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Atomistic Molecular Dynamics Simulations of Dendrimers and their Complexes with
Linear Polyelectrolytes
ABSTRACT
I. Tanis * , K. Karatasos
Aristotle University of Thessaloniki, Department of Chemical Engineering, Physical Chemistry Lab,
54124 Thessaloniki, Greece
*itanis@auth.gr
The aim of this project was to investigate the mechanisms that influence the ability of aqueous solutions of dendrimers or
complexes of them with linear polyelectrolytes to act as solubility enhancement agents, as well as the examination of the
mechanisms related to their capacity to adsorb/release polar molecules in a controlled manner. For that purpose molecular
dynamics simulations were conducted in aqueous solutions of dendrimers of different generations. These simulations were
performed with and without the presence of linear polyelectrolyte.
INTRODUCTION
Dendrimers are well-defined, globular, synthetic polymers. They are built up one monomer layer at a time, referred to as a
generation, starting from a core molecule, known as generation 0. This procedure results in structures of high molecular size,
large number of surface groups and low polydispersity. Studies of dendrimers as potential delivery systems indicated that a
microenvironment can arise in the dendrimer core because of the limited diffusion of solvent molecules into it[1]. For
example, dendrimers dissolved in polar solvents such as water can have an unpolar interior allowing organic molecules to be
encapsulated and carried in aqueous media [2]. The necessity for a detailed atomistic study of these systems becomes clear,
since (as has been shown by pertinent experiments) slight structural differences (for instance in surface groups) or variations
related to the electrolytic and solution properties may incur drastic changes in the behavior of such systems particularly
when biological applications are targeted. Moreover, because the number of surface functional groups (which more than
doubles when moving to the next generation) are expected to play a crucial role to the ability of these molecules to absorb
other compounds, a thorough examination of systems of different sizes is needed.
SIMULATION DETAILS
The systems that were examined represent aqueous solutions of 3 rd and 4 th generation poly(amidoamine) (PAMAM)
dendrimers with and without the presence of poly (ethylene oxide) (PEO). In addition, a system containing pure water was
constructed. All constructed models correspond to dilute solutions at density 0.98 gr/cm 3 . In systems that contained linear
chain molecule, the number of chain monomer units equals the number of the dendrimer terminal groups. We used AMBER
force field to describe the interactions for all atoms in polymer molecules including a hydrogen-bonding term. TIP3P [3]
force field parameters were used for water. The atomic charges needed for describing the coulomb interactions are calculated
from the Gasteiger [4] method. In total, the systems are neutrally charged. 3-dimensional representations of systems of 4 th
generation are shown in figures 1-4.
Figure 1. Generation 3 PAMAM-H 2 O
Figure 2. Generation 3 PAMAM-PEO-H 2 O
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