Transverse Magnetic Relaxation Research Articles

Study of magnetic phase transitions by helium-3 in DyF3 nanoparticles

The spin kinetics of liquid 3He in contact with a mixture of LaF3 (99.7%) and DyF3 (0.3%) powders at temperatures of 1.5–3 K was studied by pulsed nuclear magnetic resonance. DyF3 particles have ellipsoidal shape and average size 225 × 153 nm with the magnetic phase transition at temperature Tc = 2.45 K. The temperature dependence of the longitudinal and transverse magnetization relaxation rates of 3He nuclei with a mixture of LaF3 and DyF3 powders has a broad maximum near Tc, which is related to the magnetic phase transition. It is shown that the adsorbed layer of 3He is extremely sensitive to magnetic phase transitions. Preplating the particles surface with adsorbed nitrogen layers allowed to vary the distance from 3He nuclei to the surface of particles in a controlled way. Calculations of the nuclear magnetic relaxation rates with a change in the distance of helium-3 from the particle surface have been carried out, which is in good agreement with experimental data. It was shown that helium-3 is extremely sensitive to surface magnetism and can be used to study surface effects and surface magnetism.

Multienzyme-Mediated Dual-Channel Magnetic Relaxation Switching Taste Biosensor (D-MRSTB) for Simultaneous Detection of Umami Compounds and Synergistic Enhancement in Food.

Umami substances play a significant role in the evaluation of food quality, and their synergistic enhancement is of great importance in improving and intensifying food flavors and tastes. Current biosensors available for umami detection still confront challenges in simultaneous quantification of multiple umami substances and umami intensities. In this study, an innovative dual-channel magnetic relaxation switching taste biosensor (D-MRSTB) was developed for the quantitative detection of representative umami substances. The multienzyme signal of D-MRSTB specifically catalyzes the umami substances of interest to generate hydrogen peroxide (H2O2), which is then used to oxidate Fe2+ to Fe3+. Such a valence-state transition of paramagnetic ions was utilized as a magnetic relaxation signaling switch to influence the transverse magnetic relaxation time (T2) within the reaction milieu, thus achieving simultaneous detection of monosodium glutamate (MSG) and inosine 5'-monophosphate (IMP). The biosensor showed good linearity (R2 > 0.99) in the concentration range of 50-1000 and 10-1000 μmol/L, with limits of detection (LOD) of 0.61 and 0.09 μmol/L for MSG and IMP, respectively. Furthermore, the biosensor accurately characterized the synergistic effect of the mixed solution of IMP and MSG, where ΔT2 showed a good linear relationship with the equivalent umami concentration (EUC) of the mixed solution (R2 = 0.998). Moreover, the D-MRSTB successfully achieved the quantitative detection of umami compounds in real samples. This sensing technology provides a powerful tool for achieving the detection of synergistic enhancement among umami compounds and demonstrates its potential for application in the food industry.

Hydrogen Peroxide-Triggered Disassembly of Boronic Ester-Cross-Linked Brush-Arm Star Polymers.

The concentrations of reactive oxygen species (ROS), e.g., H2O2, are often elevated in diseased tissue microenvironments. Therefore, the selective detection of ROS could enable new diagnostic methods or tools for chemical biology. Here, we report the synthesis of boronic ester-bis-norbornene core-cross-linked brush-arm star polymers (BASPs) with polyethylene glycol (PEG) or PEG-branch-spirocyclohexyl nitroxide (chex) shells. Size exclusion chromatography (SEC) and dynamic light scattering (DLS) showed that these BASPs have narrowly dispersed molar masses and average hydrodynamic diameters of 23 ± 2 nm, respectively. Moreover, due to their core-shell structures, these BASPs disassemble into bottlebrush fragments with improved selectivity for H2O2 over ROS such as peroxynitrite (ONOO-) and hypochlorite (-OCl). Finally, H2O2 induced disassembly of chex-containing BASPs induces a change in transverse magnetic relaxivity that can be detected via magnetic resonance imaging (MRI). Chex-BASPs may represent a valuable new diagnostic tool for H2O2 sensing.

Myocardial Tissue Characterization in Cardiac Magnetic Resonance Studies of Patients Recovering From COVID-19: A Meta-Analysis.

Background Meta-analysis can identify biological factors that moderate cardiac magnetic resonance myocardial tissue markers such as native T1 (longitudinal magnetization relaxation time constant) and T2 (transverse magnetization relaxation time constant) in cohorts recovering from COVID-19 infection. Methods and Results Cardiac magnetic resonance studies of patients with COVID-19 using myocardial T1, T2 mapping, extracellular volume, and late gadolinium enhancement were identified by database searches. Pooled effect sizes and interstudy heterogeneity (I2) were estimated with random effects models. Moderators of interstudy heterogeneity were analyzed by meta-regression of the percent difference of native T1 and T2 between COVID-19 and control groups (%ΔT1 [percent difference of the study-level means of myocardial T1 in patients with COVID-19 and controls] and %ΔT2 [percent difference of the study-level means of myocardial T2 in patients with COVID-19 and controls]), extracellular volume, and the proportion of late gadolinium enhancement. Interstudy heterogeneities of %ΔT1 (I2=76%) and %ΔT2 (I2=88%) were significantly lower than for native T1 and T2, respectively, independent of field strength, with pooled effect sizes of %ΔT1=1.24% (95% CI, 0.54%-1.9%) and %ΔT2=3.77% (95% CI, 1.79%-5.79%). %ΔT1 was lower for studies in children (median age: 12.7 years) and athletes (median age: 21 years), compared with older adults (median age: 48 years). Duration of recovery from COVID-19, cardiac troponins, C-reactive protein, and age were significant moderators for %ΔT1 and/or %ΔT2. Extracellular volume, adjusted by age, was moderated by recovery duration. Age, diabetes, and hypertension were significant moderators of the proportion of late gadolinium enhancement in adults. Conclusions T1 and T2 are dynamic markers of cardiac involvement in COVID-19 that reflect the regression of cardiomyocyte injury and myocardial inflammation during recovery. Late gadolinium enhancement and to a lesser extent extracellular volume, are more static biomarkers moderated by preexisting risk factors linked to adverse myocardial tissue remodeling.

Longitudinal differences in iron deposition in periaqueductal gray matter and anterior cingulate cortex are associated with response to erenumab in migraine.

The objective of this longitudinal study was to determine whether brain iron accumulation, measured using magnetic resonance imaging magnetic transverse relaxation rates (T2*), is associated with response to erenumab for the treatment of migraine. Participants (n = 28) with migraine, diagnosed using international classification of headache disorders 3rd edition criteria, were eligible if they had six to 25 migraine days during a four-week headache diary run-in phase. Participants received two treatments with 140 mg erenumab, one immediately following the pre-treatment run-in phase and a second treatment four weeks later. T2* data were collected immediately following the pre-treatment phase, and at two weeks and eight weeks following the first erenumab treatment. Patients were classified as erenumab responders if their migraine-day frequency at five-to-eight weeks post-initial treatment was reduced by at least 50% compared to the pre-treatment run-in phase. A longitudinal Sandwich estimator approach was used to compare longitudinal group differences (responders vs non-responders) in T2* values, associated with iron accumulation. Group visit effects were calculated with a significance threshold of p = 0.005 and cluster forming threshold of 250 voxels. T2* values of 19 healthy controls were used for a reference. The average of each significant region was compared between groups and visits with Bonferroni corrections for multiple comparisons with significance defined as p < 0.05. Pre- and post-treatment longitudinal imaging data were available from 28 participants with migraine for a total of 79 quantitative T2* images. Average subject age was 42 ± 13 years (25 female, three male). Of the 28 subjects studied, 53.6% were erenumab responders. Comparing longitudinal T2* between erenumab responders vs non-responders yielded two comparisons which survived the significance threshold of p < 0.05 after correction for multiple comparisons: the difference at eight weeks between the erenumab-responders and non-responders in the periaqueductal gray (mean ± standard error; responders 43 ± 1 ms vs non-responders 32.5 ± 1 ms, p = 0.002) and the anterior cingulate cortex (mean ± standard error; responders 50 ± 1 ms vs non-responders 40 ± 1 ms, p = 0.01). Erenumab response is associated with higher T2* in the periaqueductal gray and anterior cingulate cortex, regions that participate in pain processing and modulation. T2* differences between erenumab responders vs non-responders, a measure of brain iron accumulation, are seen at eight weeks post-treatment. Less iron accumulation in the periaqueductal gray and anterior cingulate cortex might play a role in the therapeutic mechanisms of migraine reduction associated with erenumab.

Investigations on asphaltene aggregate formation by high-field diffusion NMR and low-field ghost solvent NMR relaxometry

Aggregation of asphaltenes remains a scientific challenge. In the present contribution, at first, transverse magnetization relaxation (T2) data from low-field NMR measurements of the asphaltenes from heavy, medium-heavy, or light crude oil samples were recovered. Following this, diffusion ordered spectroscopy nuclear magnetic resonance (NMR) spectra of these asphaltenes were acquired to obtain average molecular weights (M w) of asphaltene aggregates. Analyzing the relaxation and diffusion behavior of asphaltene aggregates as a function of solution percentage and hence molecular weights are utilized to explain the difference between light, medium-heavy and heavy crude oil asphaltenes in aggregate formation. The main results suggest that light crude oil asphaltenes form a small but significant number of aggregates. In contrast, heavy crude oil asphaltenes demonstrate a more complicated picture at high concentrations with small, medium, and large aggregates. The relaxation behavior of medium-heavy asphaltenes is similar to those of heavy crude oil asphaltenes in diluted solutions and similar to light crude oil asphaltenes in concentrated solutions. Diffusion NMR results showed that the light crude oil asphaltene samples have a relatively smaller aggregate size, higher diffusion coefficient, and hence a smaller molecular weight than the samples extracted from heavy crude oils.

Better neural images by combining ultrahigh field strength MRI with innovative MRI sequences

Better MRI scanning technologies and protocols can provide insights into neurological disorders. In this review, we describe the basic concepts of MRI and, in the process, we convey to the reader the relevance of MRI as a high-resolution imaging modality of tissue structure and metabolism. We outline the main parameters for improving MRI resolution and sensitivity for the ultimate goal of optimizing the diagnosis of neurological diseases. A key to obtaining high-resolution images by MRI is the strength of the magnet’s external field strength (Bo). The higher the field strength, the better the signal-to-noise (SNR) of acquired signals. Hence, this results in improved sensitivity and resolution of the reconstructed images. This article recapitulates the advancement of MRI technology towards Ultra-High-Field Strength (UHF) apparatus and the consequent benefits in SNR. Other keys towards improving MRI images include deftly modifying the parameters of longitudinal magnetization relaxation time (T1), transverse magnetization relaxation time (T2), repetition times between radiofrequency (RF) pulses (TR), and the time of reading post-pulse (TE). Such parameters can be controlled through acquisition software associated with the MRI machines. The review profiles the cumulative efforts by researchers to complement UHF-MRI hardware with innovative RF pulse sequences protocols such as Diffusion Weighted Imaging (DWI), Pulse Gradient Spin Echo (PGSE), Oscillating Gradient Spin Echo (OGSE), Blood Oxygen Level Dependent (BOLD)-MRI and Arterial Spin Label (ASL)-MRI. Collectively, these advances in both MRI hardware and software have pushed the field to attain a mesoscopic level of resolution. Further enhancements in analyzing MRI images through Artificial Intelligence (AI) algorithms may advance resolutions beyond the mesoscopic stage and perhaps even toward the microscopic resolution of living tissue.

Step Activity Monitoring in Boys with Duchenne Muscular Dystrophy and its Correlation with Magnetic Resonance Measures and Functional Performance.

Muscles of boys with Duchenne muscular dystrophy (DMD) are progressively replaced by fatty fibrous tissues, and weakness leads to loss of ambulation (LoA). Step activity (SA) monitoring is a quantitative measure of real-world ambulatory function. The relationship between quality of muscle health and SA is unknown in DMD. To determine SA in steroid treated boys with DMD across various age groups, and to evaluate the association of SA with quality of muscle health and ambulatory function. Quality of muscle health was measured by magnetic resonance (MR) imaging transverse magnetization relaxation time constant (MRI-T2) and MR spectroscopy fat fraction (MRS-FF). SA was assessed via accelerometry, and functional abilities were assessed through clinical walking tests. Correlations between SA, MR, and functional measures were determined. A threshold value of SA was determined to predict the future LoA. The greatest reduction in SA was observed in the 9- < 11years age group. SA correlated with all functional and MR measures.10m walk/run test had the highest correlation with SA. An increase in muscle MRI-T2 and MRS-FF was associated with a decline in SA. Two years prior to LoA, SA in boys with DMD was 32% lower than age matched boys with DMD who maintained ambulation for more than two-year period. SA monitoring can predict subsequent LoA in Duchenne, as a daily step count of 3200 at baseline was associated with LoA over the next two-years. SA monitoring is a feasible and accessible tool to measure functional capacity in the real-world environment.

The in-situ NMR evidence of gas hydrate forming in micro-pores in the Shenhu area, South China Sea

Nuclear magnetic resonance (NMR) measurement could provide information during the formation and dissociation of gas hydrate on the pore structure properties which are of great important to understand the gas production behavior. In this study, the in–situ NMR and other well logging data achieved during the natural gas hydrate drilling program were used to study the pore size and hydrate formation properties in the Shenhu area, South China Sea by comparing transverse magnetic relaxation time (T2) distributions between the gas hydrate zone and the upper water–saturated zone whose properties represent the virgin status. Compared with those of the upper water–saturated layer, increasing resistivity, higher–than–baseline shear modulus, less–than–density–porosity NMR porosity, shortening T2 peak time, reducing amplitude and covered area of T2 distributions and decreasing water–filling pore size denote the association of hydrate. Based on eight bin porosities distribution derived from user-defined time intervals of the T2 distribution for researching the hydrate formation characteristic in different pore size, macro–pores (T2 ≥ 10 ms, rc≥ 0.9 μm), meso–pores (3 ms ≤ T2 < 10 ms, 0.27 μm ≤rc<0.9μm) and micro–pores (T2 < 3 ms, rc< 0.27 μm) were divided. It was found that the meso–pores are the dominant pore size in the Shenhu area, but hydrate form more easily in the macro–pores. Just as the previous experience, gas hydrate forms primarily in macro–pores and meso–pores resulting in an increase of micro–pores. In addition, another mode was achieved that gas hydrate forms in the three types of pore spaces leading to a decrease of micro–pores. Both forming modes can develop reservoirs with high hydrate saturation that can exceed 30%.

Nanostructuring the Interior of Stimuli-Responsive Microgels by N-Vinylimidazoles Quaternized with Hydrophobic Alkyl Chains

The functionality of stimuli-responsive microgels can be tailor-made by manipulating their internal nanostructure induced by the chemical composition and morphology of the polymer network. Microgels with phase-separated domains on a nanoscopic length scale were synthesized by copolymerization of N-vinylcaprolactam (VCL) and amphiphilic-to-hydrophobic 1-vinyl-3-alkylimidazolium (VIM+CnH2n+1) bromides (Br–) of different alkyl chain lengths (n = 12, 14, 16) as comonomers. These quaternized imidazoles provide dual functionality for immobilization of payload by electrostatic and hydrophobic interactions. The morphologies and properties of synthesized poly(VCL-co-VIM+CnH2n+1Br–) microgels with 10 mol % comonomer were investigated systematically by 1H and 13C high-resolution NMR spectroscopy and relaxometry. Chemical side-selective information about the monomers’ volume-phase transition temperatures, width of transition, and change in transition entropy was reported and correlated to the alkyl chain length of the VIM+CnH2n+1Br– comonomer. 13C NMR spectroscopy reveals the existence of trans and gauche conformers of alkyl chains, which depends on the alkyl chain length and temperature. Morphologies and dynamic contrasts of alkyl chain domains and VCL moieties of poly(VCL-co-VIM+CnH2n+1Br–) microgels were investigated by 1H transverse magnetization relaxation (T2-relaxation). Finally, the microgels were successfully applied in the uptake of the hydrophobic dye Nile red, proving their ability to solubilize hydrophobic substances. In addition, the poly(VCL-co-VIM+CnH2n+1Br–) microgels were utilized in electrostatic interactions, as well as simultaneous addition of hydrophobic and negatively charged payload as a proof of concept for dual functionality. This investigation will allow for a better understanding of the internal nanophase structure of complex poly(N-vinylcaprolactam) (PVCL)-based microgels comprising pH-independent positive charges, as well as hydrophobic compartments, which have potential application as dual-functional delivery systems.

Experimental investigation of effects of mica content, Fe and pressure on the pore size distribution and permeability of sandy sediment using proton nuclear magnetic resonance

Sediment permeability, an important factor for evaluating groundwater flow in slope and/or ground and oil and natural gas reservoirs in sandy sediments, can be estimated using transverse magnetic relaxation time (T2) measurements by 1H nuclear magnetic resonance (NMR). However, the performance of this method is influenced by the mineralogy and the pore and grain size distributions of the tested material. Therefore, NMR estimations for sandy sediments must first be validated against flow-based measurements. A good relationship between the mercury porosimetry (DHG) and T2 peaks was obtained for samples with different mica content (0–10 wt%). However, the faster T2 relaxation and higher surface relaxivity coefficient depended on the mica content with increasing Fe concentration for the sand-mica mixtures (mica content >20 wt%). The measurement permeability results were compared with estimates from NMR spectra using the Schlumberger Doll Research and Timur–Coates models. While both models provided estimates consistent with flow measurements at 0.1 MPa, the permeabilities were overestimated by 1–2 orders of magnitude at 1.0 MPa for the samples of mica content 20–50 wt%. The results show that the permeability estimated by NMR in mica-rich sediments is overestimated at greater pressure (at approximately 100 m depth).

Asialoglycoprotein receptor targeted optical and magnetic resonance imaging and therapy of liver fibrosis using pullulan stabilized multi-functional iron oxide nanoprobe

Early diagnosis and therapy of liver fibrosis is of utmost importance, especially considering the increased incidence of alcoholic and non-alcoholic liver syndromes. In this work, a systematic study is reported to develop a dual function and biocompatible nanoprobe for liver specific diagnostic and therapeutic applications. A polysaccharide polymer, pullulan stabilized iron oxide nanoparticle (P-SPIONs) enabled high liver specificity via asialogycoprotein receptor mediation. Longitudinal and transverse magnetic relaxation rates of 2.15 and 146.91 mM−1 s−1 respectively and a size of 12 nm, confirmed the T2 weighted magnetic resonance imaging (MRI) efficacy of P-SPIONs. A current of 400A on 5 mg/ml of P-SPIONs raised the temperature above 50 °C, to facilitate effective hyperthermia. Finally, a NIR dye conjugation facilitated targeted dual imaging in liver fibrosis models, in vivo, with favourable histopathological results and recommends its use in early stage diagnosis using MRI and optical imaging, and subsequent therapy using hyperthermia.

Expanding the Ligand Classes Used for Mn(II) Complexation: Oxa-aza Macrocycles Make the Difference.

We report two macrocyclic ligands based on a 1,7-diaza-12-crown-4 platform functionalized with acetate (tO2DO2A2−) or piperidineacetamide (tO2DO2AMPip) pendant arms and a detailed characterization of the corresponding Mn(II) complexes. The X−ray structure of [Mn(tO2DO2A)(H2O)]·2H2O shows that the metal ion is coordinated by six donor atoms of the macrocyclic ligand and one water molecule, to result in seven-coordination. The Cu(II) analogue presents a distorted octahedral coordination environment. The protonation constants of the ligands and the stability constants of the complexes formed with Mn(II) and other biologically relevant metal ions (Mg(II), Ca(II), Cu(II) and Zn(II)) were determined using potentiometric titrations (I = 0.15 M NaCl, T = 25 °C). The conditional stabilities of Mn(II) complexes at pH 7.4 are comparable to those reported for the cyclen-based tDO2A2− ligand. The dissociation of the Mn(II) chelates were investigated by evaluating the rate constants of metal exchange reactions with Cu(II) under acidic conditions (I = 0.15 M NaCl, T = 25 °C). Dissociation of the [Mn(tO2DO2A)(H2O)] complex occurs through both proton− and metal−assisted pathways, while the [Mn(tO2DO2AMPip)(H2O)] analogue dissociates through spontaneous and proton-assisted mechanisms. The Mn(II) complex of tO2DO2A2− is remarkably inert with respect to its dissociation, while the amide analogue is significantly more labile. The presence of a water molecule coordinated to Mn(II) imparts relatively high relaxivities to the complexes. The parameters determining this key property were investigated using 17O NMR (Nuclear Magnetic Resonance) transverse relaxation rates and 1H nuclear magnetic relaxation dispersion (NMRD) profiles.

Sense current dependent coercivity and magnetization relaxation in Gd-Fe-Co Hall bar

The understanding of the characteristics of a magnetic layer in a different environment is crucial for any spintronics application. Before practical applications, thorough scrutiny of such devices is compulsory. Here we study such a potential Hall device of MgO-capped Hf/GdFeCo bilayer (FeCo-rich) for magnetization relaxation around nucleation fields at different voltage probe line widths and dc sensing currents. The device is characterized by anomalous Hall measurements in transverse and longitudinal Hall geometries for two different probe widths A (5 µm) and B (1 µm). The coercivities of the Hall loops (ρxy-H and Rxx-H) drop with increasing the sense current for both the probes. For probe B, the sharp and large drop in coercivity (ρxy-H loops) at comparatively lower sensing currents is observed, which is attributed to the negligible current shunting and presence of pinning site at B caused by the patterning process. The average domain wall velocities at various sensing currents for probe B are found to be smaller than probe A, from the transverse and longitudinal Hall geometry magnetization relaxation measurements, which agrees with pinning sites and Joule heating effect at probe B. The notch position in the pattern and the longitudinal Hall resistance curve peak shape suggest the domain wall propagation direction from probe B to probe A in the current channel. This study highlights the domain wall propagation at different nucleation fields, sensing currents, and the Hall probe aspect ratios.

Uncovering the Magnetic Particle Imaging and Magnetic Resonance Imaging Features of Iron Oxide Nanocube Clusters.

Multifunctional imaging nanoprobes continue to garner strong interest for their great potential in the detection and monitoring of cancer. In this study, we investigate a series of spatially arranged iron oxide nanocube-based clusters (i.e., chain-like dimer/trimer, centrosymmetric clusters, and enzymatically cleavable two-dimensional clusters) as magnetic particle imaging and magnetic resonance imaging probes. Our findings demonstrate that the short nanocube chain assemblies exhibit remarkable magnetic particle imaging signal enhancement with respect to the individually dispersed or the centrosymmetric cluster analogues. This result can be attributed to the beneficial uniaxial magnetic dipolar coupling occurring in the chain-like nanocube assembly. Moreover, we could effectively synthesize enzymatically cleavable two-dimensional nanocube clusters, which upon exposure to a lytic enzyme, exhibit a progressive increase in magnetic particle imaging signal at well-defined incubation time points. The increase in magnetic particle imaging signal can be used to trace the disassembly of the large planar clusters into smaller nanocube chains by enzymatic polymer degradation. These studies demonstrate that chain-like assemblies of iron oxide nanocubes offer the best spatial arrangement to improve magnetic particle imaging signals. In addition, the nanocube clusters synthesized in this study also show remarkable transverse magnetic resonance imaging relaxation signals. These nanoprobes, previously showcased for their outstanding heat performance in magnetic hyperthermia applications, have great potential as dual imaging probes and could be employed to improve the tumor thermo-therapeutic efficacy, while offering a readable magnetic signal for image mapping of material disassemblies at tumor sites.

Dysprosium and Holmium Vanadate Nanoprobes as High-Performance Contrast Agents for High-Field Magnetic Resonance and Computed Tomography Imaging.

We describe a wet chemical method for the synthesis of uniform and well-dispersed dysprosium vanadate (DyVO4) and holmium vanadate (HoVO4) nanoparticles with an almost spherical shape and a mean size of ∼60 nm and their functionalization with poly(acrylic acid). The transverse magnetic relaxivity of both systems at 9.4 T is analyzed on the basis of magnetic susceptibility and magnetization measurements in order to evaluate their potential for application as high-field MRI contrast agents. In addition, the X-ray attenuation properties of these systems are also studied to determine their capabilities as computed tomography contrast agent. Finally, the colloidal stability under physiological pH conditions and the cytotoxicity of the functionalized NPs are also addressed to assess their suitability for bioimaging applications.

Chain Heterogeneity in Simulated Polymer Melts: Segment Orientational Autocorrelation Function

The dynamic heterogeneity of polymer chains is characterized by the lower correlation times of its end Kuhn segments with respect to those of the middle segments. In this study, the heterogeneity was investigated using molecular dynamics simulation of freely jointed chains of various lengths in the melt. Our characterization of the segmental dynamics along the chain additionally revealed the heterogeneity of rotational anisotropy, which was also lower for chain-end segments compared to those for chain-middle ones. This heterogeneity can be quantitatively characterized by intra-segmental residual dipolar coupling, which influences the transverse magnetic relaxation rate of the various chain segments and, ultimately, defines the free induction decay shape for chains of any length. Further, in the second part of this report, the origin of this relationship is discussed in detail.

Prediction of gas hydrate saturation using machine learning and optimal set of well-logs

Resistivity and acoustic logs are widely used to estimate gas hydrate saturation in various sedimentary systems using one of the two popular methods ((1) acoustic velocity and (2) electrical resistivity), but the limitations of these two methods are often overlooked, which include (i) well-specific calibration of empirical exponents in the electrical resistivity method, (ii) assumption of known pore morphology for gas hydrates in the acoustic velocity method, and (iii) presence of unknown mineralogy and bulk modulus terms in the acoustic velocity method. NMR-density porosity-derived gas hydrate saturation based on the analysis of the transverse magnetization relaxation time (T2) is considered the most precise method, but acquisition of NMR-based logs is limited at relatively recent drilled sites; additionally, its use in conventional oil and gas reservoirs is not that common due to higher cost and operational deployment limitations associated with acquiring NMR well-logs. This study proposes a new method that predicts gas hydrate saturation (Sh) for any well using porosity, bulk density, and compressional wave (P wave) velocity well-logs with neural network (or stochastic gradient descent regression) without any well-specific calibration and/or other aforementioned shortcomings of the existing methods. The method is developed by examining the underlying dependency between Sh and different combinations of well-logs, chosen from 6 routine logs, with 12 different machine learning (ML) algorithms. The accuracy of the proposed method in predicting Sh is ~ 84%, which is better than the accuracy of seismic and electrical resistivity methods (≤ 75%) per the results reported by three different studies. The robustness of the method in the specific case of permafrost-associated gas hydrates is demonstrated with well-log data from two wells drilled on the Alaska North Slope.

CALX-CBD1 Ca2+-Binding Cooperativity Studied by NMR Spectroscopy and ITC with Bayesian Statistics

The Na+/Ca2+ exchanger of Drosophila melanogaster, CALX, is the main Ca2+-extrusion mechanism in olfactory sensory neurons and photoreceptor cells. Na+/Ca2+ exchangers have two Ca2+ sensor domains, CBD1 and CBD2. In contrast to the mammalian homologs, CALX is inhibited by Ca2+ binding to CALX-CBD1, whereas CALX-CBD2 does not bind Ca2+ at physiological concentrations. CALX-CBD1 consists of a β-sandwich and displays four Ca2+-binding sites at the tip of the domain. In this study, we used NMR spectroscopy and isothermal titration calorimetry (ITC) to investigate the cooperativity of Ca2+ binding to CALX-CBD1. We observed that this domain binds Ca2+ in the slow exchange regime at the NMR chemical shift timescale. Ca2+ binding restricts the dynamics in the Ca2+-binding region. Experiments of 15N chemical exchange saturation transfer and 15N R2 dispersion allowed the determination of Ca2+ dissociation rates (∼30 s−1). NMR titration curves of residues in the Ca2+-binding region were sigmoidal because of the contribution of chemical exchange to transverse magnetization relaxation rates, R2. Hence, a novel, to our knowledge, approach to analyze NMR titration curves was proposed. Ca2+-binding cooperativity was examined assuming two different stoichiometric binding models and using a Bayesian approach for data analysis. Fittings of NMR and ITC binding curves to the Hill model yielded nHill ∼2.9, near maximal cooperativity (nHill = 4). By assuming a stepwise model to interpret the ITC data, we found that the probability of binding from 2 up to 4 Ca2+ is approximately three orders of magnitude higher than that of binding a single Ca2+. Hence, four Ca2+ ions bind almost simultaneously to CALX-CBD1. Cooperative Ca2+ binding is key to enable this exchanger to efficiently respond to changes in the intracellular Ca2+ concentration in sensory neuronal cells.

Design of a nanoprobe for high field magnetic resonance imaging, dual energy X-ray computed tomography and luminescent imaging

The combination of different bioimaging techniques, mainly in the field of oncology, allows circumventing the defects associated with the individual imaging modalities, thus providing a more reliable diagnosis. The development of multimodal endogenous probes that are simultaneously suitable for various imaging modalities, such as magnetic resonance imaging (MRI), X-ray computed tomography (CT) and luminescent imaging (LI) is, therefore, highly recommended. Such probes should operate in the conditions imposed by the newest imaging equipment, such as MRI operating at high magnetic fields and dual-energy CT. They should show, as well, high photoluminescence emission intensity for their use in optical imaging and present good biocompatibility. In this context, we have designed a single nanoprobe, based on a core-shell architecture, composed of a luminescent Eu3+:Ba0.3Lu0.7F2.7 core surrounded by an external HoF3 shell that confers the probe with very high magnetic transverse relaxivity at high field. An intermediate, optically inert Ba0.3Lu0.7F2.7 layer was interposed between the core and the shell to hinder Eu3+–Ho3+ cross-relaxation and avoid luminescence quenching. The presence of Ba and Lu, with different K-edges, allows for good X-ray attenuation at high and low voltages. The core-shell nanoparticles synthesized are good potential candidates as trimodal bioprobes for MRI at high field, dual-energy CT and luminescent imaging.