Darrel D. Nicholas

Naturally durable heartwood: evidence for a proposed dual defensive function of the extractives

We previously proposed that extractives in highly durable heartwood may protect wood against fungal colonization and subsequent degradation by dual mechanisms: the extractives have some fungicidal activity and are also free radical scavengers (antioxidants). In short-term laboratory decay tests using two different wood species and decay fungi, the antioxidant 2,6-dimethyl-di-tert-butyl-4-methylphenol (BHT) alone had little or no preservative effect. In contrast, the combination of BHT with different organic commercial biocides always showed an increase in efficacy compared to the organic biocide alone. Consequently, we conclude that the combination of a commercial antioxidant and biocide is synergistic. This implies that extractives may protect wood by more than simply being fungicidal.

Development of environmentally-benign wood preservatives based on the combination of organic biocides with antioxidants and metal chelators.

Wood extractives can be envisaged to protect heartwood by at least three different mechanisms, i.e. fungicide, free radical scavengers/antioxidants and as metal chelators. In short-term laboratory decay tests using two different wood species and decay fungi, the combination of different organic fungicides with various antioxidants and/or metal chelators gave enhanced activity as compared to the organic biocide alone, with the best results usually obtained with all three compounds. Outdoor ground-contact stakes treated with a biocide and antioxidant combination and exposed for 30 months also gave enhanced protection against both decay fungi and termites. It was concluded that the combination of an organic biocide with metal chelating and/or antioxidant additives gives enhanced protection to wood against fungi as compared to the biocide alone and, consequently, it may be possible to develop environmentally-benign wood preservative systems based on this idea.

Role of stilbenes in the natural durability of wood: Fungicidal structure-activity relationships

Abstract The fungicidal bioactivity of a number of ( E )-4-hydroxy-3′- and/or 4 - substituted stilbenes and related analogues was measured against the white-rot fungus Coriolus versicolor and the brown-rot fungi Gloeophyllum trabeum and Poria placenta using the agar plate technique. The bioactivity of didecyldimethylammonium chloride (DDAC), an effective wood preservative, was also determined for comparison purposes. Only DDAC and a (reduced) bibenzyl derivative with a 4′-hydrogen showed fungicidal activity against the white-rot fungus. Against the two brown-rot fungi all stilbenes with a 4′-hydrogen and also a (reduced) bibenzyl compound with a 4′-hydrogen had greater activity than DDAC. A quantitative structure-activity relationship study found that stilbene brown-rot bioactivity was linearly related to hydrophobicity. The results of this study and a review of the prior literature suggests that stilbene phytoalexins may be modified in vivo by partial methylation to further enhance their bioactivity.

Durability of angiosperm heartwood : the importance of extractives

Analysis of osage orange (Maclura pomifera) heartwood extractives showed that two compounds were present at much higher levels than previously reported, the flavanonol dihydromorin (2.51%) and the stilbene oxyresveratrol (2.65%). All compounds present in osage orange heartwood that were tested had low activity against wood-decaying fungi. The agar plate test showed no synergistic effect, but the soil block test usinh white-rot fungi suggested synergism. The high durability of osage orange heartwood may be due to the large amounts of oxyresveratrol and dihydromorin. High levels of one or two monomeric compounds may also explain the exceptionally good durability of black locust and red mulberry heartwood

Structural characterization of brown-rotted lignin.

On etudie la structure de la lignine de sapin Douglas degradee par les basidiomycetes responsables de la pourriture brune

Structure-fungicidal properties of some 3- and 4-hydroxylated stilbenes and bibenzyl analogues

Abstract The fungicidal activity of some substituted hydroxylated stilbenes and bibenzyls was measured against three wood-destroying fungi using the agar plate technique. Four 3-hydroxystilbene derivatives and 3-hydroxy-bibenzyl were active against the white-rot fungus Coriolus versicolor . A tentative structure-activity relationship was proposed for stilbene C. versicolor activity. The previously proposed hypothesis that white-rot extracellular enzymes oxidatively degrade stilbenes which makes white-rot fungi immune to stilbenes may need to be reexamined. No structure-activity relationship was apparent for stilbenes tested against the two brown-rot fungi Gloeophyllum trabeum and Poria placenta . Of the two natural hydroxylated stilbenes studied, pinosylvin was slightly more active against G. trabeum and C. versicolor than pinosylvin monomethyl ether. Surprisingly, neither of these two natural stilbenes showed much activity against the copper-tolerant fungus P. placenta .

Biological resistance of southern pine and aspen flakeboards made from acetylated flakes

Abstract Standard soil block tests can be used for southern pine and aspen flskeboards made with phenol-formaldehyde adhesive if the boards are first leached to remove toxic residual chemicals which inhibit fungal attack. Standard fungal cellar and termite tests can be applied directly without leaching. Flakeboards made from flakes acetylated by a new simplified dip acetic anhydride procedure are resistant to attack by brown-, white-, and soft-rot fungi and tunneling bacteria at acetyl weight gains above 15%. Acetylated flakeboards at 18 to 21% acetyl weight gains are not completely resistant to attack by subterranean termites.

Comparison of the fungicidal activities of (E)-4-hydroxylated stilbenes and related bibenzyls

Abstract The fungicidal activities of ( E )-4-hydroxylated stilbenes and related bibenzyls were measured by the agar plate procedure and selected active compounds by the soil block method. In the agar plate test, stilbenes with 3′-substituents were all active against two brown-rot ( G. trabeum and P. placenta ) fungi, with the activity having a parabolic hydrophobic relationship. A highly fungitoxic monomer was used to synthesize a dehydrogenative dimer which showed no brown-rot activity. No stilbene was active against the white-rot fungi C. versicolor while three bibenzyls had white-rot activity. Most bibenzyls had moderate brown-rot fungicidal activity. No structural requirement was apparent for bibenzyl brown-rot activity in contrast to the stilbenes. No synergism was observed when various combinations of stilbenes and bibenzyls were tested by the agar plate procedure. Similarities were observed between the agar plate activity and soil block results, although the soil block required higher levels of the stilbene/bibenzyl. No synergism was observed in the soil block results for stilbene and/or bibenzyl combinations. Stilbenes and/or bibenzyls in combination with didecyldimethylammonium chloride, however, showed some synergism.

Wood Enhancement Treatments I. Impregnation of Southern Yellow Pine with Melamine-Formaldehyde and Melamine-Ammeline-Formaldehyde Resins

Abstract Southern yellow pine (SYP) was impregnated with melamine-formaldehyde (MF) or melamine-ammeline-formaldehyde (MAF) resins. The dimensional stability, strength properties, weathering, fire resistance and chemical resistance of the impregnated wood were examined. The wood treated with two commercial MF resins or with a synthesized MAF resin exhibited greatly enhanced dimensional stability, fire resistance and resistance to weathering. The chemical resistance increased moderately.

Mineralization of the methoxyl carbon of isolated lignin by brown-rot fungi under solid substrate conditions

SummaryThe objectives of this work were to begin developing an experimental system for studying the demethylation of lignin by brown-rot fungi and to examine the influence of selected culture parameters. As substrate for demethylation, we used partially 3-O-demethylated lignin that had been isolated earlier from brown-rotted spruce wood; we remethylated with14CH3I, giving a lignin with both [3-14C]methoxyl and [4-14C]methoxyl groups. This lignin was added to pine wood flakes, which were incubated with selected brown-rot fungi, and the evolved14CO2 was trapped and measured. Of eight fungi examined,Gloeophyllum trabeum andWolfiporia cocos gave the highest rates of mineralization of the14C-methoxyl carbons. With the former but not the latter fungus, methoxyl mineralization was over twice as fast in an atmosphere of O2 than in air. Amending the cultures with ammonium tartrate suppressed mineralization to some extent. Further studies withG. trabeum showed that glutamate lowered the rate of mineralization and that glucose and glycerol sharply suppressed it. Addition of Fe2+ and Mn2+ slightly increased the rate of mineralization. Our results suggest that in unsupplemented cultures the rate-limiting step in methoxyl mineralization is the initial demethylation. Thus the two likely initial C1 products, methanol and formaldehyde (as14C compounds), were mineralized much more rapidly than the methoxyl carbon of the lignin (as was formic acid), and no low molecular weight labeled intermediates from the [14C]-methoxyl lignin accumulated in the cultures. Our results also provide evidence that the spruce lignin was partially polymerized byG. trabeum. Mineralization of the methoxyl carbon of a synthetic [3-14C]-methoxyl lignin was slower than that of the spruce lignin, suggesting either that the synthetic lignin was more recalcitrant or that the [4-14C]methoxyl group in the [3,4-14C]-methoxyl spruce lignin was attacked more readily.