Hydrated complexes of tryptophan: ion dip infrared spectroscopy in the molecular fingerprint region, 100–2000 cm^–1

The infrared spectra of hydrated complexes of tryptophan have been recorded in the gas phase over the range 160–800 cm–1 using double resonance IR-UV ion dip spectroscopy. Despite the problems arising from severe UV spectral overlap of unresolved resonances, the IR measurements, combined with new DFT and ab initio calculations have allowed a re-assessment of the spectral assignments proposed in an earlier combined near-infrared/quantum computational investigation [L. C. Snoek, R. T. Kroemer and J. P. Simons, Phys. Chem. Chem. Phys. 2002, 4, 2130]. It has reinforced the conclusion that hydration leads to conformational restructuring and also served to focus attention on the information that can be provided by spectroscopic measurements obtained in the mid and far IR