Lyotropic model membrane structures of hydrated DPPC: DSC and small-angle X-ray scattering studies of phase transitions in the presence of membranotropic agents

Abstract

Multibilayer structures of hydrated phospholipids, often considered as model biological membranes, are, from the physical viewpoint, lyotropic liquid crystalline systems undergoing temperature-induced mesomorphic phase transitions. Effects of silver nitrate and urocanic acid on lyotropic phase states of hydrated L-α-dipalmitoylphosphatidylcholine (DPPC) have been studied by small-angle X-ray scattering and differential scanning calorimetry (DSC). Both methods show increase of the main phase-transition temperature (T_m) of hydrated DPPC upon introduction of AgNO₃ or urocanic acid, decrease of pre-transition temperature (T_p) in the presence of urocanic acid and its increase in the presence of AgNO₃. Thus, urocanic acid widened the ripple-phase temperature region. Silver nitrate caused the appearance of an additional high-temperature peak on DSC thermograms, evidencing phase separation in the system. Both agents caused minor effects on DPPC lipid bilayer repeat distance (D) in gel phase, but resulted in noticeable increase of D in the liquid crystal phase with temperature as compared to undoped DPPC structures.

Keywords:

• lyotropic liquid crystal
• hydrated DPPC
• urocanic acid
• silver nitrate
• small-angle X-ray scattering
• differential scanning calorimetry
• phase transitions
• drug–membrane interaction

Disclosure statement

No potential conflict of interest was reported by the authors.

Funding

We acknowledge support of this work by the Russian Foundation for Basic Research (Research projects 13-04-91320 and 13-02-01460A) and by the MIPT ‘5Top100’ program of the Ministry of Education and Science of the Russian Federation.