Synthesis, Characterization and Biological Applications of New Guanidinium and Aminoguanidinium Salts of 6-Hydroxypyridine-3-Carboxylic Acid

The reaction of 6-hydroxypyridine-3-carboxylic acid with guanidine bicarbonate and aminoguanidine hydrogen carbonate, in different molar ratios (1:1, 1:2, and 2:1) yield salts of composition[GunH][C₆H₄NO₃]. H₂O(1),[GunH][C₆H₄NO₃][C₆H₅NO₃](2),[GunH]₂[C₆H₃NO₃]. H₂O(3),[AmguH][C₆H₄NO₃](4),[AmguH][C₆H₄NO₃][C₆H₅NO₃](5),[AmguH]₂[C₆H₃NO₃](6). The physicochemical techniques like elemental, spectral and thermal studies were employed to characterize the compounds. All the six as prepared compounds were found to be polycrystalline in nature. The N-N stretching frequency of aminoguanidine moiety appear in the range of 989–914 cm⁻¹. Proton nuclear magnetic resonance (¹H NMR) results show signals at7.5–7.9 δ for NH₂ protons (1–6). Thermal data of all the as prepared salts exhibit continuous decomposition to produce carbon residue as end products. Density functional theoretical studies were carried out to optimize the structure of the compounds theoretically. The lower molecular orbital energy reveal, the high biological activity of the compounds. The broth disk diffusion method was used to examine the antibacterial activities of compounds (1–6) against Gram-negative and Gram-positive bacterial pathogens. The compound 3 showed potential antibacterial activity against Escherichia coli and Staphylococcus aureus bacteria showing 24 and 20 mm, zone of inhibition respectively. Molecular docking (MD) studies were performed for the compounds, with protein structures of Staphylococcus aureus (5CZZ) and Escherichia coli (3T88). The results were consistent with the experimental data obtained from the antibacterial activity.