Structural investigation of sulfobetaines and phospholipid monolayers at the air-water interface

Naomi Elstone, Thomas Arnold, Maximilian W.A. Skoda, Simon E. Lewis, Peixun Li, Gavin Hazell, Karen J. Edler

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Mixtures of sulfobetaine based lipids with phosphocholine phospholipids are of interest in order to study the interactions between zwitterionic surfactants and the phospholipids present in cell membranes. In this study we have investigated the structure of mixed monolayers of sulfobetaines and phosphocholine phospholipids. The sulfobetaine used has a single 18-carbon tail, and is referred to as SB3-18, and the phospholipid used is DMPC. Surface pressure-area isotherms of the samples were used to determine whether any phase transitions were present during the compression of the monolayers. Neutron and X-ray reflectometry were then used to investigate the structure of these monolayers perpendicular to the interface. We found that the average headgroup and tail layer thickness was reasonably consistent across all mixtures, with a variation of less than 3 Å reported in the total thickness of the monolayers at each surface pressure. However, by selective deuteration of the two components of the monolayers, it was found that the two components have different tail layer thicknesses. For the mixture with equal compositions of DMPC and SB3-18 or with a higher composition of DMPC the tail tilts were found to be constant, resulting in a greater tail layer thickness for SB3-18 due to its longer tail. For the mixture higher in SB3-18 this was not the case, the tail tilt angle for the two components was found to be different and DMPC was found to have a greater tail layer thickness than SB3-18 as a result.

Original languageEnglish
Pages (from-to)22679-22690
Number of pages12
JournalPhysical Chemistry Chemical Physics
Issue number37
Early online date6 Sept 2022
Publication statusPublished - 6 Sept 2022

Bibliographical note

Funding Information:
N. E. gratefully acknowledges PhD studentship funding via the EPSRC Centre for Doctoral Training in Sustainable & Circular Technologies, grant number: EP/L016354/1. We also thank the ISIS Pulsed Neutron and Muon Source for allocation of experimental beamtime on INTER under project RB1610351 ( ) and the Diamond Light Source for the allocation of experimental beamtime on I07 under project SI11542-1. Thanks are extended to I07 and Inter beamline staff as well as members of the Edler group for their assistance in the collection of NR and XRR data. We are also thankful to Piexun Li at the ISIS deuteration facility for the provision of deuterated compounds used to synthesize the surfactants within this study. Data supporting this article have been made freely available via the University of Bath Research Data Archive system at DOI: 10.15125/BATH-00917.

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry


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