Structure of Charged Poly(propylene imine) Dendrimers: Theoretical Investigation

Abstract

A mean‐field model for charged dendrimers has been elaborated and applied to Astramol dendrimers of 5th generation in salt‐free solution. The free energy of a dendrimer molecule was minimized with respect to the dendrimer size and to the profile of counterion distribution. The model of highly stretched freely jointed chain was used to describe the elasticity of long branches, the dissociated groups were assumed to be localized mostly on the periphery of the molecule, and the electrostatic interactions were described in the Poisson‐Boltzmann approximation. It was found that the osmotic pressure of counterions leads to moderate expansion of dendrimer molecules upon charging, and a significant fraction of counterions is localized within the dendrimer molecule under typical experimental conditions.The schematic structure of poly(propylene imine) dendrimers for the 4th generation.imageThe schematic structure of poly(propylene imine) dendrimers for the 4th generation.

Mean field theory of charged dendrimer molecules

“…This result is consistent with the predictions of the scaling in the quasi-neutral regime (Eq. (19)). As the charge fraction is increased, the size behavior of the dendrimer is seen to approach the high salt osmotic regime scaling (Eq.…”

“…Adding charged groups to dendrimers was proposed as a way to achieve open core conformations desired for drug delivery applications. Such considerations have motivated a number of theoretical [17][18][19][20][21][22][23][24][25][26][27][28][29] and experimental [30][31][32][33][34] studies of charged dendrimer molecules. For instance, Welch and Muthukumar 17 used Monte Carlo simulations to show that the size and conformations of dendrimers with charged branch and terminal points are strongly dependent on the salt concentration.…”

“…However, their model for electrostatic effects treated the counterions only at an implicit level and incorporated instead Debye-Huckel interactions between the charged groups. Subsequent work using scaling analysis 35 and computer simulations 19,[21][22][23][24][25][26][27][28][29][36][37][38] have shown that counterion localization becomes an important factor for highly branched polymeric structures. Such a phenomenon reduces the electrostatic interactions between the charged monomers and endows nontrivial dependencies for the conformations of the dendrimer as a function of number of dissociatable groups, salt concentrations, etc.…”

The Structure of Dendrimers with Charged Terminal Groups: Monte Carlo Simulations

“…Some examples of their use include lithographic materials, nanoscale catalysts, drug delivery systems, rheology modifiers, bioadhesives, and magnetic resonance imaging (MRI) contrast agents [3]. Though experimental studies [4][5][6][7][8][9], theory and simulations [10][11][12][13][14] have already brought about some insight into the way charged dendrimers react to various conditions, the research on them is far from being completed. For instance, the number of simulation papers is still very limited and some predictions reported in them contrast with experimental results.…”

The adsorption-desorption transition of double-stranded DNA interacting with an oppositely charged dendrimer induced by multivalent anions

“…Besides, the molecular volume of dendrimers also depends on terminal groups which prevent the core of dendrimers from other molecules. 14 Recently, experimental, 15,16 analytical, 17 and computational [18][19][20][21][22][23][24][25] studies of these novel macromolecules have focused on charged dendrimers. Welch and Muthukumar studied first the charged dendrimers by using Monte Carlo simulations with implicit conversions, and they found that the ion strength of solution is an important parameter for controlling the behavior of charged dendrimers.…”