Self-Assembly of Lysine-Based Dendritic Surfactants Modeled by the Self-Consistent Field Approach

Implementing a united atom model, we apply self-consistent field theory to study structure and thermodynamic properties of spherical micelles composed of surfactants that combine an alkyl tail with a charged lysine-based dendritic headgroup. Following experiments, the focus was on dendron surfactants with varying tail length and dendron generations G0, G1, G2. The heads are subject to acetylation modification which reduces the charge and hydrophilicity. We establish a reasonable parameter set which results in semiquantitative agreement with the available experiments. The critical micellization concentration, aggregation number, and micelle size are discussed. The strongly charged dendronic surfactants micelles are stable for generation numbers G0 and G1, for progressively higher ionic strengths. Associates of G2 surfactants are very small and can only be found at extreme surfactant concentration and salt strengths. Micelles of corresponding weaker charged acetylated variants exist up to G2, tolerate significantly lower salt concentrations, but lose the spherical micelle topology for G0 at high ionic strengths

Structure of asymmetrical peptide dendrimers : Insights given by self-consistent field theory

Structural properties of asymmetric peptide dendrimers up to the 11th generation are studied on the basis of the self-consistent field Scheutjens-Fleer numerical approach. It is demonstrated that large scale properties such as, e.g., the gyration radius, are relatively weakly affected by the asymmetry that is, by difference in the length of short and long spacers. However, the asymmetry has strong influence on the internal structure of the dendrimers and on the radial distribution of polymer density and terminal segments. In particular, symmetrical and weakly asymmetrical dendimers are characterized by quasi-uniform intramolecular concentration profiles of monomer units whereas strongly asymmetric dendrimers are characterized by sharply decreasing in a radial direction polymer density profile reminiscent to that in star-shaped polymers. This finding may have important implication for the use of peptide dendrimers as carriers for biologically active molecules

Effect of an asymmetry of branching on structural characteristics of dendrimers revealed by Brownian dynamics simulations

Dendrimers in dilute solution with asymmetry of branching were simulated by the Brownian dynamics method. In this simulation a coarse-grained dendrimer model and athermal solvent conditions were implemented, extending previous work to a wider range of branch asymmetries at fixed average spacer lengths and high generation numbers close to the theoretical limit. We considered both global and local structural characteristics of dendrimers. The global ones, such as the average distance of ends from the center, the radius of gyration, the hydrodynamic radius and the dendrimer shape anisotropy, are practically insensitive to the asymmetry of branching. The effect of the spacer asymmetry is revealed mainly in the local structure of dendrimers. In particular the radial density profile changes its shape from a convex to a concave one with an increase of the asymmetry. As compared to symmetrical case, the distribution of terminal monomer units in asymmetrical dendrimers shifts towards the dendrimers periphery. The terminal monomers in an asymmetrical dendrimer are on average in a denser environment compared to their symmetrical analogs. The shorter spacers are less stretched and more turned back to the core than the longer ones located at the same topological distance from the dendrimer periphery. The simulations also demonstrated that the asymmetry of branching leads to a smaller radial overlap of dendron fragments inside the dendrimer as compared to the symmetrical case. However, the total overlap was found to be independent of the asymmetry of branching

Computer Simulations of Hyperbranched Polymers: the Influence of the Wiener Index on the Intrinsic Viscosity and Radius of Gyration

The influence of the Wiener index on solution properties of trifunctional hyperbranched polymers has been investigated using Brownian dynamics simulations with excluded volume and hydrodynamic interactions. A range of degrees of polymerization (N) and degrees of branching (DB) were used. For each DB and N, several molecules with different Wiener indices (W) were simulated, where W depends on the arrangement of branch points. The intrinsic viscosity and the radius of gyration (Rg) of HPs were both observed to scale with W at a constant N via a power law relationship, as found in the literature. Through their relationships to W, an expression relating intrinsic viscosity to Rg was obtained. This relationship is found to fall centrally between the predictions of Flory and Fox for linear polymers and that of Zimm and Kilb for branched polymers. Molecular shape in solution is also found to depend on W and N, as observed through the W dependence of the ratio of Rg to the hydrodynamic radius, Rh