6 research outputs found
A Unique Discrete Tetranuclear Cuā²āCu(N-N)<sub>2</sub>CuāCuā² Copper(II) Complex, Built from a Ī¼<sub>3</sub>ā1,2,4-Triazolato-Ī¼-carboxylato Ligand, as an Effective DNA Cleavage Agent
The title compound, characterized by means of an X-ray
structure
analysis, represents an easy example of a noncatena ā1 + 2
+ 1ā tetranuclear copperĀ(II) Ī¼<sub>3</sub>-triazolate
compound. [Cu<sub>4</sub>(atc)<sub>2</sub>(dien)<sub>4</sub>(ClO<sub>4</sub>)<sub>2</sub>]Ā(ClO<sub>4</sub>)<sub>2</sub>Ā·2H<sub>2</sub>O (<b>1</b>), where H<sub>2</sub>atc = 5-amino-l,2,4-triazole-3-carboxylic
acid and dien = diethylenetriamine = 1,4,7-triazaheptane, contains
two copper atoms linked by a double diazinic bridge, each of which
is further connected to a third and fourth copper atom (Cuā²)
through the triply bridging triazolato ring and the bidentate carboxylato
group of the atc<sup>2ā</sup> ligands. The copperācopper
distances within the tetranuclear unit are CuāCu = 4.059 Ć
,
CuāCuā² = 5.686 and 6.370 Ć
, and Cuā²āCuā²
= 11.373 Ć
. The compound self-assembles into a tridimensional
hydrogen-bonded network to generate a MOF. <b>1</b> exhibits
antiferromagnetic behavior with <i>g</i> = 2.10(1), <i>J</i> = ā34.1(2) cm<sup>ā1</sup> and <i>j</i> = ā5.50(3) cm<sup>ā1</sup>, where <i>J</i> is the coupling constant of the central CuāCu pair and <i>j</i> the coupling constant of the two CuāCuā²
(Cu<sub>central</sub>āCu<sub>pheripheral</sub>) pairs, as defined
by <b>H</b> = ā<i>J</i> <b>S</b><sub>2</sub><b>S</b><sub>2a</sub> ā <i>j</i> (<b>S</b><sub>1</sub><b>S</b><sub>2</sub> + <b>S</b><sub>2a</sub><b>S</b><sub>1a</sub>). Complex <b>1</b> has
been tested as nuclease mimic. It shows good binding propensity to
calf thymus DNA, with a binding constant value of 6.20 Ć 10<sup>6</sup> M<sup>ā1</sup> (<i>K</i><sub>app</sub>)
and Ī<i>T</i><sub>m</sub> = 18.3 Ā°C. Moreover,
the compound displays efficient oxidative cleavage of pUC18 DNA, even
at low concentration, in the presence of a mild reducing agent (ascorbate),
with a rate constant for the conversion of supercoiled to nicked DNA
(<i>k</i><sub>obs</sub>) of ā¼0.126 min<sup>ā1</sup>. The good reactivity of <b>1</b> toward DNA is explained from
the electrostatic interactions of the cationic species produced in
solution
A Unique Discrete Tetranuclear Cuā²āCu(N-N)<sub>2</sub>CuāCuā² Copper(II) Complex, Built from a Ī¼<sub>3</sub>ā1,2,4-Triazolato-Ī¼-carboxylato Ligand, as an Effective DNA Cleavage Agent
The title compound, characterized by means of an X-ray
structure
analysis, represents an easy example of a noncatena ā1 + 2
+ 1ā tetranuclear copperĀ(II) Ī¼<sub>3</sub>-triazolate
compound. [Cu<sub>4</sub>(atc)<sub>2</sub>(dien)<sub>4</sub>(ClO<sub>4</sub>)<sub>2</sub>]Ā(ClO<sub>4</sub>)<sub>2</sub>Ā·2H<sub>2</sub>O (<b>1</b>), where H<sub>2</sub>atc = 5-amino-l,2,4-triazole-3-carboxylic
acid and dien = diethylenetriamine = 1,4,7-triazaheptane, contains
two copper atoms linked by a double diazinic bridge, each of which
is further connected to a third and fourth copper atom (Cuā²)
through the triply bridging triazolato ring and the bidentate carboxylato
group of the atc<sup>2ā</sup> ligands. The copperācopper
distances within the tetranuclear unit are CuāCu = 4.059 Ć
,
CuāCuā² = 5.686 and 6.370 Ć
, and Cuā²āCuā²
= 11.373 Ć
. The compound self-assembles into a tridimensional
hydrogen-bonded network to generate a MOF. <b>1</b> exhibits
antiferromagnetic behavior with <i>g</i> = 2.10(1), <i>J</i> = ā34.1(2) cm<sup>ā1</sup> and <i>j</i> = ā5.50(3) cm<sup>ā1</sup>, where <i>J</i> is the coupling constant of the central CuāCu pair and <i>j</i> the coupling constant of the two CuāCuā²
(Cu<sub>central</sub>āCu<sub>pheripheral</sub>) pairs, as defined
by <b>H</b> = ā<i>J</i> <b>S</b><sub>2</sub><b>S</b><sub>2a</sub> ā <i>j</i> (<b>S</b><sub>1</sub><b>S</b><sub>2</sub> + <b>S</b><sub>2a</sub><b>S</b><sub>1a</sub>). Complex <b>1</b> has
been tested as nuclease mimic. It shows good binding propensity to
calf thymus DNA, with a binding constant value of 6.20 Ć 10<sup>6</sup> M<sup>ā1</sup> (<i>K</i><sub>app</sub>)
and Ī<i>T</i><sub>m</sub> = 18.3 Ā°C. Moreover,
the compound displays efficient oxidative cleavage of pUC18 DNA, even
at low concentration, in the presence of a mild reducing agent (ascorbate),
with a rate constant for the conversion of supercoiled to nicked DNA
(<i>k</i><sub>obs</sub>) of ā¼0.126 min<sup>ā1</sup>. The good reactivity of <b>1</b> toward DNA is explained from
the electrostatic interactions of the cationic species produced in
solution
Antisymmetric Exchange in Triangular Tricopper(II) Complexes: Correlation among Structural, Magnetic, and Electron Paramagnetic Resonance Parameters
Two new trinuclear copperĀ(II) complexes, [Cu<sub>3</sub>(Ī¼<sub>3</sub>-OH)Ā(daat)Ā(Hdat)<sub>2</sub>(ClO<sub>4</sub>)<sub>2</sub>(H<sub>2</sub>O)<sub>3</sub>]Ā(ClO<sub>4</sub>)<sub>2</sub>Ā·2H<sub>2</sub>O (<b>1</b>) and [Cu<sub>3</sub>(Ī¼<sub>3</sub>-OH)Ā(aaat)<sub>3</sub>(H<sub>2</sub>O)<sub>3</sub>]Ā(ClO<sub>4</sub>)<sub>2</sub>Ā·3H<sub>2</sub>O (<b>2</b>) (daat = 3,5-diacetylamino-1,2,4-triazolate,
Hdat = 3,5-diamino-1,2,4-triazole, and aaat = 3-acetylamino-5-amino-1,2,4-triazolate),
have been prepared from 1,2,4-triazole derivatives and structurally
characterized by X-ray crystallography. The structures of <b>1</b> and <b>2</b> consist of cationic trinuclear copperĀ(II) complexes
with a Cu<sub>3</sub>OH core held by three <i>N</i>,<i>N</i>-triazole bridges between each pair of copperĀ(II) atoms.
The copper atoms are five-coordinate with distorted square-pyramidal
geometries. The magnetic properties of <b>1</b> and <b>2</b> and those of five other related 1,2,4-triazolato tricopperĀ(II) complexes
with the same triangular structure (<b>3ā7</b>) (whose
crystal structures were already reported) have been investigated in
the temperature range of 1.9ā300 K. The formulas of <b>3ā7</b> are [Cu<sub>3</sub>(Ī¼<sub>3</sub>-OH)Ā(aaat)<sub>3</sub>(H<sub>2</sub>O)<sub>3</sub>]Ā(NO<sub>3</sub>)<sub>2</sub>Ā·H<sub>2</sub>O (<b>3</b>), {[Cu<sub>3</sub>(Ī¼<sub>3</sub>-OH)Ā(aat)<sub>3</sub>(Ī¼<sub>3</sub>-SO<sub>4</sub>)]Ā·6H<sub>2</sub>O}<sub><i>n</i></sub> (<b>4</b>), and [Cu<sub>3</sub>(Ī¼<sub>3</sub>-OH)Ā(aat)<sub>3</sub>AĀ(H<sub>2</sub>O)<sub>2</sub>]ĀAĀ·<i>x</i>H<sub>2</sub>O [A = NO<sub>3</sub><sup>ā</sup> (<b>5</b>), CF<sub>3</sub>SO<sub>3</sub><sup>ā</sup> (<b>6</b>), or ClO<sub>4</sub><sup>ā</sup> (<b>7</b>); <i>x</i> = 0 or 2] (aat =3-acetylamino-1,2,4-triazolate). The magnetic
and electron paramagnetic resonance (EPR) data have been analyzed
by using the following isotropic and antisymmetric exchange Hamiltonian: <i>H</i> = ā<i>J</i>[<i>S</i><sub>1</sub><i>S</i><sub>2</sub> + <i>S</i><sub>2</sub><i>S</i><sub>3</sub>] ā <i>j</i>[<i>S</i><sub>1</sub><i>S</i><sub>3</sub>] + <i>G</i>[<i>S</i><sub>1</sub> Ć <i>S</i><sub>2</sub> + <i>S</i><sub>2</sub> Ć <i>S</i><sub>3</sub> + <i>S</i><sub>1</sub> Ć <i>S</i><sub>3</sub>]. <b>1</b>ā<b>7</b> exhibit strong antiferromagnetic coupling
(values for both ā<i>J</i> and ā<i>j</i> in the range of 210ā142 cm<sup>ā1</sup>) and antisymmetric
exchange (<i>G</i> varying from to 27 to 36 cm<sup>ā1</sup>). At low temperatures, their EPR spectra display high-field (<i>g</i> < 2.0) signals indicating that the triangles present
symmetry lower than equilateral and that the antisymmetric exchange
is operative. A magneto-structural study showing a lineal correlation
between the CuāOāCu angle of the Cu<sub>3</sub>OH core
and the isotropic exchange parameters (<i>J</i> and <i>j</i>) has been conducted. Moreover, a model based on Moriyaās
theory that allows the prediction of the occurrence of antisymmetric
exchange in the tricopperĀ(II) triangles, via analysis of the overlap
between the ground and excited states of the local CuĀ(II) ions, has
been proposed. In addition, analytical expressions for evaluating
both the isotropic and antisymmetric exchange parameters from the
experimental magnetic susceptibility data of triangular complexes
with local spins (<i>S</i>) of <sup>1</sup>/<sub>2</sub>, <sup>3</sup>/<sub>2</sub>, or <sup>5</sup>/<sub>2</sub> have been
purposely derived. Finally, the magnetic and EPR results of this work
are discussed and compared with those of other tricopperĀ(II) triangles
reported in the literature
Two Novel Ternary Dicopper(II) Ī¼āGuanazole Complexes with Aromatic Amines Strongly Activated by Quantum Dots for DNA Cleavage
Two
novel (Ī¼-guanazole)-bridged binuclear copperĀ(II) complexes
with 1,10-phenanthroline (phen) or 2,2ā²-bipyridine (bipy),
[Cu<sub>2</sub>(Ī¼-<i>N</i>2,<i>N</i>4-Hdatrz)Ā(phen)<sub>2</sub>(H<sub>2</sub>O)Ā(NO<sub>3</sub>)<sub>4</sub>] (<b>1</b>) and [Cu<sub>2</sub>(Ī¼-<i>N</i>1,<i>N</i>2-datrz)<sub>2</sub>(Ī¼-OH<sub>2</sub>)Ā(bipy)<sub>2</sub>]Ā(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 CuĀ·Ā·Ā·Cuā²-bridging system.
Compound <b>1</b>, which contains two mono-bridged copper ions,
represents the first example of a discrete Cuā(<i>N</i>C<i>N</i>-trz)āCuā² complex. Compound <b>2</b>, with two triply bridged copper ions, is one of the few
compounds featuring a Cuā[(<i>NN</i>-trz)<sub>2</sub> + (<i>O-</i>aquo)]āCuā² unit. Both compounds
display antiferromagnetic coupling but of different magnitude: <i>J</i> (Ī¼<sub>2,4</sub>-triazole) = ā52 cm<sup>ā1</sup> for <b>1</b> and <i>J</i> (Ī¼<sub>1,2</sub>-triazolate) = ā115 cm<sup>ā1</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 coreāshell 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
(metalāmetal, metalāhydrogen bonding, metalāintercalation,
and metalānanoparticle). 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 copperĀ(II) centers for
the generation of CuĀ(I) and reactive oxygen species
Two Novel Ternary Dicopper(II) Ī¼āGuanazole Complexes with Aromatic Amines Strongly Activated by Quantum Dots for DNA Cleavage
Two
novel (Ī¼-guanazole)-bridged binuclear copperĀ(II) complexes
with 1,10-phenanthroline (phen) or 2,2ā²-bipyridine (bipy),
[Cu<sub>2</sub>(Ī¼-<i>N</i>2,<i>N</i>4-Hdatrz)Ā(phen)<sub>2</sub>(H<sub>2</sub>O)Ā(NO<sub>3</sub>)<sub>4</sub>] (<b>1</b>) and [Cu<sub>2</sub>(Ī¼-<i>N</i>1,<i>N</i>2-datrz)<sub>2</sub>(Ī¼-OH<sub>2</sub>)Ā(bipy)<sub>2</sub>]Ā(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 CuĀ·Ā·Ā·Cuā²-bridging system.
Compound <b>1</b>, which contains two mono-bridged copper ions,
represents the first example of a discrete Cuā(<i>N</i>C<i>N</i>-trz)āCuā² complex. Compound <b>2</b>, with two triply bridged copper ions, is one of the few
compounds featuring a Cuā[(<i>NN</i>-trz)<sub>2</sub> + (<i>O-</i>aquo)]āCuā² unit. Both compounds
display antiferromagnetic coupling but of different magnitude: <i>J</i> (Ī¼<sub>2,4</sub>-triazole) = ā52 cm<sup>ā1</sup> for <b>1</b> and <i>J</i> (Ī¼<sub>1,2</sub>-triazolate) = ā115 cm<sup>ā1</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 coreāshell 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
(metalāmetal, metalāhydrogen bonding, metalāintercalation,
and metalānanoparticle). 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 copperĀ(II) centers for
the generation of CuĀ(I) and reactive oxygen species
Two Novel Ternary Dicopper(II) Ī¼āGuanazole Complexes with Aromatic Amines Strongly Activated by Quantum Dots for DNA Cleavage
Two
novel (Ī¼-guanazole)-bridged binuclear copperĀ(II) complexes
with 1,10-phenanthroline (phen) or 2,2ā²-bipyridine (bipy),
[Cu<sub>2</sub>(Ī¼-<i>N</i>2,<i>N</i>4-Hdatrz)Ā(phen)<sub>2</sub>(H<sub>2</sub>O)Ā(NO<sub>3</sub>)<sub>4</sub>] (<b>1</b>) and [Cu<sub>2</sub>(Ī¼-<i>N</i>1,<i>N</i>2-datrz)<sub>2</sub>(Ī¼-OH<sub>2</sub>)Ā(bipy)<sub>2</sub>]Ā(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 CuĀ·Ā·Ā·Cuā²-bridging system.
Compound <b>1</b>, which contains two mono-bridged copper ions,
represents the first example of a discrete Cuā(<i>N</i>C<i>N</i>-trz)āCuā² complex. Compound <b>2</b>, with two triply bridged copper ions, is one of the few
compounds featuring a Cuā[(<i>NN</i>-trz)<sub>2</sub> + (<i>O-</i>aquo)]āCuā² unit. Both compounds
display antiferromagnetic coupling but of different magnitude: <i>J</i> (Ī¼<sub>2,4</sub>-triazole) = ā52 cm<sup>ā1</sup> for <b>1</b> and <i>J</i> (Ī¼<sub>1,2</sub>-triazolate) = ā115 cm<sup>ā1</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 coreāshell 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
(metalāmetal, metalāhydrogen bonding, metalāintercalation,
and metalānanoparticle). 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 copperĀ(II) centers for
the generation of CuĀ(I) and reactive oxygen species