A study on spin-labelled oligonucleotide synthesis and its electron spin resonance behavior in solution.

An oligonucleotide spin-labelled with 4-amino-2,2,6,6-tetramethylpiperidine-N-oxyl (4-amino-TEMPO) at the internucleotide bond (d-Tp(L)TpTpTpT) prepared by oxidation of the pentanucleotide containing the H-phosphonate diester (d-Tp(H)TpTpTpT) in the presence of 4-amino-TEMPO, was separated and identified by high-performance, reverse-phase liquid chromatography combined with detection by electron spin resonance spectroscopy. This spin-labelled oligonucleotide produced a triplet with the slightly broadened M1 = -1 ESR component, while a triplet with almost equal intensities was obtained from the spin-label. The M1 = -1 component from the labelled oligonucleotide was further broadened in the presence of poly(A) which forms a complementary double strand with this molecule.