Infrared Free-Electron Laser: A Versatile Molecular Cutter for Analyzing Solid-State Biomacromolecules

Free-electron lasers that oscillate in the infrared (IR) range of 1000 (10 μm) to 4000 cm^-1 (2.5 μm) were applied to irradiate solid-phase polysaccharides and aromatic biomacromolecules. Synchrotron radiation IR microscopy (SR-IRM) and electrospray ionization mass spectroscopy (ESI-MS) analyses showed that <i>N</i>-acetyl glucosamine was isolated from the powdered exoskeleton of crayfish by irradiation at 1020 cm^-1 (9.8 μm), resonating with the C-O stretching mode (νC-O). Irradiation at 3448 cm^-1 (2.9 μm), which is resonant with the O-H stretching vibration (νO-H) of sulfonated lignin, dissociates the aggregate state and releases coniferyl aldehyde substituted with sulfinate, as shown by scanning electron microscopy, terahertz-coherent edge radiation spectroscopy, SR-IRM, and ESI-MS. These vibrational excitation reactions proceed at room temperature in the absence of solvent. Current and previous studies have demonstrated that intense IR lasers can be used as versatile tools for unveiling the internal structures of persistent biomacromolecules.