Investigation of lignin models of the biphenyl type by X-ray crystallography and NMR spectroscopy

Brunow, Gösta; Karhunen, Pirkko; Lundquist, Knut; Olson, Solveig; Stomberg, Rolf

doi:10.1007/bf01666186

Cited by 18 publications

(7 citation statements)

References 12 publications

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“…The lowest energy conformer of DBDO alongside its chemical structure is shown in Figure a. It is in agreement with X‐ray data of similar molecules . One methoxy group is not planar with the ring to which it is attached; this seems to be due to steric hindrance with the G‐ring.…”

Section: Resultssupporting

confidence: 90%

“…It is in agreement with X-ray data of similar molecules. [50,51] One methoxy group is not planar with the ring to which it is attached; this seems to be due to steric hindrance with the G-ring. However, this is in contradiction to the aforementioned X-ray studies, where the aryl-methoxy groups are always found to be in plane with the ring.…”

Section: Molecular Structurementioning

confidence: 99%

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Infrared and Raman spectra of lignin substructures: Dibenzodioxocin

Bock

Nousiainen

Elder

et al. 2020

J Raman Spectroscopy

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Vibrational spectroscopy is a very suitable tool for investigating the plant cell wall in situ with almost no sample preparation. The structural information of all different constituents is contained in a single spectrum. Interpretation therefore heavily relies on reference spectra and understanding of the vibrational behavior of the components under study. For the first time, we show infrared (IR) and Raman spectra of dibenzodioxocin (DBDO), an important lignin substructure. A detailed vibrational assignment of the molecule, based on quantum chemical computations, is given in the Supporting Information; the main results are found in the paper. Furthermore, we show IR and Raman spectra of synthetic guaiacyl lignin (dehydrogenation polymer—G‐DHP). Raman spectra of DBDO and G‐DHP both differ with respect to the excitation wavelength and therefore reveal different features of the substructure/polymer. This study confirms the idea previously put forward that Raman at 532 nm selectively probes end groups of lignin, whereas Raman at 785 nm and IR seem to represent the majority of lignin substructures.

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Section: Resultssupporting

confidence: 90%

Section: Molecular Structurementioning

confidence: 99%

Infrared and Raman spectra of lignin substructures: Dibenzodioxocin

Bock

Nousiainen

Elder

et al. 2020

J Raman Spectroscopy

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“…Another 13 C NMR study confirmed these data (Capanema et al 2004). In contrast, it is difficult to validate these data because of the overlapping NMR signals of biphenyl structures with other signals (Brunow et al 1995).…”

Section: Introductionmentioning

confidence: 54%

Revisiting alkaline nitrobenzene oxidation: quantitative evaluation of biphenyl structures in cedar wood lignin (Cryptomeria japonica) by a modified nitrobenzene oxidation method

Tamai

Goto

Akiyama³

et al. 2014

Holzforschung

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A modified alkaline nitrobenzene oxidation (NBO) method was developed to enable the analysis of the biphenyl structures of cedar wood lignin. The most essential point of the process is a modified work-up process in pyridine and a prolonged gas chromatography analysis of the silylated products. By applying this mean to cedar wood meal, a novel biphenyl product, dehydrovanillin-vanillic acid (1-carboxy-1′-formyl-4,4′-dihydroxy-3,3′-dimethoxy-5,5′-biphenyl), was detected together with known products, dehydrodivanillin and dehydrodivanillic acid. The highest total yield of biphenyl products was detected when NBO was carried out for 2-4 h at 170°C. The workup procedure was slightly modified so that the biphenyl products can be quantified. The NBO conversion rates of biphenyl linkages of lignin were also examined with a biphenyl-type lignin model compound, and this gave rise to 75% biphenyl-type NBO degradation products. Under the same condition, the total yield of vanillin and vanillic acid (VA) from a non-condensed-type β-O-4 model compound was 89%. Because the latter did not exhibit any peak of the biphenyl products, it can be concluded that all the biphenyl products obtained by NBO (0.17 mmol g -1 ) were from the lignin of the native wood. It was calculated that at least 6.7 of 100 phenylpropanoid units of cedar lignin were involved in biphenyl structures even if the NBO conversion rate was not taken into consideration. The synthesis and analytical data of 11 lignin model compounds is described.

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“…13 C NMR studies also indicated that 0.24-0.26 per C 6 -C 3 unit (Drumond et al 1989) and 0.24-0.27 per C 6 -C 3 unit (Capanema et al 2004) were involved in the biphenyl structures in spruce MWLs. Brunow et al (1995) pointed out the difficulty in validating the biphenyl content determined by 13 C NMR analysis due to the overlap of the NMR signals of biphenyl structures with other signals. Such a signal overlap may possibly lead to an overestimation of the biphenyl content.…”

Section: Introductionmentioning

confidence: 99%

Variation of the contents of biphenyl structures in lignins among wood species

et al. 2019

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Biphenyl structures (5–5 linkages) are one of the significant structural units in plant cell wall lignin. They can potentially play a role in providing branch points in lignins and influence the polymer structure of lignins. Variation of the biphenyl content was investigated for 21 wood species by alkaline nitrobenzene oxidation. The total yields of biphenyl-type products were similar among the six softwoods, and at least 6% of the phenylpropanoid units in lignin were involved in the biphenyl structures (>0.06 per C6-C3). The biphenyl product yield of the 15 hardwoods ranged widely (0.002–0.05 per C6-C3) and was lower in species having a higher syringyl/guaiacyl ratio (i.e. a species with less guaiacyl units). In addition, the proportion of biphenyl products in all guaiacyl-type products was not constant but decreased as the proportion of syringyl units increased. This indicates that the content of guaiacyl units is not likely the only factor influencing the biphenyl content.

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Investigation of lignin models of the biphenyl type by X-ray crystallography and NMR spectroscopy

Cited by 18 publications

References 12 publications

Infrared and Raman spectra of lignin substructures: Dibenzodioxocin

Infrared and Raman spectra of lignin substructures: Dibenzodioxocin

Revisiting alkaline nitrobenzene oxidation: quantitative evaluation of biphenyl structures in cedar wood lignin (Cryptomeria japonica) by a modified nitrobenzene oxidation method

Variation of the contents of biphenyl structures in lignins among wood species

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