B.— CHE^IISTIIV. 41 



Tlic unit of stai'cli lias l)ccii c-lainicd to lie: — 



J. [i-glucosan . . . (PicLet)'" 



2. Aniiydro-nmltose . . (Karrer)"" 



3. Triainylose . . . (Prinssheim)'"' 



It is possible to lest these views by the methylation method. 



The first successful methylation of starch was effected by Denham 

 and ^YoodhoLlse,-- and the reaction was afterwards adopted by Karrer.--' 

 He was, however, unable to complete the alkylation, the substitution 

 being arrested, as we ascertained many years ago, when the methoxyl 

 content was of the order 35 per cent. This value is slightly higher than 

 that demanded for a dimethyl starch, but is considerably lower than 

 that calculated for a trimethyl derivative. It is significant that Prings- 

 heini encountered similar difficulty in methylating tlie amyloses, diamyl- 

 ose giving a tetramethyl compound, whilst a-tetramylose was converted 

 into the corresponding octamethyl derivative. Pringsheim's combined 

 results lead him to tlie conclusion that the molecule of starch is built 

 up of not more than 4-6 glucose residues, and, on the whole, he is 

 disposed to retain triamylose as the basis of the polysaccharide. 



On the other hand, Karrer "s view that starch is a polymerised 

 anhydro-maltose rests upon very insecure evidence. The claim that 

 the action of acetyl bromide on the amyloses gives practically quantita- 

 tive yields of heptacetyl bromo-maltose has been adequately repudiated 

 by Pringsheim. It is, moreover, possible to dispose completely of 

 Karrer's formula for starch by the results now submitted. 



When the polysaccharide is methylated repeatedly by the methyl 

 sulphate method, the reaction ceases when the methoxyl content is 

 37 per cent. It is to be noted that this maximum is not reached when 

 the silver oxide and methyl iodide reaction is employed, as the substitu- 

 tion then stops definitely at the dimethyl stage. Now, the higher value 

 for methoxyl corresponds exactly with the theoretical amount calcu- 

 lated on the basis that one hexose residue has acquired three methyl 

 groups, while four are shared by two glucose residues. Ultimate 

 analysis is also in agreement with this view. Hydrolysis of the methyl- 

 ated starch has shown that this is not a fortuitous coincidence, and 

 we thus obtain a direct clue to the magnitude of the unit which goes 

 to form the starch molecule. When digested with methyl alcohol con- 

 taining hydrogen chloride the methylated polysaccharide was converted 

 into trimethyl methylglucoside and dimethyl methylglucoside. These 

 were purified by distillation in a high vacuum, and thereafter hydrolysed 

 to give the parent sugars. A totally unexpected result was encountered 

 in that the trimethyl glucose actually isolated proved to be the crystalline 

 form in which the methyl groups occupy the 2,3,G-positions. This 

 sugar has been shown to have the constitution given in Formula XIV., 

 and the linkage of one glucose unit in the starch molecule is thus 

 established (Formula XV.). It is to be noted that this particular type 

 of structui-e is not present in maltose, but is characteristic of cellobiose 

 and lactose. 



