Single Electron Transfer Mechanism Research Articles

Why Does Monoamine Oxidase (MAO) Catalyze the Oxidation of Some Tetrahydropyridines?

Results pertaining to the mechanism of the oxidation of the tertiary amine 1-methyl-4-(1-methyl-1-H-pyrrol-2-yl)-1,2,3,6-tetrahydropyridine (MMTP, a close analog of the Parkinsonism inducing compound MPTP) by 3-methyllumiflavin (3MLF), a chemical model for the FAD cofactor of monoamine oxidase, are reported. MMTP and related compounds are among the few tertiary amines that are monoamine oxidase B (MAO-B) substrates. The MMTP/3MLF reaction is catalytic in the presence of O2 and the results under anaerobic conditions strongly suggest the involvement of radical intermediates, consistent with a single electron transfer mechanism. These observations support a new hypothesis to explain the MAO-catalyzed oxidations of amines. In general, electron transfer is thermodynamically unfavorable, and as a result, most 1° and 2° amines react via one of the currently accepted polar pathways. Steric constraints prevent 3° amines from reacting via a polar pathway. Those select 3° amines that are MAO substrates possess certain structural features (e. g., a C-H bond that is α- both to nitrogen and a C=C) that dramatically lower the pKa of the corresponding radical cation. Consequently, the thermodynamically unfavorable electron transfer equilibrium is driven towards products by an extremely favorable deprotonation step in the context of Le Chatelier's principle.

N‐Bu4NI/K2S2O8‐Mediated C–N Coupling between Aldehydes and Amides

n‐Bu4NI/K2S2O8‐mediated C‐N coupling between aldehydes and amides is reported. A strong electronic effect is observed on the aromatic aldehyde substrates. The transformylation from aldehyde to amide takes place exclusively when an aromatic aldehyde bears electron‐donating groups at either the ortho or para position of the formyl group, while the cross‐dehydrogenative coupling dominates in the absence of these groups. Both the density functional theory (DFT) thermochemistry calculations and experimental data support the proposed single electron transfer mechanism with the formation of an acyl radical intermediate in the cross‐dehydrogenative coupling. The n‐Bu4NI/K2S2O8 mediated oxidative cyclization between 2‐aminobenzamide and aldehydes is also reported, with four quinazolin‐4(3H)‐ones prepared in 65‐99% yields.

Primary Antioxidant Power and Mpro SARS-CoV-2 Non-Covalent Inhibition Capabilities of Miquelianin.

The antioxidant power of quercetin-3-O-glucuronide (miquelianin) has been studied, at the density functional level of theory, in both lipid-like and aqueous environments. In the aqueous phase, the computed pKa equilibria allowed the identification of the neutral and charged species present in solution that can react with the ⋅OOH radical. The Hydrogen Atom Transfer (HAT), Single Electron Transfer (SET) and Radical Adduct Formation (RAF) mechanisms were considered, and the individual, total and fraction corrected rate constants were obtained. Potential non-covalent inhibition of Mpro from SARS-CoV-2 by miquelianin has been also evaluated.

Sustainable cycling and mechanism of Co(II)/Co(IV)/Co(III) with S(IV) highly triggered by Co(IV) in E/Co(II)/S(IV) for enhanced removal of reactive brilliant red X-3B

The massive discharge and inadequate treatment of dye wastewater have led to the extensive accumulation of azo dyes in natural water bodies, which is a severe threat to human health. In this study, a novel homogeneous electrochemical system, denoted E/Co(II)/S(IV), was developed by the incorporation of an electric field and cobalt/sulfite. Notably, the decontamination efficiency of the E/Co(II)/S(IV) system for reactive brilliant red X-3B (X-3B) was 95.14 % within 10 min, which was accomplished by utilizing only a trace amount of Co(II). The entire process exhibited an exceptionally low energy consumption of only 0.331 kWh/m3. Single-factor experiments were conducted to explore the influence of various operational parameters and water matrix components on the system decontamination efficiency. By combining the chelator EDTA and chemical probe PMSO, the presence of Co(III) and Co(IV) was detected. The results showed that Co(IV) mainly triggered the chain reaction. The activation products of S(IV), including SO3•−, SO4•−, SO5•− and HO∙, played a dominant role in the degradation of X-3B, with SO4•− having the most substantial contribution. Under anodic oxidation, Co(II) underwent double-electron transfer, leading to the conversion of Co(II) into Co(IV). Subsequently, Co(IV) activated S(IV) via a single-electron transfer mechanism, initiating a free radical chain reaction. During the reaction, Co(IV) transformed into Co(III) and Co(II), thus achieving the Co(II)/Co(IV)/Co(III) cycle. The generation of oxygen as a result of the electrochemical process offers a viable solution for addressing the issue of hypoxia stemming from the rapid activation of S(IV). The active sites in the X-3B molecule were elucidated through density functional theory predictions, and three degradation pathways for X-3B were identified via mass spectrometry analysis. The toxicological characteristics of both X-3B and its degradation products were comprehensively assessed using toxicity estimation software tool and algal culture experiments. This research offers valuable insights into the refinement of cobalt/sulfite systems and introduces innovative concepts for electrochemical applications, which have broad-reaching implications for dye wastewater purification.

Optimization, Metabolomic Analysis, Antioxidant Potential andDepigmenting Activity of Polyphenolic Compounds fromUnmature Ajwa Date Seeds (Phoenix dactylifera L.) Using Ultrasonic-Assisted Extraction.

This study sought to optimize the ultrasonic-assisted extraction of polyphenolic compounds from unmature Ajwa date seeds (UMS), conduct untargeted metabolite identification and assess antioxidant and depigmenting activities. Response surface methodology (RSM) utilizing the Box-Behnken design (BBD) and artificial neural network (ANN) modeling was applied to optimize extraction conditions, including the ethanol concentration, extraction temperature and time. The determined optimal conditions comprised the ethanol concentration (62.00%), extraction time (29.00 min), and extraction temperature (50 °C). Under these conditions, UMS exhibited total phenolic content (TPC) and total flavonoid content (TFC) values of 77.52 ± 1.55 mgGAE/g and 58.85 ± 1.12 mgCE/g, respectively, with low relative standard deviation (RSD%) and relative standard error (RSE%). High-resolution mass spectrometry analysis unveiled the presence of 104 secondary metabolites in UMS, encompassing phenols, flavonoids, sesquiterpenoids, lignans and fatty acids. Furthermore, UMS demonstrated robust antioxidant activities in various cell-free antioxidant assays, implicating engagement in both hydrogen atom transfer and single electron transfer mechanisms. Additionally, UMS effectively mitigated tert-butyl hydroperoxide (t-BHP)-induced cellular reactive oxygen species (ROS) generation in a concentration-dependent manner. Crucially, UMS showcased the ability to activate mitogen-activated protein kinases (MAPKs) and suppress key proteins including tyrosinase (Tyr), tyrosinase-related protein-1 and -2 (Trp-1 and -2) and microphthalmia-associated transcription factor (MITF), which associated melanin production in MNT-1 cell. In summary, this study not only optimized the extraction process for polyphenolic compounds from UMS but also elucidated its diverse secondary metabolite profile. The observed antioxidant and depigmenting activities underscore the promising applications of UMS in skincare formulations and pharmaceutical developments.

A density functional study of the photocatalytic degradation of polycaprolactone by the decatungstate anion in acetonitrile solution.

A recent experimental study has reported that decatungstate [W10O32]4- can degrade various polyesters in the presence of light and molecular oxygen [Li et al., Nanoscale, 2023, 15, 15038]. We apply density functional theory to the photocatalyst-polycaprolactone model complex in acetonitrile solution and elucidate the degradation mechanisms and catalytic cycle. We consider hydrogen atom transfer (HAT) and single electron transfer (SET) mechanisms. The potential energy profiles show that the former proceeds exergonically in a single step but that the latter involves a subsequent proton transfer and finally yields HAT products as well. Oxygenated polymer species can regain the transferred hydrogen and regenerate the reduced photocatalyst. We propose a photocatalytic cycle that realizes both the photocatalyst regeneration and the polymer degradation.

Cobalt(II)-catalyzed peri-C(sp2)-H selective hydroxylation of naphthalene monoimides.

Reported herein is an efficient and eco-friendly peri-selective monohydroxylation of naphthalene monoimides (NMIs) to access 4-hydroxy NMIs, which possess multidisciplinary applications. The key aspect of this method is the utilization of cobalt(II)-catalysis via a single electron transfer mechanism to achieve site-selective C(sp2)-hydroxylation. Transformation of the hydroxyl group into pseudohalides reveals its applications towards cross-coupling reactions.

Chemical Mechanism of Fireworm Bioluminescence - A Theoretical Proposition.

Odontosyllis undecimdonta is a marine worm, commonly known as a fireworm, that exhibits bluish-green bioluminescence (BL). The luciferin (L) and oxyluciferin (OL) during fireworm BL have been experimentally identified in vitro. The L and OL are the respective starting point and ending point of a series of complicated chemical reactions in the BL. However, the chemical mechanism of the fireworm BL remains largely unknown. Before the experiments provided strong evidence for the mechanism, based on our previously successful studies on several bioluminescent systems, we theoretically proposed the chemical mechanism of the fireworm BL in this article. By means of the spin-flip and time-dependent density functional calculations, we clearly described the complete process from L to OL: under the catalysis of luciferase, L undergoes deprotonation and reacts with 3O2 to form a dioxetanone anion via the single-electron transfer mechanism; the dioxetanone anion decomposes into the OL at the first singlet excited state (S1) by the gradually reversible charge-transfer-induced luminescence mechanism; and the S1-OL emits light and deexcites to OL in the ground state.

Electrophilicity, mechanism and structure–reactivity relationships of cyclic secondary amines addition to 2-methoxy-3,5-dinitropyridine

The second-order rate constants (k) for the nucleophilic aromatic substitution reactions of 2‑methoxy-3,5-dinitropyridine 1 with secondary cyclic amines 2a-c in acetonitrile solution at 20 °C are reported. The logarithms of these rate constants are particularly significant as possible measures of the electrophilicity parameters E for 2‑methoxy-3,5-dinitropyridine 1 according to the linear free energy relationship log k (20 °C) = sN(N + E). Additional kinetic data for reactions of 2-methoxy-3,5-dinitropyridine 1 with a series of nitroalkyl anions in DMSO solution are also measured and found to agree with those calculated by Mayr's approach from the known two solvent-dependent parameters N and sN of nitroalkyl anions and the electrophilicity parameter E measured in this work. A Single Electron Transfer (SET) mechanism is proposed for the SNAr reactions, on the basis of the linear Brönsted plot with the βnuc value of 0.94. The validity of this mechanism is confirmed by the agreement between the rate constants, k, and the oxidation potentials E° of these series of secondary cyclic amines. Also, reactivity descriptors such as the electronic chemical potential (μ), and the chemical hardness (η) for a series of pyridine derivatives were calculated by Density Functional Theory (DFT), and it is shown that the global electrophilicity index (ω = μ2/2η) is significantly correlated with the electrophilicity parameters E.

Selective Defluoroalkylation and Hydrodefluorination of Trifluoromethyl Groups Photocatalyzed by Dihydroacridine Derivatives.

The selective functionalization of trifluoromethyl groups through C-F cleavage poses a significant challenge due to the high bond energy of the C(sp3)-F bonds. Herein, we present dihydroacridine derivatives as photocatalysts that can functionalize the C-F bond of trifluoromethyl groups with various alkenes under mild conditions. Mechanistic studies and DFT calculations revealed that upon irradiation, the dihydroacridine derivatives exhibit high reducibility and function as photocatalysts for reductive defluorination. This process involves a sequential single-electron transfer mechanism. This research provides valuable insights into the properties of dihydroacridine derivatives as photocatalysts, highlighting the importance of maintaining a planar conformation and a large conjugated system for optimal catalytic activity. These findings facilitate the efficient catalytic reduction of inert chemical bonds.

Electrochemically driven aerobic oxygenation of alkylarenes to carbonyl compounds

In this article, electrochemical aerobic oxidation method is developed that methylarenes and benzyl methylenes can be efficiently converted into the corresponding aryl aldehydes and aryl ketones using O2 as the oxygen source without any base or transition-metal catalyst. And multigram scale of aryl aldehyde and aryl ketone are also synthesized using inexpensive nickel foam as the electrode to demonstrate the practicality of this electrochemical oxidation strategy. In addition, the pharmaceutical molecule Fenbufen is facilely synthesized, implying the potential applications in pharmaceutical synthesis of this protocol. Furthermore, the control experiments suggest that the aerobic oxidation reaction undergoes a single-electron transfer (SET) mechanism.

Inner‐Sphere Single Electron Transfer in Polynuclear Gold Photocatalysis

AbstractPhoto‐induced electron transfer is a fundamental step in photochemical reactions, where light energy is used to drive chemical transformations. However, conventional outer‐sphere single electron transfer mechanisms encounter multiple limitations, notably requiring redox potential matching between photocatalysts and substrates, thereby impeding the activation of non‐activated carbon‐halogen bonds. In this concept review, we present an elucidation of the photophysical and photochemical properties exhibited by polynuclear gold photocatalysts, with a particular emphasis on their inner‐sphere single electron transfer mechanism. By exploring these intricate aspects, we endeavor to furnish readers with a more profound insight into the remarkable potential of polynuclear gold photocatalysts and the indispensable role played by inner‐sphere electron transfer in the realm of photocatalysis.

Photocatalytic breaking of C-C bonds in lignin models by combining N-doped carbon nitride and persulfate in micellar aqueous medium

Photocatalysis is thought to be a promising way to obtain aromatic compounds by depolymerizing lignin. However, the development of heterogeneous photocatalysts with high catalytic activity still faces many challenges for the high-value utilization of lignin under mild reaction conditions. Herein, N-doped graphitic carbon nitride (CN) is obtained by using dimethylformamide as a modifier. The conduction band potential of photocatalyst 15DCN (15 mL of dimethylformamide as a modifier) with optimal catalytic performance is reduced to − 1.11 eV, which has a stronger reducing ability than CN. Importantly, it can efficiently reduce potassium persulfate (KS) to produce sulfate radicals. By combining 15DCN and KS, the C-C bonds in typical β-1 lignin models are efficiently broken into benzaldehyde and benzoic acid. In addition, the enhanced photogenerated electron-hole pairs separation ability and sunlight capture ability also contribute to the high photocatalytic activity. Mechanistic studies revealed that sulfate radicals, superoxide radicals and hydroxyl radicals were generated and triggered C-C bonds breaking. Isotope experiments illustrate that water promotes the photocatalytic reaction and provides the H and O atoms required for C-C bonds cleavage, which is a critical factor for obtaining high photocatalytic efficiency. The photocatalytic reaction mainly follows the single-electron transfer mechanism and the improved Cβ radical mechanism. This study provides a new photocatalytic strategy for breaking C-C bonds using water as a solvent under mild conditions.

Photocatalytic lignin C-C bonds cleavage in lignin models via Fe-doped graphene carbon nitride in micellar aqueous medium

Photocatalytic depolymerization of lignin to prepare value-added chemicals by breaking lignin Cα-Cβ bonds (LCCD) is sustainable because of its green and mild reaction conditions. However, photocatalytic cleavage of LCCD still faces great challenges because of the complexity and stubbornness of lignin structure. Here, Fe-doped graphene carbon nitride (g-C3N4) photocatalysts were successfully prepared. The doping of Fe ions reduces the band gap of g-C3N4 and accelerates the migration ability of photogenerated carriers. 8FeCN can efficiently break LCCD in β-1 lignin model compounds and ethanol organosolv lignin, producing aromatic aldehydes, alcohol and acids as the main products. Hydroxyl radicals are generated through Fe-induced Fenton reactions, which increase the reaction pathway for breaking LCCD. The mechanism studies showed that photocatalytic cleavage of LCCD mainly followed the improved Cβ radical and single electron transfer mechanism. In addition, micellar aqueous media further accelerates the cleavage of LCCD, as water participates in the photocatalytic reaction and provided the O and H atoms needed for the formation of photocatalytic products. This work offers a fresh concept for the high-value utilization of lignin by oxidizing cleavage of LCCD.

Evaluation of Phytochemical Properties and Antioxidant Activity of Methanol Extract of Ziziphus Spina-Christi, Satureja Khuzistanica, and Salvia Rosmarinus Using FT-IR Method

Introduction: Medicinal plants have shown special application in the pharmaceutical and food industries. Chemical analysis and determination of medicinal compounds of medicinal plants attract great attention throughout the world. The present study was designed to evaluate the phytochemical properties and antioxidant activity of methanol extract of three species of aromatic plants by FTIR method. Methods: Three species of aromatic plants including Konar (Ziziphus spina-christi), rosemary (Salvia rosmarinus), and Marzeh khuzestani (Satureja khuzistanica) were prepared and studied from the cities of Dehlran and Ilam locating in the west of Iran. These medicinal plants were dried and then powdered. The active groups of the medicinal plants were identified by the FT-IR method. Total antioxidant capacity was measured based on divalent iron reducing ability (FRAP) and by a single electron transfer mechanism. Results: The FT-IR results displayed that Z. spina-christi surrounds 11 functional groups, rosemary has 13 functional groups, and Khuzestani pepper contains 12 functional groups. The antioxidant potential of the methanolic extract of Z. spina-christi was 7 mmol Fe2+/L, rosemary was 1.93 mmol Fe2+/L, and Marzeh khuzestani was 12.99 mmol Fe2+/L. Conclusion: Ziziphus spina-christi, Salvia rosmarinus, and Satureja Khuzestani have strong antioxidant properties due to their chemical compounds and can be used for medicinal purposes.

Three-component reaction of tert-butyl nitrite with indoles and halides: A facile and efficient synthesis of oxime ether derivatives

A mild and efficient one-pot method has been developed for the synthesis of oxime ether derivatives with up to 85% yield by employing tert-butyl nitrite (TBN) as nitrogen source, which occurs under room temperature and exhibits wide substrate scope. The single electron transfer mechanism and the cascade reactions approach have been confirmed.

Rational Design of Multifunctional Ferulic Acid Derivatives Aimed for Alzheimer's and Parkinson's Diseases.

Ferulic acid has numerous beneficial effects on human health, which are frequently attributed to its antioxidant behavior. In this report, many of them are reviewed, and 185 new ferulic acid derivatives are computationally designed using the CADMA-Chem protocol. Consequently, their chemical space was sampled and evaluated. To that purpose, selection and elimination scores were used, which are built from a set of descriptors accounting for ADME properties, toxicity, and synthetic accessibility. After the first screening, 12 derivatives were selected and further investigated. Their potential role as antioxidants was predicted from reactivity indexes directly related to the formal hydrogen atom transfer and the single electron transfer mechanisms. The best performing molecules were identified by comparisons with the parent molecule and two references: Trolox and α-tocopherol. Their potential as polygenic neuroprotectors was investigated through the interactions with enzymes directly related to the etiologies of Parkinson's and Alzheimer's diseases. These enzymes are acetylcholinesterase, catechol-O-methyltransferase, and monoamine oxidase B. Based on the obtained results, the most promising candidates (FA-26, FA-118, and FA-138) are proposed as multifunctional antioxidants with potential neuroprotective effects. The findings derived from this investigation are encouraging and might promote further investigations on these molecules.

Ru(bpy)3 2+ -Enabled Cell-Surface Photocatalytic Proximity Labeling toward More Efficient Capture of Physically Interacting Cells.

Intercellular proximity labeling has emerged as a promising approach to enable the study of cell-cell interactions (CCIs), but the efficiency of current platforms is limited. Here, we use Ru(bpy)3 2+ to construct an efficient photocatalytic proximity labeling (PPL) system on the cell surface that allows the highly discriminative CCI detection with spatiotemporal resolution. Through the mechanism study and quantitative characterization on living cells, we demonstrate that the singlet-oxygen (1 O2 ) mechanism is more efficient and specific than the single electron transfer (SET) mechanism in Ru-mediated PPL. Ru(bpy)3 2+ catalysts with different cell-anchoring moieties are prepared to facilitate the catalyst loading on primary cells. Finally, based on this system, we develop a "live" T cell receptor (TCR) multimer with TCR-T cells that could sensitively identify and discriminate cells presenting antigens of different affinity, providing a powerful tool to better understand the heterogeneity of antigen presenting cells.

Ru(bpy)32+‐Enabled Cell‐Surface Photocatalytic Proximity Labeling toward More Efficient Capture of Physically Interacting Cells

AbstractIntercellular proximity labeling has emerged as a promising approach to enable the study of cell‐cell interactions (CCIs), but the efficiency of current platforms is limited. Here, we use Ru(bpy)32+ to construct an efficient photocatalytic proximity labeling (PPL) system on the cell surface that allows the highly discriminative CCI detection with spatiotemporal resolution. Through the mechanism study and quantitative characterization on living cells, we demonstrate that the singlet‐oxygen (1O2) mechanism is more efficient and specific than the single electron transfer (SET) mechanism in Ru‐mediated PPL. Ru(bpy)32+ catalysts with different cell‐anchoring moieties are prepared to facilitate the catalyst loading on primary cells. Finally, based on this system, we develop a “live” T cell receptor (TCR) multimer with TCR‐T cells that could sensitively identify and discriminate cells presenting antigens of different affinity, providing a powerful tool to better understand the heterogeneity of antigen presenting cells.

Assessing radical scavenging capacity of Sempervivum tectorum L. leaf extracts: An integrated high-performance thin-layer chromatography/in silico/chemometrics approach

High-Performance Thin-Layer Chromatography (HPTLC)-radical scavenging capacity (RSC) assays are standard techniques for the separation and identification of antioxidants from complex mixtures. HPTLC coupled with DPPH· visualization of chromatograms allows for the detection of individual antioxidants. However, other HPTLC-RSC assays that recognize compounds exhibiting different mechanisms of radical-scavenging activity are rarely reported. In this study, we developed an integrated approach that combines five HPTLC-RSC assays, principal component analysis (PCA) and quantum chemical calculations to assess the antioxidant capacity of Sempervivum tectorum L. leaf extracts. Two HPTLC assays - potassium hexacyanoferrate(III) total reducing power assay (TRP) and total antioxidant capacity by phosphomolybdenum method (TAC) - were developed for the first time. The method supports a more in-depth study of the RSC of natural products, as it compares the radical scavenging fingerprints of S. tectorum leaf extracts and recognizes differences in their individual bioactive constituents. Kaempferol, kaempferol 3-O-glucoside, quercetin 3-O-glucoside, caffeic acid, and gallic acid were identified as the compounds that discriminate HPTLC-RSC assays according to their mechanism of action and capture the similarities between 20 S. tectorum samples. Additionally, DFT calculations on M06–2X/6–31+G(d,p) level were applied to map thermodynamic feasibility of hydrogen atom transfer (HAT) and single electron transfer (SET) mechanisms of the identified compounds. Based on experimental and theoretical results, a combination of HPTLC-ABTS and HPTLC-TAC assays were proposed as the optimal method for mapping the antioxidants from S. tectorum. This study represents a step forward in identifying and quantifying individual antioxidants from complex food and natural product matrices in a more rational manner.