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Comparison of the Kinetics, Mechanism, and Thermodynamics of Aqueous Iron(III) Chelation and Dissociation by Hydroxamic Oxo and Thio Acid Ligands

Publication ,  Journal Article
Fish, LL; Crumbliss, AL
Published in: Inorganic Chemistry
July 1, 1985

The kinetics and thermodynamics of aqueous iron(III) complexation by 4-CH3OC6H4C(X)N(OH)H (X = O, S) to form Fe-(H2O)4(4-CH30C6H4C(X)N(0)H)2+ are reported. These data provide a direct comparison between the iron(III) chelation chemistry of hydroxamic oxo and thio acids. A parallel-path mechanism involving Fe(H2O)63+ and Fe(H2O)5OH2+ was found to be operative for both ligands. Equilibrium quotients and microscopic rate constants for the forward and reverse directions of both paths were obtained along with the corresponding ΔH0, ΔH∗ and ΔS°, ΔS∗ values. An associative interchange (Ia) mechanism is operative for the substitution of both ligands at Fe(H2O)63+. Data are also presented that support an Ia mechanism for substitution at Fe(H2O)5OH2+, although the associative character in this path may be due to H-bonding interactions between the ligand and coordinated OH-. Initial bond formation at iron(III) for either path occurs at the >C=X (X = O, S) site. The rtoohydroxamic acid forms a more stable complex at physiological pH, and aquation by the acid-dependent and acid-independent, paths is ca. 50 times slower than for the hydroxamic acid complex. The increased kinetic stability is consistent with enhanced derealization of the N atom lone electron pair into the C-N bond in the thiohydroxamic acid complex. The chemistry of iron(III) chelation by CH3OC6H4C(S)N(OH)H suggests that siderophores may exist that use the thiohydroxamate moiety for iron(III) binding. © 1985, American Chemical Society. All rights reserved.

Duke Scholars

Published In

Inorganic Chemistry

DOI

EISSN

1520-510X

ISSN

0020-1669

Publication Date

July 1, 1985

Volume

24

Issue

14

Start / End Page

2198 / 2204

Related Subject Headings

  • Inorganic & Nuclear Chemistry
  • 3403 Macromolecular and materials chemistry
  • 3402 Inorganic chemistry
  • 0399 Other Chemical Sciences
  • 0306 Physical Chemistry (incl. Structural)
  • 0302 Inorganic Chemistry
 

Citation

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Fish, L. L., & Crumbliss, A. L. (1985). Comparison of the Kinetics, Mechanism, and Thermodynamics of Aqueous Iron(III) Chelation and Dissociation by Hydroxamic Oxo and Thio Acid Ligands. Inorganic Chemistry, 24(14), 2198–2204. https://doi.org/10.1021/ic00208a018
Fish, L. L., and A. L. Crumbliss. “Comparison of the Kinetics, Mechanism, and Thermodynamics of Aqueous Iron(III) Chelation and Dissociation by Hydroxamic Oxo and Thio Acid Ligands.” Inorganic Chemistry 24, no. 14 (July 1, 1985): 2198–2204. https://doi.org/10.1021/ic00208a018.
Fish, L. L., and A. L. Crumbliss. “Comparison of the Kinetics, Mechanism, and Thermodynamics of Aqueous Iron(III) Chelation and Dissociation by Hydroxamic Oxo and Thio Acid Ligands.” Inorganic Chemistry, vol. 24, no. 14, July 1985, pp. 2198–204. Scopus, doi:10.1021/ic00208a018.
Journal cover image

Published In

Inorganic Chemistry

DOI

EISSN

1520-510X

ISSN

0020-1669

Publication Date

July 1, 1985

Volume

24

Issue

14

Start / End Page

2198 / 2204

Related Subject Headings

  • Inorganic & Nuclear Chemistry
  • 3403 Macromolecular and materials chemistry
  • 3402 Inorganic chemistry
  • 0399 Other Chemical Sciences
  • 0306 Physical Chemistry (incl. Structural)
  • 0302 Inorganic Chemistry