Racemization barriers of 1,1'-binaphthyl and 1,1'-binaphthalene-2,2'-diol: a DFT study

Density functional theory has been applied to the study of various pathways and transition states for the configurational inversion of 1,1'-binaphthyl (1) and 1,1'-binaphthalene-2,2'-diol (2). The preferred pathway is found to be anti with centrosymmetric transition state. Whereas the reaction path of 1 goes downhill from transition to ground state, in the case of 2 it contains one unexpected local minimum. Very satisfactory agreement with available experimental values of activation Gibbs energies is achieved.     

Voltammetric behavior of DNA modified with osmium tetroxide 2,2'-bipyridine at mercury electrodes

Osmium tetroxide complexes with nitrogen ligands (L) are probes of DNA structure and electroactive labels of DNA. Here adducts of single-stranded (ss) DNA with osmium tetroxide 2,2'-bipyridine (DNA-Os,bipy) were studied by cyclic voltammetry for the first time. It was found that at neutral pH DNA-Os,bipy produces three redox couples in the potential range between 0 and -1 V (peaks I-III) and a cathodic peak at about -1.3 V (peak IV). The latter peak decreased with increasing scan rate, and peaks arising from the forward and reverse scans exhibited the same direction, suggesting catalytic nature of the electrode process. We concluded that this peak corresponds to the known differential pulse voltammetric (polarographic) peak of DNA-Os,L adducts for which catalytic hydrogen evolution is responsible. In contrast, currents of cathodic peaks II and III increased almost linearly with increasing scan rate, suggesting involvement of adsorption in the electrode processes. Adsorptive stripping square-wave voltammetry was used to analyze the DNA-Os,bipy at low concentrations. It was shown that at neutral pH, peak III can offer sensitivity in the ppb range, which is only little lower than that reached by catalytic peak IV. The latter peak is, however, superior in sensitivity at acid pH values.     

Use of molybdate as novel complex-forming selector in the analysis of polyhydric phenols by capillary zone electrophoresis

Molybdate was examined as a complex-forming additive to the CE background electrolytes (BGE) to affect the selectivity of separation of polyhydric phenols such as flavonoids (apigenin, hyperoside, luteolin, quercetin and rutin) and hydroxyphenylcarboxylic acids (ferulic, caffeic, p-coumaric and chlorogenic acid). Effects of the buffer concentrations and pH and the influence of molybdate concentration on the migration times of the analytes were investigated. In contrast to borate (which is a buffering and complex-forming agent generally used in CE at pH ≥9) molybdate forms more stable complexes with aromatic o-dihydroxy compounds and hence the complex-formation effect is observed at considerably lower pH. Model mixtures of cinnamic acid, ferulic acid, caffeic acid and 3-hydroxycinnamic acid were separated with 25 mM morpholinoethanesulfonic acid of pH 5.4 (adjusted with Tris) containing 0.15 mM sodium molybdate as the BGE (25 kV, silica capillary effective length 45 cm × 0.1 mm I.D., UV-vis detection at 280 nm). With 25 mM 2-hydroxy-3-[4-(2-hydroxyethyl)-1-piperazinyl]propanesulphonic acid/Tris of pH^* 7.4 containing 2 mM sodium molybdate in aqueous 25% (v/v) methanol as the BGE mixtures of all the above mentioned flavonoids, p-coumaric acid and chlorogenic acid could be separated (the same capillary as above, UV-vis detection at 263 nm). The calibration curves (analyte peak area versus concentration) were rectilinear (r > 0.998) for ≈8-35 μg/ml of an analyte (with 1-nitroso-2-naphthol as internal standard). The limit of quantification values ranged between 1.1 mg l⁻¹ for p-coumaric acid and 2.8 mg l⁻¹ for quercetin. The CE method was employed for the assay of flavonoids in medicinal plant extracts. The R.S.D. values ranged between 0.9 and 4.7% (n = 3) when determining luteolin (0.08%) and apigenin (0.92%) in dry Matricaria recutita flowers and rutin (1.03%) and hyperoside (0.82%) in dry Hypericum perforatum haulm. The recoveries were >96%.     

Comparison of the low-frequency magnetic field effects on bacteria Escherichia coli, Leclercia adecarboxylata and Staphylococcus aureus

This work studies biological effects of low-frequency electromagnetic fields. We have exposed three different bacterial strains-Escherichia coli, Leclercia adecarboxylata and Staphylococcus aureus to the magnetic field (t<30 min, B(m)=10 mT, f=50 Hz) in order to compare their viability (number of colony-forming units (CFU)). We have measured the dependence of CFU on time of exposure and on the value of the magnetic field induction B(m). Viability decreases with longer exposure time and/or higher induction B(m) for all strains, but the quantity of the effect is strain-dependent. The highest decrease of the viability and the biggest magnetic field effect was observed with E. coli. The smallest magnetic field effect appears for S. aureus. From the measurement of the growth dynamics we have concluded that the decrease of the CFU starts immediately after the magnetic field was switched on.     

Voltammetry of osmium-modified DNA at a mercury film electrode: application in detecting DNA hybridization

Mercury film electrodes (MFE) have recently been used in nucleic acid electrochemical analysis as alternatives to the classical mercury drop ones. DNA modified with osmium tetroxide, 2,2'-bipyridine (Os,bipy) can be detected with a high sensitivity at mercury electrodes via measurements of a catalytic osmium signal. In this paper we show that mercury film on a glassy carbon electrode can be used in voltammetric analysis of Os,bipy-modified DNA. Application of the MFE as a detection electrode in double-surface electrochemical DNA hybridization assay involving osmium labeling of target DNA is demonstrated.     

The Banach-Zarecki theorem for functions with values in metric spaces

Using an old result of Luzin about his property , we prove a general version of the Banach-Zarecki theorem (on absolute continuity and Luzin's property ).

     

Alkaloids from some amaryllidaceae species and their cholinesterase activity

Alkaloid extracts of four Amaryllidaceae species were studied with respect to their acetylcholinesterase and butyrylcholinesterase inhibitory activity and alkaloid patterns. Twenty-one alkaloids were determined by GC/MS, and seventeen of them identified from their mass spectra and retention times. The GC/MS analysis of the alkaloid extract of Nerine filamentosa is the first phytochemical investigation of this species. Promising erythrocytic acetylcholinesterase inhibitory activity was demonstrated by the alkaloid extracts of Narcissus poeticus var recurvus, Nerine filifolia and N. filamentosa (IC(50,HuAChE) = 6.0 +/- 0.1 microg/mL; IC(50,HuAChE) = 18.5 +/- 0.8 microg/mL, IC(50,HuAChE) = 21.6 +/- 1.1 microg/mL). The most potent inhibitory activity against serum butyrylcholinesterase was shown by extracts of Sternbergia lutea and Nerinefilamentosa (IC(50,HuBuChE) = 3.7 +/- 0.1 microg/mL; IC(50.HuBuChE) = 13.0 +/- 0.7 microg/mL).     

Effect of spin-orbit coupling on reduction potentials of octahedral ruthenium(II/III) and osmium(II/III) complexes

Reduction potentials of several M(2+/3+) (M = Ru, Os) octahedral complexes, namely, [M(H2O)6](2+/3+), [MCl6](4-/3-), [M(NH3)6](2+/3+), [M(en)3](2+/3+) [M(bipy)3](2+/3+), and [M(CN)6](4-/3-), were calculated using the CASSCF/CASPT2/CASSI and MRCI methods including spin-orbit coupling (SOC) by means of first-order quasi-degenerate perturbation theory. It was shown that the effect of SOC accounts for a systematic shift of approximately -70 mV in the reduction potentials of the studied ruthenium (II/III) complexes and an approximately -300 mV shift for the osmium(II/III) complexes. SOC splits the sixfold-degenerate (2)T(2g) ground electronic state (in ideal octahedral symmetry) of the M(3+) ions into the E((5/2)g) Kramers doublet and G((3/2)g) quartet, which were calculated to split by 1354-1573 cm(-1) in the Ru(3+) complexes and 4155-5061 cm(-1) in the Os(3+) complexes. It was demonstrated that this splitting represents the main contribution to the stabilization of the M(3+) ground state with respect to the closed-shell (1)A(1g) ground state in M(2+) systems. Moreover, it was shown that the accuracy of the calculated reduction potentials depends on the calculated solvation energies of both the oxidized and reduced forms. For smaller ligands, it involves explicit inclusion of the second solvation sphere into the calculations, whereas implicit solvation models yield results of sufficient accuracy for complexes with larger ligands. In such cases (e.g., [M(bipy)3](2+/3+) and its derivatives), very good agreement between the calculated (SOC-corrected) values of the reduction potentials and the available experimental values was obtained. These results led us to the conclusion that especially for Os(2+/3+) complexes, inclusion of SOC is necessary to avoid systematic errors of approximately 300 mV in the calculated reduction potentials.     

Preparation of Nanostructured Magnetic Films by the Plasma Jet Technique

 Magnetic films were prepared by the plasma jet technique from Fe, mumetal, and Fe/Hf or Fe/Ta nozzles. Two different plasma jet systems with different vacuum pumps were used to compare the quality of the produced films. The films prepared from a Fe nozzle in the two different equipments shows that oxygen in the residual atmosphere of the low vacuum reactor leads mainly to the formation of iron oxides. The Fe and mumetal films prepared in the high vacuum system contain only a very small amount of oxygen, as proved by chemical analysis and ferromagnetic resonance. The mumetal film, moreover, shows good soft magnetic properties and low magnetic damping. For the reactive plasma jet deposition of nanogranular Fe–Hf–O and Fe–Ta–O films, the low vacuum system was used. The films with higher oxygen content exhibit tunneling-type conductivity. In some films, superparamagnetic behaviour and spin-dependent tunneling magnetoresistance were observed.     

Determination of nanogram quantities of osmium-labeled single stranded DNA by differential pulse stripping voltammetry.

Earlier, we showed that using differential pulse cathodic stripping voltammetry with hanging mercury drop electrode (HMDE), single-stranded (ss) DNA modified with osmium tetroxide, pyridine reagent (Os,py) can be determined at concentrations down to about 10-5 ng/ml. Here, we show that by exchanging Os,py for osmium tetroxide, 2,2'-bipyridine (Os,bipy) and decreasing the pH of the background electrolyte from neutrality to about pH 4, ssDNA can be determined at concentrations lower by one order of magnitude. Determination of DNA at such low concentrations may find use in various areas of molecular biology and in biotechnologies, including the development of DNA sensors.