Experimental and Computational Insights of a Benzytrietylammonium [CoBr ₄ ] Salt: A Potential Photocatalyst and Inflammation-Related Enzyme Inhibitor

In this paper, we present a combined experimental and computational study of a cobalt-(II) complex with the organic ligand benzyltriethylammonium bromide. The complex was characterized by IR spectroscopy and single-crystal X-ray crystallography. The molecular geometries, electronic transitions, and vibrational frequencies were calculated using density functional theory (DFT) at the B3LYP/LanL2DZ level. Based on the unit cell parameters obtained from experimental data, DFT calculations were performed to correlate with the vibrational spectrum analysis. The theoretical parameters derived from DFT showed strong agreement with the experimental results. A qualitative description of the charge-transfer character was carried out using natural bond orbital (NBO) analysis. The energies of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were calculated, and the band gap was determined. Furthermore, the complex demonstrated significant degradation of methylene blue (MB) under sunlight irradiation. In vitro, the cobalt-(II) complex exhibited strong inhibitory activity against key inflammatory enzymes, particularly myeloperoxidase (MPO), with a half-maximal inhibitory concentration (IC₅₀) of 80.45 μM, compared to 4-aminobenzoic acid hydrazide (ABAH, IC₅₀ = 9.46 μM). It also showed potent inhibitory effects on obesity-related enzymes such as lipase (IC₅₀ = 41.93 μM) compared to orlistat (IC₅₀ = 32.75 μM). Regarding diabetes-related targets, the complex effectively inhibited α-amylase (IC₅₀ = 21.75 μM) in comparison to acarbose (ACR, IC₅₀ = 18.08 μM), and promoted insulin signaling by inhibiting dipeptidyl peptidase-4 (DPP-4, IC₅₀ = 22.01 μM) compared to sitagliptin (STG, IC₅₀ = 4.07 μM). Additionally, it exhibited moderate inhibitory activity against protein tyrosine phosphatase 1B (PTP1B, IC₅₀ = 10.88 μM), approximately 2.1 times less potent than sodium orthovanadate (SV, IC₅₀ = 5.24 μM). A molecular docking approach was employed to investigate the binding affinities and molecular interactions of the two ligands forming the Co-(II) complex with several protein targets (PDB IDs: 3BAJ, 4A5S, 1LPB, 5MFA, and 1T49). The docking results revealed that the complex, through interactions such as hydrogen bonding, π-π stacking, carbon-hydrogen interactions, π-anion, π-cation, and π-alkyl interactions, exhibits promising inhibitory potential against the selected enzymes: α-amylase, dipeptidyl peptidase-4 (DPP-4), lipase, promyeloperoxidase (proMPO), and protein tyrosine phosphatase 1B (PTP1B).