Journal of Magnetic Resonance Open最新文献

From complex-mixture analysis to in vivo molecular imaging, applications of liquid-state nuclear spin hyperpolarization have expanded widely over recent years. In most cases, hyperpolarized solutions are generated ex situ and transported from the polarization instrument to the measurement device. The sample hyperpolarization usually survives this transport, since the changes in magnetic fields that are external to the sample are typically adiabatic (slow) with respect to the internal nuclear spin dynamics. The passage of polarized samples through weakly magnetic components such as stainless steel syringe needles and ferrules is not always adiabatic, which can lead to near-complete destruction of the magnetization. To avoid this effect becoming “folklore” in the field of hyperpolarized NMR, we present a systematic investigation to highlight the problem and investigate possible solutions. Experiments were carried out on: (i) dissolution-DNP-polarized [1-¹³C]pyruvate with NMR detection at 1.4 T, and (ii) 1.5-T-polarized H${}_2$O with NMR detection at 2.5 $\mu$T. We show that the degree of adiabaticity of solutions passing through metal parts is intrinsically unpredictable, likely depending on many factors such as solution flow rate, degree of remanent ferromagnetism in the metal, and nuclear spin species. However, the magnetization destruction effects can be suppressed by application of an external field on the order of 0.1–10 mT.

A prototype scannable unilateral permanent (SUPER) magnet for use with the electron paramagnetic resonance (EPR) mobile universal surface explorer (MOUSE) is described. The unilateral magnetic field is scannable from -94 to 94 mT by changing the relative angles of two fixed position ring magnets. The angular dependence of the modeled and measured magnetic fields are in agreement. The SUPER magnet is demonstrated on both the narrow spectral line sample DPPH as well as the broad spectral line sample rhodochrosite using the EPR MOUSE.

Intrinsically disordered proteins (IDPs) and intrinsically disordered regions (IDRs) of complex multi-domain proteins are now identified as a trend topic by the scientific community. NMR constitutes a unique investigation tool to access atom resolved information on their structural and dynamic properties, in isolation or upon interaction with potential partners (metal ions, small molecules, proteins, nucleic acids, membrane mimetics etc.). Their high flexibility and disorder, in contrast to more compact structures of globular protein domains, has a strong impact on NMR observables and NMR experiments should be tailored for their investigation. In this context, ¹³C direct detection NMR has become a very useful tool to contribute to IDPs/IDRs characterization at atomic resolution. 2D CON spectra can now be collected in parallel to 2D HN ones, and reveal information, which in some cases is not accessible through 2D HN spectra only, particularly when studying proteins in experimental conditions approaching physiological pH and temperature. The 2D HN/CON spectra are thus becoming a sort of identity card of an IDP/IDR in solution. Their simultaneous acquisition through multiple receiver NMR experiments is particularly useful to investigate the properties of highly flexible intrinsically disordered regions within complex multi-domain proteins, rather than in isolation as often performed to reduce the complexity of the system, an interesting perspective in the field.

Higher magic angle spinning (MAS) frequencies than currently available are desirable to improve spectral resolution in NMR and EPR systems. While conventional strategies employ pneumatic spinning limited by fluid dynamics, this paper demonstrates the development of an optical spinning technique in which vacuum quality dictates the maximum achievable spinning frequency. Using optical traps, we levitated a range of micron-sized samples. Under vacuum we achieved optical rotation of a single ∼10 μm diameter particle of vaterite at several mbar up to hundreds of Hz and of 20 μm diameter SiO₂ particles at ≤10⁻² mbar at several kHz. At ambient conditions, we optically levitated γ-irradiated alanine particles of 20–50 μm diameter. Additionally, using a single chip EPR detector operating at 11 GHz, we measured the EPR spectrum for a 30 μm γ-irradiated alanine particle in contact with the chip surface (i.e., without optical levitation) in a single scan lasting 92 s. These observations suggest that a γ-irradiated alanine particle having a diameter in the order of 30 μm is a promising candidate for our aim of demonstrating the first magnetic resonance experiment on optically levitated samples. Furthermore, we discuss strategies, limitations, and the potential of implementing MAS with optical traps for NMR and EPR.

We describe an automated hands-off bench testing method for measuring the magnetic field profile of transceiver coils for nuclear magnetic resonance (NMR). The scattering parameter (S-parameter) data is measured using a portable network analyzer, and the results are automatically exported to a computer for plotting and viewing. This assay dramatically reduces the time needed to measure the magnetic field (B${}_1$) homogeneity profile of a transceiver coil while also improving accuracy relative to manual operation. Here, we demonstrate the method on a saddle coil of a solution-state NMR probe in comparison to profiles obtained using NMR spectroscopy measurements. We also measure the axial homogeneity of a variable-pitch solenoid.

Rapid expansion of the Li-ion pouch cell market is driven by the looming problem of permanent depletion of natural gas reservoirs and by the growing demand for high-performance portable devices and electric vehicles. Safety and performance of Li-ion cells have been two main focal points of the extensive battery research. Surface-scan Magnetic Resonance Imaging (MRI) is an operando method designed for the accurate detection of substandard battery cells and for monitoring electrochemical processes with high spatial and temporal resolutions. Intercalation-dependent magnetism and charge transfer processes in the cell's electrodes give rise to characteristic magnetic field patterns outside the cell. For accurate mapping of such patterns, we proposed the concept of a unilateral radio-frequency (RF) sensor, a flat thin resonator encapsulating a proton-rich solid-state detection medium. When the pouch cell is placed in direct contact with the sensor, the magnetic field patterns propagate inside the detection medium, and the corresponding spatial distribution of Larmor precession frequencies can be detected with MRI. In this work, we developed and evaluated a series of RF sensor configurations based on parallel-plate architecture enhanced by arrays of distributed capacitors. The parallel-plate approach does not suffer from RF interference with pouch cells and provides excellent sensitivity and B₁-field homogeneity. The optimal configuration of the parallel-plate sensor depends on the dimensions of the pouch cell and the distribution of parallel capacitors. This article includes the results of experimental tests, RF-field simulations, and strategies to further improve the surface-scan MRI method.

Here we correct an expression in a recent paper Jeschke (2023).

Signal Amplification By Reversible Exchange (SABRE) is a technique aimed at enhancing weak NMR signals of heteronuclei by utilizing the non-equilibrium spin order of parahydrogen. SABRE polarization transfer takes place by means of metalorganic complexes that interact with parahydrogen and the substrate to be polarized in a reversible manner. To achieve substrate hyperpolarization in the high magnetic field of an NMR magnet, radiofrequency (RF) excitation is required. There are two general options for the RF field amplitude: constant or modulated. To date, there has been limited optimization of the adiabatic SABRE conditions. In SABRE, the presence of chemical exchange significantly complicates the spin dynamics involved in polarization transfer and the optimization of adiabatic RF sweeps. We conducted a comprehensive analysis of high-field SABRE pulse sequences with RF sweeps on the heteronuclear channel, specifically ¹⁵N. We proposed a simple method for optimizing the amplitude modulation profile of the RF field, which is efficient for systems undergoing chemical exchange. Our approach involved utilizing the dependence of ¹⁵N polarization on the amplitude of the constant RF field on the ¹⁵N channel. By employing the "optimal" adiabatic RF profile, we achieved a 2.5-fold increase in ¹⁵N SABRE-derived polarization at high magnetic field compared to a linear sweep. We theoretically assessed the benefit of RF sweeps over constant RF fields for SABRE at high magnetic field. We demonstrated experimentally that at temperatures $-5^{\circ }$C - $+{10}^{\circ }$C RF sweeps are more efficient than constant RF field. Maximal increase in ¹⁵N polarization achieved was 1.7-fold for bound and 1.4-fold for free substrate. We attribute this increase in polarization to the adiabaticity of the polarization transfer process. This behavior was explained via numerical solution of SABRE master equation for different dissociation rate constants.

Commercial availability, ease of printing and cost effectiveness have rendered 3D printing an essential part of magnetic resonance (MR) experimental design. However, the magnetic properties of several materials contemporarily used for 3D printing are lacking in literature to some extent. A database of the magnetic susceptibilities of several commonly used 3D printing materials is provided, which may aid MR experiment design. Here, we exploit the capability of magnetic resonance imaging (MRI) to map the local magnetic field variations caused by these materials when placed in the scanner's B₀ field. Exact analytical solutions of the magnetic flux density distribution for a cylindrical geometry are utilized to fit experimentally obtained data with theory in order to quantify the magnetic susceptibilities. A detailed explanation of the data processing and fitting procedure is presented and validated by measuring the susceptibility of air along with high resolution MR measurements. Furthermore, an initiative is taken to address the need for a comprehensive database comprising of not only the magnetic susceptibilities of 3D printing materials, but also information on the 3D printing parameters, the printers used, and other information available for the materials that may also influence the measured magnetic properties. An open platform with the magnetic susceptibilities of materials reported in this work besides existing literature values is provided here, with the aim to invite researchers to enable further extension and development towards an open database to characterize commonly used 3D printing materials based on their magnetic properties.