Makuvaza James T, Kokkin Damian L, Loman John L, Reid Scott A
Department of Chemistry , Marquette University , Milwaukee , Wisconsin 53233 , United States.
J Phys Chem A. 2019 Apr 4;123(13):2874-2880. doi: 10.1021/acs.jpca.9b01020. Epub 2019 Mar 20.
Noncovalent forces such as hydrogen bonding, halogen bonding, π-π stacking, and C-H/π and C-H/O interactions hold the key to such chemical processes as protein folding, molecular self-assembly, and drug-substrate interactions. Invaluable insight into the nature and strength of these forces continues to come from the study of isolated molecular clusters. In this work, we report on a study of the isolated anisole-methane complex, where both C-H/π and C-H/O interactions are possible, using a combination of theory and experiments that include mass-selected two-color resonant two-photon ionization spectroscopy, two-color appearance potential (2CAP) measurements, and velocity mapped ion imaging (VMI). Using 2CAP and VMI, we derive the binding energies of the complex in ground, excited, and cation radical states. The experimental values from the two methods are in excellent agreement, and they are compared with selected theoretical values calculated using density functional theory and ab initio methods. The optimized ground-state cluster geometry, which is consistent with the experimental observations, shows methane sitting above the ring, interacting with anisole via both C-H/π and C-H/O interactions, and this dual mode of interaction is reflected in a larger ground-state binding energy as compared with the prototypical benzene-methane system.
诸如氢键、卤键、π-π堆积以及C-H/π和C-H/O相互作用等非共价力是蛋白质折叠、分子自组装以及药物-底物相互作用等化学过程的关键所在。对这些力的性质和强度的宝贵见解仍不断来自于对孤立分子簇的研究。在这项工作中，我们报告了一项对孤立的苯甲醚-甲烷复合物的研究，其中C-H/π和C-H/O相互作用均有可能发生，我们结合了理论和实验方法，包括质量选择双色共振双光子电离光谱、双色出现势（2CAP）测量以及速度成像离子成像（VMI）。利用2CAP和VMI，我们推导了该复合物在基态、激发态和阳离子自由基态的结合能。这两种方法得到的实验值高度吻合，并与使用密度泛函理论和从头算方法计算得到的选定理论值进行了比较。优化后的基态簇几何结构与实验观测结果一致，显示甲烷位于环上方，通过C-H/π和C-H/O相互作用与苯甲醚相互作用，与典型的苯-甲烷体系相比，这种双重相互作用模式体现在更大的基态结合能上。
