Double electron–electron resonance (DEER, also known as PELDOR) is an efficient tool to study nanoscale distances between paramagnetic species forming oligomers or arranged in clusters. DEER also may be applied to study heterogeneous systems in which large clusters of spin labels may be considered as randomly distributed species of enhanced local concentration. For these systems, information of the same kind could be obtained with a simple two-pulse Hahn’s spin-echo sequence, if a so-called instantaneous diffusion (ID) effect is separated from other dephasing processes. Comparison of DEER and ID decays performed here at X-band EPR for model systems of nitroxides dissolved in molecular glasses showed good agreement between DEER and ID data, as well as with theory for randomly distributed spins. For spin-labeled stearic acids in a model biological membrane, the obtained DEER and ID data indicate on cluster formation with enhanced local concentration. For high stearic acid concentration, the ID data were found to strongly deviate from the DEER data, which were interpreted as an evidence for correlation of mutual orientations of spin labels in the clusters.

双电子-电子共振（DEER，也称为 PELDOR）是研究形成低聚物或排列成簇的顺磁性物质之间纳米级距离的有效工具。DEER 也可用于研究异质系统，在这些系统中，自旋标签的大簇可以被认为是随机分布的局部浓度增强的物种。对于这些系统，如果将所谓的瞬时扩散 (ID) 效应与其他移相过程分开，则可以通过简单的两脉冲哈恩自旋回波序列获得相同类型的信息。在 X 波段 EPR 中对溶解在分子玻璃中的氮氧化物模型系统进行的 DEER 和 ID 衰减的比较表明，DEER 和 ID 数据以及随机分布自旋的理论之间具有良好的一致性。对于模型生物膜中的自旋标记硬脂酸，获得的 DEER 和 ID 数据表明簇形成具有增强的局部浓度。对于高硬脂酸浓度，发现 ID 数据强烈偏离 DEER 数据，这被解释为簇中自旋标签相互方向相关性的证据。