439 research outputs found
Alien Registration- Mantle, Emeline F. (Limestone, Aroostook County)
https://digitalmaine.com/alien_docs/35237/thumbnail.jp
Contribution of Organ Vasculature in Rat Renal Analysis for Ochratoxin A: Relevance to Toxicology of Nephrotoxins
Assumptions surrounding the kidney as a target for accumulation of ochratoxin A (OTA) are addressed because the contribution of the toxin in blood seems invariably to have been ignored. Adult rats were maintained for several weeks on toxin-contaminated feed. Using standard perfusion techniques, animals were anaesthetised, a blood sample was taken, one kidney was ligated, and the other kidney perfused with physiological saline in situ under normal blood pressure. Comparative analysis of OTA in pairs of kidneys showed marked reduction in the perfused organ in the range 37%–98% (mean 75%), demonstrating the general efficiency of perfusion supported also by histology, and implying a major role of blood in the total OTA content of kidney. Translation of OTA values in plasma to whole blood, and its predicted contribution as a 25% vascular compartment in kidney gave values similar to those in non-perfused kidneys. Thus, apparent ‘accumulation’ of OTA in kidney is due to binding to plasma proteins and long half-life in plasma. Attention should be re-focused on whole animal pharmacokinetics during chronic OTA exposure. Similar principles may be applied to DNA-OTA adducts which are now recognised as occurring in blood; application could also extend to other nephrotoxins such as aristolochic acid. Thus, at least, quantitative reassessment in urological tissues seems necessary in attributing adducts specifically as markers of potentially-tumourigenic exposure
Effects of surface modifications on molecular diffusion in mesoporous catalytic materials
In this work, we use pulsed-field gradient (PFG) NMR to probe molecular diffusion of liquids inside
mesoporous structures and assess the influence of surface modifications, namely, deposition of
palladium (Pd) nanoparticles over alumina (Al2O3) surfaces and passivation of titania (TiO2) surfaces
with alkyl chains, on the diffusion pattern
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Spatially-resolved 1H NMR relaxation-exchange measurements in heterogeneous media.
In the last decades, the 1H NMR T2-T2 relaxation-exchange (REXSY) technique has become an essential tool for the molecular investigation of simple and complex fluids in heterogeneous porous solids and soft matter, where the mixing-time-evolution of cross-correlated T2-T2 peaks enables a quantitative study of diffusive exchange kinetics in multi-component systems. Here, we present a spatially-resolved implementation of the T2-T2 correlation technique, named z-T2-T2, based on one-dimensional spatial mapping along z using a rapid frequency-encode imaging scheme. Compared to other phase-encoding methods, the adopted MRI technique has two distinct advantages: (i) is has the same experimental duration of a standard (bulk) T2-T2 measurement, and (ii) it provides a high spatial resolution. The proposed z-T2-T2 method is first validated against bulk T2-T2 measurements on homogeneous phantom consisting of cyclohexane uniformly imbibed in finely-sized α-Al2O3 particles at a spatial resolution of 0.47 mm; thereafter, its performance is demonstrated, on a layered bed of multi-sized α-Al2O3 particles, for revealing spatially-dependent molecular exchange kinetics properties of intra- and inter-particle cyclohexane as a function of particle size. It is found that localised z-T2-T2 spectra provide well resolved cross peaks whilst such resolution is lost in standard bulk T2-T2 data. Future prospective applications of the method lie, in particular, in the local characterisation of mass transport phenomena in multi-component porous media, such as rock cores and heterogeneous catalysts
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In situ reaction monitoring in heterogeneous catalysts by a benchtop NMR spectrometer.
Understanding the reactivity and mass transport properties of porous heterogenous catalysts is important for the development of new materials. Whereas MRI has previously been used to correlate chemical kinetics and hydrodynamics under operando conditions, this paper demonstrates that a modern benchtop NMR spectrometer is a suitable alternative to obtain diverse reaction information in porous heterogeneous catalyst materials on a smaller scale. Besides information about the chemical conversion within the pores, it can also be used to study changes of surface interaction by T1/T2 NMR relaxometry techniques and changes in mass transport by PFG NMR from a single chemical reaction
Surface diffusion in catalysts probed by APGSTE NMR
In this work we report the application of a recently developed experimental protocol using Pulsed Field Gradient (PFG) Nuclear Magnetic Resonance (NMR) techniques to simultaneously assess bulk pore and surface diffusion coefficients in liquid saturated
porous catalysts. This method has been developed to study solvent effects on the diffusion of methyl ethyl ketone (MEK) in mesoporous 1 wt% Pd/Al2O3 catalyst trilobes. The selection of solvents used in this work is known to have a complex effect on reaction rates and hence catalyst performance in heterogeneous liquid phase catalysis. Here, we report the bulk pore and surface diffusion characteristics of MEK, water and isopropyl alcohol (IPA) in 1 wt% Pd/Al2O3 catalyst trilobes. The results show that the physicochemical interactions of molecules in the porous catalyst matrix are very different for the different molecules. We also find that the mobility of water appears to be affected strongest by the catalyst surface
Sub-sampling of NMR Correlation and Exchange Experiments
Sub-sampling is applied to simulated - NMR signals and its influence
on inversion performance is evaluated. For this different levels of
sub-sampling were employed ranging from the fully sampled signal down to only
less than two percent of the original data points. This was combined with
multiple sample schemes including fully random sampling, truncation and a
combination of both. To compare the performance of different inversion
algorithms, the so-generated sub-sampled signals were inverted using Tikhonov
regularization, modified total generalized variation (MTGV) regularization,
deep learning and a combination of deep learning and Tikhonov regularization.
Further, the influence of the chosen cost function on the relative inversion
performance was investigated. Overall, it could be shown that for a vast
majority of instances, deep learning clearly outperforms regularization based
inversion methods, if the signal is fully or close to fully sampled. However,
in the case of significantly sub-sampled signals regularization yields better
inversion performance than its deep learning counterpart with MTGV clearly
prevailing over Tikhonov. Additionally, fully random sampling could be
identified as the best overall sampling scheme independent of the inversion
method. Finally, it could also be shown that the choice of cost function does
vastly influence the relative rankings of the tested inversion algorithms
highlighting the importance of choosing the cost function accordingly to
experimental intentions
Mesoscopic structuring and dynamics of alcohol/water solutions probed by terahertz time-domain spectroscopy and pulsed field gradient nuclear magnetic resonance.
Terahertz and PFG-NMR techniques are used to explore transitions in the structuring of binary alcohol/water mixtures. Three critical alcohol mole fractions (x1, x2, x3) are identified: methanol (10, 30, 70 mol %), ethanol (7, 15, 60 mol %), 1-propanol (2, 10, 50 mol %), and 2-propanol (2, 10, 50 mol %). Above compositions of x1 no isolated alcohol molecules exist, and below x1 the formation of large hydration shells around the hydrophobic moieties of the alcohol is favored. The maximum number of water molecules, N0, in the hydration shell surrounding a single alcohol molecule increases with the length of the carbon chain of the alcohol. At x2 the greatest nonideality of the liquid structure exists with the formation of extended hydrogen bonded networks between alcohol and water molecules. The terahertz data show the maximum absorption relative to that predicted for an ideal mixture at that composition, while the PFG-NMR data exhibit a minimum in the alkyl chain self-diffusivity at x2, showing that the alcohol has reached a minimum in diffusion when this extended alcohol-water network has reached the highest degree of structuring. At x3 an equivalence of the alkyl and alcohol hydroxyl diffusion coefficients is determined by PFG-NMR, suggesting that the molecular mobility of the alcohol molecules becomes independent of that of the water molecules.This is the final published version. It's also available from the Journal of Physical Chemistry B here: http://pubs.acs.org/doi/abs/10.1021/jp502799x
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