Thermodynamic and kinetic stability of zwitterionic histidine: Effects of gas phase hydration

- We calculate the structures and relative stabilities of histidine-(H2O)n (n = 0-6) clusters.
- We compare the Gibbs free energies of canonical and zwitterionic conformers.
- Six H2O are required for thermodynamically stable histidine zwitterion.
- Some canonical clusters may be kinetically stable in low temperature gas phase.