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

Eurobic9, 2-6 September, 2008, Wrocław, Poland
P20. The Coordination Abilities of the 14-membered Cyclic Tetrapeptide
with the c(β 3 homoLysDHisβ-AlaHis) Sequence
J. Brasuń a* , A. Matera-Witkiewicz a , S. Ołdziej b , A. Pratesi c , M. Ginanneschi c , L. Messori d
a*
Department of Inorganic Chemistry, Wrocław Medical University, Szewska 38, 50-139 Wrocław, Poland
e-mail: jbrasun@chnorg.am.wroc.pl
b
Laboratory of Biopolymer Structure, Intercollegiate Faculty of Biotechnology, University of Gdańsk and
Medical University of Gdańsk, Kładki 24, 80-822 Gdańsk, POLAND
c
Laboratory of Peptides and Proteins Chemistry and Biology, Department of Organic Chemistry “Ugo Schiff”,
University of Florence, Via della Lastruccia 3, 50019 Sesto Fiorentino, Firenze, Italy
d
Department of Chemistry, University of Florence, Via della Lastruccia 3, Sesto Fiorentino, Firenze, Italy
A new, 14-membered, tetraza cyclic tetrapeptide containing histidine and lysine side-chains,
c(β 3 homoLysDHisβ-AlaHis), was designed, synthesized and characterized; its copper(II) binding properties were
investigated in dependence of pH by potentiometric and spectroscopic methods. In line with previous studies of
similar systems, the progressive involvement of amide nitrogens in copper(II) coordination was evidenced upon
raising pH. At physiological pH the dominant species consists of a copper(II) center coordinated by two amide
nitrogens, an imidazole nitrogen and a water molecule. In contrast, at pH above 8.7, a copper(II) coordination
environment consisting of four amide nitrogens in the equatorial plane and the axial imidazole ligands is formed
as clearly indicated by spectroscopic data and theoretical calculations. The behavior of this 14-membered cyclic
tetrapeptide is compared to that of its 12-membered cyclic analog, particular attention being paid to the effects of
ring size on the respective copper(II) binding abilities.
%Cu 2+
100
80
60
40
20
0
CuH 2 L
Cu 2+
CuHL
CuH -1 L
CuH -2 L
CuH -3 L
4 6 8 10
pH
CuH -4 L
Figure 1. Species distribution curves for Cu 2+ -
DK14 (solid line) and Cu 2+ -DK12 data from [1] (dashed
line) complexes at 25°C and I=0.1 mol dm -3 KNO3. The
ligand concentration 1×10 -3 mol dm -3 . Ligand to metal
ratio 1.5:1.
Scheme 1. The structure of CuH-3L complex
obtained from theoretical calculations. All hydrogen
atoms are removed for clarity. The copper(II) ion is
shown in cyano, oxygen, carbon and nitrogen atoms
are shown in red, black and blue respectively.
References:
[1] J.Brasuń, A.Matera, S.Ołdziej, J.Świątek-Kozłowska, L.Messori, Ch.Gabbiani, M.Orfei, M.Ginnaneschi, J.
Inorg. Biochem., 101 452 (2007)
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