Stabilization of the Zwitterionic Structure of Proline by an Alkylammonium Ion in the Gas Phase

Separate charges: Zwitterionic proline can be effectively stabilized by protonated methylamine in the gas phase (see calculated structure; C gray, H white, N blue, O red), as shown by accurate binding-energy measurements and IR fingerprint spectra. These results imply that organic ions may provide an effective means of stabilizing the zwitterionic structures of amino acids, which are of fundamental importance in biological systems.