Ideal Two-Dimensional Solutions. Ii. A New Isotherm for Soluble and “Gaseous” Monolayers

Water at Biological Phase Boundaries: Its Role in Interfacial Activation of Enzymes and Metabolic Pathways

“…Then, the energy spent to bring w moles of water from the bulk phase to the surface is The average surface area occupied by a water molecule is 29.1 Å 2 , which is much larger than the area 9.65 Å 2 determined from the molecular volume of water (Fowkes 1962). This indicates that there is a large spatial separation between water molecules at the surface and the vacant area ( 20 Å 2 ) between water molecules at the surface might act as binding sites for surfactant molecules.…”

Regulation of the surface pressure of lipid monolayers and bilayers by the activity of water: derivation and application of an equation of state.

“…Prompted by the apparent similarities between monolayer and bilayer systems and the importance of water in determining their structures, we have derived a water-oriented, quasi-two-dimensional equation of state that accurately describes the properties of liquid-type (15,16) (17) is useful because it can be directly applied to data describing interfacial tension as a function of system composition. However, it is incomplete in that it fails to account for changes in the activity coefficients of the components as a function of their interactions across an interphase of finite thickness.…”

“…Studies of bilayer structure have also focused on the role of water as a determinant of interfacial structure. These studies have led to the recognition that at small distances water-water interaction is the principal mediator of the approach of two lipid-covered surfaces through an aqueous medium (12)(13)(14).Prompted by the apparent similarities between monolayer and bilayer systems and the importance of water in determining their structures, we have derived a water-oriented, quasi-two-dimensional equation of state that accurately describes the properties of liquid-type (15,16) (17) is useful because it can be directly applied to data describing interfacial tension as a function of system composition. However, it is incomplete in that it fails to account for changes in the activity coefficients of the components as a function of their interactions across an interphase of finite thickness.…”

“…Prompted by the apparent similarities between monolayer and bilayer systems and the importance of water in determining their structures, we have derived a water-oriented, quasi-two-dimensional equation of state that accurately describes the properties of liquid-type (15,16) (17), but these are difficult to apply experimentally. Using a firstorder treatment with the generalized Gibbs approach, Lucassen-Reynders (6, 7) has shown that the excess free energy, AGij, that interactions impart to a nonideal surface of n components, can be described by a linear function of the product of the mole fractions XjXj for each pair of interacting molecules, AG1j/X nI = E Hj Xi Xj, where Hij are proportionality constants characterizing the interaction specific for each combination of components i and j.…”

“…Hence, the mole fraction of water in the surface phase is given by a + (A -wJ)/e 1 + a + (A -oc)/< Substitution of this into Eq. 2 and rearranging gives A = c--arcs + [3] fi-expiTo)-1 flePq~k-T) (20), when the surface pressure decreases exponentially (21,22) from a value iro at the air-surface interface to zero at the surface-bulk water interface, the depth-dependent surface pressure is given by [7] which describes the Us~ing the data subsets and w, = 9.65 (16), the parameters 00, f1, and q were optimized for each lipid using a modified Levenberg-Marquardt least-squares algorithm (24). The value of (o, for each lipid was obtained by using these parameters to evaluate the function at irc, and from this and coO the hydration parameter, a, was calculated.…”