Occurrence of fatty acid methyl esters and cholesterol in a molecular complex with riboflavin. A correction

Abstract

In a previous publication [1], the occurrence of natural fatty acid methyl esters and cholesterol in an apparent association with riboflavin was reported. Further study has revealed that the methyl esters are artifacts derived from methanolysis of traces of phospholipids remaining in the Folch wash. The presence of cholesterol among these phospholipids after their separation by thin-layer chromatography remains unexplained. Part of this report is therefore invalid. Methanolysis is a well known reaction of lipids but it is invariably described as occurring in solutions of anhydrous methanolic sodium hydroxide (0.2–0.5 M). In the previous study, fatty acid methyl esters were obtained from 30% aqueous methanolic KOH solutions of pH 10–11 (0.05 M KOH) after being held at 50° C for 10 min. The large proportion of water and the weak alkalinity seemed to be incompatible with methanolysis, but tests have shown that phospholipids will produce detectable amounts of fatty acid methyl esters in 5% aqueous methanol under these conditions. The methyl esters may be transient intermediates that would not have survived longer periods of reaction.