Glycosphingolipids permethylated

Three types of carbohydrate sample have been reported to give data above mass 4000, namely, permethylated polysaccharides, permethylated glycosphingolipids, and naturally acylated forms of a mycobacterial O-methyl-D-glucose polysaccharide. All are hydrophobic, and desorption is probably facilitated by their inability to form strongly hydrogen-bonded aggregates, either with themselves or with the matrix. 

Fig. 11.—Sequence of a 2S-Sugar Residue Glycosphingolipid Isolated from Rabbit Erythrocyte Membranes. (Cleavage points, and the masses of fragment ions of the permethylated derivative, are shown. No fragment-ions were observed above 4000, because of the poor sensitivity at high mass.)...

Fig. 13.—Predicted Sequence of the Smith-Degradation Product of the Glycosphingolipid Shown in Fig. 12. (Predicted Fragment-ions for the permethylated derivative are shown.)...

In the polysaccharide and the glycoprotein series, permethylated derivatives are almost exclusively used for their solvolytic decomposition and for the analysis of the mono- and oligo-saccharides formed, whereas, in the glycosphingolipid series, the investigation of the permethylated derivatives themselves by physicochemical methods has acquired great importance. They proved to be very convenient both for mass-spectrometric analysis and for n.m.r. spectroscopy (see later). 

Direct probe mass spectrometry. Glycosphingolipids (30-100 pg) were permethylated as described (12). The samples (less than 5 p g) were subjected to electron impact/desorption analysis with a Varian MAT CH-5 DF mass spectrometer under the following conditions emission current, 300pA electron energy, 70 eV acceleration voltage, 3KV ion source temperature, 160° C emitter wire current, programed from 0 to 35mA. 

Figure 2. Mass spectra of the intact permethylated glycosphingolipids of fractions I (a), II (b), III (c), and IV (d). See Materials and Methods for conditions,...

ESI, like MALDI is compatible with negative- and positive-mode analyses and for analysis of native or permethylated neutral glycosphingolipids. The most abundant signal is also often the singly sodiated ion [M + Na]+. In-source fragmentation can be tuned by varying the ion source temperature and skimmer voltage. 

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