Graham Trent R, Chun Jaehun, Schenter Gregory K, Zhang Xin, Clark Sue B, Pearce Carolyn I, Rosso Kevin M
Pacific Northwest National Laboratory, Richland, WA 99354, USA.
Department of Chemistry, Washington State University, Pullman, WA 99164, USA.
Magn Reson Chem. 2022 Feb;60(2):226-238. doi: 10.1002/mrc.5218. Epub 2021 Oct 14.
Although nanometer-sized aluminum hydroxide clusters (i.e., ϵ-Al , [Al O (OH) (H O) ] ) command a central role in aluminum ion speciation and transformations between minerals, measurement of their translational diffusion is often limited to indirect methods. Here, Al pulsed field gradient stimulated echo nuclear magnetic resonance (PFGSTE NMR) spectroscopy has been applied to the AlO core of the ϵ-Al cluster with complementary theoretical simulations of the diffusion coefficient and corresponding hydrodynamic radii from a boundary element-based calculation. The tetrahedral AlO center of the ϵ-Al cluster is symmetric and exhibits only weak quadrupolar coupling, which results in favorable T and T Al NMR relaxation coefficients for Al PFGSTE NMR studies. Stokes-Einstein relationship was used to relate the Al diffusion coefficient of the ϵ-Al cluster to the hydrodynamic radius for comparison with theoretical simulations, dynamic light scattering from literature, and previously published H PFGSTE NMR studies of chelated Keggin clusters. This first-of-its-kind observation proves that Al PFGSTE NMR diffusometry can probe symmetric Al environments in polynuclear clusters of greater molecular weight than previously considered.
尽管纳米级氢氧化铝簇（即ε-Al，[AlO(OH)(H₂O)₅]）在铝离子形态以及矿物之间的转化过程中起着核心作用，但其平移扩散的测量通常仅限于间接方法。在此，铝脉冲场梯度刺激回波核磁共振（PFGSTE NMR）光谱已应用于ε-Al簇的AlO核心，并结合基于边界元计算的扩散系数及相应流体动力学半径的互补理论模拟。ε-Al簇的四面体AlO中心是对称的，仅表现出较弱的四极耦合，这使得其具有利于铝PFGSTE NMR研究的T₂和T₁铝NMR弛豫系数。利用斯托克斯-爱因斯坦关系将ε-Al簇的铝扩散系数与流体动力学半径相关联，以便与理论模拟、文献中的动态光散射以及先前发表的关于螯合凯gin簇的氢PFGSTE NMR研究进行比较。这一首次观察证明，铝PFGSTE NMR扩散测量法能够探测比先前认为的分子量更大的多核簇中的对称铝环境。
