Synthesis, characterization, antimicrobial activity and DFT study of some novel Schiff bases

Two new Schiff bases derived from L-cysteine and substituted benzaldehyde were synthesized: the compound 1 [2-((2-chlorobenzylidene) amino)-3-mercaptopropanoic acid] and the compound 2 [3-mercapto-2-((2-methoxybenzylidene) amino) propanoic acid]. Their structures were confirmed by experimental FT-IR, NMR (1H, 13C), and theoretical methodology DFT (density functional theory). DFT calculations were based on global chemical reactivity indices calculated using the B3LYP/6–31G*, B3LYP/6–31G**, and B3LYP/6–31+G* theory levels. Experimentally and theoretically obtained values for FT-IR and NMR (1H, 13C) of test compounds showed good agreement. The reactivity descriptors of B3LYP (E, EHOMO, ELUMO, dipole moment, ∆ɛ, μ, η, ω) were calculated to predict the stability of newly synthesized compounds. The microbiological activity of the compounds was tested on several Gram-positive bacteria: Staphylococcus aureus, Bacillus subtilis, Clostridium sporogenes, Microccocus luteus and Microccocus flavus. The following Gram-negative bacteria were used to test the compounds: Escherichia coli, Pseudomonas aeruginosa Proteus hauseri, Klebsiella pneumoniae, Salmonella enterica subsp. enterica serovar Enteritidis. Also, the activity on the following yeasts was examined: Candida albicans, Saccharomyces cerevisiae and fungal strain Aspergillus brasilliensis. The Schiff base with chlorine in the structure (the compound 1) has the best antimicrobial action against all tested microorganisms. The selected quantum chemical descriptors calculated for the compounds 1 and 2 have a close relationship with the antimicrobial activity