Formation Of Radical Anion Research Articles

Ketyl Radical Anion Mediated Radical Polymerization and Anionic Ring-Opening Polymerization to Give Polymers with Low Molecular Weight Distribution.

The development of novel polymerization capable of yielding polymers with low molecular weight distribution (Đ) is essential and significant in polymer chemistry, where monofunctional initiator contains only one initiation site in these polymerizations generally. Here, ketyl radical anion species is introduced to develop a novel Ketyl Mediated Polymerization (KMP), which enables radical polymerization at carbon radical site and anionic ring-opening polymerization at oxygen anion site, respectively. Meanwhile, polymerization and corresponding organic synthesis generally couldn't be performed simultaneously in one pot. Through KMP, organic synthesis and polymerization are achieved in one pot, where small molecules (cyclopentane derivates) and polymers with low Đ are successfully prepared under mild condition simultaneously. At the initiation step, both organic synthesis and polymerization are initiated by single electron transfer reaction with ketyl radical anion formation. Cyclopentane derivates are synthesized through 3-3 coupling reaction and cyclization. Polystyrene and polycaprolactone with low Đ and a full monomer conversion are prepared by KMP via radical polymerization and anionic ring-opening polymerization, respectively. This work therefore enables both organic synthesis and two different polymerizations from same initiation system, which saves time, labour, resource and energy and expands the reaction mode and method libraries of organic chemistry and polymer chemistry.

Ketyl Radical Anion Mediated Radical Polymerization and Anionic Ring‐Opening Polymerization to Give Polymers with Low Molecular Weight Distribution

AbstractThe development of novel polymerization capable of yielding polymers with low molecular weight distribution (Đ) is essential and significant in polymer chemistry, where monofunctional initiator contains only one initiation site in these polymerizations generally. Here, ketyl radical anion species is introduced to develop a novel Ketyl Mediated Polymerization (KMP), which enables radical polymerization at carbon radical site and anionic ring‐opening polymerization at oxygen anion site, respectively. Meanwhile, polymerization and corresponding organic synthesis generally couldn't be performed simultaneously in one pot. Through KMP, organic synthesis and polymerization are achieved in one pot, where small molecules (cyclopentane derivates) and polymers with low Đ are successfully prepared under mild condition simultaneously. At the initiation step, both organic synthesis and polymerization are initiated by single electron transfer reaction with ketyl radical anion formation. Cyclopentane derivates are synthesized through 3–3 coupling reaction and cyclization. Polystyrene and polycaprolactone with low Đ and a full monomer conversion are prepared by KMP via radical polymerization and anionic ring‐opening polymerization, respectively. This work therefore enables both organic synthesis and two different polymerizations from same initiation system, which saves time, labour, resource and energy and expands the reaction mode and method libraries of organic chemistry and polymer chemistry.

Influence of iodine substitution on electrochemical properties and energy levels of BODIPY derivatives

Four boron-dipyrromethene derivatives (BODIPYs) were investigated to assess the influence of the iodine substitution on their electrochemical properties. The performed CV and DPV scans revealed an increase in the number of redox pairs in iodine-substituted derivatives compared to unsubstituted ones, from one reduction and one or two oxidations to two reductions and two oxidations. The calculated electrochemical energy band gap was decreased by approx. 0.6 eV in the case of neutral iodinated derivative 3 compared to parent compound 1, indicating the possible future application of substituted species as semiconductors. The electrolysis of 3 and 4 showed the formation of anion radicals of BODIPYs. The additional DFT studies confirmed the decrease of the HOMO-LUMO energy band gap when the halide atom was inserted into the core and allowed to locate the orbitals.

Visible Light-Driven C(sp3)-H Carboxylation of Diverse Amines with CO2 into α-Amino Acids Using an Eco-Friendly and Reusable Covalent Organic Framework

Direct photochemical carboxylation of C(sp3)–H bonds with CO2 is an uphill task and it has attracted increasing attention. In the present study, we report an elegant strategy for visible-light-triggered C(sp3)-H carboxylation of amines with CO2 into α-amino acids using a stable crystalline polyimide-based covalent organic framework (PI-COF) as an efficient heterogeneous photocatalyst and NiO nanoparticles (NiO NPs) as a cocatalyst under ambient conditions (room temperature and atmospheric CO2 pressure). Diverse amino acids are produced in moderate-to-high yields. This methodology tolerates a range of functional groups and displays remarkable regioselectivity. Various drugs were effectively achieved using this light-assisted approach. The high chemical stability of the COF and its strong interactions with NiO NPs renders the catalytic system to be highly recyclable (i.e., over five times). More interestingly, this photoinduced carboxylation reaction occurred without the involvement of any sacrificial electron donors. Based on computational (DFT) investigations, a tentative mechanism revealed the formation of CO2 radical anion at the conduction band (CB) of the COF via single electron transfer mediated by NiO nanoparticles which combined with amine radical cation at the valence band of the COF to form α-amino acid.

Formation of stable naphthalenediimide radical anion: Substituent-directed synergistic effects of hydrogen bonding and charge transfer interactions on chromogenic response towards hydrazine

Naphthalimide-based chromogenic probes have been developed with different electron-withdrawing terminal functional groups. All the compounds showed a dose-dependent gradual change in solution color from pale yellow to dark yellow to light brown and finally dark brown upon the addition of hydrazine hydrate. Concomitantly, the appearance of intense green fluorescence is noticed. The mechanistic investigations, as supported by 1H NMR and ESR studies, indicate the hydrazine induces formation of radical anion species in the reaction medium. The presence of electron-withdrawing substituents not only improves the degree of chromogenic response but also the stability of the radical species. It is found that the substituents take an active role in the adsorption of hydrazine via hydrogen bonding interactions, which facilitates the subsequent charge transfer from hydrazine to probe molecules. In this context, a detailed density functional theory (DFT) based first-principle calculations are performed to theoretically study the cooperative effect of hydrogen bonding interaction in the sensing of hydrazine. It is observed that on changing substituents, significant changes in the numbers of possible chemisorption sites and binding energies at individual sites for hydrazine, as well as the magnitude of charge transfer from the hydrazine at individual binding sites. Finally, chemically modified biodegradable paper strips have been developed on on-location naked-eye sensing of hydrazine.

Sunlight‐Induced Degradation of Dissolved Ethyl‐Parathion and Coupled Molecular Toxicity Investigation

AbstractEthyl‐parathion (EP) is a globally‐distributed organophosphorus (OP) pesticide where environmental release is a standard use case. The present study sought to determine if sunlight degraded EP and if the degraded products were toxic to biological molecules in cell‐free assays. A 24 mg/L solution of EP (water solubility limit) was exposed to direct sunlight for 0, 1, 2, 3 and 4 hrs where as much as 64.6 % of EP was degraded relative to the 0 hr sunlight exposure. Singlet oxygen formation (1O2) increased by 15.9, 20.6, 29.8, and 64.4 % in the 1, 2, 3 and 4 hr sunlight exposures, respectively. Ultra‐high performance liquid chromatography further confirmed the sunlight‐induced transformation of EP and the increased 1O2 formation through time, likely via a type‐II photochemical mechanism. The degradation of DNA nucleotides (8‐hydroxy 2‐deoxyguanosine), the formation of superoxide anion radical (O2.‐) which was validated by significant O2.– quenching by superoxide dismutase (SOD), and peroxidation of membrane lipid (linoleic acid), increased significantly in sunlight exposures, however the presence of EP at 24 mg/L had no significant influence on this effect. Overall, sunlight quickly degraded EP in solution, however the sunlight‐irradiated EP caused no discernable toxic effects in cell‐free assays relative to sunlight alone.

Photothermal Perylene Bisimide Hydrogels.

Gels formed using a perylene bisimide (PBI) as a low molecular weight gelator can show the photothermal effect. Formation of the PBI radical anion results in new absorption bands forming, meaning that subsequent irradiation with a wavelength of light overlapping with the new absorption band leads to heating of the gel. This approach can be used to heat the gel, as well as the surrounding milieu. We show how we can use electrochemical methods as well as multicomponent systems to form the radical anion without the need for UV light, and how we can use the photothermal effect to induce phase transitions in the solutions above the gels by exploiting photothermal behavior.

Direct mass spectrometric imaging of document handwriting with laser desorption ionization and post ultraviolet photodissociation

Handwriting represents personal education and physical or psychological states. This work describes a chemical imaging technique for document evaluation that combines laser desorption ionization with post ultraviolet photo-induced dissociation (LDI-UVPD) in mass spectrometry. Taken the advantages of chromophores in ink dyes, handwriting papers were subjected to direct laser desorption ionization without additional matrix materials. It is a surface-sensitive analytical method that uses a low intensity pulsed laser at 355 nm to remove chemical components from very outermost surfaces of overlapped handwritings. Meanwhile, the transfer of photoelectrons to those compounds leads to the ionization and the formation of radical anions. The gentle evaporation and ionization property enable the dissection of chronological orders. Paper documents maintain intact without extensive damages after laser irradiation. The evolving plume resulting from the irradiation of the 355 nm laser is fired by the second ultraviolet laser at 266 nm that is in parallel to the sample surface. In contrast to collision activated dissociation in tandem MS/MS, such post ultraviolet photodissociation generates much more different fragment ions through electron-directed specific cleavages of chemical bonds. LDI-UVPD can not only provide graphic representation of chemical components but also reveal hidden dynamic features such as alterations, pressures and aging.

Theoretical and experimental evidences for the formation of carbonate anion radical (CO3−•) in the atmosphere

Troposphere is the lowest layer where the oxidation reactions responsible for the atmospheric self-purification of contaminants occur, which are initiated mostly by hydroxyl radicals (HO•). In this context, the objective of the present work was to carry out theoretical and experimental studies on the formation of the carbonate anion radical (CO3−•) in the atmosphere and evaluate the spontaneity of chemical reactions that occur at molecular. Experimental tests to evaluate the formation of CO3−• in the atmosphere were conducted using rainwater samples containing 5, 10, and 15 mg L−1 of sodium carbonate, and the addition of methylene blue dye was used to indicate the formation of the CO3−• by monitoring its degradation. Exposure of the samples to solar radiation led to a greater degradation of the dye in rainwater samples with higher concentrations of bicarbonate. The determination of the alkalinity of the samples revealed that the predominant chemical species in the medium was the bicarbonate anion and that the increase in its concentration promotes the formation of CO3−•. As a result of the simulation of the reactions with the radicals •OH, •OOH, and CO3−• at the level of theory MP2/6–311++G (2df,p), it was obtained that the formation of the radical CO3−• is possible (HO• + CO32− → HO− + CO3−• and HCO3− + HO• → H2O + CO3−•). The simulations were carried out in aqueous phase with implicit solvent, in the gas and showed the same trends. Furthermore, the reactions involving CO3−• with atmospheric molecules are spontaneous (ΔrG298 < 0) for electron-rich groups as H2S compounds, indicating that the radical CO3−• can react with some atmospheric molecules, and thus contribute to the atmospheric oxidation mechanisms.

Phenyl-substituted cibalackrot derivatives: Redox behavior, structure-properties relationships and in situ UV-vis/EPR-spectroelectrochemistry of radical ions

Redox properties and UV–vis and EPR spectroelectrochemical behavior of cibalackrot (7,14-diphenyldiindolo[3,2,1-de:3′,2′,1′-ij][1,5]naphthyridine-6,13‑dione, 1) and its six derivatives 2 - 7 carrying two substituted phenyl rings have been examined. The dyes are of potential interest for organic electronics and singlet fission for solar energy conversion. The compounds are reduced in two reversible one-electron steps under formation of a stable primary radical anion. Oxidation yields the radical cation in a first reversible step and the second step is quasireversible. The presence of radical ions was confirmed by in situ UV–vis/EPR spectroelectrochemistry. The substituents have different influence on oxidation and on reduction, as revealed using the LFER approach and interpreted with the help of calculated energies of frontier orbitals. The observed first reduction (Ered1) and first oxidation (Eox1) potentials correlate well with the calculated values and their difference (ΔE1) has photophysical relevance because it reflects the energy of HOMO-LUMO gap.

Eggshell powder as an efficient recyclable catalyst generates H2O2 prompted radicals for selective oxidative mineralization of crystal violet dye at room temperature

Eggshell powder (ESP) was explored as a selective heterogeneous catalyst for oxidative degradation of crystal violet (CV) dye in aqueous media in presence of H2O2 at room temperature. Natural but throw-away material ESP as a carbonate (CO32−) source facilitated the formation of carbonate anion radicals in presence of H2O2. Carbonate anion radicals (CO3•−), though a weaker oxidant than ∙OH radical, efficiently served as a selective oxidant. Selective degradation of CV dye in aqueous solution was confirmed from the quenching experiments. Synergistic effects of both the radicals (CO3•− and ∙OH) in the dye degradation process was experimentally verified. At a dose of 10 g/L of ESP, 91% removal of CV (initial concentration: 10 mg/L) was achieved in 60 min. The reaction kinetics followed first order rate model. Intermediate products formed during CV degradation and the extent of mineralization were confirmed from MALDI-TOF-MS and TOC analysis, respectively. The turnover number (TON) and turnover frequency (TOF) were obtained as 2.45 × 10−6 mol per g and 6.81 × 10−10 mol per g per second. A promising reusability was achieved up to seven cycles. The ESP catalyst used in this study was characterized by SEM, FTIR, XRD, XPS, BET surface area analysis, UV–visible DRS, XRF, and pHZPC analyses. The present work offers a novel facile but selective route for CV degradation and opens up newer possibilities for eggshell waste utilization as catalyst.

Reaction of FeaqII with Peroxymonosulfate and Peroxydisulfate in the Presence of Bicarbonate: Formation of FeaqIV and Carbonate Radical Anions.

Many advanced oxidation processes (AOPs) use Fenton-like reactions to degrade organic pollutants by activating peroxymonosulfate (HSO5-, PMS) or peroxydisulfate (S2O82-, PDS) with Fe(H2O)62+ (FeaqII). This paper presents results on the kinetics and mechanisms of reactions between FeaqII and PMS or PDS in the absence and presence of bicarbonate (HCO3-) at different pH. In the absence of HCO3-, FeaqIV, rather than the commonly assumed SO4•-, is the dominant oxidizing species. Multianalytical methods verified the selective conversion of dimethyl sulfoxide (DMSO) and phenyl methyl sulfoxide (PMSO) to dimethyl sulfone (DMSO2) and phenyl methyl sulfone (PMSO2), respectively, confirming the generation of FeaqIV by the FeaqII-PMS/PDS systems without HCO3-. Significantly, in the presence of environmentally relevant concentrations of HCO3-, a carbonate radical anion (CO3•-) becomes the dominant reactive species as confirmed by the electron paramagnetic resonance (EPR) analysis. The new findings suggest that the mechanisms of the persulfate-based Fenton-like reactions in natural environments might differ remarkably from those obtained in ideal conditions. Using sulfonamide antibiotics (sulfamethoxazole (SMX) and sulfadimethoxine (SDM)) as model contaminants, our study further demonstrated the different reactivities of FeaqIV and CO3•- in the FeaqII-PMS/PDS systems. The results shed significant light on advancing the persulfate-based AOPs to oxidize pollutants in natural water.

Iron Tricarbonyl Complexes Based on N,N'-Disubstituted Phenanthrenediimines

The oxidative addition of N,N'-disubstituted phenanthrenediimines to iron carbonyls was studied. The reactions of acceptor phenanthrenediimines with Fe2(CO)9 give iron(I) tricarbonyl complexes with anion-radical forms of the ligands. The synthesized compounds were characterized by NMR and IR spectroscopy. The structures of the complex based on N,N'-bis(3-trifluoromethylphenyl)phenanthrenediimine and imidazol-2-one ligand was established by X-ray diffraction (XRD) (CIF files СCDC nos. 2173471 and 2173472, respectively).

Controlling π-π Interactions of Highly Soluble Naphthalene Diimide Derivatives for Neutral pH Aqueous Redox Flow Batteries.

Organic redox-active molecules are a promising platform for designing sustainable, cheap, and safe charge carriers for redox flow batteries. However, radical formation during the electron-transfer process causes severe side reactions and reduces cyclability. This problem is mitigated by using naphthalene diimide (NDI) molecules and regulating their π-π interactions. The long-range π-stacking of NDI molecules, which leads to precipitation, is disrupted by tethering four ammonium functionalities, and the solubility approaches 1.5m in water. The gentle π-π interactions induce clustering and disassembling of the NDI molecules during the two-electron transfer processes. When the radical anion forms, the antiferromagnetic coupling develops tetramer and dimer and nullifies the radical character. In addition, short-range-order NDI clusters at 1m concentration are not precipitated but inhibit crossover. They are disassembled in the subsequent electron-transfer process, and the negatively charged NDI core strongly interacts with ammonium groups. These behaviors afford excellent RFB performance, demonstrating 98% capacity retention for 500 cycles at 25mA cm-2 and 99.5% Coulombic efficiency with 2m electron storage capacity.

Photocatalytic coupling of electron-deficient alkenes using oxalic acid as a traceless linchpin

•Oxalic acid is used as a traceless linchpin •CO2 radical anion formation via photocatalytic oxidation of oxalic acid is achieved •Homo- and cross-coupling of electron-poor alkenes is achieved Reductive alkene cross-coupling represents a straightforward strategy for the construction of C–C bonds from readily available alkene feedstocks. A one-pot protocol, utilizing oxalic acid as a traceless linchpin, has been developed to achieve direct cross-coupling of electron-deficient alkenes. The overall process is a two-step transformation involving hydrocarboxylation followed by decarboxylative cross-coupling. A dual-photocatalyst system is crucial for success and promotes the two reaction steps synergistically. This reaction supports the efficient synthesis of bioactive molecules. Photoredox catalysis provides an easy and mild pathway for the generation of a CO2 radical anion from oxalic acid, which paves the way for the broad utilization of this reactive intermediate in the synthesis of fine chemicals. Reductive alkene cross-coupling represents a straightforward strategy for the construction of C–C bonds from readily available alkene feedstocks. A one-pot protocol, utilizing oxalic acid as a traceless linchpin, has been developed to achieve direct cross-coupling of electron-deficient alkenes. The overall process is a two-step transformation involving hydrocarboxylation followed by decarboxylative cross-coupling. A dual-photocatalyst system is crucial for success and promotes the two reaction steps synergistically. This reaction supports the efficient synthesis of bioactive molecules. Photoredox catalysis provides an easy and mild pathway for the generation of a CO2 radical anion from oxalic acid, which paves the way for the broad utilization of this reactive intermediate in the synthesis of fine chemicals.

Boosting photocatalytic oxidation of organic pollutants on Z-scheme carbon nitride / Ag3PO4 / Ag composites by coupling with carbon nanotubes

ABSTRACT The present study reports the development of ternary and quaternary carbon nitride (CN) based nanocomposites through the coupling of CN with single-walled carbon nanotubes (SWCNTs), Ag3PO4 (AP) and Ag nanoparticles (NP). A facile wet-chemistry process was developed for the synthesis of the composites. The prepared materials were characterised using XRD, ATR, DR-UV-Vis, photoluminescence (PL) spectroscopy and EPR. Photocatalytic dye degradation (rhodamine b, RhB) is greatly improved in composite materials. The most active photocatalyst was the quaternary composite bearing SWCNTs, Ag3PO4 and Ag NP, that presented a 2- and a 3-fold increase in photoactivity compared with the CN functionalised only with SWCNTs and the pure CN, respectively. The enhanced activity is associated with improvements in several important materials properties. Adsorption in the visible light is improved by the presence of Ag3PO4 and Ag NP. The latter provided plasmon resonance effects, absorbing light up to 700 nm. The presence of SWCNTs reduced charge recombination phenomena reducing by half the PL intensity. In addition, charge availability was further increased due to the formation of heterojunctions through the coupling of CN with Ag3PO4 and Ag NP. The PL intensity of the ternary composite was reduced to 1% of the pure CN PL intensity. In-situ EPR spectroscopy using spin-traps revealed the formation of superoxide anion radicals () that provide evidence for charge transfer via a Z-scheme mechanism. production was enhanced 8.5 times in the ternary composite compared with the pure CN. The importance of the stepwise functionalization of CN through the formation of ternary and quaternary composites towards the development of advanced photoactive materials is highlighted herein.

The role of molecular oxygen (O2) and UV light in the anion radical formation and stability of TCNQ and its fluorinated derivatives

We report the electronic absorption spectroscopy of 7,7,8,8-tetracyanoquinodimethane (TCNQ) and its fluorinated derivatives (F2TCNQ and F4TCNQ), well-known electron-accepting molecules in common organic solvents (toluene, chlorobenzene, acetonitrile, and ethanol) under controlled exposure to air (O2) and UV light. All compounds (FxTCNQ (x = 0, 2, 4)) were stable in a neutral state (FxTCNQ0) in toluene and chlorobenzene, even under both O2 and UV light. On the other hand, in EtOH, the formation of FxTCNQ·− was monitored upon controlled exposure to O2 or UV light. Especially in air-equilibrated ethanol upon the UV-illumination, efficient α,α-dicyano-p-toluoylcyanide anion (DCTC−) and its fluorinated derivatives were generated evinced by the absorption peak near 480 nm, whereas the reaction was shut off by removing O2 or blocking UV light, thereby keeping FxTCNQ·− stable. However, even in deaerated ethanol, upon the UV-illumination, the anion formation of TCNQ and its fluorinated derivatives (FxTCNQ·−, x = 0, 2, 4) was inevitable, showing the stability of FxTCNQ0 depends on the choice of solvent.

Formation and degradation of strongly reducing cyanoarene-based radical anions towards efficient radical anion-mediated photoredox catalysis

Cyanoarene-based photocatalysts (PCs) have attracted significant interest owing to their superior catalytic performance for radical anion mediated photoredox catalysis. However, the factors affecting the formation and degradation of cyanoarene-based PC radical anion (PC•‒) are still insufficiently understood. Herein, we therefore investigate the formation and degradation of cyanoarene-based PC•‒ under widely-used photoredox-mediated reaction conditions. By screening various cyanoarene-based PCs, we elucidate strategies to efficiently generate PC•‒ with adequate excited-state reduction potentials (Ered*) via supra-efficient generation of long-lived triplet excited states (T1). To thoroughly investigate the behavior of PC•‒ in actual photoredox-mediated reactions, a reductive dehalogenation is carried out as a model reaction and identified the dominant photodegradation pathways of the PC•‒. Dehalogenation and photodegradation of PC•‒ are coexistent depending on the rate of electron transfer (ET) to the substrate and the photodegradation strongly depends on the electronic and steric properties of the PCs. Based on the understanding of both the formation and photodegradation of PC•‒, we demonstrate that the efficient generation of highly reducing PC•‒ allows for the highly efficient photoredox catalyzed dehalogenation of aryl/alkyl halides at a PC loading as low as 0.001 mol% with a high oxygen tolerance. The present work provides new insights into the reactions of cyanoarene-based PC•‒ in photoredox-mediated reactions.

Perylene diimide-based radical anions for the rapid detection of picomolar H2O2 in an aqueous medium.

The formation of radical anions (PDI 1˙-) using H2S as a sacrificial electron donor in 50% HEPES buffer-THF solution is reported. PDI 1˙- was confirmed by optical, I-V plot, CV, DPV, NOBF4 and EPR studies. PDI 1˙- has a half-life of 96 minutes in solution and 11 days in the solid state without any additive. The formation of PDI 1˙- was confirmed by AFM and SEM. PDI 1˙- can be used for the detection of 26.6 pM of H2O2 supported by optical and CV data.

Cobalt(II) coordination to an N4-acenaphthene-based ligand and its sodium complex.

A new bifunctional N4-ligand was obtained via the condensation reaction of acenaphthenequinone and 2-picolylamine. A peculiarity of this synthesis is the formation of a new intramolecular C-C bond during the reaction. The structure and redox properties of the ligand were studied. The anion-radical form of the ligand was prepared via the chemical reduction of the latter with metallic sodium as well as in situ via its electrochemical reduction in a solution. The sodium salt prepared was structurally characterized using single-crystal X-ray diffraction (XRD). New cobalt complexes with the ligand in neutral and anion-radical forms were synthesized and further studied. As a result, three new homo- and heteroleptic cobalt(II) complexes were obtained, in which the cobalt atom demonstrates different modes of coordination with the ligand. Cobalt(II) complex CoL2 with two monoanionic ligands was prepared by the electrochemical reduction of a related L2CoBr2 complex or by treating cobalt(II) bromide with the sodium salt. XRD was used to study the structures of all cobalt complexes prepared. Magnetic and electron paramagnetic resonance studies were performed: CoII ion states with S = 3/2 and S = 1/2 were found for the complexes. A quantum-chemical study confirmed that the spin density is mainly located at the cobalt center.