Cell wall penetration

A very important factor in ensuring that full cell wall penetration has occurred is to allow sufficient time for the impregnant molecules to diffuse into the intracellular spaces. Many workers allow several days (weeks in some cases) for this to occur. It is important to emphasize that pressure treatment will aid penetration of larger wood samples, but will not in any way result in cell wall penetration, which is a purely diffusion-controlled process. 

Rozman etal. (1997a) treated rubberwood by impregnation with a methanolic solution of TMPS for 24 hours, followed by curing at 110°C for 5 hours. No solvent extraction was employed after treatment. Volume increases due to treatment were considerably lower than predicted theoretically, showing that little cell wall penetration had occurred. ASE measurements were made over two cycles, and it was found that ASE increased in the second cycle. This odd behaviour was not explained and the experimental details for ASE determination were not given. 

A solution of styrene in methanol to impregnate wood samples, followed by polymerization, was used by Furuno and Goto (1979). Penetration of the monomer into the cell wall was determined by solvent extraction of samples after polymerization. This removed lumen located polymer, whilst leaving the cell wall bound polymer in place. This showed that the concentration of cell wall bound polymer increased in proportion to the monomer content in methanol, up to a maximum of 80% of the monomer in the solvent. No cell wall penetration was observed for treatment with neat monomer. This was also found for bulking of the wood, as determined from external dimensions of the samples. Improvements in ASE were obtained as a result of the presence of cell wall bound polymer. To achieve similar ASE values with lumen located polymer required very high polymer loadings. 

Chemical modification will be defined for this chapter as any chemical reaction between some reactive part of a wood cell wall component and a simple single chemical reagent, with or without catalyst, that forms a covalent bond between the two components. This excludes in situ polymerizations of monomers in the lumen structure of the wood and those reactions that result in cell wall-penetrating polymer systems that do not result in any cell wall attachment. It is well known that lumen-filling polymer treatment results in large improvements in mechanical properties, but these are mainly a result of the properties of the new polymer introduced [ 1 ]. 

Many monomers have been studied, including acrylonitrile, acrylates, methacrylates, styrene, and t-butylstyrene (ii). Most of the research done with these monomers has shown that the formed polymer is in the lumen rather than in the cell wall. Swelling, cell-wall-penetrating solvents can be used to achieve cell wall penetration, so that the polymers that form are in both the cell wall and the lumen. 

Eight classes of natural products that are inhibitors of FPTase have been described from a variety of microbial sources. Mechanistically, these compounds are competitive with FPP. All compounds, with the exception of manumycins, possess negative charges in the form of one or more carboxylic, sulfuric or phosphoric acids, and are not active in cell-based assays. The lack of cell-based activities for these classes of natural products is linked to the negative charge present in these compounds that appears to be detrimental for cell wall penetration. Manumycin, in contrast, is not only active in cell-based assays but is also active in animal models. 

Accordingly it appears that further QSAR investigations should focus separately on those parameters facilitating both cell wall penetration and those required for DNA gyrase inhibition. Then it should be possible to design structures which would maximize both responses. 

Usually, penetration of adhesives can be described as filling up the lumens by the adhesive material. Cell wall penetration [9,46], in principle, is possible, but rather appUes only to substances with low molar masses, like impregnating resins [42 14,... 

Plate 4 Soft rot attack of Alstonia spp. showing typical cavity attack (Q, cell wall erosion (E) and cell wall penetration (P). Bar = 50 pm. 

They were unable, however, to obtain good correlations with log P for other classes of compounds, and point out that there is evidence (Miller etal. 1972) that cell-wall penetration may not be the rate-limiting step in enzymatic reactions. 

The uptake of hexylresorcinol by . coli in the presence and absence of cetomacrogol exhibits the same trend as the uptake of iodine from aqueous solution and surfactant mixtures, with a marked reduction in the presence of detergent [190] the rate of uptake is not affected. Beckett et al. [190] consider that the phenol-cetomacrogol complex probably prevents cell-wall penetration. The amount of hexylresorcinol bound per organism is less than the theoretical... 

Puck, T. T., Lee, H. H. Mechanism of cell wall penetration by viruses. II. Demonstration of cyclic permeability change accompanying virus infection of Escherichia coli B cells. J. exp. Med. 101, 151-175 (1955). 

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