Nature of the Effective Interaction Between Dendrimers

TL;DR

This study uses atomistic molecular dynamics simulations to explore how the effective interactions between dendrimers can be tuned from repulsive to attractive by adjusting protonation levels, revealing detailed potential profiles.

Contribution

It provides the first detailed atomistic PMF profiles for dendrimers and challenges previous Gaussian-based models by showing a combined exponential and Gaussian fit.

Findings

Interaction can be tuned from repulsive to attractive

PMF fits combine exponential and Gaussian functions

Results differ from previous analytic and coarse-grained models

Abstract

We have performed fully atomistic classical molecular dynamics (MD) simulations to calculate the effective interaction between two polyamidoamine (PAMAM) dendrimers. Using the umbrella sampling (US) technique, we have obtained the potential of mean force (PMF) between the dendrimers and investigated the effects of protonation level and dendrimer size on the PMF. Our results show that the interaction between the dendrimers can be tuned from purely repulsive to partly attractive by changing the protonation level. The PMF profiles are well-fitted by the sum of an exponential and a Gaussian function with the weight of the exponential function dominating over that of the Gaussian function. This observation is in disagreement with the results obtained in previous analytic [Macromolecules 34, 2914 (2001)] and coarse-grained simulation [J. Chem. Phys. 120, 7761 (2004)] studies which predicted the effective interaction to be Gaussian.