Shape Transformations in the Lecithin-Bile Salt System: From Cylinders to Vesicles

Egelhaaf, Stefan U.; Schurtenberger, Peter

doi:10.1021/j100085a041

Cited by 138 publications

(184 citation statements)

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“…[34][35][36][37][38] While lecithin alone tends to form vesicles in water, the addition of bile salt transforms these vesicles into cylindrical micelles. 37,38 Such a transition implies a reduction in packing parameter from ca. 1 to ca.…”

Section: Discussionmentioning

confidence: 99%

A New Reverse Wormlike Micellar System: Mixtures of Bile Salt and Lecithin in Organic Liquids

2006

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Abstract:We report a new route for forming reverse wormlike micelles (i.e., long, flexible micellar chains) in nonpolar organic liquids such as cyclohexane and n-decane. This route involves the addition of a bile salt (e.g., sodium deoxycholate) in trace amounts to solutions of the phospholipid lecithin. Previous recipes for reverse wormlike micelles have usually required the addition of water to induce reverse micellar growth; here, we show that bile salts, due to their unique "facially amphiphilic" structure, can play a role analogous to that of water and promote the longitudinal aggregation of lecithin molecules into reverse micellar chains. The formation of transient entangled networks of these reverse micelles transforms low-viscosity lecithin organosols into strongly viscoelastic fluids. The zero-shear viscosity increases by more than 5 orders of magnitude, and it is the molar ratio of bile salt to lecithin that controls the viscosity enhancement. The growth of reverse wormlike micelles is also confirmed by small-angle neutron scattering (SANS) experiments on these fluids.

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Section: Discussionmentioning

confidence: 99%

A New Reverse Wormlike Micellar System: Mixtures of Bile Salt and Lecithin in Organic Liquids

2006

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“…We now illustrate the results using the full form of eq A26, not in the flexible coil limit, for two choices of p /d: (1) p /d ) 4, which corresponds to a value of p near the value 17 nm that we estimated above, and (2) (14) and Pederson et al (76) on bile salt-PC micellar systems. For these comparisons, we also chose ψ ) ψ* corresponding to a good solvent regime (41)(42)(43).…”

Section: B) Examination Of the First-order Effect Of Intermicellar Inmentioning

confidence: 90%

“…Mazer et al (7) found that the mixed disk model predicted the mixed micellar growth observed in model bile systems by QLS when this was achieved either by dilution or by varying the EYPC/ bile salt ratio at constant concentration. However, more recent studies employing small-angle neutron scattering (10,11), high-performance liquid chromatography (12), cryotransmission electron microscopy (13), and light scattering (14) have questioned growth of bile salt-PC mixed micelles via the mixed disk model and have shown that they may form locally cylindrical rodlike particles. In addition, octyl glucoside-PC mixed micelles appear to grow with similar morphology (3) despite the strikingly different molecular structures of octyl glucoside and common bile salts (15).…”

mentioning

confidence: 99%

Laser Light Scattering Evidence for a Common Wormlike Growth Structure of Mixed Micelles in Bile Salt− and Straight-Chain Detergent−Phosphatidylcholine Aqueous Systems: Relevance to the Micellar Structure of Bile

et al. 1998

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We employed quasielastic and static light scattering to measure apparent values of the mean hydrodynamic radii (R h ) app , molecular weights (M app ), and radii of gyration (R g ) app in solutions containing mixed micelles composed of bile salts (cholate and taurochenodeoxycholate, both cholanoyl derivatives) and the glycoacyl chain detergent, octyl glucoside, with egg yolk phosphatidylcholine (EYPC) as functions of total lipid concentration (0.1-10 g/dL), EYPC/detergent molar ratio (0-1.2), and ionic strength (0.15-0.4 M NaCl) at 20°C and 1 atm. As the mixed micellar phase boundaries were approached by dilution, (R h ) app , M app , and (R g ) app values increased markedly by up to 20-fold. For each micellar system, the scaling ratios (R h ) app /M app 1/2 and (R g ) app /(R h ) app remained essentially constant at 0.018 nm/(g/mol) 1/2 and 1.5 (dimensionless), respectively, despite large variations in total lipid concentration, detergent molecular species, and ionic strength. Refined data analysis is inconsistent with a flat "mixed-disc" model for bile salt-EYPC micelles [Mazer, N. A., Benedek, G. B., and Carey, M. C. (1980) Biochemistry 19, 601] and octyl glucoside-EYPC micelles principally because the numerical value of (R h ) app /M app 1/2 corresponds to a hypothetical disk thickness of ∼1 nm, which is 4-fold smaller than the bimolecular width of EYPC molecules, and for a disk, (R g ) app /(R h ) app ratios should be close to 1 at low total lipid concentrations. Assuming disc-shaped micelles, we show that intermicellar excluded volume interactions would have only a minor effect on M app and cannot account for the unrealistic disk thickness. Instead, locally cylindrical, semiflexible wormlike micelles of diameter d ) 4 nm and persistence length p ) 17 nm in solution are compatible with the observed (R h ) app /M app 1/2 and (R g ) app /(R h ) app values when intermicellar excluded-volume interactions are considered. With EYPC/taurochenodeoxycholate ) 0.6 and EYPC/cholate ) 1.0 in 0.15 M NaCl, independent micelles grow upon dilution and use of the second virial coefficient [Egelhaaf, S. U., and Schurtenberger, P. (1994) J. Phys. Chem. 98, 8560] is adequate for estimating micellar weights. The systems EYPC/cholate ) 1.0 in 0.4 M NaCl, EYPC/cholate ) 1.2 in 0.15 M NaCl, and EYPC/octyl glucoside ) 0.13 in 0.15 M NaCl all form highly overlapping, semidilute polymer solutions, which mimic the observed scaling ratios. In such semidilute systems, use of the second virial coefficient alone to account for intermicellar interactions is inadequate for estimating micellar weights. The results of the present study, in combination with locations of known phase boundaries of the ternary bile salt-EYPCwater phase diagram at high dilution, suggest that elongation, as well as entanglement of wormlike mixed micelles may occur at concentrations approaching the micellar phase limit.Aqueous mixed micellar solutions of steroidal or straightchain detergents with long-chain phosphatidylcholine (PC) 1 are of considerable s...

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“…44 They were also believed to be intermediate structures in lecithin-bile salt systems, 45 but recent studies clearly indicate cylindrical polymerlike micelles to be present instead. 46 Formation of disklike micelles as an intermediate geometry in micelle-to-vesicle transitions thus seems to be relatively uncommon. The change in aggregate geometry during the solubilization of phospholipid bilayers by surfactants has been recently theoretically mod- eled.…”

Section: And M+v -mentioning

confidence: 99%

Vesicle Formation and General Phase Behavior in the Catanionic Mixture SDS−DDAB−Water. The Anionic-Rich Side

et al. 1998

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Catanionic mixtures are aqueous mixtures of oppositely charged surfactants which display novel phase behavior and interfacial properties in comparison with those of the individual surfactants. One phase behavior property is the ability of these systems to spontaneously form stable vesicles at high dilution. The phase behavior of the mixture sodium dodecyl sulfate (SDS) -didodecyldimethylammonium bromide (DDAB) in water has been studied in detail, and two regions of isotropic vesicular phases (anionic-rich and cationic-rich) were identified. Cryo-transmission electron microscopy allowed direct visualization of relatively small and polydisperse unilamellar vesicles on the SDS-rich side. Monitoring of the microstructure evolution from mixed micelles to vesicles as the surfactant mixing ratio is varied toward equimolarity was also obtained. Further information was provided by water self-diffusion measurements by pulsed field gradient spin-echo NMR. Water molecules can be in fast or slow exchange between the inside and outside of the vesicle with respect to the experimental time scale, depending on membrane permeability and vesicle size. For the SDSrich vesicles, a slow-diffusing component of very low molar fraction observed for the echo decays was traced down to very large vesicles in solution. Light microscopy confirmed the presence of vesicles of several microns in diameter. Thus, polydispersity seems to be an inherent feature of the system.

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Shape Transformations in the Lecithin-Bile Salt System: From Cylinders to Vesicles

Cited by 138 publications

References 10 publications

A New Reverse Wormlike Micellar System: Mixtures of Bile Salt and Lecithin in Organic Liquids

A New Reverse Wormlike Micellar System: Mixtures of Bile Salt and Lecithin in Organic Liquids

Laser Light Scattering Evidence for a Common Wormlike Growth Structure of Mixed Micelles in Bile Salt− and Straight-Chain Detergent−Phosphatidylcholine Aqueous Systems: Relevance to the Micellar Structure of Bile

Vesicle Formation and General Phase Behavior in the Catanionic Mixture SDS−DDAB−Water. The Anionic-Rich Side

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