Electron Transfer Strategy Research Articles

Electron Transfer Mediator Modulates Type II Porphyrin-Based Metal-Organic Framework Photosensitizers for Type I Photodynamic Therapy.

Photodynamic therapy (PDT), a minimally invasive and effective local treatment, heavily depends on photosensitizer (PS) performance and oxygen availability. Despite the use of PS-based metal-organic frameworks (MOFs) to address the solubility and aggregation issues of PSs, the inherent hypoxic intolerance of mainstream Type II PDT remains challenging. Herein, we report an electron transfer strategy for the fabrication of hypoxia-tolerant Type I MOFs by encapsulating thymoquinone (TQ) into existing Type II MOFs. With TQ serving as an effective electron transfer mediator, it facilitates the electron transfer process from the MOF ligand PS to oxygen, establishing the Type I pathway and attenuating the original Type II pathway. Four representative porphyrin-based MOFs are synthesized to demonstrate the proposed strategy. Our findings reveal that TQ@MOF-1 nanoparticles (NPs) exhibit enhanced anticancer activity under hypoxic conditions and superior in vivo antitumor efficacy compared to parent MOF-1 NPs. This work offers an effective and universal strategy to modulate ROS generation in PS-based MOFs, endowing hypoxic tolerance with improved PDT performance against solid tumors.

Electron Transfer Mediator Modulates Type II Porphyrin‐Based Metal‐Organic Framework Photosensitizers for Type I Photodynamic Therapy

Photodynamic therapy (PDT), a minimally invasive and effective local treatment, heavily depends on photosensitizer (PS) performance and oxygen availability. Despite the use of PS‐based metal‐organic frameworks (MOFs) to address the solubility and aggregation issues of PSs, the inherent hypoxic intolerance of mainstream Type II PDT remains challenging. Herein, we report an electron transfer strategy for the fabrication of hypoxia‐tolerant Type I MOFs by encapsulating thymoquinone (TQ) into existing Type II MOFs. With TQ serving as an effective electron transfer mediator, it facilitates the electron transfer process from the MOF ligand PS to oxygen, establishing the Type I pathway and attenuating the original Type II pathway. Four representative porphyrin‐based MOFs are synthesized to demonstrate the proposed strategy. Our findings reveal that TQ@MOF‐1 nanoparticles (NPs) exhibit enhanced anticancer activity under hypoxic conditions and superior in vivo antitumor efficacy compared to parent MOF‐1 NPs. This work offers an effective and universal strategy to modulate ROS generation in PS‐based MOFs, endowing hypoxic tolerance with improved PDT performance against solid tumors.

Construction of electron-deficient Co on the nanoarrays enhances absorption and direct electron transfer to accelerate electrochemical nitrate reduction

Electrochemical nitrate reduction is a promising remediation strategy for nitrate-contaminated wastewater treatment, in which nitrate adsorption is a prerequisite step in the overall process. Herein, the iron-induced cobalt phosphide was grown in situ on porous nickel foam (Fe-CoP/NF) for the electrochemical nitrate reduction. Structural characterization verified doping of Fe and the uniform nanotube arrays of Fe0.03CoP/NF. Remarkably, the Fe0.03CoP/NF exhibited a high efficiency nitrate removal efficiency (99.3 %) and excellent ammonia selectivity (100 % selectivity and 0.485 mg·h−1cm−2 NH3 yield rate). Both experimental and theoretical results reveal that Fe doping alters the local charge distribution of the Co active centers to form electron-deficient Co. The Co electron-deficient regions were constructed due to the difference in electronegativity between Co and Fe. Furthermore, the formation of electron-deficient centers facilitates the reduction of charge transfer resistance. In particular, Fe0.03CoP/NF maintained an excellent conversion efficiency of nitrate to N2 (99.8 %) with 60 mM Cl−, and the selectivity of N2 is maintained above 99.1 % during long-term operation. This system possesses a low electrical consumption of 1.79 kWh·molN−1. This study designed an enhanced electrocatalyst through enhanced nitrate absorption and direct electron transfer strategies, thus providing a promising and low-power consumption approach for addressing nitrate pollution.

Photoelectrocatalytic [4+2] Annulation for S-Heterocycle Assembly Enabled by Proton-Coupled Electron Transfer (PCET).

Cross-dehydrogenative couplings (CDC) present an efficient strategy for the assembly of biorelevant heterocycles, but are thus far largely limited to toxic transition metals and rather harsh reaction conditions. In sharp contrast, we, herein report on a mild photoelectrocatalyzed CDC-[4+2] annulation enabling the synthesis of functionalized isothiochromenes enabled by a proton-coupled electron transfer (PCET) strategy. The transformative photoelectrocatalysis obviated toxic transition-metal, high reaction temperatures, and stoichiometric chemical redox reagents. This approach was characterized by exceedingly mild conditions, ample substrate scope, and a commercially available catalyst. Gram-scale reactions and a telescoped synthesis route reflected the unique potential in the green synthesis of important S-heterocycles.

The surface electron transfer strategy promotes the hole of PDI release and enhances emerging organic pollutant degradation

In semiconductor photocatalysts, the easy recombination of photogenerated carriers seriously affects the application of photocatalytic materials in water treatment. To solve the serious problem of electron−hole pair recombination in perylene diimide (PDI) organic semiconductors, we loaded ferric hydroxyl oxide (FeOOH) on PDI materials, successfully prepared novel FeOOH@PDI photocatalytic materials, and constructed a photo-Fenton system. The system was able to achieve highly efficient degradation of BPA under visible light, with a degradation rate of 0.112 min−1 that was 20 times higher than the PDI system, and it also showed universal degradation performances for a variety of emerging organic pollutants and anti-interference ability. The mechanism research revealed that the FeOOH has the electron trapping property, which can capture the photogenerated electrons on the surface of PDI, effectively reducing the compounding rate of photogenerated carriers of PDI and accelerating the iron cycling and H2O2 activation on the surface of FeOOH at the same time. This work provides new insights and methods for solving the problem of easy recombination of carriers in semiconductor photocatalysts and degrading emerging organic pollutants.

Deoxygenative radical cross-coupling of C(sp3)−O/C(sp3)−H bonds promoted by hydrogen-bond interaction

Building C(sp3)-rich architectures using simple and readily available starting materials will greatly advance modern drug discovery. C(sp3)−H and C(sp3)−O bonds are commonly used to strategically disassemble and construct bioactive compounds, respectively. However, the direct cross coupling of these two chemical bonds to form C(sp3)−C(sp3) bonds is rarely explored in existing literature. Conventional methods for forming C(sp3)−C(sp3) bonds via radical-radical coupling pathways often suffer from poor selectivity, severely limiting their practicality in synthetic applications. In this study, we present a single electron transfer (SET) strategy that enables the cleavage of amine α-C − H bonds and heterobenzylic C − O bonds to form C(sp3)−C(sp3) bonds. Preliminary mechanistic studies reveal a hydrogen bond interaction between substrates and phosphoric acid facilitates the cross-coupling of two radicals with high chemoselectivity. This methodology provides an effective approach to a variety of aza-heterocyclic unnatural amino acids and bioactive molecules.

Single-atom iron nanoatalysts facilitate electrochemiluminescence of graphitic carbon nitride for copper ion sensing

As an emerging electrochemiluminescence (ECL) nanomaterial, graphitic carbon nitride (g-C3N4) has attracted considerable attention from the scientific community due to its excellent optical properties, favorable biocompatibility, and tunable bandgap structure. However, the ECL intensity of g-C3N4 is subject to various influencing factors, including conductivity and electrode passivation, which pose notable challenges in improving its ECL performance. In this study, iron single atom nanocatalysts (Fe SAC) were introduced onto g-C3N4 sheets, and a novel approach was proposed to enhance the active sites, modulate the bandgap, and bolster the conductivity through synergistic mechanism. Furthermore, Fe SAC acted as the co-reactant promoter, amplifying the ECL signal significantly. Comparative analysis revealed a visible improvement in the ECL performance of Fe SAC-g-C3N4/K2S2O8 in a potential range of 0 to −0.9 V. Via the electron transfer strategy, a copper ion-sensitive ECL sensor based on Fe SAC-g-C3N4 was developed with the linear range of 0.01–100 μM and a detection limit of 0.75 nM. This sensor has been successfully applied in detecting copper ions in water environment and human serum samples, providing a new strategy for enhancing the ECL performance of g-C3N4 and expanding the utility of Fe SAC in ECL.

Site‐Selective Radical Aromatic C−H Functionalization of Alloxazine and Flavin through Ground‐State Single Electron Transfer

AbstractFlavins and their alloxazine isomers are key chemical scaffolds for bioinspired electron transfer strategies. Their properties can be fine‐tuned by functional groups, which must be introduced at an early stage of the synthesis as their aromatic ring is inert towards post‐functionalization. We show that the introduction of a remote metal‐binding redox site on alloxazine and flavin activates their aromatic ring towards direct C−H functionalization. Mechanistic studies are consistent with a synthetic sequence involving ground‐state single electron transfer (SET) with an electrophilic source followed by radical‐radical coupling. This unprecedented reactivity opens new opportunities in molecular editing of flavins by direct aromatic post‐functionalization and the utility of the method is demonstrated with the site‐selective C6 functionalization of alloxazine and flavin with a CF3 group, Br or Cl, that can be further elaborated into OH and aryl for chemical diversification.

Site-Selective Radical Aromatic C-H Functionalization of Alloxazine and Flavin through Ground-State Single Electron Transfer.

Flavins and their alloxazine isomers are key chemical scaffolds for bioinspired electron transfer strategies. Their properties can be fine-tuned by functional groups, which must be introduced at an early stage of the synthesis as their aromatic ring is inert towards post-functionalization. We show that the introduction of a remote metal-binding redox site on alloxazine and flavin activates their aromatic ring towards direct C-H functionalization. Mechanistic studies are consistent with a synthetic sequence involving ground-state single electron transfer (SET) with an electrophilic source followed by radical-radical coupling. This unprecedented reactivity opens new opportunities in molecular editing of flavins by direct aromatic post-functionalization and the utility of the method is demonstrated with the site-selective C6 functionalization of alloxazine and flavin with a CF3 group, Br or Cl, that can be further elaborated into OH and aryl for chemical diversification.

Synthesis of Ag2CO3/TiO2/SiC with pH stability and chloride ion boosted for efficient photodegrading tetracycline under visible light

The increasing issue of antibiotic contamination in water has sparked significant interest in seeking effective solutions. In this research, a dual Z-scheme ternary photocatalyst Ag2CO3/TiO2/SiC (ATS) was synthesized by a mechanochemical-coprecipitation method. The experimental results demonstrated that the 15 %Ag2CO3/TiO2/SiC (ATS-15) reached a remarkable tetracycline (TC) degradation efficiency of 95.87 % (k = 0.1063 min−1) after a 30 min exposure to visible light, which was 46.22 and 13.63 times more effective than SiC (k = 0.0023 min−1) and TiO2/SiC (k = 0.0078 min−1), respectively. The synergistic effect of ATS ternary structure to promote Si electron transfer and SiC surface oxidation. The photocatalytic performance of ATS-15 was greatly enhanced due to the synergistic effect of Cl− and CO3•−, achieving 95 % of TC degradation within 5 min. In the ATS-15 system, Cl− converts a portion of Ag2CO3 into AgCl and establishes a quaternary electron transfer scheme with ATS-15, thereby enhancing the performance of the photocatalyst. ATS-15 photocatalyst can maintain TC degradation rate above 90 % among pH 3 to 9. The ATS-15 system also exhibits excellent adaptability to various water environment, achieving 94.01 % TC degradation rate in natural river water, with only a 1 % reduction. A novel treatment scheme for antibiotic pollution in a complex water environment was proposed by ATS-15 photocatalyst with high pH stability and water applicability.

Asymmetric photoredox catalytic formal de Mayo reaction enabled by sensitization-initiated electron transfer.

Visible-light-driven photoredox catalysis is known to be a powerful tool for organic synthesis. Its occurrence critically depends on the twice exothermic single-electron transfer processes of photosensitizers, which are governed by the redox properties of the species involved. Hence, the inherently narrow range of redox potentials of photosensitizers inevitably constrains their further availability. Sensitization-initiated electron transfer has recently been found to effectively overcome this substantial challenge. However, feasible and practical strategies for designing such complicated catalytic systems are rather scarce. Herein we report an elaborate dual-catalyst platform, with dicyanopyrazine as a visible light photosensitizer and a pyrenyl-incorporated chiral phosphoric acid as a co-sensitizer, and we demonstrate the applicability of this sensitization-initiated electron transfer strategy in an asymmetric formal de Mayo-type reaction. The catalysis platform enables otherwise thermodynamically unfavourable electron transfer processes to close the redox cycle and allows for precise access to valuable enantioenriched 1,5-diketones with a wide substrate range.

Proton-coupled electron transfer activation of peroxydisulfate with phosphorylated zero-valent iron

Heterogeneous peroxydisulfate (PDS) activation driven by conventional electron transfer (ET) is often frustrated by low thermodynamic driving force and sluggish kinetics. Herein, we propose a proton-coupled electron transfer (PCET) strategy of PDS activation, by utilizing ball-milled phosphorylated zero-valent iron (P-ZVIbm) as a PCET platform. P-ZVIbm efficiently activated PDS to produce SO4•− and •OH for rapid degradation of 4-chlorophenol in a wide pH range of 3.5–10.5, with rate constants 3–62 times those of the ZVIbm/PDS counterpart. PCET mechanism was evidenced by the pH dependent kinetics, kinetic isotope effect, and proton inventory study. The surface-bound phosphates offer flexible pendant protons (P-O-H) through hydrogen bonds, delocalizing electrons of peroxide O to polarize the O-O bond, thereby facilitating the ET from ZVI for O-O bond cleavage. The work demonstrates the superiority of PCET strategy for heterogeneous PDS activation, and shall guide the design of high-performance Fenton-like catalysts.

Photocatalytic Proton-Coupled Electron Transfer Enabled Radical Cyclization for Isoquinoline-1,3-diones Synthesis.

Radical cyclization has been demonstrated to be an efficient method to access functionalized heterocycles from easily accessible raw materials. Described herein is the development of a photocatalytic proton-coupled electron transfer (PCET) strategy for the synthesis of isoquinoline-1,3-diones using readily prepared naphthalimide (NI)-based organic photocatalysts. The process features free metal-complex photocatalysts, acids, and mild reaction conditions. This mild radical cyclization protocol has a broad substrate scope and can be effectively applied to a variety of medicinally relevant substrates. Furthermore, control experiments were conducted to elucidate the mechanism of this visible light-induced methodology.

Outer Sphere Electron Transfer Enabling High-Voltage Aqueous Electrolytes.

Aqueous electrolytes with a low voltage window (1.23 V) and prone side reactions, such as hydrogen evolution reaction and cathode dissolution, compromise the advantages of high safety and low cost of aqueous metal-ion batteries. Herein, introducing catechol (CAT) into the aqueous electrolyte, an outer sphere electron transfer mechanism is initiated to inhibit the water reactivity, achieving an electrochemical window of 3.24 V. In a typical Zn-ion battery, the outer sphere electrons jump from CAT to Zn2+-H2O at a geometrically favorable situation and between the solvation molecules without breaking or forming chemical bonds as that of the inner sphere electron transfers. The excited state π-π stacking further leads to the outer sphere electron transfer occurring at the electrolyte/electrode interface. This high-voltage electrolyte allows achieving an operating voltage two times higher than that of the usual aqueous electrolytes and provides almost the highest energy density and power density for the V2O5-based aqueous Zn-ion full batteries. The Zn//Zn symmetric battery delivers a 4000 h lifespan, and the Zn//V2O5 full battery achieves a ∼380 W h kg-1 energy density and a 92% capacity retention after 3000 cycles at 1 A g-1 and a 2.4 V output voltage. This outer sphere electron transfer strategy paves the way for designing high-voltage aqueous electrolytes.

Deciphering Oxygen‐Independent Augmented Photodynamic Oncotherapy by Facilitating the Separation of Electron‐Hole Pairs

AbstractDeveloping Type‐I photosensitizers provides an attractive approach to solve the dilemma of inadequate efficacy of photodynamic therapy (PDT) caused by the inherent oxygen consumption of traditional Type‐II PDT and anoxic tumor microenvironment. The challenge for the exploration of Type‐I PSs is to facilitate the electron transfer ability of photosensitization molecules for transforming oxygen or H2O to reactive oxygen species (ROS). Herein, we propose an electronic acceptor‐triggered photoinduced electron transfer (a‐PET) strategy promoting the separation of electron‐hole pairs by marriage of two organic semiconducting molecules of a non‐fullerene scaffold‐based photosensitizer and a perylene diimide that significantly boost the Type‐I PDT pathway to produce plentiful ROS, especially, inducing 3.5‐fold and 2.5‐fold amplification of hydroxyl (OH⋅) and superoxide (O2−⋅) generation. Systematic mechanism exploration reveals that intermolecular electron transfer and intramolecular charge separation after photoirradiation generate a competent production of radical ion pairs that promote the Type‐I PDT process by theoretical calculation and ultrafast femtosecond transient absorption (fs‐TA) spectroscopy. By complementary tumor diagnosis with photoacoustic imaging and second near‐infrared fluorescence imaging, this as‐prepared nanoplatform exhibits fabulous photocytotoxicity in harsh hypoxic conditions and terrific cancer revoked abilities in living mice. We envision that this work will broaden the insight into high‐efficiency Type‐I PDT for cancer phototheranostics.

Deciphering Oxygen-Independent Augmented Photodynamic Oncotherapy by Facilitating the Separation of Electron-Hole Pairs.

Developing Type-I photosensitizers provides an attractive approach to solve the dilemma of inadequate efficacy of photodynamic therapy (PDT) caused by the inherent oxygen consumption of traditional Type-II PDT and anoxic tumor microenvironment. The challenge for the exploration of Type-I PSs is to facilitate the electron transfer ability of photosensitization molecules for transforming oxygen or H2O to reactive oxygen species (ROS). Herein, we propose an electronic acceptor-triggered photoinduced electron transfer (a-PET) strategy promoting the separation of electron-hole pairs by marriage of two organic semiconducting molecules of a non-fullerene scaffold-based photosensitizer and a perylene diimide that significantly boost the Type-I PDT pathway to produce plentiful ROS, especially, inducing 3.5-fold and 2.5-fold amplification of hydroxyl (OH⋅) and superoxide (O2 -⋅) generation. Systematic mechanism exploration reveals that intermolecular electron transfer and intramolecular charge separation after photoirradiation generate a competent production of radical ion pairs that promote the Type-I PDT process by theoretical calculation and ultrafast femtosecond transient absorption (fs-TA) spectroscopy. By complementary tumor diagnosis with photoacoustic imaging and second near-infrared fluorescence imaging, this as-prepared nanoplatform exhibits fabulous photocytotoxicity in harsh hypoxic conditions and terrific cancer revoked abilities in living mice. We envision that this work will broaden the insight into high-efficiency Type-I PDT for cancer phototheranostics.

Electron transfer-mediated synergistic nonlinear optical response in the Agn@C18 (n = 4–6) complexes: A DFT study on the electronic structures and optical characteristics

Seeking highly efficient and stable non-linear optical (NLO) materials is crucial yet challenging, given their promising applications in laser diodes and photovoltaics. In this study, we employ the excess electron and charge transfer strategies to theoretically design three novel complexes, namely Agn@C18 (n = 4–6), by adsorbing silver clusters onto the cyclo[18]carbon ring (C18). Our aim is to investigate the NLO characteristics of these complexes using density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. The results reveal that the adsorption of Ag clusters onto C18 leads to a decrease in excitation energy and an increase in dipole moment and oscillator strengths, thereby significantly enhancing the hyperpolarizability of the complexes. Strikingly, among all these complexes, Ag6@C18 exhibits the highest first hyperpolarizability value of approximately 109496.2620 au calculated at the B3LYP/cc-PVDZ-pp level of theory, which is about 1.3 × 106 times higher than that of pure C18. This finding validates the effectiveness of the proposed strategies in enhancing the NLO response of the species. Moreover, the calculated UV–Vis absorption spectrum demonstrates that the Agn@C18 complexes with excess electrons exhibit absorption at longer wavelengths (ranging from 385 to 731 nm) compared to C18. In addition, the stability, chemical bonding, and charge transfer characteristics of the Agn@C18 (n = 4–6) complexes were also discussed. These findings highlight the potential of these complexes for the development of highly efficient NLO devices.

Activity-Based Nitric Oxide-Responsive Porphyrin for Site-Selective and Nascent Cancer Ablation.

Nitric oxide (NO) generated within the tumor microenvironment is an established driver of cancer progression and metastasis. Recent efforts have focused on leveraging this feature to target cancer through the development of diagnostic imaging agents and activatable chemotherapeutics. In this context, porphyrins represent an extraordinarily promising class of molecules, owing to their demonstrated use within both modalities. However, the remodeling of a standard porphyrin to afford a responsive chemical that can distinguish elevated NO from physiological levels has remained a significant research challenge. In this study, we employed a photoinduced electron transfer strategy to develop a panel of NO-activatable porphyrin photosensitizers (NOxPorfins) augmented with real-time fluorescence monitoring capabilities. The lead compound, NOxPorfin-1, features an o-phenylenediamine trigger that can effectively capture NO (via N2O3) to yield a triazole product that exhibits a 7.5-fold enhancement and a 70-fold turn-on response in the singlet oxygen quantum yield and fluorescence signal, respectively. Beyond demonstrating excellent in vitro responsiveness and selectivity toward NO, we showcase the potent photodynamic therapy (PDT) effect of NOxPorfin-1 in murine breast cancer and human non-small cellular lung cancer cells. Further, to highlight the in vivo efficacy, two key studies were executed. First, we utilized NOxPorfin-1 to ablate murine breast tumors in a site-selective manner without causing substantial collateral damage to healthy tissue. Second, we established a nascent human lung cancer model to demonstrate the unprecedented ability of NOxPorfin-1 to halt tumor growth and progression completely. The results of the latter study have tremendous implications for applying PDT to target metastatic lesions.

Recent advances in photochemical strain-release reactions of bicyclo[1.1.0]butanes.

Bicyclo[1.1.0]butanes (BCBs) are attractive compounds for their beautiful "butterfly" conformations, distinctive properties, and novel reactivities. As soon as the first example had been synthesized, a wide range of strain-release reactions were explored for the preparation of cyclobutanes and bicyclic systems in the ground state or excited state. In particular, with the demand for the construction of rigid three-dimensional aliphatic skeletons to "escape from flatland" in drug discovery programs, numerous efforts have been devoted in this area to expanding the boundaries of their reactivities and broadening the chemical space of their attractive bioisosteric products. In recent years, with the great resurgence and dramatic evolution of photochemistry, photochemical strain-release reactions generally relying on single electron transfer (SET) or energy transfer (EnT) strategies can provide much more opportunities and capability for innovative transformations of BCBs. In this review, we summarize and highlight the recent advances (year > 2016) of this topic and hope that it will inspire much more wonderful chemistry of BCBs.

Photocatalytic functionalization of white phosphorus with aryl bromides and chlorides.

We report the implementation of a consecutive photoinduced electron transfer (conPET) strategy for the functionalization of white phosphorus (P4) with inexpensive and widely available aryl bromides and chlorides. By employing a well-known acridinium-based photocatalyst under near-UV irradiation, this protocol gives direct access to valuable triarylphosphines and tetraarylphosphonium salts. The reaction mechanism is elucidated by NMR spectroscopic studies and model reactions.