Morphological Characterization of DMPC/CHAPSO Bicellar Mixtures: A Combined SANS and NMR Study

Abstract

Spontaneously forming structures of a system composed of dimyristoyl phosphatidylcholine (DMPC) and 3-[(3-cholamidopropyl)dimethylammonio]-2-hydroxy-1-propanesulfonate (CHAPSO) were studied by small-angle neutron scattering (SANS), (31)P NMR, and stimulated echo (STE) pulsed field gradient (PFG) (1)H NMR diffusion measurements. Charged lipid dimyristoyl phosphatidylglycerol (DMPG) was used to induce different surface charge densities. The structures adopted were investigated as a function of temperature and lipid concentration for samples with a constant molar ratio of long-chain to short-chain lipids (= 3). In the absence of DMPG, zwitterionic bicellar mixtures exhibited a phase transition from discoidal bicelles, or ribbons, to multilamellar vesicles either upon dilution or with increased temperature. CHAPSO-containing mixtures showed a higher thermal stability in morphology than DHPC-containing mixtures at the corresponding lipid concentrations. In the presence of DMPG, discoidal bicelles (or ribbons) were also found at low temperature and lower lipid concentration mixtures. At high temperature, perforated lamellae were observed in high-concentration mixtures (≥7.5 wt %) whereas uniform unilamellar vesicles and bicelles formed in low-concentration mixtures (≤2.5 wt %), respectively, when the mixtures were moderately and highly charged. From the results, spontaneous structural diagrams of the zwitterionic and charged systems were constructed.

Characterization of Small Isotropic Bicelles with Various Compositions

“…Therefore, the effect cannot be explained by the increase of the average volume of lipid molecule in the planar region of a bicelle caused by the phase transition of lipids. Most likely, the size of the particles is increased at high q* due to the temperature-dependent mixing of lipids and detergents in the lipid bilayer region of bicelles, which was shown to occur in magnetically aligned species 36 ; or, alternatively, the observed temperature dependence is caused by the presence of rod-like or band-like particles in the solutions of high-q* isotropic bicelles above the phase transition temperature of DMPC, as was found by Cryo-EM spectroscopy 41,45 . 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 Apart from the bicelle radius, concentration of free DHPC was also found to be dependent on both temperature and q* ( Figure 1F, 2C).…”

“…DMPC/DHPC system has been studied quite thoroughly. Several models, describing the geometry of such bicelles were suggested and tested 22,36,37 , morphology of bicelles was studied by cryo-electron (cryo-EM) and freeze-fraction electron microscopy 38,39 , small angle neutron scattering (SANS) 40,41 , NMR diffusion [42][43][44] and dynamic light scattering (DLS) 45 , which allowed to plot the complex phase diagrams for DMPC/DHPC and DMPC/CHAPSO systems 38,41 . However, most of the listed studies refer to the case of large and magnetically aligned species.…”

Thermal Stabilization of Bicelles by a Bile-Salt-Derived Detergent: A Combined 31P and 2H Nuclear Magnetic Resonance Study

“…47 SANS data indicate that bicellar mixtures of the type examined here exhibit lamellar spacings on the order of 100 Å, leaving roughly 60 Å of interstitial aqueous space. 29 Thus, a nonzero residual quadrupole splitting for CHAPSO-d 6 confined between such bicellar lamella is not surprising. However, confinement alone is not sufficient to explain the quadrupole splittings detailed in Figure 10.…”

“…29 And it is certainly the case that mixtures of shortchain and long-chain phosphatidylcholines can form small, stable unilamellar vesicles. 13,14 The present NMR results do not, however, differentiate whether these are micellar or small vesicular assemblies.…”

Low-toxicity metallosomes for biomedical applications by self-assembly of organometallic metallosurfactants and phospholipids

“…S3, ESI †). 5 At this point, our results show that MTS/SPC systems allow stable aggregates that contain metal atoms in their hydrophobic domain to be obtained. The MTS to SPC molar ratio modulates the type and size of these aggregates, since vesicles (metallosomes) and small structures of about 10 nm can be obtained.…”