Route to stable nitroxides with alkoxy groups at α- carbon - the derivatives of 2- and 3-imidazolines

Oxidation of 1-hydroxy-5,5-dimethyl-3-imidazoline-3-oxides containing one or two hydrogen atoms in position 2 of the heterocycle with lead dioxide in alcohol leads to stable nitroxides with alkoxy groups at α-carbon, the derivatives of 2- and 3-imidazolines, via the intermediate formation of 4H-imidazol-1,3-dioxides.     

Structure determination of isolated metal clusters via far-infrared spectroscopy

We present a new method for the size selective structure determination of small isolated metal clusters in the gas phase. The technique is applied to cationic vanadium clusters containing 6 to 23 atoms, whose far infrared absorption spectra are measured in the 140-450 cm(-1) spectral range. The spectra are unique for each cluster size and are true fingerprints of the cluster's structure. By comparing the experimental spectra to spectra obtained from density-functional theory, the geometric cluster structure can be identified.     

Observation of giant magnetic linear dichroism in (Ga, Mn) As

Giant magnetic linear dichroism (MLD) is observed in the ferromagnetic semiconductor Ga(0.98)Mn(0.02)As. The contribution to this effect induced by the spontaneous magnetization can be clearly identified by azimuthal dependencies. The spectral dependence of the effect in the range from 1.4 to 2.4 eV shows that the MLD induced by the spontaneous magnetization is strongly enhanced for excitations from the electronic states that are responsible for the ferromagnetism in this material. This spectral sensitivity and the size of the effect makes MLD a powerful tool for the study of (III, Mn)V alloys and similar novel ferromagnetic semiconductors.     

Reactions of cyclic α-methoxy nitrones with nucleophilic reagents

Reactions of cyclic -methoxy nitrones, which are derivatives of imidazole or dihydroimidazole N-oxides, with amines, KOH, or KSH result in the replacement of the MeO group to form cyclic -amino nitrones, hydroxamic acids, or thiohydroxamic acids, respectively. Analogous reactions occur with C-nucleophiles.     

Photochemical isomerization of 2H-imidazoleN-oxides

1,3-Diaza-6-oxabicyclo[3.1.0]hex-3-enes and their 3-oxides were obtained by the photolysis of 2H-imidazole 1-oxides and 2H-imidazole 1,3-dioxides. 1,3-Diaza-6-oxabicyclo [3.1.0]hex-3-ene 3-oxides are thermally unstable and are converted to the starting 2H-imidazole 1,3-dioxides; their further photolysis affords a mixture of stereoisomeric 1,3-diaza-4,7-dioxatricyclo [4.1.0.0^3,5]heptanes.For the previous communication, see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2096–2100, December, 1993.     

2H-imidazole-N-oxides as spin traps

The capacity of 2H-imidazole-1-oxides, which contain an aldonitrone group, for spin capture was investigated. The parameters of spin adducts with^.OH,^.CH₃, and^.CH₂OH radicals are reported.Institute of Chemical Kinetics and Combustion, Siberian Branch, Russian Academy of Sciences. Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences, 630090 Novosibirsk. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 5, pp. 1064–1068, May, 1992.     

Synthesis of the tetraethyl substituted pH-sensitive nitroxides of imidazole series with enhanced stability towards reduction

The synthesis of 2,2,5,5-tetraethylimidazole nitroxides from 3-ethylpent-2-ene is described. The newly synthesized nitroxides, namely 4-methyl-2,2,5,5-tetraethyl-2,5-dihydro-1H-imidazol-1-yloxy (1), 3,4-dimethyl-2,2,5,5-tetraethylperhydroimidazol-1-yloxy (2) and 2,2,5,5-tetraethyl-4-pyrrolidin-1-yl-2,5-dihydro-1H-imidazol-1-oxyl (3), were found to be pH sensitive spin probes, with pK values of 1.2, 4.95 and 7.4, respectively. The most important finding was the fact that these new nitroxides were 20-30 times more stable in the presence of ascorbate and had significantly longer halflifes in rat blood as compared to 2,2,5,5-tetramethyl analogs. The latter observation provides a unique advantage for the application of tetraethyl substituted imidazole nitroxides as functional EPR probes.     

Uptake of Cell-Penetrating Peptide RL2 by Human Lung Cancer Cells: Monitoring by Electron Paramagnetic Resonance and Confocal Laser Scanning Microscopy

RL2 is a recombinant analogue of a human κ-casein fragment, capable of penetrating cells and inducing apoptosis of cancer cells with no toxicity to normal cells. The exact mechanism of RL2 penetration into cells remains unknown. In this study, we investigated the mechanism of RL2 penetration into human lung cancer A549 cells by a combination of electron paramagnetic resonance (EPR) spectroscopy and confocal laser scanning microscopy. EPR spectra of A549 cells incubated with RL2 (sRL2) spin-labeled by a highly stable 3-carboxy-2,2,5,5-tetraethylpyrrolidine-1-oxyl radical were found to contain three components, with their contributions changing with time. The combined EPR and confocal-microscopy data allowed us to assign these three forms of sRL2 to the spin-labeled protein sticking to the membrane of the cell and endosomes, to the spin-labeled protein in the cell interior, and to spin labeled short peptides formed in the cell because of protein digestion. EPR spectroscopy enabled us to follow the kinetics of transformations between different forms of the spin-labeled protein at a minimal spin concentration (3–16 μM) in the cell. The prospects of applications of spin-labeled cell-penetrating peptides to EPR imaging, DNP, and magnetic resonance imaging are discussed, as is possible research on an intrinsically disordered protein in the cell by pulsed dipolar EPR spectroscopy.     

Thermostressed state of a piezoelectric bodywith a plane crack under symmetric thermal load

The paper addresses a thermoelectroelastic problem for a piezoelectric body with an arbitrarily shaped plane crack in a plane perpendicular to the polarization axis under a symmetric thermal load. A relationship between the intensity factors for stress (SIF) and electric displacement (EDIF) in an infinite piezoceramic body with a crack under a thermal load and the SIF for a purely elastic body with a crack of the same shape under a mechanical load is established. This makes it possible to find the SIF and EDIF for an electroelastic material from the elastic solution without the need to solve specific problems of thermoelasticity. The SIF and EDIF for a piezoceramic body with an elliptic crack and linear distribution of temperature over the crack surface are found as an example __________ Translated from Prikladnaya Mekhanika, Vol. 44, No. 3, pp. 96–108, March 2008.     

EPR and Quantum Chemical Studies of the pH-sensitive Imidazoline and Imidazolidine Nitroxides with Bulky Substituents

The X- and W-band electron paramagnetic resonance (EPR) spectroscopies were employed to investigate a series of imidazolidine nitroxide radicals with different number of ethyl and methyl substituents at positions 2 and 5 of a heterocycle in liquid and frozen solutions. The influence of the substituents on the line shape and width was studied experimentally and analyzed using quantum chemical calculations. Each pair of the geminal ethyl groups in the positions 2 or 5 of the imidazolidine ring was found to produce an additional hyperfine splitting (hfs) of about 0.2 mT in the EPR spectra of the nitroxides. The effect was attributed to the hfs constant of only one of four methylene hydrogen atoms of two geminal ethyl substituents not fully averaged by ethyl group rotation and ring puckering. In accordance with this assumption, the substitution of hydrogen atoms of CH₂ groups in 2,2,5,5-tetraethyl-substituted imidazolidine nitroxides by deuterium leads to the substantial narrowing of EPR lines which could be useful for many biochemical and biomedical applications, including pH-monitoring. W-band EPR spectra of 2,2,5,5-tetraethyl-substituted imidazolidine nitroxide and its 2,2,5,5-tetraethyl–d₈ deuterium-substituted analog measured at low temperatures demonstrated high sensitivity of their g-factors to pH, which indicates their applicability as spin labels possessing high stability.