Measurement of Vibrational Circular Dichroism spectra using the Jasco FVS-6000

It is generally understood that chiral compounds have different bioactivities depending upon the absolute configuration of each compound. Some familiar examples include glutamic acid and thalidomide. L-glutamic acid demonstrates the “Umami” taste, while D-glutamic acid has a bitter taste, similarly, the R form of thalidomide is a sedative, but the S form has teratogenic activity. Thus, the separation and study of chiral compounds is critical for many reasons.

The functionalities of chiral compounds have been studied for the development of advanced molecules for many applications. The study of chiral compounds has spread to several fields such as natural products, pharmaceuticals and other functional molecules, and it can be pointed out that among those studies, the structural analysis of chiral compounds is a very important topic. X-ray Diffraction (XRD), Nuclear Magnetic Resonance (NMR) and Electronic Circular Dichroism (ECD) using UV/Vis light are employed as primary methods for the structural analysis of chiral compounds. In this paper, the measurement of chiral compounds by Vibrational Circular Dichroism (VCD) using infrared light will be outlined.

VCD is a method to measure the difference of absorbance intensity between left-hand and right-hand circularly polarized light. It is an advantage of VCD that this method can be applied to almost all organic compounds in the same way as infrared (IR) spectroscopy. In addition, by comparing the measurement results with calculated results by ab-initio molecular orbital calculations, the absolute configuration of the sample can be determined. However, since the peak intensity of VCD spectra are 1,000 – 10,000 times weaker than that of standard IR spectra, spectroscopic instruments with high sensitivity and stability with very small baseline fluctuations are required. The FVS-6000 VCD system has a high sensitivity detector, suitable optical filter technology and a thermostatted Photoelastic Modulator (PEM) to accurately measure the weak VCD peaks. The measurement results of typical chiral compounds and hemoglobin as a model protein using the FVS-6000 are reported.