Department of Chemistry and Konstanz Research School Chemical Biology, University of Konstanz, Universitätsstraße 10, 78464 Konstanz, Germany.
Department of Chemistry and Konstanz Research School Chemical Biology, University of Konstanz, Universitätsstraße 10, 78464 Konstanz, Germany.
J Magn Reson. 2018 Nov;296:29-35. doi: 10.1016/j.jmr.2018.08.006. Epub 2018 Aug 29.
Nanometric distance measurements with EPR spectroscopy yield crucial information on the structure and interactions of macromolecules in complex systems. The range of suitable spin labels for such measurements was recently expanded with a new class of light-inducible labels: the triplet state of porphyrins. Importantly, accurate distance measurements between a triplet label and a nitroxide have been reported with two distinct light-induced spectroscopy techniques, (light-induced) triplet-nitroxide DEER (LiDEER) and laser-induced magnetic dipole spectroscopy (LaserIMD). In this work, we set out to quantitatively compare the two techniques under equivalent conditions at Q band. Since we find that LiDEER using a rectangular pump pulse does not reach the high modulation depth that can be achieved with LaserIMD, we further explore the possibility of improving the LiDEER experiment with chirp inversion pulses. LiDEER employing a broadband pump pulse results in a drastic improvement of the modulation depth. The relative performance of chirp LiDEER and Laser-IMD in terms of modulation-to-noise ratio is found to depend on the dipolar evolution time: While LaserIMD yields higher modulation-to-noise ratios than LiDEER at short dipolar evolution times (τ=2μs), the high phase memory time of the triplet spins causes the situation to revert at τ=6μs.
纳米级距离测量的电子顺磁共振波谱学为复杂体系中大分子的结构和相互作用提供了关键信息。最近，一类新的光诱导标记物——卟啉的三重态，扩展了适用于此类测量的自旋标记物的范围。重要的是，已经报道了使用两种不同的光诱导波谱技术（光诱导）三重态-氮氧自由基的电子双共振（LiDEER）和激光诱导磁偶极子波谱（LaserIMD），在三重态标记物和氮氧自由基之间进行准确的距离测量。在这项工作中，我们旨在在 Q 波段下在等效条件下对这两种技术进行定量比较。由于我们发现使用矩形泵浦脉冲的 LiDEER 没有达到可以通过 LaserIMD 实现的高调制深度，因此我们进一步探索了使用啁啾反转脉冲改进 LiDEER 实验的可能性。使用宽带泵浦脉冲的 LiDEER 导致调制深度的大幅提高。啁啾 LiDEER 和 Laser-IMD 的相对性能（调制比噪声比）被发现取决于偶极子演化时间：虽然在短偶极子演化时间（τ=2μs）下，LaserIMD 比 LiDEER 产生更高的调制比噪声比，但三重态自旋的高相位记忆时间导致情况在 τ=6μs 时反转。
