for the 1,2-dichloroethane-water system were calculated on the assumption of ideal behaviour of the vapour phase on using the van Laar equation for activity coefficients of the components in the liquid phase. The parameters of the van Laar equation were calculated from the solubility of 1,2-dichloroethane in water and of water in 1,2-dichloroethane determined experimentally in this work. On using the solubility data, the parameters of the heteroazeotropic point at the pressure of 101.3 kPa were also calculated.
Nonclassical behaviour of binary mixtures in gas-liquid critical region and its quantitative description
Authors: Wichterle Ivan , Wagner Zdeněk
Published: May 2010

The gas-liquid critical region is described by means of an exponential relation, parameters of which are independent of system. It can be used for the preparation of nonclassical fluid phase behaviour. The isothermal vapour-liquid equilibrium data on the sulphur hexafluoride-pentane system measured in neighbourhood of the critical point of SF6 are presented.
A generalized treatment of cubic equations of state
Authors: Míka Vladimír
Published: May 2010

From the formula proposed for the van Waals type equations of state, general expressions for the compressibility factor, the departure functions and the fugacity coefficient are derived. Easy construction of the formula needed is possible for any of the equations listed in the paper. The method is applicable to other equations of this type.
Theoretical and experimental study of chemical equilibrium in the systems Si-Cl and Si-Cl-H. Calculation of chemical equilibrium in the systems Si-Cl and Si-Cl-H
Authors: Leitner Jindřich , Černý Čestmír , Voňka Petr , Mikulec Jan
Published: May 2010

From the calculations of heterogenous chemical equilibria in the systems Si-Cl and Si-Cl-H the equilibrium composition of the gas phase and the amount of deposited or reacted solid silicon have been determined. For these calculations, the method based on the minimization of the Gibbs energy of the system and critically judged and selected values of input thermodynamic data have been used. The calculations have been performed for the temperature range 1 000-1 600 K, for the pressure 101.325 kPa and 10.133 kPa and for various input compositions of the gaseous phase. In the case of the system Si-Cl, the reaction of solid leading to the formation of silicon subchlorides takes place at all conditions investigated. At atmospheric pressure and at temperatures in the neighbourhood of 1 300 K, the dominant components of the gas phase are the following substances: SiCl4, SiCl3 and SiCl2. The dependence of the amount of deposited solid silicon on temperature and on the initial composition of the gas phase in the system Si-Cl-H shows–in the investigated range of variables – a maximum, the position of which depends on the total pressure of the system. At atmospheric pressure, at temperatures around 1 300 K and at the initial molar ratio Cl/H = 0.01, the dominant components of the gas phase are the following substances: SiCl4, SiCl3, SiCl2, SiHCl3, SiH2Cl2 and HCl. The substance SiHCl which has been included into the equilibrium calculations for the first time, is present in a significant amount at higher temperatures and especially at lower pressure.
Measurement of growth rates for single crystals and pressed tablets of CuSO4.5 H2O on a rotating disc
Authors: Karel Miloslav , Nývlt Jaroslav
Published: May 2010

Measured growth and dissolution rates of single crystals and tablets were used to calculate the overall linear rates of growth and dissolution of CuSO4.5 H2O crystals. The growth rate for the tablet is by 20% higher than that calculated for the single crystal. It has been concluded that this difference is due to a preferred orientation of crystal faces on the tablet surface. Calculated diffusion coefficients and thicknesses of the diffusion and hydrodynamic layers in the vicinity of the growing or dissolving crystal are in good agreement with published values.
The effect of the cooling mode on the kinetic parameters of crystallization
Authors: Broul Miroslav , Hložný Ladislav , Provazník Luděk , Loučka Tomáš , Vaněček Vojtěch
Published: May 2010

The effect of different cooling regimes (natural, linear, and programmed cooling according to a theoretical curve) on the kinetic parameters of crystallization and on the mean product crystal size is demonstrated by an example of batch cooling crystallization of ammonium aluminium sulphate dodecahydrate. The kinetic exponent g/n determined on the basis of model experiments does not depend on the cooling regime, the system constant BN is highest for the programmed cooling. If this constant is to be a basis for the design of a cooling crystallization equipment, it is necessary to carry out its experimental determination under the same temperature regime.
Some relations between thermodynamic and kinetic parameters in heterogeneous catalysis
Authors: Quang Nguyen Xuan , Thoang Ho Si , Šípek Milan
Published: May 2010

The results of our preceding work on irreversible (rational) thermodynamics of reacting mixture of fluids and a solid substance are applied to the problem of heterogeneous catalysis. The negative effect of diffusion and the positive effect of surface forces are justified, and the Bronsted-Polanyi equation for the activation energy of surface reaction is obtained.
Influence of water on activity, selectivity and deactivation of zeolites in acetone transformation
Authors: Čejka Jiří , Jírů Pavel
Published: May 2010

The suppression of the deactivation of acid forms of zeolites in acetone transformation was studied by adding water vapours to the feed. Both conversion of acetone and yield of isobutene increased remarkably. Water prevents the substitution of bridging hydroxyls for coke species and limits the aldolization steps, which are decisive for catalyst deactivation.
Automated low gas flow-rate calibrator
Authors: Wičar Stanislav , Svozil Martin , Šimík Pavel
Published: May 2010

A new method of the absolute low gas flow measurement was developed. The method is based on the comparison of the known rate of a piston movement in a calibrated cylinder with the measured gas flow rate. Due to its compensating character, the method is extremely sensitive, and the relative error is given merely by the sensitivity of determining the pressure difference between the cylinder and atmosphere. The method is absolute as the apparatus constant is determined by such operations as weighing and frequency measurement.
Control of cascade of CSTR with an autocatalytic reaction. Isothermal regime
Authors: Horák Josef , Rosol Petr , Bartholomae Ines
Published: May 2010

Regime stability of a cascade of continuous stirred reactors operated isothermally is analyzed for a reaction with autocatalytic type of kinetic law. Consequences of the regime unstabilities are discussed and control algorithms suggested to operate the cascade in both stable and unstable operating points. Numerical simulations are used to test the algorithms. Reaction calorimetry serves as the source of information on the reactor state in conversion control in unstable states if no on-line analytical method is available to measure conversion.
Titanium-catalyzed Diels-Alder addition of bis(trimethylsilyl)acetylene to 1,3-cyclohexadiene
Authors: Mach Karel , Antropiusová Helena , Hanuš Vladimír , Sedmera Petr
Published: May 2010

The TiCl4-(C2H5)2AlCl catalyst induced the Diels-Alder addition of bis(trimethylsilyl)acetylene to 1,3-cyclohexadiene affording 2,3-bis(trimethylsilyl)bicyclo[2.2.2]octa-2,5-diene in 72% yield under mild conditions. The product eliminates ethylene upon heating to 240 °C to give 1,2-bis(trimethylsilyl)benzene.
Computer simulation of inhibitor action on singlet substrate oxidation
Authors: Wagnerová Dana M. , Mach Ivan , Luňák Stanislav , Vepřek-Šiška Josef
Published: May 2010

The new mechanism recently proposed for reactions of dioxygen with organic substrates postulates that all reactions of dioxygen are catalyzed by metal ions, sometimes even in trace concentrations. Inhibition in terms of this mechanism is interpreted as being due to the formation of catalytically inactive complexes of catalyst with inhibitor. Kinetic consequences of this mechanism were simulated on a computer as a function of various parameters, and compared with experimental results. It is shown that the new mechanism accounts for all experimentally observed inhibition effects, including those which are considered as proof of a chain mechanism.
Potential distribution in a trickle-bed electrode
Authors: Špalek Otomar , Balogh Karel
Published: May 2010

The performance of trickle-bed electrodes of crushed graphites in oxygen reduction to hydrogen peroxide has been investigated. Results are presented for the effects of the current density, gas and electrolyte flow rates, pressure, and graphite particle size on the electrode potential, voltage loss in the electrode material, and current yield of the process.
A comment on evaluation of effects of mixed solvents by means of the Born and Kirkwood method
Authors: Bekárek Vojtěch
Published: May 2010

The evaluation of the mixed solvent effect by means of the Kirkwood and Born functions of the relative permitivity of the mixed solvent has been criticized as a thermodynamically inconsistent procedure. A procedure has been suggested to estimate the composition of solvation sphere around dipolar molecules or transition states in binary mixtures of a polar and a nonpolar solvents.
Molecular orientation of liquid aliphatic hydrocarbons on the surface and at the interface with water
Authors: Kloubek Jan
Published: May 2010

The validity of the Fowkes theory for the interaction of dispersion forces at interfaces was inspected for the system water-aliphatic hydrocarbons with 5 to 16 C atoms. The obtained results lead to the conclusion that the hydrocarbon molecules cannot lie in a parallel position or be randomly arranged on the surface but that orientation of molecules increases there the ration of CH3 to CH2 groups with respect to that in the bulk. This ratio is changed at the interface with water so that the surface free energy of the hydrocarbon, γH, rises to a higher value, γ’H, which is effective in the interaction with water molecules. Not only the orientation of molecules depends on the adjoining phase and on the temperature but also the density of hydrocarbons on the surface of the liquid phase changes. It is lower than in the bulk and at the interface with water. Moreover, the volume occupied by the CH3 group increases on the surface more than that of the CH2 group. The dispersion component of the surface free energy of water, γdW = 19.09 mJ/m2, the non-dispersion component, γnW = 53.66 mJ/m2, and the surface free energies of the CH2 and CH3 groups, γ(CH2) = 32.94 mJ/m2 and γ(CH3) = 15.87 mJ/m2, were determined at 20 °C. The dependence of these values on the temperature in the range 15-40 °C was also evaluated.
Oxygen transfer during batch cultivation in an airlift tower fermentor
Authors: Potůček František
Published: May 2010

Oxygen transfer was studied in an airlift tower fermentor with motionless mixers (Kenics type). The intensity of oxygen transfer was characterized by its volumetric mass transfer coefficient, kLa, which was determined by the balance method. Experimental data of kLa were described by correlation equation and compared with results obtained for the airlift fermentor without motionless mixers with respect to energetic consumption. In addition, growth characteristics of the yeast culture Turulopsis ethanolitolerans cultivated on ethanol were also investigated.
The crystal and molecular structure of configurationally chiral unsym-fac-[N-(2-aminoethyl)-1,3-diaminopropane-(S)-aspartato]cobalt(III) perchlorate with dominating vicinal effect in its circular dichroism
Authors: Ondráček Jan , Maixner Jaroslav , Kratochvíl Bohumil , Ondráčková Jana , Jursík František
Published: May 2010

The crystal and molecular structure of unsym1-fac-Λ-(δ, chair)-(S)-[Co(aepn)(S)-Asp]ClO4(trans-6,6) was solved by the heavy atom method. The positions of the non-hydrogen atoms and their anisotropic temperature parameters were refined on the basis of 1 935 observed reflections, yielding values of R = 0.121 and wR = 0.117, affected by the undertermined position of the oxygen atoms in the ClO4-> anion. The substance crystallizes in the orthorhombic system with space group P212121; Z = 4, a = 9.664(1), b = 11.805(1), c = 13.966(2) Å. The secondary atom of the triamine has S configuration, the conformation of the five-membered chelate ring approaches that of the asymmetrical δ envelope and the six-membered ring has chair configuration. Both conformations are deformed. The donor atoms deviate from the defined planes and thus form further sources of chirality (λ) contributing to the optical activity of the isomer. These deviations lead to the similarity of the CD spectra of the isomers.
Medium effect in the aquation of pentaamine-(p-toluenesulfonamido)cobalt(III) ion
Authors: Grančičová Oľga , Holba Vladislav
Published: May 2010

The aquation kinetics of pentaamine-(p-toluenesulfonamido)cobalt(III) ion were studied in the presence of NaCl, NaBr and NaClO4 as supporting electrolytes as well as in binary aqueous-organic mixtures with methanol, isopropyl alcohol, tert-butylalcohol, dioxane and acetonitrile as non aqueous cosolvents. It was found that the association between the complex ion and Cl-, Br- and ClO4- ion takes place and the association constants were evaluated from kinetic measurements. Some conclusions concerning the effect of non aqueous component of the solvent on solvation of the initial and transition state have been drawn from the experimental data obtained.
Crystal and solution structure of (E)-1,2-bis(ethylsulphonyl)cyclobutane-1,2-dicarbonitrile
Authors: Podlaha Jaroslav , Buděšínský Miloš , Podlahová Jana , Hašek Jindřich
Published: May 2010

The unusual product of the reaction of 2-chloroacrylonitrile with ethane thiol and following hydrogen peroxide oxidation was found to be (E)-1,2-bis(ethylsulphonyl)cyclobutane-1,2-dicarbonitrile by means of X-ray crystallography. 1H and 13C NMR study of this compound has proven the same conformation of the molecule in solution.
The Bayer-Villiger oxidation of diamantanone and the structure of 11-oxo-10-oxapentacyclo[7,4,1,14,13,02,7,06,12]-pentadecane
Authors: Ondráček Jan , Janků Josef , Novotný Jiří , Vodička Luděk , Csordás László , Kratochvíl Bohumil
Published: May 2010

The studied substance was prepared by the Bayer-Villiger oxidation of diamantanone and identified by 1H and 13C NMR spectroscopy. The structure of the compound was solved by direct methods and refined to the value R = 0.052 for 845 observed reflections (I > 1.96σ(I)). The substance crystallizes in the orthorhombic space group Pnnm; a = 23.595(4), b = 10.284(2), c = 6.676(1) Å. The unit cell of the crystal structure of 11-oxo-10-oxapentacyclo[7,4,1,14,13,02,7,06,12]pentadecane contains four ordered and two disordered molecules. The disordered molecule is described by averaging the image of the ordered molecule and its inverse image. Thus, the unit cell contains 6 formula units (part of the atoms have fractional occupation factors) even though the multiplicity of the general position in the Pnnm group is 8.
Ammonolysis mediated side reactions of β-tert-butyl aspartyl peptides
Authors: Schön István , Rill Attila
Published: May 2010

Ammonolysis of Z-Asp(OBut)-Phe-NH2 and Boc-Leu-Asp(OBut)-Phe-NH2, as well as their diastereomers, resulted not only in transpeptidated, but also in epimerized peptides through a complex mechanism. Key compounds of these transformations are presumably very reactive cyclic aminosuccinyl derivatives. In some cases, the amount of α-peptide formed approached that of the β-peptide, in one case it exceeded this amount.
Synthesis, biological activity and receptor binding affinity of six new antagonists of [8-L-arginine]vasopressin
Authors: Lammek Bernard , Derdowska Izabela , Kupryszewski Gotfryd , Slaninová Jiřina , Barth Tomislav , Hrbas Pavel
Published: May 2010

Six analogues of d(CH2)5AVP, a vasopressin inhibitor, modified in positions 1, 2, 4, and 9 were synthesized and the effect of the modifications on the inhibitory potency was followed. Buly and lipophilic substitutions in position 1 in combination with Abu substitution in position 4 led to a slight decrease of antivasopressor potency and a strong decrease of the antiuterotonic potency. Alkylation of any type of carboxamide group at positions 4 and 9 strongly reduced the biological potency in all the tests.
Racemization rates of 3,4-didehydro-2-amino acids
Authors: Havlíček Libor , Hanuš Jan , Němeček Jan
Published: May 2010

The racemization rates of amino acids in acidic medium (acetic acid) were studied. The sensitivity to racemization decreases in the order (E)-3,4-didehydroornithine > (E)-Nδ-Z-3,4-didehydroornithine >> (Z)-3,4-didehydronorvaline > ornithine, norvaline. (E)-3,4-Didehydroornithine is also relatively rapidly racemized on heating with 5 M or 0.05 M-HCl (100 °C).
Does childhood and adolescence fracture influence bone mineral content in young adulthood?
Authors: Kawalilak Chantal E. , Baxter-Jones Adam D.G. , Faulkner Robert A. , Bailey Donald A. , Kontulainen Saija A.
Published: May 2010

Previous fracture may predispose an individual to bone fragility because of impaired bone mineral accrual. The primary objective of the study was to investigate the influence of fractures sustained during childhood and (or) adolescence on total body (TB), lumbar spine (LS), femoral neck (FN), and total hip (TH) bone mineral content (BMC) in young adulthood. It was hypothesized that there would be lower TB, LS, FN, and TH BMC in participants who had sustained a pediatric fracture. Participant anthropometrics, physical activity, and BMC (measured with dual energy X-ray absorptiometry) were assessed longitudinally during childhood and adolescence (from 1991 to 1997), and again in young adulthood (2002 to 2006). Sex, adult height, adult lean mass, adult physical activity, and adolescent BMC adjusted TB, LS, FN, and TH BMC in young adulthood, for those who reported 1 or more fractures (n = 42), were compared with those who reported no fractures (n = 101). There were no significant differences (p > 0.05) in adjusted BMC between fracture and nonfracture groups at the TB, LS, FN, and TH sites in young adulthood. These results suggest that fractures sustained during childhood and adolescence may not interfere with bone mass in young adulthood at clinically relevant bone sites.
The effects of 4 weeks of an arginine-based supplement on the gas exchange threshold and peak oxygen uptake
Authors: Camic Clayton L. , Housh Terry J. , Mielke Michelle , Zuniga Jorge M. , Hendrix C. Russell , Johnson Glen O. , Schmidt Richard J. , Housh Dona J.
Published: May 2010

The purpose of the present study was to examine the effects of the daily administration of an arginine-based supplement for 4 weeks on the gas exchange threshold (GET) and peak oxygen uptake. The study used a double-blind, placebo-controlled design. Forty-one college-aged males (mean age ± SD = 22.1 ± 2.4 years) were randomized into either the PLACEBO (n = 20) or ARGININE (n = 21) group. The placebo was microcrystalline cellulose. The ARGININE group ingested 3.0 g of arginine, 300 mg of grape seed extract, and 300 mg of polyethylene glycol. All subjects performed an incremental test to exhaustion on a cycle ergometer prior to supplementation (PRE) and after 4 weeks of supplementation (POST). The GET was determined by using the V-slope method of the carbon dioxide output vs. oxygen uptake relationship. The results indicated that there were significant mean increases (PRE to POST) in GET (4.1%), as well as in carbon dioxide output (4.3%) and power output (5.4%) at the GET for the ARGININE group, but no significant changes for the PLACEBO group (2.5%, 4.3%, and 3.9%, respectively). In addition, there were no significant changes in peak oxygen uptake for the ARGININE (–1.0%) or PLACEBO (–1.5%) groups. These findings supported the use of the arginine-based supplement for increasing GET and the associated power output, but not for increasing peak oxygen uptake during cycle ergometry.
Dietary fish oil alleviates soleus atrophy during immobilization in association with Akt signaling to p70s6k and E3 ubiquitin ligases in rats
Authors: You Jae-Sung , Park Mi-Na , Song Wook , Lee Yeon-Sook
Published: May 2010

Reduced muscle activity leads to impaired insulin signaling, which leads to loss of contractile proteins and muscle mass via the Akt pathway. Dietary fish oil rich in long chain n-3 polyunsaturated fatty acids has been shown to prevent insulin signaling resistance in skeletal muscle. This study was conducted to elucidate the protective effect of dietary fish oil on disuse-induced perturbations in insulin signaling and soleus muscle atrophy. To accomplish this, rats were fed a corn-oil- (control) or fish-oil-based diet for 2 weeks, and then subjected to hindlimb immobilization while still receiving the same diets. After 10 days of immobilization, the soleus muscle mass and myosin heavy chain level had markedly decreased; however, these losses were significantly suppressed in rats fed dietary fish oil, compared with the control group. Dietary fish oil nearly completely attenuated the disturbances in activation of the Akt and p70 S6 kinase proteins, as well as the gene expression of muscle-specific E3 ubiquitin ligases (muscle atrophy F-box and muscle RING finger 1). However, insulin receptor substrate 1 associated with the p85 subunit of phosphoinositide 3-kinase was not altered during immobilization. Dietary fish oil also inhibited alterations in the gene expression of cyclooxygenase-2 and inducible nitric oxide synthase, with no additional observation of oxidative stress. Collectively, these findings indicate that dietary fish oil prior to and during immobilization may alleviate the immobilization-induced soleus muscle atrophy, at least in part, via the Akt pathway through E3 ubiquitin ligases and p70s6k.
Bone formation is increased to a greater extent than bone resorption during a cycling stage race
Authors: Hinton Pamela S. , Rolleston Anna , Rehrer Nancy J. , Hellemans Ien J. , Miller Benjamin F.
Published: May 2010

This study examined the effects of participation in the Tour of Southland, a 6-day bicycle race, on serum markers of bone turnover in 5 elite male cyclists. During the race, energy intake matched expenditure. Osteocalcin was increased ~300% on days 1–5; and C-terminal telopeptide of type I collagen was elevated (43%) on day 3. Participation in a cycling stage race does not appear to have deleterious effects on bone turnover.