Stable Radical Research Articles

Anthocyanin stability and antioxidant capacity of Clitoria ternatea incorporated jelly

Antioxidants from natural sources from Clitoria ternatea (butterfly blue pea flower) have recently received great attention as an increase in oxidative stress disease is concerning. One of the most useful bioactive compounds from C. ternatea extract is anthocyanin, which is generally unstable due to various factors. Therefore, the extraction process needs to be optimized with a condition that favours the stability of anthocyanin. The effect of sugar as a preservative on the anthocyanin stability and antioxidant capacity of C. ternatea has been studied on anthocyanin-rich jelly formulated in two different conditions using dried butterfly blue pea flowers. The extract (E), jelly with sugar (JWS), and jelly without sugar (JWOS) were analyzed for their anthocyanin stability and antioxidant capacity for 11 weeks at two storage temperatures (25°C and 4°C). Total anthocyanin content was determined by the pH differential method, while antioxidant capacity was determined by a common 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. After two weeks of storage, the total anthocyanin content in the extract and jelly samples decreased over time, with no major difference between the samples in temperature and the presence of sugar. However, the extract alone possessed a higher and better stability of anthocyanin content (56.27 µg/ mL to 7.19 µg/mL) after 14 days of storage at both temperatures (25°C and 4°C) compared to the processed food. It might be due to the processing effect on jelly samples during the analysis that might influence the final anthocyanin content (TAC). On the other hand, jelly incorporated with anthocyanin gives a significantly higher and more stable free radical scavenging activity than the extract, with no remarkable difference between jelly with sugar and without sugar at a different temperature. In addition, anthocyanin pigments from extract and jelly samples steadily degrade during storage at 25°C after 35 days of storage, which dramatically impacts colour quality and may also affect its nutritional properties. In conclusion, their food preparation (in extract or processed form) and storage temperature highly affected anthocyanin stability and its antioxidant capacity. 1. Introduction The current lifestyle of commonly consuming processed foods, lack of exercise, and exposure to a wide range of toxins may lead to a condition defined as oxidative stress. It is marked by an imbalance in the formation and buildup of reactive oxygen species (ROS) in cells and tissues, with the biological system's inability to detoxify these reactive products that worsen the situation (Sharifi-Rad et al., 2020). From another point of view, modernization also brings a new chapter to technological and scientific innovation, which help

Scalable Approach for Grafting Qubit Candidates onto The Surface of MOF-808 Framework

The development of quantum bits (qubits) is crucial for the progress of quantum technologies. Among various approaches, the qubits based on paramagnetic centers have decent advantages, including their diversity and possibilities of regular ordering, for example, within the structure of metal-organic frameworks (MOFs). In the present work a simple and scalable approach to obtain qubit candidates based on stable organic radical 3-carboxy-proxyl and MOF-808 framework has been demonstrated. Investigation of the obtained compounds with different radical amounts using electron paramagnetic resonance (EPR) demonstrates the presence of two fractions of radicals, which is supported by simulations. Sufficiently long phase memory time at room temperature for the radicals adsorbed into MOF (0.39 μs), as well as the observed Rabi nutations, allow considering this material as a platform for qubits design. The developed approach is capable of incorporating various amounts of paramagnetic centers into the MOF structure and can be employed to obtain other spin qubit candidates.

A Stable Carbon-centered Radical Showing Six Amphoteric Redox States.

An air- and moisture-stable hydrocarbon radical with four six- and three five-membered rings alternately fused to a heptacycle was obtained by ortho fusion in a suitably ortho,ortho'-substituted diphenylfluorene and subsequent re-establishment of the conjugation. The radical was obtained in five consecutive steps from commercially available starting materials with a total yield of 34%; key steps are Suzuki couplings and cyclizing SEAr reactions. Mesityl substituents at the five-membered rings ensure the stability of the radical. This cyclopenta-fused polyaromatic hydrocarbon (CP-PAH) was characterized by EPR and UV/Vis spectroscopy and by cyclic voltammetry. Quantum chemical calculation disclosed further properties and led to simulated spectra (spin densities, aromaticity, orbital energies, and UV/Vis/NIR). This radical is best described with the unpaired electron centered in the outer five-membered rings; this resonance formula shows the largest number of fully intact benzene rings. Its triradical character was computed to be very small and can be neglected. The five-membered rings show notable antiaromatic character, especially in the central ring. The constitution of the radical could be further substantiated by X-ray crystallographic analysis of its direct precursor.

Donor-Acceptor Viologens with Through-Space Conjugation for Enhanced Visible-Light-Driven Photocatalysis.

A series of novel donor-acceptor (D-A) type viologens with through-space conjugation (TSC) are synthesized. The synergistic effect of D-A conjugation and TSC endow these compounds with a narrower energy gap, excellent redox properties, strong absorption in the visible range (up to 450nm), and high efficiency of intramolecular charge transfer (ICT). These compounds also exhibit a long-lived charge separation state and stable radical formation. Considering their impressive photophysical and redox properties, TSC viologens with D-A conjugation are explored for visible-light-driven photocatalysis. As a catalyst in oxidative coupling reactions under visible light, compound 9 can achieve a yield of 94%, attributed to its strong ICT effect. Additionally, hybridized into graphitic carbon nitride (g-C₃N₄), compound 9 enhances hydrogen production performance under visible light, achieving an H2 generation rate of 4102µmolh-1g-1. This study highlights the potential applications of TSC viologens in photocatalytic systems.

Colorimetric quantification of vancomycin by highly active nitroxyl radical compounds.

Nitroxyl radicals, represented by 2,2,6,6-tetramethylpiperidine N-oxyl (TEMPO), are highly stable organic free radicals with unique properties and are used as functional molecules in various fields. However, TEMPO had low reactivity and sometimes did not provide enough response. Therefore, highly active nitroxyl radical compounds have been developed in which bicyclo and tricyclo structures stabilize the radicals. In this study, we found that nortropine N-oxyl (NNO), a type of highly active nitroxyl radical, can oxidize the 2,2'-dihydroxybiphenyl structure under physiological conditions, and succeeded in the colorimetric quantification of vancomycin containing 2,2'-dihydroxybiphenyl moieties in the molecular structure. The reaction took only a few minutes to complete and could be confirmed with the naked eye, with a quantitative range of 10-100μM. High-performance analytical probes are expected to be developed that use highly active nitroxyl radical derivatives to replace TEMPO derivatives.

Luminescent Radical Polymers.

Organic radicals are gaining significant interest in luminescent materials due to their unique properties, which present unprecedented opportunities for innovation across various fields, from display technology to biomedical applications. However, addressing challenges related to stability and low fluorescence efficiency is crucial to unlocking their full potential for practical applications. Polymerization has emerged as an effective strategy to enhance intra- and interchain through-space interactions, enabling the creation of stable luminescent radicals with excellent processing and multifunctional properties. This concept emphasizes the strategic use of polymerization in designing and synthesizing stable main-chain and side-chain radical polymers. This approach not only broadens the scope of stable radicals but also improves their luminescence properties as photofunctional materials.

Propeller‐Shaped Blatter‐Based Triradicals: Distortion‐Free Triangular Spin System and Spin‐State‐Dependent Photophysical Properties

Herein, we report the synthesis and properties of triptycene‐based C3v‐ and Cs‐symmetric stable radical trimers. SQUID magnetometry showed the propeller‐shaped trimers were both an antiferromagnetic equilateral triangle spin system with small spin‐spin interaction J/kB ~ −120 K and –106 K, leading to ca. 4/6 coexistence of the doublet/quartet states in thermal equilibrium at room temperature. The trimers exhibited characteristic NIR absorption bands reaching 1000 nm, which was solely ascribed to the triradical in the doublet state by variable‐temperature spectroscopic studies and quantum chemical calculations. Taking advantage of the spin‐specific absorption feature, we found that the triradicals in the low‐spin state undergo symmetry‐breaking charge transfer, while those in the high‐spin state fall into a monomer‐like excited state.

Propeller-Shaped Blatter-Based Triradicals: Distortion-Free Triangular Spin System and Spin-State-Dependent Photophysical Properties.

Herein, we report the synthesis and properties of triptycene-based C3v- and Cs-symmetric stable radical trimers. SQUID magnetometry showed the propeller-shaped trimers were both an antiferromagnetic equilateral triangle spin system with small spin-spin interaction J/kB ~ -120 K and -106 K, leading to ca. 4/6 coexistence of the doublet/quartet states in thermal equilibrium at room temperature. The trimers exhibited characteristic NIR absorption bands reaching 1000 nm, which was solely ascribed to the triradical in the doublet state by variable-temperature spectroscopic studies and quantum chemical calculations. Taking advantage of the spin-specific absorption feature, we found that the triradicals in the low-spin state undergo symmetry-breaking charge transfer, while those in the high-spin state fall into a monomer-like excited state.

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 (1 a-c and 2 a-c), which exhibited excellent chemical stability and emission ranging from green to near-infrared (527-714 nm). Notably, the selenium-substituted radical (1 c) 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.

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

AbstractOrganic 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 (1 a–c and 2 a–c), which exhibited excellent chemical stability and emission ranging from green to near‐infrared (527–714 nm). Notably, the selenium‐substituted radical (1 c) 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.

Magnetic Circular Dichroism of Luminescent Triarylmethyl Radicals.

Stable triarylmethyl radicals are the most common carbon radical building blocks and have recently attracted much attention for their luminescent properties. However, magnetic circular dichroism (MCD) discovered by Michael Faraday and magnetic circularly polarized luminescence (MCPL) have not been observed for simple triarylmethyl radicals, probably due to their photodegradability. Here we report the first observation of MCD and MCPL of triarylmethyl radicals in solution using racemic mixtures of (3,5-dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radical (PyBTM) and (3,5-difluoro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radical (F2PyBTM), which are much more photostable than simple triphenylmethyl radical derivatives. Faraday B terms, which are at the origin of magnetic dichroism in nondegenerate systems, were calculated using TD-DFT, and the line shape of MCD spectra was well reproduced. This study provides new circular dichroism properties for luminescent triarylmethyl radicals in solution without separating enantiomers and also clarifies the origin of magnetic circular dichroism properties of stable organic radicals for the first time.

Benzylic C−H Radical Sulfation by Persulfates

AbstractSulfation is a highly valuable pathological and physiological process, yet it is often underappreciated considering the rather difficult accessibility of organosulfates. O‐sulfonation (O−SO3), a conventional and still common way to make organosulfates, restricts its applicability to hydroxyl compounds and therein lies a major challenge of library construction. Here, we describe a benzylic C−H radical sulfation with persulfates via C−O bond formation. This strategy leverages modular control over the reactivity of persulfates and the stability of sulfate radicals by coutercations. K+/NH4+ stabilized sulfate radicals act as the oxidant to generate carbon‐centered radicals from substrates, and activation of persulfates by n‐NBu4+ provides O−O resource pool to facilitate C−OSO3− bond formation via a bimolecular homolytic substitution (SH2) process.

Benzylic C-H Radical Sulfation by Persulfates.

Sulfation is a highly valuable pathological and physiological process, yet it is often underappreciated considering the rather difficult accessibility of organosulfates. O-sulfonation (O-SO3), a conventional and still common way to make organosulfates, restricts its applicability to hydroxyl compounds and therein lies a major challenge of library construction. Here, we describe a benzylic C-H radical sulfation with persulfates via C-O bond formation. This strategy leverages modular control over the reactivity of persulfates and the stability of sulfate radicals by coutercations. K+/NH4 + stabilized sulfate radicals act as the oxidant to generate carbon-centered radicals from substrates, and activation of persulfates by n-NBu4 + provides O-O resource pool to facilitate C-OSO3 - bond formation via a bimolecular homolytic substitution (SH2) process.

ESR measurement of carbonated hydroxyapatite for dosemeter.

We have examined a dosimetry characteristic of carbonate hydroxyapatite (CO3HAp), which is a dental bone graft material. The purpose of this work is to investigate the reproducibility and stability of radiation-induced radicals on CO3HAp samples and assess the feasibility of using these materials as dosemeters. CO3HAp samples were exposed to gamma rays with dose range from 10 to 10000Gy. The electron spin resonance (ESR) spectra for irradiated samples were measured. Variation of peak-to-peak amplitude of the ESR signal intensity as a function of absorbed dose for CO3HAp was compared with that for alanine dosemeters, suggesting that the CO3HAp sample has a good linear dose response in the range from 10to 10000Gy as well as does the alanine dosemeters.

Synthesis of (bicyclo[2.2.0]hex-1-yl)methanal and Arrhenius parameters for thermal rearrangement: Radical stabilizing effect of aldehyde substituents on highly strained C[sbnd]C bonds

Bicyclo[2.2.0]hexane rearranges to hexa-1,5-diene via the cyclohexane-1,4-diyl diradical. The 1-formyl substituted derivative was sought to evaluate the effect of a CHO-group on the rate of rearrangement. (Bicyclo[2.2.0]hex-1-yl)methanal was prepared for the first time in a multistep synthesis starting from hexachlorocyclopentadiene. The pivotal last step was achieved by Swern oxidation of (bicyclo[2.2.0]hex-1-yl)methanol at T = –60 °C. The carbon skeleton of the alcohol precursor remains intact under those conditions. Thermolysis of the aldehyde to 2-methylenehex-5-enal follows a first-order rate law between T = 322.85–361.51 K (Tavg = 343.30 K). Seven rate constants kT were used to plot log kT vs. 1/T, which provided the Arrhenius parameters for the rearrangement: activation energy (Ea) = 25.4 ± 1.0 kcal/mol and pre-exponential factor (A343) = 1.66 × 1012 s−1. The Ea is 10.6 kcal/mol below that of the unsubstituted archetype bicyclo[2.2.0]hexane. This sizable change in Ea reflects the radical stabilization energy of the CHO-group in 1-formylcyclohexane-1,4-diyl.

Independent LUMO Reactivity in Mesoionic N-Heterocyclic Thiones: Synthesis of a Stable Radical Anion.

Mesoionic compounds, with positive and negative charges, are expected to have dual-site highest occupied molecular orbital (HOMO, donor) and lowest unoccupied molecular orbital (LUMO, acceptor) reactivity. Herein, we report a novel class of air-stable mesoionic N-heterocyclic thiones (mNHTs) synthesized from abnormal N-heterocyclic carbenes (aNHCs). DFT studies revealed a highly polarized exocyclic thione moiety and computed Fukui function analysis suggests the dual-site HOMO/LUMO reactivity of mNHTs predicting donor property at the negatively charged 'S' center while acceptor property at the cationic imidazole ring. The independent LUMO reactivity of the mNHT was realized by its chemical reduction to an elusive radical anion, which was characterized by a single crystal X-raydiffraction study. Further, we explore the reactivity of radical anion for the activation of SO2 gas, C-Br bonds of aryl bromide and photocatalytic functionalization of C-X (X = F, Br) bonds. This work unlocks the independent LUMO reactivity of a mesoionic compound.

Independent LUMO Reactivity in Mesoionic N‐Heterocyclic Thiones: Synthesis of a Stable Radical Anion

AbstractMesoionic compounds, with positive and negative charges, are expected to have dual‐site highest occupied molecular orbital (HOMO, donor) and lowest unoccupied molecular orbital (LUMO, acceptor) reactivity. Herein, we report a novel class of air‐stable mesoionic N‐heterocyclic thiones (mNHTs) synthesized from abnormal N‐heterocyclic carbenes (aNHCs). DFT studies revealed a highly polarized exocyclic thione moiety and computed Fukui function analysis suggests the dual‐site HOMO/LUMO reactivity of mNHTs predicting donor property at the negatively charged ‘S’ center while acceptor property at the cationic imidazole ring. The independent LUMO reactivity of the mNHT was realized by its chemical reduction to an elusive radical anion, which was characterized by a single crystal X‐raydiffraction study. Further, we explore the reactivity of radical anion for the activation of SO2 gas, C−Br bonds of aryl bromide and photocatalytic functionalization of C−X (X = F, Br) bonds. This work unlocks the independent LUMO reactivity of a mesoionic compound.

Crystallization‐Induced Dimerization and Solution‐Phase Bond Dissociation of Stable Dibenzoolympicenyl Radicals

AbstractCrystallization of organic materials can lead to different assembly structure with different reactivity, but this phenomenon is rarely observed for delocalized hydrocarbon radicals. This report introduces a crystallization‐induced radical–radical coupling reaction, which employs a series of stable nonplanar organic π‐radicals as reactants. Six stable radical congeners are synthesized, resulting in radical–radical coupling at the allenyl radical site during crystallization to produce close‐shell dimers. This coupling reaction is absent in the solution phase, which highlights the importance of preorganization in the lattice. Remarkably, the attempts of cocrystallization of different congeners yielded homocoupling products instead of cross‐coupling products. In specific cases, two distinct polymorphs are observed and their reactivity is different according to the distance of the reaction sites. Theoretical calculations indicate that the transition from a metastable preorganized monomer to a dimer is barrierless and spontaneous. The dimer could regenerate free radicals by heating or photoirradiation in the solution phase. This discovery may lead to controllable molecular switches.

Crystallization-Induced Dimerization and Solution-Phase Bond Dissociation of Stable Dibenzoolympicenyl Radicals.

Crystallization of organic materials can lead to different assembly structure with different reactivity, but this phenomenon is rarely observed for delocalized hydrocarbon radicals. This report introduces a crystallization-induced radical-radical coupling reaction, which employs a series of stable nonplanar organic π-radicals as reactants. Six stable radical congeners are synthesized, resulting in radical-radical coupling at the allenyl radical site during crystallization to produce close-shell dimers. This coupling reaction is absent in the solution phase, which highlights the importance of preorganization in the lattice. Remarkably, the attempts of cocrystallization of different congeners yielded homocoupling products instead of cross-coupling products. In specific cases, two distinct polymorphs are observed and their reactivity is different according to the distance of the reaction sites. Theoretical calculations indicate that the transition from a metastable preorganized monomer to a dimer is barrierless and spontaneous. The dimer could regenerate free radicals by heating or photoirradiation in the solution phase. This discovery may lead to controllable molecular switches.

Molecular properties of a triazole-Ce(III) complex with antioxidant activity: structure, spectroscopy, and relationships with related derivatives. Influence of the ligands in the complex.

A novel Ce(III) complex with the triazole ligand 2b, which presents four H-bonded sites with amino acids of the MMP-2 receptor, was synthesized. The experimental IR and Raman spectra of this Ce(III) complex were well-interpreted based on their comparison to the theoretical scaled spectra using the scaling equations determined by two procedures and four density functional theory (DFT) levels. Therefore, the structure predicted for the synthesized Ce(III) complex was clearly characterized and confirmed. The potential antioxidant action of this complex was compared with the analogous La(III) complex, and it was found that the coordination of ligand 2b with Ce(III) improves the ligand's ability to participate in single-electron transfer (SET), as observed in the ABTS·+ assay, and this complex seems to scavenge the stable radical much more actively compared to its La(III) counterpart. Additionally, interactions with potassium superoxide and sodium hypochlorite indicate a high pro-oxidant behavior of the complex. The effects of different ligands on the geometric parameters, atomic charges, and molecular properties of the Ce(III) complex were analyzed at four DFT levels, and several relationships were clearly established. These relationships can facilitate the selection of new ligands with improved properties in the design of novel lanthanide-triazole carboxylate complexes with promising biological activity. The ligand size increase in the complexes facilitates the electronic transfer of negative charge, and the low HOMO (highest occupied molecular orbital)-LUMO (lowest unoccupied molecular orbital) energy gap indicates a large reactivity and low energy for their excitation.