Two Novel Ternary Dicopper(II) μ‑Guanazole
Complexes with Aromatic Amines Strongly Activated by Quantum Dots
for DNA Cleavage
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Abstract
Two
novel (μ-guanazole)-bridged binuclear copper(II) complexes
with 1,10-phenanthroline (phen) or 2,2′-bipyridine (bipy),
[Cu<sub>2</sub>(μ-<i>N</i>2,<i>N</i>4-Hdatrz)(phen)<sub>2</sub>(H<sub>2</sub>O)(NO<sub>3</sub>)<sub>4</sub>] (<b>1</b>) and [Cu<sub>2</sub>(μ-<i>N</i>1,<i>N</i>2-datrz)<sub>2</sub>(μ-OH<sub>2</sub>)(bipy)<sub>2</sub>](ClO<sub>4</sub>)<sub>2</sub> (<b>2</b>) (Hdatrz = 3,5-diamino-1,2,4-triazole
= guanazole), have been prepared and characterized by X-ray diffraction,
spectroscopy, and susceptibility measurements. Compounds <b>1</b> and <b>2</b> differ in the aromatic amine, which acts as a
coligand, and in the Cu···Cu′-bridging system.
Compound <b>1</b>, which contains two mono-bridged copper ions,
represents the first example of a discrete Cu–(<i>N</i>C<i>N</i>-trz)–Cu′ complex. Compound <b>2</b>, with two triply bridged copper ions, is one of the few
compounds featuring a Cu–[(<i>NN</i>-trz)<sub>2</sub> + (<i>O-</i>aquo)]–Cu′ unit. Both compounds
display antiferromagnetic coupling but of different magnitude: <i>J</i> (μ<sub>2,4</sub>-triazole) = −52 cm<sup>–1</sup> for <b>1</b> and <i>J</i> (μ<sub>1,2</sub>-triazolate) = −115 cm<sup>–1</sup> for <b>2</b>. The DNA binding and cleavage properties of the two compounds have
been investigated. Fluorescence, viscosimetry, and thermal denaturation
studies reveal that both complexes have high affinity for DNA (<b>1</b> > <b>2</b>) and that only <b>1</b> acts as
an
intercalator. In the presence of a reducing agent like 3-mercaptopropionic
acid, <b>1</b> produces significant oxidative DNA cleavage,
whereas <b>2</b> is inactive. However, in the presence of very
small quantities of micelles filled with core–shell CdSe-ZnS
quantum dots (15 nM), <b>1</b> and <b>2</b> are considerably
more active and become highly efficient nucleases as a result of the
different possible mechanisms for promoting cooperative catalysis
(metal–metal, metal–hydrogen bonding, metal–intercalation,
and metal–nanoparticle). Electrophoresis DNA-cleavage inhibition
experiments, X-ray photoelectron spectroscopy studies, and fluorescence
ethidium bromide displacement assays reveal that in these novel nucleases
the QDs act as redox-active protein-like nanoparticle structures that
bind to the DNA and deliver electrons to the copper(II) centers for
the generation of Cu(I) and reactive oxygen species
