Kinetics of the labeling reactions of thymine, cytosine and uracil with osmium tetroxide bipyridine

The electroactive complex osmium tetroxide bipyridine holds great promise as a covalent label for biosensor applications regarding nucleic acids and protein detection. Labeling can easily be performed in the laboratory. Until now, almost only DNA species have been investigated using this label. Thymine (which occurs exclusively in DNA) is known to react much faster than cytosine and uracil. In order to explore the possibilities to modify and detect also RNA species in a timely fashion, we have investigated the kinetics of reactions of osmium tetroxide bipyridine with the pyrimidine bases in the micromolar concentration range at different temperatures by means of spectrophotometry. Results were confirmed using voltammetric detection for the determination of labeled oligonucleotides. The modification reaction can be easily completed at room temperature within 7 h, even in case of cytosine and uracil. At 60 A degrees C, 3 h are sufficient for complete modification of all pyrimidine bases that are found in natural nucleic acids. These findings will be important for future biosensor applications with RNA species as target molecules.