2 THE PLANT CELL WALL 



by methods which give a minimum of contamination or artifact 

 formation; second, specific, and sensitive methods must be avail- 

 able for qualitative and quantitative measurements of the isolated 

 fractions. 



Dealing as it does with complex materials, natural products 

 chemistry cannot achieve these technical ideals in a simple, direct 

 fashion. It is only through the efforts, experiences, and ingenuity 

 of many investigators that a definitive analytical description of 

 the cell wall and similarly heterogeneous materials has been achieved. 

 No brief account can hope to convey the difficulties with which 

 this roadway is beset. Therefore, as we examine the current end- 

 product of more than a century of cell wall chemistry, it is well 

 to remember the efforts represented by the apparently "finished" 

 character of the modern techniques and the likelihood of even 

 further improvement in the future. 



Among the simpler solvents, cold dilute NaOH may be used 

 for the removal of high molecular weight carboxylic acids. Calcium 

 salts of polymeric acids may be solubilized by treatment with 

 ammonium oxalate or chelating agents which precipitate or seques- 

 ter the calcium. More concentrated alkali solubilizes neutral poly- 

 saccharides at low temperature and waxy or other lipid materials 

 when hot. A more specialized solvent for some acidic substances 

 is warm dilute H 2 2 . Hot dilute acid also solubilizes some acidic 

 components, but also hydrolyzes some neutral polysaccharides. 

 Cellulose, the most resistant carbohydrate component, may be 

 swelled and solubilized by cold sulfuric acid (72 per cent) or by 

 cupraammonium solutions which contain the ion Cu(NH 3 )4 ++ . 



The aromatic polymers of the cell wall may be partially extrac- 

 ted by organic solvents such as dioxane or hot butanol, or more 

 completely solubilized by treatment with acidic alcohols. Strong 

 alkali will also extract aromatic substances in proportion to their 

 content of phenolic OH. More general (and destructive) extract- 

 ants for aromatic compounds include bisulfites and chlorine in 

 combination with H 2 S0 3 or ethanolamine. 



By the proper application of solvents and treatments, the 

 cell wall may be fractionated into cellulose and the following 

 additional major chemical classes: 



