Solvent isotope effect in the monomer–dimer equilibrium of methylene blue

Abstract

So-called stacking forces, of particular interest in the structural stability of nucleic acids, have been studied in a simple model system of planar, non-hydrogen-bonding dye molecules (Methylene Blue). The dimerization process has been studied by spectral analyses at different concentrations and temperatures in D₂O as well as in H₂O. Computer-aided data-processing techniques have been used to obtain detailed information on the dimerization process.

Results show that the high positive (hydrophobic) contribution to the ‘unitary’ entropy term due to solute–solvent interaction changes appreciably upon H–D substitution. This illustrates the role of hydrophobic interactions in dimerization (stacking) processes.