Two Novel Ternary Dicopper(II) μ‑Guanazole Complexes with Aromatic Amines Strongly Activated by Quantum Dots for DNA Cleavage

Two
novel (μ-guanazole)-bridged binuclear copper­(II) complexes
with 1,10-phenanthroline (phen) or 2,2′-bipyridine (bipy),
[Cu2(μ-N2,N4-Hdatrz)­(phen)2(H2O)­(NO3)4] (1) and [Cu2(μ-N1,N2-datrz)2(μ-OH2)­(bipy)2]­(ClO4)2 (2) (Hdatrz = 3,5-diamino-1,2,4-triazole
= guanazole), have been prepared and characterized by X-ray diffraction,
spectroscopy, and susceptibility measurements. Compounds 1 and 2 differ in the aromatic amine, which acts as a
coligand, and in the Cu···Cu′-bridging system.
Compound 1, which contains two mono-bridged copper ions,
represents the first example of a discrete Cu–(NCN-trz)–Cu′ complex. Compound 2, with two triply bridged copper ions, is one of the few
compounds featuring a Cu–[(NN-trz)2 + (O-aquo)]–Cu′ unit. Both compounds
display antiferromagnetic coupling but of different magnitude: J (μ2,4-triazole) = −52 cm–1 for 1 and J (μ1,2-triazolate) = −115 cm–1 for 2. 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 (1 > 2) and that only 1 acts as
an
intercalator. In the presence of a reducing agent like 3-mercaptopropionic
acid, 1 produces significant oxidative DNA cleavage,
whereas 2 is inactive. However, in the presence of very
small quantities of micelles filled with core–shell CdSe-ZnS
quantum dots (15 nM), 1 and 2 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.