This change showed that a mixed monolayer of SA/BSA was successfully formed, with more interactions between SA and BSA taking place as the concentration of BSA increased. A marked shift away from the isotherm of pure SA was observed at X BSA = 0.8,

0.9 and 1.0 (the last value being pure BSA). There was no collapse pressure observed for X BSA ≥ 0.9, suggesting that a stronger interaction occurred between SA and BSA with high concentrations of BSA in the mixed monolayer system. Energetic stability of the mixed monolayers The miscibility of the mixed monolayer components can be determined by calculating the mean molecular area A 12. For ideality of mixing, A 12 is defined as (1) where A 1 and A 2 are the mean molecular areas of single components at the same surface pressure and X 1 and X 2 are the mole fractions of components Akt inhibitor ic50 1 and 2 in the mixed film. Quantitatively, these deviations can be described with the excess mean molecular area values too. (2) In Figure  2, the mean molecular area A 12 is presented against X SA at different surface pressures (5, 10, 15 and 20 mN m-1). A negative deviation from linearity was attributed to the

miscibility of both components interacting with each other at the interface. The mean molecular area declined as the surface pressure increased. There were only slight deviations from ideality at 5 mN m-1, indicating immiscibility and weak interactions in a mixed monolayer. At 20 mN m-1, a marked negative deviation indicated strong attractions between the check details molecules in the mixed monolayer as compared with the interactions in their respective pure films. Large 17-DMAG (Alvespimycin) HCl deviation observed at X SA = 0.8 and 0.9 for the selected surface pressures showed a significant influence on the molecular packing and favourable interactions between molecules in the mixed monolayers. Figure 2 Mean molecular area of SA/BSA monolayers vs X BSA on pure water subphase at 26°C. For discrete surface pressure

of 5 mN m -1 (diamond), 10 mN m -1 (circle), 15 mN m -1 (triangle), 20 mN m -1 (square) and 25 mN m -1 (right-pointing triangle). The packing density of monolayers can be evaluated and analysed by the compression modulus C s -1, which is defined as [11, 17] (3) C s -1 curves provide detailed information on phase transitions of SA/BSA monolayers. C s -1 can be classified into various phases, namely (a) liquid-expanded (LE) phase at surface pressure from 10 to 50 mN m-1, (b) liquid (L) phase from 50 to 100 mN m-1, (c) liquid-condensed (LC) phase from 100 to 250 mN m-1 and (d) solid (S) phase above 250 mN m-1. In this work, the compression moduli were obtained by numerical calculation of the first derivative from the isotherm data point using the OriginPro-8 program. The significantly large value of compression modulus for the pure SA monolayer indicates its highly condensed phase (Figure  3). At 20 to 25 mN m-1, a change of its slope was observed, corresponding to the phase transition from the liquid-condensed to the solid state.