Gas-phase reactions between urea and Ca2+: the importance of Coulomb explosions

The gas-phase reactions between urea and Ca 2+ have been investigated by means of electrospray mass spectrometry techniques. The MS/MS spectra of [Ca(urea)] 2+ and [Ca(urea-H)] + complexes show that both ions decompose by losing NH 3 and HNCO. However, for the [Ca(urea)] 2+ system, additional intense peaks are observed at m/z 44, 56 and 82. Density functional theory calculations at the B3-LYP/cc-pWCVTZ level have been used to help rationalize these observations, through an examination of the structures and bonding characteristics of the various stationary points on the [Ca(urea)] 2+ and [Ca(urea-H)] + potential energy surfaces (PESs). Analysis of the topology of these PESs allows mechanisms to be proposed for the loss of § Universida