Stereoselective Recognition in Phospholipid Monolayers
During the past ten years we have investigated the stereochemistry of intermolecular interactions in monolayers at the air-water interface,1–3 a field which has never been developed explicitly before to our knowledge. Although we demonstrated clear enantiomeric and diastereomeric interactions for a number of chiral surfactants, we found no evidence whatsoever for stereoselective interaction in dipalmitoylphosphatidylcholine (DPPC) monolayers or vesicles by standard monolayer techniques, differential scanning calorimetry or ultra-highfield NMR.4 The present article extends these observations to dimyristoyl- and dilauroylphosphatidylcholine. Results from dynamic surface tension studies are also reported. In no case could chiral recognition be demonstrated using the 95% confidence limit as the criterion.
In our previous study of DPPC mixtures with another chiral surfactant the question arose as to whether chiral interactions could be transmitted through intervening phospholipid molecules.4 This question is addressed by examining the force-area curves for a variety of mixed monolayers composed of chiral surfactants and phospholipids. We conclude that the chiral discrimination observed in some of these mixed monolayers is due to the direct interaction of chiral centers, and not due to the transmission of chirality from one stereocenter to the next through intermediate achiral molecules.
Finally, we will consider the question of why phospholipids, the most ubiquitous of natural chiral surfactants, should show so little chiral discrimination in view of the wide occurrence of high stereoselectivity in many natural processes.
KeywordsRacemic Mixture Chiral Recognition Film Composition Molecular Area Dynamic Surface Tension
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- 2.E.M. Arnett, O. Thompson, Chiral Aggregation Phenomena. 2. Evidence for Partial “Two-Dimensional Resolution” in a Chiral Monolayer, J. Am. Chem. Soc. 103:908 (1981).Google Scholar
- 6.J. Minones, M.I. Sandez Macho, E. Iribarnegaray Jado, P. Sanz Pedro, Effect of Silicic Acid on Phospholipid Monolayers. Part I. Interaction with Synthetic Lecithins, Med. Segur. Trab. 27:40 (1979).Google Scholar
- 10.N.L. Gershfeld, Film Balance and the Evaluation of Intermolecular Energies in Monolayers, in: “Techniques of Surface and Colloid Chemistry and Physics”, R.J. Good, R.R. Stromberg, and R.L. Patrick, eds., Marcel Dekker, Inc., New York, (1972).Google Scholar
- 11.O. Thompson, Doctoral Dissertation, University of Pittsburgh, 1982.Google Scholar
- 13.R. Aneja, J.S. Chada, A Total Synthesis of Phosphatidylcholines, Biochem. Biophys. Acta 248:455 (1971).Google Scholar
- 14.E. Johnson, Doctoral Dissertation, Duke University, 1985.Google Scholar
- 16.G.L. Gaines, “Insoluble Monolayers at the Liquid-Gas Interface”, Interscience, New York (1966).Google Scholar
- 17.E.M. Arnett, E.A. Johnson, D. Mirajovsky and R. Verbiar, in preparation.Google Scholar
- 19.J.M. Gold, Doctoral Dissertation, Duke University (1982).Google Scholar
- 22.R. Defay, I. Pregogine, A. Bellemans and D. Everette, “Surface Tension and Adsorption”, Wiley, New York (1966) pp. 74–78.Google Scholar
- 23.D.J. Crisp, “Surface Chemistry,” Suppl. Research, London (1949) pp. 17, 23.Google Scholar
- 24.E.M. Arnett, N. Harvey and L.G. Whitesell, unpublished data.Google Scholar