Equilibrium spreading pressure, overcompression and metastability of C10-CER

GABRIELA MARZARI; MARIA LAURA FANANI; BRUNO MAGGIO

Sierra de la Ventana

Congreso; XLIII Reunión Anual Sociedad Argentina de Biofísica; 2014

Sociedad Argentina de Biofísica

Ceramide is one of the simplest sphingolipids, consisting of a sphingosine base N-linked to a fatty acid, and is a mediator for cell-signaling events. In this work, the dependence of the interfacial organization and topography of films of ceramide N-acylated with a 10 carbon fatty acid (C10-Cer) with the compression-expansion kinetics were studied in Lagmuir monolayers. The molecular packing, the bidimensional transition, its cooperativity and the morphology of condensed domains under cycles of compression-expansion at different rates indicates that the interfacial structure is kinetically limited at the molecular and supra-molecular levels. Recent experiments indicate that at 21 °C these monolayers have an "equilibrium spreading pressure" lower than 0.5 mN/m and monolayer formation was not detected when compressed at very slow rates. Thus, at the usual compression rates, the ceramide film is in overcompressed state at all surface pressures. At these relatively faster rates isotherm having different compressions-expansion hysteresis were observed depending on the scan rate. The hysteresis thermodynamic functions point to entropic-enthalpic compensations that result in favorable enthalpic contributions derived from a more condensed packing which overcomes the unfavorable diminution of configurational entropy. These results suggest formation of kinetically limited and metastable condensed states. Suported by CONICET, FONCyT, SECyT-UNC