Gas-Phase Resonance Raman Spectroscopy Combined with IR-Laser Ablation of a Droplet Beam: Local Structural Analysis of Myoglobin.

Gas phase spectroscopy is a powerful tool for examining fundamental chemical structures and properties free from solvent molecules. We developed a gas-phase resonance Raman spectroscopy combined with IR-laser ablation of a droplet beam, which allowed us to elucidate local structures around chromophores in gas-phase proteins and DNAs. To demonstrate the potential of this approach, we applied this method to myoglobin, one of the heme proteins, and elucidated its structures in the gas phase and in aqueous solution. The experimental spectra are compared with calculated spectra of stable heme structures for the structural determination. These results show the oxidation/spin states of the Fe atom in myoglobin in the gas phase and were compared with the aqueous solution from the obtained resonant Raman spectra. The present method gives an important tool to investigate the gas-phase structure of large biomolecules.