Partitioning of macromolecules between two interconnected spherical cavities

Simulations of excluded volume macromolecular chain encased in two interconnected cavities reveal for weak confinement a strong preference for a conformation of macromolecule in one of the two cavities. For a symmetric twin-cavity system, a conformational transition from the single cavity occupation to the conformation bridging the two cavities is observed on increasing confinement of encased chain. For asymmetric system of cavities with weak confinement the partitioning of chain segments between the two cavities is governed by classical partitioning law in which partitioning free energy increases linearly with chain length. On increasing chain length (or stronger confinement), a maximum in this dependence is observed followed by a decrease. This behavior is explained by correlation between increasing confinement and increasing concentration of encased chain. The position of the maximum reflects an increasing hinderance of the macromolecule in the larger of the two cavities and the start of the population of the bridging conformation as observed from the histogram of conformations. The structure of coils in the twin cavity is reflected by typical structure factors S(q) of (1) the free excluded volume coil for the weak confinement, (2) about the 0 coil for the moderate confinement, and (3) of the polymer globule for strongly confined macromolecular chain exhibiting a break in S(q), appearing from the structure of the twin cavity.