Gastric emptying and gastrointestinal (GI) transit times in mice and humans were monitored noninvasively by using 27 Al and 19 F nuclear magnetic resonance (NMR). Al 3؉ bound to ion-exchange resin and perfluorononane were administered orally as selective and specific markers for the stomach and the entire GI tract, respectively.27 Al-and 19 F-MR spectroscopy (MRS) was employed to follow quantitatively boli of the mixed markers in awake, fed mice over a period of 48 hr. The selectivity of the markers was confirmed by whole-body 1 H-, 27 Al-, and 19 F-MRI of anesthetized mice. Gastric emptying in humans was also monitored with 27 Al-MRS of aluminum-loaded ion exchange resin. GI transit was assessed by 19 F projection imaging of pharmaceutical capsules tagged with perfluorononane. Quantitative analysis of the MR data revealed that gastric emptying in humans proceeded linearly, whereas in mice an exponential decay was observed. This difference is explained by the respective feeding patterns of humans and mice. Humans usually achieve nearly complete gastric emptying before each meal. In contrast, very short delays between successive food intakes in small animals result in successive dilution of the stomach contents. For stomach emptying in mice the exponential decay constant was 74 min, whereas the half-time of the linear gastric emptying in humans was 30 min.Magn Reson Med 48: 255-261, 2002.

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Liquid perfluorocarbons exhibit unique physical-chemical characteristics such as extraordinary stability, combined hydrophobia and lipophobia, low surface tension and a capacity to carry large quantities of gas. They have found widespread use in industry, medicine and biology even though the molecular origin of these properties is not fully understood. The objective of the present work was to elucidate the physical behavior of perfluorinated linear alkanes by investigating their intramolecular electronic environment using 13C and 19F NMR techniques in combination with theoretical calculations of molecular orbitals. Particular advantage was taken of 19F-19F through-space couplings, which led us to propose a molecular model in which delocalized p-electrons of the fluorines cover the entire surface of the molecule in two pairs of intertwined helices. Experimental data are presented for n-perfluorononane and supported by corresponding measurements with shorter and longer perfluorinated alkanes.

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