Cell wall reactivity

3 Cell Wall Reactivity 3.3.1 Cell Wall Accessibility 

It has been stated mat me reactivity of the wood cell wall polymers to acetic anhydride decreases in me order lignin hemicelluloses cellulose, both within me wood cell wall (Rowell, 1982) and with me isolated polymers (Callow, 1951 Rowell etal., 1994 Efanov, 2001). A comprehensive series of NMR studies has been performed investigating me substitution of me cell wall polymeric OH groups at various WPGs (Ohkoshi and Kato, 1992, 1993, 1997a,b). These have shown that not all of me lignin OH groups are 

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The anatomical stmcture of wood affects strength properties, appearance, resistance to penetration by water and chemicals, resistance to decay, pulp quabty, and the chemical reactivity of wood (5). To use wood most effectively requires a knowledge of not only the amounts of various substances that make up wood, but also how those substances are distributed ia the cell walls. 

A conceptualized cross section through a portion of the cell wall (rectangles), periplasmic space, and cell membrane (lipid bilayer with polar head groups in contact with cytoplasm and external medium, and hydrophobic hydrocarbon chains) of an aquatic microbe. Reactive functional groups (-SH, -COOH, -OH, -NH2) present on the wall consitutents and extracellular enzymes (depicted as shaded objects) attached by various means promote and catalyze chemical reactions extracellularly. 

The next study of wood modification was that reported by Baird (1969), who performed vapour-phase reactions of spruce with ethyl, n-butyl, /-butyl, allyl and phenyl isocyanate (PhNCO). Unfortunately, DMF was used as a catalyst for the reactions, which resulted in polymerization of PhNCO in the cell wall of the wood, leading to unpredictable results. No evidence was presented in support of the contention that polymerization had occurred, and since this requires an anionic catalyst initiator, this is considered unlikely. However, the presence of side reactions when DMF is used in conjunction with isocyanates has already been mentioned. Greater success was reported when butyl isocyanate was reacted with wood (presumably a consequence of the lower reactivity of this isocyanate... 

Epoxides can react with alcohols via acidic or basic catalysed reaction mechanisms. However, since both strong acids and bases will degrade the cell wall polymers of wood, the reaction is usually catalysed via the use of amines, which are more strongly nucleophilic than the OH group. For example, whereas the production of epoxy-phenolic resins requires temperatures in the region of 180-205 °C, reaction between epoxides and primary or secondary amines takes place at 15 °C (Turner, 1967). Reaction of epoxides with wood often involves the use of tertiary amines as catalysts (Sherman etal., 1980). The sapwood is more reactive towards epoxides than heartwood (Ahmad and Harun, 1992). 

Rowell, R.M. (1984a). Penetration and reactivity of cell wall components. In The Chemistry of Solid Wood, Rowell, R.M. (Ed.). Advances in Chemistry Series, 207, American Chemical Society, pp. 175-210. 

Rowell, R.M., Simonsen, R., Hess, S., Plackett, D.V., Cronshaw, D. and Dunningham, E. (1994). Acetyl distribution in acetylated whole wood and reactivity of isolated cell wall components to acetic anhydride. Wood and Fiber Science, 26(1), 11-18. 

Koenders MI, Rolls JR, Oppers-Walgreen B, van den Bersselaar L, Joosten LA, Schurr JR, Schwarzenberger P, van den Berg WB, Lubberts E Interleukin-17 receptor deficiency results in impaired synovial expression of interleukin-1 and matrix metalloproteinases 3, 9, and 13 and prevents cartilage destruction during chronic reactivated streptococcal cell wall-induced arthritis. Arthritis Rheum 2005 52 3239-3247. 

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