Chemistry of phenolic stains in Douglas-fir sapwood Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/12579v73w

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  • Dihydroquercetin [(2,3-trans)-3,3',4',5,7-pentahydroxyflavanonol] was shown to be the precursor to the phenolic stains that often develop in Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] sapwood. Douglas-fir sapwood was extracted with methanol and the methanol solubles were fractionated by solvent partition, thin-layer chromatography, silica-gel column chromatography, and Sephadex gelpermeation chromatography. Tyrosinase, a commercially available catechol oxidase enzyme, was used to locate and trace the precursors to color formation in the solubilized materials. Careful control of the separations and careful testing of the fractions for color formation resulted in the identification and isolation of dihydroquercetin as the precursor of the stains. It was established that neither oregonin, the color precursor of stains in red alder wood and bark, nor catechin, a flavonoid that has been associated with stains in western hemlock wood, were involved in the staining of Douglas-fir sapwood. The inhibitors, ethylenedinitrillotetraacetic acid disodium salt (EDTA), phenylthiourea, mercaptobenzothiazole, and Chloramine-T proved ineffective in preventing color formation when the methanol-extracted materials from Douglas-fir sapwood were treated with tyrosinase. An improved method of isolating dihydroquercetin from Douglas-fir bark was developed. This pure crystalline dihydroquercetin was reacted with tyrosinase to simulate the reactions that might lead to color formation in Douglas-fir sapwood. The reaction mixture became brown in color and a dark brown polymeric precipitate formed. The brown polymer was recovered and was shown to have a number of characteristics similar to the stains in Dotglas-fir sapwood by ultraviolet and infrared spectroscopy. The compounds 3,4- dihydroxybenzoic acid (protocatechuic acid), 3,4-dihydroxyphenylacetic acid, and quercetin were found in the reaction products of dihydroquercetin and tyrosinase. They were considered to be degradation products of dihydroquercetin and possible intermediates in polymeric stain formation. Thus, a relationship between the presence of dihydroquercetin, enzyme action, and the phenolic stains that often develop in Douglas-fir sapwood was established.
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