Tracing Possible Structural Asymmetry of Silica Gel Used for Precoating Thin-Layer Chromatography Plates

JPC – Journal of Planar Chromatography – Modern TLC - We have previously described unexpected two-dimensionality in the thin-layer chromatographic separation of pairs of enantiomers of...     

Thiyl radical interaction with pyrimidine C5-C6 double bond

Addition and elimination interaction of thiyl radicals with the C5-C6 double bond in pyrimidines was studied by the pulse radiolysis technique in aqueous solution with the use of different monitoring systems. For this purpose, p-thiocresol, cysteamine hydrochloride, and mercaptoethanol were used. The rate constants of addition and elimination of thiyl radicals were determined by applying the modified version of ACUCHEM (computer program for modeling complex reaction systems). Aliphatic thiyl radicals add to the pyrimidine C5-C6 double bond with k = 1.0-3.0 x 10(7) dm3 mol(-1) s(-1), whereas elimination takes place with k = 0.7-2.0 x 10(5) s(-1). Quantum chemical calculations at the B3LYP/6-31G(d)/PCM level show that the addition should occur at the C6 position of the pyrimidine ring and that the energy of interaction between thiyl radicals and the pyrimidine double bond C5-C6 is low.     

Neutrinos in general relativity: Four(?) levels of approach

The three subsequent levels of approach to the problem of the neutrino in general relativity which have been exploited till now, are:

1. ‘classical particle’ approach, i.e. a study on the neutrino as a classical particle in a classical, given gravitational field;
2. ‘quantum particle’ approach, i.e. considering the Dirac equation for the neutrino in a given gravitational field;
3. ‘classical field’ approach comprising the study of combined neutrino-gravitational fields.

Many results obtained along these lines are presented, with emphasis upon the geometrical theory of two-component neutrino-gravitational fields. A synthesis of the particle and fields aspects of the neutrino could provide a possible fourth, till now non-existing, ‘quantum field’ level of approach. This should deal with a guantized neutrino field in a curved space-time (which might be also quantized, but perhaps this should belong already to a next, fifth level of approach). Studies on the neutrino physics in gravitational fields reveal not only a series of results which are of interest in se, and which may be used as the basis to a unified theory of neutrino and gravitational fields (the Rainich problem for the neutrino). They provide in addition the necessary material for astrophysical and cosmological applications; some of these are outlined in relation to the results presented.     

On amenability of two-generator groups

A discrete group G is amenable if there exists a finitely additive probability measure on G which is invariant under left translations and is defined on all subsets of G. It is proved that if the group is generated by two elements and is amenable then there are words being relators whose most of the consecutive pairs of the letters belong to a certain four-element set of pairs. This fact is applied to reproving non-amenability of a braid group. The same group provides an example showing that such type of condition is not su?cient for amenabilty.     

Volumetric and Surface Properties of Short Chain Alcohols in Aqueous Solution–Air Systems at 293?K

From measurements of the surface tension, density, viscosity and light scattering of aqueous solutions of methanol, ethanol and propanol at 293?K, their activity in the surface monolayer, surface excess concentration, and apparent and partial molar volume were determined. The surface excess concentration of alcohols at the water?Cair interface was determined from the Gibbs equation by using both the alcohol's activity and their molar fraction in the bulk phase and recalculated by using the Guggenheim?CAdam equation. The values of the surface excess concentration determined from the Gibbs equation were also applied to determine the standard Gibbs energy of alcohol adsorption at the water?Cair interface from Langmuir??s equation and compared to those determined from that of Aronson and Rosen.     

Mikrophotometrische Bestimmung Ton Co(II)-Ionen mit Antipyrin-4-Dithiocarbonsäure

Zusammenfassung Ein kolorimetrisches Verfahren zur Kobaltbestimmung wurde ausgearbeitet. Das Kobalt wird mit Antipyrin-4-Dithiocarbonsaurem Ammonium gefällt. Der Niederschlag löst sich in Pyridin mit gelber Farbe. Im Bereich zwischen 0,2 und 1,0g Co/ml ist das Lambert-Beersche Gesetz erfüllt.

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Summary A colorimetric procedure has been worked out for determining cobalt. The cobalt is thrown down by means of antipyrine-4-dithiocarboxylic acid (ammonium salt). The precipitate yields a yellow solution in pyridine. The Lambert-Beer law is satisfied in the range between 0.2 and 1.0g Co/ml.

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Résumé On a mis au point un procédé de dosage colorimétrique du cobalt. On précipite celui-ci par l'antipyrine dithiocarbonate-4 d'ammonium. Le précipité se dissout dans la pyridine en donnant une couleur jaune. Dans les limites de 0,2 à 1,0g Co/ml la loi de Lambert-Beer est vérifiée.

     

Synthesis and Physicochemical Properties of the Complexes of Co(II), Ni(II), and Cu(II) with Chrysin

New solid complex compounds of Co(II), Ni(II), and Cu(II) with chrysin were obtained. Their composition and some physicochemical properties were studied (thermogravimetric analysis, ultraviolet, visible and infrared spectroscopy, magnetic properties). During heating, the hydrated complexesM(C₁₅H₉O₄)₂·nH₂O lose some crystallization water molecules in one or two steps, and then decompose to the oxides. A structure for the compounds was proposed.     

Composition of Surface Layer at the Water–Air Interface and Micelles of Triton X-100 + Rhamnolipid Mixtures

Measurements of the surface tensions, densities and viscosities of aqueous solutions of Triton X-100 (TX-100) and rhamnolipid (RL) mixtures, at constant concentration of RL or TX-100, were carried out. The measured values of the surface tension were compared to those determined using different theoretical models and on the basis of the surface tension of aqueous solutions of individual surfactants. From the surface tension isotherms, the Gibbs surface excess concentration of TX-100 and RL, the composition of surface layer and the standard Gibbs free energy of adsorption at the water–air interface were determined. Moreover, on the basis of surface tension, density and viscosity isotherms, the CMC of surfactants mixtures were evaluated. From the density isotherms, apparent and partial molar volumes of TX-100 and RL were also determined. These volumes were compared to those calculated from the sizes of TX-100 and RL molecules. There was observed a synergetic effect in the reduction of water surface tension and micelle formation, which was confirmed by the intermolecular interactions parameter. In the case of micelle formation, this effect was discussed based on the standard Gibbs free energy of micellization as well as of TX-100 and RL mixing in the micelles. The synergism of TX-100 and RL mixtures in the reduction of water surface tension and micelle formation was explained on the basis of electrostatic interactions between the hydrophilic part of TX-100 and RL molecules; this was supported by pH measurements.     

A new total antioxidant potential measurements using RP-HPLC assay with fluorescence detection

In this paper, an improved total antioxidant potential (TAP) estimation using high-performance liquid chromatographic (HPLC) assay with fluorometric detection has been described. The principle of this method is based on the hydroxyl radicals generated in the Fenton-like reaction and subsequently detected using hydroxyterephthalic acid (HTPA), which is a reaction product of hydroxyl radicals and terephthalic acid (TPA), working as a sensing compound. HTPA quantity in the samples was measured by fluorescence detector working at excitation and emission wavelengths equal to 312 and 428 nm, respectively. A number of key experimental conditions including the influence of the reaction (incubation) time on the surface areas of HTPA peaks, concentration of Fe(II) ions as well as the influence of concentration of TPA on the surface area of the chromatographic peak of HTPA were optimized to the characteristic feature of TAP measurements. The elaborated assay has been used to evaluate TAP values of selected low-molecular mass compounds like pyrogallol, tryptamine, and n-alcohols (methanol, ethanol, and n-propanol) as well as chlorogenic and ascorbic acids and benzoic acid derivatives, which are commonly present in the food samples.