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Os parâmetros de ligação de brometo de etídio (EtBr) com DNA em diversas proporções GC/AT foram determinados usando espectroscopia de absorção e fluorescência. Nossos dados experimentais demonstram claramente a co-existência de tipos de ligação "forte" fluorescente e não-fluorescente em baixas concentrações de EtBr. O complexo fluorescente corresponde ao modelo normal intercalante. O complexo não-fluorescente refere-se à ligação semi-intercalante de EtBr. A constante de ligação (K) e o número de pares de bases correspondentes ao sítio de ligação (n) dos tipos fluorescente (K f e n f ) e não-fluorescente (K nf , n nf ) de interações foram determinados. O tamanho médio do sítio de ligação (n) é igual a 1,5 bp (espectroscopia de absorção), e n f ca. 2 bp (espectroscopia de fluorescência). Mostrou-se que n nf é dependente da quantidade de GC e n total é independente.The binding parameters of ethidium bromide (EtBr) with DNA of various GC/AT ratios were determined using absorption and fluorescence spectroscopy. Our experimental data clearly demonstrate the co-existence of fluorescing and non-fluorescing types of "strong" binding at low concentration of EtBr. The fluorescent complex corresponds to the ordinary intercalative model. The non-fluorescent complex is referred to semi-intercalative binding of EtBr. The binding constant (K) and the number of base pairs corresponding to a binding site (n) of the fluorescent (K f and n f ) and non-fluorescent (K nf , n nf ) types of interactions were determined. The average size of binding site (n) is equal to 1.5 bp (absorption spectroscopy), and n f ca. 2 bp (fluorescence spectroscopy). It was shown that n nf is dependent on GC-content and total n is independent of it.

Aim.To investigate the thermodynamic characteristics of complexes of calf thymus double-stranded DNA with methylene blue (MB), ethidium bromide (EtBr) and Hoechst 33258 (H33258). Methods. The binding of MB with double-stranded DNA was observed by UV-melting method. Results. Several types of MB binding to DNAintercalating, semi-intercalating and electrostatic with DNA phosphate backbone, have been revealed at low concentrations of Na + (2 mM). At high concentrations of cations and low ratios of r b = [ligand]/[DNA] (£ 0.05), the molecules of ligand semi-intercalate into the space between adjacent bases. At higher concentrations of ligand the main mode becomes electrostatic binding of MB to DNA phosphate groups. Conclusions. The comparison of thermodynamic characteristics of DNA-MB complexes with those of EtBr and H33258 indicates that there is more than one mode of binding ligands to DNA: besides nonspecific, external electrostatic binding with phosphate groups, intercalation and semi-intercalation modes of interaction coexist.

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An identification of radio sources from the NVSS list with ROSAT X-ray sources was made as well as also with optical objects from SDSS DR 16. We have tried to find the connection between the fluxes of different wave ranges, for different types of objects. We also have tried to find the relationship between the sizes and polarization angles of sources with the types of objects and recurrence. The fluxes detected from X-ray, optical, and radio bands for them are compiled. This database allows an investigation on broad band energy distribution and other possible correlations among spectral indices and luminosities for various types of extragalactic objects.