Diastereoselective synthesis and ESR study of 4-phenylDEPMPO spin traps

[reaction: see text] The cis and trans diastereoisomers of 5-(diethoxyphosphoryl)-5-methyl-4-phenylpyrroline N-oxide (4-PhDEPMPOt 8 and 4-PhDEPMPOc 9) were prepared stereoselectively and used as spin traps for hydroxyl and superoxide radicals. The spin adduct formed by reaction of the cis stereoisomer 9with superoxide radical anion exhibited an 8-line ESR spectrum, showing only a reduced alternating line width phenomenon. This spectrum is simpler than the 12-line spectrum of DEPMPO-OOH, which exhibits a strong alternating line width phenomenon. The half-life times of the 4-PhDEPMPOc-OOH and DEPMPO-OOH adducts were of the same order: 14.5 and 15.5 min, respectively.     

Electrochemical and ESR studies of au-protein from Micrococcus luteus

Au-protein from Micrococcus luteus, with and without Au inactive center, and chloroauric acid (HAu ^IIICl₄·4H₂O) with the addition of rutin, catechol, and riboflavin have been studied by means of electrochemistry and ESR. The redox potentials for Au-protein, as well as for the complexes Au-rutin and Au-catechol, have been measured, and ESR spectra of complexes Au-rutin and Au-catechol have been recorded. It has been shown that the Au atom binds to Au-protein via OH-groups of rutin. Flavin does not participatein gold binding. Au-protein is characterized by two peaks of cyclic voltammogram, −0.37 and −0.54 V. Au-protein with these potentials is able to function in the electron-transport chain of membranes between flavoproteins and quinones.     

ESR spectroscopic study on the addition of PhCONHCHCO2Me radicals to alkenes and spin traps

Using ESR spectroscopy, the rate constants for the addition of PhCONHCHCO₂Me radicals to alkenes CH₂=CXY (X = Me, Y = Ph; X = H, Y = Ph; X = Me, Y = CO₂Me; X = H, Y = CO₂Me; X = H, Y = CN) and nitrosodurene were determined at 22 °C. It is shown that a linear dependence exists between the donor-acceptor properties of the substituents at the vinyl group and the rate constants for the addition.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 2124–2126, August, 1996.     

ESR spin probe studies on the alteration of water structure

The electron spin resonance (ESR) spectra of the stable organic free radical 2,2,6,6-tetramethyl piperid-4-one N-oxide (TEMPO) were measured in aqueous solutions of urea and sodium butyrate. From an analysis of the ESR spectral line-widths and tumbling correlation times, inferences have been made about the alteration in the structure of solvent water induced by these solutes.     

Preparation of N-aryl-ketonitrone spin traps

The syntheses of seven N-aryl-C,C-dialkoxycarbonylnitrones 1–7, six of which were original, were achieved from the appropriate aryl-nitroso compounds. These ketonitrones were found to trap efficiently carbon-centred free radicals in aqueous media, yielding stable aminoxyl radicals whose EPR spectra lasted several days. The two penta-deuterated compounds 6 and 7 were also found to be efficient at trapping methoxyl radical. Their various spin adducts showed simple three line signals, very sensitive to the polarity of the environment. This study represents the very first use of linear ketonitrones as spin traps.     

A new intramolecular transformation of aromatic nitroso oxides

The possibility of intramolecular interaction of a nitroso oxide group with an aromatic ring is investigated at the UB3LYP/6-311+G(d,p) and G3MP2B3 levels of theory for a wide series of aromatic nitroso oxides. It is found that this reaction leads to the formation of a dioxazole cycle, its subsequent decay resulting in opening of the benzene ring and formation of nitriloxide and carbonyl functional groups. The activation enthalpy of the transformation of phenylnitroso oxide is 75.1 kJ/mol. It is shown that various sub-stituents at ortho-position (with respect to the nitroso oxide fragment) considerably lower the activation barrier of the investigated transformation, particularly in case of o,p-dimethoxyphenylnitroso oxide ΔH ^≠ = 43.7 kJ/mol. It is concluded that in the case of polyaromatic nitroso oxides, for which intramolecular cyclization is more typical (ΔH ^≠ ∼ 50 kJ/mol), a factor favoring the attack on the ortho-carbon atom is the stabilization of the product’s diene group due to its inclusion in the polyaromatic system. It is established that sum of these effects leads to a low activation barrier for the transformation of nitroso oxide that forms during the photooxidizing of 2-azido-1-methoxyphenazine, ΔH ^≠ = 19 kJ/mol. It is proposed that due to the low activation energy of some nitroso oxides, their intramolecular cyclization may be the primary channel of their unimolecular decay.     

Phosphoryl and thiophosphoryldithioformates as spin traps: from EPR studies to practical applications

This paper is aimed at providing an overview of our studies on the title compounds as spin trapping agents, and at emphasising the links between purely cognitive, academic research and industrial applications. Phosphoryl- and thiophosphoryl-dithioformates exhibit a comparable and interesting spin trapping ability, their efficiency being analogous to that of some aromatic thioketones. The spectral hyperfine structure may provide valuable information on the nature of the trapped radical but the phosphorus hfs constant cannot be used as an useful indicator. Thionformates are less efficient spin traps than the corresponding dithioformates, being inert towards stabilised radicals such as benzyl or relatively hindered radicals as tert-butoxyl. In no case could spin adducts to thiolformates be detected, this being an indication that their carbonyl group is significantly deactivated with respect to that of organic and organometallic ketones. Because of their ability in trapping either alkyl or alkoxy radicals both kind of dithioformates were exploited as stabilisers in the processing of such polymers as polypropylene, but their outstanding performance could not compensate for some organoleptic drawbacks that were intrinsic of the thiocarbonyl function. A much more promising application of dithioesters is instead their use as RAFT chain transfer agents in the controlled polymerisation of styrene. Preliminary experiments with benzyl diethoxyphosphoryldithioformate have afforded polystyrene with a polydispersity as low as 1.17, but further studies are needed to fully elucidate the RAFT-polymerisation mechanism and to optimise its outcome.     

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.     

ESR determination of the rate constant for the addition of CpW(CO)3 to spin traps

Conclusions The reaction of [CpW(CO)₃]₂ with PhCH₂Cl and the decomposition of CpW(CO)₃Me were studied by ESR spectroscopy using 2,4,6-tri-tert-butyinitrobenzene (BNB) and -phenyl-N-tert-butylnitrone (PNB) as spin traps. The rate constants for the addition of CpW(CO)₃ radicals to the spin traps at 20°C were determined by identification of the intermediate radicals in these reactions: k _ad ^BNB =6.7·10⁵-7.0·10⁵ and k _ad ^PNB =5.8·10⁴-6.1·10⁴ liters/mole · sec.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2631–2633, November, 1984.     

Free radicals and their electron spin relaxation in cellobiose. X-band and W-band ESR and electron spin echo studies

By use of 9.7 GHz and 94 GHz ESR spectra and electron spin echo (ESE)-detected spectra the six radical centres produced by γ-irradiation of cellobiose were identified. The radicals are localized on different carbon atoms. Use of high-frequency ESR spectra with computer resolution enhancement methods enabled unique radical identification and determination of g-factors and proton hyperfine splitting, A, with high accuracy. For radiation doses below 20 kGy three radicals dominate: on C₁ with isotropic doublet A = 1.8 mT; on C₂, C₃ and C₄ with triplet A = 2.9 mT; and localized on CH₂ with anisotropic triplet. For doses above 100 kGy the radical on C₁ dominates, because of cleavage of the glycosidic bonds. Electron spin–lattice relaxation shows that radiation damage of the cellulose structure around the radical centres is significant and radical molecules do not participate in phonon dynamics of the host lattice. The relaxation is because of tunnelling motions of the ring or OH-groups, with tunnelling splitting 2.4 cm⁻¹. Electron spin echo dephasing results identify cellobiose ring torsions with activation energy 117 cm⁻¹.     

Electrochemical and ESR studies on the reduction of 3-arylimino-3H-indole-N,N′-dioxides

3-Arylimino-3H-indole-N,N′-dioxides have been reduced in DMF to the corresponding radical anions, and studied using polarographic and controlled potential electrolysis, as well as UV and ESR spectrometry. A multistep scheme has been suggested in order to explain the various experimental results. ESR spectra were explained in terms of HFSC evaluation and theoretically reconstructed in order to check the validity of the attributions. The same radicals were obtained with DMSO/t-BuOK as reducing agent.     

Electrochemical and ESR studies on the reduction of some indolinone derivatives and of their N-oxides in DMF

2-Phenyl-3-oxo-3H-indole 4 and 3-imino-, 3-iminoxy-, derivatives, the corresponding N-oxide 3, and 2-phenyl- 5 and 2-(2'-pyridyl-) isatogen 6 have been reduced in DMF and in DMF in presence of proton donors, and followed by polarography, controlled potential coulometry, cyclic voltammetry, UV, and ESR. In aprotic media, compounds 1, 4, 5 and 6, are reduced via anion radical intermediates.     

ESR spin probes in ionic liquids.

The spin probes 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL), and 2,2,6,6-tetramethyl-4-trimethylammoniumpiperidine-1-oxylIodide (CAT-1) are examined in a number of ionic liquids based on substituted imidazolium cations and tetrafluoroborate and hexafluorophosphate anions, respectively. The reorientation correlation times tau(R) of the spin probes in these systems have been determined by complete spectra simulation and, for rapid reortientation, by analysis of the intensities of the hyperfine lines of the electron spin resonance (ESR) spectra. A comparison of the results with those from the model system glycerol/water and selected organic solvents is made. Additions of diamagnetic and paramagnetic ions allow the conclusion that salt effects and spin exchange are present, and that both are superimposed by motional effects. Specific interactions in the ionic liquids, as well as between the spin-probe molecules and the constituents of the ionic liquids are reflected in the spectra of the spin probes, depending on their molecular structure.