Isolation of proton transfer complexes containing 4-picolinium as cation and pyridine-2,6-dicarboxylate complex as anion: crystallographic and spectral investigations, antioxidant activities and molecular docking studies

Abstract

Three novel complexes with stoichiometry [4-pic-H][M(pda)₂]·2H₂O [M = Cr (1), Fe (2) and Co (3); H₂pda = pyridine-2,6-dicarboxylic acid and 4-pic = 4-picoline] have been prepared. The complexes (1–3) are characterized using elemental analysis, TGA, CV, FTIR, ESI mass, ¹H & ¹³C NMR, EPR, UV Visible, fluorescence, magnetic and X-ray studies. Spectral data ascertained the bonding modes and the geometry of the complexes. Single crystal X-ray data of (2) and (3) revealed the formation of proton transfer complexes in which a proton is transferred from the H₂pda moiety to the pyridine nitrogen of 4-pic. Thermal and ESI mass data confirmed the proposed stoichiometry of the complexes. Cyclic voltammetric (CV) studies confirm the formation of M^II/M^III quasi-reversible redox couples in solution. The antioxidant activity of (3) assessed using DPPH and hydrogen peroxide assays has suggested that the present compounds may be used as potent antioxidants. Molecular docking studies performed for (2) and (3) reveal that the present complexes can efficiently bind with DNA receptor with free energy of binding (FEB) values of −314 (2) and −276.8 kcal mol⁻¹ (3). The molecular docking studies indicated a higher binding ability of (2) to DNA compared to that of (3).