ISBN: 978-83-60043-10-3 - eurobic9

Eurobic9, 2-6 September, 2008, Wrocław, Poland
P203. Complexation of Pb(II) Ions with Humic Acids and Naturally
Occurring Antioxidants; EPR and Relativistic DFT Study
M. Witwicki a , A. Jaszewski b , J. Jezierska b , A. Ożarowski c , A. Jezierski b , M. Jerzykiewicz b
a
Department of Chemistry, Wroclaw University, F. Joliot-Curie 14, Wroclaw 50-283, Poland
e-mail:mck@eto.wchuwr.pl
b
Department of Chemistry, Wroclaw University, F. Joliot-Curie 14, Wroclaw 50-283, Poland,
c
National High Magnetic Field Laboratory, Florida State University, 1800 E. Paul Dirac Drive,
Tallahassee, FL 32310, USA,
Complexation of Pb(II) with functional groups of humic acids [1, 2] and with their models, polihydroxybenzoic
acids which are present in natural products as strong antioxidants, results in the formation of new radicals whose
g values (observed in EPR spectra) are unusually low in comparison with those of parent semiquinone radicals
[2, 3].
To show the reasons of this effect we underwent the EPR studies of Pb(II) complexes with the model radical
derived from of 3, 4-dihydroxybenzoic acid. The 3, 4-dihydroxybenzoic acid is representative for other
polihydroxybenzoic acids substituted with at least two vicinal phenolic OH and one carboxylic groups which
form the radicals able to shift characteristically g parameters after Pb(II) complexation.
The role of the OH and COOH substituents of the model radical in Pb(II) coordination, leading to the
characteristic shift of g parameter, was studied by us using the relativistic DFT calculations of the expected
complexes geometries, unpaired electron delocalizations and electronic structures with ADF program. The
calculations were verified by the best agreement between the predicted and experimental g parameters.
Acknowledgement: The work was supported by Grant No. 6 PO4G 06730.
References:
[1] M. Jerzykiewicz, Geoderma 122 (2004) 305
[2] E. Giannakopoulos, K.C. Christoforidis, A. Tsipis, M. Jerzykiewicz, Y. Deligiannakis, Journal of Physical
Chemistry Part A 109 (2005) 2223.
[3] F. Czechowski, I. Golonka, A. Jezierski, Spectrochimica Acta Part A 60 (2004) 1387
_____________________________________________________________________
322