Reversal of a Single Base-Pair Step Controls Guanine Photo-Oxidation by an Intercalating Ruthenium(II) Dipyridophenazine Complex

Small changes in DNA sequence can often have major biological effects. Here the rates and yields of guanine photo-oxidation by Lambda-[Ru(TAP)(2)(dppz)](2+) have been compared in 5'-{CCGG (AT) under bar CCGG}(2) and 5'-{CCGG (TA) under bar CCGG}(2) using pico/nanosecond transient visible and time-resolved IR (TRIR) spectroscopy. The inefficiency of electron transfer in the TA sequence is consistent with the 5'-TA-3' versus 5'-AT-3' binding preference predicted by X-ray crystallography. The TRIR spectra also reveal the differences in binding sites in the two oligonucleotides.