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Quinones represent an important class of biological compounds, but are also involved with toxicological intermediates and among their hazardous effects include cytotoxicity, immunotoxicity, and carcinogenesis. The structure-toxicity relationship for quinone derivatives has been used to cytotoxicity or cytoprotective effects by redox mechanism is determined using quantum chemical calculations through the density functional theory (DFT). According to our DFT study, the electron acceptance is related with LUMO, electron affinity, and stabilization energy values. The highest spin density distribution in the heteroatoms is more favored for the more cytotoxic compounds. The electrophilic capacities of these compounds have been related with LUMO values. The cytotoxic properties of quinones are related to the stabilization energy after electron accepting by redox mechanism. Electron affinity is the most relevant parameter related to toxicity mechanism. Regioisomers has different electrophilic capacity. The electrophilicity increases on molecules containing electron-withdrawing groups (EWG) and reduces on molecules containing electron-donating groups (EDG). These results explain the toxic difference between natural and synthetic quinone derivatives and can be used in the design and study of new drugs.

The paracetamol has more antioxidant properties than the salicylic acid on the several oxidative stress-forced models and one possible mechanism is due to electron or hydrogen transfer by the evaluated hydroxyl radicals. The antioxidant mechanism for the compounds studied here was performed by molecular modeling using quantum chemical calculations at the B3LYP level of theory. Our results show that the paracetamol has more antioxidant properties than the salicylic acid in experimental and theoretical studies. The theoretical mechanism show that the hydrogen transfer is more favorable than the electron transfer. From the study it was concluded that the electron abstraction for paracetamol is more favored than salicylic acid.

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The Penicillin Binding Proteins (PBPs) are important biological target for new antibacterial drugs development. This study focused on molecular interaction between cefoxitin and the Escherichia coli PBP5 by molecular dynamics (MD) by using hybrid quantum mechanics/molecular mechanics (QM/MM) simulations approach, searching to develop a computational simulations prototype method on antimicrobial susceptibility of gram-negative bacteria against antibiotics. E. coli ATCC 8739 strain susceptibility for the drugs used in the antimicrobial susceptibility testing and selection of bioactive molecules against resistant strain. The protonation revealed a deprotonate state for His146, His151, His216 and His320 residues. The complex was stabilized after 0.6 ns of MD simulation. The global interaction means for inhibition zone diameters of E. coli ATCC8739 strain and cefoxitin was 24.33 mm no showing significant difference between computational and experimental methods. Our computational simulation method can reliably be performed as a molecular modeling prototype for gram-negative antimicrobial susceptibility testing bacteria. This article is protected by copyright. All rights reserved.