Three Schiff bases were synthesized by reaction of different benzaldehydes with amino acids. The characterization of these compounds was performed using IR spectroscopy, molecular calculations, thin-layer chromatography, determining the melting point and other physical characteristics. IR spectra for imino groups (C=N), which are characteristic of Schiff bases, show stretching frequency from 1629 to 1654 cm-1. The obtained spectral results were confirmed by molecular calculations using the density functional theory (DFT) and were performed before experimental work. The DFT global chemical reactivity descriptors were calculated and used to predict their relative stability and reactivity of synthesized compounds. The antimicrobial assay of all compounds were screened for Grampositive bacteria species: Staphylococcus aureus ATCC 25923; Methicillin-resistant Staphylococcus aureus: MRSA ATCC 33591; Bacillus subtilis ATCC 6633; and Enterococcus faecalis ATCC 29212, Gram-negative: Salmonella enterica ATCC 31194; Pseudomonas aeruginosa ATCC 9027; Escherichia coli ATCC 25922; Extended Spectrum Beta-Lactamase producing E. coli: ESBL E. coli ATCC 35218, and one yeast Candida albicans ATCC 1023.The highest values of inhibition zones were recorded for compound1, followed by the compound 3, while compound 2 performed inhibitory effect just in case of MRSA. DFT calculations show that antimicrobial activity has a good correlation with chemical reactivity descriptors obtained Schiff bases.

Oxidative stress is directly related to several diseases and symptoms, where antioxidant compounds, such as xanthenes, may become important in prevention and/or treatmant. Ten biologically active 9-aryl substituted 2, 6, 7-trihydroxyxanthen-3-one derivatives were synthesized using reliable one-pot synthesis and their structures were confirmed by IR, 1H and 13C NMR spectroscopy and mass spectrometry. Some of the synthesized compounds were scanned for their antioxidant potency using electrochemical method cyclic voltammetry of immobilized microparticles. Substitution of hydrogen at the phenyl ring of 2, 6, 7-trihydroxy-9-phenylxanthen-3-one with an electron-donating group affected the reducing power of the compounds by lowering the biological oxidation potential. These results signify the importance of xanthen-3-one derivatives as antioxidant agents and their further biological evaluation.

For some synthesized coumarin derivatives, 1H and 13C NMR isotropic chemical shifts and some other molecular properties were calculated using density functional theory. The calculations yield reliable results, that are in good correlation with experimental data. This is a good basis for the collaboration between experimentalists and quantum chemists.

In the present investigation, a series of coumarin-based compounds containing a chalcone moiety were studied for their in vitro and in silico pro- perties. The DFT global chemical reactivity descriptors (chemical hardness, total energy, electronic chemical potential and electrophilicity) were calculated for four synthesized compounds and used to predict their relative stability and reactivity. The antibacterial activities of all compounds were screened against Bacillus subtilis (ATCC 6633) and Bacillus cereus (ATCC 11778). The quantum-chemical calculations indicated that the antibacterial activity correlates well with chemical reactivity descriptors of the molecules.

Coumarin-based compounds containing a chalcone moiety exhibit antimicrobial activity. These substances are potential drugs and it is important to determine their pKa values. However, they are almost insoluble in water. The dissociation constant was experimentally determined by potentiometric titration for 3-[3-(2-nitrophenyl)prop-2-enoyl]-2H-1-benzopyran-2-one because this compound shows good activity and solubility. A number of different computer programs for the calculation of the dissociation constant of chemical compounds have been developed. The pKa value of the target compound was calculated using three different computer programs, i.e., the ACD/pKa, CSpKaPredictor and ADME/ToxWEB programs, which are based on different theoretical approaches. The analysis demonstrated good agreement between the experimentally observed pKa value of 3-[3-(2-nitrophenyl)prop-2-enoyl]-2H-1-benzopyran- 2-one and the value calculated using the computer program CSpKa.