Thermal stability of poly(A) and poly(U) complexes in H2O and D2O: isotopic effects on critical temperatures and transition widths.

This is a study of the effect of total and partial deuteration of solvent on critical temperatures and profiles of all four reactions occurring in poly(A) x n poly(U) (n = 1 or 2) aqueous systems. The study was done at observational times not longer than hydrogen exchange times at base pairs in helically ordered structures, and it was extended to a wide range of salt concentrations at neutral pH. The dependence of stability of polymer helical order on hydrogen mass does not appear to be merely attributable to the stronger intrahelical deuterium bonding. Substituting Deuterium for Hydrogen implies a probably predominant modulation of the entrophy term of polymer-solvent interactions. Effects of deuteration on the width of the 2(poly(A) x poly (U)) leads to poly(A) x 2poly(U)+poly(A) interconversion reaction were also observed. They bear on the role of polymer-solvent interaction on pattern recognition leading to formation of ordered structures. They also bear on the role of the same interaction on the "breathing" of ordered structures of this type.