Resonance raman spectroscopy with chemical state selectivity on histidine and acetamide using synchrotron radiation

We report on ultraviolet resonance Raman scattering experiments carried out on two model substances: histidine and acetamide using a UV synchrotron radiation source. In the case of aqueous histidine solution each protonated state of histidine tautomers was selectively excited by tuning the incident wavelength and the vibrational state of each protonated state was studied. We also demonstrated that the local pH condition of histidine can be identified directly from the spectra above pH 9. In the case of acetamide, the resonance Raman bands of acetamide with a stronger hydrogen bond at the NH2 site and weaker hydrogen bond at the C=O site were selectively observed. These findings will extend the selectivity and sensitivity of RR spectroscopy that is helpful to understanding protein functionality.