The Antioxidant Properties, Metabolism, Application and Mechanism of Ferulic Acid in Medicine, Food, Cosmetics, Livestock and Poultry

Ferulic acid is a ubiquitous ingredient in cereals, vegetables, fruits and Chinese herbal medicines. Due to the ferulic phenolic nucleus coupled to an extended side chain, it readily forms a resonant-stable phenoxy radical, which explains its potent antioxidant potential. In addition, it also plays an important role in anti-cancer, pro-angiogenesis, anti-thrombosis, neuroprotection, food preservation, anti-aging, and improving the antioxidant performance of livestock and poultry. This review provides a comprehensive summary of the structure, mechanism of antioxidation, application status, molecular mechanism of pharmacological activity, existing problems, and application prospects of ferulic acid and its derivatives. The aim is to establish a theoretical foundation for the utilization of ferulic acid in medicine, food, cosmetics, livestock, and poultry.

New Thiosemicarbazide Derivatives with Multidirectional Biological Action

Over the years, several new medicinal substances have been introduced for the treatment of diseases caused by bacteria and parasites. Unfortunately, due to the production of numerous defense mechanisms by microorganisms and parasites, they still pose a serious threat to humanity around the world. Therefore, laboratories all over the world are still working on finding new, effective methods of pharmacotherapy. This research work aimed to synthesize new compounds derived from 3-trifluoromethylbenzoic acid hydrazide and to determine their biological activity. The first stage of the research was to obtain seven new compounds, including six linear compounds and one derivative of 1,2,4-triazole. The PASS software was used to estimate the potential probabilities of biological activity of the newly obtained derivatives. Next, studies were carried out to determine the nematocidal potential of the compounds with the use of nematodes of the genus Rhabditis sp. and antibacterial activity using the ACCT standard strains. To determine the lack of cytotoxicity, tests were performed on two cell lines. Additionally, an antioxidant activity test was performed due to the importance of scavenging free radicals in infections with pathogenic microorganisms. The conducted research proved the anthelmintic and antibacterial potential of the newly obtained compounds. The most effective were two compounds with a 3-chlorophenyl substituent, both linear and cyclic derivatives. They demonstrated higher efficacy than the drugs used in treatment.

Neomangiferin, a Naturally Occurring Mangiferin Congener, Inhibits Sodium-Glucose Co-transporter-2: An In silico Approach

Type 2 diabetes is a major health concern contributing to most of diabetic cases worldwide. Mangiferin and its congeners are known for their diverse pharmacological properties. This study sought to investigate the inhibitory property of naturally occurring mangiferin congeners on sodium-glucose co-transporter 2 protein (SGLT-2) using comprehensive computational methods. The naturally occurring mangiferin congeners were subjected to molecular docking, molecular dynamics (MDs) simulation (100 ns), molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) binding free energy, density functional theory calculations (B3LYP 6-31G basis set), and ADMET approaches to identify potential SGLT-2 inhibitor. The molecular docking studies revealed neomangiferin (-9.0 kcal/mol) as the hit molecule compared with dapagliflozin (-8.3 kcal/mol). Root-mean-square deviation (RMSD) and root-mean-square fluctuation (RMSF) plots from the MD simulations established that neomangiferin stabilizes SGLT-2 better than the dapagliflozin, a standard drug. The MM-PBSA binding free energy calculations showed that neomangiferin (-26.05 kcal/mol) elicited better binding affinity than dapagliflozin (-17.42 kcal/mol). The electronic studies showed that neomangiferin (3.48 eV) elicited high electrophilicity index compared with mangiferin (3.31 eV) and dapagliflozin (2.11 eV). Also, the ADMET properties showed that the hit molecule is safe when administered to diabetic subjects. The current in silico studies suggest that neomangiferin could emerge as a promising lead molecule as a SGLT-2 inhibitor.

Synthesis, characterization, biological activity and computation-based efficacy of cobalt(II) complexes of biphenyl-2-ol against SARS-CoV-2 virus

Cobalt(II) complexes of biphenyl-2-ol of composition, CoCl2-n(OC6H4C6H5-2)n(H2O)4 (where n = 1 or 2), were prepared by reacting cobaltous(II) chloride with equi- and bimolar ratios of sodium salt of biphenyl-2-ol. The structural characterization of the synthesized complexes was accomplished by NMR, FTIR, thermogravimetry (TGA), high resolution mass spectroscopy (HRMS), electronic spectroscopic techniques coupled with density functional theory (DFT). The stability of the complexes in different pH media of solvent was studied. Chemical reactivity parameters of the newly synthesized complexes, computed using DFT, indicated greater reactivity of complex 2 over complex 1 and free ligand as indicated by its low HOMO-LUMO energy gap corresponding to 1.71 eV. Molecular docking (MD) studies were carried out in order to study the binding affinities between amino acid residues of DNA duplex (PDB ID: 1BNA) and SARS-CoV-2 (PDB ID: 7T9K) with newly synthesized complexes. Complex 2 has shown promising antivirus behaviour with an inhibition constant value of 0.0423 µmol-1 with amino acid residues of SARS-CoV-2 virus. Toxicity of the complexes was predicted using ProTox-II online server. Antibacterial studies have indicated the complexes to exhibit greater efficacy than the free ligand, while the antioxidant activities have suggested them to display enhanced antioxidant behaviour as compared to reference compounds.Communicated by Ramaswamy H. Sarma.

Investigation of the radical scavenging potential of vanillin-based pyrido-dipyrimidines: experimental and in silico approach

Antioxidants have a significant contribution in the cell protection against free radicals which may induce oxidative stress, and permanently damage the cells causing different disorders such as tumors, degenerative diseases, and accelerated aging. Nowadays, a multi-functionalized heterocyclic framework plays an important role in drug development, and it is of great importance in organic synthesis and medicinal chemistry. Encouraged by the bioactivity of the pyrido-dipyrimidine scaffold and vanillin core, herein, we made an effort to thoroughly investigate the antioxidant potential of the vanillin-based pyrido-dipyrimidines A-E to reveal novel promising free radical inhibitors. The structural analysis and the antioxidant action of the investigated molecules were performed in silico by DFT calculations. Studied compounds were screened for their antioxidant capacity using in vitro ABTS and DPPH assays. All the investigated compounds showed remarkable antioxidant activity, especially derivative A exhibiting inhibition of free radicals at the IC₅₀ value (ABTS and DPPH assay 0.1 mg ml^-1 and 0.081 mg ml^-1, respectively). Compound A has higher TEAC values implying its stronger antioxidant activity compared to a trolox standard. The applied calculation method and in vitro tests confirmed that compound A has a strong potential against free radicals and may be a novel candidate for application in antioxidant therapy.

Synthesis, spectroscopic findings, SEM/EDX, DFT, and single-crystal structure of Hg/Pb/Cu-SCN complexes: In silico ADME/T profiling and promising antibacterial activities

This work contemplates synthesizing M-SCN crystal compounds (M = Hg/Pb/Cu) in the presence of respective metal salts and exogenous ancillary SCN^- ion by slowly evaporating the mixed solvent (CH₃OH + ACN). The complexes were characterized by spectroscopy, SEM/EDX, and X-ray crystallography. The Hg-Complex, Pb-Complex, and Cu-Complex crystallize in the monoclinic space group (Z = 2/4). The crystal packing fascinatingly consists of weak covalent bonding and Pb⋯S contacts of tetrel type bond. Here are the incredible supramolecular topographies delineated by the Hirshfeld surface and 2D fingerprint plot. The B3LYP/6-311++G (d, p) level calculations in the gas phase optimized the compound's geometry. The energy difference (Δ) between HOMO-LUMO and global reactivity parameters investigates the complex's energetic activity. MESP highlights the electrophilic/nucleophilic sites and H-bonding interactions. Molecular docking was conceded with the Gram- + ve bacterium Bacillus Subtilis (PDB ID: 6UF6) and the Gram-ve bacterium Proteus Vulgaris (PDB ID: 5HXW) to authenticate the bactericidal activity. ADME/T explains the various pharmacological properties. In addition, we studied the antibacterial activity with MIC (μg/mL) values and time-kill kinetics against Staphylococcus aureus (ATCC 25923) and Bacillus subtilis (ATCC 6635) as Gram-positive, Pseudomonas aeruginosa (ATCC 27853) and Escherichia coli (ATCC 25922) as Gram-negative bacteria.

Theoretical study on the radical scavenging activity of gallic acid

The global descriptors of the chemical activity: ionization potential IP, electron affinity EA, chemical potential μ, absolute electronegativity χ, molecular hardness η and softness S, electrophilicity index ω, electro-donating ω^-, electro-accepting ω⁺ powers as well as Ra and Rd indexes for gallic acid (GA) in the gas phase and water medium have been determined. To this aim, the HOMO and LUMO energies were calculated using the DFT method at the B3LYP, M06-2X, LC-ωPBE, BHandLYP, ωB97XD/cc-pVQZ theory levels using C-PCM, IEF-PCM and SMD solvation models, enabling more accurate descriptor calculations than those carried out so far. Quantum-chemical computations were also applied to investigate the GA structure and thermodynamic parameters characterizing its radical scavenging properties. To this aim, the full optimization of the neutral GA and its radical, cationic and anionic forms in vacuum and water medium has been performed, and then the bond dissociation enthalpy BDE, adiabatic ionization potential AIP, proton dissociation enthalpy PDE, proton affinity PA, electron transfer enthalpy ETE, gas phase acidity H_acidity and free Gibbs acidity G_acidity in water have been determined. The calculations revealed that GA in vacuum scavenges free radicals via hydrogen atom transfer (HAT), whereas in water (polar) medium by sequential proton loss electron transfer (SPLET). Analysis of the global activity descriptors of GA indicates that only B3LYP method combined with different solvation models satisfactory reproduces LUMO-HOMO energies and provides the smallest value of the total electron energy of GA. Among the parameters of chemical activity, the indexes Ra and Rd are the most independent of the computational method and the solvation model used. They can be recommended as a reliable source of information on the antioxidant activity of chemical compounds.

Investigation and Comparison of Antioxidant Potential of Catechins Present in Green Tea: DFT Study

DFT calculations were applied to compare the antioxidant potential of four major catechins present in green tea. The thermodynamic parameters related to three key mechanisms of primary antioxidant action were investigated in detail. Molecular orbital energies, absolute hardness, electronegativity, and electrophilicity index, which contributed to the radical scavenging were also investigated. The radical scavenging potential of each hydroxyl group of these polyphenolic antioxidants were investigated independently.

Subcritical water extraction of bioactive phenolic compounds from distillery stillage

Distilleries generate huge amounts of by-products that have a negative impact on the environment, so the management of wastes generated by this sector should be improved. Because distillery by-products are a source of bioactive compounds, the recovery of these compounds not only reduces issues with environmental protection but also provides the basis for a waste-to-profit solution. Following the latest trends in the search for so-called green extraction techniques for recovering valuable products, this study investigated the effect of subcritical water extraction (SWE) conditions (temperature (25-260 °C), time (5-90 min), and solid-to-solvent ratio (1:5-1:50, w:v)) on the efficiency of recovery of bioactive compounds, i.e., polyphenols from distillery stillage, and on the antioxidant activity of the extracts. The highest extraction yield was obtained with 30-min SWE with a solid-to-solvent ratio of 1:15 at either 140 °C (for total polyphenol content and phenolic acid content) or 200 °C (for total flavonoid content), as indicated by the Response Surface Methodology analysis. Phenolic acids in the extracts were present mainly in free forms (up to 88% of the total content). The antioxidant activity, which was measured using several assays, correlated positively with the content of phenolic acids, which confirmed their significant contribution to the bioactive properties of the extracts. The antioxidant effects of the extracts were mostly due to hydroxycinnamic acids (especially ferulic and p-coumaric acids). Principal component analysis showed that the temperature and time of SWE were the factors that can explain the greatest amount of variation in the extraction yield, composition, and bioactive properties of the polyphenols. These results will influence the design of further processes, such as purification and concentration, which are necessary before using the extracted compounds as substrates that are applicable in various industries. Based on the analysis of the elemental composition, the biomass remaining after SWE was evaluated to consider the possibilities of its further utilization.

Antioxidant capacity and interaction of endogenous phenolic compounds from tea seed oil

Endogenous phenols play a significant role in delaying oil rancidity. In this study, the profile of 22 endogenous phenols was determined from tea seed oil by UPLC-MS/MS, of which 15 phenols were identified for the first time. Then seven phenols with high content and strong antioxidant capacity were selected to investigate interaction using the DPPH· and Rancimat. It was found that the interaction of combinations was inconsistent in different media. Combined quercetin + esculetin, caffeoyl tartaric acid + esculetin, caffeoyl tartaric acid + gentisic acid and esculetin + gentisic acid showed synergistic antioxidant effects in oil and ethanol systems. Moreover, through the evaluation of the lipid oxidation process, combined esculetin + gentisic acid exhibited the greatest synergistic antioxidant effect. Notably, combined quercetin + esculetin had an inhibitory effect on the formation of volatile compounds. These findings may provide a basis for explaining the oxidation stability of tea seed oil.

Synthesis of some novel coumarin isoxazol sulfonamide hybrid compounds, 3D-QSAR studies, and antibacterial evaluation

With the progressive and ever-increasing antibacterial resistance pathway, the need for novel antibiotic design becomes critical. Sulfonamides are one of the more effective antibiotics against bacteria. In this work, several novel sulfonamide hybrids including coumarin and isoxazole group were synthesized in five steps starting from coumarin-3-carboxylic acid and 3-amino-5-methyl isoxazole and assayed for antibacterial activity. The samples were obtained in good to high yield and characterized by FT-IR, ¹³C-NMR, ¹H-NMR, CHN and melting point techniques. 3D-QSAR is a fast, easy, cost-effective, and high throughput screening method to predict the effect of the compound's efficacy, which notably decreases the needed price for experimental drug assay. The 3D-QSAR model displayed acceptable predictive and descriptive capability to find r2 and q2 the pMIC of the designed compound. Key descriptors, which robustly depend on antibacterial activity, perhaps were explained by this method. According to this model, among the synthesized sulfonamide hybrids, 9b and 9f had the highest effect on the gram-negative and gram-positive bacteria based on the pMIC. The 3D-QSAR results were confirmed in the experimental assays, demonstrating that our model is useful for developing new antibacterial agents. The work proposes a computationally-driven strategy for designing and discovering new sulfonamide scaffold for bacterial inhibition.

A pH-Triggered Polymer Degradation or Drug Delivery System by Light-Mediated Cis/Trans Isomerization of o-Hydroxy Cinnamates

A new methodology for the pH-triggered degradation of polymers or for the release of drugs under visible light irradiation based on the cyclization of ortho-hydroxy-cinnamates (oHC) to coumarins is described. The key oHC structural motif can be readily incorporated into the rational design of novel photocleavable polymers via click chemistry. This main-chain moiety undergoes a fast photocleavage when irradiated with 455 nm light provided that a suitable base is added. A series of polyethylene glycol-alt-ortho-hydroxy cinnamate (polyethylene glycol (PEG)_n -alt-oHC)-based polymers are synthesized and the time-dependent visible-light initiated cleavage of the photoactive monomer and polymer is investigated in solution by a variety of spectroscopic and chromatographic techniques. The photo-degradation behavior of the water-soluble poly(PEG₂₀₀₀ -alt-oHC) is investigated within a broad pH range (pH = 2.1-11.8), demonstrating fast degradation at pH 11.8, while the stability of the polymer is greatly enhanced at pH 2.1. Moreover, the neat polymer shows long-term stability under daylight conditions, thus allowing its storage without special precautions. In addition, two water-soluble PEG-based drug-carrier molecules (mPEG₂₀₀₀ -oHC-benzhydrol/phenol) are synthesized and used for drug delivery studies, monitoring the process by UV-vis spectroscopy in an ON/OFF intermittent manner.

Quantum Mechanical Predictions of the Antioxidant Capability of Moracin C Isomers

The antioxidant capability of moracin C and iso-moracin C isomers against the OOH free radical was studied by applying density functional theory (DFT) and choosing the M05-2X exchange-correlation functional coupled with the all electron basis set, 6-311++G(d,p), for computations. Different reaction mechanisms [hydrogen atom transfer (HAT), single electron transfer (SET), and radical adduct formation (RAF)] were taken into account when considering water- and lipid-like environments. Rate constants were obtained by applying the conventional transition state theory (TST). The results show that, in water, scavenging activity mainly occurs through a radical addition mechanism for both isomers, while, in the lipid-like environment, the radical addition process is favored for iso-moracin C, while, redox- and non-redox-type reactions can equally occur for moracin C. The values of pKa relative to the deprotonation paths at physiological pH were predicted in aqueous solution.

Recent Developments in Effective Antioxidants: The Structure and Antioxidant Properties

Since the last few years, the growing interest in the use of natural and synthetic antioxidants as functional food ingredients and dietary supplements, is observed. The imbalance between the number of antioxidants and free radicals is the cause of oxidative damages of proteins, lipids, and DNA. The aim of the study was the review of recent developments in antioxidants. One of the crucial issues in food technology, medicine, and biotechnology is the excess free radicals reduction to obtain healthy food. The major problem is receiving more effective antioxidants. The study aimed to analyze the properties of efficient antioxidants and a better understanding of the molecular mechanism of antioxidant processes. Our researches and sparing literature data prove that the ligand antioxidant properties complexed by selected metals may significantly affect the free radical neutralization. According to our preliminary observation, this efficiency is improved mainly by the metals of high ion potential, e.g., Fe(III), Cr(III), Ln(III), Y(III). The complexes of delocalized electronic charge are better antioxidants. Experimental literature results of antioxidant assays, such as diphenylpicrylhydrazyl (DPPH) and ferric reducing activity power assay (FRAP), were compared to thermodynamic parameters obtained with computational methods. The mechanisms of free radicals creation were described based on the experimental literature data. Changes in HOMO energy distribution in phenolic acids with an increasing number of hydroxyl groups were observed. The antioxidant properties of flavonoids are strongly dependent on the hydroxyl group position and the catechol moiety. The number of methoxy groups in the phenolic acid molecules influences antioxidant activity. The use of synchrotron techniques in the antioxidants electronic structure analysis was proposed.

Identification of new biologically active synthetic molecules: comparative experimental and theoretical studies on the structure-antioxidant activity relationship of cyclic 1,3-ketoamides

Antioxidant agent is a chemical that prevents the oxidation of other chemical substances. Its use is the most effective means of protecting the organism by neutralizing the harmful effects of free radicals caused by oxidative stress. In the present work, a series of β-ketoamides containing a variety of monosubstituted amide groups were synthesized and tested as antioxidant agents. In order to establish a possible structure-antioxidant activity relationship, we are presenting a systematic theoretical study of these molecules with the aim of clarifying the active sites. In particular, we discuss the selectivity resulting from the choice of a free radical/antioxidant system. The theoretical study of these molecules was carried out using density functional theory (DFT) calculations at the B3LYP/6-311G (d,p) level of theory. In order to shed light on the antioxidant properties of β-ketoamides, O-H bond dissociation enthalpies (BDEs), ionization potentials (IPs), electron affinities (EAs), proton affinities (PAs), and electron transfer enthalpies (ETEs) are performed in the gas phase and in ethanol. The results obtained show that the HAT mechanism is thermodynamically more favored in the gas phase, while the SPLET is preferred in the polar solvent.

Hydroxylated 3-(pyridin-2-yl)coumarins as radical scavengers with potent lipoxygenase inhibitor activity

Hydroxylated 3-(pyridin-2-yl)coumarins show radical scavenging activity and are able to inhibit soybean lipoxygenase.

New 1H-benzimidazole-2-yl hydrazones with combined antiparasitic and antioxidant activity

Parasitic infections, caused mainly by the species Trichinella spiralis (T. spiralis), are widespread around the world and lead to morbidity and mortality in the population. Meanwhile, some studies have showed that these parasites induce oxidative stress in the infected host. With the aim of developing a class of compounds combining anthelmintic with antioxidant properties, a series of new benzimidazolyl-2-hydrazones 5a-l, bearing hydroxyl- and methoxy-groups, were synthesized. The anthelmintic activity on encapsulated T. spiralis was studied in vitro thus indicating that all hydrazones were more active than the clinically used anthelmintic drugs albendazole and ivermectin. 5b and 5d killed the total parasitic larvae (100% effectiveness) after 24 hours incubation period at 37 °C in both concentrations (50 and 100 μg ml⁻¹). The antioxidant activity of the target compounds was elucidated in vitro against stable free radicals DPPH and ABTS as well as iron induced oxidative damage in model systems containing biologically relevant molecules lecithin and deoxyribose. The two 2,3- and 3,4-dihydroxy hydrazones 5b and 5d were the most effective radical scavengers in all studied systems. DFT calculations were applied to calculate the reaction enthalpies in polar and nonpolar medium and estimate the preferred mechanism of antioxidant activity. The relative radical scavenging ability of compounds 5a-l showed a good correlation to the experimentally observed trends. It was found that the studied compounds are capable to react with various free radicals – ˙OCH₃, ˙OOH and ˙OOCH₃, through several possible reaction pathways – HAT in nonpolar medium, SPLET in polar medium and RAF in both media.

The design of new drug candidates that combine anthelmintic and antioxidant actions in one molecule offers a beneficial approach in the treatment of the tissue damages, immune system dysfunction and oxidative stress caused by trichinellosis.

Computationally designed p-coumaric acid analogs: searching for neuroprotective antioxidants

Newly designed p-coumaric acid derivatives are promising candidates as multifunctional antioxidants with neuroprotective effects.

Antioxidant Potential of Novel Designed Phenolic Derivatives: Computational Insights

Density functional theory calculations were applied for designed phenolic antioxidant derivatives. The reaction enthalpies related to various mechanisms of primary antioxidant action were deliberated in detail. How antioxidant activity of designed phenolic compounds has been perturbed by electron donor and withdrawing substituents present at ortho, meta and para positions, allylic conjugation and the dimerization effect were computed.

Exploration of Chromone-Based Thiosemicarbazone Derivatives: SC-XRD/DFT, Spectral (IR, UV-Vis) Characterization, and Quantum Chemical Analysis

By the condensation of thiosemicarbazide with coumarin aldehyde, two novel substituted thiosemicarbazones with chemical formulae C24H25N3O3S (3a) and C26H23N3O3S (3b) have been synthesized. The synthesized compounds were resolved using SC-XRD, and structure elucidation was carried out using 1H NMR, 13C NMR, UV-visible, and FT-IR spectroscopic analyses. Computational calculations at the B3LYP/6-311+G(d,p) level of theory were performed to countercheck the experimental (UV-vis, FT-IR) findings and explore the electronic (FMO, NBO, MEP) properties of 3a-b. The nonlinear optical (NLO) properties of 3a-b were estimated using B3LYP, HF, LC-BLYP, CAM-B3LYP, M062X, and M06 functionals in combination with the 6-311+G(d,p) basis set. The crystallographic data revealed that compounds were crystallized as an orthorhombic crystal lattice with the Pbcn space group and the triclinic crystal lattice with the P̅1 space group. A good concurrence among experimental SC-XRD-generated bond lengths, bond angles, FT-IR, UV-vis, and corresponding DFT results was found, which confirms the purity of both compounds. The NBO analysis confirmed the presence of intramolecular hydrogen bonding and hyperconjugative interactions, which not only were the pivotal cause of stability of the investigated compounds but also led to an overwhelming NLO response. The energy differences calculated for HOMO/LUMO are 3.053 and 3.118 eV in 3a and 3b, respectively. The crystal 3b showed a higher value of first-order polarizability at all levels of theory than 3a. Overall results show that the crystals under investigation are polarized in nature with a good dipole moment. A comparative analysis with urea molecules clearly indicates that the studied compounds are acceptable NLO candidates and they can be used for future technological applications.

TDDFT study on the photophysical properties of coumarinyl chalcones and sensing mechanism of a derived fluorescent probe for hydrogen sulfide

Coumarin-chalcone hybrids have attracted much attention in recent years due to their important optical properties. Herein, the photophysical properties of a series of coumarinyl chalcones and the sensing mechanism for H₂S of a related fluorescent probe CC-DNP were investigated using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. The predicted spectral properties agree well with the experimental results, which allowed an assignment of the spectra. Our calculations successfully clarified the experimental observed fluorescence "off-on" effect and the fluorescent quenching mechanism of the probe. The results revealed that the first excited state (S₁) of the probe CC-DNP is a dark state with obvious charge transfer from coumarin unit to 2,4-dinitrophenyl (DNP) moiety, which results in the fluorescence quenching via the nonradiative photoinduced electron transfer (PET) process. On the other hand, the excited state S₁ in the thiolysis product CC-OH decayed directly to S₀, and thus the fluorescence is recovered.

Structure-antioxidant activity relationship of methoxy, phenolic hydroxyl, and carboxylic acid groups of phenolic acids

The antioxidant activities of 18 typical phenolic acids were investigated using 2, 2′-diphenyl-1-picrylhydrazyl (DPPH) and ferric ion reducing antioxidant power (FRAP) assays. Five thermodynamic parameters involving hydrogen atom transfer (HAT), single-electron transfer followed by proton transfer (SET-PT), and sequential proton-loss electron transfer (SPLET) mechanisms were calculated using density functional theory with the B3LYP/UB3LYP functional and 6–311++G (d, p) basis set and compared in the phenolic acids. Based on the same substituents on the benzene ring, -CH₂COOH and -CH = CHCOOH can enhance the antioxidant activities of phenolic acids, compared with -COOH. Methoxyl (-OCH₃) and phenolic hydroxyl (-OH) groups can also promote the antioxidant activities of phenolic acids. These results relate to the O-H bond dissociation enthalpy of the phenolic hydroxyl group in phenolic acids and the values of proton affinity and electron transfer enthalpy (ETE) involved in the electron donation ability of functional groups. In addition, we speculated that HAT, SET-PT, and SPLET mechanisms may occur in the DPPH reaction system. Whereas SPLET was the main reaction mechanism in the FRAP system, because, except for 4-hydroxyphenyl acid, the ETE values of the phenolic acids in water were consistent with the experimental results.

Rational approaches, design strategies, structure activity relationship and mechanistic insights for therapeutic coumarin hybrids

Hybrid molecules, furnished by combining two or more pharmacophores is an emerging concept in the field of medicinal chemistry and drug discovery that has attracted substantial traction in the past few years. Naturally occurring scaffolds such as coumarins display a wide spectrum of pharmacological activities including anticancer, antibiotic, antidiabetic and others, by acting on multiple targets. In this view, various coumarin-based hybrids possessing diverse medicinal attributes were synthesized in the last five years by conjugating coumarin moiety with other therapeutic pharmacophores. The current review summarizes the recent development (2014 and onwards) of these pharmacologically active coumarin hybrids and demonstrates rationale behind their design, structure-activity relationships (SAR) and mechanistic studies performed on these hybrid molecules. This review will be beneficial for medicinal chemist and chemical biologist, and in general to the drug discovery community and will facilitate the synthesis and development of novel, potent coumarin hybrid molecules serving as lead molecules for the treatment of complex disorders.

Comparative Study of Antioxidant Potential of Selected Dietary Vitamins; Computational Insights

Density functional theory (DFT) was used to explore the antioxidant properties of some naturally occurring dietary vitamins, and the reaction enthalpies related to various mechanisms of primary antioxidant action, i.e., hydrogen atom transfer, single electron transfer–proton transfer, and sequential proton loss–electron transfer were discussed in detail. B3LYP, M05-2X, and M06-2X functionals were utilized in this work. For aqueous phase studies, the integral equation formalism polarized continuum model (IEF–PCM) was employed. From the outcomes, hydrogen atom transfer (HAT) was the most probable mechanism for the antioxidant action of this class of compounds. Comparison of found results with experimental data (available in literature), vitamin C possesses the lowest enthalpy values for both proton affinity (PA) and bond dissociation energy (BDE)in the aqueous phase, suggesting it as the most promising candidate as an antioxidant. Accordingly, these computational insights encourage the design of structurally novel, simple vitamins which will be more economical and beneficial in the pharmaceutical industry.

Structure-antioxidant capacity relationship of dihydrochalcone compounds in Malus

The antioxidant capacity (AC) of six dihydrochalcone compounds was evaluated using DPPH and ABTS assays. In water-based solution 3-hydroxyphlorizin exhibited the highest AC among all dihydrochalcones. In acetone and acidic solutions (pH = 2.5 or 2.0), presence of an o-dihydroxyl at the B-ring increased AC, whereas glycosylation at the A-ring decreased AC of dihydrochalcones. By comparing the AC of dihydrochalcones with similar structures, it was found that the o-dihydroxyl at the B-ring and 2'-hydroxyl group at the A-ring were critical for maintaining the AC of dihydrochalcones by promoting hydrogen atom transfer or single electron transfer mechanism. Sequential proton-loss electron transfer commonly occurred during free radical scavenging in water-based solution. Moreover, we report a unique phenomenon in which glycosylation at the 2'-position enhanced the dissociation ability of the 4'-hydroxyl group and increased the AC of dihydrochalcones containing o-dihydroxyl. We speculate that this increase in AC might occur through intramolecular electron transfer.

Theoretical insight into the substituent effects on the antioxidant properties of 8-hydroxyquinoline derivatives in gas phase and in polar solvents

The objective of this work is to perform a theoretical analysis of the antioxidant properties of a series of 8-hydroxyquinolines (8-HQs) to rationalize the available experimental results and to design new potent 8-HQ derivatives. The study was carried out in gas phase and in methanol at the DFT/B3LYP/ 6-311++G(d,p) computational level. The formation of stable ArO• radicals is discussed on the basis of different mechanisms, namely, hydrogen atom transfer (HAT), single electron transfer followed by proton transfer (SET-PT), and single proton loss electron transfer (SPLET). The obtained results show that the HAT mechanism is, thermodynamically, more favoured in gas phase, whereas the SPLET pathway is more favoured in polar solvents. The calculated thermochemical descriptors allow classification of the antioxidant power of the studied compounds.

Antioxidant properties and free radical scavenging mechanisms of cyclocurcumin

Cyclocurcumin has a strong ability to scavenge ˙OH by its 4′-OH phenolic hydroxyl via a hydrogen-atom transfer mechanism in a physiological environment.

Atypical antioxidant activity of non-phenolic amino-coumarins

Coumarin compounds have been described as anti-inflammatories, and chemotherapeutic agents as well as antioxidants. However, the origin of the antioxidant activity of non phenolic coumarins remains obscure. In the present report, we demonstrate that non-phenolic 7-dialkyl-aminocoumarins may also have significant antioxidant properties against free radicals derived from 2,2′-azobis(2-amidinopropane) dihydrochloride under aerobic conditions. This atypical behaviour is due to the presence of traces of very reactive hydroxycinnamic acid-type compounds. Changing functional groups at the C-3 and C-4 positions shifts the reactivity of the compounds from peroxyl to alkoxyl free radicals. Kinetic and theoretical studies based on Density Functional Theory support the formation of reactive hydroxycinnamic acid and directly link the antioxidant behaviour of the compounds to hydrogen atom transfer.

Relevant antioxidant properties of non-phenolic 7-dialkyl-aminocoumarins against free radicals derived from 2,2′-azobis(2-amidinopropane) dihydrochloride under aerobic conditions have been experimentally and theoretically demonstrated.

Antioxidative mechanisms in chlorogenic acid

Although chlorogenic acid (5CQA) is an important ingredient of various foods and beverages, mechanisms of its antioxidative action have not been fully clarified. Besides electron spin resonance experiment, this study includes thermodynamic and mechanistic investigations of the hydrogen atom transfer (HAT), radical adduct formation (RAF), sequential proton loss electron transfer (SPLET), and single electron transfer - proton transfer (SET-PT) mechanisms of 5CQA in benzene, ethanol, and water solutions. The calculations were performed using the M06-2X/6-311++G(d,p) level of theory and CPCM solvation model. It was found that SET-PT is not a plausible antioxidative mechanism of 5CQA. RAF pathways are faster, but HAT yields thermodynamically more stable radical products, indicating that in acidic and neutral media 5CQA can take either HAT or RAF pathways. In basic environment (e.g. at physiological pH) SPLET is the likely antioxidative mechanism of 5CQA with extremely high rate.