Inhibitory Effect of Ascorbic Acid on the Hydrolytic Polymerization of Iron and a Consideration of the Effect in the Intestinal Absorption of Iron

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  • アスコルビン酸による鉄の加水分解重合阻止とその鉄吸収に与える効果の考察
  • アスコルビン酸による鉄の加水分解重合阻止とその鉄吸収に与える効果の考察〔英文〕
  • アスコルビンサン ニヨル テツ ノ カスイブン カイジュウゴウ ソシ ト ソノ

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Abstract

The Fe-sugar complexes prepared so far in this laboratory were found to be difficult in their intestinal absorptions. For the reason we considered the formation of high molecular weight Fe-polymers under the experimental conditions. Therefore, the inhibitory effects of glucose, fructose, sorbitol, and ascorbic acid (AsA) on the hydrolytic polymerization of Fe were examined in this work. As the Fe-salt, FeCl3 was used in the concentrations of 1×10^-2－1×10^-4M. The amounts of Fe were determined by the o-phenanthroline method and the polymerization degree of Fe was obtained from the difference between the amounts of the total Fe and the ionic Fe in the sample solutions. On the basis of the change in the absorption spectra of the FeCl3 solutions at various pH values, we concluded that the hydrolytic polymerization of Fe occurs rapidly even in acidic media, especially in aqueous media of above pH 4.5. The polymerization of Fe was markedly inhibited by AsA. Sorbitol also showed a considerable inhibition and its addition to the FeCl3 solution lowered the polymerization to about one-third. However, almost no effect was observed by the addition of glucose or fructose. When AsA was added to the FeCl3 solution, an Fe-AsA complex was formed. The paper electrophoretograms of the Fe-AsA complex, of which the molecular weight was rather small and presumed to be about 5,000, revealed that the charge of the complex was negative in alkaline or neutral media and was positive in acidic media. The electric charge of the complex is considered to be produced by formation of the surface complex of AsA on the surface of Fe atoms, which constitute generally a polynuclear Fe-hydroxo complex in aqueous media; AsA probably coordinates to the Fe atoms just like a cover that coats the polynuclear polymer. The changes of the dissociation of the coated AsA with pH values of the media produce the negative or the positive charges. Some nutritional considerations of the intestinal absorption of Fe were given in connection with the inhibitory effect of AsA on the hydrolytic polymerization of Fe.

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