Reactivity of Cytosine with Alkylmercury Ions in the Gas Phase: the Critical Role of the Alkyl Chain

Abstract The gas‐phase reactivity towards cytosine ( C ) of alkylmercury cations C n H 2n+1 Hg + , and more particularly CH 3 Hg + , C 2 H 5 Hg + , n‐ C 4 H 9 Hg + and t‐ C 4 H 9 Hg + , has been studied for the first time by combining tandem mass spectrometry, infrared multiple photon dissociation spectroscopy (IRMPD) and density functional theory (DFT) calculations. Under electrospray conditions, the interaction of C with the cations derived from alkylmercury chloride compounds gives rise to a single type of complex of general formula [RHg( C )] + , except for t‐ butylmercury which turned to be unreactive. Subsequent MS/MS experiments showed that [RHg] + ions (R=Me, Et, n‐Bu) exhibit a peculiar reactivity characterized by the transfer of the alkyl group, R, to the nucleobase leading to a [( C )R] + ion, accompanied by the reduction of the metal and loss of 0 Hg. As the length of the alkyl chain increases (n≥2), a new fragmentation path leading to protonated cytosine is opened, associated with the elimination of a C n ,H 2n ,Hg moiety. This latter process is clearly overwhelming with n‐ BuHg + . The mechanisms associated with both dissociation channels were examined through the use of IRMPD data in the fingerprint region, and by exploring the corresponding potential energy surfaces in the DFT framework.