NMR Spectroscopy for Assessing Pretreatment Effects of Switchgrass

Researchers from the University of Georgia report the use of nuclear magnetic resonance spectroscopy (NMR)to assess the chemical changes in switchgrass (Panicum virgatum, a potential biofuel [grass] feedstock) after subjecting it to different types of pretreatment methods. (Pretreatment by physicochemical or biological methods "deconstructs" the plant cell wall; this is the first step in biofuel ethanol production from lignocellulosics). NMR is a technique in chemistry which relies on nuclear magnetic resonance properties of certain atoms for the structural analysis of substances, including its chemical environment.

The traditional method of pretreatment assessment of lignocellulosic biomass usually involves time-consuming procedures of extraction/purification prior to spectroscopic characterization. In the NMR method, such time-consuming procedures are reported to be not necessary. It involves dissolving the lignocellulosic sample in a binary solvent system consisting of "1-methyl imidazole-d₆/DMSO-d₆". High resolution NMR spectra data can be reportedly obtained from this solvent system. The NMR spectral data allows the identification of lignin sub-units, as well as polysaccharide units in pretreated switchgrass. The methods used for the pretreatment of switchgrass include: steam explosion, lime addition, and acid pretreatment.

The NMR results from the study showed that: (1) xylan is the major hemicellulose fraction of switchgrass, (2) switchgrass lignin is composed of H, G and S monolignol subunits with significant amounts of p-coumarate and ferulate, (3) steam explosion slightly degrades lignin and partially dissolved the hemicellulose in switchgrass, (4) lime pretreatment resulted in "preferential degradation of p-hydroxy benzoyl ester, ferulate and coumarate" in lignin, and less severe dissolution of hemicellulose, (4) acid treatment was the most "harsh" pretreatment"; there was significant degradation of both lignin and hemicellulose. The full paper is published in the journal, Polymer Degradation and Stability (URL above).

Related information:Basics of NMR: http://www.cis.rit.edu/htbooks/nmr/inside.htm

Lignin: http://www.dfrc.wisc.edu/dfrcwebpdfs/jr_brazil99_paper.pdf