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The measurement of translational diffusion coefficients by nuclear magnetic resonance (NMR) spectroscopy is essential in a broad range of fields, including organic, inorganic, polymer, and supramolecular chemistry. It is also a powerful method for mixture analysis. Spatially encoded diffusion NMR (SPEN DNMR)" is a time efficient technique to collect diffusion NMR data, which is particularly relevant for the analysis of samples that evolve in time. In many cases, motion other than diffusion is present in NMR samples. This is, for example, the case of flow NMR experiments, such as in online reaction monitoring and in the presence of sample convection. Such motion is deleterious for the accuracy of DNMR experiments in general and for SPEN DNMR in particular. Limited theoretical understanding of flow effects in SPEN DNMR experiments is an obstacle for their broader experimental implementation. Here, we present a detailed theoretical analysis of flow effects in SPEN DNMR and of their compensation, throughout the relevant pulse sequences. This analysis is validated by comparison with numerical simulation performed with the Fokker–Planck formalism. We then consider, through numerical simulation, the specific cases of constant, laminar, and convection flow and the accuracy of SPEN DNMR experiments in these contexts. This analysis will be useful for the design and implementation of fast diffusion NMR experiments and for their applications. [ABSTRACT FROM AUTHOR]

Explicit phenomenological solutions to recurrence relations for the bulk transverse and longitudinal magnetization found using the Torrey–Bloch equations with relaxation effects are used to investigate nuclear magnetic resonance (NMR) diffusion measurements. Of particular interest are steady state NMR (self-)diffusion measurements that reduce experimental time that can extend the techniques to quickly reacting systems. The solutions for bulk transverse and longitudinal magnetization presented here are used to investigate the average behavior of the transverse and longitudinal magnetization in forming a steady state and are used to derive new expressions for the steady state longitudinal magnetization. These solutions can be applied to a noninteracting spin 1/2 ensemble undergoing free diffusion exposed to an arbitrary NMR pulse sequence containing arbitrary magnetic field gradient waveforms. The closed algebraic form method presented here has an advantage over iterative procedures for calculating transverse and longitudinal magnetization for the analysis and development of steady state pulse sequences. Previous theoretical results for steady state diffusion measurements are also reproduced. The Mathematica code for these solutions is provided in the supplementary material. [ABSTRACT FROM AUTHOR]

Time-dependent diffusion behavior is probed over sub-millisecond timescales in a single shot using a nuclear magnetic resonance static gradient time-incremented echo train acquisition (SG-TIETA) framework. The method extends the Carr–Purcell–Meiboom–Gill cycle under a static field gradient by discretely incrementing the π-pulse spacings to simultaneously avoid off-resonance effects and probe a range of timescales (50–500 µs). Pulse spacings are optimized based on a derived ruleset. The remaining effects of pulse inaccuracy are examined and found to be consistent across pure liquids of different diffusivities: water, decane, and octanol-1. A pulse accuracy correction is developed. Instantaneous diffusivity, Dinst(t), curves (i.e., half of the time derivative of the mean-squared displacement in the gradient direction) are recovered from pulse accuracy-corrected SG-TIETA decays using a model-free log-linear least squares inversion method validated by Monte Carlo simulations. A signal-averaged 1-min experiment is described. A flat Dinst(t) is measured on pure dodecamethylcyclohexasiloxane, whereas decreasing Dinst(t) is measured on yeast suspensions, consistent with the expected short-time Dinst(t) behavior for confining microstructural barriers on the order of micrometers. [ABSTRACT FROM AUTHOR]

Since its discovery in mid-20th century, the sensitivity of Nuclear Magnetic Resonance (NMR) has increased steadily, in part due to the design of new, sophisticated NMR experiments. Here we report on a liquid-state NMR methodology that significantly increases the sensitivity of diffusion coefficient measurements of pure compounds, allowing to estimate their sizes using a much reduced amount of material. In this method, the diffusion coefficients are being measured by analysing narrow and intense singlets, which are invariant to magnetic field inhomogeneities. The singlets are obtained through signal acquisition embedded in short (<0.5 ms) spin-echo intervals separated by non-selective 180° or 90° pulses, suppressing the chemical shift evolution of resonances and their splitting due to J couplings. The achieved 10−100 sensitivity enhancement results in a 100−10000-fold time saving. Using high field cryoprobe NMR spectrometers, this makes it possible to measure a diffusion coefficient of a medium-size organic molecule in a matter of minutes with as little as a few hundred nanograms of material. Since its discovery, the sensitivity of Nuclear Magnetic Resonance has increased steadily. Here the authors report on a liquid-state NMR methodology that increases the sensitivity of the diffusion coefficient measurements 10–100- fold, allowing to use microgram quantities of compounds, while reducing the measurement time to few minutes. [ABSTRACT FROM AUTHOR]

This article reviews different studies on the gelation mechanisms and network structural characteristics in polysaccharide gels at the different length scales of observation: macroscopic, microscopic, and molecular. Rheological and micro-DSC (Differential Scanning Calorimetry) measurements represent the macroscopic viewpoints on the gelation of pure kappa-carrageenan (KC), iotacarrageenan (IC) and KC/IC mixtures. Microscopic rheological properties observed using particle tracking experiments have been used to elucidate the formation of heterogeneous networks of KC-rich and IC-rich domains in mixed KC/IC gels, and facilitate observations of their aging process. Nuclear magnetic resonance (NMR) relaxation time measurements provide information on the tumbling motion and local mobility; these molecular-level experiments are presented for agar, agarose, native gellan and deacylated gellan chains. NMR diffusion measurements of gelling and probe polymers give insights into the conformational changes, aggregation and network formation, and aging mechanisms, and are presented for all studied polysaccharides. [ABSTRACT FROM AUTHOR]

[Display omitted] • NMR for moving samples under strong magnetic field gradients. • Diffusion. • NMR Logging-While-Drilling (LWD) simulator. Among the numerous measurements carried out during a well-logging procedure, the Nuclear Magnetic Resonance (NMR) assessment is one of the fundamental analyses in determining the economic viability of a well for the oil industry. Nowadays, two reliable approaches, Wireline Logging (WL) and Logging While Drilling (LWD), stand out. WL comprises the acquisition of NMR data under static conditions. On the other hand, in LWD, the NMR measurements happen simultaneously with the drilling process, while the NMR tool experiences translation, rotation, and vibration motions relative to the rock formation. In order to comprehend better the NMR response acquired under LWD conditions, a setup emulating an LWD tool was developed, consisting of a single-sided magnet, rf probes, and a mechanical device that emulates a relative sinusoidal movement between the sample and the applied magnetic field. A bulk sample and three representative rocks, Fontainebleau Sandstone, Berea Sandstone, and Indiana Limestone, were investigated. Even though the diffusion coefficient measurements remain neglected for their intrinsic characteristics of data acquisition, the findings demonstrate that the diffusion coefficient parameter of a fluid in a bulk sample or confined in a porous rock can be precise and accurately predicted. In strong magnetic field gradients, the Hahn spin echo is predominantly weighted by the diffusion process, an effect used to measure diffusion coefficients. Under LWD conditions, the diffusion coefficient measurement is considerably affected by signal phase modulation due to sample movement in the presence of strong magnetic field gradients, making this measurement difficult. This article present solutions for correct diffusion coefficient measurements, synchronizing Hahn spin echo experiments with sample movement. [ABSTRACT FROM AUTHOR]

The diffusion of enzymes is of fundamental importance for many biochemical processes. Enhanced or directed enzyme diffusion can alter the accessibility of substrates and the organization of enzymes within cells. Several studies based on fluorescence correlation spectroscopy report enhanced diffusion of enzymes upon interaction with their substrate or inhibitor. In this context, major importance is given to the enzyme fructose-bisphosphate aldolase, for which enhanced diffusion has been reported even though the catalysed reaction is endothermic. Additionally, enhanced diffusion of tracer particles surrounding the active aldolase enzymes has been reported. These studies suggest that active enzymes can act as chemical motors that self-propel and give rise to enhanced diffusion. However, fluorescence studies of enzymes can, despite several advantages, suffer from artefacts. Here, we show that the absolute diffusion coefficients of active enzyme solutions can be determined with Pulsed Field Gradient Nuclear Magnetic Resonance (PFG-NMR). The advantage of PFG-NMR is that the motion of the molecule of interest is directly observed in its native state without the need for any labelling. Furthermore, PFG-NMR is model-free and thus yields absolute diffusion constants. Our PFG-NMR experiments of solutions containing active fructose-bisphosphate aldolase from rabbit muscle do not show any diffusion enhancement for the active enzymes, nor the surrounding molecules. Additionally, we do not observe any diffusion enhancement of aldolase in the presence of its inhibitor pyrophosphate. [ABSTRACT FROM AUTHOR]

The diversion efficiency measures the acid capacity to change its flow direction to the lower permeability reservoir sections. A good acid diverter creates a tortuous (zigzagged) wormhole within the acidized core sample in a laboratory setup. Here, we studied two different acid diverters compared to the conventional hydrochloric acid (HCl) to investigate their efficiency in changing the wormhole direction inside the rock core. Nuclear magnetic resonance (NMR) can be used to measure the 3D tortuosity of a rock sample; hence, we propose it as a tool to measure acid diversion efficiency because it can be applied in the field and in the laboratory. Two acid systems were utilized: straight 15 wt.% HCl acid and gelled acid consisting of 15 wt.% HCl acid and polyacrylamide polymer (PAM). Four coreflooding experiments were conducted on 1.5 inch-diameter × 3 inch-length Indiana limestone samples, two with straight HCl acid and two with gelled HCl acid at different PAM concentrations. NMR was utilized to measure the T2 distribution of the rock samples and diffusion tortuosity in two orthogonal directions. Also, X-ray computed tomography (CT) of the acidized samples was taken to visualize the wormholes. Results showed that the polymer-based acid-created zigzagged paths, and more acid volume was consumed to create the wormholes using CT. NMR diffusion tortuosity measurements showed that the tortuosity was reduced along the wormhole direction in all experiments. Nevertheless, the gelled acid treatments showed a significant reduction of the tortuosity orthogonal to the main wormhole path. The diversion efficiency of the 50 lbm/ 1000 gal PAM-gelled acid was 35% higher compared to the straight HCl acid. On the contrary, the 30 lbm/ 1000 gal PAM-gelled acid gave only 10% improvement in the diversion. The index could screen quantitatively which diverting acid is more efficient. We introduced a new diversion index based on the NMR diffusion measurements in this study to quantify the diversion capacity of an acid system in carbonate rock. [ABSTRACT FROM AUTHOR]

Sodium has been suggested as a tracer for brine in reservoir formations where a significant amount of sodium ion is found mainly in the aqueous phase. Fortunately, the most abundant sodium isotope, 23Na, is Nuclear Magnetic Resonance (NMR) active, making it possible to study the structure and dynamical properties of both bulk and pore confined fluid systems. We investigated the diffusion of key dissolved sodium species in bulk solution and porous media as a function of composition, ionic strength, and permeability of the carbonate samples using NMR relaxometry and pulsed-field gradient (PFG) NMR techniques. We use Indiana limestone as an example of natural porous media and water as a freely diffusible tracer and carrier. We demonstrate apparent diffusion measurement of sodium based on changes in spin–spin relaxation time (T 2) signal in pore confinement. The diffusion rate of sodium decreases with increasing counter-ion size. This effect is greater at higher ionic strengths and lower chemical potentials in porous media. The reactive transport code, CrunchFlow, was used to complement the NMR experiments to simulate diffusion behavior in porous media. Combining these two methods provides a powerful approach to estimating effective diffusion coefficients in heterogeneous matrices. The modeling considers the influence of physical properties (porosity and tortuosity) and chemical properties (geochemical composition and chemical gradients). The results presented in this work highlight the advantage of measuring apparent diffusivity using NMR T 2 relaxometry in conjunction with numerical simulation to derive effective diffusivity and the corresponding matrix properties (i.e., tortuosity) of the system. [ABSTRACT FROM AUTHOR]

This work focuses on quantification of microscopic self-diffusion of gas molecules in mixed-matrix membranes (MMMs) formed by dispersing UiO-66-NH 2 metal–organic framework (MOF) crystals in 6FDA-Durene polyimide. Self-diffusion measurements were performed by 13C pulsed field gradient nuclear magnetic resonance (PFG NMR) for pure CO 2 and CH 4 with the spatial resolution in the range of 0.5–24 μm and for different MOF loadings between 12.5 and 50 weight percent. Diffusion measurements performed for each gas in the MMM with the lowest MOF loading of 12.5 weight percent yielded a single diffusivity for all measured diffusion times corresponding to a diffusion under the condition of a fast exchange between the UiO-66-NH 2 crystals and the surrounding polymer phase. However, as the UiO-66-NH 2 loading was increased, two molecular ensembles were observed for both CO 2 and CH 4 : 1) an ensemble corresponding to diffusion inside UiO-66-NH 2 crystals and through the MOF–polymer interfaces, and 2) an ensemble corresponding to diffusion mainly in the polymer phase of the MMMs. This behavior can be explained by the formation of MOF clusters at higher MOF loadings. Quantification of the intra-cluster diffusivity, average cluster size, and the dependence of these properties on the MOF loading are presented and discussed. The reported measurements can serve as a framework to quantify discrete microscopic diffusion characteristics and sizes of interconnected MOF clusters in MMMs as MOF loading increases to reach the desired outcome of gas percolation over a spanning MOF cluster, viz a cluster of interconnected MOF crystals spanning an entire MMM. [Display omitted] • Changes in microscopic gas diffusion in the studied membranes with MOF loading. • Quantifying intra-membrane diffusion inside MOF clusters and in the polymer phase. • Sizes of MOF clusters and intra-cluster diffusivity increase with increasing MOF loading. • Gas diffusion selectivities are quantified separately for MOF and polymer phases. [ABSTRACT FROM AUTHOR]

Lubricating greases were investigated by nuclear magnetic resonance/magnetic resonance imaging (NMR/MRI) to get insight into their structure and into their response to mechanical forces, which is related to bleeding and aging. The investigated greases are based on metallic soaps of fatty acids and oils, whereby LiOH is often used. These organic soaps act as thickeners and provide a network in which oils and their additives are embedded. Lubricating greases can thus be considered as a class of substances similar to oleogels or even hydrogels. Questions arise about translational mobility of guest molecules, mainly base oil, in these networks. Molecular structuring and interactions within the network of thickeners are of interest as they are related to macroscopic stability. Apart from NMR spectroscopy (1H‐, 7Li‐ and 31P‐NMR), spectrally resolved relaxation and diffusion measurements are used for characterization. In addition, magic angle spinning (MAS)‐NMR was combined with 1H‐MRI to investigate the impact of mechanical stress and swelling of lubricating greases. [ABSTRACT FROM AUTHOR]

Although nanometer‐sized aluminum hydroxide clusters (i.e., ϵ‐Al13, [Al13O4(OH)24(H2O)12]7+) command a central role in aluminum ion speciation and transformations between minerals, measurement of their translational diffusion is often limited to indirect methods. Here, 27Al pulsed field gradient stimulated echo nuclear magnetic resonance (PFGSTE NMR) spectroscopy has been applied to the AlO4 core of the ϵ‐Al13 cluster with complementary theoretical simulations of the diffusion coefficient and corresponding hydrodynamic radii from a boundary element‐based calculation. The tetrahedral AlO4 center of the ϵ‐Al13 cluster is symmetric and exhibits only weak quadrupolar coupling, which results in favorable T1 and T227Al NMR relaxation coefficients for 27Al PFGSTE NMR studies. Stokes–Einstein relationship was used to relate the 27Al diffusion coefficient of the ϵ‐Al13 cluster to the hydrodynamic radius for comparison with theoretical simulations, dynamic light scattering from literature, and previously published 1H PFGSTE NMR studies of chelated Keggin clusters. This first‐of‐its‐kind observation proves that 27Al PFGSTE NMR diffusometry can probe symmetric Al environments in polynuclear clusters of greater molecular weight than previously considered. [ABSTRACT FROM AUTHOR]

A pulsed field gradient spin-echo nuclear magnetic resonance (NMR) sequence with solvent suppression (PGSE-WATERGATE) was applied to accurately measure the diffusion coefficients of Rhodamine 6G (Rh6G) in low-concentration aqueous solutions. Three samples with Rh6G concentrations of CRh6G = 1,4.5, and 25 μM were investigated. The precise determination of the diffusion coefficients in this low-concentration range was made possible by using a cryogenically cooled NMR probe and by the effective solvent suppression of the PGSE-WATERGATE sequence. The present results bridge the gap between diffusion data measured by fluorescence correlation spectroscopy in the single molecule limit and diffusivities obtained by pulsed field gradient NMR (PFG-NMR) without solvent suppression at higher concentrations. To further extend the concentration range, the diffusion coefficient of Rh6G was also measured on a sample with CRh6G = 410 μM by PFG-NMR. The overall concentration dependence of the Rh6G diffusion at 25 °C is discussed in terms of dimerization of the Rh6G molecules. The concentration-dependent monomer/dimer proportion is deduced from the diffusion data. [ABSTRACT FROM AUTHOR]

ZSM‐5 zeolite nanoboxes with accessible meso‐micro‐pore architecture and strong acid sites are important in relevant heterogeneous catalysis suffering from mass transfer limitations and weak acidities. Rational design of parent zeolites with concentrated and non‐protective coordination of Al species can facilitate post‐synthetic treatment to produce mesoporous ZSM‐5 nanoboxes. In this work, a simple and effective method was developed to convert parent MFI zeolites with tetrahedral extra‐framework Al into Al‐enriched mesoporous ZSM‐5 nanoboxes with low silicon‐to‐aluminium ratios of ≈16. The parent MFI zeolite was prepared by rapid ageing of the zeolite sol gel synthesis mixture. The accessibility to the meso‐micro‐porous intra‐crystalline network was probed systematically by comparative pulsed field gradient nuclear magnetic resonance diffusion measurements, which, together with the strong acidity of nanoboxes, provided superb catalytic activity and longevity in hydrocarbon cracking for propylene production. [ABSTRACT FROM AUTHOR]

Abstract Organic-rich shales have pore size on nanometer scale and permeability on the order of nano-Darcy. These properties give rise to significant challenges in understanding and modeling flow processes during the hydrocarbon production from shale reservoirs. During production, light hydrocarbons move from nanopores in the rock matrix to fractures generated by hydraulic fracturing to the well. Diffusion becomes a key mechanism in controlling hydrocarbon transport within matrix and from matrix to fractures. However, reliable experimental data for hydrocarbon diffusion coefficients in organic-rich shales are still lacking in the literature. This study presents experimental measurements of in situ methane diffusion coefficients in shales using a pulse-field-gradient nuclear magnetic resonance method. This method measures the diffusion coefficient at equilibrium state and thus eliminates the possibility of fluid flow effects in laboratory measurement generated from pressure or concentration gradient. The measured methane diffusion coefficients in shales are two orders of magnitude smaller than those in the bulk state in the pressure range from 75 to 6000 psi. The measured data can be used to more accurately evaluate and model the production from shale reservoirs. [ABSTRACT FROM AUTHOR]

GARField 1 H NMR relaxometry experiments were done to study the drying process of two latices with different polymer T g and to elucidate water mobility behavior during this process. It was found that the hard type latex, with a polymer T g above room temperature, dries faster than the soft type latex, with a polymer T g below room temperature. Diffusion measurements by means of echo time variations at different moments in the drying process show that water auto-diffusion decreases with increasing solid content of the latex independent of particle T g . Two pools of protons with different mobilities were observed based on transversal relaxation T 2 . Determination of the long T 2, long 's and short T 2, short 's of both latex dispersions and their respective proton densities during drying at 80% RH showed evidence of particle deformation for the soft type latex and the absence thereof for the hard type latex. Additional drying of the resulting coatings with anhydrous CaCl 2 showed a higher porosity for the hard type coating based on the proton distribution profile width. Moreover, two domains with different polymer proton mobilities are found for both coatings that are both plasticized by water at 80% RH . This is more apparent for the hard type coating, suggesting that a more hydrophilic polymer gives a higher degree of plasticization. [ABSTRACT FROM AUTHOR]

Multinuclear pulsed field gradient (PFG) NMR was used to study the self-diffusion of carbon dioxide and methane as equimolar mixtures and pure gases inside ZIF-11 crystals. Diffusion measurements were performed under conditions where the length scales of displacements were comparable with or smaller than the mean size of ZIF-11 crystals. It was found for both carbon dioxide and methane that the intracrystalline diffusivity decreases with an increasing diffusion time. Quantitative analysis of these time dependencies using a previously reported model explained the dependencies by the reflections of gas molecules from the external crystal surface. This analysis also allowed the intracrystalline gas diffusivities that are not perturbed by the influence of the external crystal surface to be determined. The ratio of such true intracrystalline diffusivities for CO 2 and CH 4 is found to be greater in the mixed sorbate sample than in the single-sorbate samples when the total gas concentration in each sample was the same within experimental error. [ABSTRACT FROM AUTHOR]

Standard diffusion NMR measurements require the repetition of the experiment multiple times with varying gradient strength or diffusion delay. This makes the experiment time-consuming and restricts the use of hyperpolarized substances to boost sensitivity. We propose a novel single-scan diffusion experiment, which is based on spatial encoding of two-dimensional data, employing the spin-echoes created by two successive adiabatic frequency-swept chirp π pulses. The experiment is called ultrafast pulsed-field-gradient spin-echo (UF-PGSE). We present a rigorous derivation of the echo amplitude in the UF-PGSE experiment, justifying the theoretical basis of the method. The theory reveals also that the standard analysis of experimental data leads to a diffusion coefficient value overestimated by a few per cent. Although the overestimation is of the order of experimental error and thus insignificant in many practical applications, we propose that it can be compensated by a bipolar gradient version of the experiment, UF-BP-PGSE, or by corresponding stimulated-echo experiment, UF-BP-pulsed-field-gradient stimulated-echo. The latter also removes the effect of uniform background gradients. The experiments offer significant prospects for monitoring fast processes in real time as well as for increasing the sensitivity of experiments by several orders of magnitude by nuclear spin hyperpolarization. Furthermore, they can be applied as basic blocks in various ultrafast multidimensional Laplace NMR experiments. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Recently, there has been a surge of interest in mesogens exhibiting the twist-bend nematic (NTB) phase that is shown to be chiral even though formed by effectively achiral molecules. Although it now seems to be clear that the NTBphase in the bulk is formed by degenerate domains having opposite handedness, the presence of a supramolecular heliconical structure proposed in the Dozov model has been contradicted by the Hoffmann et al. model in which the heliconical arrangement is replaced by a polar nematic phase. The evidence in support of this is that the quadrupolar splitting tensor measured in various experiments is uniaxial and not biaxial as expected for the twist-bend nematic structure. In this debate, among other evidence, the molecular translational diffusion, and its magnitude with respect to that in the nematic phase above the NTBphase, has also been invoked to eliminate or to confirm one model or the other. We attempt to resolve this issue by reporting the first measurements of the translational self-diffusion coefficients in the nematic and twist-bend nematic phases formed 1″,7″-bis-4-(4′-cyanobiphenyl-4′-yl) heptane (CB7CB). Such measurements certainly appear to resolve the differences between the two models in favour of that for the classic twist-bend nematic phase. [ABSTRACT FROM PUBLISHER]

NMR measurements of diffusion in solution, whether primarily quantitative, or, (as in DOSY, Diffusion-Ordered Spectroscopy) qualitative, can be particularly demanding. Here we show how the use of appropriate transverse ( x , y ) pulsed field gradients, orthogonal to the more usual z axis pulsed field gradient applied along the long axis of the sample, can greatly reduce two important sources of systematic error in diffusion experiments. These are the extra signal attenuation caused by sample convection, and gradient-dependent signal phase shifts caused by the magnetic field and field-frequency lock disturbances generated by field gradient pulses. [ABSTRACT FROM AUTHOR]

Laplace NMR (LNMR) consists of relaxation and diffusion measurements providing detailed information about molecular motion and interaction. Here we demonstrate that ultrafast single- and multidimensional LNMR experiments, based on spatial encoding, are viable with low-field, single-sided magnets with an inhomogeneous magnetic field. This approach shortens the experiment time by one to two orders of magnitude relative to traditional experiments, and increases the sensitivity per unit time by a factor of three. The reduction of time required to collect multidimensional data opens significant prospects for mobile chemical analysis using NMR. Particularly tantalizing is future use of hyperpolarization to increase sensitivity by orders of magnitude, allowed by single-scan approach. [ABSTRACT FROM AUTHOR]

Thecomposition and molecular mobility within thin spherical liquidfilms have been investigated using nuclear magnetic resonance (NMR)diffusion measurements. These films were formed either on the surfaceof pores inside a sponge at low saturation or by adsorbed water onthe outside of urea prills during caking. Using pulsed field gradient(PFG) NMR experiments, the molecular mobility within these liquidfilms was determined through analysis of the conditional probabilitydensity for displacement (propagator). Molecular diffusion coefficientswere determined for films in the sponge and prill systems by fittingthe experimental propagators using a model for diffusion on an arrayof isotropically distributed infinite planes. By comparing these diffusioncoefficients with bulk diffusion coefficients for a range of concentrationsof urea solutions (2.1 M, 6.2 M and saturated), it was possible tooptimize the PFG experimental parameters to enable accurate determinationof molecular diffusion in these spherical liquid films. Determinationof the diffusion coefficients for a range of urea solutions in thesponge enabled identification of the composition of the film thatformed on the surface of the urea prills. Analysis of these data showedthat the liquid layers are composed of saturated urea solution coveringthe surface of the prills, with an estimated layer thickness on theorder of 10–5m. The shape of the propagators indicatedthe adsorbed water was uniformly distributed over the surface of theurea prills, rather than primarily in the meniscus between particles,which agrees with dye visualization experiments on a pair of ureaprills during caking. This work provides the first quantitative measurementsof diffusion in thin spherical films, which is a key parameter fordetermining what controls the presence and rate of bonding betweenadjacent particle surfaces. [ABSTRACT FROM AUTHOR]

Nuclear magnetic resonance (NMR) can be conveniently used for accurate measurement of water and ethanol concentrations in gasoline–ethanol fuel blends. The spectra also contain information on proton exchange rates. In addition, NMR pulsed-field-gradient diffusion measurement allows estimation of ethanol–water clusters and viscosity of the fuel blends. [ABSTRACT FROM AUTHOR]

Nuclear magnetic resonance (NMR) relaxometry and diffusometry are important tools for the characterization of heterogeneous materials and porous media, with applications including medical imaging, food characterization and oil-well logging. These methods can be extremely effective in applications where high-resolution NMR is either unnecessary, impractical, or both, as is the case in the emerging field of portable chemical characterization. Here, we present a proof-of-concept experiment demonstrating the use of high-sensitivity optical magnetometers as detectors for ultra-low-field NMR relaxation and diffusion measurements. [ABSTRACT FROM AUTHOR]

Abstract: In the past decade, low-field NMR relaxation and diffusion measurements in grossly inhomogeneous fields have been used to characterize pore size distribution of porous media. Estimation of these distributions from the measured magnetization data plays a central role in the inference of insitu petro-physical and fluid properties such as porosity, permeability, and hydrocarbon viscosity. In general, inversion of the relaxation and/or diffusion distribution from NMR data is a non-unique and ill-conditioned problem. It is often solved in the literature by finding the smoothest relaxation distribution that fits the measured data by use of regularization. In this paper, estimation of these distributions is further constrained by linear functionals of the measurement that can be directly estimated from the measured data. These linear functionals include Mellin, Fourier–Mellin, and exponential Haar transforms that provide moments, porosity, and tapered areas of the distribution, respectively. The addition of these linear constraints provides more accurate estimates of the distribution in terms of a reduction in bias and variance in the estimates. The resulting distribution is also more stable in that it is less sensitive to regularization. Benchmarking of this algorithm on simulated data sets shows a reduction of artefacts often seen in the distributions and, in some cases, there is an increase of resolution in the features of the T 2 distribution. This algorithm can be applied to data obtained from a variety of pulse sequences including CPMG, inversion and saturation recovery and diffusion editing, as well as pulse sequences often deployed down-hole. [Copyright &y& Elsevier]

Pulsed gradient spin echo (PGSE) is a well-known NMR technique for determining diffusion coefficients. Various signal processing techniques have been introduced to solve the task, which is especially challenging when the decay is multiexponential with an unknown number of components. Here, we introduce a new method for the processing of such types of signals. Our approach modifies the Tikhonov's regularization, known previously in CONTIN and Maximum Entropy (MaxEnt) methods, by using the l1-norm penalty function. The modification enforces sparsity of the result, which improves resolution, compared to both mentioned methods. We implemented the Iterative Thresholding Algorithm for Multiexponential Decay (ITAMeD), which employs the l1-norm minimization, using the Fast Iterative Shrinkage Thresholding Algorithm (FISTA). The proposed method is compared with the Levenberg-Marquardt-Fletcher fitting, Non-negative Least Squares (NNLS), CONTIN, and MaxEnt methods on simulated datasets, with regard to noise vulnerability and resolution. Also, the comparison with MaxEnt is presented for the experimental data of polyethylene glycol (PEG) polymer solutions and mixtures of these with various molecular weights (1080 g/mol, 11 840 g/mol, 124 700 g/mol). The results suggest that ITAMeD may be the method of choice for monodispersed samples with "discrete" distributions of diffusion coefficients. [ABSTRACT FROM AUTHOR]

The selection of proper coherence pathways is a very important aspect of the design of NMR pulse sequences. This article describes a C++ program for the calculation of coherence pathway selection via phase cycles, including a module to calculate cogwheel cycles. Cogwheel phase cycles shorter than the original ones [M.H. Levitt et al., J. Magn. Reson. 155 (2002) 300] are derived and experimentally tested for the MQMAS experiment for 3/2 spins. Some other cogwheel cycles are derived for the MQNQMAS, the STMAS experiment, and a PFG diffusion pulse sequence. This program is publicly available through our website http://www.nyu.edu/projects/jerschow with additional documentation and examples. [Copyright &y& Elsevier]

Zeolites are known to be effective catalysts in biomass converting processes. Understanding the mesoporous structure and dynamics within it during such reactions is important in effectively utilizing them. Nuclear magnetic resonance (NMR) T2 relaxation and diffusion measurements, using a high-power radio frequency probe, are shown to characterize the dynamics of water in mesoporous commercially made 5A zeolite beads before and after the introduction of xylose. Xylose is the starting point in the dehydration into furfural. The results indicate xylose slightly enhances rotational mobility while it decreases translational motion through altering the permeability, K, throughout the porous structure. The measurements show xylose inhibits pure water from relocating into larger pores within the zeolite beads where it eventually is expelled from the bead itself. [ABSTRACT FROM AUTHOR]

The new complex of N,N-Dimethylglycine (DMG) with chloranilic acid (CLA) was synthesized and examined for thermal, structural, and dynamical properties. The structure of the reaction product between DMG and CLA was investigated in a deuterated dimethyl sulfoxide (DMSO-d6) solution and in the solid state by Nuclear Magnetic Resonance (NMR) (Cross Polarization Magic Angle Spinning-CPMAS NMR). The formation of the 1:1 complex of CLA and DMG in the DMSO solution was also confirmed by diffusion measurement. X-ray single crystal diffraction results revealed that the N,N-dimethylglycine–chloranilic acid (DMG+–CLA−) complex crystallizes in the centrosymmetric triclinic P-1 space group. The X-ray diffraction and NMR spectroscopy show the presence of the protonated form of N,N-dimethylglycine and the deprotonated form of chloranilic acid molecules. The vibrational properties of the co-crystal were investigated by the use of neutron (INS), infrared (IR), and Raman (RS) spectroscopies, as well as the density functional theory (DFT) with periodic boundary conditions. From the band shape analysis of the N–CH3 bending vibration, we can conclude that the CH3 groups perform fast (τR ≈ 10−11 to 10‒13 s) reorientational motions down to a temperature of 140 K, with activation energy at ca. 6.7 kJ mol−1. X-ray diffraction and IR investigations confirm the presence of a strong N+–H···O− hydrogen bond in the studied co-crystal. [ABSTRACT FROM AUTHOR]

Core-shell tecto dendrimers (CSTDs) are a class of superstructured dendrimeric nanoconstructs with similar structural characteristics and biomedical performances to the high-generation dendrimers that can be decorated with zwitterions to be availed of good antifouling properties for different biomedical applications. Characterization of the CSTD-based dendrimeric derivatives remains to be a great challenge. Here, we attempted to utilize nuclear magnetic resonance (NMR) technologies to investigate the structure and hydrodynamic size of CSTDs functionalized with zwitterionic carboxybetaine acrylamide (CBAA) and confirmed their antifouling property through protein resistance assay. In this study, we initially prepared CSTDs by supramolecular assembly of beta-cyclodextrin (β-CD)-modified generation 5 (G5) poly(amidoamine) (PAMAM) dendrimers as cores and adamantane (Ad)-decorated G3 PAMAM dendrimers as shells, and then partially modified the CSTD terminal amines with CBAA. The dendrimeric products were thoroughly characterized. Our results show that the obtained CSTDs display strong correlation signals between the Ad and β-CD protons in the two-dimensional NMR spectrum, indicating the strong host-guest interaction existing between G3-Ad and G5-CD in the structure of CSTDs. Diffusion NMR measurements reveal that the hydrodynamic diameter of CSTDs is smaller after partial CBAA surface modification, possibly due to the tightened molecular volume after zwitterionic modification. Lastly, the CBAA-modified CSTDs were demonstrated to have good antifouling property through protein resistance assay. Our findings provide a new strategy to study the framework of the developed CSTDs and CBAA-modified CSTDs, facilitating their further design and surface modification for various biomedical applications. [Display omitted] [ABSTRACT FROM AUTHOR]

This study explored the reactive processes of atmospheric carbonation and the consequences with respect to cementitious materials. Two model pastes were used: hydrated C 3 S (including C-S-H and portlandite) and a paste prepared by hydrating a blend of C 3 S and nanosilica (including C-S-H only). The two pastes were carbonated under accelerated conditions in the laboratory. The resulting mineralogical assemblage was examined using X-ray diffraction, thermogravimetric analysis and nuclear magnetic resonance. The microstructural changes were studied by X-ray tomography and porosimetry, and their macroscopic impacts were evaluated through gas diffusion and shrinkage measurements. The use of model pastes allowed for the evaluation of the change in solid volume induced by the carbonation of C-S-H. C-S-H decalcification and subsequent silica chain polymerisation were found responsible for carbonation shrinkage (and potentially cracking). Finally, the results highlight the protective role of portlandite: portlandite helped in limiting C-S-H decalcification and then reducing carbonation shrinkage and cracking. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pulse field gradient nuclear magnetic resonance (PFG-NMR) measurement of electrolyte transport. • Proof of concept measurement on the impact dissolved gasses on D Li + . • CO 2(g) has no measurable effect on the solution phase Li+ diffusion coefficient. Electrolyte decomposition in Li-ion batteries (LIB) and its entailing gas evolution significantly impacts cell performance. CO 2 is one of the most abundantly evolved gases from common LIB electrolytes and could potentially affect Li+ solution transport during LIB operation. To this end, a comparative analysis of the Li+ diffusion coefficient (D Li + ) which governs mass transport is required. Herein a methodology is established to saturate common battery electrolytes with a soluble gas without introducing other contaminants, so as to determine D Li + in saturated and unsaturated samples. As a proof of concept, the values of D Li + are determined in 1 M LiPF 6 and 1 M LiClO 4 in ethylene carbonate (EC):dimethyl carbonate (DMC) with and without dissolved CO 2 , confirmed by gas chromatography–mass spectrometry (GC–MS). The results obtained by pulse field gradient nuclear magnetic resonance (PFG-NMR) diffusion measurements agree for both electrolytes; saturating the electrolyte with CO 2 has no measurable effect on D Li + and therefore does not hinder Li+ mass transport. [ABSTRACT FROM AUTHOR]

2-(2-Fluoro-4-biphenyl) propionic acid (flurbiprofen), from the phenylalkanoic acid family of nonsteroidal anti-inflammatory drugs (NSAID's), is currently on the pharmaceutical market as a racemate. This racemic compound was tested for its propensity to undergo the self-disproportionation of enantiomers (SDE) phenomenon by various forms of chromatography (SDEvC), such as routine gravity-driven column chromatography, medium-pressure liquid chromatography (MPLC), preparative thin-layer chromatography (PTLC), and size-exclusion chromatography (SEC), as well as by sublimation (SDEvS). Furthermore, examination by nuclear magnetic resonance (NMR) in various solvents found that flurbiprofen exhibited the phenomenon of self-induced diastereomeric anisochronism (SIDA). By measurement of the diffusion coefficient (D), the longitudinal relaxation time (T1), and the transverse relaxation time (T2) using NMR, as well as by electrospray ionization-mass spectrometry (ESI-MS) examinations, the preferred intermolecular association was found to be solvent dependent, e.g., heterochiral association was preferred in toluene, while homochiral association was preferred in more polar solvents. This study also attempted, unsuccessfully, to correlate the NMR measurements of flurbiprofen with chromatographic outcomes for the rationalization and prediction of chromatographic results based on NMR measurements. Because the intermolecular hydrogen bonding of the acid groups in flurbiprofen overwhelmingly predominates over other intermolecular interactions, flurbiprofen seemed to represent a good test case for this idea. The behavior of scalemic samples of flurbiprofen is important, as, although it is currently dispensed as a racemate, clinical applications of the R enantiomer have been investigated. SDEvC and SDEvS both have ramifications for the preparation, handling, and storage of enantioenriched flurbiprofen, and this concern applies to other chiral drugs as well. [ABSTRACT FROM AUTHOR]

• LF-NMR is an modern tool for material characterization of materials using homogeneous and inhomogeneous fields. • Fourier and inverse Laplace-like transforms are traditional primary processing methods. • The principles and perspectives of PCA are presented as tertiary level analysis for data processing. • Principal Component Analysis (PCA) can differentiate samples by their characteristics. • The perspectives of artificial neural network (ANN) used as quaternary analysis were discussed. Low field Nuclear Magnetic Resonance (LF-NMR) is a rich source of information for a wide range of samples types. These can be hard or soft solids, such as plastics or elastomers; bulk liquids or liquids absorbed in porous materials, and can come from biomaterials, biological tissues, archaeological artifacts, cultural heritage objects. LF-NMR instruments present a significant advance especially for in situ, ex situ and in vivo measurement of relaxation and diffusion. Moreover, high resolution 1D and 2D spectroscopy, as well as magnetic resonance (MR) imaging are available in these fields. In this work we discuss the advanced analysis of the data measured in LF-NMR from the perspectives of tertiary level that implies the analysis on principal components (PCA), and on the quaternary analysis that uses an artificial neural network (ANN). The principles of PCA and ANN are largely discussed. For the PCA analysis, a series of 52 spectra were analyzed, having been recorded in vivo by LF-NMR. Of these spectra, 38 were generated from normal uterus, 7 by uterus tissue with endometrial cancer, and another 7 were obtained from tissues of women with uterine cervical cancer. The PC1 vs PC2 plot was further analyzed using an artificial neural network, and the results are presented as 2D maps of probability. Furthermore, the perspectives of applying an ANN to solve the problem of Laplace-like inversion are discussed. An example of such ANN was presented and the performance was discussed. Finally, a model of complex ANN, capable to sequentially solve this kind of problems specific to LF-NMR is proposed and discussed. [ABSTRACT FROM AUTHOR]

• Four pulse sequences to obtain D-T 1 correlation maps were studied. • The IR-PGSE and SR-PGSE sequences allow to obtain signals with the highest SNR. • The fast PGSE-CWFT-T 1 and PGSE-SAFF sequences present lower SAR parameters. Longitudinal relaxation time (T 1), transverse relaxation time (T 2) and diffusion coefficient (D) values have been widely used for the characterizations of materials using low field Time Domain Nuclear Magnetic Resonance (TD-NMR). Each parameter can be determined using one-dimensional techniques or their values and correlations by multi-dimensional experiments such as T 1 -T 2 , D-T 2 , and T 1 -D-T 2. In this work, we studied four D-T 1 sequences for TD-NMR combining Stejskal-Tanner Pulse Gradient Spin Echo (PGSE) diffusion measurement with Inversion-Recovery (IR), Saturation-Recovery (SR), Small-Angle Continuous Wave Free Precession (CWFP-T 1) and Small-Angle Flip-Flop (SAFF) for T 1 measurement. The results show that rapid D-T 1 measurements can be obtained with single shot CWFP-T 1 and SAFF sequences. The two sequences were two and eight time fast than sequences based on SR and IR, respectively. Although the two fast sequences yield low signal-to-noise ratio signal, they can be as fast as the traditional D-T 2 experiment, or even faster, because it is not necessary to wait a recycle delay of 5 T 1. Another advantage of the CWFP-T 1 and SAFF methods, when compared to the one based on SR or CPMG (for D-T 2) are the low specific absorption rate (SAR) of these sequences due the low flip angles in the sequences, that reduces the sample heating problem. These sequences were initially studied using phantom samples. They also were used to study plant tissues to observe the anisotropic diffusion in asparagus. Therefore, they can be useful methods for practical application in TD-NMR. [ABSTRACT FROM AUTHOR]

We present a tutorial discussion of diffusion measurements by NMR, aimed around a specific problem. To measure diffusion in the presence of convective flow, one may use the second echo using the well‐known cancellation of phase effects from flow for the second echo. In testing this with a simple organic liquid and a static (dc) gradient at room temperature, where no convection can occur, we noticed the data from the second echo implied a substantially larger rate of diffusion than for the first echo. The error is due to the second echo being a superposition of a spin (Hahn) echo (an echo of the first echo) and a stimulated echo. We show that the stimulated echo is more attenuated by diffusion (it has a larger b value), explaining our result. A simple phase cycle is presented that suppresses the stimulated echo and leads to the correct diffusion value from the second echo. That is, the diffusion values taken from the first and second echoes are now identical. [ABSTRACT FROM AUTHOR]