Antioxidant Properties of Pterocarpans through Their Copper(II) Coordination Ability. A DFT Study in Vacuo and in Aqueous Solution

Role of the Solvent and Intramolecular Hydrogen Bonds in the Antioxidative Mechanism of Prenylisoflavone from Leaves of Vatairea guianensis

This work discusses the electron structure, antioxidative properties, and solvent contribution of two new antioxidant molecules discovered, named S10 and S11, extracted from a medicinal plant called Vatairea guianensis, found in the Amazon rain-forest. To gain a better understanding, a study using density functional theory coupled with the polarizable-continuum model and the standard 6-311++G(d,p) basis set was conducted. The results indicate that S10 has a higher antioxidant potential than S11, confirming the experimental expectations. In the gas phase, the hydrogen atom transfer route dominates the hydrogen scavenging procedure. However, in the water solvents, the antioxidant mechanism prefers the sequential proton loss electron transfer mechanism. Furthermore, the solvent plays a fundamental role in the antioxidant mechanism. The formation of an intramolecular OH···OCH3 hydrogen bond is crucial for accurately describing the hydrogen scavenging phenomenon, better aligning with the experimental data. The results suggest that the two isoflavones investigated are promising for the pharmacologic and food industries.

DFT studies of camptothecins cytotoxicity IV — active and inactive forms of irinotecan

Structures of irinotecan (CPT-11) in neutral lactone, neutral carboxyl, and anionic carboxylate forms in singlet ground states and of their complexes with Cu(II) in doublet ground states are optimized using B3LYP/6-311G* treatment. Metal ion affinities (MIA), Cu charges and Laplacians of Cu-ligand bond critical points of possible CPT active sites are evaluated. The formation of Cu(II) complexes with the anionic carboxylate ligand leads to the release of CO2 that can cause a decrease in the concentration of the active lactone form due to equilibria between all forms of the drug. MIA values and electron density transfer to Cu increase in the sequence lactone < neutral carboxyl < anionic carboxylate. Both neutral forms of irinotecan exhibit lower MIA values than those of camptothecin, unlike the anionic carboxylate form.

Phytochemical analysis and preclinical toxicological, antioxidant, and anti-inflammatory evaluation of hydroethanol extract from the roots of Harpalyce brasiliana Benth (Leguminosae)

ETHNOPHARMACOLOGICAL RELEVANCE

Harpalyce brasiliana Benth (Leguminosae) is a shrub endemic to Brazil, popularly known as "snake's root." This species is used in folk medicine for the treatment of inflammation and snakebites. However, up to now there is no scientific research to justify its popular use. The study aimed to characterize the phytochemical profile of the hydroethanol extract from the roots of H. brasiliana (Hb), to evaluate its antioxidant and anti-inflammatory potential, as well as to investigate its cytotoxicity and acute toxicity.

MATERIALS AND METHODS

The extract was obtained by maceration method using a solution of ethanol:water (70: 30, v/v). The phytochemical profile was obtained by liquid chromatography coupled to mass spectrometry. The cytotoxicity of extract (31-2000 μg/mL) was evaluated in vitro, by the 3-methyl-[4-5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) method using murine macrophage and fibroblast cell lines (RAW 247.6 and 3T3, respectively) and by the hemolytic assay. For the in vivo acute toxicity, the extract (2000 mg/kg) was administered and after 14 days the weight (body and organs) and hematological and biochemical parameters were analyzed. Chemical free radical scavenging effect of the extract (125-2000 μg/mL) was investigated through diphenylpicryl hydrazine reduction, total antioxidant capacity, reducing power, hydroxyl radical scavenging, and iron and copper chelating assays. In vitro anti-inflammatory effect of the extract (125, 500, and 2000 μg/mL) was demonstrated through of nitric oxide (NO) analyzed in lipopolysaccharides stimulated RAW 264.7 cells. In vivo anti-inflammatory activities were evaluated in carrageenan-induced paw edema and zymosan-air-pouch models, with gavage administration (post-treatment) of extract at 100, 200, and 400 mg/kg. For the first animal model, the anti-edematogenic activity and myeloperoxidase (MPO) levels were investigated, while in the zymosan-air-pouch model the leukocyte number, MPO, total protein and pro-inflammatory cytokine (IL-1β, IL-6, and TNF-α) levels were quantified. In addition, the oxidative parameters such as malondialdehyde (MDA) and reduced glutathione (GSH) were determined.

RESULTS

The phytochemical profile revealed the presence of 20 compounds, mainly prenylated and geranylated pterocarpans. The extract demonstrated no cytotoxicity in erythrocytes, macrophages and fibroblasts cells at the tested concentrations, as well as no sign of toxicity and mortality or significant alterations on the hematological and biochemical parameters in the acute toxicity model. The extract was also able to neutralize chemical free radicals, with copper and iron chelating effect. For the NO dosage, the extract evidenced the reduction of expression of NO after the administration of the extract (500 and 2000 μg/mL). The edematogenic model revealed a decrease in paw edema and MPO level, while the zymosan-air-pouch model evidenced a reduction of leukocyte number (especially of polymorphornuclears), MPO production, and total protein and cytokine levels, and demonstrated the antioxidant effect through a decrease in MDA and increase in GSH parameters.

CONCLUSION

This approach demonstrates for the first time that Hb is not cytotoxic, has low acute toxicity, and possesses antioxidant and anti-inflammatory properties in preclinical analyses, corroborating its popular use.

DFT studies of camptothecins cytotoxicity III: camptothecin, irinotecan and SN-38

Geometries of camptothecin, irinotecan, SN-38, and of their hypothetical Cu(II) complexes were optimized at the B3LYP/6-311G* level of theory. Their electron structure, evaluated in terms of Mulliken population analysis and Quantum Theory of Atoms-in-Molecule, was subsequently related to in vitro cytotoxicity. Electron density transfer from the relevant active sites to Cu decreases in the sequence irinotecan > SN-38 > camptothecin. The absolute values of their metal-ligand interaction energies exhibit the same trend. Discrepancy with the least relative in vitro cytotoxicity of irinotecan can be explained by differences in its pharmacokinetics.

Quantum-chemical studies of rutile nanoparticles toxicity II. Comparison of B3LYP and PM6 data

The relation between copper atomic charges and metal-ligand interaction energies obtained by PM6 and DFT-B3LYP methods for cytotoxicity prediction of model rutile nanoparticles [Ti40O124H81]7–, [Ti7O28H26]2–, [Ti2O10H10]2–, [Ti7O30H30]2– and their Cu(II) complexes is investigated. Except for Mulliken charges, very good statistical parameters were obtained for the linear relation between the results obtained by both methods if standard accuracy of quantum-chemical calculations is achieved.

Proportional coexistence of okanin chalcone glycoside and okanin flavanone glycoside in Bidens pilosa leaves and theoretical investigation on the antioxidant properties of their aglycones

Bidens pilosa plant has been shown to produce okanin flavanone glycoside and its chalcone derivative. In most other plants, due to chalcone isomerase enzyme, the flavanone tends to exist in higher proportions than their chalcone precursors. Herein we have utilized liquid chromatography-mass spectrometry approach and shown that within the leaves of Bidens pilosa plant the two okanin glycosides exist in unusual equal proportional distribution, which indicates that Bidens pilosa plant is an alternative rich source of these highly sought-after antioxidant molecules. The aglycone okanin chalcone (ONC) and okanin flavanone (ONF) have experimentally been shown to exhibit antioxidant activity. However, experimental findings have not conclusively determined which of the two compounds is a more potent antiradical than the other. Herein, the density functional theory (DFT) method is utilized to establish, from structural and thermodynamic energetic considerations, the preferred antioxidant molecule between the two aglycone okanins. A theoretical study on the antioxidant properties of ONC and ONF has been performed by considering their radical scavenging and metal cation (Mⁿ⁺, where M = Cu(II) or Fe (III)) chelation ability. The study has been performed using B3LYP/6-31 + G(d,p) method. In the case of the metal chelation mechanism, the LANL2DZ pseudo-potential was selected to describe the selected Mⁿ⁺ cations. The results of the study suggest that ONC is a better radical scavenger than ONF because of the extended electron delocalization on its neutral radical, which is due to the presence of conjugation within the ONC neutral radical after hydrogen atom abstraction. In the metal chelation mechanism, it is noted that the binding energies depend on the media, the nature of the ligand and the cation and the cation coordination site on the ligand. The charge and the spin density on Mⁿ⁺ decrease on coordination to the ligand. The ability of the ligands to reduce Mⁿ⁺ cations, coupled with the strong Mⁿ⁺ binding properties, has significant implication on the antioxidant ability of both okanins. However, since ONC⋅⋅⋅M⁺ⁿ interaction results in higher binding energy than ONF⋅⋅⋅M⁺ⁿ interaction, the implication is that ONC is a preferred free metal ion chelator than ONF.

Quantum-chemical studies of rutile nanoparticles toxicity I. Defect-free rod-like model clusters

Using the semiempirical PM6 method, structures of a rod-like [Ti40O124H81]7– model cluster and of [Ti40O124H81Cu]5– with Cu2+ coordinated at various sites were optimized in order to assess the toxicity of rutile nanoparticles. If the relative toxicity of individual Ti centers in rod-like rutile nanoparticles can be evaluated by the electron density transfer to a Cu2+ probe, its maximal values can be ascribed to the pentacoordinated corner and hexacoordinated edge Ti centers with three Ti—OH bonds. However, these centers exhibit the least negative interaction energies which can be compensated by the significantly better accessibility of the corner Ti center compared with that of the remaining ones. Ti centers with the most negative interaction energy parameters exhibit the lowest extent of electron density transfer to a Cu2+ probe. Rutile nanoparticles destruction starts at pentacoordinated Ti face centers.

Computational study of acylphloroglucinols: an investigation with many branches

Acylphloroglucinols (ACPLs) are a broad class of compounds structurally derived from phloroglucinol and characterised by the presence of a CRO group. They are interesting for their biological activities and their potentialities as lead compounds in drug development. The current review considers a series of works which, altogether, sum up to a systematic computational study of ACPLs in vacuo and in three solvents – chloroform, acetonitrile and water. An initial set of studies, focusing on ACPLs as a class and utilising an adequately representative selection of molecules, identified patterns in the conformational preferences and molecular properties of ACPLs, which appear valid for the whole class or for specific subclasses such as monomeric ACPLs, dimeric ACPLs, ACPLs with substituents containing C=C double bonds, etc. The validity of the identified patterns was further verified through the study of additional and significantly different ACPL molecules, as well as other molecular structures containing ACPL units. Furthermore, the computational study of ACPLs proved interesting for the insights into the factors stabilising their conformers, first of all intramolecular hydrogen bonding, which plays dominant roles in determining conformational preferences and energetics. The current review outlines the objectives, approaches and main results of these studies. The obtained information may be relevant for further studies aimed at a better understanding of the molecular bases of the biological activities of ACPLs.

Quantum-chemical study of the active sites of camptothecin through their Cu(II) coordination ability

The structures of camptothecin (CPT) lactone form and its complexes with Cu(II) were optimized at B3LYP/6-311G* level of theory. Their electronic structures were evaluated via QTAIM topological analysis of electron density and Mulliken population analysis. Stability, electron density distribution and geometrical factors of the optimized systems were compared. Both CPT nitrogen atoms show lower affinity to Cu(II) compared to the oxygen ones. Both the oxygen atom in the CPT lactone ring and the one in the neighbouring carbonyl group show the highest affinity to Cu(II) and the highest stability of Cu-CPT complexes which indicates the most probable CPT reaction sites.

Complexes of arzanol with a Cu2+ ion: a DFT study

Arzanol (C₂₂H₂₆O₇) is a naturally occurring acylphloroglucinol largely responsible for the anti-inflammatory, anti-oxidant, antibiotic and antiviral activities of Helichrysum italicum. Like all acylphloroglucinols, the molecule contains a carboxylic substituent (-COR group); for arzanol, this is a -COCH₃ group. The molecule is further characterized by the presence of an α-pyrone ring bonded in meta to -COR through a methylene bridge, and of a prenyl chain bonded to the other meta position. The molecule can form up to three intramolecular hydrogen bonds (IHB) simultaneously, and their presence and patterns are the major stabilizing factors. This work considers complexes of representative conformers of arzanol with a Cu²⁺ ion, taking into account the different possibilities for the binding of the Cu²⁺ ion to the electron-density rich sites of the molecule and including simultaneous coordination to two geometrically suitable sites. Calculations were performed at the DFT/B3LYP level, using the 6-31+G(d,p) basis set for the C, O and H atoms and the LANL2DZ pseudopotential for the Cu²⁺ ion. Interaction energies show preference for simultaneous binding of Cu²⁺ to two sites. Simultaneous binding to the O of a phenol OH neighboring the prenyl chain and to the π bond of the prenyl chain appears to be the most favorable option, followed by simultaneous binding to the sp² O of the α-pyrone ring and the O of the phenol OH ortho to -COR on the side of the α-pyrone ring. The charge of the Cu²⁺ ion is reduced to +1 or slightly less in the complexes, which is consistent with the molecules' antioxidant (reducing) ability. Graphical abstract The copper ion prefers to attach to two sites of the arzanol molecule simultaneously. The arzanol molecule reduces the charge of the copper ion from +2 to +1 by transferring an electron to it; it becomes a radical molecular cation. The distribution of the unpaired electron in the molecule (as highlighted by the spin density maps) depends on the site/s to which the Cu²⁺ ion binds and on the molecule's conformer.

A theoretical study on the antioxidant properties of methoxy-substituted chalcone derivatives: A case study of kanakugiol and pedicellin through their Fe (II and III) coordination ability

A theoretical study on the antioxidant properties of two chalcone derivatives, kanakugiol and pedicellin, is performed by considering their Fe[Formula: see text] and Fe[Formula: see text] coordination ability. The objective of the study is to elucidate the factors influencing the stability of the isolated conformers, the nature of the complexes, metal[Formula: see text]ligand stability, metal ion affinities (MIA) and electronic properties of the cations before and after coordination to the ligand. The study is performed using the B3LYP/6–311[Formula: see text]G(2d,p)//B3LYP/6–31[Formula: see text]G(d,p) method. The LANL2DZ pseudopotential is selected to describe the Fe[Formula: see text] ions. Time-dependent density functional theory (TDDFT) method is used to assess the electronic UV–Vis spectra of the isolated chalcones and their complexes with Fe[Formula: see text] ions. The results suggest that the preferred complexes are those in which the Fe ion is coordinated at the hydroxyl-methoxy and hydroxyl-keto sites for kanakugiol and methoxy-keto site for pedicellin. Both kanakugiol and pedicellin have potential to chelate iron ions as demonstrated by their high MIA values in vacuo and in water solution. However, the ability of pedicellin to chelate iron is slightly lower than that of kanakugiol, indicating that the presence of the hydroxyl group has an effect of enhancing the metal binding abilities of the chalcone derivatives. In all the complexes obtained in vacuo, kanakugiol and pedicellin exhibit the ability to reduce the Fe[Formula: see text] ion. In water solution (which mimics the environment in biological systems or studies performed in vivo), Fe[Formula: see text] is reduced to Fe[Formula: see text] upon coordination to the ligand while the oxidation number of Fe[Formula: see text] upon coordination to the ligand remains virtually unchanged.

A theoretical study on antioxidant activity of ferulic acid and its ester derivatives

Phenolic compounds play a very crucial role as antioxidant that can prevent various diseases caused by free radicals in human body. Although, lots of natural phenolic compounds having antioxidant activity are available nowadays, the modeling of compounds with naturally available phenolics as building blocks is very important in order to get enhanced antioxidant activity. In this study, Ferulic acid (FA), one natural phenolic acid present in coffee, apples, orange, etc., is taken as building block and its ester derivatives with different alkyl groups are subjected to measure the antioxidant activity by using density functional theory (DFT). Various parameters like bond dissociation enthalpy (BDE), vertical ionization potential (IP[Formula: see text]), reactivity descriptors, metal chelation ability, etc. are used to measure the antioxidant activity. All the parameters suggest that the ester derivatives are superior antioxidants to the parent FA. Since FA has been reported to be present as esters in many herbs and plants, hence our study provides a route to study the structure activity relationship of this class of natural phenolics with antioxidant activity.