Tautomerism of cytosine probed by gas phase IR spectroscopy

The tautomerism of the gaseous protonated cytosine is studied using infrared multiple photon dissociation (IRMPD) spectroscopy of singly hydrated complexes of protonated cytosine in the 2700-3750 cm(-1) wavenumber range. The hydrated complexes are formed through argon-mediated collisions between bare electrosprayed cytosine and low-pressure water vapor. In the spectra, where X-H (X=C, O, and N) stretching vibrations are probed, evidence is found for the coexistence in the gas phase of hydrated complexes of two different cytosine tautomers. As the addition of a water molecule to either tautomer of protonated cytosine is energetically highly unlikely to induce interconversion, it is deduced that both C(2)=O and N(3) protonated tautomers of cytosine are formed under electrospray conditions. (C) 2009 Elsevier B.V. All rights reserved.