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J Pharm Sci. 1995 Oct;84(10):1180-3.

Partitioning of ionizing molecules between aqueous buffers and phospholipid vesicles.

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Department of Physical Chemistry, Astra Charnwood, Loughborough, Leicestershire, United Kingdom.


The distribution of four ionizing molecules between small unilamellar vesicles of dimyristoylphosphatidylcholine (DMPC) and aqueous buffers has been studied as a function of pH using an ultrafiltration method. The results show that pH-distribution behavior observed in the standard 1-octanol-water system does not always apply in model membrane systems, since the charged form of some molecules are able to partition into a phospholipid bilayer. It was further shown that the partitioning of these charged species into the bilayer is not as a consequence of ion pairing. The results clarify reports suggesting that protonated amines have a surprisingly high membrane affinity, and the implications of these findings for drug design are discussed.

[Indexed for MEDLINE]

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