Investigations on configuration in the carbohydrate group by means of conductivity measurements in boric acid solution

• Main Author: Macpherson, Herbert Taylor
• Published: University of Edinburgh 1937
• Subjects: 547
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.657155

(1) As has been stated, the purpose of this research was to study the effects of hydroxy -compounds, more especially the simple sugars and their derivative's, on the conductivity of boric acid solution. An attempt has been made to correlate these results with the number and position of the hydroxyl groups present and thereby also to gain some insight into the structure of the molecule as a whole. (2) It is generally assumed that the increased conductivity of boric acid solution on the addition of certain hydroxy-compounds is due primarily to the formation, in solution, of cyclic complexes between the hydroxy-compound and boric acid: According to B?eseken and his co- workers, who have advanced a great deal of experimental evidence in support of this theory, such complex formation will only take place, when adjacent cis-hydroxyl groups, in the same plane as the carbon atoms to which they are attached, are available. These complexes are supposed to be dissociable to a greater extent than the boric acid itself, the varying degrees of dissociation giving rise to corresponding increases in hydrogen ion concentration and hence also in conductivity. Using 115 this hypothesis of complex formation, several conclusions have been reached from a consideration of the experimental results: - (a) With the pyranose sugars and their methylated derivatives: - The only hydroxyl groups having any positive effect on the conductivity of a boric acid solution are those on C1 and C2 No increase in conductivity is observed unless both these hydroxyl groups are unsubstituted and are in the cis-position to one another. (b) Using 3:4:6-trimethyl ?-mannopyranose, the configuration is shown to be trans - with respect to the hydroxyl groups on C1 and C2, in contradistinction to the results of B?eseken and Couvert for ?-mannose. This result was confirmed for ?-mannose itself. (c) The results for glucose, galactose and marnose (and their derivatives) appear to be best explained by the view that they possess the configuration either of the "bed" form of Sachse ring or something intermediate between this and the "flat" form proposed by Cox. (d) With open-chain polyhydroxy compounds:- No notable elevation of the conductivity of boric acid solutions is observed until the molecule possesses more than three hydroxyl groups. The elevation of conductivity increases with the number of hydroxyl groups. (e) In the case of methylglycofuranosides, the ring being flat, the question of ring-configuration does not arise, the important factor being the orientation of the hydroxyl groups. Increase in conductivity appears to depend on the number of hydroxyl groups in proximity to one another. The group -CHOH.CH(2)OH by itself appears to have no positive effect on the conductivity. (f) Sorbose brings about a very much greater increase of conductivity of boric acid solution than does fructose: this -cannot be explained on the basis of the generally accepted pyranose structures for the two compounds, and a hydrated form of the ketonic formula is suggested for sorbose in solution. (3) Examination of the viscosities of glucose and the methylated glucoses in aqueous and in boric acid solutions revealed no direct relationship between viscosity and conductivity, but in all cases very close agreement to the law that viscosity is a function of the volume of the dissolved phase was obtained.