Relaxation Rate Research Articles

Injectable Biocompatible Zeolite Nanocrystals for Enhanced Tumor Oxygenation and MRI Imaging.

Tumor hypoxia significantly limits the effectiveness of radiotherapy, as oxygen is crucial for producing cancer-killing reactive oxygen species. To address this, we synthesized nanosized faujasite (PBS-Na-FAU) zeolite crystals using clinical-grade phosphate-buffered saline (PBS) as the solvent, ensuring preserved crystallinity, microporous volume, and colloidal stability. The zeolite nanocrystals showed enhanced safety profiles in vitro and ex vivo, and in vivo studies showed no apparent toxicity to animals. They demonstrated a high oxygen capacity with a release rate of 2.68 mg/L under hypoxic conditions. The introduction of gadolinium (Gd3+) into the zeolite nanocrystals by ion exchange, replacing three monovalent cations (Na+ and K+), led to an increased oxygen capacity of the sample. In situ Fourier transform infrared (FTIR) study revealed that Gd-containing zeolite (PBS-Gd-FAU) adsorbed ∼23% more oxygen at 20 kPa compared to the as-synthesized sample (PBS-Na-FAU). In vivo magnetic resonance imaging (MRI) demonstrated targeted oxygen delivery and release within brain tumors, revealing 14.91 and 17.10% differences in cerebral blood volume (CBV) between tumor and contralateral brain tissue after 15 and 20 min, respectively, compared to the control. T1 maps at 7 T indicated a relaxation rate of 9.254 mM-1·s-1 for PBS-Gd-FAU, twice that of commercial Gd-chelates. These findings highlight the potential of Gd-containing zeolite nanocrystals synthesized in PBS as a biocompatible platform for enhancing tumor oxygenation in anticancer therapy, with significant clinical translation potential.

Composite spin probes with adjustable oxygen sensitivity for pulse electron paramagnetic resonance imaging.

Solid crystalline spin probes, such as lithium phthalocyanine (LiPc) and lithium octa-n-butoxynaphthalocyanine (LiNc-BuO), allow repeated oxygen measurement using electron paramagnetic resonance (EPR). Due to their short relaxation times, their use for pulse EPR oxygen imaging is limited. In this study, we developed and tested a new class of solid composite spin probes that modified the relaxation rates R1 and R2 of LiPc or LiNc-BuO probes, which allowed pO2 measurements in the full dynamic (0-760 torr) range. The composite probes were developed by embedding LiPc or LiNc-BuO with bonewax, beeswax, or petroleum jelly. All experiments were performed using a 25-mT EPR imager, JIVA-25®. A selected composite probe, LiPc-BW5 (LiPc + 5-times bonewax), was tested for its in vivo stability and robustness using oxygen-enhanced EPR oxygen imaging. As another application, a LiPc-BW5-based marker was tested to outline the SCC7 tumor in a C3H mouse. The composite probes showed an increased oxygen measurement range compared with unaltered probes. The in vivo experiments with LiPc-BW5 showed the stability of the probes for repeated oxygen imaging up to 4 weeks of measurements. The in vivo pO2 at the subcutaneous site changed from 26.1 ± 1.9 torr to 118.9 ± 1.9 torr when the breathing gas was changed from 21% O2 to 100% O2. The use of LiPc-BW5 as a fiducial marker showed its use in outlining the tumor boundaries. We developed a new class of robust and versatile solid composite probes with adjustable oxygen sensitivity that allows pO2 imaging in the broad dynamic range.

The influence of the molecular weight of hyaluronic acid on the mangiferin release kinetics from the polymer matrix

Introduction. Currently, the use of natural biologically active agents (BAA) as effective antibacterial drugs for both external and internal use is becoming widespread. Polyphenol mangiferin, extracted from the leaves of the Mangifera indica plant, is the most attractive BAA. Despite high antimicrobial activity against gram-positive and gram-negative strains of bacteria, the use of mangiferin is limited by its low aqueous solubility. To increase solubility and, accordingly, bioavailability, various approaches are used, in particular, encapsulation in polymer and biopolymer matrices. One of the promising biopolymers for the encapsulation of biologically active substances is hyaluronic acid, which is completely biocompatible with the tissues of a living organism and is capable of complete biodegradation under the influence of enzymes (hyaluronidases).Aim. Study of the release kinetics of the biologically active agent (mangiferin) from a polymer matrix based on hyaluronic acid with different molecular weights.Materials and methods. Polymer films obtained by casting method from 1.5 wt.% forming solutions of hyaluronic acid with a molecular weight of 1.30 and 2.48 MDa with different contents of mangiferin were used as the objects of the study. The weight ratio of hyaluronic acid to mangiferin varied from 5 to 25. Released mangiferin was measured by UV/Vis spectrophotometry at a wavelength of 237 nm. A phosphate buffered saline with pH 7.4 was used as a model medium. The mangiferin release kinetic was assessed using various mathematical models.Results and discussion. Mangiferin release kinetic from a polymer matrix based on hyaluronic acid has a release sigmoidal pattern. The release mechanism has a complex nature of the Super Case II transport type, with the exception of a sample with a low content of mangiferin and hyaluronic acid with molecular weight equal to 1.3 MDa, for which an abnormal release pattern is detected (non-Fickian diffusion), due to the hydrophilic nature of hyaluronic acid, the rapid swelling of the polymer matrix, as well as a significant leading in the diffusion of mangiferin compared to the relaxation rate of the polymer. The most suitable model is the Weibull model, which describes the mangiferin release kinetics with greater accuracy compared to other mathematical models.Conclusion. The results obtained indicate the potential possibility of using the developed polymer films as biomedical materials for external use, which provide transdermal delivery of pharmaceutical agents. The authors of the study are planning to develop a methodology for prolonged and controlled release of a loaded biologically active agent, including by various cross-linking agents.

Universal bound on the relaxation rates for quantum Markovian dynamics

Abstract Relaxation rates provide important characteristics both for classical and quantum processes. Essentially they control how fast the system thermalizes, equilibrates, {decoheres, and/or dissipates}. Moreover, very often they are directly accessible to be measured in the laboratory and hence they define key physical properties of the system. Experimentally measured relaxation rates can be used to test validity of a particular theoretical model. %In this note 
Here we analyze a fundamental question: {\em does quantum mechanics provide any nontrivial constraint for relaxation rates?} We prove the conjecture formulated a few years ago that any quantum channel implies that a maximal rate is bounded from above by the sum of all the relaxation rates divided by the dimension of the Hilbert space. It should be stressed that this constraint is universal (it is valid for all quantum systems with finite number of energy levels) and it is tight (cannot be improved). In addition, the constraint plays an analogous role to the seminal Bell inequalities and the well known Leggett-Garg inequalities (sometimes called temporal Bell inequalities). Violations of Bell inequalities rule out local hidden variable models, and violations of Leggett-Garg inequalities rule out macrorealism.
Similarly, violations of the relaxation bound rule out Markovian (meaning CP-divisible) evolution.

Cerebral Hemodynamic Responses to Disease-Modifying and Curative Sickle Cell Disease Therapies.

Sickle cell disease (SCD) is a hemoglobinopathy resulting in hemoglobin-S production, hemolytic anemia, and elevated stroke risk. Treatments include oral hydroxyurea, blood transfusions, and hematopoietic stem cell transplantation (HSCT). Our objective was to evaluate the neurologic relevance of these therapies by characterizing how treatment-induced changes in hemoglobin (Hb) affect brain health biomarkers. In this interventional study, adults with and without SCD underwent a 3T-MRI at Vanderbilt University Medical Center at 2 time points before and after clinically indicated transfusion or HSCT or at 2 time points without the introduction of a new Hb-altering therapy (adult controls and patients with SCD on hydroxyurea). Cerebral blood flow (CBF; mL/100 g/min) and cerebral venous blood relaxation rate (s-1; a marker of Hb and blood oxygen content) responses were assessed to understand how these markers of brain health vary with Hb modulation. CBF was assessed with arterial spin labeling MRI, and blood relaxation rate was assessed using T2 relaxation under spin tagging MRI. Measures were pairwise compared within each cohort using a 2-tailed Wilcoxon signed-rank test, and regression was applied to evaluate the parameter and Hb change relationships. The significance criterion was 2-sided p < 0.05. Adults with (n = 43; age 28.7 ± 7.7 years; 42% male) and without (n = 13; age 33.5 ± 12.2 years; 46% male) SCD were evaluated. In adults receiving hydroxyurea (n = 10), neither Hb, CBF, nor venous relaxation rate changed between time 1 (Hb = 8.6 ± 1.2 g/dL) and time 2 (Hb = 9.0 ± 1.8 g/dL) (all p > 0.05). In transfusion patients (n = 19), Hb increased from 8.2 ± 1.4 g/dL to 9.3 ± 1.3 g/dL before vs after transfusion (p < 0.001), paralleling a CBF decrease of 14.2 mL/100 g/min (p < 0.001) toward control levels. The venous relaxation rate did not change after transfusion (p = 0.71). In HSCT patients (n = 14), Hb increased from 8.9 ± 1.9 g/dL to 12.9 ± 2.7 g/dL (p < 0.001) before vs after transplant, paralleling CBF decreases from 68.16 ± 20.24 to 47.43 ± 12.59 mL/100 g/min (p < 0.001) and increase in venous relaxation rate (p = 0.004). Across the Hb spectrum, a CBF decrease of 5.02 mL/100 g/min per g/dL increase in Hb was observed. Findings demonstrate improvement in cerebral hemodynamics after transfusion and transplant therapies compared with hydroxyurea therapy; quantitative relationships should provide a framework for using these measures as trial end points to assess how new SCD therapies affect brain health.

Temperature Dependence of Intermolecular Dynamics and Liquid Properties of Deep Eutectic Solvent, Reline.

We investigated the temperature dependence of the intermolecular dynamics, including intermolecular vibrations and collective orientational relaxation, of one of the most typical deep eutectic solvents, reline, using femtosecond Raman-induced Kerr effect spectroscopy (fs-RIKES), subpicosecond optical Kerr effect spectroscopy (ps-OKES), and molecular dynamics (MD) simulations. According to fs-RIKES results, the temperature-dependent intermolecular vibrational band peak at ∼90 cm-1 exhibited a redshift with increasing temperature. The density-of-state (DOS) spectrum of reline by MD simulations reproduced this fs-RIKES spectral feature. The decomposition analysis of the DOS spectra showed that all constituent components, including urea, cholinium cation, and chloride anion, also exhibited similar magnitudes of redshifts upon heating, indicating that the three species intermolecularly interact one another. The temperature sensitivity of the intermolecular vibrational frequency was high compared to that of ionic liquids. According to ps-OKES results, the slow orientational relaxation rate increased with increasing temperature; however, this phenomenon was not well explained by the Stokes-Einstein-Debye hydrodynamic model. Analysis of the orientational relaxation time based on the Stokes-Einstein-Debye model indicates that the decoupling between the orientational relaxation time and viscosity occurs at temperatures below ∼330 K. Quantum chemistry calculations of urea and the cholinium cation based on the MP2/6-311++G(d,p) level of theory confirmed that the contribution of intramolecular vibrational bands to low-frequency bands below 200 cm-1 was minimal. The densities, viscosities, electrical conductivities, and surface tensions of reline at various temperatures were also estimated and compared with the dynamics data.

A Spectrochemical Series for Electron Spin Relaxation.

Controlling the rate of electron spin relaxation in paramagnetic molecules is essential for contemporary applications in molecular magnetism and quantum information science. However, the physical mechanisms of spin relaxation remain incompletely understood, and new spectroscopic observables play an important role in evaluating spin dynamics mechanisms and structure-property relationships. Here, we use cryogenic magnetic circular dichroism (MCD) spectroscopy and pulse electron paramagnetic resonance (EPR) in tandem to examine the impact of ligand field (d-d) excited states on spin relaxation rates. We employ a broad scope of square-planar Cu(II) compounds with varying ligand field strength, including CuS4, CuN4, CuN2O2, and CuO4 first coordination spheres. An unexpectedly strong correlation exists between spin relaxation rates and the average d-d excitation energy (R2 = 0.97). The relaxation rate trends as the inverse 11th power of the excited-state energies, whereas simplified theoretical models predict only an inverse second power dependence. These experimental results directly implicate ligand field excited states as playing a critical role in the ground-state spin relaxation mechanism. Furthermore, ligand field strength is revealed to be a particularly powerful design principle for spin dynamics, enabling formation of a spectrochemical series for spin relaxation.

Molecular mobility of thin films of poly(bisphenol-A carbonate) capped and with one free surface: from bulk-like samples down to the adsorbed layer.

The molecular mobility of thin films of poly(bisphenol A carbonate) (PBAC) was systematically investigated using broadband dielectric spectroscopy, employing two distinct electrode configurations. First, films were prepared in a capped geometry between aluminum electrodes employing a crossed electrode capacitor (CEC) configuration, down to film thicknesses of 40 nm. The Vogel temperature, derived from the temperature dependence of relaxation rates of the α-relaxation, increases with decreasing film thickness characterized by an onset thickness. The onset thickness depends on the annealing conditions, with less intense annealing yielding a lower onset thickness. Additionally, a broadening of the β-relaxation peak was observed with decreasing thickness, attributed to the interaction of phenyl groups with thermally evaporated aluminum, resulting in a shift of certain relaxation modes to higher temperatures relative to the bulk material. A novel phenomenon, termed the slow Arrhenius process (SAP), was also identified in proximity to the α-relaxation temperature. For films with thicknesses below 40 nm, nanostructured electrodes (NSE) were utilized, incorporating nanostructured silica spacers to establish a free surface with air. This free surface causes an enhancement in the molecular mobility for the 40 nm sample, preserving the β-relaxation as a distinct peak. The α-relaxation was detectable in the dielectric loss down to 18 nm, shifting to higher temperatures as film thickness is decreased. Notably, the onset thickness for the increase in Vogel temperature was lower in the NSE configuration compared to the CEC setup, attributed to the presence of the polymer-air interface.

Histological Validation of Multi-Echo Gradient Echo (MGRE)-Derived Myelin Water Fraction (MWF) at 9.4 T and the Influence of Orientation on Quantification.

Myelin is essential in the nervous system of mammals. As the location and degree of myelin loss can reflect varied pathophysiological status, noninvasive measurement of myelin is of high importance. The magnetic resonance imaging (MRI) technique of myelin water fraction (MWF) derived from multi-echo gradient echo (MGRE) sequence is a promising tool for the quantification of myelin content due to the low specific absorption rate (SAR) compared with the spin-echo sequence, time efficiency, and wide availability. Yet to our knowledge, MGRE-derived MWF has never been quantitatively validated with histology. The main objective of this study was to quantitatively validate the MRI findings by referencing the myelin histology using a rat model. As a second objective, we investigated how the orientation of white matter fibers with respect to the static B0 field impacted both the apparent transverse relaxation rate (R2* = 1/T2*) and the derived MWF. Moreover, MWF is known to change with age; thus, we compared rat brains of different ages. The orientation effect of MWF in a clinical setting was studied using 3 T human data. Twenty exvivo rat brains with different ages and three healthy volunteers were scanned on a 9.4 T Bruker and 3.0 T Siemens systems, respectively. The 3D MGRE and diffusion tensor imaging (DTI) data were acquired. Our results showed a highly significant correlation between MGRE-derived MWF and histological stain of myelin, and susceptibility and diffusivity also demonstrated a significant association with myelin. Both MWF and R2* (R2* = 1/T2*) values changed as a function of orientation, and the function varied with age. Furthermore, MWF and R2* were more sensitive to age than DTI. Invivo 3 T human MWF also changed substantially with the orientation as well. Our results support that MGRE-derived MWF can be used to assess the myelin content quantitatively.

Structural dynamics of calcium and integrin-binding protein 2 (CIB2) reveal uncommon flexibility and heterogeneous calcium and magnesium loading

Calcium- and Integrin-Binding protein 2 (CIB2) is a widely expressed protein with an uncertain biological role. Two of its four EF-hand motifs bind Mg(II) and/or Ca(II), thus triggering conformational changes. Although previous studies suggested that CIB2 preferentially binds Mg(II) over Ca(II) under physiological conditions, an atomic level characterization of CIB2 in the presence of both cations was lacking. Based on a combination of solution NMR, exhaustive molecular dynamics simulations and isothermal titration and differential scanning calorimetry, we characterized the interaction of CIB2 with both Ca(II) and Mg(II) ions and elucidated the protein regions involved in the interaction with the α7B integrin target. Analysis of experimental amide nitrogen relaxation rates shows that the EF4 motif exhibits high mobility regardless of the specific bound metal ion and demonstrates that the Ca(II)- and Mg(II)-bound state of CIB2 is relatively floppy, with pico-nanosecond motions induced in a region involved in target recognition. Overall, our data indicate a preferential, thermodynamically stable but structurally flexible state for CIB2, in which an Mg(II) ion is bound to EF3 and a Ca(II) ion to EF4. These results unveil the role of metal binding events in CIB2 and offer new insights into the dynamic regulation of target recognition.

Ex vivo imaging of subacute myocardial infarction with ultra-short echo time 3D quantitative T1- and T1ρ -mapping magnetic resonance imaging in mice.

The aim of this study was to develop an ultra-short echo time 3D magnetic resonance imaging (MRI) method for imaging subacute myocardial infarction (MI) quantitatively and in an accelerated way. Here, we present novel 3D T1- and T1ρ -weighted Multi-Band SWeep Imaging with Fourier Transform and Compressed Sensing (MB-SWIFT-CS) imaging of subacute MI in mice hearts ex vivo. Relaxation time-weighted and under-sampled 3D MB-SWIFT-CS MRI were tested with manganese chloride (MnCl2) phantom and mice MI model. MI was induced in C57BL mice, and the hearts were collected 7 days after MI and then fixated. The hearts were imaged with T1 and adiabatic T1ρ relaxation time-weighted 3D MB-SWIFT-CS MRI, and the contrast-weighted image series were estimated with a locally low-rank regularized subspace constrained reconstruction. The quantitative parameter maps, T1 and T1ρ , were then obtained by performing non-linear least squares signal fitting on the image estimates. For comparison, the hearts were also imaged using 2D fast spin echo-based T2 and T1ρ mapping methods. The relaxation rates varied linearly with the MnCl2 concentration, and the T1 and T1ρ relaxation time values were elevated in the damaged areas. The ischaemic areas could be observed visually in the 3D T1, 3D T1ρ , and 2D MRI maps. The scar tissue formation in the anterior wall of the left ventricle and inflammation in the septum were confirmed by histology, which is in line with the results of MRI. MI with early fibrosis, increased inflammatory activity, and interstitial oedema were determined simultaneously with T1 and T1ρ relaxation time constants within the myocardium by using the 3D MB-SWIFT-CS method, allowing quantitative isotropic 3D assessment of the entire myocardium.

Change in transverse relaxation rates (R2) and change in cognition for older African Americans

AbstractDespite transverse relaxation rate (R2) being one of the fundamental contrasts in MRI, most investigations of brain R2 and cognition have been cross‐sectional and conducted in predominantly non‐Latino White adults. We investigated the profile of R2 as related to cognition in 212 older African Americans (~75 years of age) with longitudinal 3T MRI scans and cognitive test data to determine how changes in R2 are associated with changes in cognition. For each participant, the slopes of global cognitive and five cognitive domain scores were each separately combined with voxel‐specific slopes of R2 in whole brain voxelwise analyses. Participants with less negative rates of R2 change within left basal ganglia and centrum semiovale, bilateral hippocampal complex and temporal gyri, parietooccipital white matter, as well as posterior cingulate displayed less negative slopes in global cognition. Similar associations were seen for regional R2 change and episodic memory (most robustly within bilateral hippocampi) as well as semantic memory (left greater than right hemisphere involvement). Results suggest a relatively wide distribution of regional associations between rates of changes in R2 and changes in global cognition for older African Americans; a profile that became more regionally specific when considering individual cognitive domains. Relative preservation of tissue integrity across grey and white matter, and in key regions associated with specific cognitive domains, is associated with slower cognitive decline for older African Americans. These results may lay the foundation for more directed work to support healthy brain aging in older African Americans.

Machine Learning Mapping Approach for Computing Spin Relaxation Dynamics.

In this work, a machine learning mapping approach for predicting the properties of atomistic systems is reported. Within this approach, the atomic orbital overlap, density, or Kohn-Sham (KS) Fock matrix elements obtained at a low level of theory such as extended tight-binding have been used as input features to predict the electric field gradient (EFG) tensors at a higher level of theory such as those obtained with hybrid functionals. It is shown that the machine-learning-predicted EFG tensors can be used to compute spin relaxation rates of several ions in aqueous solutions. From only a fraction of data used in direct calculation, one can predict the quadrupolar isotropic spin relaxation rates with good accuracy, achieving relative errors between about 2-8% for different ions.

Study of Thermalization Mechanisms of Hot Carriers in BABr-Added MAPbBr3 for the Top Layer of Four-Junction Solar Cells.

The hot carrier multi-junction solar cell (HCMJC) is an advanced-concept solar cell with a theoretical efficiency greater than 65%. It combines the advantages of hot carrier solar cells and multi-junction solar cells with higher power conversion efficiency (PCE). The thermalization coefficient (Qth) has been shown to slow down by an order of magnitude in low-dimensional structures, which will significantly improve PCE. However, there have been no studies calculating the Qth of MAPbBr3 quantum dots so far. In this work, the Qth values of MAPbBr3 quantum dots and after BABr addition were calculated based on power-dependent steady-state photoluminescence (PD-SSPL). Their peak positions in PD-SSPL increased from 2.37 to 2.71 eV after adding BABr. The fitting shows that, after adding BABr, the Qth decreased from 2.64 ± 0.29 mW·K-1·cm-2 to 2.36 ± 0.25 mW·K-1·cm-2, indicating a lower relaxation rate. This is because BABr passivates surface defects, slowing down the carrier thermalization process. This work lays the foundation for the theoretical framework combining perovskite materials, which suggests that the appropriate passivation of BABr has the potential to further reduce Qth and make MAPbBr3 QDs with BABr modified more suitable as the top absorption layer of HCMJCs.

Shot-noise-induced lower temperature limit of the nonneutral plasma parallel temperature diagnostic

We develop a new algorithm to estimate the temperature of a nonneutral plasma in a Penning-Malmberg trap. The algorithm analyzes data obtained by slowly lowering a voltage that confines one end of the plasma and collecting escaping charges, and is a maximum likelihood estimator based on a physically-motivated model of the escape protocol presented in (Beck in Measurement of the magnetic and temperature dependence of the electron-electron anisotropic temperature relaxation rate. PhD thesis, 1990). Significantly, our algorithm may be used on single-count data, allowing for improved fits with low numbers of escaping electrons. This is important for low-temperature plasmas such as those used in antihydrogen trapping. We perform a Monte Carlo simulation of our algorithm, and assess its robustness to intrinsic shot noise and external noise. The assumptions in this paper allow for a lower bound for measurable plasma temperatures of approximately 3K for plasmas of length 1cm, with approximately 100 particle counts needed for an accuracy of ±10%.

Molecular dynamics as an efficient process to predict 15N chemical shift anisotropy at very high NMR magnetic fields.

The emergence of very high NMR magnetic fields will certainly encourage the study of larger biological systems with their dynamics and interactions. NMR spin relaxation allows probing the dynamical properties of proteins where the 15N longitudinal (R1) and transverse (R2) relaxation rates in addition to the 1H-15N heteronuclear NOE describe the ps-ns time scale. Their analytical representation involves the chemical shift anisotropy (CSA) effect that represents the major contribution at a very high magnetic field above 18.8 T. An accurate analysis of the latter parameters in terms of model free (MF) requires considering its effect. Until now, a uniform value of -160 ppm for the CSA has been widely used to derive the backbone order parameters (S2), giving rise to a large fluctuation of its value at very high magnetic fields. Conversely, the use of a site-specific CSA improves the accurate analysis of protein dynamics but requires a cost-effective experimental multi-field approach. In the present paper, we show how the CSA mainly contributes to the relaxation parameters at 28.2 T compared to lower magnetic fields and may bias the determination of S2. We propose to replace the time-consuming measurement of spin relaxation at multiple fields by a combination of molecular dynamics (MD) and the measurement of spin relaxation at one very high magnetic field only. We applied this strategy to three well-folded proteins (ubiquitin, GB3 and ribonuclease H) to show that the determined order parameters are in good agreement with the ones obtained by means of experimental data only.

New Mechanisms of Phase Transition in Olivine‐Type LixMn0.7Fe0.3PO4 Cathodes: a Finding on Relaxation Behavior and its Implications for Battery Performance

AbstractPhosphates of the olivine type, LiMnyFe1‐yPO4 (LMFP), have garnered significant attention due to their higher energy density compared to LiFePO4 (LFP). However, their limited cycle life and rate performance remain key obstacles to their commercialization. Therefore, elucidating the intricate phase transition mechanisms during electrochemical cycling is paramount to overcoming this bottleneck. This study investigates the relaxation behavior of LixMn0.7Fe0.3PO4 (0≤x≤1) under various conditions revealed a remarkable memory characteristic in its crystal structure: the lattice parameters of different delithiated states return to their fully lithiated configuration upon complete relaxation. Moreover, the relaxation rate is influenced by the charging/discharging conditions and storage environment: higher rates, greater delithiation, and longer relaxation times are observed, as are extended relaxation time at lower temperatures and in the absence of electrolyte. These findings provide a rational explanation for the complexity of the phase transition mechanisms in LMFP and highlight the significant differences in phase transition and relaxation behaviors, advancing the understanding of LMFP materials.

Dependence of brain-tissue R2 on MRI field strength.

To quantify T2 relaxation in the brain at 3 T and 7 T to study its field dependence and correlation with iron content, and to investigate whether iron can be separated from other sources of T2 relaxation based on this field dependence. Nine subjects were scanned at both field strengths with the same acquisition technique, which used multiple gradient-echo sampling of a spin echo. This allowed for separation of T2 relaxation from static dephasing by B0 field inhomogeneities and the effects of radiofrequency refocusing imperfections. The average relaxation rates (R2 = 1/T2) in multiple regions of interest in the brain were fitted with a model linear in B0 and correlated with literature iron values. The relationship between the R2 values at the two field strengths appeared to be linear over all regions of interest. The R2 values (in s-1) in the regions of interest for which both an iron and a lipid mass fraction have been documented in the literature were fitted as , where and indicate the putative mass fractions of iron and lipid. The R2 relaxation rate is well described by a constant plus a term linear in B0, with both iron and lipid content contributing to the slope. This indicates that the contributions of lipid and iron to R2 cannot be separated based solely on the field dependence of R2 in the field range of 3-7 T.

Cation-Cation, Cation-Anion, and Anion-Anion Translation Diffusion in Ionic Liquids─Insight from NMR Relaxometry.

1H and 19F spin-lattice relaxation experiments have been performed for a series of ionic liquids: [HMIM][TFSI], [OMIM][TFSI], and [DMIM][TFSI] including the same anion and cations with progressively longer alkyl chains. The experiments were performed in a wide frequency range from 10 kHz to 10 MHz (referring to the 1H resonance frequency) versus temperature. This extensive data set has been analyzed in terms of a theoretical model including all relevant homonuclear (1H-1H and 19F-19F) and heteronuclear (1H-19F) relaxation pathways and linking the relaxation features to the relative translational diffusion between the ion pairs (cation-cation, cation-anion, and anion-anion). In addition to the comprehensive theoretical approach, closed-form expressions have been provided and applied to determine the diffusion coefficients from the slopes of the linear dependences of the relaxation rates on the square root of the resonance frequency. The combined experimental and theoretical studies have led to the determination of the complete set of diffusion coefficients, forming a consistent picture of the dynamical scenario. In addition to revealing the dynamical properties of the liquids and the influence of the subtle changes in the cation structure on the movement of both cations and anions, the theoretical means for exploiting Nuclear Magnetic Resonance relaxometry for ionic liquids have been provided.

MR Imaging Reveals Dynamic Aggregation of Multivalent Glycoconjugates in Aqueous Solution.

Glycoconjugates forming from the conjugation of carbohydrates to other biomolecules, such as proteins, lipids, or other carbohydrates, are essential components of mammalian cells and are involved in numerous biological processes. Due to the capability of sugars to form multiple hydrogen bonds, many synthetic glycoconjugates are desirable biocompatible platforms for imaging, diagnostics, drugs, and supramolecular self-assemblies. Herein, we present a multimeric galactose functionalized paramagnetic gadolinium (Gd(III)) chelate that displays spontaneous dynamic aggregation in aqueous conditions. The dynamic aggregation of the Gd(III) complex was shown by the concentration-dependent magnetic resonance (MR) relaxation measurements, nuclear magnetic resonance dispersion (NMRD) analysis, and dynamic light scattering (DLS). Notably, these data showed a nonlinear relationship between magnetic resonance relaxation rate and concentrations (0.03-1.35 mM), and a large DLS hydrodynamic radius was observed in the high-concentration solutions. MR phantom images were acquired to visualize real-time dynamic aggregation behaviors in aqueous solutions. The in situ visualization of the dynamic self-assembling process of multivalent glycoconjugates has rarely been reported.