Observations on Glyoxals,Their Determination and Behavior.

Abstract

Shaffer 1 observed that the addition of alkali cyanide in small amounts to glyoxal produces in slightly alkaline solution a very highly reducing substance, which rapidly reduces many dyes and other reagents; and he suggested that this reaction be utilized for a quantitative method for the determination of glyoxals. Among the reagents which develop color on reduction are the complex phospho-tungstic acids, and of these the arseno phospho-tungstic reagent used by Benedict 2 for uric acid was found to be well suited for our purpose. Without cyanide, glyoxal or methyl glyoxal scarcely reduces this reagent, but with cyanide reduction is rapid and proportional to the glyoxal present. Six hundredths mg. or more glyoxal may thus be determined with an accuracy of ±5 per cent. To the glyoxal solution (preferably about 0.6 mg.) are added 2 cc. of Benedict's reagent, followed by 1 cc. of M NaCN and 5 cc. of M Na₂CO₃ in the order named. A similar mixture is made with 10 cc. 0.001 M glyoxal (0.58 mg.) as a standard. After 10 minutes at room temperature the mixtures are diluted to 100 cc. and read by colorimeter.

The notable effect of cyanide, in markedly increasing the reducing power, is not limited to glyoxals, having been observed also with uric acid and with cystin, but is exceptionally striking with the glyoxals.

With this method it is possible to follow the transformation of glyoxals by alkali, by tissue extracts (glyoxalase) and by cyanides. The following observations have been made. In pure buffer sohtions at pH below 7 to 8 glyoxal and methyl glyoxal are quite stable; at higher pH the conversion to the corresponding hydroxy acid occurs, becoming rapid and complete at pH 12.5. At intermediate reactions at which the conversion is relatively slow, less lactic acid appears, then corresponds to the methyl glyoxal destroyed.