2 research outputs found
Water alignment, dipolar interactions, and multiple proton occupancy during water-wire proton transport
A discrete multistate kinetic model for water-wire proton transport is
constructed and analyzed using Monte-Carlo simulations. The model allows for
each water molecule to be in one of three states: oxygen lone pairs pointing
leftward, pointing rightward, or protonated (HO). Specific rules
for transitions among these states are defined as protons hop across successive
water oxygens. We then extend the model to include water-channel interactions
that preferentially align the water dipoles, nearest-neighbor dipolar coupling
interactions, and coulombic repulsion. Extensive Monte-Carlo simulations were
performed and the observed qualitative physical behaviors discussed. We find
the parameters that allow the model to exhibit superlinear and sublinear
current-voltage relationships and show why alignment fields, whether generated
by interactions with the pore interior or by membrane potentials {\it always}
decrease the proton current. The simulations also reveal a ``lubrication''
mechanism that suppresses water dipole interactions when the channel is
multiply occupied by protons. This effect can account for an observed
sublinear-to-superlinear transition in the current-voltage relationship