Radical Formation Research Articles

A Radical Activation Strategy for Versatile and Stereoselective N‐Glycosylation

AbstractPrevious N‐glycosylation approaches have predominately involved acidic conditions, facing challenges of low stereoselectivity and limited scope. Herein, we introduce a radical activation strategy that enables versatile and stereoselective N‐glycosylation using readily accessible glycosyl sulfinate donors under basic conditions and exhibits exceptional tolerance towards various N‐aglycones containing alkyl, aryl, heteroaryl and nucleobase functionalities. Preliminary mechanistic studies indicate a pivotal role of iodide, which orchestrates the formation of a glycosyl radical from the glycosyl sulfinate and subsequent generation of the key intermediate, a configurationally well‐defined glycosyl iodide, which is subsequently attacked by an N‐aglycone in a stereospecific SN2 manner to give the desired N‐glycosides. An alternative route involving the coupling of a glycosyl radical and a nitrogen‐centered radical is also proposed, affording the exclusive 1,2‐trans product. This novel approach promises to broaden the synthetic landscape of N‐glycosides, offering a powerful tool for the construction of complex glycosidic structures under mild conditions.

The ability of photochemical decomposition products of the Roundup to induce oxidative stress in bacterial cells

BACKGROUND: A common non-selective systemic herbicide Roundup (Glyphosate, active ingredient N-phosphonomethylglycine, N-PMG) is used to control perennial weeds. It is necessary to assess the hazard of the products of photochemical decomposition of N-FMG formed under the influence of solar UV and ozone. AIM: Using lux-biosensors based on Escherichia coli, studying the ability of N-FMG photochemical degradation products to induce oxidative stress in bacterial cells. MATERIALS AND METHODS: The work used the active substance of the herbicide Roundup N-phosphonomethylglycine (N-PMG), biosensors E. coli (pSoxS-lux), E. coli (pKatG-lux). UV radiation, Mass spectrometry. RESULTS: Using biosensors, it was shown that the products of photochemical decomposition of N-PMG (2-(N-hydroxymethyl-hydroxyamine) ethanoic acid) cause an increase in the concentration of superoxide anion radical and H2O2 in E. coli cells, which induces oxidative stress in the bacterial cell. CONCLUSIONS: The photochemical decomposition product of N-PMG (2-(N-hydroxymethyl-hydroxyamine) ethanoic acid) induces the formation of superoxide anion radical and H2O2 in bacterial cells.

A Radical Activation Strategy for Versatile and Stereoselective N-Glycosylation.

Previous N-glycosylation approaches have predominately involved acidic conditions, facing challenges of low stereoselectivity and limited scope. Herein, we introduce a radical activation strategy that enables versatile and stereoselective N-glycosylation using readily accessible glycosyl sulfinate donors under basic conditions and exhibits exceptional tolerance towards various N-aglycones containing alkyl, aryl, heteroaryl and nucleobase functionalities. Preliminary mechanistic studies indicate a pivotal role of iodide, which orchestrates the formation of a glycosyl radical from the glycosyl sulfinate and subsequent generation of the key intermediate, a configurationally well-defined glycosyl iodide, which is subsequently attacked by an N-aglycone in a stereospecific SN2 manner to give the desired N-glycosides. An alternative route involving the coupling of a glycosyl radical and a nitrogen-centered radical is also proposed, affording the exclusive 1,2-trans product. This novel approach promises to broaden the synthetic landscape of N-glycosides, offering a powerful tool for the construction of complex glycosidic structures under mild conditions.

Mechanistic Implications of the Varying Susceptibility of PAHs to Pyro-Catalytic Treatment as a Function of Their Ionization Potential and Hydrophobicity.

Transition metal catalysts in soil constituents (e.g., clays) can significantly decrease the pyrolytic treatment temperature and energy requirements for efficient removal of polycyclic aromatic hydrocarbons (PAHs) and, thus, lead to more sustainable remediation of contaminated soils. However, the catalytic mechanism and its rate-limiting steps are not fully understood. Here, we show that PAHs with lower ionization potential (IP) are more easily removed by pyro-catalytic treatment when deposited onto Fe-enriched bentonite (1.8% wt. ion-exchanged content). We used four PAHs with decreasing IP: naphthalene > pyrene > benz(a)anthracene > benzo(g,h,i)perylene. Density functional theory (DFT) calculations showed that lower IP results in stronger PAH adsorption to Fe(III) sites and easier transfer of π-bond electrons from the aromatic ring to Fe(III) at the onset of pyrolysis. We postulate that the formation of aromatic radicals via this direct electron transfer (DET) mechanism is the initiation step of a cascade of aromatic polymerization reactions that eventually convert PAHs to a non-toxic and fertility-preserving char, as we demonstrated earlier. However, IP is inversely correlated with PAH hydrophobicity (log Kow), which may limit access to the Fe(III) catalytic sites (and thus DET) if it increases PAH sorption to soil OM. Thus, ensuring adequate contact between sorbed PAHs and the catalytic reaction centers represents an engineering challenge to achieve faster remediation with a lower carbon footprint via pyro-catalytic treatment.

Photocatalyst-Free Visible Light-Induced C(sp2)-H Arylation of Quinoxalin-2(1H)-ones and Coumarins.

Herein, we describe a visible light-induced C(sp2)-H arylation method for quinoxalin-2(1H)-ones and coumarins using iodonium ylides without the need for external photocatalysts. The protocol demonstrates a broad substrate scope, enabling the arylation of diverse heterocycles through a simple and mild procedure. Furthermore, the photochemical reaction showcases its applicability in the efficient synthesis of biologically active molecules. Computational investigations at the CASPT2//CASSCF/PCM level of theory revealed that the excited state of quinoxalin-2(1H)-one facilitates electron transfer from its π bond to the antibonding orbital of the C-I bond in the iodonium ylide, ultimately leading to the formation of an aryl radical, which subsequently participates in the C-H arylation process. In addition, our calculations reveal that during the single-electron transfer (SET) process, the C-I bond cleavage in iodonium ylide and new C-C bond formation between resultant aryl radical and cationic quinoxaline species take place in a concerned manner. This enables the arylation reaction to efficiently proceed along an energy-efficient route.

Differential Incidence of Contrast-Associated Acute Kidney Injury: Comparing Intravenous and Intraarterial Contrast Administration.

Contrast-associated acute kidney injury (CA-AKI) remains a significant concern in diagnostic and invasive procedures, particularly in the context of iodinated contrast material administration. The traditional definition of CA-AKI, based on serum creatinine elevation following contrast exposure, may not accurately capture its multifactorial nature. Studies have provided new insights into the differential incidence of CA-AKI between intravenous and intraarterial contrast administration, emphasizing the importance of tailored preventative strategies for high-risk procedures. This higher risk may arise from two proposed mechanisms: one implicating free radical formation leading to cytotoxicity and apoptosis in renal cells and another suggesting that contrast media alter renal hemodynamics, particularly in the outer medulla, by constricting the vasa recta and reducing medullary flow. Advances in technology and patient care, including contemporary use of low-osmolar contrast agents and hydration protocols, mitigate CA-AKI risk. Diagnostic and invasive procedures should not be avoided solely due to concerns about renal dysfunction if the patient is likely to benefit clinically.

From Aldehyde to Ketone via Water‐Accelerated Molybdenum‐Photocatalysis

The efficient “on water” protocol was developed by employing molybdenum‐based polyoxometalate [N(C4H9)4]2[Mo6O19] as the photocatalyst. This water‐accelerated photoinduced process affords versatile ketones from aldehydes straightforwardly, showcasing exceptional substrate generality. Its applicability to life‐related molecules such as amino acids, peptides, and sugars, further demonstrates the bioorthogonal application. The mechanistic investigation highlights the hydrogen atom transfer (HAT) process between the excited‐state POM and benzaldehyde for acyl radical formation. Highly efficient gram‐scale flow operation underlines the industrial applicability of this transformative strategy.

MgAl hydrotalcite supported ultrafine PdNi bimetallic catalyst for the dehydrogenation of dodecahydro-N-ethylcarbazole

Liquid organic hydrogen storage is a promising way of storing hydrogen. The development of efficient and low-cost dehydrogenation catalysts is still required to advance the commercialization of N-ethylcarbazole/dodecahydro-N-ethylcarbazole (NEC/H12-NEC) hydrogen storage and transport system.In this paper, PdNi bimetallic catalyst (Pd3Ni1/LDHs) supported on MgAl hydrotalcite was prepared by NaBH4 and ultrasound-assisted stepwise reduction. Ultrasonic cavitation could excite the hydroxyl hydrogen of hydrotalcite in the form of hydrogen radicals to reduce PdCl42− to Pd nanoparticles (NPs), and also promoted the formation of PdNi alloys as well as the dispersion of NPs. In the Pd3Ni1/LDHs catalyst, the average particle size of NPs was 1.98 nm, suggesting an excellent dispersion of Pd, Ni, and PdNi NPs. The electronic effects of Ni and Pd significantly improved the catalytic efficiency of Pd3Ni1/LDHs in H12-NEC dehydrogenation, resulting in a hydrogen release rate of 98.4 % after 6 h at 180 °C, surpassing that of Pd/LDHs. It can be considered that the dehydrogenation performance of Pd3Ni1/LDHs for H12-NEC is related to the alloy phase, electronic structure and NPs size.

Sunlight-mediated removal of endocrine disruptors from wastewater using trimetallic core-shell Ag-TeO2@ZnO nanocomposites

The current work emphasizes the preparation of trimetallic core-shell Ag–TeO2@ZnO nanocomposites (NCs) by thermo-mechanical method for the efficient photocatalytic degradation of 2,4-Dichlorophenol and β-naphthol pollutants. FE-SEM shows that Ag and TeO2 nanoparticles are deposited on the surface of ZnO nanotubes. The band gap of pristine ZnO NPs and 5 wt% Ag–TeO2@ZnO nanocomposites are found to be 3.16 and 2.96 eV, respectively. The calculated specific surface area (SBET) of pristine ZnO NPs and 5 wt% Ag–TeO2@ZnO nanocomposites are 40.47 and 45.66 m2 g−1 respectively, confirming that Ag and TeO2 nanoparticles contribute to increasing in surface area of pure ZnO. The synthesised nanocomposite showed excellent photocatalytic performance for the degradation of β -naphthol (95.6%) in 40 min at the concentration of (0.6 mg ml−1) and 2,4-DCP (99.6%) in 180 min (0.4 mg ml−1) under natural sunlight. Cyclic Voltammetry and Electrochemical Impedance Spectroscopy were carried out to study the electrochemical properties. The determination of reactive oxygen species (ROS) confirmed that the degradation of the pollutants by 5 wt% Ag–TeO2@ZnO NCs was due to the formation of superoxide radicals. Electron paramagnetic resonance revealed the presence of sharp signals in pure ZnO nanoparticles at g ∼1.95 and oxygen vacancy peak at g ∼2.01 in 5 wt% Ag–TeO2@ZnO NCs. To study the mechanism behind the degradation of pollutants, Scavenger test using histidine and ascorbic acid (ROS scavengers) was performed. The synthesised nanocomposites are highly stable and showed enhanced efficiency up to three cycles, confirming their reusability as a photocatalyst.

A switch and a failsafe: KatG’s mechanism for preservation of catalase activity using a conformationally dynamic Arg and an active-site Trp

Many novel structural features impart a robust catalase activity to KatG that is absent from all other members of its superfamily. The conformationally dynamic “Arg switch” and oxidizable “proximal Trp” have both figured prominently in investigations of KatG structure and mechanism, but the full scope of their contributions to catalysis remains unclear. The switch (R418) appears to regulate active-site intramolecular electron transfer. The proximal Trp (W321) is a conspicuous site of radical formation, but W321•+ does not appear to participate directly in the KatG catalase cycle. To explore the extent to which these residues may cooperate in KatG’s catalase activity, we generated R418N and W321F/R418N KatG and compared their catalytic and spectroscopic properties to wt KatG. R418N KatG showed pH-independent susceptibility to H2O2-based inactivation, whereas wt KatG only showed this response under conditions where the Arg switch would be oriented away from the active site (i.e., low pH). Peroxidatic electron donors (PxEDs) prevented inactivation of wt and R418N KatG regardless of pH; however, protection of R418N KatG activity by this mechanism produced at least ten-fold greater extents of PxED oxidation. Elimination of the proximal Trp in addition to the Arg switch (i.e., W321F/R418N KatG) resulted in a near complete inability to sustain H2O2 degradation. Remarkably, W321F KatG showed resistance to H2O2-dependent inactivation indistinguishable from wt at pH 7 (i.e., when the Arg switch is oriented toward the active site) but sensitivity to H2O2-dependent inactivation indistinguishable from W321F/R418N KatG at pH 5 (i.e., when the Arg switch is oriented away from the active site). These data suggest loss of the Arg switch (either by mutagenesis or conformationally due to environmental pH) results in a KatG that is substantially compromised in the sustained degradation of H2O2. This can be overcome provided that KatG retains its ability to utilize the proximal Trp as a site of protein-based oxidation and has a PxED available to repair protein oxidation events. However, if both the Arg switch and the proximal Trp are absent, rapid H2O2-dependent inactivation is observed, and PxEDs are unable to effectively intervene to preserve KatG’s catalase activity.

A Geometrically Flexible Three-Dimensional Nanocarbon.

The development of architecturally unique molecular nanocarbons by bottom-up organic synthesis is essential for accessing functional organic materials awaiting technological developments in fields such as energy, electronics, and biomedicine. Herein, we describe the design and synthesis of a triptycene-based three-dimensional (3D) nanocarbon, GFN-1, with geometrical flexibility on account of its three peripheral π-panels being capable of interconverting between two curved conformations. An effective through-space electronic communication among the three π-panels of GFN-1 has been observed in its monocationic radical form, which exhibits an extensively delocalized spin density over the entire 3D π-system as revealed by electron paramagnetic resonance and UV-vis-NIR spectroscopies. The flexible 3D molecular architecture of GFN-1, along with its densely packed superstructures in the presence of fullerenes, is revealed by microcrystal electron diffraction and single-crystal X-ray diffraction, which establish the coexistence of both propeller and tweezer conformations in the solid state. GFN-1 exhibits strong binding affinities for fullerenes, leading to host-guest complexes that display rapid photoinduced electron transfer within a picosecond. The outcomes of this research could pave the way for the utilization of shape and electronically complementary nanocarbons in the construction of functional coassemblies.

In situ copper photocatalysts triggering halide atom transfer of unactivated alkyl halides for general C(sp3)-N couplings

Direct reduction of unactivated alkyl halides for C(sp3)-N couplings under mild conditions presents a significant challenge in organic synthesis due to their low reduction potential. Herein, we introduce an in situ formed pyridyl-carbene-ligated copper (I) catalyst that is capable of abstracting halide atom and generating alkyl radicals for general C(sp3)-N couplings under visible light. Control experiments confirmed that the mono-pyridyl-carbene-ligated copper complex is the active species responsible for catalysis. Mechanistic investigations using transient absorption spectroscopy across multiple decades of timescales revealed ultrafast intersystem crossing (260 ps) of the photoexcited copper (I) complexes into their long-lived triplet excited states (>2 μs). The non-Stern-Volmer quenching dynamics of the triplets by unactivated alkyl halides suggests an association between copper (I) complexes and alkyl halides, thereby facilitating the abstraction of halide atoms via inner-sphere single electron transfer (SET), rather than outer-sphere SET, for the formation of alkyl radicals for subsequent cross couplings.

Dual Nickel- and Photoredox-Catalyzed Asymmetric Reductive Cross-Couplings: Just a Change of the Reduction System?

ConspectusIn recent years, nickel-catalyzed asymmetric coupling reactions have emerged as efficient methods for constructing chiral C(sp3) carbon centers. Numerous novel approaches have been reported to rapidly construct chiral carbon-carbon bonds through nickel-catalyzed asymmetric couplings between electrophiles and nucleophiles or asymmetric reductive cross-couplings of two different electrophiles. Building upon these advances, our group has been devoted to interrogating dual nickel- and photoredox-catalyzed asymmetric reductive cross-coupling reactions.In our endeavors over the past few years, we have successfully developed several dual Ni-/photoredox-catalyzed asymmetric reductive cross-coupling reactions involving organohalides. While some probably think that this system is just a change of the reduction system from traditional metal reductants to a photocatalysis system, a question that we also pondered at the beginning of our studies, both the achievable reaction types and mechanisms suggest a different conclusion: that this dual catalysis system has its own advantages in the chiral carbon-carbon bond formation. Even in certain asymmetric reactions where the photocatalysis regime functions only as a reducing system, the robust reducing capability of photocatalysts can effectively accelerate the regeneration of low-valent nickel species, thus expanding the selectable scope of chiral ligands. More importantly, in many transformations, besides reducing nickel catalysts, the photocatalysis system can also undertake the responsibility of alkyl radical formation, thereby establishing two coordinated, yet independent catalytic cycles. This catalytic mode has been proven to play a crucial role in achieving diverse asymmetric coupling reactions with great challenges.In this Account, we elucidate our understanding of this system based on our experience and findings. In the Introduction, we provide an overview of the main distinctions between this system and traditional Ni-catalyzed asymmetric reductive cross-couplings with metal reductants and the potential opportunities arising from these differences. Subsequently, we outline various chiral carbon-carbon bond-forming types obtained by this dual Ni/photoredox catalysis system and their mechanisms. In terms of chiral C(sp3)-C(sp2) bond formation, extensive discussion focuses on the asymmetric arylations of α-chloroboronates, α-trifluoromethyl alkyl bromides, α-bromophosphonates, and so on. In the realm of chiral C(sp3)-C(sp) bond formation, asymmetric alkynylations of α-bromophosphonates and α-trifluoromethyl alkyl bromides have been presented herein. Regarding C(sp3)-C(sp3) bond formation, we take the asymmetric alkylation of α-chloroboronates as a compelling example to illustrate the great efficiency of this dual catalysis system. This summary would enable a better grasp of the advantages of this dual catalysis system and clarify how the photocatalysis regime facilitates enantioselective transformations. We anticipate that this Account will offer valuable insights and contribute to the development of new methodologies in this field.

Heme-catalyzed degradation of linoleate 9-hydroperoxide (9-HPODE) forms two allylic epoxy-ketones via a proposed pseudo-symmetrical diepoxy radical intermediate

Heme-initiated decomposition of unsaturated fatty acid hydroperoxides creates alkoxyl radicals that propagate a complex series of reactions to hydroxy, keto, epoxy and aldehydic products. Herein, among the products from the hematin-catalyzed degradation of 9-hydroperoxy-linoleic acid (9-HPODE), we observed a double peak on normal-phase HPLC that resolved on RP-HPLC into equal proportions of two epoxy-allylic ketones with identical UV spectra. Their proton NMR spectra were also indistinguishable and consistent with 9,10-trans-epoxy-11E-13-keto- and 9-keto-10E-12,13-trans-epoxy-octadecenoic acids. Acid hydrolysis to the corresponding dihydroxy-ketones and GC-MS analysis identified the earlier eluting product on RP-HPLC as the 9,10-epoxy regio-isomer. Starting from the C9-hydroperoxide, recovery of the two epoxy-ketones in equal proportions suggests their formation from a common intermediate. Earlier work has proposed formation of a pseudo-symmetrical diepoxy radical (9,10-epoxy-11(•)-12,13-epoxy, derived from an epoxy allylic hydroperoxide precursor) in the carbon chain fragmentation leading to aldehydic products. This intermediate in pathways of alkoxyl radical reactions forms equal pairs of aldehydes, and now also a pair of epoxy-ketones, and based on mechanism the same products arise from either 9-HPODE or 13-HPODE. Our results point to the intermediacy of this diepoxy-carbinyl radical in the origin of at least two classes of linoleate peroxidation products, and it should be considered as a viable intermediate for homo-conjugated diene peroxidation in general. The reactions could contribute to the aldehydes and epoxy-ketones in tissues undergoing oxidative transformations of polyunsaturated fatty acids.

Simulation on the effect of oxygen concentration on the positive secondary streamer generated in oxygen-rich nitrogen–oxygen mixtures under atmospheric pressure

In this study, we investigated the effect of various O2 concentrations, from 20% to 90%, in nitrogen–oxygen ( N2/O2 ) mixtures on the characteristics of secondary streamers. As oxygen molecules have different molecular characteristics from nitrogen molecules in terms of ionisation threshold and electron attachment property, streamer discharges generated under various nitrogen–oxygen ratios may exhibit differing characteristics such as electron density, electric field, and radical formation. We focused on the changes in these parameters in secondary streamers using simulations. Simulations were first performed under the same conditions as those in previous experiments to compare the results of the ozone production, discharge current, and discharge emission characteristics. To compare the ozone production characteristics, simulated O radicals–the precursor of ozone–were used in the simulation for simplicity. This comparison showed that, although the absolute values of each parameter were different, the simulation exhibited a similar trend in the case of the experimentally obtained oxygen concentration dependence. After the validity of the simulation was verified to some extent via a comparison with the experiment, the results obtained from the simulation were analysed in detail. The results showed that, although the electric field strength in the secondary streamer did not change much as the oxygen concentration increased, the decrease rate of the electron density was greatly accelerated by the electron attachment reaction of oxygen. As a result, many of the electrons had already dissipate during the development of the primary streamer, and few electrons remained when the secondary streamer was formed. This effect suggests that the ratio of the amount of O radicals produced in the primary streamer to that produced in the secondary streamer changes as the oxygen concentration changes.

Covalent electrografting of aryl groups on AA2060-T8 surfaces, and their modification with Ce(4OHcin)3 to incorporate additional anticorrosive activity

The aluminum alloys used in aerospace applications are susceptible to corrosion. This has led to the development of methodologies that ensure the durability of the parts and pieces of aircraft. These anticorrosive processes involve the use of coatings containing chromate-based corrosion-inhibitor compounds. Although these coatings provide an excellent solution to this problem, their use in protection protocols is restricted owing to their high toxicity and carcinogenic nature.This study evaluates a different process to protect aluminum alloy surfaces that incorporates the derivatization of organic compounds using potentiostatic techniques. The metallic surface was modified in situ by the potentiostatic reduction of aryl diazonium salts, leaving the surface covered with molecular grafts. The grafting of molecules onto the surface is modulated by the application of a potential that causes the formation of aryl radicals. The organic compound selected in this study was p-toluidine in protic medium. The derivatization process in the AA2060-T8 alloy was carried out at different pHs and potentials, observing from the potential/current responses in 0.1 M NaCl solution that the maximum optimization is obtained at pH 3 and -1 V.Likewise, the E/I and electrochemical impedance (EIS) responses of the electrografted samples modified and functionalized with cerium 4-hydroxycinnamate (Ce(4-OHcinn)3) revealed that the presence of this compound in the arylic structure significantly increased the protective capacity of the organic film electrografted on the aluminum alloy.The morphologies and characteristics of the modified surface were studied by SEM, TEM, and XPS. Furthermore, TEM examinations of ultramicrotomed sections of the electrografted specimens revealed the presence of a film approximately 10 nm thick on the AA2060-T8 surface.

The Effect of Irradiation on Meat Products.

The effects of irradiation on meat constituents including water, proteins, and lipids are multifaceted. Irradiation leads to the decomposition of water molecules, resulting in the formation of free radicals that can have both positive and negative effects on meat quality and storage. Although irradiation reduces the number of microorganisms and extends the shelf life of meat by damaging microbial DNA and cell membranes, it can also accelerate the oxidation of lipids and proteins, particularly sulfur-containing amino acids and unsaturated fatty acids. With regard to proteins, irradiation affects both myofibrillar and sarcoplasmic proteins. Myofibrillar proteins, such as actin and myosin, can undergo depolymerization and fragmentation, thereby altering protein solubility and structure. Sarcoplasmic proteins, including myoglobin, undergo structural changes that can alter meat color. Collagen, which is crucial for meat toughness, can undergo an increase in solubility owing to irradiation-induced degradation. The lipid content and composition are also influenced by irradiation, with unsaturated fatty acids being particularly vulnerable to oxidation. This process can lead to changes in the lipid quality and the production of off-odors. However, the effects of irradiation on lipid oxidation may vary depending on factors such as irradiation dose and packaging method. In summary, while irradiation can have beneficial effects, such as microbial reduction and shelf-life extension, it can also lead to changes in meat properties that need to be carefully managed to maintain quality and consumer acceptability.

Unravelling the role of silver in addressing the nitrate radical induced photocatalytic oxidation of olefins to epoxides or carbonyl compounds

Nitrate radicals possess the unique capability to add to unsaturated bonds, leading to the formation of carbon-centred radicals evolving to organic compounds, which cannot be achieved through more common reactive oxygen centred species. Therefore, the possibility of generating nitrate radicals through heterogeneous photocatalysis endows this technology with unprecedented possibilities in the field of green organic synthesis. In particular, previous research showcased the promising potential of nitrate radicals in selectively conducting the photocatalytic oxidative cleavage of limonene to limononaldehyde. However, the role of silver ions, required for the reaction to occur, remained uncertain. This study aims at elucidating the role of silver in determining conversion of limonene and selectivity towards the corresponding oxidized compounds. In particular, it has been demonstrated that silver ions efficiently scavenge photogenerated electrons, thus making molecular oxygen available for the nitrate radical induced production of limononaldehyde, obtained with selectivity values up to 60%. In this study it is shown that, nitrate radical formation is as well boosted by silver nanoparticles, in the absence of silver ions. However, in this case, the consequent oxidation of limonene produced both 1,2-limonene epoxide and limononaldehyde. Notably, in the absence of silver ions, molecular oxygen is the main electron scavenger and its lower availability for the oxidative cleavage mechanism addresses the reaction towards the epoxide. Ab initio calculations, confirmed this hypothesis, showing that, while formation of limononaldehyde is thermodynamically and kinetically favoured, formation of the epoxide is kinetically limited. Therefore, its formation takes place when the formation of limononaldehyde is hindered by factors such as the reduced availability of molecular oxygen. The identification of key parameters governing the process offers possibilities to tune the selectivity of the reaction towards oxidative cleavage or epoxidation. Moreover, it allows to further optimize this reaction, which may become an appealing and versatile method of chemicals green synthesis.

Textile dyes removing from the wastewater by green synthesized Cu-doped ZnO photocatalysts under the simulated sunlight illumination

Herein, Cu-doped ZnO photocatalysts were prepared via green synthesis method with utilization of Cannabis Sativa leaves. The catalytic activity was evaluated through the degradation of methylene blue (MB) and rhodamine B (RhB) under the simulated sunlight illumination. XRD, FESEM, EDAX, FTIR, BET-BJH and DRS were used for characterizations of Cu-doped ZnO. The results showed that, 3 wt % Cu-doped ZnO (CuZn3) displayed the excellent characterizations such as uniform dispersion, lower energy bandgap, smaller average particle size and greater surface area. For the photocatalysts with higher Cu loading (more than 3 wt %), non-uniform dispersion with larger particles, lower specific surface area and higher energy bandgap were found. The average particle size and energy bandgap for CuZn3 were 37.7 nm and 2.9 eV, respectively. Due to the superior properties, CuZn3 presented the highest amount of dyes degradations. After 180 min test, MB and RhB degradations by CuZn3 were 92.1 and 94.2 %, respectively. Moreover, it was found that optimum amount of CuZn3 was 100 ppm. Furthermore, applying of various scavengers revealed that hydroxyl radicals, superoxide radicals, and photo-generated electrons were the primary forms of radicals involved in dyes degradation using Cu-doped ZnO photocatalysts.

Azido derivatives of sesquiterpene lactones: Synthesis, anticancer proliferation, and chemistry of nitrogen-centered radicals

Sesquiterpene lactones (SLs) such as parthenolide (PTL) and dehydroleucodine (DhL) selectively kill cancer cells without exerting normal tissue toxicity, potentially due to presence of α-methylene-γ-lactone (αMγL) fragment. We hypothesize that the addition of an azido group to the αMγL fragment of PTL or DhL further augments their anticancer properties as well as radiation sensitivity of cancer cells. Azido-SLs containing the azido group at the C14 methyl position of PTL (i.e., azido-melampomagnolide B, AzMMB) while preserving the mechanistically crucial exomethylene unit of αMγL fragment were also prepared. Sham-irradiated (i.e., unirradiated control) or irradiated human breast cancer cells (MCF7) were treated with different concentrations of azido-PTL (AzPTL) or azido-DhL (AzDhL) along with parental SLs. Proliferation rate of MCF7 cells were measured by MTT-assay, and their colony forming ability was determined by colony formation assay. Both AzPTL and AzDhL significantly suppress proliferation rate and colony forming ability of MCF-7 cells. AzPTL suppressed colony forming ability, not cellular proliferation, following irradiation to a greater extent than PTL at lower concentrations (5 and 10 μM). Electron spin resonance (ESR) studies were performed employing gamma-irradiated homogeneous supercooled aqueous solutions to investigate radical formation through addition of radiation-mediated prehydrated electrons to the azide group of AzPTL and AzDhL and to follow subsequent reactions of these radicals. In AzPTL, formation of a tertiary carbon-centered radical plausibly via a metastable aminyl radical was observed, whereas AzDhL produced both π-aminyl and α-azidoalkyl radicals. These radicals may contribute to the antitumor activities of AzPTL and AzDhL.