Abstract
We report an analysis of Molecular Dynamics simulations carried out for the PAMAM-EDA dendrimer in water, considering neutral dendrimer, or high pH conditions, or assuming that all the amine groups are fully protonated at low pH (the addition of chloride counterions ensures the global charge neutrality of the system in this case). These simulations were performed considering the PCFF force-field with explicit consideration of hydrogen bonds and using the TIP3P molecular parameters for the water molecules. Our data indicate a remarkably different orientational distribution of dendrimer units for the two systems, low or high pH, with stronger segregation of dendrons in the former case Neutral dendrimers adsorb more water molecules.
Highlights
1 Introduction The polyamidoamine dendrimers with an ethylenediamine core (PAMAM-DEA) are commercially available and have a great potential in different applied fields [1]. Both primary and tertiary amino groups can be protonated and this protonation is strongly influenced by the physiological conditions of the medium, the solution pH. (All amine groups are expected to be fully protonated at low pH and they should be neutral in high pH solution)
We explored some features revealed from the analysis of the initial 2ns of the simulation trajectories, in particular the location of the amine groups within the dendrimer, the angular distribution of the density around the dendrimer center for conformations of neutral and charged dendrimers and the time evolution of the mean number of water molecules associated to amines located at different shells
3 Results and discussion Once we have achieved an adequate reproduction of the molecular sizes through the consideration of explicit hydrogen bond interactions, we have analyzed different conformational properties corresponding to these simulations that may help us to describe the space distribution of atoms
Summary
The polyamidoamine dendrimers with an ethylenediamine core (PAMAM-DEA) are commercially available and have a great potential in different applied fields [1] In these particular dendrimers, both primary and tertiary (or peripheral and inner) amino groups can be protonated and this protonation is strongly influenced by the physiological conditions of the medium, the solution pH. We have investigated the role of hydrogen bonds in the alternative more specific, class II, PCFF force-field [9], using the TIP3P molecular parameters and partial charges for water [10] With these specifications we have been able to find a good reproduction of the neutron scattering data for G=4 PAMAM-EDA dendrimers with different degrees of protonation [11]. We explored some features revealed from the analysis of the initial 2ns of the simulation trajectories, in particular the location of the amine groups within the dendrimer, the angular distribution of the density around the dendrimer center for conformations of neutral and charged dendrimers and the time evolution of the mean number of water molecules associated to amines located at different shells
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