Methanol Radical Research Articles

Ionic Route to Atmospheric Relevant HO2 and Protonated Formaldehyde from Methanol Cation and O2.

Gas-phase ion chemistry influences atmospheric processes, particularly in the formation of cloud condensation nuclei by producing ionic and neutral species in the upper troposphere-stratosphere region impacted by cosmic rays. This work investigates an exothermic ionic route to the formation of hydroperoxyl radical (HO2) and protonated formaldehyde from methanol radical cation and molecular oxygen. Methanol, a key atmospheric component, contributes to global emissions and participates in various chemical reactions affecting atmospheric composition. The two reactant species are of fundamental interest due to their role in atmospheric photochemical reactions, and HO2 is also notable for its production during lightning events. Our experimental investigations using synchrotron radiation reveal a fast hydrogen transfer from the methyl group of methanol to oxygen, leading to the formation of CH2OH+ and HO2. Computational analysis corroborates the experimental findings, elucidating the reaction dynamics and hydrogen transfer pathway. The rate coefficients are obtained from experimental data and shows that this reaction is fast and governed by capture theory. Our study contributes to a deeper understanding of atmospheric processes and highlights the role of ion-driven reactions in atmospheric chemistry.

Mutual Activation of Two Radical Trapping Agents: Unusual "Win-Win Synergy" of Resveratrol and TEMPO during Scavenging of dpph• Radical in Methanol.

The reaction of the 2,2'-diphenyl-1-picrylhydrazyl radical (dpph•) with resveratrol in methanol (kMeOH = 192 M-1 s-1) is greatly accelerated in the presence of stable nitroxyl radical TEMPO• (kmixMeOH = 1.4 × 103 M-1 s-1). This synergistic effect is surprising because TEMPO• alone reacts with dpph• relatively slowly (kS = 31 M-1 s-1 in methanol and 0.03 M-1 s-1 in nonpolar ethyl acetate). We propose a putative mechanism in which a mutual activation occurs within the acid-base pair TEMPO•/RSV to the resveratrol (RSV) anion and TEMPOH•+ radical cation, both being extremely fast scavengers of the dpph• radical. The fast initial reaction is followed by a much slower but continuous decay of dpph• because a nitroxyl radical is recovered from the TEMPOnium cation, which is reduced directly by RSV/RSV- to TEMPO• or recovered indirectly via a reaction with methanol, producing TEMPOH subsequently oxidized by dpph• to TEMPO•.

Evaluation of solvent effects on the DPPH reactivity for determining the antioxidant activity in oil matrix.

The online version contains supplementary material available at 10.1007/s10068-020-00874-9.

Preparation, Characterization, and Antioxidant Activity of β-Carotene Impregnated Polyurethane Based on Epoxidized Soybean Oil and Malic Acid

A new polyol was synthesized based on epoxidized soybean oil (ESO) and malic acid (MA) for the formulation of a bio-based polyurethane. The synthesized polyol was characterized by Fourier transform-infrared spectroscopy, nuclear magnetic resonance spectroscopy, and mass spectrometry. Polyurethanes were formed by reacting the synthesized ESO-MA polyol with 1,6-hexamethylene diisocyanate at different isocyanate/hydroxyl ratios. The tensile and thermal properties of the prepared polyurethanes were analyzed by differential scanning calorimetry, thermogravimetric analysis, and universal testing machine. The polyurethanes exhibited a tensile strength of 1.34–5.56 MPa, an elongation at break of 20–41%, and a glass transition temperature of − 2.7 to 0.6 °C. In addition, β-carotene, a natural antioxidant, was impregnated on the polyurethane surface and its effect on the tensile and thermal properties of polyurethane was investigated. An increase in tensile strength and a reduction in elongation at break were observed in these β-carotene impregnated polyurethane films. They also showed up to 61% radical scavenging activity against 2,2-diphenyl-1-picryhydrazyl radical in methanol. Moreover, these films retained radical scavenging activity for more than 50 days.

Degradation of Sulfamethoxazole by Electrochemically Activated Persulfate Using Iron Anode

Abstract In this study, sulfamethoxazole (SMX) was removed by electrochemically activated persulfate using iron anode. Different oxidation processes (persulfate alone, Fe2+/persulfate, electrolysis alone, electrochemically/Persulfate) were investigated, the results showed SMX could be more efficiently degraded under the electrochemically/Persulfate system. Central composite design (CCD) based Response surface methodology (RSM) was used to optimize and elucidate the individual and interactive effects of independent variables on the degradation kinetics of sulfamethoxazole. The maximum kinetics was predicted by CCD as pH 3.6, 18 mA applied current and 3.55 mM/L persulfate concentration. The results of free-radical scavenging experiments and electron paramagnetic resonance (EPR) indicated that both {\text{SO}}_4^{ \cdot - } and HO· were responsible for the degradation of SMX. The inhibition of methanol (MeOH) was lower than tertiary butanol (TBA), due to the generation of methanol radical (·CH2OH), which promoted the reduction of Fe3+to Fe2+. LC-ESI-TOF-MS analysis was done on SMX and its intermediates. The SMX degradation pathway during the electrochemical treatment was proposed. In addition, two typical inorganic anions ( {\text{C}}{{\text{l}}^ - },{\text{HCO}}_3^ -) were investigated and the inhibitory effect of {\text{HC}}O_3^ - was more obvious.

Calixapap: Calixarene-based Cluster of Acetaminophen as a Novel Antiradical Agent.

In this paper, the synthesis and free-radical scavenging capacity of novel calix[4]arene-based cluster of paracetamol was reported. The phenolic structures of acetaminophen and calix[4]arene prompted us for designing a synthetic route for calix[4]arene-based cyclic tetramer of paracetamol. The present chalice-shaped cluster is the first example of calixarene/acetaminophen hybrid and paracetamol can be considered as ¼ of the synthetic cyclic tetramer. Free-radical scavenging tests were determined by the 2,2-diphenyl-1-picrylhydrazyl radical in methanol. The results of antiradical-testing showed the enhanced free-radical scavenging capacity (~ 10-fold) for the prepared chaliced-shaped cluster with respect to the corresponding single therapeutic drug unit (acetaminophen). It is maybe attributed to the multivalency, spatial preorganization, and synergistic effect of four impacted drug units in the cluster structure (clustering effect).

Radical-Driven Silicon Surface Passivation by Benzoquinone– and Hydroquinone–Methanol and Photoinitiators

This work confirms that radical intermediates are the reactive species in quinhydrone/methanol (QHY/ME) passivation on silicon surfaces. The two constituent parts, p-benzoquinone (BQ) and hydroquinone (HQ), have been studied separately. BQ abstracts the hydrogen atom from methanol to become semiquinone radicals (QH*). Both QH* and the resulting methanol radical are responsible for the large, instantaneous increase in minority carrier lifetime in BQ/ME, obtaining the lowest surface recombination velocity of 1.6 cm/s. HQ releases a hydrogen atom to become QH*. The quinone derivatives containing a lower electronegativity group (Cl— or O═) on the benzene ring form radicals more easily, and give better passivation results. This radical-driven passivation mechanism is also valid on other radical sources. X-ray photoelectron spectroscopy (XPS) supports the radical mechanism in the observation of dominating BQ bonding after 1 h of BQ/ME treatment, and increasing methanol bonding with increasing immersion time, re...

Tunneling Isomerizations on the Potential Energy Surfaces of Formaldehyde and Methanol Radical Cations

Formaldehyde (H2CO+) and methanol (H3COH+) radical cations, well-known in mass spectrometry, potentially form from radiative ionization or ion–molecule reactions in the interstellar medium. For both ions, other tautomeric forms exist that are accessible via [1,2]hydrogen shifts involving reaction barriers in excess of 25 kcal mol–1. Here, we compute the tunneling rates of the isomerization processes connecting the hydroxymethylene radical cation (HCOH+) to its more stable formaldehyde isomer (H2CO+) and the methanol radical cation (H3COH+) to its methylene oxonium isomer (H2COH2+) using the Wentzel–Kramers–Brillouin method at the CCSD(T)/cc-pVQZ//B3LYP/cc-pVTZ level of theory. While the hydroxymethylene radical cation features a half-life of over 3500 years and thus represents a potentially observable molecule, the methanol radical cation is predicted to decay with a half-life of about 4 days and is thus not likely to be present in appreciable quantities in space. We discuss the potential relevance of the...

Calixtyrosol: a Novel Calixarene Based Potent Radical Scavenger.

The oxidative stress causes many diseases in human, therefore antioxidants have a special position in the medicinal chemistry. Tyrosol is an important antioxidant with a plenty of biological properties. There are many strategies such as clustering single drug units in order to develop new drugs. The cluster effect can increase drug effects relative to single drug unit. Calixtyrosol is the novel cluster of tyrosol that shows a more effective antioxidant activity than single tyrosol. In fact, tyrosol can be considered as 1/4 of the cluster. Four hydroxyethyl moieties have been grafted at the upper rim of the calix[4]arene in all-syn orientation, giving novel agent in the field of antioxidant agents. Free radical scavenging tests were determined by the 2, 2-diphenyl-1-picrylhydrazyl radical in methanol for four antioxidants: calixtyrosol, tyrosol, hydroxytyrosol and 3, 5-di-tert-buty l-4-hydroxytoluene to compare their antioxidant activity. Free radical scavenging test showed that calixtyrosol has enhanced antioxidant activity in comparison to the corresponding single tyrosol unit (> 5 fold), it has even more active than the other test antioxidants (2 fold). Presumably, it is attributed to tethering and arraying of four impacted tyrosol units, which make a synergistic effect in interactions with radicals for creating effective radical scavenging activity. This method is in debt of synergistic effect, tethering and arraying of single units in the cluster structure.

Evaluation of antioxidant activity of homo and copolymer of aniline and p-phenylenediamine electrosynthesized in the presence of calcium chloride

Homo and copolymer of aniline (Ani) and p-phenylenediamine (pPDA) are electrodeposited on the composite graphite (CG) in phosphoric acid (H3PO4) solution which contains calcium chloride (CaCl2) as the supporting electrolyte and different ratios of two monomers. The antioxidant activity is evaluated through the reaction of copolymers with 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical in methanol. The FTIR and UV–visible spectra indicate that the increase of the molar ratio of pPDA in polymer chain has also increased the antioxidant activity of the copolymers. The electrochemical impedance spectroscopy (EIS) is used for further investigation. It was revealed that the increase of the molar ratio of pPDA in polymeric chain decreased the charge transfer resistance (Rct) in the electrochemical content and improved the free radical scavenging activity of copolymers.

Structure and Activity of the Peptidyl-Prolyl Isomerase Domain from the Histone Chaperone Fpr4 toward Histone H3 Proline Isomerization

The FK506-binding protein (FKBP) family of peptidyl-prolyl isomerases (PPIases) is characterized by a common catalytic domain that binds to the inhibitors FK506 and rapamycin. As one of four FKBPs within the yeast Saccharomyces cerevisiae, Fpr4 has been described as a histone chaperone, and is in addition implicated in epigenetic function in part due to its mediation of cis-trans conversion of proline residues within histone tails. To better understand the molecular details of this activity, we have determined the solution structure of the Fpr4 C-terminal PPIase domain by using NMR spectroscopy. This canonical FKBP domain actively increases the rate of isomerization of three decapeptides derived from the N terminus of yeast histone H3, whereas maintaining intrinsic cis and trans populations. Observation of the uncatalyzed and Fpr4-catalyzed isomerization rates at equilibrium demonstrate Pro(16) and Pro(30) of histone H3 as the major proline targets of Fpr4, with little activity shown against Pro(38). This alternate ranking of the three target prolines, as compared with affinity determination or the classical chymotrypsin-based fluorescent assay, reveals the mechanistic importance of substrate residues C-terminal to the peptidyl-prolyl bond.

A new insight into the photocatalytic reduction of 4-nitroaniline to p-phenylenediamine in the presence of alcohols

Photoreduction of 4-nitroaniline to p-phenylenediamine over TiO2, ZnO, PbBi2Nb2O9 and CdS photocatalysts in the presence of CH3OH was investigated under light irradiation (hv≥band gap) upon purging with N2. Compared with PbBi2Nb2O9 and CdS, TiO2 and ZnO showed photocatalytic activities for the photoreduction of 4-nitroaniline. Electron spin resonance analysis results revealed that a methanol radical could be detected in the present of TiO2 and ZnO. Its formation was attributed to the reaction between the hydroxyl radical and CH3OH molecule. The species had strong reductive ability, and therefore could reduce 4-nitroaniline to p-phenylenediamine. Other alcohols (C2H5OH and i-C3H7OH) were also found to be efficient additives for the photoreduction of 4-nitroaniline. The results of the 2H-labeled experiments indicated that the p-phenylenediamine formation was formed by the hydrogen transfer reaction between the 4-nitroaniline and H2O molecules. A mechanism was proposed to explain the photoreduction of 4-nitroaniline to p-phenylenediamine in the present alcohols.

Antioxidant and antiproliferative activities of hydroxyl-substituted Schiff bases

Eight hydroxyl-substituted Schiff bases with the different number and position of hydroxyl group on the two asymmetric aromatic rings (A and B rings) were prepared by the reaction between the corresponding aromatic aldehyde and aniline. Their antioxidant effects against the stable galvinoxyl radical (GO ) in ethyl acetate and methanol, and 2,2′-azobis(2-amidinopropane hydrochloride) (AAPH)-induced DNA strand breakage, and their antiproliferative effects on human hepatoma HepG2 cells, were investigated. Structure–activity relationship analysis demonstrates that o-dihydroxyl groups on the aromatic A ring and 4-hydroxyl group attached to the aromatic B ring contribute critically to the antioxidant and antiproliferative activities.

Comparative studies on the characterization and antioxidant properties of biodegradable alginate films containing ginseng extract

The physical and antioxidant properties of alginate biodegradable film incorporating white, red and extruded white ginseng extracts were investigated. No differences in moisture contents of all alginate film samples were noticeable ( p > 0.05) except those film samples incorporated without ginseng extract, which had the highest moisture content. The addition of ginseng extract to alginate film decreased tensile strength and elastic modulus ( p < 0.05) but increased the percent elongation at break. The presence of extracts did not significantly affect the water vapor permeability of the film samples. Alginate film containing extruded white ginseng extract at a barrel temperature of 130 °C presented the highest (61.12%) free-radical scavenging activity against the 2,2-diphenyl-1-picryhydrazyl radical (DPPH) in methanol, followed by film containing white ginseng extruded at a barrel temperature of 115 °C. Following these samples in terms of free-radical scavenging activity were film samples containing red and white ginseng extracts, respectively. These results revealed that extruded white ginseng extract has good potential to be incorporated into alginate to make antioxidant biodegradable film or coating for various food applications.

The improvement of free-radical scavenging capacity of the phosphate medium electrosynthesized polyaniline

The oxidative polymerization of aniline on composite 2B pencil graphite was accomplished in phosphoric acid (H 3PO 4) containing 0.06 M calcium phosphate (Ca 3(PO 4) 2). The shifting of three pairs of redox peaks by 250 mV to the negative direction has increased antioxidant capacity of polyaniline (PAni). This was realised through reaction with 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical in methanol. The phosphate medium prepared PAni was a strong reducing agent and radical scavenger. Additionally, it was twice more effective than the one prepared in chloride medium.

Kaiware Daikon (Raphanus sativus L.) Extract: A Naturally Multipotent Chemopreventive Agent

Brassica vegetables are attracting major attention as healthy foods because of their content of glucosinolates (GLs) that release the corresponding isothiocyanates (ITCs) upon myrosinase hydrolysis. A number of studies have so far documented the chemopreventive properties of some ITCs. On the other hand, single nutrients detached from the food itself risk being somewhat "reductive", since plants contain several classes of compounds endowed with a polyhedral mechanism of action. Our recent finding that 4-methylthio-3-butenyl isothiocyanate (GRH-ITC) and 4-methylsulfinyl-3-butenyl isothiocyanate (GRE-ITC), released by the GLs purified from Japanese (Kaiware) Daikon (Raphanus sativus L.) seeds and sprouts, had selective cytotoxic/apoptotic activity on three human colon carcinoma cell lines prompted further research on the potential chemopreventive role of a standardized Kaiware Daikon extract (KDE), containing 10.5% w/w GRH and 3.8% w/w GRE, compared to its isolated components. KDE administered in combination with myrosinase at doses corresponding to 50 microM GRH-ITC plus 15 microM GRE-ITC (50 microM KDE-ITC) to three human cancer cell lines (LoVo, HCT-116 and HT-29) significantly reduced cell growth by 94-96% of control in six days (p < 0.05), outperforming pure GRH-ITC or GRE-ITC at the same dose. On the other hand, the same treatment had no significant toxicity on normal human T-lymphocytes. A 50 microM concentration of KDE-ITC had relevant apoptosis induction in all tested cancer cell lines, as confirmed by annexin V assay (e.g., 33% induction in LoVo compared to control, p < 0.05), Bax protein induction (e.g., +20% in HT-29, p < 0.05), and Bcl2 downregulation (e.g.-20% in HT-29, p < 0.05), and induced caspase-1 and PARP-1 activation in all cancer cells as shown by Western blot analysis. Unlike pure GRH or GRH-ITC, KDE also had significant chain-breaking antioxidant activity, retarding the AAPH-initiated autoxidation of methyl linoleate in SDS micelles at concentrations as low as 4.4 ppm (-50% in oxygen consumption rate), as monitored by Clark-type microelectrode oxygen-uptake kinetics, and induced very fast quenching of DPPH. radical in methanol with t(1/2) (s) = (1.47 +/- 0.25) x 10(-2)/[KDE; (g/L)], measured by stopped-flow UV-vis kinetics at 298 K. The potential chemopreventive role of KDE is discussed.

A Novel Oxidative Dimer from Protocatechuic Esters: Contribution to the Total Radical Scavenging Ability of Protocatechuic Esters

A novel oxidative dimer was isolated as a major product from a reaction mixture of methyl protocatechuate and DPPH radical in methanol. Its unusual benzobicyclo[3.2.1]octane structure was elucidated by extensive spectral analysis. This result suggests that the regeneration of catechol structures by the nucleophilic addition of an alcohol molecule on o-quinones and subsequent dimerization is one of the key reactions in the high radical-scavenging activity of protocatechuic esters in an alcoholic solvent.

Antioxidant constituents from the rhizomes of Cibotium barometz

Cibotium barometz J. Smith (Dicksoniaceae), a traditional Asian herbal medicine, was reported to have several biological activities including neuronal regeneration and an anti-inflammatory effect for the bones. Phytochemical screening of this plant revealed the presence of several compounds such as protocatechuic acid, caffeic acid and shinbarometin (2-O-(9Z,12Z-octadecadienoyl)-3-O-[α-D-galactopyranosyl-(1′′→6')-O-β-D-galactopyranosyl]glycerol). Cell damage by reactive oxygen species such as superoxide anion are generally recognized to cause many kinds of disease and promote aging to living organisms. Free radical scavenging activity is regarded as playing an important role in the prevention of various chronic diseases and the aging process. To search for antioxidant constituents from C. barometz, its rhizomes were extracted with 80% methanol and partitioned into five fractions based on their polarity. Fractionations and subfractionations were performed by bioassay-guided isolation, and bioactive compounds were separated from chloroform and n-butanol fractions showing significant antioxidant effect. Evaluation of antioxidant activity was carried out using the 1,1-diphenyl-2-picrylhydrazyl radical in methanol, and L-ascorbic acid and BHA and BHT were used as positive controls in the assay. Structures of the active compounds were elucidated by spectroscopic techniques inclusive of 2D-NMR (HMBC, HSQC), IR, UV and mass spectrometry

Investigating the free radical trapping ability of NXY-059, S-PBN and PBN

The spin trapping ability of the nitrones 2,4-disulphophenyl-N-tert-butyl nitrone (NXY-059), 2-sulphophenyl-N-tert-butyl nitrone (S-PBN) and α-phenyl-N-tert-butyl nitrone (PBN) for both hydroxyl and methanol radicals was investigated using electron paramagnetic resonance (EPR) spectroscopy. The radicals of interest were generated in situ in the spectrometer under constant flow conditions in the presence of each nitrone. The spin adducts formed were detected by EPR spectroscopy. This approach allowed for quantitative comparison of the EPR spectra of the spin adducts of each nitrone. The results obtained showed that NXY-059 trapped a greater number of hydroxyl and methanol radicals than the other two nitrones, under the conditions studied.

Multi-syringe flow injection system for the determination of the scavenging capacity of the diphenylpicrylhydrazyl radical in methanol and ethanolic media

A multi-syringe flow injection system for the determination of 2,2-diphenyl-1-picrylhydrazyl radical (DPPH•) scavenging capacity using methanol or ethanolic solutions as reaction media is presented. A stopped flow approach was implemented in order to monitor the DPPH• consumption using spectrophotometry at 517 nm. The kinetic profile for the first 3 min of reaction was determined for several antioxidant compounds and the number of DPPH• molecules reduced by one molecule of antioxidant was calculated whenever the absorbance value was stable within the period of measurement. For ascorbic acid, trolox, isoeugenol and quercetin in methanol, the values obtained were similar to those reported in the literature. It was possible to perform 14 determinations per hour, consuming 0.34 µmol of DPPH• per determination, which accounts for the application of this system as a screening tool for fast scavenger compounds.