Sorption and permeation of poly(n-hexyl l-glutamate) — organic solvent systems

To elucidate the permeation mechanism in polypeptide membranes quantitatively, sorption and permeation of organic solvents on and through poly(n-hexyl l-glutamate) (PHeLG) membrane are studied. Sorption isotherms of solvents are monotonous curves characteristic of random mixing of solvent with the side chains of PHeLG. Values obtained for the permeability and diffusion coefficients are explained systematically by the solvent size and affinity to PHeLG. The free volume fraction of PHeLG is larger than that of usual amorphous polymers. Using a membrane prepared by the application of electric field to concentrated PHeLG solution, the influence of orientation of α-helix to the permeation behaviour is examined. While the sorption is affected little by orientation, the permeability and diffusion coefficients decrease systematically with increase of orientation. It is also confirmed that the critical solvent concentration for the orientation in PHeLG-benzene system is about 40 wt %.