Pavel V. Yushmanov

Sensitive and robust electrophoretic NMR: instrumentation and experiments.

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.

Solute-solvent contact by intermolecular cross relaxation. I. The nature of the water-hydrophobic interface.

Intermolecular cross-relaxation rates between solute and solvent were measured by {1H} 19F 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.

Molecular complexation and binding studied by electrophoretic NMR spectroscopy.

Electrophoretic mobilities obtained on a molecularly selective manner by electrophoretic NMR can be used to provide a quantitative characterization of the composition and stoichiometry of molecular complexes. This is demonstrated in complexes formed by uncharged cyclodextrins which attain an electrophoretic mobility upon inclusion of charged surfactants.

Assessing the potential of 2D electrophoretic mobility spectroscopy (2D MOSY) for analytical applications

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. Copyright

Assessing 2D electrophoretic mobility spectroscopy (2D MOSY) for analytical applications: 2D MOSY for analytical applications

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. Copyright

Assessing 2D electrophoretic mobility spectroscopy (2D MOSY) for analytical applications.

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. Copyright