Class Of Radicals Research Articles

Stable Xanthene Radicals and Their Heavy Chalcogen Analogues Showing Tunable Doublet Emission from Green to Near-infrared.

Organic luminescent radicals, unlike traditional closed-shell fluorescent emitters, exhibit distinct luminescence mechanisms, offering promising potential for optoelectronic devices. To date, stable luminescent radicals have predominantly been confined to polychlorinated triphenylmethyl radicals, underscoring the need for new platforms to expand their emission spectra. In this study, we report the synthesis of stable 9-aryl-substituted xanthene radicals and their heavy chalcogen analogues (1a-c and 2a-c), which exhibited excellent chemical stability and emission ranging from green to near-infrared (527~714 nm). Notably, the selenium-substituted radical (1c) demonstrates a significantly enhanced photoluminescence quantum yield of 41% when doped into its precursor solid. Additionally, the introduction of methoxyphenyl groups has largely enhanced the stability of the radical, showcasing an excellent photostability with the longest half-life of around 1792 h. The high internal quantum efficiency of up to 81% was further validated in organic light-emitting diode. This study introduces a novel class of stable carbon-centered radicals with high tunability and functionality for photoelectric applications.

At the Speed of Light: Recent Advances on Photocatalyzed Generation and Applications of Iminyl Radicals Promoted by Visible-light

: Nitrogen-positioned radicals are chemical entities that have a lengthier history than carbon ones and their high reactivity makes them invaluable. But, despite its power, much of its chemistry is still uncharted. Currently, developed methodologies to access nitrogen-positioned radicals, such as transition metal catalysis or visible-light photoredox methods through a single-electron transfer process, avoiding the use of harmful or toxic reagents, excess raw materials, solvents as well as pre-functionalization steps or extensive synthetic routes are in continuous progress. This revision aims to depict the recent advances in the field of iminyl-radicals’ syntheses, a special class of radicals placed on nitrogen, catalyzed by transition metals or photoredox techniques for the construction of C-N bonds and their synthetic applications. This work serves as a comprehensive guide for the scope of synthetic applications that this kind of radicals could have.

Unraveling the Isotropic Hyperfine Coupling Constants of Nitroxide Radicals via Molecular Electrostatic Potential Analysis.

Nitroxide radicals have wide and promising applications as organic magnetic materials. Modulating the isotropic hyperfine coupling constants (HFCCs) of these radicals through proper structural design is an effective strategy for their application as spin probes and spin labels. In the present work, density functional theory calculations were carried out to develop a robust descriptor based on the molecular electrostatic potential for nitrogen HFCCs of nitroxide radicals. Forty nitroxide radicals from five distinct classes, namely, derivatives of cyclic, acyclic, imino, nitronyl, and benzimidazole nitronyl nitroxides, were selected, and the molecular electrostatic potential (MESP) at the nitrogen atom (VN) of the NO moiety was calculated. The VN values efficiently capture the electronic changes associated with the steric and electronic nature of these systems. A significant correlation between VN values and the experimental HFCCs of nitrogen nuclei demonstrates the applicability of VN as a simple and efficient descriptor for monitoring HFCCs. Furthermore, a good correlation between VN and experimental nitrogen HFCCs for each class of nitroxide radicals indicates the use of VN in the evaluation of the magnetic nature of the nitroxide radicals. The findings in this work are expected to facilitate the design of novel nitroxide radicals with desirable magnetic properties based on MESP topology analysis.

Highly-separated Co anchored on S, O-doped carbon nitride for enhanced peroxymonosulfate activation: Insights into radical and non-radical pathways

Understanding the various catalytic mechanisms of activated peroxymonosulfate (PMS) is crucial for designing high-efficiency metal-supported catalysts. Herein, Co, S, O co-doped carbon nitride (CoCN-x) was constructed. Density functional theory (DFT) calculations for CN doped with different elements revealed that CoCN-x exhibited improved PMS activation capabilities. Optimized CoCN-0.5 achieved a 95% removal rate of sulfamethoxazole (SMX) within 30 s, with a degradation rate constant of 2.92 min−1, which is 845.34 times higher than that of the original CN. Additionally, the activation mechanism of PMS was thoroughly investigated, revealing the presence of classical radicals such as OH, SO4− and O2− and non-radicals involving 1O2, CoO2+, and electron transfer. Potential SMX degradation pathways were also elucidated using DFT calculations, HPLC-MS, and 3D EEMs. This work provides new insights into the development of catalysts that effectively activate PMS through both radical and non-radical mechanisms.

High-Pressure Limit and Pressure-Dependent Rate Rules for β-Scission Reaction Class of Hydroperoxyl Alkyl Hydroperoxyl Radicals (•P(OOH)2) in Normal-Alkyl Cyclohexanes Combustion.

Chemical kinetic studies of the β-scission reaction class of hydroperoxyl alkyl hydroperoxyl radicals (•P(OOH)2) from normal-alkyl cyclohexanes are carried out systematically through high-level ab initio calculations. Geometry optimizations and frequency calculations for all species involved in the reactions are performed at the B3LYP/CBSB7 level of theory. Electronic single-point energy calculations are calculated at the CBS-QB3 level of theory. Rate constants for the reactions of β-scission, in the temperature range of 500-1500 K and the pressure range of 0.01-100 atm, are calculated using transition state theory (TST) and Rice-Ramsberger-Kassel-Marcus/Master-Equation (RRKM/ME) theory taking asymmetric Eckart tunneling corrections and the one-dimensional hindered rotor approximation into consideration. The rate rules are obtained by averaging the rate constants of the representative reactions of this class. These rate rules can greatly assist in constructing more accurate low-temperature combustion mechanisms for normal-alkyl cyclohexanes.

Environmental-Persistent Free Radicals Prediction by Neural Networks

Air pollution is recognized as a critical threat to human health. The link between the inhalation of fine particulate matter (PM) in combination with toxic gases and the resulting health effects is well documented. The health damages were proven to be interrelated with the free radicals caused by air pollution. Free radicals cause a destructive chain reaction by taking an electron from a stable molecule and converting it into an unstable one. Environmentally persistent free radicals (EPFRs) were not considered until the last ten years as an important part of the air pollution composition. EPFRs are a special class of free radicals with a long half-life, contributing to the development of aging-related diseases in living organisms, as well as harmful oxidative effects in lung tissue. The work is grounded on database of the routinely measured air quality parameters (air pollutants О3, CO, NO2, SO2, PM2.5) and corresponding EPFR data to develop a model for EPFR prediction. An intelligent instrument is used to perceive the pollution information and, on this basis, EPFR values without direct measurement were calculated. Applying the above approach, an average deviation of 0.73 was accomplished.

Perylene diimide-hydroxyphenyl benzothiazole-based new class of radical anions/dianions: biochemical assay for glucose detection.

We report the design, synthesis and characterization of a perylene diimide-hydroxyphenyl benzothiazole (BT-PDI) dyad as a new class for the formation of radical anion (BT-PDI˙-) and dianion (BT-PDI2-) in aqueous medium using H2S. We demonstrate the applications of BT-PDI˙- for (i) the detection of H2O2; (ii) the detection of glucose in blood serum using a biochemical assay and (iii) the reduction of Ag+ to Ag0.

Acyloxy, sulfate, and phosphate radicals as hydrogen atom transfer (HAT) agents for direct C(sp3)–H functionalization

This tutorial review focuses on the recent advancements in HAT-based direct C(sp3)–H bond functionalization with three unique classes of oxygen radicals: acyloxy, sulfate, and phosphate radicals.

A Theoretical Kinetic Study on Concerted Elimination Reaction Class of Peroxyl-hydroperoxyl-alkyl Radicals (•OOQOOH) in Normal-alkyl Cyclohexanes.

The concerted elimination reaction class of peroxyl-hydroperoxyl alkyl radicals (•OOQOOH) plays a crucial role in the low-temperature combustion of normal-alkyl cyclohexanes. The generation of the relatively unreactive HO2 radicals in this reaction is one of the factors leading to the negative temperature coefficient (NTC) behavior, which hinders the low-temperature oxidation of normal-alkyl cyclohexanes. In this study, 44 reactions are selected and divided into 4 different subclasses according to the nature of the carbon atom where the H atom is eliminated and the reaction center position. Utilizing the CBS-QB3 method, we compute the energy barriers for the concerted elimination reactions of peroxyl-hydroperoxyl alkyl radicals. Following this, we assess both the high-pressure limit and pressure-dependent rate constants for all reactions by applying TST and RRKM/ME theory. These calculations allow for the development of rate rules, which come to fruition through an averaging process involving the rate constants of representative reactions within each subclass. Our work provides accurate rate constants and rate rules for this reaction class, which can aid in constructing more accurate combustion mechanisms for normal-alkyl cyclohexanes.

Influence of Nafion and PBI Membranes on the Performance of Verdazyl Species in Aqueous Redox Flow Batteries

The concept of redox flow batteries (RFB) was originally patented in 1949 by Dr. Kangro with inorganic active materials like iron- or chromium-ions in mind.[1] Intensive research on inorganic active materials led to the proposal of vanadium based RFBs in 1985 by the Skyllas-Kazacos group, which is the most intensively studied RFB type currently.[2],[3] Organic active materials were introduced in 2009 for RFBs and offer a potential alternative to vanadium as active species, due to potentially lower costs and the replacement of rare metal ions.[4],[5] The class of verdazyl radicals has gathered interest as organic active material for the battery application since the publication of symmetrical coin cells.[6] Verdazyl radicals can be transformed into an oxidized or reduced species by a one electron reaction in organic electrolytes, which motivates the application in symmetrical RFBs.[7] Still, degradation of the verdazyl species during operation of the symmetrical battery in organic electrolytes as well as the theoretical voltage of ≈ 1 V show the need for further optimization of the material class and electrolytes.[6] While previous electrochemical investigations of verdazyl species were limited to organic electrolytes, we used a different approach and investigated the influence of acidic electrolytes on the redox chemistry of this material class.[8] Strongly acidic electrolytes lead to a disproportionation of the radical form. The resulting species differ by two electrons and two protons and show a reversible redox reaction in cyclovoltammetry measurements. This different reaction is of interest for the RFB application due to the fast rate constant as well as the utilization of two electrons.[8] Herein, we take the next step for the possible application of the redox chemistry of verdazyl species in acidic electrolytes into aqueous RFBs by analyzing the influence of the separating membranes. We use 1,3,5-triphenylverdazyl species as model compounds in 1 M sulfuric acid. To investigate the influence of the separating membranes in aqueous RFBs, we use Nafion 211 as commercial standard and compare it to self-made mPBI and O-PBI-based polybenzimidazole (PBI) membranes with a target thickness of ≈ 25 µm. When Nafion membranes are immersed in verdazyl cation solutions, they absorb ≈ 0.5 verdazyl cations per sulfonic acid group from the solution, whereas no absorption was observed for PBI membranes. UV/vis also did not show any changes in the UV/vis spectra of the solution, indicating that the verdazyl cations did not degrade. Beside the chemical stability, the permeability through the membranes is characterized, which is detrimental for the capacity retention in an RFB. To fully characterize the membranes with verdazyl species, the conductivity of the membranes is measured and the influence of the verdazyl species onto the conductivity is investigated. As a last step, symmetrical RFBs of verdazyl species in acidic electrolytes are built and the capacity retention is compared.With this study, we show the detrimental effect of using Nafion in combination with verdazyl species. Nafion 211 shows a high affinity to verdazyl cations and absorbs them from the electrolyte, leading to fast capacity fading of the RFB. PBI membranes show chemical stability as well as low absorption and permeability.Our study presents the one of the next steps towards the implementation of verdazyl species into water-based RFBs by investigating the suitability of PBI membranes for this application. PBI membranes offer overall good stability and beneficial properties for this application, while state-of-the-art Nafion is not applicable.

Direct mapping of kidney function by DCE-MRI urography using a tetrazinanone organic radical contrast agent

Chronic kidney disease (CKD) and acute kidney injury (AKI) are ongoing global health burdens. Glomerular filtration rate (GFR) is the gold standard measure of kidney function, with clinical estimates providing a global assessment of kidney health without spatial information of kidney- or region-specific dysfunction. The addition of dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) to the anatomical imaging already performed would yield a ‘one-stop-shop’ for renal assessment in cases of suspected AKI and CKD. Towards urography by DCE-MRI, we evaluated a class of nitrogen-centered organic radicals known as verdazyls, which are extremely stable even in highly reducing environments. A glucose-modified verdazyl, glucoverdazyl, provided contrast limited to kidney and bladder, affording functional kidney evaluation in mouse models of unilateral ureteral obstruction (UUO) and folic acid-induced nephropathy (FAN). Imaging outcomes correlated with histology and hematology assessing kidney dysfunction, and glucoverdazyl clearance rates were found to be a reliable surrogate measure of GFR.

High-Pressure-Limit and Pressure-Dependent Rate Rules for Intramolecular Cyclization Reactions of α,β-Hydroxyl Hydroperoxyalkyl Radicals

ABSTRACT The cyclization reaction class of hydroxyl hydroperoxyalkyl radicals is one of the crucial reaction classes in low-temperature combustion mechanism of alcohols and alkenes. However, there is a lack of reports on accurate high-pressure-limit rate rules and pressure-dependent rate rules for this reaction class in literature. In this paper, 108 reactions are selected and divided into different classes according to the type of hydroxyl hydroperoxyalkyl radicals, the ring size of the transition states, and the position of the OH group. The energy barriers of the cyclization reactions of hydroxyl hydroperoxyalkyl radicals are calculated by the isodesmic reaction method, and the high-pressure-limit rate constants and pressure-dependent rate constants of all reactions are calculated using the TST and RRKM/ME theory, from which a high-pressure-limit rate rule and pressure-dependent rate rule for each subclass are established. It found that the isodesmic reaction method gives accurate energy barriers and rate constants, and the calculated rate constants of the cyclization reactions of hydroxyl hydroperoxyalkyl radicals are different from those of analogous reactions in alkanes, which indicates the necessity of establishing the rate rules for the cyclization reactions of hydroxyl hydroperoxyalkyl radical. There are large differences in energy barriers and rate constants among the whole reaction classes of the cyclization reactions of hydroxyl hydroperoxyalkyl radicals, so it is necessary to divide the cyclization reactions class into subclasses, and it is also shown that the pressure has a significant effect on the rate constants. In summary, accurate high-pressure-limit rate rules and pressure-dependent rate rules for the cyclization of hydroxyl hydroperoxyalkyl radicals have been developed in this study, which is helpful for the automatic construction of higher accuracy combustion mechanisms for alcohols and alkenes.

1-[2,6-Dimethyl-4-(pent-4-yn-1-yloxy)phenyl]-4-phenyl-1,2,4-triazolidine-3,5-dione

Urazolyl radicals are a class of persistent nitrogen-centered radicals. In a previous work, we successfully formed self-assembled monolayers of substituted urazolyl radicals on gold surfaces. To extend the scope of these investigations, we sought to form a self-assembled monolayer using a urazolyl radical species that we knew existed predominantly in the dimerized N-N form instead of existing predominantly as free N-centered radical species, as had previously been investigated. We successfully synthesized the precursor urazole compound needed to generate the desired urazolyl radical, and completely characterized its structure. Most importantly, it was determined that the alkyne functional group that is needed to adhere to the gold surface remained intact. Unfortunately, however, we only obtained ambiguous results from attempts at forming self-assembled monolayers of this species on gold.

Investigating the kinetics of the intramolecular H-migration reaction class of methyl-ester peroxy radicals in low-temperature oxidation mechanisms of biodiesel.

Biodiesel is a promising, sustainable, and carbon-neutral fuel. However, studying its combustion mechanisms comprehensively, both theoretically and experimentally, presents challenges due to the complexity and size of its molecules. One significant obstacle in determining low-temperature oxidation mechanisms for biodiesel is the lack of kinetic parameters for the reaction class of intramolecular H-migration reactions of alkyl-ester peroxy radicals, labeled as R(CO)OR'-OO˙ (where the 'dot' represents the radical). Current biodiesel combustion mechanisms often estimate these parameters from the analogous reaction class of intramolecular H-migration reactions of alkyl peroxy radicals in alkane combustion mechanisms. However, such estimations are imprecise and neglect the unique characteristics of the ester group. This research aims to explore the kinetics of the reaction class of H-migration reactions of methyl-ester peroxy radicals. The reaction class is divided into 20 subclasses based on the newly formed cycle size of the transition state, the positions of the peroxy radical and the transferred H atom, and the types of carbons from which the H atom is transferred. Energy barriers for each subclass are calculated by using the CBS-QB3//M06-2X/6-311++G(d,p) method. High-pressure-limit and pressure-dependent rate constants ranging from 0.01 to 100 atm are determined using the transition state theory and Rice-Ramsberger-Kassel-Marcus/master-equation method, respectively. It is noted that the pressure-dependent rate constants calculated for each individual isomerization channel could bring some uncertainties while neglecting the interconnected pathways. A comprehensive comparison is made between our values of selected reactions and high-level calculated values of the corresponding reactions reported in the literature. The small deviation observed between these values indicates the accuracy and reliability of the energy barriers and rate constants calculated in this study. Additionally, our calculated high-pressure-limit rate constants are compared with the corresponding values in combustion mechanisms of esters, which were estimated based on analogous reactions of alkyl peroxy radicals. These comparative analyses shed light on the significant impact of the ester group on the kinetics, particularly when the ester group is involved in the reaction center. Finally, the high-pressure-limit rate rule and pressure-dependent rate rule for each subclass are derived by averaging the rate constants of reactions in each subclass. The accurate and reasonable rate rules for methyl-ester peroxy radicals developed in this study play a crucial role in enhancing our understanding of the low-temperature oxidation mechanisms of biodiesel.

An interesting case of symmetry breaking in the absence of symmetry: the bicarbonate radical (HCO3)

As part of a computational study of the thermochemical properties of systems related to carbonic acid (HCO), an interesting phenomenon was observed in the bicarbonate radical (HCO). This species belongs to the class of formoxyl radicals, but lacks the geometric symmetry of the more heavily-studied and prototypical HCO and FCO molecules. However, it is not immune from the problems that those molecules present to electronic structure calculations. Specifically, at geometries in the vicinity of the equilibrium structure, three solutions to the unrestricted Hartree-Fock equations can be found: two in which the unpaired spin is largely localized onto one of the (inequivalent) carbonyl oxygen atoms, and one in which the spin is delocalized. While all three of these reference functions comprise orbitals that transform as pure irreducible representations of the point group, the two localized choices qualitatively correspond to the symmetry-broken solution of the formoxyl species and the delocalized solution qualitatively corresponds to the symmetry-preserving (but orbitally unstable) solution. The three solutions are described in this work, as well as the corresponding ambiguities that result in the thermochemical characterization of this species.

Neutral Boryl Radicals in Mixed-Valent B(III) Br-B(II) Adducts.

The general strategies to stabilize a boryl radical involve single electron delocalization by π-system and the steric hinderance from bulky groups. Herein, a new class of boryl radicals is reported, with intramolecular mixed-valent B(III) Br-B(II) adducts ligated by a cyclic (alkyl)(amino)carbene (CAAC). The radicals feature a large spin density on the boron center, which is ascertained by EPR spectroscopy and DFT calculations. Structural and computational analyses revealed that the stability of radical species was assisted by the CAAC ligand and a weak but significant B(III)Br-B(II) interaction, suggesting a cooperative avenue for stabilization of boryl radicals. Two-electron reduction of these new boryl radicals provides C-H insertion products via a borylene intermediate.

Visible-Light-Induced Palladium-Catalyzed Cross-Coupling of Iodocarboranes with (Hetero)Arenes.

This work describes a general method for the efficient production of a class of cage B-centered carboranyl radicals at the B3, B4, and B9 sites via a visible-light-promoted palladium(0)/palladium(I) pathway using readily available iodo-o-carboranes as the starting materials. The electrophilicities of these hypervalent boron-centered radicals decrease in the following order: B3 > B4 > B9. They are useful intermediates for the preparation of a family of cage B-(hetero)arylated o-carboranes at ambient temperature.

Photoredox Generation of Isothiouronyl Radical Cations: A New Platform in Covalent Radical Catalysis.

Thiyl radicals offer unique catalytic patterns for the direct covalent activation of alkenes. However, important limitations in terms of structural diversity and handling have hampered the routine use of thiyl radicals in covalent radical catalysis. Herein, we report a new class of cationic sulfur-centered radicals to achieve covalent radical catalysis. Their generation from highly modular thioureas by photoredox catalysis make their utilization very simple and reliable. The synthetic potential and the versatility of the catalytic system were finally evaluated in a (3+2)-radical cascade between vinylcyclopropanes and olefins.

High-Pressure-Limit Rate Coefficients for HO2 Elimination Reactions of Hydroperoxyalkenylperoxy Radicals based on the Reaction Class Transition State Theory.

Thermokinetic parameters and transport parameters are of great importance to the combustion model and the reaction rate rules are of great importance to construct the combustion reaction mechanism for hydrocarbon fuels. The HO2 elimination reaction class for hydroperoxyalkenylperoxy radicals is one of the key reaction classes for olefin, for which the rate coefficients are lacking. Therefore, the rate coefficients and rate rules of the HO2 elimination reaction class for hydroperoxyalkenylperoxy radicals are studied in this work. The reaction class transition state theory (RC-TST) is used to calculate the rate coefficients. In addition, the HO2 elimination reaction class of hydroperoxyalkenylperoxy radicals is divided into four subclasses depending upon the type of H–Cβ bond that is broken in the reactant molecules, and the rate rules are calculated by taking the average of rate coefficients from a representative set of reactions in a subclass. The calculated kinetics data would be valuable for the construction of the combustion reaction mechanism for olefin.

Classical Radicals of Invariants of Algebraic Skew Derivations

Let [Formula: see text] be an automorphism and[Formula: see text] be a [Formula: see text]-skew [Formula: see text]-derivation of an [Formula: see text]-algebra [Formula: see text]. We prove that if [Formula: see text] is semiprimitive and [Formula: see text] is algebraic, then the subalgebra [Formula: see text] has nilpotent Jacobson radical. Using this result, we obtain similar relations for the Baer prime radical, the Levitzki locally nilpotent radical, and the Köthe nil radical when the field [Formula: see text] is uncountable. Then we apply it to actions of the [Formula: see text]-dimensional Taft Hopf algebra [Formula: see text] and the [Formula: see text]-analogue [Formula: see text] of the enveloping algebra of the Lie algebra [Formula: see text].