Engineering Ultrasoft Interactions in Stiff All‐DNA Dendrimers by Site‐Specific Control of Scaffold Flexibility

Abstract A combined experimental and theoretical study of the structural correlations in moderately concentrated suspensions of all‐DNA dendrimers of the second generation (G2) with controlled scaffold rigidity is reported here. Small‐angle X‐ray scattering experiments in concentrated aqueous saline solutions of stiff all‐DNA G2 dendritic constructs reveal a novel anomalous liquid‐like phase behavior which is reflected in the calculated structure factors as a two‐step increase at low scattering wave vectors. By developing a new design strategy for adjusting the particle's internal flexibility based on site‐selective incorporation of single‐stranded DNA linkers into the dendritic scaffold, it is shown that this unconventional type of self‐organization is strongly contingent on the dendrimer's stiffness. A comprehensive computer simulation study employing dendritic models with different levels of coarse‐graining, and two theoretical approaches based on effective, pair‐potential interactions, remarkably confirmed the origin of this unusual liquid‐like behavior. The results demonstrate that the precise control of the internal structure of the dendritic scaffold conferred by the DNA can be potentially used to engineer a rich palette of novel ultrasoft interaction potentials that could offer a route for directed self‐assembly of intriguing soft matter phases and experimental realizations of a host of unusual phenomena theoretically predicted for ultrasoft interacting systems.