Free Radical Scavenging Mechanism Research Articles

Isolation and Structural Confirmation of Xanthone Isomers from Dryopteris ramosa (Hope) C. Chr. and Their In Vitro Antioxidant Mechanism

The long history of using plant species as medicines worldwide provides clues for the search for bioactive phytochemicals. One of the important traditional medicinal plant species of Pakistan is Dryopteris ramosa (Dryopteridaceae). The fronds of Dryopteris ramosa are traditionally used for the treatment of gastric ulcer and constipation. The crude methanol extract and aqueous fraction of Dryopteris ramosa exhibited strong free radical scavenging potential. Two xanthonoid compounds, mangiferin and isomangiferin, were isolated from the aqueous fraction of Dryopteris ramosa by chromatographic techniques (CC Sephadex LH20, followed by MPLC and purified by preparative TLC). Their structures were confirmed by spectroscopic analysis MS, NMR (1H, 13C, HSQC and HMBC). This is the first report on isolation of mangiferin and isomangiferin from Dryopteris genus though previously reported in other fern genera, e.g., Cystopteris, Acystopteris, Gymnocarpium and Asplenium. The antioxidant potential of mangiferin (60.34 ± 0.14 μg/mL) and isomangiferin (55.98 ± 0.39 μg/mL) was comparable to ascorbic acid (57.97 ± 0.93 μg/mL), thus representing promising antioxidant agents against oxidative stress. The investigation of the mechanism of free radical scavenging by mangiferin and isomangiferin showed that the catechol moiety was involved in quenching of free radicals. This study justified the traditional use of Dryopteris ramosa confirming the pharmacological properties of isolated compounds. Further phytochemical studies on Dryopteris ramosa are needed for identification of new bioactive phytochemicals in this plant of ethnobotanical relevance.

Synthesis and antioxidant activity of conjugates of hydroxytyrosol and coumarin

Antioxidants have been the subject of intense research interest due to their numerous health benefits. In this work, a series of new conjugates of hydroxytyrosol and coumarin were synthesized and evaluated for their free radical scavenging, toxicity and antioxidant mechanism in vitro. The all target compounds 14a–t exhibited better radical scavenging activity than BHT, hydroxytyrosol, and coumarin in both DPPH radical and ABTS+ radical cation scavenging assays. The structure-activity relationships study indicated that the number and position of hydroxyl groups on the coumarin ring were vital to a good antioxidant capacity. Furthermore, the most promising compound 14q showed less toxicity in hemolysis assay and weaker antiproliferative effects than BHT against normal WI-38 and GES cells, and enhanced viability of H2O2-induced HepG2 cells. Additionally, 14q decreased the apoptotic percentage of HepG2 cells, reduced the ROS produce and LDH release, and improved GSH and SOD levels in H2O2-treated HepG2 cells. Lastly, 14q exhibited more stability than hydroxytyrosol in methanol solution. These results revealed that conjugations of hydroxytyrosol and coumarin show better antioxidant capacity, and are the efficacious approach to finding novel potential antioxidant.

Irvingia gabonensis Seed Extract: An Effective Attenuator of Doxorubicin-Mediated Cardiotoxicity in Wistar Rats.

Cardiotoxicity as an off-target effect of doxorubicin therapy is a major limiting factor for its clinical use as a choice cytotoxic agent. Seeds of Irvingia gabonensis have been reported to possess both nutritional and medicinal values which include antidiabetic, weight losing, antihyperlipidemic, and antioxidative effects. Protective effects of Irvingia gabonensis ethanol seed extract (IGESE) was investigated in doxorubicin (DOX)-mediated cardiotoxicity induced with single intraperitoneal injection of 15 mg/kg of DOX following the oral pretreatments of Wistar rats with 100-400 mg/kg/day of IGESE for 10 days, using serum cardiac enzyme markers (cardiac troponin I (cTI) and lactate dehydrogenase (LDH)), cardiac tissue oxidative stress markers (catalase (CAT), malonyldialdehyde (MDA), superoxide dismutase (SOD), glutathione-S-transferase (GST), glutathione peroxidase (GSH-Px), and reduced glutathione (GSH)), and cardiac histopathology endpoints. In addition, both qualitative and quantitative analyses to determine IGESE's secondary metabolites profile and its in vitro antioxidant activities were also conducted. Results revealed that serum cTnI and LDH were significantly elevated by the DOX treatment. Similarly, activities of tissue SOD, CAT, GST, and GSH levels were profoundly reduced, while GPx activity and MDA levels were profoundly increased by DOX treatment. These biochemical changes were associated with microthrombi formation in the DOX-treated cardiac tissues on histological examination. However, oral pretreatments with 100-400 mg/kg/day of IGESE dissolved in 5% DMSO in distilled water significantly attenuated increases in the serum cTnI and LDH, prevented significant alterations in the serum lipid profile and the tissue activities and levels of oxidative stress markers while improving cardiovascular disease risk indices and DOX-induced histopathological lesions. The in vitro antioxidant studies showed IGESE to have good antioxidant profile and contained 56 major secondary metabolites prominent among which are γ-sitosterol, Phytol, neophytadiene, stigmasterol, vitamin E, hexadecanoic acid and its ethyl ester, Phytyl palmitate, campesterol, lupeol, and squalene. Overall, both the in vitro and in vivo findings indicate that IGESE may be a promising prophylactic cardioprotective agent against DOX-induced cardiotoxicity, at least in part mediated via IGESE's antioxidant and free radical scavenging and antithrombotic mechanisms.

Free radical scavenging potency of ellagic acid and its derivatives in multiple H+/e‒ processes

The reaction energetics of the multiple free radical scavenging mechanisms of ellagic acid and its derivatives were studied by DFT method. Ellagic acid and its derivatives that bear catechol or guaiacyl moieties can proceed multiple free radical scavenging processes. Intramolecular hydrogen-bonds were found in the most stable geometries of the investigated compounds and can influence the antioxidant activity of the related groups and hydrogen atom/proton loss sequence. The stronger hydrogen-bond, the weaker antioxidant activity of the hydrogen atom/proton-donating group. The preferred mechanisms vary among different phases. All of the investigated compounds prefer to trap free radicals by multiple HAT mechanisms in gas and benzene phases. The second HAT reaction preferably occurs in the same catechol or guaiacyl unit of the first HAT group with the formation of stable quinone or benzodioxole. The catechol and guaiacyl moieties not only retain high free radical scavenging ability of the parent compounds but even show increased potency for the second and fourth H+/e‒ reactions. In water phase, ellagic acid and its derivatives would proceed consecutively PL reactions from the OH groups. The formed di/tri/tetra-anion would proceed one/four electron transfers following with single/double SPLET mechanism and electron donation reactions until forming the stable quinone or benzodioxole.

Highly efficient free radical-scavenging property of phenolic-functionalized chitosan derivatives: Chemical modification and activity assessment

Chitosan is an abundant and renewable polysaccharide, and chemical modification can be used to enhance the biological properties of chitosan. In this study, monophenol and ortho-diphenol were introduced to chitosan through chemical modification to get chitosan derivatives owned high antioxidant activity. Their free radical-scavenging activity against three free radicals and reduction ability was tested. Based on the four antioxidant assay, the antioxidant ability of the synthesized chitosan derivatives exhibited a remarkable improvement over chitosan. The IC50 of inhibition of DPPH, hydroxyl (OH), and superoxide (O2−) radical-scavenging was 41–172, 10–89, and 14–38 μg/mL, respectively. Meanwhile, ortho-diphenol was more efficient group than monophenol on the improvement of antioxidant ability of chitosan derivatives. The possible free radical-scavenging mechanism, including the number of the hydroxyl groups and the presence ortho-dihydroxy substitution for the antioxidant ability were discussed. In vitro studies demonstrated that the constructed chitosan derivatives have good biocompatibility, and good antioxidant capacity to reduce oxidative stress. Functionalization of chitosan with phenolic group allows the possible applications on the therapy of oxidative-related diseases.

Antioxidant activity and mechanism of dihydrochalcone C-glycosides: Effects of C-glycosylation and hydroxyl groups

Dihydrochalcones (DHCs), an important subgroup of flavonoids, have recently received much attention due to their diverse biological activities. In contrast to their O-glycosides, understanding of the antioxidant property and mechanism of DHC C-glycosides remains limited. Herein, the free radical scavenging activity and mechanism of two representative C-glycosyl DHCs, aspalathin (ASP) and nothofagin (NOT) as well as their aglycones, 3-hydroxyphloretin (HPHL) and phloretin (PHL) were evaluated using the density functional theory (DFT) calculations. The results revealed the crucial role of sugar moiety on the conformation and the activity. The o-dihydroxyl in the B-ring and the 2′,6′-dihydroxyacetophenone moiety were found significant in determining the activity. Our results showed that hydrogen atom transfer (HAT) is the dominant mechanism for radical-trapping in the gas and benzene phases, while the sequential proton loss electron transfer (SPLET) is more preferable in the polar environments. Also, the results revealed the feasibility of the double HAT and double SPLET as well as the SPLHAT mechanisms, which provide alternative pathways to trap radical for the studied DHCs. These results could deepen the understanding of the antiradical activity and mechanism of DHCs, which will facilitate the design of novel efficient antioxidants.

Molecular design of curcumin analogues with potent antioxidant properties and thermodynamic evaluation of their mechanism of free radical scavenge

BackgroundFree radical attack of cellular structures in the human system is the major cause of various forms of degenerative diseases. Consequently, recent research has been focused on the development of new antioxidants with more efficient free radical scavenging potentials. Ligand-based virtual screening was employed in the rational design of potent antioxidant derivatives of curcumin by the density functional theory method. Various antioxidant descriptors that characterize the three major mechanisms of free radical scavenge, namely, hydrogen atom transfer (HAT), single electron transfer followed by proton transfer (SET-PT), and sequential proton loss electron transfer (SPLET), were calculated. Also, the spin density distribution on the generated radicals and the frontier orbital distribution and energy of the studied compounds were evaluated in order to gain further insight on the reaction mechanism. The reaction Gibbs free energy for scavenging the two important peroxyl radicals (HOO· and CH3OO·) was calculated in order to evaluate the preferred mechanism of free radical scavenge by these compounds.ResultsThe investigated compounds were able to scavenge HOO· and CH3OO· radicals by HAT and SPLET mechanisms in the gas phase and aqueous solution, based on the computed results of reaction enthalpies and Gibbs free energy. The SET-PT mechanism for these compounds was observed to be thermodynamically unfeasible in the gas phase. However, the thermodynamic feasibility of free radical scavenge by SET-PT mechanism was observed in aqueous solution. Among the investigated compounds, MCC 009 (1E,4E)-1-(3-(aminomethyl)-4-hydroxyphenyl)-5-(4-hydroxy-3-((hydroxy (methyl)amino)methyl)phenyl)penta-1,4-dien-3-one at the 19-OH position possessed the highest capacity to scavenge both HOO· and CH3OO· radicals by HAT, SET-PT, and SPLET mechanisms. The reaction Gibbs free energy of scavenging HOO· radical by this molecule in the gas phase and aqueous solution is ∆rGBDEgas = − 58.18, {Delta _r{G}_{BDE}}_{H_2O}=-73.77 , ∆rGAIPgas = 611.48, {Delta _r{G}_{AIP}}_{H_2O}=-74305.49 , ∆rGPDEgas = − 669.66, {Delta _r{G}_{PDE}}_{H_2O}=74231.72 , ∆rGPAgas = − 271.40, {Delta _r{G}_{PA}}_{H_2O}=-73.09 ,∆rGETEgas = 213.22, and {Delta _r{G}_{ETE}}_{H_2O}=-0.69 .ConclusionNew set of curcumin derivatives with potent free radical scavenging properties was successfully designed, and their mechanism of free radical scavenging evaluated by thermodynamic studies. This research is a gateway to the exploitation of the considered curcumin derivatives in food chemistry and pharmacy.

Clerodendrum volubile Ethanol Leaf Extract: A Potential Antidote to Doxorubicin-Induced Cardiotoxicity in Rats.

Doxorubicin is widely applied in hematological and solid tumor treatment but limited by its off-target cardiotoxicity. Thus, cardioprotective potential and mechanism(s) of CVE in DOX-induced cardiotoxicity were investigated using cardiac and oxidative stress markers and histopathological endpoints. 50–400 mg/kg/day CVE in 5% DMSO in distilled water were investigated in Wistar rats intraperitoneally injected with 2.5 mg/kg DOX on alternate days for 14 days, using serum troponin I and LDH, complete lipid profile, cardiac tissue oxidative stress marker assays, and histopathological examination of DOX-treated cardiac tissue. Preliminary qualitative and quantitative assays of CVE's secondary metabolites were also conducted. Phytochemical analyses revealed the presence of flavonoids (34.79 ± 0.37 mg/100 mg dry extract), alkaloids (36.73 ± 0.27 mg/100 mg dry extract), reducing sugars (07.78 ± 0.09 mg/100 mg dry extract), and cardiac glycosides (24.55 ± 0.12 mg/100 mg dry extract). 50–400 mg/kg/day CVE significantly attenuated increases in the serum LDH and troponin I levels. Similarly, the CVE dose unrelatedly decreased serum TG and VLDL-c levels without significant alterations in the serum TC, HDL-c, and LDL-c levels. Also, CVE profoundly attenuated alterations in the cardiac tissue oxidative stress markers' activities while improving DOX-associated cardiac histological lesions that were possibly mediated via free radical scavenging and/or antioxidant mechanisms. Overall, CVE may play a significant therapeutic role in the management of DOX-induced cardiotoxicity in humans.

Microplate ORAC-pyranine spectrophotometric assay for high-throughput assessment of antioxidant capacity

Antioxidant activity assessment is crucial to establish the protective role of bioactive compounds against free radical-induced oxidative damage, a serious threat to health and food quality. For oxygen radical absorbance capacity (ORAC) assays, the target molecule employed has been indicated as a key factor to characterize free-radical scavenging mechanisms. The combined use of target molecules such as pyranine (PYR) and pyrogallol red (PGR) allows to distinguish between the stoichiometry and the chemical reactivity of free radical scavenging by antioxidants. In this work, a high-throughput microplate-based ORAC-PYR method was developed for the estimation of antioxidant capacity (stoichiometry) in a miniaturized fashion. Kinetic studies of pyranine consumption by AAPH-derived radicals were carried out to achieve high sensitivity, reduced consumption of reagents, and low generation of waste. The use of low amounts of target molecule and radical generator (2.5 ng and 2.5 µg, respectively) was feasible with a maximum time to result of 3 h for 96 simultaneous determinations. The limit of detection was 1 µM for Trolox and RSD values were <5.4% and <6.4% for intra- and inter-assay precision, respectively. A dual-probe approach (ORAC-PGR and ORAC-PYR) was implemented in microplate format and a comparative study of structure-antioxidant activity of catechol-derived compounds was performed. This strategy was also extended to the analysis of antioxidant-rich beverages for assessing the applicability of the proposed method to complex matrices.

Pharmacological potential of tocopherol and doxycycline against traumatic brain injury-induced cognitive/motor impairment in rats

ABSTRACT Primary Objective The primary objective of this study was to explore the pharmacological potential of tocopherol and doxycycline against traumatic brain injury-induced cognitive/motor impairment in rats. Research Design Weight drop model of traumatic brain injury. Methods and Procedures After TBI, the animals were treated with doxycycline (50 and 100 mg/kg; p.o), tocopherol (5 and 10 mg/kg; p.o) alone and in combination as doxycycline and tocopherol (50 and 10 mg/kg; p.o) from 1st day to 28th day. The behavioral parameters were performed on a weekly basis from 1st day to 28th day. On 29th day, animals were sacrificed and striatum and cortex were homogenized for the estimation of biochemical (LPO, nitrite, and GSH), neuroinflammatory (IL-6, IL-1β, and TNF-α), and neurotransmitters (dopamine, norepinephrine, serotonin, GABA, and glutamate) analysis. Main Outcomes and Results Induction of TBI had significantly reduced locomotor activity, recognition memory, increased neuroinflammatory markers, and imbalance neurotransmitter levels. The treatment with doxycycline and tocopherol alone and in combination significantly attenuated locomotor activity, memory recognition, reduced neuroinflammation, preserved oxidative balance, and restored the level of neurotransmitters. Conclusions The neuroprotective effect of doxycycline and tocopherol might be due to its anti-inflammatory and free radical scavenging mechanisms. Abbreviations TBI: Traumatic brain injury; Doxy: Doxycycline; Toco: Tocopherol; LPO: Lipid peroxidation; MDA: Malondialdehyde; TNF-α: Tumor necrosis factor-alpha; IL-1b: Interleukin-1 beta; GSH: Glutathione; GABA: gamma-Aminobutyric acid.

Lipid peroxidation inhibition study: A promising case of 1,3-di([1,1′-biphenyl]-3-yl)urea

In the present study eighteen inhibitors of the hydrolytic enzymes of the endocannabinoid system were investigated for antioxidant activity using lipid peroxidation (LP) method. Among the assayed compounds ten belong to carbamates with phenyl [1,1′-biphenyl]-3-ylcarbamate (6), reported for the first time, and eight are retro-amide derivatives of palmitamine. Interestingly, results indicated that most of the tested compounds have good antioxidant properties. In particular, 1,3-di([1,1′-biphenyl]-3-yl)urea (3) shows IC50 = 26 ± 6 μM comparable to ones obtained for standard antioxidants trolox and quercetin (IC50 = 22 ± 6 μM and 23 ± 6 μM, respectively). Compound 3 was investigated further by means of DFT calculations, to clarify a possible mechanism of the antioxidant action. In order to estimate the capability of 3 to act as radical scavenger the structure was optimized at B3LYP/6–311++G** level and the respective bond dissociation enthalpies were calculated. The calculations in non-polar medium predicted as favorable mechanism a donation of a hydrogen atom to the free radical and formation of N-centered radical, while in polar solvents the mechanism of free radical scavenging by SPLET dominates over HAT H-abstraction. The possible radical scavenging mechanisms of another compound with potent antioxidant properties (IC50 = 53 ± 12 μM), the retro-amide derivative of palmitamine (compound 18), was estimated computationally based on the reaction enthalpies of a model compound (structural analogue to 18). The computations indicated that the most favorable mechanisms are hydrogen atom transfer from the hydroxyl group in meta-position of the benzamide fragment in nonpolar medium, and proton transfer from the hydroxyl group in ortho-position of the benzamide fragment in polar medium.

Theoretical exploration on free radical scavenging mechanism of curcumin analogues in water solvent

One way to improve curcumin’s possibility in preventing lipid peroxidation is through modification of carbon linker, β-diketone group and aromatic rings. However, there remains a need to explore the role of carbon linker on the free radical scavenging mechanisms of curcumin. This study uses density functional theory to explore two descriptors of free radical scavenging mechanisms, which are bond dissociation enthalpy (BDE) and adiabatic ionization potential (AIP) of curcumin and its analogues. Five analogues with different amount of carbon atoms in the linker in the presence / absence of β-diketone group are chosen. Our result shows that decreasing the amount of carbon atom from 7 to 5 atoms in the linker decreases the BDE at β-diketone group of the curcumin analogue. Moreover, increasing the amount of carbon atoms in the linker decreases the AIP of the analogues.

Electron Scavenging Not Free Radical Scavenging by Fullerene Materials Protects Against Mitochondrial Oxidative Stress in Complex Organisms.

Fullerene materials are often reported to be excellent antioxidants in cells. Usually, direct free radical scavenging mechanisms, as seen in polymer and food industry research, is the proposed antioxidant mechanism. However, free radical scavenging by antioxidants in vivo is kinetically unlikely and conflicts with fullerene material’s molecular properties. Pristine fullerene materials, and many of their derivatives, are pro‐oxidant and form adducts, which are both potentially toxic mechanisms in vivo. Although they are electrophilic, and potentially oxidative molecules with an affinity for electrons, they appear to function like other non‐radical electrophilic antioxidants and stimulate enzymatic oxidative stress management and protection. We approach fullerene material’s antioxidant role from the perspective that they do not act as direct free radical scavengers. Other mechanisms have been previously proposed that are more consistent with fullerene properties, and antioxidant benefits in vivo. Here we discuss fullerene materials as electron scavenging antioxidants rather than free radical scavengers. We propose that fullerene materials scavenge excess electrons in the ETC preventing the formation of superoxide and hydroxyl radicals in the mitochondria. The scavenging of electrons would help in preventing damage to mitochondrial structures and DNA, maintaining optimum NAD+/NADH ratios, as well as in maintaining an oxidized OX/PHOS enzyme system in mitochondrial conditions resulting from excess caloric intake in the absence of cellular energy requirements and progressive mitochondrial dysfunction related to oxidative stress. Further research is needed to evaluate the utilization of fullerene materials for use in metabolic syndromes and neurodegenerative conditions complicated by progressive mitochondrial damage.Support or Funding InformationSupported by Institutional Resources of the University of Science Arts and Technology, Montserrat, BWI, The University of Health and Humanities, BVI and the Einstein Medical Institute, Florida USA.

EICOSAPENTAENOIC ACID INHIBITS OXIDATION OF VERY LARGE DENSITY LIPOPROTEINS (VLDL) IN A DOSE-DEPENDENT MANNER OVER TIME AS COMPARED TO DOCOSAHEXAENOIC ACID IN VITRO

Eicosapentaenoic acid (EPA) reduces oxidation of LDL in patients with hypertriglyceridemia, a benefit that may contribute to reduced cardiovascular (CV) risk. EPA may specifically inhibit oxidation of triglyceride-rich lipoproteins such as VLDL, through a free radical scavenging mechanism. We

Free radical scavenging mechanism of 1,3,4-oxadiazole derivatives: thermodynamics of O–H and N–H bond cleavage

The thermodynamics of free radical scavenge of 1,3,4-oxadiazole derivatives towards oxygen-centred free radicals were investigated by the density functional theory (DFT) method in the gas phase and aqueous solution. Three mechanisms of free radical scavenge namely, hydrogen atom transfer (HAT), single electron transfer followed by proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET) were considered. The antioxidant descriptors that characterize these mechanisms such as, bond dissociation enthalpy (BDE), adiabatic ionization potential (AIP), proton dissociation enthalpy (PDE), proton affinity (PA) and electron transfer enthalpy (ETE) were evaluated. The sequence of electron donation as predicted by the HOMO results were in good agreement with the sequence of ETE for the considered molecules at their favoured sites of free radical scavenge. The reaction Gibbs free energy for inactivation of the selected peroxyl radicals, show that 1,3,4-oxadiazole antioxidants are more efficient radical scavengers by HAT and SPLET mechanisms than SET-PT mechanism in vacuum. In aqueous solution, the SET-PT mechanism was observed to be the dominant reaction pathway.

Performance and mechanism of methylene blue degradation by an electrochemical process.

An exciting electrochemical oxidation (EO) process has been developed. Compared with electro-Fenton (EF) and electro-coagulation (EC) processes, this process had more advantages in the degradation of methylene blue. It is observed that methylene blue can be quickly degraded by EO, in which an iron rod is used as an anode, graphite is used as a cathode, and fly ash–red mud particles are used as particle electrodes. Compared to EC and EF processes that are affected by specific pH values, EO has excellent performance in the pH range of 3.0–11.0. In addition, the electric energy consumption (EEC) of EF, EC and EO is 81.51, 36.55 and 21.35 kW h m−3 respectively, suggesting EO is more economical. The free radical scavenging mechanism of i-PrOH is studied, and the contribution of EC, EF and fly ash–red mud particle electrodes in EO is inferred. Particle electrodes before and after use are characterized by SEM, EDS and BET to illustrate the role of particle electrodes in the EO system. Analysis of flocs and solutions by FTIR and GC-MS proves that EO can effectively degrade methylene blue, and the degradation route of methylene blue is speculated. The particle electrode dissolution experiment shows that the prepared fly ash–red mud particle electrode is considered to be suitable and safe for wastewater treatment. Finally, in actual surface water experiments, the EO process still has great potential.

Reactions of the Lipid Hydroperoxides With Aminic Antioxidants: The Influence of Stereoelectronic and Resonance Effects on Hydrogen Atom Transfer

Aminic radical-trapping antioxidants (RTAs), as one of the most important antioxidants, have not received sufficient attention yet. But, an increasing number of aminic RTAs have been identified as ferroptosis inhibitors in recent years, which can potentially mediate many pathological states including inflammation, cancer, neurodegenerative disease, as well as ocular and kidney degeneration. This highlights the importance of aminic RTAs in the field of medicine. Herein, we systematically explored the radical scavenging mechanism of aminic RTAs with a quantum chemical method, particularly emphasizing the role of stereoelectronic factors and resonance factors on the transfer of H-atom and the stability to one-electron oxidation. These theoretical results elucidate the diversity of free radical scavenging mechanisms for aminic RTAs, and has significant implications for the rational design of new aminic RTAs.

Structure-antioxidant activity relationship of ferulic acid derivatives: Effect of ester groups at the end of the carbon side chain

Differences in the antioxidant activity of ferulic acid and its nine naturally occurring derivatives with the presence of different ester groups at the end of their carbon side chains were investigated using the density functional theory (DFT) method. The thermodynamics parameters related to the double H+/e− free radical scavenging mechanisms were calculated in the gas, benzene and water phases. In the investigated phases, ferulic acid with the COOH group or COO− group and its different ester derivatives show similar antioxidant capacities. They preferentially undergo the first H+/e− reaction from the 4−OH group and then proceed to the second H+/e− reaction from the 3−H group, forming a benzodioxole. The energy cost of the second H+/e− reaction is considerably reduced. In the gas and benzene phases, ferulic acid and its derivatives have the highest probability of using the HAT mechanism in the first H+/e‒ reaction. In water, the most possible mechanism is SPLET. In the studied phases, HAT is the most likely second H+/e‒ reaction mechanism for ferulic acid and its ester derivatives trap free radicals.

Green synthesis of silver nickel bimetallic nanoparticles using plant extract of Salvadora persica and evaluation of their various biological activities

Metallic nanoparticles play vital role in the field of science, medicine, food and technology. Various strategies have been used for the synthesis of bimetallic nanoparticles to improve the physical and chemical properties of monometallic nanoparticles. The present study describes synthesis of Ag-Ni bimetallic nanoparticles, using aqueous extract of Salvadora persica. Silver and nickel ions were reduced by secondary metabolites within the extract which act as reducing as well as capping agents. UV–visible spectrum produced an absorbance band in the range of 400 nm to 450 nm due to electronic transitions associated with resonance of surface electrons that was an indication of the formation of nanoparticles. Scanning Electron Microscopy (SEM) and x-ray diffraction spectroscopy (XRD) were used for the determination of morphology and dimension of nanoparticles. Particle dimension of synthesized nanoparticles was 23.67 nm. Energy dispersive x-ray spectroscopy (EDX) was used for the elemental analysis that showed the presence of silver and nickel in elemental form. Fourier Transform Infrared Microscopy (FTIR) was used for the functional group analysis. Synthesized Ag-Ni bimetallic nanoparticles were assessed for the estimation of their antioxidant potential by three methods i.e. DPPH free radical scavenging mechanism, phosphomolybdenum complex method and determination of phenolic contents. Percent scavenging activity of synthesized Ag-Ni bimetallic nanoparticles was observed as 70.5% at 1500 μg ml−1 concentration. Total antioxidant activity calculated for synthesized nanoparticles was 0.6479 against BHT as a reference. Total phenolic contents of green synthesized nanoparticles were calculated to be 74.5 mg g−1 GAE. Different parameters like temperature, pH, effect of adsorbent concentration, time of contact, and concentration of adsorbate, were optimized for the utmost removal of congo red dye and chromium (VI).

Titanium dioxide catalytic activity contributes to the process of free radical scavenging

TiO2 crystallochemical properties have been explored and correlated with the activity of this material in the scavenging of reactive oxygen and nitrogen species (ROS/RNS). It is well known that those highly reactive species are produced by inflammatory cells and neutralized by some oxides, such a titanium dioxide under light. Nevertheless, the mechanism of action of this ceramic material is yet to be fully understood. A set of reactions have been proposed that imply the presence of different valence states of titanium as the basis for the ROS/RNS scavenging, but in this work, we have demonstrated that those species are not always detected in TiO2-based materials, which are, in addition, active in depleting ROS/RNS. TiO2 powders with undetected Ti3+ have been obtained with a range of different properties—surface area, particle size, rutile–anatase ratio, and band gap values—by varying the powder processing conditions after synthesis through the sol precipitation route. The properties of the powders have been correlated with the scavenging activity of the materials toward two reactive species, DPPH· and peroxynitrite, always conducted under dark conditions. It was observed that despite the lack of Ti3+ states, TiO2 powders can still neutralize ROS/RNS. For the first time, this study explain how the catalytic activity of different TiO2 contribute to the free radical scavenging mechanism and the differences in scavenger activity shown by different TiO2 phases and mixtures.