10 research outputs found
Photoinduced DNA Cleavage Promoted by Two Copper(II) Complexes of Tetracyclines and 1,10-Phenanthroline
In this report, we demonstrate how UV-light exposure can enhance DNA cleavage promoted by two copper(II) complexes of tetracyclines and 1,10-phenanthroline about 40 times in comparison to nonirradiated conditions. In addition, new aspects regarding their DNA binding properties, as well as the mechanism of the cleavage reaction, were also investigated
New La(III) Complex Immobilized on 3āAminopropyl-Functionalized Silica as an Efficient and Reusable Catalyst for Hydrolysis of Phosphate Ester Bonds
Described
herein is the synthesis, structure, and monoesterase and diesterase
activities of a new mononuclear [La<sup>III</sup>(L<sup>1</sup>)Ā(NO<sub>3</sub>)<sub>2</sub>] (<b>1</b>) complex (H<sub>2</sub>L<sup>1</sup> = 2-bisĀ[{(2-pyridylmethyl)-aminomethyl}-6-[<i>N</i>-(2-pyridylmethyl) aminomethyl)])-4-methyl-6-formylphenol) in the
hydrolysis of 2,4-bisĀ(dinitrophenyl)Āphosphate (2,4-BDNPP). When covalently
linked to 3-aminopropyl-functionalized silica, <b>1</b> undergoes
disproportionation to form a dinuclear species (<b>APS-1</b>), whose catalytic efficiency is increased when compared to the homogeneous
reaction due to second coordination sphere effects which increase
the substrate to complex association constant. The anchored catalyst <b>APS-1</b> can be recovered and reused for subsequent hydrolysis
reactions (five times) with only a slight loss in activity. In the
presence of DNA, we suggest that <b>1</b> is also converted
into the dinuclear active species as observed with <b>APS-1</b>, and both were shown to be efficient in DNA cleavage
Second-Coordination-Sphere Effects Increase the Catalytic Efficiency of an Extended Model for Fe<sup>III</sup>M<sup>II</sup> Purple Acid Phosphatases
Herein we describe the synthesis
of a new heterodinuclear Fe<sup>III</sup>Cu<sup>II</sup> model complex
for the active site of purple acid phosphatases and its binding to
a polyamine chain, a model for the amino acid residues around the
active site. The properties of these systems and their catalytic activity
in the hydrolysis of bisĀ(2,4-dinitrophenyl)Āphosphate are compared,
and conclusions regarding the effects of the second coordination sphere
are drawn. The positive effect of the polymeric chain on DNA hydrolysis
is also described and discussed
Second-Coordination-Sphere Effects Increase the Catalytic Efficiency of an Extended Model for Fe<sup>III</sup>M<sup>II</sup> Purple Acid Phosphatases
Herein we describe the synthesis
of a new heterodinuclear Fe<sup>III</sup>Cu<sup>II</sup> model complex
for the active site of purple acid phosphatases and its binding to
a polyamine chain, a model for the amino acid residues around the
active site. The properties of these systems and their catalytic activity
in the hydrolysis of bisĀ(2,4-dinitrophenyl)Āphosphate are compared,
and conclusions regarding the effects of the second coordination sphere
are drawn. The positive effect of the polymeric chain on DNA hydrolysis
is also described and discussed
Second-Sphere Effects in Dinuclear Fe<sup>III</sup>Zn<sup>II</sup> Hydrolase Biomimetics: Tuning Binding and Reactivity Properties
Herein,
we report the synthesis and characterization of two dinuclear Fe<sup>III</sup>Zn<sup>II</sup> complexes [Fe<sup>III</sup>Zn<sup>II</sup>LP1] (<b>1</b>) and [Fe<sup>III</sup>Zn<sup>II</sup>LP2] (<b>2</b>), in which LP1 and LP2 are conjugated systems containing
one and two pyrene groups, respectively, connected via the diamine
āHNĀ(CH<sub>2</sub>)<sub>4</sub>NHā spacer to the well-known
N<sub>5</sub>O<sub>2</sub>-donor H<sub>2</sub>L ligand (H<sub>2</sub>L = 2-bisĀ{[(2-pyridylmethyl)Āaminomethyl]-6-[(2-hydroxybenzyl)Ā(2-pyridylmethyl)]Āaminomethyl}-4-methylphenol).
The complex [Fe<sup>III</sup>Zn<sup>II</sup>L1] (<b>3</b>),
in which H<sub>2</sub>L was modified to H<sub>2</sub>L1, with a carbonyl
group attached to the terminal phenol group, was included in this
study for comparison purposes.<sup>1</sup> Both complexes <b>1</b> and <b>2</b> were satisfactorily characterized in the solid
state and in solution. Extended X-ray absorption fine structure data
for <b>1</b> and <b>3</b> in an acetonitrile solution
show that the multiply bridged structure seen in the solid state of <b>3</b> is retained in solution. Potentiometric and UVāvis
titration of <b>1</b> and <b>2</b> show that electrostatic
interaction between the protonated amino groups and coordinated water
molecules significantly decreases the p<i>K</i><sub>a</sub> of the ironĀ(III)-bound water compared to those of <b>3</b>. On the other hand, catalytic activity studies using <b>1</b> and <b>2</b> in the hydrolysis of the activated substrate
bisĀ(2,4-dinitrophenyl)Āphosphate (BDNPP) resulted in a significant
increase in the association of the substrate (<i>K</i><sub>ass</sub> ā
1/<i>K</i><sub>M</sub>) compared to
that of <b>3</b> because of electrostatic and hydrophobic interactions
between BDNPP and the side-chain diaminopyrene of the ligands H<sub>2</sub>LP1 and H<sub>2</sub>LP2. In addition, the introduction of
the pyrene motifs in <b>1</b> and <b>2</b> enhanced their
activity toward DNA and as effective antitumor drugs, although the
biochemical mechanism of the latter effect is currently under investigation.
These complexes represent interesting examples of how to promote an
increase in the activity of traditional artificial metal nucleases
by introducing second-coordination-sphere effects
Synthesis, Magnetostructural Correlation, and Catalytic Promiscuity of Unsymmetric Dinuclear Copper(II) Complexes: Models for Catechol Oxidases and Hydrolases
Herein, we report the synthesis and characterization,
through elemental
analysis, electronic spectroscopy, electrochemistry, potentiometric
titration, electron paramagnetic resonance, and magnetochemistry,
of two dinuclear copperĀ(II) complexes, using the unsymmetrical ligands <i>N</i>ā²,<i>N</i>ā²,<i>N</i>-trisĀ(2-pyridylmethyl)-<i>N</i>-(2-hydroxy-3,5-di-<i>tert</i>-butylbenzyl)-1,3-propanediamin-2-ol
(<b>L1</b>) and <i>N</i>ā²,<i>N</i>ā²-bisĀ(2-pyridylmethyl)-<i>N</i>,<i>N</i>-(2-hydroxybenzyl)Ā(2-hydroxy-3,5-di-<i>tert</i>-butylbenzyl)-1,3-propanediamin-2-ol
(<b>L2</b>). The structures of the complexes [Cu<sub>2</sub>(<b>L1</b>)Ā(Ī¼-OAc)]Ā(ClO<sub>4</sub>)<sub>2</sub>Ā·(CH<sub>3</sub>)<sub>2</sub>CHOH (<b>1</b>) and [Cu<sub>2</sub>(<b>L2</b>)Ā(Ī¼-OAc)]Ā(ClO<sub>4</sub>)Ā·H<sub>2</sub>OĀ·(CH<sub>3</sub>)<sub>2</sub>CHOH (<b>2</b>) were determined by X-ray
crystallography. The complex [Cu<sub>2</sub>(<b>L3</b>)Ā(Ī¼-OAc)]<sup>2+</sup> [<b>3</b>; <b>L3</b> = <i>N</i>-(2-hydroxybenzyl)-<i>N</i>ā²,<i>N</i>ā²,<i>N</i>-trisĀ(2-pyridylmethyl)-1,3-propanediamin-2-ol]
was included in this study for comparison purposes only (Neves et
al. <i>Inorg. Chim. Acta</i> <b>2005</b>, <i>358</i>, 1807ā1822). Magnetic data show that the Cu<sup>II</sup> centers in <b>1</b> and <b>2</b> are antiferromagnetically
coupled and that the difference in the exchange coupling <i>J</i> found for these complexes (<i>J</i> = ā4.3 cm<sup>ā1</sup> for <b>1</b> and <i>J</i> = ā40.0
cm<sup>ā1</sup> for <b>2</b>) is a function of the CuāOāCu
bridging angle. In addition, <b>1</b> and <b>2</b> were
tested as catalysts in the oxidation of the model substrate 3,5-di-<i>tert</i>-butylcatechol and can be considered as functional models
for catechol oxidase. Because these complexes possess labile sites
in their structures and in solution they have a potential nucleophile
constituted by a terminal Cu<sup>II</sup>-bound hydroxo group, their
activity toward hydrolysis of the model substrate 2,4-bisĀ(dinitrophenyl)Āphosphate
and DNA was also investigated. Double electrophilic activation of
the phosphodiester by monodentate coordination to the Cu<sup>II</sup> center that contains the phenol group with <i>tert</i>-butyl substituents and hydrogen bonding of the protonated phenol
with the phosphate O atom are proposed to increase the hydrolase activity
(<i>K</i><sub>ass.</sub> and <i>k</i><sub>cat.</sub>) of <b>1</b> and <b>2</b> in comparison with that found
for complex <b>3</b>. In fact, complexes <b>1</b> and <b>2</b> show both oxidoreductase and hydrolase/nuclease activities
and can thus be regarded as man-made models for studying catalytic
promiscuity
Synthesis, Magnetostructural Correlation, and Catalytic Promiscuity of Unsymmetric Dinuclear Copper(II) Complexes: Models for Catechol Oxidases and Hydrolases
Herein, we report the synthesis and characterization,
through elemental
analysis, electronic spectroscopy, electrochemistry, potentiometric
titration, electron paramagnetic resonance, and magnetochemistry,
of two dinuclear copperĀ(II) complexes, using the unsymmetrical ligands <i>N</i>ā²,<i>N</i>ā²,<i>N</i>-trisĀ(2-pyridylmethyl)-<i>N</i>-(2-hydroxy-3,5-di-<i>tert</i>-butylbenzyl)-1,3-propanediamin-2-ol
(<b>L1</b>) and <i>N</i>ā²,<i>N</i>ā²-bisĀ(2-pyridylmethyl)-<i>N</i>,<i>N</i>-(2-hydroxybenzyl)Ā(2-hydroxy-3,5-di-<i>tert</i>-butylbenzyl)-1,3-propanediamin-2-ol
(<b>L2</b>). The structures of the complexes [Cu<sub>2</sub>(<b>L1</b>)Ā(Ī¼-OAc)]Ā(ClO<sub>4</sub>)<sub>2</sub>Ā·(CH<sub>3</sub>)<sub>2</sub>CHOH (<b>1</b>) and [Cu<sub>2</sub>(<b>L2</b>)Ā(Ī¼-OAc)]Ā(ClO<sub>4</sub>)Ā·H<sub>2</sub>OĀ·(CH<sub>3</sub>)<sub>2</sub>CHOH (<b>2</b>) were determined by X-ray
crystallography. The complex [Cu<sub>2</sub>(<b>L3</b>)Ā(Ī¼-OAc)]<sup>2+</sup> [<b>3</b>; <b>L3</b> = <i>N</i>-(2-hydroxybenzyl)-<i>N</i>ā²,<i>N</i>ā²,<i>N</i>-trisĀ(2-pyridylmethyl)-1,3-propanediamin-2-ol]
was included in this study for comparison purposes only (Neves et
al. <i>Inorg. Chim. Acta</i> <b>2005</b>, <i>358</i>, 1807ā1822). Magnetic data show that the Cu<sup>II</sup> centers in <b>1</b> and <b>2</b> are antiferromagnetically
coupled and that the difference in the exchange coupling <i>J</i> found for these complexes (<i>J</i> = ā4.3 cm<sup>ā1</sup> for <b>1</b> and <i>J</i> = ā40.0
cm<sup>ā1</sup> for <b>2</b>) is a function of the CuāOāCu
bridging angle. In addition, <b>1</b> and <b>2</b> were
tested as catalysts in the oxidation of the model substrate 3,5-di-<i>tert</i>-butylcatechol and can be considered as functional models
for catechol oxidase. Because these complexes possess labile sites
in their structures and in solution they have a potential nucleophile
constituted by a terminal Cu<sup>II</sup>-bound hydroxo group, their
activity toward hydrolysis of the model substrate 2,4-bisĀ(dinitrophenyl)Āphosphate
and DNA was also investigated. Double electrophilic activation of
the phosphodiester by monodentate coordination to the Cu<sup>II</sup> center that contains the phenol group with <i>tert</i>-butyl substituents and hydrogen bonding of the protonated phenol
with the phosphate O atom are proposed to increase the hydrolase activity
(<i>K</i><sub>ass.</sub> and <i>k</i><sub>cat.</sub>) of <b>1</b> and <b>2</b> in comparison with that found
for complex <b>3</b>. In fact, complexes <b>1</b> and <b>2</b> show both oxidoreductase and hydrolase/nuclease activities
and can thus be regarded as man-made models for studying catalytic
promiscuity
Synthesis, Magnetostructural Correlation, and Catalytic Promiscuity of Unsymmetric Dinuclear Copper(II) Complexes: Models for Catechol Oxidases and Hydrolases
Herein, we report the synthesis and characterization,
through elemental
analysis, electronic spectroscopy, electrochemistry, potentiometric
titration, electron paramagnetic resonance, and magnetochemistry,
of two dinuclear copperĀ(II) complexes, using the unsymmetrical ligands <i>N</i>ā²,<i>N</i>ā²,<i>N</i>-trisĀ(2-pyridylmethyl)-<i>N</i>-(2-hydroxy-3,5-di-<i>tert</i>-butylbenzyl)-1,3-propanediamin-2-ol
(<b>L1</b>) and <i>N</i>ā²,<i>N</i>ā²-bisĀ(2-pyridylmethyl)-<i>N</i>,<i>N</i>-(2-hydroxybenzyl)Ā(2-hydroxy-3,5-di-<i>tert</i>-butylbenzyl)-1,3-propanediamin-2-ol
(<b>L2</b>). The structures of the complexes [Cu<sub>2</sub>(<b>L1</b>)Ā(Ī¼-OAc)]Ā(ClO<sub>4</sub>)<sub>2</sub>Ā·(CH<sub>3</sub>)<sub>2</sub>CHOH (<b>1</b>) and [Cu<sub>2</sub>(<b>L2</b>)Ā(Ī¼-OAc)]Ā(ClO<sub>4</sub>)Ā·H<sub>2</sub>OĀ·(CH<sub>3</sub>)<sub>2</sub>CHOH (<b>2</b>) were determined by X-ray
crystallography. The complex [Cu<sub>2</sub>(<b>L3</b>)Ā(Ī¼-OAc)]<sup>2+</sup> [<b>3</b>; <b>L3</b> = <i>N</i>-(2-hydroxybenzyl)-<i>N</i>ā²,<i>N</i>ā²,<i>N</i>-trisĀ(2-pyridylmethyl)-1,3-propanediamin-2-ol]
was included in this study for comparison purposes only (Neves et
al. <i>Inorg. Chim. Acta</i> <b>2005</b>, <i>358</i>, 1807ā1822). Magnetic data show that the Cu<sup>II</sup> centers in <b>1</b> and <b>2</b> are antiferromagnetically
coupled and that the difference in the exchange coupling <i>J</i> found for these complexes (<i>J</i> = ā4.3 cm<sup>ā1</sup> for <b>1</b> and <i>J</i> = ā40.0
cm<sup>ā1</sup> for <b>2</b>) is a function of the CuāOāCu
bridging angle. In addition, <b>1</b> and <b>2</b> were
tested as catalysts in the oxidation of the model substrate 3,5-di-<i>tert</i>-butylcatechol and can be considered as functional models
for catechol oxidase. Because these complexes possess labile sites
in their structures and in solution they have a potential nucleophile
constituted by a terminal Cu<sup>II</sup>-bound hydroxo group, their
activity toward hydrolysis of the model substrate 2,4-bisĀ(dinitrophenyl)Āphosphate
and DNA was also investigated. Double electrophilic activation of
the phosphodiester by monodentate coordination to the Cu<sup>II</sup> center that contains the phenol group with <i>tert</i>-butyl substituents and hydrogen bonding of the protonated phenol
with the phosphate O atom are proposed to increase the hydrolase activity
(<i>K</i><sub>ass.</sub> and <i>k</i><sub>cat.</sub>) of <b>1</b> and <b>2</b> in comparison with that found
for complex <b>3</b>. In fact, complexes <b>1</b> and <b>2</b> show both oxidoreductase and hydrolase/nuclease activities
and can thus be regarded as man-made models for studying catalytic
promiscuity
Spectroscopic and Catalytic Characterization of a Functional Fe<sup>III</sup>Fe<sup>II</sup> Biomimetic for the Active Site of Uteroferrin and Protein Cleavage
A mixed-valence complex, [Fe<sup>III</sup>Fe<sup>II</sup><b>L1</b>(Ī¼-OAc)<sub>2</sub>]ĀBF<sub>4</sub>Ā·H<sub>2</sub>O, where the ligand H<sub>2</sub><b>L1</b> = 2-{[[3-[((bisĀ(pyridin-2-ylmethyl)Āamino)Āmethyl)-2-hydroxy-5-methylbenzyl]Ā(pyridin-2-ylmethyl)Āamino]Āmethyl]Āphenol},
has been studied with a range of techniques, and, where possible,
its properties have been compared to those of the corresponding enzyme
system purple acid phosphatase. The Fe<sup>III</sup>Fe<sup>II</sup> and Fe<sup>III</sup><sub>2</sub> oxidized species were studied spectroelectrochemically.
The temperature-dependent population of the <i>S</i> = <sup>3</sup>/<sub>2</sub> spin states of the heterovalent system, observed
using magnetic circular dichroism, confirmed that the dinuclear center
is weakly antiferromagnetically coupled (<i>H</i> = ā2<i>JS</i><sub>1</sub>Ā·<i>S</i><sub>2</sub>, where <i>J</i> = ā5.6 cm<sup>ā1</sup>) in a frozen solution.
The ligand-to-metal charge-transfer transitions are correlated with
density functional theory calculations. The Fe<sup>III</sup>Fe<sup>II</sup> complex is electron paramagnetic resonance (EPR)-silent,
except at very low temperatures (<2 K), because of the broadening
caused by the exchange coupling and zero-field-splitting parameters
being of comparable magnitude and rapid spinālattice relaxation.
However, a phosphate-bound Fe<sup>III</sup><sub>2</sub> complex showed
an EPR spectrum due to population of the <i>S</i><sub>tot</sub> = 3 state (<i>J</i>= ā3.5 cm<sup>ā1</sup>). The phosphatase activity of the Fe<sup>III</sup>Fe<sup>II</sup> complex in hydrolysis of bisĀ(2,4-dinitrophenyl)Āphosphate (<i>k</i><sub>cat.</sub> = 1.88 Ć 10<sup>ā3</sup> s<sup>ā1</sup>; <i>K</i><sub>m</sub> = 4.63 Ć 10<sup>ā3</sup> mol L<sup>ā1</sup>) is similar to that of
other bimetallic heterovalent complexes with the same ligand. Analysis
of the kinetic data supports a mechanism where the initiating nucleophile
in the phosphatase reaction is a hydroxide, terminally bound to Fe<sup>III</sup>. It is interesting to note that aqueous solutions of [Fe<sup>III</sup>Fe<sup>II</sup><b>L1</b>(Ī¼-OAc)<sub>2</sub>]<sup>+</sup> are also capable of protein cleavage, at mild temperature
and pH conditions, thus further expanding the scope of this complexās
catalytic promiscuity
Spectroscopic and Catalytic Characterization of a Functional Fe<sup>III</sup>Fe<sup>II</sup> Biomimetic for the Active Site of Uteroferrin and Protein Cleavage
A mixed-valence complex, [Fe<sup>III</sup>Fe<sup>II</sup><b>L1</b>(Ī¼-OAc)<sub>2</sub>]ĀBF<sub>4</sub>Ā·H<sub>2</sub>O, where the ligand H<sub>2</sub><b>L1</b> = 2-{[[3-[((bisĀ(pyridin-2-ylmethyl)Āamino)Āmethyl)-2-hydroxy-5-methylbenzyl]Ā(pyridin-2-ylmethyl)Āamino]Āmethyl]Āphenol},
has been studied with a range of techniques, and, where possible,
its properties have been compared to those of the corresponding enzyme
system purple acid phosphatase. The Fe<sup>III</sup>Fe<sup>II</sup> and Fe<sup>III</sup><sub>2</sub> oxidized species were studied spectroelectrochemically.
The temperature-dependent population of the <i>S</i> = <sup>3</sup>/<sub>2</sub> spin states of the heterovalent system, observed
using magnetic circular dichroism, confirmed that the dinuclear center
is weakly antiferromagnetically coupled (<i>H</i> = ā2<i>JS</i><sub>1</sub>Ā·<i>S</i><sub>2</sub>, where <i>J</i> = ā5.6 cm<sup>ā1</sup>) in a frozen solution.
The ligand-to-metal charge-transfer transitions are correlated with
density functional theory calculations. The Fe<sup>III</sup>Fe<sup>II</sup> complex is electron paramagnetic resonance (EPR)-silent,
except at very low temperatures (<2 K), because of the broadening
caused by the exchange coupling and zero-field-splitting parameters
being of comparable magnitude and rapid spinālattice relaxation.
However, a phosphate-bound Fe<sup>III</sup><sub>2</sub> complex showed
an EPR spectrum due to population of the <i>S</i><sub>tot</sub> = 3 state (<i>J</i>= ā3.5 cm<sup>ā1</sup>). The phosphatase activity of the Fe<sup>III</sup>Fe<sup>II</sup> complex in hydrolysis of bisĀ(2,4-dinitrophenyl)Āphosphate (<i>k</i><sub>cat.</sub> = 1.88 Ć 10<sup>ā3</sup> s<sup>ā1</sup>; <i>K</i><sub>m</sub> = 4.63 Ć 10<sup>ā3</sup> mol L<sup>ā1</sup>) is similar to that of
other bimetallic heterovalent complexes with the same ligand. Analysis
of the kinetic data supports a mechanism where the initiating nucleophile
in the phosphatase reaction is a hydroxide, terminally bound to Fe<sup>III</sup>. It is interesting to note that aqueous solutions of [Fe<sup>III</sup>Fe<sup>II</sup><b>L1</b>(Ī¼-OAc)<sub>2</sub>]<sup>+</sup> are also capable of protein cleavage, at mild temperature
and pH conditions, thus further expanding the scope of this complexās
catalytic promiscuity