Singlet O2 Oxidation of a Deprotonated Guanine‐Cytosine Base Pair and Its Entangling with Intra‐Base‐Pair Proton Transfer. Issue 20 (9th August 2018)

• Record Type: Journal Article
• Authors: Lu, Wenchao; Sun, Yan; Tsai, Midas; Zhou, Wenjing; Liu, Jianbo
• Is Part Of: Chemphyschem. Volume 19:Issue 20(2018)
• Page Start: 2645
• Page End: 2654
• Publication Date: 2018-08-09
• Subjects: singlet oxygen -- guanine-cytosine base pair -- guided-ion-beam tandem mass spectrometry -- direct dynamics trajectory simulation -- potential energy surface; Chemistry, Physical and theoretical -- Periodicals; 541.05
• DOI: 10.1002/cphc.201800643
• Languages: English
• ISSNs: 1439-4235

Abstract

Abstract: We report an experimental and computational study on the 1 O2 oxidation of gas‐phase deprotonated guanine‐cytosine base pair [G ⋅ C−H] − that is composed of 9HG ⋅ [C−H] − and 7HG ⋅ [C−H] − (pairing 9H‐ or 7H‐guanine with N1‐deprotonated cytosine), and 9HG ⋅ [C−H] − _PT and 7HG ⋅ [C−H] − _PT (formed by intra‐base‐pair proton transfer from the N1 of guanine to the N3 of [C−H] − ). The conformer‐averaged reaction product ions and cross section were measured over a center‐of‐mass collision energy range from 0.1 to 0.5 eV using a guided‐ion‐beam tandem mass spectrometer. To explore conformation‐specific reactivity, collision dynamics of 1 O2 with each of the four [G ⋅ C−H] − conformers was simulated at B3LYP/6‐31G(d). Trajectories showed that the 1 O2 oxidation of the base pair entangles with intra‐base‐pair proton transfer, and prefers to occur in a collision when the base pair adopts a proton‐transferred structure; trajectories also indicate that the 9HG‐containing base pair favors stepwise formation of 4, 8‐endoperoxide of guanine, whereas the 7HG‐containing base pair prefers concerted formation of guanine 5, 8‐endoperoxide. Using trajectory results as a guide, potential energy surfaces (PESs) along all possible reaction pathways were established using the approximately spin‐projected ωB97XD/6‐311++G(d, p)//B3LYP/6‐311++G(d, p) method. PESs have not only rationalized trajectory findings but provided more accurate energetics and indicated that the proton‐transferred base‐pair conformers have lower activation barriers for oxidation than their non‐proton‐transferred counterparts. Abstract : The conformation‐specific singlet O2 oxidation of deprotonated guanine‐cytosine base pair is studied.