I had purify glucosinolates from seed of plant. But when i do NMR, the result showed impurities in 0-2.5 ppm. How can i solved this issue?
Dear Shazzy,
You need to give us some more details on how you isolated glucosinolates. Signals in the range that you mentioned are suggestive of some lipid impurity. For example, since you used seeds, these could be triacyl glycerols. You could easily get rid of them by extracting/washing your sample with hexane. Glucosinolates are highly polar and will not dissolve in hexane while the fatty impurities will. This is all I can help for now. Waiting for your additional info.
Best regards,
Niko
i useisolation method by Jessica barillari. i agreed that i dont defat the sample before purifying the crude extract.. the method is extracting the sample with boiling water, then sonicate. after that add zn acetate and centrifuge the sample to remove protein. The supernatant was taken. the deproteinised extract was concentrated with rotary evaporator and load on deae ephadex a-25. the elution was run with 0.1M K2S04.
The procedure appears to be fine and I would not expect any fatty contamination. What glucosinolate are you expecting to find? What was the solvent you used for NMR? D2O, CD3OD, CD3SOCD3 or some other? It would be nice if you could scan or attach in some electronic form the spectrum with the impurities visible.
i expect for benzyl glucosinolate ( 4-α-rhamnosyloxy benzyl glucosinolate), for NMR i use D20.
I took a look at the spectrum, however I could not make out the origin of the signals in the high field region of the spectrum. The spectrum clearly implies an aromatic moiety (could be a 4-hydroxybenzyl group since there is a great mess of signals there of similar shifts) and a sugar fragment. I suspect that in the best case scenario you have a mixture of several glucosinolates some of which have an aliphatic side chain. I have attached three papers to this message that deal with the NMRs of glucosinolates, one of them specifically with the one you are after. The paper from JAFC reports some NMR data on the mentioned aliphatic side chain glucosinolates. Perhaps it would be more informative if you measure a 13C NMR spectrum of your sample. You will definitely get a less crowded spectrum, and could more easily (probably all signals will be singlets) compare your chemical shift values with those from the literature.
Best regards,
Niko
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