Influence of the Environment on the Protective Effects of Guaiacol Derivatives against Oxidative Stress: Mechanisms, Kinetics, and Relative Antioxidant Activity

Theoretical insight of reactive oxygen species scavenging mechanism in lignin waste depolymerization products

Apart from natural products and synthesis, phenolic compounds can be produced from the depolymerization of lignin, a major waste in biofuel and paper production. This process yields a plethora of aryl propanoid phenolic derivatives with broad biological activities, especially antioxidant properties. Due to its versatility, our study focuses on investigating the antioxidant mechanisms of several phenolic compounds obtained from renewable and abundant resources, namely, syringol (Hs), 4-allylsyringol (HAs), 4-propenylsyringol (HPns), and 4-propylsyringol (HPs). Employing the density functional theory (DFT) approach in conjunction with the QM-ORSA protocol, we aim to explore the reactivity of these compounds in neutralizing hydroperoxyl radicals in physiological and non-polar media. Kinetic and thermodynamic parameter calculations on the antioxidant activity of these compounds were also included in this study. Additionally, our research utilizes the activation strain model (ASM) for the first time to explain the reactivity of the HT and RAF mechanisms in the peroxyl radical scavenging process. It is predicted that HPs has the best rate constant in both media (1.13 × 108 M-1 s-1 and 1.75 × 108 M-1 s-1, respectively). Through ASM analysis, it is observed that the increase in the interaction energy due to the formation of intermolecular hydrogen bonds during the reaction is an important feature for accelerating the hydrogen transfer process. Furthermore, by examining the physicochemical and toxicity parameters, only Hs is not suitable for further investigation as a therapeutic agent because of potential toxicity and mutagenicity. However, overall, all compounds are considered potent HOO˙ scavengers in lipid-rich environments compared to previously studied antioxidants.

Feruloylmonotropeins: promising natural antioxidants in Paederia scandens

Paederia scandens (Lour.) is a widely used medicinal herb in Vietnam, China, India, and Japan for the treatment of a variety of conditions, including toothache, chest pains, piles, and spleen inflammation. There is broad interest in identifying the composition of its extracts and confirming their numerous biological activities, including anti-nociceptive, antiviral, and anticancer properties. Two iridoid glucosides obtained from the MeOH extract of P. scandens, 6'-O-E-feruloylmonotropein (6-FMT) and 10'-O-E-feruloylmonotropein (10-FMT), are potential antioxidants based on their structure. In this study, the hydroperoxyl scavenging activity of 6-FMT and 10-FMT was examined in silico by using density functional theory. These FMTs are predicted to be weak antioxidants in non-polar environments, whereas a good HOO˙ scavenging activity is expected in polar environments (pH = 7.4) with k _overall = 3.66 × 10⁷ M^-1 s^-1 and 9.45 × 10⁶ M^-1 s^-1, respectively. This activity is better than many common antioxidants such as trolox and nearly equivalent to ascorbic acid and resveratrol. The hydroperoxyl scavenging activity was exerted mainly by the di-anion form of FMTs in water at physiological pH following the single electron transfer mechanism. The results suggest that FMTs are promising natural antioxidants in aqueous physiological environments.

Phenolic acids and their carboxylate anions: Thermodynamics of primary antioxidant action

Phenolic acids represent naturally occurring antioxidants and play important role in free radicals scavenging. In this work, we have studied thermodynamics of the first step of primary antioxidant action for phenolic OH groups of benzoic and cinnamic acid derivatives, and their carboxylate anions. M06-2X/6-311++G(d,p) reaction enthalpies related to Hydrogen Atom Transfer (HAT), Single Electron Transfer - Proton Transfer (SET-PT), and Sequential Proton-Loss Electron-Transfer (SPLET) mechanisms were computed for model non-polar environment (benzene) and aqueous solution. The effect of acid structure on found reaction enthalpies was investigated, as well. For HAT, representing relevant reaction path in both environments, the lowest O-H bond dissociation enthalpies, BDE, were found for sinapic acid (347 kJ mol^-1 in benzene and 337 kJ mol^-1 in water). With two exceptions, carboxylate anions show lower BDEs than parent acids. In aqueous solution, enthalpies of the first step of SPLET from phenolic OH groups are low (135-199 kJ mol^-1). It indicates thermodynamic feasibility of the mechanism for acids, as well as their carboxylate anions. Although enthalpies of electron transfer from dianions formed after successive deprotonations of carboxyl and phenolic groups in water are usually higher than BDEs, differences are within 25 kJ mol^-1. Demethylation of OCH₃ groups may affect radical scavenging activity of studied substances due to O-CH₃ BDE considerably lower (230-269 kJ mol^-1) in comparison to O-H ones.

New insights into the competition between antioxidant activities and pro-oxidant risks of rosmarinic acid

Direct and indirect antioxidant activities of rosmarinic acid (RA) based on HOO˙/CH₃OO˙ radical scavenging and Fe(iii)/Fe(ii) ion chelation were theoretically studied using density functional theory at the M05-2X/6-311++G(2df,2p) level of theory. First, four antioxidant mechanisms including hydrogen atom transfer (HAT), radical adduct formation (RAF), proton loss (PL) and single electron transfer (SET) were investigated in water and pentyl ethanoate (PEA) phases. Regarding the free radical scavenging mechanism, HAT plays a decisive role with overall rate coefficients of 1.84 × 10³ M⁻¹ s⁻¹ (HOO˙) and 4.49 × 10³ M⁻¹ s⁻¹ (CH₃OO˙) in water. In contrast to PL, RAF and especially SET processes, the HAT reaction in PEA is slightly more favorable than that in water. Second, the [Fe(iii)(H₂O)₆]³⁺ and [Fe(ii)(H₂O)₆]²⁺ ion chelating processes in an aqueous phase are both favorable and spontaneous especially at the O5, site-1, and site-2 positions with large negative Δ_rG⁰ values and great formation constant K_f. Finally, the pro-oxidant risk of RA⁻ was also considered via the Fe(iii)-to-Fe(ii) complex reduction process, which may initiate Fenton-like reactions forming reactive HO˙ radicals. As a result, RA⁻ does not enhance the reduction process when ascorbate anions are present as reducing agents, whereas the pro-oxidant risk becomes remarkable when superoxide anions are found. The results encourage further attempts to verify the speculation using more powerful research implementations of the antioxidant activities of rosmarinic acid in relationship with its possible pro-oxidant risks.

Direct and indirect antioxidant activities of rosmarinic acid (RA) based on HOO˙/CH₃OO˙ radical scavenging and Fe(iii)/Fe(ii) ion chelation were theoretically studied using density functional theory at the M05-2X/6-311++G(2df,2p) level of theory.

Natural Methoxyphenol Compounds: Antimicrobial Activity against Foodborne Pathogens and Food Spoilage Bacteria, and Role in Antioxidant Processes

The antibacterial and antioxidant activities of three methoxyphenol phytometabolites, eugenol, capsaicin, and vanillin, were determined. The in vitro antimicrobial potential was tested on three common foodborne pathogens (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus) and three food spoilage bacteria (Shewanella putrefaciens, Brochothrix thermosphacta, and Lactobacillus plantarum). The antioxidant assays were carried out for studying the free radical scavenging capacity and the anti-lipoperoxidant activity. The results showed that eugenol and capsaicin were the most active against both pathogens and spoilage bacteria. S. aureus was one of the most affected strains (median concentration of growth inhibition: IC50 eugenol = 0.75 mM; IC50 capsaicin = 0.68 mM; IC50 vanillin = 1.38 mM). All phytochemicals slightly inhibited the growth of L. plantarum. Eugenol was the most active molecule in the antioxidant assays. Only in the oxygen radical absorbing capacity (ORAC) test did vanillin show an antioxidant activity comparable to eugenol (eugenol ORAC value = 2.12 ± 0.08; vanillin ORAC value = 1.81 ± 0.19). This study, comparing the antimicrobial and antioxidant activities of three guaiacol derivatives, enhances their use in future applications as food additives for contrasting both common pathogens and spoilage bacteria and for improving the shelf life of preserved food.

Effect of pH on ·OH-induced degradation progress of syringol/syringaldehyde and health effect

Syringol and syringaldehyde are widely present pollutants in atmosphere and wastewater due to lignin pyrolysis and draining of pulp mill effluents. The hydroxylation degradation mechanisms and kinetics and health effect assessment of them under high and low-NO_x regimes in atmosphere and wastewater have been studied theoretically. The effect of pH on reaction mechanisms and rate constants in their ·OH-initiated degradation processes has been fully investigated. Results have suggested that aqueous solution played a positive role in the ·OH-initiated degradation reactions by decreasing the energy barriers of most reactions and changing the reactivity order of initial reactions. For Sy^- and Sya^- (anionic species of syringol and syringaldehyde), most initial reaction routes were more likely to occur than that of HSy and Hsya (neutral species of syringol and syringaldehyde). As the pH increased from 1 to 14, the overall rate constants (at 298 K) of syringol and syringaldehyde with ·OH in wastewater increased from 5.43 × 10¹⁰ to 9.87 × 10¹⁰ M^-1 s^-1 and from 3.70 × 10¹⁰ to 1.14 × 10¹¹ M^-1 s^-1, respectively. In the NO_x-rich environment, 4-nitrosyringol was the most favorable product, while ring-opening oxygenated chemicals were the most favorable products in the NO_x-poor environment. On the whole, the NO_x-poor environment could decrease the toxicities during the hydroxylation processes of syringol and syringaldehyde, which was the opposite in a NO_x-rich environment. ·OH played an important role in the methoxyphenols degradation and its conversion into harmless compounds in the NO_x-poor environment.

Simultaneous Determination of Six Compounds in Destructive Distillation Extracts of Hawthorn Seed by GC-MS and Evaluation of Their Antimicrobial Activity

Hawthorn seed can be used to produce various bioactive compounds through destructive distillation. In this study, an accurate and feasible analytical method based on a gas chromatography mass spectrometer (GC-MS) was developed for simultaneous determination of six major compounds (contributing to more than 3% in total peak area) in destructive distillation extracts of hawthorn seed collected at different temperatures ranging from 150 to 270 °C. Then, a broth microdilution method coupled with grey correlation analysis was engaged in the evaluation of their antimicrobial activities and the screening of primarily active compounds. Results indicate that the extract collected from 211 to 230 °C had the highest content of six major compounds (furfural, 2-methoxyphenol, 2-methoxy-4-methylphenol, 4-ethyl-2-methoxyphenol, 2,6-dimethoxyphenol, and 5-tertbutylpyrogallol) and the strongest antibacterial activity. Besides, 2,6-dimethoxyphenol was found to be a potential compound in inhibiting the growth of vaginitis pathogens. This study provided an optimum temperature for the destructive distillation of hawthorn seed, reducing the waste of energy, and saving the cost of production in the hawthorn industry.

How Does Pyridoxamine Inhibit the Formation of Advanced Glycation End Products? The Role of Its Primary Antioxidant Activity

Pyridoxamine, one of the natural forms of vitamin B6, is known to be an effective inhibitor of the formation of advanced glycation end products (AGEs), which are closely related to various human diseases. Pyridoxamine forms stable complexes with metal ions that catalyze the oxidative reactions taking place in the advanced stages of the protein glycation cascade. It also reacts with reactive carbonyl compounds generated as byproducts of protein glycation, thereby preventing further protein damage. We applied Density Functional Theory to study the primary antioxidant activity of pyridoxamine towards three oxygen-centered radicals (•OOH, •OOCH3 and •OCH3) to find out whether this activity may also play a crucial role in the context of protein glycation inhibition. Our results show that, at physiological pH, pyridoxamine can trap the •OCH3 radical, in both aqueous and lipidic media, with rate constants in the diffusion limit (>1.0 × 108 M - 1 s - 1 ). The quickest pathways involve the transfer of the hydrogen atoms from the protonated pyridine nitrogen, the protonated amino group or the phenolic group. Its reactivity towards •OOH and •OOCH3 is smaller, but pyridoxamine can still scavenge them with moderate rate constants in aqueous media. Since reactive oxygen species are also involved in the formation of AGEs, these results highlight that the antioxidant capacity of pyridoxamine is also relevant to explain its inhibitory role on the glycation process.

Polyphenolic Composition of Rosa canina, Rosa sempervivens and Pyrocantha coccinea Extracts and Assessment of Their Antioxidant Activity in Human Endothelial Cells

The aim of the present study was the investigation of the antioxidant activity of plant extracts from Rosa canina, Rosa sempervivens and Pyrocantha coccinea. The results showed that the bioactive compounds found at higher concentrations were in the R. canina extract: hyperoside, astragalin, rutin, (+)-catechin and (-)-epicatechin; in the R. sempervirens extract: quinic acid, (+)-catechin, (−)-epicatechin, astragalin and hyperoside; and in the P. coccinea extract: hyperoside, rutin, (−)-epicatechin, (+)-catechin, astragalin, vanillin, syringic acid and chlorogenic acid. The total polyphenolic content was 290.00, 267.67 and 226.93 mg Gallic Acid Equivalent (GAE)/g dw, and the total flavonoid content 118.56, 65.78 and 99.16 mg Catechin Equivalent (CE)/g dw for R. caninna, R. sempervirens and P. coccinea extracts, respectively. The extracts exhibited radical scavenging activity in DPPH and 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS)•⁺ assays and protection from ROO•-induced DNA damage in the following potency order: R. canina > R. sempervirens > P. coccinea. Finally, treatment with R. canina and P. coccinea extract significantly increased the levels of the antioxidant molecule glutathione, while R. canina extract significantly decreased Reactive Oxygen Species (ROS) in endothelial cells. The results herein indicated that the R. canina extract in particular may be used for developing food supplements or biofunctional foods for the prevention of oxidative stress-induced pathological conditions of endothelium.

Intracellular antioxidant effect of vanillin, 4-methylguaiacol and 4-ethylguaiacol: three components in Chinese Baijiu

Vanillin, 4-methylguaiacol, and 4-ethylguaiacol can improve AAPH-induced alterations in oxidative stress biomarkers and antioxidant enzymes in HepG2 cells.

Thin layer-based spectral and electrophoretic study of electro-oxidation of solid ellagic acid

Acquisition of data from both in situ spectroscopy detection and online chromatography-like separation is important for studying complex electrochemical reactions. The present work provides an example of combination of thin-layer spectral and electrophoretic electrochemistry, both based on thin-layer electrolysis. Two thin-layer electrochemical cells were used to investigate the electro-oxidation of solid ellagic acid at different potentials, in acidic, physiological, and alkaline buffer media. UV-vis spectra and cyclic voltabsorptograms of the oxidation products were recorded in situ without interference from the solid reactant. Four oxidation products, depending upon the buffer pH and the applied potential, were separated and detected by electrophoretic electrochemistry. The major products possess redox stability, possibly with a diquinonemethide structure. The minor product is considered as an o-quinone derivative with a lactone-ring-opening, which can be reduced or further oxidized at appropriate potentials. A consecutive-parallel reaction mechanism is proposed for the formation of four products of ellagic acid in different pH media, which enriches the knowledge about the oxidation pathway and antioxidant property of this biologically active polyphenol compound.

The molecular basis for the pharmacokinetics and pharmacodynamics of curcumin and its metabolites in relation to cancer

This review addresses the oncopharmacological properties of curcumin at the molecular level. First, the interactions between curcumin and its molecular targets are addressed on the basis of curcumin's distinct chemical properties, which include H-bond donating and accepting capacity of the β-dicarbonyl moiety and the phenylic hydroxyl groups, H-bond accepting capacity of the methoxy ethers, multivalent metal and nonmetal cation binding properties, high partition coefficient, rotamerization around multiple C-C bonds, and the ability to act as a Michael acceptor. Next, the in vitro chemical stability of curcumin is elaborated in the context of its susceptibility to photochemical and chemical modification and degradation (e.g., alkaline hydrolysis). Specific modification and degradatory pathways are provided, which mainly entail radical-based intermediates, and the in vitro catabolites are identified. The implications of curcumin's (photo)chemical instability are addressed in light of pharmaceutical curcumin preparations, the use of curcumin analogues, and implementation of nanoparticulate drug delivery systems. Furthermore, the pharmacokinetics of curcumin and its most important degradation products are detailed in light of curcumin's poor bioavailability. Particular emphasis is placed on xenobiotic phase I and II metabolism as well as excretion of curcumin in the intestines (first pass), the liver (second pass), and other organs in addition to the pharmacokinetics of curcumin metabolites and their systemic clearance. Lastly, a summary is provided of the clinical pharmacodynamics of curcumin followed by a detailed account of curcumin's direct molecular targets, whereby the phenotypical/biological changes induced in cancer cells upon completion of the curcumin-triggered signaling cascade(s) are addressed in the framework of the hallmarks of cancer. The direct molecular targets include the ErbB family of receptors, protein kinase C, enzymes involved in prostaglandin synthesis, vitamin D receptor, and DNA.

Renewable biofuel additives from the ozonolysis of lignin

In this investigation ozonolysis in the presence of ethanol was used to depolymerise lignin, resulting in a low conversion of oxygenated aromatics over short reaction times, or a range of saturated esters over 24 h. Short chain oxygenates can be used as fuel additives, displacing a percentage of a hydrocarbon fuel while leading to improvement in some of the fuel properties. The utility of the resulting bio-oils was therefore assessed by blending with a range of fuels. Guaiacol, a potential antioxidant, was formed over short reaction times and was found to be completely miscible with low-sulphur petrol (ULSP), diesel, aviation kerosene and rapeseed methyl ester. The mainly aliphatic proportion of the bio-oil produced over 24 h could be blended with the fuels replacing a maximum of 12-17 wt.% of the hydrocarbon fuel.