The thermolysis of 1,2,3,7a-tetrahydroimidazo[1,2-b]isoxazole derivatives results in intramolecular rearrangements by two main pathways. One rearrangement affords azomethine ylide derivatives. Another rearrangement leads to the migration of the substituent from position 7a to the nitrogen atom. The rate constants of these reactions were determined. Quantum chemical calculations by the DFT method were carried out. Based on the data for the migration of the substituent, the concerted mechanism was proposed.

Methods for the synthesis and transformations of 2,3-dihydroisoxazole derivatives are reviewed. Data on reduction and oxidation reactions and intramolecular rearrangements are generalized; their mechanisms are discussed.

Method of time-resolved fluorescence was applied to study the luminescent properties of several 3-and 2-imidazoline derivatives of naphthalene. For 2-imidazoline derivatives in which the imidazoline fragment is directly bound to the naphthalene fragment, a weak (quantum yield φ < 0.001) luminescence of common π-system containing the radical group and the naphthalene core was recorded. 3-imidazoline derivatives, in which naphthalene and imidazoline fragments are separated by an ethylene bridge, demonstrate luminescence with the spectrum similar to that of free naphthalene. Quantum yield of luminescence and life-time of singlet excited state of 3-imidazoline derivatives are ca. 50 times less than for free naphthalene, because of intramolecular quenching of the luminophore luminescence by a stable radical.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

AbstractReview: methods for the synthesis and transformations; 106 refs.

Chelate complexes of copper(II) and nickel(II) with anions of nitroxide radical ethyl-2-(1-oxyl-2,2,5,5-tetramethylimidazolidin-4-yliden)-3-oxopropanoate (HL) are synthesized. The compounds have molecular structure and zero magnetic dimensionality. CuL(2) crystallizes as two polymorphs having mononuclear structure. Ni(2)L(4) forms dimeric molecules by virtue of the bridging function of the aldehyde oxygen atoms. Magnetic properties of Ni(2)L(4) are determined by antiferromagnetic exchange interactions between the Ni(II) ions (-48(1) K) propagated through the oxygen bridges.

Electron spin echo (ESE) spectroscopy as applied to nitroxide spin probes in glasses is sensitive to molecular motions of two types. The first type of motion is fast stochastic librations, with correlation times on the scale of nanoseconds. In this work, these librations were found in glassy glycerol above ∼190K and in glassy o-terphenyl above ∼250K (glass transition temperatures for these two solvents are Tg=185K and Tg=243K, respectively). Most likely, these librations are of the same origin as anharmonic atomic vibrations, as seen in glasses by neutron scattering above a so-called dynamical transition temperature. The second type of motion is slow millisecond inertial rotations, which are observed in the experimentally accessible microsecond time scale as developing within an angular range of ∼0.1–2°. Over the temperature range studied, the square of the characteristic rotation rate was found to be proportional to the dielectric α-relaxation rate that is known for glycerol and o-terphenyl from literature. This empirical fact probably means that small-angle inertial rotations of spin probes and dielectric α-relaxation in the solvent are interrelated phenomena.

Mechanisms of carbazole photoluminescence quenching by the free and chemically bound nitroxyl radicals in the model bound system “carbazole (CBZ)—imidazolidine nitroxyl radical R • ” were investigated and the photophysical properties of the system were studied and compared with those of free CBZ and R • in solution. The quantum yield and lifetime of fluorescence from the local singlet excited state of the carbazole moiety in the bound CBZ—R • system is three orders of magnitude lower than in free CBZ. The lifetime of the local triplet excited state of the carbazole moiety in the bound system is shorter than 50 ns. The rate constants for intermolecular quenching of the singlet and triplet excited states of free CBZ by R • in acetonitrile were found to be (1.4±0.1)·10 10 and (1.5±0.2)·10 9 L mol −1 s −1 , respectively. The most plausible mechanisms of both free and covalently bound carbazole luminescence quenching by nitroxyl radicals are exchange energy transfer and acceleration of internal conversion due to electron exchange.

2,2′-Diaryl-5,5,5′,5′-tetramethyl-3,3′-bi(pyrrol-3-ylidene)-4,4′(5H,5′H)-dione 1,1′-dioxides containing a carboxy, alkoxycarbonyl, or carbamoyl group in the para position of one or both benzene rings were synthesized. These compounds may be regarded as cyclic dinitrones with conjugated C=C bond. Mild aminolysis of carboxy groups in the title compounds may be used to introduce dinitrone fragments into oligonucleotide or polypeptide structures. Electrochemical reduction of the resulting amides involves reversible oneelectron transfer in the first step at a near-zero potential, which makes it possible to use the title compounds as electrochemically active labels in applied bioorganic electrochemistry.

In some cases, the reactions of enaminones of the imidazolidine 1-oxide series with the Vilsmeier reagent afford electrophilic substitution products containing the dimethyl-aminomethylene group. In an acidic medium, these products undergo either hydrolytic elimination of the dimethylaminomethylene moiety or hydrolysis of the latter to form the aldehyde group. The reaction of nitroenamine, which is a derivative of imidazolidine 1-oxide, with the Vilsmeier reagent produces furoxane, viz., the nitroxyl biradical. Reduction of the latter affords the dioxime biradical.

It has been shown by cyclic voltammetry for the first time for nitrons that the first step of electrochemical reduction of 3,3′-bi(2-R-5,5-dimethyl-4-oxopyrrolinylidene)-1,1′-dioxides in water and its binary mixtures with acetonitrile is a reversible one-electron process. The potentials of the first one-electron reduction peaks shift toward less negative values with an increase in the water content in the binary mixture, being in water equal to −0.14, −0.09, −0.08, and +0.19 V vs. saturated calomel electrode for dinitrons with R = Me, Ph, But, and CF3, respectively. Such very low reduction potentials allow one to use derivatives of these dinitrons as redox-active labels in applied bioorganic electrochemistry.

Syntheses of a nitroxide radical 2-(1-oxyl-2,2,5,5-tetramethyl-imidazolin-4-yliden)-3-oxo-5-phenylpentannitrile \((HL^{CH_2 CH_2 Ph} )\) and its copper(II) complex are reported. The coordination compound is characterized by the single crystal X-ray diffraction analysis (a = 11.647(2) Å, b = 13.269(3) Å, c = 13.844(3) Å, α = 61.83(2)°, β = 88.13(2)°, γ = 74.12(2)°, space group \(P\bar 1\)). The \(Cu(L^{CH_2 CH_2 Ph} )_2 (H_2 O)\) complex has a molecular structure.

Two competitive processes - 1,3-dipolar cycloaddition and nucleophilic addition - in the reaction of 4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole 3-oxides with asymmetrically substituted alkynes were shown to occur. The influence of solvents and the nature of substituents in the reagent and substrate molecules on the rate ratio of these competitive processes were studied.

The influence of solvents and different structural factors on the rate of 1,3-dipolar cycloaddition reaction of the 4,5-dihydro-1H-imidazole 3-oxide derivatives with alkynes have been studied. Nitrones and alkynes have been ranged by their relative activity in this reaction. Using the DFT calculation with the triple zets basis set, the energy profile of the reaction has been plotted, and the structures and energy characteristics of the transition states have been determined. The mechanism of this reaction has been shown to be concerted and asynchronous. The validity of the used computational approach for the detailed investigation of 1,3-dipolar cycloaddition of nitrones has been demonstrated.

Recently we demonstrated the principal possibility of application of 19F NMR spin-trapping technique for in vivo *NO detection [Free Radic. Biol. Med. 36 (2004) 248]. In the present study, we employed this method to elucidate the significance of *NO availability in animal models of hypertension. In vivo *NO-induced conversion of the hydroxylamine of the fluorinated nitronyl nitroxide (HNN) to the hydroxylamine of the iminonitroxide (HIN) in hypertensive ISIAH and OXYS rat strains and normotensive Wistar rat strain was measured. Significantly lower HIN/HNN ratios were measured in the blood of the hypertensive rats. The NMR data were found to positively correlate with the levels of nitrite/nitrate evaluated by Griess method and negatively correlate with the blood pressure. In comparison with other traditionally used methods 19F NMR spectroscopy allows in vivo evaluation of *NO production and provides the basis for in vivo *NO imaging.