Site-selective electron transfer from purines to electrocatalysts: voltammetric detection of a biologically relevant deletion in hybridized DNA duplexes

Background: The one-electron oxidation of guanine nucleobases is of interes t for understanding the mechanisms of mutagenesis, probing electron-transfe r reactions in DNA, and developing sensing schemes for nucleic acids. The e lectron-transfer rates for oxidation of guanine by exogenous redox catalyst s depend on the base paired to the guanine. An important goal in developing the mismatch sensitivity is to identify a means for monitoring the current resulting from electron transfer at a single base in the presence of nativ e oligonucleotides that contain all four bases. Results: The nucleobase 8-oxo-guanine (8G) is selectively oxidized by the r edox catalyst Os(bpy)(3)(3+/2+) (bpy = 2,2'-bipyridine) in the presence of native guanine. Cyclic voltammograms of Os(bpy)(3)(2+) show current enhance ments indicative of nucleobase oxidation upon addition of oligonucleotides that contain 8G, but not in the presence of native guanine. As expected, si milar experiments with Ru(bpy)(3)(2+) show enhancement with both guanine an d 8G. The current enhancements for the 8G/Os(III) reaction increase in the order 8G-C similar to 8G.T < 8G.G < 8G.A < 8G, the same order as that obser ved for guanine/Ru(III). This site-selective mismatch sensitivity can be ap plied to detection of a TTT deletion, which is important in cystic fibrosis . Conclusions: The base 8G can be effectively used in conjunction with a low- potential redox catalyst as a probe for selective electron transfer at a si ngle site. Because of the high selectivity for 8G, rate constants can be ob tained that reflect the oxidation of only one base. The mismatch sensitivit y can be used to detect biologically relevant abnormalities in DNA.