Lignin plants

It weis found that hardwood lignins yielded both guaiacyl and syringyl units on oxidation, whereas softwood lignins yielded only guaiacyl units. Hibbert and co-workers (20), (21) distinguished perennial plant lignins... 

Since the oxidative polymerization of phenols is the industrial process used to produce poly(phenyleneoxide)s (Scheme 4), the application of polymer catalysts may well be of interest. Furthermore, enzymic, oxidative polymerization of phenols is an important pathway in biosynthesis. For example, black pigment of animal kingdom "melanin" is the polymeric product of 2,6-dihydroxyindole which is the oxidative product of tyrosine, catalyzed by copper enzyme "tyrosinase". In plants "lignin" is the natural polymer of phenols, such as coniferyl alcohol 2 and sinapyl alcohol 3. Tyrosinase contains four Cu ions in cataly-tically active site which are considered to act cooperatively. These Cu ions are presumed to be surrounded by the non-polar apoprotein, and their reactivities in substitution and redox reactions are controlled by the environmental protein. 

As to the origins of the major N compounds identified, it is possible that at least a portion of some of these compounds are pyrolysis products of amino acids, peptides, proteins, [18] and porphyrins (a component of chlorophyll), [19] or originate from the microbial decomposition of plant lignins and other phenolics in the presence of ammonia. [20] Of considerable interest are the identifications aromatic and aliphatic nitriles. Nitriles can be formed from amines with the loss of 2 H2, from amides with the loss of H20, and also by reacting n-alkanoic acid with NH3. [21] The detection of long-chain alkyl- and dialkyl-nitriles points to the presence in the soil or SOM of long-chain amines... 

For example, the dynamic state of backbone sites in synthetic block copolyesters, as well as the chemical bonding patterns in plant lignins, have been elucidated (4-6). 

Haider, K., Martin, J. P., and Rietz, E. (1977). Decomposition of 14C-labelled coumaryl alcohols free and linked to dehydropolymer and plant lignins and model humic acids. Soil. Sci. Soc. Am. J. 41, 556-562. 

Even the structural material of plants, lignin, comes from the shikimic acid pathway. Lignin—from which wood is made—has a variable structure according to the plant and the position in the plant. A typical splinter is shown here. 

High-temperature cupric oxide (CuO) oxidation of vascular plant lignins yields the eight simple phenols illustrated here as major reaction products. These reaction products comprise monomethoxylated (vanillyl) and dimethoxylated (syringyl) phenols, which occur primarily as aldehydes, along with smaller amounts of the corresponding ketones and acids. Two cinnamyl phenols (p-coumaric and ferulic acid) are also produced that retain the three-carbon side chain of the original structural units and terminate in a carboxyl. 

Terrestrial organic matter is derived mainly from higher plants lignin and cuticular waxes are its most stable constituents. In contrast, organic matter... 

Source Landucci, L.L., lEA Presymposium on Analysis of Wood, Annual Plant lignins, New Orleans, LA., 1991. 

Plants - Lignin, tannins, and pigments, flavor components of spices (cinnamon oil, wintergreen oil, bitter almond, nutmeg, cayenne pepper, vanilla bean, clove, and ginger) are derived from coniferyl alcohol. Coniferyl alcohol, in turn, is derived from phenylalanine and tyrosine. Phenylalanine is also a precursor of plant pigments and related polyphenolic compounds called flavonoids. The biosynthetic scheme leads to a class of flavonoids called anthocyanins, which are common flower pigments.. An offshoot of this pathway leads to the synthesis of cocaine. 

Phenol Hydroxy benzene biopolymers built with phenol-based compounds that have oxygen-containing groups attached to the central aromatic ring are common in higher plants (lignins and tannins), but they are rare in algae and animals. 

In the last years, presence of new structures in plant lignins has been reported (Fig. 8.6). 

The interesting aspect of one of these examples (Figure 3.20) is the inclusion of carbon dioxide within the cycle. Both postulates recognize the production of carbon dioxide from coal, thereby pointing out the relationship of carbon dioxide and coal but recognition of carbon dioxide as part of the natural cycle between plants, lignin, humus, and coal underscores the closeness of the relationship and the end product of the environmental aspects of coal use. 

---