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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Dynamics and Multiconfiguration Potential Energy Surface for the Singlet O2 Reactions with Radical Cations of Guanine, 9-Methylguanine, 2′-Deoxyguanosine, and Guanosine
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Dynamics and Multiconfiguration Potential Energy Surface for the Singlet O2 Reactions with Radical Cations of Guanine, 9-Methylguanine, 2′-Deoxyguanosine, and Guanosine

机译：动力学和多组廓流潜在能量表面为鸟嘌呤，9-甲基胍，2'-脱氧核苷酸和鸟苷的自由基O2反应

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Reactions of electronically excited singlet oxygen (~(1)O_(2)) with the radical cations of guanine (9HG~(?+)), 9-methylguanine (9MG~(?+)), 2′-deoxyguanosine (dGuo~(?+)), and guanosine (Guo~(?+)) were studied in the gas phase by a combination of guided-ion-beam mass spectrometric measurement of product ions and cross sections as a function of collision energy (E _(col)) and electronic structure calculations of the reaction potential energy surface (PES) at various levels of theory. No product could be captured in the ~(1)O_(2) reaction with bare 9HG~(?+) or 9MG~(?+), because energized products decayed rapidly to reactants before being detected. To overcome this unfavorable kinetics, monohydrated 9HG~(?+)·H_(2)O and 9MG~(?+)·H_(2)O were used as reactant ions, of which the peroxide product ions were stabilized by energy relaxation via elimination of the water ligand. Reaction cross sections for 9HG~(?+)·H_(2)O and 9MG~(?+)·H_(2)O decrease with increasing E _(col), becoming negligible above 0.6 eV. This indicates that the reactions are exothermic with no barriers above reactants and the heat of formation of the products is sufficiently large to overcome their water ligand elimination energy (0.7 eV). Peroxide product ions were also detected in the ~(1)O_(2) reactions with unhydrated dGuo~(?+) and Guo~(?+), in which intramolecular vibrational redistribution was able to stabilize oxidation products. 9MG~(?+) was utilized as a model system to explore the reaction PES for the initial ~(1)O_(2) addition to the guanine radical cation. Calculations were carried out using single-reference ωB97XD, RI-MP2, and DLPNO-CCSD(T) and multireference CASSCF and CASPT2. Although the same PES profile was obtained at different levels of theory, the energies of the mixed open- and closed-shell ~(1)O_(2) reactant and the open-shell reaction intermediates, transition states, and products are sensitive to the theories. By taking into account both static and dynamic electron correlations, the CASPT2 PES has provided the best agreement with the experimentally measured reaction thermodynamics and predicted 8-peroxide as the most probable initial oxidation product of the guanine radical cation.
机译：电子激发单线态氧（~（1）O_（2））与鸟嘌呤（9HG~（？））、9-甲基鸟嘌呤（9MG~（？））、2′-脱氧鸟苷（dGuo~（？））等自由基阳离子的反应，在气相中，通过引导离子束质谱测量产物离子和截面作为碰撞能量（E（col））的函数，以及在不同理论水平上计算反应势能面（PES）的电子结构，研究了鸟苷（Guo~（？））。在与裸9HG~（？+）或9MG~（？+）的~（1）O_2）反应中，由于通电产物在被检测之前迅速衰变为反应物，因此不能捕获任何产物。为了克服这种不利的动力学，一水化9HG~（？+）·H_（2）O和9MG~（？+）·H_（2）O被用作反应离子，其中过氧化物产物离子通过消除水配体通过能量弛豫而稳定。9HG~（？）·H_（2）O和9MG~（？）·H_（2）O的反应截面随着E_col的增加而减小，在0.6eV以上变得可以忽略不计。这表明反应是放热的，反应物上方没有障碍物，产物的生成热足够大，足以克服其水配体消除能（0.7 eV）。在与未水合的dGuo~（？+）和Guo~（？+）的~（1）O_2）反应中也检测到过氧化物产物离子，其中分子内振动再分布能够稳定氧化产物。以9MG~（？+）为模型体系，研究了鸟嘌呤阳离子与~（1）O_2的初始加成反应。使用单参考ωB97XD、RI-MP2和DLPNO-CCSD（T）以及多参考CASSCF和CASPT2进行计算。尽管在不同的理论水平上获得了相同的PES分布，但开壳和闭壳~（1）O_2）反应物和开壳反应中间体、过渡态和产物的能量对这些理论很敏感。通过考虑静态和动态电子关联，CAPT2 PES与实验测量的反应热力学最为一致，并预测8-过氧化物是鸟嘌呤自由基阳离子最可能的初始氧化产物。

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