Strong Solvent Imprint

Abstract

The optical rotation of polarized light caused by chiral molecules dissolved in solution is usually attributed to the interaction of the light field with the electronic distribution of the solute. However, the solvent shell around the molecule can also exert strong effects; for example, the sign of the optical rotation of (S)-methyloxirane switches from positive to negative when the solvent is changed from water to benzene. Previous theoretical work has shown that the interaction of (S)-methyloxirane with water accounts for most of the optical rotary dispersion (ORD) in aqueous media. Mukhopadhyay et al. now present time-dependent density functional theory calculations of ORD for Monte Carlo simulations of (S)- and (R)-methyloxirane solvated with benzene. They show that for an explicit solvent model, the dissymmetric benzene solvent shell, rather than the solute itself, dominates the ORD. This effect was not seen with implicit solvent molecules or with an achiral solute (ethylene oxide). — PDS