Jäger H, Koch A, Maus V, Spiess H W, Jeschke G
Max Planck Institute for Polymer Research, Mainz, Germany.
J Magn Reson. 2008 Oct;194(2):254-63. doi: 10.1016/j.jmr.2008.07.012. Epub 2008 Jul 18.
Distance measurements by electron paramagnetic resonance techniques between labels attached to biomacromolecules provide structural information on systems that cannot be crystallized or are too large to be characterized by NMR methods. However, existing techniques are limited in their distance range and sensitivity. It is anticipated by theoretical considerations that these limits could be extended by measuring the enhancement of longitudinal relaxation of a nitroxide label due to a lanthanide complex label at cryogenic temperatures. The relaxivity of the dysprosium complex with the macrocyclic ligand DOTA can be determined without direct measurements of longitudinal relaxation rates of the lanthanide and without recourse to model compounds with well defined distance by analyzing the dependence of relaxation enhancement on either temperature or concentration in homogeneous glassy frozen solutions. Relaxivities determined by the two calibration techniques are in satisfying agreement with each other. Error sources for both techniques are examined. A distance of about 2.7 nm is measured in a model compound of the type nitroxide-spacer-lanthanide complex and is found in good agreement with the distance in a modeled structure. Theoretical considerations suggest that an increase of the upper distance limit requires measurements at lower fields and temperatures.
通过电子顺磁共振技术对附着在生物大分子上的标记物之间进行距离测量，可为无法结晶或体积太大而无法用核磁共振方法表征的系统提供结构信息。然而，现有技术在距离范围和灵敏度方面存在局限性。从理论上考虑，预计通过在低温下测量镧系元素配合物标记导致的氮氧化物标记纵向弛豫增强，可以扩展这些限制。通过分析均匀玻璃态冷冻溶液中弛豫增强对温度或浓度的依赖性，无需直接测量镧系元素的纵向弛豫率，也无需借助距离明确的模型化合物，就可以确定带有大环配体DOTA的镝配合物的弛豫率。通过两种校准技术确定的弛豫率彼此吻合良好。对两种技术的误差来源进行了研究。在氮氧化物-间隔物-镧系元素配合物类型的模型化合物中测量到约2.7纳米的距离，发现与建模结构中的距离吻合良好。理论上考虑表明，提高距离上限需要在更低的场强和温度下进行测量。
