Experimental studies on the nature of bonding of DNA*bipyridyl-(ethylenediamine)platinum(II) and DNA*netropsin complexes in solution and oriented wet-spun films

Abstract

The stability of complexes of NaDNA with bipyridyl- (ethylenediamine)platinum(II) (abbreviated [(bipy)Pt(en)](2+)) and with netropsin has been studied using two techniques: (i) ultraviolet (UV) melting experiments were done on NaDNA* [(bipy)Pt(en)](2+), showing that the [(bipy)Pt(en)](2+) ligand stabilizes the DNA double helix structure; and (ii) swelling measurements (via optical microscopy) as a function of relative humidity were done on wet-spun oriented films of NaDNA*[(bipy)Pt(en)](2+) and of NaDNA*netropsin. The swelling data shows that an irreversible transition of the films occurs at high relative humidity, first for the NaDNA*netropsin, then for pure NaDNA, and lastly for the NaDNA*[(bipy)Pt(en)](2+). These results are indicative that the [(bipy)Pt(en)](2+) complex stabilizes the intermolecular bonds which mediate the film swelling characteristics. A model is suggested for the binding of [(bipy)Pt(en)](2+) to DNA to explain why the swelling experiments show this ligand as increasing the intermolecular bond strength between the DNA double helices, while netropsin decreases this degree of stabilization.