Page 52 - ILL Annual Report 2019

SOFT CONDENSED MATTER
Yuri Gerelli. Italian
The ILL
‘I am the co-ordinator of the Partnership
for Soft Condensed Matter at the ILL. My research focuses on the study of the structural dynamics in thin films.’
Phase transitions in a single supported phospholipid bilayer: real-time determination by neutron reflectometry
Vertical reflectometer D17 and PSCM
A lack of information on the phase transition behaviour of systems with
low dimensionality, such as supported lipid bilayers (SLBs), still exists. Using D17, we identified the presence of an isothermal phase transition characterised by a symmetrical rearrangement of
lipid molecules in both bilayer leaflets, followed by the main thermotropic phase transition characterised by
an independent melting of the two leaflets. These results are highly relevant for the further understanding of co-operative structural dynamics
in SLBs and for the investigation of thermally activated processes.
AUTHORS
Y. Gerelli (ILL) ARTICLE FROM
Phys. Rev. Lett. (2019)—doi: 10.1103/PhysRevLett.122.248101
REFERENCES
[1] B.R. Olden, C.R. Perez, A.L. Wilson, I.I. Cardle, Y.-S. Lin, B. Kaehr, J.A. Gustafson, M.C. Jensen and S.H. Pun, Adv. Healthc. Mater. (2018) 1801188
[2] E.T. Castellana and P.S. Cremer, Surf. Sci. Rep. 61 (2006) 429
[3] H.-L. Wu, Y. Tong, Q. Peng, N. Li and S. Ye, Phys. Chem. Chem.
Phys. 18 (2016) 1411
Solid-supported lipid bilayers (SLBs) are widely used tools in biological and technological studies for investigating interactions and molecular processes involved in cell function and disease and for sensing applications [1, 2]. Moreover, SLBs are one of the prototypes of natural self- assembling systems.
Phase transitions in lipid bilayers have been widely studied in solution aggregates such as vesicles, and in solid-supported stacks of hundreds of bilayers in controlled humidity environments. However, in the case of SLBs, effects of supporting interfaces, finite size and planarity may have a large impact and modify the phase behaviour of these self-assembled systems. It is accepted that the main phase transition (known as order–disorder or gel-fluid transition) of bi-dimensional bilayers is characterised by
a substantial broadening with respect to that observed
in free-standing bilayers in solution. In addition, atomic force microscopy (AFM) experiments [3] have reported that the main phase transition in SLBs is mediated by the formation and growth of nanosized fluid-in-gel domains
as the temperature is increased; such coexistence was detected up until the growing domains entirely replaced the starting phase. Moreover, these experiments indicated a decoupling between the thermodynamic behaviour
of the lipid molecules ‘strongly’ interacting with the solid substrate (forming the proximal leaflet) and those facing the water reservoir (forming the distal leaflet). In particular, they hypothesised that the melting of the proximal leaflet is preceded by the complete melting of the distal one.
ANNUAL REPORT 2019