How to make a molecular light switch sequence-specific: tethering of an oligonucleotide to a dipyridophenazine complex of ruthenium (II)

Abstract

Considerable attention has been given recently to the design and development of nonradiative methods of recognizing DNA in a sequence-specific manner. Earlier, we reported that Ru(bpy)_2dppz^(2+)(bpy equals 2,2'-bipyridine, dppz equals dipyrido[3,2:a-2',3':c]phenazine) shows no luminescence in aqueous solution, but upon intercalation into double-helical DNA, bright photoluminescence is observed (A. E. Friedman, et al., J. Am. Chem. Soc., 1990, 112, 4960). Based upon this observation, a sequence-specific molecular light switch has been designed in which a dppz complex of ruthenium(II) is tethered onto an oligonucleotide. An oligonucleotide modified at its 5 foot end has been constructed by coupling the sequence 5'-H_2N(CH_2)_6AGTGCCAAGCTTGCA-3' to Ru(phen')_2dppz^(2+) (phen' equals 5-amido-glutaric acid-1,10-phenanthroline). Like the parent complex Ru(bpy)_2dppz^(2+), the single-stranded metal-oligonucleotide conjugate shows little detectable luminescence in aqueous solution. Addition of the complementary strand results in intense photoluminescence; time-resolved studies show that the emission is biphasic with excited state lifetimes of 500 (60%) and 110 (40%) ns. As expected, addition of a non- complementary strand produces no luminescence enhancement over that of the single-stranded metal-oligonucleotide. These results demonstrate that this oligonucleotide derivatized metal complex can be used to recognize and target specific sequences on DNA, a valuable feature which may lead to interesting and novel applications in hybridization technology.

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