bluuebunny/crossref_metadata_2025 huggingface dataset:
Antimycobacterial 2-Arylamino-2-Thioxoacetamides
Authors: Waisser Karel , Macháček Miloš , Odlerová Želmíra , Thiel Wilfried , Mayer Roland
Published: April 2003

A series of 13 2-arylamino-2-thioxoacetamides was tested against Mycobacterium tuberculosis and M. kansasii. Structure-activity relationships were analyzed quantitatively using the Free-Wilson method. Evaluation of the antimycobacterial profile with regard to equipotency of both activities was accomplished by means of a recently proposed method for evaluation of activity profile with respect to intended therapeutical use.
Electrochemical Study of cis-Cyanoaquobis(ethylenediamine)chromium(III) Ion and Its Adducts with Hg(II) and Ag(I)
Authors: Rievaj Miroslav , Korgová Elena , Bustin Dušan
Published: April 2003

The paper describes voltammetric and polarographic properties of the cis-cyanoaquobis(ethylenediamine)chromium(III) complex and the kinetics of its acid hydrolysis. The reactions of this complex with Hg(II) and Ag(I) ions were studied. Formation of di- and trinuclear adducts was found. Linkage isomerisation of CN bridging group in these adducts (Cr-NC-Hg and Cr-NC-Ag) was proposed on the basis of their electrochemical properties. The kinetics of formation and decomposition of [Cr(CN)(en)2(H2O)]2+ adducts with Hg(II) and Ag(I) are described and the factors affecting them are discussed.
The Structure and Hydration of Composite Membranes Based on Polyacrylonitrile
Authors: Tishchenko Galina A. , Bleha Miroslav , Tyráčková Věra , Sukhanova Tatyana E. , Gulevskaya Svetlana A. , Koshcheenko Kira A. , Shataeva Larisa K.
Published: April 2003

The morphology of polyacrylonitrile composite membranes containing microdispersions of ion exchange resins was investigated by gas adsorption, mercury porosimetry, and scanning and transmission electron microscopy. The relation between the structure, hydration and permeability of composite membranes at the transmembrane difference of pH and pNa was studied.
Thermodynamics of Adsorption of Methyl Formate on Metal Dopant/Active Carbon Systems
Authors: Afzal Muhammad , Mahmood Fazal
Published: April 2003

It has been found that doping of active carbon with metals (Ni, Cu, Zn, Cd) decreases its surface area due to dispersion of metal resides on the surface. A detailed examination of nitrogen adsorption indicates differences in the mode of dispersion of metals on the surface of active carbon. The adsorbing behavior of metal doped carbon for methyl formate was also studied as a function of temperature. From adsorption data, thermodynamic parameters such as free energy, enthalpy and entropy of adsorption were calculated using virial isotherm expression and interpreted. Results show that metal dopant/active carbon systems are synergic, exhibiting greater adsorption affinity for methyl formate than the sum of its constituents.
The Extraction Transfer of H+-18-Crown-6 Species across the Water-Nitrobenzene Phase Boundary in the Extraction of Aqueous Solutions of Perchloric Acid by Nitrobenzene in the Presence of 18-Crown-6
Authors: Vaňura Petr , Juklíková Iveta
Published: April 2003

A study was made of the extraction of perchloric acid in water-nitrobenzene-18-crown-6 (hereafter L) systems. The experimental data was interpreted on the basis of the assumption that the extraction occurs according the equations H+aq + ClO4,aq- ↔ H+org + ClO4,org- and H+aq + Laq + ClO4,aq- ↔ HL+org + ClO4,org-. Crown is also protonated in the aqueous phase according to the equation H+aq + Laq ↔ HL+aq. The values of the corresponding extraction constants, the protonation constants of 18-crown-6 in nitrobenzene and water and the individual extraction constants of the HL+ species in the water-nitrobenzene system were determined, along with the magnitude of the molar free enthalpy for the transfer of these species across the given phase boundary.
Effect of Sulfide Ions on the Corrosion Behaviour of Mild Steel in Acetate Buffer
Authors: Rehan Hyman H. , Salih Said A. , El-Daley Hassan , Gad-Allah Ahmed G.
Published: April 2003

The corrosion behaviour of mild steel was investigated in acidic acetate buffer solution using impendance and potential measurements. It was found that there are two dissolution rates resulting from the duplex nature of the formed oxides. The dissolution rates were found to depend on the dissolving acetate buffer solution pH and the dissolution temperature. In all cases, the film thickness was found to decrease with time of corrosion according to the relation Cm-1 = (Cm0)-1 - kdt1/2. It was found that addition of sulfide ions increases the dissolution rate and increases the rate of hydrogen evolution reaction but does not affect the mechanism of cathodic process. The role of sulfide ions on the corrosion behaviour of steel in acetate buffer solutions is revealed by the complex plane impendance analysis.
Simple Preparation of 4,5-Disubstituted 2-Cyclopentenones
Authors: Šafář Peter , Považanec František , Zalibera Lubomír , Berkeš Dušan
Published: April 2003

(E-2-Formyl-3-(2-furyl)propenenitrile (I) reacts with primary aromatic amines under formation of 3-(arylamino)-2-[5-(arylamino)-2-oxo-3-cyclopenten-1-yl]propenenitriles (IVa-IVi). Condensation of I with salts of nitrogen bases in pyridine affords 2-(R-aminomethylidene)-3-(2-furyl)propenenitriles (Va-Vm).
Cyclic Phenylboronates of Ecdysteroids as Products of Regiospecific Reaction with Phenylboronic Acid
Authors: Píš Jaroslav , Hykl Jiří , Buděšínský Miloš , Harmatha Juraj
Published: April 2003

The diol system in the side-chain of ecdysteroids reacts with phenylboronic acid under formation of cyclic esters. Phenylboronates of ecdysteroids I - V were prepared. The regiospecific reaction course was confirmed by 1H NMR spectra of the products. The reaction conditions were studied for 20-hydroxyecdysone (I). The phenylboronate can be prepared in high yields even in aqueous solutions. The liberation of the ecdysteroid I from the corresponding phenylboronate VI was performed using various reagents - diols or carboxylic acids.
Syntheses of Enantiomeric N-(3-Hydroxy-2-phosphonomethoxypropyl) Derivatives of Purine and Pyrimidine Bases
Authors: Holý Antonín
Published: April 2003

Methods of preparation of N-(3-hydroxy-2-phosphonomethoxypropyl) (HPMP) derivatives of (2S)- and (2R)-configuration (compounds I and XXVII, respectively) are described. The general method starts from the corresponding N-(2,3-dihydroxypropyl) derivatives which were converted either into the (R)-enantiomers XIII by reaction of the base with (R)-glycidol butyrate (XII) in the presence of cesium carbonate and subsequent methanolysis, or into the (S)-enantiomers XI by alkylation of the base with (R)-2,2-dimethyl-4-tosyloxymethyl-1,3-dioxolane (V) in the presence of the same reagent. The amino groups on the heterocyclic base in compounds XI and XIII were benzoylated by silylation followed by reaction with benzoyl chloride and the obtained N-benzoates XV and XVII on reaction with trityl chloride afforded the corresponding 3'-O-trityl derivatives XVI and XVIII. These compounds were condensed with bis(2-propyl) p-sulfonyloxymethylphosphonate (XXIII) in dimethylformamide in the presence of sodium hydride to give the fully protected diesters XXIV and XXVIII. These compounds could be selectively acid-hydrolyzed to remove the trityl group only under formation of compounds XXXV, or methanolyzed and then acid-hydrolyzed to remove the trityl and N-benzoyl groups and lead to compounds XXVI and XXX, or treated with bromotrimethylsilane to remove the trityl and 2-propyl group to give phosphonates of the type XXXI. All the three types of compounds were then converted into free phosphonates of the (S)-series (I) and the (R)-series (XXVII). Derivatives of cytosine (Ia, XXVIIa), adenine (Ib, XXVIIb), 2,6-diaminopurine (Ic, XXVIIc) and guanine (Id, XXVIId) were prepared. Condensation of the partially blocked adenine deriavtive XXXV with the tosyl derivative XXIII and subsequent deprotection afforded 9-(S)-(2,3-diphosphonomethoxy propyl)adenine (XLIII). Reaction of the same compound XXXV or its (R)-enantiomer XXXVIII with diethyl phosphonate , followed by deblocking, afforded 3'-O-phosphoryl derivatives (S)-HPMPA (XXXVII) and (R)-HPMPA (XL).
An Alternative Approach for Constructive Enumeration of Graphs
Authors: Pospíchal Jiří , Kvasnička Vladimír
Published: April 2003

An efficient method for constructive enumeration of graphs is suggested. The method is based on the so called semicanonical numbering of graphs, that is a numbering much more restrictive than the cooperative numbering. Graph-theoretical properties of the semicanonical numbering make it possible to formulate an exhaustive and nonredundant constructive enumeration of graphs. The approach allows an easy introduction of specifications for molecular graphs.
Structure of Adeninium Chloroacetate-Chloroacetic Acid Solvate C5H6N5+ ClCH2COO- . ClCH2COOH
Authors: Maixner Jaroslav , Zachová Jana , Huml Karel
Published: April 2003

The structure adeninium chloracetate-chloroacetic acid solvate was solved by direct methods and refined anisotropically to R = 0.085 for 1978 unique observed reflections (I 33 σ(I). The title compound is orthorhombic, a = 24.138(4), b = 15.525(2), c = 7.136(1) Å. Pccn, Z = 8. The adenine molecule, which is protonated at N(1), is almost planar with a dihedral angle of 0.3(2)° between the imidazole and the pyrimidine rings. The chloroacetate is partially distorted. A dimensional net of H-bonds between adenine, chloroacetic acid and chloroacetate is formed.
Free-Fall of Solid Particles through Fluids
Authors: Hartman Miroslav , Yates John G.
Published: April 2003

A comprehensive, up-to-date review is presented of predictive relationships for the terminal, free-fall velocity of solid particles falling in an infinite Newtonian fluid. The study explores accuracy of the implicit and explicit equations in terms of the drag coefficient and the terminal velocity. Problems of predicting the terminal velocity of non-spherical, isometric as well as non-isometric, particles is discussed.
Thermodynamic and Kinetic Investigation of the Solvent Effect on the Oxidation of [Co(en)2SCH2COO]+ with S2O82- In Water-Methanol and Water-tert-Butyl Alcohol Mixtures
Authors: Vollárová Oľga , Benko Ján
Published: April 2003

The kinetics of oxidation of [Co(en)2SCH2COO]+ with S2O82- was studied in water-methanol and water-tert-butyl alcohol mixtures. Changes in the reaction activation parameters ∆H≠ and ∆S≠ with varying concentration of the co-solvent depend on the kind of the latter, which points to a significant role of salvation effects. The solvation effect on the reaction is discussed based on a comparison of the transfer functions ∆Ht0, ∆St0 and ∆Gt0 for the initial and transition states with the changes in the activation parameters accompanying changes in the CO-solvent concentration. The transfer enthalpies of the reactant were obtained from calorimetric measurements.
Modelling of Steam Cracking. I. Simplified Mathematical Model of Steam Cracking Furnace and Its Identification
Authors: Horák Josef , Bělohlav Zdeněk
Published: April 2003

A simplified mathematical model of a steam cracking furnace was constructed. The model involves adjustable parameters, values of which are to be evaluated on the basis of measurements available in industrial reactors. The following adjustable parameters are considered: the effective radiative heat transfer coefficient, the convective heat transfer coefficient, the mean relative reactivity of the reaction mixture. The sources of information which can be utilized in the model identification are discussed. A numerical procedure was developed for finding the best set of the adjustable parameters. The procedure is based on the analogy with single-input single-output control loops.
The Measurement of Voidage of Nonuniformly Fluidized Bed by Means of the Wall Pressure Signal
Authors: Beňa Ján , Havalda Ivan
Published: April 2003

By the wall pressure signal, ∆px, from a nonuniformly fluidized bed is here termed the excess pressure at a wall of open column over the atmospheric pressure measured at a distance x from distributor. The relation was investigated between the wall pressure signal, ∆px, and some specifically defined voidages of a so-called standard bubbling bed characterized by the fact that the ratio of the experimentally determined pressure drop for minimum fluidization, ∆p0,mf, and of the theoretical pressure drop, ∆pt, is approximately equal to the unity. We have shown that under certain conditions, the time-volume averaged voidage, ε, of this bed can be determined in terms of simple relation (13).
Mass Transfer in Liquid in an Apparatus with Mobile Packing. Application of a Dispersion Model
Authors: Palatý Zdeněk
Published: April 2003

The paper deals with the mass transfer in a liquid on a plate with mobile packing. A procedure has been suggested which enables estimation of the mass transfer coefficients from experimental data considering the dispersion flow of the liquid. The results obtained from the desorption of CO2 from water are presented graphically and in the form of empirical equation.
Equilibrium and Kinetics of the Extraction of Gallium(III) from Sodium Hydroxide Solutions with 7-Dodecenyl-8-quinolinol (Kelex 100)
Authors: Mitrovic Aleksandra A. , Milonjic Slobodan K. , Ilic Zoja E. , Stevanovic Radomir V.
Published: April 2003

The influence of hydroxide ions concentration of the aqueous sodium hydroxide solution, at constant sodium concentrations, on the gallium extraction with Kelex 100 was examined in the hydroxide concentration range from 0.02 to 0.5 mol dm-3. The percentage of extracted gallium increases from 51% to 98% within the investigated hydroxide concentration range. The influence of sodium concentrations (from 1 to 6 mol dm-3) on the gallium extraction was also studied at constant pH values. The decrease of extracted gallium is slight for the sodium concentration up to 3 mol dm-3, while for the higher ones it is pronounced. The extraction kinetics was studied using a mixer-type apparatus. The rate expression of the extraction reaction of gallium with Kellex 100, for both lower and higher hydroxide concentrations are ascertained.
Synthesis of Some New Type of Naphthothiazole Triazoles from Lawsone
Authors: Rajeswar Rao Vedula , Sharma Vedula M. , Padmanabha Rao Tadepally V.
Published: April 2003

A series of 3-aryl naphto[2',3':4,5]thiazolo[3,2-b-1,2,4-triazolo-5,10-diones (V) have been prepared by the condensation of bromo lawsone (I) with 5-mercapto-3-substituted 1,2,4-triazole (II) followed by cyclization of the resulting uncyclized products (IV) with alkohol and sulfuric acid. The products are identical with the condensation products of 2,3-dichloro naphthoquinone (III) with 5-mercapto-3-substituted 1,2,4-triazoles in the presence of anhydrous alcohol containing fused sodium acetate.
Electrochemical Behaviour of 3-Pyridyl-N,N-bis[(8-quinolyl)amino]methane
Authors: Loeches Angeles , Teijeiro Carmen , Marín Dolores
Published: April 2003

3-Pyridyl-N,N-bis[(8-quinolyl)amino]methane was studied by DC polarography, coulometry, cyclic voltammetry and differential pulse polarography in a system comprising Britton-Robinson buffer and 15 vol.% ethanol at pH 7.0. The nature of the waves was investigated, and the reduction mechanism is suggested. DPP was also used for a quantitative determination of the substance, and a limit of detection of 3 μmol l-1 was obtained.
Photocatalytic Oxidation of p-Cresol in Aqueous Titanium Dioxide Suspension
Authors: Brezová Vlasta , Brandšteterová Eva , Čeppan Michal , Pieš Juraj
Published: April 2003

The reaction products of the photocatalytic oxidation of p-cresol were characterized by high performance liquid chromatography. The influence of p-cresol concentration as well as the presence of dioxygen and hydrogen peroxide on the rate of photocatalytic oxidation was studied. The p-cresol concentration in the irradiated systems was determined by spectrophotometric method using α-nitroso-β-naphtol or by the Principal Component Regression method (in the sample with hydrogen peroxide added). The reaction pathway of the photocatalytic oxidation of p-cresol in TiO2 suspension was suggested.
Electron Spin Resonance Linewidth Studies of Vanadyl Tetraphenylporphyrin
Authors: Al-Mowali Ali H. , Girgees Alhan D.
Published: April 2003

The linewidths of the hyperfine components of the ESR spectra of vanadyl tetraphenylporphyrin in liquid toluene have been measured as a function of temperature and analyzed in detail. This has allowed the separate contributions to the observed ESR line widths from spin rotational, g tensor anisotropy, hyperfine anisotropy and unresolved nitrogen hyperfine coupling to be evaluated. These results have been used to estimate the size of the nitrogen isotropic hyperfine coupling constant and thus the extent of delocalization of the unpaired electron onto the nitrogen atoms.
The Effect of Tensides on the Dissociation of Azure B
Authors: Dušková Martina , Němcová Irena
Published: April 2003

A study was carried out of the effect of an anionogenic and cationogenic tenside on the dissociation of azure B. It was found that, in the presence of sodium lauryl sulfate, the pH value of the solution affects both the dissociation and the ratio of the contents of the monomer, dimer and higher aggregates of the dye at various concentrations of the tenside. The dependences of pKa on the concentration of the given kind of tenside and its variation in the presence of an inorganic salt (NaNO3) were found.
Errors in Measurement of Interfacial Area and Mass Transfer Coefficient in Liquid in Apparatus with Mobile Packing
Authors: Palatý Zdeněk
Published: April 2003

The paper deals with an analysis of errors of measurement of interfacial area and mass transfer coefficient in liquid in an absorber with mobile packing. The system of CO2-NaOH has been used for the testing with recirculation of the adsorption solution. The error of measurement of the absorption solution temperature, CO2 concentration in the gas, the composition of absorption solution, the mass transfer coefficient in gas, and the volume of absorption solution at the beginning and at the end of the measurement have been investigated with regard to their effects upon the resulting values of specific interfacial area and mass transfer coefficient in liquid. From the simulation calculations if follows that the interfacial areas most strongly affected by the error of measurement of CO2 concentration in gas, whereas the mass transfer coefficient in liquid is considerably affected by inaccuracies in measuring the volume of absorption solution at the beginning and at the end of experiment.
New Metabolites of Streptomyces globisporus and Streptomyces griseus
Authors: Jizba Josef , Sedmera Petr , Beran Marian
Published: April 2003

5,6,7,7a-Tetrahydro-3H-pyrrolizin-7a-ol-3-one (VI) and N-[2-(1-hydroxy-4-methylpentyl)]acetamide (VII) were isolated from submerged cultures of the macrotetrolide-producing strains Streptomyces globisporus and S. griseus. Proposed structures are based on spectroscopic measurements.
Unique Dialkylsulfonio-Methylation of the 7,8-C2B9H12(-) Ion to the 9-R2S-CH2-7,8-C2B9H11 Zwitterions by Formaldehyde and Dialkyl Sulfides. General Synthesis of the Compounds 10-R2E-7,8-C2B9H11 (E = O, S)
Authors: Plešek Jaromír , Jelínek Tomáš , Mareš František , Heřmánek Stanislav
Published: April 2003

Dialkylsulfonio-methylation has been observed on the treatment of the 7,8-C2B9H12(-) ion with formaldehyde and dialkyl sulfides in aqueous acidic medium. Four zwitterions of the type 9-R2S-CH2-7,8-C2B9H11 were formed with dimethyl and diethyl sulfide, tetrahydrothiophene and thioxane. In contrast, dialkyl ethers (diethyl ether, tetrahydrofuran, dioxane) afforded low amounts of the 10-R2O-7,8-C2B9H11 zwitterions, with the carborane 4,5- C2B7H13 being the principal product. Using acetaldehyde instead of formaldehyde, moderate yields of the 10-R2O- and high yields of the 10-R2S-7,8-C2B9H11 derivatives were obtained. With tertiary amines, only corresponding ammonium salts precipitated. Possible reaction pathways for these transformations are discussed and compared with the specific degradation of the 7,8-C2B9H12(-) ion to the arachno-4,5- C2B7H13 carborane.
Decomposition of High Temperature Superconductors in Water
Authors: Smrčková Olga , Sýkorová Dagmar , Svoboda Pavel , Vašek Petr
Published: April 2003

Changes of magnetic susceptibility and electrical resistivity of ceramic superconductors of nominal composition YBa2Cu3O7-y and Bi1.4Pb0.6Sr2Ca2Cu3.6Ox observed during their soaking in water are reported. It was found that the YBa2Cu3O7-y superconductor is destroyed in few minutes by boiling water. At lower temperatures the hydrolysis reduces the volume of the superconductive phase, as seen from the susceptibility measurements. Reaction of Bi1.4Pb0.6Sr2Ca2Cu3.6Ox with water causes a decrease of the relative volume of both superconducting phases at a rate substantially higher for the high temperature one (Tc = 110 K).
Ten-Vertex Polyhedral Rhodadicarbaborane Chemistry. Molecular Structure, NMR Properties, and Cluster Dynamic Behaviour of [2,2,2-(PPh3)2H-closo-2,1,6-RhC2B7H9]
Authors: Nestor Karl , Murphy Michael , Štíbr Bohumil , Spalding Trevor R. , Fontaine Xavier L. R. , Thornton-Pett Mark , Kennedy John D.
Published: April 2003

The compound previously described as [6,6,6-(PPh3)2H-closo-6,3,3-RhC2B7H9] is shown by detailed multielement NMR studies and single-crystal X-ray diffraction analysis to be its isomer [2,2,2-(PPh3)2H-closo-2,1,6-RhC2B7H9] Crystals (from pentane-diethyl ether) were monoclinic, space group P21/n, with Z = 4, and with a = 1 222.2(1) pm, b = 1 598.7(2) pm, c = 1 836.7(1) pm, and β = 91.86(1)°. The structure was refined to R(Rw) 0.0295(0.0414)using 6 819 observed data [I > 2.0 σ(I)] out of 8 541 collected at 200 K. The {RhC2B7} cluster structure is to a first approximation classically closo, with the metal and two carbon atoms in adjacent 2, 1, and 6 positions, respectively. Both enantiomers exist in the unit cell, and variable temperature NMR studies show that the molecule is fluxional (∆G355 ≈ 60 kJ mol-1) between enantiomers via a diamond-square diamond cluster rearrangement.
Preparation, Spectroscopic, Magnetic, Conductometric and Polarographic Characterization of Cobalt(II)-1-phenyl-4,6-dimethylpyrimidine-2-thione Complexes
Authors: Borsari Marco , Battistuzzi Gianantonio , Battistuzzi Raffaele
Published: April 2003

The following coordination compounds of cobalt(II) with 1-phenyl-4,6-dimethylpyrimidine-2-thione: CoLX2 . n H2O ( X = Cl-, n = 1; X = Br-, n = 2; X =SCN-, n = 0; X = NO3-, n = 4), Co2L3Cl4 . H2O, CoL2X2 (X = Br-, I-, SCN-, NO3-), CoL2X2 . n H2O . p Me2CO (X = I-, ClO4-, n = p = 2; X = NO3-, n = 1, p = 0), CoL3(ClO4)2 . 0.5 Me2CO, Co2L5(NO3)4 and Co2L7X4 (X = Cl-, Br-, I-) have been isolated and characterized by chemical analyses, visible and IR spectra, paramagnetic susceptibility, conductivity and polarographic measurements. Solid phase IR spectra suggest that the heterocyclic ligand is almost always bonded through non-substituted ring nitrogen and exocyclic sulfur atoms. The solid compounds with the exception of the [CoL(SCN)2]2, [CoL2(H2O)2][CoCl4] and [CoL3][CoCl4] . H2O have originally a distorted octahedral geometry. By grinding the solid [CoL2(SCN)2], Co2L7Cl4 and all the bromide complexes the cobalt(II) coordination undergo octahedral (T> tetrahedral geometry change. Spectral evidences and polarographic results in DMF solution have shown that for these and [CoL(SCN)2]2, [CoL2(H2O)2][CoCl4] and [CoL3][CoCl4] . H2O complexes, the solvolysis gives rise to equilibria between tetrahedral anionic [CoX4]2- (X = SCN-, Cl-), [CoX3(DMF)]- (X = SCN-, Cl-, Br-) and some possible [Co(DMF)6]2+, [CoX(DMF)5]+, [CoXL(DMF)4]+, [CoL(DMF)5]2+ (L = N-monodentate ligand) cationic octahedral species. Polarographic data for perchlorate complexes and for [Co(DMF)6](ClO4)2-L system at increasing ligand concentration have shown that in DMF solution the solved ions [Co(DMF)6]2+ are the prevailing species and that the thiopyrimidine-containing species [CoL(DMF)5]2+ (β = 3.78 . 105) and [CoL2(DMF)4]2+ (β =9.59 . 107) can be formed only in presence of large excess of the free ligand.
Synthesis of N-(3-Fluoro-2-phosphonomethoxypropyl) (FPMP) Derivatives of Heterocyclic Bases
Authors: Jindřich Jindřich , Holý Antonín , Dvořáková Hana
Published: April 2003

A new group of compounds has been prepared: N-(3-fluoro-2-phosphonomethoxypropyl) (FPMP) derivatives of purine and pyrimidine bases which exhibit a significant selective activity against a broad spectrum of retroviruses. Racemic N-(3-fluoro-2-phosphonomethoxypropyl) derivatives of adenin (V), guanine (IX), cytosine (XIII), 2,6-diaminopurine (XXI), 3-deazaadenin e(XVII), xanthine (X) and hypoxanthin (VI) were prepared from the corresponding N-(3-fluoro-2-hydroxypropyl) derivatives after protection of amino group at the heterocyclic ring by selective benzoylation, reaction with diisopropyl p-toluenesulfonyloxymethylphosphonate (II), and subsequent removal of the protecting groups. Chiral FPMP derivatives were prepared by reaction of heterocyclic base with the corresponding chiral synthon (XXX, XXXVII) followed by deprotection. The required chiral synthons were obtained from enantiomeric 3-fluoro-1,2-propanediols by two methods. In the first, the primary hydroxyl group was tritylated, the obtained derivative was reacted with compound II, the trityl group was removed and the product was mesylated to give synthon XXXVII. The second pathway consisted in selective tosylation of the primary hydroxyl group and conversion of the secondary hydroxyl into the acetoxymethyl ether via the methoxymethyl ether; treatment of the acetoxy compound with bromotrimethylsilane and triisopropyl phosphite afforded the desired synthon XXX.
Spiroheterocyclic Systems. V. Synthesis of 3-Substituted-10-spiro(1'-cycloalkane)-thiazolo[4,3-a]quinazolin-4-ones
Authors: Hozien Zeinab A. , Abdel-Hafez Ali A. , Awad Ibrahim M. A. , El-Zohry Maher F.
Published: April 2003

Synthesis of a series of 3-substituted-10-spiro(1'-cycloalkane)-thiazolo[4,3-a]quinazolin-4-ones is described.
Kinetic Study of the Oxidation of Alcohols with Quaternary Ammonium Permanganates
Authors: Šumichrast Robert , Holba Vladislav
Published: April 2003

Kinetics of the oxidation of 2-propanol, 1-butanol, and 1-pentanol with tetraalkylammonium permanganates have been investigated as function of temperature. The studied reactions are partly autocatalytic, colloidal manganese dioxide as one of the reaction products has been identified as the autocatalyst.A computerized iterative procedure has been used in order to obtained the rate constants of both non-catalytic and catalytic reaction steps together with the thermodynamic activation parameters.
Modification of Clinoptilolite by Synthetic Zeolite
Authors: Medvecký Ľubomír , Briančin Jaroslav , Mihalik Ján
Published: April 2003

The sol-gel process allows to modify clinoptilolite by the nucleation of synthetic zeolite. From the viewpoint of methanol conversion, the obtained high Al content nucleation-deposited zeolite decreases the catalytic activity of clinoptilolite. Therefore, it is necessary to optimize the selection of suitable synthetic zeolite as to its composition. Contamination of zeolite surfaces by carbonaceous fragments during catalytic process results from physico-chemical properties of the used and processed zeolite, and according to DTA and TG analysis it significantly affects the readsorption of water vapours and likely also the zeolite activity in methanol conversion.
Catalyzed Alkaline Hydrolysis of Substituted Phenyl Acetates
Authors: Kulič Jiří , Ptáček Aleš
Published: April 2003

2-Iodosobenzoic acid forming strong nucleophile in alkaline medium - 1-oxido-1,2-benziodoxol-3(1H)-one, was used as a catalyst of alkaline hydrolysis of substituted phenyl acetates (4-NO2, 3-NO2, 3-Cl, 4-Br, H, 4-CH3, 3-CH3, 4-OCH3, 3-OCH3) in the presence of hexadecyltrimethylammonium bromide as a micellar agent. It was found that the observed first-order rate constants kobs can be correlated by the Hammett equation: log kobs = (-3.29 ± 0.03) + (1.77 ± 0.001) σ.
Kinetics of the Crystallization of Potassium Sulfate
Authors: Karel Miroslav , Nývlt Jaroslav
Published: April 2003

The kinetics of the crystallization of potassium sulfate has been determined using the MSMPR technique. Values of the nucleation and crystal growth rates evaluated from the experimental data are compared with the corresponding literature data.
Differential Enthalpies of Solution of Components in Binary Systems 2 CaO . Al2O3 . SiO2-CaO . Al2O3 . 2 SiO2, CaO . SiO2-CaO . Al2O3 . 2 SiO2 and CaO . SiO2-2 CaO . Al2O3 . SiO2
Authors: Kosa Ladislav , Nerád Ivan , Strečko Jozef , Proks Ivo , Adamkovičová Katarína
Published: April 2003

Differential enthalpies of solution of components in binary systems 2 CaO . Al2O3 . SiO2-CaO . Al2O3 . 2 SiO2, CaO . SiO2-CaO . Al2O3 . 2 SiO2 and CaO . SiO2-2 CaO . Al2O3 . SiO2 as the function of composition and temperature were determined on the base of isothermal composition dependences of enthalpies of mixing and temperature dependences of heats of fusion of their pure components. From the values of the first differential heat of solution of CaO . Al2O3 . 2 SiO2 and 2 CaO . Al2O3 . SiO2 in CaO . SiO2 over temperature range considered we can conclude that the reactions were closed chains of SiO4 tetrahedra in CaO . SiO2 melt break, are exothermic. On the other hand positive values of this quantity for CaO . SiO2 in CaO . Al2O3 . 2 SiO2 and 2 CaO . Al2O3 . SiO2 led us to the conclusion that the progressive breaking originally closed chains in CaO . SiO2 melt has endothermic character.
Preparation and Characterization of Mixed Anhydrides of O-Acylarylcarbohydroximic Acid
Authors: Sharma Rajinder P. , Sharma Kusum , Lakhanpal Sunita , Sharma Namita , Misra Bhupendra N.
Published: April 2003

A number of N,O-diacylhydroxylamines have been prepared by the reaction of potassium salts of hydroxamic acids with variety of acylating agents which include: benzoyl, p-nitrobenzoyl, anisoyl, p-chlorobenzyl and lauroyl chlorides in dioxane under reflux. The structure of resulting N,O-diacylhydroxylamines has been determined by spectral analysis, Attempted have been made to prepare mixed anhydrides of several N,O-diacylhydroxylamines by the acylation reaction in the cold (below 10 °C) using acetyl, benzoyl, p-nitrobenzoyl, anisoyl and p-toluensulfonyl chlorides as acylating agents in dioxane using triethylamine as a base. Structures of the resulting mixed anhydrides have been elucidated by spectral methods.
[5-(Adenin-9-yl)-5-deoxy-L-pentofuranosyl]phosphonates - A Novel Type of Nucleotide Analogs Related to HPMPA. II. Synthesis of L-ribo and L-xylo Configurated Derivatives by Recyclization of Diethyl (5-RS)-[1,2-O-Isopropylidene-5-O-methanesulfonyl-D-pentofuranos-5-C-yl]phosphonates under Acidic Conditions
Authors: Otmar Miroslav , Rosenberg Ivan , Masojídková Milena , Holý Antonín
Published: April 2003

Further cyclic analogs of the antiviral (S)-9-(3-hydroxy-2-phosphonomethoxypropyl)adenine (I) were prepared: both anomers of [5-(adenin-9-yl)-5-doxy-L-ribofuranosyl]phosphonic acid (α-IId and β-IId) and [5-(adenin-9-yl)-5-doxy-α-L-ribofuranosyl]phosphonic acid (IIe). Recyclization reaction of diethyl (5RS-(3-O-benzyl-1,2-O-isopropylidene-5-O-methanesulfonyl-D-ribofuranos-5-C-yl)phosphonate (IVb) and diethyl (5RS-(3-O-benzyl-1,2-O-isopropylidene-5-O-methanesulfonyl-D-xylofuranos-5-C-yl)phosphonate (IVd) in trifluoroacetic acid led to cyclic aldehydes Va and Vb which were reduced to diethyl α- and β-L-ribofuranosylphosphonates VIb and α-L-xylofuranosylphosphonate VIIb. Conversion to the protected 5-O-tosylates VId and VIId, followed by reaction with adenine and deprotection, afforded the mentioned nucleotide analogs IId and IIe. An attempt to prepare L-pentofuranosylphosphonates Vc and XIII, suitable for the synthesis of nucleotide analogs of 3-deoxy-L-erythro and L-xylo configuration (IIf and IIg, respectively) by the recyclization reaction of the corresponding 5-O-methanesulfonyl derivatives IVf and XIIb failed. In this case, anhydro derivatives IXa, XVa and XVIa were isolated and identified.
The Wichterle Reaction
Authors: Hudlický Miloš
Published: April 2003

The Wichterle reaction is a conversion of vinylic chlorides to ketones by sulfuric acid. Most of the applications are transformations of γ-chlorocrotyl (3-chloro-2-butenyl) derivatives to 3-oxobutyl derivatives. The ketones thus formed may undergo subsequent reactions in compounds containing reactive centers. Thus intramolecular aldol-type condensations occur in compounds containing carbonyl groups, and Friedel-Crafts-type cyclizations in compounds containing aromatic rings. The reaction can be used as an alternative to Robinson's annelation.
Light Scattering from Polystyrene-block-poly(ethylene-co-propylene) in Decane and in Dioxane
Authors: Stejskal Jaroslav , Koňák Čestmír , Helmstedt Martin , Kratochvíl Pavel
Published: April 2003

Polystyrene-block-poly(ethylene-co-propylene) solutions in decane have been investigated by dynamic and static light scattering. The dissolution of the diblock copolymer in a solvent, which is selective of aliphatic blocks, yields well-defined metastable micellar structures. These structures are converted into equilibrium micelles on heating and change into frozen micelles when cooled. A similar pattern is observed also in dioxane, which is a selective solvent for polystyrene blocks.
Liquid-Liquid Phase Separation in Multicomponent Polymer Systems: Influence of Molar-Mass Distribution on Shadow Curve and Phase-Volume Ratio
Authors: Koningsveld Ron , Šolc Karel
Published: April 2003

The effect of the molar-mass distribution (MMD), in particular the effect of a few higher molar-mass averages, on liquid-liquid phase behaviour is studied with the aid of data based on the Flory-Huggis-Staverman model. The critical concentration and the critical slopes of the cloud-point curve and the shadow curve appear to be quite sensitive to mz and mz+1, and, theoretically, they could serve as a unique data source for estimating these averages. In practice, however, experimental difficulties and errors encountered, especially with the shadow-curve slope determination, are probably too great for these data to be of any use. Next, the entire cloud-point and shadow-curves, and phase-volume ratios are examined with respect to the possible use to supply information on the MMD. At constant weight- and number-average molar mass, the cloud-point curve does not appear to be overly sensitive to Mz-average in the studied range. As to the other curves, no simple relationship evolves either, higher averages and details of the MMD both determining shape and location of shadow and phase-volume curves. An alternative procedure is suggested which consists of fitting a set of delta functions to a series of data points.
Block Copolymer Micelles in Aqueous Media
Authors: Tuzar Zdeněk , Kratochvíl Pavel , Procházka Karel , Munk Petr
Published: April 2003

Micellization of di- and triblock copolymers, poly(methacrylic acid)-block-polystyrene and poly(methacrylic acid)-block-polystyrene-block-poly(methacrylic acid), varying in molecular weight and composition, has been studied by static and dynamic light scattering, and sedimentation velocity. Micelles with polystyrene cores were prepared in water-dioxane mixtures, rich in dioxane, and transferred into water-rich mixtures, water, and aqueous buffers via stepwise dialysis. It has been shown that, in dioxane-rich mixtures, the micellar system was in dynamic equilibrium, while in water-rich solvents, water, and aqueous buffers the micellization equilibrium was frozen and micelles behaved like autonomus particles. Under certain conditions, micelles were accompanied by independent large particles. This phenomenon, known from other micellar systems as an "anomalous micellization", is discussed.
NMR and X-ray Diffraction Study of the Conformational Structure of Poly[N5-(2-hydroxyethyl)-L-glutamine] and Poly[N5-(2-hydroxyethyl)-L-glutamine-co-γ-L-glutamylhydrazide]
Authors: Hlavatá Drahomíra , Pivcová Hana , Spěváček Jiří , Nosková Dagmar , Rypáček František
Published: April 2003

The conformation of poly[N5-(2-hydroxyethyl)L-glutamine] (P(HEG-GH)), in solid state was studied by 13C CP/MAS NMR spectrometry and X-ray diffraction. The association of copolymers in dichloroacetic acid was investigated by following the temperature dependence of their 1H NMR spectra, PHEG and P(HEG-GH) were prepared by the reaction of poly(benzyl γ-L-glutamate) with 2-aminoethanol and 2-aminoethanol-hydrazine mixtures, respectively. The conformation of the copolymers depends on the reaction conditions. While PHEG and the copolymers prepared with the mole ratio of hydrazine to the benzyl ester nH/nB = 0.25 were almost amorphous in solid state and had a random coil conformation and/or randomly oriented helices, at increased concentration of hydrazine (nH/nB = 0.5 and 1.0) P(HEG-GH) formed more or less ordered structure characterized by assemblies of α-helices. The copolymers prepared at nH/nB 3 2.0 showed features of β-sheets. The tendency of the copolymers to form associates in Cl2CHCOOH solutions correlated well with their tendency to form ordered structures in solid state.
Revival of the Induction Time Concept in the Theory of Polymer Crystallization
Authors: Lednický František , Muchová Miroslava
Published: April 2003

To monitor early stages of spherulite growth, a microscopical method has been worked out based on the photometrical measurement of the intensity of depolarized light during isothermal crystallization. Application of the technique to polypropylene yields the evidence of existence of nucleation induction time which reflects the processes taking place prior to the onset of spherulite growth, viz. the formation of stable crystal nuclei. Using the method, it is possible to evaluate also systems with a dispersed phase, the interfacial relations being reflected in the induction time of the nucleation on the surface of the dispersed phase. Application to the model PP/carbon fibres system yields differing results for carbon fibres of various provenance and of various properties.
Effect of Coagulative Mechanism of Particle Growth on the Structural Heterogeneity of Ethyl Acrylate-Methacrylic Acid Copolymer Latex Particles
Authors: Šňupárek Jaromír , Bradna Pavel , Mrkvičková Libuše , Lednický František , Quadrat Otakar
Published: April 2003

Latex particles of ethyl acrylate-methacrylic acid copolymers prepared by semicontinuous emulsion polymerization with a monomer emulsion feed were found to disintegrate into smaller subparticles on alkalization. The phenomenon observed by light scattering and scanning electron microscopy is explained in terms of heterogeneous structure of latex particles which are agglomerates of small particles formed by coagulation during polymerization. The influence of particle size and polymerization route on particle heterogenity is discussed.
Oxidation of 3β,28-Diacetoxy-18-lupen-21-one with Peroxy Acids: A Way to Des-E-lupane Derivatives
Authors: Klinotová Eva , Rejzek Martin , Zůnová Hana , Sejbal Jan , Klinot Jiří , Urban Jiří
Published: April 2003

Oxidation of 3β,28-diacetoxy-18-lupen-21-one (I) and its 18β, 19β-epoxy derivative III with peracetic acid, catalyzed with strong acids, proceeds with cleavage of the bond between C-19 and C-21 under formation of E-seco derivatives with hydroxyl and isobutyryl groups on C-18 (spiro lactones V - VII and acid VIII). Oxidative removal of the isobutyryl fragment in spiro lactone VI by treatment with lead tetraacetate leads to the tetranor derivative - keto lactone XI which in an alkaline medium loses formaldehyde from C-17 to give des-E acid XVI.
From Chlorobenzene to a Carbohydrate in Two Steps. A New Chemoenzymatic Synthesis of 2,3-O-Isopropylidene-D-erythruronolactone
Authors: Mandel Martin , Hudlický Tomáš , Kwart Lawrence D. , Whited Gregg M.
Published: April 2003

Controlled oxidation of chloroepoxide V with two equivalents of sodium periodate furnished 2,3-O-isopropylidene-D-erythruronolactone (I) in 63% yield. This procedure was augmented by combining the protection of diol III, the oxidation of acetonide IV to V, and the subsequent oxidative cleavage to I into one operation which yielded, on medium scale, the title lactone in 51% yield. detailed procedure of preparation and physical constants are provided for lactone I.
On the Definition and Use of Deviation Functions for Treatment of Quasi-Elastic Light Scattering Data
Authors: Sundelöf Lars-Olof , Porsch Bedřich
Published: April 2003

A theory for deviation functions defined as the deviation from strict gaussian behaviour of electric field correlation functions obtained from Quasi-Elastic Light Scattering experiments is presented. Its application to systems with different types of particle size distributions is treated both theoretically and by numerical examples. Expressions are given for distributions where the correlation function can be expressed as Laplace transform in closed form. The theory is also compared with experiments on solutions of polymers with a variety of molecular mass distributions. It is concluded that even if the procedure based on deviation functions cannot compete with other numerical inversion methods in the direct determination of molecular size distributions it may substantially help to visualize the magnitude of the effect of polydispersity and serve as a prerequisite for a decision concerning how far it is meaningful to purse more precise calculations. This is essentially equivalent to a judgment of the noise level of the experiment and of the "information content" to be expected.
Polymerization of Vinyl Chloride by Organometallic Compounds. Effect of Moisture in the Monomer
Authors: Kolínský Miloslav , Michalcová Jaroslava , Jíšová Václava , Lukáš Rudolf
Published: April 2003

The effect of moisture in vinyl chloride (VC) on its polymerization initiated with tert-butyllithium was investigated. The conversion curves thus obtained and the dependences of molecular weights of isolated products show that within range 6.5 - 80 ppm. vol. water in vinyl chloride and the mole ration t-BuLi/VC 0.0004 - 0.03 the conversion of vinyl chloride decreases, while the molecular weight of PVC increases. The distribution curves of molecular weights become broader with increasing water content in the monomer, and their maxima are shifted to higher molecular weights. The water content up to 40 ppm. vol. in vinyl chloride does not affect the heat stability of PVC. At higher water contents the stability decreases.
Block Copolymers Poly(2,6-dimethyl-1,4-phenylene oxide)-poly(6-hexanelactam). Preparation and Composition
Authors: Stehlíček Jaroslav , Puffr Rudolf
Published: April 2003

Poly(2,6-dimethyl-1,4-phenylene oxide)-poly(6-hexanelactam) diblock copolymers were prepared from low-molecular weight poly(2,6-dimethyl-1,4-phenylene oxide) by transforming its phenolic end groups via the reaction with 2,4-tolylene diisocyanate and 6-hexanelactam to polymeric initiators and the subsequent anionic polymerization of 6-hexanelactam. The polymerization of 6-hexanelactam was carried out in bulk or toluene solution. The content of the 6-hexanelactam homopolymer was estimated by TLC showing that the pure diblock copolymer can be prepared in toluene. The reason for relatively low yields is discussed.
Excess Volumes of Mixtures of Some Alkyl Esters and Ketones with Alkanols
Authors: Qin Anwei , Hoffman Dolly E. , Munk Petr
Published: April 2003

Excess volumes were calculated from measured densities of binary mixtures of five linear alkanols (methanol, ethanol, 1-propanol, 1-butanol, and 1-pentanol) with five n-alkyl acetates (methyl, ethyl, propyl, butyl, and pentyl acetates) and with two ketones (acetone and 2-butanone) at 20 °C. The whole composition range was studied for all thirty-five binary systems. For a given alcohol, the ∆V/φ1ϑ2 value decreases with increasing size of the carbonyl compound. For a given carbonyl compound, it increases with the length of the alkanol. Systems with methyl acetate as one component have relatively large ∆V/φ1ϑ2 values, while systems with methanol display different compositional dependency in respect to systems with other alcohols.
Surface-Enhanced Raman Scattering (SERS) Spectroscopy with Borohydride-Reduced Silver Colloids: Controlling Adsorption of the Scattering Species by Surface Potential of Silver Colloid
Authors: Čermáková Kateřina , Šesták Ondřej , Matějka Pavel , Baumruk Vladimír , Vlčková Blanka
Published: April 2003

Formation of Ag colloid/adsorbate SERS-active systems (upon adsorption of the selected adsorbates on the surface of Ag colloidal particles) as a function of (i) NaBH4 to AgNO3 molar ratio in the preparation protocol of Ag colloid, and (ii) aging of the colloid has been investigated by Surface-enhanced Raman scattering (SERS) spectroscopy. Oligomeric synthetic polypeptides, bovine serum albumin, phosphate coadsorbed with CuTMePyP [copper(II) derivative of 5,10,15,20-tetrakis-(N-methylpyridinium-4-yl)porphyrin chloride] and borates in systems with N-containing bases were selected as model adsorbates. Both (i) a decrease of NaBH4 to AgNO3 molar ratio upon preparation and (ii) aging of Ag colloid affect adsorption of the adsorbates and consequently, their SERS spectra, in the same manner. Aging of Ag colloid is thus viewed as a slow hydrolysis of BH4- anions. The actual concentration of BH4- in the system is identified as the most important factor controlling adsorption of all the selected adsorbates on the surface of Ag colloid. As this factor can be related to the surface potential, the conditions controlling adsorption of the selected adsorbates are specified in terms of a more negative and/or more positive surface potential of Ag colloidal particles. A more positive surface potential promotes adsorption of polypeptides, bovine serum albumin and phosphate while observation of spectral features of borates in the SERS spectra of N-containing bases in alkaline solutions is conditioned by a more negative surface potential.
FEM Study CO and H2 Interaction with a Supported Bimetallic Catalyst: Mo-Pd/Al2O3/W
Authors: Šotola Jan , Knor Zlatko
Published: April 2003

Palladium and molybdenum were deposited onto a continuous layer of Al2O3 covering a tungsten field emitter. The adsorption of CO at 300 K on such a model system shows unexpected increase in the electron emission from both metals. This effect can either be understood in terms of a resonance enhancement of electron tunneling, or it can result from specific interactions of CO with supported clusters as compared to CO interaction with bulk metals. Coadsorption of CO and H2 on the mixed molybdenum and palladium surface exhibits features different from coadsorption on the individual metals.
Ten-Vertex Polyhedral Monocarbaborane Chemistry. The Novel High-Yield Formation of the Ten-Vertex closo Compound [6-(PMe2Ph)-closo-1-CB9H9] from the Thermolysis of [8,8-(PMe2Ph)2-nido-8,7-PtCB9H11]
Authors: Jones Jane H. , Štíbr Bohumil , Kennedy John D. , Thornton-Pett Mark
Published: April 2003

Thermolysis of [8,8-(PMe2Ph)2-nido-8,7-PtCB9H11] in boiling toluene solution results in an elimination of the platinum centre and cluster closure to give the ten-vertex closo species [6-(PMe2Ph)-closo-1-CB9H9] in 85% yield as a colourles air stable solid. The product is characterized by NMR spectroscopy and single-crystal X-ray diffraction analysis. Crystals (from hexane-dichloromethane) are monoclinic, space group P21/c, with a = 903.20(9), b = 1 481.86(11), c = 2 320.0(2) pm, β = 97.860(7)° and Z = 8, and the structure has been refined to R(Rw) = 0.045(0.051) for 3 281 observed reflections with Fo > 2.0σ(Fo). The clean high-yield elimination of a metal centre from a polyhedral metallaborane or metallaheteroborane species is very rare.