bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Simulation of the Flow Around a Circular Cylinder Following a Figure-8-Like Path
Authors: Baranyi La´szlo´
Published: March 2011

This numerical study investigates a circular cylinder placed in a uniform stream and moving along a slender figure-8 path. A 2D computational method based on the finite difference method was used. Two aspects were investigated separately: the effect of in-line amplitude of oscillation and the effect of the frequency ratio. Computations for varying amplitude values were carried out at Re = 150, 200 and 250. Time-mean and rms values of force coefficients yielded smooth curves and tended to increase with amplitude. When plotted against frequency ratio in the domain of 0.69 to 0.98 at Re = 250, a jump was found in the time-mean values of lift and torque. This was also present in the energy transfer curves, and positive and negative values were found. Limit cycle curves from before and after a jump were symmetric, mirror images, and quite complex. Vorticity contours also showed a mirror image pre- and post-jump. These results indicate the possibility of symmetry-breaking bifurcation.
Computational Fluid-Structure Interaction of DGB Parachutes in Compressible Fluid Flow
Authors: Pantano-Rubino Carlos , Karagiozis Kostas , Kamakoti Ramji , Cirak Fehmi
Published: March 2011

This paper describes large-scale simulations of compressible flows over a supersonic disk-gap-band parachute system. An adaptive mesh refinement method is used to resolve the coupled fluid-structure model. The fluid model employs large-eddy simulation to describe the turbulent wakes appearing upstream and downstream of the parachute canopy and the structural model employed a thin-shell finite element solver that allows large canopy deformations by using subdivision finite elements. The fluid-structure interaction is described by a variant of the Ghost-Fluid method. The simulation was carried out at Mach number 1.96 where strong nonlinear coupling between the system of bow shocks, turbulent wake and canopy is observed. It was found that the canopy oscillations were characterized by a breathing type motion due to the strong interaction of the turbulent wake and bow shock upstream of the flexible canopy.
Theoretical Stability Analysis of Self-Excited Vibration in a Thin Film Wrapped Around an Air-Turn Bar
Authors: Watanabe Masahiro , Hara Kensuke
Published: March 2011

This paper deals with a theoretical stability analysis of a self-excited vibration generated in a film wrapped around an air-turn bar. In this paper, firstly, vibration characteristics of the self-excited vibration are examined experimentally, and it is shown that two different types of self-excited vibration, which are low-frequency and high-frequency modes, occur in the film. Secondly, stability of the low-frequency mode is examined theoretically. A theoretical model of the film wrapped around the air-turn bar is developed. Basic equations of the air flow in the gap between the film and air-turn bar, and pressurized air flow inside the air-turn bar are derived. The characteristics equation of the system is derived from the basic equations of motion of the film coupled with the air flow. Instability condition in which the self-excited vibration occurs is shown as a function of air flow rate and tension applied to the film. Moreover, instability mechanism of the self-excited vibration is discussed based on the theoretical model.
An Analytical Study of the Dynamics of Pipes Conveying Fluid of Axially Varying Density
Authors: Giacobbi Dana , Semler Christian , Pai¨doussis Michael
Published: March 2011

This paper investigates the dynamics of a slender, flexible pipe, conveying a fluid whose density varies axially along the length of the pipe. Specific applications for this system have appeared in the mining of submerged methane crystals [1], but a general interest also exists due to more common situations in which fluid density changes along the length of the pipe, such as when a gas is conveyed at high velocity. Therefore, following a brief review of related work and of the well-established theory concerning pipes conveying fluid of constant density, the current problem is approached from an analytical perspective. In particular, a linear model describing the system is derived using a Hamiltonian approach, for the cases of (i) a pipe clamped at both ends and (ii) a cantilevered pipe, and results obtained using a Galerkin approach. Ultimately, it is shown that, in both the cantilevered and clamped-clamped cases, the behaviour of the system is similar to that of a pipe conveying fluid of constant density — that is, loss of stability by flutter and buckling respectively — save for two crucial differences. The first and most important is that it is the density at the discharging end which has the most significant effect on the critical flow velocities, rather than any other. Second, in the case of a cantilevered pipe, the magnitude of the density change can strongly influence in which mode the system loses stability, thereby also impacting the critical flow velocities. The specifics of both these effects are addressed in the paper.
Nonlinear Stability of a Fluid-Conveying Cantilevered Pipe With End Mass in Case of Horizontal Excitation at the Upper End
Authors: Furuya Hiroaki , Yamashita Kiyotaka , Yabuno Hiroshi
Published: March 2011

Nonplanar vibrations of a cantilevered pipe with an end mass is studied. We have already clarified the nonplanar vibrations with a single frequency component when the pipe conveys fluid whose velocity is slightly over the critical value, above which the lateral vibration of the pipe is self-excited due to the internal flow. Moreover, for the case that the upper end of the pipe is excited periodically in the horizontal direction, we have shown in the previous paper that the nonplanar limit cycle motions start complex spatial transients and settle down to stationary planar forced-excited vibration when the excitation frequency is near the nonplanar limit cycle frequency. The purpose of this paper is to examine the stability of the nonplanar pipe vibrations when the nonplanar self-excited pipe vibrations are subjected to the excitation at the upper end. A set of ordinary differential equations, which govern the amplitudes and phases of unstable mode vibration and contain the effect of excitation at the upper end are derived. Stability analysis of these equations clarifies the nonlinear interactions between nonplanar self-excited pipe vibrations and the forced excitation. Second, the experiments are conducted with a silicon rubber pipe conveying water, confirming the dynamic features of pipe vibrations for the horizontal excitation.
Science Signaling
Podcast: 8 March 2011
Authors: González-Gaitán Marcos , Jülicher Frank , VanHook Annalisa M.
Published: March 2011

Mathematical analysis reveals how a graded signal can induce a homogeneous response across a field of cells.
mTORC Acid Test
Authors: VanHook Annalisa M.
Published: March 2011

Amino acids induce signaling through mTORC2.
Netting Pancreatic Cancer Genes
Authors: Kiberstis Paula A.
Published: March 2011

A rare but deadly form of human pancreatic cancer harbors mutations in chromatin remodeling genes.
4-Aminoquinolines Active against Chloroquine-Resistant Plasmodium falciparum: Basis of Antiparasite Activity and Quantitative Structure-Activity Relationship Analyses
Authors: Hocart Simon J. , Liu Huayin , Deng Haiyan , De Dibyendu , Krogstad Frances M. , Krogstad Donald J.
Published: March 2011

Chloroquine (CQ) is a safe and economical 4-aminoquinoline (AQ) antimalarial. However, its value has been severely compromised by the increasing prevalence of CQ resistance. This study examined 108 AQs, including 68 newly synthesized compounds. Of these 108 AQs, 32 (30%) were active only against CQ-susceptible
Plasmodium falciparum
strains and 59 (55%) were active against both CQ-susceptible and CQ-resistant
P. falciparum
strains (50% inhibitory concentrations [IC
50
s], ≤25 nM). All AQs active against both CQ-susceptible and CQ-resistant
P. falciparum
strains shared four structural features: (i) an AQ ring without alkyl substitution, (ii) a halogen at position 7 (Cl, Br, or I but not F), (iii) a protonatable nitrogen at position 1, and (iv) a second protonatable nitrogen at the end of the side chain distal from the point of attachment to the AQ ring via the nitrogen at position 4. For activity against CQ-resistant parasites, side chain lengths of ≤3 or ≥10 carbons were necessary but not sufficient; they were identified as essential factors by visual comparison of 2-dimensional (2-D) structures in relation to the antiparasite activities of the AQs and were confirmed by computer-based 3-D comparisons and differential contour plots of activity against
P. falciparum
. The advantage of the method reported here (refinement of quantitative structure-activity relationship [QSAR] descriptors by random assignment of compounds to multiple training and test sets) is that it retains QSAR descriptors according to their abilities to predict the activities of unknown test compounds rather than according to how well they fit the activities of the compounds in the training sets.
Pharmacokinetic Interactions of Maraviroc with Darunavir-Ritonavir, Etravirine, and Etravirine-Darunavir-Ritonavir in Healthy Volunteers: Results of Two Drug Interaction Trials
Authors: Kakuda Thomas N. , Abel Samantha , Davis John , Hamlin Julia , Schöller-Gyüre Monika , Mack Rebecca , Ndongo Noella , Petit Wendy , Ridgway Caroline , Sekar Vanitha , Tweedy Sarah , Hoetelmans Richard M. W.
Published: March 2011

The effects of darunavir-ritonavir at 600 and 100 mg twice daily (b.i.d.) alone, 200 mg of etravirine b.i.d. alone, or 600 and 100 mg of darunavir-ritonavir b.i.d. with 200 mg etravirine b.i.d. at steady state on the steady-state pharmacokinetics of maraviroc, and vice versa, in healthy volunteers were investigated in two phase I, randomized, two-period crossover studies. Safety and tolerability were also assessed. Coadministration of 150 mg maraviroc b.i.d. with darunavir-ritonavir increased the area under the plasma concentration-time curve from 0 to 12 h (AUC12) for maraviroc 4.05-fold relative to 150 mg of maraviroc b.i.d. alone. Coadministration of 300 mg maraviroc b.i.d. with etravirine decreased the maraviroc AUC12by 53% relative to 300 mg maraviroc b.i.d. alone. Coadministration of 150 mg maraviroc b.i.d. with etravirine-darunavir-ritonavir increased the maraviroc AUC123.10-fold relative to 150 mg maraviroc b.i.d. alone. Maraviroc did not significantly affect the pharmacokinetics of etravirine, darunavir, or ritonavir. Short-term coadministration of maraviroc with darunavir-ritonavir, etravirine, or both was generally well tolerated, with no safety issues reported in either trial. Maraviroc can be coadministered with darunavir-ritonavir, etravirine, or etravirine-darunavir-ritonavir. Maraviroc should be dosed at 600 mg b.i.d. with etravirine in the absence of a potent inhibitor of cytochrome P450 3A (CYP3A) (i.e., a boosted protease inhibitor) or at 150 mg b.i.d. when coadministered with darunavir-ritonavir with or without etravirine.
Novel Mutations in a Patient Isolate of Streptococcus agalactiae with Reduced Penicillin Susceptibility Emerging after Long-Term Oral Suppressive Therapy
Authors: Longtin Jean , Vermeiren Christie , Shahinas Dea , Tamber Gurdip Singh , McGeer Allison , Low Donald E. , Katz Kevin , Pillai Dylan R.
Published: March 2011

Penicillin nonsusceptibility has been demonstrated in group B streptococci (GBS), but there is limited information regarding mechanisms of resistance. We report a case of GBS with reduced susceptibility to penicillin emerging after long-term suppressive oral penicillin therapy for a prosthetic joint infection. Molecular characterization of the isolate before and after long-term penicillin therapy revealed 5 mutations in the ligand-binding regions of PBP1a, -2a, and -2x not previously reported in GBS.
Preclinical Characterization of Naturally Occurring Polyketide Cyclophilin Inhibitors from the Sanglifehrin Family
Authors: Gregory Matthew A. , Bobardt Michael , Obeid Susan , Chatterji Udayan , Coates Nigel J. , Foster Teresa , Gallay Philippe , Leyssen Pieter , Moss Steven J. , Neyts Johan , Nur-e-Alam Mohammad , Paeshuyse Jan , Piraee Mahmood , Suthar Dipen , Warneck Tony , Zhang Ming-Qiang , Wilkinson Barrie
Published: March 2011

Cyclophilin inhibitors currently in clinical trials for hepatitis C virus (HCV) are all analogues of cyclosporine (CsA). Sanglifehrins are a group of naturally occurring cyclophilin binding polyketides that are structurally distinct from the cyclosporines and are produced by a microorganism amenable to biosynthetic engineering for lead optimization and large-scale production by fermentation. Preclinical characterization of the potential utility of this class of compounds for the treatment of HCV revealed that the natural sanglifehrins A to D are all more potent than CsA at disrupting formation of the NS5A-CypA, -CypB, and -CypD complexes and at inhibition of CypA, CypB, and CypD isomerase activity. In particular, sanglifehrin B (SfB) was 30- to 50-fold more potent at inhibiting the isomerase activity of all Cyps tested than CsA and was also shown to be a more potent inhibitor of the 1b subgenomic replicon (50% effective concentrations [EC
50
s] of 0.070 μM and 0.16 μM in Huh 5-2 and Huh 9-13 cells, respectively). Physicochemical and mouse pharmacokinetic analyses revealed low oral bioavailability (
F
< 4%) and low solubility (<25 μM), although the half-lives (
t
1/2
) of SfA and SfB in mouse blood after intravenous (i.v.) dosing were long (
t
1/2
> 5 h). These data demonstrate that naturally occurring sanglifehrins are suitable lead compounds for the development of novel analogues that are less immunosuppressive and that have improved metabolism and pharmacokinetic properties.
PER-7, an Extended-Spectrum β-Lactamase with Increased Activity toward Broad-Spectrum Cephalosporins in Acinetobacter baumannii
Authors: Bonnin Rémy A. , Potron Anaïs , Poirel Laurent , Lecuyer Hervé , Neri Rita , Nordmann Patrice
Published: March 2011

Acinetobacter baumannii
isolate AP2 was recovered from a bronchial lavage sample of a patient hospitalized in Paris, France.
A. baumannii
AP2 was resistant to all β-lactams, including carbapenems, and expressed the extended-spectrum β-lactamase (ESBL) PER-7, which differs from PER-1 by 4 amino acid substitutions. Compared to PER-1, PER-7 possessed higher-level hydrolytic activities against cephalosporins and aztreonam. The
bla
PER-7
gene was chromosomally located and associated with a mosaic class 1 integron structure. Additionally, isolate AP2 expressed the carbapenem-hydrolyzing oxacillinase OXA-23 and the 16S RNA methylase ArmA, conferring high-level resistance to aminoglycosides.
Oscillations of the enol form of 2,4-pentanedione during Belousov-Zhabotinskii reaction
Authors: Tkáč Ivan , Treindl Ľudovít
Published: March 2011

In the Belousov-Zhabotinskii oscillation reaction with 2,4-pentanedione and Mn2+ /Mn3+ redox catalyst, also the enol form of the substrate has an oscillating concentration. The decrease of the concentration of the enol form is due to its reaction with bromine and Mn3+ ions; its increase corresponds to the reestablishment of the keto-enol equilibrium, when the concentrations of bromine and Mn3+ ions are low. An oscillating time-course was observed also with the concentration of the intermediate product of the reaction, of 2,4-pentanedione with Mn3+ ions, probably an intermediate complex [Mn(III)-enol], which oscilated with a phase shift against Mn3+ ions.
(E-Z) Isomerization of α,β-unsaturated ketones
Authors: Vondrák Tomáš , Procházka Miloš
Published: March 2011

Thermodynamic parameters have been determined for the (E-Z) equilibria of title ketones X-CH=CH-CO-CH3(X = Cl, CH3, OCH3); the energy difference of the isomers calculated by the MO CNDO/2 method for optimum conformations is lower than ΔH by 7-8 kJ mol-1.
S-Substituted derivatives of 8-chloro-6-(2-chlorophenyl)-1-mercaptomethyl-4H-s-triazolo[4,3-a]-1,4-benzodiazepine; Synthesis and pharmacology
Authors: Vejdělek Zdeněk J. , Metyš Jan , Protiva Miroslav
Published: March 2011

Reactions of 7-chloro-5-phenyl-1,3-dihydro-1,4-benzodiazepin-2-thione (XVIII) and its 5-(2-chlorophenyl) analogue XIX with hydrazines of methylthio-, ethylthio-, cyclohexylthio-, phenylthio-, 4-tolylthio-, 4-chlorophenylthio-, benzylthio-, S-(2-dimethylaminoethyl)thio-, 2-furfurylthio- and 3-pyridylmethylthioacetic acid in boiling butanol gave substance VII and the title compounds VIII-XVII. The synthesis of hydrazines XXVIII-XXXII is described. The compounds prepared are very little toxic, have strong discoordinating activity and are very potent as anticonvulsant agents. In this line they are substantially more active than alprazolam (II) and are not far behind triazolam (III).
Rearrangement of the 16,17-cyclopropano derivatives
Authors: Kohout Ladislav , Kasal Alexander , Šanda Vlastimil , Velgová Helena
Published: March 2011

Some reactions of the isomeric cyclopropano derivatives II and V leading to D-homo steroids are described and the mechanism of these reactions is discussed.
Immobilization of enzymes introducing spacers. A synthesis of carriers with spacers of various length
Authors: Flemming Christian , Gabert Anton , Wand Helmut , Zemek Jiří
Published: March 2011

A synthesis of spacers of various length and type, utilizing α,ω-dicarboxylic acids, α,ω-diaminoalkanes and succinic anhydride, condensation with carbodiimide, or introduction of -NCS functional groups is described. Carriers with a spacer were prepared by a method of binding the already synthesized spacer to the carrier (glass), and alternatively, by a stepwise synthesis of the spacer on the carrier surface. Carriers containing functional groups (37.2 - 39.3 μmol/g - NCS and 25 - 41.5 μmol/g - COOH) prepared in this way had total length of the spacer 0.62 - 3.92 nm. Whereas the length of the spacer is if no substantial importance for the reaction with low-molecular substances (L-valine, L-cysteine and 2-mercaptoethanol), the optimum length of the spacer for high-molecular compounds (albumin) is about 1.75 - 2.05 nm. The hydroxyl group adjacent to the functional group of the spacer (1,3-diaminopropan-2-ol) is also of noticeable influence.
Evaluation of the dependence of excess volume of the benzene-cyclohexane mixture on composition at 298.15 K from literature data
Authors: Cibulka Ivan , Holub Robert
Published: March 2011

The results of foregoing attempts in the literature to evaluate the mean dependence of excess volume of the benzene-cyclohexane mixture on composition at 298.15 K are summarized and a new equation for this dependence is presented. This equation is compared with the literature data.
Transport parameters of monodisperse porous catalysts
Authors: Fott Pavel , Petrini Guido , Schneider Petr
Published: March 2011

A method has been developed of evaluating the transport parameters of porous catalysts using the mean transport pore model (MTPM). The method has been based on combining results of permeation and diffusion measurements while taking into account the different reliability of results of both methods. The approach has been applied to six catalysts for the conversion of water gas with monodisperse pore distribution. Various simple gases have been used to test the MTPM, i.e. the independence of transport parameters on experimental conditions. The results have pointed at the shortcomings of estimating the mass transport in porous structures using pore distribution determined by conventional methods.
Some derivatives of 4-[(2-amino-6-hydroxy-4-oxo-3,4-dihydro-5-pyrimidinyl)methyl] benzoic acid
Authors: Kotva Rudolf , Vachek Jaroslav , Křepelka Jiří
Published: March 2011

Esterification of the title acid (I) gave esters II - VI. Halogenation of the acid I afforded its 5-chloro and 5-bromo derivatives, VII and VIII. Condensation of triesters XIV - XVII and of tetraester XVIII with guanidine, followed by hydrolysis, led to acids IX - XIII. Some of these compounds had a weak antineoplastic activity in animals with experimental transplantable tumours.
Oxygen cathodes based on carbon promoted with silver. I. Some electrochemical parameters of the electrodes
Authors: Musilová Miroslava , Wedell Martin , Mrha Jiří , Smrček Karel
Published: March 2011

A comparison of the electrochemical parameters of oxygen gas diffusion electrodes made of teflonized carbon black ( the hydrophobic component) and of a catalyst - consisting either of pure silver or silver promoted active carbon (the hydrophilic component) - enabled to investigate the influence of the silver presence in this type of electrodes. The characteristics obtained with the pure and air oxygen permitted, in combination with other measurements, to explain the role of the silver catalyst. It was found that this catalyst has a positive effect on the electroreduction of oxygen but that it also, due to its structural properties, influences in a negative way the distribution of the gas and electrolyte filled pores - which, in consequence, leads to gas transport problems in the active layer. Comparative measurements, carried out with electrodes on the silver-teflon basis have supported the assumption that both the above types of pores influence the transport processes in the active layer. The measurements showed also the advantages of the silver-teflon electrodes with pure oxygen, as well as, their disadvantages when air oxygen was used.
Phenazines from Streptomyces cinnamonensis
Authors: Tax Jiří , Sedmera Petr , Vokoun Jindřich , Urban Jiří , Karnetová Jaroslava , Stajner Karel , Vaněk Zdenko , Krumphanzl Vladimír
Published: March 2011

Phenazine-1-carboxylic acid (Ia) and 6-(3-methyl-2-butenyl)phenazine-1-carboxylic acid (IIa) were isolated from the mycelium of the strain Streptomyces cinnamonensis ATCC 15 413. Identification and structure elucidation were performed by spectroscopic methods. Both compounds weakly inhibit the growth of gram-positive bacteria.
Absorption, luminiscence, and polarisation spectra of 1,4-tetracenequinone
Authors: Gaš Bohuslav , Štěpán Václav , Titz Miloš , Kratochvíl Václav , Nepraš Miloš
Published: March 2011

Absorption electronic spectrum of 1,4-tetracenequinone has been interpreted on the basis of excitation polarisation spectrum of fluorescence and dichroism on oriented polyvinyl alcohol sheet. The theoretical spectrum has been obtained by the PPP method in the approximation of variable integrals βc and γ.
The reduction of cobalt (II) ion in thiocyanate media by pulse polarography
Authors: Bolzan Jorge Alfredo , Tokoro Robert
Published: March 2011

The electroreduction of cobalt(II) in aqueous thiocyanate solutions at the dropping mercury electrode depends on the thiocyanate concentration. At [SCN-] = 0.3 mol/l the intermediate cobalt(I)-thiocyanate complex does exist electrokinetically and may be responsible for the appearance of a peaked catalytic wave. The predecessor species of this intermediate may be CoSCN+ and Co(SCN)2 in similarity to the behaviour of cobalt(II) with cyanide and azide ions.
Chemical transformations of ethyl 3,5-dicyano-2,4,4,6-tetramethyl-1,4-dihydro-1-pyridyl acetate, sythesis of a new N-vinyl monomer
Authors: Paleček Jaroslav , Pavlík Manfred , Kuthan Josef
Published: March 2011

Ethoxycarbonyl group in the title compound I undergoes regioselective functional transformations to give the amide II and the carboxylic acid III. Reduction with lithium aluminium hydride gave the alcohol V whose p-toluenesulfonate was converted directly or via 2-iodoethyl derivative VIII into the N-vinyl monomer IX. Absorption molecular spectra of the synthesized compounds I-IX, as well as their fragmentation by electron impact, are discussed.
Preparation and antibacterial activity of di-, tri- and tetraoic acids derived from 3,4-secolupane
Authors: Valterová Irena , Klinot Jiří , Vystrčil Alois
Published: March 2011

Diacids XXIII and XXIV, triacid XXVII and tetraacid XVI were prepared from 3,4-secodiacid V and from nitrile XVII by modifying the isopropenyl groups in position 5 and 19. Procedures for selective esterification of the acids and the hydrolysis of their esters in position 3, 23 and 28 were elaborated and the methyl esters VII, XI, XII, XXVI, XXVIII, XXX and XXXI prepared. The structures of the derivatives prepared were confirmed by mass spectra. The antibacterial activity of the series of 3,4-secoacids derived from lupane and 19β,28-epoxy-18α-oleanane was also determined.
Effect of scale-up on rate of interfacial mass transfer in shallow-bed bubble column reactors
Authors: Rylek Milan , Svoboda Karel , Zahradník Jindřich
Published: March 2011

Absorption rates of CO2 into aqueous solutions of sodium hydroxide were measured in shallow-bed bubble columns with sieve trays as gas distributors. Experiments were carried out in two cylindrical columns (ID 0.15 and 0.30 m) and in a rectangular unit with square cross-section 1 m2. Liquid side mass transfer coefficients (kL) and specific interfacial area (a) were evaluated from experimental data of absorption rates. The effect of bubble-bed dimensions on mass transfer characteristics is discussed and recommendations for scale-up of bubble column reactors are presented.
Dipole moment of the intramolecular hydrogen bond. 2-Nitrophenol and its derivatives
Authors: Exner Otto , Koudelka Juraj , Vašíčková Soňa
Published: March 2011

Dipole moments of substituted 2-nitrophenols VIa-VIf and substituted 2-nitroanisoles VIIa to VIIf were measured in benzene and dioxan solutions. Infrared spectroscopy confirmed that nitrophenols VI exist either solvent and at different concentrations as non-associated molecules with an intramolecular hydrogen bond. Therefore, the difference between the experimental dipole moment and that calculated from group moments can be attributed to charge redistribution raised by the hydrogen bond. Only a minute part of it may be due to electron transfer through the ring (conjugation of the functional groups) as follows particularly from he comparison with nitroanisoles VII. Nevertheless, the charge transfer, expressed as the vector μH, amounts only 1.7 . 10-30 Cm (at an angle of 138° to the H-O bond), i.e. several times less than observed previously in compounds with more powerful hydrogen acceptors. CNDO/2 and MNDO calculations agree fairly with the gross dipole moments of the compounds investigated but are unable to predict μH, not even as far as its direction is concerned.
Deesterification mode of pectin by pectin esterases of Aspergillus foetidus, tomatoes and alfalfa
Authors: Kohn Rudolf , Markovič Oskar , Machová Eva
Published: March 2011

The effect of microbial pectin esterases (Aspergillus foetidus) and higher plants (tomatoes, alfalfa) on high-esterified pectin was investigated. Pectin derivatives of esterification degree E 42-66% were prepared by a partial deesterification catalyzed by the above-mentioned enzymes. The distribution pattern of free and esterified carboxyl groups in the linear pectin macromolecule was determined on the basis of activity coefficients of counterions γCa2+ as found in solutions of the proper calcium pectinates. The activity coefficients γCa2+ were compared with the corresponding γCa2+ values determined in pectins partially deesterified with alkali, with a random distribution pattern of free carboxyl groups. The plant pectin esterases under investigation lead to a block-wise arrangement of the free carboxyl groups in the pectin molecule, whereas A. foetidus pectin esterase cleaves randomly the ester groups in the same mode as do the alkali hydroxides. Significant differences were observed with final products of enzyme deesterification of pectin even in the selectivity of Ca2+ 2K+ cation exchange, as documented by the change of electrostatic free enthalpy of exchange of these cations. The different mechanism of action of plant and A. foetidus pectin esterases was thus unambiguously proved by a physico-chemical method.
A biospecific membrane sensor for the determination of sucrose
Authors: Macholán Lumír , Konečná Hana
Published: March 2011

The paper describes a rapid method for the biospecific determination of sucrose using an oxygen electrode of the Clark type or a platinum disc anode, the measuring part of which is coated by a thin film of invertase, mutarotase and glucose oxidase co-crosslinked by glutardialdehyde together with serum albumin. After injecting the sample into the reaction vessel the current corresponding to the decrease of the oxygen content or to the formation of hydrogen peroxide in the enzyme reaction layer is registered. The steady state electrode response is proportional to the concentration of sucrose within the range of 0.03 to 1.5 mmol . l-1 and is attained during 1-2 minutes with a reproducibility of 3-4%.
An approximate solution of transient diffusion through laminated membranes
Authors: Kubín Miroslav
Published: March 2011

Approximate relations have been derived for the initial transient diffusion through laminated membranes of the AB or ABC type for boundary conditions corresponding to the time-lag method. It is shown that in the initial stages of diffusion the behaviour of laminated membranes can be approximated by hypothetical simple membranes of the same thickness, the diffusion and partition coefficient of which can be determined from the corresponding characteristics (and thickness) of the constituent layers.
Kinetics and mechanism of hydrolysis of aryl N-methoxycarbamates and their derivatives
Authors: Mindl Jaromír , Štěrba Vojeslav
Published: March 2011

Hydrolysis kinetics have been studied of 3- and 4-substituted phenyl N-methoxycarbamates and their N-methyl derivatives in aqueous buffers at 60 °C. The N-methyl derivatives show linear dependence of the rate constants on concentration of hydroxyl ion in the pH range measured. Hydrolysis of aryl N-methoxycarbamates is independent of hydroxyl ion concentration at higher pH values. Logarithms of the rate constants have been correlated with the substituent constants σ. The calculated values 0.9 for N-methyl derivatives, 4.5 and 3.3 for aryl N-methoxy-carbamates in the region of linear pH-dependency and pH-independency, respectively, suggest that the hydrolysis follows the BAC2 and ElcB mechanisms in the case of the N-methyl derivatives and aryl N-methoxycarbamates, respectively. Difference between the two ρ constants for the hydrolysis of aryl N-methoxycarbamates agrees with the found value ρ = 1.2 for dissociation constants of these compounds. The elimination mechanism has been confirmed by reaction of the isocyanate formed with added aniline to give the respective urea.
Electrocapillary measurements at low concentrations of surfactants: Adsorption of tetrabutylammonium cation
Authors: Novotný Ladislav , Smoler Ivan , Kůta Jaroslav
Published: March 2011

Using drop-time technique with long drop-times achieved by means of a spindle-type capillary with the combination of a interrupted convection the surface tension data of tetrabutylammonium perchlorate in 0.1 mol l-1 NaClO4 in the concentration range 3 . 10-3 mol l-1 down to 10-7 mol l-1 could be measured. The corresponding adsorption parameters have been evaluated both from Langmuir (for Θ ⪬ 0.8) and Frumkin isotherm. The maximum energy of adsorption amounts to -48.1 kJ . mol-1. The dependence of E vs log c (Yesin-Markov plot) carried out in the concentration range 10-7 to 10-3 mol l-1 showed a S-shaped curve.
Determination of coupling constants of nitrogen in amino group of nitroanilines by means of relaxation times in rotating frame
Authors: Mlynárik Vladimír
Published: March 2011

One-bond coupling constants of amino nitrogen in 2-, 3- and 4-nitroanilines have been calculated on the basis of 1H and 13C relaxation times in rotating frame (T1ρ) which are affected by interaction with rapidly relaxing 14N nucleus. A method has been suggested and tested for calculation of 14N-13C couplings with elimination of effects of other relaxation mechanisms. Dependence of 1J(14N13C) on position of nitro group in the aromatic nucleus has been observed.
Oxidation of triamantane by sulphuric acid
Authors: Kafka Zdeněk , Vodička Luděk , Hájek Milan
Published: March 2011

The oxidation of triamantane by sulphuric acid was studied in various reaction conditions. 8-Triamantanone, 8,16-triamantanedione, and 15-hydroxy-8-triamantanone were isolated and identified as reaction products. The reaction was monitored and the purity of the compounds prepared was checked by gas chromatography and mass spectrometry, the position of the functional groups was determined by 13C NMR spectrometry.
Detection of electrode reactions intermediate products by electrochemical methods and study of their properties
Authors: Kozin L. F. , Lepesov K. K. , Nagibin S. N. , Kozina S. A.
Published: March 2011

It is shown that the rotating disc-ring electrode (R.R.D.E.) method may be used for the study of complexing reactions. Monovalent indium complex of the composition InCl32- has been determined as an example of the successful applicability of the R.R.D.E. techniques.
Digital polarograph-impedancemeters for frequency range of 10-3-10-5 Hz
Authors: Novitskii S. P. , Burenkov I. I. , Kenzin V. I. , Beck R. Yu.
Published: March 2011

Design, principal function and technical parameters of two polarograph-impendancemeters are given. The instruments are suitable both for analytical applications and for investigation of the kinetics and mechanism of electrode processes.
A conductivity detector for liquid chromatography with a cell volume of 0.1 μl
Authors: Kouřilová Danuše , Šlais Karel , Krejčí Miloš
Published: March 2011

A conductivity detector with a cell volume of 0.1 μl has been devised to fit glass micropacked columns with an inner diameter of 0.5 mm. D.c. current was used in the measurements, the voltage applied to the electrodes was 30 V. Organic acids separated in a reverse-phase system were detected; the minimum detectable concentrations were 6 . 10-7 - 1 . 10-5 mol l-1 according to the acid concerned and the composition of the mobile phase. The linear range of the detector is 400.
Application of the Crytur 20-15 Ca2+-selective electrode in volumetric analysis
Authors: Kalous Jaromír , Vytřas Karel , Terberová Alena
Published: March 2011

Some possibilities have been studied of application of the Crytur 20-15 Ca2+-selective electrode in volumetric analysis especially for determination of the compounds which react with calcium(II) salts to form precipitates or complexes. Titrations with standard calcium(II) nitrate solution have particularly proved useful for determination of aminocarboxylic acids, but sufficiently developed potentiometric titration curves have also been obtained in titrations of fluoride, oxalate and higher carboxylic acid anions (soaps). Also reliable results have been obtained in titrations of Ca2+ besides Mg2+ with standard EGTA solution.
Synthesis of diamantanedicarboxylic acids with the carboxy groups bonded at tertiary carbon atoms
Authors: Vodička Luděk , Janků Josef , Burkhard Jiří
Published: March 2011

The preparation of diamantanedicarboxylic acids with the carboxy groups at the tertiary carbon atoms of the diamantane skeleton is described. The procedure comprises bromination or oxidation of 1- and 4-diamantanecarboxylic acid and Koch-Haaf carboxylation of the reaction products. Of the four diamantanedicarboxylic acids synthesized, two - 1,4- and 1,7-diamantanedicarboxylic acids - have not been so far described.
4-Thia-5-cholesten-3-one and some further steroidal δ-thioenol lactones
Authors: Kasal Alexander
Published: March 2011

δ-Oxo acids VI-IX and XIV were converted to δ-thioenol lactones X-XIII and XV on reaction with phosphorus pentasulfide in pyridine. Under these conditions the ε-oxo acid XVI affords B-norsteroids XVII and XVIII. The proposed structures are confirmed by a number of physico-chemical data. The reduction of these thienol lactones with hydrides is also described.
Differential heats of dissolution of potassium nitrate in water at 298.15 K near the saturation concentration
Authors: Kolařík Stanislav , Pekárek Vladimír , Hostomský Jiří
Published: March 2011

Differential heats of dissolution of potassium nitrate in water at 298.15 K were measured on an 8 700 LKB calorimeter over a molality range 3-3.5 mol/kg. The dependence of the differential heat of dissolution, ΔLm (kJ/mol), on the molality can be described over the above range by the relation ΔLm = -33.933 + 3.635m. The value of the endothermic last dissolution heat obtained by extrapolation to the saturation concentration of 3.75 mol/kg was found to be -20.303 kJ/mol, with a standard deviation of 0.37 kJ/mol.
On separation of inductive and resonance effect
Authors: Ponec Robert
Published: March 2011

On the basis of minimization of the properly defined objective function, a general method for separation of inductive and resonance effect has been proposed. Comparison of the so calculated results with characteristics obtained independently by perturbation theory of substituent effect made it possible to discuss mechanism of the transmission of inductive effect in aromatic and aliphatic series.
Basicity of carbonfunctional organosilicon compounds and mechanism of the α effect
Authors: Ponec Robert , Kučera Jan , Chvalovský Václav
Published: March 2011

On the basis of decomposition of the protonation energy resulting from Longuet-Higgins theory of proton affinity, the significant stereospecific effect of silyl substituents that manifests itself in basicity trends in a series of carbonfunctional organosilicon compounds has been analysed.
On chemical form of Na+ ion in aqueous solutions
Authors: Čeleda Jiří
Published: March 2011

Experimental densities of mixed aqueous solutions of sodium and potassium salts have been compared with the densities calculated for various alternative models to show that Na+ ion (in contrast to bulkier cations K+, Rb+, Cs+) is present as a NaH2O+ particle analogous to hydroxonium ion H3O+. The experimental data also suggest that apparent molar volumes of ions in aqueous solutions depend on the degree of „filling" of the solution with the ion volumes, or otherwise, on volume fraction of the water left in the solution for formation of electrostatically bound hydration sheaths of the ions. The observed increase of apparent volumes of electrolytes with their concentration is due to degradation of these close-packed hydration sheaths with decreasing proportion of water in the system.
Molybdenum area and hydrogenation and hydrogenolytic activities of hydrorefining catalysts
Authors: López Rafael , Kraus Miloš
Published: March 2011

A series of nickel or cobalt promoted molybdenum catalysts and one nickel-tungsten catalyst have been studied by oxygen chemisorption on reduced oxidic samples, by activities of oxidic and sulphided samples for 1-hexene hydrogenation and by activities of sulphided samples for benzothiophen and pyridine hydrogenolyses. A good correlation was obtained between oxygen chemisorption and hydrogenation activity on oxidic, partially reduced, forms of the catalysts, and a limited correlation for activities of sulphided forms. Parallel activities for hydrogenation and hydrogenolyses were observed.
Pyrolysis of 2-acetoxycarboxylic acids
Authors: Galoci Ján , Procházka Miloš , Klinotová Eva
Published: March 2011

The pyrolysis of 2-acetoxycarboxylic acids may be described by the competing reactions R1R2C.(OCOCH3)COOH → (a) R1R2CO + CH3COOH + CO; (b) R1R2CO + CH3CHO + CO2; (c) CH3COOH + unsaturated acid. The formation of a carbonyl compound is the general character of the pyrolysis of this group of substances.
Etude des interactions entre fonctions alcool et amine. Evolution thermique d'hydroxydes et de sels d'ω-trialkylammonio alcanols-1
Authors: Barbry Didier , Hasiak Bruno
Published: March 2011

The thermolysis of ω-hydroxyalkyltrialkylammonium hydroxides (Φ = 4-8) was investigated. Elimination to alkenol competes with substitution to amino alcohol; the hydroxy group can be alkylated into aliphatic ethers by an intermolecular process; the intramolecular cyclization into cyclic ethers is important only when ω = 4. Substitution reaction in amino alcohols is the main pathway for the thermolysis of ω-hydroxyalkyltrimethylammonium acetates (ω = 5, 6) and chloride (ω = 6).
The synthesis of some alcohols derived from 1,2,3,4-tetrahydroisoquinoline and from 1,2,3,4-tetrahydroquinoline
Authors: Ferles Miloslav , Šilhánková Alexandra , Kafka Stanislav , Taufmann Petr , Motáček Tomáš
Published: March 2011

Reduction of ethyl esters of ω-(1,2,3,4-tetrahydro-2-isoquinolyl)alkanoic acids IVa-e by means of LiAlH4 was used for the preparation of corresponding primary alcohols Ia-e. 6-(1,2,3,4-Tetrahydro-2-isoquinolyl)-1-hexanol (Ie) was also obtained on reduction of ester amide VII. Reduction of 2-(2-hydroxypropanoyl)-1,2,3,4-tetrahydroisoquinoline (V) with LiAlH4 gave secondary alcohol II; in the quinoline series alcohol IIIa was obtained in a similar manner by reduction of ethyl 3-(1,2,3,4-tetrahydro-1-quinolyl)propanoate (IIIb).
Stereochemistry of epoxidation and hydroboration of some 4,4-dimethyl-A-homo-5-cholestene derivatives
Authors: Velgová Helena
Published: March 2011

Stereochemistry of epoxidation and hydroboration of some 3-substituted 4,4-dimethyl-A-homo-5-cholestene derivatives was studied. These reactions afforded predominantly products of addition from the less hindered β-side of the cyclic system. Reduction of the 5β,6β-epoxide ring in the 3β-acetoxy derivative IV led to product of diaxial opening, i.e. the 3β,6β-diol VII, whereas in the case of the 3α-acetoxy derivative XIV the reductive as well as alkaline opening of the 5β,6β-epoxide afforded product of 5(O)n participation of the 3α-substituent, i.e. the 3α,5α-transannular epoxide XV.
Reduction of glycosylnitromethanes to glycosylmethylamines with ferrous salts
Authors: Petruš Ladislav , Mihálov Vincent
Published: March 2011

Reduction of β-D-galactopyranosylnitromethane, β-D-glucopyranosylnitromethane and 1-deoxy-1-nitro-D-glycero-L-manno-heptitol with ferrous hydroxide afforded β-D-galactopyranosylmethylamine (I), β-D-glucopyranosylmethylamine (II) and 1-amino-1-deoxy-D-glycero-L-manno-heptitol (III), respectively. Thanks to the high conversion of the nitro derivatives and the simple isolation, this method is very suitable for preparation of glycosylmethylamines. The structure of products in their underivatized form was proved by mass spectrometry.
The synthesis and reactions of arylfurocondensed derivatives
Authors: Krutošíková Alžbeta , Kováč Jaroslav , Kraľovičová Eva
Published: March 2011

The preparation of new 9-arylfuro[2',3':4,5]pyrrolo[1,2-d]-1,2,4-triazolo[3,4-f]-1,2,4-triazines (V) and 7-aryl-1,4-dioxo-1,2,3,4-tetrahydrofuro[2',3':4,5]pyrrolo[1,2-d]-1,2,4-triazines (VII) from 2-aryl-4H-furo[3,2-b]pyrrole-5-carbohydrazides (I) is described. Reaction of I with triethyl orthoformate or acetate afforded 7-aryl-1,2-dihydrofuro[2',3':4,5]pyrrolo[1,2-d]-1,2,4-triazin-1-ones, or their 4-methyl analogues II giving with phosphorus pentasulfide thiones III, reacting with hydrazine to the corresponding hydrazides IV. Cyclization of IV with orthoformates, or orthoacetates led to V. Methylchloro formate reacted with I to yield N-methoxycarbonyl-2-aryl-4H-furo[3,2-b]pyrrole-5-carbohydrazides VI undergoing cyclization in an alkaline medium to VII.
Synthesis of pyridinium and picolinium salts of 5-nitro-2-vinylfuran having antibacterial properties
Authors: Végh Daniel , Kováč Jaroslav , Dandárová Miloslava , Briš Vladimír , Seman Milan
Published: March 2011

Quaternization of pyridine, 2-, 3-, or 4-picoline with (Z)-, or (E)-5-nitro-2-furylvinyl bromide is described and the addition-elimination mechanism of the nucleophilic substitution to yield the respective (Z)-, or (E)-vinylammonium salts is discussed.
11-(Dimethylaminoalkyl)-6,11-dihydrodibenzo[b,e]thiepin-11-carbonitriles and some related compounds
Authors: Šindelář Karel , Holubek Jiří , Ryska Miroslav , Svátek Emil , Urban Jiří , Protiva Miroslav
Published: March 2011

The title compounds II and III were obtained by alkylations of 6,11-dihydrodibenzo[b,e]thiepin-11-carbonitrile (I) with 2-dimethylaminoethyl chloride and 3-dimethylaminopropyl chloride in the presence of sodium hydride or sodium amide. Hydrolysis of the nitrile II with potassium hydroxide in ethanol resulted in a small amount of the amino acid X and in the amine XI as the main product. Alkylations of I with 1,2-dibromoethane and 1,3-dibromopropane in the presence of sodium hydride gave the bromoalkylnitriles IV and V and the alkylenebisnitriles XIII and XIV. The preparation of the methylpiperazinopropyl derivative VI proved the usefulness of compounds IV and V in the synthesis of further aminonitriles of this series. Alkylation of the nitrile I with 1,2-dibromoethane in the presence of sodium hydroxide or potassium carbonate and benzyltriethylammonium chloride afforded three isomeric nitriles C17H13NS: the vinyl derivative IX, the 6,11-ethano-6H, 11H-dibenzo[b,e]thiepin derivative XV and finally the 1a,11b-dihydro-1H,7H-dibenzo[b,f]cyclopropa[d]thiocin derivative XVI. Compounds II, III, VI and XII showed some spasmolytic effects but their central neurotropic activity is insignificant.
Calculation of the phase diagram for the system water-dimethyl sulphoxide
Authors: Horsák Ivan , Sláma Ivo
Published: March 2011

Liquidus curves of the phase diagram for the system water-dimethyl sulphoxide (DMSO) have been calculated in such a way as to give a good fit to experimental data for the phase diagram. The calculation is based on the assumption of an equilibrium chemical reaction yielding DMSO.3 H2O, and on the relation for the excess Gibbs energy in a ternary system composed of the two starting components and their compound. The data for the temperature dependence of the difference in the heat capacities of the liquid and solid phases of the pure components in the supercooling region have been obtained by extrapolation of experimental data in the case of DMSO, and for water by adopting published data measured down to -40 °C and by estimating their further trend.
Calcium tetra(4-chlorophenyl) borate complexes of some new macrocyclic polyetherdiamides and their membrane selectivity
Authors: Petránek Jaromír , Ryba Olen
Published: March 2011

Preparation of some new macrocyclic polyetherdiamides and their complexes with calcium and tetra(4-chlorophenyl) borate is described. The selectivities of these compounds for calcium with respect to ions of the other alkaline earth and alkali metals in poly(vinyl chloride) membranes plasticized with 2-nitro-1-octyloxybenzene are compared.
Thermal decomposition of magnesium sesquicarbide
Authors: Hájek Bohumil , Karen Pavel , Brožek Vlastimil
Published: March 2011

The structure of Mg2C3 and the course of its decomposition were studied. The powder X-ray diffraction patterns were analyzed to obtain the lattice parameters for hexagonal Mg2C3, a = 743.4 ± 0.5 pm, c = 1 056.4 ± 1.6 pm. Thermal decomposition data were obtained for temperatures 670-740 °C and pressure 130 Pa; they could be fitted satisfactorily by kinetic equations for various processes, including the 1 st order decomposition reaction, and so the controlling phenomenon of the reaction cannot be deduced based on the kinetic data. The 1 st order rate constants and reaction halflives were evaluated for various temperatures and approximated by the Arrhenius equation to calculate the parameters AA = 1.97 . 1014 s-1, EA = 333 kJ mol-1. The conditions of synthesis of Mg2C3 are discussed from the point of view of the choice of a suitable hydrocarbon for the reaction with magnesium. The thermal stability of the sesquicarbide increases with increasing pressure; it could be formed from dicarbide and sustained even at a temperature of 1 450 °C by applying a pressure as high as 6 GPa.