Electron Paramagnetic Resonance Pattern Research Articles

Investigation of Paraffin-embedded Basal Cell Carcinoma Using Electron Paramagnetic Resonance.

Basal cell carcinoma (BCC) in paraffin-embedded specimens was investigated by nondestructively electron paramagnetic resonance (EPR) and X-band (9.45 GHz) EPR imaging (EPRI). A histopathological examination of specimens showed the melanin contents and revealed that they were predominantly of the nodular types. A single-line EPR pattern was observed in the BCC specimens, and the spectra of the samples were analyzed using linewidth and spectral pattern parameters. The eumelanin-related radical was observed in paraffin-embedded BCC specimens. The stability of the radical was supported by sepia pigment experiments. The g-value and peak-to-peak linewidths (ΔHpp) were 2.0046 and 0.61 ± 0.02 mT (mean ± SEM), respectively. Strong EPRI signals correspond to areas of strong pigmentation in the samples. Thus, histopathological examination, EPR, and EPRI of BCC specimens showed that the radical distribution reflects on the spatial distribution of pigments in the samples.

Structural, morphological and magnetic properties of Zn1−xCoxO prepared by sol—gel and hydrothermal method combined**Project supported by the 46th Institute of China Electronics Technology Group Corporation (No. 0231182346).

Cobalt-doped ZnO powder samples were prepared by sol—gel and hydrothermal method combined. The prepared powder samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), electron paramagnetic resonance (EPR) and vibrating sample magnetometry (VSM). XRD patterns show that all the samples have a single pure phase with wurtzite structure suggesting that Co2+ occupied Zn2+ sites in the ZnO crystal lattice. SEM images show that crystal grains of cobalt-doped ZnO are hexagonal cone or spheroidal. EPR pattern shows that all of the samples possess oxygen vacancy. Measurement of magnetism indicates that all the samples exhibit room temperature ferromagnetism (RTFM) embedded in a dominant diamagnetic or paramagnetic signal. The dominant signal turns from diamagnetic to paramagnetic with the increase of Co concentration. The magnetic behavior can attribute to defects and Co doping.

Reversible mechanical switching of magnetic interactions in a molecular shuttle.

Invited for this months cover are the groups of Professors Marco Lucarini and Alberto Credi at the University of Bologna. The cover picture shows coupled and uncoupled states of a [2]rotaxane incorporating stable nitroxide radical units in both the ring and dumbbell components. Interaction between nitroxide radicals could be switched between noncoupled (three-line electron paramagnetic resonance (EPR) spectrum) and coupled (five-line EPR spectrum) upon deprotonation of the rotaxane NH2+ centers that effects a quantitative displacement of a dibenzocrown macroring to a 4,4’-bipyridinium recognition site. The complete base- and acid-induced switching cycle of the EPR pattern was repeated several times without an appreciable loss of signal, highlighting the reversibility of the process. Hence, this molecular machine is capable of switching on/off magnetic interactions by chemically driven reversible mechanical effects. For more details, see the Communication on p. 18 ff.

Cover Picture: Reversible Mechanical Switching of Magnetic Interactions in a Molecular Shuttle (ChemistryOpen 1/2015)

The cover picture shows coupled and uncoupled states of a [2]rotaxane incorporating stable nitroxide radical units in both the ring and dumbbell components. Interaction between nitroxide radicals could be switched between noncoupled (three-line electron paramagnetic resonance (EPR) spectrum) and coupled (five-line EPR spectrum) upon deprotonation of the rotaxane NH2 + centers that effects a quantitative displacement of a dibenzocrown macroring to a 4,4’–bipyridinium recognition site. The complete base and acid-induced switching cycle of the EPR pattern was repeated several times without an appreciable loss of signal, highlighting the reversibility of the process. Hence, this molecular machine is capable of switching on/off magnetic interactions by chemically driven reversible mechanical effects. For more details, see the Communication on p. 18 ff.

Reversible mechanical switching of magnetic interactions in a molecular shuttle.

An acid–base switchable molecular shuttle based on a [2]rotaxane, incorporating stable radical units in both the ring and dumbbell components, is reported. The [2]rotaxane comprises a dibenzo[24]crown-8 ring (DB24C8) interlocked with a dumbbell component that possesses a dialkylammonium (NH2+) and a 4,4′-bipyridinium (BPY2+) recognition site. Deprotonation of the rotaxane NH2+ centers effects a quantitative displacement of the DB24C8 macroring to the BPY2+ recognition site, a process that can be reversed by acid treatment. Interaction between stable 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radicals connected to the ring and dumbbell components could be switched between noncoupled (three-line electron paramagnetic resonance (EPR) spectrum) and coupled (five-line EPR spectrum) upon displacement of the spin-labelled DB24C8 macroring. The complete base- and acid-induced switching cycle of the EPR pattern was repeated six times without an appreciable loss of signal, highlighting the reversibility of the process. Hence, this molecular machine is capable of switching on/off magnetic interactions by chemically driven reversible mechanical effects. A system of this kind represents an initial step towards a new generation of nanoscale magnetic switches that may be of interest for a variety of applications.

Electron Paramagnetic Resonance Spectroscopic Study of Copper Hopping in Doped Bis(l-histidinato)cadmium Dihydrate

Electron paramagnetic resonance (EPR) spectroscopy was used to study Cu(II) dynamic behavior in a doped biological model crystal, bis(L-histidinato)cadmium dihydrate, in order to gain better insight into copper site stability in metalloproteins. Temperature-dependent changes in the low temperature X-band EPR spectra became visible around 100 K and continued up to room temperature. The measured 298 K g-tensor (principal values: 2.17, 2.16, 2.07) and copper hyperfine coupling tensor (principal values: -260, -190, -37 MHz) were similar to the average of the 77 K tensor values pertaining to two neighboring histidine binding sites. The observed temperature dependence was interpreted using Anderson's theory of motional narrowing, where the magnetic parameters for the different states are averaged as the copper rapidly hops between sites. The EPR pattern was also found to undergo a sharp sigmoidal-shaped, temperature-dependent conversion between two species with a critical temperature T(c) ≈ 160 K. The species below T(c) hops between the two low temperature site patterns, and the one above T(c) represents an average of the molecular spin Hamiltonian coupling tensors of the two 77 K sites. In addition, the low and high temperature species hop between one another, contributing to the dynamic averaging. Spectral simulations using this 4-state model determined a hop rate between the two low temperature sites ν(h4) = 4.5 × 10(8) s(-1) and between the low and high temperature states ν(h2) = 1.7 × 10(8) s(-1) at 160 K. An Arrhenius relationship of hop rate and temperature gave energy barriers of ΔE4 = 389 cm(-1) and ΔE2 = 656 cm(-1) between the two low temperature sites and between the low and high temperature states, respectively.

Polymer-Bound Oxidovanadium(IV) and Dioxidovanadium(V) Complexes As Catalysts for the Oxidative Desulfurization of Model Fuel Diesel

The Schiff base (Hfsal-dmen) derived from 3-formylsalicylic acid and N,N-dimethyl ethylenediamine has been covalently bonded to chloromethylated polystyrene to give the polymer-bound ligand, PS-Hfsal-dmen (I). Treatment of PS-Hfsal-dmen with [V(IV)O(acac)(2)] in the presence of MeOH gave the oxidovanadium(IV) complex PS-[V(IV)O(fsal-dmen)(MeO)] (1). On aerial oxidation in methanol, complex 1 was oxidized to PS-[V(V)O(2)(fsal-dmen)] (2). The corresponding neat complexes, [V(IV)O(sal-dmen)(acac)] (3) and [V(V)O(2)(sal-dmen)] (4) were similarly prepared. All these complexes are characterized by various spectroscopic techniques (IR, electronic, NMR, and electron paramagnetic resonance (EPR)) and thermal as well as field-emission scanning electron micrographs (FE-SEM) studies, and the molecular structures of 3 and 4 were determined by single crystal X-ray diffraction. The EPR spectrum of the polymer supported V(IV)O-complex 1 is characteristic of magnetically diluted V(IV)O-complexes, the resolved EPR pattern indicating that the V(IV)O-centers are well dispersed in the polymer matrix. A good (51)V NMR spectrum could also be measured with 4 suspended in dimethyl sulfoxide (DMSO), the chemical shift (-503 ppm) being compatible with a VO(2)(+)-center and a N,O binding set. The catalytic oxidative desulfurization of organosulfur compounds thiophene, dibenzothiophene, benzothiophene, and 2-methyl thiophene (model of fuel diesel) was carried out using complexes 1 and 2. The sulfur in model organosulfur compounds oxidizes to the corresponding sulfone in the presence of H(2)O(2). The systems 1 and 2 do not loose efficiency for sulfoxidation at least up to the third cycle of reaction, this indicating that they preserve their integrity under the conditions used. Plausible intermediates involved in these catalytic processes are established by UV-vis, EPR, (51)V NMR, and density functional theory (DFT) studies, and an outline of the mechanism is proposed. The (51)V NMR spectra recorded for solutions in methanol confirm that complex 4, on treatment with H(2)O(2), is able to generate peroxo-vanadium(V) complexes, including quite stable protonated peroxo-V(V)-complexes [V(V)O(O)(2)(sal-dmen-NH(+))]. The (51)V NMR and DFT data indicate that formation of the intermediate hydroxido-peroxo-V(V)-complex [V(V)(OH)(O(2))(sal-dmen)](+) does not occur, but instead protonated [V(V)O(O)(2)(sal-dmen-NH(+))] complexes form and are relevant for catalytic action.

Structure of Radicals from X-Irradiated Guanine Derivatives. 2. An Experimental and Computational Study of 9-Ethylguanine Single Crystals

An EPR (electron paramagnetic resonance) and ENDOR (electron-nuclear double resonance) study of 9-ethylguanine crystals X-irradiated at 10 K detected evidence for three radical forms. Radical R1, characterized by three proton and two nitrogen hyperfine interactions, was identified as the product of net hydrogenation at N7 of the guanine unit. R1, which evidently formed by protonation of the primary electron addition product, exhibited an unusually distorted structure leading to net positive isotropic components of the alpha-coupling to the hydrogen attached to C8 of the guanine unit. Radical R2, characterized by two nitrogen and three proton hyperfine couplings, was identified as the primary electron loss product, *G+. Distinguishing between *G+ and its N1-deprotonated product is difficult because their couplings are so similar, and density functional theory (DFT) calculations were indispensable for doing so. The results for R2 provide the most complete ENDOR characterization of *G+ presented so far. Radical R3 exhibited a narrow EPR pattern but could not be identified. The identification of radicals R1 and R2 was supported by DFT calculations using the B3LYP/6-311+G(2df,p)//6-31+G(d,p) approach. Radical R4, detected after irradiation of the crystals at room temperature, was identified as the well-known product of net hydrogenation at C8 of the guanine component. Spectra from the room temperature irradiation contained evidence for R5, an additional radical that could not be identified. Radical concentrations from the low temperature irradiation were estimated as follows: R1, 20%; R2, 65%; R3, 15%.

Identification and stability study of irradiated chicken, pork, beef, lamb, fish and mollusk shells by electron paramagnetic resonance (EPR) spectroscopy

The application of electron paramagnetic resonance (EPR) spectroscopy to the detection of irradiation treatment of bones of chicken, pork, beef, lamb, fish and mollusk shells was described. Induced radicals in irradiated samples gave distinguishable EPR patterns for differentiation from the unirradiated samples. The EPR signals were found to be relatively stable in mammalian bones and mollusk shells; but significant loss was observed in fish samples. Dose–response relationships of the samples were found to be linear at 0–5 kGy range (r2>0.95). Using calibration curve method, the irradiation status of all the 64 blind samples (14 unirradiated and 50 irradiated) was correctly identified. The estimation of irradiation doses was satisfactory with mean values ranging from 86 to 116% of those of the nominal values, and precision (%RSD) ranged from 15 to 29%. The validated analytical procedure was applied in the surveillance monitoring of about 400 food samples during the period of 2001–2004.

Roles of Chloride Ion in Microvia Filling by Copper Electrodeposition: II. Studies Using EPR and Galvanostatic Measurements

The interactions among additives employed in acidic copper plating solution for microvia filling are characterized by galvanostatic measurement (GM) and electron paramagnetic resonance (EPR), respectively. These additives include polyethylene glycol (PEG), chloride ion, 3-mercapto-1-propanesulfonate (MPS), and bis-(3-sulfopropyl) disulfide (SPS). EPR patterns show that MPS can reduce to before electrochemical reduction. However, the GMs show that MPS is an inhibiting reagent for copper electrodeposition. An inhibition mechanism of the MPS is proposed according to the EPR patterns. GMs also revealed that the combination of MPS and could result in a strongly catalytic effect on the reduction rate. This synergistic effect between MPS and on enhancing copper electrodeposition is attributed to an inner sphere electron transfer net constructed by a competitive coordination of MPS and on complexes. SPS also exhibits similar electrochemical behavior to MPS. However, the response speed of SPS in enhancing the reduction rate is slower than that of MPS. GM results obtained by adopting two different rotating speeds of the working electrode demonstrate that PEG competes with MPS to grab through and that the competitive adsorption between PEG- and on the cathodic surface is strongly convection-dependent. © 2005 The Electrochemical Society. All rights reserved.

EPR investigation of superparamagnetism in nanometric-size LaFeO3±δ and La2NiO4±δ perovskites

Two LaFeO3±δ and La2NiO4±δ catalysts characterized by high thermal stability and phase purity have been prepared. Scanning electron microscopy analysis showed that they consisted of 20–60 nm spheroids, generally clustered in one order of magnitude larger particles. Electron paramagnetic resonance (EPR) spectroscopy showed that both samples possess superparamagnetic properties, connected with ca. 20 nm diameter particles. Furthermore, the EPR patterns were broader in La2NiO4±δ than in LaFeO3±δ, indicating a greater amount of local disorder in the former. This was attributed to the presence of more oxygen vacancies in the Ni-based than in the Fe-based sample, in agreement with what was elsewhere hypothesized on the basis of catalytic properties of the two samples for the flameless combustion of methane.

Coordination scheme and stereochemical configuration of manganese(II) adenosine 5'-diphosphate at the active site of 3-phosphoglycerate kinase.

The structure of the MnIIADP complex at the active site of 3-phosphoglycerate kinase from yeast has been investigated by electron paramagnetic resonance (EPR) spectroscopy. Inhomogeneous broadening in the EPR signals for Mn(II) resulting from unresolved superhyperfine coupling to 17O regiospecifically incorporated into ADP shows that Mn(II) is coordinated to the alpha- and beta-phosphate groups of ADP at the active site of the enzyme. The EPR pattern for the enzyme-MnIIADP complex is characteristic of a predominantly axially symmetric zero-field splitting tensor. The symmetry and magnitude of the zero-field splitting interaction suggest that there is an additional negatively charged oxygen ligand in the coordination sphere of Mn(II). EPR measurements for solutions of the enzyme-MnIIADP complex in 17O-enriched water indicate that there are also two or three water molecules in the coordination sphere of the metal ion. EPR data for complexes with the two epimers of [alpha-17O]ADP have been used to determine the stereochemical configuration of the MnIIADP complex at the active site. EPR spectra for Mn(II) in the enzymic complex with (Rp)-[alpha-17O]ADP show an inhomogeneous broadening due to superhyperfine coupling with 17O whereas spectra for (Sp)-[alpha-17O]ADP complexes are indistinguishable from those for matched samples with unlabeled ADP. These results show that 3-phosphoglycerate kinase selectivity binds the alpha configuration of the alpha, beta chelate of MnIIADP. Addition of 3-phosphoglycerate to form the dead-end complex (enzyme-MnIIADP-3-phosphoglycerate) does not alter the EPR spectrum, but addition of vanadate to this complex causes marked changes in the spectral parameters.(ABSTRACT TRUNCATED AT 250 WORDS)

A model for the irradiative coloration of smoky feldspar and the inhibiting influence of water

Radiation-induced smoky color and associated electron paramagnetic resonance (EPR) signals develop only in potassium feldspar (KalSi_3O_8) free of structurally bound molecular water. Fluid inclusion water does not influence coloration. The integrated intensity of each of the four bands (11,600, 16,200, 19,100, and 27,200 cm^(−1)) in the optical absorption spectra are linearly correlated with the doubly-integrated intensity of a broad, asymmetric first derivative at g_(eff)=2.027 in EPR spectra. In microcline, the EPR pattern is resolved into an asymmetric six-line pattern at g_(eff)=2.024 and a single derivative at g_(eff)=2.009 which, based on analogy to alkali-silicate glass, are due respectively to [SiO_4/K^+]^(2+) and a hole shared between two nonbonding oxygens on Si. We propose that structural water inhibits formation of smoky centers in feldspar by releasing atomic hydrogen during irradiation which destroys centers while diffusing towards a stable site.

Reorientation Motions of theHA(Li+)Center in KCl:Li+

Through a combined electron paramagnetic resonance (EPR) and optical-absorption investigation, it is shown that the ${H}_{A}({\mathrm{Li}}^{+})$ interstitial center in KCl: ${\mathrm{Li}}^{+}$ exhibits two well-defined motions, the pyramidal motion (P. M.) and the restricted interstitial motion (R. I. M.). The P. M. possesses ${C}_{4v}$ symmetry around 100>: The ${\mathrm{Cl}}_{2}^{\ensuremath{-}}$ jumps around a given 100> direction among the four {110} half-planes. This thermally activated motion is responsible for the disorientation temperature ${T}_{D}(\mathrm{P}.\mathrm{M}.)=23.5$ K, around which all optical anisotropy produced at 4.2 K with 110> polarized light disappears, and for the lifetime broadening of the EPR lines above ${T}_{\mathrm{LB}}(\mathrm{P}.\mathrm{M}.)=75$ K. The P. M. is basically the same as the reorientation motions of the $H$ and ${H}_{{A}^{\ensuremath{'}}A}$ centers. The R. I. M. possesses ${C}_{3v}$ symmetry around 111>: The interstitial Cl exchanges molecular bonds with the three substitutional ${\mathrm{Cl}}^{\ensuremath{-}}$ ions that surround it. This motion is very similar to the ${V}_{K}$-center reorientation process. The thermally activated R. I. M. is responsible for the broadening of the EPR lines above ${T}_{\mathrm{LB}}(\mathrm{R}.\mathrm{I}.\mathrm{M}.)=29$ K, and at 75 K a motionally averaged ${\mathrm{Cl}}_{4}^{3\ensuremath{-}}$ EPR pattern of ${C}_{3v}$ symmetry is indeed observed. However, in the optical-anisotropy measurements no ${T}_{D}(\mathrm{R}.\mathrm{I}.\mathrm{M}.)$ is observed. It is concluded that the R. I. M. does not freeze in at low temperatures but goes over into a tunneling motion. As a result no optical anisotropy can be produced at 4.2 K with 100> polarized light. No differences have been observed so far for the R. I. M. and the P. M. between ${H}_{A}(^{6}\mathrm{Li}^{+})$ and ${H}_{A}(^{7}\mathrm{Li}^{+})$. A few comments are also made on the ${H}_{A}({\mathrm{Na}}^{+})$ center in KCl: ${\mathrm{Na}}^{+}$.

Studies of Trace Metal Metabolism: Electron Paramagnetic Resonance of Manganese in Ribonucleic Acids.

SummaryIn an attempt to elucidate the intramolecular bonding of trace metals in ribonucleic acids, measurements have been made of the electron paramagnetic resonance (EPR) spectrums of 36 samples of RNA isolated from human and rat tissues. The EPR pattern of manganese was readily detected in all of the samples of RNA. The resonance patterns indicate that manganese is present in RNA in a divalent state and suggest that manganese is located at the center of a distorted octahedron of oxygen atoms. From the intensity of nominally forbidden resonances, the crystal field splitting parameter D was estimated to be 0.02 cm-1.