Park JJ, Lee CS, Han SY. Proton Transfer Accounting for Anomalous Collision-Induced Dissociation of Proton-Bound Hoogsteen Base Pair of Cytosine and Guanine.
JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2018;
29:2368-2379. [PMID:
30215166 DOI:
10.1007/s13361-018-2060-5]
[Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/19/2018] [Revised: 08/08/2018] [Accepted: 08/08/2018] [Indexed: 06/08/2023]
Abstract
To understand the anomalous collision-induced dissociation (CID) behavior of the proton-bound Hoogsteen base pair of cytosine (C) and guanine (G), C:H+∙∙∙G, we investigated CID of a homologue series of proton-bound heterodimers of C, 1-methylcytosine, and 5-methylcytosine with G as a common base partner. The CID experiments were performed in an energy-resolved way (ER-CID) under both multiple and near-single collision conditions. The relative stabilities of the protonated complexes examined by ER-CID suggested that the proton-bound complexes produced by electrospray ionization in this study are proton-bound Hoogsteen base pairs. On the other hand, in contrast to the other base pairs, CID of C:H+∙∙∙G exhibited more abundant productions of C:H+, the fragment protonated on the moiety with a smaller proton affinity, than that of G:H+. This appeared to contradict general prediction based on the kinetic method. However, further theoretical exploration of potential energy surfaces found that there can be facile proton transfers in the proton-bound Hoogsteen base pairs during the CID process, which makes the process accessible to an additional product state of O-protonated C for C:H+ fragments. The presence of an additional dissociation channel, which in other words corresponds to twofold degeneracy in the transition state leading to C:H+ fragments, effectively doubles the apparent reaction rate for production of C:H+. In this way, the process gives rise to the anomaly, the observed pronounced formation of C:H+ in the CID of the proton-bound Hoogsteen base pair, C:H+∙∙∙G. Graphical Abstract ᅟ.
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