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A proposed mechanism for toxicity of trans-dehydrocrotonin was performed by means of density functional theory calculations related to exploration of its electronic structure. The preferential electron transfer was located mainly under furan ring as nucleophilic moiety. The HOMO values and the highest spin density contribution at the furan ring can be related with a probable and preferential metabolism by means of oxidation reaction such as epoxidation. Simplified derivatives show great impact on electron donating capacity for each moiety. Furan and cycle-hexenone increase electron donating capacity by synergistic effect. Lactone moiety decreases electron donating capacity. A toxicity mechanism on furan ring as nucleophilic moiety was proposed to give epoxide and aldehyde as reactive intermediate.

The electronic performance between mangiferin and isomangiferin as antioxidants was achieved using electron and hydrogen atom transfer mechanisms at DFT/B3LYP/6-31+G(d,p) level. According to theoretical properties of these molecules a structural and electronic symmetry among 3-hydroxyl of xanthone, 2’-hydroxyl of sugar, and ether moiety of sugar were stablished. The sugar moiety changes on 2 and 4 positions showed that isomangiferin is more potent than mangiferin by electron transfer and mangiferin by hydrogen transfer. Hydrogen bonds between sugar and resorcinol rings can be involved to their electronic behavior and favored conformations of low energies. Sugar moiety in both compounds is responsible for the antioxidant capacity increase in xanthone ring.

Quantum chemical calculations at the B3LYP level of theory, together with the 6-31G ∗ basis sets, were employed to obtain electronic properties of the dapsone and related derivatives in order to study their methemoglobinemia mechanism. The electronic properties such as HOMO, LUMO, ionization potential, MEPs, and spin densities were correlated to redox properties of the compounds studied. The results show that the amine linked to the aniline moiety at the para-position is the main contributor to methemoglobin property. The sulfone moiety is responsible for the electron transition between both aniline rings. The lowest ionization potential is related with the increase of methemoglobinemia.

Nucleo de Estudos e Selecao de Biomoleculas da Amazonia, Faculdade de Farmacia, Instituto de Ciencias da Saude,Universidade Federal do Para 66075-110, Belem, PA, BrasilThe metronidazole metabolism has been explained by a mechanism involving single electron trans-fer using quantum chemistry calculations at the B3LYP theory level, together with the 6-31+G(d,p)basis set. These methods were employed to obtain energy (E), ionization potential (IP), spin-densitydistribution, and LUMO and MEPs of the metronidazole. Our results using DFT/B3LYP/6-31+G(d,p)calculations show the ionization potential and spin densities of metronidazole can be used in oxida-tion or reduction prediction of its metabolism. The positive charge radical is stabilized by resonance.These properties were observed by spin density distribution. The bond dissociation energy is relatedwith hydrogen abstraction and a possible hydroxylation via cytochrome P-450. An increase of spindistributions on C

The conformational studies for three rotenone isomers, using a simple rotenoids model has been analyzed by DFT method in B3LYP level of theory and 6-31G∗ basis set to obtain energy. This study shows how a systematic theoretical conformational analysis contributes to understanding molecular level of chemical processes. The gas phase structures are discussed based on thermodynamic values. The results supported that the biological effects of rotenone can be a consequence of conformational restriction and cis preference. The significance of these results is identifying the rotenone toxicity mechanism.