Mechanism of ligand substitution on high-spin iron(III) by hydroxamic acid chelators. Thermodynamic and kinetic studies on the formation and dissociation of a series of monohydroxamatoiron(III) complexes

Experimental and theoretical vibrational spectroscopy studies of acetohydroxamic acid and desferrioxamine B in aqueous solution: Effects of pH and iron complexation

“…2), DFT calculations showed that the high-spin Fe(III) complex (S ϭ 6) is energetically more favorable than the low-spin Fe(III) complex in the ground state. This is consistent with the experimental studies on the Fe(aHa) 3 complex (Monzyk and Crumbliss, 1979). All calculated normal modes fall into doubly degenerate (E x,y ), and total symmetric representations (A z ) within the C 3 point group.…”

“…However, calculations also indicated that the addition of solvated water molecules stabilized O-deprotonated species more than the N-deprotonated species (Ventura et al, 1993). Complexation of aHa with Fe(III) shows that the Fe(aHa) 3 is the dominant species in the pH range of 4 -10 (Holmen et al, 1997;Farkas et al, 1998), with aHa forming three five-membered rings around Fe (Monzyk and Crumbliss, 1979;Brink and Crumbliss, 1984;Crumbliss, 1990).…”

The effect of organic compounds in the oxidation kinetics of Cr(III) by H2O2

“…Considering the hydrolysis of CrðH 2 OÞ 6 3þ and the hydroxamic acid dissociation equilibrium (pK a = 9.37 and 8.79 for Aha and Bha, respectively, Schwarzenbach and Schwarzenbach, 1963), the following mechanisms may be hypothesized (Monzyk and Crumbliss, 1979) CrðH 2 OÞ 5 OH 2þ þ RCONHOH…”

Structures of two isomeric hydroxamic acids: N-methyl-p-toluohydroxamic acid (MTH) and N-(4-methylphenyl)acetohydroxamic acid (MPA)

“…As a consequence of this latter property, a large number of naturally occurring iron(III) chelating agents of procaryotic and eucaryotic origin (siderophores) utilize hydroxamate functional groups for ferric ion coordination (Hider, 1984). The specificity and high stability of these complexes is dependent on the geometric and electronic arrangements of the ligating O atoms in the five-membered ferric-hydroxamate chelate ring, which in turn can be influenced markedly by inductive and resonance effects introduced into the ligand and chelate by the carbon (R1) and nitrogen (R2) substituents of the hydroxamate functionality (Monzyk & Crumbliss, 1979;Brink & Crumbliss, 1984). There has been considerable interest in the design for clinical use of synthetic secondary hydroxamic • acids (R2 ;~ H) with simpler stereochemistry than that possessed by siderophores.…”

“…There has been considerable interest in the design for clinical use of synthetic secondary hydroxamic • acids (R2 ;~ H) with simpler stereochemistry than that possessed by siderophores. A series of substituted N-phenylacetohydroxamic and N-methylbenzohydroxamic acids has been synthesized and studied to determine the effect of electron-releasing and withdrawing substituents on the acidity of the ligand, and the kinetic and thermodynamic stability of their (monohydroxamato)iron(III) complexes (Monzyk & Crumbliss, 1979Brink & Crumbliss, 1984;Brink, Fish & Crumbliss, 1985). In our• continuing study of the molecular structures of iron-chelating agents (siderophores) and their metal chelates, we have previously reported the structures of several of these secondary hydroxamic acids (Mocherla, Powell, Barnes & van der Helm, 1983;Mocharla, Powell & van der Helm, 1984;Powell & van der Helm, 1987).…”