Kajian Struktur dan Dinamika Solvasi Ion Ac3+ dalam Air Menggunakan Simulasi Dinamika Molekul MP2-DKH2/MM

Muhammad Aditya Abimanyu, Dr. rer. nat. Niko Prasetyo, S.Si., M.Sc.; Mokhammad Fajar Pradipta, S.Si., M.Eng.

2024 | Skripsi | KIMIA

Kajian struktur dan dinamika solvasi ion Ac3+ dalam air berdasarkan simulasi dinamika molekuler MP2-DKH2/MM telah dilakukan. Tujuan penelitian ini adalah melakukan kajian teoritis pembentukan kompleks [Ac(H2O)n]3+ dan kestabilannya dalam larutan berair serta mempelajari sifat struktur dan dinamika solvasi ion Ac3+ dalam air secara komputasi. Analisis trajektori dilakukan untuk mempelajari sifat struktur dan dinamika solvasi ion Ac3+ dalam air yang meliputi fungsi distribusi radial (RDF), distribusi bilangan koordinasi (CND), fungsi distribusi sudut (ADF), waktu tinggal rata-rata ligan (MRT), vibrasi ulur Ac3+-O, dan local density corrected three-body distribution functions.

Simulasi dinamika molekul MP2-DKH2/MM menggunakan metode ab initio MP2. Himpunan basis relativistik SARC-DKH-TZVP diberlakukan untuk ion Ac3+ dan himpunan basis 6-31G* untuk air. Koreksi efek relativistik untuk ion Ac3+ dihitung menggunakan metode DKH2. Ekuilibrasi sistem dilakukan selama 5 ps yang kemudian dilanjutkan dengan proses sampling data selama 100 ps. Hasil penelitian menunjukkan bahwa kulit solvasi pertama bersifat rigid/kaku yang membentuk kompleks stabil oktahidrat ([Ac(H2O)8]3+) yang tertata dalam geometri Square Antiprism (SA) dan nonahidrat ([Ac(H2O)9]3+) yang tertata pada geometri Gyro-elongated Square Antiprism (GySA) di mana terdapat 8 hingga 9 molekul H2O. Sudut ikatan yang diperoleh sebesar 72,5º dan 138,5º pada jarak 2,68 Å. Kulit solvasi kedua dan ketiga bersifat dinamis dan memiliki fleksibilitas tinggi dibuktikan dengan waktu tinggal ligannya yang cukup singkat yaitu berturut-turut sebesar 6,46 ps dan 2,67 ps.

A study of solvation structure and dynamics of Ac3+ ion in water based on MP2-DKH2/MM molecular dynamics simulation has been carried out. The aims of this research are to conduct a theoretical study of  formation  [Ac(H2O)n]3+  complex and its stability in aqueous solution and to study the structural properties and dynamics of solvation of the Ac3+ ion in water using computational method. Trajectory analysis was carried out to study the structural properties and dynamics of solvation of Ac3+ ions in water which includes Radial Distribution Function (RDF), Coordination Number Distribution (CND), Angular Distribution Function (ADF), Mean Residence Time (MRT), stretching vibration of Ac3+-O, and local density corrected three-body distribution functions.

MP2-DKH2/MM molecular dynamics simulations used the MP2 ab initio method. The SARC-DKH-TZVP relativistic basis set was applied to Ac3+ ion and 6-31G* basis set was applied to water molecules. The correction of relativistic effect for Ac3+ ion was calculated using the DKH2 method. System equilibration was carried out for 5 ps which was then continued with a sampling process for 100 ps. The result of this research shows that the first solvation shell is rigid which forms a stable complex of octahydrate actinium complex ([Ac(H2O)]3+) which is arranged in Square Antiprism (SA) geometry and nonahydrate actinium complex ([Ac(H2O)9]3+) which is arranged in Gyro-elongated Square Antiprism (GySA) geometry where there are 8 until 9 H2O molecules. The obtained bond angles were 72.5º and 138.5º at a distance of 2.68 Å. The second and third solvation shells are dynamic and have high flexibility as evidenced by their relatively short ligand residence times, namely 6.46 ps and 2.67 ps respectively.

Kata Kunci : Ac3+, air, MP2-DKH2/MM, relativistik, solvasi