A Mechanistic Study on Iron-Based Styrene Aziridination: Understanding Epoxidation via Nitrene Hydrolysis.

Transition-metal-catalyzed nitrene transfer reactions are typically performed in organic solvents under inert and anhydrous conditions due to the involved air and water-sensitive nature of reactive intermediates. Overall, this study provides insights into the iron-based ([Fe(PBI)](CFSO) (1), where PBI = 2-(2-pyridyl)benzimidazole), catalytic and stoichiometric aziridination of styrenes using PhINTs ([(-tosylimino)iodo]benzene), highlighting the importance of reaction conditions including the effects of the solvent, co-ligands (-substituted pyridines), and substrate substituents on the product yields, selectivity, and reaction kinetics. The aziridination reactions with /PhINTs showed higher conversion than epoxidation with 1/PhIO (iodosobenzene).

Contributions of fossil and non-fossil fractions to total carbon in urban aerosols in Bratislava (Slovakia).

Radiocarbon measurements of total carbon (TC) fraction of aerosol samples collected at the campus of the Comenius University in Bratislava (Slovakia) during 2022-2023 were carried out. Based on radiocarbon activity of these samples and a source apportionment model we have determined the relative proportion of fossil and non-fossil carbon in collected atmospheric aerosols. The carbon from non-fossil sources (biomass burning and biogenic emissions) was dominant in this time period, on average it formed 72% of carbon present in the aerosols from the atmosphere of Bratislava.

Assessment of environmental impacts from authorized discharges of tritiated water from the Fukushima site to coastal and offshore regions.

In August 2023, the long-planned discharging of radioactive wastewater from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) started after the confirmation of its feasibility and safety. As this water contains elevated amounts of tritium even after being diluted, a lot of resources have been invested in the monitoring of the Fukushima coastal region where the discharge outlet is located. We compare the first H surface activity concentrations from these measurements (up to the end of November 2023) with the available background values to evaluate a possible impact of the long-term discharging on humans and environmental levels of the radionuclide of interest in the same or nearby area.

Effect of monodentate heterocycle co-ligands on the μ-1,2-peroxo-diiron(III) mediated aldehyde deformylation reactions.

Peroxo-diiron(III) species are present in the active sites of many metalloenzymes that carry out challenging organic transformations. The reactivity of these species is influenced by various factors, such as the structure and topology of the supporting ligands, the identity of the axial and equatorial co-ligands, and the oxidation states of the metal ion(s). In this study, we aim to diversify the importance of equatorial ligands in controlling the reactivity of peroxo-diiron(III) species.

Long-term radiocarbon variation studies in the air and tree rings of Slovakia.

Fifty-five years of radiocarbon variation studies are reviewed with an emphasis on a better understanding of the impacts of the Bohunice nuclear power plant and fossil fuel CO on the atmosphere and biosphere of Slovakia. The maximum ΔC levels in the air up to about 1200‰ were observed during the 1970s at the Žlkovce monitoring station, which after 2005 decreased to <30‰. A relative decrease in the atmospheric ΔC levels due to increasing levels of fossil CO in the atmosphere has also been significant, for example, in Bratislava down to about -330‰, but after 2005 they were only <50‰ below the Jungfraujoch European clean-air level.

Influence of Equatorial Co-Ligands on the Reactivity of LFeOIPh.

Previous biomimetic studies clearly proved that equatorial ligands significantly influence the redox potential and thus the stability/reactivity of biologically important oxoiron intermediates; however, no such studies were performed on FeOIPh species. In this study, the influence of substituted pyridine co-ligands on the reactivity of iron(III)-iodosylbenzene adduct has been investigated in sulfoxidation and epoxidation reactions. Selective oxidation of thioanisole, -cyclooctene, and - and -stilbene in the presence of a catalytic amount of [Fe(PBI)](OTf) with PhI(OAc) provide products in good to excellent yields through an FeOIPh intermediate depending on the co-ligand (4R-Py) used.

Mechanisms of Sulfoxidation and Epoxidation Mediated by Iron(III)-Iodosylbenzene Adduct: Electron-Transfer vs. Oxygen-Transfer Mechanism.

The mechanisms of sulfoxidation and epoxidation mediated by previously synthesized and characterized iron(III)-iodosylbenzene adduct, Fe(OIPh) were investigated using para-substituted thioanisole and styrene derivatives as model substrates. Based on detailed kinetic reaction experiments, including the linear free-energy relationships between the relative reaction rates (log) and the (4R-PhSMe) with = -0.65 (catalytic) and = -1.

Effect of Redox Potential on Diiron-Mediated Disproportionation of Hydrogen Peroxide.

Heme and nonheme dimanganese catalases are widely distributed in living organisms to participate in antioxidant defenses that protect biological systems from oxidative stress. The key step in these processes is the disproportionation of HO to O and water, which can be interpreted via two different mechanisms, namely via the formation of high-valent oxoiron(IV) and peroxodimanganese(III) or diiron(III) intermediates. In order to better understand the mechanism of this important process, we have chosen such synthetic model compounds that can be used to map the nature of the catalytically active species and the factors influencing their activities.

Impact of the Fukushima Accident on H and C Environmental Levels: A Review of Ten Years of Investigation.

The investigation of the impact of the Fukushima accident is still going on although more than ten years have passed since the disaster. The main goal of this paper was to summarize the results of tritium and radiocarbon determinations in different environmental samples, possibly connected with the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. A document containing compiled data may serve as a solid basis for further research in the selected fields.

Stoichiometric Alkane and Aldehyde Hydroxylation Reactions Mediated by In Situ Generated Iron(III)-Iodosylbenzene Adduct.

Previously synthesized and spectroscopically characterized mononuclear nonheme, low-spin iron(III)-iodosylbenzene complex bearing a bidentate pyridyl-benzimidazole ligands has been investigated in alkane and aldehyde oxidation reactions. The in situ generated Fe(III) iodosylbenzene intermediate is a reactive oxidant capable of activating the benzylic C-H bond of alkane. Its electrophilic character was confirmed by using substituted benzaldehydes and a modified ligand framework containing electron-donating (Me) substituents.

Tritium and radiocarbon in the water column of the Red Sea.

Despite being the busiest transient sea in the world due to the Suez Canal, radionuclide distribution studies in seawater and sediment of the Red Sea remain rare. A sampling expedition in the Red Sea was conducted from June 9 to July 6, 2021, visiting a transect of several deep sampling stations located along the central axis of the basin from the Gulf of Aqaba to the southern Red Sea (near Farasan Island, Saudi Arabia). The collected seawater profile samples were analyzed for tritium, radiocarbon and oxygen-18.

Sequential scavenging and measurement of seawater radiocesium concentrations and plutonium isotopic ratios offshore Fukushima.

The scientific interest in radiocesium and plutonium found in the oceans and seas has increased enormously in the past years as a consequence of the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident and is expected to be ongoing due to many unresolved questions. Hence, continuous development of new and verification of old analytical methods should be at the top of the list of the community, working on the topic. In this study, we processed and analyzed several seawater samples, collected in different time frames (2011-2015) from the North Pacific Ocean offshore Fukushima, to determine their radiocesium activities, Cs/Cs activity ratios and Pu/Pu isotopic ratios using the sequential scavenging method, gamma spectrometry and accelerator mass spectrometry (AMS).

Catalytic and Stoichiometric Oxidation Mediated by Nonheme Peroxo-Diiron(III), Acylperoxo, and Iodosylbenzene Iron(III) Intermediates.

In this paper we describe a detailed mechanistic studies on the [Fe(PBO)(CFSO)] (), [Fe(PBT)(CFSO)] (), and [Fe(PBI)](CFSO) ()-catalyzed (PBO = 2-(2'-pyridyl)benzoxazole, PBT = 2-(2'-pyridyl)benzthiazole, PBI = 2-(2'-pyridyl)benzimidazole) oxidation of cycloketones by dioxygen with cooxidation of aldehydes and peroxycarboxylic acids, including the kinetics on the reactivity of (μ-1,2-peroxo)diiron(III), acylperoxo- and iodosylbenzene-iron(III) species as key intermediates.

Distribution of Am and Pu isotopes in the Curonian Lagoon and the south-eastern Baltic Sea seawater, suspended particles, sediments and biota.

Distribution trends and temporal variations of Am and Pu isotopes in the south-eastern Baltic Sea during the study period of 1999-2001 and 2011-2015 were investigated with the aim to study temporal changes of radionuclide levels in seawater, suspended particles and sediment, to estimate Am and Pu levels in marine biota and to assess the radiation doses received by the biota. The activities of Am and Pu were measured by alpha spectrometry after radiochemical purification. Pu was determined radiometrically via the ingrown daughter Am after 10-12 years of storage, while the Pu/Pu atom ratio of was measured by accelerator mass spectrometry.

Nonheme Diiron Oxygenase Mimic That Generates a Diferric-Peroxo Intermediate Capable of Catalytic Olefin Epoxidation and Alkane Hydroxylation Including Cyclohexane.

Herein are described substrate oxidations with HO catalyzed by [Fe(IndH)(CHCN)](ClO) [IndH = 1,3-bis(2'-pyridylimino)isoindoline], involving a spectroscopically characterized (μ-oxo)(μ-1,2-peroxo)diiron(III) intermediate () that is capable of olefin epoxidation and alkane hydroxylation including cyclohexane. Species also converts ketones to lactones with a decay rate dependent on [ketone], suggesting direct nucleophilic attack of the substrate carbonyl group by the peroxo species. In contrast, peroxo decay is unaffected by the addition of olefins or alkanes, but the label from HO is incorporated into the the epoxide and alcohol products, implicating a high-valent iron-oxo oxidant that derives from O-O bond cleavage of the peroxo intermediate.

Disproportionation of HO Mediated by Diiron-Peroxo Complexes as Catalase Mimics.

Heme iron and nonheme dimanganese catalases protect biological systems against oxidative damage caused by hydrogen peroxide. Rubrerythrins are ferritine-like nonheme diiron proteins, which are structurally and mechanistically distinct from the heme-type catalase but similar to a dimanganese KatB enzyme. In order to gain more insight into the mechanism of this curious enzyme reaction, non-heme structural and functional models were carried out by the use of mononuclear [Fe(L)(solvent)](ClO) (-) (L = 1,3-bis(2-pyridyl-imino)isoindoline, L = 1,3-bis(4'-methyl-2-pyridyl-imino)isoindoline, L = 1,3-bis(4'-Chloro-2-pyridyl-imino)isoindoline, L = 1,3-bis(5'-chloro-2-pyridyl-imino)isoindoline) complexes as catalysts, where the possible reactive intermediates, diiron-perroxo [Fe(μ-O)(μ-1,2-O)(L-L)(Solv)] (-) complexes are known and well-characterized.

Comparison of Nonheme Manganese- and Iron-Containing Flavone Synthase Mimics.

Heme and nonheme-type flavone synthase enzymes, FS I and FS II are responsible for the synthesis of flavones, which play an important role in various biological processes, and have a wide range of biomedicinal properties including antitumor, antimalarial, and antioxidant activities. To get more insight into the mechanism of this curious enzyme reaction, nonheme structural and functional models were carried out by the use of mononuclear iron, [Fe(CDA-BPA*)] () [CDA-BPA = ,,','--(2-pyridylmethyl)-cyclohexanediamine], [Fe(CDA-BQA*)] () [CDA-BQA = ,,','--(2-quinolilmethyl)-cyclohexanediamine], [Fe(Bn-TPEN)(CHCN)] () [Bn-TPEN = -benzyl-,','-tris(2-pyridylmethyl)-1,2-diaminoethane], [Fe(O)(Bn-TPEN)] (), and manganese, [Mn(N4Py*)(CHCN)] () [N4Py* = ,-bis(2-pyridylmethyl)-1,2-di(2-pyridyl)ethylamine)], [Mn(Bn-TPEN)(CHCN)] () complexes as catalysts, where the possible reactive intermediates, high-valent Fe(O) and Mn(O) are known and well characterised. The results of the catalytic and stoichiometric reactions showed that the ligand framework and the nature of the metal cofactor significantly influenced the reactivity of the catalyst and its intermediate.

A nonheme peroxo-diiron(III) complex exhibiting both nucleophilic and electrophilic oxidation of organic substrates.

The complex [FeIII2(μ-O2)(L3)4(S)2]4+ (L3 = 2-(4-thiazolyl)benzimidazole, S = solvent) forms upon reaction of [FeII(L3)2] with H2O2 and is a functional model of peroxo-diiron intermediates invoked during the catalytic cycle of oxidoreductases. The spectroscopic properties of the complex are in line with those of complexes formed with N-donor ligands. [FeIII2(μ-O2)(L3)4(S)2]4+ shows both nucleophilic (aldehydes) and electrophilic (phenol, N,N-dimethylanilines) oxidative reactivity and unusually also electron transfer oxidation.

Radiocarbon analysis of carbonaceous aerosols in Bratislava, Slovakia.

Aerosols dispersed in the atmosphere represent important factors influencing not only the environment, but also human health. Carbonaceous aerosols are one of the main components of total atmospheric aerosols, and their sources are of great interest. Radiocarbon analysis provides an excellent way to determine the fraction of fossil and non-fossil aerosols in the atmosphere.

Temporal changes in tritium and radiocarbon concentrations in the western North Pacific Ocean (1993-2012).

The western North Pacific is one of the most studied oceanic basins due to its diverse structure and important role in connection with the adjacent reservoirs. Tritium (H) and radiocarbon (C) have been frequently exploited as oceanographic tracers due to their suitable properties; several extensive observation projects, such as GEOSECS, WOCE and WOMARS, used these two radionuclides to investigate different oceanographic processes, pathways, ocean currents and time scales of deep and bottom water formation. Here we evaluate temporal changes in H and C levels in seawater of the western North Pacific Ocean from 1993 to 2012.

Radiocarbon and Cs dating of wines.

Wine dating methods based on anthropogenic C and Cs, as well as on the cosmogenic C were studied with the aim to improve the accuracy and precision of the dating results. While the C dating method has proved to be useful for dating young and old wines, the Cs has been effective for dating of wines originating around the Cs bomb-peak observed in 1963. A new method was developed for simultaneous C and Cs dating of wines, which helped to distinguish wines originating before or after the bomb peak.

Functional models of nonheme diiron enzymes: reactivity of the μ-oxo-μ-1,2-peroxo-diiron(iii) intermediate in electrophilic and nucleophilic reactions.

The reactivity of the previously reported peroxo-adduct [FeIII2(μ-O)(μ-1,2-O2)(IndH)2(solv)2]2+ (1) (IndH = 1,3-bis(2-pyridyl-imino)isoindoline) has been investigated in nucleophilic (e.g., deformylation of alkyl and aryl alkyl aldehydes) and electrophilic (e.

Geant4-based electromagnetic background model for the CRESST dark matter experiment.

The CRESST (Cryogenic Rare Event Search with Superconducting Thermometers) dark matter search experiment aims for the detection of dark matter particles via elastic scattering off nuclei in crystals. To understand the CRESST electromagnetic background due to the bulk contamination in the employed materials, a model based on Monte Carlo simulations was developed using the Geant4 simulation toolkit. The results of the simulation are applied to the TUM40 detector module of CRESST-II phase 2.

Stability and Catalase-Like Activity of a Mononuclear Non-Heme Oxoiron(IV) Complex in Aqueous Solution.

Heme-type catalase is a class of oxidoreductase enzymes responsible for the biological defense against oxidative damage of cellular components caused by hydrogen peroxide, where metal-oxo species are proposed as reactive intermediates. To get more insight into the mechanism of this curious reaction a non-heme structural and functional model was carried out by the use of a mononuclear complex [Fe(N4Py*)(CHCN)](CFSO) (N4Py* = ,-bis(2-pyridylmethyl)- 1,2-di(2-pyridyl)ethylamine) as a catalyst, where the possible reactive intermediates, high-valent Fe=O and Fe-OOH are known and spectroscopically well characterized. The kinetics of the dismutation of HO into O and HO was investigated in buffered water, where the reactivity of the catalyst was markedly influenced by the pH, and it revealed Michaelis-Menten behavior with K = 1.