Carbon Radicals Research Articles

Molecular surface engineering via collision-induced-dissociation-assisted grafting of antimicrobial molecules on self-assembled-silanized glass

The surface of a glass plate was molecularly engineered to become antimicrobial by coating it with a self-assembled layer of (3-aminopropyl) trimethoxysilane (APTMS) and then with an overlayer of antimicrobial benzyldodecyldimethylammonium bromide (BAB). Hyperthermal H2 molecules with a kinetic energy of about 15 eV were used as “bullets” to collide with BAB and APTMS to selectively cleave the CH bonds in them. Subsequent recombination of the carbon radicals thus formed lead to the crosslinking and fixation of BAB to APTMS which is itself strongly bonded to the glass surface via silanization. Molecular dynamics simulations were conducted to validate this peculiar hyperthermal hydrogen induced cross-linking (HHIC) mechanism, and hyperthermal hydrogen molecules with a high flux density over 1 × 1015 H2/cm2s for completing the HHIC process in 10 s in reaction-time were experimentally generated with a specifically designed instrument. The glass silanization with APTMS and the fixation of BAB molecules were assessed and confirmed by water contact angle (WCA) measurements, X-ray photoelectron spectroscopy (XPS), as well as atomic force microscopy (AFM). The antimicrobial activity against staphylococcus aureus was confirmed with the standard ISO/DIS 22196 test-method.

Tunable Nanoparticles with Aggregation-Induced Emission Heater for Precise Synergistic Photothermal and Thermodynamic Oral Cancer Therapy of Patient-Derived Tumor Xenograft.

The fluorophores in the second near-infrared (NIR-II) biological window (1000 - 1700nm) show great application prospects in the fields of biology and optical communications. However, both excellent radiative transition and nonradiative transition cannot be achieved simultaneously for the majority of traditional fluorophores. Herein, tunable nanoparticles formulated with aggregation-induced emission (AIE) heater are developed rationally. The system can be implemented via the development of an ideal synergistic system that can not only produce photothermal from nonspecific triggers but also trigger carbon radical release. Once accumulating in tumors and subsequently being irradiated with 808nm laser, the nanoparticles (NMB@NPs) encapsulated with NMDPA-MT-BBTD (NMB) are splitted due to the photothermal effect of NMB, leading to the decomposition of azo bonds in the nanoparticle matrix to generate carbon radical. Accompanied by second near-infrared (NIR-II) window emission from the NMB, fluorescence image-guided thermodynamic therapy (TDT) and photothermal therapy (PTT) which significantly inhibited the growth of oral cancer and negligible systemic toxicity is achieved synergistically. Taken together, this AIE luminogens-based synergistic photothermal-thermodynamic strategy brings a new insight into the design of superior versatile fluorescent NPs for precise biomedical applications and holds great promise to enhance the therapeutic efficacy of cancer therapy.

Reductive Deoxygenative Functionalization of Alcohols by First‐Row Transition Metal Catalysis

Comprehensive SummaryAlcohols are among the most accessible functionalities. Catalytic deoxygenative functionalization of alcohols is highly synthetically appealing. While significant progress has been made on the reactions with nucleophiles, the reactions with electrophilic coupling partners remain a real challenge. This manuscript highlights the advance in this direction, which is mainly achieved by the first‐row transition metals. The low‐valent titanium catalyst has shown the unique reactivity to homolytically cleave the C—OH bonds. The formed carbon radicals could either undergo reduction to give protonation products or couple with carbon fragments to form C—C bonds. This chemistry is initially realized using a stoichiometric amount of titanium reagents and later extended to catalytic variants. Nickel features a variety of oxidation states ranging from Ni0 to NiIV, and both two‐electron oxidative addition and single‐electron process are involved in their activation of an electrophile. These properties enable nickel to catalyze reductive C—C coupling of alcohols with R–X electrophiles. The reaction is first reported on the reactions of allylic alcohols, then extended to benzylic alcohols and, very recently non‐activated alcohols. Recent effort has resulted in many invaluable methodologies that highly improve the reaction efficiency for the construction of aliphatic C—C bonds. The use of cobalt and copper catalysts not only expands the substrate scope of these reactions but also shows the new reactivity and selectivity issues.

Comparative 6+studies of environmentally persistent free radicals on nano-sized coal dusts

Coal dust is the major hazardous pollutant in the coal mining environment. Recently environmentally persistent free radicals (EPFRs) were identified as one of the key characteristics which could impart toxicity to the particulates released into the environment. The present study used Electron Paramagnetic Resonance (EPR) spectroscopy to analyze the characteristics of EPFRs present in different types of nano-size coal dust. Further, it analyzed the stability of the free radicals in the respirable nano-size coal dust and compared their characteristics in terms of EPR parameters (spin counts and g-values). It was found that free radicals in coal are remarkably stable (can remain intact for several months). Also, Most of the EPFRs in the coal dust particles are either oxygenated carbon centered or a mixture of carbon and oxygen-centered free radicals. EPFRs concentration in the coal dust was found to be proportional to the carbon content of coal. The characteristic g-values were found to be inversely related to the carbon content of coal dust. The spin concentrations in the lignite coal dust were between 3.819 and 7.089 μmol/g, whereas the g-values ranged from 2.00352 to 2.00363. The spin concentrations in the bituminous coal dust were between 11.614 and 25.562 μmol/g, whereas the g-values ranged from 2.00295 to 2.00319. The characteristics of EPFRs present in coal dust identified by this study are similar to the EPFRs, which were found in other environmental pollutants such as combustion-generated particulates, PM2.5, indoor dust, wildfires, biochar, haze etc., in some of the previous studies. Considering the toxicity analysis of environmental particulates containing EPFRs similar to those identified in the present study, it can be confidently hypothesized that the EPFRs in the coal dust might play a major role in modulating the coal dust toxicity. Hence, it is recommended that future studies should analyze the role of EPFR-loaded coal dust in mediating the inhalation toxicity of coal dust.

Controlled Vertical Transfer of Individual Au Atoms Using a Surface Supported Carbon Radical for Atomically Precise Manufacturing

To explore a proof-of-concept for atomically precise manufacturing (APM) using scanning probe microscopy (SPM), first principle theoretical calculations of atom-by-atom transfer from the apex of an SPM tip to an individual radical on a surface-bound organic molecule have been performed. Atom transfer is achieved by spatially controlled motion of a gold terminated tip to the radical. Two molecular tools for SPM-based APM have been designed and investigated, each comprising an adamantane core, a radical end group, and trithiol linkers to enable strong chemisorption on the Au(111) surface: ethynyl-adamantane-trithiol and adamantyl-trithiol. We demonstrate the details of controlled Au atom abstraction during tip approach toward and retraction from the radical species. Upon approach of the tip, the apical Au atom undergoes a transfer toward the carbon radical at a clearly defined threshold separation. This atomic displacement is accompanied by a net energy gain of the system in the range −0.5 to −1.5 eV, depending on the radical structure. In the case of a triangular pyramidal apex model, two tip configurations are possible after the tip atom displacement: (1) an Au atom is abstracted from the tip and bound to the C radical, not bound to the tip base anymore, and (2) apical tip atoms rearrange to form a continuous neck between the tip and radical. In the second case, subsequent tip retraction leads to the same final configuration as the first, with the abstracted Au atom bound to radical carbon atom of the molecular tool. For the less reactive adamantyl-trithiol radical molecular tool, Au atom transfer is less energetically favored, but this has the advantage of avoiding other apex gold atoms from rearrangement.

Deconstructive Cyanomethylation Enabled by Radical Cross‐Coupling through Multiple C−C Bond and C−H Bond Cleavage

AbstractBeing in its infancy, radical cross‐coupling is highly efficient for C−C bond construction, though suffers from selectivity problems and limited reaction types. New methodologies to realize radical cross‐coupling selectively are highly desired. Herein, an iron catalyzed deconstructive cyanomethylation of unstrained cyclic and linear alcohols with acetonitrile has been developed through radical cross‐coupling. The unprecedented method enables a ring‐opening functionalization of cyclohexanols to produce α‐cyanomethyl ketones. Notably, the highly challenging reaction involves twice C−C single bond cleavage through β‐scission of alkoxyl radical intermediates, and twice C(sp3)−H bond transformation via hydrogen atom transfer (HAT) procedures, resulting in two carbon radical species that realize a radical cross‐coupling process to form a new C(sp3)−C(sp3) bond selectively. α‐arylketo and α‐aryl substituted tertiary alcohols can also be applied as substrates, leading to terminal cyano‐functionalized linear products, with ketone as the leaving fragment. Mechanistically, a new procedure to generate alkoxyl radical with chlorine radical through the in‐situ formed intermediate cycloalkyl hypochlorite was suggested.magnified image

Thermal stability and decomposition mechanism analysis of 1, 1’-Azobis(cyclohexanecarbonitrile) by STA, DSC, ARC and TG-FTIR

1, 1′-Azobis(cyclohexanecarbonitrile) (ABCN) is a kind of azo compound, which is widely used as an initiator in the polymer industry. Plenty of heat will be released during the thermal decomposition, and fire or explosive accidents could happen when the cooling system of the polymerization reactor fails. In this manuscript, the thermal decomposition behavior of ABCN under a dynamic temperature environment was investigated by simultaneous thermogravimetric analyzer (STA). Differential scanning calorimeter (DSC) was used to detect the thermal effects of different stages of mass loss. The apparent activation energy was calculated by Kissinger-Akahira-Sunose methods (K-A-S methods). The thermal runaway behavior was investigated by accelerating rate calorimeter (ARC), which was used to predict time to maximum rate under adiabatic condition (TMRad). The results show that the temperatures at TMRad = 8 h and 24 h are 93.0 °C and 89.7 °C, respectively. The self-accelerating decomposition temperature (SADT) is 86.6 °C, which is calculated based on the thermal theory of Semenov. Since ABCN is used at 60–90 °C, a major accident could happen when the heat accumulated in the reactor is not removed timely. The risk of thermal runaway reactions for ABCN was defined against the risk matrix as level Ⅲ, which is an unacceptable risk. The carbon radicals and nitrogen were released during the decomposition of ABCN based on the experiment result of thermal gravimetric analyzer-Fourier transform infrared spectrometer (TG-FTIR) system. Several safety assessment parameters could supply references for the industry to alleviate thermal hazards and prevent critical incidents.

Boryl Radical-Promoted Dehydroxylative Alkylation of 3-Hydroxyoxindole Derivatives

A boryl radical-promoted dehydroxylative alkylation of 3-hydroxy-oxindole derivatives is achieved. The reaction starts from addition of 4-dimethylaminopyridine (DMAP)-boryl radical to the amide carbonyl oxygen atom, which induces a spin-center shift process to promote the C-O bond cleavage. The elimination of a hydroxide anion from a free hydroxy group is also accomplished. Capture of the generated carbon radical with alkenes furnishes a variety of C-3 alkylated oxindoles. This method features a simple operation and broad substrate scope.

Visible-Light Photocatalytic Barbier-Type Reaction of Aziridines and Azetidines with Nonactivated Aldehydes

AbstractBarbier-type reactions are a classic group of reactions for carbon–carbon bond formation; however, their common use of stoichiometric metals restricts their widespread application. Considering the ready availability and diversity of cyclic amines, we report a visible-light photocatalytic Barbier-type reaction of aziridines and azetidines with nonactivated aldehydes. A series of important γ- and δ-amino alcohols were synthesized in the presence of amines as electron donors. Moreover, this transition-metal-free protocol displays mild reaction conditions, broad functional-group tolerance, and a wide substrate scope. Mechanistic investigations indicated that carbon radicals and carbanions might be generated as key intermediates.

Photoadsorption and reaction mechanism of periwinkle shell ash in the removal of hazardous dye

AbstractCombined adsorption and photocatalysis synergy was explored in this research because the porosity of activated carbon and hydroxyl radicals' generation are the main drivers of the adsorption and photodecomposition efficiency of dyes. In this study, periwinkle shell ash (PSA) activated at 800 °C was used for the adsorption of toxic crystal violet (CRV) dyes. The PSA was characterized by scanning electron microscope, Fourier transform infrared spectroscopy, thermogravimetric analysis, Brunauer–Emmett–Teller surface area analysis, and X-ray diffraction. Findings showed that CRV adsorption was dependent on the dosage, pH, contact time, and initial concentration. The adsorption capacity was 46.82 at pH (9) for CRV, dosage amount of 0.2 g/L, and an adsorbate concentration of 70 mg/L. Pseudo-second order gave a perfect fitting-chemisorption mechanism with values >0.98 (R2). Maximum photodegradation (93–98%) was achieved when the catalyst dosage increased to 0.75 g. Thermodynamics confirmed a spontaneous/exothermic process. The photocatalysis process confirmed that the combined process was effective and determined to be the rate-determining step by Langmuir–Hinshelwood. The study concluded that PSA was an efficient adsorbent, and TiO2 was a key factor in the reaction mechanism and recommended for potential synthesis of membrane substrates, high performance, efficiency, and cost reduction.

Synthesis of α‐Aryl Carbonyls via Photoinduced Formation of C−C Bonds

AbstractThe present review aims to provide an overview of recent developments in photochemical and photocatalyzed synthesis of α‐aryl carbonyls via formation of C(sp)2−C(sp)3bonds. The approaches described are based on the use of light as the exclusive energy source for the generation of highly reactive carbon radicals, cations or radical ions as the key intermediates of the process. Such strategies efficiently compete with traditional routes, that require the combined use of transition metal complexes, ligands, additives and often harsh reaction conditions.

Reaction between 1,3,5-Triisopropylbenzene and Elemental Sulfur Extending the Scope of Reagents in Inverse Vulcanization.

Inverse vulcanization utilizes an organic compound as reagent for crosslinking elemental sulfur to result in corresponding polymeric material with a high sulfur content. This work, employing 1,3,5-triisopropylbenzene (TIPB) as the reagent, demonstrates the first attempt on extending the scope of crosslinking agents of inverse vulcanizationtosaturatecompounds. Under nuclearmagneticspectroscopic analysis, the reactions between TIPB and elemental sulfur take places through ring-opening reaction of S8 resulting in sulfur radicals at sulfur chain ends, radicals transferring to isopropyl groups of TIPB, and radical coupling reactions between carbon radicals and sulfur radicals. The obtained products are similar to the sulfur polymers from conventional inverse vulcanization processes and show self-healing property.

Preferential Adsorption of Ethylene Oxide on Fe and Chlorine on Ni Enabled Scalable Electrosynthesis of Ethylene Chlorohydrin

AbstractIndustrial manufacturing of ethylene chlorohydrin (ECH) critically requires excess corrosive hydrochloric acid or hypochlorous acid with dealing with massive by‐products and wastes. Here we report a green and efficient electrosynthesis of ECH from ethylene oxide (EO) with NaCl over a NiFe2O4nanosheet anode. Theoretical results suggest that EO and Cl preferentially adsorb on Fe and Ni sites, respectively, collaboratively promoting the ECH synthesis. A Cl radical‐mediated ring‐opening process is proposed and confirmed, and the key Cl and carbon radical species are identified by high‐resolution mass spectrometry. This strategy can enable scalable electrosynthesis of 185.1 mmol of ECH in 1 h with 92.5 % yield at a 55 mA cm−2current density. Furthermore, a series of other chloro‐ and bromoethanols with good to high yields and paired synthesis of ECH and 4‐amino‐3,6‐dichloropyridine‐2‐carboxylicacid via respectively loading and unloading Cl are achieved, showing the promising potential of this strategy.

Preferential Adsorption of Ethylene Oxide on Fe and Chlorine on Ni Enabled Scalable Electrosynthesis of Ethylene Chlorohydrin.

Industrial manufacturing of ethylene chlorohydrin (ECH) critically requires excess corrosive hydrochloric acid or hypochlorous acid with dealing with massive by-products and wastes. Here we report a green and efficient electrosynthesis of ECH from ethylene oxide (EO) with NaCl over a NiFe2 O4 nanosheet anode. Theoretical results suggest that EO and Cl preferentially adsorb on Fe and Ni sites, respectively, collaboratively promoting the ECH synthesis. A Cl radical-mediated ring-opening process is proposed and confirmed, and the key Cl and carbon radical species are identified by high-resolution mass spectrometry. This strategy can enable scalable electrosynthesis of 185.1 mmol of ECH in 1 h with 92.5 % yield at a 55 mA cm-2 current density. Furthermore, a series of other chloro- and bromoethanols with good to high yields and paired synthesis of ECH and 4-amino-3,6-dichloropyridine-2-carboxylicacid via respectively loading and unloading Cl are achieved, showing the promising potential of this strategy.

Mechanistic Study of Chemoselectivity for Carbon Radical Hydroxylation versus Chlorination with FeIII (OH)(Cl) Complexes.

The FeIII (OH)(Cl) complex resembles the key intermediate proposed for the non-heme iron halogenases. Goldberg and co-workers reported that the FeIII (OH)(Cl) RC reacts with triphenylmethyl radical 1 to give an exclusive hydroxylation product. To understand the chemoselectivity of the reaction of RC with 1, density functional theory (DFT) calculations have been conducted. From RC, the competing pathways were identified as the OH-transfer, Cl-transfer, and isomerization pathways. The direct Cl-transfer is more favorable than direct OH-transfer by 2.8 kcal/mol. The hydrogen bonding interactions between the hydroxyl group and the pendent amine ligand impede the direct OH-transfer from RC. Compared with the direct Cl-transfer pathway, the isomerization pathways require lower barriers. In isomer RCiso2 , the equatorial hydroxyl group, which has smaller diabatic bond dissociation energy, prefers to transfer to form the hydroxylation product. In FeIII (Cl)2 RC2 and RC2iso , the equatorial chloride group also prefers to transfer to give the chlorination product.

Chlorine Atom Transfer of Unactivated Alkyl Chlorides Enabled by Zirconocene and Photoredox Catalysis

Alkyl chlorides are robust precursors to carbon radicals; however, their relative inertness has hampered their practical use. Although modern photochemical strategies have greatly enhanced the utility of alkyl chlorides as radical precursors, these methods often depend on strongly reducing conditions leading to unproductive side reactions. Here, we report a catalytic radical generation from 1°, 2°, and 3° unactivated alkyl chlorides with zirconocene and photoredox catalysis, which enables both hydrogenation and borylation on a range of structurally complex molecules. This mild zirconocene-catalyzed protocol shows that zirconium can render the C–Cl bond cleavage more exergonic and can lower the activation energy of the transition state, amplifying the ability of metallocenes toward halogen atom transfer.

Visible-Light-Mediated Photoredox Carbon Radical Formation from Aqueous Sulfoxonium Ylides.

The visible-light-induced photoredox carbon radical formation from aqueous sulfoxonium ylides has been demonstrated for the first time. While direct reduction of sulfoxonium ylides by H2O efficiently generates the corresponding hydrocarbon compounds, the use of additional alkenes as radical acceptors alters the chemical reactivity to achieve alkene carboarylation of N-arylacrylamides. Mechanistic studies reveal two different reaction pathways involved in the carbon radical formation from aqueous sulfoxonium ylides resulting in reduction to release dimethyl sulfone and carboarylation to form DMSO.

Photocatalytic Carboxylation of C-N Bonds in Cyclic Amines with CO2 by Consecutive Visible-Light-Induced Electron Transfer.

Visible-light photocatalytic carboxylation with CO2 is highly important. However, it still remains challenging for reluctant substrates with low reduction potentials. Herein, we report a novel photocatalytic carboxylation of C-N bonds in cyclic amines with CO2 via consecutive photo-induced electron transfer (ConPET). It is also the first photocatalytic reductive ring-opening reaction of azetidines, pyrrolidines and piperidines. This strategy is practical to transform a variety of easily available cyclic amines to valuable β-, γ-, δ- and ϵ-amino acids in moderate-to-excellent yields. Moreover, the method also features mild and transition-metal-free conditions, high selectivity, good functional-group tolerance, facile scalability and product derivations. Mechanistic studies indicate that the ConPET might be the key to generating highly reactive photocatalysts, which enable the reductive activation of cyclic amines to generate carbon radicals and carbanions as the key intermediates.

Photocatalytic Carboxylation of C−N Bonds in Cyclic Amines with CO2 by Consecutive Visible‐Light‐Induced Electron Transfer

AbstractVisible‐light photocatalytic carboxylation with CO2 is highly important. However, it still remains challenging for reluctant substrates with low reduction potentials. Herein, we report a novel photocatalytic carboxylation of C−N bonds in cyclic amines with CO2 via consecutive photo‐induced electron transfer (ConPET). It is also the first photocatalytic reductive ring‐opening reaction of azetidines, pyrrolidines and piperidines. This strategy is practical to transform a variety of easily available cyclic amines to valuable β‐, γ‐, δ‐ and ϵ‐amino acids in moderate‐to‐excellent yields. Moreover, the method also features mild and transition‐metal‐free conditions, high selectivity, good functional‐group tolerance, facile scalability and product derivations. Mechanistic studies indicate that the ConPET might be the key to generating highly reactive photocatalysts, which enable the reductive activation of cyclic amines to generate carbon radicals and carbanions as the key intermediates.

Photosynthesis of 3-Alkylated Coumarins from Carboxylic Acids Catalyzed by a Na2S-Based Electron Donor-Acceptor Complex.

A simple and practical electron donor-acceptor (EDA) strategy to synthesize various 3-alkylated coumarins from easily available coumarins and naturally abundant carboxylic acids under photocatalyst-, oxidant-, and additive-free and mild conditions is reported. Using Na2S as the catalytic electron donor, a series of primary, secondary, and tertiary carbon radicals can be efficiently generated, and the EDA complex can be regenerated without an alkaline additive.