Formation of methyl radicals derived from cumene hydroperoxide in reconstructed human epidermis: an EPR spin trapping confirmation by using 13 C-substitution

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Disentangling magnetic hardening and molecular spin chain contributions to exchange bias in ferromagnet/molecule bilayers

We performed SQUID and FMR magnetometry experiments to clarify the relationship between two reported magnetic exchange effects arising from interfacial spin-polarized charge transfer within ferromagnetic metal (FM)/molecule bilayers: the magnetic hardening effect, and spinterface-stabilized molecular spin chains. To disentangle these effects, both of which can affect the FM magnetization reversal, we tuned the metal phthalocyanine molecule central site's magnetic moment to selectively enhance or suppress the formation of spin chains within the molecular film. We find that both effects are distinct, and additive. In the process, we 1) extended the list of FM/molecule candidate pairs that are known to generate magnetic exchange effects, 2) experimentally confirmed the predicted increase in anisotropy upon molecular adsorption; and 3) showed that spin chains within the molecular film can enhance magnetic exchange. This magnetic ordering within the organic layer implies a structural ordering. Thus, by distengangling the magnetic hardening and exchange bias contributions, our results confirm, as an echo to progress regarding inorganic spintronic tunnelling, that the milestone of spintronic tunnelling across structurally ordered organic barriers has been reached through previous magnetotransport experiments. This paves the way for solid-state devices studies that exploit the quantum physical properties of spin chains, notably through external stimuli.Comment: Non

Encoding information onto the charge and spin state of a paramagnetic atom using MgO tunnelling spintronics

An electrical current that flows across individual atoms or molecules can generate exotic quantum-based behavior, from memristive effects to Coulomb blockade and the promotion of quantum excited states. These fundamental effects typically appear one at a time in model junctions built using atomic tip or lateral techniques. So far, however, a viable industrial pathway for such discrete state devices has been lacking. Here, we demonstrate that a commercialized device platform can serve as this industrial pathway for quantum technologies. We have studied magnetic tunnel junctions with a MgO barrier containing C atoms. The paramagnetic localized electrons due to individual C atoms generate parallel nanotransport paths across the micronic device as deduced from magnetotransport experiments. Coulomb blockade effects linked to tunnelling magnetoresistance peaks can be electrically controlled, leading to a persistent memory effect. Our results position MgO tunneling spintronics as a promising platform to industrially implement quantum technologies

Revisiting the pro-oxidant activity of copper: interplay of ascorbate, cysteine and glutathione

Copper (Cu) is essential for most organisms, but it can be poisonous in excess, through mechanisms such as protein aggregation, trans-metallation and oxidative stress. Latter could implicate the formation of potentially harmful Reactive Oxygen Species (ROS: O2•–, H2O2 and HO•) via the redox cycling between Cu(II)/Cu(I) states in the presence of dioxygen and physiological reducing agents such as ascorbate (AscH), cysteine (Cys) and the tripeptide glutathione (GSH). Although the reactivity of Cu with these reductants has been previously investigated, the reactions taking place in a more physiologically-relevant mixture of these biomolecules are not known. Hence, we report here on the reactivity of Cu with binary and ternary mixtures of AscH, Cys and GSH. By measuring ascorbate and thiol oxidation, as well as HO• formation, we show that Cu reacts preferentially with GSH and Cys, halting AscH oxidation and also HO• release. This could be explained by the formation of Cu-thiolate clusters with both GSH and, as we first demonstrate here, Cys. Moreover, we observed a remarkable acceleration of Cu-catalysed GSH oxidation in the presence of Cys. We provide evidence that both thiol-disulfide exchange and the generated H2O2 contribute to this effect. Based on these findings, we speculate that Cu-induced oxidative stress may be mainly driven by GSH depletion and/or protein disulfide formation rather than by HO• and envision a synergistic effect of Cys on Cu toxicity

Potential of EPR spin-trapping to investigate in situ free radicals generation from skin allergens in reconstructed human epidermis: cumene hydroperoxide as proof of concept

The first step in the development of skin sensitisation to a chemical, and in the elicitation offurther allergic contact dermatitis (ACD), is the binding of the allergen to skin proteins after pene-trating into the epidermis. The so-formed antigenic adduct is then recognised by the immunesystem as foreign to the body. Sensitising organic hydroperoxides derived from autoxidation ofnatural terpenes are believed to form antigens through radical-mediated mechanisms, althoughthis has not yet been established. So far,in vitroinvestigations on reactive radical intermediatesderived from these skin sensitisers have been conducted in solution, yet with experimental condi-tions being far away from real-life sensitisation. Herein, we report for the first time, the potentialuse of EPR spin-trapping to study thein situgeneration of free radicals derived from cumenehydroperoxide CumOOH in a 3D reconstructed human epidermis (RHE) model, thus much closerto what may happenin vivo. Among the undesirable effects associated with dermal exposure toCumOOH, it is described to cause allergic and irritant dermatitis, being reported as a significantsensitiser. We considered exploiting the usage of spin-trap DEPMPO as an extensive view of allsort of radicals derived from CumOOH were observed all at once in solution. We showed that inthe EpiskinTMRHE model, both by incubating in the assay medium and by topical application,carbon radicals are mainly formed by redox reactions suggesting the key role of CumOOH-derived carbon radicals in the antigen formation process

Nucleic Acids Res

Site-directed spin labeling is emerging as an essential tool to investigate the structural and dynamical features of RNA. We propose here an enzymatic method, which allows the insertion of a paramagnetic center at a specific position in an RNA molecule. The technique is based on a segmental approach using a ligation protocol with T4 RNA ligase 2. One transcribed acceptor RNA is ligated to a donor RNA in which a thio-modified nucleotide is introduced at its 5'-end by in vitro transcription with T7 RNA polymerase. The paramagnetic thiol-specific reagent is subsequently attached to the RNA ligation product. This novel strategy is demonstrated by introducing a paramagnetic probe into the 55 nucleotides long RNA corresponding to K-turn and Specifier Loop domains from the Bacillus subtilis tyrS T-Box leader RNA. The efficiency of the coupling reaction and the quality of the resulting spin-labeled RNA were assessed by Mass Spectrometry, Electron Paramagnetic Resonance (EPR) and Nuclear Magnetic Resonance (NMR). This method enables various combinations of isotopic segmental labeling and spin labeling schemes, a strategy that will be of particular interest to investigate the structural and dynamical properties of large RNA complexes by NMR and EPR spectroscopies

Oxidative stress on biomaterials:from molecules to cells

Reactive Oxygen Species (ROS) is a family of oxygen-based active molecules, which are deeply involved in numerous crucial processes of cellular metabolism, where the redox equilibrium is very important. An imbalance between ROS and the cell ability to neutralize them with antioxidants results in an Oxidative Stress (OS). This leads to cell alterations and impaired physiological functions. OS is involved in a growing list of human pathologies, from brain disorder, like Alzheimer and Parkinson's disease, to various forms of cancer (skin melanoma) and eye pathologies (cataract, macular disease), as well as in the aging process. Sometimes, inducing OS selectively in diseased cells can also act as a powerful therapy. This is the basis of PhotoDynamic Therapy (PDT), a newly developed medical application to cure cancer. It is based on ROS generation through photo-sensitive molecules (also referred to as PhotoSensitizers, or PS) under specific illumination. The goal of this work was to develop an efficient way to tune and characterize OS and related damage to biological systems. For this purpose, we synthesized a water-soluble derivative of fullerene-based PS, since the pristine molecule is known to generate ROS under visible illumination at very high yield. The efficiency of our custom-made PS in generating ROS was characterized by Electron Spin Resonance (ESR). Parallel studies were performed on a porphyrin-based PS and on TiO2 nanoparticles. The effects of oxidative stress provoked via PS were investigated for selected proteins and for a large variety of cells. The extent of OS was finely tuned by adjusting the experimental conditions such as PS concentration in the buffer. The changes upon OS were studied by three modern experimental techniques: ESR, Synchrotron Infrared MicroSpectroscopy (SIRMS) and Atomic Force Microscopy (AFM). We have obtained a promising set of data on the consequences of OS detected by these local techniques. During the OS certain chemical bonds are interrupted and others are created which manifest in the change of the lattice vibrations detected for entire cells using SIRMS. These stresses affect, first of all, the constituents of the cells. For example, OS on a protein induces conformational changes as measured by ESR using spin labeled proteins. We have shown that larger organizations of proteins like cytoskeletal filaments must also change under OS, since the cell stiffness decreases considerably. AFM measurements on various cell types (neurons, fibroblast, bladder cell, glioblastoma…) and on healthy and cancerous cells have clearly shown the progressive decrease of the Young's modulus as OS was switched on

Cu(II) Binding to the N-Terminal Model Peptide of the Human Ctr2 Transporter at Lysosomal and Extracellular pH

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