Reaction Monitoring Using Mid-Infrared Laser-Based Vibrational Circular Dichroism

Abstract

Changes in vibrational circular dichroism (VCD) were recorded on-line during a chemical reaction. The chiral complex nickel-(–)-sparteine chloride was hydrolyzed to free (–)-sparteine base in a biphasic system of sodium hydroxide solution and chloroform (CHCl3). Infrared (IR) and VCD spectra were iteratively recorded after pumping a sample from the CHCl3 phase through a lab-built VCD spectrometer equipped with a tunable mid-IR quantum cascade laser light source, which allows for VCD measurements even in the presence of strongly absorbing backgrounds. Time-dependent VCD spectra were analyzed by singular value decomposition and global exponential fitting. Spectral features corresponding to the complex and free (–)-sparteine could be clearly identified in the fitted amplitude spectrum, which was associated with an exponential decay with an apparent time constant of 127 min (t½ = 88 min).