Exploring transport and selectivity in salt-rejecting membranes using transition-state theory

The theory of transition states was formulated by Eyring and coworkers in 1935. This theory provides a physical explanation for transition states by determining their location on the potential energy surface. It can also explain pre-exponential factors and activation energies in terms of entropy changes.

Transition state theory can be applied to any elementary chemical reaction, including diffusion. Diffusion involves solute molecules detaching from water molecules, entering a high energy state, and stabilizing in the next coordinate. This process is thermally activated and can be described using transition state theory.

When considering membrane permeability, multiple diffusion jumps must be accounted for. Solute molecules must partition into the membrane, face barriers inside the membrane, and then partition back out. Eyring's later work in 1949 connected his original theory to membrane permeability, showing that intrinsic permeability is equal to the product of partition coefficients and diffusion coefficients.