Borel Alain, Laus Sabrina, Ozarowski Andrzej, Gateau Christelle, Nonat Aline, Mazzanti Marinella, Helm Lothar
Laboratoire de Chimie Inorganique et Bioinorganique, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.
J Phys Chem A. 2007 Jun 28;111(25):5399-407. doi: 10.1021/jp066921z. Epub 2007 Jun 1.
In the search for highly efficient magnetic resonance imaging contrast agents, polyamino polypyridine carboxylate complexes of Gd3+ have shown unusual properties with both very rapid and very slow electron spin relaxation in solution observed by electron paramagnetic resonance. Since the relationship between the molecular structure and the electron spin properties remains quite obscure at this point, detailed studies of such complexes may offer useful clues for the design of Gd3+ compounds with tailored electronic features. Furthermore, the availability of very high-frequency EPR spectrometers based on quasi-optical components provides us with an opportunity to test the existing relaxation theories at increasingly high magnetic fields and observation frequencies. We present a detailed EPR study of two gadolinium polyamino polypyridine carboxylate complexes, [Gd(tpaen)]- and [Gd(bpatcn)(H2O)], in liquid aqueous solutions at multiple temperatures and frequencies between 9.5 and 325 GHz. We analyze the results using the model of random zero-field splitting modulations through Brownian rotation and molecular deformations. We consider the effect of concentration on the line width, as well as the possible existence of an additional g-tensor modulation relaxation mechanism and its possible impact on future experiments. We use (17)O NMR to characterize the water exchange rate on [Gd(bpatcn)(H2O)] and find it to be slow (approximately 0.6 x 10(6) s-1).
在寻找高效磁共振成像造影剂的过程中，钆（Gd3+）的聚氨基聚吡啶羧酸盐配合物表现出不同寻常的性质，通过电子顺磁共振观察到其在溶液中的电子自旋弛豫既非常快又非常慢。由于目前分子结构与电子自旋性质之间的关系仍相当模糊，对这类配合物的详细研究可能为设计具有定制电子特性的钆化合物提供有用线索。此外，基于准光学组件的甚高频电子顺磁共振光谱仪的出现，为我们提供了一个机会，可在越来越高的磁场和观测频率下检验现有的弛豫理论。我们对两种钆聚氨基聚吡啶羧酸盐配合物[Gd(tpaen)]-和[Gd(bpatcn)(H2O)]在液态水溶液中、9.5至325吉赫兹的多个温度和频率下进行了详细的电子顺磁共振研究。我们使用通过布朗旋转和分子变形的随机零场分裂调制模型来分析结果。我们考虑了浓度对线宽的影响，以及可能存在的额外g张量调制弛豫机制及其对未来实验可能产生的影响。我们使用（17）O核磁共振来表征[Gd(bpatcn)(H2O)]上的水交换速率，发现其较慢（约0.6×10（6）秒-1）。
