DNA-BINDING OF DELTA-[RU(PHEN)2DPPZ]2-[RU(PHEN)2DPPZ]2+( AND LAMBDA)

Linear dichroism (LD) spectroscopy and steady-state as well as time-re solved luminescence spectroscopy have been used to investigate the int eraction of the DELTA and LAMBDA enantiomers of Ru(phen)2DPPZ2+ (phen = 1,10-phenanthroline; DPPZ = dipyrido[3,2-a:2',3'-c]phenazine) with D NA. The pure enantiomers, which were difficult to separate by traditio nal resolving methods, were synthesized via a chiral precursor. Change s in luminescence, isotropic absorption and excited state lifetimes up on binding, and the LD observed in flow-oriented DNA systems provide d etailed information about the DNA binding of the enantiomers. Flow LD shows that both enantiomers bind to DNA in a well-defined manner with an orientation of the dipyridophenazine chromophore consistent with in tercalation of this moiety between base-pairs. Both enantiomers are fo und to show luminescence in the presence of DNA to which they bind ver y strongly (K almost-equal-to 10(8) M-1); however, the relative lumine scence quantum yield of the bound DELTA enantiomer is 6-10 times large r than that of the bound LAMBDA enantiomer. Furthermore, for each enan tiomer two distinct excited state lifetimes are found in varying propo rtions depending on the binding ratio. The large difference in lumines cence quantum yield between the enantiomers is interpreted in terms of slightly different intercalation geometries of the dipyridophenazine ligand, resulting in different protections from quenching by solvent w ater and diastereomeric differences in the interactions between enanti omers bound in contigue on DNA.