HISTOCHEMICAL ACYLATION OF ALDEHYDES PRODUCED BY PERIODIC ACID OXIDATION

Aldehydes produced in tissue sections by periodic acid oxidation are readily acetylated or benzoylated so as to weaken or completely prevent the Schiff and other chromogenic reactions. The reactivity of acylated aldehydes to Schiff reagent is promptly restored by saponification in alcoholic potassium hydroxide solution (10-20 min, 1% KOH, 70% ethanol). Benzoylation with 5-10% benzoyl chloride in pyridine gave the promptest, most complete and consistent aldehyde blockade, which was somewhat inferior on addition of 0.5% sulfuric acid. Pyridine acetic anhydride mixtures, 25, 40 and 50% gave partial to complete blockade. Addition of 0.25-0.5% sulfuric acid did not give consistent effects. Acetic anhydride at 60°C gave partial blockade at ½-5 hr, on addition of 0.01-0.25% sulfuric acid total or subtotal blockade was achieved. Acetylation in alcohol gave inferior resutlts. Use of 25% acetic anhydride ims glacial acetic acid gave inferior results; addition of 0.25% sulfuric acid produced total to subtotal blockade at 4-5 hr. Glacial acetic acid was without appreciable blockade effect. Sulfation in 10% and 25% H2SO4/glacial acetic acid failed to blockade aldehydes. Experiments with the peracetic acid Schiff reaction for ethylene groups indicate that some proportion of enol monobenzoate may be formed, and that with the various acetylation techniques a smaller or negligible proportion of enol acetate is formed. Acetic anhydride with 0.25% H2S04 at 60° appears to form only aldehyde diacetate. Experiments with the bromination silver techniques did not give satisfactory results.