Molecular salts of terephthalic acids with 2-aminopyridine and 2-aminothiazole derivatives as potential antioxidant agents; Base-Acid-Base type architectures

Abstract Molecular salts of terephthalic acid (TA) with 2-amino-4-chloropyridine (ACP), 2-amino-6-methylpyridine (AMP), 2-aminothiazole (AT) and 2-amino-5-methylthiazole (AMT), were prepared with an intent to get new crystalline materials with improved physical properties. Crystals of the desired compounds were obtained through slow evaporation technique. The solid state structures reveal that proton transfer from acid to aromatic nitrogen of the base occurs, thus affording molecular salts of general representation AT-TA-AT (1), AMT-TA-AMT (2), AMP-TA-AMP (3) and ACP-TA-ACP (4). The NH2 group at position 2 of each amino base is still available to interact with C O to afford planar fragment. The COOH functional groups in TA at para position with respect to each other accommodated the respective base in a 1:2 M ratio (acid:base, respectively) to give almost planar Base-Acid-Base (BAB) fragments. The resultant molecular salts were structurally characterized with the help of FT-IR and X-ray diffraction. The antimicrobial (selected strains), antioxidant (2,2-DiPheny-1-Picry-l-Hydrazyl, DPPH and 2,2′-Azino-Bis(3-ethylbenzoThiazoline-6-Sulphonic acid, ABTS) and enzyme inhibition (AChE, BChE and AGS) potencies of the synthesized Base-Acid-Base type, molecular salts were explored. In addition to improved physical properties, all molecular salts showed promising biological activities. The optimization, natural bonding orbitals (NBOs) and IR analysis of the molecular salts were carried out by DFT/B3LYP/6-311G (d,p) level in PCM model with ethanol solvent. However, frontier molecular orbitals (FMOs) analysis was performed utilizing TD-DFT/B3LYP/6-311G (d,p) level. A comparative analysis reveals that consistency is found between the experimental and theoretical findings of geometric parameters and vibrational frequencies. The inter-molecular hydrogen bond (IHB) and hyper conjugative interactions are characterized by NBO analysis. The chemical stability of the molecules is evaluated by FMOs. The energies of FMOs are also used to calculate the global reactivity descriptor parameters. The obtained high softness values indicated that entitled compounds might be biological active.