Complexation of Some Plant Auxins with Metal Ions of Biological Interest

Department of Chemistry, V. S. S. D. College (Kanpur University),Kanpur-208 002, India

Manuscript received 12 October 1979, accepted 30 December 1979

In order to investigate chelation as a possible mode of action of plant auxins, the complexation of indole-3-acetic acid (IAA), indole-3-propanoic acid (IPA), indole-3- butanoic acid (IBA) and naphthalene-1-acetic acid (NAA) with Mg(II), AI(Ill), Ca(ll), Fe(III), Co(II), Ni(II), Cu(II), Zr(IV), La(III) and Th(IV) have been investigated potentiometrically. Protonation constant of ligands and stepwise stability constant for metal-ligand complexes are reported at constant ionic strength (0.01M, KNO₃) and constant temperature (30°) in 50% aqueous dioxane (V/V). The general order of these stability constants with above auxins is found to be Th(IV)>Zr(IV)>AI(III)>Co(II)> Cu(ll)- Ni(II)> Fe( III). The stability constants of these metal-complexes are found to be almost same in the cases of IAA, IP A and IBA but are somewhat higher in the case of NAA. Since all auxins are biologIcaly active and have approximately same value of stability constant, thus present investigation supports chelation as a possible mode of action of these auxins.