NMR Relaxation Times Research Articles

Inverting surface NMR free induction decay data in a voltage-time data space

Envelope detection is an integral step of the surface NMR data processing workflow. A promising approach to produce high signal-to-noise ratio envelopes involves a scheme referred to as spectral analysis (SA) envelope detection – a scheme based upon a series of discrete Fourier transforms for sliding windows of observed NMR data. This method has the advantage that it naturally handles the narrow-band character of the NMR signal without corrupting the early portion of the time-series – both of which are challenges confronting traditional surface NMR processing schemes. However, SA estimated envelopes are weighted by the NMR relaxation time during processing and the envelopes have units of volt-seconds, whereas the unit of the data space employed by traditional surface NMR forward models is volts. To better integrate the SA envelope detection scheme within the surface NMR workflow, we propose to modify the surface NMR forward model such that it predicts data directly in the voltage-time data space. Synthetic and field data inversions, as well as a parameter resolution study, are presented to demonstrate advantages of pairing the SA envelope detection scheme with a forward model that works in the voltage-time data space. The method is shown to improve parameter resolution and does not require significant modifications to existing surface NMR inversion platforms.

Single‐Ion Conducting Poly(Ethylene Oxide Carbonate) as Solid Polymer Electrolyte for Lithium Batteries

AbstractSingle‐ion conducting polymer electrolytes (SIPE) have attracted a lot of interest for application in high energy density lithium metal batteries. SIPEs possess lithium transport numbers close to unity, which does not provoke concentration gradients and holds the promise of limiting lithium dendrite formation. In this article, we have optimized a single‐ion polymer incorporating the most successful chemical units in polymer electrolytes, such as ethylene oxide, carbonate, and a lithium sulfonimide. This single‐ion poly(ethylene oxide carbonate) copolymer was synthesized by polycondensation between polyethylene glycol, dimethyl carbonate, and a functional diol including the pendant sulfonamide anionic group and the lithium counter‐cation. By playing with the monomer stoichiometry, the crystallinity and ionic conductivity were optimized. The best copolymer showed high ionic conductivity values of 1.2×10−4 S cm−1 at 70 °C. Lithium interactions and mobility were studied by lithium‐pulsed field gradient, lithium diffusion, NMR relaxation time measurements, and FTIR‐ATR analysis. High lithium mobility is observed, which is due to the weakly coordinating chemical environment in the polymer and also that the sulfonamide in the SIPE adopts to a greater extent the cis conformation, which is known to promote lithium mobility. Finally, the performance of the singe‐ion conducting poly(ethylene oxide carbonate) was compared in lithium symmetric cells versus an analogous conventional salt in polymer electrolyte, showing improved performance in lithium plating and stripping.

Paper aging and degradation monitoring by the non-destructive two-dimensional micro-Raman mapping.

The aim of this research is the identification of main and common physical-chemical parameters which induce paper degradation. A simple protocol to monitor the quality and molecular structure of ancient papers under natural degradation processes was proposed. Two-dimensional micro-Raman mapping were carried out. Then, point to point, the changes of both the cellulose Raman signature and fluorescence signal intensity were analysed. Modern papers were artificially aged to simulate the natural degradation and a comparison with the trend found for the ancient paper was presented and discussed. Cellulose degradation involves different mechanisms such as dehydration, cleaving of cellulose-glycosidic bonds and glucopyranose rings oxidation, that induce a reduction in the polymerization degree. As shown by the changes of Raman and fluorescence signals and NMR relaxation times, the rate of each processes depends on the initial amount of glycosidic bonds in the cellulose amorphous and crystalline regions, respectively. All these informations are useful both to define procedures to restore old documents and also to preserve the quality of modern papers for a long-term time.

Integrated analysis of modified Japanese cypress using solid-state NMR spectra and nuclear magnetic relaxation times

Acetylation and resin impregnation of Japanese cypress and subsequent heating of these modified cypresses were examined using an integrated analysis of solid-state NMR spectra and relaxation times. The 1H magic angle spinning NMR showed altered moisture balance after chemical and thermal modifications because of changed hydrophobicity. The 13C cross-polarization/magic angle spinning (CP-MAS) NMR spectra showed that acetylation predominately occurred for carbohydrates while phenol formaldehyde (PF) and melamine formaldehyde (MF) resins permeated all biomass constituents in cypress samples. Spin–lattice relaxation times in the laboratory frame, T1H and T1C, increased with chemical modifications although T1C decreased with the curing of both resins. In contrast, 1H spin–lattice relaxation in the rotation frame, T1ρH, increased with the curing as well as acetylation. The tendencies of relaxation times with curing suggested that faster molecular motions were suppressed in the MHz frequency range, and slower molecular motions were enhanced in the kHz frequency range, which generally matched with the signal changes in the 13C pulse saturation transfer/magic angle spinning NMR spectra. Scanning electron microscope observation showed different adhesion distribution between PF and MF resins, affecting the cellulose signals of 13C CP-MAS NMR and T1H change due to the curing.

Topological superconductivity of spin- 3/2 carriers in a three-dimensional doped Luttinger semimetal

We investigate topological Cooper pairing, including gapless Weyl and fully gapped class DIII superconductivity, in a three-dimensional doped Luttinger semimetal. The latter describes effective spin-3/2 carriers near a quadratic band touching and captures the normal-state properties of the 227 pyrochlore iridates and half-Heusler alloys. Electron-electron interactions may favor non-$s$-wave pairing in such systems, including even-parity $d$-wave pairing. We argue that the lowest energy $d$-wave pairings are always of complex (e.g., $d + i d$) type, with nodal Weyl quasiparticles. This implies $\varrho(E) \sim |E|^2$ scaling of the density of states (DoS) at low energies in the clean limit, or $\varrho(E) \sim |E|$ over a wide critical region in the presence of disorder. The latter is consistent with the $T$-dependence of the penetration depth in the half-Heusler compound YPtBi. We enumerate routes for experimental verification, including specific heat, thermal conductivity, NMR relaxation time, and topological Fermi arcs. Nucleation of any $d$-wave pairing also causes a small lattice distortion and induces an $s$-wave component; this gives a route to strain-engineer exotic $s+d$ pairings. We also consider odd-parity, fully gapped $p$-wave superconductivity. For hole doping, a gapless Majorana fluid with cubic dispersion appears at the surface. We invent a generalized surface model with $\nu$-fold dispersion to simulate a bulk with winding number $\nu$. Using exact diagonalization, we show that disorder drives the surface into a critically delocalized phase, with universal DoS and multifractal scaling consistent with the conformal field theory (CFT) SO($n$)${}_\nu$, where $n \rightarrow 0$ counts replicas. This is contrary to the naive expectation of a surface thermal metal, and implies that the topology tunes the surface renormalization group to the CFT in the presence of disorder.

Self-Association Behavior of Cell Membrane-Inspired Amphiphilic Random Copolymers in Water.

Water-soluble and amphiphilic random copolymers (P(MPC/DMAx)) composed of hydrophilic 2-methacryloyloxyethyl phosphorylcholine (MPC) and hydrophobic n-dodecyl methacrylate (DMA) were prepared via reversible addition-fragmentation chain transfer (RAFT) controlled radical polymerization. The compositions of DMA unit (x) in the copolymer were in the range of 0 to 38 unit mol %. The degree of polymerization of P(MPC/DMAx) was adjusted to about 200. Since the monomer reactivity ratios of MPC and DMA are 1.01 and 1.00, respectively, ideal free radical copolymerization occurred. In aqueous solutions, interpolymer aggregation occurred due to the hydrophobic pendant n-dodecyl groups. The aggregation number (Nagg) increased with an increasing x. The mobilities of the DMA and MPC pendant groups in aqueous solutions were restricted, as confirmed by 1H NMR relaxation time measurements, because a part of the MPC units were trapped in the hydrophobic microdomain formed from the pendant n-dodecyl groups. The polarity of the hydrophobic microdomain formed from P(MPC/DMA38) in water was similar to that of ethyl acetate according to fluorescence probe experiments. No specific interactions were found in water between P(MPC/DMAx) and bovine serum albumin because the surface of the interpolymer aggregates contained only hydrophilic MPC units.

Hydration and Water Molecules Mobility in Acid Form of Nafion Membrane Studied by 1H NMR Techniques

Hydration of perfluorinated sulfonic cation-exchange membrane Nafion 117 in acidic ionic form was investigated. It was shown that cation H+ is coupled with two water molecules and hydroxonium ion H5O2+ at low water content is formed. The main feature of the temperature dependence of the self-diffusion coefficients is the increasing curve slopes in low-temperature regions. At high humidity activation energies do not depend on the water content above 0 °C and are close to the bulk water activation energy. The changes in slopes of self-diffusion coefficients and proton conductivity temperature dependencies are usually explained by the freezing of free water at temperatures below 0 °C. This explanation contradicts the temperature dependence of the amount of mobile water. Water does not freeze till λ = 9–10 (λ is the number of water molecules per sulfonate group), but, anyway, ice-like phase DSC peak is observed at λ ≤ 9. From analysis of the 1H NMR relaxation time temperature dependences, it was proposed that at the temperatures below 0 °C water molecules are associated, but are not able to form ice phase because part of their hydrogen bonds are occupied by sulfonate group oxygen and H+ cation. The mobility of these associates is rather high at negative temperatures; however, these associates show a DSC peak.

Variable temperature solid-state NMR spectral and relaxation analyses of the impregnation of polyethylene glycol (PEG) into coniferous wood.

To investigate the behaviours of polyethylene glycol (PEG) and its interaction with biomass constituents in coniferous wood (Japanese cypress), variable temperature solid-state NMR spectra and relaxation times were measured from 20–80 °C. Signal intensities in the 1H and 13C PST-MAS NMR spectra changed depending on both the measurement temperature and the melting point of the impregnated PEG. In the 13C CP-MAS NMR spectra with increasing temperature, although the signal intensities of biomass constituents slightly decreased, signal intensities of PEG molecules in the cypress maximized at 80 °C. PEG impregnation into cypress decreased the T1H values at 80 °C for short to medium chain PEG in the liquid phase while it decreased T1H values at ambient temperature for long chain PEG in the solid phase because the interactions of PEG molecules and the biomass constituents of coniferous wood were different for different chain lengths of the PEG. These variable temperature measurements of both solid-state NMR spectra and relaxation time indicated that impregnation of longer chain PEG molecules produced higher hydrophobicity because of the increased steric hinderance of PEG attached to carbohydrates. The variable temperature measurements also showed that long chain PEG molecules were restricted to the lumen while short to medium chain length PEG molecules infiltrated into the intercellular region of the cell wall in addition to the lumen. These results obtained from the variable temperature NMR measurements were also supported by ATR-IR spectroscopy analyses.

Exploiting enhanced paramagnetic NMR relaxation for monitoring catalyst preparation using T1–T2 NMR correlation maps

A new method to characterise the evolution of surface sites during metal-supported catalyst preparation has been developed, which exploits NMR relaxation times and their sensitivity to paramagnetic ions.

Understanding substrate substituent effects to improve catalytic efficiency in the SABRE hyperpolarisation process.

The use of parahydrogen based hyperpolarisation in NMR is becoming more widespread due to the rapidly expanding range of suitable target molecules and low-cost of parahydrogen production. Hyperpolarisation via SABRE catalysis employs a metal complex to transfer polarisation from parahydrogen into a substrate whilst they are bound. In this paper we present a quantitative study of substrate-iridium ligation effects by reference to the substrates 4-chloropyridine (A), 4-pyridinecarboxaldehyde methyl hemiacetal (B), 4-methylpyridine (C) and 4-methoxypyridine (D), and evaluate the role they play in the SABRE catalysis. Substrates whose substituents enable stronger associations yield slower substrate dissociation rates (k d). A series of variable temperature studies link these exchange rates to optimal SABRE performance and reveal the critical impact of NMR relaxation times (T 1). Longer catalyst residence times are shown to result in shorter substrate T 1 values in solution as binding to iridium promotes relaxation thereby not only reducing SABRE efficiency but decreasing the overall level of achieved hyperpolarisation. Based on these data, a route to achieve more optimal SABRE performance is defined.

Effect of secondary heat-induced aggregation on pork meat batter protein conformation, hydration characteristics, textural quality and in vitro digestibility.

Secondary heating (SH, 30 min at 100 °C), which has a great influence on elastic gels, has been widely applied to emulsified meat products to extend their shelf life. The effects of SH on the textural and nutritional qualities, water migration of meat batter and on the conformations, aggregation and in vitro digestibility of the meat proteins were investigated. Various heat treatments were tested, and the results revealed that an initial heating at 75 °C yielded the highest low-field NMR relaxation time T22 and peak area P22 and the highest in vitro digestibility. As this initial heating time was increased, the α-helix content, water-holding capacity (WHC) and protein digestibility all decreased. Furthermore, SH yielded a much more obvious decrease in the pepsin activity on the protein digestibility than just the initial heating, and also yielded increases in β-sheet content, hardness, gumminess, and chewiness. This result implied that gel shrinkage and protein aggregation occurred, causing decreased WHC and protein digestibility. Also, SH resulted in significantly decreased (P < 0.05) intensities of myosin light chain gel electrophoresis bands. Therefore, SH was concluded to have reduced the textural quality and nutritional value of the meat.

19F MRI of Polymer Nanogels Aided by Improved Segmental Mobility of Embedded Fluorine Moieties.

Using fluorinated probes for 19F MRI imaging is an emerging field with potential utility in cellular imaging and cell tracking in vivo, which complements conventional 1H MRI. An attractive feature of 19F-based imaging is that this is a bio-orthogonal nucleus and the naturally abundant isotope is NMR active. A significant hurdle however in the 19F MRI arises from the tendency of organic macromolecules, with multiple fluorocarbon substitutions, to aggregate in the aqueous phase. This aggregation results in significant loss of sensitivity, because the T2 relaxation times of these aggregated 19F species tend to be significantly lower. In this report, we have developed a strategy to covalently trap nanoscopic states with an optimal degree of 19F substitutions, followed by significant enhancement in T2 relaxation times through increased segmental mobility of the side chain substituents facilitated by the stimulus-responsive elements in the polymeric nanogel. In addition to NMR relaxation time based evaluations, the ability to obtain such signals are also evaluated in mouse models. The propensity of these nanoscale assemblies to encapsulate hydrophobic drug molecules and the availability of surfaces for convenient introduction of fluorescent labels suggest the potential of these nanoscale architectures for use in multimodal imaging and therapeutic applications.

Solvent molecule mobilities in propylene carbonate-based electrolyte solutions coexisting with fumed oxide nanoparticles

Non-aqueous LiClO4 solutions kneaded with various fumed oxides (fumed silica, fumed alumina, and fumed titania) were employed as model systems of lithium ion batteries. The properties of the solid phase and Li+ ions, which affect solvent molecules, were evaluated using 1H NMR spectroscopy and 1H NMR relaxation time (T1, T2) measurements. The 1H NMR signals of propylene carbonate (PC) molecules were influenced by the coexisting solid phase in the LiClO4-PC solution/fumed oxide nanoparticle dispersion. The mobilities of the PC molecules drastically decreased in the presence of only 1–2 vol% of the solid phase (liquid phase thickness is 15–20 nm or less), regardless of the fumed oxide employed. In the IR spectra of the PC/fumed alumina systems, the vibrations at higher wavenumbers were predominantly observed because of indirect electron-donation from the solid surface. The 1H NMR signal detection ratios depended on the fraction of the liquid phase influenced by the solid phase. In the LiClO4-PC solution/fumed alumina systems, the 1H NMR signal detection ratios greatly decreased because of this influence; here, the large positive zeta potential of the solid phase surface of fumed alumina attracted the PC molecules, which had local negative electric fields owing to polarization. Moreover, the T1 and T2 results confirmed that the interaction between the solid phase and PC molecules is much smaller than that between the solid phase and water molecules. Additionally, it was seen that the PC solution system was more significantly affected than the aqueous solution system; the network structure of the entire PC solvent is greatly affected by the addition of the Li+ ion, and the relaxation time decreased significantly.

Effect of magnetic field on diffusion of ethylammonium nitrate – water mixtures confined between polar glass plates

We used 1H NMR diffusometry to study mixtures of ethylammonium nitrate (EAN) with water (3.1–12.4 mol% of added H2O) confined between polar glass plates and exposed to a static magnetic field of 9.4 T. The presence of such restrictions reverses the concentration dependence of the diffusivities of the EA (ethylammonium) cation and water typical for the bulk system. The presence of water weakens the effects of a static magnetic field on diffusion of the EA cation as well as on proton exchange of –NH3 groups. Surprisingly, the amplitude of the echo signal of water protons decreases during exposure to the magnetic field and finally disappears, a phenomenon that depends on the concentration of water in the system. Based on experimental data, we suggest that water in the system is present in two states with different dynamic properties. One type of water formed in confinement possesses NMR relaxation time typical for liquids; its diffusivity can be measured by 1H NMR. The second type of water is formed upon exposure of the sample of the first type to the magnetic field and eventually includes all the water in the system. This type of water possesses “solid-like” NMR relaxation features that makes it “invisible” to the NMR diffusometry technique. We suggest that this second type of water is adsorbed onto the glass plates. Correspondingly, EAN exists in two liquid phases: the first one contains an EAN-water mixture, while the second one contains neat EAN, and forms on the microscopic scale range under the influence of a static magnetic field.

Diffusion of water in industrial cement and concrete

We propose a deuterium diffusion tracer approach to measure diffusion coefficient in the case of very short NMR relaxation times, too short for NMR pulsed field gradient sequences (T1 or T2 below 1 ms). We also treat the case of porous media containing metallic fibers (such as reinforced concrete) strongly disturbing the magnetic field, and the case of inhomogeneous porous media containing large non porous granulates. For the latter, we propose a hollow geometry maximizing the investigated volume and minimizing the experimental time. The method is a 3D diffusion technique in which samples are immersed in deuterium and the water content inside the sample is monitored as a function of time. Water diffusing outside the sample with very long relaxation times can be subtracted either from T2 relaxation time distribution or not polarizing these components using a short repeat delay. Using analytical formulations describing the concentration of a tracer diffusing out of a cylinder or a hollow cylinder, we can calculate the corresponding pore diffusion coefficient.

Direct Correlation between Adsorption Energetics and Nuclear Spin Relaxation in a Liquid-saturated Catalyst Material.

The ratio of NMR relaxation time constants provides a non-destructive indication of the relative surface affinities exhibited by adsorbates within liquid-saturated mesoporous catalysts. In the present work we provide supporting evidence for the existence of a quantitative relationship between such measurements and adsorption energetics. As a prototypical example with relevance to green chemical processes we examine and contrast the relaxation characteristics of primary alcohols and cyclohexane within an industrial silica catalyst support. values obtained at intermediate magnetic field strength are in good agreement with DFT adsorption energy calculations performed on single molecules interacting with an idealised silica surface. Our results demonstrate the remarkable ability of this metric to quantify surface affinities within systems of relevance to liquid-phase heterogeneous catalysis, and highlight NMR relaxation as a powerful method for the determination of adsorption phenomena within mesoporous solids.

Molecular Interactions and Mechanisms in the 1H NMR Relaxation of Residual CHCl3 in Deuterochloroform Solution of a Two-Chain Ionic Surfactant

1H NMR spin–lattice (T1) and spin–spin (T2) relaxation times have been measured for the residual CHCl3 component of deuterochloroform (99.8 atom% D) in neat solvent samples and in a series of isotropic solutions of the ionic surfactant n-octylammonium-n-octadecanoate and also in degassed/dried and aerated solvent systems at 298 K. Analysis of the proton relaxation times as composite values from various relaxation mechanisms suggests that the spin–lattice process is predominantly via spin–rotation while spin–spin relaxation principally involves 1H–Cl scalar coupling. Rotational correlation times from relaxation rates via the dipolar and spin–rotation mechanisms reveal similar fast picosecond molecular rotation of chloroform in the different samples. The presence of surfactant in the solution appreciably affects the 1H NMR spin–lattice relaxation time of CHCl3 and the chemical shift, which is concentration dependent owing to weak intermolecular interactions. Effects of sample condition and solvent degassing, drying, and aeration treatments on the NMR relaxation times and line shape properties of the residual CHCl3 isotopomers are also examined.

Product Inhibition in Glycerol Oxidation over Au/TiO2 Catalysts Quantified by NMR Relaxation

Liquid-phase catalytic oxidation of glycerol in aqueous solutions using porous solid catalysts represents a viable strategy for the sustainable production of fine chemicals from renewable resources. Various aspects of these novel types of reactions are still under investigation. Catalyst deactivation is one of those issues that need to be understood and addressed in order to make these processes commercially viable. In a previous study, it has been reported that the catalytic activity of Au/TiO2 catalysts for the oxidation of glycerol with O2 under basic conditions can be severely inhibited by some reaction intermediates or products. It was suggested that the presence of certain species blocks the active sites of the catalyst, preventing the adsorption of glycerol, which in turn results in a decrease of reaction rate. In this work, we used NMR relaxation time measurements in order to assess surface interactions of glycerol in a Au/TiO2 catalyst pretreated with aqueous solutions of various oxygenates, incl...

Rotational and translational dynamics and their relation to hydrogen bond lifetimes in an ionic liquid by means of NMR relaxation time experiments and molecular dynamics simulation.

We report a concerted theoretical and experimental effort to determine the reorientational dynamics as well as hydrogen bond lifetimes for the doubly ionic hydrogen bond +OH⋯O- in the ionic liquid (2-hydroxyethyl)trimethylammonium bis(trifluoromethylsulfonyl)imide [Ch][NTf2] by using a combination of NMR relaxation time experiments, density functional theory (DFT) calculations, and molecular dynamics (MD) simulations. Due to fast proton exchange, the determination of rotational correlation times is challenging. For molecular liquids, 17O-enhanced proton relaxation time experiments have been used to determine the rotational correlation times for the OH vectors in water or alcohols. As an alternative to those expensive isotopic substitution experiments, we employed a recently introduced approach which is providing access to the rotational dynamics from a single NMR deuteron quadrupolar relaxation time experiment. Here, the deuteron quadrupole coupling constants (DQCCs) are obtained from a relation between the DQCC and the δ 1H proton chemical shifts determined from a set of DFT calculated clusters in combination with experimentally determined proton chemical shifts. The NMR-obtained rotational correlation times were compared to those obtained from MD simulations and then related to viscosities for testing the applicability of popular hydrodynamic models. In addition, hydrogen bond lifetimes were derived, using hydrogen bond population correlation functions computed from MD simulations. Here, two different time domains were observed: The short-time contributions to the hydrogen lifetimes and the reorientational correlation times have roughly the same size and are located in the picosecond range, whereas the long-time contributions decay with relaxation times in the nanosecond regime and are related to rather slow diffusion processes. The computed average hydrogen bond lifetime is dominated by the long-time process, highlighting the importance and longevity of hydrogen-bonded ion pairs in these ionic liquids.

Determination of quantitative pore‐size distribution of soils with 1H NMR relaxometry

SummaryThe determination of pore‐size distribution (PSD) in soil by conventional methods can be time‐ and effort‐consuming. Therefore, several attempts have been made recently to assess and implement proton nuclear magnetic resonance relaxometry (1H NMR relaxometry) to determine PSDs quantitatively. The 1H NMR relaxometry promises not only to be more time‐ and effort‐saving but also offers a broader range for the estimation of pore size, better resolved results and non‐destructive measurements. To evaluate these possibilities, we tested the extent to which a single calibration curve for the estimation of surface relaxivity of soil, derived from seven soil samples, can be applied to unknown soils. For validation, the quantitative PSDs of seven additional soil samples were determined from the distributions of NMR relaxation times of water saturated samples using this calibration curve; they were compared with their classical water retention curves (WRCs). In general, the quantitative PSDs determined by this approach described the classical WRCs quite well. The best results were obtained for sandy, silty and loam soils. The largest differences were for soils with large clay (47%) and SOM contents (10 and 21%). Our results suggest that these differences derive from swelling processes.Highlights Can NMR relaxometry be used to quantify soil pore‐size distribution without individual calibration? Soil pore size assessment by NMR is fast, detailed and independent of conventional methods NMR method describes the pore‐size distribution of various soil types and soil compositions. NMR method can assess quantitative effects of SOM and swelling of clay in soil.