| 1. |
- Banyai, Istvan, et al.
(författare)
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Simple O-17 NMR method for studying electron self-exchange reaction between UO22+ and U4+ aqua ions in acidic solution
- 2016
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Ingår i: Magnetic Resonance in Chemistry. - : WILEY-BLACKWELL. - 0749-1581 .- 1097-458X. ; 54:6, s. 444-450
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Tidskriftsartikel (refereegranskat)abstract
- O-17 NMR spectroscopy is proven to be suitable and convenient method for studying the electron exchange by following the decrease of O-17-enrichment in (UOO2+)-O-17 ion in the presence of U4+ ion in aqueous solution. The reactions have been performed at room temperature using I=5MClO(4)(-) ionic medium in acidic solutions in order to determine the kinetics of electron exchange between the U4+ and UO22+ aqua ions. The rate equation is given as R = a[H+](-2) + R, where R is an acid independent parallel path. R depends on the concentration of the uranium species according to the following empirical rate equation: R = k(1)[UO2+](1/2)[U4+](1/2) + k(2)[UO2+](3/2)[U4+](1/2). The mechanism of the inverse H+ concentration-dependent path is interpreted as equilibrium formation of reactive UO2+ species from UO22+ and U4+ aqua ions and its electron exchange with UO22+. The determined rate constant of this reaction path is in agreement with the rate constant of UO22+-UO2+, one electron exchange step calculated by Marcus theory, match the range given experimentally of it in an early study. Our value lies in the same order of magnitude as the recently calculated ones by quantum chemical methods. The acid independent part is attributed to the formation of less hydrolyzed U(V) species, i.e. UO3+, which loses enrichment mainly by electron exchange with UO22+ ions. One can also conclude that O-17 NMR spectroscopy, or in general NMR spectroscopy with careful kinetic analysis, is a powerful tool for studying isotope exchange reactions without the use of sophisticated separation processes. Copyright (C) 2015 John Wiley amp; Sons, Ltd.
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| 2. |
- Elwinger, Fredrik, et al.
(författare)
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C-13 SPE MAS measurement of ligand concentration in compressible chromatographic beads
- 2015
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 53:8, s. 572-577
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Tidskriftsartikel (refereegranskat)abstract
- A method for measuring the ligand concentration in heterogeneous materials like chromatography media is described. In this method, C-13 single pulse excitation magic angle spinning NMR experiment with broadband H-1 decoupling is used to determine the peak integrals for a butyl ligand in the spectrum of a dried chromatography medium. Within a carefully controlled protocol, those integrals compared with that of the internal reference compound dimethyl sulfone provide the required volume concentration with an accuracy of ca 2%. The effects of temperature, degree of hydration, and other experimental parameters are discussed. Copyright (C) 2015 The Authors. Magnetic Resonance in Chemistry published by John Wiley & Sons Ltd.
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| 3. |
- Elwinger, Fredrik, et al.
(författare)
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High-resolution magic angle spinning H-1 NMR measurement of ligand concentration in solvent-saturated chromatographic beads
- 2016
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley-Blackwell. - 0749-1581 .- 1097-458X. ; 54:4, s. 291-297
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Tidskriftsartikel (refereegranskat)abstract
- A method based on H-1 high-resolution magic angle spinning NMR has been developed for measuring concentration accurately in heterogeneous materials like that of ligands in chromatography media. Ligand concentration is obtained by relating the peak integrals for a butyl ligand in the spectrum of a water-saturated chromatography medium to the integral of the added internal reference. The method is fast, with capacity of 10min total sample preparation and analysis time per sample; precise, with a reproducibility expressed as 1.7% relative standard deviation; and accurate, as indicated by the excellent agreement of derived concentration with that obtained previously by C-13 single-pulse excitation MAS NMR. The effects of radiofrequency field inhomogeneity, spin rate, temperature increase due to spinning, and distribution and re-distribution of medium and reference solvent both inside the rotor during spinning and between bulk solvent and pore space are discussed in detail.
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| 4. |
- Fang, Yuan, et al.
(författare)
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Assessing the potential of 2D electrophoretic mobility spectroscopy (2D MOSY) for analytical applications
- 2017
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Ingår i: Magnetic Resonance in Chemistry. - : John Wiley & Sons. - 0749-1581 .- 1097-458X. ; 55:6, s. 584-588
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Tidskriftsartikel (refereegranskat)abstract
- Electrophoretic displacement of charged entity phase modulates the spectrum acquired in electrophoretic NMR experiments, and this modulation can be presented via 2D FT as 2D mobility spectroscopy (MOSY) spectra. We compare in various mixed solutions the chemical selectivity provided by 2D MOSY spectra with that provided by 2D diffusion-ordered spectroscopy (DOSY) spectra and demonstrate, under the conditions explored, a superior performance of the former method. 2D MOSY compares also favourably with closely related LC-NMR methods. The shape of 2D MOSY spectra in complex mixtures is strongly modulated by the pH of the sample, a feature that has potential for areas such as in drug discovery and metabolomics.
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| 5. |
- Filippov, Andrei, et al.
(författare)
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Dynamic Properties of Imidazolium Orthoborate Ionic Liquids Mixed with Polyethylene Glycol Studied by NMR Diffusometry and Impedance Spectroscopy
- 2018
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Ingår i: Magnetic Resonance in Chemistry. - : John Wiley & Sons. - 0749-1581 .- 1097-458X. ; 56:2, s. 113-119
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Tidskriftsartikel (refereegranskat)abstract
- We used 1H pulsed field gradient (PFG) NMR to study the self-diffusion of polyethylene glycol (PEG) with average molecular mass of 200 and ions in mixtures of PEG with imidazolium bis(mandelato)borate (BMB) and imidazolium bis(oxalato)borate (BOB) ionic liquids (ILs). The ionic liquid was mixed with PEG in the concentration range of 0–100 wt%. Within the temperature range of 295 to 353 K, the diffusion coefficient of BMB is slower than that of the imidazolium cation. The diffusion coefficients of PEG, as well as the imidazolium cation and BMB anions, differ under all experimental conditions tested. This demonstrates that the IL in the mixture is present in at least a partially dissociated state. Generally, increasing the concentration of PEG leads to an increase in the diffusion coefficients of PEG and both the ions, and decreases their activation energy for diffusion. NMR chemical shift alteration analysis showed that the presence of PEG changes the chemical shifts of both ions but in different directions. Impedance spectroscopy was used to measure the ionic conductivity of the ionic liquids mixed with PEG.
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| 6. |
- Filippov, Andrei, et al.
(författare)
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Self-diffusion and interactions in mixtures of imidazolium bis(mandelato)borate ionic liquids with polyethylene glycol : H-1 NMR study
- 2015
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 53:7, s. 493-497
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Tidskriftsartikel (refereegranskat)abstract
- We used H-1 nuclear magnetic resonance pulsed-field gradient to study the self-diffusion of polyethylene glycol (PEG) and ions in a mixture of PEG and imidazolium bis(mandelato)borate ionic liquids (ILs) at IL concentrations from 0 to 10 wt% and temperatures from 295 to 370 K. PEG behaves as a solvent for these ILs, allowing observation of separate lines in H-1 NMR spectra assigned to the cation and anion as well as to PEG. The diffusion coefficients of PEG, as well as the imidazolium cation and bis(mandelato) borate (BMB) anion, differ under all experimental conditions tested. This demonstrates that the IL in the mixture is present in at least a partially dissociated state, while the lifetimes of the associated states of the ions and ions with PEG are less than similar to 30ms. Generally, increasing the concentration of the IL leads to a decrease in the diffusion coefficients of PEG and both ions. The diffusion coefficient of the anion is less than that of the cation; the molecular mass dependence of diffusion of ions can be described by the Stokes-Einstein model. NMR chemical shift alteration analysis showed that the presence of PEG changes mainly the chemical shifts of protons belonging to imidazole ring of the cation, while chemical shifts of protons of anions and PEG remain unchanged. This demonstrated that the imidazolium cation interacts mainly with PEG, which most probably occurs through the oxygen of PEG and the imidazole ring. The BMB anion does not strongly interact with PEG, but it may be indirectly affected by PEG through interaction with the cation, which directly interacts with PEG. Copyright (C) 2015 John Wiley & Sons, Ltd.
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| 7. |
- Galvosas, P., et al.
(författare)
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Rheo-NMR in food science - Recent opportunities
- 2019
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 57:9, s. 757-765
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Tidskriftsartikel (refereegranskat)abstract
- For over 25years, nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) techniques have been used to study materials under mechanical deformation. Collectively, these methods are referred to as Rheo-NMR. In many cases, it provides spatially and temporally resolved maps of NMR spectra, intrinsic NMR parameters (such as relaxation times), or motion (such as diffusion or flow). Therefore, Rheo-NMR is complementary to conventional rheological measurements. This review will briefly summarize current capabilities and limitations of Rheo-NMR in the context of material science and food science in particular. It will report on recent advances such as the incorporation of torque sensors or the implementation of large amplitude oscillatory shear and point out future opportunities for Rheo-NMR in food science. © 2019 John Wiley & Sons, Ltd.
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| 8. |
- Kazimierczuk, Krzysztof, et al.
(författare)
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Non-uniform sampling: Post-Fourier era of NMR data collection and processing
- 2015
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 53:11, s. 921-926
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Tidskriftsartikel (refereegranskat)abstract
- The invention of multidimensional techniques in the 1970s revolutionized NMR, making it the general tool of structural analysis of molecules and materials. In the most straightforward approach, the signal sampling in the indirect dimensions of a multidimensional experiment is performed in the same manner as in the direct dimension, i.e. with a grid of equally spaced points. This results in lengthy experiments with a resolution often far from optimum. To circumvent this problem, numerous sparse-sampling techniques have been developed in the last three decades, including two traditionally distinct approaches: the radial sampling and non-uniform sampling. This mini review discusses the sparse signal sampling and reconstruction techniques from the point of view of an underdetermined linear algebra problem that arises when a full, equally spaced set of sampled points is replaced with sparse sampling. Additional assumptions that are introduced to solve the problem, as well as the shape of the undersampled Fourier transform operator (visualized as so-called point spread function), are shown to be the main differences between various sparse-sampling methods. Copyright © 2015 John Wiley & Sons, Ltd.
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| 9. |
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| 10. |
- Liebau, Jobst, et al.
(författare)
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Characterization of fast-tumbling isotropic bicelles by PFG diffusion NMR
- 2017
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 55:5, s. 395-404
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Forskningsöversikt (refereegranskat)abstract
- Small isotropic bicelles are versatile membrane mimetics, which, in contrast tomicelles, provide a lipid bilayer and are at the same time suitable for solution-state NMR studies. The lipid composition of the bilayer is flexible allowing for incorporation of various head groups and acyl chain types. In bicelles, lipids are solubilized by detergents, which are localized in the rimof the disk-shaped lipid bilayer. Bicelles have been characterized by a broad array of biophysical methods, pulsed-field gradient NMR (PFG NMR) being one of them. PFG NMR can readily be used to measure diffusion coefficients of macromolecules. It is thus employed to characterize bicelle size and morphology. Even more importantly, PFG NMR can be used to study the degree of protein association to membranes. Here, we present the advances that have been made in producing small, fast-tumbling isotropic bicelles from a variety of lipids and detergents, together with insights on the morphology of such mixtures gained from PFG NMR. Furthermore, we review approaches to study protein-membrane interaction by PFG NMR.
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