Synthesis And Biological Activity Of Some Mono-and Di-thiocarbohydrazones Schiff Base And Their Mn(Ⅱ) Complex

Schiff base, containing the group, has some specialities. Its atom N with several lone pair electrons p and sp² hybridized orbit is inclined to coordinate with metals and to be ring formation. It seems to be useful to synthesize Schiff base with chemical and biological active. Up to now, researchers in the world have synthesized and charactered kinds of Schiff base and its metal complexes. And they exploited many uses such as medicines, catalyst, material, titrate and simulating biology mechanism et al. Schiff base containing sulfur and its complexes are given more attention because of their significant antitumor and antibacterial activities.Because the two -NH＿2 groups have the same reaction activity, we first prepared the symmetrical bis-Schiff bases easily, using the symmetrical diamine-thiocarbohydrazide as the parent reactants. By controlling the molar ratio of ketone-2-acetylpyrazine to thiocarbohydrazide (1:1), we could get the product of monocondensation through slow addition of the former to an excess of the later reactant. Because of the exist of free -NH₂ group, the product of monocondensation could also condense with substituted salicylaldehydes and benzaldehydes. A new simpler method was developed to synthesis asymmetrical bis-Schiff base. One mono-thiocarbohydrazones Schiff base and five new asymmetrical bis-Schiff bases have been synthesized. Melting Point, IR, UV, Mass spectrum, element analyses and ¹H NMR have been tested and their composition and probably structure have been conjectured. Among these, six compound have not been reported by literatures. Using acetylpyrazine thiocarbohydrazone (1), 1-acetylpyrazine -5-5-chlorosalicylaldehyde dithiocarbohydrazone (2b) and 1-acetyl-pyrazine-5-4-methoxybenzaldehyde dithiocarbohydrazone (3b) as ligand, and three Mn(â…¡) complexes have been synthesized. Molar conductance, melting point, element analysis, IR and UV have been measured, and their probably structures have been conjectured.The antibacterial activities of acetylpyrazine thiocarbohydrazone (1), 1-acetylpyrazine-5-5-bromosalicylaldehyde dithiocarbohydrazone(2a), 1-acetylpyrazine -5-5-chlorosalicylaldehyde dithiocarbohydrazone (2b) and their Mn(â…¡) complexes have been tested against gram-positive(Staphylococcus aureus, Bacillus thuringiensis, Bacillus subtills) and gram-negative bacterium (Escherichia coli., Pseudomomas aeruginosa). Using disc diffusion assay method, we found that all the Schiff bases have anti-bacterial ability. We measured the diameter of circles of different...