Origins and Information Content of Vibrational Optical Activity Spectra
Wednesday, March 10, 2021: 9:15 AM - 9:50 AM
Vibrational optical activity (VOA) consists principally of infrared vibrational circular dichroism (VCD) and vibrational Raman optical activity (ROA) . Both VCD and ROA can be used as insightful probes of molecular chirality ranging from small molecules to proteins and nucleic acids. Both VCD and ROA can be calculated accurately using density functional theory (DFT) and both can be measured with multiplex instrumentation that includes Fourier transform infrared (FT-IR) for FT-VCD and charge coupled detector (CCD) multichannel arrays spectrometers for CCD-ROA. A significant challenge for most VOA measurements is long collection times, ranging from minutes to hours, since VOA intensities are between three to five orders of magnitude smaller than their parent IR and Raman intensities. For some samples, however, VOA intensities can be enhanced by one to several orders of magnitude, making such phenomena interesting both from theoretical and practical perspectives. In addition, VOA spectra contain rich information about solvent solute interactions and here 2D-COS can be a valuable elucidation tool. In this presentation a variety of examples of VOA spectra will be presented and progress toward their more complete understanding will be discussed. These include: 1) Unusually large VCD in protein fibril supramolecular chirality , 2) Resonance ROA (RROA) in the near single electronic state (SES) limit , 3) Enhanced VCD from molecules with magnetically allowed low-lying electronic states (LLES) and 4) 2D-COS VCD spectra of amino acids as a function of pH .  Nafie LA. Vibrational Optical Activity: Principles and Applications. Chichester: John Wiley & Sons, Ltd; 2011. .Ma S, Cao X, Mak M, Sadik A, Walkner C, Freedman TB, Lednev IK, Dukor RK, Nafie LA. JACS. 2007;129:12364-12365.  Nafie LA. Chem Phys. 1996;205:309-322.  Nafie LA. JPC A. 2004;108:7222-7231.  Ma S, Freedman TB, Cao X, Nafie LN, J Mol Struc. 2006;799:226-238.
Keywords: Please select up to 4 keywords ONLY:
Biospectroscopy,Infrared Spectroscopy,Raman/Surface Enhanced Raman Spectroscopy,Spectroscopy