[Distribution of tributyltin between water and liposome]

Distribution of the tributyltin (TBT) between egg-phosphatidylcholine membranes (liposome) and water under different pH and a comparison between the partition of TBT into lipid membranes and into octanol were studied. The distribution of this compound into both lipid membranes and octanol increased with pH. The major difference was that at lower pH, where ionized TBT dominated distribution was greater into lipid membranes compared to that of octanol. At high pH, where TBT predominates as neutral species, the distribution ratios were very similar in the octanol and the liposome-water system. These differences can be attributed to the properties of the biomembrane. The results indicated that the liposome-water partition model appears to be a better molecular descriptor for ionogenic organic compounds.