Conformational landscapes in amino acids: infrared and ultraviolet ion-dip spectroscopy of phenylalanine in the gas phase

A full structural assignment of the most stable conformers of phenylalanine, based upon a combination of ultraviolet and infrared ion-dip spectroscopy of the jet-cooled amino acid, coupled with high-level ab initio computation is presented for the first time. The results are discussed in relation to aliphatic amino acids to highlight the importance of ring–side chain interactions; the question of zwitterion formation is also discussed.