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Kinetics and Thermodynamics of Complex Formation between Fe III and Two Synthetic Chelators of the Dicatecholspermidine Family
Author(s) -
Chahine JeanMichel El Hage,
Bauer AnneMarie,
Baraldo Karin,
Lion Claude,
Ramiandrasoa Florence,
Kunesch Gerhard
Publication year - 2001
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/1099-0682(200109)2001:9<2287::aid-ejic2287>3.0.co;2-7
Subject(s) - chemistry , catechol , dissociation (chemistry) , ammonium , reaction rate constant , kinetics , acid dissociation constant , dissociation constant , medicinal chemistry , stability constants of complexes , stereochemistry , chelation , ligand (biochemistry) , inorganic chemistry , aqueous solution , organic chemistry , biochemistry , physics , receptor , quantum mechanics
This report deals with a kinetic and thermodynamic study of complex formation between Fe III and a new series of synthetic chelators, 2,3‐ (FR401) and 3,4‐dicatecholspermidine (FR295). For the following data, the first value concerns FR295 and the second FR401. Each ligand undergoes five acid‐base dissociations, four of which involve the hydroxy groups of the catechol moieties and the final one the central ammonium group. They occur with average at p K 2a = 8.40 and 7.95 for the first two hydroxy groups, p K 3a = 12.6 and 12.20 for the two remaining hydroxy groups and p K 1a = 5.50 and 4.90 for the ammonium group. Complex formation with both chelators occurs rapidly in acidic media (pH < 2), resulting in the second‐order complex formation rate constants k 1 = 450 M −1 s −1 and 500 M −1 s −1 and first‐order complex dissociation rate constants k −1 = 0.82 s −1 and 0.28 s −1 . From these two elementary rates, the complex dissociation constant is determined in acidic media: K 1 = 1.82·10 −3 M and 5.6·10 −4 M . The Fe III complexes also undergo five proton dissociations with marked decreases in the catechol p K a value: Δp K 1a = 1.25 and 1.25, Δp K 2a = 6.60 and 6.50, Δp K 3a = 6.55 and 6.95. From Δp K a and K 1 , the affinity of both FR295 and FR401 for Fe III is determined: log β = 29 and 31 with pFe = 22 and 25. This new series of chelators is aimed for antibiotic targeting. It proved efficient in inhibiting Plasmodium falciparum growth and delivered iron ions to Gram‐negative bacteria.