Location of deep‐sea shark (Centrophorus squamosus) glycerol ether lipid double bonds by nitric oxide chemical ionization mass spectrometry

Abstract

Chemical ionization mass spectrometry with nitric oxide as the reactant gas has proved to be an efficient tool for locating the double bond in monoalkenylglycerols of type HO-CH 2 -CHOH-CH 2 -O-(CH 2 ) n-1 -CH=CH-(CH 2 ) n-2 -CH 3 . These monoalkenylglycerols were extracted from the liver oil of the shark Centrophorus squamosus, which lives at depths ranging from 1000 m and deeper. The presence of characteristic acylium ions R 1 CO + and/or R 2 CO + allowed location of the double-bond position. JAOCS 74, 923-926 (1997). KEY WORDS:Characteristic acylium ions, chemical ionization with NO + , ether di-O-methylglycerols, gas chromatography/mass spectrometry, Glycerol ethers, hexadec-9-enylglycerol, liver oil of shark Centrophorus squamosus, location of double bond in monoalkenylglycerols, octadec-9-enylglycerol, selachyl alcohol. (1), Einhorn (2-4), and Budzikiewicz (5,6) on the reaction of NO + with olefins, chemical ionization nitric oxide mass spectrometry (CI/NO + /MS) was used for locating double bonds in aliphatic compounds. The purpose of this study was to examine the possible application of CI/NO + /MS for double-bond location in 1-O-monoalkenylglycerols isolated from the liver oil of the shark Centrophorus squamosus, which are glycerol ether lipids as shown in Scheme 1. Subsequent to studies by Hunt and HarveyWe recently reported (7) the characterization of fatty acid methyl esters from this liver oil by gas chromatography-mass spectrometry (GC-MS), and the purification of two of them, namely docosahexaenoic acid (DHA or 22:6) and docosamonoenoic acid (DMA or 22:1), by countercurrent chromatography. We then directed our investigations to the unsaponifiable complementary fraction, more particularly to the glycerol ether fraction (8), because of its potential applications in industry.The unsaponifiable matter of this liver oil contains glycerol ethers in addition to squalene. These molecules exhibit bacteriostatic (9) and antiinflammatory properties (10) and hemopoietic effects (11,12); they are also believed to protect against radiation damage (13) and possess antitumor properties (14).Electronic impact (EI) of pure NO in a conventional CI source produces NO + in good yield with lesser amounts of the dimeric ion (NO) 2 +• . In general, three alternative reaction channels (15) are observed and give (M + NO) + , (M − H) + , and M +• ions.Apparently two distinct processes may occur (3,4):Step 1: oxidative cleavage of the double bond and neutral-neutral reaction catalyzed by the source surface : [1] which may be followed by Step 2: hydride ion abstraction, classically observed with NO as reactant gas: [2] The ions R 1 CO + and/or R 2 CO + are acylium diagnostic ions. The most important prerequisites for the formation of these acylium ions are a low ion-source temperature (16) and a small amount of sample at the given NO pressure (3,4). EXPERIMENTAL PROCEDURESShark liver oil was obtained from IS-France Company (Lorient, France). By a procedure already described (8), the oil was saponified and esterified with BF 3 ...

Fatty acids, fatty acid analogues and their derivatives

“…465,466 Chemical ionization mass spectrometry with nitric oxide as the reactant gas has been used for the determination of the position of the double bond in monoalkenylglycerols isolated from the liver oil of the shark Centrophorus squamosus. 467 Mass spectrometric analysis of triacylglycerols using negativeion chemical ionization with ammonia was found to be a rapid method for the semiquantitative determination of triacylglycerol mixtures of various fats and oils. 468 A useful method for the identification of fatty acid hydroperoxides by electrospray ionization-tandem mass spectrometry has been described.…”