tokens: The imino proton of T3 in the O6meG . T 12 - mer and G3 in the O6meG . N 12 - mer helix , which are associated with the modification site , resonate at unusually high field ( 8 . 5 to 9 . 0 ppm ) compared to imino protons in Watson - Crick base pairs ( 12 . 5 to 14 . 5 ppm ) .