The behavior and solubility of monoglycerides in dilute, micellar bile-salt solution

Abstract

1. 1. The behavior and solubility of a number of pure monoglycerides in dilute, micellar bile-salt solution has been studied in vitro, using experimental conditions simulating those present in human small-intestinal content during fat digestion with respect to Na + (0.15 M), pH (6.3) and temperature (37°). 2. 2. Monoglycerides with a chain length of 10 carbon atoms or more have a low solubility in buffer alone, although certain unsaturated monoglycerides ( e.g. 1-mono-olein, 1-monolinolein, 2-monoolein) may interact with buffer to form liquid crystalline states; these, however, disperse poorly. 3. 3. In bile-salt solution, the solubility of monoglycerides is greater and their behavior and solubility is chiefly related to melting point. At 37°, monoglycerides with melting point under about 65° have a striking micellar solubility, being solubilized as amphiphiles. Higher-melting-point monoglycerides ( e.g. 1-monopalmitin or 1-monomyristin) are solubilized as non-polar solutes and have much lower solubilities. 4. 4. 1-Monoolein and 2-monoolein are solubilized identically by bile-salt solutions. 2-Monopalmitin has a higher solubility than 1-monopalmitin, but the difference may only reflect the former's lower melting point. 2-Monolein and 2-monopalmitin isomerize slowly in dilute bile-salt solution (5% in 1 h; 55% in 24 h) with the experimental conditions cited. 5. 5. If two amphiphilic monoglycerides are equilibrated with bile-salt solution, they are solubilized competitively; however, the solubilization of an amphiphilic monoglyceride generally enhances the solubility of a higher-melting-point (non-polar) monoglyceride. 6. 6. Glycerol 1-monoethers and 1-monoglycerides containing the same alkyl radical are solubilized identically by bile-salt solutions, with the appropriate experimental conditions.