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

Eurobic9, 2-6 September, 2008, Wrocław, Poland
P8. Spectroscopic Study of the Interaction of Ni II -5-triethyl Ammonium
Methyl Salicylidene orto-phenylendiiminato with Native DNA
G. Barone a , N. Gambino a , A. Ruggirello b , A. Silvestri a , A Terenzi a , V. Turco Liveri b
a Dipartimento di Chimica Inorganica e Analitica “S. Cannizzaro”, Università di Palermo, Viale delle Scienze,
Parco d’Orleans II, Edificio 17, 90128 Palermo, Italy
e-mail: gbarone@unipa.it.
b Dipartimento di Chimica Fisica “F. Accascina”, Università di Palermo, Viale delle Scienze, Parco d’Orleans
II, Edificio 17, 90128 Palermo, Italy.
The interaction of native calf thymus DNA with cationic complexes of 5-triethyl ammonium methyl salicylidene
orto-phenylendiimine (ML 2+ ), in 1 mM Tris-HCl aqueous solutions at neutral pH (M=Cu II and Zn II ) [1], and in
inverse micelles to simulate the intracellular solution environment (M=Cu II ) [2], has been recently reported.
The interaction has been monitored as a function of the metal complex-DNA molar ratio by UV absorption
spectrophotometry, circular dichroism (CD) and fluorescence spectroscopy. Here we report on preliminary
results of analogous studies performed on the interaction of DNA with the cationic Ni(II) complex of the same
ligand (NiL 2+ ).
The dramatic modification of the DNA CD spectrum, the appearance of a broad induced CD band in the range
350-450 nm, the strong increase of the DNA melting temperature (Tm) and the fluorescence quenching of
ethidium bromide-DNA solutions, in the presence of increasing amounts of the NiL 2+ metal complex, support the
existence of a tight intercalative interaction of NiL 2+ with DNA, analogous to that recently found for both ZnL 2+
and CuL 2+ [1]. The intrinsic binding constant (Kb) and the interaction stoichiometry (s), determined by UV
spectrophotometric titration, are equal to 4.3x10 6 M -1 and 1.0 base pair per metal complex, respectively.
Interestingly, the value of Kb is slightly higher than and more than 10 times higher than that relative to the
CuL 2+ -DNA and the ZnL 2+ -DNA systems, respectively.
Speculations can be performed of the observed trend, on the basis of the electronic and geometrical structures of
the three complexes of the same ligand, characterized by a square planar coordination geometry of the metal
centre.
Analogously to what observed for CuL 2+ , the shape of the CD of the NiL 2+ -DNA system, at NiL 2+ -DNA molar
ratios higher than 0.5 is indicative of the formation of supramolecular aggregates in solutions, as a possible
consequence of the electrostatic interaction between the cationic complex and the negatively charged phosphate
groups of DNA.
References:
[1] A. Silvestri, G. Barone, G. Ruisi, D. Anselmo, S. Riela and V. Turco Liveri, J. Inorg. Biochem. 101, 841
(2007).
[2] G. Barone, A. Longo, A. Ruggirello, A. Silvestri, A. Terenzi, V. Turco Liveri, Dalton Trans., in press.
_____________________________________________________________________
127