| 1. |
- Baranowska, Irena, et al.
(författare)
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Use of multivariate statistical techniques to optimize the separation of isoflavones by liquid chromatography
- 2011
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Ingår i: Central European Journal of Chemistry. - : Springer Verlag (Germany). - 1895-1066 .- 1644-3624. ; 9:6, s. 972-981
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this paper is to optimize and validate a high performance liquid chromatography (HPLC) method for separation and quantification of five isoflavones. A statistical central composite design was used to separate all peaks. These multivariate procedures were efficient in determining the optimal separation condition using resolution, capacity factor, asymmetry and number of theoretical plates. less thanbrgreater than less thanbrgreater thanThe effective separation of the examined compounds was applied on a Develosil RP Aqueous AR 5 RP-30 column with a gradient mobile phase system and a DAD detector. less thanbrgreater than less thanbrgreater thanThe isolation and preconcentration of the isoflavones from urine and plasma samples were conducted by means of the solid-phase extraction (SPE). For optimize SPE conditions various sorbents were tested. Furthermore, high recoveries and good relative standard deviations were obtained when the samples were passed through the Oasis HLB column. The developed method was validated and successfully applied for determination of isoflavones in urine and plasma.
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| 2. |
- Baykal, Abdulhadi, et al.
(författare)
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Sonochemical synthesis and chracterization of Mn3O4 nanoparticles
- 2010
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Ingår i: Central European Journal of Chemistry. - : Walter de Gruyter GmbH. - 1895-1066. ; 8:3, s. 633-638
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Tidskriftsartikel (refereegranskat)abstract
- We report on the synthesis of Mn3O4 nanoparticles (NPs) using a novel sonochemical method without requiring any pH adjustment. Synthesized material was identified as tetragonal hausmannite crystal structure model of Mn3O4 from XRD analysis. Crystallite size was estimated from x-ray line profile fitting to be 17 +/- 5 nm. FTIR analysis revealed stretching vibrations of metal ions in tetrahedral and octahedral coordination confirming the crystal structure. TEM analysis revealed a dominantly cubic morphology of NPs with an average size of similar to 20 nm. Magnetic evaluation revealed a blocking temperature, T-B of 40 K above which the material behaves paramagnetic. Asymmetric coercive field is attributed to the interaction between ferromagnetic Mn3O4 and antiferromagnetic Mn oxide at the surface of nanoparticles.
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| 3. |
- Kosa, Ladislav, et al.
(författare)
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Phase transitions of K2TaF7 within 680-800 degrees C
- 2008
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Ingår i: Central European Journal of Chemistry. - : Walter de Gruyter GmbH. - 1895-1066. ; 6:1, s. 27-32
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Tidskriftsartikel (refereegranskat)abstract
- Three thermal effects on heating/cooling of K2TaF7 in the temperature interval of 680-800 degrees C were investigated by the DSC method. The values determined for the enthalpy change of the individual processes are: Delta H-transII(m)(K2TaF7; 703 degrees C) = 1.7(2) kJ mol(-1), Delta H-transI(m)(K2TaF7; 746 degrees C) = 19(1) kJ mol(-1) and Delta H-transIII(m)(K2TaF7; 771 degrees C) = 13(1) kJ mol(-1). The first thermal effect was attributed to a solid-solid phase transition; the second to the incongruent melting of K2TaF7 and the third to mixing of two liquids. These findings are supported by in situ neutron powder diffraction experiments performed in the temperature interval of 654-794 degrees C.
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| 4. |
- Nikoleli, Georgia-Paraskevi, et al.
(författare)
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Potentiometric cholesterol biosensing application of graphene electrode with stabilized polymeric lipid membrane
- 2013
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Ingår i: Central European Journal of Chemistry. - : Springer Verlag (Germany). - 1895-1066 .- 1644-3624. ; 11:9, s. 1554-1561
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Tidskriftsartikel (refereegranskat)abstract
- A novel potentiometric cholesterol biosensor has been fabricated through the immobilization of the stabilized polymeric lipid membrane onto graphene electrode. The stabilized polymeric lipid membrane is composed of cholesterol oxidase enzyme and polymerization mixture; which holds paramount influence on the properties of the cholesterol biosensor. The presented biosensor reveals an appreciable reproducibility, good selectivity and high sensing capability with a linear slope curve of similar to 64 mV per decade. The strong biocompatibility among stabilized polymeric lipid membranes and human biofluids provides the possibility to use for real blood samples and other biological applications.
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| 5. |
- Pucetaite, Milda, et al.
(författare)
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Microspectroscopic infrared specular reflection chemical imaging of multi-component urinary stones: MIR vs. FIR
- 2014
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Ingår i: Central European Journal of Chemistry. - : Walter de Gruyter GmbH. - 1895-1066. ; 12:1, s. 44-52
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Tidskriftsartikel (refereegranskat)abstract
- Specular reflection infrared microspectroscopy was used for chemical imaging of cross-sectioned urinary stones to determine their chemical composition and morphology simultaneously. Absorption spectral bands were recovered from reflection spectra by Kramers-Kronig transform. FUse of far-infrared radiation provides high-contrast images and allows more precise constituent distribution determinations than mid-infrared because band asymmetry after the transform caused by diffuse reflection is less in the far-infrared.
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| 6. |
- Roth, Olivia, et al.
(författare)
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Oxidation of UO2(s) in aqueous solution
- 2008
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Ingår i: Central European Journal of Chemistry. - : Walter de Gruyter GmbH. - 1895-1066. ; 6:1, s. 1-14
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Tidskriftsartikel (refereegranskat)abstract
- In this review the kinetics and mechanism of oxidative dissolution of UO2(s), mainly under conditions of relevance for the safety assessment of a deep geological repository for spent nuclear fuel, are discussed. Rate constants for the elementary processes involved (oxidation of UO2 and dissolution of oxidized UO2) are used to calculate the rates of oxidative UO2(s) dissolution under various conditions (type of oxidant, oxidant concentration and HCO3-/CO32- concentration) for which experimental data are also available. The calculated rates are compared to the corresponding experimental values under the assumption that the experimental numbers reflect the steady-state conditions of the system. The agreement between the calculated rates and the corresponding experimental ones is very good, in particular for the higher rates. In general, the calculated rates are somewhat higher than the experimental numbers. This can be due partly to the use of initial concentrations rather than steady-state concentrations in the calculations. The kinetic data are also used to quantitatively discuss the dynamics of spent nuclear fuel dissolution under deep geological repository conditions.
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| 7. |
- Shahid, Robina, et al.
(författare)
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Low temperature synthesis of cubic phase zinc sulfide quantum dots
- 2012
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Ingår i: Central European Journal of Chemistry. - : Walter de Gruyter GmbH. - 1895-1066 .- 1644-3624. ; 10:1, s. 54-58
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we report on a new method for the synthesis of ZnS quantum dots (QDs). The synthesis was carried out at low temperature by a chemical reaction between zinc ions and freshly reduced sulfide ions in ethanol as reaction medium. Zinc chloride and elemental sulfur were used as zinc and sulfur sources, respectively and hydrazine hydrate was used as a strong reducing agent to convert elemental sulfur (S(8)) into highly reactive sulfide ions (S(2-)) which react spontaneously with zinc ions. This facile, less toxic, inexpensive route has a high yield for the synthesis of high quality metal sulfide QDs. Transmission electron microscopy (TEM) image analysis and selected area electron diffraction (SAED) reveal that ZnS QDs are less than 3 nm in diameter and are of cubic crystalline phase. The UV-Vis absorption spectrum shows an absorption peak at 253 nm corresponding to a band gap of 4.9 eV, which is high when compared to the bulk value of 3.68 eV revealing strong quantum confinement. PL emission transitions are observed at 314 nm and 439 nm and related to point defects in ZnS QDs.
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| 8. |
- Sladkovicova, Mariana, et al.
(författare)
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DFT and neutron diffraction study of 1,6-anhydro-beta-D-glucopyranose (levoglucosan)
- 2007
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Ingår i: Central European Journal of Chemistry. - : Walter de Gruyter GmbH. - 1895-1066. ; 5:1, s. 55-70
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Tidskriftsartikel (refereegranskat)abstract
- Geometries of 27 generated conformers of levoglucosan were optimized in vacuo at DFT level of theory combining several functionals with high quality basis sets. For the sake of comparison a reference molecular and crystal geometry obtained from 30 K single crystal neutron diffraction data was used. Analysis of the conformers' geometries revealed that in all stable conformers intramolecular two- or three centre hydrogen bonds were formed. Relative energy of the conformer, which approximated the molecule in the crystal structure the most, was only similar to 3 kcal/mol higher, than the energy of the most stable conformer in vacuo. The largest discrepancies between the geometries calculated in vacuo and experimental geometry concentrated in the vicinity of anomeric C1. These differences were reduced by involving O1 to intermolecular hydrogen bond using a simple model of the respective hydrogen bond in the crystal.
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| 9. |
- Tafti, Mohsen Yakshi, et al.
(författare)
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Fabrication and characterization of nanostructured thermoelectric FexCo1-xSb3
- 2015
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Ingår i: Open Chemistry. - : Walter de Gruyter GmbH. - 2391-5420. ; 13:1, s. 629-635
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Tidskriftsartikel (refereegranskat)abstract
- A novel synthesis route for the fabrication of p-type nanostructured skutterudite, FexCo1-xSb3 in large quantity is reported. This scalable synthesis route provides nano-engineered material with less impact on the environment compared to conventional synthesis procedures. Several Fe substituted compositions have been synthesized to confirm the feasibility of the process. The process consists of a nano-sized precursor fabrication of iron and cobalt oxalate, and antimony oxides by chemical co-precipitation. Further thermochemical processes result in the formation of iron substituted skutterudites. The nanopowders are compacted by Spark Plasma Sintering (SPS) technique in order to maintain nanostructure. Detailed physicochemical as well as thermoelectric transport properties are evaluated. Results reveal strongly reduced thermal conductivity values compared to conventionally prepared counterparts, due to nanostructuring. P-type characteristic was observed from the Seebeck measurements while electrical conductivity is high and shows metallic behavior. The highest TE figure of merit of 0.25 at 800 K has been achieved, which is strongly enhanced with respect to the mother compound CoSb3. This suggests the promise of the utilized method of fabrication and processing for TE applications with improved performance.
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