Mass spectrometry and computational study of collision-induced dissociation of 9-methylguanine–1-methylcytosine base-pair radical cation: intra-base-pair proton transfer and hydrogen transfer, non-statistical dissociation, and reaction with a water ligand

Abstract

<p>A combined experimental and theoretical study is presented on the collision-induced dissociation of 9-methylguanine–1-methylcytosine base-pair radical cation ([9MG·1MC]˙⁺) and its monohydrate ([9MG·1MC]˙⁺·H₂O) with Xe and Ar gases.</p>

Dynamics and Multiconfiguration Potential Energy Surface for the Singlet O2 Reactions with Radical Cations of Guanine, 9-Methylguanine, 2′-Deoxyguanosine, and Guanosine

“…, solvent and pH). In neutral aqueous solution, free G •+ (and that within single-stranded DNA) undergoes deprotonation through the loss of the imino proton at N1 to water and yields a neutral radical [G – H]• within 56 ns. , In contrast, G •+ within double-stranded DNA is stabilized through Watson–Crick base paring which diminishes the probability of deprotonation . The fates of G •+ and [G – H] • are distinctively different by following different transformations and producing different end products. − This implies that a direct measurement of G • + with 1 O 2 in aqueous solution is not feasible, because deprotonation of G •+ may be faster than oxidation and the oxidation behavior of deprotonated [G – H] • may not faithfully mimic that of G •+ within DNA .…”

Flying DNA Cation Radicals in the Gas Phase: Generation and Action Spectroscopy of Canonical and Noncanonical Nucleobase Forms

“…Distonic ions are a special class of ion-radical species in which the formal charge and radical are at different and remote atoms. , Collision-induced dissociation (CID) of the (2′-deoxyguanosine–2′-deoxycytidine) +• complex involved fragmentation in the deoxyribose rings, which was related to the propagation of radiation damage in DNA . A recent study reported CID and computational investigations of the cation radical of the 9-methylguanine–1-methylcytosine (9MG–1MC) +• complex and its water adduct . Energy-resolved CID was used to identify the dissociation thresholds for the competing formation of 9MG +• and protonated 1-methylcytosine, (1MC + H) + .…”

“…Energy-resolved CID was used to identify the dissociation thresholds for the competing formation of 9MG +• and protonated 1-methylcytosine, (1MC + H) + . The authors concluded that the complex consisted of a mixture of the major 9MG +• –1MC structure and a minor [9MG – H] • –[1MC + H] + component formed by proton transfer from 9MG +• to 1MC …”

“…32 A recent study reported CID and computational investigations of the cation radical of the 9-methylguanine−1-methylcytosine (9MG−1MC) +• complex and its water adduct. 35 Energyresolved CID was used to identify the dissociation thresholds for the competing formation of 9MG +• and protonated 1methylcytosine, (1MC + H) + . The authors concluded that the complex consisted of a mixture of the major 9MG +• −1MC structure and a minor [9MG − H] • −[1MC + H] + component formed by proton transfer from 9MG +• to 1MC.…”

“…The authors concluded that the complex consisted of a mixture of the major 9MG +• −1MC structure and a minor [9MG − H] • −[1MC + H] + component formed by proton transfer from 9MG +• to 1MC. 35 A stable noncanonical isomer has been identified as a major product in the formation of gas-phase cation radicals of 1methylcytosine. 36 The neutral nucleobase binds to Cu(terpy) 2+• as the canonical 2-oxo tautomer, which forms the by far most stable ternary complex.…”