Molecular Associations in Lipid-carotenoid Monolayers
The properties of monomolecular films composed of binary mixtures of membrane components can provide useful information relevant to the interaction between molecules. We have used this system to examine interactions between 1, 2-distearoyldigalactosylglycerol (DGDG) and 1, 2-distearoylphosphatidylcholine (DSPC) and astaxanthin (AX; all-trans-3, 3′-dihydroxy-4, 4′-dioxo-β-carotene) and found that the collapse pressure of the mixed monolayers was greater than would be predicted on the basis of perfect behaviour of the mixture (Tomoaia-Cotişel et al., 1984). The increased stability of mixed monolayers of DGDG and AX could be explained on the basis of regular behaviour of the components allowing the derivation of an apparent interaction parameter, ξM, representing the attraction between molecules of DGDG and AX in the film. The numerical value of this parameter was -0.87, however, the standard deviation of the experimental data from the theoretical curve is rather high, viz. Δ= 1.106 m N. m-1 In the case of DSPC: AX monolayers the regular solution approximation does not fit at all. We have therefore undertaken an examination of the collapse pressure vs composition curves of AX with DGDG and DSPC to determine whether they conform to behaviour according to inter molecular associations.
KeywordsFatty Acid Ester Molecular Association Mixed Monolayer Molecular Area Regular Solution Approxim Ation
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