Department of Chemistry

Kinetics and mechanism of the reaction between chromium(III) and 3,4-dihydroxyphenylpropionic (dihydrocaffeic) acid in weak acidic aqueous solutions

English

The reaction of 3,4-dihydroxyphenylpropionic acid (dihydrocaffeic acid,
hydcafH(3)) with chromium(III) in weak acidic aqueous solutions has been
shown to take place through various oxygen-bonded intermediates. The
formation of the oxygen-bonded complexes upon substitution of water
molecules of the chromium(III) coordination sphere takes place in at
least three stages, the first of which has an observed rate constant
k(l(obs)) = k(1)K(0)([H+])(’)([hydcaffH3]) where K-0(’) corresponds
to the Cr(H2O)(6)(3+) complex dissociation equilibrium. The second and
third stages are ligand concentration independent and are thus
attributed to isomerisation and chelation processes. The corresponding
activation parameters are DeltaH(2)(not equal) = 78 +/- 3 kJ mol(-1),
DeltaS(2)(not equal) = -49 +/- 9 J K-1 mol(-1), DeltaH(3)(not equal) =
60 +/- 9 kJ mol(-1) and DeltaS(3)(not equal) = - 112 +/- 39 J K-1
mol(-1). The kinetic results support associative mechanisms and the
nature of the electronic spectra a catecholic-type of coordination at
the pH and concentration range studied and reported in this paper. The
associatively activated substitution processes are accompanied by proton
release causing a pH decrease. At lower acid concentration oxidation of
the ligand takes place with concomitant high increase in the UV and VIS
absorbance. (C) 2003 Elsevier Inc. All rights reserved.

2004

Athinoula L Petrou
Patrina Paraskevopoulou
Maria Chrysikopoulou

Journal of Inorganic Biochemistry

ELSEVIER BV

98

1

123--132

kinetic studies; activation parameters; dihydrocaffeic acid;
chromium(III); catecholic-type of coordination

Science

https://doi.org/10.1016/j.jinorgbio.2003.09.008

10.1016/j.jinorgbio.2003.09.008

https://pergamos.lib.uoa.gr/uoa/dl/object/2928869