Monomolecular films of phenolic esters.
Abstract The properties of three phenolic esters, characterized by gradual changes in their molecular constitution, have been evaluated in pure monomolecular films, as well as in mixed films with stearic acid. The pressure-area isotherms for the pure compounds reflect a similar orientation for compounds I (resorcinol monoundecanoate) and II (4-chlororesorcinol 1-undecanoate) at the air-water interface. At pressures corresponding to the limiting area per molecule, the molecules are apparently rather erect and anchored to the aqueous subphase surface by the phenolic-OH function; at lower pressures, the molecules are less erect, with their aliphatic chains randomly intertwined. The isotherm characteristics for III (4-chlorophenyl undecanoate), on the other hand, are compatible with an orientation in which the molecule is anchored to the aqueous subphase surface by its ester function, with both the aliphatic chain and the substituted phenyl ring projecting upwards. Isotherms for 1:1 mixtures of each of the phenolic esters with stearic acid indicate that the properties of the mixed films were controlled, generally, by the esters (at low pressures) and by stearic acid (at high pressures), after the esters had been forced out of area-determining positions in the films. The experimentally derived isotherms for the mixtures were compared with those calculated from the isotherms of the pure components, and observed deviations from additive behavior discussed.
Monomolecular films of mixtures: I. Stearic acid with isostearic acid and with tri-p-cresyl phosphate. Comparison of components with octadecylphosphonic acid and with tri-o-xenyl phosphate
Abstract Pressure-area isotherms have been obtained for mixed monolayers of pure compounds whose structures are related to those of lubricant additives. Individually, stearic acid and octadecylphosphonic acid with long unbranched chains form strong films. Isostearic acid has a larger molecular area and a much lower collapse pressure than stearic acid. This difference demonstrates the great sensitivity of monolayers to a single methyl side chain. Tri- p -cresyl phosphate and tri- o -xenyl phosphate have much larger areas and lower collapse pressures. An equimolar mixture of two similar compounds, stearic acid and isostearic acid, has monolayer properties close to the calculated average. An equimolar mixture of dissimilar compounds, stearic acid and tri- p -cresyl phosphate, shows film properties of the phosphate at low pressures, expulsion of the phosphate from the monolayer at intermediate pressures, and properties of stearic acid at high pressures.
Interactions of Veratrum Alkaloids, Procaine, and Calcium with Monolayers of Stearic Acid and Their Implications for Pharmacological Action
The interactions of veratridine, cevadine, veracevine, and veratramine with monolayers of stearic acid show marked differences. Veratridine and cevadine, at concentrations that are known from potential, ionic flux, and other measurements to affect living membranes, react strongly with the film and appear to cause an "interfacial dissolution" whereby both the alkaloid and the stearate leave the surface. Veracevine at the same concentration does not interact with the film. The veratramine reaction is weak, much like that of the local anesthetic procaine. The veratridine and cevadine effects are antagonized by 10-3 M Ca++, low pH, and 3.7 and 7.4 x 10-3 M procaine. These differences among the veratrum alkaloids and the antagonisms parallel effects observed in living systems. Such parallelism suggests that similar physical interactions are involved in the stearate film and in natural membranes.