Heterocyclic Schiff Bases of 3-Aminobenzanthrone and Their Reduced Analogues: Synthesis, Properties and Spectroscopy

New substituted azomethines of benzanthrone with heterocyclic substituents were synthesized by condensation reaction of 3-aminobenzo[de]anthracen-7-one with appropriate aromatic aldehydes. The resulting imines were reduced with sodium borohydride to the corresponding amines, the luminescence of which is more pronounced in comparison with the initial azomethines. The novel benzanthrone derivatives were characterized by NMR, IR, MS, UV/Vis, and fluorescence spectroscopy. The structure of three dyes was studied by the X-ray single crystal structure analysis. The solvent effect on photophysical behaviors of synthesized imines and amines was investigated. The obtained compounds absorb at 420–525 nm, have relatively large Stokes shifts (up to 150 nm in ethanol), and emit at 500–660 nm. The results testify that emission of the studied compounds is sensitive to the solvent polarity, exhibiting negative fluorosolvatochromism for the synthesized azomethines and positive fluorosolvatochromism for the obtained amines. The results obtained indicate that the synthesized compounds are promising as luminescent dyes.

Synthesis and Characterization of New Palladium(II) Schiff Base Complexes Derived from β-Diketones and Diamines

A new series of heterocyclic Schiff bases were prepared from condensation of 1-phenyl-3-methyl-4-acetyl/benzoyl-pyrazolone with 4,4′-diaminodiphenylmethane and 4,4′-diaminodiphenyl ether, resulting in the formation of four novel Schiff base ligands. These ligands were then treated with ethanolic solution of PdCl2, to form corresponding palladium(II) complexes. These complexes were characterized by elemental analysis, IR, 1H NMR, TGA, magnetic susceptibility measurements and UV-visible absorption spectroscopy. All the Pd(II) complexes were found to have one coordinated water molecule. Schiff base ligands chelated with the metal atom through two donor sites N and O of azomethine (-C=N-) and phenolic (-OH) groups, respectively.

Synthesis and In Vitro Antibacterial Evaluation of Schiff Bases Derived FROM 2-Chloro-3-Quinolinecarboxaldehyde

Background: Design, identification, and synthesis of new antimicrobial agents along with preventive proceedings are essential to confront antibiotic-resistant pathogenic bacteria. Heterocyclic Schiff bases are biologically important compounds whose antimicrobial potentials have been proven to bacterial and fungal pathogens. Objectives: In this study, some quinoline Schiff bases were synthesized from condensation of 2-chloro3-quinolinecarboxaldehyde and aniline derivatives. Their inhibitory activities were evaluated against 6 gram-positive and 2 gram-negative bacterial pathogens. Methods: Disc diffusion, broth microdilution, and time-kill tests were applied according to the CLSI guidelines to determine IZD, MIC, and MBC values. Results: 2-Chloro-3-quinolinecarboxaldehyde Schiff bases could inhibit the growth of bacteria with IZDs of 7.5-19.8 mm, MICs of 256-2048 μg mL-1, and MBCs of 512 to ≥2048 μg mL-1. Conclusion: Moderate antibacterial effects were observed with heterocyclic Schiff bases. Complexation and structural changes can improve their antimicrobial properties.