C O M M U N I C A T I O N S
modeling showed that the spin label does not fit because of steric
clashing with the methyl groups of the flanking base pairs. We
hypothesize that this steric interaction results in displacement of
the spin-labeled base toward the major groove, resulting in increased
spin-label mobility.
In conclusion, single-base mismatches have been detected for
the first time by EPR spectroscopy using a standard X-band
continuous-wave EPR spectrometer. Furthermore, the spin label TC
can report the identity of the base to which it is paired in duplex
DNA and thereby give insights into hydrogen bonding between
bases. This study illustrates that minor structural variations in
nucleic acids can be detected with carefully chosen spin labels in
conjunction with EPR spectroscopy.
Acknowledgment. We thank Lina Olofsson for technical
assistance. This work was supported by The Icelandic Research
Fund (080041022) and by a doctoral fellowship to P.C. from the
Eimskip Fund of the University of Iceland.
Supporting Information Available: Supplementary figures and
tables, experimental procedures, and characterization of compounds and
oligomers, including spectral data. This material is available free of
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