bluuebunny/crossref_metadata_2025 huggingface dataset:
Series of sequential polypeptides containing lysine or arginine: Preparation and characterization
Authors: Pírková Jana , Churkina Svetlana , Gut Vladimír , Frič Ivo , Bláha Karel
Published: June 2010

The sequential polypeptides (Lys-Ala)n, (Lys-Ala-Ala)n, (Lys-Ala-Ala-Ala)n, (Lys-Leu-Ala)n, (Lys-Leu-Ala-Ala)n, (Lys-Leu-Ala-Ala-Ala)n, (Lys-Ala-Leu)n, (Lys-Ala-Leu-Ala)n, (Orn-Leu-Ala)n,(Arg-Ala-Ala)n, (Arg-Leu-Ala)n, (Arg-Leu-Ala-Ala)n, (Arg-Ala-Leu)n, and (Arg-Ala-Leu-Ala)n were synthesized by polymerization of active esters (1-succinimidyl or pentafluorophenyl) of the corresponding Nα-deblocked monomers. The monomers were prepared using the usual methods of peptide synthesis in solution. Upon dialysis, the average molecular weight of the polymer was 6 000-9 000 as determined by sedimentation in ultracentrifuge. Polypeptides, containing leucine in addition to the basic amino acid, showed a marked tendency to aggregation. CD spectra of the products were measured for characterization.
New nitrogen-containing compounds in Lilium candidum L.
Authors: Haladová Mária , Eisenreichová Eva , Bučková Anna , Tomko Jozef , Uhrín Dušan
Published: June 2010

1-(3’-Methyl-2’-oxo-5’-pyrrolidinyl)-3-methyl-3-pyrrolin-2-one, 1-(2’-oxo-5’-pyrrolidinyl)-3-meth-yl-3-pyrrolin-2-one and 1-(3’-methyl-2’-oxo-5’-pyrrolidinyl)-5-hydroxy-3-methyl-3-pyrrolin-2-one were isolated from petals of Lilium candidum L.(Liliaceae). Presence of these substances, obtained by column chromatography of the extract on silica gel, has not been reported in any plant material as yet; their structures were adduced from spectral data.
A vector method of representing individual types of enzymic reactions in K’mV’ coordinates
Authors: Krupyanko Vladimír I.
Published: June 2010

A vector method of representing individual types of enzymic reactions in K’mV’ coordinates is described. Equations for enzyme activation (and nontrivial inhibition) constants are deduced using the method. The inhibiting effect of Na2WO4 on the initial rates of p-nitrophenyl phosphate decomposition by calf intestinal alkaline phosphatase was studied, and the constant of enzyme inhibition by this compound was determined. Other uses of the method are discussed.
Biosynthesis of sucrose and its deoxy derivatives
Authors: Zemek Jiří , Kučár Štefan
Published: June 2010

The biosynthesis of sucrose (β-D-fructofuranosyl-α-D-glucopyranoside) was studied in the reaction catalyzed by partially purified sucrose syntheses (UDP-D-glucose: D-fructose 2glucosyltransferase) isolated from pea seedlings, bean seedlings and sugar beet roots using UDP-D-glucose and its deoxyglucosyl derivatives as donors and D-fructose and its deoxy-analogues as acceptors. It was found that none of the hydroxyl groups either of the reaction donor or the acceptor is essential for the substrate properties in the transglycosylation reaction. The affinity of these plant enzymes and the rate of hexose incorporation into sucrose decreases however in the following sequence: sucrose, 2G-deoxysucrose, 6G-deoxysucrose, 4G-deoxysucrose, and 3G-deoxysucrose for the donor and sucrose, 6F-deoxysucrose, 1F-deoxysucrose, 4F-deoxysucrose, and 3F-deoxysucrose for the acceptor.
Proteoglycan-collagen interactions. Structure in the amorphous ground substance
Authors: Scott John E.
Published: June 2010

Glycosaminoglycans occur in vivo outside the collagen fibrils. In this perifibrillar space specific interactions between proteoglycans and the collagen fibrils lead to the formation of an organized structure. Different tissues were examined by an electron histochemical method and it was concluded that the single proteoglycans have specific loci of association with the type I collagen fibril and are arrayed orthogonally in respect to the fibrils.
Study of the azo-hydrazone tautomeric equilibrium by electronic spectroscopy and quantum chemistry. I. Electronic spectra
Authors: Nepraš Miloš , Titz Miloš , Nečas Miroslav , Luňák Stanislav , Hrdina Radim , Lyčka Antonín
Published: June 2010

The azo-hydrazone tautomeric equilibrium was studied for p-hydroxy and p-amino derivatives of some arylazo compounds. Substantial differences were observed between the spectral patterns in hydrocarbon and alcoholic solutions at normal and low temperatures; these are due to shifts in the azo-hydrazone tautomeric equilibrium, which depends on the nature of the proton donor para substituent, size and topology of the system (aromatic ring fusion patterns), solvent and temperature. The spectral patterns suggest that the proton transfer from the para substituent takes place after dimerization of the molecule.
Nitrogen cross-sectional area on standard graphite
Authors: Cascarini de Torre L. E. , Llanos J. L. , Bottani E. J.
Published: June 2010

Nitrogen physical adsorption at 77.5 and 80.4 K on a standard graphite was studied with the purpose too analyze adsorption models and to determine nitrogen cross-sectional areas for each model. With this intention different models, such as Van der Waals, Langmuir, and BET, which describe the adsorption process at different surface coverages were employed. Molar differential entropies and isosteric heats of adsorption were calculated. A two-dimensional phase transition was confirmed. Adsorbed molecule cross-sectional areas were determined at different surface coverages, by direct comparison with that corresponding to argon. The values obtained varied in a wide range (0.135 to 0.166 nm2) depending on surface coverage.
Interaction between natural and forced convections at a sphere in a laminar flow regime
Authors: Kimla Arnošt , Míčka Jiří
Published: June 2010

The authors deal with the formulation and solution of a boundary value problem describing the influence of natural convection on forced convection during diffusion to a sphere in a laminar flow regime, the orientation of the natural convection being opposite to that of the forced one. The results of numerical solution are discussed and compared with the case where the orientation of both types of convection is the same. There is a good qualitative agreement with illustrative physical concepts referring both to hydrodynamics and concentrations.
Reduction and oxidation of vanadium catalysts for the NO + NH3 reaction
Authors: Čížek Milan , Pour Vladimír
Published: June 2010

The reduction of V2O5/Al2O3 (15 mass % V2O5) and V2O5 by ammonia, hydrogen, and a NO + NH3 mixture, and the oxidation of pre-reduced catalysts by oxygen and nitrogen oxide have been investigated. For both catalysts, the reduction rate increases in the sequence H2 < NH3 < NO + NH3. From the character of the temperature and concentration dependences of the oxidation state of vanadium, it has been concluded that in the temperature range 100 to 175 °C the catalysts are reduced by the NO + NH3 mixture within the surface layer only. The reaction of this mixture with oxidized surface of vanadium catalyst is of the same order with respect to NO and NH3 concentrations.
The molecular and crystal structure of benzamidinium bromoacetate
Authors: Kratochvíl Bohumil , Ondráček Jan , Malý Karel , Csordás László
Published: June 2010

The molecular and crystal structure of benzamidinium bromoacetate was solved on the basis of Patterson and Fourier synthesis. The position of all the atoms were localized and the least squares method was employed to refine the coordinates of all the atoms together with their thermal vibration parameters. A final R factor value of 0.067 was obtained for 1 349 observed reflections (I 1.96 σ(I)). The substance crystallizes in the P21/n monoclinic space group with lattice parameters of a = 1 145.7(2), b = 1 571.3(3), c = 578.3(1) pm, γ = 90.65(1)°, Z = 4. Intramolecular hydrogen bonds form ion pairs in the structure between the nitrogen atoms of the amidinium group and the oxygen atoms of the bromoacetate. Intramolecular hydrogen bonds, also between nitrogen and oxygen atoms, connect the molecules in an infinite chain. The molecular chains are joined together by van der Waals forces. The N···O distance in the hydrogen bonds varies between 280.3(8) and 284.5(8) pm.
Structure of 5-nitro-2-methylbenzoic acid: ortho Effect of the methyl group
Authors: Tinant Bernard , Declercq Jean-Paul , Van Meerssche Maurice , Exner Otto
Published: June 2010

The X-ray structure of the title compound was determined: Mr = 181.15, triclinic, P1, a = 7.628(2) Å, b = 10.475(3) Å, c = 10.522(2) Å, α = 90.61(2)°, β = 98.19(2)°, γ = 76.41(2)°, V = 808.6(4) Å3, Z = 4, Dx = 1.49 g cm-3, CuKα, λ = 1.5418 Å, μ = 10.57 cm-1, F(000) = 376, T = 291 K, R = 0.049 for 1 713 observed reflections. The deformations induced by the steric effect of the ortho-methyl group are discussed in some detail. They are partly different from those commonly considered, in particular the carboxyl group is coplanar with the benzene ring.
Rearrangement of five-membered heterocyclic enamines
Authors: Červinka Otakar , Fábryová Anna , Jursík Tomáš
Published: June 2010

Addition of bromine to 1-methyl-2-benzilidenepyrrolidine (Ia) and subsequent treatment with sodium hydroxide afforded unstable 1-methyl-2-phenyl-3-piperidone (IVa) which was reduced with lithium aluminium hydride to an isolable mixture of diastereoisomeric 1-methyl-2-phenyl-3-piperidinols (Va). Analogous reaction with 1-methyl-2-ethylidenepyrrolidine (Ib) led to mixture of products containing, in addition to diastereoisomeric 1,2-dimethyl-3-piperidinols (Vb), also the substitution products 1-methyl-2-(1-hydroxyethyl)pyrrolidines VI and 1-methyl-2-ethyl-3-pyrrolidinols VII (as detected by mass spectrometry).
Synthesis of a new type of pyrazolothiazoles
Authors: Ravinder P. , Rajeswar Rao V. , Padmanabha Rao T. V.
Published: June 2010

Pyrazolothiazoles IV have been synthesized by the condensation of appropriate 3,4,5-trisubstituted 1-thiocarbamoylpyrazoles I, II with various (ω-bromoacetyl)coumarins III.
On theory of apparent molar volumes in concentrated aqueous solutions of strong electrolytes
Authors: Čeleda Jiří
Published: June 2010

On the basis of the method reported in the previous work, according to which close-packed hydration sheaths of ions are surrounded by excess voids which in the above model were replaced by contact gap of width d0 independent of temperature and concentration, it is inferred in the present study that on extrapolating the apparent volumes of strong electrolytes to zero volume fraction of water in solution, temperature-independent water-free ion volumes Φ’i are obtained. These volumes correspond to the state in which the contact gap is shifted up to the very surface of ions, without changing its width d0 = 39 ± 2 pm. The volumes Φ’i show additivity and acquire thus the properties of parameters which are applicable to calculation of the density of aqueous solutions of strong electrolytes as well as of their mixtures up to the highest possible concentrations. With Li+ and Na+ ions, the condition of temperature invariance of Φ’i results in that the hydrate nucleus is not naked cation but a species MH2O+ analogous to H3O+ ion. This explains likely the different function of Na+ and K+ ions in biological systems (especially concerning their permeation through membranes). In the case of Mg2+, Ca2+, Sr2+, and Ba2+ ions, the hard-body centre of their hydrates is formed by hexaaqua-complexes.
Kinetic study of permanganate oxidation of L-leucine in neutral aqueous solution
Authors: Brillas Enrique , Garrido José A. , Perez-Benito Joaquin F. , Rodriguez Rosa M. , de Andres Jaime
Published: June 2010

The permanganate oxidation of L-leucine in aqueous phosphate buffers over the pH range 6.1 – 7.6 is autocatalyzed by the manganese reduction product, a soluble form of colloidal manganese dioxide. The kinetic data for both the non-catalytic and autocatalytic reaction pathways have been obtained, and mechanism in agreement with them proposed. The non-catalytic pathway takes place by reaction between either the anionic or the zwitterionic form of the amino acid and permanganate ion, whereas the autocatalytic pathway is realized by the permanganate oxidation of the amino acid previously adsorbed on the colloid surface.
Voltametric study of chlorine using a rotating gold disc electrode
Authors: Beran Přemysl , Micka Karel , Gái Vu Thi
Published: June 2010

The kinetics of hydrolysis of chlorine in acidic aqueous solutions was studied by the voltammetric method using a rotating gold disc electrode. The voltammetric curves consist of two waves, of which the more negative corresponds to reduction of hypochlorous acid and the more positive to reduction of chlorine. The wave of chlorine increases with the concentration of H+ and Cl- ions and has a kinetic character; in acetate buffer (pH 3.6) its behaviour approaches best the theory of kinetic-controlled waves. The corresponding dependences on the concentrations of H+ and Cl- ions, however, show some anomalies suggesting complications in the reaction mechanism.
Photochemical decomposition of t-butyl hydroperoxide; Photocatalytical effects of VO(II) and Co(III) 2,4-pentanedionates
Authors: Luňák Stanislav , Kokorin Aleksandr I. , Mácová Eva , Lederer Pavel
Published: June 2010

It has been found that [VO(acac)2] and [Co(acac)3] increase the rate of t-BuOOH photolysis, whereas [Fe(acac)3] has the opposite effect. Redox changes of the catalytically active [VO(acac)2] were followed using the EPR technique. An EPR signal from a free radical intermediate of photochemical decomposition of t-BuOOH was recorded, and the concentration of the intermediate was monitored during the reaction.
An investigation of the formation of molecular complexes of O-(3,5-dinitrobenzoyl)-O-acetylcellulose with n- and π-donors
Authors: Čík Gabriel , Šeršeň František , Blažej Anton , Hayden Viktor , Havlínová Bohuslava
Published: June 2010

Soluble O-(3,5-dinitrobenzoyl)-O-acetylcellulose was synthesized, and the formation of molecular complexes with n- and π-donors was investigated. The formation of complexes obeys the Langmuir adsorption isotherm adjusted for macromolecules. The formation of molecular complexes with low-molar mass compounds of the type of heterocyclic compounds, aromatic amines and condensed hydrocarbons was confirmed by electric resistance measurements. The largest decrease in the specific resistance by 2-3 orders of magnitude was observed with indole and phenothiazine, while the specific resistance of the other types of donors decreased by 1-2 orders of magnitude. A decrease in the activation energy took place with all types of complexes.
Base-catalyzed formation of spiro adduct from N-methyl-N-(2,4,6-trinitrophenyl)glycinamide, the smiles rearrangement of the amide in methanol
Authors: Kaválek Jaromír , Macháček Vladimír , Hassanien Makky M. M. , Štěrba Vojeslav
Published: June 2010

The reaction of N-methyl-N-(2,4,6-trinitrophenyl)glycinamide (Ic with methoxide in methanol produces the spiro adduct IIc(A). In methanolic acetate buffers, the equilibrium is rapidly established between the spiro adduct IIc(A) and the dipolar ion of 2-methylamino-N-(2,4,6-trinitrophenyl)acetamide (IIIc(Z)). The equilibrium constant of the reaction IIIc(Z) ⇆ IIc(A) + H+ is by eight orders of magnitude greater than that of the analogous cyclization of 2-methylamino-N-methyl-N-(2,4,6-trinitrophenyl)acetamide to the spiro adduct. In chloracetate buffers, the dipolar ion is protonated to give 2-methylammonium-N-(2,4,6-trinitrohenyl)acetamide IIIc(K). The kinetics of the reversible reaction IIIc(Z) ⇆ IIc(A) + H+ has been studied in acetate buffers, aliphatic amine – ammonium salt buffers, and methoxide solutions. In all cases, the rate-limiting step was the proton transfer with half-lives in milliseconds. In more basic methanolic buffers (pH > 10) the rate-limiting step consists in the formation of spiro adduct from the zwiterion IIIc(Z) resulting from the protonation of the anion IIIc(A). n acetate buffers, the second reaction pathway via the cation IIIc(K) is predominant.
A description of effect of composition of mixed binary solvents on processes in solutions
Authors: Pytela Oldřich , Ludwig Miroslav
Published: June 2010

A theoretical description of the effect of changed composition of mixed solvents on processes in solutions has been suggested on the basis of the proportionality between the Gibbs energy change of the process and that of the solvent due to the transition from pure components to the mixture. The additional Gibbs energy has been expressed by means of the so-called classical functions by Margules, van Laar-Wohl, and van Laar-Null. The application to 115 various processes (pK, IR, UV-VIS, NMR, log k, and others) has confirmed that the theoretical presumptions are justified, the most suitable being Margules' 4th order model which shows a statistically significant difference from the models of lower orders.
Maxima in pulse polarography
Authors: Bolzan Jorge A.
Published: June 2010

Maxima may occur in pulse polarography under certain circumstances. They have been found in solutions of Zn2+ and Cd2+ ions with very dilute supporting electrolytes. The possibility of adsorption phenomena, which may cause another kind of maxima, has been excluded. Due to the fact that maxima have not yet been systematically studied with the present technique, it is premature to assign them to any particular kind, although they somewhat resemble to classical d.c. polarographic maxima of the first kind. It is shown that larger peak maxima are obtained at short pulse widths and, mainly, at short decay times and that they disappear by increasing either the decay time or the measuring time, or both; by shortening the delay time or by turning to the differential pulse polarographic technique. Some considerations are made on the influence of the double layer and or surface phenomena on the dropping mercury electrode.
Effect of surface active cations undergoing interfacial rearrangements on deposition type electrode reactions
Authors: Anastopoulos Anastos , Christodoulou Anastasia
Published: June 2010

The influence of the adsorption of methyltriphenyl- and cyclopropyltriphenylphosphonium cations on simple deposition reactions of Cd2+ and Zn2+ at the dropping mercury electrode, is studied by polarographic techniques. The size parameters of the activated complex, r≠, and adsorbate particles, ri, are determined and discussed. It is shown that for substances undergoing interfacial rearrangements, i.e. condensation and reorientation, the values of the size ratio r≠/ri can hardly be correlated to independently determined values of r≠ and ri. Electrode coverages are related to formal rate constants and an elucidation of the inhibition mechanism is attempted.
IR study of water and 2-propanol adsorption on alumina
Authors: Malysheva L. V. , Morávek Vladimír , Paukshtis E. A. , Yurchenko E. N.
Published: June 2010

The adsorption of water and 2-propanol on alumina has been studied by means of IR spectroscopy. Low temperature adsorption of CO has revealed that evolution of Lewis acid sites begins at 80 °C in vacuo when still about 40% of molecular water is present on the surface. The thermodesorption of water proceeds by recombination of neighbouring OH groups. The adsorption of 2-propanol increases the concentration of the nonisolated OH groups and decreases the concentration of isolated ones. The irreversible adsorption influences mostly the C-O and Cβ-H bonds in 2-propanol.
Determination of gallium in aluminium compounds by atomic absorption spectrometry
Authors: Tokarová Věnceslava , Mareček Josef
Published: June 2010

A method is suggested for the determination of gallium in aluminium oxide and in raw materials for its production (aluminium sulphates, alums) by atomic absorption spectrometry with electrothermal atomization, based on direct injection of a suspension of Al2O3 in an ethanol-water 9 : 1 mixture into a tungsten atomizer. Suspensions of Al2O3 with known amounts of Ga embedded in the solid phase are found to suit best for calibration. Optimum heat treatment and atomization conditions are established. The behaviour of gallium in aqueous solutions and in Al2O3 suspensions during their heat treatment is compared for atomization in a tungsten atomizer and in a graphite furnace.
Influence of liquid properties on mass transfer coefficients in bubble columns
Authors: Winkler Kurt , Kaštánek František , Kratochvíl Jan
Published: June 2010

The gas phase holdup, the specific interfacial area a, and the liquid-side volumetric mass transfer coefficient kLa have been determined for two selected binary systems water-butanol and butanol-2-ethylhexanol in a short bubble column of 150 mm i.d. at gas phase velocities (air) in the range of uG = (0.31-2.52) . 10-2 m s-1. The kLa-uG dependences show characteristic maxima which only partially can be explained by molecular and surface force interactions, induced by the liquid phase. The main parameter, influencing the kLa-values, is a. At small gas velocities some irregularities in the Sauter diameter d32 and in the values of separated kL are observed.
The preparation and stereochemistry of the ternary cobalt(III) complex of (2R,2'S)-2,2'-ethylene-bis(2-aminobutanoic) acid and ethylenediamine
Authors: Strašák Milan , Kederová Milena , Novák Vladimír
Published: June 2010

The ternary cobalt(III) complex [Co(EDDB)(en)]+ was prepared by oxidation of an aqueous solution of a cobalt(II) salt and the ligands by an equimolar amount of PbO2. Chromatographic separation on a cation exchanger yielded two geometric isomers, that were characterized by their electronic absorption, 13C NMR and IR spectra. Gel permeation chromatography was used to partially separate the two geometric isomers to yield the corresponding enantiomers, whose absolute configuration was found by CD.
A new variant of the synthesis of disparlure via acetylenic intermediates
Authors: Jonas Jaroslav , Slanina Pavel , Humpa Otakar , Mazal Ctibor
Published: June 2010

Disparlure, the sexual feromone of the Gypsy Moth, has been prepared via the known intermediate 2-methyl-7-octadecyne, using a new constructional principle: C9 + C10 → C19. The so far undescribed 7-methyl-1-octyne was used as the C9 component. The advantages of this procedure consist in higher yields of disparlure and in a substantial simplification of the method of purification of 2-methyl-7-octadecyne.
Electron transfer between ferrocene and hexacyanoferrate(III) across the water/1,2-dichloroethane interface
Authors: Hanzlík Josef , Hovorka Jan , Samec Zdeněk , Toma Štefan
Published: June 2010

Kinetics of electron transfer between ferrocene or its derivative (1,1'-diethyl- or 1,1'-distearoylferrocene) in dichloroethane and hexacyanoferrate(III) in water was studied by means of convolution potential sweep voltammetry. Within the accessible range of experimental conditions no effect of either the potential or concentrations of reactants on the rate constant of electron transfer from the organic to the aqueous phase (ko→w = 1 . 10-7 m4 mol-1 s-1) was observed. Electron transfer was shown to occur far from the potential range, in which the ferricenium ion transfer can take place. However, the reaction was complicated by the chemical decomposition of ferricenium in dichloroethane (k = 0·346 s-1).
Influence of extraction properties of PVC plasticizer membrane on the response of coated wire type ion selective electrode
Authors: Halámek Emil , Čapoun Tomáš , Souček Jan
Published: June 2010

The authors studied the influence of the extraction properties of a PVC membrane plasticizer of a coated-wire type ion-selective electrode on its response in titrations of brucine and atropine with sodium tetraphenyl borate, as well as in potentiometric determinations of these compounds. The highest attainable value of the ion pair concentration in the plasticizer, which is limited by the distribution coefficient of the ion pair, determines the interval in which the electrode potential can be changed; and a linear dependence of the potential range of the titration curves on the logarithm of the ion-pair distribution coefficient was found. The slope of the dependence of the electrode potential on the logarithm of the ion concentration to be determined, found in potentiometric measurements, is proportional to the distribution coefficient of the ion which forms a pair with the ion to be determined and in whose solution the electrode membrane is activated between the measurements. The dependence of the slope of the electrode function on the logarithm of the product of the mentioned distribution coefficients is linear.
The polarographic and voltammetric determination of trypane blue
Authors: Barek Jiří , Balsiene Janina , Tietzová Barbara , Zima Jiří
Published: June 2010

The reduction of mutagenic bisazodye trypane blue has been studied at a mercury electrode, a mechanism has been proposed and optimal conditions found for its analytical application. The use of a dropping mercury electrode with a renewable surface yielded a detection limit of 8 . 10-7 mol l-1 for TAST polarography, and 8 . 10-8 mol l-1 for differential pulse polarography; the use of a hanging mercury drop electrode with an unrenewed surface during the measurement yielded detection limit of 6 . 10-8 mol l-1 for fast scan differential pulse voltammetry and 4 . 10-8 mol l-1 for linear scan voltammetry. Preliminary adsorptive accumulation of the determined substance on the surface of the hanging mercury drop electrode led to a decrease in the detection limit to 5 . 10-9 mol l-1 for linear scan voltammetry.
A feedback reactor with continuous injection of one reaction component using spectrophotometric indication I
Authors: Skopal František
Published: June 2010

The time dependence of the volume of solution of one reaction component injected continuously to the solution of the other reaction component is derived for the case that the injection is controlled by feedback to hold the absorbance of the reaction mixture constant. An experimental apparatus based on this principle has been set up and its function tested on two 2nd order reactions, whereby the theoretical relations derived for the determination of the rate constants have also been verified.
Complexes of N-methyliminobis(methylenephosphonic) acid with cobalt, nickel, copper, and zinc
Authors: Lukeš Ivan , Kváča Zdeněk , Dominák Ivor
Published: June 2010

The 1 : 1 cobalt, nickel, copper and zinc complexes of N-methyliminobis(methylenephosphonic) acid, and 1 : 2 cobalt and nickel complexes were prepared. The effect of alkali and alkali earth metals as "external cations" on the crystallization and stoichiometry of solid cobalt complex was investigated. Infrared and electronic spectra and magnetic susceptibilities indicate that cobalt and nickel form high-spin complexes. The coordination sphere of the central atom is formed by a distorted octahedron of the ligand oxygen atoms.
A mathematical model of the synthon
Authors: Koča Jaroslav
Published: June 2010

A mathematical model of the synthon is suggested. The term synthon is used to denote one or several molecules or their part(s) with free valences. The notion of isomeric synthons on a set of atoms A and that of the Family of Isomeric Synthons FIS(A) are introduced. Matrix operators are defined for modelling the elementary steps of reorganization of electrons during reactions. A new notion of the reaction distance of isomeric synthons is introduced as the smallest number of elementary steps of reorganization of electrons during the reaction transforming one synthon into another.
In vitro release of chloramphenicol from poly[N-(2-hydroxypropyl)methacrylamide] carriers by Cathepsin B
Authors: Ulbrich Karel , Nazarova Olga , Panarin Eugenii , Baudyš Miroslav , Solovskii Michail V.
Published: June 2010

It has been shown in recent years that copolymers of N-(2-hydroxypropyl)methacrylamide may be used as targeted polymer drug carriers. The wide-spectrum antibiotic chloramphenicol has been bound to these carriers by means of biodegradable oligopeptidic sequences. The rate of drug release from the carrier in aqueous buffer solutions pH 7·4 and 6·0 was measured and the rates were compared with that of the enzymatic drug release from the carrier by means of the enzyme Cathepsin B. It was shown that the active drug may be released from the carrier by simple hydrolysis or by acting with an enzyme and that the rate of drug release depends on the structure of the oligopeptidic sequence which acts as a link between the drug and the polymer. The results obtained may be employed in the synthesis of a polymer compound potentially possessing antimicrobial activity.
Synthesis of the carboxy-terminal octapeptide of cholecystokinin (CKK-8) based on incorporation of O4-sulfotyrosine by enzymatically catalyzed formation of peptide bonds
Authors: Čeřovský Václav , Hlaváček Jan , Slaninová Jiřina , Jošt Karel
Published: June 2010

Papain-catalyzed condensation of sodium salt of tert-butyloxycarbonyl-β-tert-butyloxyaspartyl-O4-sulfotyrosine (fragment 1-2) with methionyl-glycyl-tryptophyl-methionyl-aspartyl-phenylalanine amide (fragment 3-8) has been elaborated. Deprotection of the thus-obtained octapeptide afforded CCK-8 which exhibited full biological activities. Benzyloxycarbonylaspartyl-phenylalanine amide (fragment 7-8) was prepared using thermolysin without protecting the aspartic acid side chain. Attempted condensation of tert-butyloxycarbonylmethionyl-glycyl-tryptophan (fragment 3-5) with methionyl-aspartyl-phenylalanine amide (fragment 6-8), catalyzed by α-chymotrypsin, subtilisin or proteinase K, afforded the product (fragment 3-8) in only low yields. Further use of proteolytic enzymes for preparing other peptide fragments of the CCK-8 molecule without side chain protection is investigated.
An alternative model of the vibronic coupling in octahedral complexes
Authors: Breza Martin , Pelikán Peter
Published: June 2010

It is suggested that for some transition metal hexahalo complexes, the Eg-(a1g + eg) vibronic coupling model is better suited than the classical T2g-(a1g + eg) model. For the former, alternative model, the potential constants in the analytical formula are evaluated from the numerical map of the adiabatic potential surface by using the linear regression method. The numerical values for 29 hexahalo complexes of the 1st row transition metals are obtained by the CNDO/2 method. Some interesting trends of parameters of such Jahn-Teller-active systems are disclosed.
The determination of Cu, Ni, and Co using 2-(2-pyridylazo)-1-naphtol-4-sulfonic acid by multicomponent flow injection analysis (MC-FIA)
Authors: Doležel Petr , Kubáň Vlastimil
Published: June 2010

2-(2-Pyridylazo)-1-naphthol-4-sulfonic acid (1PAN4S) was used to develop a method for the simultaneous spectrophotometric determination of Cu(II), Ni(II), and Co(III) by reverse flow injection analysis (FIA) using a multichannel UV-VIS detector with a diode array. The method can be used to determine the individual ions in the range 5-50 μmol dm-3 Ni(II) or Cu(II) and 5-60 μmol dm-3 Co(III) in binary and ternary mixtures at ratios of 1 : 1 to 1 : 10 with a maximal relative deviation of units of per cent for the major components and tens of per cent for the minor components. The precision and accuracy of the determination are the same or slightly worse than for stationary measurements with half to one fifth the sensitivity. Measurement of the absorption spectra for the maximum analytical signal in digital form for c(1PAN4S) = 0·12 mmol dm-3, c(NaIO4) = 1·2 mmol dm-3 in 0·2M acetate buffer medium at pH 5·00 permits rapid determination (15 s per sample) of all the components using a simple program for multicomponent analysis in "overdetermined" systems.
Analytical description of the solid phase particle distribution in a mechanically agitated system
Authors: Sýsová Marie , Fořt Ivan , Kudrna Vladimír
Published: June 2010

A mathematical model of the solid particle random motion in a turbulent liquid flow was developed which resulted in an unconventional form of diffusion equation. The diffusion equation derived describes quantitatively the local extremes of the solid phase concentrations in the charge mixed which were verified experimentally. The comparison of the experimental and calculated distribution of local concentrations in the system shows an adequate qualitative agreement. The system consisted of a cylindrical conical-bottomed vessel with baffles and cylindrical draft-tube. A six-blade impeller with inclined (at α = 45° plane blades was used for agitating.
Transport properties of porous γ-alumina from diffusion in liquids and gases
Authors: Uchytil Petr , Schneider Petr
Published: June 2010

Transport characteristics of four porous samples with bidisperse or broad monodisperse pore structure were determined by combination of diffusion and permeation measurements with simple gases and compared with results obtained from diffusion of toluene or α,α,α-trifluorotoluene in cyclohexane in liquid phase. From comparison of both types of results it followed that all pores are decisive for the rate of diffusional transport in liquids, whereas only the wide transport pores are significant in gas diffusion.
Dialysis experiments with asymmetric cellulose acetate membranes
Authors: Schwarz Hans-Hartmut , Lukáš Jaromír , Vacík Jiří
Published: June 2010

Cellulose acetate membranes for ultrafiltration produced by phase inversion have an asymmetric structure in the cross-section. In spite of this assymetry it is possible to characterize such membranes by dialysis. The asymmetry has no influence on the permeability for solute poly(oxyethylene). The membrane structure was varied systematically by annealing. The influence of solution concentration, dialysis time and temperature was also investigated. Statements are made on the annealing influence. A relationship between diffusion permeability and the true rejection is discussed.
Kinetics of alkaline hydrolysis of 3,4-thiophenedicarboxylic acid monomethyl ester in aqueous-nonaqueous media
Authors: Benko Ján , Vollárová Oľga
Published: June 2010

The kinetics of alkaline hydrolysis of 3,4-thiophenedicarboxylic acid monomethyl ester has been studied in mixed solvents water-methyl alcohol, water-tert-butyl alcohol, and water-dioxane. The specific effects causing different courses of these dependences have been evaluated. The greatest changes in the thermodynamic activation parameters have been observed in the medium of water-methyl alcohol.
Uv-light- and radiation-initiated addition of acetaldehyde to allyl alkanoates
Authors: Liška František , Valenta Miroslav , Fikar Jiří , Jandová Martina , Pešek Miroslav , Trška Petr
Published: June 2010

UV-light- and γ-60Co-initiated addition of acetaldehyde to allyl formate (I) and allyl acetate (II) yielded the 1:1 adducts - 4-oxopentyl formate (III) and 4-oxopentyl acetate (IV), respectively, together with the 1:2 telomers - 7-formyloxy-4-formyloxymethyl-2-heptanone (V) and 7-acetoxy-4-acetoxymethyl-2-heptanone (VI). The initial radiation yields are: G(III) = 200·8, G(IV) = 211·3, G(V) = 39·5, G(VI) = 37·9. Base-catalyzed transesterification of oxopentyl alkanoates III and IV afforded 5-hydroxy-2-pentanone (XIV), the same reaction of dialkylalkanoates VI and VII gave 5-hydroxy-4-hydroxymethyl-2-heptanone (XV).
Synthesis of pyridazines via furan vinamidinium salts
Authors: Gracza Tibor , Arnold Zdeněk , Kováč Jaroslav
Published: June 2010

Reaction of 5-(N,N-dimethylamino)-2-furfurylidene-N,N-dimethyliminium bromide (I) with hydrazine affords 3-hydrazono-2,3,4,5-tetrahydro-6-methylenehydrazonopyridazine (III). 5-(N,N-Dialkylamino)-2-arylazofuran salts II react with the same reagent to give 3,6-disubstituted pyridazines V. The structure of the synthesized compounds was identified by 1H NMR and mass spectra.
Partial reduction of quinoxaline 1,4-dioxide derivatives with L-ascorbic acid
Authors: Nováček Libor , Nechvátal Miloslav
Published: June 2010

Partial reduction of quinoxaline 1,4-dioxide derivatives with L-ascorbic acid has been elaborated. Quinoxaline 1,4-dioxide, 2,3-dimethylquinoxaline 1,4-dioxide, 2-methylquinoxaline 1,4-dioxide and 2-(N-(2-hydroxyethyl)carbamoyl)-3-methylquinoxaline 1,4-dioxide afforded monoxides. In the monomethyl derivatives the more distant N-O bond is reduced. In addition to the monoxide, quinoxaline 1,4-dioxide afforded small amount of quinoxaline. Structures of all the compounds have been confirmed by 1H and 13C NMR spectroscopy.
Structure of penta-O-acetylsucroses formed by deacetylation of octa-O-acetylsucrose. Reaction of 2,3,4,6,6'-penta-O-acetylsucrose
Authors: Čapek Karel , Vydra Tomáš , Sedmera Petr
Published: June 2010

Chromatographic separation of penta-O-acetylsucrose fraction from deacetylation of octa-O-acetylsucrose by treatment with aluminium oxide impregnated by potassium carbonate gave 1',3,4,6,6'-penta-O-acetylsucrose (XII), 1,2,3,4,6-penta-O-acetylsucrose (XIII), and the prevailing 2,3,4,6,6'-penta-O-acetylsucrose (XIV). Reaction of compound XIV with two equivalents of p-toluenesulfonyl chloride in pyridine produced besides the 1'-O-p-toluenesulfonyl derivative XXI and 1',3',4'-tri-O-tosyl derivative XXII also 1',3'-di-O-tosyl derivative XXIII and 1',4'-di-O-tosyl derivative XX. 1',2-anhydro-(3,4,6-tri-O-acetyl-α-D-glucopyranosyl 6'-O-acetyl-3',4'-anhydro-β-D-ribo-hexulofuranoside) (X) and 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl 1,6-di-O-acetyl-3,4-anhydro-β-D-ribo-hexulofuranoside (VIII) were prepared from compound XXIII by two minutes boiling with 1M sodium methoxide, evaporation of the reaction mixture, and acetylation (method A). Compound XX gives under reaction conditions of method A 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl 1,6-di-O-acetyl-3,4-anhydro-β-D-lyxo-hexulofuranoside (IX) only. However, upon 24h boiling with 1M sodium methoxide, neutralization, evaporation, and acetylation of the reaction mixture (method B), we obtained 3,3',4,6,6'-penta-O-acetyl-1',2-anhydro-4'-O-methylsucrose (XXIV), 1',2,3,3',4,6,6'-hepta-O-acetyl-4'-O-methylsucrose (XXV), and 1',2-anhydro-(3,4,6-tri-O-acetyl-α-D-glucopyranosyl 3',4',6'-tri-O-acetyl-β-D-xylo-hexulofuranoside) (XXVI). Compounds XXV and XXVI are also formed by reaction of epoxide IX with sodium methoxide according to method B. Compound XXVI can be prepared by hydrolysis of the dianhydro derivative X followed by acetylation. A reaction mechanism for compound XXVI formation from the epoxide IX is proposed. It assumes an intramolecular opening of the oxirane ring in compound IX under formation of α-D-glucopyranosyl 1,3-anhydro-β-D-xylo-hexulofuranoside (XLVI). The 1'-O-tosyl derivative XXI reacts with sodium methoxide according to method B to give 3,3',4,4',6,6'-hexa-O-acetyl-1',2-anhydrosucrose (XXVIII), octa-O-acetylsucrose, and 2,3,3',4,6,6'-hexa-O-acetyl-1',4'-anhydrosucrose XL.
Empirical approach to description of solvent effect on processes in solutions: A review
Authors: Pytela Oldřich
Published: June 2010

The review summarizes and evaluates the empirical models used for description of effects of solvents and solvent mixtures on processes in solutions. Analyzed are the principles of application of the empirical relations and their theoretical basis. A survey is given about empirical parameters of individual solvents with respect to the model process and also about the parameters derived by mathematical-statistical treatment. Also analyzed is the relation between the individual parameter scales, and their physical meaning is evaluated. Furthermore the review gives a survey of relations with empirical parameters used for description of effects of individual solvents on processes in solutions and presents results of tests of selected equations with a set of 368 experimental data series. The Kamlet & Taft equation in the basic version (only with the π*, α, and β parameters), has been evaluated as the best one, the best parameter according to the STEPWISE procedure being the π* parameter by Kamlet & Taft and the BASITY parameter by Swain et al. The best fit has been found for the processes involving electronic excitation of molecules in absorption and fluorescence spectroscopy. The section concerning mixed solvents presents a survey of empirical models used for description of effect of changes in composition of solvent mixtures on processes in solutions. The testing with 29 data series has shown the practically advantageous properties of the relations based on application of the additional Gibbs function expressed by empirical linear expansion (Margules).
Certain problems with the application of stochastic diffusion processes for description of chemical engineering phenomena; Modelling of processes by means of stochastic differential equations
Authors: Kudrna Vladimír
Published: June 2010

The paper points at certain problems associated with direct use of stochastic differential equations for description of chemical engineering processes or with the use of corresponding diffusion equations. It is shown that on the basis of various definitions one can write down three types of stochastic differential equations which might, in principle, describe the same process. One of these types is at the same time equivalent to the classic transport equations common in chemical engineering. A method is described removing these inconsistencies.
Synthetic utilization of N-diformylmethylazoles: The preparation of 1-heteryl-4-nitropyrazoles
Authors: Král Vladimír , Kanishchev Mikhail Ivanovich , Semenov Viktor Vladimirovich , Arnold Zdeněk , Shevelev Svyatoslav Arkadievich , Fainzilberg Albert Aleksandrovich
Published: June 2010

1-Diformylmethyl-4-nitropyrazole serves to show the potential synthetic utilization of N-diformylmethylazoles as suitable synthons for building heterocyclic systems.
Synthesis of 2-methyl-3-(1-aryl-1H-tetrazol-5-yl)-1,8-naphthyridines
Authors: Mogilaiah Kaleru , Reddy Kamreddy Rajendar , Rama Rao Gurram , Sreenivasulu Bathula
Published: June 2010

2-Methyl-3-(1-aryl-1H-tetrazol-5-yl)-1,8-naphthyridines III have been synthesized by the reaction of 2-methyl-N-aryl-1,8-naphthyridine-3-carboxyamides (I) with phosphorus pentachloride and azidolysis of the resulting imidoyl chlorides. Structures of these compounds have been established by means of their elemental analyses and spectral data.
Preparation and some reactions of bis(2',3'-O-carbonyl-6-azauridine) 5',5''-carbonate
Authors: Drašar Pavel , Beránek Jiří
Published: June 2010

Reaction of 6-azauridine (I) with phosgene and hexamethylphosphoramide afforded the title compound II. Both its 2',3'-cyclic carbonate groups were selectively deblocked with methanolic sodium methoxide under preservation of the internucleoside carbonate bridge. The carbonate II was also converted into the 5',5''-carbonyloxybis(2,2'-anhydro) derivative III by heating with imidazole in N,N-dimethylformamide. Several analogues of II were prepared by reaction of 1,1'-carbonyldiimidazole with the corresponding nucleosides in N,N- dimethylformamide.
Irreversible (rational) thermodynamics of mixtures of a solid substance with chemically reacting fluids
Authors: Quang Nguyen Xuan , Samohýl Ivan , Thoang Ho Si
Published: June 2010

The method of rational thermodynamics of Truesdell's school (non-linear thermomechanics of continuum) has been applied to mixtures of a solid substance with chemically reacting fluids. The kinematics, balances, and stoichiometry in such mixtures are formulated, and constitutive equations are proposed involving the effects of diffusion, heat conduction, and long-term memory expressed by internal parameters. The final form of the constitutive equations has been obtained by applying the constitutive entropic principle of Coleman and Noll. The equilibrium in the mixture is discussed.
The limit of determination and the limit of nonzero information content
Authors: Eckschlager Karel
Published: June 2010

The limit of nonzero information content, which is the lowest result of quantitative determination that is accurate and precise enough to have nonzero information content, is suggested to serve as the lowest limit of applicability of an analytical method whose results involve a systematic error. The limit of determination at which the relative precision of results is σr = 10% can be used as the lowest limit of applicability of a method whose results are accurate.
Atropine and quinine ionic associates with some acid dyes
Authors: Souček Jan , Halámek Emil , Kysilka Roman
Published: June 2010

The formation of ionic associates of atropine and quinine with bromothymol blue, metanil yellow and cresol red was studied by extraction spectrophotometry. In aqueous solutions, formation of ionic associates was only observed for quinine with bromothymol blue; ionic associates of both dyes with all of the three dyes could be, however, studied by their extraction into chloroform. The conditional extraction constants were calculated for the equilibria involved. The ability of atropine, quinine and bromothymol blue to be extracted into chloroform was examined in dependence on pH and ionic strength of the aqueous phase. The pH1/2 value corresponding to 50% extraction recovery decreases with increasing ionic strength for quinine whereas for atropine the extraction recovery is only slightly affected by a higher ionic strength and for bromothymol blue the pH1/2 (E = 50%) value increases with increasing ionic strength.
Mathematical modelling of absorption with chemical reaction in liquid phase in a tray column
Authors: Kaspar Vladislav , Eckert Egon , Vaněk Tomáš , Marek Miloš
Published: June 2010

A methodology for the modelling and simulation of tray columns in which gas absorption is accompanied by a chemical reaction is suggested. The presented model is based on the concept of a non-equilibrium stage and the effect of chemical reaction is described by enhancement factors. Pseudo-enhancement factors are introduced for components in liquid phase which take part in the reaction but are not transferred through the gas-liquid interface. A method for calculation of these factors from enhancement factors of components in gas phase and reaction stoichiometry is suggested. The advantages of the so-called global approach to the solution of the system of non-linear algebraic equations forming the column model are shown; this approach enables simply to combine universal equations with specific equations valid for a particular case. An example of CO2 absorption into aqueous solution of K2CO3 and KHCO3 in a tray column illustrates the usefulness of the approach. The proposed model is compared with simplified models and models in which the concept of pseudo-enhancement factors is not included. The comparison proves the superiority of the presented model.
Kinetics of ammonia recovery from soda-plant liquor by burnt magnesite
Authors: Glaser Vladimír , Vídenský Jan
Published: June 2010

The kinetics of the reaction of a soda-plant liquor containing ammonium chloride and sodium chloride with softly burnt magnesite have been investigated using a modified distillation test. Evaluation of the kinetic data has shown that the reaction rate is controlled by the dissolution of the solid phase. The kinetic equation for this variant of reaction mechanism has been modified to obtain a form suitable for chemical engineering calculations. A procedure of determining the adjustable parameters of this equation is illustrated by treating the obtained experimental data.
Preparation of graft copolymers by the reaction of polymeric acyl chlorides with monohydroxy-terminated polymers: An introductory study
Authors: Horská Jitka , Stejskal Jaroslav , Kratochvíl Pavel , Jenkins Aubrey D. , Tsartolia Eugenia , Walton David R. M.
Published: June 2010

An attempt was made to prepare well-defined graft copolymers by the coupling reaction between acyl chloride groups located along the backbone chain and monohydroxy-terminated grafts prepared separately. The molecular weights and the parameters of heterogeneity in chemical composition of the products were determined by light scattering and osmometry. The determination of molecular characteristics revealed that the degree of grafting was low. The results therefore could not be confronted with a statistical model at this stage. The problems encountered in the synthesis, e.g., gel formation, and the data relating to the soluble products are discussed.