| 1. |
- 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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| 2. |
- Hallberg, Fredrik, et al.
(författare)
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Molecular complexation and binding studied by electrophoretic NMR spectroscopy
- 2008
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 130:24, s. 7550-
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Tidskriftsartikel (refereegranskat)abstract
- Electrophoretic mobilities obtained on a molecularly selective manner by electrophoretic NMR can be used to proved a quantitative characterization of the composition and stoichiometry of molecular complexes. This is demonstrated in complexes formed by uncharge cyclodextrins which attain an electrophoretic mobility upon inclusion of charged surfactants.
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| 3. |
- Hallberg, Fredrik, et al.
(författare)
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Sensitive and robust electrophoretic NMR : Instrumentation and experiments
- 2008
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Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 192:1, s. 69-77
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Tidskriftsartikel (refereegranskat)abstract
- Although simple as a concept, electrophoretic NMR (eNMR) has so far failed to find wider application. Problems encountered are mainly due to disturbing and partly irreproducible convection-like bulk flow effects from both electro-osmosis and thermal convection. Additionally, bubble formation at the electrodes and rf noise pickup has constrained the typical sample geometry to U-tube-like arrangements with a small filling factor and a low resulting NMR sensitivity. Furthermore, the sign of the electrophoretic mobility cancels out in U-tube geometries. We present here a new electrophoretic sample cell based on a vertically placed conventional NMR sample tube with bubble-suppressing palladium metal as electrode material. A suitable radiofrequency filter design prevents noise pickup by the NMR sample coil from the high-voltage leads which extend into the sensitive sample volume. Hence, the obtained signal-to-noise ratio of this cell is one order of magnitude higher than that of our previous U-tube cells. Permitted by the retention of the sign of the displacement-related signal phase in the new cell design, an experimental approach is described where bulk flow effects by electro-osmosis and/or thermal convection are compensated through parallel monitoring of a reference signal from a non-charged species in the sample. This approach, together with a CPMG-like pulse train scheme provides a superior first-order cancellation of non-electrophoretic bulk flow effects.
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| 4. |
- Nordstierna, Lars, et al.
(författare)
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Solute-Solvent Contact by Intermolecular Cross Relaxation : II. The Water-Micelle Interface and the Micellar Interior
- 2006
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 110:51, s. 25775-25781
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Tidskriftsartikel (refereegranskat)abstract
- The intermolecular dipole-dipole cross-relaxation is measured between F-19 nuclei of sodium perfluorooctanoate in micelles and H-1 nuclei of the water solvent. The cross-relaxation rates for fluorines in the different moieties along the surfactant vary strongly by the resonance frequency in the investigated range of 188-470 MHz. This frequency dependence indicates that the cross-relaxation between water and amphiphilic aggregates is not controlled solely by the fast local water dynamics but significantly contributed to by the long-range translational diffusion of water. The cross-relaxation rates, analyzed in the framework of a model (Nordstierna, L.; Yushmanov, P. V.; Furo, I. J. Chem. Phys. 2006, 125, 074704), provide information about the dynamic retardation of water molecules by the micellar headgroup region and the location of the various moieties along the hydrophobic tail with respect to the water-micelle interface. Both intermolecular cross-relaxation and aggregation-induced F-19 chemical shift changes indicate no direct water contact to fluorines except for those closest to the head group.
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| 5. |
- Nordstierna, Lars, et al.
(författare)
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Solute-Solvent Contact by Intermolecular Cross Relaxation : I. The Nature of the Water-Hydrophobic Interface
- 2006
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 125:7, s. 074704-
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Tidskriftsartikel (refereegranskat)abstract
- Intermolecular cross-relaxation rates between solute and solvent were measured by {H-1} F-19 nuclear magnetic resonance experiments in aqueous molecular solutions of ammonium perfluoro-octanoate and sodium trifluoroacetate. The experiments performed at three different magnetic fields provide frequency-dependent cross-relaxation rates which demonstrate clearly the lack of extreme narrowing for nuclear spin relaxation by diffusionally modulated intermolecular interactions. Supplemented by suitable intramolecular cross-relaxation, longitudinal relaxation, and self-diffusion data, the obtained cross-relaxation rates are evaluated within the framework of recent relaxation models and provide information about the hydrophobic hydration. In particular, water dynamics around the trifluoromethyl group in ammonium perfluoro-octanoate are more retarded than that in the smaller trifluoroacetate
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| 6. |
- Yushmanov, Pavel V., et al.
(författare)
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A rapid-mixing design for conventional NMR probes
- 2005
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Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 175:2, s. 264-270
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Tidskriftsartikel (refereegranskat)abstract
- A simple stopped-flow design for rapid mixing of two liquids within the NMR probe is presented. The device uses no switches or relays but exploits instead the torque exerted by the magnetic field on a current-leading-coil to open and close the start and stop valves. Two serially arranged tangential jet mixer blocks provide a homogeneous mixture with, depending on conditions and requirements, a filling time in the 50-100 ms range and a subsequent stabilization time in the range of 10-40 ms as tested by mixing various combinations of liquids and observing their 1H NMR spectrum. Factors influencing the mixing process are analyzed.
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| 7. |
- Yushmanov, Pavel V.
(författare)
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NMR Studies of Colloidal Systems in and out of Equilibrium
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Thesis describes (i) the development of add-on instrumentation extending the capabilities of conventional NMR spectrometers and (ii) the application of the designed equipments and techniques for investigating various colloidal systems. The new equipments are: Novel designs of stopped-flow and temperature–jump inserts intended for conventional Bruker wide-bore superconductive magnets. Both inserts are loaded directly from above into the probe space and can be used together with any 10 mm NMR probe with no need for any auxiliary instruments. A set of 5 mm and 10 mm 1H – 19F – 2H NMR probes designed for heteronuclear 1H – 19F cross-relaxation experiments in Bruker DMX 200, AMX 300 and DMX 500 spectrometers, respectively. A two–stage low-pass filter intended for suppressing RF noise in electrophoretic NMR experiments. The kinetics of micellar dissolution and transformation in aqueous solutions of sodium perfluorooctanoate (NaPFO) is investigated using the stopped-flow NMR instrument. The sensitivity of NMR as detection tool for kinetic processes in micellar solutions is clarified and possible artefacts are analysed. In the NaPFO system, the micellar dissolution is found to proceed faster than 100 ms while surfactant precipitation occurs on the time scale of seconds-to-minutes. The kinetics of the coil-to–globule transition and intermolecular aggregation in a poly (Nisopropylacrylamide) solution are investigated by the temperature-jump NMR instrument. As revealed by the time evolution of the 1H spectrum, the T2 relaxation time and the self-diffusion coefficient D, large (>10 nm) and compact aggregates form in less than 1 second upon fast temperature increase and dissolve in less than 3 seconds upon fast temperature decrease. The intermolecular 1H – 19F dipole-dipole cross-relaxation between the solvent and solute molecules, whose fast rotational diffusion is in the extreme narrowing limit, is investigated. The solutes are perfluorooctanoate ions either in monomeric or in micellar form and trifluoroacetic acid and the solvent is water. The obtained cross-relaxation rates are frequency-dependent which clearly proves that there is no extreme narrowing regime for intermolecular dipole-dipole relaxation. The data provide strong constraints for the dynamic retardation of solvent by the solute.
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| 8. |
- Yushmanov, Pavel V., et al.
(författare)
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Stopped-flow F-19 NMR studies of surfactant precipitation
- 2006
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Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 291:1-3, s. 59-62
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Tidskriftsartikel (refereegranskat)abstract
- The kinetics of the phase change in surfactant solutions is studied by F-19 stopped-flow NMR. In the aqueous solution of sodium perfluooctanoate, we observe precipitation and crystal growth induced by the addition of NaCl solution to the system. The time dependences of the NMR signal intensity and chemical shift, evaluated in the framework of a single model, narrow the range of possible scenarios, the most plausible of which is monomer incorporation into the growing crystals. In accordance to existing models of crystallization, both the nucleation rates and the crystal growth rates are strongly dependent on the magnitude of supersaturation.
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