Indole-3-carbaldehyde Semicarbazone Derivatives: Synthesis, Characterization, and Antibacterial Activities

Four indole-3-carbaldehyde semicarbazone derivatives, 2-((5-bromo-1H-indol-3-yl)methylene)hydrazinecarboxamide (1), 2-((5-chloro-1H-indol-3-yl)methylene)hydrazinecarboxamide (2), 2-((5-methoxy-1H-indol-3-yl)methylene)hydrazinecarboxamide (3), and 2-((4-nitro-1H-indol-3-yl)methylene)hydrazinecarboxamide (4) were synthesized and characterized by ESI-MS and spectroscopic (FT-IR, 1H NMR, and 13C NMR) techniques. The two-dimensional NMR (in acetone-d6) spectral data revealed that the molecules 1 and 2 in solution are in the cisE isomeric form. This evidence is supported by DFT calculations at the B3LYP/6-311++G(d,p) level of theory where it was shown that the corresponding most stable conformers of the synthesized compounds have a cisE geometrical configuration, in both the gas and liquid (acetone and DMSO) phases. The in vitro antibacterial activity of compounds 1–4 was determined against Gram-positive (Staphylococcus aureus and Bacillus subtilis) and Gram-negative (Pseudomonas aeruginosa and Escherichia coli) bacteria. Among all the tested semicarbazones, 1 and 2 exhibited similar inhibitory activities against Staphylococcus aureus (MIC = 100 and 150 μg/mL, respectively) and Bacillus subtilis (MIC = 100 and 150 μg/mL, respectively). On the other hand, 3 and 4 were relatively less active against the tested bacterial strains compared with 1, 2, and tetracycline.

CALCULATIONS AND EXPERIMENTAL STUDIES OF THE AGGREGATION OF MOLECULES OF LIQUID ACETONE BY SPECTRA OF RAMAN SCATTERING

Experimental studies of the Raman scattering of the band of C = O vibrations of acetone (1710 cm–1) showed that the parallel and perpendicular polarized components have a large half-width (respectively, 11.6 and 18 cm–1) and also the bands' maxima of these components are shifted by ~5 cm–1. In the neutral solvent (heptane), the difference of the maxima position of the bands decreases. Calculations showed that the molecules of acetone can aggregate to form a dimer with the energy gain of 10.1 kJ/mole. In the dimer several hydrogen bonds are formed between the oxygen atom of one molecule and the hydrogen atoms of CH3 -group of another molecule. In an aqueous mixture of acetone, according to calculations, there is a possibility for formation of dimers and closed trimer aggregates with the energy gain, respectively, 19.1 and 45.8 kJ/mole. Calculation showed that symmetric and antisymmetric O–H vibrations of water are displaced in the interaction with acetone to lower frequencies, respectively, to 3808.4 and to 3931.8 –1.