Bio-Nanotechnology Center, Department of Chemistry, Pohang University of Science and Technology, San 31 Hyojadong Namgu, Pohang, Kyungbuk 790-784, Korea.
J Phys Chem A. 2010 Nov 4;114(43):11376-85. doi: 10.1021/jp1033855.
Noncovalent interactions between protonated porphyrin and fullerenes (C₆₀ and C₇₀) were studied with five different meso-substituted porphyrins in the gas phase. The protonated porphyrin-fullerene complexes were generated by electrospray ionization of the porphyrin-fullerene mixture in 3:1 dichloromethane/methanol containing formic acid. All singly protonated porphyrins formed the 1:1 complexes, whereas porphyrins doubly protonated on the porphine center yielded no complexes. The complex ion was mass-selected and then characterized by collision-induced dissociation with Xe. Collisional activation exclusively led to a loss of neutral fullerene, indicating noncovalent binding of fullerene to protonated porphyrin. In addition, the dissociation yield was measured as a function of collision energy, and the energy inducing 50% dissociation was determined as a measure of binding energy. Experimental results show that C₇₀ binds to the protonated porphyrins more strongly than C₆₀, and electron-donating substituents at the meso positions increase the fullerene binding energy, whereas electron-withdrawing substituents decrease it. To gain insight into π-π interactions between protonated porphyrin and fullerene, we calculated the proton affinity and HOMO and LUMO energies of porphyrin using Hartree-Fock and configuration interaction singles theory and obtained the binding energy of the protonated porphyrin-fullerene complex using density functional theory. Theory suggests that the protonated porphyrin-fullerene complex is stabilized by π-π interactions where the protonated porphyrin accepts π-electrons from fullerene, and porphyrins carrying bulky substituents prefer the end-on binding of C₇₀ due to the steric hindrance, whereas those carrying less-bulky substituents favor the side-on binding of C₇₀.
在气相中，使用五种不同的中位取代卟啉研究了质子化卟啉与富勒烯（C60 和 C70）之间的非共价相互作用。通过在含甲酸的 3:1 二氯甲烷/甲醇混合物中电喷雾电离卟啉/富勒烯混合物，生成了质子化卟啉-富勒烯配合物。所有单质子化卟啉都形成了 1:1 的配合物，而卟啉中心双质子化的卟啉则没有形成配合物。将配合物离子进行质量选择，然后用 Xe 通过碰撞诱导解离进行表征。碰撞激活仅导致中性富勒烯的损失，表明富勒烯与质子化卟啉的非共价结合。此外，还测量了作为碰撞能函数的离解产率，并将引起 50%离解的能量确定为结合能的度量。实验结果表明，C70 与质子化卟啉的结合比 C60 更强，而中位取代的供电子取代基增加了富勒烯的结合能，而吸电子取代基则降低了它。为了深入了解质子化卟啉与富勒烯之间的π-π相互作用，我们使用 Hartree-Fock 和组态相互作用单重理论计算了卟啉的质子亲和能和 HOMO 和 LUMO 能量，并使用密度泛函理论获得了质子化卟啉-富勒烯配合物的结合能。理论表明，质子化卟啉-富勒烯配合物通过π-π相互作用稳定，其中质子化卟啉接受来自富勒烯的π电子，而带有大取代基的卟啉由于空间位阻而优先选择 C70 的端接结合，而带有较小取代基的卟啉则优先选择 C70 的侧接结合。
