| Popis: |
A model of the lipid bilayer is described constituting a system of interacting aliphatic chains tied by one of the ends to a flat impermeable surface and capable of shifting along it. To maintain constant density periodic boundary conditions are introduced. The transitions between states (conformational changes of the chains and their disposition within the isolated cell) have been simulated with a computer by the Monte Carlo method. The details of chemical structure of the chains, the braking and correlation of internal rotations and the fluctuation of the valent and torsional angles are taken into account. Depending on the area A per chain the author has calculated the mean square size of the chains 〈r2〉), the parameter of the orientation order S and the mean number of the contacts between the monomer units 〈W〉 and the characteristics of the distribution of the monomer units in space (g2(R), ϱ1, etc.). It is shown that with fall in A (starting from A ∼ 〈r2〉0 where the value 〈r2〉0 refers to the isolated chain tied by an end to the impermeable surface) the system passes into the state with a clearly marked orientation ordering of the chains. The main role is played by the steric interactions of the chains. On the basis of the theory of similitude it is shown that for A ⪡ 〈r2〉0, 〈r2〉 ∼ l 103 N2 (p/A)23 and S∼l43 (p/A)23 (l is length of the skeletal bond; N is the number of bonds in the chain; p=a/d; a is the persistent length; d, the diameter of the chain). The expressions obtained are compared with the data of computer calculation and the experimental findings. |
