TY - JOUR
TI - Kinetics and mechanism of the reaction between chromium(III) and 3,4-dihydroxyphenylpropionic (dihydrocaffeic) acid in weak acidic aqueous solutions
AU - Athinoula L Petrou
AU - Patrina Paraskevopoulou
AU - Maria Chrysikopoulou
JO - Journal of Inorganic Biochemistry
PY - 2004
VL - 98
TODO - 1
SP - 123--132
PB - ELSEVIER BV
SN - 0162-0134
TODO - 10.1016/j.jinorgbio.2003.09.008
TODO - kinetic studies; activation parameters; dihydrocaffeic acid;
chromium(III); catecholic-type of coordination
TODO - 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.
ER -