Surface areas of naturally occurring lipid classes and the quantitative microdetermination of lipids

Abstract

The surface area (A) of a lipid was directly proportional to the amount of lipid in a surface film (A = k μmoles) measured at constant surface pressure, temperature, and subphase composition. A surface area of 2300 cm2/μmole was obtained for cholesterol isolated from human adrenal and aorta and for cholesterol from hydrolysates of cholesteryl esters isolated from the same tissues. Unsaturated methyl esters that contained from one to four cis double bonds had the same surface area, 39.4 Å2/molecule. AS a consequence, naturally occurring triglyceride mixtures which had similar saturated–unsaturated fatty acid ratios had the same surface area, 6090 cm2/μmole. Naturally occurring phospholipid mixtures had the same surface area, 4590 cm2/μmole, and it appeared that the composition of these mixtures was regulated to control the physical properties of the mixtures. Surface area was much more sensitive than colorimetric procedures for the estimation of cholesterol and triglycerides. The surface areajmolecule was a criterion of purity and an expanded surface area/molecule was an indication of autoxidation. Thus, surface area measurements were valuable for both the microdetermination and the characterization of lipid classes.

Keywords

• Langmuir trough
• piston oils
• cholesterol
• cholesteryl esters
• methyl esters
• triglycerides