Complexation of anions to gas-phase amino acids: Conformation is critical in determining if the global minimum is canonical or zwitterionic

- Br− can stabilize the zwitterionic form of arginine in an isolated cluster.
- Zwitterionic and canonical minima are very close in energy for Br−·Arg.
- The canonical tautomer is lower in energy for the Cl−·Arg cluster.
- Conformation is crucial in determining canonical vs zwitterion relative energies.
- Comparison to experiment suggests that messenger tagged IR experiments are vital.