Synthesis of Cu2O micro/nanocrystals with tunable morphologies using coordinating ligands as structure controlling agents and antimicrobial studies

Amino acid based reduced Schiff base ligands that have often produced intriguing supramolecular coordination polymeric structures with metal ions have been used as structure controlling agents in the synthesis of Cu2O micro/nanocrystals. Cu2O micro/nanocrystals in the form of solid spheres, cubes, rods, flat surfaced powders, spheres with rough surfaces and octahedra were obtained by changing the amino acid structure, hydroxyl functionality and oxidizing agent. The absorption studies revealed that the Cu2O micro/nanocrystals with different morphologies exhibited tunable optical band gaps between 1.71 eV and 2.44 eV. Antibacterial studies of Cu2O with different morphologies showed that Cu2O crystals dispersed in liquid are highly effective against both Gram-positive and Gram-negative bacteria whereas, when tested by the agar diffusion method, they were effective only against Bacillus subtilis. All six morphologies exhibited a similar effect, and the antibacterial effect could possibly be attributed to the altered membrane permeability caused by the Cu2O micro/nanocrystals. Comparatively higher membrane permeability was observed in the case of Gram-negative bacteria relative to Gram-positive bacteria.