¹³C-NMR of the Deoxyribose Sugars in Four DNA Oligonucleotide Duplexes: Assignment and Structural Features

Natural-abundance ¹³C-NMR spectra have been obtained for four self-complementary DNA oligonucleotides: [d(TAGCGCTA)]₂, [d(GGTATACC)]₂, [d(CG)₃]₂, and [d(TCGCG)]₂; this paper focuses on the deoxyribose resonances. Assignments were made by a combination of the two-dimensional protondetected heteronuclear correlation experiment and comparison of 1D spectra, accounting for ³¹P coupling, base composition, and similarities in chemical shift versus temperature profiles (δ vs T). Large shielding and deshielding of the sugar resonances (between 2.0 and -1.9 ppm) are observed upon thermal dissociation of the duplex. The shapes of the δ vs T profiles correlate strongly with the purine/pyrimidine nature of the base attached at C1′ in these duplexes that have a substantial fraction of residues within alternating purine-pyrimidine sequences. The correlation is primarily associated with changes in the equilibrium distribution of furanose pseudorotational states that may arise in part from the relief of interstrand purine-purine steric clashes.