COMPUTATIONAL STUDY OF CU(II)-GALLATE AND MN(II)- GALLATE MONONUCLEAR COMPLEXES AND THEIR POTENTIAL AS ANTIOXIDANTS USING DENSITY FUNCTIONAL THEORY (DFT)

• Main Author: Fauzan Hamzah, Muh.
• Format: Theses
• Language: Indonesia
• Subjects: Kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/83515
• Institution: Institut Teknologi Bandung

Gallic acid (3,4,5- trihydroxybenzoic acid, symbolized as H4G) is one of polyphenol compounds which recognized as a good antioxidant agent. As a polyphenol compound, gallic acid can also act as ligands that will form coordination bond with transition metal ions. Gallic acid is also a polyprotic acid that can undergo various stages of ionization in an aqueous solution, which has a value of pKa1 = 4,0, pKa2 = 8,7, pKa3 = 11,4, dan pKa4 > 13. The equilibrium of gallic acid in water can produce several ions, namely H3G?, H2G 2?, HG3?, dan G4?. Therefore, the formation of transition metal ion complex compounds with gallic acid is strongly influenced by the solution's pH. Several researchers reported that gallic acid can form mononuclear complexes with transition metal ions M(II) (M = Cu, Mn, Fe, Co, Ni, Zn, Cd) and gallate ions as bidentate ligands using the O atom of the phenolic group position 3 and 4 as an atom donor. In addition, gallic acid can also act as a bridging ligand and produce polymeric complexes with MOF frameworks. Based on previous studies of mononuclear complexes, the coordination bond between the transition metal ion and the gallate ligand is via the phenolic group which has a pKa value that is greater than the carboxylate group. The smallest pKa value for gallic acid is located in the carboxylic group, so the carboxylate group is much easier to deprotonate, and has more potential as donor group than the phenolic group for mononuclear complexes. The aim of this research is to examine mononuclear complexes of Cu(II) and Mn(II) and gallate ligands with O atoms in deprotonated carboxylates and phenolics as atom donors. The research was carried out computationally using the DFT (Density Functional Theory) method with B97-3c and B3LYP LANL2DZ D4 approach to study the structure and various properties of the complex, including its potential as an antioxidant. From the research results it was found that the Cu(II)-gallate and Mn(II)-gallate complexes were more stable with the O atom of the carboxylate group on the gallate ligand as the atom donor. The Cu(II)-gallate complex is more stable in the form of 4 coordination compared to 6 coordination. FMO (Frontier Molecular Orbital) analysis shows that Cu(II)-gallate more easily captures electrons, while Mn(II)-gallate more easily releases electrons. Antioxidant potential studies show that the Cu(II)-gallate complex has more potential as an antioxidant through the HAT (Hydrogen Atom Transfer) mechanism.