15N and 13C nuclear magnetic resonance of deoxydinucleotide monophosphates. II. Protonation of the homo dimers deoxycytidylyl-(3?,5?)-deoxycytidine, thymidylyl-(3?,5?)-thymidine, and deoxyadenylyl-(3?,5?)-deoxyadenosine in dimethyl sulfoxide

The preferential protonation sites of the homo dimers deoxycytidylyl-(3?,5?)-deoxycytidine, thymidylyl-(3?,5?)-thymidine, and deoxyadenylyl-(3?,5?)-deoxyadenosine were established by nitrogen-15 and carbon-13 NMR in dimethyl sulfoxide, in the presence of varying amounts of CF3COOH. The nitrogen-15 NMR data show that in d(CpC) the capability of the two N3 nitrogens to accept the proton is slightly different. In d(TpT) and d(ApA) the protonation of the phosphate group leads to significant variations of the chemical shift of the carbons adjacent to phosphorus. Keywords: deoxydinucleotides, protonation, 15N and 13C NMR.