Peter E. Laks

Flavonoid biocides: wood preservatives based on condensed tannins

Summary The condensed tannins are natural wood preservatives found in high concentrations in the bark and wood of some tree species. Condensed tannin-containing bark extracts from loblolly pine (Pinus taeda) were evaluated as wood preservatives using standard methods. Bark extracts by themselves did not cause any reduction in weight loss of pressure-treated wood blocks at the retentions tested. However, they do have efficacy as wood preservatives when complexed with copper (II) ions. The best experimental wood preservative formulation was a dual treatment using a sulphited bark extract first, followed by a Cu~ treatment. At some retentions, this method yielded wood blocks with greater resistance to decay by Corio/us versicolor than pentachlorophenol. A single stage treatment of extract plus copper using an aqueous ammoniacal solvent was also successful but not as effective as the dual treatment.

Flavonoid biocides: Structure/activity relations of flavonoid phytoalexin analogues

Abstract Two sets of semisynthetic flavonoid phytoalexin analogues were synthesized and their lipophilicity ( R M ) correlated with their antifungal and antibacterial activity. Two natural phytoalexins, pisatin and maackiain, were also tested under these same conditions, and their R M s determined. The observed structure/activity relationships suggest that these analogues, and the phytoalexins, function primarily as uncouplers of oxidative phosphorylation. The relative acidity and number of hydroxyl groups per molecule appear to be the main factors affecting the antifungal activity of flavonoids. with the bacterium, Streptococcus faecium , there is not the same simple correlation between lipophilicity and antibacterial activity for the two sets of analogues, implying they have different modes of action.

Use of nanoparticles for controlled release of biocides in solid wood

The fungicides tebuconazole and chlorothalonil were successfully incorporated into polymeric nanoparticles with median particle diameters of 100–250 nm. Polyvinylpyridine (PVPy) and polyvinylpyridine-co-styrene (10% styrene and 30% styrene) were employed as the polymer matrix. The size of the nanoparticle increased with increased styrene content. The biocide also affected particle size, with chlorothalonil consistently yielding larger nanoparticles than tebuconazole. The release of the biocides from the polymeric nanoparticles was studied by suspending them in water. The release rate of both tebuconazole and chlorothalonil decreased with increased styrene content in the matrix, and chlorothalonil consistently released more slowly from the polymeric nanoparticles than did tebuconazole. It was found that biocides were successfully introduced into solid wood by incorporating them within polymeric nanoparticles, suspending the nanoparticles in water, and using the suspension to treat the wood with conventional pressure treatments. Once in the wood, the polymer matrix serves as a reservoir for the biocide and controls its release rate into the wood. Southern pine sapwood samples were treated with biocide-containing nanoparticles suspended in water, then exposed to the wood decay fungus Gloeophyllum trabeum using a simple wafer test. Samples exhibited fungal resistance at appropriate levels of biocide incorporation.

Flavonoid biocides: Phytoalexin analogues from condensed tannins

Abstract Flavonoids containing a single alkyl chain can be synthesized from condensed tannins by thiolysis with an alkyl thiol to give epicatechin-4-alkylsulphides. A number of flavonoid derivatives were made with side chains ranging from C 6 to C 16 and tested for fungitoxic and bactericidal activities. Maximum activity was usually found for the decane derivative. Minimum inhibitory concentrations varied with the organism tested, from about 10 ppm for some rapidly growing fungi and Gram-positive bacteria, to over 500 ppm for other fungi and Gram-negative bacteria. The structural and toxicity characteristics of the epicatechin-4-alkylsulphides suggests they are acting as analogues of prenylated isoflavonoid phytoalexins.

A Method for Digital Color Analysis of Spalted Wood Using Scion Image Software

Color analysis of spalted wood surfaces requires a non-subjective, repeatable method for determining percent of pigmentation on the wood surface. Previously published methods used human visual perception with a square grid overlay to determine the percent of surface pigmentation. Our new method uses Scion Image©, a graphical software program used for grayscale and color analysis, to separate fungal pigments from the wood background. These human interface processes render the wood block into HSV (hue, saturation, value, within the RGB color space), allowing subtle and drastic color changes to be visualized, selected and analyzed by the software. Analysis with Scion Image© allows for a faster, less subjective, and easily repeatable procedure that is superior to simple human visual perception.

Condensed tannins. Base-catalysed reactions of polymeric procyanidins with phloroglucinol: Intramolecular rearrangements

Reactions of polymeric procyanidins with phloroglucinol at pH 12.0 and temperatures of 23 or 50 °C gave epicatechin-(4β)-phloroglucinol (7), by cleavage of the interflavanoid bond between procyanidin units with subsequent addition of phloroglucinol, and (+)-catechin from the terminal unit. The phloroglucinol adduct (7) rearranged to an enolic form of 8-(3,4-dihydroxyphenyl)-7-hydroxy-6(2,4,6-trihydroxyphenyl)bicyclo[3.3.1]nonane-2,4,9-trione (9). Rearrangement of a dimeric procyanidin phloroglucinol adduct resulted in the formation of 3′-{8-(3,4-dihydroxyphenyl)-7-hydroxy-2,4,9-trioxobicyclo[3.3.1 ]nonan-6-yl}-4-(3,4-dihydroxyphenyl)-2′,3,4′,5,6′,7-hexahydroxyflavan (10), also in an enolic form. (+)-Catechin, from the terminal unit, gave catechinic acid, an enolic form of 6-(3,4-dihydroxyphenyl)-7-hydroxybicyclo[3.3.1]nonane-2,4,9-trione (4).

Condensed tannins: base-catalysed reactions of polymeric procyanidins with toluene-α-thiol. Lability of the interflavanoid bond and pyran ring.

Reaction of polymeric procyanidins (condensed tannins) with toluene-α-thiol at pH 12.0 and 23 °C gave predominantly one stereoisomer of 1,3-bisbenzylthio-1-(3,4-dihydroxyphenyl)-3-(2,4,6-trihydroxyphenyl) propan-2-ol (10) by stereoselective reaction at C-4 and C-2 of the quinone methide derived from the upper 2,3-cis procyanidin units. Smaller amounts of two isomers of 1-benzylthio-1-(3,4-dihydroxyphenyl)-3-(2,4,6-trihydroxyphenyl)propan-2-ol (4) were obtained by reaction at the C-2 of catechin obtained from the terminal units. At higher temperatures, (10) loses toluene-α-thiol preferentially from C-1 to give 1-benzylthio-1-(3,4-dihydroxyphenyl)-3-(2,4,6-trihydroxyphenyl)propan-2-one (11) by a tautomeric rearrangement of the quinone methide via an enol to the ketone. Loss of toluene-α-thiol from (4) gave 1-(3,4-dihydroxyphenyl)-3-(2,4,6-trihydroxyphenyl)propan-2-one (5) by a similar rearrangement. This compound further rearranges to 1-(3,4-dihydroxyphenyl)-4,6-dihydroxyindan-2-one (6).

Effects of substrate on laboratory spalting of sugar maple

Abstract Spalting is the coloration of wood caused by fungal colonization. Woodturners, craftspeople, and artists appreciate spalted wood for its aesthetic appeal and uniqueness. Laboratory-induced spalting aims at a repeatable procedure in which wood is inoculated with selected fungi to obtain natural color with high aesthetic appeal, low weight loss and good machinability. Vermiculite (a natural clay with a high capacity for water holding and cation exchange) has been the primary incubation substrate for spalting research despite soil being the standard substrate for soil block decay testing. In this research, we explored the differences between these two substrates and their effects on the growth of spalting fungi on sugar maple (Acer saccharum) wood. Five fungi, Trametes versicolor, Xylaria polymorpha, Arthrographis cuboidea, Ceratocystis pilifera, and Ceratocystis virescens, were tested for their weight loss and spalting abilities on 14-mm sugar maple cubes incubated in both soil and vermiculite. Weight losses from all fungi were either unaffected or reduced by incubation in vermiculite compared to soil. In vermiculite, X. polymorpha produced more zone lines and A. cuboidea produced more pigment than blocks incubated in soil. Growth in vermiculite decreased weight loss of blocks inoculated with T. versicolor and X. polymorpha, while bleaching was unaffected regardless of substrate. External blue stain was higher on blocks inoculated with either Ceratocystis species and incubated in soil. These results indicate that vermiculite is a better substrate for spalting regardless of fungus due to the higher external pigmentation, lower weight loss, and better color contrast on the sugar maple blocks incubated in this substrate.

Condensed Tannins: A Proposed Route to 2R,3R-(2,3-cis)-Proanthocyanidins

The biogenesis of 2R,3R-(2,3-cis)-proanthocyanidins from 2R,3R-(2,3-trans)-dihydroflavonols can be accounted for by tautomerism between quinone methide and flav-3-en-3-ol intermediates.

CONDENSED TANNINS: DESULFONATION OF HYDROXYBENZYLSULFONIC ACIDS RELATED TO PROANTHOCYANIDIN DERIVATIVES

Abstract Studies on the desulfonation of 2,4,6-trihydroxybenzylsulfonic acid and sodium epicatechin-(4β)-sulfonate showed that sulfonates α to a phloroglucinol ring are good leaving groups at ambient temperature and pH greater than 8.0. In contrast, hydroxybenzylsulfonic acids with resorcinol or phenol hydroxyl functionality resist desulfonation even at pH 12 and 90°C. It was also not possible to make (2,4,6-trihydroxyphenyl), (4-hydroxyphenyl)-methane or (2,4,6-trihydroxyphenyl),(2,4-dihydroxyphenyl)-methane by slow addition of 2,4,6-trihydroxybenzylsulfonic acid to alkaline solutions of phenol or resorcinol. However, facile desulfonation of 2,4,6-trihydroxybenzylsulfonic acid derivatives permits the use of condensed tannins from most conifer barks as intermediates for the formulation of water-resistant, cold-setting, wood-laminating adhesives. Under typical adhesive formulation conditions, the sulfonic acid groups on tannin derivatives from conifer barks will he displaced, resulting in water-insoluble p...