Comparative study of conformational behavior of hydroxyl-terminated carbosilane dendrimers at water–toluene and water–air interfaces

Abstract

In this study, we investigate how molecular density—governed by dendrimer generation and branching functionality—influences the conformational behavior and hydrogen bonding of OH-terminated carbosilane dendrimers in water, air, toluene, and at water–air and water–toluene interfaces by atomistic molecular dynamics simulations. We focus on the 4-3 series (G2–G4), featuring a tetrafunctional core and trifunctional branching, and compare it with the denser, more rigid 4-4G3 dendrimer of the third generation (tetrafunctional at both core and branching points). In hydrophobic environments, terminal OH groups form linear intramolecular aggregates; the 4-4G3 exhibits markedly reduced toluene uptake (10% vs 40% volume change for 4-3G4) and severely restricted intramolecular dynamics, with some OH groups remaining kinetically trapped near the core—a phenomenon requiring microsecond-scale simulations for proper characterization. In aqueous solution, 4-3 dendrimers expose OH groups at their periphery to form hydrogen bonds with water, whereas 4-4G3 retains a significant fraction of OH groups internally, forming intramolecular H-bonds instead. At interfaces, 4-3 dendrimers adopt flattened “umbrella” conformations to maximize interfacial H-bonding with water, swelling slightly into toluene to form biconvex shapes, while 4-4G3 remains nearly spherical due to steric constraints, forming over four times more intramolecular H-bonds and fewer with water than the more flexible 4-3G4. These findings establish molecular density as a key determinant of solvation, dynamics, and interfacial adaptability, providing a foundation for understanding structure–composition–property relationships in dendrimer monolayers under lateral confinement.