Chemistry of Bark

The chemical composition of bark is complicated, varies among the different tree species and also depends on the morphological elements involved. Many of the constituents present in wood also occur in bark, although their proportions are different. Typical of bark is its high content of certain soluble constituents (extractives) such as pectin and phenolic compounds as well as suberins. The mineral content of bark is also much higher than that in wood. 

Bark can roughly be divided into the following fractions fibers, cork cells, and fine substance including the parenchyma cells. The fiber fraction is chemically similar to that of the wood fibers and consists of cellulose, hemicelluloses, and lignin. The other two fractions contain large amounts of extractives. The walls of the cork cells are impregnated with suberin, whereas the polyphenols are concentrated in the fine fraction. 

The lipophilic fraction, extractable with nonpolar solvents (ethyl ether, dichloromethane, etc.) consists mainly of fats, waxes, terpenes and terpenoids, and higher aliphatic alcohols (cf. Sections 5.3.1 and 5.3.2). Terpenes, resin acids, and sterols are located in the resin canals present in the bark and also occur in the cork cells and in the pathological exudate (oleore-sin) of wounded bark. Triterpenoids are abundant in bark /3-sitosterol occurs in waxes, as an alcohol component, and the cork cells in the outer bark (periderm) of birch contain large amounts of betulinol (cf. Fig. 5-6). 

Minor amounts of soluble carbohydrates, proteins, vitamins, etc., are present in the bark. In addition to starch and pectins, oligosaccharides, including raffinose and stachyose have been detected in phloem exudates. 

Polysaccharides, lignin, and suberins are the principal cell wall constituents of bark. 

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Jensen W, Fremer K E, Sierila P, Wartiovaara V 1963 The chemistry of bark. In Browning B L (ed) The chemistry of wood. Wiley-Interscience New York London, 587-666... 

Raymond-Hamet has published, with a bibliography, a critical historical account of the botany and chemistry of pereiro bark, the botanical source of which he suggests should be named Geissospermum Iceve (Vellozo) Baillon. There seems to be some doubt as to whether vellosine was actually obtained from this species. 

The Chemistry of Birch Bark and Birch Bark Tars... 

Aveling, E.M. and Heron, C. (1998). The chemistry of birch bark tars at Mesolithic Star Carr. Ancient Biomolecules 2 69-80. 

Hartley, F. R., "The Chemistry of Platinum and Palladium. Applied Science Publ., Barking, 1973. 

Bast or Bass is the fibrous inner bark of linden, lime and some milkweed trees. It is used for ropes, mats, peasant shoes(such as Rus"lapti"). The term blast fiber is applied to fibers obtained from the inner bark of flax, hemp, jute, ramie, etc. They contain a considerable amt of cellulose and can be nitrated to NC. However, these substances are more valuable as fabric materials than as sources of NC. Ramie has been used in France for prepn of pure NC Ref J.T.Marsh F.C.Wood, "An Introduction to the Chemistry of Cellulose",Chapman Hall, London( 1945), 1,3 12... 

Timell, T. E. (1965). Wood and bark polysaccharides. In "Cellular Ultrastructure of Woody Plants" (W. A. C6te, Jr., ed.), pp. 127-156. Syracuse Univ. Press, Syracuse, New York. Timell, T. E. (1967). Recent progress in the chemistry of wood hemicelluloses. Wood Sci. Technol. 1,45-70. 

Following World War II, extensive investigative effort was initiated to find new uses for the mountains of bark generated as byproducts of the West Coast forest products industry in the United States and Canada. This work was carried out at the Institute of Paper Chemistry (sponsored by the Pacific Lumber Company of Scotia, California), the Oregon Forest Products Laboratory, Rayonier Incorporated, the Weyerhaueser Company, and the Forest Products Laboratory on the University of British Columbia campus. 

Tannins. Herb Hergert s introduction (Chapter 12) to the use of condensed tannins in adhesives is especially interesting because he provides some reasons why commercial success is lacking in the use of condensed tannins from conifer barks despite substantial effort worldwide to parallel the South African success in the use of wattle tannins. Much of the problem in the use of conifer bark tannins remains centered on our inadequate understanding of the fundamental chemistry of these polymers. For example, Lawrence Porter (Chapter 13) provided the first measurements of the viscosities of solutions of purified condensed tannin isolates of known molecular weight and the reactions of these polymers with formaldehyde. It is incredible that this has not been done previously considering the hundreds of papers that have been published on tannin use in wood adhesives. Further evidence for the comparatively limited knowledge... 

Some aspects of the chemistry of lauren-l-ene, including the remote functionalization of other rings based on the I2-Pb(OAc)4 oxidation of laurenan-2-ols, have been described.158 X-Ray crystallographic evidence has been presented for the structure (92) of cinncassiol D, a pentacyclic diterpenoid from the dried bark of Cinnamomum cassia possessing anti-complement activity.159... 

The chemistry and biochemistry of wood have been summarized in several monographs. Numerous reviews of the chemistry of the hemi-celluloses are also available. " The chemistry of the polysaccharides associated with wood cellulose and the structural chemistry of the hemi-celluloses have previously been discussed in this Series. In the following, the structures and properties of all wood hemicelluloses will be considered in detail, and brief reference will also be made to their location in the wood. Topics not reviewed are evolution of wood hemicelluloses, their biosynthesis, their possible association with lignin in the wood, and their behavior in the technical pulping and bleaching processes. The hemicelluloses occurring in the bark of trees have also been omitted. 

Tanaecium noctumum . A psychoactive snuff called koribo is prepared by Brasilian Paumari Indians from roasted, pulverized leaves of this plant with tobacco (Prance etal. 1977). Tea of the root-bark is also psychoacdve, apparently sedative (Schultes Hofmann 1980). It has been reported that merely smelling plant has provoked psychoactive effects in researchers (Schultes Hofinann 1980). The chemistry of this intriguing drug is obscure. 

BYERS, J.A., Host-tree chemistry affecting colonization of bark beetles, in Chemical Ecology of Insects 2 (R.T. Carde and W.J. Bell, eds,). Chapman and Hall, New York. 1995, pp. 154-213. 

The presence of acetate substituents on the side chain at C-6 is very common. Compounds (40) and (41) were isolated by Drewes et al from the bark of Cryptocarya latifolia trees in their investigations of the chemistry of plants used for magical and medicinal purposes by the Zulu people (55). The CD spectra of these two compounds show a positive Cotton effect and hence they possess the (67 )-configuration. Saponification followed by acetonide formation of (40) afforded two acetonides (42) and (43) (50). A (2 7 ,6 5)-stereochemistry followed from application of the MTPA determination rule (24) to the (/ )- and (5)-MTPA esters of these acetonides. A (4 5)-stereochemistry was assigned from the syn-diol relationship of the two acetal oxygen atoms in (42) and (43) as determined from their C NMR spectra (57). Thus the acetonide rings in both compounds possessed chair conformations with the alkyl... 

Nomura, T., T. Fukai, Y. Momose, and T. Narita Structures of the Hypotensive Constituents of the Root Bark of the Mulberry Tree Moms alba l.), 23rd Symposium on the Chemistry of Natural Products, Symposium Paper, p 552, Oct., 1980, Nagoya, Japan. 

Hano, Y., T. Fukai, H. Tsubura, and T. Nomura Some Pigments and Related Compounds of Morus Root Bark, 27th Symposium on the Chemistry of Natural Products, Abstract Paper, p 710, Oct. Hiroshima, Japan, 1985. 

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