title: Infrared multiple-photon dissociation spectroscopy of deprotonated 6-hydroxynicotinic acid.
abstract: BACKGROUND
  Hydroxynicotinic acids (2-, 4-, 5- and 6-hydroxy) are widely used in the manufacture of industrial products, and hydroxypyridines are important model systems for study of the tautomerization of N-heterocyclic compounds. Here we determined the gas-phase structure of deprotonated 6-hydroxynicotinic acid (6OHNic).
  
  
  METHODS
  Anions were generated by electrospray ionization, and isolated and stored in a Fourier transform ion cyclotron resonance mass spectrometer. Infrared (action) spectra were collected by monitoring photodissociation yield versus photon energy. Experimental spectra were then compared with those predicted by density functional theory (DFT) and second-order Møller-Plesset (MP2) perturbation theory calculations.
  
  
  RESULTS
  For neutral 6OHNic, DFT and MP2 calculations strongly suggest that the 6-pyridone tautomer is favored when solvent effects are included. The lowest energy isomer of deprotonated 6OHNic, in the aqueous or gas phase, is predicted to be the 6-pyridone structure deprotonated by the carboxylic acid group.
  
  
  CONCLUSIONS
  The deprotonated, 6-pyridone structure is confirmed by comparison of the infrared multiple-photon photodissociation (IRMPD) spectrum in the region of 1100-1900 cm(-1) with those predicted using DFT and MP2 calculations.
authors.affiliation: Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, PA, USA; Agilent Center of Excellence in Mass Spectrometry, Duquesne University, Pittsburgh, PA, USA.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: van Stipdonk
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Kullman
authors.forename: Giel
authors.initials: G
authors.lastname: Berden
authors.forename: Jos
authors.initials: J
authors.lastname: Oomens