Demay-Drouhard Paul, Ching H Y Vincent, Akhmetzyanov Dmitry, Guillot Régis, Tabares Leandro C, Bertrand Hélène C, Policar Clotilde
Ecole Normale Supérieure-PSL Research University, Département de Chimie, Sorbonne Universités-UPMC Univ Paris 06, CNRS UMR 7203 LBM, 24 rue Lhomond, 75005, Paris, France.
Institute for Integrative Biology of the Cell (I2BC), Department of Biochemistry, Biophysics and Structural Biology, Université Paris-Saclay, CEA, CNRS UMR 9198, Gif-sur-Yvette, F-91198, France.
Chemphyschem. 2016 Jul 4;17(13):2066-78. doi: 10.1002/cphc.201600234. Epub 2016 Apr 18.
High-spin gadolinium(III) and manganese(II) complexes have emerged as alternatives to standard nitroxide radical spin labels for measuring nanometric distances by using pulsed electron-electron double resonance (PELDOR or DEER) at high fields/frequencies. For certain complexes, particularly those with relatively small zero-field splitting (ZFS) and short distances between the two metal centers, the pseudosecular term of the dipolar coupling Hamiltonian is non-negligible. However, in general, the contribution from this term during conventional data analysis is masked by the flexibility of the molecule of interest and/or the long tethers connecting them to the spin labels. The efficient synthesis of a model system consisting of two Mn(dota) (MnDOTA; DOTA(4-) =1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate) directly connected to the ends of a central rodlike oligo(phenylene-ethynylene) (OPE) spacer is reported. The rigidity of the OPE is confirmed by Q-band PELDOR measurements on a bis-nitroxide analogue. The Mn(II) -Mn(II) distance distribution profile determined by W-band PELDOR is in reasonable agreement with one simulated by using a simple rotamer analysis. The small degree of flexibility arising from the linking MnDOTA arm appears to outweigh the contribution from the pseudosecular term at this interspin distance. This study illustrates the potential of MnDOTA-based spin labels for measuring fairly short nanometer distances, and also presents an interesting candidate for in-depth studies of pulsed dipolar spectroscopy methods on Mn(II) -Mn(II) systems.
高自旋钆（III）和锰（II）配合物已成为标准氮氧化物自由基自旋标记的替代品，用于在高场/高频下通过脉冲电子-电子双共振（PELDOR或DEER）测量纳米距离。对于某些配合物，特别是那些具有相对较小的零场分裂（ZFS）且两个金属中心之间距离较短的配合物，偶极耦合哈密顿量的赝久期项不可忽略。然而，一般来说，在传统数据分析过程中，该项的贡献被感兴趣分子的灵活性和/或连接它们与自旋标记的长链所掩盖。本文报道了一种模型体系的高效合成，该体系由两个直接连接到中心棒状聚（亚苯基乙炔）（OPE）间隔物两端的[Mn（dota）]（2-）（MnDOTA；DOTA（-4）=1,4,7,10-四氮杂环十二烷-1,4,7,10-四乙酸）组成。通过对双氮氧化物类似物的Q波段PELDOR测量证实了OPE的刚性。通过W波段PELDOR测定的Mn（II）-Mn（II）距离分布轮廓与使用简单旋转异构体分析模拟的结果合理吻合。在这个自旋间距离处，连接MnDOTA臂产生的小程度灵活性似乎超过了赝久期项的贡献。这项研究说明了基于MnDOTA的自旋标记在测量相当短的纳米距离方面的潜力，并且还为深入研究Mn（II）-Mn（II）体系的脉冲偶极光谱方法提供了一个有趣的候选物。
