Abstract
Dipalmitoyl- and dihexanoylphosphatidylcholine have been synthesized using fatty acids which have the acyl carbonyl carbons enriched with carbon-13. The chemical shifts of these carbonyl carbons, which are known to be sensitive to intermolecular interactions, have been measured in a variety of solvents, including aqueous dispersions. The use of dihexanoylphosphatidylcholine permits the observation of molecules in both monomer and micelle forms in aqueous solutions. Carbon-13-proton two- and three-bond coupling constants have also been measured. From these data, it can be concluded that, when the molecules are in bilayers, the observed shifts are determined by hydrogen bonding of the carbonyl oxygens with the water, even though there is partial exclusion of water molecules from this region of the bilayer. The extent of water exclusion can be quantified and taken as a measure of molecular packing. The hydration difference between carbonyls of molecules on the the inside and outside of small single-walled vesicles is found to be 0.05. Furthermore, the relative shifts of the two carbonyl carbon-13's indicate that the fatty acid esterified to the 1-carbon of the glycerol is less accessible to water than that esterified to the 2-carbon of glycerol.
Original language | English |
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Pages (from-to) | 3948-3954 |
Number of pages | 7 |
Journal | Biochemistry |
Volume | 16 |
Issue number | 18 |
DOIs | |
State | Published - 1 Sep 1977 |
Externally published | Yes |