Multidimensional Vibrational Circular Dichroism Apparatus Equipped with Quantum Cascade Laser and Its Use for Investigating Some Peptide Systems Containing D-Amino Acids

We developed a multidimensional vibrational circular dichroism system with a positional coordinate, making it possible to move in both x- and y-directions using an automatic stage. Quantum cascade laser (QCL) was used as a light source to achieve high intensity and narrow focusing. The QCL emitted light in the wavenumber range of 1500-1740 cm(-1), which encompassed absorption bands assigned to the stretching vibrations of amides I and II. The operation of the instrument was analyzed for samples containing amide groups. An aqueous solution of Gly-L-Leu or GIy-D-Leu was measured under the background absorbance as high as 3.5 due to the water medium. The spectra were recorded by scanning at 1.0 cm(-1) steps. The time required for performing measurement at each wavenumber was less than 1 s. The mirror-image relation was maintained between the optical antipodes. A peak assigned to amide II appeared clearly at around 1580 cm(-1). In the case of KBr pellets containing the same compounds, peaks assigned to amide I and II were observed. For two-dimensional pattering, a KBr pellet comprising two domains of amino acids (or L-Ala and D-Ser) was investigated. The distribution of each component within the pellet was obtained under the two-dimensional alignment at the spatial interval of 2.5 mm.

Automated summary

A multidimensional vibrational circular dichroism system with a positional coordinate was developed, utilizing a Quantum cascade laser as a high-intensity light source for precise focusing. The instrument was operated to analyze samples containing amide groups, including measurements in high background absorbance due to water medium. The system allowed for movement in both x and y directions, maintaining a mirror-image relation between optical antipodes.