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Detection of superoxide produced by living cells has been an on-going challenge in biology for over forty years. Various methods have been proposed to address this issue, among which spin trapping with cyclic nitrones coupled to EPR spectroscopy, the gold standard for detection of radicals. This technique is based on the nucleophilic addition of superoxide to a diamagnetic cyclic nitrone, referred to as the spin trap, and the formation of a spin adduct, i.e. a persistent radical with a characteristic EPR spectrum. The first application of spin trapping to living cells dates back 1979. Since then, considerable improvements of the method have been achieved both in the structures of the spin traps, the EPR methodology, and the design of the experiments including appropriate controls. Here, we will concentrate on technical aspects of the spin trapping/EPR technique, delineating recent breakthroughs, inherent limitations, and potential artifacts., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Bispidine containing a paramagnetic group was obtained for the first time by the Mannich reaction using the 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO) free radical as a reagent. The structure of the target compound, tert-butyl 9-oxo-7-(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)-3,7-diazabicyclo[3.3.1]nonane-3-carboxylate, was confirmed by mass spectrometry and ESR spectroscopy, the molecular and crystal structure was established by X-ray diffraction analysis. In the synthesis of the starting 4-amino-TEMPO by the reductive amination reaction, the by-product of the further reaction of 4-amino-TEMPO with the starting ketone, the free biradical N-(2,2,6,6-tetramethyl-1-oxylpiperidin-4-yl)-2,2,6,6-tetramethyl-4-aminopiperidine-1-oxyl, was isolated and structurally characterized. [ABSTRACT FROM AUTHOR]

Conjugates of bispidines and free radicals of the (2,2,6,6-tetramethylpiperidin-1-yl)-oxyl type were synthesized for the first time. The conjugates were obtained by the alkylation reaction of NH-bispidines with electrophilic chloro derivatives containing a free radical. The structure of the latter was established by X-ray diffraction analysis. The products obtained were characterized by IR spectroscopy, ESR spectroscopy, and high-resolution mass spectrometry. [ABSTRACT FROM AUTHOR]

ESR spectra of asphaltenes from a series of crude oils from the Devonian and Carboniferous deposits of the South-Tatar Dome in Tatarstan with low vanadium content and of vanadiferous crude oils from deposits of the Melekess depression in Tatarstan are analyzed. For asphaltenes from Devonian oils, the correlation between the concentrations of stable free radicals (SFR) and vanadyl complexes (VCs) has direct trend, whereas for asphaltenes from Carboniferous oils the trend is inverse. Taking into account the previously revealed inverse trend for asphaltenes of vanadium-enriched highly viscous crude oils [1], the opposite trends in SFR–VC correlations (direct and inverse) suggest different structures of asphaltene molecules in oils with different vanadium content and, correspondingly, different sources and conditions of the formation of oil deposits. Specific features of the ESR characteristics of asphaltenes of core and extractable oils and of oils from Devonian and Carboniferous deposits are revealed. [ABSTRACT FROM AUTHOR]

A combined electron spin resonance (ESR) and density functional theory study has been carried out to obtain deeper insight in the reaction mechanism of the photorearrangement of 3-hydroxyindolic nitrones. Also, in this case, the combination of these techniques constitutes a powerful tool when discriminating between different reaction pathways. In particular, density functional theory calculations played an important role for unraveling the overlapping of signals coming from different species in the ESR spin trapping experiments. In the present study, the computed energies and the corresponding ESR parameters of each possible isomer hypothesized have been considered, taking also into account their different possibilities of intramolecular H-bond formation. However, the results obtained indicate that the possibility of intramolecular H-bonding did not play a determinant role in this case. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Synopsis Objective Cosmetic formulations are influenced by environmental impacts and ageing, resulting in rancidity and change of colour and structure. These changes are caused by free radicals ( FRs). The sensitivity of cosmetics generating FRs is a metric for its quality and should be determined. Methods Electron spin resonance spectroscopy in combination with UV irradiation tested cosmetics such as creams, milks, lotions and fragrances. The probes were directly measured without expensive preparation. Results Nine formulations are tested for its radical generation and ranked corresponding to the radical power. The transformation of the FR properties of three formulations to skin is measured by the radical skin status factor ( RSF) method. It shows that the higher the radical power (RP) is, the lower the radical status RSF of skin will be. Conclusion The knowledge of the sensitivity of cosmetics to generate FRs is necessary for its stabilization and prevention of potential damages to skin. It is a new way in development of cosmetics which has to be considered. [ABSTRACT FROM AUTHOR]

1H-Benzo[b]pyrrole samples were irradiated in the air with gamma source at 0.969 kGy per hour at room temperature for 24, 48 and 72 h. After irradiation, electron spin resonance, thermogravimetry analysis (TGA) and differential thermal analysis (DTA) measurements were immediately carried out on the irradiated and unirradiated samples. The ESR measurements were performed between 320 and 400 K. ESR spectra were recorded from the samples irradiated for 48 and 72 h. The obtained spectra were observed to be dependent on temperature. Two radical-type centres were detected on the sample. Detected radiation-induced radicals were attributed to R-+•NH and R=•CC2H2. Theg-values and hyperfine constants were calculated by means of the experimental spectra. It was also determined from TGA spectrum that both the unirradiated and irradiated samples were decomposed at one step with the rising temperature. Moreover, a theoretical study was presented. Success of the machine learning methods was tested. It was found that bagging techniques, which are widely used in the machine learning literature, could optimise prediction accuracy noticeably. [ABSTRACT FROM PUBLISHER]

This paper attempts to lead the reader an understanding of what free radicals are and how they can form during lipid oxidation. Also, it provides some information out natural antioxidants (tocopherols and tocotrienols flavonoids, polyphenols, tannines, melanoidihes, carotenoids, ascorbates) and the echanisms of their protection from radical damage. The sources of natural antioxidants are: oil seeds, teas, vegetables, fruits, spices and herbs.

• ESR can be used to evaluate oxidative stability of beer. • Dry-hopping at 20 °C improves oxidative stability of beer better than at 5 °C. • Dry-hopping at 20 °C prolong lag time of beer (the time after which the reactions of free radical formation initiate, which is a good indicator of the antioxidant potential of beer). • The oxidative stability of beer depends on the variety of hops used for dry-hopping. • The lag time is strongly correlated with the concentration of polyphenols in beer. Electron spin resonance (ESR) spectroscopy was used to determine the effect of dry hopping on the oxidative stability and antioxidative potential of beer. Commercial beer was dry-hopped at 5 °C and 20 °C with six hop varieties (Polish and American). The rate of radical formation and lag time were found to depend on the variety of hop used. An increase in the lag time and a decrease in the rate of radical formation occurred when dry-hopping was performed at 20 °C for all hop varieties (at 5 °C in some varieties). The lag time had a strong correlation with the TPC (total polyphenols content) in beer. The rate of radical formation was correlated with the iron content of the beer. A decrease in iron concentration was observed after dry-hopping at 20 °C. Overall, the evaluation of free radical formation using ESR is useful for predicting oxidative changes in beer during storage. [ABSTRACT FROM AUTHOR]

Abstract: Reactive oxygen species are by-products of aerobic metabolism involved in the onset and evolution of various pathological conditions. Among them, the superoxide radical is of special interest as the origin of several damaging species such as H2O2, hydroxyl radical, or peroxynitrite (ONOO−). Spin trapping coupled with ESR is a method of choice to characterize these species in chemical and biological systems and the metabolic stability of the spin adducts derived from reaction of superoxide and hydroxyl radicals with nitrones is the main limit to the in vivo application of the method. Recently, new cyclic nitrones bearing a triphenylphosphonium or permethylated β-cyclodextrin moiety have been synthesized and their spin adducts demonstrated increased stability in buffer. In this article, we studied the stability of the superoxide adducts of four new cyclic nitrones in the presence of liver subcellular fractions and biologically relevant reductants using an original setup combining a stopped-flow device and an ESR spectrometer. The kinetics of disappearance of the spin adducts were analyzed using an appropriate simulation program. Our results highlight the interest of the new spin trapping agents CD-DEPMPO and CD-DIPPMPO for specific detection of superoxide with high stability of the superoxide adducts in the presence of liver microsomes. [Copyright &y& Elsevier]

Abstract: 4,4′-Bis(chloroacetyl)diphenylether was synthesized and its polycrystal form was produced. This polycrystal sample was irradiated by gamma rays (60Co) for 72h. The ESR method was used to observe formation of free radical on the sample. ESR signal was not recorded from the non-irradiated sample, but the irradiated polycrystal sample exhibited complex ESR spectra. The measurements were carried out in the temperature range of 120–450K. It was observed that the shape of the spectrum was dependent on the temperature. Two identical radicals were determined on the irradiated sample. Respectively, the spin density, hyperfine, and g values were found to be , and g 1 =2.0115 for the Radical I; , and g 2 =2.0383 for the Radical II. [Copyright &y& Elsevier]

Abstract: The objective of this study was to determine the effect of (bi)sulfite (hydrated sulfur dioxide) on human neutrophils and the ability of these immune cells to produce reactive free radicals due to (bi)sulfite oxidation. Myeloperoxidase (MPO) is an abundant heme protein in neutrophils that catalyzes the formation of cytotoxic oxidants implicated in asthma and inflammatory disorders. In this study sulfite (•SO3 −) and sulfate (SO4 •−) anion radicals are characterized with the ESR spin-trapping technique using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) in the reaction of (bi)sulfite oxidation by human MPO and human neutrophils via sulfite radical chain reaction chemistry. After treatment with (bi)sulfite, phorbol 12-myristate 13-acetate-stimulated neutrophils produced DMPO–sulfite anion radical, –superoxide, and –hydroxyl radical adducts. The last adduct probably resulted, in part, from the conversion of DMPO–sulfate to DMPO–hydroxyl radical adduct via a nucleophilic substitution reaction of the radical adduct. This anion radical (SO4 •−) is highly reactive and, presumably, can oxidize target proteins to protein radicals, thereby initiating protein oxidation. Therefore, we propose that the potential toxicity of (bi)sulfite during pulmonary inflammation or lung-associated diseases such as asthma may be related to free radical formation. [Copyright &y& Elsevier]

Abstract: In this study, to obtain guanosine polycrystalline, novel crystallization method was performed on powder guanosine material. Effective crystallization conditions were achieved by adjustment of the concentration of the metal ions, chemical solutions, NaCl, KCl, glacial acetic acid, nitric oxide, perchloric acid, glutamic acid, and pH of buffer. Behaviors of the guanosine polycrystal samples exposed to high-energy values were investigated using ESR method. The polycrystal samples were exposed to gamma-rays for 48 and 72h. ESR signals were not recorded from the non-irradiated sample and the sample irradiated for 48h, but the polycrystalline sample irradiated for 72h exhibited complex ESR spectra. ESR measurements were taken on the irradiated sample in temperature range from 300 to 450K. On the basis of all these measurements dependence temperature, it can be said that the shape of the spectrum was to be dependent on temperature slightly. Hence, we assume that the radical structure occurred was resistance to high temperature. Two radicals were determined in the structure irradiated and these were called radical I and radical II. The g, hyperfine constants, and spin density were found to be ρ =0.96, , , a N =0.35mT and g 1 =2.0093 for the radical I; a N =4.7mT and g 2 =2.0094 for the radical II. [Copyright &y& Elsevier]

Abstract: Soups based on cauliflower soup powders, prepared by dry mixing of ingredients and rapeseed oil, showed a decrease in quality, as evaluated by a sensory panel, during the storage of the soup powder in the dark for up to 12weeks under mildly accelerated conditions of 40°C and 75% relative humidity. Antioxidant, shown to be effective in protecting the rapeseed bulk oil, used for the powder preparation, had no effect on storage stability of the soup powder. The freshly prepared soup powder had a relatively high concentration of free radicals, as measured by electron spin resonance spectroscopy, which decreased during storage, and most remarkably during the first two weeks of storage, with only marginal increase in lipid hydroperoxides as primary lipid oxidation products, and without any increase in secondary lipid oxidation products. Analyses of volatiles by SPME-GC–MS revealed a significant increase in concentrations of 2-methyl- and 3-methyl butanals, related to Maillard reactions, together with an increase in 2-acetylpyrrole concentration. The soup powders became more brown during storage, as indicated by a decreasing Hunter L-value, in accord with non-enzymatic browning reactions. A significant increase in the concentrations of dimethyl disulfide in soup powder headspace indicated free radical-initiated protein oxidation. Protein degradation, including Maillard reactions and protein oxidation, is concluded to be more important than lipid oxidation in determining the shelf-life of dry cauliflower soup powder. [Copyright &y& Elsevier]

The addition of CCl and Bu radicals to (η-C)Os(CO)(PPh)(CNBu) ( 1) and (η-C)[Os(CO)(PPh)(CNBu)] ( 3) was studied by ESR spectroscopy. The metal fragment in complex 1 does not influence the regioselectivity of the addition of the radicals to it. The stability of the spin adducts formed upon addition of free radicals to complexes 1 and 3 is mainly governed by delocalization of the unpaired electron over three hexagonal rings. [ABSTRACT FROM AUTHOR]

Abstract: Heat-induced paramagnetic centers in modern and archaeological lentils (Lens culinaris, Medik.) were studied by X-band (9.3GHz) electron spin resonance (ESR) technique. The modern red lentil samples were heated in an electrical furnace at increasing temperatures in the range 70–500°C. The ESR spectral parameters (the intensity, g-value and peak-to-peak line width) of the heat-induced organic radicals were investigated for modern red lentil (Lens culinaris, Medik.) samples. The obtained ESR spectra indicate that the relative number of heat-induced paramagnetic species and peak-to-peak line widths depends on the temperature and heating time of the modern lentil. The g-values also depend on the heating temperature but not heating time. Heated modern red lentils produced a range of organic radicals with g-values from g =2.0062 to 2.0035. ESR signals of carbonised archaeological lentil samples from two archaeological deposits of the Van province in Turkey were studied and g-values, peak-to-peak line widths, intensities and elemental compositions were compared with those obtained for modern samples in order to assess at which temperature these archaeological lentils were heated in prehistoric sites. The maximum temperatures of the previous heating of carbonised UA5 and Y11 lentil seeds are as follows about 500°C and above 500°C, respectively. [Copyright &y& Elsevier]

Abstract: Single-crystal X-ray study of 6,9,12,15,18-pentamethyl-1,6,9,12,15,18-hexahydro(C60-I h)[5,6]fullerene (C60Me5H) has been reported. In crystal packing, the stacking self-organization of molecules is realized. It is concluded that the formation of such polar columns is a general rule for crystals of C60R5H independent of the nature of the R group. An ESR spectrum of the stable fullerenyl radical of the cyclopentadienyl-type, C60Me5, was observed in a sample of the pentamethylated[60]fullerene. Rotation of methyl groups around C–C bonds is restricted on the ESR scale time and therefore protons within each methyl group are non-equivalent. [Copyright &y& Elsevier]

Abstract: Throughout the body, melanin is a homogenous biological polymer containing a population of intrinsic, semiquinone-like radicals. Additional extrinsic free radicals are reversibly photo-generated by UV and visible light. Melanin photochemistry, particularly the formation and decay of extrinsic radicals, has been the subject of numerous electron spin resonance (ESR) spectroscopy studies. Several melanin monomers exist, and the predominant monomer in a melanin polymer depends on its location within an organism. In skin and hair, melanin differs in content of eumelanin or pheomelanin. Its bioradical character and its susceptibility to UV irradiation makes melanin an excellent indicator for UV-related processes in both skin and hair. The existence of melanin in skin is strongly correlated with the prevention against free radicals/ROS generated by UV radiation. Especially in the skin melanin (mainly eumelanin) ensures the only natural UV protection by eliminating the generated free radicals/ROS. Melanin in hair can be used as a free radical detector for evaluating the efficacy of hair care products. The aim of this study was to investigate the suitability of melanin as protector of skin against UV generated free radicals and as free radical indicator in hair. [Copyright &y& Elsevier]

Abstract: In the past few years, the cellular effects of ultraviolet (UV) irradiation induced in skin have become increasingly recognized. Indeed, it is now well known that UV irradiation induces structural and cellular changes in all the compartments of skin tissue. The generation of reactive oxygen species (ROS) is the first and immediate consequence of UV exposure and therefore the quantitative determination of free radical reactions in the skin during UV radiation is of primary importance for the understanding of dermatological photodamage. The RSF method (radical sun protection factor) herein presented, based on electron spin resonance spectroscopy (ESR), enables the measurement of free radical reactions in skin biopsies directly during UV radiation. The amount of free radicals varies with UV doses and can be standardized by varying UV irradiance or exposure time. The RSF method allows the determination of the protective effect of UV filters and sunscreens as well as the radical induction capacity of self-tanning agents as dihydroxyacetone (DHA). The reaction of the reducing sugars used in self-tanning products and amino acids in the skin layer (Maillard reaction) leads to the formation of Amadori products that generate free radicals during UV irradiation. Using the RSF method three different self-tanning agents were analyzed and it was found, that in DHA-treated skin more than 180% additional radicals were generated during sun exposure with respect to untreated skin. For this reason the exposure duration in the sun must be shortened when self-tanners are used and photoaging processes are accelerated. [Copyright &y& Elsevier]

Abstract: Free radicals/reactive oxygen species (ROS) generated in skin by UV irradiation were measured by electron spin resonance (ESR). To increase the sensitivity of measurement the short life free radicals/ROS were scavenged and accumulated by using the nitroxyl probe 3-carboxy-2,2,5,5-tetrametylpyrrolidine-1-oxyl (PCA). The spatial distribution of free radicals/ROS measured in pig skin biopsies with ESR imaging after UV irradiation corresponds to the intensity decay of irradiance in the depth of the skin. The main part of free radicals/ROS were generated by UVA (320–400nm) so that the spatial distribution of free radicals reaches up to the lower side of the dermis. In vivo measurements on human skin were performed with a L-band ESR spectrometer and a surface coil integrating the signal intensities from all skin layers to get a sufficient signal amplitude. Using this experimental arrangement the protection of UVB and UVA/B filter against the generation of free radicals/ROS in skin were measured. The protection against ROS and the repair of damages caused by them can be realized with active antioxidants characterized by a high antioxidative power (AP). The effect of UV filter and antioxidants corresponding to their protection against free radicals/ROS in skin generated by UVAB irradiation can be quantified by the new radical sun protection factor (RSF). The RSF indicates the increase of time for staying in the sun to generate the same number of free radicals/ROS in the skin like for the unprotected skin. Regarding the amount of generated free radicals/ROS in skin as an biophysical endpoint the RSF characterizes both the protection against UVB and UVA radiation. [Copyright &y& Elsevier]

There is a body of evidences demonstrating, in biological systems, a cooperative interaction between tocopherols and carotenoids. FeAOX-6 is a novel antioxidant that combines the chroman head of α-tocopherol and a fragment of the isoprenyl chain of lycopene. We have tested its antioxidant effect on different radical species generated in a chemical system, where peroxyl, alkoxyl and methyl radicals are generated by the ferrous ion-mediated decomposition of tert -butyl hydroperoxide. We found that FeAOX-6 has the same effectiveness of α-tocopherol in quenching peroxyl radical with no contribution by lycopene. The antioxidant activity of FeAOX-6 on alkoxyl and methyl radicals is comparable to that of the equimolar mixture of the parent compounds. Lycopene is able to quench alkoxyl radical, while it has no effect on peroxyl radical, showing a different antioxidant activity compared to other carotenoids, such as β-carotene and lutein. [ABSTRACT FROM AUTHOR]

Abstract: Samples of egg shell powder were annealed in air in the temperature range 298–1173K. Samples were analyzed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis and electron spin resonance (ESR). ESR measurements were made on annealed egg shells before and after gamma irradiation at 4kGy. Annealing egg shells produced a range of organic radical with g-values from g=2.005 to 2.002. The thermal dependence of this signal may provide valuable information about the extent of the thermal treatment that the sample was subjected to. Samples irradiated from 3Gy to 10kGy were analyzed by ESR in order to obtain the response curve and to show ESR signal behavior. [Copyright &y& Elsevier]

The interaction of organometallic chromium‐centered free radicals generated by the homolytic dissociation of (pentamethylcyclopentadienyl)chromiumtricarbonyl dimer in toluene with single‐walled carbon nanotubes (SWNT) was investigated using ESR spectroscopy. Low values of g‐factors of the radical species formed from chromium‐centered free radicals and SWNT as well as invariability of disorder mode (D band) intensity in Raman spectra of pristine and functionalized SWNT after this reaction indicated that chromium‐centered free radicals added to the surface of nanotubes through rather oxygen atoms than to sidewall carbon atoms. This is the first chromium‐derivatization of carbon nanotubes. [ABSTRACT FROM AUTHOR]

Abstract: The results of the treatment of activated carbons prepared from Turkish Elbistan lignite with γ-irradiation from a 60Co source are presented and associated volatilization of surface material of the activated carbon as a means to obtain a physical modification of the material is discussed in terms of changes in surface area, free radical concentrations and structural changes determined with FTIR and solid-state 13C NMR spectroscopical methods. BET areas of irradiated samples are measured to be greater than those of non-irradiated samples; this might be considered as an indication to some loss of material from the surface by γ-irradiation. γ-Irradiation caused remarkable erosion on the surface with the loss of some carbonaceous matter by probable bond cleavage reactions. As the activation temperature was raised, both of the carbon content and the intensities of the carbon functionalities decreased in the 13C NMR spectra. The observation of symmetric shapes in the ESR spectra might be considered as an indication to the delocalization of the electrons over the graphite-like microcrystallites present in the active carbons. The broadening of the ESR signals in the present work might be both due to the effect of oxygen during the measurements in lower activation temperatures and the enhanced effect of the presence of Fe3+ ion in the form of pyrites in the mineral matter the lignite used. Increase of the relative intensities of free radicals with activation temperature may be indicative of some molecular cracking leading to organic radicals. Irradiation of the activated carbon samples seemed to increase the peak widths and g-values. g-value of 2.003 was due to semiquinone-type free radical which was probably created in oxidation reaction during activation processes. [Copyright &y& Elsevier]

Organic matter plays a major role in the chemical and physical attributes of highly weathered soils usually found in tropical and subtropical regions. In the present work, soil organic matter (SOM) of six representative Brazilian Ferralsol profiles was examined by chemical analyses, solid state 13C and 15N nuclear magnetic resonance (NMR) spectroscopy and electron spin resonance (ESR) spectroscopy. The HF treatment, realized with the soil samples prior to the spectroscopic analysis, promoted both C and N enrichment, and no selective dissolution of specific C-compounds was identified. The recovery of C and N ranged between 47% and 66% in the A horizon and decreased pronouncedly with depth. The solubility of SOM after HF treatment, especially in deeper horizons, was related to its occurrence in organo-mineral associates. The results obtained by 13C NMR revealed that the SOM of A horizons of the Brazilian Ferralsols is characterized by a considerable amount of O-alkyl (29–38%), followed by lower proportions of alkyl (24–30%) and aromatic structures (10–14%). The organic nitrogen occurred mainly as amide, as indicated by the 15N NMR analysis. A similar pattern was exhibited by the SOM of lower horizons. The C/N ratio varied between 8 and 21 and tended to decrease with depth. The same trend was found for the semiquinone-type free radicals concentrations, determined by ESR spectroscopy. The occurrence of a SOM showing a medium decomposition degree containing structures of low chemical recalcitrance points to a stabilization of organic matter mainly through surface interactions with iron oxides and kaolinite. [Copyright &y& Elsevier]

We have evaluated the effects of DMPO, CMPO, EMPO, BMPO, and DEPMPO on functioning CHO cells and the stability of the radical adducts in the presence of cells. The potential toxic effects of the spin traps were measured by two estimates of cell viability (trypan blue exclusion and colony formation) and one of cell function (rate of oxygen consumption). We also studied the effects of the spin traps on colony formation in a second cell line, 9L tumor cells. Toxicity varied with the type of cell line and the parameter that was measured. In aqueous solutions the order of stability for all spin adducts was SO3 > OH > CH3, while in cell suspensions it was SO3 > OH ≈ CH3. The radical adducts of the new spin traps have significantly increased stability as compared to DMPO. These results indicate that the new spin traps potentially offer increased stability of spin adducts in functioning cells. It also is clear that it is necessary to carry out appropriate studies of the stability and toxicity in the system that is to be studied for any particular use of these spin traps. It then should be feasible to select the spin trap(s) best suited for the proposed study. [Copyright &y& Elsevier]

A new procedure for quantum-chemical estimates of the constants of isotropic hyperfine coupling (IHFC) with protons using the orbital spin populations calculated in the basis set of symmetrically orthogonalized (according to Löwdin) atomic orbitals is tested taking 16 well-studied simplest π-electron and σ-electron radicals as examples. The most probable reasons for and possible ways of correcting large deviations of calculated IHFC constants from experimental values are considered. The efficiency of the semiempirical MNDORU scheme, which makes it possible to consistently estimate the delocalization and spin-polarization contributions to the constants of IHFC with protons in free radicals, is demonstrated. [ABSTRACT FROM AUTHOR]

The magnetic and dynamic properties of tris(2,6-di- tert-butyl-4-hydroxybenzyl)amine free radical was studied by ESR spectroscopy in the temperature range from 170 to 350 K in toluene. Symmetrical conformers in the rigid toluene matrix with characteristic angles θ = 26° and θ = 60° between the symmetry axis of the 2p-orbital on the C atom of the phenoxyl ring and the direction of the C-C bond of the CH fragment were determined. The activation energy of transition between the conformers was determined to be 8.2 kcal mol. The correlation time of transition between the conformers was established as 8.2·10 s. [ABSTRACT FROM AUTHOR]

The rate constants for addition of the Me2 ·CCN, Me2 ·CPh, and CCl3 at 22 °C were determined by ESR spectroscopy using spin trapping technique. [ABSTRACT FROM AUTHOR]2 ·CHPh radicals to fullerene C60 at 22 °C were determined by ESR spectroscopy using spin trapping technique. [ABSTRACT FROM AUTHOR]