The Equilibria of Sphingolipid-Cholesterol and Sphingolipid–Sphingolipid in Monolayers at the Air–Water Interface

Abstract

Monolayers of sphingomyelin (SM), ceramide (Cer) and cholesterol (Ch) and binary mixtures SM–Ch, SM–Cer and Cer–Ch were investigated at the air–water interface. SM, Cer and Ch were used in the experiment. The surface tension values of pure and mixed monolayers were used to calculate π-A isotherms. Surface tension measurements were carried out at 22 °C using a Teflon trough and a Nima 9000 tensiometer. Interactions between sphingolipid and Ch as well as sphingolipid and another sphingolipid result in significant deviations from the additivity rule. An equilibrium theory to describe the behavior of monolayer components at the air–water interface was developed in order to obtain the stability constants and Gibbs free energy values of SM–Ch, SM–Cer and Cer–Ch complexes. We considered the equilibrium between the individual components and the complex and established that sphingolipid and Ch as well as sphingolipid and another sphingolipid formed highly stable 1:1 complexes.

The Equilibria Between Monovalent Ions and Phosphatidylcholine Monolayer at the Air/Water Interface

“…The surface area for the PC molecule in pure water is 56 Å 2 . This value agrees with values reported in the literature (Brzozowska and Figaszewski 2002; Petelska and Figaszewski 2013a, b). The surface areas for the lecithin molecule in the presence of 2.5 × 10 −4  M Li + , Na + and Cs + ion concentrations are 59, 60 and 65 Å 2 , respectively, which are presented in Fig.…”

“…The PC isotherm is in satisfactory agreement with that previously reported (Brzozowska and Figaszewski 2002; Petelska and Figaszewski 2013a, b). The surface area for the PC molecule in pure water is 56 Å 2 .…”

“…In water, the phase behavior of PC has been well documented (Brzozowska and Figaszewski 2002; Aroti et al 2004, 2007; Sovago et al 2007; Petelska and Figaszewski 2013a, b). With decreasing surface area, the following regions have been identified: a gas phase, a liquid-expanded (LE) phase, a plateau characteristic of the coexistence of the LE and the liquid-condensed (LC) phase and the pure LC phase.…”

“…Langmuir monolayers provide a unique way of studying two-dimensional (2D) materials at air/water interfaces, and investigations of Langmuir monolayers have uncovered a rich variety of physicochemical phenomena (Shapovalov 1998; Lee 2008; Fragneto et al 2013; Petelska and Figaszewski 2013a). Langmuir monolayers are excellent model systems for membrane biophysics since a biological membrane can be considered as two weakly coupled monolayers.…”

Equilibria in DPPC-Diosgenin and DPPC-Diosgenin Acetate Bilayer Lipid Membranes: Interfacial Tension and Microelectrophoretic Studies

“…Since no accurate data of the stability constants for forming connections exist in the literature, our team, as a first, has determined these parameters and introduced them to the world. This represents an original contribution to the knowledge of the biochemistry and biophysics of lipid membranes [30][31][32][33][34][35][36][37].…”