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Flavonoids are a big class of natural product and have a wide range of biological activities. Some of these applications depend on its antioxidant capacity. Nevertheless, another mechanism can be involved by means of alkylation reaction on α,β-unsaturated carbonyl system. This study aimed to evaluate the antioxidant capacity and the chemical reactivity among simplified flavonoid derivatives and isoxazolone analogous as Michael system by using B3LYP functional and 6–311 g(d,p) basis set. Frontier molecular orbital, ionization potential (IP), spin density contributions, and Fukui index explain the antioxidant capacity and reactivity index on isoxazolone and its related derivatives. The best contribution at β-alkene moiety is related to better reactivity of α,β-unsaturated carbonyl group. A decrease in antioxidant capacity is related to an increase in the chemical reactivity index. The frontier molecular orbitals show that aurone is more reactive than isoxazolone. In accordance with Fukui index, isoxazolone can be better inhibitor as Michael system when compared to flavonoid derivatives.

Flavonoids are a big class of natural product and have a wide range of biological activities. Some of these applications depend on its antioxidant capacity. Nevertheless, another mechanism can be involved by means of alkylation reaction on α,β-unsaturated carbonyl system. This study aimed to evaluate the antioxidant capacity and the chemical reactivity among simplified flavonoid derivatives and isoxazolone analogous as Michael system by using B3LYP functional and 6-311 g(d,p) basis set. Frontier molecular orbital, ionization potential (IP), spin density contributions, and Fukui index explain the antioxidant capacity and reactivity index on isoxazolone and its related derivatives. The best contribution at β-alkene moiety is related to better reactivity of α,β-unsaturated carbonyl group. A decrease in antioxidant capacity is related to an increase in the chemical reactivity index. The frontier molecular orbitals show that aurone is more reactive than isoxazolone. In accordance with Fukui index, isoxazolone can be better inhibitor as Michael system when compared to flavonoid derivatives. Graphical abstract.

Sesamol is a phenolic derivative. Its antioxidant activity is low than that of Trolox and depends on benzodioxole moiety. Thus, a molecular modification strategy through alkylation, inspired by natural and synthetic antioxidants, was studied by molecular modeling at the DFT/B3LYP level of theory by comparing the 6-31+G(d,p) and 6-311++G(2d,2p) basis sets. All proposed derivatives were compared to classical related antioxidants such as Trolox, t-butylated hydroxytoluene (BHT) and t-butylated hydroxyanisole (BHA). According to our results, molecular orbitals, single electron or hydrogen-atom transfers, spin density distributions, and alkyl substitutions at the ortho positions related to phenol moiety were found to be more effective than any other positions. The trimethylated derivative was more potent than Trolox. t-Butylated derivatives were stronger than all other alkylated derivatives and may be new alternative forms of modified antioxidants from natural products with applications in the chemical, pharmaceutical, and food industries., PROPESP/UFPA, National Council for Scientific and Technological Development (CNPq)

β-Nitro-styrenes among other nitroderivatives are known due to their high electrophilicity and low electron donation capacities. A preferential molecular modification on 1-nitro-2-phenylethene was analyzed by DFT method in B3LYP/6-311++G(2d,2p) level of theory on gas phase seeking to increase its electron donating capacity. For this, four molecular modifications were proposed showing the impact of alkene moiety, substitutions on β or para positions using electron donating groups (EDGs) or electron withdrawing groups (EWGs). The para is the preferential position for methylation when compared to ortho or meta positions. Our results show that EDGs increase the redox capacity in β and para positions and decrease the electrophilicity when compared to EWGs. The increase on electron donation capacity is in accordance with DPPH evaluation and β-nitro-phenylethene derivatives still are poor antioxidants. Therefore, the antioxidant capacity on β-nitro-phenylethene can be increased by using EDGs substituted on β or para positions.

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.

1-Nitro-2-phenylethene (NPe) induces a more potent vasorelaxant effect in rat aorta than its structural analog 1-nitro-2-phenylethane, but mediated through a different mechanism, independent of soluble guanylate cyclase (sGC) stimulation. We hypothesized that introducing an electron donor into the aromatic moiety might stabilize NPe, enhancing its potency and/or interaction with sGC. Therefore, trans-4-methoxy-β-nitrostyrene (T4MN) was synthesized, and mechanisms underlying its vasorelaxant effects were studied in rat aortic ring preparations. In endothelium-intact preparations, T4MN fully relaxed contractions induced by phenylephrine (PHE) with a potency similar to that of its parent drug, NPe. This vasorelaxant effect that was unchanged by endothelium removal, pretreatment with L-NAME, indomethacin, or MDL-12,330 A, but was significantly reduced by tetraethylammonium, 4-aminopyridine, methyl blue, or ODQ. Under Ca 2+ -free conditions, T4MN did not alter contractions evoked by caffeine, but significantly reduced, in an ODQ-preventable manner, those induced by either PHE or extracellular Ca 2+ restoration following depletion of intracellular Ca 2+ stores in thapsigargin-treated aortic preparations. Under the same conditions, T4MN also reduced contractions induced by protein kinase C activator phorbol-12,13-dibutyrate with a potency similar to that evoked by this nitroderivative against PHE-induced contractions. In conclusion, T4MN induces potent vasorelaxation in rat aorta by stimulating the sGC-cGMP pathway through a NO-independent mechanism. Introduction of a methoxy group into the aromatic moiety apparently stabilizes NPe, thereby enhancing its interaction with sGC.

This theoretical and experimental study describes the design and evaluation of the free-radical scavenging effect for the molecular association of 4-aminophenol and salicylate derivatives. For this purpose, we employed theoretical methods for the selection of antioxidant drugs and the rapid methods of evaluation: the 1,1-diphenyl-2-picrylhydrazyl radical and the thiobarbituric acid reactive substances in the lipid peroxidation initiated by Fe 2+ and ascorbic acid in human erythrocytes. The associate derivatives exhibited a more potent inhibition than the salicylic acid, while the benzoyl compound exhibited a more potent inhibition than paracetamol. The molecular parameters related to the electron distribution and structure (ionization potential and energy of the highest occupied molecular orbital) correlated very well with the antioxidant action of the compounds studied here in different tests.

Mechanisms underlying the vasorelaxant effects of trans-4-methyl-β-nitrostyrene (T4MeN) were studied in rat aortic rings. In endothelium-intact preparations, T4MeN fully and similarly relaxed contractions induced by phenylephrine (PHE) (IC50 = 61.41 [35.40-87.42] μmol/L) and KCl (IC50 = 83.50 [56.63-110.50] μmol/L). The vasorelaxant effect of T4MeN was unchanged by endothelium removal, pretreatment with L-NAME, indomethacin, tetraethylammonium, ODQ or MDL-12,330A. Under Ca2+ -free conditions, T4MeN significantly reduced with a similar potency: (i) phasic contractions induced by PHE, but not by caffeine; (ii) contractions due to CaCl2 in aortic preparations stimulated with PHE (in the presence of verapamil) or high KCl; (iii) contractions evoked by the restoration of external Ca2+ levels after depletion of intracellular Ca2+ stores in the presence of thapsigargin. In contrast, T4MeN was more potent at inhibiting contractions evoked by the tyrosine phosphatase inhibitor, sodium orthovanadate, than those induced by the activator of PKC, phorbol-12,13-dibutyrate. These results suggest that T4MeN induces an endothelium- independent vasorelaxation that appears to occur intracellularly through the inhibition of contractions that are independent of Ca2+ influx from the extracellular milieu but involve phosphorylation of tyrosine residues.

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.

A structural and computational study of the morphine mechanism as an antioxidant or oxidant compound is performed by density functional theory (DFT) calculations. The geometry was obtained using the B3LYP/6-31G(d,p) method. The antioxidant property of morphine is related to the highest occupied molecular orbital (HOMO) energy, ionization potential (IP), stabilization energy (ΔEiso), bond dissociation energy (BDE), and spin density distribution for the electron abstraction at the amine position, which is more favored than other positions for morphine. The decrease in the HOMO and IP values, together with the increase in the ΔEiso values, is related to amine groups, ether and alkyl moieties, benzene rings, hydroxyls, and double bonds. The hydrogen abstraction in the phenol position is more favored than the other positions in morphine. The prevalent spin contribution for these groups is important for the highest stability free radical and other resonance structures. Morphine is more powerful antioxidant than its de-methylated or hydroxylated derivatives.

This theoretical and experimental study describes the design and evaluation of the free-radical scavenging effect for the molecular association of 4-aminophenol and salicylate derivatives. For this purpose, we employed theoretical methods for the selection of antioxidant drugs and the rapid methods of evaluation: the 1,1-diphenyl-2-picrylhydrazyl radical and the thiobarbituric acid reactive substances in the lipid peroxidation initiated by Fe(2+) and ascorbic acid in human erythrocytes. The associate derivatives exhibited a more potent inhibition than the salicylic acid, while the benzoyl compound exhibited a more potent inhibition than paracetamol. The molecular parameters related to the electron distribution and structure (ionization potential and energy of the highest occupied molecular orbital) correlated very well with the antioxidant action of the compounds studied here in different tests.

In this study, 1-nitro-2-phenylethane was evaluated with respect to its effects in edema models of acute inflammation induced with carrageenan, dextran, and croton oil. 1-Nitro-2-phenylethane produced inhibition of rat paw edema induced by carrageenan and dextran at the doses of 25 and 50 mg/kg. The same doses caused an inhibition of croton oil-induced ear edema in mice. Our results suggest that 1-nitro-2-phenylethane has anti-inflammatory activity, probably of peripheral origin, acting in the synthesis and/or release of inflammatory mediators. A conformational study of 1-nitro-2-phenylethane was carried out using density functional theory calculations, showing three different groups of conformers corresponding to energy minimum geometries. The stereoelectronic repulsions are responsible for conformational preferences and the one most stable conformer. The prostaglandin endoperoxide synthase mechanism is related more to electrophilic than nucleophilic properties.