RESUMO
Viomycin is a basic peptide antibiotic, which is among the most effective agents against multidrug-resistant tuberculosis. In this paper we provide the characteristics of its acid base properties, coordination preferences towards the Cu(ii) ions, as well as the reactivity of the resulting complexes against plasmid DNA and HDV ribozyme. Careful coordination studies throughout the wide pH range allow for the characterisation of all the Cu(ii)-viomycin complex species. The assignment of proton chemical shifts was achieved by NMR experiments, while the DTF level of theory was applied to support molecular structures of the studied complexes. The experiments with the plasmid DNA reveal that at the physiological levels of hydrogen peroxide the Cu(ii)-viomycin complex is more aggressive against DNA than uncomplexed metal ions. Moreover, the degradation of DNA by viomycin can be carried out without the presence of transition metal ions. In the studies of antigenomic delta ribozyme catalytic activity, viomycin and its complex are shown to modulate the ribozyme functioning. The molecular modelling approach allows the indication of two different locations of viomycin binding sites to the ribozyme.
Assuntos
Antituberculosos/química , Complexos de Coordenação/química , Cobre/química , RNA Catalítico/metabolismo , Viomicina/química , Antituberculosos/farmacologia , Sítios de Ligação , Dicroísmo Circular , Complexos de Coordenação/farmacologia , Fragmentação do DNA/efeitos dos fármacos , Espectroscopia de Ressonância de Spin Eletrônica , Ligação de Hidrogênio , Peróxido de Hidrogênio/química , Peróxido de Hidrogênio/metabolismo , Concentração de Íons de Hidrogênio , Conformação Molecular , Conformação de Ácido Nucleico , Potenciometria , RNA Catalítico/química , Viomicina/farmacologiaRESUMO
The interaction of apramycin with copper at different pH values was investigated by potentiometric titrations and EPR, UV-vis and CD spectroscopic techniques. The Cu(II)-apramycin complex prevailing at pH 6.5 was further characterized by NMR spectroscopy. Metal-proton distances derived from paramagnetic relaxation enhancements were used as restraints in a conformational search procedure in order to define the structure of the complex. Longitudinal relaxation rates were measured with the IR-COSY pulse sequence, thus solving the problems due to signal overlap. At pH 6.5 apramycin binds copper(II) with a 2 : 1 stoichiometry, through the vicinal hydroxyl and deprotonated amino groups of ring III. Plasmid DNA electrophoresis showed that the Cu(II)-apramycin complex is more active than free Cu(II) in generating strand breakages. Interestingly, this complex in the presence of ascorbic acid damages DNA with a higher yield than in the presence of H(2)O(2).
Assuntos
Cobre/química , DNA/química , Nebramicina/análogos & derivados , Estresse Oxidativo/efeitos dos fármacos , Plasmídeos/química , Antioxidantes/farmacologia , Ácido Ascórbico/farmacologia , Dicroísmo Circular , Cobre/metabolismo , DNA/metabolismo , Espectroscopia de Ressonância de Spin Eletrônica , Peróxido de Hidrogênio/farmacologia , Concentração de Íons de Hidrogênio , Espectroscopia de Ressonância Magnética , Modelos Químicos , Nebramicina/química , Nebramicina/metabolismo , Oxidantes/farmacologia , TermodinâmicaRESUMO
Coordination of Cu(II) to lincomycin was studied by potentiometry, UV-Vis, circular dichroism (CD), EPR, NMR, cyclic voltammetry (CV) and ESI-MS. Only mononuclear complexes of stoichiometries ranging from CuL to CuH(-3)L were found. In the main species present at neutral pH, CuH(-2)L, lincomycin bonds Cu(II) through both of its nitrogen donors, and a deprotonated oxygen donor at C4 of the sugar moiety. High pressure liquid chromatography (HPLC) of products of 2'-deoxyguanosine (dG) oxidation and agarose gel electrophoresis of plasmid DNA confirmed that lincomycin complexes effectively facilitate dG oxidation by H2O2, but are not able to cleave double-stranded plasmid DNA.