Mass spectra f fatty alchls. Part 1. ictinate derivatives. MASS SPECTRA OF FATTY ALCOHOLS Part 1. ictinate Derivatives Fatty alchls can be characterized by GC-MS mst readily as the nictinate derivatives, first described by Vetter and Meister (1981). These are structurally analgus t 3-pyridylcarbinl esters and fragment in much the same way. Indeed, with alkyl mieties f the same basic structure, nictinates and 3-pyridylcarbinl esters have identical mlecular weights. The tw mst abundant ins at = 7 and crrespnd t fragmentatin at the carbxyl miety. Thereafter, interpretatin f spectra is very similar t that fr 3-pyridylcarbinl esters. ictinates are als very useful fr structural determinatin f diacylglycerls and related lipids. a 7 a D.J. Harvey was respnsible fr much f the early wrk n nictinates, and his review article is mst valuable (Harvey, 1992). The preparatin prcedure used in ur labratry is described belw. The mass spectra f the nictinates f fatty alchls illustrated belw were btained in a study f fish waxes (Jh et al., 1995). Saturated and Branched-Chain Fatty Alchls The mass spectrum f the nictinate derivative f hexadecanl is illustrated first 7 69 78 192 262 4 137 164 178 6 234 248 276 318 332 347 1 1 1 1 2 2 2 2 3 As with 3-pyridylcarbinl esters, interpretatin is easiest if we start with the mlecular in and wrk backwards (see the web pages n 3-Pyridylcarbinl esters f saturated and branched-chain fatty acids ). There is a gap f 15 amu fr lss f the terminal methyl grup t = 332, and then a series f ins 14 amu apart fr fragmentatins at successive methylene grups, until the characteristic ins at = and 7 are reached. W.W. Christie lipidlibrary.acs.rg 1
Mass spectra f fatty alchls. Part 1. ictinate derivatives. The same features are seen in the mass spectrum f the nictinate derivative f ctadecanl - 7 151 165 1926 2 248 262 2 4 318 346 375 3 1 1 1 1 2 2 2 2 3 3 3 Branched fatty alchls can als be identified by this means in a similar manner t 3- pyridylcarbinl esters, thus in the spectrum f the nictinate derivative f 14-methyl-hexadecanl (anteis-) 332 4 7 4 77 137 164 183 193 2 262 276 332 2 346 234 361 1 1 1 1 2 2 2 2 3 3 - the gap f 28 amu between = 4 and 332 reflects cleavage n either side f the carbn carrying the methyl grup. As might be expected, this gap is shifted t between = 318 and 346 in the spectrum f the is-ismer (15-methyl-hexadecanl) next 318 346 78 69 7 318 151 178 2 234 262 2 4 192 248 346 361 1 1 1 1 2 2 2 2 3 3 W.W. Christie lipidlibrary.acs.rg 2
Mass spectra f fatty alchls. Part 1. ictinate derivatives. Mnenic Fatty Alchls The mass spectrum f the nictinate derivative f ctadec-9-en-1-l fllws 234 2 373 7 288 274 178 151 164 6 2 2 234 2 3163 358 1 1 1 1 2 2 2 2 3 3 3 Again, the spectrum resembles that fr a 3-pyridylcarbinl ester (see the web pages n 3-Pyridylcarbinl esters f mnenic fatty acids ). The duble bnd is lcated by the gap f 28 amu between = 234 and 2, while the dublet at = 274 and 288 are invaluable guides (identical ins are present in the spectrum f 3-pyridylcarbinyl leate). The mass spectrum f the nictinate derivative f ctadec-11-en-1-l 288 262 373 7 2 316 192 6 288 3 2 248 151165 262 358 1 1 1 1 2 2 2 2 3 3 3 Here, the diagnstic ins are shifted upwards by 28 amu, i.e. fr the duble bnd t between = 262 and 288, with the dublet at = 392 and 316. A further shift upwards f 28 amu fr the diagnstic ins is then seen in the spectrum f the nictinate f eics-13-en-1-l (ver page) - W.W. Christie lipidlibrary.acs.rg 3
Mass spectra f fatty alchls. Part 1. ictinate derivatives. 316 2 78 7 151 344 3 2 178 234248 276 316 358 192 2 372 1 1 2 3 Di- and Plyenic Fatty Alchls The spectra reprted here were frm the first definitive finding f such fatty alchls in a fish il (Jh et al. (1995)). The mass spectrum f the nictinate derivative f ctadeca-9,12-dien-1-l (the analgue f linleic acid) is - 234 274 2 67 6 371 151 164 178 2 6 234 2 274 314 328 1 1 1 1 2 2 2 2 3 3 The duble bnds in psitins 9 and 12 can be lcated by the gaps f 26 amu between = 234 and 2, and 274 and, respectively. On the ther hand, the limited infrmatin available suggests that a gap f 12 amu, analgus t that fund with DMOX derivatives may be mre useful with nictinates, i.e. frm = 234 t 246, and 274 t 286, respectively. W.W. Christie lipidlibrary.acs.rg 4
Mass spectra f fatty alchls. Part 1. ictinate derivatives. In the mass spectrum f the nictinate derivative f ctadeca-11,14-dien-1-l, the diagnstic ins are again shifted upwards by 28 amu frm the previus example. 288 328 262 2 371 67 6 288 192 6 2 342 2 248 328 151165 262 356 1 1 1 1 2 2 2 2 3 3 The mass spectrum f the nictinate derivative f eics-5,8,11,14,17-pentaen-1-l 284 364 91 6 324 175 145 284 324 393 2 232 258 338 364 378 1 1 1 1 2 2 2 2 3 3 3 Here, nly the terminal duble bnds can be lcated with cnfidence, and these by the gaps f amu fr the methylene grups fllwed by the duble bnd, i.e. frm = 284 t 324, and 324 t 364, fr the duble bnds in psitins 14 and 17 respectively. The mass spectrum f the nictinate derivative f dcs-7,,13,16,19-pentaen-1-l 67 91 7 272 312 352 392 133 159 175 215 247 272 312 338 352 392 421 1 2 3 W.W. Christie lipidlibrary.acs.rg 5
Mass spectra f fatty alchls. Part 1. ictinate derivatives. Again, the duble bnds in psitins 13, 16 and 19 nly can be lcated frm the gaps f amu between = 272 and 312, 312 and 352, and 352 and 392 respectively. There has been a suggestin in the literature that rather than preparing 3-pyridylcarbinl esters f fatty acids fr structural analysis, better results might be btained by reducing them t the aliphatic alchls and then preparing nictinates fr mass spectrmetry. Frm my admittedly limited experience f nictinates relative t piclinyl esters, I have t disagree. Alkan-2-ls Frm the limited number f mass spectra available t us, thse f nictinates f alkan-2-ls are almst indistinguishable in terms f which ins are frmed frm thse f alkan-1-ls. Fr example, the mass spectrum f the nictinate f hexadecan-2-l is illustrated next CH 3 COOCH 6 78 69 135 151 192 6 234 262 248 276 4 318 332 347 1 1 1 1 2 2 2 2 3 Essentially the same ins are present in the spectra f bth ismers, but their relative abundances in the spectrum f the 2-alkanl derivative are lwer in the high mass range. In cntrast, 1- and 2- alkanls are readily distinguishable as the trimethylsilyl ether derivatives (see the apprpriate web page). Diacylglycerls Derived frm Phsphlipids A cmmn apprach t the analysis f phsphlipids cnsists in enzymatic hydrlysis t the diacylglycerls fllwed by cnversin t UV-absrbing derivatives fr separatin by liquid chrmatgraphy. While mst such derivatives ffer little useful structural infrmatin when subjected t mass spectrmetry, nictinates are an imprtant exceptin. t nly d they permit identificatin f which fatty acid is esterified t each psitin, but they allw lcatin f the duble bnds in the fatty acyl chains. Separatins can als be mnitred by UV absrptin. The fllwing spectra were btained by separatin f mlecular species by reversed-phase HPLC n a basedeactivated ODS clumn, with particle-beam electrn-impact mass spectrmetry (Dbsn et al., 1998). The spectra belw have been adapted frm this paper, where much mre detailed interpretatin is ffered than is apprpriate here. W.W. Christie lipidlibrary.acs.rg 6
Mass spectra f fatty alchls. Part 1. ictinate derivatives. Fr example, the mass spectrum f the nictinate derivative f 1,2-dilein is illustrated first - 3 572 626 612 725 H C OOC 6 462 x3 626 164 1 339 393 444 3 572 612 682 1 2 3 4 5 6 There is an abundant mlecular in, tgether with the ins at = 6/7 and fr fragmentatins at the nictinyl miety. Ins at = 444 ([M-RCOO] + ) and 462 ([M-RCO+2] + ) establish the size f the acyl mieties. The distinctive fragments shwn serve t lcate the duble bnds in the chain. It is ntewrthy that there is n dubiety abut the mlecular in. ext fllw the mass spectra f the nictinate derivatives f bth 1-palmityl-2-leyl-glycerl and 1-leyl-2-palmityl-glycerl 3 544 699 H C OOC 4 546 436 x 5 6 166 198 3 4 444 418 461 239 313 339 576 614 544/6 656 1 2 3 4 5 6 491 546 699 6 166 H 198 C OOC 239 3 544 313 339 461 3 576 436 491 614 418 533 544/6 444 1 2 3 4 5 6 x 5 656 W.W. Christie lipidlibrary.acs.rg 7
Mass spectra f fatty alchls. Part 1. ictinate derivatives. The spectra are qualitatively similar, but differ in the relative abundance f specific ins that serve t determine the nature f the acyl-chains, specifically at = 436 (M-RCO+2), and 461 (M-R CO+1; nt at = 462 as fr dilein). Mass spectrum f nictinate derivative f 1,2-palmityl/linleyl-glycerl, in which the reverse ismers may be present, althugh nly ne frmula is illustrated - 6 1 514 H C OOC 4 542 546 598 626 626 6 436 x 7 697 574 198 1 598 514 6 164 459 418 4 546 626 239 313 442 542 337 1 2 3 4 5 6 668 - and lastly, this may be true als fr the nictinate f 1,2-linleyl/linlenyl-glycerl - 499 512 568 8 622 662 648 H C OOC 719 6 C OOCH 2 1 514 5 6 624 6 663 x 7 6 4 8/ 648/ 164 198 335/7 4/2 458/ 512/4 499/ 527 1 568 596 663 6 4 1 2 3 4 5 6 Preparatin f ictinates The fllwing methd was used t prepare the nictinate derivatives fr the abve spectra (Dbsn et al. (1998)). It was adapted frm a prcedure by Zllner and Schmid (1996). Prtcl: At ºC,, -dicyclhexylcarbdiimide (Cautin carcingenic!) ( mg) was added t a slutin f fatty alchls (up t 2 mg), nictinic acid ( mg) and 4- dimethylaminpyridine (2 mg) in dichlrmethane (3 ml). After 5 minutes, the mixture was allwed t warm t rm temperature and left vernight. Hexane (2 ml) was then added and the prduct filtered thrugh a cttn wl plug pre-washed with hexane. After taking t dryness, the prduct was purified by slid-phase extractin thrugh a bnded H 2 clumn. After pre-washing the clumn with hexane, the prduct was applied in hexane and washed with hexane (8 ml). The required prduct was recvered by elutin with hexane-acetne (95:5, v/v; ml). W.W. Christie lipidlibrary.acs.rg 8
Mass spectra f fatty alchls. Part 1. ictinate derivatives. We have sme spectra f further nictinate derivatives f fatty alchls n file in ur Archive pages, but withut interpretatin. References Dbsn, G., Itabashi, Y., Christie, W.W. and Rbertsn, G.W. Liquid chrmatgraphy with particle-beam electrn-impact mass spectrmetry f diacylglycerl nictinates. Chem. Phys. Lipids, 97, 27-39 (1998). Harvey, D.J. Mass spectrmetry f piclinyl and ther nitrgen-cntaining derivatives f lipids. In: 'Advances in Lipid Methdlgy - One', pp. 19- (edited by W.W. Christie, Oily Press, Ayr) (1992). Jh, Y.-G., Brechany, E.Y. and Christie, W.W. Characterizatin f wax esters in the re il f the amber fish Serila aurevittata, by silver in high-perfrmance liquid chrmatgraphy. J. Am. Oil Chem. Sc., 72, 7-713 (1995). Vetter, W. and Meister, W. ictinates as derivatives fr the mass spectrmetry investigatin f lng chain alchls. Org. Mass Spectrm., 16, 118-122 (1981) Zllner, P. and Schmid, R. Utility f nictinyl derivatives in structural studies f mn- and diacylglycerls by GC/MS. Part 3. Applicatin t acylglycerls with methyl branchings and epxy and cyclprpyl rings. J. Mass Spectrm., 31, 411-417 (1996). William W. Christie James Huttn Institute (and Mylnefield Lipid Analysis), Invergwrie, Dundee (DD2 5DA), Sctland Last updated: September 2 nd, 13 W.W. Christie lipidlibrary.acs.rg 9