Thermodynamic behavior and epifluorescence microscopy of mixed DOPC/Cho monolayers at the air / water interface

COLMANO, G. N.; MOTTOLA, MILAGRO; PERILLO, M. A.

Santiago del Estero

Congreso; XLIV Reunión Anual de la Sociedad Argentina de Biofísica; 2015

Sociedad Argentina de Biofísica

The present study investigated the thermodynamic behavior and topography of mixed 1, 2-Dioleoyl-sn-glycero-3-phosphocholine (DOPC) /Cholesterol (Cho) monolayers at the air/water interface, self-organized over aqueous subphases containing Hepes, CaCl2 or both, at room temperature. Surface pressure ()?mean molecular area (Mma) isotherms were obtained with a computer-controlled film balance and the topographic analysis was done by epifluorescence microscopy (EFM). Cho induced positive deviations from the ideality at all compositions and compressions, probably due to its disturbing effect on DOPC molecular packing, mainly at high  and Cho contents [1]. In accordance with previous data [2], Ca2+ expanded PC monolayers. Hepes also affected the molecular packing in the same direction as Ca2+but at a lower extent. EFM showed a lateral phase separation in monolayers prepared over a H2O subphase at low  and at xCho ≥ 0.4. In the presence of Hepes, Ca2+ or both, this phenomenon occurred at lower xCho. The lateral phase separation observed with increasing xCho may be a result of the segregation of Cho-rich domains (dark phases that preferentially exclude the fluorescent probe) dispersed within liquid ordered DOPC/Cho phases (bright fluorescent). While  increases, the Cho domains fused together turn into a homogeneous dark phase, with a miscibility critical pressure dependent on Cho content, as shown with POPC/Cho monolayers [3].Referencias:1 Tzung-Han Chou et al. Colloids and Surfaces B: Biointerfaces 17 (2000) 71?79.2 Aneta D. Petelska et al. Langmuir 26, (2010) 13359?13363.3 Lynn-Ann D. Worthman et al. Biophyscal Journal 72 (1997) 2569-2580.Agradecimientos: FONCyT, CONICET, SeCyT-UNC.