Organic Substances 55 



being oxidized by periodate may prove exceptionally resist- 

 ant^*^ (cellobiose, some methylglycosides ) ; the reasons for 

 this irregular behavior are not clear. 



The amount of aldehyde formed from C4-linked polysac- 

 charides does not depend on the degree of polymerism, be- 

 cause of the availability of two vicinal OH groups (C2-C3) 

 in every one of the carbohydrate units. On the other hand, 

 in Cs-linked polysaccharides, only the temiinal units can be 

 oxidized. For this reason, the relative yield of aldehyde w^ill 

 increase with decreasing chain length. 



The mechanism of other oxidants has not been studied in 

 sufficient detail, but it seems to be essentially similar to that 

 of periodate, although there are minor quantitative or quali- 

 tative differences. Periodate appears to be the most specific 

 for glycolic linkages proper; the aldehyde groups are not 

 further oxidized, even on prolonged exposure to the oxidant. 

 Chromic acid, another popular oxidant, is less energetic as 

 far as attacking all glycolic linkages is concerned; its action 

 is limited almost exclusively to glycogen and mucin; glyco- 

 proteins are quite resistant to its action. The aldehyde groups 

 are destroyed after prolonged exposure and cannot be dem- 

 onstrated after a certain time. Acidified permanganate, as 

 used by Casella,^^ combines the properties of periodate and 

 chromic acid in that it seems to attack all glycol linkages but, 

 on prolonged action, destroys the aldehydes formed. 



In the case of nucleic acids, aldehydes cannot be produced 

 by oxidative procedures. As mentioned before, desoxyribo- 

 furanose, the carbohydrate component of DNA, does not 

 possess a glycolic group. In ribofuranose, the carbohydrate 

 moiety of RNA, phosphoric acid residues in position 3 block 

 the reaction. If the latter are removed by mild hydrolysis, 

 the depolymerized nucleic acid becomes diffusible and will 

 be lost from the section. 



10. Jeanloz, R.: Science, 111:289, 1950. 



11. Casella, C: Anat. Anz., 93:289, 1942. 



