Wu R R, Rodgers M T
Department of Chemistry, Wayne State University, Detroit, Michigan 48202, USA.
Phys Chem Chem Phys. 2016 Jun 21;18(23):16021-32. doi: 10.1039/c6cp01445c. Epub 2016 May 31.
Our previous gas-phase infrared multiple photon dissociation action spectroscopy study of protonated 2'-deoxyadenosine and adenosine, dAdo+H and Ado+H, found that both N3 and N1 protonated conformers are populated with the N3 protonated ground-state conformers predominant in the experiments. Therefore, N-glycosidic bond dissociation mechanisms of N3 and N1 protonated dAdo+H and Ado+H and the associated quantitative thermochemical values are investigated here using both experimental and theoretical approaches. Threshold collision-induced dissociation (TCID) of dAdo+H and Ado+H with Xe is studied using guided ion beam tandem mass spectrometry techniques. For both systems, N-glycosidic bond cleavage reactions are observed as the major dissociation pathways resulting in production of protonated adenine or elimination of neutral adenine. Electronic structure calculations are performed at the B3LYP/6-311+G(d,p) level of theory to probe the potential energy surfaces (PESs) for N-glycosidic bond cleavage of dAdo+H and Ado+H. Relative energetics of the reactants, transition states, intermediates and products along the PESs for N-glycosidic bond cleavage are determined at the B3LYP/6-311+G(2d,2p), B3LYP-GD3BJ/6-311+G(2d,2p), and MP2(full)/6-311+G(2d,2p) levels of theory. The predicted N-glycosidic bond dissociation mechanisms for the N3 and N1 protonated species differ. Base rotation of the adenine residue enables formation of a strong N3H(+)O5' hydrogen-bonding interaction that stabilizes the N3 protonated species and its glycosidic bond. Comparison between experiment and theory indicates that the N3 protonated species determine the threshold energies, as excellent agreement between the measured and B3LYP computed activation energies (AEs) and reaction enthalpies (ΔHrxns) for N-glycosidic bond cleavage of the N3 protonated species is found.
我们之前对质子化的2'-脱氧腺苷和腺苷（dAdo+H和Ado+H）进行的气相红外多光子解离作用光谱研究发现，N3和N1质子化构象异构体均存在，且在实验中以N3质子化基态构象异构体为主。因此，本文采用实验和理论方法研究了N3和N1质子化的dAdo+H和Ado+H的N-糖苷键解离机制以及相关的定量热化学值。使用导向离子束串联质谱技术研究了dAdo+H和Ado+H与Xe的阈值碰撞诱导解离（TCID）。对于这两个体系，均观察到N-糖苷键断裂反应是主要的解离途径，导致产生质子化腺嘌呤或消除中性腺嘌呤。在B3LYP/6-311+G(d,p)理论水平上进行电子结构计算，以探究dAdo+H和Ado+H的N-糖苷键断裂的势能面（PESs）。在B3LYP/6-311+G(2d,2p)、B3LYP-GD3BJ/6-311+G(2d,2p)和MP2(full)/6-311+G(2d,2p)理论水平上确定了沿N-糖苷键断裂的PESs的反应物、过渡态、中间体和产物的相对能量。预测的N3和N1质子化物种的N-糖苷键解离机制不同。腺嘌呤残基的碱基旋转能够形成强大的N3H(+)O5'氢键相互作用，从而稳定N3质子化物种及其糖苷键。实验与理论之间的比较表明，N3质子化物种决定了阈值能量，因为在N3质子化物种的N-糖苷键断裂的测量活化能（AEs）和反应焓（ΔHrxns）与B3LYP计算值之间发现了极好的一致性。
