Electron Magnetic Resonance Spectroscopy Research Articles

Selection rules in electron magnetic resonance (EMR) spectroscopy and related techniques: Fundamentals and applications to modern case systems

Allowed transitions observed using electron magnetic resonance (EMR) in transition metal (3dN or 4fN) complexes may be predicted by the selection rules. Non-standard selection rules justified by mixing of wavefunctions emerge for nominally forbidden transitions. We present tutorial guide on selection rules in EMR, optical, and inelastic neutron scattering spectroscopy. This includes basic concepts in quantum mechanics and group theory underlying derivations of selection rules and useful rules for nonzero matrix elements. These rules provide crucial information for practitioners. Survey of usage of selection rules in EMR and related studies of novel systems in emerging areas is provided at an introductory level. Applications to modern case systems include: parallel field EMR excitations for integer spin vs half-integer spin ions, nitrogen vacancies in diamond, Haldane gap systems, exchange coupled systems and molecular nanomagnets, and magnetic adatoms on surfaces. Various misconceptions concerning crucial notions, which constitute terminological confusion, have been clarified.

OXİDATİVE CONVERSİON OF METHANE. EFFECT OF CATALYST AND PERSPECTİVE DİRECTİONS OF REACTİON

The well-known MnNaW catalysts based on SiO2 for oxidative condensation of methane (OCM) were synthesized by various methods, characterized by X-ray diffractometry (XRD), scanning electron microscopy with energy dispersive elemental analysis (SEM/EDX), electron magnetic resonance (EMR) spectroscopy, N2 adsorption-desorption measurements, and tested as OCM catalysts at atmospheric pressure to convert into a mixture of ethylene + carbon oxides for further hydroformylation to propylene. The structural and catalytic features of the synthesized systems are discussed. The necessity of using mainly X-ray diffraction, Raman, and EMR methods for studying catalysts in situ mode in combination with online MS analysis of gasphase reaction products to establish the nature of catalytically active phases, centers, their mechanism of functioning, activation of CH4 with the formation of C-C bond for the synthesis of hydrocarbons C2 and C2+ is considered. Keywords: oxidative conversion of methane, NaMnW/SiO2 catalyst, ethylene-carbon monoxide mixture, magnetic, texture properties

Structural and magnetic study of the iron cores in iron(III)-polymaltose pharmaceutical ferritin analogue Ferrifol®

Iron(III)-polymaltose pharmaceutical ferritin analogue Ferrifol® was investigated by high resolution transmission electron microscopy (HRTEM), X-ray diffraction, thermogravimetry, electron magnetic resonance (EMR) spectroscopy, direct current magnetization measurements and 57Fe Mössbauer spectroscopy to get novel information about the structural arrangement of the iron core. The Ferrifol® Mössbauer spectra measured in the range from 295 K to 90 K demonstrated non-Lorentzian two-peak pattern. These spectra were better fitted using a superposition of 5 quadrupole doublets with the same line width. The obtained Mössbauer parameters were different and an unusual line broadening with temperature decrease was observed. Measurements of the Ferrifol® Mössbauer spectra from 60 K to 20 K demonstrated a slow decrease of magnetic relaxation in the iron core. Zero-field-cooled and field-cooled magnetization measurements revealed a blocking temperature at ~33 K and a paramagnetic state of the Ferrifol® iron core at higher temperatures. Isothermal magnetization measurements at 5 K show that the saturation magnetic moment is ~0.31 emu/g. X-band EMR spectroscopy measurements revealed the presence of different magnetic species in the sample. Transmission electron microscopy demonstrated that the size of the iron cores in Ferrifol® is in the range 2–6 nm. The lattice periodicity in these iron cores, measured on the HRTEM images, vary in the range 2.2–2.7 Å. This can be best understood as sets of close packed O(OH) layers in ferrihydrite cores without long range correlation.

Radical Intermediates in Reactions of Mixed Phosphonium–Iodonium Ylides

The active intermediates generated in the photolysis of phosphonium–iodonium ylides and their reaction with acetylenes have been studied with electron and nuclear magnetic resonance spectroscopy. The radical mechanism of the ylides decomposition and of the interaction with acetylenes has been established using a stable nitroxyl radical. The radical products of these reactions have been monitored for the first time by EPR, and their spectroscopic parameters were determined. The chemical structure of the active intermediates of the reactions under study has been proposed.

The effect of preparation conditions on magnetite nanoparticles obtained via chemical co-precipitation

Chemical stability and good biocompatibility under physiological conditions render nanoparticles made of the spinel oxide magnetite a favorable choice in biomedical diagnostic and therapeutic applications that benefit from high levels of magnetization and superparamagnetism. Under ambient atmosphere, however, magnetite nanoparticles are prone to undesired oxidation leading to an at least partially oxidized form of magnetite. In the present work Fe3-xO4 nanopowders (with a particle size of 10–50 nm) were prepared under different conditions via chemical co-precipitation method, resulting in samples with different oxidation levels. The effect of oxidation of the prepared samples on their morphological, structural, electronic and magnetic properties is followed, respectively, by the means of transmission electron microscopy (TEM), powder X-ray diffractometry (PXRD), 57Fe Mössbauer spectroscopy (MS) and electron magnetic resonance (EMR) spectroscopy measurements. A novel method is applied to decompose the heavily broadened room-temperature 57Fe Mössbauer spectra of the nanoparticles into signals of intermediate valence Fe2.5+ and that of Fe3+ iron species. The results indicate that the cubic lattice parameter of non-stoichiometric magnetite nanoparticles depends on the concentration as well as on the mean oxidation level of the intermediate valence iron species. At the same time, EMR spectra of the samples indicate that oxidation influences the magnetic anisotropy of the nanoparticles, with the magnitude of the nanoparticles' magnetic anisotropy field being correlated with the concentration of the intermediate valence iron species. Malic acid, used as coating agent for several of the samples, is shown to hinder the oxidation of magnetite nanoparticles.

Proteomics-based identification of hypoxia-sensitive membrane-bound proteins in rat erythrocytes

This study examines the action of hypoxia on integrity, fluidity and protein composition of red blood cell (RBC) membrane. Twenty-min exposure to oxygen-free environment decreases rat RBC integrity documented by 3-fold elevation of hemoglobin release without any action on the membrane fluidity estimated by electron magnetic resonance spectroscopy of spin-labeled stearic acid analogues. The proteomics technology in combination with relative label free quantification analysis revealed a dozen of membrane-bound proteins, including elevated content of hemoglobin, reproducibly affected by hypoxia. Mapping the identified proteins in the KEGG pathway database we found that the proteins of multi subunit Cullin-Rbx E3 ubiquitin ligase complex are presented in normoxic RBC ghosts but not in the hypoxic samples. Our results suggest that Cullin-Rbx E3 complex, associated with RBC membrane in normoxia, provides detection and deletion of membrane proteins damaged by reactive oxygen species. In hypoxic conditions, deoxy-Hb binds to band 3 protein, resulting in dissociation of Cullin-Rbx E3 complex from RBC membrane and impaired clearance of damaged cytoskeleton proteins. These rearrangements of membrane proteins might be involved in attenuated membrane integrity revealed in hypoxic RBC. SignificanceThis study demonstrate that sustained deoxygenation of rat erythrocytes alters the composition of membrane-bound proteins including elevation of the content of hemoglobin without any changes in the viscosity of erythrocyte membrane lipid bilayer. These results suggest that the changes the composition of membrane proteins result in attenuated membrane integrity and contribute to augment release of hemoglobin seen in hypoxic conditions.

Grain Size Effect on the Magnetic Properties of Sm0.08Ca0.92MnO3 Manganite

Here we present a comparative study of the temperature dependent magnetic properties of nanosized and bulk samples of Sm0.08Ca0.92MnO3 (SCMO) manganite. Nanoparticles of SCMO (mean diameter ∼ 27, 22 and 16 nm) were synthesized by sol-gel technique and the bulk samples were obtained by sintering the nanoparticles at high temperatures. The samples were characterized by X-ray powder diffraction, energy dispersive X-ray analysis and transmission electron microscopy. The magnetic properties were studied by SQUID magnetometer and Electron magnetic resonance (EMR) spectroscopy. Temperature dependence of dc-magnetization showed that the nanoparticles underwent ferromagnetic transition at 103 K where as the bulk sample showed the same at 105 K. The field cooled curve shows that the magnetization decreases with the size reduction. The EMR studies substantiate the presence of ferromagnetism in the bulk sample as well as in nanosamples but with a weakened strength in nanosamples. In manganites linewidth shows a characteristic minimum near 1.1 TC where TC is the FM transition temperature. We observe this minimum becomes less shallow as the size decreases. The behaviour of the nanoparticles is ascribed to core shell model; reduction of magnetization in the nanoparticles is due to uncompensated surface spin.

Magnetic Resonance Spectroscopy as a Tool for Assessing Macromolecular Structure and Function in Living Cells.

Investigating the structure, modification, interaction, and function of biomolecules in their native cellular environment leads to physiologically relevant knowledge about their mechanisms, which will benefit drug discovery and design. In recent years, nuclear and electron magnetic resonance (NMR) spectroscopy has emerged as a useful tool for elucidating the structure and function of biomacromolecules, including proteins, nucleic acids, and carbohydrates in living cells at atomic resolution. In this review, we summarize the progress and future of in-cell NMR as it is applied to proteins, nucleic acids, and carbohydrates.

Intra-particle chemical homogeneity determining the exchange coupling in palladium-iron nanoparticles

The interplay between chemical inhomogeneities and magnetic properties in iron alloys is a subtle question that affects several nanoalloys with potential technological and biomedical applications. Herein below, we focus on the FCC palladium rich–iron nanoparticle system, specifically in three samples that reflect the key influence of synthesis conditions. Magnetic measurements as a function of field and temperature have allowed detecting the onset of anomalous relaxation phenomena of the magnetization due to the strong weakening of the exchange coupling in nanoparticles prepared at low temperatures. Such effects are triggered by the lack of a good inter-diffusion of atomic species during core growth and directly affect the magnetic anisotropy. Electron Magnetic Resonance spectroscopy has confirmed that iron clustering leads to a gradual transition from a superparamagnetic state at low temperatures to a nearly paramagnetic behaviour at high temperatures. The measurements of the g-factor and the average magnetic moment per Fe atom do not account for a significant polarization in Pd atoms.

An EPR Study of Small Magnetic Nanoparticles

Abstract Magnetic nanoparticles (MNPs) of spinel type iron oxide (of approximately 4 nm) mineralized inside the internal cavity of a mini ferritin-type protein have been investigated by means of electron magnetic resonance (EMR) spectroscopy. EMR measurements have been recorded at different temperatures in perpendicular and parallel configurations. The spectra have been interpreted using an approach based on the giant spin model. We confirm the quantum behavior of the MNPs, moreover, the thermal evolution of the spin system in terms of population of excited spin states is showed.

Antitumor magnetic hyperthermia induced by RGD-functionalized Fe3O4 nanoparticles, in an experimental model of colorectal liver metastases.

This work reports important advances in the study of magnetic nanoparticles (MNPs) related to their application in different research fields such as magnetic hyperthermia. Nanotherapy based on targeted nanoparticles could become an attractive alternative to conventional oncologic treatments as it allows a local heating in tumoral surroundings without damage to healthy tissue. RGD-peptide-conjugated MNPs have been designed to specifically target αVβ3 receptor-expressing cancer cells, being bound the RGD peptides by “click chemistry” due to its selectivity and applicability. The thermal decomposition of iron metallo-organic precursors yield homogeneous Fe3O4 nanoparticles that have been properly functionalized with RGD peptides, and the preparation of magnetic fluids has been achieved. The nanoparticles were characterized by transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), electron magnetic resonance (EMR) spectroscopy and magnetic hyperthermia. The nanoparticles present superparamagnetic behavior with very high magnetization values, which yield hyperthermia values above 500 W/g for magnetic fluids. These fluids have been administrated to rats, but instead of injecting MNP fluid directly into liver tumors, intravascular administration of MNPs in animals with induced colorectal tumors has been performed. Afterwards the animals were exposed to an alternating magnetic field in order to achieve hyperthermia. The evolution of an in vivo model has been described, resulting in a significant reduction in tumor viability.

Vehement Competition of Multiple Superexchange Interactions and Peculiar Magnetically Disordered State in Cu(OH)F

The mixed anion copper compound Cu(OH)F was studied in measurements of dc- and ac-magnetic susceptibility, static and pulsed field magnetization, specific heat, X-band electron magnetic resonance and muon-spin spectroscopy. In variance with its layered structure, the magnetic behavior shows no evidence of low-dimensionality. Cu(OH)F reaches short range static antiferromagnetic order at TN = 9.5–11.5 K and experiences the spin-flop transition at B ∼ 3.5 T. This behavior is in a sharp contrast with physical properties of earlier reported isostructural compound Cu(OH)Cl. The first principle calculations reveal highly competitive nature of ferromagnetic and antiferromagnetic superexchange interactions, the details being rather sensitive to choice of magnetic structure employed in the extraction of magnetic interaction. Rather broad anomaly in Cp(T) dependence at phase transition and smeared magnetization curve M(B) at low temperatures suggest static disorder at low temperatures however no frequency dependence...

EMR study and superposition model analysis of Cr3+ and Fe3+ impurity ions in mullite powders used in aerospace industry

Abstract In this work, the electron magnetic resonance (EMR) spectra of the mullites powders were measured for different grain sizes (0.07 and 0.12 mm). We have used EMR spectroscopy at X-band, combined with superposition model (SPM) calculations to reveal electronic structure and establish correlations between structure, and surroundings of these complexes.

Copper-manganese-zinc spinels in zeolites: study of EMR spectra

Abstract The aim of this study is the application of electron magnetic resonance (EMR) spectroscopy to determine the interactions between NaY and HY zeolites and Cu-Mn-Zn spinels loaded onto the zeolite surfaces. The materials were characterized using XRD and IR spectroscopies. Four types of EMR lines were observed for Cu-Mn-Zn/NaY, Cu-Mn-Zn/HY samples. The difference between the EMR spectra recorded at 77 and 293 K has been shown. The spectra recorded at 77 K allowed us to distinguish between the species formed on NaY and HY zeolites. The EMR spectrum of Cu-Mn-Zn/NaY recorded at 77 K showed only one line attributed to antiferromagnetic spinels Cu1.4Mn1.6O4 and ZnMn2O4 or/and Cu0.5Zn0.5Mn2O4. The spinels appeared to be more stable (more strongly attached) on HY zeolite than on NaY one. It was proved that different strength of interactions between the zeolites and Cu-Mn-Zn spinels was caused by differences in the acidity of NaY and HY zeolites.

Síntese e caracterização de nanopartículas de NiFe2O4 utilizando o método de sol-gel/combustão e combustão homogênea

O presente trabalho teve por finalidade a síntese de nanopartículas de NiFe2O4 utilizando o método de sol-gel/combustão e combustão homogênea. As nanopartículas foram caracterizadas por difração de raios X, ressonância magnética eletrônica (RME) e espectroscopia de infravermelho de transformada de Fourier (IV-FT). As medidas de raios X foram usadas para caracterizar e estimar o tamanho médio dos cristalitos. Nos espectros de infravermelho, são observadas a formação da fase ferrítica e a influência do tamanho médio de cristalitos em todas as amostras que apresentaram alto grau de cristalinidade, já que a banda de infravermelho na faixa de 600-550 cm-1 é característica por sítios tetraédricos da ferrita. Os espectros de ressonância magnética eletrônica mostram que as partículas sintetizadas possuem dimensão nanométrica.

Temperature dependence of electron magnetic resonance spectra of iron oxide nanoparticles mineralized in Listeria innocua protein cages

Electron magnetic resonance (EMR) spectroscopy was used to determine the magnetic properties of maghemite (γ-Fe(2)O(3)) nanoparticles formed within size-constraining Listeria innocua (LDps)-(DNA-binding protein from starved cells) protein cages that have an inner diameter of 5 nm. Variable-temperature X-band EMR spectra exhibited broad asymmetric resonances with a superimposed narrow peak at a gyromagnetic factor of g ≈ 2. The resonance structure, which depends on both superparamagnetic fluctuations and inhomogeneous broadening, changes dramatically as a function of temperature, and the overall linewidth becomes narrower with increasing temperature. Here, we compare two different models to simulate temperature-dependent lineshape trends. The temperature dependence for both models is derived from a Langevin behavior of the linewidth resulting from "anisotropy melting." The first uses either a truncated log-normal distribution of particle sizes or a bi-modal distribution and then a Landau-Liftshitz lineshape to describe the nanoparticle resonances. The essential feature of this model is that small particles have narrow linewidths and account for the g ≈ 2 feature with a constant resonance field, whereas larger particles have broad linewidths and undergo a shift in resonance field. The second model assumes uniform particles with a diameter around 4 nm and a random distribution of uniaxial anisotropy axes. This model uses a more precise calculation of the linewidth due to superparamagnetic fluctuations and a random distribution of anisotropies. Sharp features in the spectrum near g ≈ 2 are qualitatively predicted at high temperatures. Both models can account for many features of the observed spectra, although each has deficiencies. The first model leads to a nonphysical increase in magnetic moment as the temperature is increased if a log normal distribution of particles sizes is used. Introducing a bi-modal distribution of particle sizes resolves the unphysical increase in moment with temperature. The second model predicts low-temperature spectra that differ significantly from the observed spectra. The anisotropy energy density K(1), determined by fitting the temperature-dependent linewidths, was ∼50 kJ/m(3), which is considerably larger than that of bulk maghemite. The work presented here indicates that the magnetic properties of these size-constrained nanoparticles and more generally metal oxide nanoparticles with diameters d < 5 nm are complex and that currently existing models are not sufficient for determining their magnetic resonance signatures.

Comparison of magnetic properties of DNA-cetyltrimethyl ammonium complex with those of natural DNA

We prepared the DNA-cetyltrimethyl ammonium complex, as well as the same complex intercalated with stable organic free radicals, and studied their magnetic properties by electron magnetic resonance (EMR) spectroscopy and by measuring the magnetization on a superconducting quantum interference device (SQUID). The UV-vis and CD spectra of DNA-quaternary alkyl ammonium complex (DNA−-Q+) in organic solvent clearly demonstrated that it retained the double helical B-form conformation. The interhelical spacing of double strand DNA (dsDNA) increased when the counter ions (Na+) of phosphate groups of the natural DNA were replaced with the long alkyl quaternary ammonium groups. The inter-helical distance of DNA-cetyltrimethyl ammonium (CTMA) was 39.1 A as confirmed by X-ray diffractometry. In general, the magnetization of the DNA-CTMA complex solid was found to be significantly lower than that of natural DNA. Moreover, intercalation of the complex with stable organic free radicals did not improve magnetization, which again was in marked contrast to natural DNA. EMR spectroscopic behavior of the complex in the solid state also was quite different from that of natural DNA: The unique broad EMR signal of natural DNA in the low field region with g-value greater than 10 disappeared in the DNA-CTMA complex.

Adsorption of Polyethylene-Glycols by Nanosized Iron Oxides Particles in Iron Oxides/Polyethylene-Glycol/Water/ Dispersions

The successful application of dynamic light scattering and electron magnetic resonance spectroscopy technique to control the formation of nanosized particles of iron oxides in iron oxides containing aqueous polyethylene-glycol dispersions is shown. The formation of the pegylated iron oxides particles with superparamagnetic properties in this system is established.

Magnetic properties of (Fe, Fe–B)/γ-Fe 2O 3 core shell nanostructure

Temperature-dependent magnetic properties of a core/shell nanostructure are reported employing magnetometry and electron magnetic resonance (EMR) spectroscopy. Structural characterization of the sample synthesized by NaBH 4 reduction of FeCl 3 was done by x-ray diffraction, TEM and Mössbauer spectroscopy and showed a core/shell nanostructure with a core of diameter D≃20 nm consisting of α-Fe and amorphous Fe–B alloy and a shell of 7 nm thickness made up of principally γ-Fe 2O 3. Temperature-dependent EMR studies at 9.28 GHz show a narrow line with g≃2.01 superimposed on a broad line with g≃2.20. The narrow line assigned to the oxide shell disappears below about 60 K, in agreement with a blocking temperature T B≃30 K measured in SQUID magnetometry. The EMR parameters of the broad EMR line are similar to those reported for α-Fe nanoparticles imbedded in amorphous SiO 2 matrix. The magnitude of the saturation magnetization M S=70 emu/g of the nanostructure is smaller than that of bulk α-Fe ( M S=220 emu/g) and bulk γ-Fe 2O 3 ( M S=88 emu/g). Size dependence is used to interpret the absence of exchange-bias in the field-cooled sample of the nanostructure.

Temperature and size dependence of magnetic and electron magnetic resonance parameters of Fe nanoparticles embedded in an amorphous SiO2 matrix

Temperature dependence (5 K to 300 K) of the magnetic properties of two Fe/SiO2 (15/85) nanocomposites with Fe particle size D ≃ 17 nm and 30 nm is reported using magnetometry and electron magnetic resonance (EMR) spectroscopy. Structural characterization of the samples, done by X-ray diffraction, TEM, and Mössbauer spectroscopy shows the presence of α-Fe, amorphous SiO2, and some nanosize Fe3+ oxides. Both samples are ferromagnets in the 5 K to 370 K range with coercivity HC(30 nm) &amp;gt; HC(17 nm). In EMR studies, a single resonance line near g = 2.2 characteristic of α-Fe is observed in both samples at 300 K, with linewidth ΔH(30 nm) &amp;gt; ΔH(17 nm). With decreasing temperature, the EMR line shifts to lower fields and broadens, which is similar to observations in other nanoparticle systems.