I am thinking of doing research on oligomerized cinnamic acid derivatives in the plant cell wall. Given that lignans vary quite a bit in molecular weight, degree of polymerisation, and structure, I was wondering what techniques would be suitable for analysing them, especially as they are likely to occur in complex mixtures.
My own idea is that chromatographic separations would be necessary, probably by HPLC, HP-SEC (or simple SEC), GC-MS, or possibly HPTLC or CZE. Am I right? I would like to hear from someone who has experience separating similar compounds (the product of three, four or more phenolic groups).
Hello Sally,
I see this question was posted in March and you might have already embarked on a journey to the "lignan landscape"...or discarded your plans. Nevertheless, I will give a short reply.
For lignans of dibenzylbutyrolactone and dibenzylbutanediol type, LC-MS methods (e.g., LC-ESI-ion-trap-MS) could be used as they don’t require derivatization prior to analysis like GC-MS often does for lignans. For LC methods, though, the drawback is that you would need pure lignan standards. From our lab(s), see for example
Eklund, P.C; Backman, M.J; Kronberg, L.A; Smeds, A.I; Sjöholm, R.E, J. Mass Spectrom., 2008, 43, pp 97-107 or newer publications from Smeds, A.I.
Some lignans might occur as glycosides, some in free form. Depeding on your interests and your plant, you might need hydrolysis methods prior to analysis.
If the intention is to isolate pure (monomeric) lignans, or at least try to remove them from complex mixtures, small scale flash chromatography + TLC and/or preparative TLC might be of use for you. For identification of individual (monomeric) lignans, I prefer GC-MS and then NMR to confirm you have the right compound.
For oligomeric or polymeric lignans, HPSEC could be used for the molar mass distribution.
Without knowing for which plant you are planning/planned to do research, I'd still
say that you are on the right path in terms of analysis methods.
Regards,
J-E Raitanen
Thanks for the detailed and useful answer. I have put the project on hold temporarily as I am just about to start a postdoc on chitin polysaccharides at Glyndwr, but I'll bear your advice in mind.
One thing I have done is run a simulation of ferulate polymerisation in R, and my results in that strongly suggest the oxidation reactions have to run to completion before there are enough cinnamic acid oligomers of DP3+ to analyse.
Check for example
Journal of Chromatography A Volume 1112, Issues 1–2, 21 April 2006, Pages 64–77
Journal of Wood Science 2004, Volume 50, Issue 1, pp 93-96
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