Mn2+–DNA interactions in aqueous systems: A Raman spectroscopic study

Interaction of natural calf thymus DNA with Mn 2+ ions was studied by means of Raman spectroscopy. Spectra of DNA in 10 mM Na-cacodylate buffer, pH 6.2, 10 mM NaCl and in buffer containing Mn 2+ ions were measured at room temperature. Mn 2+ concentrations varied between 0 and 0.6 M. DNA backbone conformational changes and DNA denaturation were not observed in the concentration range 0 and 0.5 M, however, DNA condensation was observed at a critical concentration of 100 mM Mn 2+ that prevented the measurement of Raman spectra. Binding of Mn 2+ to the charged phosphate groups of DNA is indicated in the spectra. A high affinity of Mn 2+ for guanine N7 was obvious, and binding to adenine was barely suggested.