Inversion of DNA helicity induced by zinc (II)-macrocyclic polyamine complexes

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Abstract
Exposure of synthetic polynucleotide poly(dG-dC)·poly(dG-dC) to ZnII cyclen, 2 (cyclen = 1,4,7,10-tetraazacyclododecane), produces a dramatic change in its circular dichroism (CD) spectrum in H2O at pH 7.2, 24°C: the CD spectrum of the initial B form changes to that of the Z form (or a non-Z structure with a left-handed helix) at very low concentrations ([ZnII]/[base pair] in molar basis ≤ 1). By contrast, ZnII-[12]aneN3, 1 ([12]aneN3 = 1,5,9-triazacyclododecane), and ZnII-cyclam, 3 (cyclam = 1,4,8,11-tetraazacyclo-tetradecane), do not significantly have such a topological affect on the polynucleotide even at much higher concentrations. An increase in Na+ ionic strength nullified the effect of 2 on the CD spectrum, indicating an outside interaction (electrostatic and/or hydrogen bonding) of the DNA model. This study illustrates the significance of the macrocyclic ligand structure around the ZnII ion for specific interaction with DNA.