|Jung, Hans Joachim|
Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 5/13/2008
Publication Date: 8/25/2008
Citation: Kim, H., Ralph, J., Grabber, J.H., Jung, H.G. 2008. Rapid 2D NMR method for determining p-coumarate and ferulate levels in corn (and other grass) cell walls. In: Ferulate 08 Abstracts, August 25-27, 2008, Minneapolis, Minnesota. p. 48. Interpretive Summary:
Technical Abstract: Grass cell wall components are acylated by the hydroxycinnamates p-coumarate and ferulate. p-Coumarates largely acylate lignin sidechains, exclusively at the gamma-position, whereas ferulates primarily acylate the arabinosyl C5-position of arabinoxylans. Such components can be quantified as the corresponding acids released following saponification. For various reasons, it would be useful to determine their levels relative to other cell wall components that are difficult to measure. Recently developed dissolution and/or acylation methods for finely divided (ball-milled) plant cell walls have allowed high-resolution two-dimensional (2D) nuclear magnetic resonance (NMR) spectra to be acquired. Most recently, we have noted that the wall need not be actually dissolved to obtain well-resolved solution-state NMR spectra, but simply swollen in DMSO-based gels. Solution-state 2D 13C–1H correlated NMR (HSQC and HMQC) experiments on the gel, produced directly in the NMR tube, provide interpretable structural fingerprints of the polysaccharide and lignin components of the walls without actual solubilization, and without structural modification beyond that inflicted by the ball milling and ultrasonication steps. The method provides a rapid (as little as 0.5 h per sample) method for comparative structural evaluation of plant cell walls. Correlations for p-coumarate units in grasses are readily seen. More strikingly, a variety of the ferulate correlations are also well resolved; ferulates have previously been difficult to discern by NMR due to spectral overlap in derivatized cell wall samples. In principle, at least, these components can be quantified, along with measures such as syringyl:guaiacyl ratios that are difficult to measure representatively. This method may provide a reasonably facile screen for hydroxycinnamate ester concentrations. Also, with the new potential for chemometric analysis using the 2D NMR fingerprint, this gel-state method may find application as a secondary screen for selecting biomass lines and for optimizing biomass processing and conversion efficiencies. The method will be illustrated using various corn samples.