Gas-phase ion/ion reactions of rubrene cations and multiply charged DNA and RNA anions

Abstract

Gas-phase ion/ion reactions between multiply deprotonated DNA and RNA anions and rubrene radical cations have been investigated in this research. Ion/ion reactions of DNA 6-mer (dT6, dC6, dA6 and dG6) anions with rubrene radical cations led to negative electron transfer dissociation (nETD), complex formation, and negative electron transfer without dissociation (nET no D). The amount of nET, no D product (G>A>C>T) is inversely related to nucleobase ionization potential (G<A<C<T). On the other hand, the amount of complex formation (G<A<C<T) is positively related to the nucleobase ionization potential, with only minimal complex formation being observed for dG6. The nETD channels generally led to the generation of w/d- and a/z-ions, but were only observed when highly deprotonated precursor ions were reacted. Similar trends were observed when reacting RNA 8-mer (rU8, rC8, rA8 and rG8) anions with rubrene radical cations (i.e., the yields of nET, no D products (G>A>C>U) and complex formation (G<A<C<U) are inversely related to one another). The major nETD product ions were w/d-ions and a/z-ions, as with the DNA anions, and were only observed at relatively high precursor ion charge states. Furthermore, extensive fragmentation from the w/d- and a/z-ion channels can be obtained from simultaneous activation of the first generation nET, no D survivor radical anions (nET-CID). In comparison to the conventional collisional activation methods, the dissociation of DNA and RNA anions via either nETD or nET-CID is less affected by the structural differences on the 2′-hydroxyl group of the sugar ring.