Electron Transfer Strategy Research Articles

Radical-mediated [3 + 2 + 1] annulation of α-polyfluoromethyl alkenes with arylisocyanates enabled by C(sp3)–F activation

A conceptually novel single electron transfer strategy for C(sp3)–F activation-enabled [3 + 2 + 1] annulation of α-polyfluoromethyl alkenes is developed.

A photoinduced electron-transfer strategy for switchable fluorescence and phosphorescence in lanthanide-based coordination polymers.

Smart optical materials with tunable fluorescence and room temperature phosphorescence (RTP) exhibit promising application prospects in the field of intelligent switches, information security, etc. Herein, a tetraimidazole derivative was grafted to one-dimensional lanthanum-diphosphonate through H-bonds, generating a coordination polymer (CP), (H4-TIBP)·[La2Li(H2-HEDP)4(H-HEDP)]·3H2O (termed La; TIBP = 3,3,5,5-tetra(imidazole-1-yl)-1,1-biphenyl; H4-HEDP = 1-hydroxyethylidene-1,1-diphosphonic acid) with a three-dimensional supramolecular structure. La shows dynamic fluorescence from blue to red and switchable monotonous yellowish-green RTP, which can be manipulated by reversible photochromism. It is worth noting that Eu3+/Tb3+-doped CPs exhibit time-resolved (red to yellow) and monotonous green afterglow, respectively, which can be attributed to multiple emissions with different decay rates. The dynamic and multicolor luminescence endows these CPs with potential for application in the domains of optical communications, multi-step encryption, and anti-counterfeiting. This work not only integrates color-adjustable fluorescence, switchable RTP, and photochromism in one material, but also realizes the manipulation of the resultant optical performances via photochromism, paving the pathway for the design and synthesis of smart optical materials.

(Invited) Electroenzymatic Hydrogen Production: Mediated/Direct Electron Transfer Strategies and Continuous Product Analysis

Metalloenzymes such as hydrogenases and nitrogenases are of interest to electrochemists for mechanistic study as well as applied biotechnological hydrogen and ammonia production. In order to interface these enzymes with electrodes mediated and direct electron transfer methods have been reported, each having their strengths and weaknesses. In addition to establishing efficient electron transfer with enzymes, dynamic product analysis is also desirable since rates of product formation (and the distribution of products) can be determined during an experiment with varying electrode potential (and thermodynamic driving force for heterogeneous electron transfer).Our recent efforts concerning the design of electrode:enzyme interfaces are presented here, including (i) mediated vs. direct electron transfer strategies, (ii) rotating ring disk electrochemistry, and (iii) continuous mass spectrometry and gas chromatography [1-2]. In this work, an [FeFe]-hydrogenase is employed as a model enzyme for molecular hydrogen formation, with a view to expand these approaches towards enzymatic electrocatalytic studies of nitrogenases. Limitations and difficulties of the presented approaches will be discussed.

A Proton-Coupled Electron Transfer Strategy to the Redox-Neutral Photocatalytic CO2 Fixation.

Herein, we report our study on the design and development of a novel photocarboxylation method. We have used an organic photoredox catalyst (PC, 4CzIPN) and differently substituted dihydropyridines (DHPs) in combination with an organic base (1,5,7-triazabicyclodec-5-ene, TBD) to access a proton-coupled electron transfer (PCET) based manifold. In depth mechanistic investigations merging experimental analysis (NMR, IR, cyclic voltammetry) and density-functional theory (DFT) calculations reveal the key activity of a H-bonding complex between the DHP and the base. The thermodynamic and kinetic benefits of the PCET mechanism allowed the implementation of a redox-neutral fixation process leading to synthetically relevant carboxylic acids (18 examples with isolated yields up to 75%) under very mild reaction conditions. Finally, diverse product manipulations were performed to demonstrate the synthetic versatility of the obtained products.

2D–1D-2D multi-interfacial-electron transfer scheme enhanced g-C3N4/MWNTs/rGO hybrid composite for accelerating CO2 photoreduction

Highly-efficient supply of the photogenerated carriers is a necessary condition for excellent photocatalytic reactions. In this paper, 2D–1D-2D multi-interfacial electron transfer scheme enhanced g-C3N4/MWNTs/rGO (CMR) were prepared for CO2 photoreduction. CO2 photoreduction tests showed that the CO and CH4 yields with CMR-3 as the catalyst were about 699.69 μmol/g and 479.47 μmol/g under the UV-Vis light irradiation, which were about 21.9 and 59.3 times higher than that of pure g-C3N4. Furthermore, the obtained CMR-3 also exhibited excellent CO2 photoreduction performance under the visible light irradiation, and the obtained CO/CH4 ratio of g-C3N4 and CMR-3 were about 13.08 and 73.54, which confirmed that the CO selectivity was greatly enhanced after the co-modification of P-MWNTs and rGO. Photo-electrochemistry tests confirmed that the modification of P-MWNTs and rGO can efficiently speed up the separation efficiency of photogenerated carriers inside of g-C3N4. Besides, Zeta potential, water contact angle, and static experiment proved the co-modification of P-MWNTs and rGO could improve the dispersion of g-C3N4 in water environment. The UPS and UV-Vis DRS further confirmed the built-in electric fields at the interfaces of g-C3N4/P-MWNTs, P-MWNTs/rGO and g-C3N4/rGO, which were great beneficial for the CO2 photoreduction reaction. Finally, the multi-interfacial electron transfer scheme enhanced photoreduction process was provided.

Unraveling the phosphorus-nitrogen bridge in carbon quantum dots/carbon nitride for efficient photodegradation of organic contaminants

Limited transport and migration of photoinduced charges in polymeric carbon nitride (g-C3N4) within the planar layers remain a great challenge for achieving favorable photocatalysis. Herein, phosphorus-doped carbon quantum dots (PCDots) implanted intra-layer carbon nitride nanosheet (PCDots-C3N4) photocatalyst with phosphorus-nitrogen (P–N) bridging was prepared. The 13C and 31P of nuclear magnetic resonance, X-ray photoelectron spectroscopy, and density functional theory calculations confirmed the formation of a P–N bridge. Additionally, implanting PCDots enlarged the π-π conjugated electronic structure and modulated the plane structure of g-C3N4. The atomic-level connection by the P–N bridge dramatically extended the delocalization effect and facilitated the intramolecular charge transfer. PCDots-C3N4 demonstrated efficient photodegradation of tetracycline hydrochloride (TC) and bisphenol A (BPA) than both g-C3N4 and CDots-C3N4, reaching 76% and 100%, respectively. The possible degradation pathways of TC and BPA were also discussed. This work provides an efficient strategy for rapid electron transfer to form a new paradigm for wastewater remediation.

PCET-Mediated Ring-Opening Alkenylation of Cycloalkanols via Dual Photoredox and Cobalt Catalysis.

The construction of molecular skeletons and modification of molecules using widely available and easily prepared alcohols as radical precursors for coupling reactions are significant and challenging subjects. We herein report a straightforward strategy for the dehydrogenative ring-opening alkenylation of cycloalkanols with alkenes by combining a proton-coupled electron transfer strategy and a dual photoredox and cobalt catalysis system. With this approach, a series of distally unsaturated ketones were obtained in 17-83% yields with high E selectivity.

Light-driven progesterone production by InP–(M. neoaurum) biohybrid system

Progesterone is one of the classical hormone drugs used in medicine for maintaining pregnancy. However, its manufacturing process, coupled with organic reagents and poisonous catalysts, causes irreversible environmental pollution. Recent advances in synthetic biology have demonstrated that the microbial biosynthesis of natural products, especially difficult-to-synthesize compounds, from building blocks is a promising strategy. Herein, overcoming the heterologous cytochrome P450 enzyme interdependency in Mycolicibacterium neoaurum successfully constructed the CYP11A1 running module to realize metabolic conversion from waste phytosterols to progesterone. Subsequently, progesterone yield was improved through strategies involving electron transfer and NADPH regeneration. Mutant CYP11A1 (mCYP11A1) and adrenodoxin reductase (ADR) were connected by a flexible linker (L) to form the chimera mCYP11A1-L-ADR to enhance electron transfer. The chimera mCYP11A1-L-ADR, adrenodoxin (ADX), and ADR-related homolog ARH1 were expressed in M. neoaurum, showed positive activity and produced 45 mg/L progesterone. This electron transfer strategy increased progesterone production by 3.95-fold compared with M. neoaurum expressing mCYP11A1, ADR, and ADX. Significantly, a novel inorganic–biological hybrid system was assembled by combining engineered M. neoaurum and InP nanoparticles to regenerate NADPH, which was increased 84-fold from the initial progesterone titer to 235 ± 50 mg/L. In summary, this work highlights the green and sustainable potential of obtaining synthetic progesterone from sterols in M. neoaurum.Graphical

Photoredox-Catalyzed and Copper(II) Salt-Assisted Radical Addition/Hydroxylation Reaction of Alkenes, Sulfur Ylides, and Water

A visible light-driven photoredox-catalyzed and copper(II)-assisted three-component radical addition/hydroxylation reaction of alkenes, sulfur ylides, and water is reported. This process shows broad substrate scope and high functional group tolerance, with respect to both readily available sulfur ylides and alkenes, providing high-yielding and practical access to valuable γ-hydroxy carbonyl compounds. Key to the success of the reaction is the controlled generation of α-carbonyl carbon radicals from sulfur ylides via sulfonium salts by a visible-light-driven proton-coupled electron transfer (PCET) strategy in a mixture of 2,2,2-trifluoroethanol/CH2Cl2. Addition of Cu(TFA)2·H2O helps to accelerate the radical-cation crossover to improve the reaction efficiency. Mechanistic studies suggest that the hydroxy moiety in the products stems from water. This study also builds up a platform for further investigation into the radical synthetic chemistry of sulfur ylides.

Interfacial Electron Transfer Strategy to Improve the Hydrogen Evolution Catalysis of CrP Heterostructure.

Though several Pt-free hydrogen evolution reaction (HER) catalysts have been reported, their employment for industry is challenging. Here, a facile pyrolysis method to obtain phase-pure CrP nanoparticles supported on N, P dual-doped carbon (CrP/NPC) is reported to be tuned toward industrial HER. Interestingly, CrP/NPC exhibits excellent HER activity that requires an overpotential of 34 mV to attain a current density of 10 mA cm-2 , which is only 1 mV positive to commercial Pt/C and a potential of 55 mV to achieve a current density of 200 mA cm-2 which is better than Pt/C. In addition, the long-term durability of CrP/NPC is far superior to Pt/C due to the strong interaction between CrP and C support, restricting any agglomeration or leaching. Density functional theory (DFT) calculations suggest that electronic modulation at the interface (CrP/NPC) optimizes the hydrogen adsorption energy. The Cr-Cr bridge site with required density of states near the Fermi level is found to be the active site. Overall, this report provides a practical scheme to synthesize rarely investigated CrP based materials along with a computational mechanistic guideline for electrocatalysis that can be utilized to explore other phosphides for various applications.

Catalytic cleavage and functionalization of bulky and inert Csp3–Csp3 bonds via a relayed proton-coupled electron transfer strategy

Catalytic cleavage and functionalization of unstrained carbon–carbon bonds represent a formidable challenge for synthetic chemistry. Despite tremendous advances in transition-metal catalysis and photoredox radical chemistry, methods for the cleavage of sterically crowded inert C sp3 –C sp3 bonds remain underdeveloped. Here we describe the direct, photoredox cleavage of hindered C sp3 –C sp3 bonds of alcohols under neutral conditions. A relayed proton-coupled electron transfer (PCET) strategy is employed that overcame the previous requirement of a Brønsted base. Heavily branched alcohols with a high oxidation potential ( E ox½ > +2 V versus saturated calomel electrode) are cleaved and functionalized with remarkable efficiency and versatility. A simple, non-substituted phenyl group can promote a relayed PCET process to deliver primary, secondary, and tertiary alkyl radicals under neutral conditions. • Proton-coupled electron transfer • C–C cleavage of alcohols • Alkyl radicals • Various radicalophiles Liao et al. report a Fukuzumi acridinium salt as a catalyst for the C–C bond cleavage of linear primary, secondary, and tertiary carbinols under neutral conditions. The resulting transient alkyl radical species can be intercepted using various radicalophiles, including electron-deficient alkenes, an electrophilic SCF 3 reagent, and a range of heteroaryls.

Redox-active metal-organic frameworks for the removal of contaminants of emerging concern

The pollution due to the presence of contaminants of emerging concern (CECs) is a major cause for concern because of the serious threat it supposes to human health and ecosystem functions. Many efforts have been geared toward their removal to guarantee safer freshwater. Metal-organic frameworks (MOFs) are crystalline hybrid materials with high surface area and flexible rational design, which allows the incorporation of different active sites into a particular framework, thereby emerging as a potentially excellent candidate for water and wastewater treatment. Benefiting from the unique redox-active properties of MOFs, this review surveys literature update on their application for the removal of CECs. The underlaying electron transfer mechanism and strategies for incorporating redox-active sites into MOFs are comprehensively discussed. Different components of MOFs that are redox-active are further highlighted. This study elaborates the application of MOFs for Fenton-type and other advanced oxidation processes (AOPs) for removing emerging contaminants. AOPs generate highly reactive strong oxidants like hydroxyl and sulfate radicals that are efficient for degrading emerging pollutants with high mineralization rates. MOFs display semiconductor-like properties. Their photocatalytic use for the removal of dissolved emerging pollutants is detailed in the discussion. This review also provides an overview of the most promising directions for future research.

Investigating the Electroactivity of Salinivibrio sp. EAGSL, through Electroanalytical Techniques and Genomic Insights

Microbial electrochemical technologies are becoming an interest for the electrochemical community due to their possible applications in wastewater treatment, biosensing, biosynthesis, and bioenergy. Fundamental to these technologies is the use of electroactive microorganisms as bioelectrocatalysts. Recent studies have aimed to elucidate electron transfer strategies of electroactive microorganisms, with a keen interest in extremophilic bacteria due to their enhanced survivability in variable and extreme conditions, making them a better candidate for use in microbial electrochemical technologies. Recently, the species Salinivibrio sp. EAGSL was isolated from the Great Salt Lake, Utah, for its anodic respiration capabilities. In this work, electroanalytical techniques offer the primary information regarding the electroactive mechanisms of Salinivibrio sp. EAGSL. Additionally, measuring the current production over time shows electricity production over 3 days. Fundamental insights from the recently determined genome sequence offer possible explanations and mechanisms of this behavior and other metabolisms of interest for microbial electrochemistry. By elucidating the extracellular electron transfer pathways of Salinivibrio sp. EAGSL, the pairing of electroanalytical and genomic methods can provide a framework of study for other novel electroactive species.

Photoelectrochemical aptasensor for kanamycin determination based on exonuclease I-assisted target signal amplification and photoexcited electron transfer strategy

• Effective assembly of β-glucosidase with the design of capture DNA and hairpin DNA. • Recovery of photocurrent of TNA/g-C 3 N 4 due to catalytic hydrolysis of β-glucosidase. • Sensitive PEC aptasensing for kanamycin with Exo I-assisted recycling amplification. In the present work, graphitic carbon nitride (g-C 3 N 4 ) was generated in situ on the TiO 2 nanotube arrays (TNAs) to form TNA/g-C 3 N 4 , the capture DNA (c-DNA) was immobilized on the TNA/g-C 3 N 4 and the anti-kanamycin aptamer was assembled by the complementary base pairing to construct a TNA/g-C 3 N 4 /c-DNA-apatmer photoelectrochemical (PEC) aptasensor for kanamycin determination, which had obvious visible-light photocurrent response, and the photocurrent would decrease when immersing the aptasensor in Cu(II) solution due to the photoexcited electron transfer from g-C 3 N 4 to Cu(II). In the presence of kanamycin, the anti-kanamycin aptamer left and more β-glucosidase labeled at 3′-end of hairpin DNA was assembled on the TNA/g-C 3 N 4 with the assistance of recycling cleavage of exonuclease I (Exo I) to single-stranded aptamer. Because of the catalytic hydrolysis of linolenin by β-glucosidase, the released cyanide ion coordinated with Cu(II), hindering the photoexcited electron transfer from g-C 3 N 4 to Cu (II), and leading to the increase of photocurrent. Therefore, a simple, rapid and sensitive PEC aptasensor was constructed for kanamycin determination with good reproducibility and stability based on the Exo I-assisted target recycling signal amplification and photoexcited electron transfer strategy, in which the increased photocurrent value of the aptasensor was linear with the concentration of kanamycin in the range of 0.1–150 nM, and the limit of detection was 0.03 nM with the signal-to-noise ratio of 3, which has been successfully applied for the real food sample analysis with good precision of RSD less than 5.6% and good accuracy of the recoveries ranged from 90% to 120%.

Multicolour Fluorescence Based on Excitation-Dependent Electron Transfer Processes in o-Carborane Dyads.

Organic materials with excitation wavelength-dependent (Ex-de) emission are highly attractive for anticounterfeiting, optoelectronics and bioassay applications; however, the realization of Ex-de fluorescence, independent of aggregation states, remains a challenge. We herein report a photoinduced electron transfer (PeT) strategy to design Ex-de fluorescence materials by manipulating the relaxation pathways of multiple excited states. As expected, the o-carborane dyad presents a clear Ex-de fluorescence colour in the aggregated states, resulting from the tunable relative intensity of the dual-fluorescence spectra. Taking TP[1]B as an example, the amorphous powders emitted bright blue-violet, white and yellow colours under 390 nm, 365 nm and 254 nm UV illumination, respectively. Importantly, multicolour, flexible and transparent films as well as an anticounterfeiting application using this o-carborane dyad are demonstrated.

Multicolour Fluorescence Based on Excitation‐Dependent Electron Transfer Processes in o‐Carborane Dyads

AbstractOrganic materials with excitation wavelength‐dependent (Ex‐de) emission are highly attractive for anticounterfeiting, optoelectronics and bioassay applications; however, the realization of Ex‐de fluorescence, independent of aggregation states, remains a challenge. We herein report a photoinduced electron transfer (PeT) strategy to design Ex‐de fluorescence materials by manipulating the relaxation pathways of multiple excited states. As expected, the o‐carborane dyad presents a clear Ex‐de fluorescence colour in the aggregated states, resulting from the tunable relative intensity of the dual‐fluorescence spectra. Taking TP[1]B as an example, the amorphous powders emitted bright blue‐violet, white and yellow colours under 390 nm, 365 nm and 254 nm UV illumination, respectively. Importantly, multicolour, flexible and transparent films as well as an anticounterfeiting application using this o‐carborane dyad are demonstrated.

Multi-stepwise electron transfer via MOF-based nanocomposites for photocatalytic ammonia synthesis

Our study proposed a multi-stepwise electron transfer strategy to offer a method for designing MOF-based nanocomposite photocatalysts with the intensified electron transfer process.

Substituent-Induced Electron-Transfer Strategy for Selective Adsorption of N2 in MIL-101(Cr)-X Metal-Organic Frameworks.

N2 removal is of great significance in high-purity O2 production and natural gas purification. Here, we present a substituent-induced electron-transfer strategy for improving N2 capture performance by controlling the Lewis acidity of Cr(III) metal unsaturated sites in Cr-based metal-organic frameworks. With the enhancement of the electron-withdrawing ability of the modified group on terephthalic acid (-NO2 > -CH3), the N2 adsorption ability of MIL-101(Cr)-X was improved significantly. For MIL-101(Cr)-NO2, the adsorption enthalpy of N2 at zero coverage was 30.01 kJ/mol, which was much larger than that of MIL-101(Cr)-CH3 (14.31 kJ/mol). In situ infrared spectroscopy studies, Bader charges, and density functional theory calculations showed that the presence of -NO2 could enhance the Lewis acidity of Cr(III) metal unsaturated sites, which resulted in a strong interaction affinity for N2. The adsorption isotherms indicated that MIL-101(Cr)-NO2 had an excellent N2/O2 (79/21, v/v) selectivity of up to 10.8 and a good N2/CH4 separation performance (SN2/CH4 = 2.8, 298 K, 1 bar). Breakthrough curves showed that MIL-101(Cr)-NO2 had great potential for the efficient separation of N2/O2 and N2/CH4.

Visible-Light Induced C(sp2 )-H Amidation with an Aryl-Alkyl σ-Bond Relocation via Redox-Neutral Radical-Polar Crossover.

We report an approach for the intramolecular C(sp2 )-H amidation of N-acyloxyamides under photoredox conditions to produce δ-benzolactams with an aryl-alkyl σ-bond relocation. Computational studies on the designed reductive single electron transfer strategy led us to identify N-[3,5-bis(trifluoromethyl)benzoyl] group as the most effective amidyl radical precursor. Upon the formation of an azaspirocyclic radical intermediate by the selective ipso-addition with outcompeting an ortho-attack, radical-polar crossover was then rationalized to lead to the rearomative ring-expansion with preferential C-C bond migration.

Visible‐Light Induced C(sp2)−H Amidation with an Aryl–Alkyl σ‐Bond Relocation via Redox‐Neutral Radical–Polar Crossover

AbstractWe report an approach for the intramolecular C(sp2)−H amidation of N‐acyloxyamides under photoredox conditions to produce δ‐benzolactams with an aryl‐alkyl σ‐bond relocation. Computational studies on the designed reductive single electron transfer strategy led us to identify N‐[3,5‐bis(trifluoromethyl)benzoyl] group as the most effective amidyl radical precursor. Upon the formation of an azaspirocyclic radical intermediate by the selective ipso‐addition with outcompeting an ortho‐attack, radical–polar crossover was then rationalized to lead to the rearomative ring‐expansion with preferential C−C bond migration.