| Popis: |
The electrical interactions between the head groups of the phospholipids phosphatidyl choline and ethanolamine when packed in the natural ordered array are examined. It is shown that Langmuir films of these molecules are likely to have a domain structure in which the head group P--N+ dipoles form arrays with a net dipole moment. Taking account of dipole-dipole interactions and of pH and counterion-dependent head group charge, it is possible to calculate the Langmuir pressure-area isotherms and to predict expanded-condensed film transitions. An electric field normal to the plane of the arrays induces repulsive dipole-dipole forces in the plane which, when sufficiently large, can rupture the structure. In bilayer form the effect of the field leads to a prediction of switching phenomena which, it is believed, have been observed experimentally. |
