¹³C NMR Characterization of Guaiacyl, Guaiacyl/Syringyl and Syringyl Dehydrogenation Polymers

Abstract

Dehydrogenation polymers (DHPs) were prepared from coniferyl alcohol (CA), sinapyl alcohol (SA), and a mixture of coniferyl and sinapyl alcohol. The polymers were fully acetylated and their carbon NMR spectra were compared. Comparison of the 13 C NMR spectra of the DHPs with those of authentic tri-and tetralignols facilitated the assignment of about 85% of the 117 reported signals. Most of the unassigned signals were those from syringyl units. Major differences between the DHP prepared from CA and a pine milled wood lignin were: a relative deficiency of ß-O-4 linkages and a predominance of ß-5, ß-ß, and CA end units in the DHP. In contrast, there was no significant quantity of SA end units in a DHP prepared from SA. A major conclusion of the study confirmed that DHPs prepared from CA are relatively poor models of natural lignins isolated from gymnosperms.

Structural Characterization and Iron(III) Binding Ability of Dimeric and Polymeric Lignin Models

“…The carbonyl signals of acetyl were observed as three peaks corresponding to primary, secondary, and phenolic alcohol moieties respectively at 171.0, 170.8, and 169.1 ppm. Owing to a great number of scans (50,000) with a relaxation delay of 4 s, it was possible to relatively quantify these functional groups (20)(21)(22): about 14% of phenolic alcohol, 28% of primary alcohol, and 57% of secondary alcohol. Since the β-6, β-5, and 5-5 structures do not contain secondary hydroxy1 groups, a high content of this type of alcohol can indicate a great abundance of β-O-4 structure.…”

The molecular properties and carbohydrate content of lignins precipitated from black liquor

“…The chemical shift assignments are based on the literature (Mörck and Kringstad 1985;Pu and Ragauskas 2005) and summarized in Table 5, along with the integrated peak areas of the lignin moieties. The integral of aromatic region (102-160 ppm) was calibrated to six, which represents six aromatic carbons (Landucci et al 1998;Ralph and Landucci 2010;Min et al 2013;Wells et al 2013). Quantitative evaluation of functional groups (OH phen and OMe) and carbohydrates was thus integrated related to this value (Robert 1992;Faix et al 1994;Ralph and Landucci 2010;Choi and Faix 2011;Min et al 2013).…”

NMR Structural Characterization ofQuercus alba(White Oak) Degraded by the Brown Rot Fungus,Laetiporus sulphureus

“…[14] Solid-state cross polarization magic angle spinning (CPMAS) 13 C NMR is the traditional method of choice for solid lignin preparations. [14,18,19] This technique has also been used to analyze the structures of DHPs and natural lignin in samples whose side chains have been labeled with 13 C. [14,16] Lignin side chains may have various oxidation states, displaying a combination of hydroxyl, carbonyl, and carboxyl groups, and its monomers are bonded together in irregular patterns. Furthermore, lignin can display different stereochemical arrangements, as up to two asymmetric centers on each of its side chain units are possible.…”