Carbohydrates, compounds with lignin

More recently, Brauns and Seiler (12), (13) extracted native lignin from spruce wood and then homogenized the wood in a colloidal mill. A suspension of approximately one gram of colloidal wood per liter of water was obtained. After the colloidal wood was changed to a solid form, it was found that its cell structure was completely destroyed. However, extraction of this wood with ethyl alcohol at room temperature did not yield further quantities of native lignin. These investigators have also reported the isolation of a lignosulfonic acid-carbohydrate compound. 

One modification that pertains to the present book is the role of anthraquinone (AQ) in the pulping process. Under conditions of alkaline pulping, carbohydrates in the wood reduce AQ into an anion-radical (AQ ). Experiments with lignin quinonemethide as a model compound showed that the AQ anion-radical caused fragmentation of the quinonemethide (Scheme 8.23). 

Sippola, V., Krause, O., and Vuorinen, T., Oxidation of lignin model compounds with cobalt-sulphosalen catalyst in the presence and absence of carbohydrate model compound. Journal Of Wood Chemistry And Technology 2004,24 (4), 323-340. 

In the case of adherends such as wood, the possibility exists that the carbohydrate polymers or lignin, or both, can be modified in situ to give activated surfaces 65,66) or surfaces containing reactive groups. Then, the surfaces are bonded by direct reaction or by reaction with a reactive, gap-filling compound. 

Plant metabolism can be separated into primary pathways that are found in all cells and deal with manipulating a uniform group of basic compounds, and secondary pathways that occur in specialized cells and produce a wide variety of unique compounds. The primary pathways deal with the metabolism of carbohydrates, lipids, proteins, and nucleic acids and act through the many-step reactions of glycolysis, the tricarboxylic acid cycle, the pentose phosphate shunt, and lipid, protein, and nucleic acid biosynthesis. In contrast, the secondary metabolites (e.g., terpenes, alkaloids, phenylpropanoids, lignin, flavonoids, coumarins, and related compounds) are produced by the shikimic, malonic, and mevalonic acid pathways, and the methylerythritol phosphate pathway (Fig. 3.1). This chapter concentrates on the synthesis and metabolism of phenolic compounds and on how the activities of these pathways and the compounds produced affect product quality. 

Fraction I, which consists mainly of low molar mass compounds, also contains a small amount of high molar mass lignin derivatives eluting with relative retention volumes of 0-0.1. These derivatives are polar and some may be bound to carbohydrates, or otherwise they would have been eluted by RPC along with the hydrophobic fractions II-IV. 

---