Abstract
When the alcohol solution of retinoic acid was mixed with Tyrode's, Locke's or Krebs・Ringer bicarbonate solution, significant decrease of retinoic acid content was observed. The decrease of retinoic acid content was due to the combined effect of calcium and bicarbonate concentrations in these physiological solutions at pH 8.3. It was also found that the decrease did not occure on addition of antioxidants to the reaction mixture or under the anaerobic conditions. At the presence of Ca^<2+> in veronal or borate buffer at pH 8-9 and also in combination of CaCl_2,BaCl_2 or MgCl_2 with bicarbonate, retinoic acid was quickly destroyed. These results suggested catalytic oxidation of retinoic acid by metal ions at the suitable ranges of pH. Retinol or retinal was shown to be more resistant to similar degradation experiments, while the stability of retinoic acid to KMnO_4,HClO, H_2O_2 and other oxidizing agents was proved to similar to that of retinol.
