Longitudinal NMR Relaxation Times Research Articles

Dry-cured ham tissue characterization by fast field cycling NMR relaxometry and quantitative magnetization transfer.

Fast field cycling (FFC) and quantitative magnetization transfer (qMT) NMR methods are two powerful tools in NMR analysis of biological tissues. The qMT method is well established in biomedical NMR applications, while the FFC method is often used in investigations of molecular dynamics on which longitudinal NMR relaxation times of the investigated material critically depend. Despite their proven analytical potential, these two methods were rarely used in NMR studies of food, especially when combined together. In our study, we demonstrate the feasibility of a combined FFC/qMT-NMR approach for the fast and nondestructive characterization of dry-curing ham tissues differing by protein content. The characterization is based on quantifying the pure quadrupolar peak area (area under the quadrupolar contribution of dispersion curve obtained by FFC-NMR) and the restricted magnetization pool size (obtained by qMT-NMR). Both quantities correlate well with concentration of partially immobilized, nitrogen-containing and proton magnetization exchanging muscle proteins. Therefore, these two quantities could serve as potential markers for dry-curing process monitoring. Copyright © 2016 John Wiley & Sons, Ltd.

Amphiphiles with polyethyleneoxide–polyethylenecarbonate chains for hydrophilic coating of iron oxide cores, loading by Gd(III) ions and tuning R2/R1 ratio

The present work is aimed at the synthesis of hydrophilic colloids with convenient transverse and longitudinal NMR-relaxation times. Core-shell morphology with iron oxide cores and hydrophilic shell enriched by Gd(III) ions is the basis for the colloids with dual-mode relaxivities. Polyethyleneoxide–polyethylenecarbonate derivatives of p-tert-butylphenols are introduced as amphiphiles for efficient hydrophilization of oleate-stabilized iron oxide nanoparticles. The obtained results reveal the easy variation of the synthetic conditions as the route to switch from the recoating to the dissolution of the oleate-stabilized iron-oxide nanoparticles. The length of ethylenecarbonate chains is highlighted as the factor affecting the transverse relaxivity (R2) and the colloid properties of the synthesized colloids, evaluated from DLS data. The complex ability of ethylenecarbonate chains is the reason for loading of the synthesized colloids by Gd(III) ions in aqueous dispersions at specific conditions. These conditions are introduced herein as a route of gaining in longitudinal relaxivity (R1) and tuning R2/R1 ratio.

Suppression of problematic compound oligomerization by cosolubilization of nondetergent sulfobetaines.

Numerous small organic compounds exist in equilibrium among monomers, soluble oligomers, and insoluble aggregates in aqueous solution. Compound aggregation is a major reason for false positives in drug screening, and even soluble oligomers can interfere with structural and biochemical analyses. However, an efficient way to manage the equilibrium of aggregation-prone compounds, especially those involved with soluble oligomers, has not been established. In this study, solution NMR spectroscopy was used as a suitable technique to detect compound oligomers in equilibrium, and it was demonstrated that cosolubilization of nondetergent sulfobetaines (NDSBs) can largely suppress compound oligomerization and aggregation by shifting the equilibrium toward the monomers. The rotational correlation time was obtained from the ratio of the selective and nonselective longitudinal NMR relaxation times, which directly and quantitatively reflected the apparent sizes of the compounds in the equilibrium. The rotational correlation time of the aggregation-prone compound SKF86002 (1 mm) was substantially reduced from 0.31 to 0.23 ns by cosolubilization of 100 mm NDSB195. NDSB cosolubilization allowed us to perform successful structural and biochemical experiments with substantially fewer artifacts, which represents a strategy to directly resolve the problematic oligomerization and aggregation of compounds.

NMR Investigation of the Dynamics of Confined Water in Nafion-Based Electrolyte Membranes at Subfreezing Temperatures

The dynamical characteristics and the thermal analysis of water absorbed in filler-free Nafion and in silica or zirconia phosphate Nafion composites, between 20 and -50 degrees C, were investigated by NMR and DSC techniques. Self-diffusion coefficients and longitudinal NMR relaxation times (T(1)) put in evidence a fraction of water freezing at subzero temperatures. The complementary water fraction remains in the liquid state at least down to -50 degrees C. The freezing point (T(f)) depends on the initial water uptake of the electrolyte membrane and, for similar uptake values, water mobility is favorite in composites systems respect to the filler-free Nafion. By DSC thermograms the hydration water molecules number per sulfonic group in the filler-free Nafion was estimated, obtaining 8 molecules/SO(3)(-) group. In the Nafion/Zr(HPO(4))(2) composite, instead, the number of hydration water is about 20 molecules/ionic group, because of the acid nature of the zirconia particles. Below T(f), the presence of this nonfreezable water fraction allows proton transport, and therefore ensures ionic conductivity also at subzero temperatures.

Phase transitions in aqueous triblock copolymers: NMR relaxation studies

Longitudinal NMR relaxation times were used to investigate the thermal transitions occurring in an aqueous triblock copolymer of the poly(oxyethylene)–poly(oxypropylene)–poly(oxyethylene) family. In such a system molecule–micelle and micelle–liquid crystal transitions are observed, depending on temperature and composition. The longitudinal relaxation time, R 1, significantly changes when the aforementioned phase transitions take place. In the case of molecule–micelle equilibrium, changes in R 1 values of the methyl (and methynic) group signal, located in the lipophilic portion of block copolymers, are observed. The effect is ascribed to a significant dehydration of the poly(oxypropylene) chains, as a consequence of micelle formation. Conversely, the thermal transitions from micelles to liquid-crystalline phases are associated with significant changes in the relaxation time of poly(oxyethylene) units. The latter effect is tentatively ascribed to a partial dehydration and/or interdigitation of the poly(oxyethylene) moieties in the block copolymer.

Magnetic resonance studies on neutron irradiated quartz and amorphous silica

NMR and ESR experiments were performed on samples of neutron irradiated quartz and amorphous silica. MAS NMR and static NMR spectra (on 29Si) were acquired. Longitudinal NMR relaxation times T1 (of 29Si) were measured, both under MAS and static conditions. ESR was used to observe the paramagnetic centers in these samples, which are thought to be the main agent responsible for longitudinal NMR relaxation. Densities of these paramagnetic centers were derived from ESR spectra and the results were compared with the T1 results.

ChemInform Abstract: Mechanisms of Longitudinal 29Si Nuclear Magnetic Relaxation in Aqueous Alkali Metal Silicate Solutions.

AbstractThe results of the measurements of 29Si longitudinal NMR relaxation times (T1) in aqueous alkali metal silicate solutions indicate that the major relaxation mechanism is a dipole‐dipole interaction involving the counterion M+ (M: Na, K, Rb), probably through an intramolecular process within a silicate‐M+ ion pair.

Frequency dependence of water proton longitudinal NMR relaxation times in mouse tissues around the freezing transition

Water proton longitudinal NMR relaxation times were measured in various tissues of healthy and tumor-bearing mice. Measurements were performed as a function of the Larmor frequency ν in the range 6–90 MHz, and at two temperatures ( θ + and θ −) bracketing the ‘freezing transition’, at which the major part of the water signal disappears. At both temperatures, 1 T 1 behaves according to: 1 T 1 = A v +B A and B are obtained at θ + and θ −, and yield the proportion of bound water, which is convincingly identified with non-freezable water. The proportions found lie around 6% for tumors and 12% for other tissues. Discrimination between tissues via T 1 is demonstrated to be essentially due to the bound water proportion. Bound water on the one hand and free water on the other hand behave similarly in all tissues including tumors. The activation energy for free water is found to be identical to that of pure water, although relaxation times are markedly different. It is noticed that determining the bound water proportion by signal intensity measurements at θ + and θ − is less reliable than by the T 1 method.