1H NMR investigation of the hetero-association of phenanthridine dyes with Daunomycin: effect of substitution of amino with azido groups in the dye chromophore

• Published in: Molecular physics 2004-09, Vol.102 (18), p.1933-1942
• Main Authors: Veselkov, Dennis A., Karawajew, Leonid, Veselkov, Alexei N., Davies, David B.
• Format: Article
• Language: English
• ISSN: 0026-8976; 1362-3028
• DOI: 10.1080/00268970412331292731

1 H NMR spectroscopy at 500 Mhz has been used to determine the structures and thermodynamics in aqueous salt solution of the hetero-association of Daunomycin (DAU) with a series of phenanthridine dyes having different numbers of amino/azido groups in the chromophore, together with the self-association of the phenthridine dyes under the same solution conditions (0.1 M phosphate buffer, pD 7.1, 298 K). The NMR measurements have been analyzed using statistical-thermodynamical models of both self-association and hetero- association in which no limitation is set on the size of molecular stacks. In this work the magnitudes of the self-association parameters of Ethidium Bromide (EB) and its azido-derivatives, 8-azido-Ethidium Bromide (EMB) and 3,8-diazido-Ethidium Chloride (EDC), show a successive decrease with mono- and di-substitition of the 3,8-amino groups of EB. A similar pattern is observed for the equilibrium constants for hetero-association of the phenanthridines with DAU. The thermodynamical and structural parameters of hetero-association of the phenanthridines with DAU are consistent with an intermolecular hydrogen bond between the 3,8 amino-groups of EB and the 9MeCO group of DAU contributing to the stability of the hetero-complex in aqueous solution.