Concentration Of Paramagnetic Ions Research Articles

Anomalies in the magnetic properties of bismuth-substituted diluted yttrium iron garnet

The magnetic properties and Mössbauer spectra of the Y1.8Bi1.2Fe3.5Ga1.5O12 compound were investigated. A linear temperature dependence of the saturation magnetization, hysteresis, and stability of the coercive field in the magnetically ordered state were found. Using the Mössbauer measurements, the distribution of iron ions over octahedral and tetrahedral sites and the concentration of paramagnetic iron ions were determined. Two critical temperatures – the sublattice magnetization compensation temperature and the ferrimagnet–paramagnet transition temperature – were established. The disappear of the phonon mode in the vicinity of the magnetic transition was observed. The experimental data have been interpreted in terms of the spin–lattice interaction model.

Following Molecular Mobility during Chemical Reactions: No Evidence for Active Propulsion.

The reported changes in self-diffusion of small molecules during reactions have been attributed to "boosted mobility". We demonstrate the critical role of changing concentrations of paramagnetic ions on nuclear magnetic resonance (NMR) signal intensities, which led to erroneous measurements of diffusion coefficients. We present simple methods to overcome this problem. The use of shuffled gradient amplitudes allows accurate diffusion NMR measurements, even with time-dependent relaxation rates caused by changing concentrations of paramagnetic ions. The addition of a paramagnetic relaxation agent allows accurate determination of both diffusion coefficients and reaction kinetics during a single experiment. We analyze a copper-catalyzed azide-alkyne cycloaddition "click" reaction, for which boosted mobility has been claimed. With our methods, we accurately measure the diffusive behavior of the solvent, starting materials, and product and find no global increase in diffusion coefficients during the reaction. We overcome NMR signal overlap using an alternative reducing agent to improve the accuracy of the diffusion measurements. The alkyne reactant diffuses slower as the reaction proceeds due to binding to the copper catalyst during the catalytic cycle. The formation of this intermediate was confirmed by complementary NMR techniques and density functional theory calculations. Our work calls into question recent claims that molecules actively propel or swim during reactions and establishes that time-resolved diffusion NMR measurements can provide valuable insight into reaction mechanisms.

Electronic structure and unusual magnetic properties of diluted magnetic semiconductors Pb1-x-ySnxScyTe

We synthesize a single-crystal Pb1-x-ySnxScyTe ingot and investigate the magnetic properties (2.0 ≤ T ≤ 300 K, B ≤ 3 T) of alloys cut from it (x = 0.045–0.175, y ≤ 0.04). At low temperatures, all samples exhibit paramagnetic contribution to the magnetization, which contradicts the generally accepted model of doping-induced rearrangement of the electronic structure of alloys and is most likely due to the paramagnetism of electrically neutral Sc2+ ions or their clusters. In p-type samples, a high-temperature ferromagnetic ordering with a Curie temperature as high as TC = 145–150 K is found, presumably due to the RKKY hole-mediated interaction of Sc2+ ions. We obtain dependences of the concentration of paramagnetic ions, of the paramagnetic Curie-Weiss temperature Θ and of the Curie temperature TC on the concentrations of scandium and tin. At temperatures T < 100 K, the spin-glass-like behavior of magnetization and ferromagnetic hysteresis loops in the field dependences of magnetization are detected, indicating the formation of a mixed ferromagnetic–spin glass phase.

Magnetic levitation assisted biofabrication, culture, and manipulation of 3D cellular structures using a ring magnet based setup.

Diamagnetic levitation is an emerging technology for remote manipulation of cells in cell and tissue level applications. Low-cost magnetic levitation configurations using permanent magnets are commonly composed of a culture chamber physically sandwiched between two block magnets that limit working volume and applicability. This work describes a single ring magnet-based magnetic levitation system to eliminate physical limitations for biofabrication. Developed configuration utilizes sample culture volume for construct size manipulation and long-term maintenance. Furthermore, our configuration enables convenient transfer of liquid or solid phases during the levitation. Before biofabrication, we first calibrated/ the platform for levitation with polymeric beads, considering the single cell density range of viable cells. By taking advantage of magnetic focusing and cellular self-assembly, millimeter-sized 3D structures were formed and maintained in the system allowing easy and on-site intervention in cell culture with an open operational space. We demonstrated that the levitation protocol could be adapted for levitation of various cell types (i.e., stem cell, adipocyte and cancer cell) representing cells of different densities by modifying the paramagnetic ion concentration that could be also reduced by manipulating the density of the medium. This technique allowed the manipulation and merging of separately formed 3D biological units, as well as the hybrid biofabrication with biopolymers. In conclusion, we believe that this platform will serve as an important tool in broad fields such as bottom-up tissue engineering, drug discovery and developmental biology.

Canting of the Magnetic Moments on the Octahedral Site of an Iron Oxide Garnet in Response to Diamagnetic Cation Substitution.

Using neutron powder diffraction and magnetic susceptibility measurements, we report on the preparation and characterization of the temperature- and field-dependent properties of CaY2ZrFe4O12, a composition closely related to the high-temperature ferrimagnet Y3Fe5O12. By diluting the concentration of paramagnetic ions on the octahedral sublattice of the garnet structure, we find temperature-dependent canting of the magnetic moments. This reflects the importance of the octahedral sublattice in mediating the magnetic interactions between the tetrahedral sites and offers insight into a large number of competing magnetic interactions in the garnet structure.

NMR relaxometry for adsorption studies: Proof of concept with copper adsorption on activated alumina

Abstract Water pollution by heavy metal is a major environmental problem. Adsorption is one of the most used and promising heavy metal removal techniques. The development and evaluation of new adsorbents is thus an important topic. Some heavy metal ions – like Cu2+, Mn2+, Cr3+ … – are paramagnetic and known to affect the Nuclear Magnetic Resonance (NMR) relaxation times T1 and T2 of water protons in aqueous solutions. These relaxation times can be used to evaluate the paramagnetic ion concentration in solution. For the adsorption of Cu2+on activated alumina, we show, after a comparison with conventional methods, that NMR T2 relaxometry can be used to perform kinetics study and obtain a Langmuir isotherm. The T2 relaxometric experiment is performed at 0.47 T directly in an NMR tube with 350 µl of solution and 45 mg of adsorbent. For the kinetics study, a single tube is used since the measurement is nondestructive. The NMR experiments allow to determine a maximum Cu2+ adsorption capacity qmax = 4.32 mgCu/gAl2O3 and an equilibrium adsorption constant K = 0.61 mM−1. T1 based relaxometry can also be used to evaluate the amount of Cu2+ adsorbed on alumina, directly on the wet sorbent. Even if it is limited to paramagnetic heavy metal ion and necessitates rather high metal concentration, NMR relaxometry could become an interesting additional tool for the study of heavy metal adsorption.

Solid-state NMR and short-range order in crystalline oxides and silicates: a new tool in paramagnetic resonances.

Most applications of high-resolution NMR to questions of short-range order/disorder in inorganic materials have been made in systems where ions with unpaired electron spins are of negligible concentration, with structural information extracted primarily from chemical shifts, quadrupolar coupling parameters, and nuclear dipolar couplings. In some cases, however, the often-large additional resonance shifts caused by interactions between unpaired electron and nuclear spins can provide unique new structural information in materials with contents of paramagnetic cations ranging from hundreds of ppm to several per cent and even higher. In this brief review we focus on recent work on silicate, phosphate, and oxide materials with relatively low concentrations of paramagnetic ions, where spectral resolution can remain high enough to distinguish interactions between NMR-observed nuclides and one or more magnetic neighbors in different bonding configurations in the first, second, and even farther cation shells. We illustrate the types of information available, some of the limitations of this approach, and the great prospects for future experimental and theoretical work in this field. We give examples for the effects of paramagnetic transition metal, lanthanide, and actinide cation substitutions in simple oxides, pyrochlore, zircon, monazite, olivine, garnet, pyrochlores, and olivine structures.

Nuclear Magnetic Spectrometer for Studying Flows of Liquid Media

Elements of studies of flows of liquid media by a nuclear magnetic spectrometer are considered. Through an assessment of these features in the design of a nuclear magnetic spectrometer the relative concentrations of paramagnetic ions could be determined and the longitudinal and transverse relaxation times measured in flows of liquid media with error not more than 0.5%. A regime for recording the nuclear magnetic resonance signal of a flowing liquid of fluorine, phosphorous, lithium, boron, sodium, chlorine, and mercury nuclei is created. The results of experimental studies of flows of liquid media are presented.

Safety and Efficacy of A High Performance Graphene-Based Magnetic Resonance Imaging Contrast Agent for Renal Abnormalities.

The etiology of renal insufficiency includes primary (e.g polycystic kidney disease) or secondary (e.g. contrast media, diabetes) causes. The regulatory restrictions placed on the use of contrast agents (CAs) for non-invasive imaging modalities such as X-ray computed tomography (CT) and magnetic resonance imaging (MRI) affects the clinical management of these patients. With the goal to develop a next-generation CA for unfettered use for renal MRI, here we report, in a rodent model of chronic kidney disease, the preclinical safety and efficacy of a novel nanoparticle CA comprising of manganese (Mn2+) ions intercalated graphene coated with dextran (hereafter called Mangradex). Nephrectomized rats received single or 5 times/week repeat (2 or 4 weeks) intravenous (IV) injections of Mangradex at two potential (low = 5 mg/kg, and high = 50 mg/kg) therapeutic doses. Histopathology results indicate that Mangradex does not elicit nephrogenic systemic fibrosis (NSF)-like indicators or questionable effects on vital organs of rodents. MRI at 7 Tesla magnetic field was performed on these rats immediately after IV injections of Mangradex at one potential therapeutic dose (25 mg/kg, [Mn2+] = 60 nmoles/kg) for 90 minutes. The results indicated significant (>100%) and sustained contrast enhancement in the kidney and renal artery at these low paramagnetic ion (Mn2+) concentration; 2 orders of magnitude lower than the paramagnetic ion concentration in a typical clinical dose of long circulating Gd3+-based MRI CA gadofosveset trisodium. The results open avenues for further development of Mangradex as a MRI CA to diagnose and monitor abnormalities in renal anatomy and vasculature.

Some specific features of the NMR study of fluid flows

Some specific features of studying fluid flows with a NMR spectrometer are considered. The consideration of these features in the NMR spectrometer design makes it possible to determine the relative concentrations of paramagnetic ions and measure the longitudinal and transverse relaxation times (T1 and T2, respectively) in fluid flows with an error no larger than 0.5%. This approach allows one to completely avoid errors in determining the state of a fluid from measured relaxation constants T1 and T2, which is especially urgent when working with medical suspensions and biological solutions. The results of an experimental study of fluid flows are presented.

Special Features in Application of Nuclear Magnetic Spectroscopy to Study Flows of Liquid Media

We consider the special features involved in studying flows of liquid media using a nuclear magnetic resonance spectrometer. Taking these special features into account in the design of the NMR spectrometer lets us determine the relative concentrations of paramagnetic ions, and also lets us measure the longitudinal (T1 ) and transverse (T2 ) relaxation times within <0.5% in liquid flows. This lets us completely eliminate errors in determining the state of the flowing medium using the measured relaxation constants T1 and T2, which is especially important when working with medicinal suspensions and biological solutions. We present the results of experimental studies on flows of liquid media.

Towards An Advanced Graphene-Based Magnetic Resonance Imaging Contrast Agent: Sub-acute Toxicity and Efficacy Studies in Small Animals.

Current clinical Gd3+-based T1 magnetic resonance imaging (MRI) contrast agents (CAs) are suboptimal or unsuitable, especially at higher magnetic fields (>1.5 Tesla) for advanced MRI applications such as blood pool, cellular and molecular imaging. Herein, towards the goal of developing a safe and more efficacious high field T1 MRI CA for these applications, we report the sub-acute toxicity and contrast enhancing capabilities of a novel nanoparticle MRI CA comprising of manganese (Mn2+) intercalated graphene nanoparticles functionalized with dextran (hereafter, Mangradex) in rodents. Sub-acute toxicology performed on rats intravenously injected with Mangradex at 1, 50 or 100 mg/kg dosages 3 times per week for three weeks indicated that dosages ≤50 mg/kg could serve as potential diagnostic doses. Whole body 7 Tesla MRI performed on mice injected with Mangradex at a potential diagnostic dose (25 mg/kg or 455 nanomoles Mn2+/kg; ~2 orders of magnitude lower than the paramagnetic ion concentration in a typical clinical dose) showed persistent (up to at least 2 hours) contrast enhancement in the vascular branches (Mn2+ concentration in blood at steady state = 300 ppb, per voxel = 45 femtomoles). The results lay the foundations for further development of Mangradex as a vascular and cellular/ molecular MRI probe.

Combining Step Gradients and Linear Gradients in Density

Combining aqueous multiphase systems (AMPS) and magnetic levitation (MagLev) provides a method to produce hybrid gradients in apparent density. AMPS—solutions of different polymers, salts, or surfactants that spontaneously separate into immiscible but predominantly aqueous phases—offer thermodynamically stable steps in density that can be tuned by the concentration of solutes. MagLev—the levitation of diamagnetic objects in a paramagnetic fluid within a magnetic field gradient—can be arranged to provide a near-linear gradient in effective density where the height of a levitating object above the surface of the magnet corresponds to its density; the strength of the gradient in effective density can be tuned by the choice of paramagnetic salt and its concentrations and by the strength and gradient in the magnetic field. Including paramagnetic salts (e.g., MnSO4 or MnCl2) in AMPS, and placing them in a magnetic field gradient, enables their use as media for MagLev. The potential to create large steps in density with AMPS allows separations of objects across a range of densities. The gradients produced by MagLev provide resolution over a continuous range of densities. By combining these approaches, mixtures of objects with large differences in density can be separated and analyzed simultaneously. Using MagLev to add an effective gradient in density also enables tuning the range of densities captured at an interface of an AMPS by simply changing the position of the container in the magnetic field. Further, by creating AMPS in which phases have different concentrations of paramagnetic ions, the phases can provide different resolutions in density. These results suggest that combining steps in density with gradients in density can enable new classes of separations based on density.

Measuring the solubility product constant of paramagnetic cations using time-domain nuclear magnetic resonance relaxometry

The use of time-domain NMR relaxometry is already well established for determining the concentration of paramagnetic cations. Paramagnetic cations have unpaired electrons, and in aqueous solutions, they interact with hydrogen nuclei, changing the relaxation time of the solvent. Thus, a linear relationship can be established between the nuclear spin–lattice relaxation time, T1, or the spin–spin relaxation time, T2, and the concentration of paramagnetic ions in solution. Previous studies have shown the efficacy of using T1 and T2 for easily determining the titration equivalence point. Currently, the most practical method for determining T2 is the Carr–Purcell–Meiboom–Gill (CPMG) pulse sequence. Thus, in this paper, we used the T2 relaxation time to determine the concentration of paramagnetic ions in solution. We used T2 relaxometry as a simple and useful method for measuring the hydroxide solubility products (Ksp) of Fe(OH)3, Cu(OH)2 and Mn(OH)2 aqueous solutions as functions of pH. To our knowledge, this is the first use of T2 relaxometry to measure Ksp.

Bifunctional chelates optimized for molecular MRI.

Important requirements for exogenous dyes or contrast agents in magnetic resonance imaging (MRI) include an effective concentration of paramagnetic or superparamagnetic ions at the target to be imaged. We report the concise synthesis and characterization of several new enantiopure bifunctional derivatives of (α1R,α4R,α7R,α10R)-α1,α4,α7,α10-tetramethyl-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTMA) (and their 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) analogues as controls) that can be covalently attached to a contrast agent delivery system using either click or peptide coupling chemistry. Gd complexes of these derivatives can be attached to delivery systems while maintaining optimal water residence time for increased molecular imaging sensitivity. Long chain biotin (LC-biotin) derivatives of the Eu(III) and Gd(III) chelates associated with avidin are used to demonstrate higher efficiencies. Variable-temperature relaxometry, 17O NMR, and nuclear magnetic resonance dispersion (NMRD) spectroscopy used on the complexes and biotin–avidin adducts measure the influence of water residence time and rotational correlation time on constrained and unconstrained systems. The Gd(III)-DOTMA derivative has a shorter water residence time than the Gd(III)-DOTA derivative. Compared to the constrained Gd(III)-DOTA derivatives, the rotationally constrained Gd(III)-DOTMA derivative has ∼40% higher relaxivity at 37 °C, which could increase its sensitivity as an MRI agent as well as reduce the dose of the targeting agent.

Phase transition temperature and paramagnetic effect in Al1−xCrxK(SO4)2·12H2O (x = 0, 0.07, and 0.2) crystals studied by 27Al nuclear magnetic resonance relaxation time

The physical properties of Al1−xCrxK(SO4)2·12H2O (x = 0, 0.07, and 0.2) single crystals as a function of temperature were studied by observing their 27Al nuclear magnetic resonance spectra and relaxation times. The effects of partial replacement of Al3+ ions with paramagnetic Cr3+ ions were examined on the basis of the physical properties of pure AlK(SO4)2·12H2O crystals. The phase transition temperatures TC varied depending on the concentration of paramagnetic ions. In addition, the spin–lattice relaxation time T1 of crystals containing Cr3+ ions was shorter than that of crystals without paramagnetic ions. The paramagnetic effects on T1 and TC were strongest for 27Al in Al0.8Cr0.2 K(SO4)2·12H2O crystals with 0.2 mol. % of Cr3+ ions.

In Situ Quantification of Cu(II) during an Electrodeposition Reaction Using Time-Domain NMR Relaxometry

The use of a low-cost benchtop time-domain NMR (TD-NMR) spectrometer to monitor copper electrodeposition in situ is presented. The measurements are based on the strong linear correlation between the concentration of paramagnetic ions and the transverse relaxation rates (R(2)) of the solvent protons. Two electrochemical NMR (EC-NMR) cells were constructed and applied to monitor the Cu(2+) concentration during the electrodeposition reaction. The results show that TD-NMR relaxometry using the Carr-Purcell-Meiboom-Gill pulse sequence can be a very fast, simple, and efficient technique to monitor, in real time, the variation in the Cu(2+) concentration during an electrodeposition reaction. This methodology can also be applied to monitor the electrodeposition of other paramagnetic ions, such as Ni(2+) and Cr(3+), which are commonly used in electroplating.

Paramagnetic Ions Affect Relaxation Rate Dispersion of Blood: Implications for Magnetic Resonance Relaxation Dispersion Imaging

The proton relaxation rate dispersion of paramagnetic ions in blood samples was studied in the frequency interval from 10 kHz to 10 MHz. With the Field cycling method we applied, the samples were first magnetized by a relatively high magnetic field (0.5 T). By electronic means this field was rapidly (1 ms) reduced to a lower value in the interval 0.1 mT - 0.5 T, where the excited proton spin may relax during a time interval of about 3·T1max. Then the magnetic field is again quickly raised up to the higher level for the detection of the NMR-signal. The relaxation characteristics were analyzed by applying a model with three compartments of water proton-spin exchange. For each compartment we estimated a correlation frequency by fitting the dispersion curves to a sum of Lorentz distributions. We found that low concentrations of paramagnetic ions have a large influence on the relaxation rate dispersion in the low frequency region 100 mT) and low (<10 mT) relaxation fields. Such sequences of images could be used to study the oxygen status and metabolism of the brain as well as the generation and distribution of reactive oxygen species (ROS). This technique called “Magnetic resonance Relaxation Dispersion Imaging” (MARDI) would be particularly suitable to analyze various neurological diseases such as stroke, MS, Alzheimer´s disease as well as brain tumor progression. It might also be suitable for imaging of tumour oxygenation and in vivo ROS distributions in radiation therapy, which could be used in dose planning and for analyzing and optimizing the effect of various radiation therapy regimes.

Magnetooptical Properties of (Ga,Fe)N Layers

Numerous works on diluted magnetic semiconductors carried out over the last decade have aimed in examining intricate interplay of ferromagnetic and semiconducting properties [1]. Wide band gap semiconductors such as GaN and ZnO doped with magnetic ions are particularly interesting in view of their wide ranging applications. Here we present results of magnetic circular dichroism (MCD) and Magneto-optical Kerr effect (MOKE) measurements in the excitonic spectral region performed on (Ga,Fe)N layers. In contrast to previous magnetooptical studies [2], we focus here on possible magnetoptical signatures of Fe-rich nanocrystals that appear in (Ga,Fe)N films obtained under suitable growth conditions [3]. We compare magnetoptical properties of two layers with similar concentrations of paramagnetic Fe ions (310cm and 210cm, respectively), one containing Fe-rich nanocrystals, the other not, according to extensive SQUID, XRD, and HRTEM characterization. As found in SQUID measurements, the sample with Fe-rich nanocrystals reveals a ferromagnetic response persisting up to above room temperature for two orientations of the magnetic field in respect to the c-axis. Reflectivity and MOKE measurements are performed in the Faraday configuration with the c-axis parallel to the incident beam in the magnetic field up to 7 T at 2 K. The sample is illuminated by a Xe lamp. We find that the field dependent magnitudes of MCD and Kerr rotation angle in the excitonic region are well descried by the paramagnetic Brillouin function in both samples. This means that ferromagnetic features, clearly seen in SQUID magnetometry, are not contributing to the magnetooptical response. We conclude that either character of nanocrystal magnetoptical properties or the nanocrystal distribution and density are not optimized to result in sizable magnetoptical phenomena. Instead, the presence on Fe-rich nanocrystals reduces the magnitude of the paramagnetic-like magnetooptical signals. In line with this observation, we find that a large magnetooptical response can be recovered by Ar sputtering of the sample surface, the finding consistent with the location of nanocrystals near the film surface [3].

Fluorescent and Paramagnetic Chitosan Nanoparticles that Exhibit High Magnetic Resonance Relaxivity: Synthesis, Characterization and &lt;I&gt;In Vitro&lt;/I&gt; Studies

We report water-in-oil (W/O) microemulsion synthesis of fluorescently bright and paramagnetically strong bimodal chitosan nanoparticles (BCNPs). The W/O microemulsion system provides a confined environment for producing monodispersed BCNPs. Average particle size as estimated by the Transmission Electron Microscopy was 28 nm. The water to surfactant molar ratio of 22 produced small size fairly monodispersed BCNPs. Fluorescein isothiocyanate (FITC, a fluorescent dye) and Gd-DOTA (a paramagnetic Gd ion chelating agent) were covalently attached to chitosan polymer backbone prior to BCNP synthesis. The purpose of the covalent attachment of fluorescent and paramagnetic labels to chitosan is to prevent leakage of these labels from the BCNPs. The BCNPs were cross-linked with tartaric acid using water-soluble carbodiimide coupling chemistry in order to maintain particulate integrity. Zeta potential value of +27.6 mV confirmed positive surface charge of cross-linked BCNPs. Fluorescence excitation and emission spectra of BCNPs were similar to that of bare FITC spectra, showing characteristic 520 nm emission at the 490 excitation. Paramagnetic gadolinium ion (Gd3+) concentration in the BCNPs was determined by inductively coupled plasma (ICP) emission spectroscopy. The longitudinal (T1) and transverse (T2) proton relaxation times were determined as a function of Gd3+ concentration in the BCNPs at 4.7 Tesla. Proton relaxivity (R1 value) of BCNPs was calculated to be 41.1 mM Gd(-1)s(-1). The reported R1 value of Gd-DOTA chelates is however 5.8 mM Gd(-1)s(-1). High proton relaxivity of BCNPs is attributed to hydrated chitosan environment around Gd chelates which additionally contributed to overall water exchange process. To demonstrate in vitro bioimaging capability, J774 macrophage cells were incubated with BCNPs. Confocal images clearly showed BCNP uptake by J774 cells. Internalization of BCNPs was confirmed by co-labeling J774 cells with a red-emitting membrane dye. BCNP green emission was mostly observed from middle of cells and within the red-emitting membrane boundary.