Study structural effects on the ionization response of lignin model compounds during electrospray ionization.

The potential use of biomass for fuel production is a hotbed of research. Degradation and fermentation of cellulose to produce “drop-in” transportation fuels is complicated by the presence of two other plant derived biopolymers, lignin and hemicellulose. Lignin is the second most abundant polymer present in plant cell walls and consists of 3 phenylpropanoid units, polymerized by oxidative radical coupling resulting in complex heterogeneous bio-macromolecules. Because of structural heterogeneity, extensive carbon-carbon crosslinking and aromaticity, lignin remains very resistive to general degradation requiring chemical pretreatments to improve cellulose accessibility during biofuel production. We are part of a large multi-institute, multi-college study to develop “on farm” biofuels production from biomass resources. This group is studying alternative lignin degradation and developing improved analytical methods to support the entire project. Since lignin represents a nearly intractable analytical problem we chose to focus on synthesized dehydrogenation polymers as lignin model compounds and study these products using high-resolution accurate mass (HRAM) mass spectrometry.

Because the acidity of phenolic hydroxyl group in lignin, the negative ion mode is usually considered more sensitive than the positive ion mode when using electrospray ionization. However, during our preliminary studies of dehydrogenation polymers (DHPs), we observed structural based differences in ionization response in the positive ion mode using cationization and the negative ion mode by deprotonation. We have chemically isolated and fully characterized three model lignin trimers and observe differences in their ionization response. We plan to use computational chemistry to elucidate the relationship between cation binding energy and three-dimensional structures of these trimers and understand mechanisms behind the ionization process.

We plan to use Gaussian to perform density functional theory calculations to model the ionization process during electrospray ionization. The geometries of each trimer (with and without associated cations) will be optimized using semi-empirical quantum chemical method PM3. These geometries and frequencies of these systems will be further optimized using density functional theory and Becke’s three-parameter exchange functional combined with the gradient-corrected functional of Lee, Yang and Parr (B3LYP functional) on the 6-31+G* basis set.

Research Personnel

Bert C Lynn (PI)
Fan Huang (graduate student)

Poornima R Sunder (graduate student)

Kimberly (Kimmy) Dean (graduate student) 05/18/2019

Software

Gaussian

Funding:

“On-Farm Biomass Processing: Towards an Integrated High-Solids Transporting/Storing/ Processing System” (PI. S.E. Nokes, CoPI B.C. Lynn (one of twelve) USDA-ARS Biomass Research Development Initiative, $1,000,000 Year 1 ($6,932,786 Total project), 7/1/2011 – 6/30/2015

Patents:

“On Farm, Integrated High-Solids Processing System for Biomass” US Patent application #14/603,616, under review.

Publications:

K.R. Dean, B.C. Lynn, “Monolignol Lithium Cation Basicity Estimates and Lithium Adduct Ion Optimized Geometries” In Press, Int. J Mass Spectrom. 442, 109-116 (2019).

Lynn, Bert C D.M. Kato, N. Ella, M. Flythe, B.C.Lynn, “Pretreatment of Lignocellulosic Biomass using Fenton Chemistry” Bioresource Technology, 162, 273-278 (2014).
Lynn, Bert C A.E. Harman-Ware, M. Crocker, A.P. Kaur, M.S. Meier, D. Kato, B.C. Lynn, “Pyrolysis-GC/MS of sinapyl and coniferyl alcohol” J. Analytical and Applied Pyrolysis, 99, 161-169 (2013).
Lynn, Bert C H.F. Li, B.L. Knutson, S.E. Nokes, B.C. Lynn, M.D. Flythe “Metabolic control of Clostridium thermocellum via inhibition of hydrogenase activity and the glucose transport rate” App.l Microbiol. Biotechnol., 93(4),: 1777-84 (2012)

Posters:

Elucidation of synthetic lignin oligomers by tandem mass spectrometry. American Society for Mass Spectrometry. June, 2014 Accepted: Structural effects on the ionization response of lignin model compounds during electrospray ionization. American Society for Mass Spectrometry. June 3, 2015

Other Funding:

“Modulation of microRNA Pathways by Gemfibrozil in Predementia Alzheimer Disease” (PI. Gregory Jicha CoI B.C. Lynn (one of nine) National Institutes of Health RO1, $486.839 (Year 1), total project 07/15/13 - 06/30/16.