Journal article
Structural analysis of phosphatidylcholines by post-source decay matrix-assisted laser desorption/ionization time-of-flight mass spectrometry
Journal of the American Society for Mass Spectrometry, Vol.14(4), pp.373-382
04/2003
Handle:
https://hdl.handle.net/2376/114432
PMID: 12686484
Abstract
The utility of post-source decay (PSD) matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was investigated for the structural analysis of phosphatidylcholine (PC). PC did not produce detectable negative molecular ion from MALDI, but positive ions were observed as both [PC+H](+) and [PC+Na](+). The PSD spectra of the protonated PC species contained only one fragment corresponding to the head group (m/z 184), while the sodiated precursors produced many fragment ions, including those derived from the loss of fatty acids. The loss of fatty acid from the C-1 position (sn-1) of the glycerol backbone was favored over the loss of fatty acid from the C-2 position (sn-2). Ions emanating from the fragmentation of the head group (phosphocholine) included [PC+Na-59](+), [PC+Na-183](+) and [PC+Na-205](+), which corresponded to the loss of trimethylamine (TMA), non-sodiated choline phosphate and sodiated choline phosphate, respectively. Other fragments reflecting the structure of the head group were observed at m/z 183, 146 and 86. The difference in the fragmentation patterns for the PSD of [PC+Na](+) compared to [PC+H](+) is attributed to difference in the binding of Na(+) and H(+). While the proton binds to a negatively charged oxygen of the phosphate group, the sodium ion can be associated with several regions of the PC molecule. Hence, in the sodiated PC, intermolecular interaction of the negatively charged oxygen of the phosphate group, along with sodium association at multiple sites, can lead to a complex and characteristic ion fragmentation pattern. The preferential loss of sn-1 fatty acid group could be explained by the formation of an energetically favorable six-member ring intermediate, as apposed to the five-member ring intermediate formed prior to the loss of sn-2 fatty acid group.
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Details
- Title
- Structural analysis of phosphatidylcholines by post-source decay matrix-assisted laser desorption/ionization time-of-flight mass spectrometry
- Creators
- Khalid A Al-Saad - Department of Chemistry, Washington State University, Pullman, USAWilliam F SiemsH H HillVladimir ZabrouskovN Richard Knowles
- Publication Details
- Journal of the American Society for Mass Spectrometry, Vol.14(4), pp.373-382
- Academic Unit
- Chemistry, Department of
- Publisher
- United States
- Identifiers
- 99900548267801842
- Language
- English
- Resource Type
- Journal article