Hydrogen-bonding effects and 13 of the DNA double helix

Abstract
13C-nmr chemical shifts of the nucleotides in DNA are sensitive to hydrogen bonding, especially for three of the carbons immediately bonded to exocyclic oxygen or nitrogen atoms acting as H-bond acceptors or donors. GuoC2, GuoC6 and ThdC4 are strongly deshielded (about 1 ppm) upon Watson-Crick pairing in oligodeoxynucleotide duplexes, regardless of the base sequence. Deshielding at these sites may be useful to distinguish bases involved in Watson-Crick pairs from upaired bases.