The combination of continuous wave electron paramagnetic resonance (cw-EPR) with electrochemistry is highly attractive as it allows a clean in-situ generation and the subsequent spectroscopic characterisation of radical ions, which are important intermediates in many photocatalytic cycles as well as light-induced processes occurring in biological systems or optoelectronic devices. Although commercial setups for spectroelectrochemical EPR are available, they are often expensive and tailored to a particular spectroscopic setup.  Here we present a design for a low-cost electrochemical EPR cell that can be used in combination with any commercial cw-EPR instrumentation. The cell design is compared to existing setups and the performance of the cell is evaluated by comparison of EPR spectra obtained by chemical and electrochemical oxidation of a graphene fragment.

Pulsed electron-electron double resonance (PELDOR) spectroscopy is a powerful method for determining nucleic acid (NA) structure and conformational dynamics. PELDOR with molecular dynamics (MD) simulations opens up unique possibilities for defining the conformational ensembles of flexible, three-dimensional, self-assembled complexes of NA. Understanding the diversity and structure of these complexes is vital for uncovering matrix and regulative biological processes in the human body and artificially influencing them for therapeutic purposes. To explore the reliability of PELDOR and MD simulations, we site-specifically attached nitroxide spin labels to oligonucleotides, which form self-assembled complexes between NA chains and exhibit significant conformational flexibility. The DNA complexes assembled from a pair of oligonucleotides with different linker sizes showed excellent agreement between the distance distributions obtained from PELDOR and calculated from MD simulations, both for the mean inter-spin distance and the distance distribution width. These results prove that PELDOR with MD simulations has significant potential for studying the structure and dynamics of conformational flexible complexes of NA.

The synthesis of diradical organic compounds has garnered significant attention due to their thermally accessible spin inversion and optoelectronic properties. Yet, preparing such stable structures with high open-shell behavior remains challenging. Herein, we report the synthesis and properties of four π-extended, fused fluorene derivatives with high diradical character, taking advantage of a molecular design where the closed-shell does not include any Clar sextet, comparatively to a maximum of 5 in the corresponding open-shell state. This led to an unusual open-shell triplet ground state with an outstanding singlet-triplet energy difference (ΔEST) of ca. 19 kcal/mol, one of the highest values reported to date for an all-carbon conjugated scaffold. Incorporation of dithiafulvene units at each end of the molecule (at the five-membered rings) furnishes extended tetrathiafulvalenes (TTFs) undergoing reversible oxidations to the radical cation and diradical dication. The various pro-aromatic structures presented herein show highly localized spin density and a limited conjugation due to the confined π-electrons in the aromatic cycles, as supported by 1H NMR, UV-visible, EPR spectroscopy and DFT calculations.

Copper-exchanged zeolite omega (Cu-omega) is a potent material for the selective conversion of methane-to-methanol (MtM) via the oxygen looping approach. However, its performance exhibits substantial variation depending on the operational conditions. Under an isothermal temperature regime, Cu-omega demonstrates subdued activity below 230 °C, but experiences a remarkable increase in activity at 290 °C. Applying a high-temperature activation protocol at 450 °C causes a rapid deactivation of the material. This behavioral divergence is investigated by combining reactivity studies, neutron and in situ high-resolution anomalous X-ray powder diffraction (HR-AXRPD), as well as electron paramagnetic resonance spectroscopy, to reveal that the migration of Cu throughout the framework is the primary cause of these behaviors, which in turn is governed by the degree of hydration of the system. This work suggests that control over the Cu migration throughout the zeolite framework may be harnessed to significantly increase the activity of Cu-omega by generating more active sites for the MtM conversion. These results underscore the power of in situ HR-AXRPD for unraveling the behavior of materials under reaction conditions and suggest that a re-evaluation of Cu-zeolites priorly deemed inactive for the MtM conversion across a broader range of conditions and looping protocols may be warranted.

New cobalt(II)-based complexes with [N2O2] coordination formed by two bis-chelate ligands were synthesized and characterized by a multi-technique approach. The complexes possess an easy-axis anisotropy (D < 0) and magnetic measurements show a field-induced slow relaxation of magnetization. The spin-reversal barriers, i.e., the splitting of the two lowest Kramers doublets (UZFS), have been measured by THz-EPR spectroscopy, which allows to distinguish the two crystallographically independent species present in one of the complexes. Based on these experimental UZFS energies together with those for related complexes reported in literature, it was possible to establish magneto-structural correlations. UZFS linearly depends on the elongation parameter εT of the (pseudo-)tetrahedral coordination, which is given by the ratio between the average obtuse and acute angles at the cobalt(II) ion, while UZFS was found to be virtually independent of the twist angle of the chelate planes. With increasing deviation from the orthogonality of the latter, the rhombicity (|E/D|) increases.

Oxidative stress is a major source of ROS-mediated damage to macromolecules, tissues, and the whole body. It is an important marker in the severe picture of pathological conditions. The discovery of free radicals in biological systems gives a \"start\" to studying various pathological processes related to the development and progression of many diseases. From this moment on, the enrichment of knowledge about the participation of free radicals and free-radical processes in the pathogenesis of cardiovascular, neurodegenerative, and endocrine diseases, inflammatory conditions, and infections, including COVID-19, is increasing exponentially. Excessive inflammatory responses and abnormal reactive oxygen species (ROS) levels may disrupt mitochondrial dynamics, increasing the risk of cell damage. In addition, low serum albumin levels and changes in the normal physiological balance between reduced and oxidized albumin can be a serious prerequisite for impaired antioxidant capacity of the body, worsening the condition in patients. This review presents the interrelationship between oxidative stress, inflammation, and low albumin levels, which are hallmarks of COVID-19.

The heme synthase AhbD catalyzes the last step of the siroheme-dependent heme biosynthesis pathway, which is operative in archaea and sulfate-reducing bacteria. The AhbD-catalyzed reaction consists of the oxidative decarboxylation of two propionate side chains of iron-coproporphyrin III to the corresponding vinyl groups of heme b. AhbD is a Radical SAM enzyme employing radical chemistry to achieve the decarboxylation reaction. Previously, it was proposed that the central iron ion of the substrate iron-coproporphyrin III participates in the reaction by enabling electron transfer from the initially formed substrate radical to an iron-sulfur cluster in AhbD. In this study, we investigated the substrate radical that is formed during AhbD catalysis. While the iron-coproporphyrinyl radical was not detected by electron paramagnetic resonance (EPR) spectroscopy, trapping and visualization of the substrate radical was successful by employing substrate analogs such as coproporphyrin III and zinc-coproporphyrin III. The radical signals detected by EPR were analyzed by simulations based on density functional theory (DFT) calculations. The observed radical species on the substrate analogs indicate that hydrogen atom abstraction takes place at the β-position of the propionate side chain and that an electron donating ligand is located in proximity to the central metal ion of the porphyrin.

Reaction of a molecular zinc-hydride [{(ArNCMe)2CH}ZnH] (Ar = 2,6-di-isopropylphenyl) with 0.5 equiv. of [Ni(CO)Cp]2 led to the isolation of a nickel-zinc hydride complex containing a bridging 3-centre,2-electron Ni-H-Zn interaction. This species has been characterized in the solid-state by single crystal X-ray diffraction. DFT calculations are consistent with its formulation as a σ-complex derived from coordination of the zinc-hydride to a paramagnetic nickel(I) fragment. Continuous wave and pulse EPR experiments suggest that this species is not stable in solution and suggest that this species is labile in solution. Further experiments show that in the presence of catalytic quantities of nickel(I) precursors, zinc-hydride bonds can undergo either H/D-exchange with D2 or dehydrocoupling to form Zn-Zn bonds. In combination, the data support the activation and functionalisation of zinc-hydride bonds at nickel(I) centres.

Nitroxides are stable organic radicals with exceptionally long lifetimes, which render them uniquely suitable as observable probes or polarising agents for spectroscopic investigation of biomolecular structure and dynamics. Radical-based probes for biological applications are ideally characterized by both robustness towards reductive degradation and beneficial electron spin relaxation parameters. These properties are largely influenced by the molecular structure of the nitroxide scaffold, and also by the conformations it prefers to adopt. In this study we present the synthesis of the first nitroxides based on a spirocyclic pyrrolidine scaffold with an exocyclic methylene substituent. The conformations adopted by these nitroxides were evaluated by X-ray crystallography, both with single nitroxide crystals and by inclusion of nitroxides in a microporous crystalline sponge. The kinetic and thermodynamic stability of the new nitroxides towards reduction was investigated by electron paramagnetic resonance (EPR) spectroscopy and cyclic voltammetry (CV). In combination with EPR measurements of electron spin relaxation properties, these results suggest that this new family of nitroxides can provide access to multifunctionalized probes and polarising agents suitable for use in biological environments at elevated temperatures.

Ovalbumin (OVA), a protein vital for chick embryo nutrition, hydration, and antimicrobial protection, together with other egg-white proteins, migrates to the amniotic fluid and is orally absorbed by the embryo during embryogenesis. Recently, it has been shown that for optimal eggshell quality, the hen diet can be supplemented with manganese. Although essential for embryonic development, manganese in excess causes neurotoxicity. This study investigates whether OVA may be involved in the regulation of manganese levels. The binding of Mn(II) to OVA was investigated using electron paramagnetic resonance (EPR) spectroscopy. The results show that OVA binds a maximum of two Mn(II) ions, one with slightly weaker affinity, even in a 10-fold excess, suggesting it may have a protective role from Mn(II) overload. It seems that the binding of Mn(II), or the presence of excess Mn(II), does not affect OVA\'s tertiary structure, as evidenced from fluorescence and UV/vis measurements. Comparative analysis with bovine and human serum albumins revealed that they exhibit higher affinities for Mn(II) than OVA, most likely due to their essentially different physiological roles. These findings suggest that OVA does not play a role in the transport and storage of manganese; however, it may be involved in embryo protection from manganese-induced toxicity.