Alkylation of uracil and thymine in the gas phase through interaction with alkylmercury compounds

The gas-phase interactions of uracil and thymine with alkylmercury cations, in particular [CHHg], n-BuHg and t-BuHg, were studied through the use of electrospray ionization coupled to tandem mass spectrometry. We observed that the interaction of akylmercury compounds with the nucleobases (NB) gives rise to a single type of complex of general formula [RHg(NB)], except for t-butyl-mercury (no interaction). The subsequent MS/MS experiments show that the [RHg] ions (R = Me, n-Bu) exhibit a peculiar reactivity characterized by the transfer of the alkyl group to the nucleobases. Indeed, the main fragmentation process observed leads to the loss of neutral Hg, producing [(NB)R] ions. Only when the length of the alkyl chain increases, as in the case of reactions with [n-BuHg], a new fragmentation path is opened, yielding the protonated nucleobase, [(NB)H], with the concomitant elimination of 2 CH + Hg. A thorough analysis of the mechanisms behind both dominant processes was carried out through the use of Infrared Multiple Photon Dissociation (IRMPD) in the fingerprint region, combined with an analysis of the corresponding potential energy surfaces by using high-level density functional theory (DFT) calculations.The CLIO team (J. M. Ortega, G. Perilhous, J. P. Berthet) as well asP. Maître, D. Scuderi and V. Steinmetz are warmly acknowledgedfor their support during the FEL experiments. This work has beenalso partially supported by the “Fonds pour le Rayonnement dela Recherche (FRR, Université d’Evry Val d’Essonne) and by theProjects CTQ2015-63997-C2 and CTQ2016-76061-P of the Minis-terio de Economía y Competitividad of Spain, FOTOCARBON-CMS2013/MIT-2841 of the Comunidad Autónoma de Madrid and bythe COST Action CM1204 of the EU Framework Programme. Hori-zon 2020. Computational time at Centro de Computación Científica(CCC) of Universidad Autónoma de Madrid is also acknowledged

Alkylation of uracil and thymine in the gas phase through interaction with alkylmercury compounds

International audienceThe gas-phase interactions of uracil and thymine with alkylmercury cations, in particular [CH3Hg]+, n-BuHg+ and t-BuHg+, were studied through the use of electrospray ionization coupled to tandem mass spectrometry. We observed that the interaction of akylmercury compounds with the nucleobases (NB) gives rise to a single type of complex of general formula [RHg(NB)]+, except for t-butyl-mercury (no interaction). The subsequent MS/MS experiments show that the [RHg]+ ions (R = Me, n-Bu) exhibit a peculiar reactivity characterized by the transfer of the alkyl group to the nucleobases. Indeed, the main fragmentation process observed leads to the loss of neutral Hg, producing [(NB)R]+ ions. Only when the length of the alkyl chain increases, as in the case of reactions with [n-BuHg]+, a new fragmentation path is opened, yielding the protonated nucleobase, [(NB)H]+, with the concomitant elimination of 2 C4H4 + Hg. A thorough analysis of the mechanisms behind both dominant processes was carried out through the use of Infrared Multiple Photon Dissociation (IRMPD) in the fingerprint region, combined with an analysis of the corresponding potential energy surfaces by using high-level density functional theory (DFT) calculations