The interaction of native DNA with Zn(II) and Cu(II) complexes of 5-triethyl ammonium methyl salicylidene orto-phenylendiimine

Abstract

The interaction of native calf thymus DNA with the Zn(II) and Cu(II) complexes of 5-triethyl ammonium methyl salicylidene ortophenylendiimine (ZnL 2+ and CuL 2+ ), in 1 mM Tris-HCl aqueous solutions at neutral pH, has been monitored as a function of the metal complex-DNA molar ratio by UV absorption spectrophotometry, circular dichroism (CD) and fluorescence spectroscopy. The results support for an intercalative interaction of both ZnL 2+ and CuL 2+ with DNA, showing CuL 2+ an affinity of approximately 10 times higher than ZnL 2+ . In particular, the values of the binding constant, determined by UV spectrophotometric titration, equal to 7.3 · 10 4 and 1.3 · 10 6 M À1 , for ZnL 2+ and CuL 2+ , respectively, indicate the occurrence of a marked interaction with a binding size of about 0.7 in base pairs. The temperature dependence of the absorbance at 258 nm suggests that both complexes strongly increase the DNA melting temperature (Tm) already at metal complex-DNA molar ratios equal to 0.1. As evidenced by the quenching of the fluorescence of ethidium bromide-DNA solutions in the presence of increasing amounts of metal complex, ZnL 2+ and CuL 2+ are able to displace the ethidium cation intercalated into DNA. A tight ZnL 2+ -DNA and CuL 2+ -DNA binding has been also proven by the appearance, in both metal complex-DNA solutions, of a broad induced CD band in the range 350-450 nm. In the case of the CuL 2+ -DNA system, the shape of the CD spectrum, at high CuL 2+ content, is similar to that observed for w-DNA solutions. Such result allowed us to hypothesize that CuL 2+ induces the formation of supramolecular aggregates of DNA in aqueous solutions.

Pyrophosphate-bridged complexes with picomolar toxicity

“…Similarly, in the presence of 3 the shift observed in the spectral profile has an overall change of $12 nm (from 273 nm to 261 nm). This blue shift is indicative of conformational changes and destabilization of the DNA helix [65]. The positive signal observed in the CD is characteristic of external interactions or groove binding to DNA [64,66].…”

Fluorescence emission and enhanced photochemical stability of ZnII-5-triethyl ammonium methyl salicylidene ortho-phenylendiiminate interacting with native DNA

“…The complex ZnL 2+ was synthesized as recently reported [22] by the reaction of 5-(triethylammoniummethyl) salicylaldehyde chloride, 1,2 phenylendiamine and zinc(II) acetate in a 2:1.1:1 molar ratio [13], in doubly distilled water, and isolated as perchlorate salts. The 5-(triethylammoniummethyl) salicylaldehyde chloride ligand was prepared from 5-chloromethyl salicylaldehyde [24] and triethylamine in THF.…”

“…In fact, we have recently reported on the interaction of native DNA with NiL 2+ , CuL 2+ and ZnL 2+ complexes [21,22], CuL 2+ also confined in reverse micelles to simulate the intracellular solution environment [23]. The results obtained by UV spectrophotometric titrations, circular dichroism, DNA thermal denaturation measurements, and fluorescence quenching of ethidium bromide-DNA solutions, collectively show that ML 2+ (M= Ni II , Cu II , and Zn II ) strongly interact with native DNA, by a combined electrostatic and intercalative mechanism [21,22]. Considering the photophysical properties of Zn II -Schiff base complexes described above, fluorescence spectroscopy measurements were mainly exploited, as supported by quantum chemical calculations.…”

(Dipyrido[3,2-a:2′,3′-c]phenazine)(glycinato)copper(II) perchlorate: A novel DNA-intercalator with anti-proliferative activity against thyroid cancer cell lines

“…We have recently studied the interaction of different copper(II) complexes with native calf thymus DNA [39][40][41][42][43]. In a few cases, the cytotoxic activity of these copper(II) complexes was correlated to their DNA-binding properties [40,43].…”