SANS Study on the Effect of Lanthanide Ions and Charged Lipids on the Morphology of Phospholipid Mixtures

Abstract

The structural phase behavior of phospholipid mixtures consisting of short-chain (dihexanoyl phosphatidylcholine) and long-chain lipids (dimyristoyl phosphatidylcholine and dimyristoyl phosphatidylglycerol), with and without lanthanide ions was investigated by small-angle neutron scattering (SANS). SANS profiles were obtained from 10 degrees C to 55 degrees C using lipid concentrations ranging from 0.0025 g/ml to 0.25 g/ml. The results reveal a wealth of distinct morphologies, including lamellae, multi-lamellar vesicles, unilamellar vesicles, and bicellar disks.

Highly Stable Phospholipid Unilamellar Vesicles from Spontaneous Vesiculation: A DLS and SANS Study

“…Beyond this range, DMPC/DHPC/DMPG mixtures form discoidal bicelles or MLV. [23][24][25][26] A structural phase diagram of lipid mixtures in the dilute regime (C lp < 1.00 wt %) is presented. It is found that under numerous experimental conditions the ULV size is insensitive to both C lp and C s .…”

Effects of Charge Density and Thermal History on the Morphologies of Spontaneously Formed Unilamellar Vesicles

“…Earlier studies examining the effect of charge on ULV formation have demonstrated that insufficient or excess charge densities can inhibit their formation and instead, result in the formation of MLVs (insufficient charge) or bicelles (excess charge). 21 Here we focused on a narrower range of charge densities (i.e., [DMPG]/[DMPC] ) 0.3, 0.8, and 1.5%) in order to gain a more detailed understanding of the system studied, as summarized in Figure 8. 21 In the case where there is an insufficient amount of charge to cause bilayers to unbind, MLVs are the stable morphology.…”

“…21 Here we focused on a narrower range of charge densities (i.e., [DMPG]/[DMPC] ) 0.3, 0.8, and 1.5%) in order to gain a more detailed understanding of the system studied, as summarized in Figure 8. 21 In the case where there is an insufficient amount of charge to cause bilayers to unbind, MLVs are the stable morphology. 32 The present system forms an opaque liquid indicative of MLVs for all temperatures studied, a result confirmed by SANS.…”

“…15,16 The size of low temperature bicelles has been reported to be weakly dependent on C lp . 21,25 If we assume that the collision frequency of aggregates in the case of higher C lp samples is greater than that of lower C lp samples, it then follows that larger ULVs are expected to form in the case of high C lp samples. The present SANS data only show small differences in ULV size between C lp ) 0.3 and 0.1 wt % samples, probably due to the already low frequency of bicelle coalescence in C lp ) 0.3 wt % samples.…”

“…20 A previous report showed a non DMPG doped system ([DMPG]/[DMPC] ) 0) formed MLVs due to insufficient Coulombic repulsion between bilayers, while a highly doped system ([DMPG]/ [DMPC] ) 6.7%) formed bicelles which were unable to fuse and form ULVs at T > T c . 21 The present study focuses on the kinetics of aggregate structures that evolve from the bicelle-to-ULV transition under different temperature protocols as determined by small angle neutron scattering (SANS). The influence of charge density with regards to ULV size and polydispersity are also investigated.…”