Triarylmethyl-based biradical as a superoxide probe

Trityl isocyanide as a general reagent for visible light mediated photoredox-catalyzed cyanations

A photoredox catalytic strategy has been developed to enable the functionalization of a variety of commercially available, structurally different radical precursors by the use of a bench-stable isonitrile as an efficient cyanating reagent. Specifically, a radical-based reaction has provided a mild and convenient procedure for the cyanation of primary, secondary and tertiary radicals derived from widely accessible sp3-hybridized carboxylic acids, alcohols and halides under visible light irradiation. The reaction tolerates a variety of functional groups and it represents a complementary method for the cyanation of structurally different scaffolds that show diverse native functionalities, expanding the scope of previously reported methodologies.

Rapid Scan EPR Oxygen Imaging in Photoactivated Resin Used for Stereolithographic 3D Printing

Oxygen plays a critical role in the photopolymerization process resulting in the formation of solid structures from liquid resins during three-dimensional (3D) printing: it acts as a polymerization inhibitor. Upon exposure to light, oxygen is depleted. As a result, the polymerization process becomes activated. Electron paramagnetic resonance (EPR) imaging is described as a tool to visualize changes in oxygen distribution caused by light exposure. This nondestructive method uses radio waves and, therefore, is not constrained by optical opacity offering greater penetrating depth. Three proof-of-principle imaging experiments were demonstrated: (1) spatial propagation of the photopolymerization process; (2) oxygen depletion as a result of postcuring; and (3) oxygen visualization in a 3D printed spiral model. Commercial stereolithography (SLA) resin was used in these experiments. Lithium octa-n-butoxynaphthalocyanine (LiNc-BuO) probe was mixed with the resin to permit oxygen imaging. Li-naphthalocyanine probes are routinely used in various EPR applications because of their long-term stability and high functional sensitivity to oxygen. In this study, we demonstrate that EPR imaging has the potential to become a powerful visualization tool in the development of 3D printing technology, including bioprinting and tissue engineering.

Perchlorinated Triarylmethyl Radical 99% Enriched 13C at the Central Carbon as EPR Spin Probe Highly Sensitive to Molecular Tumbling

Soluble stable radicals are used as spin probes and spin labels for in vitro and in vivo electron paramagnetic resonance (EPR) spectroscopy and imaging applications. We report the synthesis and characterization of a perchlorinated triarylmethyl radical enriched 99% at the central carbon, ¹³C₁-PTMTC. The anisotropy of the hyperfine splitting with the ¹³C₁ (A_x = 26, A_y = 25, A_z = 199.5 MHz) and the g (g_x = 2.0015, g_y = 2.0015, g_z = 2.0040) are responsible for a strong effect of the radical tumbling rate on the EPR spectrum. The rotational correlation time can be determined by spectral simulation or via the line width or the apparent A_z after calibration, so the spin probe ¹³C₁-PTMTC can be used to measure media microviscosity with high sensitivity.

Immobilization of Heteroatom-Doped Carbon Dots onto Nonpolar Plastics for Antifogging, Antioxidant, and Food Monitoring Applications

This work presents the facile synthesis of heteroatom-doped fluorescent carbon quantum dots (C-dots), which could serve as an antioxidant. Herein, nitrogen, phosphorous, and sulfur codoped carbon dots (NPSC-dots) have been synthesized by a single-step hydrothermal strategy. Owing to the radical scavenging activity of the NPSC-dots, they were tested against several methods as well as in practical applications. The antioxidant ability of the NPSC-dots was efficiently utilized on plastic films by coating with these NPSC-dots. For the very first time, NPSC-dots were immobilized onto nonpolar plastic films (polypropylene) via photochemical covalent grafting to extend the shelf life of food items or storage without affecting the quality of plastic films. The NPSC-dot-coated PP film with negligible deterioration of transparency was extensively studied using scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared (FTIR) analysis, X-ray photoelectron spectroscopy (XPS), contact angle measurement, and thermogravimetric analysis (TGA). The fluorescent character, antioxidant ability, and durability under different solvent systems of the coated film were examined. Also, the coated films were extensively and rigorously evaluated against simulated drastic environmental conditions to ensure the durability and antifogging application.

Highly luminescent N-doped carbon dots from black soya beans for free radical scavenging, Fe3+ sensing and cellular imaging

The novel N doped carbon dots (N-CDs) were readily fabricated through one-step pyrolysis method from black soya beans. The obtained N-CDs possessed excellent photoluminescence properties with quantum yield of 38.7 ± 0.64% and dual responsive properties towards free radical and Fe3+. The N-CDs exhibited favorable radical scavenging activity (RSA) against 1,1-diphenyl-2-picrylhydrazyl (DPPH) and superoxide anion radicals. Fe3+ could induce photoluminescence quenching of N-CDs through static quenching characteristics. The possible quenching mechanism was presented. Combining with negligible toxicity and preferable biocompatibility, the N-CDs were extended to imaging intracellular Fe3+. As an attractive candidate, the N-CDs demonstrated a great potential in free radical scavenging, sensing and cellular imaging.

Molecular Probes for Evaluation of Oxidative Stress by In Vivo EPR Spectroscopy and Imaging: State-of-the-Art and Limitations

Oxidative stress, defined as a misbalance between the production of reactive oxygen species and the antioxidant defenses of the cell, appears as a critical factor either in the onset or in the etiology of many pathological conditions. Several methods of detection exist. However, they usually rely on ex vivo evaluation or reports on the status of living tissues only up to a few millimeters in depth, while a whole-body, real-time, non-invasive monitoring technique is required for early diagnosis or as an aid to therapy (to monitor the action of a drug). Methods based on electron paramagnetic resonance (EPR), in association with molecular probes based on aminoxyl radicals (nitroxides) or hydroxylamines especially, have emerged as very promising to meet these standards. The principles involve monitoring the rate of decrease or increase of the EPR signal in vivo after injection of the nitroxide or the hydroxylamine probe, respectively, in a pathological versus a control situation. There have been many successful applications in various rodent models. However, current limitations lie in both the field of the technical development of the spectrometers and the molecular probes. The scope of this review will mainly focus on the latter.

Comparison of different methods for measuring the superoxide radical by EPR spectroscopy in buffer, cell lysates and cells

As superoxide anion is of keen interest in biomedical research, it is highly desirable to have a technique allowing its detection sensitively and specifically in biological media. If electron paramagnetic resonance (EPR) techniques and probes have been individually described in the literature, there is actually no comparison of these techniques in the same conditions that may help guiding researchers for selecting the most appropriate approach. The aim of the present study was to compare different EPR strategies in terms of sensitivity and specificity to detect superoxide (vs. hydroxyl radical). Three main classes of EPR probes were used, including paramagnetic superoxide scavengers (such as nitroxides TEMPOL and mitoTEMPO as well as trityl CT-03), a spin trap (DIPPMPO), and diamagnetic superoxide scavengers (such as cyclic hydroxylamines CMH and mitoTEMPO-H). We analysed the reactivity of the different probes in the presence of a constant production of superoxide or hydroxyl radical in buffers and in cell lysates. We also assessed the performances of the different probes to detect superoxide produced by RAW264.7 macrophages stimulated by phorbol 12-myristate 13-acetate. In our conditions and models, we found that nitroxides were not specific for superoxide. CT-03 was specific, but the sensitivity of detection was low. Comparatively, we found that nitrone DIPPMPO and cyclic hydroxylamine CMH were good candidates to sensitively and specifically detect superoxide in complex biological media, CMH offering the best sensitivity.