1H NMR Microimaging Research Articles

Assessing the performance of commercial and biological gas hydrate inhibitors using nuclear magnetic resonance microscopy and a stirred autoclave

The formation kinetics of methane/ethane/propane hydrate in the presence of kinetic inhibitors was investigated using 1H nuclear magnetic resonance imaging (MRI) as well as a more-traditional method using a stirred autoclave. These studies were facilitated by fabricating a multi-drop insert for 1H NMR micro-imaging, which allowed the comparison of the performance of microliter quantities of several inhibitors simultaneously and under the same conditions. Both methods showed that hydrate nucleation and growth were delayed significantly in the presence of inhibitors, which included two biological inhibitors (antifreeze proteins) and a commercial inhibitor. The results demonstrate that MRI is a useful tool for the visualization and evaluation of the performance of kinetic inhibitors on mixed gas hydrate formation. The MRI technique should prove especially valuable in the case of analysis of potential inhibitors, pre-commercialization, which are available in only limited quantities, such as biological inhibitors. This technique may also find utility in the exploration of differences in inhibitor performance, which may suggest distinct mechanisms of inhibitor action.

Spatially Resolved Solid-State 1H NMR for Evaluation of Gradient-Composition Polymeric Libraries

Polyurethane libraries consisting of films with composition gradients of aliphatic polyisocyanate and hydroxy-terminated polyacrylate resin were characterized using methods of (1)H NMR microimaging (i.e., magnetic resonance imaging, (MRI)) and solid-state NMR. Molecular mobilities and underlying structural information were extracted as a function of the relative content of each of the two components. Routine NMR microimaging using the spin-echo sequence only allows investigations of transverse relaxation of magnetization at echo times >2 ms. A single-exponential decay was found, which is likely due to free, noncross-linked polymer chains. The mobility of these chains decreases with increasing content of the aliphatic polyisocyanate. The concept of a 1D NMR profiler is introduced as a novel modality for library screening, which allows the convenient measurement of static solid-state NMR spectra as a function of spatial location along a library sample that is repositioned in the rf coil between experiments. With this setup the complete transverse relaxation function was measured using Bloch decays and spin echoes. For all positions within the gradient-composition film, relaxation data consisted of at least three components that were attributed to a rigid highly cross-linked resin, an intermediate cross-linked but mobile constituent, and the highly mobile free polymer chains (the latter is also detectable by MRI). Analysis of this overall relaxation function measured via Bloch decays and spin echoes revealed only minor changes in the mobilities of the individual fractions. Findings with respect to the most mobile components are consistent with the results obtained by NMR microimaging. The major effect is the significant increase in the rigid-component fraction with the addition of the hydroxy-terminated polyacrylate resin.

Relationships between solid dispersion preparation process, particle size and drug release – An NMR and NMR microimaging study

Solid dispersion tablets prepared by either spray drying or rotoevaporation and exhibiting different grain and pore sizes were investigated under the process of hydration-swelling-gelation. 2H and 1H NMR microimaging experiments were used to selectively follow water penetration and polymer mobilization kinetics, respectively, while the drug release kinetics was followed by 1H NMR spectroscopy. The obtained data, in combination with morphological information by scanning electron microscopy (SEM), reveal a complex process that ultimately leads to release of the drug into the aqueous phase. We find that the rate of water ingress has no direct influence on release kinetics, which also renders air in the tablets a secondary factor. On the other hand, drug release is directly correlated with the polymer mobilization kinetics. Water diffusion into the originally dry polymer grains determines the rate of grain swelling and the hydration within the grains varies strongly with grain size. We propose that this sets the stage for creating homogeneous gels for small grain sizes and heterogeneous gels for large grain sizes. Fast diffusion through water-rich sections of the inhomogeneous gels that exhibit a large mesh size is the factor which yields a faster drug release from tablets prepared by rotoevaporation.

Biochemical consequences of alginate encapsulation: A NMR study of insulin-secreting cells

In this study we explore the biochemical consequences of alginate encapsulation on βTC3 cells. 13C NMR spectroscopy and isotopomer analysis were used to investigate the effects of encapsulation on several enzymatic processes associated with the TCA cycle. Our data show statistically significant differences in various enzymatic fluxes related to the TCA cycle and insulin secretion between monolayer and alginate-encapsulated cultures. The principal cause for these effects was the process of trypsinization. Embedding the trypsinized cells in alginate beads did not have a compounded effect on the enzymatic fluxes of entrapped cells. However, an additional small but statistically significant decrease in insulin secretion was measured in encapsulated cells. Finally, differences in either enzymatic fluxes or glucose consumption as a function of bead diameter were not observed. However, differences in T 2, assessed by 1H NMR microimaging, were observed as a function of bead diameter, suggesting that smaller beads became more organized with time in culture, while larger beads displayed a looser organization.

Characteristics of drying and active component distribution in alumina monoliths using 1H-NMR imaging

The distribution of water in the impregnated monolithic substrates was visualized by 1H-NMR imaging. The two-dimensional water content maps along the axial and radial directions have been collected for different monoliths at variation of the drying conditions. Using the blow-through air for drying of the substrate with coated external walls and with free access of air to external walls leads to the parabolic profile of water concentration along the axial direction of the sample. Drying of the monoliths with open external walls proceeds more uniformly in the radial and axial directions of the substrate. Characteristics of drying of alumina monoliths, calcined at 600, 900 and 1200 °C having differences in the pore structure and pore distribution, are studied. During drying of the impregnated washcoated monolith the certain part of the introduced active component precursor (H 2PtCl 6 or H 2PdCl 4) is transported from the substrate macropores to the mesoporous washcoated layer which leads to enrichment of the washcoat of the final catalyst by active component. The non-destructive character of 1H-NMR microimaging demonstrated its capability to visualize the water content maps in monoliths in the presence of Pt and Pd.

Efficient Recovery of CO2 from Flue Gas by Clathrate Hydrate Formation in Porous Silica Gels

Thermodynamic measurements and NMR spectroscopic analysis were used to show that it is possible to recover CO2 from flue gas by forming a mixed hydrate that removes CO2 preferentially from CO2/N2 gas mixtures using water dispersed in the pores of silica gel. Kinetic studies with 1H NMR microimaging showed that the dispersed water in the silica gel pore system reacts readily with the gas, thus obviating the need for a stirred reactor and excess water. Hydrate phase equilibria for the ternary CO2-N2-water system in silica gel pores were measured, which show that the three-phase hydrate-water-rich liquid-vapor equilibrium curves were shifted to higher pressures at a specific temperature when the concentration of CO2 in the vapor phase decreased. 13C cross-polarization NMR spectral analysis and direct measurement of the CO2 content in the hydrate phase suggested that the mixed hydrate is structure I at gas compositions of more than 10 mol % CO2, and that the CO2 molecules occupy mainly the more abundant 5(12)6(2) cages. This makes it possible to achieve concentrations of more than 96 mol % CO2 gas in the product after three cycles of hydrate formation and dissociation. 1H NMR microimaging showed that hydrate yields of better than 85%, based on the amount of water, could be obtained in 1 h when a steady state was reached, although approximately 90% of this yield was achieved after approximately 20 min of reaction time.

Liquid and gas flow and related phenomena in monolithic catalysts studied by 1H NMR microimaging

NMR is employed to study liquid and gas flow in a tube and in the channels of shaped catalysts, mass transport during drying of water saturated porous monoliths, and gas adsorption by porous alumina pellets. NMR flow imaging and pulsed field gradient NMR are shown to yield the same average propagators for liquid and gas flow in a straight circular tube. The complicated patterns of gas or liquid flow in shaped reactors are characterized successfully by NMR flow imaging through the detection of all three flow velocity components.

Application of the 1H NMR Microimaging Technique to in situStudies of Evaporation of Liquids from Objects Modeling Porous Solids

Application of the 1H NMR Microimaging Technique to in situStudies of Evaporation of Liquids from Objects Modeling Porous Solids

Thermally polarized (1)H NMR microimaging studies of liquid and gas flow in monolithic catalysts

The feasibility of gas flow imaging in moderately high magnetic fields employing thermally polarized gases at atmospheric pressures is demonstrated experimentally. Two-dimensional spatial maps of flow velocity distributions for acetylene, propane, and butane flowing along the transport channels of shaped monolithic alumina catalysts were obtained at 7 T by (1)H NMR, with true in-plane resolution of 400 &mgr;m and reasonable detection times. The resolution is shown to be limited by the echo attenuation due to rapid molecular diffusion in the imaging gradients of magnetic field. All gas flow images exhibit flow patterns that are not fully developed, in agreement with the range of Reynolds numbers (190-570) and the length of the sample used in gas flow experiments. The flow maps reveal the highly nonuniform spatial distribution of shear rates within the monolith channels of square cross-section, the kind of information essential for evaluation and improvement of the efficiency of mass transfer in shaped catalysts. The water flow images were obtained at lower Re numbers for comparison. These images demonstrate the transformation of a transient flow pattern observed closer to the inflow edge of a monolith into a fully developed one further downstream. Copyright 2000 Academic Press.

An 1H NMR Microimaging Visualization of Hexachloroplatinate Dianion Redistribution within a Porous γ-Al2O3 Pellet in the Course of Supported Catalyst Preparation

The application of the 1H NMR microimaging technique to the indirect mapping of the spatial distribution of hexachloroplatinate dianion within porous alumina pellets is reported. It is demonstrated that the nuclear spin−lattice relaxation times of liquids filling the pores of the pellet increase in the presence of the adsorbed hexachloroplatinate dianion. The microimaging results for the supported catalysts with two types of platinum distribution (egg-shell and egg-white) are shown to be consistent with the results obtained by the staining method and electron probe microanalysis. Finally, the microimaging technique is employed for a nondestructive visualization of the dynamics of the active component redistribution in the course of the supported catalyst preparation by competitive adsorption.

In Vivo1H‐NMR microimaging with respiratory triggering for monitoring adoptive immunotherapy of metastatic mouse lymphoma

The metastatic ESb-MP murine lymphoma in DBA/2 mice has been used as a model for investigating metastatic disease and its cure by adoptive immunotherapy (ADI) as monitored by in vivo multislice spin-echo 1H NMR microimaging at 7 T. isoflurane inhalation anesthesia facilitated long measurement sessions, and respiratory gating with a fiber-optic sensor greatly reduced motional artifacts. With T2 weighting (TR = 2 s, TE = 30 ms) mean signal-to-noise ratios of 30 and 15 for kidney and liver, respectively, were achieved in 20 min (100-micron pixels, 1-mm slices, 25-mm field of view). Without the use of contrast agents, metastases with diameters > or = 0.3 mm in the imaged plane could be detected as hyperintense lesions in kidney (contrast ratio ca. 1.4) and liver (contrast ratio ca. 2) with a confidence level of > 98%. For the first time the complete eradication of late-stage macroscopic metastases by ADI could be demonstrated noninvasively by MRI.

Skin layer effects on the diffusion of carbon tetrachloride into injection moulded polypropylene studied by 1H NMR microimaging

Skin layer effects on the diffusion of carbon tetrachloride into injection moulded polypropylene studied by 1H NMR microimaging

Measurements of the growth and distribution of mammalian cells in a hollow-fiber bioreactor using nuclear magnetic resonance imaging.

We have used diffusion-weighted 1H NMR micro-imaging and localized spectroscopy techniques to monitor the growth and distribution of mammalian cells in a hollow-fiber bioreactor. Non-invasive NMR measurements of this type should also allow investigation of metabolic heterogeneity and assist in future designs of hollow-fiber systems.

Histological and biochemical differences of slightly and severely injured spruce needles of two stands in northrhine westphalia

Histological structures and phenolic composition of first and second year needles of Norway spruce trees of a severely polluted stand of the Eggegebirge, and a healthy-to-slightly polluted stand of the Rothaargebirge are compared. Histological analysis of the spruce needles revealed quantitative differences between the two stands. Measurements of water content and mapping of water in living needles by 1H-NMR microimaging indicated an increased amount of water in the needles of the Eggegebirge stand, possibly due to: (1) a reduced evaporation rate caused by a degradation of tubular waxes and (2) an early formation of wax layers covering the needle surface. HPLC-measurements suggest differences in the composition of intermediates of the phenolic pathway. The highest amounts of phenolic compounds, e.g. picein and catechin, were found at the Eggegebirge stand.

1H-NMR Micro-Imaging and Correlated Sem Studies of Spruce Needles from Healthy and Declined Forest Sites

Abstract 1H-NMR micro-imaging is a technique for measuring mobile proton density and for obtaining cross-sectional pictures of quantitative distribution of water in living tissues. An application comparing healthy and damaged Norway spruce needles of a slightly polluted stand of the Sauerland area, Germany, and a severely polluted stand of the Eggegebirge, Germany, is presented. Damaged needles show a higher proton signal intensity and a different distribution of free water in the needle tissues compared with healthy needles. 1H-NMR microimaging and correlated SEM studies give rise to an integrated interpretation of symptoms caused by air pollution.