Studies of some bio-inspired liquid crystals

ABSTRACT

The main phase transition of lipid bilayers corresponds to a defined change from an ordered (gel) to a disordered (fluid liquid crystal) state of hydrocarbon chains, occurring in general at a defined temperature T_m. However, aqueous dispersions of pure anionic phospholipids, and particularly DMPG, may exhibit a ‘melting regime’, from T_m^on until T_m^off, over ~10°C. The melting process depends on pH, ionic strength and several details of sample preparation. This paper makes a review on seven papers of the author with different collaborations, with the original proposal of pores in the DMPG melting transition. The focus is on structural results obtained from X-ray scattering, varying concentration and temperature, but integrating with results from other experimental techniques. Initially the effect of salt addition was separated from the effect of DMPG concentration. At DMPG concentrations higher than 70 mM a lamellar phase starts and a detailed study of the temperature variation of 150 mM DMPG allowed arrival to detailed pore model, focused in the surface fractions of pores in the bilayers. The model admits large and small pores in the melting regime and agrees with the new Lamellar Phase with pores (Lp) starting at T_3. The large biological relevance is stressed.

GRAPHICAL ABSTRACT

KEYWORDS:

• Pore model
• DMPG
• abnormal melting regime
• concentration variation
• X-ray scattering
• liquid crystal structures

Acknowledgments

Karin A. Riske helped in the preparation of the Graphical Abstract and had punctual discussions with me on this work; Department of Applied Physics and IFUSP together give me academic support as Senior Professor and Project INCT of Complex Fluids 2014/50983-3 (FAPESP) payed the registration fee for ILCC 2022 online meeting.

Disclosure statement

No potential conflict of interest was reported by the author(s).