Six novel Ln(III) Schiff base complexes were synthesized using rare earth metals with threonine and 5-bromosalicylaldehyde, namely Pr(III), Sm(III), Gd(III), Tb(III), Er(III) and Yb(III) Schiff bases. These complexes were characterized using elemental analysis, molar conductivity, Fourier transform infrared and UV-visible spectroscopies, and thermogravimetry-differential thermal analysis. The general formula of the complexes is [Ln(L)(NO 3 ) 2 (H 2 O)].NO 3 (L = Schiff base ligand). The spectroscopic data reveal that the Schiff base ligand behaves as a tridentate ligand with ONO donor atoms sequencing towards the central metal ion. An investigation of fluorescence properties of the Sm(III), Er(III) and Tb(III) complexes shows that the Ln(III) ions can be sensitized efficiently by the ligand to some extent. Antimicrobial activity testing indicates that all six complexes exhibit antibacterial and antifungal ability against microbes with broad antimicrobial spectra. In addition, the antioxidant properties of the complexes were also screened.

Objective: Aim of this work is to synthesize and characterization of the hydroxyl group the hydroxyl group substituted L-phenylalanine Schiff bases to compare their predicted quantitative structure-activity relationship (QSAR) and molecular docking against Escherichia coli protein ZipA (1s1j) outcomes with the antibacterial activity and brine shrimp lethal assay (BSLA) results. Methods:The Schiff bases of L-Phenylalanine were synthesized by the simple condensation reaction using methanol, water in 2:1 ratio at reflux and were characterized by spectral techniques. QSAR parameters of the Schiff bases were predicted using java-based online and offline tools. Molecular docking carried through online mcule server and CLC Drug Discovery Workbench 3. Antibacterial activity and toxicity studies were conducted using broth dilution and brine shrimp lethal assay methods, respectively. Results:The Schiff bases fulfilled the QSAR drug-likeness parameters and showed the docking score between −6.8 and −6.0 Kcal/mol which are higher than amoxilicillin and gentamicin like standard drugs. They also possess good inhibition for urinary tract infection causing E. coli bacteria, and minimum inhibitory concentrations (MIC) exists between 3.25 and 5.25 µg/ml. The brine shrimp lethal concentration for 50% mortality [LC 50 ]) between 58.73 and 135.6 µg/ml. Conclusion:Para, meta and 2,4 hydroxyl substituted Schiff bases exhibited good inhibition against Gram-negative E. coli bacteria at low concentration and the MIC exists below the LC 50 value. The Schiff base showed high drug score, high docking score, and low toxicity than other Schiff base. Docking score, high inhibition, low clogP, low MIC