Modeling the action of environment on proton tunneling in the adenine-thymine base pair.

Effect of environment coupling on the quantum-biological phenomenon of proton tunneling in the hydrogen bonds of the adenine-thymine base pair in DNA was modeled within the framework of quantum statistics and perturbation theory. A number of important thermodynamic indicators including partition function, free energy, and entropy were then calculated and examined. The proton was then assumed to be subject to an attraction represented by a double-well potential energy surface with a small asymmetry, which was considered as the perturbation introduced to the system. The action of environment manifested itself in the form of a global minimum in the free energy curve, as an implicit implication of the tendency of the system toward randomness and disorder, at which no spontaneous change such as quantum tunneling will accordingly occur. Furthermore, assuming the free energy to be in a close neighborhood of its minimum truly explained the smallness of the contribution of environment coupling to the tunneling probability reported in the literature based on the fact that the closer the free energy to its minimum, the less the transition probability to this point.