Kinetics and mechanisms of Fe(III) complexation by lipophilic 3-hydroxy-2-methyl-1(γ-stearoamidopropyl)-4-pyridinone (HMSP)

The kinetics of Fe(III) complexation by lipophilic 3-hydroxy-2-methyl-1(gamma-stearoamidopropyl)-4-pyridinone (HMSP) were studied when [Fe(III)] much greater than [HMSP] in MeOH/H2O mixed solvent and [Fe(III)] much less than [HMSP] in MeOH, respectively. When Fe(III) was in excess, the observed rate constants depend on [Fe(III)](tot)(2) and on the reciprocal of [H+] and decrease with increasing pressure. Delta V-double dagger values are around + 8.0 cm(3) mol(-1). A mechanism consisting of the complexations of the hydrolyzed monomer Fe(H2O)(5)OH2+ and dimer species Fe-2(H2O)(7) (mu-OH)(2)OH3+ by HMSP is proposed. This mechanism is supported by the solvent effect and the work of other researchers. When HMSP is in excess, Fe(HMSP), is formed and three kinetic steps on different time-scales are observed. An "intermolecular chelate ring-closure" mechanism is proposed, differing from the "intramolecular chelate ring-closure" complexation reported for the formation of ferrioxamine B.