Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL 60115, USA.
J Am Soc Mass Spectrom. 2012 Jun;23(6):1135-46. doi: 10.1007/s13361-011-0330-6. Epub 2012 Apr 12.
The Co(II) complexes of twelve meso-tetraaryl-porphyrins, -chlorins, and chlorin analogues containing non-pyrrolic heterocycles were synthesized and converted in situ to the corresponding Co(III) complexes coordinated to one or two imidazoles. Electrospray ionization tandem mass spectrometry (ESI-MS/MS) in conjunction with the energy-variable collision-induced dissociation (CID) technique was used to compare the relative gas-phase binding strength of the axially coordinated imidazoles to the octahedral and square planar Co(III) porphyrinoid complex ions. The observed binding energies of these ligands were rationalized in terms of the effects of porphyrinoid core structure and meso-substitution on the electron density on the central Co(III) centers. Some of these trends were supported by DFT-based computational studies. The study highlights to which extend porphyrins vary from chlorins and chlorin analogues in their coordination abilities and to which extraordinary degree meso-thienyl-substituents influence the electronic structure of porphyrins. The study also defines further the scope and limits CID experiments can be used to interrogate the electronic structures of metalloporphyrin complexes.
合成了 12 种含有非吡咯杂环的meso-四芳基卟啉、氯卟啉和氯卟啉类似物的 Co(II)配合物，并将其原位转化为与一个或两个咪唑配位的相应 Co(III)配合物。采用电喷雾串联质谱（ESI-MS/MS）结合能量可变碰撞诱导解离（CID）技术，比较了轴向配位咪唑与八面体和平面正方形 Co(III)卟啉配合物离子的相对气相结合强度。根据卟啉核心结构和中位取代对中心 Co(III)中心电子密度的影响，对这些配体的观察到的结合能进行了合理化解释。这些趋势中的一些得到了基于密度泛函理论（DFT）的计算研究的支持。该研究强调了卟啉在配位能力上与氯卟啉和氯卟啉类似物的差异程度，以及中位噻吩取代基对卟啉电子结构的影响程度。该研究还进一步定义了 CID 实验可用于研究金属卟啉配合物电子结构的范围和限制。
