Noncovalent and Site‐Directed Spin Labeling of Nucleic Acids

Spin label parking: The rigid spin label ç (magenta), which is an analogue of cytidine, binds site-specifically to abasic sites in duplex DNAs, through hydrogen bonding to guanine (blue) and π stacking with the flanking base pairs. EPR spectroscopy shows complete binding of ç to the abasic site at low temperatures. This new spin-labeling strategy gives easy access to spin-labeled nucleic acids for structural studies by pulsed EPR techniques.