Nitroxide Spins Research Articles

Imaging Reactive Oxygen Radicals in Excised Mouse Lung Trapped by Reaction with Hydroxylamine Probes Using 1 GHz Rapid Scan Electron Paramagnetic Resonance.

Oxidative stress is proposed to be critical in acute lung disease, but methods to monitor radicals in lungs are lacking. Our goal is to develop low-frequency electron paramagnetic resonance (EPR) methods to monitor radicals that contribute to the disease. Free radicals generated in a lipopolysaccharide-induced mouse model of acute respiratory distress syndrome reacted with cyclic hydroxylamines CPH (1-hydroxy-3-carboxy-2,2,5,5-tetramethylpyrrolidine hydrochloride) and DCP-AM-H (4-acetoxymethoxycarbonyl-1-hydroxy-2,2,5,5-tetramethylpyrrolidine-3-carboxylic acid), which were converted into the corresponding nitroxide radicals, CP• and DCP•. The EPR signals of the nitroxide radicals in excised lungs were imaged with a 1 GHz EPR spectrometer/imager that employs rapid scan technology. The small numbers of nitroxides formed by reaction of the hydroxylamine with superoxide result in low signal-to-noise in the spectra and images. However, since the spectral properties of the nitroxides are known, we can use prior knowledge of the line shape and hyperfine splitting to fit the noisy data, yielding well-defined spectra and images. Two-dimensional spectral-spatial images are shown for lung samples containing (4.5 ± 0.5) ×1014 CP• and (9.9 ± 1.0) ×1014 DCP• nitroxide spins. These results suggest that a probe that accumulates in cells gives a stronger nitroxide signal than a probe that is more easily washed out of cells. The nitroxide radicals in excised mouse lungs formed by reaction with hydroxylamine probes CPH and DCP-AM-H can be imaged at 1 GHz.

FTIR study of thermally induced magnetostructural transitions in breathing crystals.

"Breathing crystals" based on copper(II) hexafluoroacetylacetonates and pyrazolyl-substituted nitronyl nitroxides comprise the exchange-coupled clusters within the polymeric chains. Owing to an interplay of exchange interaction between copper(II) and nitroxide spins and Jahn-Teller nature of copper(II) complex, the breathing crystals demonstrate thermally and light-induced magnetostructural transitions in many aspects similar to the classical spin crossover. Herewith, we report the first application of variable temperature (VT) far/mid Fourier transform infrared (FTIR) spectroscopy and mid FTIR microscopy to breathing crystals. This VT-FTIR study was aimed toward clarification of the transitions mechanism previously debated on the basis of superconducting quantum interference device, X-ray diffraction, and electron paramagnetic resonance data. VT-FTIR showed the onset of new vibrational bands during phase transitions occurring at the expense of several existing ones, whose intensity was significantly reduced. The most pronounced spectral changes were assigned to corresponding vibrational modes using quantum chemical calculations. A clear-cut correlation was found between temperature-dependent effective magnetic moment of studied compounds and the observed VT-FTIR spectra. Importantly, VT-FTIR confirmed coexistence of two types of copper(II)-nitroxide clusters during gradual magnetostructural transition. Such clusters correspond to weakly coupled and strongly coupled spin states, whose relative contribution depends on temperature. The pronounced difference in the VT-FTIR spectra of two states in breathing crystals is a fingerprint of magnetostructural transition, and understanding of these characteristics achieved by us will be useful for future studies of breathing crystals as well as their diamagnetic analogues.

Spin‐Labeled Fulleropyrrolidines

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Spin-labeled fulleropyrrolidines

Abstract We describe the synthesis and properties of a series of fulleropyrrolidines bearing stable nitroxide free radical moieties covalently linked to the [60]fullerene cage. The nitroxide electron spin functions as a weakly interacting probe for the investigation of radical anions and paramagnetic excited states of functionalized fullerenes. Electron transfer processes, spin coupling in polyradical adducts, and interactions between radical and fullerene excited triplet unpaired electrons have been studied through electron paramagnetic resonance. Photogenerated quartet and quintet high spin species, obtained from the spin coupling of the fullerene triplet with the nitroxide spins, have been observed for the first time at room temperature. To cite this article: C. Corvaja et al., C. R. Chimie 9 (2006).

Magnetic behavior of a manganese(II) complex of nitroxide-substituted 1,3-di(4-pyridyl)benzene

Magnetic interaction between two magnetic metals separated by a sizable diamagnetic ligand is generally very weak. A new spin-introduced bidentate, N- t-butyl- N-oxy-3,5-dipyridylaniline ( 1) was designed and synthesized to explore the spin-introducing effect on sizable ligands. A Mn(hfac) 2 complex of 1 was prepared and its structure was elucidated by X-ray structure analysis. The complex 1·Mn(hfac) 2 has a one-dimensional helical alternate-chain structure; a double-helix structure is constructed by the two chains. The ferromagnetic interaction between Mn(II) and the nitroxide spins was observed. The analysis using Seiden's model allows the estimation of J = + 0.33 K for Mn(II)–nitroxide interaction. In accordance with this result, the N- t-butyl- N-oxy-3-pyridylaniline ( 2)-derived Mn(hfac) 2 complex, 2 2·Mn(hfac) 2, revealed a comparable magnetic interaction between the Mn(II) spin and the nitroxide spins, showing J = + 0.19 K by a trimer model analysis. Thus, the magnetic interaction between the Mn(II) ions can be improved by introduction of the nitroxide group into the diamagnetic bidentate through the spin communication between the nitroxide and Mn(II) spins.

Low temperature magnetic properties of a molecular compound (abstract)

In molecular compounds, the magnetic properties depend on the coupling between the magnetic moments of transition metal ions, rare earth ions, and/or free radicals. This coupling is often antiferromagnetic, but can give a high spin moment in some particular cases. When organic molecules form crystals, again the coupling between molecules can be antiferromagnetic or ferromagnetic like. In a few cases the ferromagnetism, only due to nitroxide radicals, has been observed at low temperature. We present here a more general case of a manganese(II) derivative of an ‘‘imidazole substituted nitronyl nitroxide’’ with complex behavior. The high temperature properties can be explained by ferrimagnetic coupling between the Mn and nitroxide spins. At low temperature a weak intermolecular coupling appears below 10 K, as well as a weak ferromagnetic component below 4.5 K. These low temperature properties might be due to the canting of antiferromagnetically coupled spins.