High resolution membrane structures within hybrid lipid-polymer vesicles revealed by combining x-ray scattering and electron microscopy

ChemRxiv

Abstract

Hybrid vesicles consisting of phospholipids and block-copolymers are increasingly finding applications in science and technology. Herein, small angle X-ray scattering (SAXS) and cryo-electron tomography (cryo-ET) were used to obtain detailed structural information about hybrid vesicles with different ratios of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and poly(1,2-butadiene-block-ethylene oxide) (PBd22-PEO14, Ms = 1800 gmol-1) . Using single particle analysis (SPA) we were able to further interpret the information gained from SAXS and cryo-ET experiments, showing that increasing PBd22-PEO14 mole fraction increases the membrane thickness from 52 Å for a pure lipid system to 97 Å for pure PBd22-PEO14 vesicles. We find two vesicle populations with different membrane thicknesses in hybrid vesicle samples. As these lipids and polymers are known to homogeneously mix, bistability is inferred between weak and strong interdigitation regimes of PBd22-PEO14 within the hybrid membranes. It is hypothesized that membranes of intermediate structure are not energetically favourable. Therefore, upon formation, each vesicle selects one of these two membrane structures, which are assumed to have comparable free energies. We conclude that, by combining biophysical methods, an accurate determination of the influence of composition on the structural properties of hybrid membranes is achieved, revealing that two distinct membranes structures can coexist in homogeneously mixed lipid-polymer hybrid vesicles.

Authors 10

1. Rashmi Seneviratne

   University of Leeds

   Affiliation as printed

   University of Leeds

2. Georgina Coates

   University of Leeds

   Affiliation as printed

   University of Leeds

3. Zexi Xu

   University of Leeds

   Affiliation as printed

   University of Leeds

4. Caitlin E. Cornell

   University of California, Berkeley

   Affiliation as printed

   University of California, Berkeley

5. Rebecca F. Thompson

   University of Leeds

   Affiliation as printed

   University of Leeds

6. Amin Sadeghpour

   University of Leeds

   Affiliation as printed

   University of Leeds

7. Daniel P. Maskell

   University of Leeds

   Affiliation as printed

   University of Leeds

8. Lars J. C. Jeuken Aachen

   Leiden University

   Affiliation as printed

   Leiden University

9. Michael Rappolt

   University of Leeds

   Affiliation as printed

   University of Leeds

10. Paul A. Beales

    University of Leeds

    Affiliation as printed

    University of Leeds