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A paramagnetic ferroferric oxide-calcined layered double hydroxide core–shell adsorbent was prepared with high selectivity to anionic pollutions. [Display omitted] • Fe 3 O 4 @cLDH core–shell adsorbent was prepared by the calcination of PB@LDH. • Fe 3 O 4 @cLDH adsorbent exhibits high anionic dye selectivity. • The paramagnetic Fe 3 O 4 @cLDH can be easily collected by a magnet. • The adsorption capability is affected by the pH and soluble CO 2 in aqueous solution. Adsorption is one of the most common methods of pollution treatment. The selectivity for pollutants and recyclability of adsorbents are crucial to reduce the treatment cost. Layered double hydroxide (LDH) materials are one type of adsorbent with poor recyclability. Prussian blue (PB) is a sturdy and inexpensive metal–organic framework material that can be used as the precursor for synthesizing paramagnetic ferroferric oxide (Fe 3 O 4). It is intriguing to build some reusable adsorbents with magnetic separation by integrating LDH and PB. In this work, paramagnetic Fe 3 O 4 -calcined LDH (Fe 3 O 4 @cLDH) core–shell adsorbent was designed and prepared by the calcination of PB-ZnAl layered double hydroxide (PB@LDH) core–shell precursor, which exhibits high anionic dyes selectivity in wastewater solutions. The paramagnetism and adsorption capability of Fe 3 O 4 @cLDH come from the Fe 3 O 4 core and calcined ZnAl-LDH shell, respectively. Fe 3 O 4 @cLDH shows an adsorption capacity of 230 mg g−1 for acid orange and a high selectivity for anionic dyes in cation–anion mixed dye solutions. The regeneration process indicates that the high selectivity for anions is related to the specific hydration recovery process of ZnAl-LDH. The synergistic effect of the paramagnetic Fe 3 O 4 core and calcined ZnAl-LDH shell makes Fe 3 O 4 @cLDH an excellent magnetic separation adsorbent with high selectivity to anions. [ABSTRACT FROM AUTHOR]

A new alkaline-earth and Gd3+ borate, Ba 5 Gd 3 (BO 3) 6 F, has been successfully grown through a high-temperature solution method employing a BaF 2 -NaF-B 2 O 3 flux. This compound crystallizes in the monoclinic space group P 2 1 / c with lattice parameters of a = 13.679(4) Å, b = 8.694(3) Å, c = 7.664(2) Å, β = 99.116(7)°, V = 899.9(5) Å3, and Z = 1. Its three-dimensional structure consists of the [Ba/GdO] polyhedra and [FBa 4 Gd 2 ] octahedra layers. Magnetic analysis reveals that Ba 5 Gd 3 (BO 3) 6 F exhibits a magnetocaloric effect with a maximum −ΔS m of 29.86 J kg–1 K–1 at 3 K and 9 T. Additionally, the thermal stability, along with infrared (IR) and ultraviolet–visible–near-infrared (UV–Vis–NIR) diffuse reflectance spectra, were thoroughly examined. First-principles calculations further explored the electronic band structure and densities of states. A new Ba 5 Gd 3 (BO 3) 6 F single crystal has been obtained using a high-temperature solution method with BaF 2 -NaF-B 2 O 3 system as flux. Ba 5 Gd 3 (BO 3) 6 F exhibits paramagnetism and demonstrates a magnetocaloric effect with a –ΔS m value of 29.86 J kg−1 K−1 at 3 K and 9 T, approaching its paramagnetic limit. [Display omitted] • A new borate, Ba 5 Gd 3 (BO 3) 6 F, was obtained. • The magnetocaloric properties of Ba 5 Gd 3 (BO 3) 6 F were investigated. • Ba 5 Gd 3 (BO 3) 6 F exhibits a maximum −ΔS m reaching 88.11 % of the theoretical value. • Ba 5 Gd 3 (BO 3) 6 F has high stability. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract This paper presents a comprehensive experimental study of the effects of vertically and horizontally applied magnetic fields on the dynamics of magnetowetting and the formation of satellite droplet. Besides explaining the physics of the transient variation of different drop shape parameters, the role of a magnetic field on controlling the dynamics of spreading is also presented. Ultimately the magnetic field maneuvers the droplet spreading without altering the surface chemistry. The morphological evolution and dynamics of an impacting ferrofluid droplet has also been studied. By observing the spreading at an appropriate time scale, the contrary spreading behavior of the paramagnetic ferrofluid under the effect of magnetic field is noticed. Special attention is given to the droplet break-up and satellite droplet formation. A universal relationship is presented between the drop shape parameters before and after the impact. The destination and travel path of the satellite droplet is also analyzed in a vertical as well as horizontal magnetic field, which governs the satellite droplet merging with the already deposited parent droplet. [ABSTRACT FROM AUTHOR]

O 2 -titrations accompanying ESR, adsorption isotherm and TPD studies of well-crystallised powdered rutile provide insights into the nature of the reduced surface following adsorption of propan-2-ol at 300 K. Estimates have been made of the mean dimensions of the octa-decahedral micro-crystallites, and of the manner in which UV-A radiation penetrates into a randomised particle-bed. The reduced surface contains a small fractional coverage (0.003monolayer) of paramagnetic Ti 3+ A sites (1.1 × 10 16  m −2 ) that appear to be associated mainly with the crystallite edges, and a large majority (>98%) of diamagnetically-coupled Ti 3+ A-B spin-pairs arranged in the form of extended defects on the crystallite faces. UV-A is found to activate only a thin layer of particles at the bed exterior (0.83%) on which a large fraction (>30%) of the Ti 4+ oct sites become reduced to paramagnetic Ti 3+ A at 78 K, and mainly to spin-pairs at 300 K, with implications for their subsequent reactivity with oxidising gases. [ABSTRACT FROM AUTHOR]

Functional MRI (fMRI) at 7 T and above provides improved Signal-to-Noise Ratio and Contrast-to-Noise Ratio compared to 3 T acquisitions. In addition to the beneficial effects on spin polarization and magnetization of deoxyhemoglobin, the increased applied field also further magnetizes air and tissue. While the magnets themselves typically provide a static B 0 field with sufficient spatial homogeneity, the diamagnetism of tissue and the paramagnetism of air causes local field deviations inside the human head. These spatially-varying field offsets (ΔB 0 ) cause image artifacts, especially in single shot EPI, including geometric distortion, signal dropout, and blurring. These effects are particularly strong near air-tissue interfaces such as the frontal sinus, and ear canals. Furthermore, if the field offsets are dynamically modulated through physiological processes such as respiration or motion, then the effect on the image time-series can be even more problematic. While post-processing methods have been developed to mitigate these effects, the ideal solution would be to reduce the ΔB 0 variations at their source. Typically 7 T scanners contain 2nd and some 3rd order spherical harmonic shim coil terms to cancel static ΔB 0 variations of low spatial order. In this article, we will motivate the need for improved, higher-order compensation for B 0 inhomogeneity and potentially add dynamic control of these fields. We discuss and compare several promising hardware approaches for static and dynamic B 0 shimming using either higher-order spherical harmonic shim coils or multi-coil shim arrays as well as passive shimming approaches, and active variants such and adaptive current networks. [ABSTRACT FROM AUTHOR]

A series of Ba 2 GdF 7 :Yb 3+ , Tm 3+ nanophosphors (NPs) with dual-mode (down-conversion (DC) and upconversion (UC)) luminescence were successfully prepared by hydrothermal method at 180 °C. The NPs have sphere-like morphology and cubic structure. Under the excitation of ultraviolet 355 nm and near-infrared 980 nm, Yb 3+ and Tm 3+ ions co-doped Ba 2 GdF 7 phosphors exhibit bright blue dual-mode emission. The mechanism of UC emissions was determined three-photon absorption. The energy transfer processes from Yb 3+ to Tm 3+ were discussed in detail. The up-conversion luminescence of Ba 2 GdF 7 :Yb 3+ /Tm 3+ nanophosphors were enhanced by introducing the sensitizer Yb 3+ ions and modifying the cetyltrimethylammonium bromide (CTAB) surfactant, respectively. Moreover, the as-prepared samples exhibit paramagnetic properties at room temperature. This type of multifunctional nanophosphors have promising applications in anti-counterfeiting, drug delivery, solid state lasers, biolabels, MRI, light emitting diodes (LEDs). [ABSTRACT FROM AUTHOR]

1T-TiSe 2 is one of the layered transition metals dichalcogenides (LTMDs) which exhibits charge density wave (CDW), but doesn't show superconductivity. However, interesting properties such as superconductivity, antiferromagnetism, ferromagnetism etc. can be induced by intercalation of suitable ions in the 1T-TiSe 2 structure. In this article, we have investigated the structural and magnetic properties of Dy intercalated TiSe 2. The powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM) analysis confirm pure (single) phase formation and layered morphology of Dy x TiSe 2 (x ​= ​0, 0.02, 0.04, 0.06, 0.08). Intercalation process is further confirmed by Raman study as no new peak appeared with intercalation. XPS spectra shows the trivalent, tetravalent and divalent nature of Dy, Ti and Se respectively. Further, it also confirms the transfer of charge from Ti to Dy as result of intercalation in TiSe 2. The magnetic measurements on 1T–TiSe 2 show Pauli paramagnetic behavior, while Dy intercalated samples with x ​= ​0.06 and 0.08 show antiferromagnetic ordering below 4 ​K. Dy is found to be electrostatically interacting with the TiSe 2 layers resulting nominal structural alteration. Dy intercalation aided transformation of the magnetic properties from Pauli paramagnetism to antiferromagnetism in Dy x TiSe 2. [Display omitted] • Synthesis of Dy x TiSe 2 (x ​= ​0, 0.02, 0.04, 0.06, 0.08) by high temperature solid state method (sealed tube method). • XPS studies of Dy 0.08 TiSe 2 shows the valence states of Ti4+, Se2− and Dy3+. • Dy intercalation in Dy x TiSe 2 induces antiferromagnetism for x ​= ​0.06, 0.08. [ABSTRACT FROM AUTHOR]

Doping in nanocrystals is a challenging process because of the self- purification mechanism which tends to segregate out the dopants resulting in a greater dopant concentration near the surface than at the interior of nanocrystals. In the present work nanocrystals of TiO 2 doped with different atom % of Co were synthesized by peroxide gel method. XRD analysis confirmed the tetragonal anatase structure and HRTEM images showed the rod-like morphology of the samples. Raman modes of anatase phase of TiO 2 along with weak intensity peaks of Co 3 O 4 for higher Co dopant concentrations were observed for the samples. EPR measurements revealed the presence of cobalt in +2 oxidation state in the TiO 2 matrix. SQUID measurements indicated paramagnetic behavior of the Co doped TiO 2 nanocrystals. The paramagnetic behavior is attributed to an increased concentration of Co 2+ ions and an increased presence of Co 3 O 4 phase near the surface of the TiO 2 nanocrystals due to self-purification mechanism. [ABSTRACT FROM AUTHOR]

Behavior of water molecules entrapped in nanochannels of zeolite mordenite has been investigated by 1 H NMR technique. The 1 H spectra and spin-lattice relaxation times in the laboratory and rotating frames, T 1 and T 1ρ , respectively, as well as the dipolar relaxation time T 1 D have been measured in the temperature range from 96 to 351 K. Diffusion of water molecules along the channels was observed above ~200 K. While in bulk liquid the dipolar ordered state of nuclear spins is not formed owing to complete motional average of dipolar interactions, we show that such a state is observed for mobile molecules confined in a restricted geometry. At temperatures below ~140 K the relaxation was found to be mainly caused by interaction of 1 H nuclear spins with paramagnetic impurities. Complete lost of the fine structure of 1 H spectra above ~320 K is attributed to isotropic molecular reorientation or/and proton exchange. We show that the dipolar relaxation in mordenite is responsive to slow 180° reorientations of water molecules. The correlation times of nuclear and electron spin fluctuations were determined. [ABSTRACT FROM AUTHOR]

We have developed and explored the use of a new Automatic Tuning Matching Cycler (ATMC) in situ NMR probe system to track the formation of intermediate phases and investigate electrolyte decomposition during electrochemical cycling of Li- and Na-ion batteries (LIBs and NIBs). The new approach addresses many of the issues arising during in situ NMR, e.g., significantly different shifts of the multi-component samples, changing sample conditions (such as the magnetic susceptibility and conductivity) during cycling, signal broadening due to paramagnetism as well as interferences between the NMR and external cycler circuit that might impair the experiments. We provide practical insight into how to conduct ATMC in situ NMR experiments and discuss applications of the methodology to LiFePO 4 (LFP) and Na 3 V 2 (PO 4 ) 2 F 3 cathodes as well as Na metal anodes. Automatic frequency sweep 7 Li in situ NMR reveals significant changes of the strongly paramagnetic broadened LFP line shape in agreement with the structural changes due to delithiation. Additionally, 31 P in situ NMR shows a full separation of the electrolyte and cathode NMR signals and is a key feature for a deeper understanding of the processes occurring during charge/discharge on the local atomic scale of NMR. 31 P in situ NMR with “on-the-fly” re-calibrated, varying carrier frequencies on Na 3 V 2 (PO 4 ) 2 F 3 as a cathode in a NIB enabled the detection of different P signals within a huge frequency range of 4000 ppm. The experiments show a significant shift and changes in the number as well as intensities of 31 P signals during desodiation/sodiation of the cathode. The in situ experiments reveal changes of local P environments that in part have not been seen in ex situ NMR investigations. Furthermore, we applied ATMC 23 Na in situ NMR on symmetrical Na–Na cells during galvanostatic plating. An automatic adjustment of the NMR carrier frequency during the in situ experiment ensured on-resonance conditions for the Na metal and electrolyte peak, respectively. Thus, interleaved measurements with different optimal NMR set-ups for the metal and electrolyte, respectively, became possible. This allowed the formation of different Na metal species as well as a quantification of electrolyte consumption during the electrochemical experiment to be monitored. The new approach is likely to benefit a further understanding of Na-ion battery chemistries. [ABSTRACT FROM AUTHOR]

The valence state of iron in Cu 12− x Fe x Sb 4 S 13 tetrahedrites have been revisited by the combination of the crystallographic results, Mössbauer spectroscopy, and magnetization measurements. The crystal structure solution for Cu 11.0 Fe 1.0 Sb 4 S 13 (space group I 4 ¯ 3 m , a =10.3253(12), z =2, R =0.011) proved that iron substitutes for copper only in the Cu1 position. At the iron content of x =0.8, 1.0, and 1.2, the presence of two nonequivalent and non-interacting Fe 3+ cations was inferred from Mössbauer spectra. At higher levels of substitution ( x =1.5 and 2.0), room-temperature Mössbauer spectra indicate the electron hopping between part of Fe 3+ and Fe 2+ centers, whereas the rest of iron atoms exists as valence-localized Fe 3+ and Fe 2+ cations. Electron transfer is frozen out at 77 K, where a combination of two Fe 3+ sites and one high-spin Fe 2+ site is observed. Paramagnetic effective moments extracted from the magnetic susceptibility data point at the Fe 3+ state of iron at x =0.8, while a mixture of Fe 2+ and Fe 3+ is presumed in the samples with higher Fe content. [ABSTRACT FROM AUTHOR]

Magnetically responsive oil-in-water emulsions are effectively stabilized by a halloysite nanotube supported superparamagnetic iron oxide nanoparticle system. The attachment of the magnetically functionalized halloysite nanotubes at the oil–water interface imparts magnetic responsiveness to the emulsion and provides a steric barrier to droplet coalescence leading to emulsions that are stabilized for extended periods. Interfacial structure characterization by cryogenic scanning electron microscopy reveals that the nanotubes attach at the oil–water interface in a side on-orientation. The tubular structure of the nanotubes is exploited for the encapsulation and release of surfactant species that are typical of oil spill dispersants such as dioctyl sulfosuccinate sodium salt and polyoxyethylene (20) sorbitan monooleate. The magnetically responsive halloysite nanotubes anchor to the oil–water interface stabilizing the interface and releasing the surfactants resulting in reduction in the oil–water interfacial tension. The synergistic adsorption of the nanotubes and the released surfactants at the oil–water interface results in oil emulsification into very small droplets (less than 20 μm). The synergy of the unique nanotubular morphology and interfacial activity of halloysite with the magnetic properties of iron oxide nanoparticles has potential applications in oil spill dispersion, magnetic mobilization and detection using magnetic fields. [ABSTRACT FROM AUTHOR]

We study the spin–lattice relaxation of the nuclear spins in a liquid or a gas entrapped in nanosized ellipsoidal cavities with paramagnetic impurities. Two cases are considered where the major axes of cavities are in orientational order and isotropically disordered. The evolution equation and analytical expression for spin lattice relaxation time are obtained which give the dependence of the relaxation time on the structural parameters of a nanocavity and the characteristics of a gas or a liquid confined in nanocavities. For the case of orientationally ordered cavities, the relaxation process is exponential. When the nanocavities are isotropically disordered, the time dependence of the magnetization is significantly non-exponential. As shown for this case, the relaxation process is characterized by two time constants. The measurements of the relaxation time, along with the information about the cavity size, allow determining the shape and orientation of the nanocavity and concentration of the paramagnetic impurities. [ABSTRACT FROM AUTHOR]

Within the present contribution, we describe solid-state NMR spectroscopic studies of the paddle wheel unit in the prototypic flexible MOF compound DUT-8(M) (M = Ni, Co, Zn). The 13C NMR chemical shift of these carboxylates shows a remarkable behavior. The pure 2,6-H 2 ndc linker carboxylates as well as DUT-8(Zn) exhibit a13C chemical shift of only about 170 ppm. In contrast, much higher values are observed for DUT-8(Ni) and especially DUT-8(Co). In the open pore state, the shift strongly depends on the solvent polarity in these two latter cases. The present contribution elucidates the reason for this solvent influence. It is concluded that the solvent mainly modifies the isotropic Fermi contact coupling constant for the excited high-spin states in DUT-8(Ni) and DUT-8(Co). [Display omitted] • Solid-state NMR of 13C-labelled carboxylate carbons provides information about flexible MOFs. • Paramagnetic effects are detected in DUT-8(Co) and DUT-8(Ni). • Solvent polarity influences the hyperfine coupling constant. [ABSTRACT FROM AUTHOR]

Present work investigates the crossover from paramagnetism to superparamagnetism as a function of crystallite size in zinc ferrite nanoparticles using near edge X-ray absorption spectroscopy. Synthesized paramagnetic and superparamagnetic nanoparticles exhibit presence of Fe 2+ and Fe 3+ ions with dominant concentration of Fe 3+ ions. Fe L - and O K -edges spectra of paramagnetic nanoparticles consist of more intense spectral features compared to that of superparamagnetic nanoparticles. This reflects enhanced t 2 g and e g symmetry states of Fe–O hybridized states in paramagnetic nanoparticles induced by increased degree of crystallization. [ABSTRACT FROM AUTHOR]

Paramagnetism-based nuclear pseudocontact shifts and spin relaxation enhancements contain a wealth of information in solid-state NMR spectra about electron–nucleus distances on the ∼20 Å length scale, far beyond that normally probed through measurements of nuclear dipolar couplings. Such data are especially vital in the context of structural studies of proteins and other biological molecules that suffer from a sparse number of experimentally-accessible atomic distances constraining their three-dimensional fold or intermolecular interactions. This perspective provides a brief overview of the recent developments and applications of paramagnetic magic-angle spinning NMR to biological systems, with primary focus on the investigations of metalloproteins and natively diamagnetic proteins modified with covalent paramagnetic tags. [ABSTRACT FROM AUTHOR]

When combined with high-frequency (currently ∼60 kHz) magic-angle spinning (MAS), proton detection boosts sensitivity and increases coherence lifetimes, resulting in narrow 1 H lines. Herein, we review methods for efficient proton detected techniques and applications in highly deuterated proteins, with an emphasis on 100% selected 1 H site concentration for the purpose of sensitivity. We discuss the factors affecting resolution and sensitivity that have resulted in higher and higher frequency MAS. Next we describe the various methods that have been used for backbone and side-chain assignment with proton detection, highlighting the efficient use of scalar-based 13 C– 13 C transfers. Additionally, we show new spectra making use of these schemes for side-chain assignment of methyl 13 C– 1 H resonances. The rapid acquisition of resolved 2D spectra with proton detection allows efficient measurement of relaxation parameters used as a measure of dynamic processes. Under rapid MAS, relaxation times can be measured in a site-specific manner in medium-sized proteins, enabling the investigation of molecular motions at high resolution. Additionally, we discuss methods for measurement of structural parameters, including measurement of internuclear 1 H– 1 H contacts and the use of paramagnetic effects in the determination of global structure. [ABSTRACT FROM AUTHOR]

Highlights: [•] Paramagnet induced quenching and relaxation in MAS–DNP experiments. [•] Comparison of four fundamentally different polarizing agents. [•] Optimization of paramagnet concentration. [•] Cross effect biradicals are superior to monoradicals. [•] MAS mediates quenching equally for TOTAPOL and trityl. [ABSTRACT FROM AUTHOR]

Abstract: Reported are the synthesis and the structural characterization of an extended family of rare-earth metal–lithium–antimonides with the formula RELi3Sb2 (RE=Ce–Nd, Sm, Gd–Ho). They crystallize in the trigonal space group (No. 164, Pearson symbol hP6) with a structure, best viewed as a filled derivative of the common CaAl2Si2 structure type (ternary variant of α-La2O3). Across the series, the lattice parameters monotonically decrease, following the lanthanide contraction. Temperature-dependent magnetic susceptibility measurements for CeLi3Sb2, PrLi3Sb2 and TbLi3Sb2 reveal paramagnetic behavior in the high temperature range, and the obtained effective moments are consistent with the expected ones for the free-ion RE 3+ ground state. Possible ferromagnetic ordering for PrLi3Sb2 and antiferromagnetic ordering for TbLi3Sb2 are observed in the low temperature range (below 20K). Tight-binding muffin-tin orbital electronic band structure calculations for LaLi3Sb2 are presented and discussed as well. [Copyright &y& Elsevier]

Novel RNi6Si6 compounds adopt the new CeNi6Si6-type structure for R=La–Ce (tP52, space group P4/nbm N 125-1) and new YNi6Si6-type structure for R=Y, Sm, Gd–Yb (tP52, space group N 117) that are tetragonal derivative of NaZn13-type structure, like LaCo9Si4-type. The CeNi6Si6, GdNi6Si6, TbNi6Si6, DyNi6Si6 and HoNi6Si6 compounds are Curie–Weiss paramagnets down to ~30K, and do not order magnetically down to 5K. However, the inverse paramagnetic susceptibility of LaNi6Si6 does not follow Curie–Weiss law. The DyNi6Si6 shows ferromagnetic-like saturation behaviour at 5K in applied fields of 50kOe, giving rise to a magnetic moment value of 6.5μB/f.u. in 50kOe. The powder neutron diffraction study in zero applied filed indicates square modulated the c-collinear antiferromagnetic ordering of TbNi6Si6 with K=[±1/4, ±1/4, 0] wave vector below ~10K. [ABSTRACT FROM AUTHOR]

Highlights: [•] DANTE 1D excitation in solids works better under ultra-fast MAS. [•] Paramagnetic samples can be excited with weak rf-field. [•] Integer-spin quadrupolar nuclei, such as 14N, can be manipulated with DANTE. [•] Overtone DANTE can be used for 90° excitation, not for 180° inversion. [•] Overtone DANTE works well for excitation of large quadrupole interaction. [ABSTRACT FROM AUTHOR]

Abstract: Careful NMR measurements on a very lightly-doped reference silicon sample provide a convenient highly precise and accurate secondary chemical shift reference standard for 29Si MAS-NMR applicable over a wide temperature range. The linear temperature-dependence of the 29Si chemical shift measured in this sample is used to refine an earlier presentation of the paramagnetic (high-frequency) 29Si resonance shifts in heavily-doped n-type silicon samples near the metal–nonmetal transition. The data show systematic decreases of the local magnetic fields with increasing temperature in the range 100–470K for all samples in the carrier concentration range from 2×1018 cm−3 to 8×1019 cm−3. This trend is qualitatively similar to that previously observed for the two-orders of magnitude larger 31P impurity NMR resonance shifts in the same temperature and concentration ranges. The 29Si and 31P resonance shifts are not related by a simple scaling factor, however, indicating that impurity and host nuclei are affected by different subsets of partially-localized extrinsic electrons at all temperatures. [Copyright &y& Elsevier]

Highlights: [•] Challenges of in situ NMR of Li-ion batteries containing paramagnetic electrodes are described. [•] The orientation dependence of BMS effects is evaluated using a dipolar coupling model. [•] The shape and packing density dependence of BMS effect of paramagnetic electrodes are discussed. [•] The BMS induced shift can be minimized by orienting the battery at a rotation angle of 54.7°. [ABSTRACT FROM AUTHOR]

Highlights: [•] Spins are not directly observable, only the magnetic moment. [•] Magnetic moment behaves differently than spin with g-anisotropy. [•] Bloch-like equations for the magnetic moment with g anisotropy are derived. [•] The length of the magnetic moment oscillates to obey conservation of energy. [•] Relaxation of anisotropic magnetic moment has two relaxation times T 1 and T 2. [ABSTRACT FROM AUTHOR]

Abstract: Zn1− x Fe x O thin films with different Fe (0⩽ x ⩽0.20) content were produced by sol–gel dip coating method. The influence of Fe doping on the structural, optical and magnetic properties of ZnO thin films was investigated. X-ray diffraction has shown that the films are polycrystalline and textured with c-axis of the hexagonal structure along the growth direction. Scanning electron microscope has indicated that the surface of the films is homogeneous with no cracking and the grain sizes tend to decrease with the increase of Fe-doping concentration. Ultraviolet–visible measurements show a reduction in band gap of the films with increase in Fe content from 3.27eV to 3.10eV. The magnetic measurements performed at 5, 100, 200 and 300K using a SQUID magnetometer revealed the dominant paramagnetic behavior until Fe doping ratio of 10% and clear magnetic hysteresis loops at 5 and 100K for the highest Fe doping ratio of 20%. The observed ferromagnetic behavior is likely related to a partial incorporation of Zn into the Fe3O4, i.e. Fe3− x Zn x O4 composition or disorders as well as some defects. [Copyright &y& Elsevier]

Abstract: Submicron-sized superparamagnetic magnetite colloid nanocrystal clusters (MCNCs) composed of many interconnected tiny Fe3O4 nanoparticles provide a new avenue for constructing highly magnetic polymer submicrospheres for biotechnological and medical applications. Herein, a facile and efficient method is described for the synthesis of Fe3O4@poly(methacrylic acid) (PMAA) core–shell submicrospheres using the MCNCs modified with polymerizable vinyl groups as the submicronic cores. The controlled encapsulation of the MCNCs with PMAA shells was achieved via precipitation polymerization mediated by a reversible addition–fragmentation chain transfer (RAFT) agent. A variety of factors influencing the formation of PMAA layers were examined, such as the loading amounts of the magnetic seeds and monomers, polymerization time, and the MCNCs’ surface chemistry. Compared with previous approaches, much higher seed dosage could be employed in the polymerization system without leading to significant particle conglutination. The shell thickness was readily tailored via varying two synthesis parameters, that is, monomer dosage and reaction time. The resulting hybrid particles showed high saturation magnetization and pH responsiveness. Also, this method was successfully extended to coating other hydrophilic polymer shells over the MCNCs and hence may be a general way for the synthesis of magnetic polymer submicrospheres. [Copyright &y& Elsevier]

Abstract: The structure and elementary physical properties of a new intermetallic compound, , are reported. has a tetragonal structure (space group I4/mmm) with lattice constants of a=3.7634(11)Å and c=13.499(4)Å. The structure, which consists of double layers of Hf stacked with edge-sharing CuGe4 squares, is not typical for intermetallic compounds and appears to be a new structure type. The compound is a weak paramagnet and a normal metal down to 0.4K. [Copyright &y& Elsevier]

Abstract: The incommensurate structure of the GdBaCo2O5+δ (δ∼0.38) paramagnetic phase was studied using the single-crystal X-ray diffraction. The basic structure of the compound is a double-layered perovskite with an alternating layer sequence of [GdO δ ]–[CoO2]–[BaO]–[CoO2] along the c axis. The crystal belongs to the five-dimensional superspace group P4/mmm(α00)0000(0α0)0000, α=0.3368(1), with a 1×1×2-type tetragonal fundamental unit cell of a=3.8934(1)Å and c=7.5267(1)Å. The structure was refined to R=0.028 for all the observed 2216 reflections with I>3σ(I), including 331 main reflections (R=0.017), 1039 observed first-order satellites (R=0.033), and 846 observed second-order satellites (R=0.045). The crystal has oxygen deficiency that occurs only in the [GdO δ ] layer; however, it causes many positional modulations of the constituent atoms throughout the crystal in association with a valence fluctuation of Co between the divalent and trivalent states. Because the value of α was very close to 1/3, the structure was also investigated using both the commensurately modulated approach and the conventional three-dimensional approach assuming a 3×3×2 supercell of P4/mmm symmetry. These approaches successfully reproduced a prime structure of the compound that consists of intersecting CoO5 pyramidal arrays parallel to a or b axes. The bond valence sum and the charge neutrality principle suggested that the divalent and trivalent cobalt cations are distributed in an ordered way. The incommensurate approach also indicated the possible presence of a local disorder having a structural similarity with that of a high-temperature modification. [Copyright &y& Elsevier]

Abstract: Oxygen uptake by the pulmonary circulation is a chemical reaction. The physicochemical attributes of oxygen are critical when studying pulmonary oxygen toxicity. Extent of lung injury depends on the percentage of oxygen in an oxygen–nitrogen mix in polybaric circumstances (Shanklin, 1969). Further change in extent of lesion follows when other gases are used in the inhalant mix instead of nitrogen (Shanklin and Lester, 1972), with oxygen at 21–100% of the mix. Comparative subatmospheric oxygen levels down to 3% in hydrogen, helium, nitrogen, argon, or sulfur hexafluoride, were run with and without ventilatory distress by the Farber (1937) model, bilateral cervical vagotomy (BCV). This yielded coherent results indicating a need to consider molecular characteristics at the atomic level. Molecular mass and size, gas viscosity, and thermal conductivity yielded no obvious correlates to lung injury. Saturation of the outer electron shells of the diluents fit the empiric data, prospectively an interaction between oxygen and nitrogen from their electronegativity and closely approximate molecular mass, size, and shape. The lesion is essentially eliminated at 7% oxygen in nitrogen. At 3% oxygen, the least lesion is found with N2, H2, and SF6, all gases with incomplete outer electron shells, allowing for transient, possibly polarized, covalent bonding with oxygen as the significant minority component in the mix. Argon and helium do not interfere with oxygen. With 3% oxygen in argon without BCV, the experiments ran so long (>70hours) they were terminated once the point had been made. 3% oxygen in argon after BCV yielded a mean survival more than twice that of BCV in air, indicating a remarkable degree of nitrogen interference with oxygen in the respiratory medium of terrestrial animal life. Argon displayed other advantages for the lung compared to nitrogen. Hydrogen, nitrogen, and oxygen are diatomic molecules, a feature which does relate to the extent of lung injury, but only oxygen is paramagnetic. Magnetic effects on lesion formation were tested: [1] with ventilatory distress induced in newborn rabbits, and [2] in young adult female white mice exposed to 100% oxygen without added mechanical distress. A noninvasive model for ventilatory distress, thoracic restraint (TR), with longer mean survivals of 40–50hours, was employed rather than the Farber model. Parallel runs with TR, one subset receiving 100% oxygen in a plastic chamber resting on six strong ring magnets with measured fields up to +1200 gauss, the other plain 100% oxygen, were performed. Both subsets developed moderate metabolic acidosis with average weight losses circa 25%, but over different time courses, 82.89±4.91hours in magnetized oxygen, 55.4% longer than the 53.34±9.82hours in plain oxygen (p <0.001). The longer survival in magnetized oxygen meant extensive lung injury (99.57±0.42% pleural surface, versus 83.86±14.03%), but the rate of lesion formation was 30.89% faster in plain oxygen (1.5722% per hour) than in magnetized oxygen (1.2012% per hour), a difference significant at p <0.001. The effect of oxygen without mechanical ventilatory distress was examined in female adult white mice exposed to oxygen or magnetized oxygen. Similar survivals and weight losses were achieved. The rate of lung lesion formation was different, 1.2617% per hour in plain oxygen, 46.13% faster than 0.8634% per hour in magnetized oxygen. A variable magnetic field, with animals moving and breathing in chambers flooded with oxygen, has both systemic and pulmonary effects which alter the rate of lesion formation due to oxygen toxicity. Paramagnetic oxygen in a magnetic field influences the effect of oxygen toxicity on the lung but at these strengths of field it does not overcome significant mechanical disturbance. [Copyright &y& Elsevier]

Abstract: The novel R 3Co2Ge3 compounds with R=Y, Sm, Tb–Tm adopt the Hf3Ni2Si3-type structure (ordered variant of the Ca3Ga5-type one, space group Cmcm). Sm3Co2Ge3, Tb3Co2Ge3, Ho3Co2Ge3 and Er3Co2Ge3 undergo an antiferromagnetic-type ordering and Tb3Co2Ge3 demonstrates a field-sensitive magnetic behavior. Tm3Co2Ge3 is a pure paramagnet down to 5K, whereas Y3Co2Ge3 demonstrates Pauli paramagnetism down to ∼120K. In zero applied field and between ∼50 and ∼15K Tb3Co2Ge3 shows a non-collinear antiferromagnetic ordering with wave vectors K 0=[0, 0, 0] and K 1=[±1/3, 0, 0] and a magnetic unit cell , whereas below ∼15K it exhibits a complex antiferromagnetic ordering with K 0=[0, 0, 0], K 1=[±1/3, 0, 0] and K 2=[1/2, 0, 0] wave vectors and magnetic unit cell . [Copyright &y& Elsevier]

Abstract: Herein, we report the synthesis of three covalently linked superparamagnetic nanocrystal-multi-walled carbon nanotube (MWCNT) composites. A generic strategy for amphiphilic polymer coating of nanocrystals and further functionalization for amide bond formation with the MWCNTs is discussed. This approach can in principle allow attachment of any colloidal nanocrystal to the MWCNTs. The materials were characterized at each stage of the syntheses using DLS, zeta-potential measurements, FT-IR, TEM, and XPS techniques. The practicality of this linkage is demonstrated by the reversible magnetic immobilization of these materials on an electrode during non-aqueous electrochemistry. [Copyright &y& Elsevier]

Abstract: Heavily doped Zn1− x Mn x O (x =0.3) films were prepared by polymeric precursor method onto glass substrates and their structural, morphological, optical and magnetic properties carefully studied. Undoped ZnO films were also prepared for the purpose of comparison. The polymeric precursor method consists in preparing a coating solution from the Pechini process followed by a three-step thermal treatment of the as deposited films at temperatures up to 550°C for 30min. X-ray diffraction (XRD) analysis reveals the typical hexagonal wurtzite structure of the undoped ZnO film. The addition of Mn ions leads to a dramatic reduction of the crystalline quality of film although no evidence of affectation by secondary phases is found. The affectation of the ZnO structure may be due to the formation of Mn clusters and generation of defects such as vacancies and interstitials. Here, the solubility limit of the Mn ions in ZnO should play an important role and it is discussed in the framework of ionic radius and valence states. The scanning electron microscopy (SEM) analysis shows that the surface of the doped sample was affected by the presence of cracks due, probably, to the expansion of the lattice constant of Zn0.7Mn0.3O caused by the Mn incorporation in the ZnO lattice. The existence of cluster-type structures on the surface is corroborated by atomic force microscopy (AFM). The EDX analysis, carried out on some areas in the film, yielded Mn/Zn ratios of about 0.3, which points out to an effective Mn incorporation in the film. On the other hand, the absorption edge of the doped films is red shifted to 2.9eV (3.24eV for undoped ZnO film) and the absorption edge is less sharp due, probably, to amorphous states appearing in the band gap. No evidence of dilute magnetic semiconductor mean-field ferromagnetic behavior is observed. The temperature dependence of the magnetization follows a Curie law suggesting pure paramagnetic behavior. The very small s-shape behavior of M versus H (without hysteresis) observed at room temperature on selected areas would stem from Mn clusters which are easily formed in transition metal doped ZnO. [Copyright &y& Elsevier]

Abstract: The influence of g tensor anisotropy on spin dynamics of paramagnetic centers having real or effective spin of 1/2 is studied. The g anisotropy affects both the excitation and the detection of EPR signals, producing noticeable differences between conventional continuous-wave (cw) EPR and pulsed EPR spectra. The magnitudes and directions of the spin and magnetic moment vectors are generally not proportional to each other, but are related to each other through the g tensor. The equilibrium magnetic moment direction is generally parallel to neither the magnetic field nor the spin quantization axis due to the g anisotropy. After excitation with short microwave pulses, the spin vector precesses around its quantization axis, in a plane that is generally not perpendicular to the applied magnetic field. Paradoxically, the magnetic moment vector precesses around its equilibrium direction in a plane exactly perpendicular to the external magnetic field. In the general case, the oscillating part of the magnetic moment is elliptically polarized and the direction of precession is determined by the sign of the g tensor determinant (g tensor signature). Conventional pulsed and cw EPR spectrometers do not allow determination of the g tensor signature or the ellipticity of the magnetic moment trajectory. It is generally impossible to set a uniform spin turning angle for simple pulses in an unoriented or ‘powder’ sample when g tensor anisotropy is significant. [Copyright &y& Elsevier]

Abstract: Powder samples and single crystals of the new complex boride series Cr x (Rh1−y Ru y )7−x B3 (x=0.88–1; y=0–1) have been synthesized by arc-melting the elements under purified argon atmosphere on a water-cooled copper crucible. The products, which have metallic luster, were structurally characterized by single-crystal and powder X-ray diffraction as well as EDX measurements. Within the whole solid solution range the hexagonal Th7Fe3 structure type (space group P63 mc, no. 186, Z=2) was identified. Single-crystal structure refinement results indicate the presence of chromium at two sites (6c and 2b) of the available three metal Wyckoff sites, with a pronounced preference for the 6c site. An unexpected Rh/Ru site preference was found in the Ru-rich region only, leading to two different magnetic behaviors in the solid solution: The Rh-rich region shows a temperature-independent (Pauli) paramagnetism whereas an additional temperature-dependent paramagnetic component is found in the Ru-rich region. [Copyright &y& Elsevier]

Abstract: Multifunctional fluorescent and superparamagnetic Fe3O4/poly(fluorescein O-methacrylate) [Fe3O4/poly(FMA)] nanoparticles with core/shell structure were synthesized via surface-initiated polymerization. First, polymerizable double bonds were introduced onto the surface of Fe3O4 nanoparticles via ligand exchange and a condensation reaction. A fluorescent monomer, FMA, was then polymerized to the double bonds at the surface via free-radical polymerization, leading to form a fluorescent polymer shell around the superparamagnetic Fe3O4 core. The resultant Fe3O4/poly(FMA) nanoparticles were characterized by Fourier transform infrared, nuclear magnetic resonance, and X-ray diffraction spectroscopy to confirm the reactions. Transmission electron microscopy images showed that the Fe3O4/poly(FMA) nanoparticles have a spherical and monodisperse core/shell morphology. Photoluminescence spectroscopy and superconducting quantum interference device magnetometer analyses confirmed that the Fe3O4/poly(FMA) nanoparticles exhibited fluorescent and superparamagnetic properties, respectively. In addition, we demonstrated the potential bioimaging application of the Fe3O4/poly(FMA) nanoparticles by visualizing the cellular uptake of the nanoparticles into A549 lung cancer cells. [Copyright &y& Elsevier]

Abstract: Single crystals of have been grown by flux method and characterized by means of X-ray diffraction, magnetic, heat capacity and electrical transport measurements. The compound exhibits weakly temperature-dependent, moderately exchange-enhanced Pauli paramagnetism and shows regular metallic conductivity. [Copyright &y& Elsevier]

Abstract: The nanoparticle with simultaneous combination of magnetic and fluorescent properties was prepared by immobilization of fluorescein isothiocyanate (FITC) onto magnetic polymeric nanoparticle (MPNP). The MPNP with 41% magnetic content was obtained from incorporating Fe3O4 magnetic nanoparticles (MNPs) into poly(styrene/divinyl benzene/acrylic acid) via the miniemulsion polymerization. Before labeling with FITC, the carboxylated MPNP was coated with chitosan (CS) having low, medium, or high molecular weight (MW) in order to avoid quenching of the fluorescent by iron oxide. Data obtained from TEM, size and zeta potential measurements clearly indicated the presence of CS as a shell surrounding the superparamagnetic MPNP core. The zeta potential, FTIR, and fluorescent spectroscopies confirmed the attachment of FITC to the MPNP-CS via covalent bonding. The higher MW or longer chains of CS (300kDa) offered the larger spacer with multiple sites for the FITC binding and, thus, provided the higher fluorescent emission intensity. The MPNP-CS immobilized with FITC would be useful for cell-labeling application. [Copyright &y& Elsevier]

Abstract: A theoretical treatment is provided for the calculation of EPR (electron paramagnetic resonance) lineshape as affected by interactions with paramagnetic ions in the vicinity. The internal fields seen by the various paramagnetic ions due to interactions with paramagnetic ions in their vicinity, as well as the resulting lineshapes, become quite significant at high magnetic fields required in high-frequency (HFHF) EPR. The resulting EPR signals for the various ions are therefore characterized by different g-shifts and lineshapes, so that the overall EPR lineshape, which is an overlap of these, becomes distorted, or even split in HFHF EPR, from that observed at lower frequencies. The observed EPR lineshapes in MnSO4⋅H2O powder and K3CrO8 single-crystal samples have been simulated here taking into account g-shifts and modified lineshapes. These simulations show that in these samples, concentrated in paramagnetic spins, the position and lineshapes of EPR signals are significantly modified in HFHF EPR involving very high magnetic fields. [Copyright &y& Elsevier]

Abstract: The effects of Ti, Fe and Co substitutions for Ir on the structure and on the physical properties of Sr2IrO4 are investigated. A complete solid solution Sr2Ir1−x Ti x O4 is obtained while both Fe and Co doping are relatively limited. In each case however, the c-axis cell parameter and the initial IrO6 octahedra tilting decreases with substitution. Doping with Ti, Fe and Co results in a decrease of the magnetic susceptibility and in an increase in the paramagnetic effective moment for Co and Fe doped samples and a suppression of the weak ferromagnetic ordering observed for Sr2IrO4. [Copyright &y& Elsevier]

Abstract: Internalisation of nanoparticles conjugated with cell penetrating peptides is a promising approach to various drug delivery applications. Cell penetrating peptides such as transactivating transcriptional activator (TAT) peptides derived from HIV-1 proteins are effective intracellular delivery vectors for a wide range of nanoparticles and pharmaceutical agents thanks to their amicable ability to enter cells and minimum cytotoxicity. Although different mechanisms of intracellular uptake and localisation have been proposed for TAT conjugated nanoparticles, it is necessary to visualise the particles on a 3-D plane in order to investigate the actual intracellular uptake and localisation. Here, we study the intracellular localisation and trafficking of TAT peptide conjugated superparamagnetic ion oxide nanoparticles (TAT-SPIONs) using 3-D electron tomography. 3-D tomograms clearly show the location of TAT-SPIONs in a cell and their slow release from the endocytic vesicles into the cytoplasm. The present methodology may well be utilised for further investigations of the behaviours of nanoparticles in cells and eventually for the development of nano drug delivery systems. [Copyright &y& Elsevier]

Abstract: The formation of spherical superparamagnetic colloidal aggregates of magnetite nanoparticles by emulsification of a ferrofluid and subsequent solvent evaporation has been systematically studied. The colloidal aggregates occur as a dense sphere with magnetite nanoparticles randomly packed and preserved particle–particle separation due to chemisorbed oleic acid. The voids between nanoparticles are filled with solvent and free oleic acid. The latter was found to influence the formation of colloidal aggregates and their surface properties. The choice of surfactant, whether low molecular weight or polymeric, was shown to lead to the colloidal aggregates having tailored interfacial behavior. Magnetization measurements at ambient temperature revealed that the magnetite colloidal aggregates preserve the superparamagnetic properties of the starting nanoparticle units and show high saturation magnetization values up to 57emu/g. The size distribution of magnetite nanoparticle colloidal aggregates produced by such an approach was found to be a function of emulsion droplet breakup – coalescence and stabilization kinetics and therefore is influenced by the emulsification process conditions and concentrations of the emulsion compounds. [Copyright &y& Elsevier]

Abstract: We present the preparation and the characterization of the solution behavior and functional properties of superparamagnetic and/or fluorescent, thermo-responsive inorganic/organic hybrid particles with an intermediate protective silica shell and a smart polymer corona. These well-defined multifunctional nanogels were prepared via two consecutive encapsulation processes of superparamagnetic Fe2O3 nanoparticles (NPs) and/or fluorescent CdSe(ZnS) semiconductor nanocrystals with a silica layer and a crosslinked poly(N-isopropylacrylamide) (PNIPAAm) polymer shell. First, the different NPs were entrapped into a silica shell using a microemulsion process. Therein, the precise adjustment of the conditions allows to entrap either several particles or single ones and to tailor the thickness of the silica shell in the range of 20–60nm. In a second step, a polymer coating, i.e. thermosensitive PNIPAAm, was attached onto the surface of the multifunctional core–shell particles via free radical precipitation polymerization, furnishing multifunctional core–shell–corona hybrid nanogels. Analyses of the functional properties, i.e. optical brightness and magnetic moments, along with transmission electron microscopy reveal near monodisperse hybrid nanoparticles that retain the intrinsic properties of the original nanocrystals. Additionally, we demonstrate the drastically increased chemical stability due to the barrier properties of the intermediate silica layer that protects and shields the inner functional nanocrystals and the responsive character of the smart PNIPAAm shell. [Copyright &y& Elsevier]

Abstract: Although quadruplex nucleic acids are thought to be involved in many biological processes, they are massively overwhelmed by duplex DNA in the cell. Small molecules, able to probe quadruplex nucleic acids with high optical selectivity, could possibly achieve the visualization of these processes. The aim of the method described herein is to evaluate quickly the optical selectivity of quadruplex nucleic acid probes, in isothermal conditions, using widely available materials, small quantities of oligonucleotides and virtually any kind and quantity of biological competitor. The assay relies on the use of streptavidin-coated paramagnetic particles and biotinylated quadruplex forming oligonucleotides, allowing a quick and easy separation of the quadruplex target from the competitor. In the present study, two quadruplex nucleic acids (the DNA and RNA human telomeric repeats) have been used as targets while a duplex DNA oligonucleotide, total DNA, total RNA, another quadruplex nucleic acid and a protein have been used as competitors. The optical selectivity of various probes, displaying different photophysical properties and binding selectivities, has been successfully examined, allowing the identification of a best candidate for further cell microscopy experiments. This assay allows a quick and reliable assessment of the labeling properties of a quadruplex binder in cellular environment conditions. It is an interesting alternative to gel electrophoresis experiments since it is performed in solution, has a well-resolved separation system and allows easy quantifications. [Copyright &y& Elsevier]

Abstract: Double Electron–Electron Resonance (DEER) has emerged as a powerful technique for measuring long range distances and distance distributions between paramagnetic centers in biomolecules. This information can then be used to characterize functionally relevant structural and dynamic properties of biological molecules and their macromolecular assemblies. Approaches have been developed for analyzing experimental data from standard four-pulse DEER experiments to extract distance distributions. However, these methods typically use an a priori baseline correction to account for background signals. In the current work an approach is described for direct fitting of the DEER signal using a model for the distance distribution which permits a rigorous error analysis of the fitting parameters. Moreover, this approach does not require a priori background correction of the experimental data and can take into account excluded volume effects on the background signal when necessary. The global analysis of multiple DEER data sets is also demonstrated. Global analysis has the potential to provide new capabilities for extracting distance distributions and additional structural parameters in a wide range of studies. [Copyright &y& Elsevier]

Abstract: The potential of magnetic grain-size variations as an obsidian source characteristic is investigated using geological and archaeological obsidians from five islands of the Mediterranean Sea: Lipari, Sardinia, Palmarola, Pantelleria, Melos. Four parameters are used: magnetic (χ) and anhysteretic (χ a) susceptibilities, saturation isothermal remanent magnetizations at room (SIRM293) and liquid nitrogen (SIRM77) temperature. The ratio S T = SIRM77/SIRM293, which depends on the superparamagnetic grains relative abundance, varies little in each individual site, with the exception of Lipari which is characterized by large variations and the highest content of superparamagnetic grains. The χ a vs. χ plot () shows some within-site dispersion of the samples; but the ratio Q a = χ a/χ, which is strongly influenced by the single domain grains content, is characteristic for each site. The combined use of the King and Q a vs. S T plots discriminates the samples from most of the sites and suggests that the grain-size analysis is a promising approach in sourcing obsidian archaeological artefacts. Moreover, the measurements of the four parameters used are simple, quick and feasible with no or little damage to archaeological finds. [Copyright &y& Elsevier]

Abstract: Determination of three-dimensional structures of biological macromolecules by magic-angle spinning (MAS) solid-state NMR spectroscopy is hindered by the paucity of nuclear dipolar coupling-based restraints corresponding to distances exceeding 5Å. Recent MAS NMR studies of uniformly 13C,15N-enriched proteins containing paramagnetic centers have demonstrated the measurements of site-specific nuclear pseudocontact shifts and spin relaxation enhancements, which report on electron–nucleus distances up to ∼20Å. These studies pave the way for the application of such long-distance paramagnetic restraints to protein structure elucidation and analysis of protein–protein and protein–ligand interactions in the solid phase. Paramagnetic species also facilitate the rapid acquisition of high resolution and sensitivity multidimensional solid-state NMR spectra of biomacromolecules using condensed data collection schemes, and characterization of solvent-accessible surfaces of peptides and proteins. In this review we discuss some of the latest applications of magic-angle spinning NMR spectroscopy in conjunction with paramagnetic probes to the structural studies of proteins in the solid state. [Copyright &y& Elsevier]

Abstract: The effectiveness of two different selective inversion methods is investigated to determine timescales of Li ion mobility in paramagnetic Li intercalation materials. The first method is 1D exchange spectroscopy, which employs a 90°–τ 1–90° sequence for selective inversion of a Li resonance undergoing site exchange. The experiment is most easily applied when the first delay period, τ 1, is set to the frequency difference between two resonances undergoing ion exchange. This enables the determination of ion hopping timescales for single exchange pair systems only. To measure ion dynamics in systems having more than one exchange process, a second selective inversion method was tested on two paramagnetic Li intercalation materials. This second technique, replaces the 90°–τ 1–90° portion of 1D EXSY with a long, selective shaped pulse (SP). Two paramagnetic solid-state materials, which are both cathode materials for lithion ion batteries, were chosen as model compounds to test the effectiveness of both the selective inversion methods. The first compound, Li2VPO4F, was chosen as it hosts two Li sites with 1-exchange process. The second model compound is a 3-site, 3-exchange process system, Li2VOPO4. For the 2-site material, Li2VPO4F, the timescales of the single A–B exchange process were found to be within error of one another regardless of the inversion method. For the 3 Li-site material Li2VOPO4, the three exchange processes, AB, BC, and AC, were found to be on the millisecond timescale as revealed using the SP method. These timescales were determined over a variable temperature range where activation energies extended from 0.6±0.1eV up to 0.9±0.2eV. [Copyright &y& Elsevier]

Abstract: With the technique of dynamic nuclear polarization (DNP) signal intensity in solid-state MAS-NMR experiments can be enhanced by 2–3 orders of magnitude. DNP relies on the transfer of electron spin polarization from unpaired electrons to nuclear spins. For this reason, stable organic biradicals such as TOTAPOL are commonly added to samples used in DNP experiments. We investigated the effects of biradical concentration on the relaxation, enhancement, and intensity of NMR signals, employing a series of samples with various TOTAPOL concentrations and uniformly 13C, 15N labeled proline. A considerable decrease of the NMR relaxation times (T 1, , and T 1 ρ ) is observed with increasing amounts of biradical due to paramagnetic relaxation enhancement (PRE). For nuclei in close proximity to the radical, decreasing T 1 ρ reduces cross-polarization efficiency and decreases in broaden the signal. Additionally, paramagnetic shifts of 1H signals can cause further line broadening by impairing decoupling. On average, the combination of these paramagnetic effects (PE; relaxation enhancement, paramagnetic shifts) quenches NMR-signals from nuclei closer than 10Å to the biradical centers. On the other hand, shorter T 1 times allow the repetition rate of the experiment to be increased, which can partially compensate for intensity loss. Therefore, it is desirable to optimize the radical concentration to prevent additional line broadening and to maximize the signal-to-noise observed per unit time for the signals of interest. [Copyright &y& Elsevier]

Abstract: A technique that is increasingly being used to determine the structure and conformational flexibility of biomacromolecules is Pulsed Electron–Electron Double Resonance (PELDOR or DEER), an Electron Paramagnetic Resonance (EPR) based technique. At X-band frequencies (9.5GHz), PELDOR is capable of precisely measuring distances in the range of 1.5–8nm between paramagnetic centres but the orientation selectivity is weak. In contrast, working at higher frequencies increases the orientation selection but usually at the expense of decreased microwave power and PELDOR modulation depth. Here it is shown that a home-built high-power pulsed W-band EPR spectrometer (HiPER) with a large instantaneous bandwidth enables one to achieve PELDOR data with a high degree of orientation selectivity and large modulation depths. We demonstrate a measurement methodology that gives a set of PELDOR time traces that yield highly constrained data sets. Simulating the resulting time traces provides a deeper insight into the conformational flexibility and exchange coupling of three bisnitroxide model systems. These measurements provide strong evidence that W-band PELDOR may prove to be an accurate and quantitative tool in assessing the relative orientations of nitroxide spin labels and to correlate those orientations to the underlying biological structure and dynamics. [Copyright &y& Elsevier]

Abstract: This work proposes the use of TurboSPI, a multi-echo single point imaging sequence, for the quantification of labeled cells containing moderate to high concentrations of iron oxide contrast agent. At each k-space location, TurboSPI acquires several hundred time points during a spin echo, permitting reliable relaxation rate mapping of large- materials. An automatic calibration routine optimizes image quality by promoting coherent alignment of spin and stimulated echoes throughout the multi-echo train, and this calibration is sufficiently robust for in vivo applications. In vitro relaxation rate measurements of SPIO-loaded cervical cancer cells exhibit behavior consistent with theoretical predictions of the static dephasing regime in the spin echo case; the relaxivity measured with TurboSPI was 10.47±2.3s−1/mG, comparable to the theoretical value of 10.78s−1/mG. Similar measurements of micron-sized iron oxide particles (0.96μm and 1.63μm diameter) show a reduced relaxivity of 8.06±0.68s−1/mG and 7.13±0.31s−1/mG respectively, indicating that the static dephasing criterion was not met. Nonetheless, accurate quantification of such particles is demonstrated up to s−1, with a potentially higher upper limit for loaded cells having a more favorable ratio. Based on the cells used in this study, reliable quantification of cells loaded with 10pg of iron per cell should be possible up to a density of 27millioncells/mL. Such quantification will be of crucial importance to the development of longitudinal monitoring for cellular therapy and other procedures using iron-labeled cells. [Copyright &y& Elsevier]