Download structural investigation on cation recognition molecules

STRUCTURAL INVESTIGATION ON CATION RECOGNITION MOLECULES
O.Cozar1, N. Leopold1, L. David1, V. Chis1, M. Tomoaia-Cotisel2, A. Mocanu2
Babeş-Bolyai University, Faculty of Physics, Kogălniceanu 1,
RO-400084 Cluj-Napoca, Romania
2
Babes-Bolyai University Cluj-Napoca, Faculty of Chemistry
1
Many spectroscopic methods (IR, Raman, EPR, NMR) were used for the structural
investigation of the chelator desferrioxamine B and its Fe(III) complex, ferrioxamine B.
The “recognition” properties of some molecules are very important for many
biological processes and generally for life [1]. The proteins in our food bind to other proteins,
called enzymes, which catalyze – that is accelerate – their breakdown. Other compounds
recognize ions, such as sodium and potassium, and transport them in and out of the living cell.
Our biological defense against intruders is based on the formation of antibodies, which
recognize the enemy, the antigen, and disarm him by forming harmless complexes. Our whole
life, our consciousness, our instincts are governed by signal substances that are recognized by
various receptors. The biological recognition is very specific and selective. The two
molecules have to fit like a key in a lock. However, the lock is always a very complicated
molecule of high molecular weight (supramolecule), a protein or a nucleic acid. The
mechanisms by which ligand discrimination is made are critically important to understanding
the structure and function of different proteins [2,3].
Comparing the FT-IR absorptions of desferrioxamine B and ferrioxamine B, the
structural changes due to the Fe(III) chelation were clearly evidenced by the spectra. Despite
the intense C=O stretching vibration (1629 cm-1) from the spectrum of desferrioxamine B, in
two bands at 1577 cm-1 and 1636 cm-1 in the IR spectrum of ferrioxamine B (DFO:Fe)
suggests the appearance of a resonative process in the O=C-N bond by chelating the Fe(III).
The new bonds at 1577 cm-1 and 1043 cm-1 from DFO:Fe spectrum are due to the C=N and CO bonds, respectively. This fact contributes to the homogenization of the electronic charge of
oxygen environment around ferric ion in the octahedral Fe chelate [4].
1
H and 13C NMR spectra show that the high stability of octahedral Fe chelate formed
in ferrioxamine B (DFO:Fe) is due to the high coordinative energy of hydroxamic acid for
Fe3+ and also to the number and spacing of the coordinative groups.
EPR spectra suggest also that Fe3+ ions are situated in a hexacoordinated distorted
octahedral symmetry subjected to strong crystal field effects. DFOB has the same ability to
chelate the Mn2+ ions, which have a similar electronic configuration (3d5, 6s5/2) with Fe3+ ions.
References:
[1] G. Winkelmann, Handbook of microbial iron chelates, CRC Press, Boca Raton, 1991
[2] Z. Yehuda, Y. Hadar, Y. Chen, Journal of Agricultural and Food Chemistry, 51, 5996 (2003)
[3] R. Ludwig, N. T. K. Dzung, Sensors, 2, 397 (2002)
[4] O. Cozar, N. Leopold, M. Tomoaia-Cotisel, A. Mocanu, C. Jelic, L. David, V. Chis, J. Molec. Structure
(in press)