H-1 NMR of compounds with low water solubility in the presence of erythrocytes: effects of emulsion phase separation

When lipophilic compounds like diethyl phthalate (DEP) were added to water, two sets of resonances appeared in the H-1 NMR spectrum, whereas when adde d in concentrations above similar to3.5 mM to erythrocytes in a high haemat ocrit suspension, only one set of resonances was observed at the low-freque ncy position. The appearance of one set of resonances at lower frequency wa s found to be common to a series of lipophilic compounds in erythrocytes. T he appearance of the NMR spectra is ascribed to the existence of an emulsio n, meaning two different phases of a compound: a "droplet" (resonances to l ower frequency) and aqueous dissolved phase (resonances to higher frequency ). The absence of the resonances from the dissolved phase in erythrocyte so lution is ascribed to exchange broadening. The absolute chemical shift of t he compound in its "droplet'' phase was also measured using a cylindrical/s pherical microcell. This arrangement mimicked the geometry of the dissolved versus the phase-separated species and thus obviated the effect of a diffe rence in magnetic susceptibility between the "droplet" solute and its aqueo us solution. Factors influencing the formation of emulsion phases such as e rythrocytes, haemoglobin and smaller proteins were investigated; they are f ound to be effective in the order given.