Extending the applications of circular dichroism in structure elucidation: aqueous environment breaks the symmetry of tartrate dianion

Abstract

Electronic circular dichroism and quantum mechanical studies show that in aqueous solution tartrate dianions are non-symmetrically hydrated and their expected C2 symmetry is reduced to C1 while preserving the conformation of the carbon skeleton. Our results indicate that inclusion of explicit solvent (water) molecules in quantum mechanical calculations is instrumental in detailed studies on molecular structure in solution. Moreover, the presented combined experimental and theoretical approach is a unique demonstration of the capability of ECD spectroscopy to detect subtle structural changes of molecules in solution. In addition to the n-π* Cotton effect at ca. 212 nm, the CD spectra of (R,R)-tartrates in aqueous solution reveal the presence of a Cotton effect at ca. 193 nm which is, at least partly, the result of n-σ* excitation.