Reative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by
Reative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).Molecules 2021, 26, 6468. https://doi.org/10.3390/moleculeshttps://www.mdpi.com/journal/moleculesMolecules 2021, 26,2 ofBesides electrospray ionization, atmospheric-pressure chemical ionization (APCI) can also be applied for localizing double bonds in HPLC/MS [183]. The approaches rely on PF-05105679 In Vitro acetonitrile-related reactive species formed in the ion sources. The use of even-electron (1-methyleneimino)-1-ethenylium as a reagent for derivatizing double bonds was initially developed for chemical ionization [247] and later applied in APCI-MS [18]. Utilizing helium as a nebulizing gas, C3 H4 N+ adducts ([M + 54]+ ) of triacylglycerols (TGs) were formed, and their CID spectra indicated the positions on the original double bonds [18]. Later, we showed that APCI sources operated under traditional situations with Guretolimod Cancer nitrogen nebulizing gas yield odd-electron C3 H5 N+adducts ([M + 55]+) [19]. The collision activation in the adducts induced cleavages of C bonds next towards the original double bond, top to pairs of diagnostic fragments indicating the double bond position. The advantage of this method lies in its simplicity: the only requirement for an HPLC/APCI-MS2 strategy will be the presence of acetonitrile in the mobile phase. The method has been applied for the structure elucidation of various unsaturated lipids, which includes FAMEs [20,28], hydroxy-FAMEs [23], wax esters [19], diol diesters [22], or TGs [21]. To date, only some solutions for figuring out the position of triple bonds in lipids have already been published [27,292]. Triple bonds in FAs might be pinpointed just after DMOX derivatization utilizing GC/MS [31]. Even though a conjugated method of double bonds manifests itself by a series of fragments differing by 12 Da, triple bond-related fragments differ by 10 Da. It allows for the structural characterization of conjugated ene ne acids. Nonetheless, the fragmentation of conjugated yne ne or yne ne ne bonds is a lot more complicated, as well as the spectra are tough to interpret [30]. Applying this strategy, many acetylenic lipids happen to be identified in plants [29,30,32]. The position of a triple bond may also be determined working with acetonitrile chemical ionization determined by (1-methyleneimino)-1-ethenylium adducts formation [27]. To the greatest of our knowledge, no system for localizing triple bonds applying HPLC/MS has appeared within the literature so far. Double bond positions in FAs reflect specificities of desaturases involved in their biosynthesis. Most monounsaturated FAs possess a double bond in 9-position. Other positions are also relatively typical, for instance, 7-position in algae, 5- and 10-positions in bacteria, or 6-position in plants [33]. Double bonds in polyunsaturated FAs are generally spaced by a single methylene group (methylene interrupted). FAs with double bonds separated by two or far more methylene units are identified, as an example, in marine sponges Microciona prolifera (FA 26:2n-17,21 and FA 26:3n-7,17,21) [34,35], Dysidea fragilis (FA 25:3n-8,16,20; FA 25:3n6,16,20; FA 24:3n-7,15,19 and FA 24:2n-7,17) [36], or Hymeniacidon sanguinea (e.g., FA 28:2n9,19,23; FA 26:2n-17,21; FA 26:3n-7,17,21; FA 24:2n-15,19 and FA 24:3n-7,15,19) [37]. A lot more than twenty various FAs with double bonds separated by two or a lot more methylene units have been identified within the gonads of limpets Cellana grata [38], Collisella dorsuosa [38], and Cellana toreum [39,40]. Unusual FAs with 24, 26, and 28 carbon atoms had been identified in TGs isolated in the f.
