Stereodynamics of ribodinucleoside monophosphates in aqueous solution

Abstract
Arguments are presented which show that conformations II and III proposed by Lee and Tinoco for ribodinucleoside monophosphates in aqueous solution are untenable. Ribodinucleoside monophosphates exist in aqueous solution as an equilibrium blend of the classically recognized right-handed stack (g-g-), loop stack (g+g+), skewed (g+t), and extended arrays. In order to determine the effect of .epsilon.A base on the conformer distribution in the equilibrium blend, detailed ring-current calculations were performed and the isoshielding curves for .epsilon.A were derived. Use of these curves vis-a-vis dimerization shift data indicates that introduction of .epsilon.A perturbs the equilibrium blend which causes an increase in the population of skewed (g+t) arrays.