Ru(phen)(2)dppz(2+) Luminescence: Dependence on DNA Sequences and Groove-Binding Agents.
Emission of Delta-Ru(phen)(2)dppz(2+) bound to nucleic acid polymers of different sequence has been investigated by time-resolved luminescence spectroscopy and the effect of major and minor groove DNA binding agents on the luminescence profile of the complex evaluated. In the presence of a 1:1 mixture of poly d(AT) and poly d(GC), the excited-state decay of Delta-Ru(phen)(2)dppz(2+) can be described by a linear combination of the decay profiles in the presence of poly d(AT) and poly d(GC) independently. This analysis indicates that approximately 85% of the complexes are bound to poly d(AT) and that the metallointercalator preferentially occupies AT sites in mixed-sequence polymers such as calf thymus or T4 DNA. When rac-Ru(phen)(2)dppz(2+) bound to [d(5'-GAGTGCACTC-3')(2)] is titrated with the major groove intercalator Delta-alpha-[Rh[(R,R)-Me(2)trien]phi](3+), the ruthenium emission yield decreases while the absorbance of the pi-pi transition centered on the dppz ligand increases, until saturation behavior is observed at a 1:1 Rh/duplex ratio. These titrations indicate that Ru(phen)(2)dppz(2+) is displaced from the major groove by the rhodium complex. In contrast, for rac-Ru(phen)(2)dppz(2+) bound to poly d(AT), addition of the minor groove binding agent distamycin produces an increase in ruthenium emission which saturates at approximately 1 distamycin/5 bp, consistent with the double helix being able to accommodate major and minor groove binders simultaneously. Distamycin has no effect on the emission of Ru(phen)(2)dppz(2+) emission bound to poly d(GC). These photophysical studies establish a sequence preference in binding to DNA by Ru(phen)(2)dppz(2+) as well as providing support for the original assignment by NMR of ruthenium intercalation from the major groove side of the DNA helix.
Holmlin
R. Erik
RE
Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125.
Stemp
Eric D. A.
ED
Barton
Jacqueline K.
JK