Structural, spectral, computational, thermal and antibacterial studies on a co-crystal: 2-Aminopyrazine phthalic acid

Abstract

In the present work, the crystal growth of a new co-crystal of aminopyrazine with phthalic acid (APPA) and the corresponding structural, vibrational, thermal and antibacterial characteristics have been reported. Crystals of aminopyrazine phthalicacid (PAPA) were grown by slow solvent evaporation technique. Single crystal X-ray diffraction analysis revealed that the present crystal structure is monoclinic system with P21/n space group. In the crystal structure, molecules were connected via NH⋯O and OH⋯N intermolecular hydrogen bonds with R22(8) and R44(18) ring motifs thus forming a C22(10) chain motif along the b axis. The crystal structure was dominated by NH⋯O and weak OH⋯N interactions and it was quantitatively analyzed by Hirshfeld surface and fingerprint analysis. The molecular geometry of the grown crystal was optimized theoretically by using density functional theory with B3LYP/cc-PVTZ basis set. The optimized molecular geometry and computed vibrational spectra were compared with experimental results which showed noteworthy agreement. Thermal stability was determined as 148 °C for APPA crystal using TG/DTA study. The atomic charge distribution on atoms of APPA molecule has been calculated by Mulliken charge analysis. Energy gap, ionization potential and chemical hardness of the APPA molecule were carried out by HOMO–LUMO plot. In which, the frontier orbitals has lower band gap value indicating the possible bio activity of the molecule. The natural bond orbital analysis was carried out to interpret the stability of the molecule and charge delocalization within the molecule. The antibacterial activity of the compound was tested and found increased significantly against all bacteria. Enhanced antibacterial activity of the APPA was attributed to the synergistic effects of intermolecular hydrogen-bonding interactions NH⋯O and OH⋯N between APZ and PA. The molecular docking study supported the antibacterial activity and exhibiting the binding energy.