Intermolecular Association of Deoxycytidylyl-(3?,5?)deoxy-guanosine and Thymidylyl-(3?,5?)-deoxyadenosine in Dimethylsulfoxide

We have recently shown by nitrogen-15 and carbon-13 NMR in dimethylsulfoxide that, contrary to expectations, in the homodimer d(ApA) protonation of the phosphate group is competitive with protonation of the N1 nitrogen of adenine (1).