Behavior of Individual Lipolytic Products in Water

To describe the behavior of a lipid in water, it is customary to use a phase diagram in which the physical state or molecular arrangement of the lipid or the system is shown in relation to the composition of the mixture (Fig. 1). Composition is usually expressed in percentage by weight (abscissa), and the ordinate is temperature. In two-component systems, called binary 

It should be noted that pH is not usually considered an independent variable in such systems. In systems containing fatty acids and soap mixtures, the bulk pH is influenced by the buffering capacity of the ionizable lipids which are present, and this buffering capacity depends on the concentration and temperature of the system. Customarily, one measures the pH at equilibrium. Although body temperature is fixed, it is also often useful to vary temperature experimentally in order to distinguish effects of, for example. 

A detailed consideration of the behavior and solubility of lipolytic products in aqueous systems not containing bile acids has two justifications. First, digestion is an aqueous process and significant intestinal absorption of certain lipolytic products may occur in the absence of bile acids, despite their low solubility. It is a reasonable assumption that such absorption occurs from a molecular solution, or at lest a nonmicellar solution, and we therefore seek information on molecular solubility or types of aggregation or both in aque-our systems. Second, behavior of lipolytic products in the absence of bile acids provides a framework from which to predict the behavior of these compounds when bile acids are added. 

The predominant form of monoglyceride present in intestinal content during fat digestion is the 2-isomer, which is unstable, slowly isomerizing to the 1-isomer. Few studies have compared the physical properties of the 1-and 2-isomers, but glyceryl monoethers, which are nearly isosteric and should have fairly similar physical properties, are prepared without difficulty. It would seem both feasible and interesting to examine the phase equilibria as well as molecular solubility of glyceryl 1- and 2-monounsaturated ethers. 

TABLE I. Transition Temperatures CC) for Monoglycerides and Fatty Acids in Water  

---