SCF Theory of Uniformly Charged Dendrimers: Impact of Asymmetry of Branching, Generation Number, and Salt Concentration

Polyelectrolyte
dendrimers attract large interest and find multiple
applications in many fields. The majority of theoretical and simulation
works consider dendrimers with symmetrical branching where all spacers
have the same length. In the present work, we for the first time systematically
studied the effect of asymmetry of branching in flexible uniformly
charged dendrimers on their structural properties. Lysine dendrimers
with lysine amino acid residues as branching units and with spacers
consisting of uniformly charged linear lysine (or arginine) peptides
of two different lengths are an example of such dendrimers. The Scheutjens–Fleer
self-consistent field approach was used to study the dendrimers with
different asymmetries of branching and different generation numbers
in solution at different salt concentrations. Three regimesosmotic,
salt-dominant, and quasi-neutralwere distinguished, and corresponding
theoretical scaling dependencies have been verified. It was demonstrated
that large-scale conformational properties practically do not depend
on asymmetry of branching, but in the osmotic regime, the gyration
radius weakly depends on it. The asymmetry of branching is manifested,
however, in the internal structure of dendrimers, such as the radial
distributions of monomer units, branching points, and terminal segments.
The asymmetry of branching significantly affects also electrostatic
properties of the dendrimers in the low-salt regime. While dendrimers
with symmetric branching behave as a uniformly charged sphere with
the maximum of electrostatic field on its surface, dendrimers with
asymmetric branches behave as a sphere with decaying local charge
density. The effective radius of an equivalent charged sphere increases
and the surface electrostatic potential (ζ-potential) decreases
with an increase of asymmetry of branching.