Mass Spectrometry of 3-Pyridylcarbinol Esters
Dicarboxylic Fatty Acids
Dicarboxylic fatty acids are not often present as such in nature, although they are occasionally found in plants and especially in the suberin in plant cuticles. For example, they are major components of cork, i.e., a product of the outer layer of the bark of the cork oak (Quercus suber). Short-chain dicarboxylic acids may be encountered in the oxidative degradation of lipids, but that utilized for the mass spectra of the 3‑pyridylcarbinol ester discussed here is of a commercial standard. Spectra for methyl esters and DMOX derivatives with pyrrolidides for a much wider range of such fatty acids are described in separate documents.
Di-3-pyridylcarbinol ('picolinyl') esters are probably not the best for mass spectrometry of these fatty acids, as the additional molecular weight and polarity increases the difficulties for gas chromatography in that relatively high column temperatures are required. Harvey (1984) has discussed the mass spectrum of di‑(3‑pyridylcarbinyl)-1,12-dodecanedioate, but this appears to be the only one to have been published elsewhere.
In contrast to methyl esters, the mass spectra of 3-pyridylcarbinol esters of saturated dicarboxylic acids have good molecular ions, although the rest of the spectra are relatively uninteresting, since they are dominated by ions related to the pyridine ring. The mass spectrum of di‑(3‑pyridylcarbinyl) 1,9‑nonanedioate (azeleate) is -
Because of having two nitrogen atoms, the molecular ion is now even numbered (as are those from all the widely used nitrogen-containing derivatives of these fatty acids). In the low molecular mass range, the main ions are at m/z = 92, 108, 151 and 164 (see the web page on 3‑pyridylcarbinol esters of saturated fatty acids for interpretation). At higher masses, the related ions representing [M‑108]+, [M‑150/1]+ and [M‑164]+, i.e., in this instance at m/z = 262, 220 and 206, respectively, are most abundant.
The mass spectra of 3-pyridylcarbinol esters of two more dicarboxylic acids are available in an Archive section of these web page but without interpretation.
References
- Harvey, D.J. Picolinyl derivatives for the structural determination of fatty acids by mass spectrometry. Applications to polyenoic acids, hydroxy acids, di-acids and related compounds. Biomed. Mass Spectrom., 11, 340-347 (1984); DOI.
| © Author: William W. Christie |  |
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