Organotin compounds alter the physical organization of phosphatidylcholinemembranes

Organotin compounds have a broad range of biological activities and are ubi quitous contaminants in the environment. Their toxicity mainly lies in thei r action on the membrane. In this contribution we study the interaction of tributyltin and triphenyltin with model membranes composed of phosphatidylc holines of different acyl chain lengths using differential scanning calorim etry, P-31-nuclear magnetic resonance, X-ray diffraction and infrared spect roscopy. Organotin compounds broaden the main gel to liquid-crystalline pha se transition, shift the transition temperature to lower values and induce the appearance of a new peak below the main transition peak. These effects are more pronounced in the case of tributyltin and are quantitatively large r as the phosphatidylcholine acyl chain length decreases. Both tributyltin and triphenyltin increase the enthalpy change of the transition in all the phosphatidylcholine systems studied except in dilauroylphosphatidylcholine. Organotin compounds do not affect the macroscopic bilayer organization of the phospholipid but do affect the degree of hydration of its carbonyl moie ty. The above evidence supports the idea that organotin compounds are locat ed in the upper part of the phospholipid palisade near the lipid/water inte rface. (C) 2001 Elsevier Science B.V. All rights reserved.