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

COLMANO GN; MOTTOLA M; PERILLO MA

Santiago del Estero

Congreso; XLIV Reunión Anual de la Sociedad Argentina de Biofísica (SAB); 2015

Sociedad Argentina de Biofísica

The present study investigated thethermodynamic behavior and topography of mixed 1, 2-Dioleoyl-sn-glycero-3-phosphocholine(DOPC) /Cholesterol (Cho) monolayers at the air/water interface, self-organizedover aqueous subphases containing Hepes, CaCl2 or both, at roomtemperature. Surface pressure (p)?mean molecular area (Mma) isotherms were obtained with acomputer-controlled film balance and the topographic analysis was done byepifluorescence microscopy (EFM). Cho induced positive deviations from theideality at all compositions and compressions, probably due to its disturbingeffect on DOPC molecular packing, mainly at high p and Cho contents [1]. Inaccordance with previous data [2], Ca2+ expanded PC monolayers.Hepes also affected the molecular packing in the same direction as Ca2+butat a lower extent. EFM showed a lateral phase separation in monolayers preparedover a H2O subphase at low p and at xCho ≥ 0.4. In the presenceof Hepes, Ca2+ or both, this phenomenon occurred at lower xCho. The lateral phaseseparation observed with increasing xChomay be a result of the segregation of Cho-rich domains (dark phases thatpreferentially exclude the fluorescent probe) dispersed within liquid orderedDOPC/Cho phases (bright fluorescent). While p increases, the Cho domainsfused together turn into a homogeneous dark phase, with a miscibility criticalpressure dependent on Cho content, as shown with POPC/Cho monolayers [3].