Separation of triacylglycerols containing allenic and acetylenic fatty acids by enantiomeric liquid chromatography-mass spectrometry

Chiral high-performance liquid chromatography analysis of mono-, di-, and triacylglycerols with amylose- and cellulose-phenylcarbamate-based stationary phases

The ever-increasing technological advancement in the (ultra)high-performance liquid chromatography tandem (high-resolution) mass spectrometry platforms have largely contributed to steeply intensify the interest towards lipidomics research. However, mass spectrometers alone are unable to distinguish between enantiomers. This obstacle is especially evident in the case of glycerolipids analysis due the prochiral nature of glycerol. Until a couple of decades ago, the stereoselective analysis of triacylglycerols (TAGs) was performed on the end products generated either from their enzymatic or chemical hydrolysis, namely on mono- or diacyl-sn-glycerols (MAGs and DAGs, respectively). These were then mostly analyzed with Pirkle-type chiral stationary phases (CSPs) after dedicated multi-step derivatization procedures. One of the most significant drawbacks of these traditional methods for enantioselective TAGs analysis (actually of the produced MAGs and DAGs, often investigated as target species per se) was the difficulty to totally abolish the migration of fatty acyls between glycerol positions. This made difficult to control and keep unaltered the stereochemistry of the original molecules. Over the last two decades, it has been widely demonstrated that the enantioselective analysis of intact TAGs as well as of non-derivatized MAGs and DAGs can be efficiently obtained using polysaccharide-based CSPs incorporating either amylose- or cellulose-phenylcarbamate derivatives chiral selectors. In this paper, the enantioselective methods developed with these CSPs for the enantioselective direct LC analysis of MAGs, DAGs and TAGs embedding different types of fatty acid residues are comprehensively reviewed.

Separation of triacylglycerols containing positional isomers of hexadecenoic acids by enantiomeric liquid chromatography-mass spectrometry

Triacylglycerols (TAGs) containing positional isomers of hypogeic (Hy), palmitoleic (Po), and palmitvaccenic (Pv) acids from three microorganisms (top-fermenting brewer's yeast Saccharomyces cerevisiae, green alga Coccomyxa elongata, and arbuscular mycorrhizal (AM) fungus Rhizophagus irregularis) were analyzed. Dozens of regioisomers and enantiomers of TAGs containing one, two or three hexadecenoic acids have been identified by means of reversed phase chromatography/mass spectrometry (RP-HPLC/MS). The regioisomers of TAGs containing two palmitic acids and any hexadecenoic acid were separated. Analysis of regioisomers of TAGs having one Pv residue showed that asymmetric molecular species such as PvPP or PPPv were dominant in Rhizophagus. TAGs were also analyzed on a chiral phase column and nine molecular species of TAGs containing two palmitic and any of three hexadecenoic acids were separated and identified. In the case of TAGs containing one palmitic and two hexadecenoic acids, the separation was successful only if the hexadecenoic acids were identical. Separation of TAGs containing three hexadecenoic acids was successful only if all three hexadecenoic acids were identical. Regardless of the type of TAG, it was found that TAGs in the AM fungus and containing palmitvaccenic acid bound at the sn-1 position of the glycerol backbone were dominant, suggesting similarity in the biosynthesis of the different TAGs. The covalent adduct chemical ionization method was used for identification of TAGs as adduct with (1-methyleneimino)-1-ethenyl ion, which reacted with double bond of the unsaturated fatty acid. Tandem MS thus makes it possible to identify TAGs containing various hexadecenoic acids.

Structural Characterization of Mono- and Dimethylphosphatidylethanolamines from Various Organisms Using a Complex Analytical Strategy Including Chiral Chromatography

Two minor phospholipids, i.e., mono- and/or dimethylphosphatidylethanolamines, are widespread in many organisms, from bacteria to higher plants and animals. A molecular mixture of methyl-PE and dimethyl-PE was obtained from total lipids by liquid chromatography and further identified by mass spectrometry. Total methyl-PE and dimethyl-PE were cleaved by phospholipase C, and the resulting diacylglycerols, in the form of acetyl derivatives, were separated into alkyl-acyl, alkenyl-acyl, and diacylglycerols. Reversed-phase LC/MS allowed dozens of molecular species to be identified and further analyzed. This was performed on a chiral column, and identification by tandem positive ESI revealed that diacyl derivatives from all four bacteria were mixtures of both R and S enantiomers. The same applied to alkenyl-acyl derivatives of anaerobic bacteria. Analysis thus confirmed that some bacteria biosynthesize phospholipids having both sn-glycerol-3-phosphate and sn-glycerol-1-phosphate as precursors. These findings were further supported by data already published in GenBank. The use of chiral chromatography made it possible to prove that both enantiomers of glycerol phosphate of some molecular species of mono- and dimethylphosphatidylethanolamines are present. The result of the analysis can be interpreted that the cultured bacteria do not have homochiral membranes but, on the contrary, have an asymmetric, i.e., heterochiral membranes.

Shotgun Lipidomic Analysis for Differentiation of Niche Cold Pressed Oils

The fast-growing food industry is bringing significant number of new products to the market. To protect consumers’ health and rights, it is crucial that food control laboratories are able to ensure reliable quality testing, including product authentication and detection of adulterations. In our study, we applied a fast and eco-friendly method based on shotgun-lipidomic mass spectrometry for the authentication of niche edible oils. Comprehensive lipid profiles of camelina (CA), flax (FL) and hemp (HP) seed oils were obtained. With the aid of principal component analysis (PCA), it was possible to detect and distinguish each of them based on their lipid profiles. Lipidomic markers characteristic ofthe oils were also identified, which can be used as targets and expedite development of new multiplexed testing methods.

Regio- and Stereospecific Analysis of Triacylglycerols—A Brief Overview of the Challenges and the Achievements

The efforts to reveal, in detail, the molecular and intramolecular structures of one of the main lipid classes, namely, triacyl-sn-glycerols, which are now known to affect their specific and important role in all living organisms, are briefly overviewed. Some milestones of significance in the gradual but continuous development and improvement of the analytical methodology to identify the triacylglycerol regio- and stereoisomers in complex lipid samples are traced throughout the years: the use of chromatography based on different separation principles; the improvements in the chromatographic technique; the development and use of different detection techniques; the attempts to simplify and automatize the analysis without losing the accuracy of identification. The spectacular recent achievements of two- and multidimensional methods used as tools in lipidomics are presented.

Detailed structural characterization of cardiolipins from various biological sources using a complex analytical strategy comprising fractionation, hydrolysis and chiral chromatography

Cardiolipins (1,3-bis(sn-3'-phosphatidyl)-sn-glycerol) (CLs) are widespread in many organisms, from bacteria to higher green plants and mammals. CLs were observed in Gram-positive bacterium of the genus Kocuria, brewer's yeast Saccharomyces, the green alga Chlamydomonas, spinach and beef heart. A mixture of molecular species of CLs was obtained from total lipids by hydrophilic interaction liquid chromatography (HILIC), and these were further separated and identified by reversed phase LC/MS with negative tandem electrospray ionization. The majority of CLs molecular species from each organism were cleaved using phospholipase C from Bacillus cereus. This phospholipase cleaves CLs into 1,2-diglycerols and phosphatidylglycerol 3-phosphates, which were then separated. After CLs cleavage, diacylglycerols such as sn-1,2-diacyl-3-acetyl-glycerols (i.e., triacylglycerols) were separated and identified by chiral chromatography/MS-positive tandem ESI. Significant differences in the composition of the molecular species between the 3-(3-sn-phosphatidyl) and 1-(3-sn-phosphatidyl) moieties of CLs were found in all organisms tested. Molecular species of CLs that contained four different fatty acids were identified in all five samples, and CLs containing very long chain fatty acids were identified in yeast. In addition, CLs containing both enantiomers (at the sn-2 carbon) were present in the bacterium tested. These findings were further supported by data already published in GenBank where, in the same family - Micrococcaceae - both enzymes responsible for chirality in the sn-2 position, glycerol-3-phosphate and glycerol-1-phosphate dehydrogenases, were present.