Spread mixed monolayers of deoxycholic and dehydrocholic acids at the air?water interface, effect of subphase pH. Characterization by axisymmetric drop shape analysis

PAULA V. MESSINA ; MARCOS D. FERNÁNDEZ-LEYES; GERARDO PRIETO; JUAN M. RUSO; FÉLIX SARMIENTO; PABLO SCHULZ

BIOPHYSICAL CHEMISTRY

Elsevier

Año: 2008 vol. 132 p. 39 - 46

0301-4622

Bile acids (deoxycholic and dehydrocholic acids) spread mixed monolayers behavior at the air/water interface were studied as a function of subphase pH using a constant surface pressure penetration Langmuir balance based on the Axisymmetric Drop Shape Analysis (ADSA). We examined the influence of electrostatic, hydrophobic and hydration forces on the interaction between amphiphilic molecules at the interface by the collapse area values, the thermodynamic parameters and equation of state virial coefficients analysis. The obtained results showed that at neutral (pH=6.7) or basic (pH=10) subphase conditions the collapse areas values are similar to that of cholanoic acid and consistent with the cross-sectional area of the steroid nucleus (approximately 40 A(2)). The Gibbs energy of mixing values (DeltaG(mix)