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

Abstract

Dedicated to Prof. Helmut Schwarz on the occasion of his 75 th birthday. Number of pages (including Tables, Figures, legends and schemes): 37

Open questions on toxic heavy metals Cd, Hg and Pb binding small components of DNA and nucleobases. Are there any predictable trends?

“…This mechanism is therefore much more favorable than the one postulated in our previous publication, and more in line with the dominant protonation of uracil as compared to butyl transfer. 58 The dominant protonation path is also consistent with the transition state associated with the butyl chain transfer located 83.2 kJ mol −1 above the reactants, and therefore well above the one found for proton transfer. Finally, it is worth noting that the observation in the gas phase of the dienolic form of protonated uracil shown in Fig.…”

“…The isomers for the different uracil protonated structures were already available from our previous investigations, 58 whereas the ethyl uracil and ethylmercury uracil cations were obtained for the present work. The uracil molecule presents several O, N and C binding sites, from which the ones leading to the most stable structures are carbon C6 in the case of the ethyl chains (Fig.…”

“…In a previous work, we studied the processes associated with the complexation between uracil and two alkyl mercury cations of different lengths, methyl mercury and n -butyl mercury, performed in the gas phase through electrospray ionization coupled to tandem mass spectrometry. 58 Very importantly, the length of the chain was shown to be crucial for the final products observed in the laboratory, being predominantly methyl uracil cation in the first case (methylation occurring onto the carbonyl group(s) of uracil according to InfraRed Multiple Photon Dissociation experiments), and protonated uracil in the second case. Our hypothesis, supported by theoretical studies, is that the different behavior is due to the flexibility of the butyl group, which allows a different pathway for a proton transfer towards uracil and the corresponding elimination of mercury and alkyl residues.…”

“…9 was not considered in our previous theoretical study regarding the reactivity between the n -butylmercury cation and uracil. 58 Once this structure was located for the EtHg + /uracil system, we searched for a similar transition state for the butyl case. This new transition state is found 19.7 kJ mol −1 above the entrance channel and leads to protonated uracil plus mercury and 1-butene, which are the result of an exothermic process (−95.9 kJ mol −1 ).…”

Synergy Effects in Heavy Metal Ion Chelation with Aryl- and Aroyl-Substituted Thiourea Derivatives

“…Quantum chemistry emerges as a reliable tool to predict ionophore properties of organic compounds. Indeed, the investigation of interactions between metallic cations and organic compounds has attracted huge interest in the last few decades, where an important activity has been developed by means of computational chemistry. − In many studies, the theory has been combined with experiments, typically carried out with mass spectrometry techniques. − The nature of the metal ion–molecule interaction, the reactivity of the new compounds, and the change in structural and spectroscopic properties of the organic molecules upon ion complexation are among the most important aspects investigated in these studies.…”