Application of positron annihilation lifetime spectroscopy (PALS) to study the nanostructure in amphiphile self-assembly materials: phytantriol cubosomes and hexosomes

Abstract

Self-assembled amphiphile nanostructures of colloidal dimensions such as cubosomes and hexosomes are of interest as delivery vectors in pharmaceutical and nanomedicine applications. Translation would be assisted through a better of understanding of the effects of drug loading on the internal nanostructure, and the relationship between this nanostructure and drug release profile. Positron annihilation lifetime spectroscopy (PALS) is sensitive to local microviscosity and is used as an in situ molecular probe to examine the Q2 (cubosome) → H2 (hexosome) → L2 phase transitions of the pharmaceutically relevant phytantriol-water system in the presence of a model hydrophobic drug, vitamin E acetate (VitEA). It is shown that the ortho-positronium lifetime (τ) is sensitive to molecular packing and mobility and this has been correlated with the rheological properties of individual lyotropic liquid crystalline mesophases. Characteristic PALS lifetimes for L2 (τ4∼ 4 ns) ∼ H2 (τ4∼ 4 ns) > Q(2 Pn3m) (τ4∼ 2.2 ns) are observed for the phytantriol-water system, with the addition of VitEA yielding a gradual increase in τ from τ∼ 2.2 ns for cubosomes to τ∼ 3.5 ns for hexosomes. The dynamic chain packing at higher temperatures and in the L2 and H2 phases is qualitatively less "viscous", consistent with rheological measurements. This information offers increased understanding of the relationship between internal nanostructure and species permeability.

Cubic and hexagonal liquid crystals as drug carriers for the transdermal delivery of triptolide

“…PT-water systems can form the V 2 phase at 20 °C, with a transformation to H 2 at a higher temperature (Barauskas & Landh, 2003; Barauskas et al., 2005). In addition, the V 2 phase can be converted into the H 2 phase by adding vitamin E acetate (VitEA) at 20 °C (Dong et al., 2006; 2015).…”

Free‐Standing Phytantriol Q224 Cubic‐Phase Films: Resistivity Monitoring and Switching

“…These range from use in pharmaceutical sciences for drug delivery vessels and biosensors, to materials templates for fuel cells, solar cells, and for photonic crystals . When combined with a “capping agent”, phytantriol can be converted into stable “cubosome” or “hexosome” particles . Key to mesophase properties and to applications is the ionic transport through the water channels.…”

Positron annihilation lifetime spectroscopy (PALS): a probe for molecular organisation in self-assembled biomimetic systems

“…During the past several decades, artificial cell morphologies such as micelles, 89 vesicles 20,90 and liposomes 23 comprised of endogenous phospholipids (Fig. [44][45][46]75 The application of PALS in the domain of drugmembrane interactions is currently putative and requires further substantiation. Phosopholipids such as DPPC (1,2dipalmitoyl-sn-glycero-3-phosphocholine) have often been the lipid of choice in these studies, as not only is it a major membrane constituent but the phase diagram is well known (Fig.…”