ISSN:
0947-3440
Keywords:
Cyclic phosphate amphiphiles
;
Micellization
;
Vesicle fusion
;
Bilayer packing
;
Vesicles
;
Amphiphiles
;
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Herein we describe the synthesis and aggregation of the sodium salts of a series of 5-alkyl-2-hydroxy-1,3,2-dioxaphosphorinan-2-ones and 5,5-dialkyl-2-hydroxy-1,3,2-dioxaphosphorinan-2-ones in aqueous solution. The results are compared with properties of previously studied sodium di-n-alkyl phosphates. The single-tailed surfactants (6a, b, g) form micelles whereas the double-tailed ones (6f, h-k) form vesicles, as revealed by transmission electron microscopy (TEM). Critical micelle concentrations (CMC) for 6a, b, g were determined using different techniques: UV spectroscopy, microcalorimetry, and conductometry. Phase transition temperatures of the bilayers were measured by differential scanning calorimetry (DSC) and by fluorescence depolarization. Fusion of the vesicles was studied employing the resonance energy transfer (RET) assay based on lipid mixing and TEM. Vesicles of 6h-k fuse upon addition of Ca2+ or Mg2+ ions, to almost the same extent in each case. Fusion only takes place above the phase transition temperature (Tc) of the different bilayers. The threshold concentrations of Ca2+ and Mg2+ ions for fusion of the different vesicles are below 0.1 mM. The initial rate of fusion is high and precludes the measurement of accurate rate constants. Upon addition of calcium chloride different processes occur. Vesicle fusion, crystallization, and formation of multilamellar sheets were observed, as was apparent from experiments with vesicles formed from 6h. Leakage through the vesicular bilayer of 6h was determined by measuring the carboxyfluorescein release from the aqueous compartment of the vesicles. All data are consistent with the notion that the alkyl chain packing in the bilayers of the vesicles formed from the cyclic phosphates is less efficient than that in the bilayers of vesicles composed of di-n-alkyl phosphates.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jlac.199719970817
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