An ESR study of the adducts of phosphonyl radicals with fullerene-70

A. N. Nesmeyanov Institute of Organometallic Compounds, Russian Academy of Sciences, 117813 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 8, pp. 1938–1940, August, 1992.     

An EPR and molecular mechanics study of radical adducts of phosphonyl radicals with 2-hydroperfluoro-4-methyl-and 4,4-dimethyl-2-pentene

EPR spectra of radical adducts of phosphonyl radicals with 2-hydroperfluoro-4-methyl- and 4,4-dimethyl-2-pentene have been studied. The molecular mechanics method has been used to determine the preferred conformation of the (CF₃)₂CF-CF-HCF₃P(O)(OMe)₂ radical. The eclipsed conformation of the C–P bond and 2p _z -orbital of an unpaired electron is stabilized due to steric factor and hyperconjugation.A. N. Nesmeyanov Institute of Organoelemental Compounds, Russian Academy of Sciences, 117813 Moscow. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 11, pp. 2550–2554, November, 1992.     

Molecular and crystal structure of derivatives of higher internal perfluoroalkenes

Institute of Heteroorganic Compounds, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 2, pp. 199–203, March–April, 1989.     

Electron spin resonance spectra of some phosphonyl radicals and related species

The isotropic ESR spectra of a number of phosphonyl radicals (X₂$\text{P}$O), the dimethylphosphinyl radical, and the phosphoranyl radical (MeO)₃$\text{P}$OBu-t, are described, and accurate values of the phosphorus hyperfine splittings and g-factors are reported. For X₂$\text{P}$O, the value of a(P) increases and the g-factor decreases as the electronegativity of X increases. There is a linear relationship between a(P) for X₂$\text{P}$O and ¹J(PH) for X₂P(O)H, but the same relationship does not hold for Me₂P- and Me₂PH. The spectrum of the di-n-hexylphosphonyl radical shows coupling to two pairs of α-methylene protons, and this non-equivalence is attributed to the pyramidal structure of the phosphonyl radical.     

EPR study of rearrangement of ω-carbalkoxyalkyl radicals using spin traps

Conclusions The rearrangement of the radicals CH₂(CH₂)_nCH₂CO₂R to CH₃(CH₂)_nCHCO₂R (n=1-4) was studied by the EPR method at room temperature, with a recording of the intermediate radicals as the spin-adducts with nitrosodurene. The ratio of the yields of the rearranged radicals with the 1,6-, 1,5-, 1.4-, and 1,3-migration, of hydrogen was, respectively, equal to 0.251 0.10 0.03.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2628–2631, November, 1977.     

Reaction of phosphonyl radicals with substituted orthobenzoquinones

Conclusions The reaction of a diethylphosphonyl radical with substituted orthobenzoquinones proceeds in two directions: addition to an oxygen atom, to form a phenoxyl-type radical, or to the ring, to form a cyclohexadienyl-type radical.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2563–2569, November, 1987.     

EPR study of free radicals in bread

The features of the recorded EPR spectra of paramagnetic species formed in bread and rusk are reported. The appearance of free radicals in them is only connected with their thermal treatment since the starting materials (flour and grains) exhibit very weak EPR signal. The obtained EPR spectra are complex and indicate that: (i) the relative number of paramagnetic species depends on the temperature and treating time of the raw product; (ii) the g-values are strongly temperature dependent with a tendency to coincide at t > or = 220 degrees C. Because of the relatively low (150-220 degrees C) temperature of thermal treatment, the studied free radicals can be assumed to appear in the course of the browning (Maillard) reaction and not to the carbonization of the material.     

EPR study of the transformations of fluoroalkenyl radicals

Conclusions Fluorinated alkenyl radicals containing a double bond at position 4 or 5 relative to the radical site are converted into relatively stable radicals, apparently due to their cyclization.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 706–708, March, 1989.We express our gratitude to A. L. Blyumenfel'd for compiling a program for calculation of the EPR spectra.     

EPR and ENDOR study of thermally produced triphenylmethyl radicals

The ENDOR spectrum of the triphenylmethyl radical formed by heat treatment of triphenylmethane has been measured in solution at 131°C. The derived hyperfine coupling constants of 2.770, 2.556 and 1.138 G were used to simulate the extremely well resolved EPR spectrum. These coupling constants are in good agreement with spin densities determined for the planar radical by the McLachlan method.     

An HPLC and EPR investigation on the stability of DMPO and DMPO spin adducts in vivo

Application of the spin trapping technique in intact animals requires an understanding of the stability and distribution of the spin traps and their spin adducts in vivo. We studied the stability of DMPO in vivo in mice using HPLC and the stability of spin adducts of DMPO by EPR in plasma, whole blood, peritoneal fluid, and homogenized heart tissue of the rat. At 15 minutes after intraperitoneal injection DMPO had similar concentrations in the liver, heart, and blood of the mice and 40% remained in the organs 2 hours after the injection. In contrast, the spin adduct DMPO-OH was short lived, with a half-life of 3.0 minutes in plasma, and was not detectable 1 minute after formation in whole blood and homogenized heart tissue. The carbon centered spin adduct DMPO-CH(OH)CH₃ was more stable, having half-lives of 16, 11, 3.6, and 0.79 minutes in plasma, peritoneal fluid, whole blood, and homogenized heart tissue, respectively. The spin adduct DMPO-SO₃ was sufficiently stable for the adduct to be observed directly from living mice.     

ESR study of radicals obtained from vinylalkoxysilanes and their adducts with branched fluoroalkenes

ESR spectra of radicals obtained by abstracting a hydrogen atom from methylvinyldimethoxysilane and methylvinyldiethoxysilane through the action of thetert-butoxy radical were studied. It was shown that the radicals appearing react with branched fluorinated olefins to give relatively stable radical adducts.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 538–540, March, 1994.     

EPR spin probe study of polymer associative systems

Molecular dynamics of polyacrylamide gels, polymeric micelles and hydrogel of polyacrylic acid and macrodiisocyanate was investigated by the ESR spectroscopy of spin probes. The local mobility in network junction of polyacrylamide gels is found to be essentially slower than that in the micelles created by the low molecular weight detergents and does not depend on the amount and length of hydrophobic groups (C9 or C12) in the polymer chain. The immersion of 10-30 mol.% of ionic monomers into the polymer chain (sodium acrylate) influences insufficiently on the local mobility of network junctions. In aqueous solutions, polystyrene-block-poly-(N-ethyl-4-vinylpyridinium bromide) block copolymers create polymeric micelles. The local mobility in the polystyrene core of the micelles is about twice as much as that in the solid polystyrene. Partially swellable polymer network in aqueous solutions was synthesized from polyacrylic acid and macrodiisocyanate. The local mobility in hydrophobic regions of the gel is substantially lower than that in the hydrophilic regions. It was concluded that the hydrophobic and hydrophilic regions and the local dynamics of them dictate practical application of the polymer associative systems.     

Identification of isomeric spin adducts of Leu-Tyr and Tyr-Leu free radicals using liquid chromatography-tandem mass spectrometry

Free radical species are generally short-lived due to their high reactivity and thus direct measurement and identification are often impossible. In this study we used a spin trap, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), to trap radical intermediates formed during the oxidation of isomeric dipeptides tyrosine-leucine (Tyr-Leu) and leucine-tyrosine (Leu-Tyr), induced by the hydroxyl radical. To investigate the influence of the amino acid position in the peptide chain on the oxidation and free radical generation, the spin adducts were characterized using LC-MS and MS(n) . We detected carbon and oxygen DMPO adducts and adducts bearing two DMPO, which were analyzed by MS(n) . Both alkoxyl and peroxyl radicals were identified. Radical intermediates were localized in Tyr during oxidation of Tyr-Leu, while radicals were identified in Leu and Tyr during oxidation of Leu-Tyr. DMPO adducts of acyl radical species formed from cleavage of the peptide backbone, promoted by the alkoxyl radical in α carbon of the N-terminal amino acid were observed. The results show that the amino acid position has an influence in the oxidation process, at least on small peptides, and that the α carbon of the N-terminal amino acid is more vulnerable to the attack of the electrophilic hydroxyl radical.