The Dissolution State of a Triglyceride Molecule in Water and Its Orientation State at the Air-Water Interface

Abstract

The relations between the surface tension and the concentration of the aqueous solutions of triacetin, tripropionin, tributyrin, tricaproin, and tricaprylin were determined at 37°. The solubilities and the adsorbed amounts of triglycerides were obtained from these results. Since the solubilities of tricaproin and tricaprylin were extremely low, the corrections for adsorption at the interfaces were necessary to obtain their solubilities. The linear relationship between the logarithm of solubility and the total surface area of hydrophobic groups in a triglyceride molecule which could contact maximally with the water, was found to hold. The smallness of the slope of this straight line in comparison with those of hydrocarbon and alcohol, was interpreted as showing that three hydrophobic chains in a triglyceride molecule may aggregate intramolecularly with one another in the water; three-fifths of the total surface area of hydrophobic group are in contact with water and the two-fifths are in contact with hydrophobic group. Moreover, from the molecular area occupied at the air-water interface, it was suggested that the hydrophobic chains in adsorbed monolayer of triacetin might correspond to the “tune-forming” conformation like the β-form crystal of triglyceride; the chains in 1- and 3-position were directed toward the air and the chain in 2-position was directed toward the water. © 1976, The Pharmaceutical Society of Japan. All rights reserved.