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Title: Comparison of Multistandard and TMS-Standard Calculated NMR Shifts for Coniferyl Alcohol and Application of the Multistandard Method to Lignin Dimers

Abstract

Coniferyl alcohol is a monomeric building block of lignin, the second most abundant biopolymer. During lignification, the monomer forms a variety of linkages through free radical additions. A large NMR database has been constructed that reports the {sup 1}H and {sup 13}C chemical shifts for thousands of lignin oligomers. Herein, Boltzmann averaged {sup 1}H and {sup 13}C GIAO NMR calculations were performed on coniferyl alcohol and four of its dimers, β-O-4, β-β, β-5, and 5-5, to compare the calculated chemical shifts with experiment. Six B3LYP/6-311++G(d,p) energy-minimized conformational isomers of coniferyl alcohol were subjected to single-point GIAO NMR calculations. Initially, four NMR shift calculation methods were compared: three were performed using the TMS-standard method at the HF/6-311+G(2d,p), B3LYP/6-311+G(2d,p), and mPW1PW91/6-31G(d) theory levels, and the fourth was performed with a multistandard approach using a mPW1PW91/6-31G(d) theory level. For the multistandard method, benzene was used as the standard for aromatic C and H atoms and methanol was used for aliphatic C and H atoms. The hydroxyl-H of methanol was used as the standard for hydroxyl-H atoms. The Boltzmann averaged results for six conformers showed that the multistandard method is more accurate for coniferyl alcohol and its dimers than the often used TMS-standard method,more » based on the mean unsigned, root-mean-squared, and maximum errors, as well as linear correlations between observed and calculated values. The {sup 13}C results were more accurate than the 1H results, due to poorer agreement between calculated hydroxyl-H results and observed data. Further Boltzmann-averaged, multistandard NMR calculations compared the {sup 13}C and {sup 1}H chemical shifts with experiment for the four stereoisomers of the β-O-4 dimer, as well as the 5-5, β-5, and β-β dimers of coniferyl alcohol. The {sup 13}C results correlated well with experiment (r2 > 0.99) for all dimers and showed small statistical errors, compared with experiment. The correlation with experiment for 1H NMR was generally inferior to the {sup 13}C NMR results for the dimers.« less

Authors:
; ;
Publication Date:
Research Org.:
Energy Frontier Research Centers (EFRC); Center for Lignocellulose Structure and Formation (CLSF)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1065359
DOE Contract Number:  
SC0001090
Resource Type:
Journal Article
Journal Name:
J. Phys. Chem. B
Additional Journal Information:
Journal Volume: 115 (9); Journal Issue: 9; Related Information: CLSF partners with Pennsylvania State University (lead); North Carolina State University; University of Rhode Island; Virginia Tech University; Journal ID: ISSN 1520--6106
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; biofuels (including algae and biomass), bio-inspired, membrane, carbon sequestration, materials and chemistry by design, synthesis (self-assembly)

Citation Formats

Watts, Heath D, Mohamed, M. Nasser Ali, and Kubicki, James D. Comparison of Multistandard and TMS-Standard Calculated NMR Shifts for Coniferyl Alcohol and Application of the Multistandard Method to Lignin Dimers. United States: N. p., 2011. Web. doi:10.1021/jp110330q.
Watts, Heath D, Mohamed, M. Nasser Ali, & Kubicki, James D. Comparison of Multistandard and TMS-Standard Calculated NMR Shifts for Coniferyl Alcohol and Application of the Multistandard Method to Lignin Dimers. United States. doi:10.1021/jp110330q.
Watts, Heath D, Mohamed, M. Nasser Ali, and Kubicki, James D. Thu . "Comparison of Multistandard and TMS-Standard Calculated NMR Shifts for Coniferyl Alcohol and Application of the Multistandard Method to Lignin Dimers". United States. doi:10.1021/jp110330q.
@article{osti_1065359,
title = {Comparison of Multistandard and TMS-Standard Calculated NMR Shifts for Coniferyl Alcohol and Application of the Multistandard Method to Lignin Dimers},
author = {Watts, Heath D and Mohamed, M. Nasser Ali and Kubicki, James D},
abstractNote = {Coniferyl alcohol is a monomeric building block of lignin, the second most abundant biopolymer. During lignification, the monomer forms a variety of linkages through free radical additions. A large NMR database has been constructed that reports the {sup 1}H and {sup 13}C chemical shifts for thousands of lignin oligomers. Herein, Boltzmann averaged {sup 1}H and {sup 13}C GIAO NMR calculations were performed on coniferyl alcohol and four of its dimers, β-O-4, β-β, β-5, and 5-5, to compare the calculated chemical shifts with experiment. Six B3LYP/6-311++G(d,p) energy-minimized conformational isomers of coniferyl alcohol were subjected to single-point GIAO NMR calculations. Initially, four NMR shift calculation methods were compared: three were performed using the TMS-standard method at the HF/6-311+G(2d,p), B3LYP/6-311+G(2d,p), and mPW1PW91/6-31G(d) theory levels, and the fourth was performed with a multistandard approach using a mPW1PW91/6-31G(d) theory level. For the multistandard method, benzene was used as the standard for aromatic C and H atoms and methanol was used for aliphatic C and H atoms. The hydroxyl-H of methanol was used as the standard for hydroxyl-H atoms. The Boltzmann averaged results for six conformers showed that the multistandard method is more accurate for coniferyl alcohol and its dimers than the often used TMS-standard method, based on the mean unsigned, root-mean-squared, and maximum errors, as well as linear correlations between observed and calculated values. The {sup 13}C results were more accurate than the 1H results, due to poorer agreement between calculated hydroxyl-H results and observed data. Further Boltzmann-averaged, multistandard NMR calculations compared the {sup 13}C and {sup 1}H chemical shifts with experiment for the four stereoisomers of the β-O-4 dimer, as well as the 5-5, β-5, and β-β dimers of coniferyl alcohol. The {sup 13}C results correlated well with experiment (r2 > 0.99) for all dimers and showed small statistical errors, compared with experiment. The correlation with experiment for 1H NMR was generally inferior to the {sup 13}C NMR results for the dimers.},
doi = {10.1021/jp110330q},
journal = {J. Phys. Chem. B},
issn = {1520--6106},
number = 9,
volume = 115 (9),
place = {United States},
year = {2011},
month = {3}
}