Increased promotion by deposition of Co acetylacetonate over sulphided Mo/TiO2 hydrodesulphurization catalyst

CoMo/TiO₂ catalysts prepared by deposition of Co acetylacetonate on presulphided Mo/TiO₂ catalyst in methanol exhibited higher promotion of hydrodesulphurization activity than catalysts prepared by conventional impregnation of Mo/TiO₂ by a solution of Co nitrate.     

Enzyme nanoparticles-based electronic biosensor

A simple and effective method to prepare an enzyme electronic biosensor by immobilizing enzyme nanoparticles directly onto the gold electrode surface is described; prepared horseradish peroxidase nanoparticles have been successfully used to develop reagentless electronic biosensors for H2O2 detection without promoters and mediators and offer great potential to develop enzyme-based electronic biosensors.     

Ring-substituted benzohydroxamic acids: 1H, 13C and 15N NMR spectra and NH-OH proton exchange

NMR spectra (1H, 13C, 15N) of para- and meta-substituted benzohydroxamic acids were studied in dry dimethyl sulfoxide solutions. The 13C chemical shifts were very close to those found by cross-polarization magic angle spinning in solids, the hydroxamic (not hydroximic) structure of which is unambiguous. The hydroxamic structure of these acids in DMSO solutions was proved independently by their 15N chemical shifts. The 15N and 1H chemical shifts of the NH-OH fragment showed excellent mutual dependences and dependences on the nature of the ring substituent. According to these dependences and ab initio energy calculations, all the acids assume the same Z conformation. Proton exchange between hydroxamic OH and NH groups in DMSO proceeded by both intra- and intermolecular exchange and the rates did not exhibit any simple relationship to the substituent constants.     

Tungsten atomizer--theory of atomization mechanism of some volatile analytes

Several types of chemical reactions may participate in the evolution of free atoms in a tungsten furnace. Reactions may take place either in the homogeneous or heterogeneous phase. The assumed reactions may be classified into four types according to the phases in which they take place. Reactions occurring in the gaseous phase, i.e. in the inner volume of the furnace, are kinetically more significant. However, for atomization of easily volatile analytes heterogeneous reaction between gaseous compounds and between condensed salts of analytes and the solid surface of the furnace become significant. With regards to the reaction mechanisms during drying, pyrolysis and atomization of nitrates of volatile analytes, three basic types of chemical reactions may be assumed. Free atoms of analytes arise by evaporation of the elementary form of analytes at atomization temperature, where the particular analyte in its elementary form is produced by direct reduction of analyte nitrate by tungsten or by hydrogen at higher temperatures. Precursory reactions of atom formation are reduction reactions which occur between analyte nitrates and tungsten, between analyte nitrates and hydrogen, as well as reactions of thermal dissociation of relevant nitrates. The importance of particular types of precursory reactions for formation of metallic analytes or their oxides is documented by dependence of Gibbs energy values of particular reactions on the temperature.     

Catalytic signal of rabbit liver metallothionein on a mercury electrode: a combination of derivative chronopotentiometry with adsorptive transfer stripping

Constant current chronopotentiometric stripping analysis (CPSA) in combination with adsorptive transfer stripping (AdTS) technique was used to study the rabbit liver metallothionein (MT) on a hanging mercury drop electrode (HMDE). Metallothionein yielded a distinct, sharp chronopotentiometric signal at very negative potentials (about -1.7 V), also known as the "peak H". The height and potential of this peak were dependent on experimental conditions, such as buffer composition, pH, and the presence oxygen in solutions. The peak H was highest in borate buffer with pH close to the isoelectric point (pI) of MT. The chronopotentiometric results contribute to a deeper understanding of the nature of catalytic hydrogen evolution and demonstrate the usefulness of the peak H in peptide and protein research.     

Simultaneous determination of quinoline yellow and brilliant blue FCF in cosmetics by solid-phase spectrophotometry

A method for the simultaneous determination of quinoline yellow (QY) and brilliant blue FCF (BB) in mixtures by solid-phase spectrophotometry has been developed. Both colorants were isolated in Sephadex DEAE A-25 gel showing maximum absorbances at 632 nm and 415 nm for BB and QY respectively. The applicable concentration ranges were between 25.0 and 500.0 mug 1(-1) for BB and between 50.0 and 750.0 mug 1(-1) for QY. The detection limits were 6.1 and 13.4 mug (-1) for BB and QY respectively. Application of the method to real samples (colognes, after shave lotions and shampoo gels) involves a previous extraction process of the colorants before their isolation on the gel.     

Mechanochemistry as a versatile and scalable tool for nanomaterials synthesis: Recent achievements in Košice,Slovakia

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Correlation energy functionals dependent on an effective number of electrons: charged species and equilibrium geometries

Recently proposed spin-dependent and spin-independent correlation energy functionals [Perez-Jimenez et al., J. Chem. Phys. 116, 10571 (2002)] based on an effective number of electrons N are extended to deal with charged systems. By introducing the concept of an effective atomic number Z analogous to N, the spin-dependent functional in combination with Becke's exchange [Becke, Phys. Rev. A 38, 3098 (1988)] yields a mean absolute error (MAE) of 5.4 kcal/mol for the 88 ionization potentials and 58 electron affinities included in the extended G2 set, and a MAE of 4.1 kcal/mol for the 312 data comprising the above plus the 148 enthalpies of formation of the extended G2 set and the 18 total energies of the neutral atoms H through Ar. Geometry optimizations performed on the 53 molecules of the G2-1 test set with the above combination of exchange and correlation functionals yield MAEs of 0.017 A and 1.5 degrees for the 68 bond lengths and 29 angles analyzed as compared with the experimental estimates.     

Gas chromatographic determination of S-alk(en)ylcysteine sulfoxides

A new GC method for determination of S-alk(en)ylcysteine sulfoxides, important secondary metabolites occurring in many plant genera, has been developed. The method is based on isolation of the amino acid fraction by ion-exchange chromatography followed by derivatization with ethyl chloroformate at ambient temperature and reduction of derivatized S-alk(en)ylcysteine sulfoxides by sodium iodide. The main advantages of the new method are its high sensitivity, excellent resolution capability, accuracy and reliability, as well as the possibility to identify unknown compounds by means of GC-MS. The content of alliin and other S-alk(en)ylcysteine sulfoxides was determined in nine different samples of garlic (Allium sativum L.) originating from the Czech Republic, France, and China. The total content of S-alk(en)ylcysteine sulfoxide pool ranged between 0.53 and 1.3% fresh weight, with S-allylcysteine sulfoxide (alliin) being predominant. A novel S-alkylcysteine derivative, S-ethylcysteine sulfoxide (ethiin), not previously reported to occur in Allium species, was found in some of the samples examined.     

Current-voltage curves for a cation-exchange membrane in methanol-water electrolyte solutions

The current-voltage curves for a cation-exchange membrane separating two equal methanol-water electrolyte solutions were determined under different experimental conditions. From these curves, the values of the limiting current density, I(L), were determined. The influence of the volume percentage of methanol in the solvent on the results was analyzed. The presence of methanol in the solutions was shown not to affect the shape of the current-voltage curves typical of aqueous solutions. However, the system resistance and the values of the limiting current density were both greatly influenced by the content of methanol. Thus, the value of the resistance increased and the limiting current decreased with increasing methanol content of the solution.