Solvent can dominate optical rotation

The three-dimensional arrangement of achiral solvent molecules surrounding chiral solute molecules has been shown to make an unexpectedly large contribution to the optical properties of the solution. Achiral solvents are known to affect the experimentally measured optical rotation of chiral solutes, but the magnitude and fundamental nature of such effects were unknown until now. David N. Beratan of Duke University, Peter Wipf of the University of Pittsburgh, and coworkers find that the optical properties of a solution of methyloxirane in benzene are dominated not by the chiral solute but by the arrangement of the achiral solvent molecules (Angew. Chem. Int. Ed., DOI: 10.1002/anie.200702273). They believe this to be the first evidence of a chiroptical property dominated by induced solvent dissymmetry. This type of solvent effect "has to be playing a role in all chiral molecular recognition events," Wipf says. He notes that this effect will have to be accounted for in the kinetics and thermodynamics of processes such as protein-substrate and protein-inhibitor binding and homogeneous and heterogeneous catalysis.