Kinetics of stepwise hydrolysis of ferrioxamine B and of formation of diferrioxamine B in acid perchlorate solution

Article abstract of DOI:10.1021/ic00254a009

Kinetic and thermodynamic parameters for the hydrolysis of ferrioxamine B, Fe(HDFB)⁺ + 3H⁺ ? Fe³⁺ + H₄DFB⁺, in 0.005-11.0 M acid at 25°C and ionic strength 2.0 M (NaClO₄/HClO₄) have been obtained by stopped-flow and rapid-scan spectral methods. Four stages can be separated. These consist of (a) Fe(HDFB)⁺ + H⁺ ? Fe(H₂DFB)²⁺, (b) transformation of Fe(H₂DFB)²⁺ to another form Fe(H₂DFB)²⁺* without H⁺ change, (c) Fe(H₂DFB)²⁺* + H⁺ ? Fe(H₃DFB)³⁺, and (d) Fe(H₃DFB)³⁺ + H⁺ ? Fe³⁺ + H₄DFB⁺. The equilibrium constants for each stage were determined by rapid-scan spectral methods and the rate laws by stopped-flow methods. The kinetics of stage d were checked by examining the reverse direction. Agreement between equilibrium constants determined by spectral means and from the kinetics was fair to good. The results were compared with those of previous investigators. The kinetics of formation and decomposition of the binuclear complex Fe₂(HDFB)⁴⁺ from Fe³⁺ and Fe(HDFB)⁺ were also determined at 25°C and ionic strength 2.0 M (NaClO₄/HClO₄). A relationship between the hydrolysis and the formation of the dimer was shown.