Resonance and Non-Resonance Raman Optical Activity in Pharmaceutical Analgesic Molecules

Abstract

Raman optical activity (ROA)1, the difference in Raman scattering intensity for right and left circularly polarized incident and/or Raman scattered radiation, has emerged as a technique for investigating the solution structure of chiral molecules, and has been applied to biomolecules in aqueous solution. 1, 2 Resonance Raman spectroscopy is well established as a technique for probing the structure and dynamics of appropriate chromophores in biomolecules. However, resonance Raman optical activity (RROA) has not been reported. Recently, the theory of Raman optical activity has been extended to the case of strong resonance with a single electronic state.3 The theory predicts that, in this limit, the RROA bands will all have the same sign (opposite in sign to the pure electronic circular dichroism of the resonant electronic transition) and will be proportional in intensity to the parent resonance Raman bands. We provide here evidence for both resonance and non-resonance ROA in the spectra of the analgesics naproxen and ibuprofen in basic and nonaqueous solution.