Gas-phase IR spectroscopy of deprotonated amino acids: Global or Local minima?

Density functional theory calculations for the structure and IR spectroscopy of deprotonated tyrosine and cysteine molecules in gas phase have been carried out to resolve the on-going debate about the global minimum of deprotonated amino acids. It is found that the global minimum of the deprotonated specie is not always directly produced from the most stable neutral conformer. Depending on the setup, the experimental IR spectroscopy of deprotonated amino acids could only give the information of the local minima of the deprotonated species.