Phase Behavior of Mixed Aqueous Dispersions of Dipalmitoylphosphatidylcholine and Dodecyl Glycosides:  A Differential Scanning Calorimetry and X-ray Diffraction Investigation

Abstract

Partial pseudo-binary-phase diagrams of dipalmitoylphosphatidylcholine (DPPC) and two glycosidic surfactants, dodecyl-β-d-maltoside (DM) and dodecyl-β-d-glucopyranoside (DG) in excess aqueous buffer were investigated by differential scanning calorimetry and X-ray diffraction, in the 10−50 °C (DPPC−DG) and 20−50 °C (DPPC−DM) temperature intervals and in the 0−1.8 range of surfactant molar ratios. At low levels, both DG and DM behaved as lipid-soluble impurities, preserving the lamellar organizations of the pure phospholipid in excess water. With an increase in the surfactant contents, the phase behaviors of DPPC in mixture with DG or DM diverged: while the DPPC−DG system exhibited only mixed lamellar structures, the DPPC−DM system underwent bilayer-to-micelle transitions beyond nearly 1 DM molecule per 2 phospholipids. For both systems, the melting of the DPPC hydrocarbon chains induced two isothermal (solid → solid + liquid) reactions, indicating a nonideal mixing in the surfactant-rich solid phases. At low temperatures, DPPC−DG and DPPC−DM mixtures formed likewise lamellar organizations with straight hydrocarbon chains. However, at DM molar ratios >0.4, the lamellar structures were broken up into micelle-like aggregates with a solid core. At high temperatures, both pseudobinary diagrams showed the existence of fluid lamellar phases, the periodicity of which was governed by the DG or DM insertion but depending on the surfactant headgroup. DG principally decreased the bilayer thickness due to the reduction of the mean chain length of the DPPC−DG mixtures. At molar ratios <0.4, DM followed the DG behavior, while at higher contents a significant lamellar swelling was observed that coincided with the appearance of mixed micelles.

A new nanomedicine based on didanosine glycerolipidic prodrug enhances the long term accumulation of drug in a HIV sanctuary

“…SAXS and WAXS patterns of pure DPPC vesicles prepared using the Bangham method ( Fig. 7a and b) presented the already reported diagrams (Forte et al, 1998;Carion-Taravella et al, 2002) at room temperature and in excess of water. DPPC was in the lamellar gel phase L␤ (d-spacing = 64Å) in which extended chains were tilted with respect to the bilayer plane and arranged in a pseudohexagonal subcell.…”

Focused ultrasound influence on calcein-loaded thermosensitive stealth liposomes

“…CHOL-free liposomes (DPPC/DSPE-PEG2000 95:5 mol%) exhibited the typical pre-transition corresponding to the conversion of the lamellar gel phase L b' into the ripple gel phase P b', and the main transition related to the passage from the P b' phase to the lamellar liquidcrystalline phase L a (Figure 3, inset) [42]. The pre-transition occurred at T onset 34.6 C with an enthalpy DH of 2.8 J/g of DPPC, and the main phase transition at T onset 41.9 C with an enthalpy of DH of 35.9 J/g of DPPC (Figure 4).…”

Influence of Long-Tailed Alcohols on the Solubilisation of Cationic DHAB Bilayers

“…Considering the DSC results, these changes are probably accompanied by changes in the packing of the DHAB/C 10 OH bilayers [42,45].…”

“…Up to 20 mol% of C 10 OH T m decreases until about 23°C. Generally a lowering in T m is explained by a decreased packing of the chains [21,42]. Upon further addition of C 10 OH the T m increases again, reaching 30°C at 50 mol% of C 10 OH.…”