Entropy effects in self-assembling mechanisms: Also a view from the information theory

At first sight, formation of self-assembled structures such as micelles, bilayers, DNA-cationic bilayers complexes, and the enzyme-substrate complexation in biological catalytic reactions look as totally different phenomena. However, common in all of them is the effective attractive interactions among the self-assembled molecular components that are required to occur. In general, the direct interactions among the components of an assembled structure are not sufficiently attractive to justify self-assembling by itself. Furthermore, in some cases these direct interactions are repulsive as in the case of like charged particles. In this paper, by means of theory and simulation, we consider the effective interactions of the following simple systems: 1) two like-charged parallel rods immersed in an electrolyte solution, 2) two like-charged parallel rods confined between two parallel plates, and 3) a sphere with an open cavity and a spherical macroparticle, both immersed in a hard sphere fluid. In the first two systems we show that effective attractive interaction among the components of a self-assembled structure may only occur when they are in high electrolyte volume fractions. In the lock-key system (3rd case), it is demonstrated that the perfect match between the spherical cavity and macroparticle is the most favorable condition for their self-assembly to occur. All these are examples of attraction driven by the need of the systems to optimize the available volume. That is, self-assembling is driven by the maximum entropy principle, or maximum missing information, as in information theory.