Evaluation of Biopolymer Conformations: Substituent Electronegativity in Nucleosides

Coupling constants J_ij for resonating vicinal protons i and j in NMR are studied theoretically and computationally. Electronegativity as a source of an additive correction for J_{1′, 2′} and J_{2′, 3′}, in two families of nucleosides is examined. Variations in J_{1′, 2′} + J_{3′, 4′} and J_{2′, 3′} are explained by conformational changes only. Variations in J_{1′, 2′} and J_{3′, 4′} are partially explained by a change of conformation, but mainly by variation in population caused by the 2′ substituents and by bee changes. Moreover, the changes of populations are quantifiable with respect to the substituent in 1′ or 2′. A computer program called SEARCH has been developed which optimizes the phase angle of pseudorotation P and the degree of pucker τ_m for a set of ring sugar coupling constants.