bluuebunny/crossref_metadata_2025 huggingface dataset:
Density and viscosity of the system Ca(NO3)2-H2O-dimethyl sulphoxide
Authors: Kodejš Zdeněk , Novák Jindřich , Sláma Ivo
Published: March 2011

The density and viscosity of the ternary system Ca(NO3)2-H2O-dimethyl sulphoxide were measured over the temperature range 0 < t < 60 °C, with the mole fraction of the salt in the system varied in the range 0.05 < x < 0.16. The temperature and concentration dependences of density and viscosity have been described by empirical equations. The viscosity data show a pronounced dependence on the solvent composition. Maximum deviations of viscosity from the ideal additive behaviour of the two salt-solvent binary systems occur at a mole fraction of DMSO in the mixed solvent of 0.3. The observed dependence is discussed in relation to the structure of the solution.
Pertrimethylsilylation as a method for improvement of chemical shift additivity through conformational homogenization. 1H and 13C NMR spectra of pertrimethylsilylated derivatives of methyl β-D-xylopyranosides
Authors: Schraml Jan , Petráková Eva , Pihar Otomar , Hirsch Ján , Chvalovský Václav
Published: March 2011

All possible mono-, di-, and tri- O-methyl, O-benzyl, O-benzoyl, and O-acetyl derivatives of methyl β-D-xylopyranoside were fully trimethylsilylated and their 1H and 13C NMR spectra measured in deuteriochloroform solutions. The spectra were analysed and the chemical shifts completely assigned on the basis of decoupling experiments. The proton-proton coupling constants vary only very little throughout the series. Conformer population analysis by the method of average coupling constants shows that trimethylsilylation increases the C1 conformer population and makes the series conformationally homogenous. Owing to this conformational homogeneity chemical shifts (both 1H and 13C) satisfy very well direct additivity rule. It is suggested that pertrimethylsilylation should be employed whenever deviations from chemical shift additivity are caused by conformational mobility of the investigated series of compounds and when bulky groups can stabilize one of the conformers.
Reactions of ethyl 2-alkyl-3-oxobutanoate with thiourea and methylthiourea
Authors: Kaválek Jaromír , Macháček Vladimír , Štěrba Vojeslav
Published: March 2011

The reaction of ethyl 3-oxobutanoate with N-methylthiourea in alkoxide medium gives a mixture (1 : 20) of 1,6-dimethyl-2-thiouracil and 3,6-dimethyl-2-thiouracil: the latter isomer has been isolated from the mixture and the former isomer has been prepared by independent synthesis. Dissociation constants of ethyl 2-alkyl-3-oxobutanoates (alkyl = methyl, butyl, or isopropyl) have been measured in methanol. Reaction of these esters with thiourea and N-methylthiourea gives the corresponding alkyl derivatives of 6-methyl-2-thiouracil. Kinetics of these reactions have been measured in methoxide medium. Effects of the alkyl groups on the reaction rates have been investigated, and a reaction mechanism is suggested.
Synthesis and reactions of trimethylammonium salts of 5-nitro-2-furan and 5-nitro-2-thiophene. The preparation of 5-nitro-2-furyl- and 5-nitro-2-thienyl azide
Authors: Végh Daniel , Kováč Jaroslav , Dandárová Miloslava
Published: March 2011

Preparation of new water-soluble derivatives of 5-nitro-2-furan and 5-nitro-2-thiophene from 2-bromo-5-nitrofuran (Ia) or 2-bromo-5-nitrothiophene (Ib) and trimethylamine is described. The trimethylammonium derivatives IIa, IIb react with the azide or cyanide anion in water to afford azides IVa, IVb or nitriles Va, Vb of 5-nitro-2-furan or 5-nitro-2-thiophene. The reactivity of these azides with dimethyl 2-butinedioate and triphenyl phosphine was studied.
Effects of two new additives on the initial rate of peroxodisulphate electrosynthesis
Authors: Balej Jan , Kadeřávek Martin , Matschiner Hermann , Thiele Wolfgang
Published: March 2011

Two new additives, dipotassium cyanimidodithiocarbonate (DKDK) and 5-thio-2-imido-3,4-disulphazolidine (TIDSAL), were tested for the effect they have on the initial rate of peroxodisulphate ion formation in 5M-H2SO4 solution. The concentrations of the additives ranged from 10-4 to 10-2 mol dm-3. Both substances were found to increase current yields of peroxodisulphates as well as oxygen overpotential on the platinum anode. The additive concentration at which a maximum increase was achieved was about 1 . 10-2 mol dm-3 in both cases. Maximum current yields attained under the applied reaction conditions were, however, somewhat lower than those observed with an optimum addition of SCN-.
Complexes of copper(II) and nickel(II) with a Schiff base bonded to a polymeric support
Authors: Kálalová Eliška , Populová Olga , Štokrová Štěpánka , Stopka Pavel
Published: March 2011

Copper(II) and nickel(II) ions were bonded in complexes of salicylideneimine type on a glycidyl methacrylate-ethylenedimethacrylate copolymer. The geometry of the complexes on the polymer was studied by measuring their magnetic properties, EPR spectra, and ultraviolet-visible spectra.Only paramagnetic complexes possessing a pseudo-tetrahedral configuration were found. The effect of the polymer matrix and of the immobility of the bonded Schiff base on the distortion of the coordination sphere of the central ion is discussed.
NMR line-shape analysis of swollen crosslinked poly(ethylene oxide) using an orientation-dependent Gaussian broadening function with varying width
Authors: Jakeš Jaromír
Published: March 2011

NMR line shapes of swollen crosslinked poly(oxyethylene) were analysed as a convolution of a narrow Lorentzian function governed by rapid segmental motions, and a dipolar broadening function. An orientation-dependent Gaussian function with some distribution of its width was chosen for the dipolar broadening function. For the distribution of the width a function similar to the χ2 distribution was used. An appreciable improvement compared to the previous analysis with the orientation-dependent Lorentz function was only obtained if the distribution used contained an essential amount of narrow widths close to zero. With this approach, it was possible to simulate the experimental spectra obtained in the CDCl3 swelling agent at various temperatures within experimental accuracy. With the CCl4 swelling agent, the agreement was slightly worse in the peak area, apparently due to the distribution of the width of the narrow Lorentzian function governed by rapid segmental motions. Even in this case, an improvement compared to the previous analysis was obtained. It was found that a simple Gaussian distribution function with the maximum at zero width, which is a special case of the general distribution function used, can reproduce the experimental spectra with almost the same accuracy as the general distribution function.
Raman and infrared spectra and the structure of the dimethyl ester of 2,2,4,4-tetramethylglutaric acid
Authors: Dybal Jiří , Štokr Jan , Schneider Bohdan
Published: March 2011

Raman and infrared spectra of the dimethyl ester of 2,2,4,4-tetramethylglutaric acid in the solid and liquid states and the temperature dependence of the spectra were measured. The behaviour of some bands in the spectra indicates the presence of three conformers in the liquid state. Local order of the molecules due to dipolar interactions of ester groups was observed.
Preparation of N-acetylnormuramyl-α-aminobutyryl-D-isoglutaminyl-lysyl-lysyl-lysine
Authors: Krchňák Viktor , Ježek Jan , Zaoral Milan
Published: March 2011

The title compound (I) has been prepared by solid-phase synthesis. In aqueous solution the compound I forms a mixture of α- and β-anomers.
Glucan isolated from leaves of Althaea officinalis L.
Authors: Kardošová Alžbeta , Rosík Jozef , Toman Rudolf , Capek Peter
Published: March 2011

A water-soluble low-molecular D-glucan was isolated from leaves of the medicinal plant marsh-mallow (Althaea officinalis L.). The results of methylation analysis, partial hydrolysis, periodate oxidation, and 13C NMR data indicated a virtually linear structure with α-(1→6) glycosidic bonds.
Growth inhibition of Escherichia coli B by nucleoside analogs
Authors: Bártová Markyta , Ryba Miloš , Jedličková Zdena , Novotný Ladislav , Hřebabecký Hubert , Beránek Jiří
Published: March 2011

The inhibition of growth of Escherichia coli B by series of 6-azaanalogs of pyrimidine nucleosides, their precursors, and analogs of cancerostatic agents 5-fluorouracil and arabinosylcytosine is reported. A very high antibacterial activity is observed with most of the 5-fluorouracil nucleosides where a cleavage (30%) to 5-fluorouracil is observed at the most active compounds (5-fluorouridine, 5-fluoro-2'-deoxyuridine). Arabinosylcytosine and its derivatives express very low activity.
Isopropylbenzene decomposition and high temperature adsorption of pyridine on hydrorefining catalysts
Authors: López Rafael , Ramos Iran , Villalba Victor , García Juan José
Published: March 2011

The acidic properties of various oxidic and sulphided hydrorefining catalysts have been studied by means of isopropylbenzene decomposition at 400 °C in a pulse reactor, and of the adsorption of pyridine at 300 °C. Isopropylbenzene reacted in two parallel reactions, forming benzene and propene by cracking, and α-methylstyrene by dehydrogenation. Sulphidation influences more the strength than the concentration of acidic sites. A correlation between the rate constants for the cracking of isopropylbenzene and the b constants of Langmuir isotherm for pyridine adsorption is presented.
Generation of the system of equations for equationally oriented global simulation of complex systems
Authors: Vrba Josef
Published: March 2011

Generation of the system of equations from equational models of standard unit operations used for solution of global simulation of a complex system in steady state is considered. The procedure is illustrated on a simple example.
Potential hypnotics and anxiolytics in the 4H-s-triazolo[4,3-a]-1,4-benzodiazepine series: 8-Chloro-6-(2-chlorophenyl)-1-[4-(2-methoxyethyl)piperazino]-4H-s-triazolo[4,3-a]-1,4-benzodiazepine and some related compounds
Authors: Polívka Zdeněk , Ryska Miroslav , Holubek Jiří , Svátek Emil , Metyš Jan , Protiva Miroslav
Published: March 2011

1-Bromo derivatives XIIa and XIIb were prepared by bromination of 8-chloro-6-phenyl-4H-s-triazolo[4,3-a]-1,4-benzodiazepine (XIa) and its 6-(2-chlorophenyl) analogue XIb with bromine in chloroform in the presence of pyridine. Substitution reactions with 1-(2-methoxyethyl)piperazine (XIVb), 1-(3-methoxypropyl)piperazine (XVb), 1-(2-ethoxyethyl)piperazine (XVIb) and 1-(2-methylthioethyl)piperazine (XVIIb) afforded the title compound IIb and analogues IIa and IIIb-Vb. A substitution reaction of the bromo derivative XIIb with piperazine gave the 1-piperazino derivative VIIIb which was alkylated with 2-phenoxyethyl bromide and 2-phenylthioethyl bromide to give compounds VIb and VIIb. The title compound IIb has very high anticonvulsant and discoordinating activities in mice. The enlargement of the substituent R1 (compounds IIIb-VIIb) results in a gradual decrease of the effects mentioned.
Further band theory arguments elucidating the nature of the ordered state of the CsCl type alloy β'-CuZn
Authors: Tomášek Mojmír , Pick Štěpán , Šob Mojmír
Published: March 2011

Partial wave analysis together with the qualitative analysis of hybridization in β'-CuZn is used to shed more light on special bonding conditions in which stability of this phase might originate. Results support the legitimacy of the so-called polar model of this phase. Analogy to the ordered Cu3Au alloy is mentioned, the difference being that the latter stabilizes due to a pure superstructure effect. Shockley surface states found recently on the (111) surface of Cu3Au are to be expected on the same face of α-CuZn as well.
PMO treatment of structure-reactivity relationships. Polar effects in the free radical addition reactions
Authors: Ponec Robert , Hájek Milan , Málek Jaroslav
Published: March 2011

The electronic nature of free radicals in the addition to substituted styrenes was studied by a simple perturbation approach utilizing delocalisability Dr as a static index of reactivity. In agreement with experimental results, the calculations reproduce correctly the change in the sign of the Hammett ρ constants in going from electronegative to electropositive radicals.
On the observability of heat dispersion parameters of the pseudohomogeneous model of heat transfer in packed beds
Authors: Staněk Vladimír , Vychodil Petr
Published: March 2011

Solution has been obtained of the pseudohomogeneous model of heat dispersion in a packed bed under simultaneous radial and axial dispersion of heat using Danckwerts' boundary condition. The obtained solution has been used to evaluate parameters of the model from experimental data based on the least sum of square deviations of the temperature profiles. Maps have been constructed of the joint confidence regions in the parameter domain. The results have shown the method to be suitable for the determination of radial thermal dispersion while suppressing the effects of structural disturbances of the bed near the containing walls.
29Si NMR chemical shifts in pertrimethylsilylated 1,6-anhydro-β-D-glucopyranose derivatives. Empirical assignment from Hammett type dependence of the chemical shifts
Authors: Schraml Jan , Včelák Jaroslav , Černý Miloslav , Chvalovský Václav
Published: March 2011

29Si chemical shift of Si-3 silicon atom of the trimethylsiloxy group attached to C(3) carbon atom in 1,6-anhydro-β-D-glucopyranose derivatives correlates linearly with the sum of Taft polar constants σσ of substituents R2 and R4 on C(2) and C(4) carbon atoms. Quality of this correlation allows assignment of Si-3 line in the spectra of derivatives containing two or three trimethylsilyl groups in the molecule. The shielding order δ(Si-4) < δ(Si-3) found in 1,6-anhydro-2,3,4-O-tris(trimethylsilyl)-β-D-glucopyranose is the same as recently found in other pyranose derivatives with the same configuration of substituents but the order is reversed by strong polar effect of the substituent in 1,6-anhydro-2-O-p-toluenesulphonyl-3,4-O-bis(trimethylsilyl)-β-D-glucopyranose. This finding warns against indiscriminate use of empirical assignment rules based on simple shielding order without considering possible substituent effects.
Affinity chromatography of rat liver S-adenosyl-L-homocysteine hydrolase
Authors: Votruba Ivan , Holý Antonín , Rosenberg Ivan
Published: March 2011

A comparison of eight types of carriers for purification of S-adenosyl-L-homocysteine hydrolase by affinity chromatography is described. The Sepharose-based carriers contained stereoisomeric eritadenines bonded by the carboxyl function or neutral aliphatic adenine derivatives bonded by the amino group of substituent on the heterocyclic nucleus or in the side-chain. Materials with bonded isomeric 9-(RS)-(3(2)-(3-aminopropylamino)-2(3)-hydroxypropyl)-8-hydroxyadenines (VIIIb, IXb) appeared to be carriers of choice which enabled an efficient affinity purification of the enzyme from rat liver. SAH-Hydrolase was liberated only upon elutions with dilute adenosine solutions.
Analysis of the system precipitation-separation unit. Effect of filtration pressure drop on relation among filtration properties of suspensions and reaction conditions at precipitation
Authors: Söhnel Otakar
Published: March 2011

Filtration characteristics of BaCO3 and SrCO3 suspensions precipitated batchwise at differing conditions were studied in dependence on the used filtration pressure drop. Both compounds form compressible filtration cakes whose behaviour is described by an exponential function. Parameters of this function determined experimentally for ΔP = 20 to 80 kPa are given. Theoretical relation between initial supersaturation at precipitation and filtration resistance of the formed suspension (Eq. (14)) hold for both compounds in the whole studied range of filtration pressure drops ΔP from 20 to 80 kPa. Two groups of compounds were found; for the first one the parameters of Eq. (14) are not a function of ΔP, whereas for the second one the dependence of parameters in Eq. (14) on ΔP is significant.
Isotopic solvent effect in hydrogenation on a supported nickel catalyst
Authors: Kudláček Rostislav , Judlová Alena
Published: March 2011

A supported nickel catalyst, commonly applied in industrial hydrogenation of fatts and oils, was used to study the effect of replacement of the light water solvent, with heavy water, on the addition of hydrogen on a double bond of maleic acid. The effect was investigated of the composition and temperature of the solution, on the reaction rate, as well as, the relation between the reaction rate and the amount of the acid absorbed on the catalyst. Reaction mechanism with respect to the hydrogenated organic compound is proposed.
Polarographic determination of some nitro group-containing pesticides
Authors: Beňadiková Hana , Popl Milan , Jakubíčková Věra
Published: March 2011

The differential pulse polarography technique was applied to the determination of some pesticides containing nitro groups in their molecules. The nitro groups were found to be reduced to hydroxylamines or to the corresponding amines. The effect of medium, particularly of pH of the supporting electrolyte, was examined. The pesticides were determined in concentrations less than 10 μg l-1, which shows primose for the application of the technique to environmental water purity monitoring.
Aliphatic and aromatic 5-nitro-2-furylamines and aromatic 5-nitrofurfuryl ethers
Authors: Mocelo Raul , Kováč Jaroslav
Published: March 2011

Tertiary 5-nitrofurylamines were prepared by a nucleophilic substitution of 5-nitro-2-furfuryl bromide (I) with aliphatic secondary amines. According to reaction conditions N-(5-nitro-2-furfuryl)-X-phenylamines or their mixture with N,N-di(5-nitro-2-furfuryl)-X-phenylamines were obtained from the reaction of I with substituted primary aromatic amines. Compound I gave with 2-aminophenol a mixture of O- and N-mono- and disubstituted derivatives, and with ethyl salicylate ethyl 2-(5-nitro-2-furfuryloxy)benzoate.
Structure of sodium tetracaprolactamatoaluminate. 1H NMR spectra of sodium isobutylcaprolactamatoaluminates
Authors: Kříž Otomar , Fusek Jiří , Čásenský Bohuslav
Published: March 2011

Sodium tetracaprolactamatoaluminate (I) exists in benzene solution predominantly as a dimer. Its structure was proposed on the basis of molecular weight studies, infrared, and 1H NMR spectra of sodium isobutylcaprolactamatoaluminates (II). Two modes of dimerization are supposed: an eight-membered cyclic caprolactam bridge between two aluminum atoms or the coordination of the caprolactam ligands belonging to two different aluminum atoms to one sodium atom.
Determination of crystallization kinetics from batch experiments II
Authors: Nývlt Jaroslav , Žáček Stanislav
Published: March 2011

Relations have been derived for the size distribution of crystal product of batch crystallization with constant and variable supersaturation, applicable where the distribution cannot be approximated by the relation holding for continuous MSMPR crystallizers. In the cases considered, relative kinetic data, but not the kinetic exponents of nucleation and crystal growth, can be evaluated for model experiments involving any variation of supersaturation with time. Application of the relationships is illustrated by treating data for potassium aluminium sulphate precipitation.
Study of the formation of complexes of 2-hydroxy-1,3-propanediamine-N,N,N',N'-tetraacetic acid with Zn(II), Cd(II) and Pb(II) ions using NMR spectroscopy
Authors: Novomeský Pavol , Balgavý Pavol , Majer Jaroslav
Published: March 2011

2-Hydroxy-1,3-propanediamine-N,N,N',N'-tetraacetic acid (HPDTA) forms complexes of the ML type with Zn(II) and Cd(II) ions in the pDH ranges 5.0-11.5 and 7.3-8.6, respectively. In these complexes, there are coordinated oxygen atoms of four carboxylate groups and nitrogen atoms of two amino-groups. Formation of the Pb2L type complex was observed in the pDH region 5.9-11.5. HPDTA is a heptadentate ligand in this complex. The two glycinate rings correspond to one Pb(II) ion and are nonequivalent. During formation of the hydroxocomplexes of Pb2L and CdL in alkaline solutions, the HPDTA carboxylate groups become substituted by OH- ion in the coordination sphere of the metal ion.
Chelates of vanadium(V) with organic hydroxy compounds in aqueous solutions
Authors: Bartušek Miloš , Šustáček Vladimír
Published: March 2011

The formation of vanadium(V) complexes has been examined potentiometrically by the method of acidimetric titrations of aqueous solutions at pH 7-5. The composition has been determined and the formation constants have been calculated for the oxalate chelates VO2Ox23- and VO2Ox . (OH)2-, the maltol chelate VO2A2-, the ternary complex VO2OxA2-, and for binuclear and tetranuclear complexes with tartarate, glycolate, sorbitol, and mannitol. The structure of the complexes is discussed in terms of the consumption of protons for their formation.
Structure effects in oxidation of aliphatic ketones by thallium(III) sulphate
Authors: Pechál Miroslav , Strašák Milan
Published: March 2011

Oxidation kinetics of 11 aliphatic ketones (R1COR2) by thallium(III) sulphate in dilute sulphuric acid have been studied by UV spectrophotometry. The oxidation of methylalkylketones (R2 > CH3) follows the first order kinetics, that of higher dialkyl ketones (R1, R2 > CH3) obeys the second order kinetic equation. Polar and steric effects in the oxidation of aliphatic ketones have been separated by application of LFER to the chosen sets of methyl alkyl ketones (R2 > CH3) and dialkyl ketones (R1, R2 > CH3). Structural factors have a certain effect on the oxidation rate of methyl alkyl ketones, the changes in the reaction rate being ascribable almost exclusively to steric effects of the R2 substituents. The polar effects are very important in the oxidation of dialkyl ketones. Results of the application of LFER suggest that enol formation is the rate-determining step in the oxidations of the two sets of ketones.
Chiroptical properties and conformation of N-acetyl-L-amino acids N'-methylamides with aliphatic side chains
Authors: Maloň Petr , Pančoška Petr , Buděšínský Miloš , Hlaváček Jan , Pospíšek Jan , Bláha Karel
Published: March 2011

CD and 1H NMR spectra of L-alanine (I), L-leucine (II), L-valine (III) and L-tert-leucine (IV) N-acetyl N'-methylamides were measured at various experimental conditions involving changes of temperature, concentration and solvent polarity. The least flexible tert-leucine derivative IV exists predominantly either in right handed α-helical (αR) conformation (fluorinated alcohols, ethanol) or in extended (C5) conformation (cyclohexane, acetonitrile). In this compound the Φ angle is constrained to about -120°, excepting aqueous solution. The flexible amides I and II exhibit more complex conformational equilibria involving probably the 310, αR and C5 conformations. The 310 helical conformation is favoured in water, acetonitrile and non-fluorinated alcohols, while a higher participation of αR conformation is observed in strongly polar fluorinated alcohols. Conformational distribution of the valine derivatve III is similar to IV in fluorinated alcohols and to amides I and II in other solvents. The C7eq conformation is clearly detected only in cyclohexane solutions of non-associated forms of I and II.
A canonical ensemble derivation of the McMillan-Mayer solution theory
Authors: Kodýtek Vilém
Published: March 2011

A special free energy function is defined for a solution in the osmotic equilibrium with pure solvent. The partition function of the solution is derived at the McMillan-Mayer level and it is related to this special function in the same manner as the common partition function of the system to its Helmholtz free energy.
NMR spectra (29Si and 13C) of trimethylsilylated cyclic acyloins and ketones
Authors: Schraml Jan , Šraga Ján , Hrnčiar Pavel
Published: March 2011

13C and 29Si NMR chemical shifts are reported for several 1-trimethylsiloxycycloalkenes and 1,2-bis(trimethylsiloxy)cycloalkenes, (CH3)3SiO)xCnH2n-2-x (x = 1,2), dissolved in hexadeuterioacetone. Several correlations of the chemical shifts with structural parameters (ring size, interatomic distances etc.) are noted and an attempt is made to explain the found strong dependence of the 29Si chemical shifts on the ring size. Steric crowding with the nearest CH2 group drives the trimethylsilyl group out of the double bond plane and thus causes steric inhibition of the resonance of unshered oxygen electron pairs with electrons of the double bond. Since the crowding becomes more accute with increasing ring size, the ring size is in this way projected into the chemical shifts of silicon and olefinic carbons. This mechanism provides a united interpretation of all observed NMR chemical shifts.
Relation between the conditions of preparation and the activity of supported platinum catalysts
Authors: Hanika Jiří , Hao Le Hoang , Růžička Vlastimil
Published: March 2011

The preparation was studied of supported catalysts with different contents of platinum (0.21 to 9.25%) on activated carbon, suitable for liquid phase hydrogenations in mild conditions. The catalyst activity was tested in hydrogenations of nitrobenzene and 1-octene in ethanolic solutions at 25 °C and atmospheric pressure of hydrogen. The highest specific activity was achieved by applying the following conditions: content of the active metal 0.5% Pt/C, calcination temperature 200 °C, and temperature of the subsequent reduction with hydrogen 100 °C.
Bromine oxidation of N-(3 or 4-substituted phenyl)-N'-3-phenylpropenoylthioureas
Authors: Dzurilla Milan , Kristian Pavol , Imrich Ján , Štec Juraj
Published: March 2011

Bromine oxidation of N-(3 or 4-substituted phenyl)-N'-3-phenylpropenoylthioureas in chloroform afforded either derivatives of benzylidenethiazoline or benzothiazole depending on the structure of the aniline residue. The structure of the title products was proved by elemental analysis, IR, 1H NMR and 13C NMR spectral data.
Site-selectivity of 1,3-dipolar cycloadditions to 2,3-dimethoxycarbonyl-7-oxabicyclo[2,2,1]heptadiene
Authors: Fišera Lubor , Považanec František , Zálupský Peter , Kováč Jaroslav , Pavlovič Dušan
Published: March 2011

Site-selectivity of dipolar cycloaddition to the title compound was studied. Azomethine X afforded a 1 : 1 cycloadduct XI at the deactivated double bond at room temperature; upon thermolysis at 110 °C it afforded the acetylated enamine XIII which was formed via a direct cycloaddition at the mentioned temperature. The cycloaddition course was investigated in various solvents; the enamine XIV formed by solvolysis of XIII was the final product in methanol. Cycloaddition of the title compound to azides, benzoylnitrile N-oxide and C-acetyl-N-phenylnitrilimine furnished the product of cycloreversion instead of the not isolable 1 : 1 cycloadducts. 5-Azido-2-furancarbaldehyde and 4-nitrophenylazide yielded cycloaddition products to both multiple bonds in an approximately 1 : 1 ratio; NH3, tosylazide, benzoylnitrile N-oxide and C-acetyl-N-phenylnitrilimine gave the addition products to the deactivated double bond. The solvent-effect of site-selectivity of 1,3-dipolar cycloaddition was investigated and the title compound was found to be an excellent synthetic equivalent for acetylene and dimethyl butinedioate.
Kinetics of catalytic reduction of nitrogen oxide by carbon monoxide on CuO/Al2O3 catalyst
Authors: Musil Zdeněk , Pour Vladimír
Published: March 2011

The kinetics of the reduction of nitrogen oxide by carbon monoxide on CuO/Al2O3 catalyst (8.36 mass % CuO) were determined at temperatures between 413 and 473 K. The reaction was found to be first order in NO and zero order in CO. The observed kinetics are consistent with a rate equation derived from a mechanism proposed on the basis of IR spectroscopic measurements.
Quantum-chemical study of N-methylacetamide and N,N-dimethylacetamide as models for peptidic bond in hydrogen-bond interaction with water, methanol and phenol
Authors: Remko Milan , Sekerka Ivan , Frecer Vladimír
Published: March 2011

The PCILO quantum-chemical method with geometry optimization has been used to study rotation barriers of methyl groups in N-methylacetamide and N,N-dimethylacetamide. In all the cases studied, the eclipsed conformation have been found to be the most stable. Cis form of N-methylacetamide is less stable than the corresponding trans form by 2.0 kJ mol-1. Moreover, the PCILO method has been used to study linear n-mers (n = 4) of N-methylacetamide. On going from the dimer to tri- and tetramers, the hydrogen-bond energies have been found non-additive, and positive cooperativity has been observed. Finally, hydrogen-bond complexes have been studied which were formed by C=O groups of N-methylacetamide and N,N-dimethylacetamide with water, methanol or phenol as proton-donors. The said proton-donors have been found to act as breakers of inter-peptide hydrogen bonds N-H...O=C. The hydrogen bonds formed by methanol are somewhat stronger than those formed by water. In accordance with experiment, the strongest hydrogen bonds with the studied proton-acceptors are formed by phenol.
Belousov-Zhabotinskii reaction with ethyl ester of 3-oxobutanoic acid
Authors: Treindl Ľudovít , Nagy Arpád
Published: March 2011

The modified Belousov-Zhabotinskii oscillation reaction with ethyl ester of 3-oxobutanoic acid is remarkable in that it does not yield carbon dioxide and the reaction system is closed and homogeneous until an emulsion of a bromo derivative of the substrate appears. As long as the system is homogeneous, it oscillates even in the motionless state and its oscillation behaviour in the absence of oxygen is independent of the intensity of stirring. The results obtained by polarography with a rotating platinum electrode are in agreement with those obtained by spectrophotometry.
Kinetics of temperature-programmed reactivation of a hydrodesulphurization catalyst
Authors: Fott Pavel , Šebesta Pavel
Published: March 2011

The kinetic parameters of reactivation of a carbonized hydrodesulphurization (HDS) catalyst by air were evaluated from combined thermogravimetric (TG) and differential thermal analysis (DTA) data. In addition, the gaseous products leaving a temperature-programmed reactor with a thin layer of catalyst were analyzed chromatographically. Two exothermic processes were found to take part in the reactivation, and their kinetics were described by 1st order equations. In the first process (180-400 °C), sulphur in Co and Mo sulphides is oxidized to sulphur dioxide; in the second process (300-540 °C), in which the essential portion of heat is produced, the deposited carbon is oxidized to give predominantly carbon dioxide. If the reaction heat is not removed efficiently enough, ignition of the catalyst takes place, which is associated with a transition to the diffusion region. The application of the obtained kinetic parameters to modelling a temperature-programmed reactivation is illustrated on the case of a single particle.
A versatile correlation of liquid hold-up under the single-phase trickle flow in a packed bed
Authors: Jiřičný Vladimír , Staněk Vladimír
Published: March 2011

The paper gives a review of present approaches to the problem of a single- and two-phase flow in a packed bed. A new definititon has been given of the flooding point, which, as far as the theory is concerned, rigorously defines critical values of the quantities in the flooding point. At the same time, the definition enables a unambiguous experimental determination of the flooding point from experimental dependence sof the hold-up or pressure drop on the flow rate of phases. Based on extensive experimental data three alternative forms have been proposed of the versatile correlation of liquid hold-up on the velocity of liquid at the zero velocity of gas. The correlations have been formulated on the principle of automodel properties and define the appropriate relationships in terms of normalized variables related to the newly defined flooding point. The dependences on the geometry parameters of the packing and physical properties of liquid appear in the versatile correlations only implicitly. A new possibility has been shown of inverse utilization of the versatile correlations for the determination of the critical values (the flooding point) from two independent measurements of liquid hold-up in a real apparatus.
The effect of 1,4-phenylenediamine antidegradants on the photo-oxidation of selected liquid hydrocarbons
Authors: Kotulák Ludovít , Rotschová Jitka , Pospíšil Jan
Published: March 2011

The effect of six N,N'-disubstituted 1,4-phenylenediamines (I) and four derivatives of 1,4-benzoquinonediimine (II) on the photo-oxidation of tetralin, squalane and squalene at 35 °C and radiation 300-400 nm was investigated by oxygen uptake measurements. Due to irradiation, the antioxidant effectiveness of I is so restricted that the induction period did not appear in any of the photo-oxidized hydrocarbons. On the other hand, however, owing to the presence of I, there is a strong retardation of the photo-oxidation of hydrocarbons connected with the transformation of I in the oxidized hydrocarbon to II. Benzoquinonediimines are able to scavenge radicals involved in the propagation step and provide a screening effect. The retardant efficiency of II was proved by model investigation. Hence, II play a pronounced role in the mechanism of photo-oxidation of hydrocarbons stabilized with I.
Electrochemical dehalogenation of open-chain vicinal dihalides at mercury cathodes: The effect of leaving group identity on E1/2 values and on steric course
Authors: Závada Jiří , Krupička Josef , Kocián Oldřich , Pánková Magdalena
Published: March 2011

The title problem has been investigated polarographically in the homologous series of erythro and threo-5,6-dihalodecanes (X = Br, Y = I; X == Cl, Y = I; X = F, Y = I; X = Br, Y = Br; X = Cl, Y = Br; X = F, Y = Br; X = Cl, Y = Cl; X = F, Y = Cl). Each dihalide from the series gave a single two-electron wave. A very pronounced dependence of half-wave potential on halogen group identity was found in the series, the E1/2 values ranging from -0.3 V (X = Br, Y = I) to -2.8 V (X = F, Y = Cl). Controlled-potential electrolyses of the dihalides were accomplished at mercury pool electrode affording always cis- and/or trans-5-decene as the sole product, in almost quantitative (>90%) yields. Stereochemistry of the dehalogenation was deduced from the olefin-isomer distribution data determined by VPC. Very marked differences were found in the series, the elimination stereochemistry ranging between a clean anti and a prevalent syn, in dependence on the identity and configuration of the halogen groups.
Absolute configuration of (1R,2S,4R,6S,7R)-(+)-3-oxotricyclo[2,2,1,02,6]heptane-7-carboxylic acid
Authors: Červinka Otakar , Habartová Eliška
Published: March 2011

The title acid was assigned absolute configuration on the basis of stereoselective condensation with optically active amines.
Participation by some oxygen containing groups in hypobromous acid addition to double bond
Authors: Kočovský Pavel
Published: March 2011

5(O)n and 6(O)π,n participations by some oxygen containing functional groups in the course of reaction with hypobromous acid have been studied on olefinic models of steroid type (I and II). The ability of these groups to participate has been compared on the basis of their relative reactivity with water (as externally attacking nucleophile) competing with participation. The results of the product analysis show that the ability to react with 5(O)n participation decreases in the order HO > CH3O ≃ CH3OCH2O > CH3CO2 > HCO2 > CH3SO3 ≥ (C2H5O)2PO2 > C6H5CO2 > O2NO ≫ CF3CO2, C2H5OCO2; in the last two functional groups is this ability completely suppressed. The 6(O)π,n participation comes in consideration only for compounds of the type II bearing the groups with the -X=O moiety which are ordered in the following sequence: C2H5OCO2 ≃ CH3CO2 ≥ (C2H5O)2PO2 > HCO2 > C6H5CO2. The remaining functional groups (CF3CO2, O2NO and CH3SO3do not undergo this process. Generally, it is valid that introduction of electron-withdrawing substituents into a participating group impedes or completely suppresses its ability to participate.
Improvement of Menopausal Symptoms with Acupuncture Not Reflected in Changes to Heart Rate Variability
Authors: Wright Cheryl L , Aickin Mikel
Published: March 2011

Hypothesis

Studies indicate that menopausal symptoms are relieved by acupuncture. Additional studies have suggested that acupuncture may affect heart rate variability (HRV). This paper reports a pilot study that investigated whether menopausal symptoms responded to acupuncture, and if changes in the spectral analysis of HRV, either suppression of low frequency or augmentation of high frequency bands, corresponded with symptom report.

Methods/interventions

12 healthy menopausal subjects were enrolled in this feasibility study. At baseline, subjects were experiencing moderately distressing menopausal symptoms, scoring at least 22 of a possible 44 points on the Menopausal Rating Scale. 10 traditional Chinese medicine-based, protocol acupuncture treatments were administered over a 4 week period, three times a week for 2 weeks, followed by twice a week for 2 weeks.

Outcome measures

Menopausal Rating Scale questionnaire, 11 menopausal symptoms were evaluated on a zero to four severity scale via self-administered daily checklist for 4 weeks. Dynamic measures of HRV (autoregressive model) were captured before, during and after acupuncture at each session. Spectral analysis of the heart rate was used to compute power in the low frequency and high frequency bands, and their ratio.

Results

All subjects complied fully with the protocol without any reported adverse events. While all 11 symptoms showed significant improvement, and one HRV measure changed, on average over the study period, there was essentially no support for a relationship between HRV, menopausal symptom report and acupuncture intervention.
The Effect of Acupuncture on Postmenopausal Symptoms and Reproductive Hormones: A Sham Controlled Clinical Trial
Authors: Sunay Didem , Ozdiken Muruvvet , Arslan Huseyin , Seven Ali , Aral Yalcin
Published: March 2011

Background

Acupuncture is commonly used to treat menopausal symptoms and other gynaecological conditions. In this study, the authors aimed to investigate whether acupuncture has an effect on menopausal symptoms and to explore whether this effect is related to changes in hormone levels.

Materials and methods

A total of 53 postmenopausal women were alternately assigned into two treatment groups: acupuncture (n=27) and sham acupuncture (n=26). Menopausal symptoms were assessed using the Menopause Rating Scale (MRS). The serum oestradiol, follicular stimulating hormone (FSH) and luteinising hormone (LH) levels were measured at baseline and again after the first and last sessions. The Student t test was used for normally distributed data and the Wilcoxon signed rank test for not normally distributed data. The group differences in MRS scores were assessed using non-parametric Mann–Whitney U test.

Results

After treatment, total MRS, and the somatic and psychological subscale scores were significantly lower in the acupuncture group than the sham group (all p=0.001). The severity of hot flushes was found to be significantly decreased after treatment in acupuncture group (p=0.001). In the acupuncture group LH levels were lower and oestradiol levels were significantly higher than sham group (p=0.046 and p=0.045, respectively) after treatment, but there was no difference in FSH levels.

Conclusion

Acupuncture was effective in reducing menopausal complaints when compared to sham acupuncture and can be considered as an alternative therapy in the treatment of menopausal symptoms.
An unusual gait following the discovery of a new disease
Authors: Keogh M J , Khan A , Gorman G , McNeill A , Horvath R , Burn J , Chinnery P F
Published: March 2011

A 39-year-old woman presented to the neurology clinic with an abnormal gait. Subsequent investigations confirmed a rare neurodegenerative disease. This case highlights the key clinical features and diagnostic approach to neuroferritinopathy, and describes the discovery of the disease in a family from Cumbria in the north west of England.
MULTIPLE Dp-BRANES AS A Dp+2-BRANE
Authors: GANJALI M. A. , ALI-AKBARI M.
Published: March 2011

From BFSS matrix theory considerations, it is expected that a single D p+2-brane action can be obtained from N D p-brane action in large N limit. We examine and confirm this expectation by working out the details of DBI and Chern–Simons terms of D p+2-brane action from D p-brane action. We show that the same relation works for non-BPS, as well as BPS branes.
A NONPERTURBATIVE MODEL FOR THE STRONG RUNNING COUPLING WITHIN POTENTIAL APPROACH
Authors: BELYAKOVA YU. O. , NESTERENKO A. V.
Published: March 2011

A nonperturbative model for the QCD invariant charge, which contains no low-energy unphysical singularities and possesses an elevated higher-loop corrections stability, is developed in the framework of potential approach. The static quark–antiquark potential is constructed by making use of the proposed model for the strong running coupling. The obtained result coincides with the perturbative potential at small distances and agrees with relevant lattice simulation data in the nonperturbative physically-relevant region. The developed model yields a reasonable value of the QCD scale parameter, which is consistent with its previous estimations obtained within potential approach.
KAGOME APPROXIMATION FOR 3He ON HUSIMI LATTICE WITH TWO- AND THREE-SITE EXCHANGE INTERACTIONS
Authors: ANANIKIAN N. S. , HOVHANNISYAN V. V. , LAZARYAN H. A.
Published: March 2011

The Ising approximation of the Heisenberg model in a strong magnetic field, with two-, and three-spin exchange interactions are studied on a Husimi lattice. This model can be considered as an approximation of the third layer of 3 He absorbed on the surface of graphite (kagome lattice). Using dynamic approach, we have found exact recursion relation for the partition function. For different values of exchange parameters and temperature, the diagrams of magnetization are plotted and showed that magnetization properties of the model vary from ferromagnetic to antiferromagnetic depending on the value of model parameters. For antiferromagnetic case magnetization plateau at 1/3 of saturation field is obtained. Lyapunov exponent for recursion relation are considered and showed absence of bifurcation points in thermodynamic limit. The Yang–Lee zeros are analyzed in terms of neutral fixed points and showed that Yang–Lee zeros of the model are located on the arcs of the circle with the radius R = 1.
STRUCTURAL EVOLUTIONS OF STOCK MARKETS CONTROLLED BY GENERALIZED ENTROPY PRINCIPLES OF COMPLEX SYSTEMS
Authors: WANG YI JIAO , FENG QING YI , CHAI LI HE
Published: March 2011

As one of the most important financial markets and one of the main parts of economic system, the stock market has become the research focus in economics. The stock market is a typical complex open system far from equilibrium. Many available models that make huge contribution to researches on market are strong in describing the market however, ignoring strong nonlinear interactions among active agents and weak in reveal underlying dynamic mechanisms of structural evolutions of market. From econophysical perspectives, this paper analyzes the complex interactions among agents and defines the generalized entropy in stock markets. Nonlinear evolutionary dynamic equation for the stock markets is then derived from Maximum Generalized Entropy Principle. Simulations are accordingly conducted for a typical case with the given data, by which the structural evolution of the stock market system is demonstrated. Some discussions and implications are finally provided.
ON THE CALCULATION OF THE OPTICAL AND REACTIVE PROPERTIES OF THE POLYCYCLIC AROMATIC HYDROCARBONS (PAHS), BY USING THE FROZEN SPIN MOLECULAR ORBITAL (SMO) HARTREE-FOCK (HF) APPROACH
Authors: ALVAREZ-COLLADO J. R.
Published: March 2011

The polycyclic aromatic hydrocarbons (PAHs) are chemical compounds of obvious technical and medical interest. In the present work, we analyze the optical and reactive properties of several small (6–50 Carbon atoms) and large (100–5000 Carbon atoms) irregular PAHs. These properties have been calculated by using the (Frozen) spin molecular orbital (SMO) Hartree-Fock (HF) approach, referred to as FHF, because of its high computational efficiency. There is a reasonable agreement of our results with those previously obtained by other authors. The FHF approach is (about 1000 times) faster than the conventional semi-empirical methods, and only requires the chemical formula of the PAH as input.
A POSTERIORI ERROR ANALYSIS OF THE METHOD OF CHARACTERISTICS
Authors: BERNARDI CHRISTINE , HECHT FRÉDÉRIC , VERFÜRTH RÜDIGER
Published: March 2011

We consider a two- or three-dimensional time-dependent diffusion–convection–reaction problem and its discretization by the method of characteristics and standard finite elements. We perform the a posteriori error analysis of this discretization and prove optimal error estimates, which lead to an efficient adaptivity strategy both for the time step and the spatial mesh. The estimates are robust with respect to the ratios of the diffusion to the reaction or convection. Some numerical experiments support the theoretical results.
IDENTIFYING AND RECONSTRUCTING LATERAL TRANSFERS FROM DISTANCE MATRICES BY COMBINING THE MINIMUM CONTRADICTION METHOD AND NEIGHBOR-NET
Authors: THUILLARD MARC , MOULTON VINCENT
Published: March 2011

Identifying lateral gene transfers is an important problem in evolutionary biology. Under a simple model of evolution, the expected values of an evolutionary distance matrix describing a phylogenetic tree fulfill the so-called Kalmanson inequalities. The Minimum Contradiction method for identifying lateral gene transfers exploits the fact that lateral transfers may generate large deviations from the Kalmanson inequalities. Here a new approach is presented to deal with such cases that combines the Neighbor-Net algorithm for computing phylogenetic networks with the Minimum Contradiction method. A subset of taxa, prescribed using Neighbor-Net, is obtained by measuring how closely the Kalmanson inequalities are fulfilled by each taxon. A criterion is then used to identify the taxa, possibly involved in a lateral transfer between nonconsecutive taxa. We illustrate the utility of the new approach by applying it to a distance matrix for Archaea, Bacteria, and Eukaryota.
APPLICATION OF POINT INTERPOLATION METHOD IN JOINTED ROCK MASS
Authors: HAJIAZIZI M. , ASHORY M. R.
Published: March 2011

In this paper, point interpolation method (PIM) is applied to analyze the nonlinear and elastoplastic behavior of jointed rock masses. PIM is advantageous over the other meshless methods that are based on moving least square (MLS) technique. On the other hand in this study, element-free Galerkin method (EFGM) has been applied to analyze a jointed rock mass for comparison purposes. The domain of jointed rock mass is represented by a set of arbitrary distributed nodes. The essential boundary conditions are imposed in EFGM using penalty method. Mohr–Coulomb failure criterion is used for analyzing the behavior of joint failure. Two numerical examples are considered to demonstrate the effectiveness of method in predicting the elastoplastic behavior of jointed rock mass. The results are compared with those of finite difference method (FDM).