Consider a phospholipid bilayer membrane consisting of a mixture of 90% uncharged lipid and 10% singly charged acid lipid. Assume 68 Å^2 surface area per lipid head group, and assume further that the charged lipids are uniformly distributed and immobile. The membrance is in contact with an aqueous solution of NaCl at 25 ˚C. The alt concentration is c = 100mM.
What is the electrostatic energy (in kT units) of binding to the membrane of a trivalent positive ion such as spermidine assuming that:
(a) binding occurs at the membrane surface?
(b) owing to steric factors the charges of the bound spermidine stay in the water 5 Å distance from the membrane surface?
The Attempt at a Solution
The electric potential at the surface and at 5 Å must be known to find the energy of the binding, and I can find that potential. But what tells me the binding energy? I just don't know. Thanks.