Single Electron Transfer Process Research Articles

Phosphine-catalyzed acyl-transfer of heteroaryl ketones for the construction of N-fused heterocycles

An inexpensive phosphine catalyst was used effectively for a transition-metal-free acyl-transfer of N-containing heteroaryl ketones for the rapid synthesis of N-fused heterocycles. The key pre-aromatic spirocyclic intermediate initialized by the single electron transfer (SET) process of Togni's reagent II promoted by the tertiary phosphine resulted in an intriguing and alternative tactic for the cleavage of C‒C bonds. By using inexpensive tertiary phosphine as the catalyst, this skeleton-reorganizing approach of N-containing heteroaryl ketones allows a streamlined assembly of complex N-fused heterocycles with broad functional group tolerance.

Redox-Neutral Intramolecular Dearomative Spirocyclization of Phenols Induced by Visible Light

Described herein is a redox-neutral intramolecular dearomative spirocyclization induced by visible light. The photochemical cyclization was catalyzed by a phenolate anion-derived photocatalyst and delivered the spirocyclohexadienone. Mechanistic experiments revealed that the aryl halide was reduced to aryl radical via the single-electron transfer (SET) process under visible light irradiation. The electrophilic addition of an aryl radical with the phenolate anion moiety gave a radical anion intermediate, which recycled the photocatalyst by a second SET process.

Novel Organic Superbase Dopants for Ultraefficient N-Doping of Organic Semiconductors.

Doping is a powerful technique for engineering the electrical properties of organic semiconductors (OSCs), yet efficient n-doping of OSCs remains a central challenge. Herein, the discovery of two organic superbase dopants, namely P2-t-Bu and P4-t-Bu as ultra-efficient n-dopants for OSCs is reported. Typical n-type semiconductors such as N2200 and PC61 BM are shown to experience a significant increase of conductivity upon doping by the two dopants. In particular, the optimized electrical conductivity of P2-t-Bu-doped PC61 BM reaches a record-high value of 2.64Scm-1 . The polaron generation efficiency of P2-t-Bu-doped in PC61 BM is found to be over 35%, which is 2-3 times higher than that of benchmark n-dopant N-DMBI. In addition, a deprotonation-initiated, nucleophilic-attack-based n-doping mechanism is proposed for the organic superbases, which involves the deprotonation of OSC molecules, the nucleophilic attack of the resulting carbanions on the OSC's π-bonds, and the subsequent n-doping through single electron transfer process between the anionized and neutral OSCs. This work highlights organic superbases as promising n-dopants for OSCs and opens up opportunities to explore and develop highly efficient n-dopants.

Enhanced Peroxidase-Mimic Catalytic Activity via Cerium Doping of Strontium-Based Metal–Organic Frameworks with Design of a Smartphone-Based Sensor for On-Site Salivary Total Antioxidant Capacity Detection in Lung Cancer Patients

The development of artificial nanozymes with superior catalytic performance and excellent stability has been a long-standing objective for chemists. The total antioxidant capacity (TAC) is one of the most important bioanalytical measures of oxidative stress in the body. The present work aims to develop a smartphone-assisted visual detection sensor using cerium-doped strontium-based metal-organic frameworks (Ce-SrMOFs) as peroxidase-like nanozymes for the rapid, low-cost, on-site detection of TAC. The pristine SrMOF functioned as a peroxidase nanozyme, and its enzymatic activity was enhanced after doping it with Ce(IV) ions because of the multivalent nature and synergistic impact of the heteroatoms. The Ce-SrMOFs were sensitive to the single electron transfer and hydrogen atom transfer processes, which implies that the Ce-SrMOFs can serve as an ideal nanozyme candidate for TAC analysis. The investigated mechanism revealed that •OH is the most active oxygen species for the peroxidase-like activity. The Ce-SrMOFs exhibited a strong affinity for 3,3',5,5'-tetramethylbenzidine (TMB) and H2O2, with Km values of 0.082 and 0.427 mM, which are 5.29- and 8.67-fold lower than those of horseradish peroxidase (HRP), respectively. The Ce-SrMOFs were used for the detection of ascorbic acid, cysteine, and glutathione, with limits of detection of 44, 53, and 512 nM, respectively. The proposed method proved effective in measuring the TAC in saliva samples from lung cancer patients, thereby yielding results with satisfactory precision and accuracy.

Endo/Exo-Controllable Photocyclization by EnT-SET-Switch.

CBZ6, a redox-neutral non-donor-acceptor-type organo-photocatalyst, presents a strong reductive potential with an oxidative potential of -2.16 V (vs SCE). It can work as a photosensitizer for both single-electron transfer and triplet energy transfer processes. This feature enables site-selective control in the intramolecular hydroarylation of acrylamides. Both 5-exo-trig and 6-endo-trig cyclization products could be prepared regiospecfically under mild conditions. No transition metal, halogen-containing reagents, or additional reductant or oxidant is involved. This process provides a concise and environmentally sustainable access to a series of oxindoles and dihydroquinolinones.

Iron-Catalyzed C–C Bond Cleavage of Oximes for Direct Coupling of Benzothiazole in Water

An Fe-catalyzed coupling reaction between oxime ester and benzothiazole is described, which involves C-C bond cleavage of oxime ester via a single-electron transfer process. This iron catalytic system performed in water under mild reaction conditions offers a streamlined strategy to the construction of alkyl nitrile substituted benzothiazole derivatives. Application of this strategy for the synthesis of some key important compounds including 4-heterocyclic-3-arylbutanoic acid is also reported.

NIR-II driven photocatalytic hydrogen peroxide-supply on metallic copper-nickel selenide (Cu-Ni0.85Se) nanoparticle for synergistic therapy

Currently, finite intratumoral H2O2 content has restricted the efficacy of chemodynamic therapy (CDT). Here, Cu-Ni0.85Se@PEG nanoparticles are constructed to display intracellular NIR-II photocatalytic H2O2 supplement. The formation mechanism is explored to discover that H2O2 generation is dominated by photo-excited electrons and dissolved O2 via a typical sequential single-electron transfer process. Both density functional theory calculation and experimental data confirm its metallic feature that endows the great NIR-II absorption and photothermal conversion efficiency (59.6 %, 1064 nm). Furthermore, the photothermal-assisting consecutive interband and intraband transition in metallic catalyst contributes to the high redox capacity and efficient separation/transfer ability of photo-generated charges, boosting H2O2 production under 1064 nm laser irradiation. In addition, Cu-Ni0.85Se@PEG possess mimic peroxidase and catalase activity, leading to in-situ H2O2 activation to produce ∙OH and O2 for the enhanced CDT and hypoxia relief. What’s more, the nanomaterials reveal novel biodegradation that is derived from oxidation from insolvable selenide into soluble selenate, resulting in elimination via feces and urine within 2 weeks. Synergistic CDT and photothermal therapy (PTT) further lead to great tumor inhibition and immune response for anti-tumor. The antitumor mechanism and the potential biological process also are investigated by high-throughput sequencing of expressed transcripts (RNAseq). The great treatment performance is responsible for the regulation of related oxidative stress and stimulus genes to induce organelle (mitochondrial) and membrane dysfunction. Besides, the synergistic therapy also can efficiently evoke immune response to further fight against tumor.

Influence of the 1,2,4-Tri-tert-butylcyclopentadienyl Ligand on the Reactivity of the Uranium Bipyridyl Metallocene [η5-1,2,4-(Me3C)3C5H2]2U(bipy)

The uranium bipyridyl metallocene, [η5-1,2,4-(Me3C)3C5H2]2U(bipy) (2), prepared from [η5-1,2,4-(Me3C)3C5H2]2UCl2 (1) and 2,2′-bipyridine in the presence of potassium graphite (KC8) has been evaluated in small-molecule activation. In contact with AgF, Ph2E2 (E = S, Se), (PhNH)2, (PhCH═N)2, diazenes, pyridine N-oxide, organic azides, diazoalkanes, Ph2CS, and Ph2CO, it behaves as a synthon for the [η5-1,2,4-(Me3C)3C5H2]2U(II) fragment. In contrast, C–C bond coupling occurs when 2 is treated with (CH2)5CO, p-MePhCHO, and p-ClPhCHO to furnish [η5-1,2,4-(Me3C)3C5H2]2U[(bipy){(CH2)5CO}] (19), [η5-1,2,4-(Me3C)3C5H2]2U[(bipy)(p-MePhCHO)] (20), and [η5-1,2,4-(Me3C)3C5H2]2U[(bipy)(p-ClPhCHO)] (21), respectively. Moreover, a single-electron transfer (SET) process ensues after the addition of CuI to 2 to yield the uranium(III) iodide complex [η5-1,2,4-(Me3C)3C5H2]2UI (3). A comparison with the other uranium bipyridyl metallocene derivatives shows that minor variations in the coordinated cyclopentadienyl ligands changes the reactivity of these compounds.

Efficient three-step strategy for reduction recovery of high purity uranium oxide from nuclear wastewater

Resource utilization of uranium from the nuclear wastewater is of significance, and the facile strategy to recover high purity uranium oxide directly from wastewater is urgent to develop. Herein, a three-step uranium oxide reduction recovery process (URRP), that is integrated solid–liquid separation (SLS) and electrochemical purification (EP) together with solid-phase uranium re-recovery (SUR), is designed and applied for uranium reduction and purification. The SEM and ICP results were used to determine the carbonate system as the optimal separation system and the Ti electrode as the optimal electrochemical purification electrode. The single electron transfer process of uranyl ions in carbonate was established using cyclic voltammetry. Such three-step recovery process achieves a high-efficient recovery of uranium with a purity of over 99.9% in complex wastewater systems, and an improved return rate of uranium as high as 98.6%. Furthermore, the concentration of metal ions in wastewater is reduced to the standard set by the World Health Organization. Such a URRP offers a very promising solution for the treatment of wastewater and the recovery of high purity uranium.

Insights on the antiradical capacity and mechanism of phytocannabinoids: H-abstraction and electron transfer processes in physiological media and the influence of the acid-base equilibrium

Phytocannabinoids are natural products primarily isolated from Cannabis sativa that exhibit the typical C21 terpenophenolic skeleton. This class of compounds has been shown to be effective in the treatment of various oxidation-related diseases, which has made their antioxidant properties the focus of increasing interest. In the present contribution, the primary antioxidant properties of eight representative phytocannabinoids have been systematically studied against a variety of biologically significant radical species using the density functional theory (DFT) method. The findings demonstrated that phytocannabinoids, in water at physiological pH, exhibit excellent radical scavenging capacity, mainly exerted by the single electron transfer (SET) process from the deprotonated state. In contrast, phytocannabinoids are moderate radical scavengers in non-polar environment via the formal hydrogen atom transfer (fHAT) process. Among the compounds examined, cannabichromene (CBC) and cannabifuran (CBF) had the greatest free radical scavenging capacity in water, surpassing even common antioxidants like BHT and Trolox. CBF is expected to have potent antiradical action toward peroxyl radicals, alkoxy radicals, and nitrogen dioxide in water at physiological pH. These results provide supporting evidence that phytocannabinoids may be useful in scavenging harmful free radicals in physiological environments.

The Implications of Coupling an Electron Transfer Mediated Oxidation with a Proton Coupled Electron Transfer Reduction in Hybrid Water Electrolysis.

Electrolysis of water is a sustainable route to produce clean hydrogen. Full water-splitting requires a high applied potential, in part because of the pH-dependency of the H2 and O2 evolution reactions (HER and OER), which are proton-coupled electron transfer (PCET) reactions. Therefore, the minimum required potential will not change at different pHs. TEMPO [(2,2,6,6-tetramethyl-1-piperidin-1-yl)oxyl], a stable free-radical that undergoes fast electro-oxidation by a single-electron transfer (ET) process, is pH-independent. Here, we show that the combination of PCET and ET processes enables hydrogen production from water at low cell potentials below the theoretical value for full water-splitting by simple pH adjustment. As a case study, we combined the HER with the oxidation of benzylamine by anodically oxidized TEMPO. The pH-independent electrocatalytic oxidation of TEMPO permits the operation of a hybrid water-splitting cell that shows promise to perform at a low cell potential (≈1 V) and neutral pH conditions.

Degradation of Diethyl Phthalate by HO• and SO4• – in the Aqueous Phase: Mechanisms, Kinetics, and Toxicity

The chemical degradation processes of diethyl phthalate (DEP) induced by HO• and SO4• – in aqueous solution were studied in a theoretical way. Not only radical addition and H-abstraction reactions but also single-electron transfer processes of DEP were considered. The thermodynamic and kinetic results indicate that the more favorable pathways are the H abstraction occurring in aliphatic side chains for all HO•/SO4• –-initiated degradation reactions of DEP. Subsequent reaction mechanisms of crucial primary intermediates were taken into account. At 298 K, the total rate constants for DEP degradation reactions induced by HO• and SO4• – are 2.34 × 109 and 1.24 × 108 M–1 s–1, respectively. They are in accordance with the experimental data. In comparison to SO4• –, HO• has higher reactivity toward DEP in the research temperature range of 273–303 K. Considering the impact on the water eco-environment and human health, DEP and its 10 products have no bioaccumulation potential, but most products are developmentally toxic, except for (Z)-ethyl-2,5-dioxopent-3-enoate. Moreover, (Z)-ethyl-2,5-dioxopent-3-enoate is acutely toxic to fish; phthalic acid is mutagenicity positive; and we should pay more attention to them in the future.

Revisiting the Reaction of IPr with Tritylium: An Alternative Mechanistic Pathway.

Despite a recent proposal on the mechanism of a single-electron transfer (SET) process between tritylium and 2,6-bis(diisopropylphenyl)imidazol-2-ylidene (IPr) based on evidence of transient IPr radical cation intermediate ([IPr]⋅+ ) formation, such oxidation is still contentious because of the high oxidation potential of N-heterocyclic carbenes. Our experimental analysis indicates that the appearance of deep purple color, previously considered to be from transient [IPr]⋅+ , originates from a zwitterionic intermediate (3 a), not a radical cation. Here, we propose an alternative mechanism for the reaction involving tritylium and IPr. This mechanism is noteworthy for explaining how [NHC-H]+ can be generated without the formation of transient [NHC]⋅+ , which has been frequently proposed as an intermediate for the reaction between NHC and oxidants. These results also show that a transient strong single-electron donor (3 a) could be generated by the alternative mechanism for oxidants using NHCs, which is a more feasible explanation for the reactivity of NHCs with oxidants.

Visible-light driven acetoxylation and dioxygenation of indoles via electron donor-acceptor complexes.

A photoresponsive electron donor-acceptor (EDA) complex, formed by indole and hypervalent iodine such as diacetoxyiodobenzene (DAIB/PIDA, etc.), was detectable through absorption and emission spectroscopy. Irradiation of the EDA complex with visible light triggered photoinduced single electron transfer (SET) processes that were synthetically useful for the catalyst-free, regioselective acetylation of indoles. The photocatalytic reaction with excess DAIB was also used for the synthesis of isatins. The synthetic protocols were tolerant of a wide variety of substituents on the indole ring, including N-substitutions. DFT and TD-DFT studies were performed to model the excited states of the EDA complex and validate the photoinduced SET mechanism.

Photoinduced copper-catalyzed selective three-component 1,2-amino oxygenation of 1,3-dienes.

This study presents a highly effective method for the photoinduced copper-catalyzed 1,2-amino oxygenation of 1,3-dienes. This synthetic strategy involves the dual roles of a single copper catalyst, which can act as a photosensitizer to generate nitrogen radicals and can also react with allyl radicals via single electron transfer (SET) processes. The method produces a range of quaternary carbon-centered allyl carboxylic esters and tertiary ethers with high yields and excellent regioselectivity under mild reaction conditions.

Combined molecular dynamics and coordinate driving method for automatically searching complicated reaction pathways.

The combined molecular dynamics and coordinate driving (MD/CD) method is updated and generalized in this work to broaden its applications in automatically searching reaction pathways for complicated reactions. In this updated version, MD simulations are performed with the GFN's family of methods to systematically sample conformers for almost any systems with atomic numbers Z ≤ 86. The improved CD procedure is greatly accelerated by applying a pre-screening stage at the semiempirical GFN2-xTB level. An automatic module based on the Marcus theory and its improved version (the Wolynes theory) is designed to include single electron transfer (SET) processes into reaction pathways. The capabilities of this method are demonstrated by exploring the most possible reaction pathways of three experimentally reported reactions: the organophosphine-catalyzed trans phosphinoboration, the Fe(II) complex-mediated C(sp2)-H borylation reaction, and the SET-triggered deaminative radical cross-coupling reaction. Comprehensive reaction networks are obtained for all three reactions with reasonable computational costs. Detailed mechanisms for these reactions can account for the reported experimental facts.

Transition-metal-mediated benzylation of C60 with benzyl chlorides.

Benzyl bromides have been widely used for fullerene functionalization. However, the use of benzyl chlorides, a more affordable but less reactive counterpart of benzyl bromides, has been rarely reported. Herein, a new metal-mediated benzylation of C60 with benzyl chlorides is presented. In this method, with the combinatorial use of Mn powder and Cu(OAc)2, various benzyl chloride derivatives could react with C60 to afford 1,4-dibenzylated products in 12-53% yields. A mechanistic study by in situ visible near infrared (vis-NIR) spectroscopy and various control experiments suggests that, unlike the conventional anionic pathway that uses benzyl bromides, the transition-metal-mediated benzylation of C60 with benzyl chlorides proceeds via a metal-mediated iterative single electron transfer process.

Synthesis of C2-Carbonyl Indoles via Visible Light-Induced Oxidative Cleavage of an Aminomethylene Group.

A strategy for photochemical oxidative cleavage of the aminomethylene group at the C2 position of indole was developed to synthesize C2-carbonyl indoles. The reaction was initiated by the photochemical oxidation of N1, followed by a water-assisted concerted H-shift by abstracting hydrogen from aminomethylene. Bromopyridine was discovered to play dual roles as an oxidant for the regeneration of photocatalysts and as an accelerant for the single-electron transfer process.

Comprehensive Characterization of Chemical Composition and Antioxidant Activity of Lignan-Rich Coniferous Knotwood Extractives.

A knotwood of coniferous trees containing large amounts of polyphenolic extractives is considered a promising industrial-scale source of lignans possessing antioxidant properties and other bioactivities. The present study is aimed at a detailed characterization of the chemical composition and antioxidant activity of lignan-rich extractives obtained from the knotwood of the Norway spruce, Scotch pine, Siberian fir, and Siberian larch growing in the European North of Russia as a region with a highly developed forest industry. To achieve this, a comprehensive approach based on a combination of two-dimensional NMR spectroscopy with high-performance liquid chromatography-high-resolution Orbitrap mass spectrometry, and the determination of antioxidant activity by the three complementary methods were proposed. The studied knotwood samples contained from 3.9 to 17% of extractive substances and were comparable to Trolox's antioxidant activity in the single-electron transfer processes and superoxide radical scavenging, which is associated with the predominance of polyphenolic compounds. The latter was represented by 12 tentatively identified monolignans and 27 oligolignans containing 3-5 phenylpropane units in their structure. The extracts were characterized by an identical set of lignans and differed only in the ratios of their individual compounds. Other components of the knotwood were flavonoids taxifolin, quercetin (Siberian larch), and three stilbenes (pinosylvin, its methyl ester, and pterostilbene), which were identified in the Scotch pine extractives. Sesquiterpene juvabione and its derivatives were found in extracts of Siberian larch knotwood.

Site-Selective Pyridine C-H Alkylation with Alcohols and Thiols via Single-Electron Transfer of Frustrated Lewis Pairs.

A unified strategy for the deoxygenative or desulfurative pyridylation of various alcohols and thiols has been developed through a single-electron transfer (SET) process of frustrated Lewis pairs (FLPs) derived from pyridinium salts and PtBu3 . Mechanistic studies revealed that N-amidopyridinium salts serve as effective Lewis acids for the formation of FLPs with PtBu3 , and the generated phosphine radical cation ionically couples with the in situ generated xanthate, eventually affording the alkyl radical through facile β-scission under photocatalyst-free conditions. The reaction efficiency was further accelerated by visible-light irradiation. This method is conceptually appealing by using encounter complexes in FLP chemistry to promote SET, which provides a previously unrecognized opportunity for the selective heteroarylation of a diverse range of alcohols and thiols with various functional groups, even in complex settings under mild reaction conditions.