Magnetic susceptibility: Solutions, emulsions, and cells

Abstract

Differences in magnetic susceptibility between various compartments in heterogeneous samples can introduce unanticipated complications to NMR spectra. On the other hand, an understanding of these effects at the level of the underlying physical principles has led to the development of several experimental techniques that provide data on cellular function that are unique to NMR spectroscopy. To illustrate some key features of susceptibility effects we present, among a more general overview, results obtained with red blood cells and a recently described model system involving diethyl phthalate in water. This substance forms a relatively stable emulsion in water and yet it has a significant solubility of ϳ5 mmol L Ϫ1 at room temperature; thus, the NMR spectrum has twice as many resonances as would be expected for a simple solution. What determines the relative intensities of the two families of peaks and can their frequencies be manipulated experimentally in a predictable way? The theory used to interpret the NMR spectra from the model system and cells was first developed in the context of electrostatics nearly a century ago, and yet some of its underlying assumptions now warrant closer scrutiny. While this insight is used in a practical way in this article, the accompanying article deals with the mathematics and physics behind this new analysis.

Diffusion NMR Spectroscopy in Supramolecular and Combinatorial Chemistry: An Old Parameter—New Insights

“…In addition, because of the non-invasiveness of the technique and the fact that the current technology is suitable for studying compartments of only a few microns in size, qspace diffusion MR was recently used to study biological systems. [23][24][25] Very recently, we expanded this approach to qspace MRI of the CNS. [26,27] Callaghan and others have used diffusion NMR spectroscopy and MRI to study complex fluids.…”

Further conventions for NMR shielding and chemical shifts (IUPAC Recommendations 2008)

“…In addition, various NMR methods have been proposed for measuring magnetic susceptibility, some depending on the use of the geometry of an iron-core magnet in which the sample tube axis is at 90°to the magnetic field axis [18,19]. Others employ a spherical sample holder inside a cylindrical sample tube [19,20] or rely on gross distortion of line-shape when the bottom of the sample tube is close to the receiver coil [16]. (14,16,18, and 20 mm) below the receiver-coil center.…”

Magnetic properties of materials for MR engineering, micro-MR and beyond

“…The value for ethylene glycol in [2] is probably not correct. In [35], the authors calculated a value of -8.77 ppm (without an error figure) from the molar susceptibility value in [8] [9] and their difference (central two columns) and to the results of [2]. The reader should keep in mind the uncertainty of typically ±0.25ppm in the central columns, the uncertainty in the right column is unknown.…”