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.

本研究合成并通过X射线衍射（X-ray diffraction）、光谱学及磁化率测量（susceptibility measurements）表征了两种新型(μ-胍唑)桥联双核铜(II)配合物，二者分别以1,10-邻菲啰啉（1,10-phenanthroline, phen）和2,2'-联吡啶（2,2′-bipyridine, bipy）作为辅助配体，化学式分别为[Cu2(μ-N2,N4-Hdatrz)(phen)2(H2O)(NO3)4] (1)与[Cu2(μ-N1,N2-datrz)2(μ-OH2)(bipy)2](ClO4)2 (2)，其中Hdatrz为3,5-二氨基-1,2,4-三唑（3,5-diamino-1,2,4-triazole，又称胍唑guanazole）。

两种配合物的差异在于作为辅助配体的芳香胺种类，以及Cu···Cu'的桥联体系。配合物1含有两个单桥联铜离子，是首例离散型Cu–(NCN-三唑)–Cu'配合物。配合物2含有两个三重桥联铜离子，是少数具有Cu–[(NN-三唑)₂ + (水配体桥)]–Cu'结构单元的化合物之一。两种配合物均表现出反铁磁耦合（antiferromagnetic coupling），但耦合强度存在差异：配合物1的耦合常数J(μ2,4-三唑)为−52 cm⁻¹，配合物2的耦合常数J(μ1,2-三唑盐)为−115 cm⁻¹。

本研究还探究了两种配合物的DNA结合与切割性能。荧光光谱法、粘度法及热变性实验结果显示，两种配合物均对DNA具有较高结合亲和力（配合物1强于2），且仅配合物1可作为DNA插入剂（intercalator）。当存在3-巯基丙酸（3-mercaptopropionic acid）等还原剂时，配合物1可显著催化氧化性DNA切割，而配合物2无此活性。

然而，当加入极少量负载核壳型CdSe-ZnS量子点（core–shell CdSe-ZnS quantum dots, QDs）的胶束（micelle）（浓度为15 nM）时，两种配合物的活性均显著提升，成为高效核酸酶（nuclease），这归因于多种可能的协同催化机制：金属-金属相互作用、金属-氢键作用、金属-插入作用以及金属-纳米粒子相互作用。

凝胶电泳DNA切割抑制实验、X射线光电子能谱（X-ray photoelectron spectroscopy）分析以及溴化乙锭荧光置换实验表明，在这类新型核酸酶中，量子点可作为具有氧化还原活性的类蛋白质纳米结构，结合至DNA并向铜(II)中心传递电子，进而生成铜(I)与活性氧物种（reactive oxygen species）。