Tris (phenanthroline) Metal Complexes: Probes for DNA Helicity
The intercalative binding of chiral tris(phenanthroline) metal complexes to DNA is stereo-selective. The enantiomeric selectivity is based upon the differential steric interactions between the two non-intercalating phenanthroline ligands of each isomer with the DNA phosphate backbone. Gel electrophoretic assays of helical unwinding, optical enrichment studies by equilibrium dialysis and luminescence titrations with separated enantiomers of (phen)_3Ru^(2+) all indicate that the delta isomer binds preferentially to the right-handed duplex. The chiral discrimination is governed by the DNA helical asymmetry. Complete stereospecifity is seen with isomers of the bulkier RuDIP (tris-4,7-diphenylphenanthrolineruthenium(II)). While both isomers bind to Z-DNA, a poor template for discrimination, binding of Λ-RuDIP to B-DNA is precluded. These chiral complexes therefore serve as a chemical probe to distinguish left and right-handed DNA helices in solution.
© 1983 Adenine Press. Date received: September 8, 1983. The financial support of the National Institutes of Health (GM32203) is very gratefully acknowledged. It is also a pleasure to thank Dr. J. J. Dannenberg for stimulating collaborations and discussions, Dr. O. J. Miller and Dr. Dorothy Miller for an already fruitful collaboration, and my new eager and curious students, Adrienne Raphael, Avis Danishefsky, Lena Basile, Jon Goldberg, and Andrei Alexandrescu.