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.     

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.     

Electrochemical and ESR studies of aromatic nitroso spin traps

The oxidation and reduction potentials of 23 nitroso compounds among which were included the most important spin traps have been determined by means of cyclic voltammetry and voltammetry at the rotating electrode. The electron transfer generally involved one electron, leading to the corresponding ion radicals. When persistent species resulted from the electron transfer, their ESR spectra were recorded and analyzed with the help of EHT calculations. The observed anion radicals are typical delocalized Π radicals, while the cation radicals are Σ radicals with a SOMO orthogonal to the Π system. Secondary species formed from these primary ion radicals were also observed and identified by e.s.r.     

Thioketones as spin traps for group VI radicals

Dyaryl-, dialkyl-, and aryltriphenylsilyl- thioketones have been shown to efficiently scavenge thiyl, sulphonyl and selenyl radicals affording adducts identified by ESR spectroscopy. Unprecedented evidence of the trapping of ^tBuO· radicals by thiones has also been obtained.     

EPR spin probe and spin label studies of some low molecular and polymer micelles

The rotational mobility of spin probes of different shape and size in low molecular and polymer micelles has been studied. Several probes having nitroxide fragment localized either in the vicinity of micelle interface or in the hydrocarbon core have been used. Upon increasing the number of carbon atoms in hydrocarbon chain of detergent from 7 to 13 (sodium alkyl sulfate micelles) or from 12 to 16 (alkyltrimethylammonium bromide micelles) the rotational mobility of spin probes is decreased by the factor 1.5–2.0. The spin probe rotational mobility in polymer micelles (the complexes of alkyltrimethylammonium bromides and polymethacrylic or polyacrylic acids) is less than mobility in free micelles of the same surfactants. The study of EPR-spectra of spin labeled polymethacrylic acid (PMA) indicated that formation of water soluble complexes of polymer and alkyltrimethylammonium bromides in alkaline solutions (pH 9) does not affect the polymer segmental mobility. On the other hand, the polymer complexes formation in slightly acidic water solution (pH 6) breaks down the compact PMA conformation, thus increasing the polymer segmental mobility. Possible structures of polymer micelles are discussed.     

EPR spin labelling studies of molecular dynamics in elastomer-silica composites

Novel methods of nitroxyl spin labelling suitable for molecular dynamics studies within the interface regions of SBR elastomer/silica composites have been developed and used together with the nitroxyl spin probe technique. Fast and slow motional components have been identified within the interface regions and the corresponding rotational diffusion tensors have been measured as a function of the temperature and the SiO₂ concentration. The fast rotational frequency is found to be orders of magnitude slower than that measured in the absence of SiO₂. This difference is suggested to arise from a closer packing of the macromolecules near the silica surface caused by the van der Waals bonding interactions. Increase of the SiO₂ concentration results in a decrease of the molecular mobility. This effect has been imputed to the overlapping of the bonding interaction regions. Spin probe measurements in the SBR-SiO₂ matrices using TEMPO, strongly suggest that the hindrance to chain segmental motion induced by the SiO₂-SBR interactions propagates beyond the interface regions thus involving the bulk polymer matrix. It is suggested that the information on the segmental chain dynamics obtained through the spin labelling and spin probe measurements can be developed as a method for investigating the polymer/filler interactions within the reinforcing mechanism by the filler.     

NO spin trapping and EPR studies on the photochemistry of aliphatic aldehydes

Radicals, such as acyl, hydrated acyl, alkyl and ketyl radicals, from aliphatic aldehyde photochemistry were detected by NO spin trapping and EPR techniques. Deuterium effects on EPR spectra and the generation of radicals by 2-amido-2-propyl radical attack on substrate molecules in aqueous solution via hydrogen-atom abstraction were applied to identify radicals produced photochemically from aldehydes. Aliphatic aldehydes used in the present investigation were formaldehyde, acetaldehyde, acetaldehyde-d4, propionaldehyde, isobutyraldehyde, isopentanal and tert-pentanal. Possible reaction mechanisms are suggested.     

Thermoresponsive copolymers: from fundamental studies to applications

Thermoresponsive copolymers have attracted considerable interest in both the polymer and biomaterial literature. They show interesting fundamental behaviour (thermally triggered contraction and aggregation) as well as potentially useful properties (reversible gelation). Biocompatible thermoresponsive copolymers are being developed for application in drug delivery and regenerative medicine. This review focuses on the fundamental aspects of thermally triggered conformational changes with an emphasis on copolymer design. Also, the ability to use these copolymers to produce thermoresponsive colloidal dispersions is discussed. Recent examples from within our group and elsewhere are considered in order to illustrate structure–property relationships. The review focuses on copolymers involving N-isopropylacrylamide. However, non-acrylamide thermoresponsive copolymers are also considered in detail. Emerging areas that appear likely to be actively pursued in the future are also discussed.     

Determination of rate constants for rearrangement of ω-carbalkoxyalkyl radicals by the EPR method employing spin traps

Conclusions The rate constants for the rearrangement of-carbalkoxyalkyl radicals, with 1,6-, 1,5-,and 1,4-migration of the hydrogen atom, were determined.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 891–893, April, 1979.     

Thioketone spin traps as mediating agents for free radical polymerization processes

Thioketones are demonstrated to be suitable agents for controlling free radical polymerization processes: the polymerizations carry (pseudo) living characteristics indicating that the control process is induced by a persistent radical effect.     

Predicting protein disorder and induced folding: from theoretical principles to practical applications

In the last years there has been an increasing amount of experimental evidence pointing out that a large number of proteins are either fully or partially disordered (unstructured). Intrinsically disordered proteins are ubiquitary proteins that fulfil essential biological functions while lacking highly populated and uniform secondary and tertiary structure under physiological conditions. Despite the large abundance of disorder, disordered regions are still poorly detected. Recognition of disordered regions in a protein is instrumental for reducing spurious sequence similarity between disordered regions and ordered ones, and for delineating boundaries of protein domains amenable to crystallization. As presently none of the available automated methods for prediction of protein disorder can be taken as fully reliable on its own, we present a brief overview of the methods currently employed highlighting their philosophy. We show a few practical examples of how they can be combined to avoid pitfalls and to achieve more reliable predictions. We also describe the currently available methods for the identification of regions involved in induced folding and provide a few practical examples in which the accuracy of predictions was experimentally confirmed.     

Gas chromatography on carbon adsorbents: Characterization, systematization, and practical applications to catalytic studies

The results of the characterization of graphite-like carbon materials by X-ray diffraction, electron microscopy, and adsorption and gas chromatography are discussed. All carbon-containing adsorbents are systematized in accordance with their structure and adsorption characteristics, chemical nature, and chromatographic surface properties. The adsorption and gas-chromatographic properties of carbons and other adsorbents are compared. The purposeful regulation of the chemical nature of carbon adsorbent surfaces is considered; it significantly extended the gas-chromatographic capabilities of carbon-containing materials, in particular, in studies of the product composition of catalytic reactions.     

Nanoscale heterogeneities in ionic liquids: insights from EPR of spin probes

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Rate constants for addition of triethylsilyl radicals to spin traps

Conclusions The rate constants for the addition of triethylsilyl radicals to -phenyl-N-tert-butylnitrone (k_add=(11±5)·10⁶ liter/mole·sec) and 2,4,6-tri-tert-butylnitrosobenzene (k_add= (1.5±0.3)·10⁹ liter/mole·sec) at 20°C were determined by the EPR method.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 938–941, April, 1984.     

Microchip-based cellular biochemical systems for practical applications and fundamental research: from microfluidics to nanofluidics

By combining cell technology and microchip technology, innovative cellular biochemical tools can be created from the microscale to the nanoscale for both practical applications and fundamental research. On the microscale level, novel practical applications taking advantage of the unique capabilities of microfluidics have been accelerated in clinical diagnosis, food safety, environmental monitoring, and drug discovery. On the other hand, one important trend of this field is further downscaling of feature size to the 10¹–10³ nm scale, which we call extended-nano space. Extended-nano space technology is leading to the creation of innovative nanofluidic cellular and biochemical tools for analysis of single cells at the single-molecule level. As a pioneering group in this field, we focus not only on the development of practical applications of cellular microchip devices but also on fundamental research to initiate new possibilities in the field. In this paper, we review our recent progress on tissue reconstruction, routine cell-based assays on microchip systems, and preliminary fundamental method for single-cell analysis at the single-molecule level with integration of the burgeoning technologies of extended-nano space.     

A modular approach toward functionalized three-dimensional macromolecules: from synthetic concepts to practical applications

A new strategy for the preparation of functional, multiarm star polymers via nitroxide-mediated "living" radical polymerization has been explored. The generality of this approach to the synthesis of three-dimensional macromolecular architectures allows for the construction of nanoscopically defined materials from a wide range of different homo, block, and random copolymers combining both apolar and polar vinylic repeat units. Functional groups can also be included along the backbone or as peripheral/chain end groups, thereby modulating the reactivity and polarity of defined portions of the stars. This modular approach to the synthesis of three-dimensional macromolecules permits the application of these tailored materials as multifunctional hosts for hydrogen bonding, nanoparticle formation, and as scaffolds for catalytic groups. Examples of applications of the functional stars in catalysis include their use in a Heck-type coupling as well as an enantioselective addition reaction.     

Synthesis of new functionalized 5,5-dimethyl-1-pyrroline 1-oxides and their investigation as spin traps

The reactions of 5,5-dimethyl-3-oxo-1-pyrroline 1-oxide (3-oxo-DMPO, 1) with NH₂OH and N₂H₄ afforded oxime (2a) and hydrazone (2b), respectively. The reaction products were studied as spin traps for the short-lived radicals HO^·, Ph^·, PhCO₂ ^·, NC(Me₂)C^·, and NC(Me₂)CO^·. The nitroxides generated in the reactions of the above-mentioned short-lived radicals with nitrones 1 and 2a,b were characterized by ESR spectroscopy. Of these nitrones, oxime 2a is the most effective radical trap.     

High resolution spin labeled fatty acid: synthesis and EPR spectral characteristics

Stearic acid spin label substituted with deuterium in all positions and¹⁵N in the paramagnetic group has been synthesized and was found to display a 5.5 fold gain in sensitivity in the EPR spectrum and a 60% decrease in linewidth compared to the unmodified analog.     

EPR fine structure and spin densities in TCNQ salts

The spin density distributions in TCNQ anion-radicals are estimated from experimental fine structure parameters and crystallographic data of five TCNQ salts of 1—1 stoichiometry.     

NMR and EPR studies of the reaction of nucleophilic addition of (bi)sulfite to the nitrone spin trap DMPO

The reaction of the nitrone spin trap 5,5‐dimethylpyrroline‐N‐oxide (DMPO) with sodium (bi)sulfite in aqueous solutions was investigated using NMR and EPR techniques. Reversible nucleophilic addition of (bi)sulfite anions to the double bond of DMPO was observed, resulting in the formation of the hydroxylamine derivative 1‐hydroxy‐5,5‐dimethylpyrrolidine‐2‐sulfonic acid, with characteristic ¹H and ¹³C NMR spectra. The reaction mechanism was suggested and corresponding equilibrium constants determined. The mild oxidation of the hydroxylamine results in the formation of an EPR‐detected spectrum identical with that for the DMPO adduct with sulfur trioxide anion radical. The latter demonstrates that a non‐radical addition reaction of (bi)sulfite with DMPO may contribute to the EPR detection of SO₃^?? radical. This possibility must be taken into account in spin trapping analysis of sulfite radical. Copyright © 2003 John Wiley & Sons, Ltd.