Olof Samuelson

Reducing end groups in brich xylan and their alkaline degradation

SummaryThe structure of the reducing end group in xylan can be written: -β-D-Xylp-(1→4)-β-D-Xylp-(1→3)-α-L-Rhap-(1→2)--α-D-GalpA-(1→4)-D-XylIn alkaline media the reducing xylose group is easily isomerized and removed by a β-elimination which leads to a reducing galacturonic acid end group. The 1, 2-linkage between rhamnose and the galacturonic acid explains the retarding effect on the alkaline peeling. Even under fairly mild conditions the galacturonic acid group is converted to other groups which are very stable in alkaline media. Model experiments permit the conclusion that OH-3 in the reducing group is subjected to β-hydroxyelimination. The 3-deoxy-2-O-α-L-rhamnopyranosyl-D-threo-hex-2-enuronic acid group formed is unstable in acid medium and escapes observation by the techniques employed for determination of the end groups.Upon prolonged alkaline treatment and increased proportion of these groups is lost and a rapid peeling proceeds until a xylose group with a 4-O-methylglucuronic acid substituent is liberated. The consecutive reactions of this group are similar to those of the galacturonic acid groups.The formation of 3-deoxyaldonic acid end groups, an important stopping reaction in cellulose, is of minor importance in xylan.

Structure of the reducing end-groups in spruce xylan

Abstract Borohydride reduction of spruce meal followed by mild hydrolysis with acid gave a large proportion of 4- O -(α- d -galactopyranosyluronic acid)- d -xylitol. When the reduction was preceded by mild treatment with alkali, galactonic acid end-groups were formed. Enzymic degradation of holocellulose from reduced spruce-meal followed by ion-exchange chromatography led to the isolation of a tetrasaccharide having a xylitol end-group. Its structure revealed that the reducing end-group in spruce xylan has the structure β- d -Xyl p -(1→3)-α- l -Rha p -(1→2)-α- d -Gal p A-(1→4)- d -Xyl, which is the same as that in hardwood xylan.

Partition chromatography of sugars on ion-exchange resins

Abstract In separations of monosaccharides in aqueous ethanol on ion-exchange resins in their lithium and sulfate forms, the sugas are eluted, with few exceptions, in the order of an increased number of hydroxyl groups. With oligomers there exists a straight-line relationship between the logarithm of the distribution coefficient and the number of monomeric units. Higher saccharides of various types exhibit large individual differences.

Chromatography of oligosaccharides from xylan by various techniques

Abstract Chromatographic studies of the oligomeric sugars obtained from birch xylan by acid hydrolysis revealed oligosaccharides containing 2–18 D -xylose residues. The results indicate that the 4-O-methyl- D -glucuronic acid groups are randomly distributed in the xylan. The nonasaccharide and the lower homologues were isolated by chromatography on charcoal-Celite and by partition chromatography on ion-exchange resins using aqueous ethanol. At a high concentration of ethanol, the sugars are eluted in order of increasing molecular weight, whereas the order is reversed at a low concentration of ethanol. At one critical concentration, which depends upon the type of resin, there is no separation at all. The validity of Martins rule is demonstrated for partition chromatography on ion-exchange resins, as well as for permeation chromatography on ion exchangers and polyacrylamide gel.

Separation of alditols and aldoses by partition chromatography on ion-exchange resins

Abstract An automated method for the determination of alditols and aldoses in complicated mixtures is described. The solutes were separated on a column of anion-exchange resin in its sulfate form, using water-ethanol as the eluant. The eluate was analysed automatically by periodate oxidation and subsequent colorimetric determination of released formaldehyde, using pentane-2,4-dione.

Automated chromatography of uronic acids on anion-exchange resins

Abstract An automatic system is described for the determination of various uronic and biouronic acids after chromatographic separation on an anion-exchange column. Elution is carried out with sodium acetate or acetic acid, and the colors developed with carbazole and after oxidation with chromic acid are determined in a multichannel photometer and recorded continuously.

Automated ion exchange chromatography of organic acids in acetate media

Abstract The chromatographic separation of 44 organic acids, mainly hydroxy acids, on anion exchange resins has been studied using sodium acetate and acetate and acetic acid as eluants. By a combination of both media most species can be separated and determined automatically.

Automatic chromatography of hydroxy acids on anion-exchange resins

Abstract Hydroxy acids are separated on an anion-exchange column and determined automatically by three colorimetric methods: chromic acid oxidation, periodate oxidation and the carbazole reaction. The simultaneous application of three methods facilitates both identification and determination.

A colorimetric method for the determination of carbonyl groups in cellulose

Abstract A method is suggested for the determination of carbonyl groups in cellulose based on the reaction with hydrazine. After washing with water, the cellulose hydrazone is dissolved in sulfuric acid and hydrolyzed. The liberated hydrazine is determined colorimetrically with p -dimethylamino-benzaldehyde. Possible interferences from carboxyl groups are discussed.

Partition chromatography on ion-exchange resins separation of sugars

Abstract Factors affecting the Chromatographic separation of sugars in ethanol-water solutions by means of anion-exchange resins in the sulfate form have been studied. When proper conditions are chosen a satisfactory separation of mono-, di-, tri-, tetra-, and pentasaccharides from one another can be achieved. In some cases it is possible to separate sugars of similar molecular weight.