Molecular Dynamics Simulation of Sorbitol-Based Surfactants with Different Chiral Configurations at the Gas/Liquid Interface

The self-assembly behavior of chiral surfactants has attracted much attention because of their crucial role in functional materials such as asymmetric catalysis and chiral separation. In this study, molecular dynamics simulations were performed to systematically investigate the effect of different chiral configurations of the sorbitol-alkylamine surfactant (SAAS-C12) on its interfacial self-assembly behavior at the gas/liquid interface. The microscopic action rules of the hydrogen-bond network regulating the interfacial directional assembly of SAAS-C12 molecules were preliminarily revealed, and the important regulatory role of chiral configuration was discussed. It is found that the interfacial self-assembly behavior of SAAS-C12 chiral isomers exhibits obvious configuration-dependent regularity. Enantiomers (such as RRRR and SSSS) show similar self-assembly behaviors due to mirror symmetry, as reflected in their nearly identical rising heights. Among diastereoisomers, some chiral molecules achieve symmetrical arrangement perpendicular to the interface through the inherent symmetry of the chiral configurations (as observed in RRRR and RSSR) or through the cooperative regulation of hydrogen-bond numbers between hydroxyl groups and water molecules (as observed in RSRS and RRSS). In contrast, the other chiral configurations (RRRS, RRSR, RSRR, and RSSS) present asymmetric interfacial distributions. The self-assembly of most chiral configurations is dominated by surfactant-water hydrogen bonds, and the increase in hydrogen-bond numbers promotes the penetration of headgroup oxygen atoms into the aqueous phase and reduces the rise height of the connected carbon atoms. Differently, the assembly behavior of the RSSS configuration is jointly regulated by intramolecular, intermolecular, and surfactant-water hydrogen bonds because of its weak hydrogen-bond stability. This study systematically compares the interfacial assembly differences of multiple stereoisomers under the same molecular framework, clarifies the synergistic regulation mechanism of chiral configurations and hydrogen-bonding networks, and fills a partial gap in the research on the interfacial assembly rules of sugar alcohol surfactants with multiple chiral centers.