The Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital , Harvard Medical School , 149 Thirteenth Street, Suite 2301, Charlestown, Massachusetts 02129, United States.
J Am Chem Soc. 2013 Dec 11;135(49):18600-8. doi: 10.1021/ja4094132. Epub 2013 Oct 24.
Here we describe a simple method to estimate the inner-sphere hydration state of the Mn(II) ion in coordination complexes and metalloproteins. The line width of bulk H2(17)O is measured in the presence and absence of Mn(II) as a function of temperature, and transverse (17)O relaxivities are calculated. It is demonstrated that the maximum (17)O relaxivity is directly proportional to the number of inner-sphere water ligands (q). Using a combination of literature data and experimental data for 12 Mn(II) complexes, we show that this method provides accurate estimates of q with an uncertainty of ±0.2 water molecules. The method can be implemented on commercial NMR spectrometers working at fields of 7 T and higher. The hydration number can be obtained for micromolar Mn(II) concentrations. We show that the technique can be extended to metalloproteins or complex:protein interactions. For example, Mn(II) binds to the multimetal binding site A on human serum albumin with two inner-sphere water ligands that undergo rapid exchange (1.06 × 10(8) s(-1) at 37 °C). The possibility of extending this technique to other metal ions such as Gd(III) is discussed.
在这里，我们描述了一种简单的方法来估计配合物和金属蛋白中 Mn(II) 离子的内球水合状态。在存在和不存在 Mn(II)的情况下测量体相 H2(17)O 的线宽作为温度的函数，并计算横向 (17)O 弛豫率。结果表明，最大 (17)O 弛豫率与内球水分子配位数 (q) 成正比。通过结合文献数据和 12 个 Mn(II) 配合物的实验数据，我们表明该方法可以以 ±0.2 个水分子的不确定度准确估计 q。该方法可以在工作场强为 7 T 及更高的商用 NMR 光谱仪上实现。可以获得微摩尔 Mn(II)浓度下的水合数。我们表明，该技术可以扩展到金属蛋白或复合物：蛋白质相互作用。例如，Mn(II)与人血清白蛋白上的多金属结合位点 A 结合，有两个内球水分子配体发生快速交换（37°C 时为 1.06×10(8) s(-1)）。讨论了将该技术扩展到其他金属离子（如 Gd(III)）的可能性。
