Brugh Alexander M, Wang Ruobing, Therien Michael J, Forbes Malcolm D E
Center for Photochemical Sciences, Department of Chemistry, Bowling Green State University, Bowling Green, Ohio 43403, United States.
Department of Chemistry, French Family Science Center, Duke University, Durham, North Carolina 27708, United States.
ACS Omega. 2021 Oct 18;6(42):27865-27873. doi: 10.1021/acsomega.1c03490. eCollection 2021 Oct 26.
An investigation of spin and conformational dynamics in a series of symmetric Cu-Cu porphyrin dimer solutions is presented using electron paramagnetic resonance (EPR) spectroscopy. Previous spectral simulations focused on the isotropic exchange interaction ( ) between the Cu centers. In this work, an additional line broadening parameter ( ) is explored in detail via variable temperature X-band EPR in liquid solution for several different structures. The phenomenon is due to fluctuations in the spin exchange interaction caused by conformational motion of the porphyrin planes. The parameter scales with the inverse of the rotational barriers that determine the Boltzmann-weighted torsional angle distribution between neighboring porphyrin planes. Arrhenius plots allow for extraction of the activation energies for rotation, which are 5.77, 2.84, and 5.31 kJ/mol for ethyne-bridged (porphinato)copper(II)-(porphinato)copper(II), butadiyne-bridged (porphinato)copper(II)-(porphinato)copper(II), and ethyne-bridged (porphinato)copper(II)-(porphinato)zinc(II)-(porphinato)copper(II) complexes, respectively. DFT calculations of these torsional barriers match well with the experimental results. This is the first report of a analysis within a highly anisotropic hyperfine field and demonstrates the utility of the theory for extraction of dynamic information.
本文利用电子顺磁共振（EPR）光谱对一系列对称的铜-铜卟啉二聚体溶液中的自旋和构象动力学进行了研究。先前的光谱模拟主要关注铜中心之间的各向同性交换相互作用（ ）。在这项工作中，通过在液体溶液中进行变温X波段EPR，对几种不同结构详细探究了一个额外的线宽参数（ ）。 现象是由于卟啉平面的构象运动引起的自旋交换相互作用的波动所致。 参数与决定相邻卟啉平面之间玻尔兹曼加权扭转角分布的旋转势垒的倒数成比例。阿累尼乌斯图允许提取旋转的活化能，对于乙炔桥联（卟啉基）铜（II）-（卟啉基）铜（II）、丁二炔桥联（卟啉基）铜（II）-（卟啉基）铜（II）和乙炔桥联（卟啉基）铜（II）-（卟啉基）锌（II）-（卟啉基）铜（II）配合物，其活化能分别为5.77、2.84和5.31 kJ/mol。这些扭转势垒的密度泛函理论（DFT）计算与实验结果吻合良好。这是在高度各向异性超精细场中进行 分析的首次报道，并证明了该理论在提取动态信息方面的实用性。
