Comparative Study of Conformational Behavior and Hydrogen Bonding of Hydroxyl-terminated Carbosilane Dendrimers in Toluene and Aqueous Solution

Abstract

Amphiphilic dendrimers, which contain segments of hydrophobic and hydrophilic nature in one molecule, have attracted increasing attention due to their high potential for use in a variety of practical applications, in particular as surface modifiers and molecular nanocontainers for drug delivery. A thorough comprehension of the structure-composition-properties relationship in these systems is of paramount importance for the targeted design of new materials. In this paper, we examine the conformational behavior of amphiphilic G2–G4 carbosilane dendrimers with hydroxyl-modified terminal groups in toluene and aqueous solutions through atomistic molecular dynamics simulations. By explicitly simulating the solvent, we were able to elucidate the effect of the solvent nature on the distribution of various structural elements, such as branches and terminal groups, inside the dendrimer as a function of generation number. In aqueous solutions, the dendrimers adopt a dense globular conformation with a large fraction of hydroxyl groups concentrated in the periphery and participating in hydrogen bonding with water molecules. In toluene, the dendrimers swell, the solvent uptake reaches 30–40 vol %, which is in good agreement with existing experimental data. In the hydrophobic medium, hydroxyl groups form intramolecular hydrogen bonds, resulting in clusters of preferentially linear geometry. The cluster size distribution is very broad and there is a non-zero probability of clusters containing almost all OH groups of the dendrimer. The results obtained are important for a better understanding of the self-assembly and surface activity of amphiphilic dendrimers and for the design of new materials based on them.