Single Resonance Line Research Articles

Pure Shift Nuclear Magnetic Resonance: a New Tool for Plant Metabolomics.

Nuclear Magnetic Resonance (NMR) is one of the most powerful tools used in metabolomics. It stands as a highly accurate and reproducible method that not only provides quantitative data but also permits structural identification of the metabolites present in complex mixtures. Metabolic profiling by 1H NMR has proven useful in the study of various types of plant scenarios, which include the evaluation of cropconditions, harvest and post- harvest treatments, metabolic phenotyping, metabolic pathways, gene regulation, identification of biomarkers, chemotaxonomy, quality control, denomination of origin, among others. However, signal overlapping of the large number of resonances with expanded J-coupling multiplicities complicates the spectra analysis and its interpretation, and represents a limitation for classical 1H NMR profiling. In the last decade, novel NMR broadband homonuclear decoupling techniques through which multiplet signals collapse into single resonance lines - commonly called Pure Shift methods - have been developed to overcome the spectra resolution problem inherent to 1H NMR classical spectra. Here a step-by-step protocol of the plant extract preparation and the procedure to record optimal Pure Shift PSYCHE and SAPPHIRE-PSYCHE spectra in three different plant matrices - Vanilla plantleaves, potato tubers (S. tuberosum), and Cape gooseberries (P. peruviana) - is presented. The effect of the gain in resolution in metabolic identification, correlation analysis and multivariate analyses, as compared against classical spectra, is discussed.

Miniaturized integrated spectrometer using a silicon ring-grating design.

We introduce and experimentally demonstrate a miniaturized integrated spectrometer operating over a broad bandwidth in the short-wavelength infrared (SWIR) spectrum that combines an add-drop ring resonator narrow band filter with a distributed Bragg reflector (DBR) based broadband filter realized in a silicon photonic platform. The contra-directional coupling DBR filter in this design consists of a pair of waveguide sidewall gratings that act as a broadband filter (i.e., 3.9 nm). The re-directed beam is then fed into the ring resonator which functions as a narrowband filter (i.e., 0.121 nm). In this scheme the free spectral range (FSR) limitation of the ring resonator is overcome by using the DBR as a filter to isolate a single ring resonance line. The overall design of the spectrometer is further simplified by simultaneously tuning both components through the thermo-optic effect. Moreover, several ring-grating spectrometer cells with different central wavelengths can be stacked in cascade in order to cover a broader spectrum bandwidth. This can be done by centering each unit cell on a different center wavelength such that the maximum range of one-unit cell corresponds to the minimum range of the next unit cell. This configuration enables high spectral resolution over a large spectral bandwidth and high extinction ratio (ER), making it suitable for a wide variety of applications.

Evidence of surface spin-glass behavior in NiFe2O4 nanoparticles determined using magnetic resonance technique

Abstract Nanosized nickel ferrite (NiFe2O4) is successfully synthesized by the sol-gel method using citric acid (C6H8O7) as fuel. The X-ray diffraction pattern of the as-synthesized sample shows formation of NiFe2O4 nanoparticles (NPs) as the main phase, with mean crystalline size ∼50 nm. While transmission electron microscopy (TEM) reveals nearly spherical morphology with mean particle diameter of 41 ± 5 nm, high-resolution TEM shows inter-planar distance (2.55 A) corresponding to the (1 1 3) plane of the spinel structure. Additionally, the Raman spectrum exhibits five Raman active modes (two A1g at 575 cm−1 and 710 cm−1; two Eg at 345 cm−1 and 670 cm−1; and one T2g at 497 cm−1) typical of NiFe2O4. X-band magnetic resonance (MR) data reveal a single broad resonance line in the whole temperature range (3.8 K ≤ T ≤ 300 K), with g-value decreasing monotonically from 3.10 ± 0.01 at 3.8 K to 2.77 ± 0.01 at 300 K. The temperature dependence of both resonance field and resonance linewidth show a remarkable change in the range of 60–70 K, herein credited to surface spin-glass behavior. The model picture used to explain the MR data assumes NPs with a core-shell structure. Below about 60–70 K the shell’s spin system progressively reveals a paramagnetic to spin-glass-like transition upon cooling, with a freezing temperature estimated at 2.1 ± 0.1 K. However, above about 60–70 K spins in the paramagnetic shell align along the NP’s core dipolar field, resulting in an effective enlarged nanoparticle size.

Evidence and evolution of magnetic polaron in HgCr2Se4 investigated by electron spin resonance

The evidence and evolution of magnetic polarons (MPs) in HgCr2Se4 have been studied by electron spin resonance (ESR), magnetism and conductivity measurements in a temperature range of 5–300 K. A single paramagnetic resonance line is observed in the high-temperature range while multiple resonance lines appear in the low-temperature range. As temperature decreases, the peak-to-peak linewidth ΔHpp shows a minimum at Tmin ≈ 210 K, with the activation energy fitted by small polaron hopping model consistent with the bottleneck mechanism, providing an evidence for existence of small MPs above Tmin. The analysis of the temperature dependence of ΔHpp, double integrated intensity I, and g factor of ESR signals, combined with the temperature dependence of magnetization and conductivity, reveals an evolution process from small MPs at zone I (T > Tmin) to correlated MPs at zone II (Tc < T* ⩽ T ⩽ Tmin) in the paramagnetic regime. Three critical temperatures, Tmin (≈210 K), Tth (≈175 K), and T* (≈121 K), which determine the evolution characteristics of MPs, are distinguished. The magnetic correlation length ξ of Cr3+–Se2−–Cr3+ should account for the evolution of MPs.

Plasmonic Surface Lattice Resonances: A Review of Properties and Applications.

When metal nanoparticles are arranged in an ordered array, they may scatter light to produce diffracted waves. If one of the diffracted waves then propagates in the plane of the array, it may couple the localized plasmon resonances associated with individual nanoparticles together, leading to an exciting phenomenon, the drastic narrowing of plasmon resonances, down to 1–2 nm in spectral width. This presents a dramatic improvement compared to a typical single particle resonance line width of >80 nm. The very high quality factors of these diffractively coupled plasmon resonances, often referred to as plasmonic surface lattice resonances, and related effects have made this topic a very active and exciting field for fundamental research, and increasingly, these resonances have been investigated for their potential in the development of practical devices for communications, optoelectronics, photovoltaics, data storage, biosensing, and other applications. In the present review article, we describe the basic physical principles and properties of plasmonic surface lattice resonances: the width and quality of the resonances, singularities of the light phase, electric field enhancement, etc. We pay special attention to the conditions of their excitation in different experimental architectures by considering the following: in-plane and out-of-plane polarizations of the incident light, symmetric and asymmetric optical (refractive index) environments, the presence of substrate conductivity, and the presence of an active or magnetic medium. Finally, we review recent progress in applications of plasmonic surface lattice resonances in various fields.

In vivo estimation of transverse relaxation time constant (T2 ) of 17 human brain metabolites at 3T.

The transverse relaxation times T2 of 17 metabolites in vivo at 3T is reported and region specific differences are addressed. An echo-time series protocol was applied to one, two, or three volumes of interest with different fraction of white and gray matter including a total number of 106 healthy volunteers and acquiring a total number of 128 spectra. The data were fitted with the 2D fitting tool ProFit2, which included individual line shape modeling for all metabolites and allowed the T2 calculation of 28 moieties of 17 metabolites. The T2 of 10 metabolites and their moieties have been reported for the first time. Region specific T2 differences in white and gray matter enriched tissue occur in 16 of 17 metabolites examined including single resonance lines and coupled spin systems. The relaxation time T2 is regions specific and has to be considered when applying tissue composition correction for internal water referencing. Magn Reson Med 80:452-461, 2018. © 2018 International Society for Magnetic Resonance in Medicine.

Antiferromagnetic coupling between martensitic twin variants observed by magnetic resonance in Ni-Mn-Sn-Co films

Magnetic properties of $\mathrm{N}{\mathrm{i}}_{46.0}\mathrm{M}{\mathrm{n}}_{36.8}\mathrm{S}{\mathrm{n}}_{11.4}\mathrm{C}{\mathrm{o}}_{5.8}/\mathrm{MgO}(001)$ epitaxial thin film, which undergo a martensitic phase transformation from cubic austenitic phase to a twinned orthorhombic martensitic phase at 270 K, were studied by the magnetic resonance at the microwave frequency of 9.45 GHz. It was found that the single resonance line observed in the austenite splits into three lines in the martensitic phase. A theoretical approach was developed to show that the additional resonance lines are caused by the weak antiferromagnetic coupling of the ferromagnetic twin components across twin boundaries. Fitting of the experimental resonance lines to model gives an effective field of antiferromagnetic coupling of about 1.5 kOe, which is two or three orders of magnitude lower than in the conventional antiferromagnetic solids because the number of magnetic ions interacting antiferromagnetically through the twin boundary is much less than the total number of magnetic ions in the twin. This feature shows a strong resemblance between the submicron twinned martensite and artificial antiferromagnetic superlattices, whereby providing a distinctive insight into magnetism of the studied magnetic shape memory material.

Crystal Structure, Magnetism, 89Y Solid State NMR, and 121Sb Mössbauer Spectroscopic Investigations of YIrSb

The ternary antimonide YIrSb was synthesized from the binary precursor YIr and elemental antimony by a diffusion controlled solid‐state reaction. Single crystals were obtained by a flux technique with elemental bismuth as an inert solvent. The YIrSb structure (TiNiSi type, space group Pnma) was refined from single‐crystal X‐ray diffractometer data: a = 711.06(9), b = 447.74(5), c = 784.20(8) pm, wR2 = 0.0455, 535 F2 values, 20 variables. 89Y solid state MAS NMR and 121Sb Mössbauer spectra show single resonance lines in agreement with single‐crystal X‐ray data. YIrSb is a Pauli paramagnet.

Exchange interaction between S = 1/2 centers bridged by multiple noncovalent interactions: Contribution of the individual chemical pathways to the magnetic coupling

We report EPR and magnetic measurements of diaqua-(pyridine-2,6-dicarboxylato)Copper(II) together with computational calculations. This compound consists of an extended lattice of magnetically equivalent copper(II) ions in which the copper centers are linked by hydrophobic interactions such as π–π, π–metal, and Y–X…π, and hydrogen bonds involving different topologies, viz., CuOeq…OeqCu, CuOeq…OapCu, and CuOeq…OCOeqCu. The powder EPR spectrum shows nearly axial symmetry with non-resolved hyperfine structure with the copper nucleus, suggesting the presence of intercenter isotropic exchange interactions. Single crystal EPR experiments show a single lorentzian resonance line for all the magnetic field orientations investigated, typical of an extended exchange coupled system. Susceptibility measurements showed weakly antiferromagnetically coupled Cu(II) ions (J=−0.79 (4) cm−1). Using Anderson’s exchange narrowing model for the collapse of the hyperfine structure, EPR yielded |J|=0.6 (1) cm−1. The distinct contributions of the different chemical pathways to the experimentally determined J-value are analyzed through first principle computational calculations.

Solid-state 13 C, 15 N and 29 Si NMR characterization of block copolymers with CO2 capture properties.

Natural abundance solid-state multinuclear (13 C, 15 N and 29 Si) cross-polarization magic-angle-spinning NMR was used to study structures of three block copolymers based on polyamide and dimethylsiloxane and two polyamides, one of which including ferrocene in its structure. Assignment of most of the resonance lines in 13 C, 15 N and 29 Si cross-polarization magic-angle-spinning NMR spectra were suggested. A comparative analysis of 13 C isotropic chemical shifts of polyamides with and without ferrocene has revealed a systematic shift towards higher δ -values (de-shielding) explained as the incorporation of paramagnetic ferrocene into the polyamide backbone. In addition, the 13 C NMR resonance lines for ferrocene-based polyamide were significantly broadened, because of paramagnetic effects from ferrocene incorporated in the structure of this polyamide polymer. Single resonance lines with chemical shifts ranging from 88.1 to 91.5 ppm were observed for 15 N sites in all of studied polyamide samples. 29 Si chemical shifts were found to be around -22.4 ppm in polydimethylsiloxane samples that falls in the range of chemical shifts for alkylsiloxane compounds. The CO2 capture performance of polyamide-dimethylsiloxane-based block copolymers was measured as a function of temperature and pressure. The data revealed that these polymeric materials have potential to uptake CO2 (up to 9.6 cm3 g-1 ) at ambient pressures and in the temperature interval 30-40 °C. Copyright © 2016 John Wiley & Sons, Ltd.

Dielectric relaxation and ferromagnetic resonance in magnetoelectric (Polyvinylidene-fluoride)/ferrite composites

In this work the dielectric properties and ferromagnetic resonance of Polyvinylidene-fluoride embedded with 10 wt. % of NiFe2O4 or Ni0.5Zn0.5Fe2O4 nanoparticles are presented. The mechanisms of the dielectric relaxation in these two composites do not differ from each other. For more precise characterization of the dielectric relaxation, a two dimensional distribution of relaxation times was calculated from the temperature dependencies of the complex dielectric permittivity. The results obtained from the 2D distribution and the mean relaxation time are found to be consistent. The dynamics of the dielectric permittivity is described by the Arrhenius law. The energy and attempt time of the dielectric relaxators lie in a narrow energy and time region thus proving that the single type chains of polymer are responsible for a dispersion. The magnetic properties of the composites were investigated using the ferromagnetic resonance. A single resonance line was observed for both samples. From the temperature dependence (100 K - 310 K) of the resonance field and linewidth, the origin of the observed line was attributed to the NiFe2O4 and Ni0.5Zn0.5Fe2O4 superparamagnetic nanoparticles. By measuring films at different orientations with respect to the external magnetic field, the angular dependence of the resonance was observed, indicating the magnetic dipolar in-plane interactions.

Detection and original dose assessment of egg powders subjected to gamma irradiation by using ESR technique

Abstract ESR (electron spin resonance) techniques were applied for detection and original dose estimation to radiation-processed egg powders. The un-irradiated (control) egg powders showed a single resonance line centered at g =2.0086±0.0005, 2.0081±0.0005, 2.0082±0.0005 (native signal) for yolk, white and whole egg, respectively. Irradiation induced at least one additional intense singlet overlapping to the control signal and caused a significant increase in signal intensity without any changes in spectral patterns. Responses of egg powders to different gamma radiation doses in the range 0–10 kGy were examined. The stability of the radiation-induced ESR signal of irradiated egg powders were investigated over a storage period of about 5 months. Additive reirradiation of the egg powders produces a reproducible dose response function, which can be used to assess the initial dose by back-extrapolation. The additive dose method gives an estimation of the original dose within ±12% at the end of the 720 h storage period.

Molecular motion of alcohols adsorbed in ACF hydrophobic nanoslits as studied by solid-state NMR

The molecular motion and local structure of methanol-d1 (CH3OD) and ethanol-d1 (C2H5OD) in activated carbon fiber (ACF) with a slit width of 0.7 and 1.1 nm have been investigated by solid-state 1H and 2H NMR. 2H NMR spectra for alcohols confined in ACF gave a so-called Pake doublet below 140 K, which were characterized by the 2H quadrupole coupling constant (QCC) of 185 kHz and the asymmetric parameter of the electric-field-gradient tensor (η) of 0.1. The QCC value of the deuteron was indicative of the hydrogen bond formation with the O···O distance of ca. 0.27 nm, suggesting the solid-like feature of alcohols in ACFs. The quadrupole broadening vanished on heating and the single isotropic resonance line was observed. Alcohol molecules were undergoing a rapid motion like as in the bulk liquid, indicating a transition from solid to liquid in ACFs. Temperature-dependent 1H NMR spectra were used for evaluating the Ea value for reorientation in solid-like alcohols, whereas the 2H NMR spectra were used for obtaining the translation accompanying reorientation in liquid-like alcohols. Alcohols with a bilayered structure in ACF with a slit width of 1.1 nm gave similar Ea values, whereas C2H5OD in ACF with a slit width of 0.7 nm, in which a monolayered structure is expected, exhibited a cross-over of two activation processes at 172 K. The variation in Ea was probably caused by the structural relaxation concerning with the hydrogen bonding formation and/or excitation of the large amplitude local motion. The competition of the directionality of hydrogen bonds and a freedom of molecular orientation plays an important role to characterize the intermolecular structure as well as the physicochemical properties in amphipathic molecules in confinement.

Magnetocrystalline interactions and oxidation state determination of Mn(2−x)V(1+x)O4 (x=0, 1/3 and 1) magnetorresistive spinel family

Abstract Oxidation states of transition metal cations in spinels-type oxides are sometimes extremely difficult to determine by conventional spectroscopic methods. One of the most complex cases occurs when there are different cations, each one with several possible oxidation states, as in the case of the magnetoresistant Mn(2−x)V(1+x)O4 (x=0, 1/3 and 1) spinel-type family. In this contribution we describe the determination of the oxidation state of manganese and vanadium in Mn(2−x)V(1+x)O4 (x=0, 1/3,1) spinel-type compounds by analyzing XANES and high-resolution Kβ X-ray fluorescence spectra. The ionic models found are Mn2+2V4+O4, Mn2+5/3V3.5+4/3O4 and Mn2+V3+2O4. Combination of the present results with previous data provided a reliable cation distribution model. For these spinels, single magnetic electron paramagnetic resonance (EPR) lines are observed at 480 K showing the interaction among the different magnetic ions. The analysis of the EPR parameters show that g-values and relative intensities are highly influenced by the concentration and the high-spin state of Mn2+. EPR broadening linewidth is explained in terms of the bottleneck effect, which is due to the presence of the fast relaxing V3+ ion instead of the weak Mn2+ (S state) coupled to the lattice. The EPR results, at high temperature, are well explained assuming the oxidation states of the magnetic ions obtained by the other spectroscopic techniques.

Easily available, low cost 19F MRI agents: Poly(ethylene-glycol)-functionalized fluorinated ethers

A simple derivatisation of commercially available poly(ethylene-glycols) of different molecular weight followed by the reaction with the selected fluorinated organic molecule, perfluoro-tertbutanol, allowed an easy synthesis of several novel polymers of different fluorine content. The properties of the new materials as MRI agents were preliminarily investigated. In all cases a single 19F signal at NMR in deuterated chloroform and D2O was registered; for a few fluorinated polymeric candidates a good solubility in water was observed and MR imaging of the fluorinated polymer successfully provided images. Most interesting results were obtained with the sample of 1436MW (24% fluorine content) that not only gave a spectrum with a single resonance line, but, most importantly, was tolerated in low doses when in vivo experiments on animals (mice) were conducted.

Deuterium nuclear magnetic resonance unambiguously quantifies pore and collagen-bound water in cortical bone

Bone water (BW) plays a pivotal role in nutrient transport and conferring bone with its viscoelastic mechanical properties. BW is partitioned between the pore spaces of the Haversian and lacuno-canalicular system, and water predominantly bound to the matrix proteins (essentially collagen). The general model of BW is that the former predominantly experiences fast isotropic molecular reorientation, whereas water in the bone matrix undergoes slower anisotropic rotational diffusion. Here, we provide direct evidence for the correctness of this model and show that unambiguous quantification in situ of these two functionally and dynamically different BW fractions is possible. The approach chosen relies on nuclear magnetic resonance (NMR) of deuterium ((2) H) that unambiguously separates and quantifies the two fractions on the basis of their distinguishing microdynamic properties. Twenty-four specimens of the human tibial cortex from 6 donors (3 male, 3 female, ages 27-83 years) were cored and (2) H spectra recorded at 62 MHz (9.4 Tesla) on a Bruker Instruments DMX 400 spectrometer after exchange of native BW with (2) H(2) O. Spectra consisted of a doublet signal resulting from quadrupole interaction of water bound to collagen. Doublet splittings were found to depend on the orientation of the osteonal axis with respect to the magnetic field direction (8.2 and 4.3 kHz for parallel and perpendicular orientation, respectively). In contrast, the isotropically reorienting pore-resident water yielded a single resonance line superimposed on the doublet. Nulling of the singlet resonance allowed separation of the two fractions. The results indicate that in human cortical bone 60% to 80% of detectable BW is collagen-bound. Porosity determined as the difference between total BW and collagen bound water fraction was found to strongly parallel micro-computed tomography (µCT)-based measurements (R(2) = 0.91). Our method provides means for direct validation of emerging relaxation-based measurements of cortical bone porosity by proton MRI.

Interaction between magnetic agglomerates and an extended free radicals network studied by magnetic resonance

Abstract Solids containing an extended network of free radicals have been prepared and studied by magnetic resonance techniques in the 4–290 K temperature range. One solid contained additionally a small amount of magnetic γ-Fe2O3 in the form of nanoparticle agglomerates. The solid without agglomerates displayed only a narrow, single resonance line centered at g eff = 2.0043. The magnetic resonance measurements of the solid with γ-Fe2O3 agglomerates gave a spectrum composed of two lines attributed to two different magnetic centers: a narrow line due to free radicals and a broad line arising from magnetic iron oxide agglomerates. In the high temperature range the integrated intensities of both lines decreased with decreasing temperature. The resonance field of the broad line shifted to lower magnetic fields upon lowering the temperature with the gradient ΔH r/ΔT = 2.3 G/K, while the narrow line shifted towards higher magnetic fields. The linewidth of the broader line increased with decreasing temperature while for the narrow lines in both samples this change was small. The magnetic iron oxide clusters produce a magnetic field which acts on the free radicals network and its strength depends essentially on the concentration of clusters. The reorientation process in the free radicals network is more intense in the sample without magnetic clusters.

A Molecular Antenna Coordination Polymer from Cadmium(II) and 4,4’-Bipyridine Featuring Three Distinct Polymer Strands in the Crystal

Reaction of cadmium perchlorate and the prototypical linear bridging ligand 4,4’-bipyridine (4,4’-bipy) in an ethanol/water mixture affords the one-dimensional coordination polymer, [{Cd(m-4,4’-bipy)(4,4’-bipy)2(H2O)2}(ClO4)2 × 2 4,4’-bipy × 4.5 H2O]n (1). The Cd2+ ions adopt an octahedral coordination sphere and are joined into linear chains by 4,4’-bipy via two trans coordination sites. The remaining two trans sites in the equatorial plane carry terminally monodentate-bound 4,4’-bipy ligands, resulting in a molecular antenna arrangement. The two axial sites of each Cd2+ ion are occupied by aqua ligands. Compound 1 crystallizes in the non-centrosymmetric, monoclinic space group C2 with three similar, crystallographically independent, cationic coordination polymer strands in the unit cell, which essentially differ only in the conformations of the 4,4’-bipyridyl ligands. Consistent with the similarity of the local coordination environments of the three independent Cd atoms in the structure, 113Cd MAS NMR spectroscopy reveals a single resonance line at 89 ppm.

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.

Electron Spin Resonance in EuB&lt;sub&gt;6&lt;/sub&gt;

Cavity measurements of a high frequency (60 GHz) electron spin resonance (ESR) have been carried our for a single crystal of EuB6 at temperatures 4.2-50K in magnetic field up to 7 T, which has been aligned along [001] crystallographic direction. The influence of the experimental geometry on the parameters of the resonance line has been studied. It is found that in conditions of a homogeneous magnetic field the ESR spectrum in EuB6 is formed by a single resonance line at all temperatures including the ferromagnetic ordering region. The presence of the gradient of the magnetic field in the sample causes strong broadening of the resonance line at low temperatures and even may induce a double peak ESR structure. The analysis of the linewidth temperature dependence in EuB6 shows the anomalous growth of the line width below Curie temperature TC ~15 K.