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
The effect of copper(II) ions on the probabilities of existence of the four detectable conformers of the tetrapeptide Tyr-Pro-Phe-Pro (beta-casomorphin 4) in [2H6]DMSO was investigated by 1H NMR spectroscopy. Integration of the Phe-NH signals provided the relative populations in the free state as tt/tc/ct/cc=28:34:29:9 at 293 K (c=cis, t=trans). Copper(II) was shown to bind to all four isomers, yielding complexes with two different structures, depending on the conformation of Pro(2). The interpretation of paramagnetic relaxation rates of Pro(2)-Halpha signals provided the corresponding isomeric probabilities in the metal-bound state as 13:36:20:31. The observed stabilization of the conformation with the lowest probability of existence (cc) may be relevant for the biological role of copper and other metal ions.
Assuntos
Cobre/química , Endorfinas/química , Fragmentos de Peptídeos/química , Prolina/química , Modelos Moleculares , Ressonância Magnética Nuclear Biomolecular/métodos , Conformação Proteica , Soluções , Estereoisomerismo , TermodinâmicaRESUMO
The copper (II) complex of amikacin in water solution at pH 5.5 was investigated by 13C-NMR. The temperature dependence of spin-lattice relaxation rates was measured and fast exchange conditions were shown to apply. The motional correlation time of the complex was approximated by the pseudo-isotropic rotational correlation time of free amikacin in water solution (tau c = 0.17 ns at 300 K). Formation of a pseudo-tetrahedral 1:1 complex was demonstrated by relaxation rates analysis and also by UV-Vis spectrophotometry. Two amino nitrogens of amikacin, together with the amide nitrogen and the hydroxyl in the hydroxyl-aminopropyl carbonyl side chain, were assigned as the copper-binding sites and a model of the complex was built by using copper-carbon distances obtained by NMR analysis as input parameters.
Assuntos
Amicacina/química , Antibacterianos/química , Configuração de Carboidratos , Sequência de Carboidratos , Isótopos de Carbono , Cobre/química , Concentração de Íons de Hidrogênio , Espectroscopia de Ressonância Magnética , Modelos Moleculares , Dados de Sequência Molecular , Soluções , ÁguaRESUMO
A method was developed for delineating the structure of paramagnetic metal complexes. The selective disappearance of cross-peaks in proton-carbon shift correlated 2D NMR maps was shown to uniquely depend upon the scalar and/or dipolar interaction between ligand nuclei and the unpaired electron(s), thus providing a means of identifying binding sites. Copper(II) was shown to form metal complexes with both Penicillin (PNC) and Pilocarpine (PLC) and the structure of the two 1:2 complexes in water solution at physiological pH were determined.
RESUMO
The interaction between the antimalarial drug chloroquine and red blood cells was investigated by measuring 1H NMR spin-lattice relaxation rates upon double-selective excitation of dipolarly connected spin pairs within the ligand molecule. Geometric and dynamic features were inferred, for the free as well as for the bound ligand, by the cross-relaxation terms between protons at fixed and time-dependent distances, respectively. A change in orientation of the side chain in respect of the aromatic moiety was shown to result from the binding interaction.