Unexpected cytosine–AuCl₄⁻ interaction under electrospray ionization mass spectrometry conditions—Formation of cytosine–Au(I) complexes

The interaction of cytosine with AuCl₄⁻, under electrospray ionization mass spectrometric conditions, is discussed. On the basis of respective full scan mass spectra and product ion spectra, obtained in positive and negative ion mode, it has been deduced that cytosine is very prone to form Au(I)-containing complexes. The complexes may be formed in the gas phase by decomposition of Au(III)-containing complexes and also in the electrospray ionization source as a result of the occurrence of redox process. It has also been found that the interaction of cytosine with Au⁺ is stronger than that with Cu⁺ or Ag⁺, although taking into account the electrostatic attraction, it is not expected.