Center for Biomedical EPR Spectroscopy and Imaging, The Davis Heart and Lung Research Institute, Division of Cardiovascular Medicine, Department of Internal Medicine, College of Medicine, The Ohio State University, Columbus, Ohio 43210, USA.
J Am Chem Soc. 2013 Feb 13;135(6):2350-6. doi: 10.1021/ja311571v. Epub 2013 Jan 30.
Highly asymmetric exchange-coupled biradicals, e.g., the trityl-nitroxides (TNs), possess particular magnetic properties that have opened new possibilities for their application in biophysical, physicochemical, and biological studies. In the present work, we investigated the effect of the linker length on the spin-spin coupling interaction (J) in TN biradicals using the newly synthesized biradicals CT02-GT, CT02-AT, CT02-VT, and CT02-PPT as well as the previously reported biradicals TNN14 and TN1. The results show that the magnitude of J can be easily tuned from ~4 G (conformer 1 in CT02-PPT) to >1200 G (in TNN14) by varying the linker separating the two radical moieties and changing the temperature. Computer simulations of EPR spectra were carried out to estimate J values of the TN biradicals directly. In addition to the spin-spin coupling interaction of TN biradicals, their g, hyperfine-splitting, and zero-field-splitting interactions were explored at low temperature (220 K). Our present study clearly shows that varying the spin-spin interaction as a function of linker distance and temperature provides an effective strategy for the development of new TN biradicals that can find wide applications in relevant fields.
高度不对称的交换耦合双自由基，例如三苯甲基-氮氧自由基（TNs），具有特殊的磁性质，为其在生物物理、物理化学和生物学研究中的应用开辟了新的可能性。在本工作中，我们使用新合成的双自由基 CT02-GT、CT02-AT、CT02-VT 和 CT02-PPT 以及之前报道的双自由基 TNN14 和 TN1 研究了连接体长度对 TN 双自由基中自旋-自旋耦合相互作用（J）的影响。结果表明，通过改变连接两个自由基部分的连接体并改变温度，J 的大小可以很容易地从~4 G（CT02-PPT 中的构象 1）调谐到>1200 G（在 TNN14 中）。我们还进行了电子顺磁共振（EPR）谱的计算机模拟，以直接估算 TN 双自由基的 J 值。除了 TN 双自由基的自旋-自旋耦合相互作用外，我们还在低温（220 K）下研究了它们的 g、超精细分裂和零场分裂相互作用。本研究清楚地表明，通过改变自旋-自旋相互作用作为连接体距离和温度的函数，为开发新的 TN 双自由基提供了一种有效的策略，这些双自由基可以在相关领域得到广泛应用。
