Formation of free radicals in photoirradiated cellulose. VI. Effect of lignin

Hon, Nyok‐Sai

doi:10.1002/pol.1975.170131201

Cited by 42 publications

(14 citation statements)

References 14 publications

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“…Studies of wood photodegradation suggest that the photon energy absorbed by cellulose in the UV range is likely to delocalize and transfer to lignin, causing degradation of the latter (27). The presence of lignin is therefore actually predicted to protect cellulose from photodegradation, a phenomenon that has been documented to some extent and attributed to the strong light absorption of lignin and its high capacity for autoxidation (27,32). Our results support the idea that lignin was the primary loss product due to photodegradation in our standard substrates, and they are consistent with observations indicating the disappearance of lignin in litter exposed to high natural UV-B radiation (20) and increased biotic lability of plant litter after solar radiation exposure (21,26).…”

Section: Resultsmentioning

confidence: 99%

Dual role of lignin in plant litter decomposition in terrestrial ecosystems

Austin

Ballaré

2010

Proc. Natl. Acad. Sci. U.S.A.

402

320

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Plant litter decomposition is a critical step in the formation of soil organic matter, the mineralization of organic nutrients, and the carbon balance in terrestrial ecosystems. Biotic decomposition in mesic ecosystems is generally negatively correlated with the concentration of lignin, a group of complex aromatic polymers present in plant cell walls that is recalcitrant to enzymatic degradation and serves as a structural barrier impeding microbial access to labile carbon compounds. Although photochemical mineralization of carbon has recently been shown to be important in semiarid ecosystems, litter chemistry controls on photodegradative losses are not understood. We evaluated the importance of litter chemistry on photodegradation of grass litter and cellulose substrates with varying levels of lignin [cellulose-lignin (CL) substrates] under field conditions. Using wavelength-specific light attenuation filters, we found that light-driven mass loss was promoted by both UV and visible radiation. The spectral dependence of photodegradation correlated with the absorption spectrum of lignin but not of cellulose. Field incubations demonstrated that increasing lignin concentration reduced biotic decomposition, as expected, but linearly increased photodegradation. In addition, lignin content in CL substrates consistently decreased in photodegradative incubations. We conclude that lignin has a dual role affecting litter decomposition, depending on the dominant driver (biotic or abiotic) controlling carbon turnover. Under photodegradative conditions, lignin is preferentially degraded because it acts as an effective light-absorbing compound over a wide range of wavelengths. This mechanistic understanding of the role of lignin in plant litter decomposition will allow for more accurate predictions of carbon dynamics in terrestrial ecosystems.

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Section: Resultsmentioning

confidence: 99%

Dual role of lignin in plant litter decomposition in terrestrial ecosystems

Austin

Ballaré

2010

Proc. Natl. Acad. Sci. U.S.A.

402

320

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“…É conhecido que o cerne concentra maior quantidade de extrativos (Kollmann e Côté, 1968). Vários autores (Hon, 1975); Desh e Dinwoodie (1993) relatam que a definição da cor na madeira é fortemente influenciada pela quantidade de extrativos presentes no cerne, onde os componentes fenólicos desempenham importante papel (Scalbert et al, 1987;Janin et al, 1990a). Quanto à lignina, observando-se a Tabela 1, nota-se que as médias de lignina total, lignina solúvel e lignina insolúvel são diferentes entre os clones, mas não variam entre as duas posições longitudinais estudadas.…”

Section: Resultados E Discussõesunclassified

Influência das características tecnológicas na cor da madeira de eucaliptos.

Mori

Mori²,

Lima³

et al. 2004

Ciênc. Florest.

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RESUMODevido à importância da cor da madeira como componente de descrição da mesma, é que se realizou um estudo procurando verificar a influência dos componentes químicos na cor da madeira de diferentes clones de eucaliptos. Foram verificadas as quantidades de lignina e polifenoís nas madeiras das mesmas, as dimensões das fibras e a sua massa específica. As medições colorimétricas foram efetuadas através de um espectrofotômetro Data Color 200d. Microflash. Verificou-se que, das características das madeiras estudadas, a quantidade de extrativos, basicamente polifenoís, tem alta correlação com a cor da madeira.Palavras-chave: caracterização tecnológica; cor; eucalipto. ABSTRACTDue to importance of the color of the wood as a component of its description this study was undertaken to verify the influence of chemical components in the color of wood of various clones of eucalypt. The amount of lignin and polyphenols in the wood, the fibres dimensions and its specific gravity were determined. The colorimetric measurements were made through a specterphotometer Data Color 200d Microflash. It was verified by the characteristics of the wood studied, that the amount of extractives, basically polyphenols, had high correlation with the color of the wood.Key words: technological characterization; color; eucalypt. INTRODUÇÃOCaracterísticas como a densidade, textura, grã e dureza são bastante utilizadas na classificação e avaliação da qualidade da madeira. Recentemente, a cor vem sendo considerada como um índice de classificação e qualidade da madeira.O padrão de coloração de uma madeira pode variar em tonalidades que vão desde o bege claro até o marrom escuro, quase preto. Dentro dessa variação, existem madeiras amarelas, avermelhadas, roxas e alaranjadas. Segundo Mady (2000), a cor da madeira deriva da composição química das substâncias presentes no xilema: polifenóis, flavonóides, estilbenos, quinonas, dentre outros, conferindo diferenciadas cores no lenho. Características anatômicas, como camadas de crescimento, vasos, raios e tipos de parênquima axial, podem influenciar na cor da madeira. A variação da cor natural da madeira é facilmente perceptível aos olhos humanos. Essa variação é devido à impregnação de diversas substâncias orgânicas nas paredes celulares, sendo depositada de forma mais acentuada no cerne (Tsoumis, 1968).

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“…We also took into account results from previous extensive ESR studies of cellobiose, cellulose, and other disaccharides (Kawano and Logarezzi 1995;Kuzuya and Yamauchi 1998;Ershov 1998;Wach et al 2004;Mohanty and Singh 1988;Wach et al 2003;Hon 1975;Ershov and Isakova 1984;Yamauchi et al 1999;Kuzina et al 2004;Engalytcheff et al 2004;Kuzuya et al 1999;Ershov et al 1977). The X-band ESR spectra were typical of radicals in saccharides with a relatively low total radical concentration (approx.…”

Section: Radical Identification and Esr Parametersmentioning

confidence: 99%

“…Abstraction of H-atom at C 1 position can, moreover, induce cleavage of the glucosidic link with formation of an alkoxy RO Á radical giving a singlet ESR line. Intermediate transient radical centres have also been observed, as hydrogen atoms (doublet with 50.8 mT splitting) (Hon 1975), formyl radicals (doublet with 12.9 mT splitting) (Hon 1975), and O Á H and other oxygen-centred radicals. It has been also reported that after cleavage of glucosidic bonds at low temperatures the two radicals appear on the pyranose rings and are converted to allylic radicals on heating (Ershov and Isakova 1984).…”

Section: Introductionmentioning

confidence: 95%

Free radicals and their electron spin relaxation in cellobiose. X-band and W-band ESR and electron spin echo studies

Wencka

Wichlacz²,

Kasprzyk³

et al. 2006

Cellulose

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By use of 9.7 GHz and 94 GHz ESR spectra and electron spin echo (ESE)-detected spectra the six radical centres produced by c-irradiation of cellobiose were identified. The radicals are localized on different carbon atoms. Use of high-frequency ESR spectra with computer resolution enhancement methods enabled unique radical identification and determination of g-factors and proton hyperfine splitting, A, with high accuracy. For radiation doses below 20 kGy three radicals dominate: on C 1 with isotropic doublet A = 1.8 mT; on C 2 , C 3 and C 4 with triplet A = 2.9 mT; and localized on CH 2 with anisotropic triplet. For doses above 100 kGy the radical on C 1 dominates, because of cleavage of the glycosidic bonds. Electron spin-lattice relaxation shows that radiation damage of the cellulose structure around the radical centres is significant and radical molecules do not participate in phonon dynamics of the host lattice. The relaxation is because of tunnelling motions of the ring or OH-groups, with tunnelling splitting 2.4 cm -1 . Electron spin echo dephasing results identify cellobiose ring torsions with activation energy 117 cm -1 .

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Formation of free radicals in photoirradiated cellulose. VI. Effect of lignin

Cited by 42 publications

References 14 publications

Dual role of lignin in plant litter decomposition in terrestrial ecosystems

Dual role of lignin in plant litter decomposition in terrestrial ecosystems

Influência das características tecnológicas na cor da madeira de eucaliptos.

Free radicals and their electron spin relaxation in cellobiose. X-band and W-band ESR and electron spin echo studies

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