Kinetics and thermodynamics of complex formation between Fe-III and two synthetic chelators of the dicatecholspermidine family

Citation
Jme. Chahine et al., Kinetics and thermodynamics of complex formation between Fe-III and two synthetic chelators of the dicatecholspermidine family, EUR J INORG, (9), 2001, pp. 2287-2296
Citations number
34
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Inorganic & Nuclear Chemistry
Journal title
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY
ISSN journal
1434-1948 → ACNP
Issue
9
Year of publication
2001
Pages
2287 - 2296
Database
ISI
SICI code
1434-1948(200109):9<2287:KATOCF>2.0.ZU;2-U
Abstract
This report deals with a kinetic and thermodynamic study of complex formati on 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 d issociations, four of which involve the hydroxy groups of the catechol moie ties and the final one the central ammonium group. They occur with average at pK(2a) = 8.40 and 7.95 for the first two hydroxy groups, pK(3a) = 12.6 a nd 12.20 for the two remaining hydroxy groups and pK(1a) = 5.50 and 4.90 fo r the ammonium group. Complex formation with both chelators occurs rapidly in acidic media (pH < 2), resulting in the second-order complex formation r ate constants k(1) = 450 M-1 s(-1) and 500 M-1 s(-1) and first-order comple x 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 a cidic media: K-1 = 1.82.10(-3) M and 5.6-10(-4) M. The Fe-III complexes als o undergo five proton dissociations with marked decreases in the catechol p K(a) value: Delta pK(1a) = 1.25 and 1.25, Delta pK(2a) = 6.60 and 6.50, Del ta pK(3a) = 6.55 and 6.95. From Delta pK(a) and K-1, the affinity of both F R295 and FR401 for Fe-III is determined: log beta = 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.