Periodicity in proton conduction along a H-bonded chain. Application to biomolecules

摘要

Molecular complexes are constructed to simulate proton transfer channels of the influenza A virus and of the active site of carbonic anhydrase. These complexes consist of proton donor and acceptor groups connected by a chain of water molecules. Quantum chemical calculations on the methylimidazole(H+)-H2O-CHCOO- model of the M2 virus channel indicate free translational motion of the water molecule between donor and acceptor, as well as concerted transfer of both H-bond protons. The proton transfer barrier does not depend on the position of the bridged water molecule and varies linearly with the difference of electrostatic potentials between the donor and acceptor. When the water chain is elongated, and with various donor and acceptor models, periodicity appears in the H-bond lengths and the progression of proton transfer in each link. This "wave" is shown to propagate along the chain, as it is driven by the displacement of a single proton. One can thereby estimate the velocity of the proton wave and proton conduction time. Computations are performed to examine the influence of immersing the system within a polarizable medium. (C) 2007 Wiley Periodicals, Inc.