Alanís-Manzano Emiliano Isaías, León-Pimentel C I, Maron Laurent, Ramírez-Solís Alejandro, Saint-Martin Humberto
Instituto de Ciencias Físicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos 62210, México.
Departamento de Matemáticas/Fisicoquímica, Facultad de Química, Universidad Nacional Autónoma de México, Ciudad de Mexico 04510, México.
ACS Omega. 2024 Dec 16;9(52):50978-50991. doi: 10.1021/acsomega.4c04947. eCollection 2024 Dec 31.
Born-Oppenheimer molecular dynamics (BOMD) simulations were performed to investigate the structure and dynamics of the first hydration shells of five trivalent lanthanide ions (Ln) at room temperature. These ions are relevant in various environments, including the bulk aqueous solution. Despite numerous studies, accurately classifying the molecular geometry of the first hydration sphere remains a challenge. To addres this, a cluster microsolvation approach was employed to study the interaction of Ln ions (La, Nd, Gd, Er, and Lu) with up to 27 explicit water molecules. Electronic structure calculations were performed with the composite rSCAN-3c method. The results demonstrate that this method offers an optimal balance between precision and computational efficiency. Specifically, it accurately predicts average Ln-O distances (MAE = 0.02 Å) of the first hydration sphere and preferred coordination numbers (CN) for the different lanthanide cations as compared to reported data in bulk. Highly dynamic first hydration shells for the examined Ln ions were found, with noticeable and rapid rearrangements in their coordination geometries, some of which can be recognized as the tricapped trigonal prism (TTP) and the capped square antiprism (CSAP) for CN = 9, and as the square antiprism (SAP), the bicapped trigonal prism (BTP), and the trigonal dodecahedron (DDH) for CN = 8. However, ca. 70% of the nonacoordinated configurations did not meet the criteria of TTP or CSAP structures. For CN = 8, the percentage of configurations that could not be assigned to SAP, BTP, or DDH was lower, around 30%. The theoretical EXAFS spectra obtained from the BOMD simulations are in good agreement with the experimental data and confirm that model microsolvated environments accurately represent the near-solvation structure of these trivalent rare-earth ions. Moreover, this demonstrates that the faster dynamics of the first hydration shell can be studied separately from the dynamics of water exchange in the bulk aqueous solution.
进行了玻恩-奥本海默分子动力学（BOMD）模拟，以研究室温下五种三价镧系离子（Ln）的第一水合层的结构和动力学。这些离子在包括本体水溶液在内的各种环境中都很重要。尽管有大量研究，但准确分类第一水合球的分子几何结构仍然是一个挑战。为了解决这个问题，采用了团簇微溶剂化方法来研究Ln离子（La、Nd、Gd、Er和Lu）与多达27个明确水分子的相互作用。使用复合rSCAN-3c方法进行电子结构计算。结果表明，该方法在精度和计算效率之间提供了最佳平衡。具体而言，与本体中报道的数据相比，它准确地预测了第一水合层的平均Ln-O距离（平均绝对误差=0.02 Å）以及不同镧系阳离子的优选配位数（CN）。发现所研究的Ln离子的第一水合层具有高度动态性，其配位几何结构有明显且快速的重排，其中一些可以被识别为配位数为9时的三棱柱封顶（TTP）和反棱柱封顶（CSAP），以及配位数为8时的反棱柱（SAP）、双三棱柱封顶（BTP）和三角十二面体（DDH）。然而，约70%的九配位构型不符合TTP或CSAP结构的标准。对于配位数为8的情况，无法归为SAP、BTP或DDH的构型百分比较低，约为30%。从BOMD模拟获得的理论扩展X射线吸收精细结构（EXAFS）光谱与实验数据吻合良好，并证实模型微溶剂化环境准确地代表了这些三价稀土离子的近溶剂化结构。此外，这表明可以将第一水合层较快的动力学与本体水溶液中的水交换动力学分开研究。
