Chelation or Complex-formation by Indoleacetic Acid in vitro

Abstract

AFTER a long series of attempts to demonstrate chelation or complex-formation between 3-indoleacetic acid and metal ions in vitro, which were unsuccessful presumably because of the very low concentrations of indoleacetic acid inevitable in the aqueous solutions used, we repeated the experiments of Cohen et al. ¹, using, as they did, cupric nitrate and indoleacetic acid in 50 per cent ethanol. Essentially similar results were obtained, except that our value for log K by the Bjerrum method was 3.0 as compared with theirs of 5.4; we were also not entirely satisfied that a discontinuity in our curve for absorption at 360 mµ, versus composition occurred at a ratio of 1 copper : 2 indoleacetic acid and there was no indication of a break at 1 copper : 1 indoleacetic acid (cf. their Fig. 2).