Understanding the cosolvation effect of dendrimers

Molecules that are virtually insoluble in certain solvents may be uploaded to "hostile" phases by dendrimers. Prime examples of this phenomenon are Eosin Y, EY, and Rose Bengal, RB, that are not soluble in CH2Cl2 where they can, however, be solvated through the interaction with a fourth generation dendrimer of polypropylene amine, POPAM-4D. The two dyes share the same carbon framework and differ for the pattern of halogenation, and yet their cosolvation varies over a factor of 4: six Eosin Y and similar to 25 Rose Bengals are solvated by the macromolecule. Leveraging on a previous report where molecular dynamics simulations of 12 EY@ POPAM-4D in CH2Cl2 showed a reduction to the experimental limit of 6, we now perform similar calculations with an excess, i.e., 40, of RB@POPAM-4D. The simulations quantitatively reproduce the cosolvation effect. They also provide a microscopic understanding of its origin and of motions-interactions of the macromolecule and both of its guests.