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| 2. |
- Akiyama, T., et al.
(författare)
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Absolute Configuration of β- and α-Asymmetric Carbons within β-O-4-Structures in Hardwood Lignin
- 2014
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Ingår i: Journal of Wood Chemistry and Technology. - : Informa UK Limited. - 1532-2319 .- 0277-3813. ; 35:1, s. 8-16
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we investigated the proportion of erythro-and threo-forms of beta-O-4-ether structures and their enantiomeric compositions in hardwood lignin by applying the ozonation method to birch wood meal. Optical activity was not substantially observed in either the erythronic or threonic acids obtained as the ozonation products of beta-O-4-structures in birch wood meal. The proportions of the four stereoisomeric forms {(alpha S,beta R)-erythro, (alpha R,beta R)-threo, (alpha S,beta S)-threo, and (alpha R,beta S)-erythro forms} were estimated to be 37-38%, 13-14%, 12-13%, and 36-37% based on the yields of erythronic and threonic acids, and on their optical activities. The proportions suggest that the entire components of beta-O-4-ether structures in birch wood lignin have R-and S-configurations at the beta-carbon in approximately the same quantities {(beta R)-beta-O-4-structure: (beta S)-beta-O-4structure = 50-52: 48-50}; i.e., that the beta-ether structures are essentially racemic. This estimation implies that, during lignin biosynthesis, an equal number of enantiomeric forms of beta-O-4-bonded quinone methides were formed by radical coupling reactions.
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| 3. |
- Albinsson, Bo, 1963, et al.
(författare)
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The origin of lignin fluorescence
- 1999
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Ingår i: Journal of Molecular Structure. - 0022-2860. ; 508:1-3, s. 19-27
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Tidskriftsartikel (refereegranskat)abstract
- Spruce lignin exhibits fluorescence emission spectra that peaks at approximate to 360 nm on excitation at wavelengths ranging from 240 to 320 nm. This can be explained by non-radiative energy transfer from lignin chromophores, that are excited in the wavelength range 240-320 nm, to an acceptor that emits fluorescent Light at approximate to 360 nm. Examinations of lignin samples and model compounds suggest that small amounts of phenylcoumarone structures in the lignin is a conceivable acceptor. Such structures and stilbene structures are formed from structural elements in lignin of the phenylcoumaran type on various treatments. The photophysical properties of models for phenylcoumarone structures [2-(3,4-dimethoxyphenyl)-7-methoxy-3-methyo[b]-furan, 2-(3,4-dimethoxyphenyl)-3-hydroxymethyl-7-methoxybenzo[b]furan] and stilbene structures (the E and Z forms of 2-hydroxy-3,3',4'-trimethoxystilbene) have been examined and are discussed on the basis of crystal structure determinations. (C) 1999 Elsevier Science B.V. All rights reserved.
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| 7. |
- Bohlin, Christina, 1979-, et al.
(författare)
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Diastereomer selectivity in the degradation of a lignin model compound of the arylglycerol β-aryl ether type by white-rot fungi
- 2008
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Ingår i: Enzyme and Microbial Technology. - : Elsevier BV. - 0141-0229 .- 1879-0909. ; 43:2, s. 199-204
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Tidskriftsartikel (refereegranskat)abstract
- Mixtures of about equal amounts of the diastereomers of arylglycerol β-aryl ether 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol (1) were added to cultures of Trametes versicolor, Phanerochaete chrysosporium, and Pycnoporus cinnabarinus. Samples taken from the fungal cultures were analyzed with respect to the fraction of 1 degraded, the erythro:threo ratio in the remaining 1, and the product profile, using HPLC and UV-diode array detector. The P. cinnabarinus cultures exhibited laccase activity and partially decolorized Remazol Brilliant Blue R (RBBR), but they did not degrade 1 under the conditions studied. Cultures of T. versicolor and P. chrysosporium preferentially degraded the threo isomer of 1. This is consistent with the fact that the product profiles showed larger amounts of threo- than erythro-veratrylglycerol. The results can be discussed in relation to the diastereomer selectivity of various oxidants implicated in lignin degradation by white-rot fungi. Preferential degradation of the threo isomer of arylglycerol β-aryl ethers is not in agreement with the action of Fenton's reagent, since this reagent does not exhibit any stereopreference.
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| 8. |
- Bohlin, Christina, et al.
(författare)
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Differences in stereo-preference in the oxidative degradation of diastereomers of the lignin model compound 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol with enzymic and non-enzymic oxidants
- 2007
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Ingår i: Journal of Molecular Catalysis - B Enzymatic. - : Elsevier BV. - 1381-1177 .- 1873-3158. ; 45:1-2, s. 21-26
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Tidskriftsartikel (refereegranskat)abstract
- Mixtures of equal amounts of the erythro and the threo forms of the β-O-4 lignin model compound 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol were oxidized with different ligninolytic enzymes and non-enzymic oxidants. The oxidants included cerium(IV)ammonium nitrate (CAN), Fenton’s reagent, lead(IV) tetraacetate (LTA), laccase, laccase–mediator systems (based on the mediators ABTS, HBT,TEMPO, and VLA), and lignin peroxidase. The stereo-preference of the different oxidants was compared based on analyses of remaining substrateusing HPLC and UV-diode array detector or 1H NMR spectroscopy. Fenton’s reagent was the only oxidant tested that did not show preferentialdegradation of either the erythro or the threo form. CAN, LTA and lignin peroxidase preferentially oxidized the threo form. The stereo-preferenceof the laccase–mediator systems depended on the mediator. Oxidation mediated by HBT, TEMPO or VLA resulted in a preferential degradationof the threo form. Laccase/ABTS was the only system tested that showed preferential oxidation of the erythro form. The stereo-preference of theoxidants is discussed based on their redox potentials and their classification as outer-sphere and inner-sphere oxidants.
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| 10. |
- Bohlin, Christina, et al.
(författare)
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Product profiles in enzymic and non-enzymic oxidations of the lignin model compound erythro-1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol
- 2005
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Ingår i: Journal of Molecular Catalysis - B Enzymatic. - : Elsevier BV. - 1381-1177 .- 1873-3158. ; 35:4-6, s. 100-107
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Tidskriftsartikel (refereegranskat)abstract
- The erythro form of the lignin model compound 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol (1) was oxidized with laccase/ABTS, lead(IV) tetraacetate (LTA), lignin peroxidase/H2O2, cerium(IV) ammonium nitrate (CAN) and Fenton's reagent. The product profiles obtained with the different oxidants were compared after separation, identification and quantification of the products using HPLC, UV-diode array detector and electrospray ionization mass spectrometry in positive ionization mode. The oxidants generated different product profiles that reflected their different properties. Oxidation with laccase/ABTS resulted almost exclusively in formation of 1-(3,4-dimethoxyphenyl)-3-hydroxy-2-(2-methoxyphenoxy)-1-propanone (2). Oxidation with LTA resulted in more 3,4-dimethoxybenzaldehyde (3) than ketone 2. Lignin peroxidase and CAN gave similar product profiles and aldehyde 3 was the predominant product (only small amounts of ketone 2 were formed). Oxidation with Fenton's reagent resulted in the formation of more aldehyde 3 than ketone 2 but the yields were very low. CAN served as an excellent model for the lignin peroxidase-catalyzed oxidation, while the laccase-mediator system, LTA and Fenton's reagent provided distinctly different product profiles. Erythro-1-(3,4-dimethoxyphenyl)-1,2,3-propanetriol was present among the products obtained on oxidation with LTA, lignin peroxidase, CAN and Fenton's reagent. The differences in redox potential between the oxidants afford an explanation of the diverse product patterns but other factors may also be of importance. The reactions leading to cleavage of the β-ether bond with formation of 1-(3,4-dimethoxyphenyl)-1,2,3-propanetriol (veratrylglycerol) were found to proceed without affecting the configuration at the β-carbon atom.
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