Structural and antioxidant properties of guanylhydrazinium pyrazine-2-carboxylate

In general, molecules with certain functional groups such as amine (-NH 2 ) and carboxyl (-COOH) can promote the growth of co-crystals leading to the formation of supramolecular networks. However, if the differences in the pKa values of the two molecules are large [pKa (base)—pKa (acid)], salts can result instead of ‘real’ co-crystals. Here, we report the formation of such salt by letting pyrazine-2-carboxylic acid (pKa = 2.9) crystallize together with aminoguanidine (pKa = 11.5; high Δpka = 8.6) a nitrogen-rich organic base. The title salt has been prepared by slow evaporation of an equimolar ratio of guanylhydrazine bicarbonate (i.e., aminoguanidine bicarbonate (AgunH.HCO 3 )) and pyrazine-2-carboxylic acid (Pymca) in aqueous medium. The salt was characterized by IR spectroscopy, powder and single-crystal X-ray diffraction techniques. This material shows enhanced antioxidant activity and this is due to the crucial role of hydrazinic moiety in the aminoguanidinium salt.