Effects of cholesterol on the structure and collapse of DPPC monolayers

Structural determinants of collapse by a monomolecular mimic of pulmonary surfactant at the physiological temperature

“…35,36 Two cycles of slow expansion and compression at surface pressures below 45 mN m À1 served to anneal the film. 16 A pulsed compression then raised surface pressure to the target value, which was held constant using simple feedback (ESI †). 32 The initial slope of semilogarithmic plots of area versus time provided the rate of collapse.…”

“…1 (left panels) and 2). 16 The two peaks indicated a centeredrectangular unit cell. Off-equatorial scattering, at q z 4 0, indicated tilt of the acyl chains (Table 1).…”

“…At temperatures below its main transition temperature, for instance, monolayers of dipalmitoyl phosphatidylcholine (DPPC) form a two-dimensional centered-rectangular structure that resists collapse. 16 The films readily undergo compression to very low surface tensions. Above the melting temperature, 17,18 disordered films of that compound collapse at the equilibrium spreading tension.…”

“…In sufficient amounts, that compound makes films of pulmonary surfactant susceptible to collapse. [20][21][22] The steroid also promotes collapse of DPPC monolayers 16,23 and alters their structure. 16 At ambient laboratory temperatures, the dose-response of the changes in structure and rates of collapse are discordant.…”

“…[20][21][22] The steroid also promotes collapse of DPPC monolayers 16,23 and alters their structure. 16 At ambient laboratory temperatures, the dose-response of the changes in structure and rates of collapse are discordant. 16 Doses of cholesterol that first change the structure of the DPPC monolayer are well below the levels at which collapse abruptly accelerates.…”