Coadsorption of the complementary base pair adenine-thymine at the mercury/electrolyte interface

The condensation behaviour of adenine was investigated with respect to a possible reorientation during the phase transition. It was found that, in contrast to thymine, randomly adsorbed adenine yields a negative dipole contribution with regard to the displaced water molecules. During the condensation reorientation takes place in such a way that this negative dipole contribution is reinforced. Coadsorption of the complementary DNA bases adenine and thymine leads to destabilisation of both the condensed and the randomly adsorbed layers. In place of the attractive lateral forces between adenine or thymine in a pure condensed monolayer, another kind of interaction occurs between adenine and thymine in a mixed adsorbate. Hence, the phase transition disappears when a critical ratio of adenine to thymine is reached.