Guest Uptake by Rigid Polyphenylene Dendrimers Acting As a Unique Dendritic Box in Solution Proven by Isothermal Calorimetry

Abstract

The existence of a dendritic box in polyphenylene dendrimers is demonstrated by isothermal titration calorimetry (ITC). The thermodynamic parameters of the uptake process of a variety of small guest molecules into the dendrimers are measured. ITC revealed that for dendrimers with an unpolar interior this process is mainly entropically driven. Two processes have been elucidated for the entropy gain: (i) the release of solvent molecules which solvate the guests and (ii) solvent molecules in the voids of the dendrimers which are replaced by the guests. For dendrimers which are substituted with polar functionalities in the core, enthalpic effects become more dominant as some hydrogen bonds and π–π-interaction come into play. Because of the rigidity of the dendrimer host, these less specific interactions can only occur in the core of the differently functionalized interior of the dendrimers since the surface is the same all over. Thereby, it is evidenced that guest molecules can be selectively trapped inside the dendrimer and not on the surface. For different host–guest pairs ITC resulted in characteristic thermodynamic parameters for the uptake. These values might give guidelines to estimate and model the binding strength and the release properties between a drug and dendritic carrier.