A Computational Study of Removal of Heavy Metal Pollutants Cr^{+3, +6}, Ni⁺², Cu⁺², Zn⁺², As⁺³, Hg⁺² & Pb⁺² from Soil Using Tri-Catecholate Protochelin Siderophore: A DFT Study

In this work, we computationally investigated the effectiveness of heavy metal removal utilizing the siderophore, i.e. protochelin by calculating the siderophore's interaction & Gibb’s free energy with various heavy metal pollutants. In this work, DFT was used to calculate the interaction & Gibb’s free energy of Protochelin with several metals, including (Cr⁺⁶, Cr⁺³, Ni⁺², Cu⁺², Zn⁺², As⁺², Hg^+2, and Pb⁺²) using hybrid DFT functional PBE0 along with basis set def2-SVP and def2-TZSVP. Cr shows a high chelating affinity for Protochelin compared to other metals in order of (Protochelin-Cr⁺⁶ > Protochelin-As⁺³ > Protochelin-Cr⁺³ > Protochelin- Fe⁺³ > Protochelin-Ni⁺² > Protochelin-Cu⁺² > Protochelin-Pb⁺² > Protochelin-Zn⁺² > Protochelin-Hg⁺²). The research results indicate that a siderophore would be an excellent choice as a metal-chelating chemical. These results are further supported by various computational analyses such as FMOs analysis & DOS spectra (indicating there is a decrease in band gap in metal-protochelin complexes). Non-covalent Interaction (NCI) analysis was further employed to provide further insight into the nature and strength of intermolecular forces between protochelin and the targeted metal pollutants (Cr, Ni, Cu, Zn, As, Hg, Pb. Additionally, RMSD analysis showed minimal structural changes within a 2000 fs simulation at 25°C, 50°C, 75°C and 100°C proving that both protochelin and its metal complexes do not exhibit any physical changes at any of the mentioned temperatures thereby indicating the stability of protochelin-metal complexes. It is now viable to create plants and bacteria that may be utilized efficiently to sequester metal pollutants from the soil and water using various approaches, such as genetic engineering.