Infrared spectroscopic confirmation of α-lactone formation in the dissociation of a gaseous amino acid

The product obtained upon collision-induced dissociation of sulfonated phenylalanine in the gas phase has been investigated by using infrared multiphoton dissociation spectroscopy with a free-electron laser. This confirms that the product formed by loss of ammonia from the amino acid is the α-lactone, as had been deduced previously based on qualitative analysis and electronic structure calculations. Spectroscopically, the structure is confirmed by the presence of the carbonyl stretching peak at 1915 cm−1 and supported by excellent agreement between the predicted and observed S–O stretching bands. The agreement between predicted relative intensities is not as good, but can be attributed to the nonlinear process of IRMPD. Copyright © 2016 John Wiley & Sons, Ltd.