Structural study of complex lipids present in soils: Characterization of monocarboxylic acids resulting from polar lipids fraction alkaline hydrolysis

摘要

In acid soils such as turf, the biological activity is reduced, so lipids tend to accumulate. Those lipids are made of two fractions: one fraction, named “simple lipids”, directly analyzable, and the other, named “polar lipids” or “complex lipids”. The structure and origin of these “polar lipids” had been investigated using chemical degradation methods. The degradation procedure consisted in an alkaline hydrolysis, where 18-crown-6 ether was used as a phase transfer catalyst. This operation yielded a large amount of acids and hydroxyl functions. Gas chromatography (GC) displayed similar distributions of monocarboxylic acids in simple lipids and in hydrolyzed polar lipids, except the eicosanoic acid which was abundant in polar lipids. Gas chromatography-mass spectrometry (GC-MS) analysis of monocarboxylic acids showed large quantities of aliphatic acids. Some hopanoic acids were also found. It seems that monocarboxylic acids were chemically linked to the polar matrix by ester group.