Nuclear Relaxation Time Research Articles

Effect of subfreezing storage on the qualities of dough and bread containing pea protein.

In this paper, -6, -9 and -12 °C were selected as subfreezing temperatures of dough containing pea protein based on the results of low-field nuclear magnetic relaxation time. The effect of storage at subfreezing temperatures on dough properties was then investigated and compared with sample storage at -18 °C. The pH value, springiness, resilience, cohesiveness of dough and sensory score of bread gradually decreased and the hardness and water loss rate of dough gradually increased with the extension of storage time. However, dough hardness, viscoelasticity and fermentation volume were maintained more effectively in subfreezing storage than in -18 °C storage. The subfreezing temperature could alleviate the damage of gluten network structure in frozen dough by ice crystals and was beneficial in maintaining the elasticity of gluten proteins. The network system of pea protein, gluten protein and starch granules in dough storage at -9 and -12 °C was more tightly connected and the microstructure was similar to that at -18 °C. There was no significant difference between the quality of bread made from the dough stored at subfreezing temperature and that stored at -18 °C for 1-6 weeks, and the preservation effect at -12 °C was closer to that at -18 °C. Subfreezing storage can keep the stability of dough containing pea protein close to traditional frozen storage (-18 °C), which provides a new method for storage and transportation of frozen dough. © 2022 Society of Chemical Industry.

Monitoring electron spin fluctuations with paramagnetic relaxation enhancement

The magnetic interactions between the spin of an unpaired electron and the surrounding nuclear spins can be exploited to gain structural information, to reduce nuclear relaxation times as well as to create nuclear hyperpolarization via dynamic nuclear polarization (DNP). A central aspect that determines how these interactions manifest from the point of view of NMR is the timescale of the fluctuations of the magnetic moment of the electron spins. These fluctuations, however, are elusive, particularly when electron relaxation times are short or interactions among electronic spins are strong. Here we map the fluctuations by analyzing the ratio between longitudinal and transverse nuclear relaxation times T1/T2, a quantity which depends uniquely on the rate of the electron fluctuations and the Larmor frequency of the involved nuclei. This analysis enables rationalizing the evolution of NMR lineshapes, signal quenching as well as DNP enhancements as a function of the concentration of the paramagnetic species and the temperature, demonstrated here for LiMg1−xMnxPO4 and Fe(III) doped Li4Ti5O12, respectively. For the latter, we observe a linear dependence of the DNP enhancement and the electron relaxation time within a temperature range between 100 and 300 K.

PH-Responsive Association Behavior of Biocompatible Random Copolymers Containing Pendent Phosphorylcholine and Fatty Acid.

Well-defined pH-responsive biocompatible random copolymers composed of 2-(methacryloyloxy)ethyl phosphorylcholine and varying quantities of sodium 11-(acrylamido)undecanoate (AaU) (fAaU = 0-58 mol %) were synthesized via reversible addition-fragmentation chain transfer radical polymerization. The pH-responsive association and dissociation behavior of the random copolymers was studied via turbidity, 1H nuclear magnetic resonance relaxation time, dynamic light scattering, static light scattering (SLS), and fluorescence measurements. At basic pH levels, the random copolymers dissolved in water in a unimer state because the AaU units behaved in a hydrophilic manner as a result of the ionization of the pendent fatty acids. The random copolymers with fAaU < 52 mol % associated intramolecularly within a single polymer chain to form unimer micelles at pH 3 because of the protonation of the pendent fatty acids. On the other hand, the random copolymer with fAaU ≥ 52 mol % formed intermolecular aggregates composed of four polymer chains at pH 3, as established by the SLS measurements. The random copolymers displayed the ability to solubilize hydrophobic guest molecules, such as N-phenyl-1-naphthylamine, into the hydrophobic microdomain formed by the pendent dehydrated fatty acids at acidic pHs. At pH 4, 1-pyrememethanol is captured by the random copolymer with fAaU = 52 mol %, and it is released from the random copolymer above pH 9. Furthermore, the mucoadhesive properties of the random copolymer with fAaU = 9 mol % were studied using a surface plasmon resonance technique. The copolymer was adsorbed onto mucin at pH 3; however, the adsorption decreased at pH 7.4.

Measurement of sub-zero temperatures in MRI using T1 temperature sensitive soft silicone materials: Applications for MRI-guided cryosurgery.

One standard method, proton resonance frequency shift, for measuring temperature using magnetic resonance imaging (MRI), in MRI-guided surgeries, fails completely below the freezing point of water. Because of this, we have developed a new methodology for monitoring temperature with MRI below freezing. The purpose of this paper is to show that a strong temperature dependence of the nuclear relaxation time T1 in soft silicone polymers can lead to temperature-dependent changes of MRI intensity acquired with T1 weighting. We propose the use of silicone filaments inserted in tissue for measuring temperature during MRI-guided cryoablations. The temperature dependence of T1 in bio-compatible soft silicone polymers was measured using nuclear magnetic resonance spectroscopy and MRI. Phantoms, made of bulk silicone materials and put in an MRI-compatible thermal container with dry ice, allowed temperature measurements ranging from -60°C to + 20°C. T1 -weighted gradient echo images of the phantoms were acquired at spatially uniform temperatures and with a gradient in temperature to determine the efficacy of using these materials as temperature indicators in MRI. Ex vivo experiments on silicone rods, 4mm in diameter, inserted in animal tissue were conducted to assess the practical feasibility of the method. Measurements of nuclear relaxation times of protons in soft silicone polymers show a monotonic, nearly linear, change with temperature (R2 >0.98) and have a significant correlation with temperature (Pearson's r>0.99, p<0.01). Similarly, the intensity of the MR images in these materials, taken with a gradient echo sequence, are also temperature dependent. There is again a monotonic change in MRI intensity that correlates well with the measured temperature (Pearson's r<-0.98 and p<0.01). The MRI experiments show that a temperature change of 3°C can be resolved in a distance of about 2.5mm. Based on MRI images and external sensor calibrations for a sample with a gradient in temperature, temperature maps with 3°C isotherms are created for a bulk phantom. Experiments demonstrate that these changes in MRI intensity with temperature can also be seen in 4mm silicone rods embedded in ex vivo animal tissue. We have developed a new method for measuring temperature in MRI that potentially could be used during MRI-guided cryoablation operations, reducing both procedure time and cost, and making these surgeries safer.

Measurement of nuclear spin relaxation time in lanthanum aluminate for development of polarized lanthanum target

The nuclear spin–lattice relaxation time (T1) of lanthanum and aluminum nuclei in a single crystal of lanthanum aluminate doped with neodymium ions is studied to estimate the feasibility of the dynamically polarized lanthanum target applicable to beam experiments. The application of our interest is the study of fundamental discrete symmetries in the spin optics of epithermal neutrons. This study requires a highly flexible choice of the applied magnetic field for neutron spin control and favors longer T1 under lower magnetic field and at higher temperature. The T1 of 139La and 27Al was measured under magnetic fields of 0.5–2.5 T and at temperatures of 0.1–1.5 K and found widely distributed up to 100 h. The result suggests that the T1 can be as long as T1∼ 1 h at 0.1 K with a magnetic field of 0.1 T, which partially fulfills the requirement of the neutron beam experiment. Possible improvements to achieve a longer T1 are discussed.

A laboratory study of the effect of clay, silt, and sand content on low-field nuclear magnetic resonance relaxation time distributions

We have developed a laboratory nuclear magnetic resonance (NMR) study to investigate the effect of clay, silt, and sand content on the NMR relaxation time distribution. Transverse NMR relaxation times ([Formula: see text]) are determined for water-saturated unconsolidated sediment mixtures of 1%–60% kaolinite clay, 5%–85% silt-size glass beads, and 8%–94% quartz sand by mass. Nearly all of the mixtures are characterized by a unimodal [Formula: see text] distribution. When clay is present in quantities greater than 10%, the clay content dominates the response. For these samples, the mean-log relaxation times ([Formula: see text]) range from 0.03 to 0.06 s, regardless of silt or sand content. For mixtures with [Formula: see text] clay, [Formula: see text] decreases with increasing clay content. When the clay content is kept the same, [Formula: see text] decreases with increasing silt content and increases with the increasing sand content. The strong effect of the clay content on the NMR response is due to the high specific surface area of the clay and the distribution of clay throughout the samples. These results will help improve the interpretation of NMR field data in soils and unconsolidated sediments.

Quantitative MRI to Characterize the Nucleus Pulposus Morphological and Biomechanical Variation According to Sagittal Bending Load and Radial Fissure, an ex vivo Ovine Specimen Proof-of-Concept Study

Background and context: Low back pain is a dramatic burden worldwide. Discography studies have shown that 39% of chronic low back pain patients suffer from discogenic pain due to a radial fissure of intervertebral disc. This can have major implications in clinical therapeutic choices. The use of discography is restricted because of its invasiveness and interest in it remains low as it represents a static condition of the disc morphology. Magnetic Resonance Imaging (MRI) appears to be less invasive but does not describe the biomechanical dynamic behavior of the fissure.Purpose: We aimed to seek a quantitative MRI protocol combined with ex vivo sagittal loading to analyze the morphological and biomechanical changes of the intervertebral disc structure and stress distribution.Study design: Proof of concept.Methods: We designed a proof-of-concept ovine study including 3 different 3.0 T-MRI sequences (T2-weighted, T1 and T2 mapping). We analyzed 3 different mechanical states (neutral, flexion and extension) on a fresh ovine spine specimen to characterize an intervertebral disc before and after puncturing the anterior part of the annulus fibrosus. We used a mark tracking method to calculate the bending angles and the axial displacements of the discal structures. In parallel, we created a finite element model to calculate the variation of the axial stress and the maximal intensity shear stress, extrapolated from our experimental boundary conditions.Results: Thanks to an original combination of specific nuclear relaxation time quantifications (T1, T2) of the discal tissue, we characterized the nucleus movement/deformation into the fissure according to the synchronous mechanical load. This revealed a link between disc abnormality and spine segment range of motion capability. Our finite element model highlighted significant variations within the stress distribution between intact and damaged disc.Conclusion: Quantitative MRI appears to provide a new opportunity to characterize intra-discal structural morphology, lesions and stress changes under the influence of mechanical load. This preliminary work could have substantial implications for non-invasive disc exploration and could help to validate novel therapies for disc treatment.

A Needless but Interesting Controversy with Pedagogical Overtones

A decade ago four independent groups, using four independent methods, reported the unanticipated and still surprising result that the bending modulus KC of bilayers of DOPC, unlike other standard lipids, does not increase with addition of cholesterol. A recent paper, using neutron spin echo (NSE) and nuclear magnetic resonance relaxation times (NMRτ), reports that the bending modulus of DOPC increases three fold with increasing cholesterol concentration up to 50%. It would appear that this has become a controversial topic. This controversy is needless because NSE and NMRτ do not measure the bending modulus as it has been defined for decades. Each measures important, complementary, properties that could enrich our understanding of bilayer properties, notably membrane viscosity and location of the neutral plane employed in membrane mechanics. The resolution of this controversy rests on elucidating the difference between measurements on a system in equilibrium that lead directly to equilibrium properties like the bending modulus, and measurements on the same equilibrium system that lead to more complex results involving both static moduli and transport properties. While the difference between static and non-equilibrium quantities is well understood in the physical sciences and statistical thermodynamics, this emerging controversy seems to warrant a pedagogical reminder.

Nuclear spin relaxation as a probe of zeolite acidity: a combined NMR and TPD investigation of pyridine in HZSM-5.

The relative surface affinities of pyridine within microporous HZSM-5 zeolites are explored using two-dimensional 1H nuclear magnetic resonance (NMR) relaxation time measurements. The dimensionless ratio of longitudinal-to-transverse nuclear spin relaxation times T1/T2 is shown to exhibit strong sensitivity to the silica/alumina ratio (SAR) of these zeolites, which is indicative of material acidity. This trend is interpreted in terms of increased pyridine surface affinity with decreasing SAR. Temperature programmed desorption (TPD) analysis corroborates this observation, revealing a distinct increase in the heat of desorption associated with adsorbed pyridine as a function of decreasing SAR. A direct correlation between NMR and TPD data suggests NMR relaxation time analysis can be a valuable tool for the non-invasive characterisation of adsorption phenomena in microporous solids.

Nuclear Magnetic Relaxation Time near the Compensation Temperature in a Ferrimagnetic Insulator

The nuclear magnetic relaxation time $T_1$ in ferrimagnetic insulators is calculated by a Raman process of hyperfine interaction with a meanfield approximation. It is found that the 1/$T_1$ on one site rapidly increases near the compensation temperature $T_0$, whereas that on another site does not increase up to Curie temperature $T_c$. This is due to that the band width of soft magnon becomes comparable to $T_0$. The increasing behavior of 1/$T_1$ below $T_c$ is found also in another type ferrimagnet, which shows hump structure in the temperature dependence of magnetization instead of compensation. Also in this case, we find the rapid increase of 1/$T_1$ below $T_c$, even though the magnetization does not show the compensation. Such a coexistence of soft and hard magnons will lead to remarkable properties of ferrimagnet.

Enantiospecific Response in Cross-Polarization Solid-State Nuclear Magnetic Resonance of Optically Active Metal Organic Frameworks.

We report herein on a NMR-based enantiospecific response for a family of optically active metal-organic frameworks. Cross-polarization of the 1H-13C couple was performed, and the intensities of the 13C nuclei NMR signals were measured to be different for the two enantiomers. In a direct-pulse experiment, which prevents cross-polarization, the intensity difference of the 13C NMR signals of the two nanostructured enantiomers vanished. This result is due to changes of the nuclear spin relaxation times due to the electron spin spatial asymmetry induced by chemical bond polarization involving a chiral center. These experiments put forward on firm ground that the chiral-induced spin selectivity effect, which induces chemical bond polarization in the J-coupling, is the mechanism responsible for the enantiospecific response. The implications of this finding for the theory of this molecular electron spin polarization effect and the development of quantum biosensing and quantum storage devices are discussed.

Understanding the role of d‐Allulose and soy protein addition in pectin gels

Abstractd‐Allulose (a monosaccharide and C3 epimer of fructose), one of the common rare sugars is getting attention due to its low caloric values. In this study, d‐Allulose was used as a replacement of sucrose at different ratios (d‐Allulose/Sucrose: 35/0, 20/15, 10/25, 0/35) to formulate pectin‐based soft confectionery gels. Soy protein isolate was also added to increase the protein content. Physical properties, such as hardness, moisture content, pH, and color, were measured for the gels. Higher hardness values were obtained for the soy protein containing gels due to pectin–soy protein interaction (p &lt; 0.05). Also, higher moisture content was observed in soy protein containing gels (p &lt; 0.05). In addition, nuclear magnetic resonance T2 relaxation times were measured at low field (~0.5 T) to determine how the water distribution in the samples changed and to observe how d‐Allulose affected the polymer–water interactions. The study also showed that the presence of d‐Allulose increased the crystallization tendency (% crystallinity of 7.9) of the pectin gels. X‐ray diffraction results showed the d‐allulose peaks at 33.76 and 48.68oθ. Morphologies of the gels were also examined by scanning electron microscope. Sugar type and soy protein isolate addition were found to have significant impact on the gel formulations.

CT, MR and EPR imaging of graphene oxide aerogels

The shape and intrinsic pore structure of pristine and partially reduced graphene oxide (prGO) aerogels/hydrogels was imaged using three complementary techniques: Magnetic Resonance Imaging (MRI), Computer Tomography (CT) and Electron Paramagnetic Resonance Imaging (EPRI). Each method is sensitive to different features of the sample: CT images are contrasted with mass density changes across sample, MRI with hydrogen density, nuclear relaxation times, diffusion, and finally EPRI with radical density. The complementarity of the techniques is presented on exemplary chosen prGO aerogels, which are currently researched for variety of applications, such as biomaterials in tissue engineering. All techniques have their strengths and weaknesses which are thoroughly pointed out and discussed. EPRI technique, which has been perfected only during last years, is used here for the first time to image carbon-based foams. Finally scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS) is used to characterize surface and elemental content of fabricated prGO aerogels/hydrogels.

Structure and Role of BCOR PUFD in Noncanonical PRC1 Assembly and Disease.

Polycomb repression complex 1 (PRC1) is a multiprotein assembly that regulates transcription. The Polycomb group ring finger 1 protein (PCGF1) is central in the assembly of the noncanonical PRC1 variant called PRC1.1 through its direct interaction with BCOR (BCL-6-interacting corepressor) or its paralog, BCOR-like 1 (BCORL1). Previous structural studies revealed that the C-terminal PUFD domain of BCORL1 is necessary and sufficient to heterodimerize with the RAWUL domain of PCGF1 and, together, form a new protein-protein binding interface that associates with the histone demethylase KDM2B. Here, we show that the PUFD of BCOR and BCORL1 differ in their abilities to assemble with KDM2B. Unlike BCORL1, the PUFD of BCOR alone does not stably assemble with KDM2B. Rather, additional residues N-terminal to the BCOR PUFD are necessary for stable association. Nuclear magnetic resonance (NMR) structure determination and 15N T2 relaxation time measurements of the BCOR PUFD alone indicate that the termini of the BCOR PUFD, which are critical for binding PCGF1 and KDM2B, are disordered. This suggests a hierarchical mode of assembly whereby BCOR PUFD termini become structurally ordered upon binding PCGF1, which then allows stable association with KDM2B. Notably, BCOR internal tandem duplications (ITDs) leading to pediatric kidney and brain tumors map to the PUFD termini. Binding studies with the BCOR ITD indicate the ITD would disrupt PRC1.1 assembly, suggesting loss of the ability to assemble PRC1.1 is a critical molecular event driving tumorigenesis.

Programmable Nuclear-Spin Dynamics in Ti(IV) Coordination Complexes.

Interstitial patterning of nuclear spins is a nascent design principle for controlling electron spin superposition lifetimes in open-shell complexes and solid-state defects. Herein we report the first test of the impact of the patterning principle on ligand-based nuclear spin dynamics. We test how substitutional patterning of 1H and 79/81Br nuclear spins on ligands modulates proton nuclear spin dynamics in the ligand shell of metal complexes. To do so, we studied the 1H nuclear magnetic resonance relaxation times (T1 and T2) of a series of eight polybrominated catechol ligands and six complexes formed by coordination of the ligands to a Ti(IV) ion. These studies reveal that 1H T1 values can be enhanced in the individual ligands by a factor of 4 (from 10.8(3) to 43(5) s) as a function of substitution pattern, reaching the maximum value for 3,4,6-tribromocatechol. The T2 for 1H is also enhanced by a factor of 4, varying by ∼14 s across the series. When complexed, the impact of the patterning design strategy on nuclear spin dynamics is amplified and 1H T1 and T2 values vary by over an order of magnitude. Importantly, the general trends observed in the ligands also match those when complexed. Hence, these results demonstrate a new design principle to control 1H spin dynamics in metal complexes through pattern-based design strategies in the ligand shell.

Determining effect of partial substitution of paramagnetic Mn2+ ions in perovskite (MA)2Zn1-xMnxCl4 mixed crystals through MAS NMR relaxation times

This study discusses the effects of the partial replacement of Zn2+ ions with paramagnetic Mn2+ ions (x = 0.1, 0.3, 0.5, and 0.7) in ecofriendly (MA)2Zn1-xMnxCl4 lead-free perovskite crystals through magic angle spinning nuclear magnetic resonance relaxation times. These crystals are grown and their structures are measured through X-ray diffraction experiments. Further, the spin-lattice relaxation time, T1ρ, in the rotating frame is measured for 1H and 13C nuclei of (MA)+ cations to understand the local environments with respect to the Mn2+ ion content. The structures and chemical shifts for CH3 and NH3 with x = 0.1 and 0.3 were highly similar to those with x = 0, whereas those for CH3 and NH3 with x = 0.5 and 0.7 were highly similar to those with x = 1. Nonetheless, the 1H T1ρ depending on the paramagnetic ion content became shorter because (MA)+ cations were bound to the paramagnetic Mn2+ layer through N–H⋯Cl bonds. The main effects were the differences in the metal Zn2+ and Mn2+ ions.

Characterization of the Nuclear Magnetic Resonance Relaxivity of Gadolinium Functionalized Magnetic Nanoparticles

The need to develop specific magnetic nanostructures for resonance imaging becomes more evident by the day. In this study, iron oxide magnetic nanoparticles stabilized with ethylenediaminetetraacetic acid (EDTA), followed by a gadolinium (Gd) ion chelation reaction Gd-EDTA-MNPs were synthesized and evaluated as a potential magnetic resonance imaging contrast agent. The contrast agent has been developed by a facile and universal coordination chemistry method. The compositions, structures, as well as the physicochemical characterization techniques, are reported. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy demonstrate the success of gadolinium complexation by the carboxyl group of EDTA coated iron oxide nanoparticles. Cytotoxicity measurements have been performed using a cell culture of normal human keratinocytes (HaCaT cell line) and human malignant melanoma (A375). Our results show a significant increase in the transverse relaxivity induced by the complexation with gadolinium, 540 mM−1 s−1 for Gd-EDTA-MNPs. The longitudinal relaxation dispersion curves show one order of magnitude enhancement of the longitudinal relaxivity from 2.2 mM−1 s−1 (EDTA-MNPs) to 29.6 mM−1 s−1 (Gd-EDTA-MNPs) at a 20 MHz resonance frequency. The results suggest that Gd complexation may represent a viable approach in obtaining contrast agents able to reduce both T1 and T2 nuclear relaxation times.

1H-NMR-relaxation and colorimetry for evaluating nanopolymeric dispersions as stone protective coatings

• New nano-latexes were tested as stone protective agents. • 1 H NMR relaxometry provides pore size distribution in stone samples. • Changes in pore size distribution and moisture content reflect treatments’ efficacy. • Non-destructive techniques allowed the selection of experimental nano-products. Non-destructive and non-invasive assessment of new nanopolymeric dispersions for protecting stone materials was accomplished; the effectiveness of five formulations was tested regarding commercial products widely used in conservation on Lecce, Montescaglioso and Matera stones. We observed the specimens’ wettability during capillary water absorption up to saturation by nuclear magnetic transverse relaxation time measurements, using a surface and portable probe. The comparison between treated and the untreated ones, concerning their specific hydration behavior, allowed establishing the effects of the polymer films. Finally, color evaluations were performed to inspect differences induced by treatments. The data analysis enabled to select the most satisfactory protective coating for each lithotype.

New Approach to Analyze 2D Map T1–T2

Based on the method of two-dimensional (2D) nuclear magnetic resonance (NMR) relaxometry, a technique was developed for determining the joint distribution of the correlation time $$ \tau_{c} $$ and the Van Vleck second moments $$ \Delta \omega^{2} $$. The field of application is the study of slow molecular motions corresponding to the condition of the ratio of nuclear magnetic relaxation times T1/T2 > 1.05 (the relation of spin–lattice relaxation time T1 to spin–spin relaxation time T2). The technique is based on the use of a priori information about the mechanism of nuclear magnetic relaxation in a system. The technique has used this information in the regularization solution of an inverse problem. In contrast to the known method for calculating 2D maps of the joint distribution P2 (T1, T2), the proposed method for constructing a 2D map of the joint distribution $$ Q_{2} \left( {\tau_{c} ,\Delta \omega^{2} } \right) $$ does not depend on the main characteristic of the NMR relaxometer—the resonance frequency $$ \omega_{0} $$. The technique was used to analyze the characteristics of sorbed water in clay rocks–argillite.

Experiment on determination of ethanol chemical shift and concentration of ethanol solution based on nuclear magnetic resonance instrument

In this designing experiment, a nuclear magnetic resonance instrument was used to study the chemical shift properties of ethanol based on the principle of magnetic shielding effect. At the same time, the nuclear magnetic resonance method was used to study the transverse relaxation time and signal strength of ethanol aqueous solution in the range of 5%to 40%. The relationship between different mass fraction of ethanol-aqueous solution and nuclear magnetic resonance signal intensity, relaxation time and solution concentration were analysed. According to the results, due to the limitation of experimental instruments, no regular changes were observed. The results show that the addition of copper sulphate can increase the ethanol content and the effect of the ethanol content on the lateral relaxation time: the ethanol content varies between 5% and 40%, and the lateral relaxation time changes from 8.42ms to 40.35ms.According to the experimental results, the empirical formulas of the concentration and lateral relaxation time of ethanol aqueous solution with fixed amount of copper sulphate were fitted. Using this relationship, the NMR measurement of the concentration of ethanol-water solution can be achieved, which provides a new method for the convenient and accurate measurement of the concentration of ethanol solution.