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Title:Alkali cation chelation in cold β-o-4 tetralignol complexes
Author(s):DeBlase, Andrew F.
Contributor(s):Zwier, Timothy S.; McLuckey, Scott A.; Kenttamaa, Hilkka I.; Burke, Nicole L.; Hopkins, John R.; Dziekonski, Eric T.
Subject(s):Spectroscopy in Traps
Abstract:Lignins are the second most abundant naturally occurring polymer class, contributing to about 30\% of the organic carbon in the biosphere. Their primary function is to provide the structural integrity of plant cell walls and have recently come under consideration as a potential source of biofuels because they have an energy content similar to coal. Herein, we employ cold ion spectroscopy (UV action and IR-UV double resonance) to unravel the spectroscopic signatures of G-type alkali metal cationized (X = Li$^{+}$, Na$^{+}$, K$^{+}$) lignin tetramers connected by $\beta$-O-4 linkages. The conformation-specific spectroscopy reveals a variety of conformers, each containing distinct infrared spectra in the OH stretching region building on recent studies on the neutral and alkali metal cationized $\beta$-O-4 dimers. Based on comparisons of our infrared spectra to density functional theory [M05-2X/6-31+G] harmonic level calculations for structures derived from a Monte Carlo conformational search, the alkali metal ion is discovered to engage in M$^{+}$-OH-O interactions as important motifs that determine the secondary structures of these complexes. This interaction disappears in the major conformer of the K$^{+}$ adduct, suggesting a reemergence of a neutral dimer segment as the metal binding energy decreases. Chelation of the metal cation by oxygen lone pair(s) of nearby oxygens in the $\beta$-O-4 linkage is observed to be the predominant driving force for 3D structure around the charge site, relegating OH-O H-bonds as secondary stabilizing elements.
Issue Date:2016-06-21
Publisher:International Symposium on Molecular Spectroscopy
Genre:Conference Paper/Presentation
Rights Information:Copyright 2016 by the authors
Date Available in IDEALS:2017-01-26

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