Nuclear-magnetic Interference Research Articles

Magnetic resonance investigation of conformational responses of tau protein to specific phosphorylation

Intrinsically disordered proteins (IDPs) are known to adopt many rapidly interconverting structures, making it difficult to pinpoint the specific conformational states that are relevant for their function. Tau is an important IDP, and its conformation is known to be affected by post-translational modifications (PTMs), such as phosphorylation. To investigate the effect of specific phosphorylation on full-length Tau's dynamic global conformation, we employed a combination of nuclear magnetic resonance-based paramagnetic relaxation interference methods and electron paramagnetic resonance spectroscopy. By reproducing the AT8 epitope, comprising exclusive phosphorylation at residues S202 and T205, we were able to identify conformations specific to phosphorylated Tau, which exhibited a tendency towards less compact states. These mechanistic details are of significance to understand the path leading from soluble Tau to the ordered structure of Tau fibers. This approach proved to be successful for studying the conformational changes of (phosphorylated) full-length Tau and can potentially be extended to the study of other IDPs that undergo various PTMs.

P53 Transactivation Domain Mediates Binding and Phase Separation with Poly-PR/GR

The most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) is the presence of poly-PR/GR dipeptide repeats, which are encoded by the chromosome 9 open reading frame 72 (C9orf72) gene. Recently, it was shown that poly-PR/GR alters chromatin accessibility, which results in the stabilization and enhancement of transcriptional activity of the tumor suppressor p53 in several neurodegenerative disease models. A reduction in p53 protein levels protects against poly-PR and partially against poly-GR neurotoxicity in cells. Moreover, in model organisms, a reduction of p53 protein levels protects against neurotoxicity of poly-PR. Here, we aimed to study the detailed molecular mechanisms of how p53 contributes to poly-PR/GR-mediated neurodegeneration. Using a combination of biophysical techniques such as nuclear magnetic resonance (NMR) spectroscopy, fluorescence polarization, turbidity assays, and differential interference contrast (DIC) microscopy, we found that p53 physically interacts with poly-PR/GR and triggers liquid–liquid phase separation of p53. We identified the p53 transactivation domain 2 (TAD2) as the main binding site for PR25/GR25 and showed that binding of poly-PR/GR to p53 is mediated by a network of electrostatic and/or hydrophobic interactions. Our findings might help to understand the mechanistic role of p53 in poly-PR/GR-associated neurodegeneration.

Magnetic Order and Sign of the Dzyaloshinskii–Moriya Interaction in 2-D Antiferromagnet Ba2CoGe2O7 Under Applied Magnetic Field

The Dzyaloshinskii–Moriya interaction (DMI), i.e., the antisymmetric part of the exchange coupling tensor, favors the perpendicular arrangement of magnetic moment, thus inducing canting in otherwise collinear structures. The DMI is the prerequisite for the emergence of weak ferromagnetism in antiferromagnets, but can stabilize twisted magnetic textures, such as spin spirals, soliton lattices, and magnetic skyrmions. While the magnitude of the DMI determines the canting angle of adjacent spins, its sign dictates the sense of the spin rotation. Based on focused polarized neutron diffraction (PND) study, combined with symmetry analysis, we determine the sign of the DMI in the unconventional multiferroic Ba <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> CoGe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> and reveal its detailed magnetic structure in magnetic fields applied in the tetragonal plane. As PND gives unique access to the scattering contribution from the phase-sensitive nuclear-magnetic interference, it is a valuable tool for a straightforward DMI sign determination in bulk materials and allows to disclose even very weak magnetic moments. Remarkably, the sign of the DMI could be determined from the PND measurement of a single reflection, which is demonstrated to be reliable for a large range of applied magnetic field directions and values.

SANS and neutron diffraction study of ausformed EUROFER97/2 ferritic/martensitic steel

Abstract Small-angle neutron scattering (SANS) and neutron diffraction have been utilized for micro-structural characterization of Eurofer97/2 heats submitted to thermo-mechanical treatments, with the aim to investigate macroscopic material volumes and to complete the local information provided by scanning electron microscopy. The measurements were carried out at MLZ in Garching, utilizing for SANS also a polarized neutron beam. The investigated samples had been submitted to austenitization and tempering at different temperatures, as well as to double austenitization and to “ausforming”, that is austenitization followed by hot rolling. For most of the examined treatments, nearly identical SANS cross-sections were measured, close to the one of Eurofer97/1. In the ausformed sample the nuclear SANS cross-section is also nearly identical to the other samples but the magnetic one is one order of magnitude higher. Furthermore, over a wide experimental interval its nuclear-magnetic interference, measured by polarized SANS, is of opposite sign with respect to the non-ausformed samples. Neutron diffraction measurements provided strong evidence that the origin of such effects is due to the presence of the non-magnetic austenite phase in the ausformed sample, with an estimated volume fraction of 0.17 ± 0.02; within the experimental resolution, it disappears after subsequent tempering.

Total interference between nuclear and magnetovibrational one-phonon scattering cross sections

A full phonon intensity cancellation is reported in a longitudinal polarized inelastic neutron scattering experiment performed on the magnetocaloric compound MnFe4Si3, a ferromagnet with TCurie ≈ 305 K. The TA[100] phonon polarized along the c-axis measured from the Brillouin zone center G=(0, 0, 2) is observed only in one () of the two non-spin-flip polarization channels and is absent in the other one () at low temperatures. This effect disappears at higher temperatures, in the vicinity of TCurie, where the phonon is measured in both channels with nonetheless marked different intensities. The effect is understood as originating from nuclear-magnetic interference between the nuclear one-phonon and the magnetovibrational one-phonon scattering cross-sections. The total cancellation reported is accidental, i.e. does not correspond to a systematic effect, as established by measurements in different Brillouin zones.

Polarized-neutron investigation of magnetic ordering and spin dynamics in BaCo2(AsO4)2 frustrated honeycomb-lattice magnet

The magnetic properties of the cobaltite BaCo2(AsO4)2, a good realization of the quasi two-dimensional frustrated honeycomb-lattice system with strong planar anisotropy, have been reinvestigated by means of spherical neutron polarimetry with CRYOPAD. From accurate measurements of polarization matrices both on elastic and inelastic contributions as a function of the scattering vector Q, we have been able to determine the low-temperature magnetic structure of BaCo2(AsO4)2 and reveal its puzzling in-plane spin dynamics. Surprisingly, the ground-state structure (described by an incommensurate propagation vector k1=(kx,0,kz), with kx=0.270±0.005 and kz≈−1.31) appears to be a quasi-collinear structure, and not a simple helix, as previously determined. In addition, our results have revealed the existence of a non-negligible out-of-plane moment component ≈0.25μB/Co2+, representing about 10% of the in-plane component, as demonstrated by the presence of finite off-diagonal elements Pyz and Pzy of the polarization matrix, both on elastic and inelastic magnetic contributions. Despite a clear evidence of the existence of a slightly inelastic contribution of structural origin superimposed to the magnetic excitations at the scattering vectors Q=(0.27,0,3.1) and Q=(0.73,0,0.8) (energy transfer ΔE≈2.3 meV), no strong inelastic nuclear-magnetic interference terms could be detected so far, meaning that the nuclear and magnetic degrees of freedom have very weak cross-correlations. The strong inelastic Pyz and Pzy matrix elements can be understood by assuming that the magnetic excitations in BaCo2(AsO4)2 are spin waves associated with trivial anisotropic precessions of the magnetic moments involved in the canted incommensurate structure.

Effect of double nuclear scattering on nuclear-magnetic interference in experiment with small-angle diffraction of polarized neutrons

An experiment on small-angle polarized-neutron diffraction by a two-dimensional spatially ordered array of nickel nanowires embedded in a porous anodic alumina matrix is discussed. The contributions of nonmagnetic (nuclear) structures and nuclear magnetic interference indicating the correlation between magnetic and nuclear structures are discussed. Magnetic scattering is two orders of magnitude smaller than nuclear scattering and, hence, turns out to be weakly distinguishable. The ordered magnetic composite nanostructure of a sample leads to strong interaction between the neutron wave and the structure itself, which, in turn, implies a twofold (miltiple scattering) nuclear scattering process. Nuclear magnetic interference scattering must be analyzed allowing for twofold scattering conditions, which substantially distorts the intensity distribution of the interference contribution of first-order diffraction peaks.

Small-angle polarized neutron scattering study of the mesostructure of phase precipitates in the steel P91 after heat treatment

This paper reports on the results of the analysis of the mesostructure of phase precipitates formed in the steel P91 during heat treatment in the temperature range of 600–820°C after quenching at 1050°C for 30 min. Measurements have been performed by the small-angle polarized neutron scattering (SAPNS) method with the separation of nuclear-magnetic interference scattering. The characteristic sizes of the phases precipitated during heat treatment have been determined to be in the range of 150–450 A. It has been demonstrated that the method is highly effective for solving problems of this class, which is based on the possibility to separate and investigate nuclear-magnetic contrast scattering against the background of the total nuclear and magnetic small-angle scattering.

Study of ferromagnetic correlations caused by impurities in nonmagnetic materials by the method of small-angle scattering of polarized neutrons

The possibility of the study of ferromagnetic correlations caused by d-metal impurities in nonmagnetic matrices is discussed. The polarization and magnetic-nuclear interference obtained by analyzing the small-angle scattering of polarized neutrons in a CuZn(20) alloy with Ni impurity (1 at %) are reported. It has been shown that Ni is clustered in the CuZn matrix with the characteristic correlation radius in the range 100 A < Rc < 5000 A depending on the thermal processing of the samples. The cross correlation function determining magnetic-nuclear interference is satisfactorily approximated by the exponential exp(−r/Rc), where r is the distance. It has been found that the nonmagnetic matrix CuZn(20) with an almost uniform distribution of 1% Ni impurity has metamagnetic properties in the field H ≈ 0.5 T at room temperature.

Magnetic properties of cobalt nanowires: Study by polarized SANS

Structural and magnetic properties of two-dimensional spatially ordered system of ferromagnetic cobalt nanowires embedded into Al2O3 matrix have been studied using polarized small-angle neutron scattering. A comprehensive analysis of contributions to the scattering intensity was carried out, including nonmagnetic (nuclear) contribution, magnetic contribution depending on the magnetic field, and nuclear–magnetic interference indicating the correlation between the magnetic and nuclear structures. Experiments have revealed an anomalously low value of the magnetic contribution as compared to the nuclear one. This behavior is interpreted in terms of low coherence of the magnetic structure caused by the anisotropy of Co crystallites as compared with the large coherency of nuclear structure of nanowires.

Two-dimensional spatially ordered arrays of cobalt nanowires: polarized SANS study

Structural and magnetic properties of two-dimensional spatially ordered system of ferromagnetic cobalt nanowires embedded into Al2O3 matrix have been studied using polarized small-angle neutron scattering. The small-angle scattering pattern exhibits many diffraction peaks (up to the third reflection order), which corresponds to the scattering from highly correlated hexagonal structure of pores and magnetic nanowires. A comprehensive analysis of contributions to the scattering intensity, including nonmagnetic (nuclear) contribution, magnetic contribution depending on the magnetic field, and nuclear-magnetic interference indicating the correlation between the magnetic and nuclear structures was carried out. A detailed pattern of the remagnetization of an ordered array of the magnetic nanowires has been obtained. It has been illustrated that polarized neutron scattering provides unique information inaccessible by the standard magnetometry techniques.

10.1007/s11448-008-1004-x

This work is devoted to a small-angle polarized neutron scattering study of the structure and magnetic properties of nickel inverted photonic crystals. Depending on the intensity of the small-angle scattering, diffraction maximums up to fourth-order reflections, which correspond to scattering from the highly ordered structures of the test samples, are observed. Several contributions to the scattering are analyzed: a nuclear contribution; a magnetic contribution; a contribution depending on an external magnetic field; and a nuclear magnetic interference, which shows a correlation between magnetic and nuclear structures. It is found that a magnetization reversal process, which was represented by a standard hysteresis curve, for weak fields was accompanied by both domain formation and coherent magnetization rotation from the field direction to directions caused by geometric structure peculiarities.

Two-dimensional NMR relaxation study of the pore structure in silicone hydrogel contact lenses

A combination of two-dimensional nuclear magnetic resonance (NMR) proton relaxometry and differential interference contrast optical microscopy is used to compare the pore structures of hydroxyethyl methacrylate-based hydrogels used in conventional contact lenses with three silicone hydrogels primarily developed for continuous-wear contact lenses. It is shown that both types of hydrogel have a connected network of nanopores but that, in addition, the silicone hydrogels contain pores on the micrometer scale that enhances their permeability. The potential of other two-dimensional NMR relaxation and diffusion methods for detailed characterization of hydrogels is discussed.

Structural and magnetic properties of inverse opal photonic crystals studied by x-ray diffraction, scanning electron microscopy, and small-angle neutron scattering

The structural and magnetic properties of nickel inverse opal photonic crystal have been studied by complementary experimental techniques, including scanning electron microscopy, wide-angle and small-angle diffraction of synchrotron radiation, and polarized neutrons. The sample was fabricated by electrochemical deposition of nickel in voids in a colloidal crystal film made of 450 nm polystyrene microspheres followed by their dissolving in toluene. The microradian small-angle diffraction of synchrotron radiation was used to reveal the opal-like large-scale ordering proving its tendency to the face-centered-cubic fcc structure with the lattice constant of 65010 nm. The wide-angle x-ray powder diffraction has shown that nanosize fcc nickel crystallites, which form an inverse opal framework, have some texture prescribed by principal directions in inverse opal on a macroscale, thus showing that the atomic and macroscopic structures are correlated. The polarized small-angle neutron scattering is used on the extreme limit of its ability to detect the transformation of the magnetic structure under applied field. Different contributions to the neutron scattering have been analyzed: the nonmagnetic nuclear one, the pure magnetic one, and the nuclear-magnetic interference. The latter in the diffraction pattern shows the degree of the spatial correlation between the magnetic and nuclear reflecting planes and gives the pattern behavior of the reversal magnetization process for these planes. The field dependence of pure magnetic contribution shows that the three-dimensional geometrical shape of the structure presumably leads to a complex distribution of the magnetization in the sample.

Magnetic inverted photonic crystals: A polarized neutron scattering study

This work is devoted to a small-angle polarized neutron scattering study of the structure and magnetic properties of nickel inverted photonic crystals. Depending on the intensity of the small-angle scattering, diffraction maximums up to fourth-order reflections, which correspond to scattering from the highly ordered structures of the test samples, are observed. Several contributions to the scattering are analyzed: a nuclear contribution; a magnetic contribution; a contribution depending on an external magnetic field; and a nuclear magnetic interference, which shows a correlation between magnetic and nuclear structures. It is found that a magnetization reversal process, which was represented by a standard hysteresis curve, for weak fields was accompanied by both domain formation and coherent magnetization rotation from the field direction to directions caused by geometric structure peculiarities.

Spatially ordered arrays of magnetic nanowires: Polarized-neutron scattering investigation

The structure and magnetic properties of magnetically ordered arrays of magnetic nanowires formed on the basis of porous aluminum oxide films have been investigated by the small-angle polarized-neutron scattering method. Small-angle scattering intensity patterns exhibit several diffraction maxima (up to the third reflection order), which correspond to scattering from the highly ordered porous structure of the matrix and on the hexagonal packing of magnetic nanowires. The observed reflections are imposed on noticeable diffuse scattering associated with the defects of the structure. A theoretical solution is obtained for describing neutron diffraction in the dynamical limit on the superstructure of magnetic nanowires incorporated into the diamagnetic matrix. Several contributions to scattering that have been analyzed are the nonmagnetic (nuclear) contribution, the magnetic contribution depending on a magnetic field, and the nuclear-magnetic interference indicating the correlation between the magnetic and nuclear structures. A detailed pattern of the remagnetization of an ordered array of the magnetic nanowires has been obtained and it has been shown that polarized neutron scattering provides information inaccessible by the standard magnetometric methods.

Polarized small-angle neutron scattering study of two-dimensional spatially ordered systems of nickel nanowires

The magnetic and structural properties of two-dimensional spatially ordered systems of ferromagnetic nickel nanowires embedded into an Al2O3 matrix have been studied using polarized small-angle neutron scattering (polarized SANS). We measured the total (nuclear and magnetic) scattering I(q) as a polarization-independent scattering, the field-dependent scattering as IH(q) = I(q, H) − I(q, 0), where H is the magnetic field, and the nuclear-magnetic interference as a polarization-dependent (P) scattering ΔI(q, P). A typical scattering pattern is composed of the diffuse small-angle scattering and the Bragg peak. It is shown that the introduction of Ni into the matrix does not change the position of the Bragg peak but results in an increase of the scattering intensity both in the small-angle region and at the Bragg positions. An external magnetic field was applied perpendicular or parallel to the long dimension of the nanowires in order to reveal the anisotropic properties of the magnetic system. It is shown that, firstly, the magnetic-field-dependent scattering IH(q) provides new and principally different information as compared with the interference term ΔI(q). Secondly, two contributions to the interference term ΔI(q) (ascribed to the diffuse scattering and to the diffraction peaks) have different signs indicating different origins of the scattering objects. Thirdly, polarized SANS gives a detailed picture of the magnetization process, which could not be obtained by methods of standard magnetometry.

Polarized SANS study of spatially ordered magnetic nanowires

Polarized small-angle neutron scattering (SANS) technique is used to study spatially ordered one-dimensional (ID) magnetic nanowires. In our experiments a typical q-dependence consists of the diffuse small-angle scattering and the Bragg peak corresponding to the scattering on the regular structure of the porous matrix. We measured the total (nuclear and magnetic) scattering and the nuclear–magnetic interference as a polarization-dependent part of the scattering. The field- and temperature-dependent scattering intensity is extracted as I { H , T }( q)= I( q, H, T)− I( q, 0, T R). It is shown that the magnetic scattering I { H , T }( q), obtained from the polarization-independent part, brings new and principally different information as compared to the interference term Δ I( q). We present Co embedded into mesoporous aluminosilicate matrices (MAS) as an example of investigations of the spatially ordered one-dimensional magnetic nanosystems.

Spin correlations and a mesoscopic structure in Ni-Mn-Ga

The mesoscopic structures of the Heusler alloys Ni49.1Mn29.4Ga21.5 and Ni2MnGa are studied by small-angle polarized neutron scattering in the temperature range 15 < T < 400 K. The characteristic temperatures of phase transformations (ferromagnetic, martensitic, and premartensitic transformations) and the characteristic sizes of mesoscopic inhomogeneities in them have been determined. Differences in the spin dynamics of these phases and magnetic-nuclear interference upon neutron scattering have been revealed. The evolutions of the mesoscopic structures in the nonstoichiometric and stoichiometric alloys are found to be substantially different.

Iron nanowires embedded in mesoporous silica: Polarized neutron scattering study

Magnetic iron nanowires embedded in the mesoporous silica matrix have been studied by Small Angle Polarized Neutron Scattering. Magnetic nanocomposites were prepared by a novel variant of the synthesis based on the introduction of the hydrophobic metal compound, Fe(CO) 5, into the hydrophobic part of as-prepared mesoporous silica-surfactant composite. The mesoporous silica represents a highly regular hexagonal structure of mesopores. A diffraction peak in SAPNS at q c≈1.55 nm −1 is observed, which corresponds to a hexagonal structure with a periodicity of a 0≈4.6 nm. The scattering pattern of the pure matrix SiO 2 is well fitted by a sum of the contributions: the scattering on a powder consisting of large particles (1/ q 4) and the scattering on the regular structure of pores (diffraction peak). The samples with iron inside the pores give additional scattering. This scattering depends significantly on the annealing temperature what demonstrates the different degrees of crystallization process. The latter is fitted as a scattering on the bunches of the nanowires with average radius R b and with its spread Δ R . The nuclear–magnetic interference in scattering of polarized neutrons was also studied. We observe no interference scattering on the periodical structure. Instead, a significant interference scattering is detected, which may be directly related to the bunches of the nanowires created during the crystallization process.