Kuzin Sergei, Syryamina Victoriya N, Qi Mian, Fischer Moritz, Hülsmann Miriam, Godt Adelheid, Jeschke Gunnar, Yulikov Maxim
Department of Chemistry and Applied Biosciences, ETH Zurich, Vladimir-Prelog-Weg 2, 8093 Zurich, Switzerland.
Voevodsky Institute of Chemical Kinetics and Combustion, Institutskaya str. 3, Novosibirsk 630090, Russia.
Magn Reson (Gott). 2025 Mar 10;6(1):93-112. doi: 10.5194/mr-6-93-2025. eCollection 2025.
The intermolecular hyperfine relaxation-induced dipolar modulation enhancement experiment (ih-RIDME) is a pulse electron paramagnetic resonance (EPR) experiment that can be used to probe the properties of a nuclear spin bath in the vicinity of an unpaired electron. The underlying mechanism is the hyperfine spectral diffusion of the electron spin during the mixing block. A quantitative description of the diffusion kinetics being applied to establish the ih-RIDME data model allows one to extend this method to systems with heterogeneous nuclear arrangements assuming a distribution of the local nuclear densities. The heterogeneity can stem from the solvent or the intrinsic nuclei of a structurally flexible (macro)molecule. Therefore, the fitted distribution function can further serve as a method for heterogeneity characterization, quantification and structure-based analysis. Here, we present a detailed introduction to the principles of ih-RIDME application to heterogeneous systems. We discuss the spectral resolution, determination of the spectral diffusion parameters and influence of noise in the experimental data. We further demonstrate the application of the ih-RIDME method to a model spin-labelled macromolecule with unstructured domains. The fitted distribution of local proton densities was reproduced with the help of a conformational ensemble generated using the Monte Carlo approach. Finally, we discuss several pulse sequences exploiting the HYperfine Spectral Diffusion Echo MOdulatioN (HYSDEMON) effect with an improved signal-to-noise ratio.
分子间超精细弛豫诱导偶极调制增强实验（ih-RIDME）是一种脉冲电子顺磁共振（EPR）实验，可用于探测未配对电子附近核自旋浴的性质。其潜在机制是混合模块期间电子自旋的超精细光谱扩散。应用扩散动力学的定量描述来建立ih-RIDME数据模型，可使该方法扩展到具有异质核排列的系统，前提是假设局部核密度存在分布。这种异质性可能源于溶剂或结构灵活的（大）分子的固有核。因此，拟合的分布函数可进一步用作异质性表征、量化和基于结构分析的方法。在此，我们详细介绍ih-RIDME应用于异质系统的原理。我们讨论光谱分辨率、光谱扩散参数的确定以及实验数据中噪声的影响。我们还展示了ih-RIDME方法在具有无结构域的模型自旋标记大分子上的应用。借助使用蒙特卡罗方法生成的构象集合，重现了局部质子密度的拟合分布。最后，我们讨论了几种利用超精细光谱扩散回波调制（HYSDEMON）效应且具有改进信噪比的脉冲序列。
