Microbicidal Studies of AMIC Acids Based Novel Ligands and Their Metal Complexes

The increasing resistance of microorganisms to conventional antimicrobial agents has encouraged the search for new chemotherapeutic compounds with enhanced biological activity. Amic acids, which are mono-amide derivatives of dicarboxylic acids containing both amide (–CONH–) and carboxylic (–COOH) functional groups, are well known for their strong chelating ability and versatile coordination behavior. Owing to the presence of mixed donor atoms (O and N), amic acid–based ligands can form stable complexes with transition metal ions and exhibit significant biological relevance. In the present study, a series of newly synthesized amic acids based novel ligands (L-1 to L-8) and their transition metal complexes with Cu(II), Zn(II), Co(II), Ni(II), and Mn(II) were evaluated for their antifungal and antibacterial properties. Antifungal activity was assessed against five plant pathogenic fungi using the poisoned food technique at 1000 ppm concentration, while antibacterial activity was determined by the disc diffusion method against selected Gram-positive and Gram-negative bacterial strains. The results revealed that metal chelation significantly enhances antimicrobial activity compared to free ligands, which may be attributed to increased lipophilicity and improved penetration of the metal complexes into microbial cell membranes. Among the metal ions studied, copper complexes exhibited the highest antimicrobial efficacy. The overall activity trend followed the order Cu > Zn > Co > Ni > Mn. These findings suggest that amic acids based metal complexes possess promising potential as effective antimicrobial agents for agricultural and pharmaceutical applications.