Multinuclear NMR Study of the Interaction of DNA Liquid Crystalline Phases with Intercalators and Divalent Metal Ions

It is assessed that intercalators, such as antibiotics and dyes, and particular divalent metal ions are activators or inhibitors of important processes, such as the replication, the transcription and the translation of the genetic code. Therefore, it is of great interest to analyse in detail the structural variations induced on DNA liquid crystals by these agents and to reveal possible correlations between the DNA structure and its biological activity.
To get these objectives, methodologies of experimental investigation based on the use of the multinuclear NMR spectroscopy have been employed, allowing the acquisition of set of information on the structural and dynamic properties of DNA-exogenous agents systems. To this aim, DNA liquid crystalline samples, at different temperatures and concentrations, have been analysed by means of 31P, 23Na, 2H and 17O NMR Spectroscopy. In particular, various spectroscopies have contributed to monitor simultaneously DNA structure and physical state (31P NMR), interactions between DNA and sodium counterions (23Na NMR), and the degree of order of examined liquid crystals and of the water (2H and 17O NMR). Moreover, the employment of the Polarized Light Optical Microscopy has provided complementary information for the characterisation of the DNA liquid crystalline phases. In the present work the following exogenous agents have been analysed: the classical intercalator ethidium bromide (EB), divalent metal ions Mg2+, Mn2+, Ni2+ and Cd2+, and the intercalating platinum complex Chloro(2,2’:6’,2’’-Terpyridine)Platinum(II) Chloride [Pt(Terpy)Cl]Cl (PtTCC).