EPR Spin Probe Research Articles

Density of states and magnetic correlations in the La 2- xSr xCuO 4 system studied by EPR of Fe spin probes

EPR of Fe 3+ ions doped to La 2- x Sr x CuO 4 samples with various Sr content ( x=0-0.25) has been carried out. In the high-temperature region the EPR linewidth was determined by the Korringa relaxation. By extracting the Korringa contribution, we were able to evaluate a dependence of the density of states N F on x. It has been found that N F continuously grows with Sr doping from under- to overdoped regimes. The obtained N F( x) dependence indicates that the insulator-metal transition near x=0.06 is driven by hole delocalization. In the low-temperature region the relaxation rate was determined by spin-spin relaxation. The low-temperature upturn observed for the temperature dependence of the EPR linewidth can be understood by a slowing down of spin fluctuations due to spin freezing and/or carrier localization. We suggest that carrier localization enhancement plays an important role in the occurrence of the well known anomaly of T c near x=0.125 (so-called 1 8 problem).

NMR determination of EPR hyperfine coupling constants of some 5-(n-alkyl)-1,1,3,3-tetrakis(trideuteriomethyl)isoindolin-2-yloxyls

2D 1H–13C chemical shift correlation spectroscopy has been used to determine some small 1H and 13C EPR hyperfine interaction constants in some 5-(n-alkyl)isoindolin-2-yloxyl radicals. In the methodology used, it was necessary to measure the chemical shifts of both the isoindolines and of the cognate isoindolin-2-yloxyl radicals. The latter n-alkyl-substituted radicals have considerable potential as EPR spin probes in lipid systems.

EPR-spin probe studies of model polymers: separation of covalent cross-linking effects from hydrogen bonding effects in swelled Argonne premium coal samples

The swelling behavior of 2-12 % cross-linked polystyrene-divinylbenzene (PSDVB) copolymers was examined by an EPR-spin probe technique. It was observed that the mechanism of spin probe inclusion was the intercalation into the matrix rather than diffusion into the pores. The disruption of van der Waals forces between adjacent aromatic rings appeared to be the primary mechanism for pyridine swelling of PSDVB. By comparing the data to results from coal swelling studies it was also inferred that the extent of hydrogen bonding in coal will have a much greater impact on its swelling properties than its covalently cross-linked character

Coupling constant versus density of states in La2-xSrxCuO4 as revealed by EPR of Gd spin probes.

By analyzing the Korringa contribution to the EPR linewidth of ${\mathrm{Gd}}^{3+}$ ions doped to high-quality ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_{4}$ samples with various Sr content (x=0.08--0.35) a dependence of the density of states N(${\mathit{E}}_{\mathit{F}}$) on x has been extracted. The analysis of the observed dependence together with that for the critical temperature ${\mathit{T}}_{\mathit{c}}$(x) enabled us to study the relation between the coupling constant \ensuremath{\lambda} and N(${\mathit{E}}_{\mathit{F}}$) in course of Sr doping. We found that up to the optimum Sr concentration of x=0.15 the coupling constant \ensuremath{\lambda} increases correspondingly to increasing of the density of states. At the same time \ensuremath{\lambda} rapidly decreases in the overdoped region (x>0.15) while N(${\mathit{E}}_{\mathit{F}}$) continuously grows. The possible reasons for such a behavior are discussed.

Spin-probe EPR study of some sugars in connection with desiccation tolerance of biological objects

EPR spectra of the nitroxide radical Tempone introduced in trehalose, sucrose, glucose and in sucrose-raffinose and sucrose-glucose mixtures have been studied at different temperatures above the room temperature. The sugars similar to those found in desiccation tolerant biological organisms (trehalose, sucrose-raffinose mixture) are distinguished from the others by the stability of their phase state and by lower values of the effective activation energies for rotational molecular motion. Probably these properties are important for the mechanism by which sugars act to protect the cell during desiccation.

Phase equilibria and formation of vesicles of dioleoylphosphatidylcholine in glycerol / water mixtures

The lipid 1,2-dioleoyl- sn-glycero-3-phosphocholine (DOPC) forms a lamellar liquid crystalline phase (L α) in arbitrary mixtures of glycerol and water. The phase has been characterized by means of X-ray diffraction, 31P-NMR spectroscopy and differential scanning calorimetry (DSC). In the L α state, and for DOPC concentrations greater than 50% (w/w), the thickness of the lipid bilayer decreases, while the area of the polar head group increases with increasing glycerol concentration. The phase transition from gel to L α state occurs in the range of 240 to 260 K. Contrary to a previous (McDaniel, R.V., McIntosh, T.J. and Simon, S.A. (1983) Biochim. Biophys. Acta 731, 97) study of 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC) we find that in the gel state, the thickness of the DOPC lipid bilayer is greater than that in the L α state. This suggests that in the gel state, the lipid acyl chains of DOPC are in extended configuration. The lamellar phase reaches its maximum swelling at about 50% (w/w) of DOPC. At lower DOPC concentrations a two-phase system is formed where the lamellar phase exists in equilibrium with excess of solvent. Unilamellar vesicles can be prepared from a diluted suspension of the lamellar phase either by using the sonicator or extruder technique. We show this by means of 31P-NMR, EPR and flourescence spectroscopy. The mean radius of the vesicles, prepared by a sonicator, has been determined at different glycerol/water mixtures. It is found to decrease continously from 100 Å at 100% water to a minimum of 75 Å at about 50% water in the solvent mixture. By further decreasing the water content in the solution, the radius rapidly increases, and a mean radius of 450 Å is estimated at a water content of 10%. The rotational relaxation times of a fluorescent probe and two EPR spin probes, solubilized in DOPC vesicles, have been measured at different glycerol/water mixtures. It is found that the rotational rates are always much slower in the systems containing glycerol.

An EPR investigation of non-haem iron sites in Escherichia coli bacterioferritin and their interaction with phosphate : A study using nitric oxide as a spin probe

EPR studies of bacterioferritin (BFR), an iron-storage protein of Escherichia coli [1993, Biochem. J. 292, 47-56.], have revealed the presence of non-haem iron (III) (NHI) sites within the protein coat which may be involved in iron uptake and release. When nitric oxide was used as an EPR spin probe of the Fe(II) state of the NHI sites, two distinct mononuclear NHI species were found. Under certain conditions, an iron dimer was also observed. The reaction of phosphate with NHI species has been investigated. Results point to a function for this anion in core nucleation.

Use of merocyanine (MC540) in quantifying lipid domains and packing in phospholipid vesicles and tumor cells

The fluorescent probe merocyanine (MC540) reports qualitatively on several membrane events. Here we demonstrate that MC540 fluorescence can quantity the degree of coexisting liquid-crystalline and gel states in mixed monotectic phosphatidylcholine (PC) bilayers. The probe exhibits disparate fluorescence wavelength maximas and intensities when incorporated into liquid-crystalline and gel state membranes. The fluorescence measurements parallel partitioning of the EPR spin probe TEMPO between the aqueous environment and the membrane fluid phase. While both techniques can accurately assess the phase transition of synthetic PCs, only MC540 can distinguish between liquid-crystalline phases of different composition. MC540 fluorescence for single-component PC bilayers correlates quantitatively with estimates of the area/molecule determined from surface area/pressure isotherms of lipid monolayers, whereas partitioning of TEMPO fails to assess the relative degree of lipid packing in various fluid state membranes. Additionally, MC540 fluorescence characterizes the interaction of cholesterol with membranes made from condensable (18:0, 18:1-PC) and non-condensable (18:0,22:6-PC) lipids. Finally MC540 distinguishes tumor cell membranes differing only in the amount of docosahexaenoic acid (DHA). Thus we conclude that MC540 can be used quantitatively to study phospholipid packing and membrane phases with lipid vesicles and to sense subtle differences in the arrangement of phospholipids in biological membranes.

Determination of the London penetration depth with EPR of surface spin probes

Evaluating the temperature dependent line broadening of paramagnetic spins on the surface of superconductors in the model of an ideal vortex state, an upper limit for λ ∥ < 500 nm was determined for single crystalline Bi2212. The temperature dependence follows a (1-t 4) law. The same “two-fluid” behaviour was also found for polycrystalline Bi 2Sr 1.3Ca 0.7CuO 6.15 sample. However, evidence temperature law was observed for c-oriented epitactic Bi- and YBCO thin films. However, evidence for a dominant contribution of magnetic field gradients on a larger scale than the lattice constant of the ideal vortex state was found for the GdBCO system by evaluating EPR line narrowing for a spin probe with fast spin diffusion.

Formation by NO of nitrosyl adducts of redox components of the Photosystem II reaction center. I. NO binds to the acceptor-side non-heme iron

NO is a good electrophile and EPR spin probe, carrying an unpaired electron ( S = 1 2 ). Exposure of Photosystem II reaction centers to NO results in the appearance of an EPR signal at g = 4. Dark titration with NO shows a K d ≈ 30 μM in spinach chloroplasts and 250 μM in BBY preparations. Successive cycles of illumination at 200 K, followed by incubation at 245 K, results in binary oscillations of the amplitude of the g = 4 signal in spinach chloroplasts. This signal is small in states Q − AQ B, Q − AQ − B, but large in states Q AQ B and Q AQ BH 2 of the PS II acceptor side. NO slows electron transfer between Q A and Q B (Diner, B.A and Petrouleas, V. (1990) Biochim. Biophys. Acta 1015, 141–149) and modifies the Mössbauer spectrum of the non-heme Fe(II). These results strongly support the assignment of the g = 4 EPR signal to an acceptor side Fe(II)-NO adduct in an S = 3 2 state. Exchange coupling of this species with the S = 1 2 semiquinones results in an integral spin system, not detectable in X-band EPR. The g = 4 spectrum can be described by a spin hamiltonian. The rhombicity parameter E D is in all cases small (⩽ 0.015), implying a near axial environment. NO can donate electrons to PS II. Charge recombination, following a light flash in the presence of DCMU, is blocked by NO ( Km ≈ 30 μM, 25°C). NO also reacts reversibly in the dark with D + (an oxidized secondary donor), resulting in the disappearance of Signal II dark with a K d of 3 μM. Pumping off of NO in the dark results in full recovery of the signal.

Accessibility, reactive site distribution, and swelling properties of Argonne Premium Coal Samples studied by a spin probe EPR method

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAccessibility, reactive site distribution, and swelling properties of Argonne Premium Coal Samples studied by a spin probe EPR methodJanina Goslar and Lowell D. KispertCite this: Energy Fuels 1989, 3, 5, 589–594Publication Date (Print):September 1, 1989Publication History Published online1 May 2002Published inissue 1 September 1989https://doi.org/10.1021/ef00017a011RIGHTS & PERMISSIONSArticle Views52Altmetric-Citations3LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (713 KB) Get e-Alerts Get e-Alerts

Molecular motion in supercooled liquids and glasses

Recently obtained data on dielectric and NMR relaxation, pulsed EPR, and other methods indicate the presence in glassy liquids of two types of molecular rotational motion. One type corresponds to macroscopic motion of the molecules and is apparent in measurements of mechanical relaxation, macroviscosity, and dielectric ..cap alpha.. relaxation. A small number of molecules display the second type of motion, which is distinguished from the first type by much higher frequency of motion and is apparent in dielectric ..beta.. relaxation, NMR relaxation, and pulsed EPR of spin probes. It is especially characteristic for impurity molecules. We discuss the connection between molecular motion and the structural features of glasses. We indicate examples of chemical reactions whose kinetics are determined by the second type of motion.

Abnormal membrane properties of the sarcoplasmic reticulum of pigs susceptible to malignant hyperthermia: Modes of action of halothane, caffeine, dantrolene, and two other drugs

The role of sarcoplasmic reticulum (SR) in malignant hyperthermia (MH) was studied using the heavy microsomal fraction prepared from semitendinosus muscles of both normal and genetically MH-susceptible pigs. In the presence of ATP, SR was loaded with 70 nmol Ca 2+/mg SR protein. Under these conditions, MH-SR demonstrated Ca 2+-induced Ca 2+ release (Ca-ICaR) and halothane-induced Ca 2+ release (halothane-ICaR; halothane concentrations as low as 10 μ m). Normal SR did not demonstrate these release phenomena. Dantrolene inhibited the halothane-ICaR, but did not inhibit the Ca-ICaR. Ruthenium red and tetracaine inhibited both types of Ca 2+ release. From the measurement of passive Ca 2+ efflux, it was shown that dantrolene did not affect the Ca 2+ permeability of the SR itself, but suppressed only the halothane-induced increment of the permeability. The membrane order parameter of the SR, as measured by the spin-probe EPR technique, indicated that halothane disordered the lipid bilayer of MH-SR to a greater extent than it did of normal SR. This halothane disordering effect on MH-SR was antagonized by dantrolene. Ruthenium red and tetracaine did not antagonize the halothane disordering effect. These results raise the possibility that halothane could disturb the structure of the lipoprotein complex in MH-SR in such a way that it could open the Ca 2+-release channels. The Ca 2+ thus released further opens the channel through the Ca-ICaR mechanism in a positive feedback fashion, thus triggering the MH syndrome. The efficacy of dantrolene in ameliorating the MH syndrome might be related to the inhibition of this halothane effect.

An EPR spin probe study of the glass transition in MBBA

EPR evidence is presented to support the literature contention that a small spherical probe will detect chain melting while a longer probe will detect the glass transition of MBBA. One finds DTA/DSC values for T g from both probes when using the Grest-Cohen model near room temperature.

An EPR determination of the helix pitch and relative handedness of some induced cholesteric mesophases

The pitch of weakly cholesteric mesophases obtained by dissolving a chiral compound in the nematic liquid crystal MBBA, has been determined by an EPR spin probe technique. The measured values are in excellent agreement with those obtained by the Grandjean-Cano microscopic method. Once a sufficiently large number of EPR simulated spectra have been computed, the experimental procedure for the determination of the pitch is shown to be faster and as reliable as other methods. The handedness of the mesophase can also be easily established by observing the spectral variations which follow the addition of a cholesteric of known handedness to a given sample.

Effect of hyperalphalipoproteinemia on structural characteristics of plasma lipoproteins as revealed by EPR spin probes

Effect of hyperalphalipoproteinemia on structural characteristics of plasma lipoproteins as revealed by EPR spin probes

A simple, accurate method of correcting for unresolved hyperfine broadening in the EPR of nitroxide spin probes to determine the intrinsic linewidth and heisenberg spin exchange frequency

A method of correcting the EPR linewidth of a nitroxide that is inhomogeneously broadened by unresolved hyperfine structure is presented. Two simple equations are presented which allow the accurate deduction of the intrinsic linewidth and the Heisenberg spin exchange frequency, respectively, from the measured linewidths. The method allows correction for the inhomogeneous broadening in practically all cases in which the nitroxide tumbles in the motional narrowing region by using only a hand-held programmable calculator, thus eliminating the need for calibration libraries. The accuracy of the two equations is demonstrated for three nitroxides.