Antimicrobial efficacies and molecular 3D modeling of novel biopolymer derivatives extracted from biowaste using a solid-state mechanochemical technique.

The biomass source, lobster shell waste, was converted into a useful biopolymer by acid-base treatment through a solid-state mechanochemical technique using ball milling. Cobalt(ii), copper(ii), and zinc(ii) metal ion-inserted, novel biologically active, water-soluble nitrogen-nitrogen-oxygen (N,N,O) polydentate donor hydrazide-grafted O-carboxymethyl chitosan (O-CMCS) Schiff base metal complexes were prepared. Computational studies, including 3D molecular modeling and selected bond lengths and bond angles of metal complexes, were carried out using the PerkinElmer ChemDraw Professional 16.0 software. The complex formation between the novel Schiff base ligands and metal ions dramatically changed the bond angles and bond lengths of the Schiff base ligand due to the lone pair-lone pair repulsion in the active molecules. Fourier-transform infrared (FT-IR) and ultraviolet (UV)-visible spectral analyses confirmed the formation of metal complexes through the metal-oxygen (M-O) and metal-nitrogen (M-N) bonds. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to investigate the surface and internal morphological characteristics of the metal complexes. The bactericidal actions of the compounds were evaluated against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Bacillus subtilis using a nutrient agar medium by the agar well-diffusion method. In addition, the O-CMCS Schiff base derivatives were tested against a few fungi. Candida albicans and Aspergillus niger showed higher percentages of growth inhibition, and the Zn(ii) metal complexes exhibited better antifungal efficacy than the Co(ii) and Cu(ii) metal complexes.