N,N′-Dihydroxy-N,N′-diisopropylhexanediamide, a siderophore analogue, as a possible iron chelating agent for hydroponic conditions: metal equilibrium studies

Synthetic iron chelates are the most efficient iron fertilizers. The stability in solution of the iron chelates in the presence of other metal cations that may compete with iron for the chelating agent in nutrient solutions is crucial for its effectiveness in supplying iron to plants. In this work, the chelating properties of N,N-dihydroxy-N,N′-diisopropylhexanediamide (DPH), a biological model of the natural siderophore rhodotorulic acid, were evaluated in order to assess its potentialities for being used, as an iron chelate, in hydroponic cultures. For this purpose, the complexation for the metals [Ca(II), Cu(II), Mg(II), Mn(II) or Zn(II)]–DPH–OH systems has been studied using pH potentiometry and the overall stability constants have been determined for the first time. For all M–DPH–OH systems, MHL and ML species were identified. For [Cu(II), Mn(II) or Zn(II)]–DPH–OH systems, the M₂L₃ species was detected, whereas formation of ML(OH) species was found in the [Ca(II) or Mg(II)]–DPH–OH systems. Finally, the chemical stability of iron chelated with DPH in hydroponic conditions was assessed by computer chemical simulations and compared with the one predicted when iron is chelated with ethylenediamine-N,N′-bis(o-hydroxyphenyl)acetic acid (o,o-EDDHA) in similar conditions.