PLANT CELL-WALL CONSTITUENTS PLANT CELL-WALL C O N S T I T U E N T S
Oximation a n d Methylation Shed Light on Lignin Structure • Specifically labeled cellulose biosynthesis aids degradation studies • Supersonic sound waves degradation
prepared
used for
by
dextran
• N e w method for determination of aldehyde groups in cellulose developed P W E D I S H and American chemists backed *^ up by several outstanding workers from other countries continue to pile up evi dence which will ultimately result in a clear-cut and undisputed structure of lig nin. Much of such evidence was reported before the section on Plant Cell-Wall Constituents. Sessions on biosynthesis, starch, hemicellulose, and cellulose rounded out the full four-day program of the section. Oximation and Methylation. T h e alka line degradation of lignosulfonic acids pretreated by oximation and methylation has been studied in an effort to elucidate the structure of the aldehyde-yielding groups. Erich Adler, Lars Ellmer and Bjorn Rabbing, Swedish Forest Products Laboratory, treated lignosulfonates with diazomethane. When heated with 3 Ν sodium hydroxide, the highest methylated products yielded only one third of the amount of vanillin obtained from the nonmethylated lignosulfate, Adler said. The yield of acetaldehyde was much less af fected by the methylation. Since carbonyl groups should have reacted w i t h diazo methane, Adler explained, such groups are apparently not present in the sul fonated Co-Os units. Pretreatment of the lignosulfonates with hydroxylamine led to the same conclusion. Adler said that these sulfonated oximes yielded normal amounts of vanillin and increased amounts of acetaldehyde. The same experimental procedure was carried out using coniferaldehyde oxime and acetaldoxime. These substances were found to be practically stable under those con ditions. This indicated that the aldehyde group of the acetaldehyde formed from lignosulfonic acid cannot be preformed in the sulfonated C e -C 3 units, Adler said. The experiments in the Swedish Forest Products Laboratory did not establish the unit yielding the vanillin, but they have precluded several possibilities, Adler con cluded.
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C o l o r Reactions of Lignin. A spectro scopic comparison of the color reactions of w o o d treated with hydrochloric acid and of known substances also acid treated has l e d to a better insight into the nature of the reactions. J, C . Pew, Forest Prod ucts Laboratory, explained that the treated wood gave an instantaneous yellow color followed in about a minute by develop ment of a green tint. If the temperature was h e l d to —10° C. the change in color was arrested at the yellow stage, he said. This color was found to correspond t o those produced by acid action o n model substituted cinnamaldehydes. Untreated wood sections were shown to contain t h e substituted cinnamaldehyde groups. T h e absorption spectra of spruce sections were plotted on the same axis with a blank prepared by bleaching a section with alkaline peroxide. Bleaching destroyed the substituted cinnamaldehyde groups without removal of lignin, P e w explained. The corrected curve, P e w con tinued, gave a maximum of 350/A as c o m pared with 347μ for coniferyl aldehyde and 354μ for sinaldehyde. The yellow color of the treated spruce w o o d is d e stroyed by alkali; t h e same is true of substituted cinnamaldehydes with no free hydroxls. From this observation, Pew con cluded that there are no free hydroxyls i n the coniferyl aldehyde group of spruce wood. M o r e on Spruce W o o d Reactions. Work reported by F. E . Brauns and Heinz Seller, Institute of Paper Chem istry, indicates that homogenized spruce wood behaves like a lignin-carbohydrate compound. The lignin is chemically c o m bined with carbohydrates in the w o o d , Brauns declared. I n addition to exhaus tive solvent extraction examinations, t h e existence of a lignin-carbohydrate linkage is further supported by the fact that a carbohydrate-lignosulfonic acid has b e e n isolated b y a sulfite treatment of spruce wood at room temperature, Brauns said.
. SEPTEMBER
2 4,
1951
Harry F . L e w i s , chairman of the executive committee, discusses the Plant-Cell Wall Constituents program w i t h committee member E . C. J aim Lignin D e g r a d a t i o n . During alkaline coking, lignin is degraded to low molec ular w e i g h t , ether-soluble compounds Terje Enkvist, Swedish Forest Products Laboratory, told the groixp. Among these are acetovaniilone and further derivatives of dirners of the phenyl propane unit in lignin, h e said. Isolated lignin precipitated from black liquor by hydrochloric acid also can b e degraded to similar products by degradation w i t h lye a t about 170° C , he continued. Molecular weights of these products w e r e in many cases as low as 200 to 50O. B o Alfredsson was collabo rator o n t h e research.
^Biosynthesis o f Specifically L a b e l e d Cellulose U s i n g a carbon 14 labeled monosac charide, a specifically labeled cellulose has been prepared w i t h the organism Acetobacter xylinum. T h e work was re ported in a paper by A . M. Schwartz, F. W . Minor, G. A. Greathouse, and Milton Harris, Harris Research Labora tories. W h e n a 1-6 C u mannitol was used as the substrate, the biosynthesized cellu lose w h e n hydrolyzed to glucose was found to have radioactivity at all six positions, Minor said. Their determinations on the glucose hydrolyzate showed 3 3 % of the total activity in the number 1 position and 5 0 % in t h e number 6 position, however. The activity at all six positions appears to rule out a simple six carbon polymeriza tion to form the cellulose, Minor declared. Questions from the floor brought out the fact that t h e biosynthesis was not a cata lytic but a metabolic process and the pos sibility of a polymerization through an intermediate step. Other specifically labeled sugars from
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INTERNATIONAL CONGRESS the National Bureau of Standards are being used to prepare other labeled cellu loses, Minor said. H e emphasized the value of these labeled celluloses as tools for degradation studies. φ-Enzyme Studies. A n e w synthesis of starch using Polytomella coeca and a Co enzyme was reported by A. Bebbington, E. J. Bourne, M. Stacey, and I. A. Wilkin son, University of Birmingham. The en zyme used was purified and found to be quite similar to the potato Q-enzyme, Stacey said. The biosynthesis of arnyiopectins with Q-enzymes reported by W. Z, Hassid, University of California, sub stantiated the enzyme work of the Birming ham group and presented additional in formation on the subject. Hassid reported the synthesis of an amylopectin with mo lecular weight of approximately 50,000.
• Supersonic Sound f o r D extra η ùeqradafion Supersonic sound waves are much more satisfactory than acid hydrolysis for deg-
F. E . Brauns, Institute of Paper Chemistry, discussed reactions with homogenized spruce wood radation of dextrans, M. Stacey, University of Birmingham, told the group. However, for economic reasons, the acid hydrolysis, as used in the United States, still must be considered the most important method at this time. Supersonic degradation converts as high as 6 0 % of the dex*xans compared with a 10% yield usually experienced with the acid hydrolysis, Stacey declared. "The proportion of the branched molecular components does not vary in supersonic methods, and in this respect the technique is also superior to acid hydrolysis," he said. H e mentioned that a new and vastly superior method was now under investigation in England but would not reveal any clue as to its nature. Stacey called for international coopera-
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tion and exchange of information relative to dextrans in view of their medicinal i m portance. H e said that it was a problem of particular interest t o carbohydrate chemists; it is not a problem for the h i g h polymer chemists, according to Stacey. The paper provoked considerable c o m ment from the floor. H. S. Isbell, National Bureau of Standards, said " . . . . w e a^e all anxious to obtain the best plasma substitute in the shortest possible time." Several others defended the light scattering technique (used by the high polymer chemists ) as the best method for molecular weight deterniination. Addition Compounds of Amy I o s e . T h e first x-ray evidence demonstrating t h e identity of successive residues in t h e amylose chain was presented in a paper i>y F. R. Senti, Northern Regional Research Laboratory, and L. F. Witnauer, of the Eastern Regional Laboratory. Addition compound of alkali amylose studied b y the x-ray diffraction method included these formed with the iodine, bromide, formate, acetate, propionate of potassium, and w i t h sodium bromide and arnmonium fluoride. The filaments are held taut during the exchange in order to retain orientation, Senti, said. Oligosaccharides Containing Pentoses. The first isolation of crystalline oligosaccharides containing pentose sugars w a s reported b y R. L. Whistler and C . C. T u , Purdue University. The acid hydrolyzates of corn cob xylan were fractionated in an automatic chromatographic column to obtain crystalline xylobiose, xylotriose, and xylotetrose, WKistier explained. T h e s e particular oligosaccharides are of interest in making comparisons with t h e similar homologous series from cellulose. Whistler pointed out that they differed structurally only in lacking the projecting hydroxymethyl or carbon atom CU on each ring unit.
Alexander Meller, Australian Paper Mfgrs.* Ltd., discussed the kinetics of removal of the easily accessible fraction from cellulose fibers in acid hydrolysis
Chromatographic fractionation was also found to be a satisfactory method for the separation and purification of some of the oligosaccharides present in sulfite waste liquor. J. E . Milks and H. B. Marshall, Ontario Research Foundation, reported that four of the oligosaccharides which were isolated appeared to b e associated with a methoxyl-containing substance of aromatic nature. The raw material used for the investigation was a commercial fermented liquor, free of glucose and mannose, prepared from spruce and balsam. Milks explained.
• N e w M e t h o d f o r Aldehyde Groups in Cellulose Developed A n e w method for determining aldehyde groups in cellulose was described in a paper b y W_ K. Wilson, H. F . Launer, and Alice Padgett, National Bureau of Standards. Chlorous acid is used to oxidize aldehyde quantitatively to carboxyl. The aldehyde content can b e determined in the range of 0.001 to 0.15 millimoles per gram of cellulose with a precision within 59k, according to Wilson. The deterrnination is carried out at 40° C. and a pH of 3.5. T h e low pH results in an unstable chlorite solution, but a satisfactory correction can be made by using a control, Wilson explained. The catalytic action of iron which was troublesome at first has been overcome by addition of sodium oxalate, he said. Indicating that work was being continued on the method, Wilson called his paper a "progress report." G. F. D a v i d s o n , who served as honorary chairman of the cellulose sessions, commented from the floor that considerable work on the same subject was being done by his own group at the Shirley Institute. H e called attention to the difficulty' in carrying the reactions to completion or to deterniining just w h e n the reaction had reached completion. Formaldehyde f o r W o o d Stabilization. High dimensional stabilization of wood has been obtained by vapor phase treatment with formaldehyde using a mineral acid catalyst. The work was carried out at the Forest Products Laboratory by Harold Tarkow and A. J. Stamm. The acetal cross links desirable for stabilization were not formed when aqeous formaldehyde with or without catalyst was used, Stamm reported. For the vapor phase treatment either nitric or hydrochloric acids were satisfactory catalysts, but organic acids were unsuited. The immediate application of the findings is limited because of the loss of abrasion resistance and embrittleness of the treated w o o d , he said. Other aldehydes and chloral have been tried but the extremely acetic conditions ( p H of 1.0 or lower) necessary for the cross-linking have always resulted in these undesirable properties in the stabilized wood, Stamm concluded.
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