bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spectral and electrochemical study of coordination molecules Cu4OX6L4: 3-Methylpyridine and 4-Methylpyridine Cu4OBrnCl(6−n)L4 complexes
Authors: Ondrejovič G. , Kotočová A. 
Published: August 2006

AbstractThe tetranuclear Cu4OBrnCl(6-n)L4 complexes, where L = 3-methylpyridine (3-Mepy), 4-methylpyridine (4-Mepy) and n=0–6 with trigonal bipyramidal coordination of copper(II) were prepared and their infrared and electronic absorption spectra as well as cyclic voltammograms in nitromethane solutions were measured. The polyhedra in Cu4OBrnCl(6−n) (3-Mepy)4 molecules are less distorted comparing with those of 4-Mepy analogues as indicated by infrared Cu4O absorptions, far infrared Cu—Br, Cu—Cl, and Cu—N absorptions, d—d bands in electronic spectra and potentials, measured by cyclic voltammetry. The 3-Mepy complexes exhibit strong single infrared Cu4O absorptions, while for related 4-Mepy complexes doubly split Cu4O bands were observed. Two strongly overlapped d—d bands in electronic absorption spectra of the 3-and 4-Mepy complexes in nitromethane were resolved by Gaussian fitting. The 4-Mepy ligand produces slightly stronger ligand field than its 3-Mepy analogue. The maxima of high-energy d—d bands are in a linear correlation with the number of bromide ligands. The correlations for corresponding low-energy bands are considerably deviated from linearity. The halfwave potentials of the complexes in nitromethane correlate with both the number of bromides and the data of electronic absorption spectra suggesting that the reducing electron at the electrode process enters the half-filled d z 2 orbital of the copper(II) atom. The origin of a difference between the 3-and 4-Mepy complexes in their spectral and electrochemical properties is also discussed.
Anodic stripping voltammetric determination of lead and cadmium in soil extracts
Authors: Rúriková D. , Kudravá M. 
Published: August 2006

AbstractTwo single-step extraction procedures validated by BCR, extraction with 0.43 mol dm−3 acetic acid and 0.05 mol dm−3 EDTA, are used for assessing bioavailable species of Pb and Cd in soils. After an extensive study of interferences of humic substances and using standard additions procedures, the extractable contents of Pb and Cd have been determined by DPASV directly in soil extracts with a good reproducibility (RSD varied from 1.0 to 7.9 %). Pb(II) and Cd(II) were released from complex in EDTA extracts by pH adjustment to 1 with 1 mol dm−3 HCl. The results were compared with those obtained with atomic absorption spectrometry and indicated reasonable agreement of both methods. Exchangeable forms represented 0.2 to 3.3 % and 13.0 to 63.6 % of total content of Pb and Cd in soils, respectively. EDTA extraction released from soils 7.9 to 29.9 % and 33.5 to 59.6 % of total content of Pb and Cd, respectively.
Gold and silver determination in Waters by SPHERON® Thiol 1000 preconcentration and ETAAS
Authors: Medveď J. , Matúš P. , Bujdoš M. , Kubová J. 
Published: August 2006

AbstractA reliable procedure for the electrothermal atomic absorption spectrometry (ETAAS) determination of gold and silver in waters at trace level is described. The method is based on prior separation and preconcentration of the metals using a chelating sorbent SPHERON® Thiol 1000 after acidification of water samples (pH < 3) with nitric acid. Optimization of analytical variables during enrichment and ETAAS determination of the metals are discussed. The accuracy of the method is verified by analysis of certified reference materials. The limits of determinations based on 10 σ definition were 0.005 ng cm−3 for Au and 0.02 ng cm−3 for Ag. Precision of studied elements determination expressed by relative standard deviation varied in the range from 2.9 % to 16.4 %.
Syntheses, geometry optimization, and electronic structure of N-and C-substituted benzonaphthyridines
Authors: Deska M. , Śliwa W. 
Published: August 2006

AbstractSynthesis of N-and C-substituted derivatives of benzo[h][1,6]naphthyridine, bearing 2-hydroxyethyl group has been made by quaternization reaction and by condensation of corresponding methylbenzonaphthyridines with formaldehyde. For six derivatives of isomeric benzo[c][1,5]-, benzo[h][1,6]-, and benzo[f][1,7]naphthyridines the 13C NMR spectra are discussed.For ten compounds the geometry was optimized with the AM1 and, in one case also with the ab initio 6–31G method; their effective charge values have also been calculated.
Synthesis, spectral description, and lipophilicity parameters determination of phenylcarbamic acid derivatives with integrated N-phenylpiperazine moiety in the structure
Authors: Malík I. , Sedlárová E. , Csöllei J. , Andriamainty F. , Kurfürst P. , Vančo J. 
Published: August 2006

AbstractThe phenylcarbamic acid derivatives with N-phenylpiperazine moiety in the molecule have been prepared. The structure has been confirmed by elemental analysis, IR, 1H NMR, and mass spectral data. For the prepared set of the compounds the lipophilicity parameters have been determined. The experimentally obtained lipophilicity parameters have been correlated with theoretical entries obtained by different computer programs based on the neural network and fragmental methods.
New methods in synthesis of acetylcholinesterase reactivators and evaluation of their potency to reactivate cyclosarin-inhibited AChE
Authors: Musílek K. , Lipka L. , Račáková V. , Kuča K. , Jun D. , Dohnal V. , Doležal M. 
Published: August 2006

AbstractNine potential AChE reactivators were synthesized using modification of currently known synthetic pathways. Their potency to reactivate AChE inhibited by cyclosarin nerve agent was tested in vitro. According to the previous results, 1,4-bis(2-hydroxyiminomethylpyridinium)butane dibromide seems to be the most potent AChE reactivator. The reactivation potency of these compounds depends on structural factors such as presence of quaternary nitrogens, length of the linking chain between both pyridinium rings, and position of the oxime moiety at the pyridinium ring.
Furan-containing thiacyanine analogs and their antimicrobial activity
Authors: Kortišová I. , Foltínová P. , Halgaš J. 
Published: August 2006

AbstractCondensation of quaternary 2-methylbenzothiazolium bromides with 5-(dialkylamino)furan-2-carbaldehydes afforded a series of new thiacyanine analogs. The compounds exhibit significant activities against several bacterial, yeast, and mould strains. Derivatives with dipropylamino substituents showed higher inhibitory effects than those with cyclic secondary amino groups. Hence, the biological activity may have been influenced by the lipophilicity of the compounds. The effect on growth and on the plastid system of the unicellular flagellate Euglena gracilis was also studied.
Synthesis and biological activity of new 1,3,4-thiadiazole derivatives
Authors: Aly A. , El-Sayed R. 
Published: August 2006

AbstractThe aminothiadiazole (II) on treatment with aromatic aldehydes yielded Schiff bases, which cyclized to thiazolidinone derivatives by reaction with thioglycolic acid. Reaction of II with phenyl isocyanate and phenyl isothiocyanate afforded the carbamide and carbothiamide derivatives, respectively, which on reaction with malonic acid in acetyl chloride gave barbituric and thiobarbituric acid derivatives. However, reaction of carbon disulfide and methyl iodide with II gave dithiocarbamidate derivative which on treatment with ethylenediamine or o-phenylenediamine gave the condensed N-imidazolylthiadiazolylamine derivatives.
Synthesis and characterization of oligosalicylaldehyde-based epoxy resins
Authors: Sahmetlioglu E. , Mart H. , Yuruk H. , Surme Y. 
Published: August 2006

AbstractThe synthesis of a new epoxy resin of oligosalicylaldehyde by the reaction with epichlorohydrin is reported. New resin’s epoxy value and chlorine content were determined and found to be 25% and 1%, respectively. The characterization of the new resin was instrumented by FTIR, 1H NMR, scanning electron microscopy, and thermal gravimetric analyses. TGA results showed that the cured epoxy resin has a good resistance to thermal decomposition. The mass losses of cured epoxy resin were found to be 5%, 10%, 50% at 175°C, 240°C, and 400°C, respectively. On the curing procedure the resin was cured with polyethylenepolyamine at 25 °C for 8 h and 100°C for 1.5 h. The FTIR spectrum of new epoxy resin gave the peak of oxirane ring at ṽ = 918 cm−1.
Extracellular polysaccharides produced by acapsular mutant of Cryptococcus laurentii
Authors: Dudíková J. , Kolarova N. 
Published: August 2006

AbstractHeterogeneous extracellular polysaccharide galactoxylomannan has been isolated from the culture medium of the acapsulated mutant Cryptococcus laurentii 17-3-6 as the main extracellular polysaccharide (90%). Size-exclusion chromatography of precipitated polysaccharides afforded two molecular fractions with molecular mass 75 kDa and 20 kDa. Mannose, galactose, glucose, and xylose ratios were 1.00: 1.16: 0.04: 0.88 and 1.00: 0.25: 0.07: 0.24, respectively.
Liquid chromatography of synthetic polymers under limiting conditions of insolubility. I. Principle of the method
Authors: Berek D. 
Published: August 2006

AbstractA novel liquid chromatographic procedure is presented. It is based on differences in the transport velocities of the fast-moving, pore-excluded macromolecules and slow-progressing, pore-permeating small molecules of an auxiliary liquid. A barrier of small molecules selectively decelerates certain kind of macromolecules while other kind remains unhindered. As a result, polymers of different nature are efficiently separated. In this new approach, the barrier is formed by a zone of a non-solvent injected immediately before the sample solution. The resulting method is denoted liquid chromatography under limiting conditions of insolubility.
Transport velocities of different particulate materials in pneumatic conveying
Authors: Hartman M. , Phořelý M. , Trnka O. 
Published: August 2006

AbstractParticle horizontal transport and vertical entrainment of widely different materials (silica sand, alumina, ceramsite, dry sludge, and wood shreds) are explored by experimental measurements. Experiments have been performed with two very narrow fractions of solids (0.315–0.50 mm and 1.4–1.6 mm) on a laboratory setup. Simple empirical correlations are proposed in terms of the Reynolds and Archimedes criteria for the commencement of the horizontal conveying as well as the vertical entrainment of particles in pipelines.
Chemistry for the design and better understanding of cement-based materials and composites
Authors: Drábik M. , Gáliková L’. , Slade R. 
Published: August 2006

AbstractMacrodefect-free (MDF) materials are one example of “hot topics” in the field of cement-based materials and composites exerting new possibilities of the exploitation of added value. These are formed through cross-linking reactions of atoms at the interfaces of cement grains and functional polymers, when medium pressure and twin-rolling procedure are applied. The MDF-relevance of the system of Portland cement + polyphosphate is reported, together with optimal synthesis conditions and limiting rules. The chemistry knowledge about MDF materials has been shown critical for both procedure design and exploitation. Chemical shifts in both 27Al and 31P MAS NMR spectra confirm Al(6)—O—P(4) cross-linking in virgin probes and indicate secondary hydrolysis during moisture uptake in domains free of cross-links. Thermogravimetric identification of the contents of hydrated and cross-linked phases in virgin and in moisture-attacked MDF probes displays that moisture uptake is accompanied by an increase in content of cementitious hydrates and CaCO3. The key phenomena governing the moisture sensitivity/resistance are the density and compactness of interfacial Al(6)—O—P(4) cross-links vs. the access of the moist environment to the unreacted cement residue.
Surface modifications of natural clinoptilolite-dominated zeolite for phenolic pollutant mitigation
Authors: Chmielewska E. , Pilchowski K. 
Published: August 2006

AbstractA novel carbonized clinoptilolite-rich tuff was studied for phenol removal from water. Zeolite sample carbonization was accomplished in a plasmachemical reactor (pyrolytic chamber) using several types of waste, here specifically waste vegetable residues and starch. Phenol adsorption experiments were performed in the batch system. An industrial activated charcoal and a clinoptilolite-rich tuff hydrofobized with an organic ammonium base were used as the related materials to compare phenol removal efficiency.
Trace analysis of lead by anodic stripping voltammetry with collection at interdigitated microelectrodes in small-volume samples
Authors: Rievaj M. , Dovalovská Z. , Bustin D. 
Published: August 2006

AbstractA simple and sensitive electroanalytical method was developed for microvolume trace elements determination. Commercially available interdigitated microelectrodes (IDA) from ALS Japan Inc. based on a thin carbon film technology were used. Anodic stripping voltammetry with collection at IDA was applied. Carbon IDA microbands were coated with a pre-deposited mercury film for better performance. The method with this sensor enables analysis of some heavy metals in total sample volumes as small as 0.05 cm3. The method was applied to Pb in blood samples determination by a standard addition method.
Investigation of the solid samples evaporation from the auxiliary DC arc discharge in the atomic emission spectroscopy
Authors: Ružičková S. , Koller L. , Matherny M. 
Published: August 2006

AbstractEfficiency of the suggested tandem technique of Marinković burner was studied in terms of the influence of the PC-controlled DC arc of the different intensities (10 A, 15 A, 20 A, 25 A) on the evaporation process. Higher intensities than 25 A did not allow to use the given experimental equipment since they cause plasma instability and periodic plasma quenching. The suggested method was evaluated by the determination of the half (t 50%) and total (t 100%) evaporation time and by determination of the signal/background ratio for the chosen elements (Al, Ca, Cr, Fe, Mg, Ni, Si, and V) in the model graphite matrix.
Determination of bioavailable iron in noncontaminated Slovak soils by flame atomic absorption spectrometry
Authors: Barteková J. , Žemberyová M. , Bajčan D. , Vyšinská D. 
Published: August 2006

AbstractA method for the extraction of bioavailable iron from soils from various parts of Slovakia using a buffered diethylenetriaminepentaacetic acid (DTPA) solution was utilized. The extractant consists of 0.005 mol dm−3 DTPA, 0.1 mol dm−3 CaCl2, and 0.1 mol dm−3 triethanolamine with pH of 7.3. DTPA was selected as the chelating agent because it can effectively extract micronutrient metal, iron. Distribution of iron in the horizons of various types of soils with respect to bioavailable iron was evaluated. The bioavailable iron in the extracts was determined by flame atomic absorption spectrometry. The calibration standards were prepared in the same surroundings as the extracts. Comparing to the average of 2.7–3.7 % total iron contents in Slovak soils, the available amounts of iron represent in average only very small amounts, approximately 0.3 % in comparison to total amounts.
Determination of technetium-99 in soils and radioactive wastes using ICP-MS
Authors: Bartošová A. , Rajec P. , Klimeková A. 
Published: August 2006

AbstractThree methods have been used for the determination of 99Tc in soils and solid radioactive wastes using 99mTc as a yield monitor. In the method one and three the samples were leached in low concentrated nitric and sulphuric acid. Many contaminants were then co-precipitated with Fe(OH)3 in alkali media and Tc in the supernatant was separated using anion-exchange extraction chromatography. There were made also some studies how to improve the chemical recovery of 99mTc in the process of chromatography. In the method two the sample was ashed and then leached in 8 mol dm−3 HNO3 and after iron precipitation, technetium was separated on chromatographic column. The chemical recovery of 99mTc was optimized in the process of chromatography and leaching. Typical recoveries of technetium determined with 99mTc tracer for all these methods were in the range 39 %–87 %.The 99Tc activity was measured using proportional low-background beta detector after one week of staying to allow decay of 99mTc activity. 99Tc was also determined by the non-radiometric method using inductively coupled plasma mass spectrometer.
Spectrophotometric determination of nickel(II) in different samples by complexation with some triazolylazo dyes
Authors: Khedr A. 
Published: August 2006

AbstractA new sensitive spectrophotometric method for the determination of nickel(II) with 3-(2-hydroxy-5-acetyl-(L1),-5-ethoxycarbonyl-(L2),-5-methyl-(L3),-5-formyl-(L4),-5-bromophen-1-ylazo)-1,2,4-triazole (L5), and 3-(2,4-dihydroxyphen-1-ylazo)-1,2,4-triazole (L6) in aqueous media containing 40 vol. % methanol has been developed. The method is based on the formation of stable coloured Ni(II) complexes with stoichiometric ratios 1: 1 and 1: 2 (n(M): n(L)). Linear calibration graphs are obtained up to 7.04 µg cm−3 of nickel(II) under optimum conditions attained from investigation of complex formation. The absorption maxima varied from 485 nm to 545 nm and the molar absorptivities ranged from 0.84 × 104 to 4.65 × 104 dm3 mol−1 cm−1 for 1: 1 and 1: 2 (n(M): n(L)) complexes with varying the substituent on the phenolic ring. The optimum ranges for the direct determination of nickel(II) (Ringbom) and the stability constants of the formed complexes are determined. The developed method was applied to the spectrophotometric determination of nickel(II) in some samples with satisfactory results.
Complexes of biologically important ligands. I. Ternary complexes of nickel(II) comprising 1,10-o-phenanthrolineazosulfonamide derivatives and alkyldithiophosphates
Authors: Aly A. , Awad I. , Abd El-Mottaleb M. , Abd El-Aal K. 
Published: August 2006

Abstract5-[p-(R-Sulfonyl)phenylazo]-1,10-o-phenanthroline (L) and its octahedral complexes of the type [Ni(R2dtp)2(L)] (where R2dtp = diethyl-or dipropyldithiophosphate) with the core NiN2S4 have been prepared and characterized by spectral, magnetic, and thermogravimetric methods. The thermal decomposition mechanism of the compounds was proposed and the kinetic parameters of decomposition were calculated making use of the Coats—Redfern and Horowitz—Metzger equations.
Effects of Cd(II) and Zn(II) complexes with bioactive ligands on some photosynthesizing organisms
Authors: Král’ová K. , Masarovičová E. , Lešíková J. , Ondrejkovičová I. 
Published: August 2006

AbstractThe effects of the complexes of the type M(L)2(nia)2 (M = Cd or Zn; L = acetate (ac) or NCS−; nia = nicotinamida) on reduction of chlorophyll content in suspensions of Chlorella vulgaris and inhibition of photosynthetic electron transport in spinach chloroplasts were investigated. The inhibitory effects of the studied compounds depended on the central metal atom as well as on the structure of L ligands. In general, the toxicity of M(NCS)2(nia)2 was higher than that of M(ac)2(nia)2 and the compounds containing cadmium were more toxic than those with Zn.Dry mass of plants cultivated in the presence of the studied complexes (c = 100 µmol dm−3) showed a decrease related to control plants. The uptaken metal (Cd or Zn) was accumulated mainly in the roots. In general, application of M(ac)2(nia)2 compounds led to higher accumulated metal content in dry mass of plant organs (in mg g−1) related to M(NCS)2(nia)2 administration. In plants treated with Zn(NCS)2(nia)2 lower content of essential metals Mn and Cu was found than in those treated with Zn(ac)2(nia)2.Toxic effects of the studied M(L)2(nia)2 compounds could be caused by exchange of their ligands with potential “biotic S-, O-, and N-donor ligands” occurring in the plant cells.
Efficiency of a fixed-bed and a gas-lift three-column reactor for continuous production of ethanol by pectate-and alginate-immobilized Saccharomyces cerevisiae cells
Authors: Valach M. , Navrátil M. , Horváthová V. , Zigová J. , Šturdík E. , Hrabárová E. , Gemeiner P. 
Published: August 2006

AbstractEthanol-tolerant and thermo-tolerant yeast strain Saccharomyces cerevisiae C11-3 cells immobilized in calcium pectate and calcium alginate gels were used for ethanol fermentation in a three-reactor system with a gradient temperature control. The fermentation process has been tested in a fixed-bed and a gas-lift arrangement. The gas-lift system was more efficient due to a better mass transport between the phases. Abrasion was more evident in calcium alginate particles, while calcium pectate beads were not significantly damaged. Two different concentrations of alginate were tested and calcium pectate gel was demonstrated to be more suitable as an immobilization material in comparison with calcium alginate due to its mechanical resistance and favourable diffusion parameters, providing an ethanol production of more than 7.5 g dm−3 h−1 over a period of 630 h.
Calibrationless determination of electroactive species using chronoamperograms at collector segment of interdigitated microelectrode array
Authors: Jenčušová P. , Tomčík P. , Bustin D. , Rievaj M. , Dovalovská Z. 
Published: August 2006

AbstractThe possibility of calibrationless chronoamperometric determination is described using a pair of individually addressable and diffusion layers interacting segments of interdigitated microelectrode array (IDA). It utilizes dual voltammetric mode where the first segment is polarized with potential corresponding to the limiting current of determined species electrode reaction and the second segment is polarized with potential corresponding to the opposite electrode reaction limiting current. Time at which the current of the collector segment reaches one half of the steady state is hyperbolically dependent on the diffusion coefficient of analyte. The determination of diffusion coefficient allows direct calculation of bulk concentration avoiding calibration with a standard solution. The equipment for measuring of fast response of IDA arrays in dual mode has been developed using a bipotentiostat connected with A/D transducer. It allows less than 1 ms sampling period for ultrafast registration of chronoamperogram. The method was tested and validated with [Fe(CN)6]4−, [Ru(NH3)6]Cl3, and ferrocene model samples using various types of IDA arrays.
The β-carotene dilemma: ESR study with coordinated peroxyl radicals
Authors: Tkáč A. , Scott G. 
Published: August 2006

AbstractThe apparently unpredictable behaviour of β-carotene in the supplementation of the diet of smokers is discussed in the light of the reactions of peroxyl radicals with β-carotene in the absence of oxygen. The decay of tert-butylperoxyl radicals in the presence of β-carotene was studied at ambient temperature in non-polar solvents by ESR spectroscopy. The primary reaction in the absence of oxygen is interpreted as a spin-trapping effect of a peroxyl radical by β-carotene producing an intermediate labile free radical, which disappears after recombination with a second tert-butylperoxyl radical. The result is the transformation of β-carotene to a diamagnetic compound with two peroxy bonds. In the presence of chelating transition metals with unpaired d-electrons as electron donors the peroxy group of the oxidized β-carotene can be split to alkoxyl free radicals. The primary attack of tert-butylperoxyl radicals is completely inhibited in the presence of vitamin E followed by production of free aryloxy radicals and the presence of oxygen has no significant effect on this reaction. Spin-trapping of peroxyl radicals by the double bond of vitamin A leads to its oxidation in the absence of vitamin E.Transition metal ions such as Co, Cr, Fe, and Mn, known to be present in the aerosol of cigarette smoke, homolyse the peroxyl bonds of peroxidised β-carotene, which results in cell damage.