Electrochemical Activity of Wedelolactone and Probing its Interaction with DNA Using Voltammetry at a Carbon Electrode

Wedelolactone (WLA) is a polyphenolic coumestan derivative found in extracts of plants used in traditional medicine. Due to its cytostatic activity, WLA is one of natural compounds tested as potential anticancer drugs. In this work we for the first time studied electrochemical properties of WLA using cyclic (CV) and square‐wave (SWV) voltammetry at the basal‐plane pyrolytic graphite electrode. A reversible pair of peaks, corresponding to catechol/o‐benzoquinone redox system, was observed using CV around 0.275 V vs. Ag|AgCl|3 M KCl reference electrode. Measurements of SWV signal of WLA in the presence of single‐ or double‐stranded DNA suggested a weak interaction without evident preference for double‐stranded DNA. An indirect assay, employing electroactive DNA intercalator doxorubicin as competitor, confirmed absence of intercalative DNA binding of WLA.     

Determination of acid volatile sulphur in river sediments by ICP-OES coupled with purge and trap method

The developed and tested method is based on the acid volatile sulphur (AVS) releasing from a sample of sediment by acidification with hydrochloric acid and sequential absorption of released hydrogen sulphide into the absorption solution of sodium hydroxide. Total sulphur absorbed in the absorption solution is subsequently determined by inductively coupled plasma optical emission spectrometry (ICP-OES) technique. The method was tested using both model and real samples of the river sediment. Obtained results were compared with the results of iodometric determination as the method routinely used for the AVS determination. In case of using ICP-OES with purge and trap, there is no spectral interference of calcium; therefore for the determination of sulphur, it is possible to use atomic emission line of sulphur S I 180.7 nm. The tested method provides the results comparable with the iodometric method within the range of tested concentrations. The detection limit (LOD) of this method is 0.09 mg· S^2? ? L^?1 in the absorption solution which corresponds to 0.23 mg S^2?·kg^?1 in a sediment. Value of LOD is comparable with the iodometric determination.     

Nitrogen heteroaromatic cations by [2+2+2] cycloaddition

A modular approach to the construction of monocationic quaternary N-heteroaromatic frameworks was developed capitalizing on a direct pyridine-type nitrogen quaternization followed by metal-catalyzed [2+2+2] cycloaddition with gaseous acetylene. The flexibility of the route is demonstrated on 12 diverse scaffolds based on pyridinium, quinolinium, thiazolium, benzothiazolium, imidazolium, and pyrimidinium. Electrochemical study revealed a quinolinium redox system with two electrochemically distinct forms that are interconverted by a homogeneous chemical reaction triggered by fast electron transfers (reduction at -0.7 V and oxidation at -0.05 V).     

A semiclassical model of the interior of Uranus

Abstract

Using the mass and radius of Uranus, as determined by Voyager, and a particular semiclassical theory of dense matter, a model of its interior has been developed. Details of the model, the underlying theory and possible sources of discrepancies with recent work on this topic are briefly presented.     

Interplay of exciton or electron transfer and relaxation: Time-convolution generalized master equation approach

Generalized Master Equation theory of the time-convolution type for exciton or electron interacting with harmonic phonons is suggested yielding the full single-carrier density matrix. A new form of the projection superoperator used makes the initial condition term zero for a broad class of initial conditions with a partially formed polaron cloud around carrier. Specification to a particle in a symmetric dimer and comparison with standard Haken-Strobl-Reineker model is performed. The theory is shown to yield that, surprisingly, in the resulting memory functions, apart of information about initial polaron cloud survives even after a short redressing time-interval following each individual (and not only initial) carrier hop.The author is really indebted to Prof. Max Wagner and University of Stuttgart for inviting him and hospitality during the author's stay in Stuttgart 1992–3. Financial support of the Max-Planck-Gesellschaft and hospitality of the Max-Planck-Institut für Festkörperforschung, Stuttgart making this stay possible are also gratefully acknowledged.     

Difference scheme for a parabolic problem with changing time direction

Institute of Mathematics and Informatics, Akademijos 4, 2600 Vilnius, Lithuania. Translated from Lietuvos Matematikos Rinkinys, Vol. 35, No. 1, pp. 37–51, January–March, 1995.     

Current-voltage characteristic and parameters of the current filament region of an amorphous gallium telluride-crystalline silicon barrier negistor structure

The transient I-V characteristic of an amorphous GaTe₃-crystalline n-Si barrier negistor structure under negative differential resistance (NDR) conditions is studied. The basic parameters (cross-section radius, current density, and resistivity) of the current filament region in the amorphous layer of the structure are determined. Results obtained are compared with the associated parameters of the current filament in a C-amorphous GaTe₃-C reference barrier-free structure. Under NDR conditions, the conductivity of the filament region in this heterostructure is shown to be governed largely by processes occurring in the crystalline component.