INVERSION OF DNA HELICITY INDUCED BY ZINC (II)-MACROCYCLIC POLYAMINE COMPLEXES

Exposure of synthetic polynucleotide poly (dG-dC)(.)poly(dG-dC) to Zn- II-cyclen (cyclen 1,4,7,10-tetraazacyclododecane), produces a dramatic change in its circular dichroism (CD) spectrum in water at pH 7.2: th e 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 concentration ([Zn-cyclen]/[base pairs] less than or equal to 1). An increase in sod ium perchlorate concentration (up to 50 mM) nullified the effect of th e Zn-cyclen complex on the CD spectrum, indicating an outside interact ion (electrostatic and/or hydrogen bonding) of the DNA model. In contr ast, zinc complexes of either 1,5,9-triazacyclododecane or 1,4,8,11-te traazacyclotetradecane do not have such a significant topological effe ct on the polynucleotide even at much higher concentrations. This stud y illustrates the significance of the macrocyclic ligand structure aro und the Zn-II ion for specific interaction with DNA.