Electron Paramagnetic Resonance Spectroscopy Spectra Research Articles

The Influence of Blood and Serum Microenvironment on Spin-Labeled Magnetic Nanoparticles

The investigation and clarification of the properties of surface-functionalized superparamagnetic nanoparticles in a biological environment are key challenges prior to their medical applications. In the present work, electron paramagnetic resonance spectroscopy (EPR) combined with the spin labeling technique was utilized to better understand the behavior of nitroxides attached to magnetite nanoparticles dispersed in body fluid. EPR spectra of spin-labeled, silane-coated Fe3O4 nanoparticles in human serum and whole blood were recorded and analyzed for both room- and low-temperature values. In all cases, the obtained EPR signal consisted of a broad line from magnetite cores and a characteristic signal from the attached 4-Amino-2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO). Even for liquid samples, the anisotropic components of magnetic tensors did not fully average out, which was reflected in the differences in the intensity of three narrow hyperfine lines from nitroxide. At 230 K the irregular slow-motion signal from the attached radical was also simulated using the EasySpin toolbox, which allowed to determine the parameters related to magnetic tensors and the dynamics of the spin label. The study showed that the anisotropy of the motion of the spin label 4-amino-TEMPO reflects its interactions with the surrounding medium and the manner of the attachment of the nitroxide to the surface of nanoparticles.

Thermal stability of artificial radiation-induced defects in kaolinite: Enhancing EPR dating protocol

Kaolinite naturally contains radiation-induced electron defects in its structure induced by ionizing radiations and can be analyzed with electron paramagnetic resonance spectroscopy (EPR). They include the so-called A-center, which is crucial for geochronological applications due to its stability at the scale of geological periods. Indeed, previous studies have substantiated the thermal stability of naturally occurring A-centers in kaolinite through annealing experiments. However, the stability of artificially created A-centers, which are used to determine paleodose through calibration via irradiation experiments and subsequent dating of kaolinite formation, still needs to be more adequately specified to confirm their relevance. Therefore, this research probed the thermal stability of A-centers produced by ionizing 1.5 MeV He+ beams in two samples, i.e., the reference KGa-2 and a very disordered lateritic soil kaolinite. Heating experiments showed that the annealing of irradiated samples at 250 °C was relevant to determining A-center concentration. Second, the annealing of artificial A-centers at higher temperatures was found to be a second-order process, as for natural A-centers. Annealing parameters such as activation energy (2–2.6 eV) were determined with estimates of half-life at 300 K, which was found to be >1012 years for natural and artificial A-centers. Thus, the parameters for artificial A-centers are consistent with the thermal annealing behavior of their natural counterparts. These new findings affirm that artificially generated A-centers mimic natural ones in terms of EPR spectra and thermal stability, enhancing the reliability and precision of the EPR dating methodology used in kaolinite dating.

Application of electron paramagnetic resonance spectroscopy to examine free radicals formed in indapamide and torasemide storage under UV irradiation and at the higher temperatures which appear under light exposition

Free radical formation in two diuretics: indapamide and torasemide was examined during UV irradiation and storage at higher temperatures using X-band (9.3 GHz) electron paramagnetic resonance spectroscopy (EPR). The aim of this study was to investigate the possibility of storing indapamide and torasemide under UV irradiation and at higher temperatures, which may occur during exposure to light. The diuretic samples were exposed to UVA irradiation for 15, 30 and 45 minutes, and stored at temperatures of 40 °C and 50 °C by 30 minutes. The EPR spectra were analyzed to determine the amplitudes (A), linewidths (ΔBpp), and integral intensities (I) and g factors. The concentrations of free radical (N) in the diuretic samples were also determined. The influence of microwave power on amplitudes, linewidths and the asymmetry parameter were evaluated. The result showed that the tested indapamide and torasemide samples exhibited high free radical concentrations in the range of 1018-1019 spin/g after UV irradiation and heat treatment. Therefore, due to the significant free radical formation indapamide and torasemide should not be stored under UV light and at temperatures of 40 °C and 50 °C. The complex character of free radical systems in the diuretic samples was proved as evidenced by the changes of the asymmetry parameters of the EPR lines with increasing microwave power. Fast spin-lattice relaxation processes were observed in all tested diuretic samples, regardless of the storage conditions. Electron paramagnetic resonance spectroscopy is proposed as a useful method in pharmacy to determine the appropriate storage conditions for diuretics.

Interaction of magnesium ions with semiquinone radicals of tiron used as an indicator of reactive oxygen species

Electron paramagnetic resonance spectroscopy (EPR) and quantum chemical calculations based on density functional theory were used to demonstrate that the earlier observed changes in the EPR spectra of Tiron semiquinone radical dissolved in sea water solution occur due to interaction of Mg2+ ions with Tiron radical. This interaction is caused by electrostatic attraction between Mg2+ ions and Tiron radicals, which bears great charges of opposite sign (+2 and -3), on the one hand, and due to the ability of Mg2+ ion to bind to bidentate oxygen-containing ligands efficiently, on the other hand. The formation of tight contact ion pairs leads to electron and spin density redistribution in the Tiron radical, as can been seen by the observed changes in the EPR spectra of the radical.

Optical, magnetic and spin resonance studies of MFe2O4 (M = Mn, Co, Zn) ferrites

MFe2O4 (M = Mn, Co, Zn) ferrites have been prepared using citric acid assisted sol–gel autocombustion technique. Structural, microstructural, optical, magnetic and spin resonance studies have been carried out using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscope (FESEM), UV–Visible spectroscopy, Vibrating sample magnetometer (VSM) and Electron spin resonance spectroscopy (ESR) respectively. The crystallite size determined using Scherrer method lies between 12 nm and 21 nm. From the UV–Visible absorption spectra the optical band gap energy, refractive index and optical dielectric constant have been estimated. The magnetic parameters have been obtained from the room temperature M−H loop of the ferrite samples. ESR spectra obtained at X-band microwave energy have been fitted using Lorentzian function to determine the spin resonance parameters like gyromagnetic ratio, peak to peak linewidth and resonance field. CoFe2O4 has the largest linewidth of 4874 Oe. The observed broad ESR linewidth of the investigated samples may find suitability as radar absorbing materials for microwave applications.

Oxygen Vacancy-Mediated Activates Oxygen to Produce Reactive Oxygen Species (ROS) on Ce-Modified Activated Clay for Degradation of Organic Compounds without Hydrogen Peroxide in Strong Acid.

The treatment of acid wastewater to remove organic matter in acid wastewater and recycle valuable resources has great significance. However, the classical advanced oxidation process (AOPs), such as the Fenton reaction, encountered a bottleneck under the conditions of strong acid. Herein, making use of the oxidation properties of CeAY (CeO2@acid clay), we built an AOPs reaction system without H2O2 under a strong acid condition that can realize the transformation of organic matter in industrial wastewater. The X-ray photoelectron spectroscopy (XPS) proved that the CeAY based on Ce3+ as an active center has abundant oxygen vacancies, which can catalyze O2 to produce reactive oxygen species (ROS). Based on the electron spin-resonance spectroscopy spectrum and radical trapping experiments, the production of •O2- and •OH can be determined, which are the essential factors of the degradation of organic compounds. In the system of pH = 1.0, when 1 mg CeAY is added to 10 mL of wastewater, the degradation efficiency of an aniline solution with a 5 mg/L effluent concentration is 100%, and that of a benzoic acid solution with a 100 mg/L effluent concentration is 50% after 10 min of reaction. This work may provide novel insights into the removal of organic pollutants in a strong acid water matrix.

In Situ Mapping and Local Negative Uptake Behavior of Adsorbates in Individual Pores of Metal-Organic Frameworks.

Herein, we report the adsorbate behavior in individual local pores of MIL-101, which is a metal-organic framework (MOF) with two heterogeneous mesopores and different metal sites, by combining adsorbate isotherms and in situ crystallography profiles. The in situ mapping shows that the substrate-adsorbate interaction affects the initial adsorption and pore condensation steps. The monolayer adsorption gradient changes greatly depending on the framework metal-adsorbate attraction force. Also, broad inflection points are found in adsorption isotherms, and the initial shape depends on the different metals. Besides, the capillary condensation at a pore draws adsorbates from other local pores. This leads to the local negative uptake behavior in individual pore isotherms. At higher pressure, they move to a larger space, whereas in a relatively low-pressure range the attraction force between the MOF framework and guest molecule influences the amount of rearranged guest molecules. Furthermore, the origin of the characteristic adsorption behavior based on the metals constituting the MOFs and the relative strength of substrate-adsorbate and adsorbate-adsorbate interactions are elucidated through the combined study of electron densities in pores, electron paramagnetic resonance spectroscopy spectra, and density functional theory and Monte Carlo simulations to uncover the previously veiled information on adsorption behavior.

Interaction kinetics and accessibility of sulfadiazine in model clay-humic acid suspension: Electron spin resonance investigations with nitroxide spin label

The characterization of the interaction of sulfonamides with soil is of particular interest in environmental risk and persistence assessment. In the present work electron spin resonance spectroscopy (ESR) was used to investigate the interaction kinetics of spin labelled sulfadiazine (SL-SDZ) with model clay-humic acid suspensions. The ESR spectra showed that SL-SDZ incubated with Leonardite humic acid (LHA) and Ca-hectorite as model clay was immobilized due to covalent binding of its aniline moiety to LHA. From the immobilization kinetics measured over a period of 1200 h a pseudo-first order reaction with a time constant of 82.6 ± 25.0 h of covalent binding was determined. Additionally, SL-SDZ was strongly sorbed by LHA immediately after incubation but not durably sequestered. Compared to incubation without Ca-hectorite the covalent binding kinetics of SL-SDZ as well as its strong sorption were retarded.

Electron Paramagnetic Resonance Gives Evidence for the Presence of Type 1 Gonadotropin-Releasing Hormone Receptor (GnRH-R) in Subdomains of Lipid Rafts.

This study investigated the effect of type 1 gonadotropin releasing hormone receptor (GnRH-R) localization within lipid rafts on the properties of plasma membrane (PM) nanodomain structure. Confocal microscopy revealed colocalization of PM-localized GnRH-R with GM1-enriched raft-like PM subdomains. Electron paramagnetic resonance spectroscopy (EPR) of a membrane-partitioned spin probe was then used to study PM fluidity of immortalized pituitary gonadotrope cell line αT3-1 and HEK-293 cells stably expressing GnRH-R and compared it with their corresponding controls (αT4 and HEK-293 cells). Computer-assisted interpretation of EPR spectra revealed three modes of spin probe movement reflecting the properties of three types of PM nanodomains. Domains with an intermediate order parameter (domain 2) were the most affected by the presence of the GnRH-Rs, which increased PM ordering (order parameter (S)) and rotational mobility of PM lipids (decreased rotational correlation time (τc)). Depletion of cholesterol by methyl-β-cyclodextrin (methyl-β-CD) inhibited agonist-induced GnRH-R internalization and intracellular Ca2+ activity and resulted in an overall reduction in PM order; an observation further supported by molecular dynamics (MD) simulations of model membrane systems. This study provides evidence that GnRH-R PM localization may be related to a subdomain of lipid rafts that has lower PM ordering, suggesting lateral heterogeneity within lipid raft domains.

A Global Minimization Toolkit for Batch-Fitting and χ2 Cluster Analysis of CW-EPR Spectra

Electron paramagnetic resonance spectroscopy (EPR) is a uniquely powerful technique for characterizing conformational dynamics at specific sites within a broad range of molecular species in water. Computational tools for fitting EPR spectra have enabled dynamics parameters to be determined quantitatively. These tools have dramatically broadened the capabilities of EPR dynamics analysis, however, their implementation can easily lead to overfitting or problems with self-consistency. As a result, dynamics parameters and associated properties become difficult to reliably determine, particularly in the slow-motion regime. Here, we present an EPR analysis strategy and the corresponding computational tool for batch-fitting EPR spectra and cluster analysis of the χ2 landscape in Linux. We call this tool CSCA (Chi-Squared Cluster Analysis). The CSCA tool allows us to determine self-consistent rotational diffusion rates and enables calculations of activation energies of diffusion from Arrhenius plots. We demonstrate CSCA using a model system designed for EPR analysis: a self-assembled nanoribbon with radical electron spin labels positioned at known distances off the surface. We anticipate that the CSCA tool will increase the reproducibility of EPR fitting for the characterization of dynamics in biomolecules and soft matter.

High promoting of selective oxidation of ethylbenzene by Mn-ZSM-5 synthesized without organic template and calcination

Acetophenone is a valuable and widely applied intermediate in chemical industry, but limited by the synthesis with low-cost and efficient heterogeneous catalyst. Herein, we report tetrahedral coordination manganese-incorporated ZSM-5 zeolite (Mn-ZSM-5) by three steps involving acid hydrolysis of Mn(NO3)2 with tetraethylorthosilicate, basic aging and hydrothermal crystallization without organic template and calcination. Mn-ZSM-5 was identified by characterizations such as X-ray diffraction, Fourier transform infrared spectra (FTIR), field emission scanning electron microscopy, inductively coupling plasma spectrometer, N2-adsorption/desorption and FTIR, X-ray photoelectron spectroscopy (XPS), electron spin-resonance spectroscopy (ESR), NH3-TPD and H2-TPR. Moreover, tetrahedral coordination Mn atoms successfully incorporate into the framework of ZSM-5 demonstrated by ESR and XPS spectra. Furthermore, Mn-ZSM-5 with high crystallinity performs high and stable catalytic activity in the oxidation of ethylbenzene owing to tetrahedral Mn3+ in the framework of ZSM-5 as catalytic active sites. Tetrahedral coordination manganese-incorporated ZSM-5 zeolites synthesized without organic template and calcination performed high and stable catalytic activity on the oxidation of ethylbenzene owing to tetrahedral Mn3+ as catalytic active sites.

The effect of pH and ionic strength on the adsorption of glyphosate onto ferrihydrite

Although, glyphosate (N-(phosphonomethyl) glycine) is one of the most widely used herbicides in the world, its interaction with poorly crystalline iron oxides, such as ferrihydrite, is not well studied. In this research, we examined the adsorption of glyphosate onto ferrihydrite using infrared spectroscopy (FT-IR), electron paramagnetic resonance spectroscopy (EPR), adsorption kinetic models and adsorption isotherm models. The effect of pH and sodium chloride concentration on the adsorption of glyphosate onto ferrihydrite as well as the effect of extractors (CaCl2 0.010 mol L−1 and Mehlich) on the desorption of glyphosate were also evaluated. There are two important findings described in this work. First, 84% of adsorbed glyphosate strongly interacted to ferrihydrite as an inner-sphere complex and phosphate and amine groups are involved in this interaction. Second, an increase of sodium chloride salt concentration increased the adsorption of glyphosate onto ferrihydrite. The non-linear Langmuir model and pseudo second order model showed a good agreement of theoretical limit of glyphosate adsorbed onto ferrihydrite, 54.88 µg mg−1 and 48.8 µg mg−1, respectively. The adsorption of glyphosate onto ferrihydrite decreased when the pH increased. Under the conditions used in this work, EPR spectra did not show dissolution of ferrihydrite. Surface area, pore volume and pHpzc of ferrihydrite decreased after adsorption of glyphosate.

Probing Structure, Topology and Dynamics of KCNE3 in Proteoliposomes using Site-Direct Spin Labeling and EPR Spectroscopy

KCNE3 (E3) is a β-subunit of voltage gated potassium ion channels (Kv) that modulates the function of Kv by interacting with its a subunits including KCNQ1 and KCNQ4 (known as Q1 and Q4). Compared to other Kv channels, E3-Q1 interactions have been well studied in intestinal and tracheal epithelial cells where the complex maintains ion homeostasis. E3 interaction with Q1 allows Ky to act as a voltage independent and constitutively active channel that facilitates transepithelial Cl- ion secretion. Mutations in KCNE3 are responsible for diseases related to salt and fluid disorders including cystic fibrosis. Hence, it is important to elucidate KCNE3 structural and dynamic information with functional studies. Previously, the structure of E3 has been studied in a bicelle environment. However, in physiological conditions, lipids are organized into bilayers instead of single sheets of molecules. This research has been focused on protein structure, dynamic and topology of KCNE3 membrane protein in POPC/POPG vesicle usingSite-Directed Spin Labeling (SDSL) and Electron Paramagnetic Resonance Spectroscopy (EPR)techniques. EPR coupled with SDSL provides structural and dynamic information about proteins. In this study we have successfully introduced S-(2,2,5,5-tetramethyl-2,5-dihydro-1H-pyrrol-3-yl) methyl methanesulfonothioate spin label (MTSL) on several site-specific position of E3 by site-directed mutagenesis to obtain EPR spectra. CW-EPR (Continuous Wave Electron Paramagnetic Resonance)line shape analysis has been performed to investigate the dynamic of the protein in a lipid bilayer, while EPR power saturation has been used to study the topology of KCNE3 in a vesicle. Our data are consistent with the model of KCNE3 in a bicelle and revealed more promising structure and dynamic information for the protein in a native membrane environment.

Spin label EPR suggests the presence of cholesterol rich domains in cultured insect cell membranes

Different spin labels were incorporated to the membranes of cultured insect UFL-AG-286 cells in order to characterize their physical properties by Electron Paramagnetic Resonance spectroscopy (EPR). The spectrum of the spin label 12-SASL incorporated to cell membranes was similar as those obtained in membrane model systems composed of eggPC/cholesterol. However, the spectrum of the spin label CSL, chemically related to cholesterol, was drastically different in the two systems. Interestingly, when cell cholesterol content was reduced using methyl beta cyclodextrin, an EPR spectrum similar to those of model membranes was obtained. The analysis of these experiments suggests the existence of cholesterol rich regions in UFL-AG-286 cell membranes.

XRD, FE-SEM, FT-IR and ESR studies of cation deficient potassium tris(oxalato)ferrate(III)trihydrate

Cation deficient potassium tris(oxalato)ferrate(III)trihydrate {K2.72[Fe(C2O4)3]·3.17H2O} crystals were characterized by X-ray powder diffractogram, Fourier Transform Infrared Spectroscopy (FT-IR), quantitative elemental analysis of EDAX, Field Emission Scanning Electron Microscope (FE-SEM), Electron Spin Resonance Spectroscopy (ESR) and Thermogravimetry And Diffrential thermal analysis (TG-DTA). This compound crystallizes in the monoclinic system with P21/c space group and shows three-dimensional (3D) chain structure. The elements present in the grown crystal were confirmed by the energy dispersive X-ray analysis (EDAX). The microstructural features on the surface of the single crystals were determined using FE-SEM. Powder X-ray diffraction results indicate the polycrystalline nature of the material. Infrared spectroscopy was used to study the vibrational modes of the compound. The room temperature crystalline ESR spectra indicate the high-spin (S = 5/2) of Fe(III) ion. Thermal behaviour of the compound has been studied using thermogravimetry and diffrential thermal analysis.

Electron spin resonance spectroscopy for immunoassay using iron oxide nanoparticles as probe.

With the help of iron oxide nanoparticles, electron spin resonance spectroscopy (ESR) was applied to immunoassay. Iron oxide nanoparticles were used as the ESR probe in order to achieve an amplification of the signal resulting from the large amount of Fe3+ ion enclosed in each nanoparticle. Rabbit IgG was used as antigen to test this method. Polyclonal antibody of rabbit IgG was used as antibody to detect the antigen. Iron oxide nanoparticle with a diameter of either 10 or 30nm was labeled to the antibody, and Fe3+ in the nanoparticle was probed for ESR signal. The sepharose beads were used as solid phase to which rabbit IgG was conjugated. The nanoparticle-labeled antibody was first added in the sample containing antigen, and the antigen-conjugated sepharose beads were then added into the sample. The nanoparticle-labeled antibody bound to the antigen on sepharose beads was separated from the sample by centrifugation and measured. We found that the detection ranges of the antigen obtained with nanoparticles of different sizes were different because the amount of antibody on nanoparticles of 10nm was about one order of magnitude higher than that on nanoparticles of 30nm. When 10nm nanoparticle was used as probe, the upper limit of detection was 40.00μgmL-1, and the analytical sensitivity was 1.81μgmL-1. When 30nm nanoparticle was used, the upper limit of detection was 3.00μgmL-1, and the sensitivity was 0.014 and 0.13μgmL-1 depending on the ratio of nanoparticle to antibody. Graphical abstract Schematic diagram of procedure and ESR spectra.

Formation and decay of radicals during Vacuum-UV irradiation of poly(dimethylsiloxane)

Formation of radicals in a poly(dimethylsiloxane) (PDMS) elastomer upon 172 nm vacuum-UV (VUV) irradiation was investigated by electron paramagnetic resonance spectroscopy (EPR). Kinetics of radical buildup and decay was investigated under varying conditions and found to depend strongly on the degree of pre-modification of the polymer. Furthermore, radicals were observed only when oxygen was absent during in situ VUV irradiation. The EPR spectrum is dominated by a broad signal, assignable to unspecified carbon-centered radicals. Stationary radical concentrations during VUV irradiation in nitrogen atmosphere can reach 0.2 mol/L in an about 260 nm thick surface layer, consistent with the remaining carbon concentration in the modified PDMS as measured by XPS. Gas diffusion is not limiting kinetics of the modification process. Our findings are consistent with a mechanism where oxygen molecules from the atmosphere diffuse in PDMS and quench radical sites in the polymer.

On the formation of solid solutions with blödite- and kröhnkite-type structures

In this contribution, we provide experimental results on the synthesis and some properties (structural, spectroscopic and thermal) of limited solid solutions Na2Ni1−xCux(SO4)2·4H2O (0 < x ≤ 0.17). Based on different experimental methods—vibrational spectroscopy (infrared and Raman), X-ray powder diffraction at ambient and elevated temperature, electron paramagnetic resonance spectroscopy (EPR) and TG–DTA–DSC methods, it has been established that the copper ions are included in the nickel blodite-type structure up to about 17 mol%. However, the nickel ions are not able to accept the coordination environment of the copper ions in the strongly distorted [Cu(H2O)2O4] clusters due to the Jahn–Teller effect, thus resulting in the crystallization of a krohnkite free from nickel ions. The X-ray powder diffraction data show that the included copper ions do not influence considerably on the lattice parameters of the blodite matrix owing probably to the buffer effect of the sodium ions and hydrogen bonds. The vibrational spectra are interpreted in the light of their crystal structures. The TG and DTA methods combined with X-ray powder diffraction at elevated temperature reveal that the dehydration of Na2Ni(SO4)2·4H2O and Na2Ni1−xCux(SO4)2·4H2O solid solutions occurs stepwise, thus forming dihydrates and anhydrous compounds—Na2Ni(SO4)2 and Na2Ni1−xCux(SO4)2 of the same structures. It has been found that the increased amount of copper ions causes increasing in the values of ΔH deh and decreasing in the values of ΔH f of the solid solutions. EPR spectra of the solid solutions are presented and compared to that of Na2Zn0.86Cu0.14(SO4)2·4H2O.

Rigid Spin Labels for Improved Distance and Dynamics in Intrinsically Disordered Proteins and Peptides

Spin-labeling and Electron Paramagnetic Resonance spectroscopy (EPR) have become powerful tools for structure determination in proteins and biomacromolecules. Usual spin labels, such as the disulfide-linked MTSL labels are flexible, owing to multiple single bonds separating the nitroxide from the protein backbone. We investigate spin labels rigidly linked to the backbone in a series of peptides derived from the KVKVLGDVIEV peptide[1], with the 4-amino-1-oxyl-2,2,6,6-tetramethylpiperidine-4-carboxylic acid (TOAC). These peptides mimic amyloid-aggregation proteins. They were found to form stable oligomers that are cell-toxic, and enabled X-ray crystallography to determine their structures[1].We synthesized and characterized three TOAC-peptides (TOAC1 -3) and one reference peptide (EZ). We show that the EPR rotation correlation times differ depending on TOAC position. Only one of the TOAC variants (peptide TOAC2) showed aggregation by CD signatures similar to[1], same as the non-TOAC containing EZ peptide. Changes in room temperature EPR spectra suggestive of amyloid aggregation were found in TOAC2, but not in the other TOAC variants.Peptide sequences:Peptides: TOAC1: KVKVT∗GDVIEV; TOAC2: T∗KVKVLGDVIEVG; TOAC3: KVKVLGDVIEVT∗G; EZ: KVKVLGDVIEVGG, where T∗ stands for TOAC.ResultsTOAC2 and EZ acquire β sheet character under aggregation conditions (in H2O, shaking at 1000 rpm at 310 K). Rotation correlation times (τr) by continuous wave EPR at 9 GHz are: TOAC1: 0.398 ± 0.018 ns; TOAC2: 0.122 ± 0.005 ns; TOAC3: 0.316 ± 0.028 ns. For TOAC2 τr increases to 0.162 ± 0.007 ns upon aggregation.Conclusions:We propose that for rigid spin labels such as TOAC, the spin label position and the peptide host are crucial and that the TOAC label may interfere with peptide properties. The results are essential to design spin-labeled constructs for the investigation of intrinsically disordered proteins.[1] Laganowsky et al., Science 335 (2012) 1228.

Characterization of free radicals by electron spin resonance spectroscopy in biochars from pyrolysis at high heating rates and at high temperatures

The concentration and type of free radicals from the decay (termination stage) of pyrolysis at slow and fast heating rates and at high temperatures (above 1000°C) in biomass char have been studied. A room-temperature electron spin resonance spectroscopy study was conducted on original wood, herbaceous biomass, holocelluloses, lignin and their chars, prepared at high temperatures in a wire mesh reactor, an entrained flow reactor, and a tubular reactor. The radical concentrations in the chars from the decay stage range up between 7·1016 and 1.5·1018 spins g−1. The results indicated that the biomass major constituents (cellulose, hemicellulose, lignin) had a minor effect on remaining radical concentrations compared to potassium and silica contents. The higher radical concentrations in the wheat straw chars from the decay stage of pyrolysis in the entrained flow reactor compared to the wood chars were related to the decreased mobility of potassium in the char matrix, leading to the less efficient catalytic effects of potassium on the bond-breaking and radical re-attachments. The high Si levels in the rice husk caused an increase in the char radical concentration compared to the wheat straw because the free radicals were trapped in a char consisting of a molten amorphous silica at heating rates of 103–104 K s−1. The experimental electron spin resonance spectroscopy spectra were analyzed by fitting to simulated data in order to identify radical types, based on g-values and line widths. The results show that at high temperatures, mostly aliphatic radicals (g = 2.0026–2.0028) and PAH radicals (g = 2.0027–2.0031) were formed.