DFT study of the effect of solvent on the H-atom transfer involved in the scavenging of the free radicals (·)HO2 and (·)O2(-) by caffeic acid phenethyl ester and some of its derivatives

Evaluation of Free Radical Scavenging Ability of Triazole-3-Thiol: A Combination of Experimental and Theoretical Approaches

An assessment of the free radical scavenging potential of 4-amino-5-phenyl-4H-1,2,4-triazole-3-thiol (AT) and 4-amino-5-(4-pyridyl)-4H-1,2,4-triazole-3-thiol (AP) involved a combination of experimental methodologies and theoretical calculations. In the 2,2-diphenyl-1-picrylhydrazyl (DPPH•) assay, AT exhibited an heightened efficacy in scavenging DPPH• radicals compared to AP. This was evidenced by the notably lower IC50DPPH value observed for AT (1.3 × 10-3 ± 0.2 × 10-3 M) in comparison to AP (2.2 × 10-3 ± 0.1 × 10-3 M). Similarly, in the 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS• +) test, AT exhibited superior ability in neutralizing ABTS•+ free radical cations compared to AP, with the computed IC50ABTS values of 4.7 × 10-5 ± 0.1 × 10-5 M for AT and 5.5 × 10-5 ± 0.2 × 10-5 M for AP. Density functional theory served as the tool for evaluating the correlation between structural attributes and the antioxidant efficacy of the studied molecules. The findings highlighted the flexibility of hydrogen atoms within NH and NH2 groups to nucleophilic attacks, indicative of their pivotal role in the scavenging mechanism. Furthermore, investigations into the interactions between AT and AP with the free radical HOO• revealed predominantly the reaction via the hydrogen atom transfer mechanism. Both experimental observations and theoretical deductions collectively affirmed AT's superior free radical scavenging ability over AP in the gas phase and ethanol.

Anti-Inflammatory Potential of Seasonal Sonoran Propolis Extracts and Some of Their Main Constituents

Biological properties of Sonoran propolis (SP) are influenced by harvest time. Caborca propolis showed cellular protective capacity against reactive oxygen species, which might be implicated in anti-inflammatory effects. However, the anti-inflammatory activity of SP has not been investigated so far. This study investigated the anti-inflammatory activity of previously characterized seasonal SP extracts (SPE) and some of their main constituents (SPC). The anti-inflammatory activity of SPE and SPC was evaluated by measuring nitric oxide (NO) production, protein denaturation inhibition, heat-induced hemolysis inhibition, and hypotonicity-induced hemolysis inhibition. SPE from spring, autumn, and winter showed a higher cytotoxic effect on RAW 264.7 cells (IC₅₀: 26.6 to 30.2 µg/mL) compared with summer extract (IC₅₀: 49.4 µg/mL). SPE from spring reduced the NO secretion to basal levels at the lowest concentration tested (5 µg/mL). SPE inhibited the protein denaturation by 79% to 100%, and autumn showed the highest inhibitory activity. SPE stabilized erythrocyte membrane against heat-induced and hypotonicity-induced hemolysis in a concentration-dependent manner. Results indicate that the flavonoids chrysin, galangin, and pinocembrin could contribute to the anti-inflammatory activity of SPE and that the harvest time influences such a property. This study presents evidence of SPE pharmacological potential and some of their constituents.

Protective Effect of Flavonoids from Mulberry Leaf on AAPH-Induced Oxidative Damage in Sheep Erythrocytes

To evaluate the antioxidant activity of flavonoids extracted from Chinese herb mulberry leaves (ML), flavonoids from mulberry leaves (FML) were extracted and purified by using ultrasonic-assisted enzymatic extraction and D101 macroporous resin. Using LC-MS/MS-Liquid Chromatography with tandem mass spectrometry analysis, hesperidin, rutoside, hyperoside, cyanidin-3-o-glucoside, myricitrin, cyanidin, and quercetin were identified, and NMR and UV were consistent with the verification of IR flavonoid characteristics. The antioxidant activity of FML has also been evaluated as well as the protective effect on 2,2 0-azobis (2-amidinopropane) dihydrochloride (AAPH)-induced oxidative stress. The results showed that FML exhibited powerful antioxidant activity. Moreover, FML showed dose-dependent protection against AAPH-induced sheep erythrocytes’ oxidative hemolysis. In the enzymatic antioxidant system, pretreatment with high FML maintained the balance of SOD, CAT, and GSH-Px; in the non-enzymatic antioxidant system, the content of MDA can be effectively reduced after FML treatment. This study provides a research basis for the development of natural products from mulberry leaves.

Antioxidant activity of delphinidin and pelargonidin: Theory and practice

The quantum chemical density functional theory and in vitro chemical-based antioxidant assays were used to research the reaction mechanism of delphinidin/pelargonidin with free radicals including superoxide anion radicals (O₂ ^- ∙) and hydroperoxide radicals (OOH∙). The geometric configuration, bond dissociation energy, PCM (polarizable continuum model) solvent model reaction enthalpy changes were studied to explain the transition states, and the reaction enthalpy change value was calculated to determine the active site. From the results of spatial configuration, delphinidin showed a stronger conjugation effect than that of pelargonidin. The dihedral angle between the three rings of delphinidin was almost 180°, and the angle between the B and C rings was only -2.81868°. Both coplanar and antioxidant activity of delphinidin was better than pelargonidin. The consequences of reaction enthalpy change in PCM were consistent with the bond dissociation energy. The phenolic hydroxyl bond dissociation energy of delphinidin was slightly smaller than that of pelargonidin. Moreover, the C4' site of delphinidin and the C3 site of pelargonidin were the active sites for scavenging free radicals. The free radical scavenging ability of delphinidin was marginally higher than that of pelargonidin. On the other hand, in vitro antioxidant results proved the scavenging ability of delphinidin and pelargonidin on superoxide anions, DPPH, and ABTS^∙+ free radicals. It was shown that the chemical-based antioxidant activity was consistent with the theoretical calculation results, with delphinidin showing greater antioxidant activity. These results could explain the antioxidant mechanism of delphinidin/pelargonidin in scavenging free radicals from chemical reactions. PRACTICAL APPLICATIONS: This manuscript explained the antioxidant mechanism of delphinidin/pelargonidin in scavenging free radicals through the analysis of the geometric configuration of delphinidin/pelargonidin and the theoretical calculation of the reaction transition state. It could also speculate on the possible reaction sites, and provide a basis for judging how to efficiently select antioxidants with great antioxidant activity.

Temperature-dependent oxidation of BSCAPE molecule in methanol medium

Temperature-dependent solvation free energy and oxidation by free energy of ionization of 2-Phenylethyl (2E)-3-(1-benzenesulfonyl-4,5-dihydroxyphenyl) acrylate (BSCAPE) in methanol medium are the concerns of the present work. This molecule is a relevant phenolic acid enclosing multiple bioactivities. The explicit, implicit and discrete-continuum models of solvation were used. The methanol molecules were coordinated to this acid to form cluster complexes. The dual method M06-2X/6-31++G(d,p)//B3LYP/6-31G(d) was employed along with basis set superposition error correction. The results show that, the free energy of coordination and solvation are distant. Both quantities increase with temperature. From discrete-continuum treatment, there is non-spontaneity of solvation process, while coordination yielded spontaneity and non-spontaneity at cold and hot room temperatures, respectively. The ionization potential in gas phase, decreases with temperature. All the solvation models yielded lower ionization potential than that of gas phase. Thus, it follows that, the increase of temperature and methanol medium favours the oxidation of BSCAPE. Consequently, this favours its metabolism processes.

Antioxidant and Anticancer Properties of Functionalized Ferrocene with Hydroxycinnamate Derivatives-An Integrated Experimental and Theoretical Study

Two ferrocenyl derivatives, Fc-CA and Fc-FA, were synthesized by a condensation reaction between the amino ferrocene and hydroxycinnamic acids, that is, caffeic acid (CA) and ferulic acid (FA). The structures and purity of all compounds were characterized by ¹H- and ¹³C NMR spectroscopies, Mass spectrometry (MS), and elemental analysis. The antioxidant properties of Fc-CA and Fc-FA and of its ligand were studied for free radical scavenging activity toward DPPH^•, superoxide anion (O₂^•-), NO^•, and ABTS^•+ by UV-vis and electron spin resonance spectroscopies. The cytotoxicity of Fc-CA and Fc-FA against MCF-7 and MDA-MB-231 breast cancer cells and MRC-5 human lung fibroblasts cell was higher than that of cisplatin. The geometry and electronic structures of all compounds were then simulated using density functional theory at M05-2X/6-311+G(d,p) level of theory. Thermodynamics of the free radical quenching reactions by common mechanisms reveal the higher antioxidant properties of the Fc-CA and Fc-FA in comparison to their ligands. An in-depth study of the free radical scavenging activity against HOO^• and HO^• radicals was performed for two of the most favorable and competitive mechanisms, the hydrogen transfer (either hydrogen atom transfer or proton-coupled electron transfer mechanisms) and the radical adduct formation. The in silico studies indicated that ferrocenyl derivatives exhibited prominent binding affinity to protein models in comparison to CA and FA. Their dock scores were notable at ligand binding sites of ERα, Erβ, and JAK2 proteins. Dock pose analysis also shed light into the possible mechanism of action for the studied compounds.

Infrared spectra of PEHA molecule and its resistance to oxidation in water and methanol media at 298.15 K: solvent cluster size dependency

The present work investigates the infrared spectra and solvation free energies (SE) of PEHA ((E)-2-(Pyridin-2-yl) ethyl 3-(3,4-dihydroxyphenyl) acrylate) and their impact on the oxidation. The latter was examined through the ionization potential parameter (IP). These investigations were carried out by the DFT method at B3LYP/6-31G(d) for optimization and frequency calculations and corrected for BSSE. X3LYP/6-311++G(2d,2p) was employed for single-point energy calculations. Water and methanol cluster sizes were used for solvation through the explicit solvent model. Thus, the infrared spectra show that the overview frequencies of PEHA compare well with the experimental results. The intense infrared absorptions of complexes are due to the stretching of O-H bonds of solvent clusters in the range 2600-3850 cm^-1. The binding energy per solvent molecule of complexes was calculated and shows that water and methanol clusters mimic the liquid state as from 5 to 10 solvent molecules. The SE of PEHA increases with the increase of the cluster size of water and methanol in the direction of the limit. The latter was censured by the solvation done using the combined explicit-implicit solvent model. As for IP parameter, the results are largely above the IP limit and lower than the IP from gas phase. Thus, water and methanol media have an effect of lowering the IP of PEHA compound. Consequently, both media favour the oxidation of PEHA molecule, which facilitates its metabolism in human organism.

Comparative Analysis of Radical Adduct Formation (RAF) Products and Antioxidant Pathways between Myricetin-3-O-Galactoside and Myricetin Aglycone

The biological process, 3-O-galactosylation, is important in plant cells. To understand the mechanism of the reduction of flavonol antioxidative activity by 3-O-galactosylation, myricetin-3-O-galactoside (M3OGa) and myricetin aglycone were each incubated with 2 mol α,α-diphenyl-β-picrylhydrazyl radical (DPPH^•) and subsequently comparatively analyzed for radical adduct formation (RAF) products using ultra-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry (UPLC-ESI-Q-TOF-MS) technology. The analyses revealed that M3OGa afforded an M3OGa–DPPH adduct (m/z 873.1573) and an M3OGa–M3OGa dimer (m/z 958.1620). Similarly, myricetin yielded a myricetin–DPPH adduct (m/z 711.1039) and a myricetin–myricetin dimer (m/z 634.0544). Subsequently, M3OGa and myricetin were compared using three redox-dependent antioxidant analyses, including DPPH^•-trapping analysis, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide radical (PTIO^•)-trapping analysis, and ^•O₂ inhibition analysis. In the three analyses, M3OGa always possessed higher IC₅₀ values than those of myricetin. Conclusively, M3OGa and its myricetin aglycone could trap the free radical via a chain reaction comprising of a propagation step and a termination step. At the propagation step, both M3OGa and myricetin could trap radicals through redox-dependent antioxidant pathways. The 3-O-galactosylation process, however, could limit these pathways; thus, M3OGa is an inferior antioxidant compared to its myricetin aglycone. Nevertheless, 3-O-galactosylation has a negligible effect on the termination step. This 3-O-galactosylation effect has provided novel evidence that the difference in the antioxidative activities of phytophenols exists at the propagation step rather than the termination step.

Thermodynamic of solvation, solute - Solvent electron transfer and ionization potential of BSCAPE molecule and its UV-vis spectra in aqueous solution

The molecular system 2-Phenylethyl (2E)-3-(1-benzenesulfonyl-4,5-dihydroxyphenyl) acrylate (BSCAPE) is a phenolic acid that covers a large spectrum of biological properties. The investigations of solvation and oxidation processes of BSCAPE molecule by computational means were the challenge of this present work. Water was required for solvation throughout the work. The explicit H₂O were sequentially added to form the complexes BSCAPE(H₂O)_n=0-11. The discrete - continuum model was at the heart of this work. DFT and TD-DFT both associated to the continuum model SMD were required. Hence, the structures, the solvation energies, the energies of solute - solvent electron transfer (SSET), the ionisation potential (IP), and the UV-vis spectra were studied. It comes out that, the structure of the CAPE part included in BSCAPE agrees well with the available experimental values of CAPE but with a minor influence due to the presence of benzensulfonyl group. The enthalpy and free energy of solvation increase linearly with nH₂O. The global reactivity indexes were assessed to appreciate the oxidation of BSCAPE. The latter quality was strongly assessed by the enthalpy and free energy of SSET and IP. The SSET potential increase with nH₂O and the size of water clusters. The values 723.16 and 711.62 kJ/mol were found for enthalpy and free energy of IP respectively. Then in aqueous solution, the results fall down and upon addition of nH₂O, they approach gas phase value for 11H₂O and still are not stabilized. Therefore, the resistance to oxidation starts to raise at this level. Elsewhere, the UV-vis spectra of BSCAPE present four important peaks about 279.3, 234.8, 208.4 and 199.4 nm in gaseous state. The excitation shifts to the red as the number of H₂O increase. Their oscillator strengths also increase with solvation.

A Null B-Ring Improves the Antioxidant Levels of Flavonol: A Comparative Study between Galangin and 3,5,7-Trihydroxychromone

To clarify the role of the B-ring in antioxidant flavonols, we performed a comparative study between galangin with a null B-ring and 3,5,7-trihydroxychromone without a B-ring using five spectrophotometric assays, namely, ^•O₂^--scavenging, 1,1-diphenyl-2-picrylhydrazyl radical (DPPH^•)-scavenging, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide radical-scavenging, 2,2'-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid) radical-scavenging, and Fe³⁺-reducing activity. The DPPH^•-scavenging reaction products of these assays were further analyzed by ultra-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry (UPLC-ESI-Q-TOF-MS/MS) technology. In the five spectrophotometric assays, galangin and 3,5,7-trihydroxychromone dose-dependently increased their radical-scavenging (or Fe³⁺-reducing) percentages. However, galangin always gave lower IC₅₀ values than those of 3,5,7-trihydroxychromone. In the UPLC-ESI-Q-TOF-MS/MS analysis, galangin yielded galangin-DPPH adduct MS peaks (m/z 662, 434, 301, 227,196, and 151) and galangin-galangin dimer MS peaks (m/z 538, 385, 268, 239, 211, 195, and 151). 3,5,7-Trihydroxychromone, however, only generated m/z 3,5,7-trihydroxychromone-DPPH adduct MS peaks (m/z 586, 539, 227, 196, and 136). In conclusion, both galangin and 3,5,7-trihydroxychromone could similarly undergo multiple antioxidant pathways, including redox-dependent pathways (such as electron transfer (ET) and ET plus proton transfer (PT)) and a non-redox-dependent radical adduct formation (RAF) pathway; thus, the null B-ring could hardly change their antioxidant pathways. However, it did improve their antioxidant levels in these pathways. Such improvement of the B-ring toward an antioxidant flavonol is associated with its π-π conjugation, which can provide more resonance forms and bonding sites.

E-Configuration Improves Antioxidant and Cytoprotective Capacities of Resveratrols

The antioxidant and cytoprotective capacities of E-resveratrol and Z-resveratrol were compared using chemical and cellular assays. Chemical assays revealed that the two isomers were dose-dependently active in •O₂^--scavenging, ferric reducing antioxidant power (FRAP), Cu²⁺-reducing antioxidant capacity (CUPRAC), 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide radical (PTIO•)-scavenging (pH 7.4 and pH 4.5), and 1,1-diphenyl-2-picryl-hydrazyl (DPPH•)-scavenging assays. The cellular assay indicated that the two isomers could also increase cell viabilities. However, quantitative analyses suggested that E-resveratrol exhibited stronger effects than Z-resveratrol in all chemical and cellular assays. Finally, the conformations of E-resveratrol and Z-resveratrol were analyzed. It can be concluded that both E-resveratrol and Z-resveratrol can promote redox-related pathways to exhibit antioxidant action and consequently protect bone marrow-derived mesenchymal stem cells (bmMSCs) from oxidative damage. These pathways include electron transfer (ET) and H⁺-transfer, and likely include hydrogen atom transfer (HAT). The E-configuration, however, improves antioxidant and cytoprotective capacities of resveratrols. The detrimental effect of the Z-configuration may be attributed to the non-planar preferential conformation, where two dihedral angles block the extension of the conjugative system.

Antioxidant Structure⁻Activity Relationship Analysis of Five Dihydrochalcones

The study determined the comparative antioxidant capacities of five similar dihydrochalcones: phloretin, phloridzin, trilobatin, neohesperidin dihydrochalcone, and naringin dihydrochalcone. In the ferric-reducing antioxidant power (FRAP) assay, the antioxidant activities of pairs of dihydrochalcones had the following relationship: phloretin > phloridzin, phloretin > trilobatin, trilobatin > phloridzin, trilobatin > naringin dihydrochalcone, and neohesperidin dihydrochalcone > naringin dihydrochalcone. Similar relative antioxidant levels were also obtained from 1,1-diphenyl-2-picryl-hydrazl radical (DPPH•)-scavenging, 2,2′-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid) (ABTS•⁺)-scavenging, and superoxide radical (•O₂⁻)-scavenging assays. Using ultra-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry (UPLC−ESI−Q−TOF−MS/MS) analysis for the reaction products with DPPH•, phloretin, phloridzin, and trilobatin were found to yield both dihydrochalcone-DPPH adduct and dihydrochalcone-dihydrochalcone dimer, whereas naringin dihydrochalcone gave a naringin dihydrochalcone-DPPH adduct, and neohesperidin dihydrochalcone gave a dimer. In conclusion, the five dihydrochalcones may undergo redox-based reactions (especially electron transfer (ET) and hydrogen atom transfer (HAT)), as well as radical adduct formation, to exert their antioxidant action. Methoxylation at the ortho-OH enhances the ET and HAT potential possibly via p-π conjugation, whereas the glycosylation of the –OH group not only reduces the ET and HAT potential but also hinders the ability of radical adduct formation. The 2′,6′-di-OH moiety in dihydrochalcone possesses higher ET and HAT activities than the 2′,4′-di-OH moiety because of its resonance with the adjacent keto group.

A DFT Study of Structural and Bonding Properties of Complexes Obtained from First-Row Transition Metal Chelation by 3-Alkyl-4-phenylacetylamino-4,5-dihydro-1H-1,2,4-triazol-5-one and Its Derivatives

Density functional calculations were used to explore the complexation of 3-alkyl-4-phenylacetylamino-4,5-dihydro-1h-1,2,4-triazol-5-one (ADPHT) derivatives by first-row transition metal cations. Neutral ADPHT ligand and mono deprotonated ligands have been used. Geometry optimizations have been performed in gas-phase and solution-phase (water, benzene, and N,N-dimethylformamide (DMF)) with B3LYP/Mixed I (LanL2DZ for metal atom and 6-31+G(d,p) for C, N, O, and H atoms) and with B3LYP/Mixed II (6-31G(d) for metal atom and 6-31+G(d,p) for C, N, O, and H atoms) especially in the gas-phase. Single points have also been carried out at CCSD(T) level. The B3LYP/Mixed I method was used to calculate thermodynamic energies (energies, enthalpies, and Gibb energies) of the formation of the complexes analyzed. The B3LYP/Mixed I complexation energies in the gas phase are therefore compared to those obtained using B3LYP/Mixed II and CCSD(T) calculations. Our results pointed out that the deprotonation of the ligand increases the binding affinity independently of the metal cation used. The topological parameters yielded from Quantum Theory of Atom in Molecules (QTAIM) indicate that metal-ligand bonds are partly covalent. The significant reduction of the proton affinity (PA) observed when passing from ligands to complexes in gas-phase confirms the notable enhancement of antioxidant activities of neutral ligands.

Role of the p-Coumaroyl Moiety in the Antioxidant and Cytoprotective Effects of Flavonoid Glycosides: Comparison of Astragalin and Tiliroside

The aim of this study was to explore the role of p-coumaroyl in the antioxidant and cytoprotective effects of flavonoid glycosides. The antioxidant effects of astragalin and tiliroside were compared using ferric ion reducing antioxidant power, DPPH• scavenging, ABTS•⁺ scavenging, •O₂^– scavenging, and Fe²⁺-chelating assays. The results of these assays revealed that astragalin and tiliroside both exhibited dose-dependent activities; however, tiliroside exhibited lower IC₅₀ values than astragalin. In the Fe²⁺-chelating assay, tiliroside gave a larger shoulder-peak at 510 nm than astragalin, and was also found to be darker in color. Both of these compounds were subsequently evaluated in a Fenton-induced mesenchymal stem cell (MSC) damaged assay, where tiliroside performed more effectively as a cytoprotective agent than astragalin. Tiliroside bearing a 6′′-O-p-coumaroyl moiety exhibits higher antioxidant and cytoprotective effects than astragalin. The 6′′-O-p-coumaroyl moiety of tiliroside not only enhances the possibility of electron-transfer and hydrogen-atom-transfer-based multi-pathways, but also enhances the likelihood of Fe-chelating. The p-coumaroylation of the 6"-OH position could therefore be regarded as a potential approach for improving the antioxidant and cytoprotective effects of flavonoid glycosides in MSC implantation therapy.

Solvent effects on the triplet–triplet annihilation upconversion of diiodo-Bodipy and perylene

Solvent effect plays a very important role in triplet–triplet annihilation (TTA) upconversion system and the upconversion efficiency is controlled by different solvent viscosity and polarity.

Comparison of the Antioxidant Effects of Quercitrin and Isoquercitrin: Understanding the Role of the 6″-OH Group

The role of the 6″-OH (ω-OH) group in the antioxidant activity of flavonoid glycosides has been largely overlooked. Herein, we selected quercitrin (quercetin-3-O-rhamnoside) and isoquercitrin (quercetin-3-O-glucoside) as model compounds to investigate the role of the 6″-OH group in several antioxidant pathways, including Fe²⁺-binding, hydrogen-donating (H-donating), and electron-transfer (ET). The results revealed that quercitrin and isoquercitrin both exhibited dose-dependent antioxidant activities. However, isoquercitrin showed higher levels of activity than quercitrin in the Fe²⁺-binding, ET-based ferric ion reducing antioxidant power, and multi-pathways-based superoxide anion-scavenging assays. In contrast, quercitrin exhibited greater activity than isoquercitrin in an H-donating-based 1,1-diphenyl-2-picrylhydrazyl radical-scavenging assay. Finally, in a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl assay based on an oxidatively damaged mesenchymal stem cell (MSC) model, isoquercitrin performed more effectively as a cytoprotector than quercitrin. Based on these results, we concluded that (1) quercitrin and isoquercitrin can both indirectly (i.e., Fe²⁺-chelating or Fe²⁺-binding) and directly participate in the scavenging of reactive oxygen species (ROS) to protect MSCs against ROS-induced oxidative damage; (2) the 6″-OH group in isoquercitrin enhanced its ET and Fe²⁺-chelating abilities and lowered its H-donating abilities via steric hindrance or H-bonding compared with quercitrin; and (3) isoquercitrin exhibited higher ROS scavenging activity than quercitrin, allowing it to improve protect MSCs against ROS-induced oxidative damage.

Protective Effects of Dihydromyricetin against •OH-Induced Mesenchymal Stem Cells Damage and Mechanistic Chemistry

As a natural flavonoid in Ampelopsis grossedentata, dihydromyricetin (DHM, 2R,3R-3,5,7,3',4',5'-hexahydroxy-2,3-dihydroflavonol) was observed to increase the viability of •OH-treated mesenchymal stem cells using a MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl] assay and flow cytometry analysis. This protective effect indicates DHM may be a beneficial agent for cell transplantation therapy. Mechanistic chemistry studies indicated that compared with myricetin, DHM was less effective at ABTS⁺• (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid radical) scavenging and reducing Cu(2+), and had higher •O₂(-) and DPPH• (1,1-diphenyl-2-picrylhydrazyl radical) scavenging activities. Additionally, DHM could also chelate Fe(2+) to give an absorption maximum at 589 nm. Hence, such protective effect of DHM may arise from its antioxidant activities which are thought to occur via direct radical-scavenging and Fe(2+)-chelation. Direct radical-scavenging involves an electron transfer (ET) pathway. The hydrogenation of the 2,3-double bond is hypothesized to reduce the ET process by blocking the formation of a larger π-π conjugative system. The glycosidation of the 3-OH in myricitrin is assumed to sterically hinder atom transfer in the •O₂(-) and DPPH• radical-scavenging processes. In DHM, the Fe(2+)-chelating effect can actually be attributed to the 5,3',4',5'-OH and 4-C=O groups, and the 3-OH group itself can neither scavenge radicals nor chelate metal.