MASS SPECTRA OF 3-PYRIDYLCARBIOL ESTERS Part 3. Dienic Fatty Acids This sectin describes mass spectra f 3-pyridylcarbinl ester derivatives under the headings Methylene-interrupted dienic fatty acids Cnjugated dienic fatty acids Bis-methylene-interrupted dienic fatty acids Plymethylene-interrupted dienic fatty acids Here, the electrn-impact mass spectra f 3-pyridylcarbinl esters f thse dienic acids that are mst likely t be encuntered in nature, tgether with sme useful mdel cmpunds, are described. The widely used term 'piclinyl ester' is inaccurate and shuld nw be avided see ur webpage n the saturated derivatives). There is a separate dcument dealing with Mass spectrmetry f allenic fatty acids. Methylene-Interrupted Dienic Fatty Acids The mass spectra f 3-pyridylcarbinl esters f dienic fatty acids, like thse f mnenes, tend t be distinctive and permit lcatin f the duble bnd. As an example, the mass spectrum f 3-pyridylcarbinyl 9,12-ctadecadienate (linleate r 18:2(n-6)), the mst imprtant dienic fatty acid in nature, is illustrated belw (Harvey, 1982) - 2 2 0 234 8 2 6 2 0 123 234 0 1 1 1 1 0 2 2 2 2 0 3 3 As with 3-pyridylcarbinl esters f saturated and mnenic fatty acids, interpretatin is easiest if we start with the mlecular in and wrk dwn the chain. Ins crrespnding t cleavage n either side f the terminal duble bnd are seen at = 0 and (26 amu apart), there is then a gap f 14 amu t = 2, then ne f 26 amu fr the internal duble bnd t = 234. When examining the spectra f unknwns, hwever, it is ften easier t lcate gaps f amu fr the duble bnd and the assciated methylene grup n the carbxyl side, i.e. in this instance between = 0 and 2, and between 2 and 2. Regular series f ins 14 amu apart n either side f the duble bnd cnfirm that there are n further functinal grups in these regins f the mlecule. W.W. Christie lipidlibrary.acs.rg 1
Similar series f ins are seen in spectra frm 3-pyridylcarbinl esters f mst methyleneinterrupted dienes, but it is advantageus t have access t spectra f authentic standards when the duble bnds are clse t either end f the mlecule when cnfusin is mst likely t arise. Details f the spectra f the cmplete series f ismeric methylene-interrupted ctadecadienates have been published (Christie, Brechany and Hlman, 1987a), but nly a few f the spectra were depicted in the paper fr practical reasns. All are nw illustrated belw, but please cnsult the riginal reference fr tabulated data. Sme f these may nt ccur in nature, but a surprising number d. Spectra f ther hmlgus fatty acid ismers displaying the same diagnstic features may have been described elsewhere. Spectra fr the cmplete C 18 series fllw. 3-Pyridylcarbinyl 2,5-ctadecadienate (2,5-18:2) (Christie et al., 1987a) - 214 2 8 2 214 1 244 258 0 342 0 1 1 1 1 0 2 2 2 2 0 3 3 The mlecular in is the base peak, presumably because f the duble bnd in cnjugatin with the carbxyl grup. Ins that identify the psitin f the duble bnd are nt apparent, but the dublet f ins at = 214 and 2 are a useful indicatr (see the web pages n 3- pyridylcarbinl esters f mnenes). The regular series f ins 14 amu apart between = 214 and the mlecular in cnfirm that there are n functinal grups in this part f the alkyl chain. 3-Pyridylcarbinyl 3,6-ctadecadienate (3,6-18:2) - 93 177 1 216 244 2 8 1 65 216 244 121 177 2 4 258 288 0 342 0 1 1 1 1 0 2 2 2 2 0 3 3 In this spectrum, the gaps f 26 amu between = and 177, and 1 and 216 serve t lcate the duble bnds in psitins 3 and 6, respectively. W.W. Christie lipidlibrary.acs.rg 2
3-Pyridylcarbinyl 4,7-ctadecadienate (4,7-18:2). Sme f the marked ins that lcate the duble bnds wuld be difficult t identify frm first principles, s a mdel spectrum is essential. 8 191 4 2 244 258 65 258 121 4 244 191 2 0 0 1 1 1 1 0 2 2 2 2 0 3 3 3-Pyridylcarbinyl 5,8-ctadecadienate (5,8-18:2) this fatty acid is a majr cmpnent f human sebum lipids. As the distance f duble bnds frm the carbxyl grup increases, the expected fragmentatin patterns fr the duble bnds emerge as marked. 93 4 244 8 4 0 1 1 1 1 0 2 2 2 2 0 3 3 244 258 272 0 316 3-Pyridylcarbinyl 6,9-ctadecadienate (6,9-18:2). Here, and with many f the subsequent spectra in this series, the duble bnds are easily lcated. 258 1 8 272 1 258 0 0 1 1 1 1 0 2 2 2 2 0 3 3 W.W. Christie lipidlibrary.acs.rg 3
3-Pyridylcarbinyl 7,-ctadecadienate (7,-18:2). 6 272 8 1 6 0 1 1 1 1 0 2 2 2 2 0 3 3 272 0 3-Pyridylcarbinyl 8,11-ctadecadienate (8,11-18:2) - 2 CH 2 OOC 2 8 0 2 62 0 1 1 1 1 0 2 2 2 2 0 3 3 3-Pyridylcarbinyl 9,12-ctadecadienate - see the start f this sectin. 3-Pyridylcarbinyl,13-ctadecadienate (,13-18:2) - 8 248 288 234 288 342 6 2 248 0 1 1 1 1 0 2 2 2 2 0 3 3 W.W. Christie lipidlibrary.acs.rg 4
3-Pyridylcarbinyl 11,14-ctadecadienate (11,14-18:2) (Christie et al.,1987a) - 8 6 2 248 262 262 288 288 2 2 342 0 1 1 1 1 0 2 2 2 2 0 3 3 3-Pyridylcarbinyl 12,15-ctadecadienate (12,15-18:2) - 2 342 276 316 8 2 6 2 248 262 276 316 342 0 1 1 1 1 0 2 2 2 2 0 3 3 3-Pyridylcarbinyl 13,16-ctadecadienate (13,16-18:2) - 8 2 316 3 316 123 62 234 262 276 2 3 0 1 1 1 1 0 2 2 2 2 0 3 3 W.W. Christie lipidlibrary.acs.rg 5
3-Pyridylcarbinyl 14,17-ctadecadienate (14,17-18:2). It is pssible even with this last f the ismers t lcate the duble bnds by the specific fragments marked, especially if we lk fr the gaps f amu as well as thse f 26 amu. 2 4 3 344 8 3 133 62 248 262 276 2 4 344 0 1 1 1 1 0 2 2 2 2 0 3 3 Spectra f 3-pyridylcarbinl esters f many mre methylene-interrupted dienic fatty acids f this type f differing chain lengths are illustrated in ur Archive sectin, but withut interpretatin. Many f these have nt been frmally published elsewhere. Cnjugated Dienic Fatty Acids 3-Pyridylcarbinl esters may nt be the best derivatives fr fatty acids with cnjugated duble bnd systems, and fr example, DMOX derivatives may be better in this instance (see Mass spectra f DMOX derivatives dienic fatty acids), r MTAD adducts f methyl esters are uniquely valuable (see Mass spectra f methyl esters f fatty acids. Part 6. Further derivatizatin), especially fr the cmplex mixtures fund in cmmercial cnjugated linleic acid (CLA) and sme natural samples. Hwever, 3-pyridylcarbinl esters can be useful if authentic standards are available fr cmparisn, especially when ismers are well reslved n the GC clumn. The mass spectrum f 3-Pyridylcarbinyl 9-cis,11-trans-ctadecadienate, the mst abundant natural ismer (e.g. in cws' milk fat), fllws - 2 234 8 123 62 0 234 262 0 1 1 1 1 0 2 2 2 2 0 3 3 W.W. Christie lipidlibrary.acs.rg 6
There is a gap f 52 amu between = 234 and at either end f the cnjugated duble bnd system, with intervals f 14 amu n either side fr cleavage at successive methylene grups. The mlecular in at = is the base peak. 3-Pyridylcarbinyl -trans,12-cis-ctadecadienate - 8 123 6 2 234 248 0 0 1 1 1 1 0 2 2 2 2 0 3 3 In this instance, the diagnstic ins are shifted up by 14 amu frm the previus spectrum, but nt very cnvincingly if a definitive identificatin were t be required. These spectra d nt appear t have been published frmally elsewhere. Bis-Methylene-Interrupted Dienic Fatty Acids It is becming apparent that bis- and plymethylene-interrupted dienic fatty acids are mre cmmn in nature than may have been suppsed. In particular, fatty acids with a 5,9-duble bnd system and their chain elngatin prducts are cmmn in seed ils frm Gymnsperms r in certain marine invertebrates such as spnges. The spectrum f 5,9-18:2 and f sme synthetic fatty acids with the bis-methylene-interrupted duble bnds (useful fr cnfirming fragmentatin mechanisms) fllw next (Christie et al., 1987b). 3-Pyridylcarbinyl 5,9-ctadecadienate (5,9-18:2) (Hierr et al., 1996) - 93 8 219 258 6 65 121 6 219 0 1 1 1 1 0 2 2 2 2 0 3 3 258 272 0 316 W.W. Christie lipidlibrary.acs.rg 7
The truly distinctive feature is the in at = 219 (unusual in being dd-numbered) representing cleavage at the centre f the bis-methylene-interrupted duble bnd system. In additin, gaps f 26 amu, between = and 6 and = and 258 help t lcate the duble bnds in psitins 5 and 9, respectively. 3-Pyridylcarbinyl 2,6-ctadecadienate (2,6-18:2) - 177 177 216 1 8 65 231 132 1 216 244258 0 1 1 1 1 0 2 2 2 2 0 3 3 In this spectrum (unpublished), the in at = 177 representing cleavage at the centre f the bismethylene-interrupted duble bnds is the base peak in fact. The expected in at = is missing, but the ins at = 1 and 216 lcate the duble bnd in psitin 6. 3-Pyridylcarbinyl 6,-ctadecadienate (6,-18:2) (Christie et al., 1987b) - 69 8 1 0 1 1 1 1 0 2 2 2 2 0 3 3 1 233 233 272 272 0 342 All the ins that lcate the duble bnds (marked) are easily lcated, and the same is true fr the 7,11-ismer (nt illustrated). It appears that ins diagnstic fr the psitins f the duble bnds becme easier t lcate as they mve further frm the carbxyl grup. With 3-pyridylcarbinyl 8,12-ctadecadienate (8,12-18:2) (ver page) (Christie et al, 1987b), the in representing cleavage at the centre f the bis-methylene-interrupted duble bnds is nw even numbered ( = 2). The same is true f the 9,13-ismer as in 3-pyridylcarbinyl 9,13- eicsadienate illustrated in the Archive pages f this website. W.W. Christie lipidlibrary.acs.rg 8
2 2 8 69 0 6 2 0 1 1 1 1 0 2 2 2 2 0 3 3 Spectra f 3-pyridylcarbinl esters f many mre bis-methylene-interrupted dienic fatty acids are illustrated in ur Archive sectin, but withut interpretatin. Many f these have nt been frmally published elsewhere. Ply-Methylene-Interrupted Dienic Fatty Acids Fatty acids with mre than tw methylene grups between duble bnds are perhaps less cmmn in nature than bis-methylene-interrupted ismers, but sme examples f mass spectra f 3-pyridylcarbinl esters f synthetic and natural fatty acids f this type are illustrated belw. Spectra frm tw synthetic fatty acids are available (Christie et al.,1987b), and the first f these has been fund naturally in a spnge (Carballeira and Maldna, 1989). 3-Pyridylcarbinyl 6,11-ctadecadienate (6,11-18:2) has three methylene grups between the duble bnds- 8 1 233 2 1 0 1 1 1 1 0 2 2 2 2 0 3 3 233 2 0 There are prminent ins fr cleavages between the duble bnds, i.e. at = 233 and (ne dd-numbered), and the duble bnds themselves can be lcated by the usual means as marked. W.W. Christie lipidlibrary.acs.rg 9
3-Pyridylcarbinyl 7,12-ctadecadienate (7,12-18:2) - 2 247 2 8 247 121 1 6 0 342 0 1 1 1 1 0 2 2 2 2 0 3 3 3 The spectrum is very similar t the previus, except that the key ins are all shifted by 14 amu upwards, as might be expected. 3-Pyridylcarbinyl 5,11-ctadecadienate (5,11-18:2) has fur methylene grups between the duble bnds and is present in the seeds f Gingk bilba. Its mass spectrum has been published (Wlff et al., 1999)) - 93 2 8 4 4 0 1 1 1 1 0 2 2 2 2 0 3 3 2 0 342 In this instance, the duble bnds are lcated in the same way as fr islated mnenes, with that fr psitin 5 being determined by the gap f 26 amu between = and 4, and fr psitin 11 by that between = 2 and. Direct cmparisn with the mass spectrum f 5-18:1 is invaluable here, fr cnfirmatin f the psitin f the first duble bnd. 3-Pyridylcarbinyl 5,11- eicsadienate has a very similar spectrum (see the Archive sectin). W.W. Christie lipidlibrary.acs.rg
3-Pyridylcarbinyl 6,12-ctadecadienate (6,12-18:2). This spectrum resembles that f the 5,11- ismer except that the diagnstic ins are all 14 amu higher. 8 1 0 1 1 1 1 0 2 2 2 2 0 3 3 2 0 3-Pyridylcarbinyl 5,13-eicsadienate - frm (Christie et al., 1988). As with the previus, interpretatin f the spectrum is similar t thse f islated mnenes, and this is als true f the next spectrum. 219 288 8 399 342 2 219 288 383 0 1 1 1 1 0 2 2 2 2 0 3 3 3 3 3-Pyridylcarbinyl 9,19-hexacsadienate (9,19-26:2) (Christie et al., 19)) - 2 398 234 372 8 288 2 358 6 234 2 2 133 344 372 412 426 398 454 0 1 0 2 0 3 0 4 483 W.W. Christie lipidlibrary.acs.rg 11
My clleagues and I have encuntered a few lng-chain fatty acids with mre than fur (six) methylene grups between duble bnds and the last tw examples were frm marine invertebrates. Spectra f 3-pyridylcarbinl esters f many mre dienic fatty acids, including sme branchedchain ismers, are illustrated in ur Archive sectin, but withut interpretatin. Many f these have nt been published frmally elsewhere. References Carballeira,.M. and Maldna, M.E. On the islatin f the new fatty acid 6,11-eicsadienic (:2) and related 6,11-dienic acids frm the spnge Euryspngia rsea. Lipids, 24, 665-668 (1989). Christie, W.W., Brechany, E.Y. and Hlman, R.T. Mass spectra f the piclinyl esters f ismeric mnand dienic fatty acids. Lipids, 22, 224-228 (1987a). Christie, W.W., Brechany, E.Y., Gunstne, F.D., Lie Ken Jie, M.S.F. and Hlman, R.T. Mass spectra f the piclinyl esters f sme nn-methylene-interrupted ctadecadienic acids. Lipids, 22, 664-666 (1987b). Christie, W.W., Brechany,E.Y. and Stefanv, K. Silver in high-perfrmance liquid chrmatgraphy and gas chrmatgraphy-mass spectrmetry in the analysis f cmplex fatty acid mixtures: applicatin t marine invertebrates. Chem. Phys. Lipids, 46, 127-136 (1988). Christie, W.W., Brechany, E.Y., Stefanv, K. and Ppv, S. The fatty acids f the spnge Dysidea fragilis frm the Black Sea. Lipids, 27, 6-644 (19). Harvey, D.J. Piclinyl esters as derivatives fr the structural determinatin f lng chain branched and unsaturated fatty acids. Bimed. Mass Spectrm., 9, 33-38 (1982). Hierr, M.T.G., Rbertsn, G., Christie, W.W. and Jh, Y.-G. The fatty acid cmpsitin f the seeds f Ginkg bilba. J. Am. Oil Chem. Sc., 73, 575-579 (1996). Wlff, R.L., Christie, W.W. and Marpeau, A.M. Reinvestigatin f the plymethylene-interrupted 18:2 and :2 acids f Ginkg bilba seed lipids. J. Am. Oil Chem. Sc., 76, 273-276 (1999). William W. Christie James Huttn Institute (and Mylnefield Lipid Analysis), Invergwrie, Dundee (DD2 5DA), Sctland Last updated: August 7 th, 13 W.W. Christie lipidlibrary.acs.rg 12