Analysis Of Electron Paramagnetic Resonance Spectra Research Articles

Structural and optical properties of silicon oxycarbide thin films using silane based precursors via sol-gel process

Silicon oxycarbide (SiCxOy) is a candidate material for white luminescence. This work investigates the formation of SiCxOy thin film coating by sol-gel route using various silanes namely, methyltrimethoxy silane (MTMS) with or without using tetraethyl orthosilicate, vinyltrimethoxysilane and polydimethyl siloxane, followed by calcination at 1000 °C/1 h under Ar atmosphere. The structural and optical properties of the developed films were studied by X-ray diffractomete (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), electron paramagnetic resonance (EPR) spectroscopy and Photoluminescence (PL). XRD plot shows amorphous nature of silicon oxycarbide (SiCxOy) while FTIR reveals Si-C band at 795 cm−1 and Si-O-Si band at 1085 cm−1 confirming the presence of SiCxOy. XPS analysis of MTMS derived coating revealed stoichiometry of SiC0.3O2.25 which is comparable to SiCxOy (0.2<x<0.6, y<1.6). EPR spectra analysis shows presence of Si-dangling bond which could be the probable cause of luminescence center in SiCxOy as observed from PL study. FESEM shows uniform coating of thickness ∼200 nm. PL spectra shows blue and green emission peaks at ∼ 403–452 and ∼ 483–560 nm, respectively.

Influence of rare-earth La3+ ion doping on microstructural, magnetic and dielectric properties of Mg0.5Ni0.5Fe2-xLaxO4 (0 ≤ x ≤ 0.1) ferrite nanoparticles

A series of La3+ ion doped magnesium nickel ferrites, Mg0.5Ni0.5Fe2-xLaxO4 (0 ≤ x ≤ 0.1) having a cubic spinel structure were prepared by the co-precipitation method. Various characterization techniques, including X-ray diffractometer (XRD), high resolution transmission electron microscopy (HR-TEM), electron spin resonance (ESR) and vibrating sample magnetometer (VSM) were used to investigate structural and magnetic properties. The average crystallite size decreases and lattice parameter increases with La3+ ion doping and lie in the range of 12–7 nm and 8.347–8.361 Å respectively. Analysis of ESR spectra reveals that, g-value with La3+ ion addition decreases from 2.57 to 2.12. The saturation magnetization and the coercivity decrease with increasing rare-earth content. Magnetic-hysteresis (M − H) loop shifts from a ferromagnetic to a superparamagnetic nature with La3+ ion addition. The dielectric study was carried out in the frequency range of 1 KHz to 4000 KHz and temperature ranging 30 °C–350 °C using the impedance analyzer. The dielectric constant decreases with increasing frequency and the La3+ ion concentration. The dielectric loss of the sample increases with increasing temperature. The magnetic properties of the synthesized nanoparticles make them a potential material for stable ferrofluid application and the low tangent loss value makes these material a potential candidate for frequency-based applications.

Sucrose enhances the chromogenic ability ofStaphylococcus xylosusby improving nitric oxide synthase activity

AbstractIn this paper, the effect of different concentrations of sucrose stress on color formation of the Staphylococcus xylosus was investigated. The results showed that the highest a* value and the best coloring effect similar to those of nitrite were observed after the addition of 0.05 g/mL sucrose to stress the S. xylosus. UV-Vis and electron spin resonance spectra analysis showed that production of coloring product Mb-NO was significantly enhanced after 0.05 g/mL sucrose stress. The growth curve, reactive oxygen content, cell cycle, nitric oxide synthase (NOS) activity, zeta potential, cell size, and protein composition of S. xylosus were investigated to reveal the mechanism of sucrose stress to enhance the coloring effect of the strain. The result showed that sucrose inhibited the growth of S. xylosus, which changed the physiological state by activating the oxidative stress response. The stress altered the rate of intracellular metabolism of S. xylosus by delaying the cell cycle and increasing cell surface zeta potential and cell particle size. These changes altered the protein composition of the cells and significantly enhanced the activity of intracellular NOS, which could improve the chromogenic ability of S. xylosus. This study will provide theoretical support for sucrose stress on S. xylosus to enhance its coloring effect, and sucrose stress for S. xylosus might be a promising biological alternative to nitrite in meat products.

Generation of hydroxyl radicals via activation of Cr(VI) by UVA-LED for rapid decontamination: The important role of Cr(V).

Hexavalent chromium (Cr(VI)) was activated by ultraviolet-A light-emitting diode (UVA-LED), resulting in efficient removal of various pollutants, including dye, pharmaceuticals, and pesticides, with pseudo-first-order rate constants of 0.0610-0.159min-1. Comparatively, UVA-LED or Cr(VI) alone barely degraded selected pollutants. Both HO• and Cr(V) were produced in the UVA-LED/Cr(VI) system based on scavenging and probing experiments, UV-visible and electron spin resonance spectra analysis. HO• was demonstrated to be the dominant reactive species via stepwise regeneration of Cr(V) to Cr(VI). The quantum yield of HO• was determined to be 7.79×10-4 mol Es-1 at a Cr(VI) dosage of 0.5mM and pH of 6.0. Additionally, the degradation efficiency of sulfamethoxazole (SMX) as a model compound decreased linearly as UVA-LED wavelengths increased from 365 to 405nm, while SMX was barely degraded at visible light irradiation wavelength ranges (449-505nm). SMX degradation efficiency increased from 71.0 % to 97.5 % as Cr(VI) dosage increased from 0.05 to 0.7mM. pH displayed a negative impact on SMX degradation with its removal efficiency decreasing from 99.4 % to 13.3 % as pH increased from 3.0 to 9.0. This study first reported that HO• was generated via activation of Cr(VI) by UVA-LED, which is instructive for the removal of pollutants co-existed in chromium-containing wastewater.

Methodology and Instrumentation for Electron Paramagnetic Resonance Dosimetry With Tooth Enamel

Abstract When tooth enamel is exposed to ionizing radiation, it generates a dose-dependent concentration of free radical centers (i.e., unpaired electrons). The concentration of these free radical centers is identified and quantified using electron paramagnetic resonance (EPR) spectroscopy in the form of an EPR spectrum. The intensity of the spectrum is proportional to the absorbed dose. Four international intercomparisons have already demonstrated that the EPR tooth enamel dosimetric technique is reliable for retrospective dose assessment in acute and chronic exposure scenarios. Additionally, EPR dosimetry is regarded same as a gold standard for reconstructing the total lifetime dose of individuals using tooth enamel. The accuracy and reproducibility of EPR dose reconstruction depend on the sample preparation, spectrum acquisition, and EPR spectra analysis techniques. So, this paper reviews some of the widely applied and accepted laboratory protocols or methodologies for the EPR dosimetric methods. The minimum detection limit in tooth enamel using this technique was 30 mGy. So, this review aims to share these protocols so that it would be easy to reconstruct the accident doses or chronic exposures with reliable accuracy and precision. Different bands (e.g., L, X, Q, etc.) continuous wave (CW) EPR spectrometers have been used in many historical and accident dose reconstructions; however, due to the availability, moderate price, and not being much influenced by the small amount of moisture in a sample, the X-band has been widely used. A well-developed methodology, a highly sensitive EPR spectrometer, and a well-trained operator are vital for the reliable measurements of absorbed low doses in EPR dosimetry with tooth enamel.

Characterization of Paramagnetic Iron-Sulfur Clusters Using Electron Paramagnetic Resonance Spectroscopy.

Continuous-wave (CW) electron paramagnetic resonance (EPR) spectroscopy is a powerful ally in characterizing the multitude of redox-active iron-sulfur cluster-containing ([Fe-S]) species present in biological samples. The technique detects only those clusters that are paramagnetic-having a nonzero total electron spin (S>0)-thus, it can discriminate between clusters in different oxidation states. The low-temperature CW-EPR spectrum of an [Fe-S] yields the three magnetic g-values that serve as a fingerprint of its electronic structure. This chapter briefly describes the underlying theory that defines this electronic structure and provides a recipe for the acquisition and analysis of EPR spectra of [Fe-S] proteins.

Facile preparation of PAN@Ag–Ag2O/TiO2 nanofibers with enhanced photocatalytic activity and reusability toward oxidation of As(III)

Visible light response PAN@Ag–Ag2O/TiO2 (PAN@AT) nanofibers with different mass ratios between Ag–Ag2O and TiO2 were synthesized via a facile electrospinning technique and pH-induced precipitation reaction. X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscope analyses manifest the formation of Ag–Ag2O/TiO2 heterojunctions, and Ag–Ag2O/TiO2 nanoparticles are evenly distributed on PAN nanofibers. The fabricated nanofibers show a highly photocatalytic performance toward As(III) oxidation under visible light, and the conversion is 92.1% after 120-min reaction at pH 5.0 in the system of PAN@AT4. Furthermore, conversion of As(III) can retain 88.6% of the original activity after repeating four cycles, indicating the good recyclability of PAN@AT4 nanofibers. Quenching experiments and electron spin resonance spectra analysis further demonstrate that the predominate active species for As(III) oxidation by PAN@AT4 are h+ and ·OH. The enhanced catalytic activity of PAN@AT4 is therefore ascribed to the formation of Ag–Ag2O/TiO2 heterojunctions on PAN surface and the efficient separation of photoinduced electron–hole pairs. This study provides a new material to oxidize reducing pollutants [such as As(III)] and also sheds light on the fabrication of recyclable photocatalysts.

Activated peroxydisulfate by sulfidated zero-valent iron for enhanced organic micropollutants removal from water

Recently, sulfidation of zerovalent iron (S-ZVI) has gained increasing attention due to its merits to mediate the electron transfer from Fe0 core to reactants at the water-particle interface. However, few studies have attempted so far to use the unique properties of S-ZVI to activate peroxydisulfate (PDS) under both oxic and anoxic conditions. Hence, in this study, the performance of S-ZVI in activating PDS was systematically evaluated at various conditions. As expected, under oxic conditions, S-ZVI could enhance the acetaminophen (ACT) removal rate by 2.4–5.1 folds compared to unmodified ZVI, and this enhancing effect works well over the tested initial pH range of 3.0–8.5. Likewise, under anoxic conditions, S-ZVI still performed better than unmodified ZVI. But interestingly, both ZVI and S-ZVI achieved better PDS activation with the absence of O2, despite in which comparable or much less Fe0 were consumed. This may be ascribed to the multiple roles of O2 which could not only enhance the Fe0 to generate Fe2+ but also compete with PDS significantly for the generated Fe2+. Through quenching experiments and electron spin resonance spectra analysis, SO4•− and HO• were identified to be involved in Fe0/PDS process. Moreover, taking PMSO as a probe, Fe(IV) was also confirmed to be generated in both ZVI/PDS and S-ZVI/PDS systems. Taking four other microcontaminants and a real groundwater sample, the broad applicability of S-ZVI/PDS was further evaluated. All these results would favor the fundamental understanding of Fe0/PDS process and thus help to facilitate its application.

Strategic combination of N-doped graphene and g-C3N4: Efficient catalytic peroxymonosulfate-based oxidation of organic pollutants by non-radical-dominated processes

In this study, two metal-free materials, i.e., N-doped graphene (rGO-N) and g-C3N4, were strategically combined to prepare a novel g-C3N4/rGO-N composite for activating peroxymonosulfate (PMS). The g-C3N4/rGO-N composite showed large specific surface area and high graphite-rich N content, and hence, exhibited excellent catalytic performance because of the synergistic effect of g-C3N4 and rGO-N. The oxidative system could effectively degrade various pollutants (e.g., acid orange 7, orange G, ciprofloxacin, and bisphenol A). The radical quenching experiments and electron paramagnetic resonance spectra analysis revealed that the novel carbonaceous composite could realize PMS-based non-radical oxidative degradation of pollutants unlike the previously reported catalysts, observed the degradation via a radical-dominated pathway. The real-time water treatment experiments demonstrated the potential of the oxidative system to environmental remediation applications. The combination strategy provides an innovative approach to fabricate binary metal-free carbonaceous catalysts for carrying out PMS-based non-radical oxidative degradation of pollutants.

Competition between Singlet Fission and Spin-Orbit-Induced Intersystem Crossing in Anthanthrene and Anthanthrone Derivatives.

Singlet and triplet excited-state dynamics of anthanthrene and anthanthrone derivatives in solution are studied. Triisopropylsilyl- (TIPS) or H-terminated ethynyl groups are used to tune the singlet and triplet energies to enable their potential applications in singlet fission and triplet fusion processes. Time-resolved optical and electron paramagnetic resonance (EPR) spectroscopies are used to obtain a mechanistic understanding of triplet formation. The anthanthrene derivatives form triplet states efficiently at a rate (ca. 107 s-1 ) comparable to radiative singlet fluorescence processes with approximately 30 % triplet yields, despite their large S1 -T1 energy gap (>1 eV) and the lack of carbonyl groups. In contrast, anthanthrone has a higher triplet yield (50±10 %) with a faster intersystem crossing rate (2.7 108 s-1 ) because of the n-π* character of the S1 ←S0 transition. Analysis of time-resolved spin-polarized EPR spectra of these compounds reveals that the triplet states are primarily generated by the spin-orbit-induced intersystem crossing mechanism. However, at high concentrations, the EPR spectrum of the 4,6,10,14-tetrakis(TIPS-ethynyl)anthanthrene triplet state shows a significant contribution from a non-Boltzmann population of the ms =0 spin sublevel, which is characteristic of triplet formation by singlet fission.

Spectroscopic Study of Mn2+ Doped PbS Nanocrystals

Mn2+ doped PbS (PbS:Mn2+) semiconductor nanocrystals have been synthesized by standard chemical method and characterized using various techniques for possible applications in quantum dots. This work describes new physical properties of these nanocrystals that have emerged from our investigations. The PbS:Mn2+ nanocrystals have cubic structure (space Group Fm3m) and the average crystallite size lies between 5 and 10 nm as characterized by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) analysis. The structural properties of PbS:Mn2+ nanoparticles are also studied by UV/Vis absorption spectrum and High-Resolution Transmission Electron Microscopy (HRTEM). The quantitative chemical analysis of pure and Mn2+ doped PbS nanocrystals has been done by Energy Dispersive Spectroscopy (EDS) spectra. The energy band gaps have been determined by UV/Vis absorption study using Tauc Plot as (in eV):1.79, 1.90, 2.23, and 2.39 for Mn2+ concentration equal to 0, 0.05, 0.26, and 0.52%, respectively. The luminescence behavior of the nanocrystals has been studied by photoluminescence (PL) spectra. The magnetic and electronic properties of PbS:Mn2+ nanocrystals were studied using Electron Paramagnetic Resonance (EPR) spectroscopy. Analysis of EPR spectra enabled determination of the electronic g-factor, the second-rank axial zero-field splitting parameter D and the hyperfine parameter A.

Probing the orientation of porphyrin oligomers in a liquid crystal solvent – a triplet state electron paramagnetic resonance study

ABSTRACTLinear porphyrin oligomers have found various applications as synthetic molecular wires in the context of light harvesting, solar energy conversion and molecular electronics. In many of these applications a partial ordering of the molecules helps to improve the reaction efficiency or device performance. In this work we study the orientational properties of the building blocks of such porphyrin-based molecular wires, namely a porphyrin monomer and the corresponding butadiyne-bridged dimer. The porphyrins have been embedded in the nematic liquid crystal solvent 4-cyano-4'-pentylbiphenyl (5CB) and the anisotropic properties of their photogenerated triplet states were characterised by transient electron paramagnetic resonance (EPR) spectroscopy. When aligned in strong magnetic fields, the liquid crystal molecules impose their orientational anisotropy onto the solute guest molecules whose orientation-dependent magnetic properties can then be explored. The line shape analysis of the porphyrin triplet state EPR spectra – highly sensitive to small conformational changes – confirms the orientation of the zero-field-splitting (ZFS) tensors previously determined for these molecules by magnetophotoselection experiments. A biaxial distribution function is shown to be necessary to simulate the experimental EPR data. The biaxial behaviour, in conjunction with symmetry considerations, allows an unambiguous assignment of the three ZFS tensor axes to the molecular axes. From the determined orientational distributions of the porphyrins in 5CB, the biaxial order parameters for both molecules were calculated.

Electron beam irradiation studies of polyethylene maleic anhydride on their Chemical and Thermal properties.

The electron beam (e-beam) irradiation effects on polyethylene maleic anhydride (MANPE) are investigated by spectroscopic and thermal methods. The MANPE irradiated with electron beam to a radiation dose of 30, 60 and 90 K Gy and the resultant changes in their chemical structure and thermal properties have been investigated by Electron spin resonance (ESR), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods. The irradiated MANPE has shown complex ESR line shapes under different conditions. The analysis of ESR spectra suggests the formation of macro-radicals of the type (–CH 2 -ĊH-CH 2 -)(I) and peroxy radicals of the ROO (II). The temperature dependent ESR studies suggest that the free radicals are trapped in the amorphous regions of the polymer. The g- values of free radicals at different temperatures are measured and reasons for variation in g- values is explained. Bloch analysis is used to calculate activation energy associated with the decay of free radicals. The FTIR analysis indicates the shifting of absorption bands and formation of new absorption bands corresponding to unsaturated groups and carbonyl groups centered around 1600 cm and 929 cm -1 . The e-beam irradiation of MANPE caused the decrease of transition temperature and increase of melting enthalpy and degree of crystallinity with increase of radiation dose as per differential scanning calorimeter studies. The results indicate that on irradiation MANPE preferably undergo degradation at low dose of irradiation and preferably undergo crosslinking at high doses.

Inactivation Efficacy of Nonthermal Plasma-Activated Solutions against Newcastle Disease Virus.

ABSTRACTIn recent years, plasma-activated solutions (PASs) have made good progress in the disinfection of medical devices, tooth whitening, and fruit preservation. In this study, we investigated the inactivation efficacy of Newcastle disease virus by PASs. Water, 0.9% NaCl, and 0.3% H2O2 were excited by plasma to obtain the corresponding solutions PAS(H2O), PAS(NaCl), and PAS(H2O2). The complete inactivation of virus after PAS treatment for 30 min was confirmed by the embryo lethality assay (ELA) and hemagglutination (HA) test. Scanning electron microscopy (SEM) results showed that the morphology of the viral particle changed under PAS treatments. The total protein concentration of virus decreased as measured by a Bradford protein assay due to PAS treatment. The nucleic acid integrity assay demonstrated that viral RNA degraded into smaller fragments. Moreover, the physicochemical properties of PASs, including the oxidation-reduction potential (ORP), electrical conductivity, and H2O2 concentration, and electron spin resonance spectra analysis indicated that reactive oxygen and nitrogen species play a major role in the virus inactivation. Therefore, the application of PASs, as an environmentally friendly method, would be a promising alternative strategy in poultry industries.IMPORTANCE Newcastle disease (ND), as an infectious viral disease of avian species, caused significant economic losses to domestic animal and poultry industries. The traditional chemical sanitizers, such as chlorine-based products, are associated with risks of by-product formation with carcinogenic effects and environmental pollution. On the basis of this, plasma-activated water as a green disinfection product is a promising alternative for applications in stock farming and sterilization in hospitals and public places. In this study, we explored the inactivation efficacy of different plasma-activated solutions (PASs) against ND virus (NDV) and the possible underlying mechanisms. Our results demonstrated that reactive oxygen and nitrogen species detected in PASs, including short-lived OH˙ and NO˙ and long-lived H2O2, changed the morphology, destroyed the RNA structure, and degraded the protein of the virus, consequently resulting in virus inactivation. These lay a foundation for the application of PASs to resolve the issues of public health and environmental sanitation.

Роль патогенних мікроорганізмів у накопиченні біогенних магнітних наночастинок у тканинах легень

Мета: У цій роботі досліджується роль патогенних мікроорганізмів у накопиченні біогенних магнітних наночастинок у тканинах легень. Основна мета даного дослідження – довести, що біогенні магнітні наночастинки можуть потрапляти у тканини легень разом з патогенними мікроорганізмами та накопичуватись там при відповідних захворюваннях. Методи дослідження: Попарне та множинне вирівнювання амінокислотних послідовностей, електронний парамагнітний резонанс. Результати: Продуценти біогенних магнітних наночастинок були знайдені серед патогенних мікроорганізмів, що є збудниками захворювань легень. Біогенні магнітні наночастинки можуть потрапляти у тканини легень разом з патогенними мікроорганізмами та накопичуватись там при відповідних захворюваннях. Наявність біогенних магнітних наночастинок у тканинах легень була експериментально доведена в ході аналізу спектра електронного парамагнітного резонансу. Обговорення: Результати даного дослідження можуть бути використані для запобігання та розуміння можливих причин токсичного, алергічного впливу і закупорки судин під час неконтрольованого накопичення магнітних наночастинок в різних органах та тканинах через їх магнітні диполь-дипольні взаємодії з біогенними магнітними наночастинками на клітинних мембранах.

Hydrothermal Carbon-Mediated Fenton-Like Reaction Mechanism in the Degradation of Alachlor: Direct Electron Transfer from Hydrothermal Carbon to Fe(III).

As Fenton systems suffer from the undesirable Fe(III)/Fe(II) cycle, great efforts were made to realize the effective reduction of Fe(III) to Fe(II). The effects of hydrothermal carbon (HTC) on the Fe(III)/H2O2 Fenton-like reaction and the subsequent degradation of alachlor in water was systematically investigated, and the results indicated that HTC could enhance alachlor degradation in Fe(III)/H2O2 by promoting the Fe(III)/Fe(II) cycle via electron transfer from HTC to Fe(III) ions. The apparent alachlor degradation rate constant in the HTC-G/Fe(III)/H2O2 system (7.02 × 10-2 min-1) was about 3 times higher than that in the Fe(III)/H2O2 system (2.25 × 10-2 min-1). The electron spin resonance spectra analysis revealed that HTC consists of abundant carbon-centered persistent free radicals to act as the electron donor. Meanwhile, the hydroxyl groups on the surface of HTC also played an important role in the enhanced alachlor degradation because the decrease in the surface hydroxyl groups on HTC significantly decreased the degradation of alachlor. On the basis of these results, an Fe(III) complex with surface hydroxyl groups on HTC was proposed to favor the electron transfer from the hydroxyl groups to Fe(III), and then, the simultaneously produced Fe(II) could accelerate the catalytic decomposition of H2O2 to facilitate alachlor degradation. These findings shed new light on the possible roles of carbon materials in a natural aquatic environment and provide a new pathway for environmental pollutant control and remediation of organic contaminants by HTC.

Hydrated and anhydrous forms of copper(II) complex of 3-methylpicolinic acid, and spectroscopic studies of their ROS-inducing and proteasome inhibition

The hydrated and anhydrous forms of the copper(II) complex of 3-methylpicolinic acid, monomeric [Cu(3Me-pic)2(H2O)]·H2O 1 and polymeric [Cu(3Me-pic)2]n2, were synthesized and characterized by FTIR, UV–visible spectroscopy, conductivity measurement, magnetic susceptibility determination, electron paramagnetic resonance (EPR) and light scattering. Crystal structure analysis of 2 shows that it has a doubly-bridged polymeric structure, involving diagonally stacked Cu(3Me-pic)2 units which are linked via carbonyl oxygen atoms of the 3Me-pic moieties. Analysis of EPR spectra at 133 K and 293 K suggests isotropic intermolecular spin interaction only in 2. Complex 2 dissolved in DMF and DMSO solvents to yield nano-size particles. Solution studies show aqueous solutions of 1 and 2 contain the same neutral Cu(3Me-pic)2 species, which generates less hydroxyl radicals from the reaction with hydrogen peroxide than their precursor CuCl2. The Cu(3Me-pic)2 species exhibit more selective inhibition of the β2 site of the 20S proteasome, among the three proteolytic sites.

Resonance local phonon mode and electron spin-lattice relaxation of formate-type free radicals studied by electron spin echo in Cd(HCOO)2·2H2O crystal

The results of X-band electron spin resonance (ESR) and electron spin echo (ESE) measurements for free radicals generated in Cd(HCOO)2·2H2O single crystal are presented. From ESR spectra analysis the radicals were identified as after x-ray irradiation and as HOCO after γ-ray irradiation. The room temperature g-factors are: g|| = 1.9969 and g⊥ = 2.0024 for and g1 = 2.0087, g2 = 2.0029 and g3 = 1.9960 for HOCO. Axial g-tensor symmetry for is due to fast reorientation of the radical molecule around the g||-axis. Assignment of HOCO is confirmed by hyperfine splitting (Amax = 0.4 mT) from a single distant proton. Spin lattice relaxation rate was determined from ESE measurements in temperature range 4–250 K. Both radicals relax via local resonance mode lying within acoustic phonon branch. The existing theories of electron spin-lattice relaxation via local resonance mode are critically reviewed and compared with experimental data. A new approximation is proposed giving local mode energy = 56 cm−1 for and = 44 cm−1 for the HOCO-radical.

Role of nitrogen on the magnetic properties of MBE grown Mn0.04Ge0.96 films

We report the role of nitrogen on the distribution of Mn atoms and ferromagnetism in Mn0.04Ge0.96 films. High quality Mn0.04Ge0.96 films are obtained by sequential evaporation of stacked Mn and Ge layers on Si (100) substrate in N2 environment. The experimental results reveal that the films grown under 5×10−5Torr N2 partial pressure exhibit improved crystallinity and magnetic properties when compared to vacuum deposited films. Correlating the results of electron spin resonance (ESR) and x-ray photoelectron spectroscopy (XPS) studies with magnetic measurements, we have found that introduction of N2 during growth effects the distribution of Mn atoms in Ge. Incorporation of nitrogen into the films and degree of magnetic ordering was obtained from XPS spectra and line shape analysis of ESR spectra. In the presence of nitrogen, enhancement in Curie temperature is associated with the increase in the number of active Mn atoms, however promoted Mn diffusion leads to formation of Mn5Ge3 clusters.

An Electron Paramagnetic Resonance Method for Measuring the Affinity of a Spin-Labeled Analog of Cholesterol for Phospholipids

Cholesterol (chol)-lipid interactions are thought to play an intrinsic role in determining lateral organization within cellular membranes. Steric compatibility of the rigid steroid moiety for ordered saturated chains contributes to the high affinity that holds chol and sphingomyelin together in lipid rafts whereas, conversely, poor affinity of the sterol for highly disordered polyunsaturated fatty acids (PUFAs) is hypothesized to drive the formation of PUFA-containing phospholipid domains depleted in chol. Here, we describe a novel method using electron paramagnetic resonance (EPR) to measure the relative affinity of chol for different phospholipids. We monitor the partitioning of 3β-doxyl-5α-cholestane (chlstn), a spin-labeled analog of chol, between large unilamellar vesicles (LUVs) and cyclodextrin (mβCD) through analysis of EPR spectra. Because the shape of the EPR spectrum for chlstn is sensitive to the very different tumbling rates of the two environments, the ratio of the population of chlstn in LUVs and mβCD can be determined directly from spectra. Partition coefficients (K(B)(A)) between lipids derived from our results for chlstn agree with values obtained for chol and confirm that decreased affinity for the sterol accompanies increasing acyl chain unsaturation. The virtue of this EPR method is that it provides a measure of chol binding that is quick, employs a commercially available probe and avoids the necessity for physical separation of LUVs and mβCD.