bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of the Tacticity of Poly(methyl methacrylate) by Hydrolysis Rate Measurements
Authors: Mikeš František , Pecka Jan
Published: June 2004

The rate of hydrolysis of poly(methyl methacrylate) increases with the content of meso(isotactic) diads in the polymer. The increase in the rate of hydrolysis of isotactic polymers is due to an intramolecular nucleophilic attack by the adjacent carboxylic ion on the carbonyl carbon atom in the ester group. An analysis of the content of sequences of variously arranged ester and carboxylic groups shows that the hydrolysis of s-poly(methyl methacrylate) is a random process, while i-poly(methyl methacrylate) is hydrolyzed gradually (by zip mechanism), starting from the carboxylate group formed by an external attack by hydroxylic ions. The kinetic data thus obtained cannot be interpreted in terms of a simple kinetic model. The tacticity of poly(methyl methacrylate) may be estimated from the dependence of the rate of hydrolysis on the content of meso diads determinated by NMR spectrometry. The rate of hydrolysis depends not only on the tacticity of the polymer, but probably also on its configurational sequence statistics.
Glucosylation of Some Steroidal 17-Hydroxy Derivatives
Authors: Černý Ivan , Pouzar Vladimír , Drašar Pavel , Havel Miroslav
Published: June 2004

Eight 17-monoglucosides derived from androst-5-ene-3,17-diol, 14β-androst-5-ene-3,17-diol, 5β-androstane-3,17-diol and estradiol derivatives differing in configuration in the positions 17 and 3, have been prepared. The silver silicate - catalyzed glycosylation with 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide gave 43-72% of the corresponding peracetylated β-D-glucopyranosides. The starting selectively protected 5β-androstane-3,17-diol derivatives were synthesized by a procedure utilizing orthogonality of the pivalate, acetate and nitrate protecting groups.
The Synthesis and NMR Study of 2,4-Diaryl-6-(fluoren-2-yl)pyridines
Authors: Hrabal Richard , Lhoták Pavel , Kurfürst Antonín
Published: June 2004

The reaction of 2-cinnamoylfluorene II with quaternary pyridinium salts IIIa, IIIb in the presence of ammonium acetate, gave 2-fluorenyl-2,6-diarylpyridines IV. The complete assignment of 1H and 13C resonances by 2D NMR methods is given.
(-)-Mitorubrinol and Phthaldehydic Acids, New Metabolites of Penicillium vermiculatum DANG.
Authors: Proksa Bohumil , Uhrín Dušan , Fuska Ján , Michálková Eva
Published: June 2004

Three new metabolites - (-)-mitorubrinol, 2-formyl-3,5-dihydroxy-4-methylbenzoic and 2-formyl-3,5-dihydroxy-4-hydroxymethylbenzoic acids - were isolated from the culture medium of Penicillium vermiculatum DANG. Hexane extract of the mycelium contained ergosterol and esters of fatty acids, linoleic, oleic and palmitic acids being the dominating ones.
Electrochemical Properties of Electrode Coatings Containing Highly Oxidatively Active Platinum Oxides
Authors: Hlavatý Jaromír , Volke Jiří
Published: June 2004

By time-programmed anodic and cathodic polarization (galvanostatic conditions and undivided cell) chemically stable coatings of hydrated higher valency platinum oxides were deposited from a 10% aqueous solution of alkali hydroxide saturated with PtO2 on platinum, nickel, titanium, iron and glassy-carbon electrode supports. Their voltammograms yield anodic and cathodic peaks over the whole pH region (0.15 to 13.20). The peaks corresponding to the transformation of higher valency platinum oxides are developed at more positive values (cathodic peaks between +0.57 and -0.35 V, and anodic peaks from +0.88 to -0.23 V vs SCE). The peaks corresponding to the transformations of PtO2 are located in a more negative region. Upon adding toluene or its derivatives their electrocatalytic oxidation over the whole pH region is intensified by increasing the temperature to 80 °C. The preparative coatings of hydrated platinum oxides prepared by the same technique on platinum grids were only deposited on a part of the electrode surface. The preparative electrolytic oxidation of toluene on these coatings leads only to low material yields: in 0.5 M H2SO4 it gives 4% benzaldehyde and in 0.25 M NaOH even less, i.e. 3%. The linear dependence of the increase of peak currents in voltammograms of coatings plotted as a function of the cathodic polarization potential (applied in the preceding preparation in strongly acidic media) points to a liberation of alkali metal cations intercalated in the coating of hydrated higher valency platinum oxides during their deposition.
Synthesis of o-Carboranylmethyl Ethers of Steroids as Potential Target Substrates for Boron Neutron Capture Therapy
Authors: Schneiderová Lenka , Štrouf Oldřich , Grüner Bohumír , Pouzar Vladimír , Drašar Pavel , Hampl Richard , Kimlová Irena
Published: June 2004

o-Carboranylmethyl ethers of steroids were synthesized by insertion of steroidal 2-propynyloxy derivatives into 6,9-bis(acetonitrile)decaborane (12). This reaction afforded compounds with estrane and androstane skeleton, potentionally useful in boron neutron capture therapy of hormone-sensitive forms of cancer: 17β-o-carboranylmethyl ether of estradiol IXb (yield 14%) and 3β- and 17β-carboranylmethyl ethers of androstenediol Vb and VIIb (yield 12% and 13%, respectively). Jones oxidation afforded carboranyl derivative of androsten-17-one VIb in 75% yield. As shown by a study of insertion of 3β-(2-propynyloxy)cholest-5-ene (IVa), the low yields of the insertion reaction cannot be increased by change in the reaction conditions. The relative binding affinity of compound IXb to estrogen receptor from rat uterine and human breast tumor cytosol was 3.0 and 0.29% respectively, of that of estradiol.
Preparation of 20R and 20S Acetylamino-30-norlupane Derivatives
Authors: Křeček Václav , Buděšínský Miloš , Vystrčil Alois
Published: June 2004

A series of epimeric pairs of 20R and 20S acetylamino derivatives VIII-XI have been prepared by reduction and subsequent acetylation of the oximes I, III, IV and VI. Their absolute configuration at C-20 (20R and 20S for the series a and b, respectively) has been suggested on the basis of their physical and spectral properties. The correctness of this assignment was confirmed by the synthesis of the acetylamino derivatives Xa and Xb from the acids XIIa and XIIb, respectively, with known configuration at C-20.
Quaternary Alkaloids from Thalictrum minus subsp. elatum (JACQ.) STOY. et STEFANOV
Authors: Slavík Jiří , Slavíková Leonora
Published: June 2004

Quaternary alkaloids berberine (chloride, 0.18%) and, after transformation into the iodides, magnoflorine (iodide, 1.06%), jatrorrhizine (iodide, 0.066%), thalphenine (iodide, 0.040%) and thalifendine (iodide, 0.021%) were isolated, after separation of the tertiary bases (0.38%) from the root of Thalictrum minus subsp. elatum (JACQ.) STOJ. et STEFANOV of Czechoslovak origin (1.8% alkaloid content). The aerial parts (0.013% alkaloids) in their quaternary fraction contain only negligible amounts of magnoflorine, berberine, and coptisine (which is the first time coptisine was found in the Thalictrum genus).
Antifungal Antibiotic from the Mushroom Agrocybe aegerita (BRIG.) SING.
Authors: Stránský Karel , Semerdžieva Marta , Otmar Miroslav , Procházka Želimír , Buděšínský Miloš , Ubik Karel , Kohoutová Jitka , Streinz Ludvík
Published: June 2004

An extract from a submersed culture of the mushroom Agrocybe aegerita (BRIG.) SING., containing antifungal antibiotic compounds was chromatographed on a silica gel column. Compounds from fractions which displayed the highest biological activity were concentrated and isolated by means of preparative thin-layer chromatography and preparative high-performance liquid chromatography, and were further characterized by means of gas chromatography, mass spectrometry and nuclear magnetic resonance. They are sesquiterpenic diols predominantly with an illudine skeleton. Structural formulae are proposed for some of them.
Amino and Deamino Analogs of 8-D-Homoarginin-vasopressin with Modified Tyrosine in Position 2: Synthesis and Some Biological Properties
Authors: Žertová Miroslava , Procházka Zdenko , Slaninová Jiřina , Škopková Jana , Barth Tomislav , Lebl Michal
Published: June 2004

Solid phase methodology on benzhydrylamine or p-methylbenzhydrylamine resin was used for the synthesis of seven analogs of amino or deamino vasopressin with non-coded amino acid, D-homoarginine, in position 8 and D- or L- O-methyl or O-ethyl tyrosine in position 2. [L-Tyr-(Me)2, D-Har8]vasopressin (I), [D-Tyr(Me)2, D-Har8]vasopressin (II), [L-Tyr(Et)2, D-Har8]vasopressin (III), [D-Tyr(Et)2, D-Har8]vasopressin (IV), [Mpr1, L-Tyr(Me)2, D-Har8]vasopressin (V), [Mpr1, D-Tyr(Me)2, D-Har8]vasopressin (VI) and [Mpr1, D-Tyr(Et)2, D-Har8]vasopressin (VII) were synthesized. All analogs have very low antidiuretic activity. Analogs containing O-methyltyrosine of D-configuration or O-ethyltyrosine of both D- and L-configuration are low pressor inhibitors. All analogs were found to be uterotonic inhibitors, the most potent one in vitro being [Mpr1, D-Tyr(Me)2, D-Har8]vasopressin (VI) with pA2 = 9.0 and [Mpr1, D-Tyr(Et)2, D-Har8]vasopressin (VII) with pA2 = 8.8.
Sequence Modification in Neurohypophyseal Hormones
Authors: Ježek Rudolf , Franc Jan , Slaninová Jiřina , Lebl Michal
Published: June 2004

Lysine vasopressin with tyrosine and phenylalanine interchanged was resynthesized in an attempt to explain recent results of biological testing of analogs modified in position 3. However, negligible activities found by Boissonnas and Guttmann in 1960 were only confirmed. The second analog, [Leu7,Pro8]dCOT-1, proved the positive influence of deamino and carba modifications on the biological activity of neurohypophyseal hormones. This analog was found to be very selective in its oxytocin-like activity.
Effect of Methanol on the Structure of Human Blood Serum Orosomucoid (Acid α1-Glycoprotein)
Authors: Karpenko Vladimír , Šinkorová Ludmila , Kodíček Milan
Published: June 2004

The effect of methanol (volume fraction 0-70%) on the optical properties of human blood serum orosomucoid (acid α1-glycoprotein) was studied over the pH range 5-12. The changes of these properties were correlated with the concept of three-dimensional arrangement of the orosomucoid molecule as obtained by a prediction study based on refined conformational preferences. From a complex analysis of the data obtained following conclusions on the orosomucoid structure in solution could be made: 1) α-helix content increases at constant pH with the methanol volume fraction exceeding 30%. 2) α-helix content at constant methanol concentration is maximal at pH 9-10. 3) The changes in conformation brought about by the presence of methanol result in the masking of 1 tyrosine and 1-tryptophan residue in 70% alcohol. It has been observed that the complex action of even the lowest alcohol leads to marked changes at the various levels of the three-dimensional organization of the orosomucoid molecule.
Numerical Simulation of the Generalized Maxwell-Stefan Model for Multicomponent Diffusion in Microporous Sorbents
Authors: Loos Jan-Baptist W. P. , Verheijen Peter J. T. , Moulijn Jacob A.
Published: June 2004

The results of simulations of transient multicomponent surface diffusion in a microporous adsorbent are given for various conditions. The generalized Maxwell-Stefan theory was applied to describe the diffusion phenomena. The diffusion equations were solved numerically. The transient uptake of a binary mixture and the counterdiffusion of two sorbate species in a slab were simulated. Some striking phenomena of multicomponent diffusion are presented. The relation to the approximate solution obtained by the linearized theory of multicomponent mass transfer is discussed. The simulations are compared with various results found in the literature.
IR Studies of Acid Properties of H-Boralites Activated at Various Temperatures
Authors: Datka Jerzy , Kawałek Marek
Published: June 2004

Four kinds of hydroxyls are present in H-boralite: 3450 cm-1 (Si-OH...O), 3670 cm-1 (B-OH), 3700-3720 cm-1 (Si-OH...B) and 3740 cm-1 (Si-OH). Only 3700-3720 cm-1 (Si-OH...B) hydroxyls are Bronsted acid sites. Their concentration, as well as the concentration of Lewis acid sites, was found to be independent of the activation temperature (in the range 473-873 K). On the other hand, both 3450 and 3670 cm-1 hydroxyls are very prone to dehydroxylation which starts at as low temperature as 473 K. This is due to a reaction: Si-OH + O(H)-B → SiOB + H2O. It has been found that the stretching frequency of Si-OH···B groups (Bronsted acid sites) depends on the activation temperature (3700 cm-1 at 573 K and 3720 cm-1 at 773 K) suggesting a variation of the properties of Bronsted sites with temperature. We explain it by the loss of Si-OHO and B-OH hydroxyls situated in close vicinity of Si-OH...B ones.
Influence of Substituting Al by Mg-Co and Mn-Co on the Properties of AlPO4-5
Authors: Changsheng Liao
Published: June 2004

Two kinds of crystalline microporous metal aluminophosphate molecular sieves, magnesium cobalt aluminophosphate (MgCoAPO-5) and manganese cobalt aluminophosphate (MnCoAPO-5), were synthesized by hydrothermal crystallization method in order to improve the surface acidity and catalytic activity of AlPO4-5. The results of X-ray diffraction, infrared spectra and chemical compositions of MgCoAPO-5 and MnCoAPO-5 indicate that Mg-Co or Mn-Co enter the framework of AlPO4-5 molecular sieve without disrupting the microporous framework. However, the results of catalytic studies show that MgCoAPO-5 and MnCoAPO-5 possess much higher surface acidity and catalytic activity than the unmodified AlPO4-5.
Studies of the Synthesis of Large VAPO-5 Crystals and Incorporation of Vanadium Ions
Authors: Kornatowski Jan , Sychev Mikhail , Baur Werner H. , Finger Gerd
Published: June 2004

The molecular sieve VAPO-5 has been synthesized hydrothermally in form of large crystals up to 660 μm in length. They have been used as a model substance for the study of vanadium incorporation into the framework. Our results show that vanadium was incorporated into the framework though in relatively small amounts. The results are in agreement with earlier findings for powder preparations of VAPO-5, except for the oxidation state of the vanadium ions and its stability. These conclusions agree with those arrived at previously for vanadium silicate KVS-5.
Structure and Shape-Selective Properties of MFI Type Ferrisilicates. A Comparison with Aluminosilicate Analogues
Authors: Wichterlová Blanka , Vorbeck Gert , Fricke Rolf , Richter-Mendau J. , Čejka Jiří
Published: June 2004

A comparison of H-forms of Fe- and Al-substituted silicates of MFI structure and of a comparable crystal size is given from the point of view of the acidity of SiOHMe groups, activity as well as para-selectivity in toluene disproportionation and toluene alkylation with ethylene. It has been found that SiOHFe groups exhibit weaker acidity than SiOHAl groups which is reflected in ammonia desorption at lower temperatures and lower toluene conversion for ferrisilicates. The ferrisilicates exhibit lower para-selectivity compared to aluminosilicates; moreover, higher coking is observed. While the aluminosilicates contain mostly aluminum in the framework sites forming SiOHAl groups, the ferrisilicates contain, beside Fe linked in SiOHFe groups, also tricoordinated Fe3+ cations or even extraframework Fe species. The latter two species can be responsible for a considerably higher coking of ferrisilicates compared to aluminosilicates. Simultaneously, such Fe species can contribute to observed lower para-selectivity of ferrisilicates in comparison with aluminosilicates, when they are located on the outer surface of zeolite crystals.
Formation of Reactive Clusters in Pd-Y Zeolite by Reduction-Reoxidation Treatment
Authors: Matsumoto Hiroshige , Tanabe Shuji
Published: June 2004

Preparation of a finely dispersed Pd-Y zeolite has been investigated by temperature-programmed reduction (TPR) and extended X-ray absorption fine structure (EXAFS) techniques. Upon the treatment by a sequence of calcination, reduction, and reoxidation, the original Pd(NH3)42+ ions in the zeolite transformed to reactive species, which were reduced with hydrogen at room temperature and characterized as small PdO clusters of about 25 Pd atoms.
Characterization of Mo-Containing Systems Supported on AlPO4-5 and Aluminium Phosphate and Their Behavior in Thiophene Conversion
Authors: Spojakina Alla A. , Kostova Nina G. , Dimitrov Ljubomir
Published: June 2004

The properties of AlPO4-5 with zeolite-like structure and amorphous aluminium phosphate modified by nickel and/or molybdenum (1 wt.% and 10 wt.%, respectively) have been studied using ESR and IR spectroscopy and catalytic testing in hydrodesulfurization (HDS) of thiophene. The chemical interaction between all components of catalysts with formation of polymolybdate structures is revealed. The impact of the support is reflected in the difference of composition of polymolybdates, and different interactions with the hydrogen sulfide eliminated in thiophene conversion. The selectivity of the thiophene conversion and adsorption of H2S eliminated depend on the method of introduction of components only for AlPO4-5.
Changes in Physico-Chemical and Catalytic Properties of Synthetic Erionite after Various Treatment
Authors: Hudec Pavol , Novanský Jozef , Bučinská Anna , Morávek Štefan , Židek Zdenek
Published: June 2004

Influence of decationization by ammonium ions and dealumination by HCl as well as calcination under self-steaming conditions at 1053 K with following treatment by ammonium ions or by HCl solution on the extent of alkali metals extraction was studied together with surface, sorption, acidic and catalytic properties of synthetic erionite. Samples were also characterized by X-ray diffraction spectra and IR skeletal vibration spectra. Results showed increasing catalytic activity and acidity after thermal treatment, followed by ion exchange with HCl or ammonium ions, which can be connected with deeper substitution of potassium cations of erionite. At the same time by the treatment under self-steaming conditions, as a result of framework dealumination, the zeolite obtained a secondary pore system, which resulted in increasing sorption capacity for aromatics, suppression of coking during o-xylene conversion and also increased diffusion of Hammet indicators into the zeolite.
Transalkylation of Benzene by the Fraction of Diisopropylbenzenes on ZSM-5 Zeolite Catalysts
Authors: Mravec Dušan , Schnierer Adrián , Riečanová Denisa , Herain Jiří , Macho Vendelín
Published: June 2004

The possibility of transalkylation of benzene by diisopropylbenzenes present in residual fraction from the production of cumene was tested on H-ZSM-5 zeolite catalysts. In this work the influence of: (i) the molar ration SiO2/Al2O3 in zeolites, (ii) reaction temperature, (iii) WHSV and (iv) the molar ratio of benzene and diisopropylbenzenes in the feed on the conversion and selectivity of the reaction were studied. The best yield of cumene was obtained at a temperature of 225 °C and WHSV = 1 h-1, at molar ratio benzene/ΣDIPB = 4 on the H-ZSM-5 zeolite with molar ratio SiO2/Al2O3 = 20.
The Templating Role of Cyclohexylamine in the Synthesis of Microporous Aluminophosphates
Authors: Zubowa Heide-Lore , Fricke Rolf , Kosslick Hendrik , Neissendorfer F. , Schreier E.
Published: June 2004

The investigation of the synthesis of AlPO4 molecular sieves from orthophosphoric acid and pseudoboehmite in the presence of cyclohexylamine shows that in this case the amine plays the role of template in the sense of "Template theory". The geometric shape of the template determines the dimensions of the channels within the AlPO4-lattices. The amount of template in the gel influences the void volumes, leading to different structures, however, with similar dimensions. The product composition is largely determined by the ratio amine/(Al,P)O2. The molecular sieves have been characterized by IR, X-ray, TG and DTA measurements.
Small Pore AlPO4/SAPO Structures Formed in Dependence on the Silicon Content of the Synthesis Gel
Authors: Girnus Irina , Löffler Elke , Lohse Ursula , Neissendorfer Frank
Published: June 2004

The synthesis of small pore AlPO4/SAPO molecular sieves (structures 14, 17, 18, 34) has been investigated at varying silicon content in the gel and with different kinds of templating agents. The samples were characterized by X-ray diffraction, adsorption, thermoanalysis and infrared spectroscopy. Independently of the kind of template at high silicon offer in the gel the crystallization of SAPO-34 is favoured whereas e.g. the formation of SAPO-17 is suppressed. Without silicon, AlPO4-18 is formed instead of AlPO4-34. The nature of template-framework interaction is discussed as a structure-directing factor.
The Adsorption of Iodide Anion on the Dropping Mercury Electrode in Water + 10% Ethanol Mixture
Authors: Pérez Oliva Luis , Carro Pilar , Hernández Creus Alberto , Morales José
Published: June 2004

The adsorption of iodide anion on the dropping Hg electrode from KI + KF solutions at a constant ionic strength in water and water + 10% ethanol mixture at 25 °C has been studied. Results show that I- adsorption is qualitatively similar in both systems. The adsorption equilibrium in both cases can be described through a Frumkin-type adsorption isotherm, although the corresponding parameters depend on the metal charge density and the solvent composition. In the presence of ethanol, the adsorption of I- ions decreases drastically. This fact appears to be mainly related to changes in the solvent structure, rather than due to the competitive adsorption of solvent molecules and I- anions.
The Kinetics of Electrode Reactions on Metallic Bismuth in Pure Molten Bismuth Chloride
Authors: Kisza Adolf , Każmierczak Jerzy
Published: June 2004

The relaxation and impendance methods were applied to the study of electrode reaction on bismuth electrode immersed in pure molten bismuth chloride. The found kinetic and activation parameters are compared with the similar ones for other pure molten chlorides.
A Simple Probabilistic Model of Bubble Column
Authors: Vašáková Jana , Čermák Jan
Published: June 2004

A probabilistic model of bubble column was derived from a deterministic model so that noncorrelated or autocorrelated noise was added at the column outlet. A pseudo-random binary series of maximum length - PRBS was used as input signal The effect of noise was observed in terms of impulse characteristics calculated by the correlation method from the responses of model to the PRBS input. The possibilities of PRBS when simulating the behaviour of bubble column were judged in the work, and the effect of magnitude of noise amplitude on the form of impulse characteristics was evaluated.
Synthesis of 1-[4-(3-Chloropropanoyl)phenyl]-2-phenylethanedione
Authors: Lukáč Ivan , Das Mohapatra Gour K.
Published: June 2004

1-[4-(3-Chloropropanoyl)phenyl]-2-phenylethanedione (I) was prepared by Friedel-Crafts acylation of (3-chloropropyl)benzene with phenylacetyl chloride, oxidation with SeO2 of the resulting 1-[4-(3-chloropropyl)phenyl]-2-phenyl-1-ethanone (IV) to 1-[4-(3-chloropropyl)phenyl]-2-phenylethanedione (V), and subsequent transformation of its benzyl CH2 group to carbonyl, via bromo (VI), acetoxy (VII) and hydroxy (VIII) derivatives.
Sesquiterpene Lactones of Ambrosia artemisiifolia L. and Ambrosia trifida L. Species
Authors: Błoszyk Ełżbieta , Rychłewska Urszula , Szczepanska Beata , Buděšínský Miloš , Drożdż Bohdan , Holub Miroslav
Published: June 2004

In addition to the already described peruvin (I), two further lactones, 3α-hydroxy-11αH,13-dihydrodamsin (II) and, 3α-acetoxy-11αH,13-dihydrodamsin (III), were isolated from aerial parts of species Ambrosia artemisiifolia L. The full structure of these lactones was derived from their NMR and CD spectra and the X-ray structural analysis of compound III. In the aerial part of Ambrosia trifida L. species coronopilin (V) and ivoxanthin (VI) were also identified.
The Analogs of 8-D-Homoarginin-vasopressin with O-Substituted Phenylalanine in Position 2: Synthesis and Some Biological Properties
Authors: Žertová Miroslava , Procházka Zdenko , Slaninová Jiřina , Barth Tomislav , Majer Pavel , Lebl Michal
Published: June 2004

Solid phase methodology on p-methylbenzhydrylamine resin was used for the synthesis of four analogs of vasopressin with the non coded amino acids, D-homoarginine (in position 8) and o-substituted L- or D-phenylalanine (in position 2). [L-Phe(o-Me)2,D-Har8]vasopressin (I), [D-Phe(o-Me)2,D-Har8]vasopressin (II), [L-Phe(o-Et)2,D-Har8]vasopressin (III) and [D-Phe(o-Et)2,D-Har8]vasopressin (IV) were synthesized. All analogs had very low antidiuretic activity. Analogs I and IV were low pressor inhibitors. All analogs were found to be the uterotonic inhibitors, the most potent on in vitro being [D-Phe(o-Et)2,D-Har8]vasopressin with a pA2 = 8.4.
Base Catalyzed Condensation of Thiobarbituric Acid with Some Aromatic Aldehydes
Authors: Popov-Pergal Katarina , Pergal Miroslav
Published: June 2004

In this paper the base catalyzed condensation reaction of 2-thiobarbituric acid with some aromatic aldehydes resulting in the formation of 5-arylidene-2-thiobarbituric acids is described. The condensation reaction of 2-thiobarbituric acid was carried out with 4-methoxybenzaldehyde, 4-ethoxybenzaldehyde, 4-benzyloxybenzaldehyde, and 1-naphthaldehyde using morpholine as a catalyst.
Does a Molecule Remember the Way It Was Energized?
Authors: Šolc Milan , Herman Zdeněk
Published: June 2004

Intramolecular vibrational redistribution (IVR) is the key phenomenon in unimolecular decomposition of polyatomic molecules energized in collisions, by photon absorption, or formed by association of radical particles. On an ultrashort time scale, the excitation energy is localized at some place (bond) of the molecule. On a middle time scale, energy irreversibly flows from the excited place to the rest of the molecule. On a long time scale fluctuations of the internal energy are reminiscent of a quasiperiodic process. Almost all the relevant experimental data and model calculations suggest that the information concerning the place of excitation in the molecule is lost during 100 fs - 10 ps after excitation. It seems that due to the rapid IVR the laser selective chemistry has in general no promising perspectives.
High Level ab initio Calculations on Acetylene Dimer - A Prototype for Estimation of the Accuracy of the Benzene Dimer Stabilization Energy
Authors: Hobza Pavel , Selzle Heinrich L. , Schlag Edward W.
Published: June 2004

High level ab initio calculations (up to MP4/DZ + (2df,2p)) on acetylene dimer permit the evaluation of a highly accurate stabilization energy of the dimer (5.9 kJ/mol) and hence serves as a test case for the error limit for lower level calculations. This error limit was employed to estimate the stabilization energy and enthalpy in the benzene dimer calculation. From this the theoretical value of formation enthalpy at 0 K (11.3 kJ/mol) is obtained which is larger than the corresponding experimental value (6.7 ± 2.1 kJ/mol).
Certain Problems with the Application of Stochastic Diffusion Processes for the Description of Chemical Engineering Phenomena. Relations between Different Types of Diffusion Equations
Authors: Kudrna Vladimír , Turzík Daniel
Published: June 2004

The dependence is discussed between the "clasical" diffusion equation commonly used in chemical engineering and the stochastic differential equations which describe this diffusion from the point of view of micromotion of individual particles. The resulting equations can be useful above all for the modelling of more complex diffusion processes.
17O NMR Spectra of Acylated Ureas and Thioureas
Authors: Jirman Josef , Pech Pavel
Published: June 2004

17O NMR spectra of ten acyl- and diacylureas (I-V) and thioureas (VII-X) were measured. 17O NMR chemical shifts of the ureido oxygen in the ureas range from 240 to 310 ppm, those of the acyl oxygens from 377 to 400 ppm (acetyl groups) and 359 to 389 ppm (benzoyl groups), the half-widths being tens to hundreds Hz. Acylation of urea to the diacyl stage has an almost twice as large effect on the chemical shift of the ureido oxygen than has the monoacylation. From the viewpoint of 17O NMR shifts, no significant differences has been found in the influence of ureido and thioureido groups on the transfer of electronic effects in 1,3-diacylureas and 1,3-diacylthioureas.
3-Alkyl-6-methyl-5,7-dioxo-4,5,6,7-tetrahydro-1,2,3-triazolo[4,5-d]pyrimidines and Their Alkylations
Authors: Bozóová Alena , Rybár Alfonz , Alföldi Juraj , Bašnáková Gabriela
Published: June 2004

Alkylation of 3-alkyl-6-methyl-5,7-dioxo-4,5,6,7-tetrahydro-1,2,3-triazolo[4,5-d]pyrimidines I with alkyl halides in dimethylformamide in the presence of potassium carbonate, or by analogous alkylation of sodium salts of compounds I afforded the respective 4-alkyl derivatives III but not 5-alkyloxy-3-alkyl-6-methyl-7-oxo-6,7-dihydro-1,2,3-triazolo[4,5-d]pyrimidines IV or isomeric 1,3-dialkyl-6-methyl-5,7-dioxo-4,5,6,7-tetrahydro-1,2,3-triazolo[4,5-d]pyrimidinium halides II.
The Structure and Photochromism of 2,4,4,6-Tetraphenyl-4H-thiopyran
Authors: Vojtěchovský Jaroslav , Hašek Jindřich , Nešpůrek Stanislav , Adamec Mojmír
Published: June 2004

2,4,4,6-Tetraphenyl-4H-thiopyran, C29H22S, orthorhombic, Pna21, a = 17.980(4), b = 6.956(2), c = 34.562(11) Å, V = 4323(2) Å3, Z = 8, Dx = 1.237 g cm-3, F(000) = 1696, λ(CuKα) = 1.54184 A, μ = 1.372 mm-2, T = 294 K. The final R was 0.050 for the unique set of 3103 observed reflections. The central 4H-thiopyran ring forms a boat conformation for both symmetrically independent molecules with average boat angles 4.4(3) and 6.8(3)° at S and C(sp3), respectively. The mean planes of phenyls at the position 2 and 6 are turned from the double plane of 4H-thiopyran by 42.5(5) and 35.8(3)°, respectively. The investigated material undergoes a photochromic change in the solid state after irradiation with UV light or X-rays. The maximum of the new absorption band is situated at 564 nm. The non-exponential time dependence of photochromic bleaching is analysed in terms of a dispersive first-order reaction.
Sorption of Lead by the Selective Ion Exchanger Ostsorb DETA
Authors: Svoboda Ladislav , Uhlíř Jan , Uhlíř Zdeněk
Published: June 2004

The properties of Ostsorb DETA, a selective ion exchanger based on modified bead cellulose with chemically bonded diethylenetriamine functional groups, were studied, and its applicability to the preconcentration of trace amounts of lead from aqueous solutions was verified. The conditions of the preconcentration procedure in the column and batch modes were optimized for this purpose. The results obtained were applied to the determination of lead in phosphoric acid.
Polyhedral Iridamonocarbaborane Chemistry. The Isolation and Characterisation of the Nine-Vertex closo-Type Species [(CO)(PPh3)2IrCB7H8] and the Partially Open Structures of Formally closo Nine-Vertex Clusters
Authors: Štíbr Bohumil , Kennedy John D. , Thornton-Pett Mark , Drdáková Eva , Jelínek Tomáš , Plešek Jaromír
Published: June 2004

Reaction of [Ir(CO)Cl(PPh3)2] with the [closo-CB7H8]- anion in dichloromethane solution at room temperature results in oxidative insertion into the cluster to give the novel nine-vertex closo-type species [(CO)(PPh3)2IrCB7H8] in 87% yield as a pale-yellow air-stable solid. Crystals (from hexane-benzene) are orthorhombic, space group P212121, with a = 1056.7(1), b = 1597.6(2), c = 2150.5(2) pm, and Z = 4. The crystal and molecular structure was refined to R (Rw) = 0.0244 (0.0250) for 3338 observed reflections with F0 > 4.0σ(F0). The cluster structure is based on a tricapped trigonal prismatic arrangement of the {IrCB7} atoms, with the iridium atom at a five-connected cluster-vertex position, and the carbon at a non-adjacent four-connected capping site. In this formally closo cluster, the distance between the two boron atoms that are bound to both iridium and carbon atoms is markedly long at 219.0(14) pm, an instance of a generally unrecognized phenomenon which is briefly discussed in the context of the other partially opened, though formally closo, nine-, ten- and eleven-vertex boron-containing cluster compounds.
Kinetics and Mechanism of Hexachloroiridate(IV) Oxidation of Arsenic(III) in Acidic Perchlorate Solutions
Authors: Hassan Refat M.
Published: June 2004

The kinetics of oxidation of arsenic(III) by hexachloroiridate(IV) at lower acid concentrations and at constant ionic strength of 1.0 mol dm-3 have been investigated spectrophotometrically. A first-order reaction in [IrCl62-] and fractional order with respect to arsenic(III) have been observed. A kinetic evidence for the formation of an intermediate complex between the hydrolyzed arsenic(III) species and the oxidant was presented. The results showed that decreasing the [H+] is accompanied by an appreciable acceleration of the rate of oxidation. The activation parameters have been evaluated and a mechanism consistent with the kinetic results was suggested.
Substituted 4-Benzylfuro[3,2-b]pyrroles
Authors: Krutošíková Alžbeta , Hanes Mikuláš
Published: June 2004

Preparation of 4-benzylfuro[3,2-b]pyrroles is described and their reactions with selected dienophiles are discussed. Utilization of 4-acetylfuro[3,2-b]pyrroles for preparation of 4-substituted derivatives of furo[3,2-b]pyrrole and the synthesis of ethyl 4-(2- and 4-nitrobenzyl)furo[3,2-b]pyrrole-5-carboxylates for fusing to a 1,4-diazepine system is presented.
New Phosgene-Free Procedure for Preparation of Methyl N-Phenylcarbamate and Dimethyl Diphenylmethane Dicarbamate as Important Precursors for Producing Iso- and Diisocyanates
Authors: Jakuš Vladimír , Bojsová Eva
Published: June 2004

Methyl N-phenylcarbamate was prepared by reductive carbonylation of nitrobenzene in the presence of methanol and a new catalytic system composed of sulfur, vanadium pentoxide and a base - alkoxides of alkali metals or hydroxides of alkali metals or alkali earths - in good yields. Reaction mechanism of this process is discussed. Diphenylmethane dicarbamates were obtained by acid-catalyzed condensation of methyl N-phenylcarbamate with formaldehyde. Concentrated and dilute sulphuric acids, dilute hydrochloric acid, a mixture of hydrochloric and sulfuric acids, and bentonite were the catalysts investigated. The influence of the catalyst used, the molar ratio of methyl N-phenylcarbamate (MPC) to formaldehyde, temperature and reaction time of yields of dimethyl 4,4'-diphenylmethane dicarbamate and its higher homologues was examined. The condensation products were analysed by high-performance liquid chromatography on reversed phases (RP-HPLC) with a favourable chemically bonded octadecyl stationary phase and a mixed mobile phase water-methanol.
Reaction of Dimethylaminoethyl Derivatives of 1-Benzylidenisoindolin-3-one with Epoxides
Authors: Proksa Bohumil , Steiner Bohumil , Uhrínová Stanislava , Koóš Miroslav
Published: June 2004

Derivatives of 1-(2-(2-dimethylaminoethyl)benzyliden)isoindolin-3-one underwent deamination on reaction with epoxides under mild conditions. Amide group of the substrate reacted slower with epoxide than the dimethylamino grouping whilst the alkanolamide was formed with a great excess of the epoxide only. Of epoxides used in this reaction 1,2-epoxy-3-phenoxypropane, 3-decyloxypropane and 3-chloro-1,2-epoxypropane, the first was found to react most rapidly.
A Conductance Investigation of Sulfamic Acid in Aqueous Solutions of Methanol, Ethanol and Isopropanol at 25 °C
Authors: Avranas Antonis , Terzoglou Vasiliki , Papadopoulos Nikos
Published: June 2004

The conductance of dilute solutions of sulfamic acid in water-methanol, water-ethanol and water-isopropanol mixture were measured at 25 °C. The experimental data were processed using the Lee and Wheaton equation to evaluate the limiting conductance Λ0 and association constant Ka. The lowest dielectric constant for each type of water-alcohol mixture was about 20.
The Hydrodynamic Oscillator and Its Use in the Investigation of Chemical Oscillators
Authors: Adamčíková Ľubica , Melichová Zuzana
Published: June 2004

Rules governing the hydrodynamic oscillator were studied with a view to using it in the examination of the coupling of two different chemical oscillators, in the periodical perturbation of the oscillatory system, or in the initiation of chemical oscillations by the self-regulating addition of one reactant to the other. The hydrodynamic oscillator can be employed in the study of the complex dynamic behaviour of chemical oscillators provided that the liquids used are not too viscous or that a vessel without a capillary is employed in order to maximally reduce the effect of viscosity.
Examination of Conditions for the Determination of Carbamate Pesticides in Soils
Authors: Tatarkovičová Věra , Stránský Zdeněk
Published: June 2004

The procedure for the determination of carbamate pesticides in soil was optimized. The following factors affecting the final results were investigated: extracting solvent, extraction procedure, extract purification procedure, and soil type. Triple extraction with acetone and purification of the extract on a two-stage purification column containing an activated carbon-silica gel 1+1 mixture were found optimal. The extracts after treatment were analyzed by RP-HPLC with UV detection. The method developed allows carbamate pesticides in soil to be determined at concentrations in excess of 30 μg kg-1.
Extraction of Selected Lanthanoids and Scandium with Bis(2-ethylhexyl)hydrogenphosphate in 1,1,2,2-Tetrachlorodifluoroethane
Authors: Sládek Petr , Navrátil Oldřich , Linhart Petr
Published: June 2004

A study was made of the extraction of Ce, Pm, Eu, Tm and Sc(III) from aqueous into organic medium of 1,1,2,2-tetrachlorodifluoroethane (CFC-112) using bis(2-ethylhexyl)hydrogenphosphate (HDEHP) as extracting reagent. On the basis of earlier work which demonstrated the usefulness of using this type of solvent for extractions with dibutylhydrogenphosphate (HDBP) and also the possibility of using CFC-112 for converting the metal chelates formed to the solid phase, the work was concentrated particularly on the dependence of the extraction of selected lanthanoids on the analytical concentration of HDEHP and also on the [H+] concentration. In addition the dimerization and distribution constants were determined for this reagent in a mixture of CFC-112 with benzene and the extraction constants were determined for the individual metals.
Synthesis of 2-Alkyl-1-allyl-3-arylsulfonyl-isothioureas
Authors: Hans Martin , Reinke Helmut , Schöffmann Thomas , Dehne Heinz , Olk Bernhard
Published: June 2004

2-Alkyl-1-allyl-3-arylsulfonyl-isothioureas III are not described in the literature. These compounds are valuable intermediate products for new potentially bioactive sulfonamide derivatives. The title compounds III can be prepared from 1-allyl-3-arylsulfonyl-thioureas I with monohalogen alkanes under alkaline conditions (method A) or from N-arylsulfonyl-iminothiocarbonic acid ester chlorides II with excess allylamine (method B).
Solid Phase Synthesis of a Somatostatin Amide Analogue Using Acid Labile t-Bumeoc Protection and an Acid Labile Anchor Group
Authors: Voelter Wolfgang , Breipohl Gerhard , Tzougraki Chryssa , Jungfleisch-Turgut Eveline
Published: June 2004

The solid phase synthesis of an amidated somatostatin analogue based on the principle of differentiated acidolysis is described. The acid labile and smoothly cleavable t-Bumeoc moiety (1% TFA/DCM) is used for temporary Nα-protection of D- and L-amino acids and [4-[[[9H-fluoren-9-yl-methoxycarbonyl]amino](4-methoxyphenyl)methyl]-2-methylphenoxy]acetic acid, attached to an aminomethylated polystyrene resin is used as acid sensitive linker of the solid carrier which releases the peptide in its amide form by treatment with TFA. Its preparation is described in detail.
Brassinosteroids with Ester Function with Five Carbon Atoms at the 20 Position
Authors: Kohout Ladislav , Strnad Miroslav
Published: June 2004

Pregnane analogues of brassinolide and castasterone have been prepared which have an ester function with five carbon atoms at the 20 position. When tested by the bean second internode bioassay, the most efficient substance is VIII.
Novel Synthesis of 4-Bromo-3-oxo-2-phenylhydrazonobutyronitrile and 4-Cyano-3-oxo-2-phenylhydrazonobutyronitrile: Synthesis of Pyridazine, Thiazole, 1,2,4-Triazine and Pyrido[2,3-e]-1,2,4-triazine Derivatives
Authors: Mohareb Rafat Milad , Abdel-Sayed Nadia Iskander
Published: June 2004

4-Bromo-3-oxo-2-phenylhydrazono-butyronitrile (II) reacted with thioamides to afford the thiazole derivatives III and VI. Compound II reacted with nucleophilic reagents to afford XIIIa and XIIIb. The reactivity of XIIIa with some chemical reagents was studied to afford pyridazine, thiazole, 1,2,4-triazine derivatives.
The Role of the Geometric Factor in Skeletal Rearrangements of Neohexane on Low-Index Surfaces of Ni and Pt Catalysts
Authors: Hejtmánek Vladimír
Published: June 2004

The steric demands of two types of adsorbed complexes of neohexane (2,2-dimethylbutane) on (100), (110) and (111) ideal surfaces of Ni or Pt catalysts were investigated with the aid of a computer. It was shown, that αγ complexes of the adsorbed noehexane were preferred in comparison to αβ ones for all studied surfaces. From the steric point of view, the feasibility of the adsorption depends on the complexity of the surface character in the following order: (111) < (100) < (110). Unfortunately, the experimentally observed discrepancies between the activity or selectivity in skeletal reactions on both types of catalysts could not be elucidated from our analyses.
Thermodynamic Functions of the Coordinated System Pb(II)-Oxalate
Authors: Rodríguez Placeres Jesús César , Ruiz Cabrera Graciliano Manuel , Alloza Moreno Ana María , Cuesta Sánchez Mariana
Published: June 2004

The coordinated Pb(II)-oxalate system has been polarographically studied in aqueous medium at 15, 20, 30 and 35 °C. The formation of the coordinated species [Pb(ox)] and [Pb(ox)2]2-, their stability constants and the values of the ∆G0, ∆H0 and ∆S0 have been determined.
Study of the Coordinated System Cd(II)-Valine-Valinate Ion
Authors: Rodríguez Placeres Jesús César , Alloza Moreno Ana María , Sosa Diaz Remedios , Ruiz Cabrera Graciliano Manuel
Published: June 2004

The polarographic method has been applied to the study of the coordinated systems Cd(II)-neutral valine and Cd(II)-valinate ion in aqueous medium and I = 1.0 mol l-1 (NaClO4). The stability constants of the complexes were determined as: [Cd(HV)]2+ (β10 = 7 ± 0.5), [Cd(HV)2]2+ (β20 = 24 ± 4), [Cd(HV)3]2+ [β30 = (1.5 ± 0.32) . 102], [Cd(V-)]+ [β01 = (4.1 ± 0.3) . 103], [Cd(V-)2] [β02 = (1.3 ± 0.2) . 107], [Cd(V-)3]- [β03 = (1.5 ± 0.3) . 109], [Cd(HV)(V-)]+ [β11 = (4.3 ± 0.8) . 104], [Cd(HV)(V-)2] [β12 = (1.7 ± 0.3) . 107] and [Cd(HV)2(V-)]+ [β21 = (1.2 ± 0.3) . 105].
Some Aspects of the Electroreduction of Niazid to Nicotinamide on Mercury Electrodes in Acidic Media
Authors: Marín Galvín Rafael , Rodríguez Mellado José Miguel
Published: June 2004

The electroreduction of niazid on mercury electrodes has been studied in acidic media (pH < 6). Tafel slopes and reaction orders were obtained at potentials corresponding to the foot of the first polarographic wave. On the basis of both polarographic and voltammetric results it has been shown that the waves appearing at more negative potentials correspond to the reduction of nicotinamide. Protonation of niazid plays an essential role in its reduction and pK values of 1.4, 3.2 and 11.5 were obtained by UV spectroscopy. The process corresponding to the first wave is irreversible, being the second one-electron transfer the rate determining step. Above pH 4 the process is complex due to the overlapping of the waves caused by the occurrence of protonation reactions.
Z-Isomers of Steroid 17β-Side Chain Methyl Acrylates
Authors: Pouzar Vladimír , Černý Ivan , Drašar Pavel
Published: June 2004

THP-Protected androstan-3-ol 17β-carboxaldehydes I-III with 3β,5-ene, 3β,5α, and 3α,5α respective arrangements, were transformed into corresponding methyl Z- and E-acrylates IVa-IXa. Peterson olefination by methyl trimethylsilylacetate gave mainly Z-isomers, whereas under conditions of Wittig-Horner reaction with trimethyl phosphonoacetate E-isomers were obtained in more stereoselective manner. THP-Ethers of methyl Z-acrylates IVa, VIa, and VIIIa were deprotected and from resulting 3-hydroxy derivatives IVb, VIb, and VIIIb the hemisuccinates IVd, VId, and VIIId and β-D-glucopyranosides IVf, VIf, and VIIIf were prepared.
1,3-Dipolar Cycloadditions of Aromatic Nitrile Oxides and Nitrones to 1,1'-(Methylenedi-4,1-phenylene)bismaleimide
Authors: Al-Timari Usama A. R. , Fišera Lubor , Prónayová Naďa
Published: June 2004

Within the scope of our research aimed at utilization of 1,3-dipolar cycloaddition reactions to heterocycles as well as to pesticide programme we report the 1,3-dipolar cycloaddition of nitrile oxides II, III and nitrones V to bis-maleiimide derivative I.
Phase Equilibria in the Water-Methyl Alcohol-Methyl tert-Butyl Ether-Ethylene Glycol System
Authors: Kubíček Vladimír , Matouš Jaroslav , Novák Josef P.
Published: June 2004

Liquid-liquid equilibria were measured at 20 °C in the W-MeOH-MTBE-EG quaternary system (W is water, MeOH is methyl alcohol, MTBE is methyl tert-butyl ether, and EG is ethylene glycol) and in the W-MeOH-MTBE, W-MTBE-EG and MeOH-MTBE-EG ternary systems. In the W-MeOH-MTBE-EG, W-MeOH-MTBE, and MeOH-MTBE-EG systems, the vapour-liquid equilibria at atmospheric pressure were also measured. The experimental data of the quaternary system were compared with those modelled by superposition of the Wilson and Redlich-Kister equations with the ternary term, whose parameters were determined based on the corresponding binary and, in some cases, ternary systems. A very good agreement was obtained for both the liquid-liquid and vapour-liquid equilibria.
Polarographic Behaviour and Physico-Chemical Characteristics of Some 5-Arylazopyrimidines of Biological Significance
Authors: Ismail Mohamed I.
Published: June 2004

The polarographic behaviour of a series of the title compounds has been investigated in aqueous alcoholic buffered media and in DMF-0.1M-LiClO4. A mechanism interpreting the electrode process was suggested and confirmed via the identification of CPE products, the use of models and the Hamett's σ-E1/2 relationship. The different physico-chemical characteristics of these compounds were also determined. A linear correlation was shown to exist between their redox potentials and spectroscopic data.
Preparation and Characterization of the High Molecular Weight [3H]Hyaluronic Acid
Authors: Chabreček Peter , Šoltés Ladislav , Hradec Hynek , Filip Jiří , Orviský Eduard
Published: June 2004

Two methods for the preparation of high molecular weight [3H]hyaluronic acid were investigated. In the first one, hydrogen atoms in the molecule were replaced by tritium. This isotopic substitution was performed in aqueous solution using Pd/CaCO3 as the catalyst. In the second method, the high molecular weight hyaluronic acid was alkylated with [3H]methyl bromide in liquid ammonia at a temperature of -33.5 °C. High-performance gel permeation chromatographic separation method was used for the isolation and characterization of the high molecular weight [3H]hyaluronic acid. Molecular weight parameters for the labelled biopolymers were Mw = 128 kDa, Mw/Mn = 1.88 (first method) and Mw = 268 kDa, Mw/Mn = 1.55 (second method). The high molecular weight [3H]hyaluronic acid having Mw = 268 kDa was degraded further by specific hyaluronidase. Products of the enzymatic depolymerization were observed to be identical for both, labelled and cold biopolymer. This finding indicates that the described labelling procedure using [3H]methyl bromide does not induce any major structural rearrangements in the molecule.