Configurations of base‐pair complexes in solutions

A theoretical search for the most stable conformations (i.e., stacked or hydrogen bonded) of the base pairs A‐U and G‐C in water, CCl₄, and CHCl₃ solutions is presented. The calculations of free energies indicate a significant role of the solvent in determining the conformations of the base‐pair complexes. The application of the continuum method yields preferred conformations in good agreement with experiment. Results of the calculations with this method emphasize the importance of both the electrostatic interactions between the two bases in a complex, and the dipolar interaction of the complex with the entire medium. In calculations with the solvation shell method, the last term, i.e., dipolar interaction of the complex with the entire medium, was added. With this modification the prediction of the solvation shell model agrees both with the continuum model and with experiment, i.e., in water the stacked conformation of the bases is preferred.