Crystalline pyrazine-2-amidoxime isolated by diffusion method and its structural and behavioral analysis in the context of crystal engineering and microbiological activity

Abstract

Pyrazine-2-amidoxime (PAOX) is a structural analogue of a popular drug, i.e. pyrazine-2-carboxamide (PZA). The crystalline PAOX was obtained by diffusion as a method of crystallization. Various types of intermolecular interactions between the H-bond donors (CH, NH, and OH) and H-bond acceptors (hydroxyl O, imino N, aza N) were found between PAOX molecules in X-ray diffraction studies. It was observed in the crystal structure that PAOX forms not only dimers but also stable helical-like polymers, stabilized by intermolecular interactions between two neighbouring molecules. Their geometric, energetic and spectroscopic properties were also characterised by DFT methods. Thermal decomposition of PAOX was examined with the use of a TG-IR analysis (20-1000 °C), and the results were further resolved. Electrochemical behaviour of the compound studied in acetonitrile in the absence or presence of methanol was described in detail, and mechanisms of the anodic oxidation and cathodic reduction were proposed. The complexometric properties of PAOX were examined against selected d-block metal ions in acetonitrile, as well as in aqueous solution. Biological assay of PAOX was performed to determine the antimicrobial activity and potential pharmaceutical applications. The minimum inhibitory (MIC) and minimal bactericidal (or fungicidal) concentrations (MBC/MFC) for PAOX were determined against six microorganisms.