Effects of solvent on stacking interactions. A spectrophotometric study of methylene blue dimerization in aqueous solutions of some monohydric alcohols

Abstract

A previous experimental study of the role of hydrophobic interactions on so-called stacking forces (of considerable interest in the conformational stability of nucleic acids) is here extended by considering alcohol solvent perturbation, as probed by dye self-association. The monomer–dimer equilibrium of Methylene Blue in aqueous solutions of methanol, ethanol, propan-1-ol and propan-2-ol has been studied using spectrophotometric techniques, microprocessor-based data acquisition and computer-aided data processing.

Results show that these alcohols mainly affect the dimerization entropy change. A linear enthalpy–entropy compensation is found, with a compensation temperature of ca. 220 K.