9 research outputs found
Synthesis, Characterization, and Spectroscopic Investigation of New Iron(III) and Copper(II) Complexes of a Carboxylate Rich Ligand and Their Interaction with Carbohydrates in Aqueous Solution
New
tetra-iron(III) (K<sub>4</sub>[<b>1</b>]·25H<sub>2</sub>O·(CH<sub>3</sub>)<sub>2</sub>CO and K<sub>3</sub>[<b>2</b>]·3H<sub>2</sub>O·(OH)) and di-copper(II) (Na<sub>3</sub>[<b>3</b>]·5H<sub>2</sub>O) complexes as carbohydrate
binding models have been synthesized and fully characterized used
several techniques including single crystal X-ray crystallography.
Whereas K<sub>4</sub>[<b>1</b>]·25H<sub>2</sub>O·(CH<sub>3</sub>)<sub>2</sub>CO and Na<sub>3</sub>[<b>3</b>]·5H<sub>2</sub>O are completely water-soluble, K<sub>3</sub>[<b>2</b>]·3H<sub>2</sub>O·(OH) is less soluble in all common solvents
including water. The binding of substrates, such as d-mannose, d-glucose, d-xylose, and xylitol with the water-soluble
complexes in different reaction conditions were investigated. In aqueous
alkaline media, complexes K<sub>4</sub>[<b>1</b>]·25H<sub>2</sub>O·(CH<sub>3</sub>)<sub>2</sub>CO and Na<sub>3</sub>[<b>3</b>]·5H<sub>2</sub>O showed coordination ability toward
the applied substrates. Even in the presence of stoichiometric excess
of the substrates, the complexes form only 1:1 (complex/substrate)
molar ratio species in solution. Apparent binding constants, p<i>K</i><sub>app</sub>, values between the complexes and the substrates
were determined and specific mode of substrate binding is proposed.
The p<i>K</i><sub>app</sub> values showed that d-mannose coordinates strongest to K<sub>4</sub>[<b>1</b>]·25H<sub>2</sub>O·(CH<sub>3</sub>)<sub>2</sub>CO and Na<sub>3</sub>[<b>3</b>]·5H<sub>2</sub>O. Syntheses, characterizations and
detailed substrate binding study using spectroscopic techniques and
single crystal X-ray diffraction are reported
New Dinuclear Cobalt(II) and Zinc(II) Complexes of a Carboxylate-Rich Dinucleating Ligand: Synthesis, Structure, Spectroscopic Characterization, and Their Interactions with Sugars
Sugar–metal ion interactions in aqueous medium
are involved
in many biochemical processes such as the transport and storage of
metals, the function and regulation of sugar-metabolizing metalloenzymes,
the mechanism of action of metal-containing pharmaceuticals, and toxic
metal metabolism. To understand such interactions we synthesized
and fully characterized two new dinuclear cobalt(II) and zinc(II)
complexes as carbohydrate binding models for xylose/glucose isomerases
(XGI). Synthesis of the dicobalt complex, Na<sub>3</sub>[Co<sub>2</sub>(ccdp)(μ-HCO<sub>2</sub>)]BF<sub>4</sub>·9H<sub>2</sub>O·2CH<sub>3</sub>OH (<b>1</b>), was performed in methanol
with stoichiometric amounts of Co(BF<sub>4</sub>)<sub>2</sub>·6H<sub>2</sub>O and the dinucleating ligand, H<sub>5</sub>ccdp (H<sub>5</sub>ccdp <i>= N,N′</i>-bis[2-carboxybenzomethyl]-<i>N,N′</i>-bis[carboxymethyl]-1,3-diaminopropan-2-ol),
in the presence of NaOH at ambient temperature in an argon glovebox.
Similarly, the dizinc complex, [NMe<sub>4</sub>]<sub>2</sub>[Zn<sub>2</sub>(ccdp)(μ-OAc)]·CH<sub>3</sub>OH (<b>2</b>), was synthesized from Zn(OAc)<sub>2</sub>·2H<sub>2</sub>O
and H<sub>5</sub>ccdp in the presence of NMe<sub>4</sub>OH at ambient
temperature in methanol. Binding of the complexes with carbohydrates
was investigated under different reaction conditions. In aqueous alkaline
media, complexes <b>1</b> and <b>2</b> showed chelating
ability towards the biologically important sugars, d-glucose
and d-xylose, and a polyalcohol enzyme inhibitor (xylitol).
In solution, each complex forms a 1:1 complex-substrate bound product
with specific binding constant values. Synthesis, characterization
details, and substrate binding using spectroscopic techniques and
single-crystal X-ray diffraction are reported
Inorganic Phosphate and Arsenate within New Tetranuclear Copper and Zinc Complexes: Syntheses, Crystal Structures, Magnetic, Electrochemical, and Thermal Studies
Three, PO<sub>4</sub><sup>3–</sup>/HPO<sub>4</sub><sup>2–</sup> and AsO<sub>4</sub><sup>3–</sup>-incorporated, new tetranuclear
complexes of copper(II) and zinc(II) ions have been synthesized and
fully characterized. In methanol–water, reactions of H<sub>3</sub>cpdp (H<sub>3</sub>cpdp = <i>N</i>,<i>N</i>′-Bis[2-carboxybenzomethyl]-<i>N</i>,<i>N</i>′-Bis[2-pyridylmethyl]-1,3-diaminopropan-2-ol) with copper(II)
chloride in the presence of either NaOH/Na<sub>2</sub>HPO<sub>4</sub>·2H<sub>2</sub>O or KOH/Na<sub>2</sub>HAsO<sub>4</sub>·7H<sub>2</sub>O lead to the isolation of the tetranuclear complexes Na<sub>3</sub>[Cu<sub>4</sub>(cpdp)<sub>2</sub>(μ<sub>4</sub>-PO<sub>4</sub>)](OH)<sub>2</sub>·14H<sub>2</sub>O (<b>1</b>)
and K<sub>2</sub>[Cu<sub>4</sub>(cpdp)<sub>2</sub>(μ<sub>4</sub>-AsO<sub>4</sub>)](OH)·16<sup>2</sup>/<sub>3</sub>H<sub>2</sub>O (<b>2</b>), respectively. Similarly, the reaction of H<sub>3</sub>cpdp with zinc(II) chloride in the presence of NaOH/Na<sub>2</sub>HPO<sub>4</sub>·2H<sub>2</sub>O yields a tetranuclear
complex, Na(H<sub>3</sub>O)<sub>2</sub>[Zn<sub>4</sub>(cpdp)<sub>2</sub>(μ<sub>4</sub>-HPO<sub>4</sub>)]Cl<sub>3</sub>·12<sup>1</sup>/<sub>2</sub>H<sub>2</sub>O (<b>3</b>). All complexes
are characterized by single-crystal X-ray diffraction and other analytical
techniques, such as Fourier transform infrared and UV−vis spectroscopy,
thermogravimetric and electrochemical studies. The solid-state molecular
framework of each complex contains two monocationic [M<sub>2</sub>(cpdp)]<sup>+</sup> (M = Cu, Zn) units, which are exclusively coordinated
to either phosphate/hydrogen phosphate or arsenate groups in a unique
mode. All three complexes exhibit a μ<sub>4</sub>:η<sup>1</sup>:η<sup>1</sup>:η<sup>1</sup>:η<sup>1</sup> bridging mode of the PO<sub>4</sub><sup>3–</sup>/HPO<sub>4</sub><sup>2–</sup>/AsO<sub>4</sub><sup>3–</sup> groups,
with each bridging among four metal ions. The thermal properties of
all three complexes have been investigated by thermogravimetric analysis.
Low-temperature magnetic studies of complexes <b>1</b> and <b>2</b> disclose moderate antiferromagnetic interactions mediated
among the copper centers through alkoxide and phosphate/arsenate bridges.
Electrochemical studies of complexes <b>1</b> and <b>2</b> in dimethylformamide using cyclic voltammetry reveal the presence
of a fairly assessable one-electron metal-based irreversible reduction
and one quasireversible oxidation couple
Inorganic Phosphate and Arsenate within New Tetranuclear Copper and Zinc Complexes: Syntheses, Crystal Structures, Magnetic, Electrochemical, and Thermal Studies
Three, PO<sub>4</sub><sup>3–</sup>/HPO<sub>4</sub><sup>2–</sup> and AsO<sub>4</sub><sup>3–</sup>-incorporated, new tetranuclear
complexes of copper(II) and zinc(II) ions have been synthesized and
fully characterized. In methanol–water, reactions of H<sub>3</sub>cpdp (H<sub>3</sub>cpdp = <i>N</i>,<i>N</i>′-Bis[2-carboxybenzomethyl]-<i>N</i>,<i>N</i>′-Bis[2-pyridylmethyl]-1,3-diaminopropan-2-ol) with copper(II)
chloride in the presence of either NaOH/Na<sub>2</sub>HPO<sub>4</sub>·2H<sub>2</sub>O or KOH/Na<sub>2</sub>HAsO<sub>4</sub>·7H<sub>2</sub>O lead to the isolation of the tetranuclear complexes Na<sub>3</sub>[Cu<sub>4</sub>(cpdp)<sub>2</sub>(μ<sub>4</sub>-PO<sub>4</sub>)](OH)<sub>2</sub>·14H<sub>2</sub>O (<b>1</b>)
and K<sub>2</sub>[Cu<sub>4</sub>(cpdp)<sub>2</sub>(μ<sub>4</sub>-AsO<sub>4</sub>)](OH)·16<sup>2</sup>/<sub>3</sub>H<sub>2</sub>O (<b>2</b>), respectively. Similarly, the reaction of H<sub>3</sub>cpdp with zinc(II) chloride in the presence of NaOH/Na<sub>2</sub>HPO<sub>4</sub>·2H<sub>2</sub>O yields a tetranuclear
complex, Na(H<sub>3</sub>O)<sub>2</sub>[Zn<sub>4</sub>(cpdp)<sub>2</sub>(μ<sub>4</sub>-HPO<sub>4</sub>)]Cl<sub>3</sub>·12<sup>1</sup>/<sub>2</sub>H<sub>2</sub>O (<b>3</b>). All complexes
are characterized by single-crystal X-ray diffraction and other analytical
techniques, such as Fourier transform infrared and UV−vis spectroscopy,
thermogravimetric and electrochemical studies. The solid-state molecular
framework of each complex contains two monocationic [M<sub>2</sub>(cpdp)]<sup>+</sup> (M = Cu, Zn) units, which are exclusively coordinated
to either phosphate/hydrogen phosphate or arsenate groups in a unique
mode. All three complexes exhibit a μ<sub>4</sub>:η<sup>1</sup>:η<sup>1</sup>:η<sup>1</sup>:η<sup>1</sup> bridging mode of the PO<sub>4</sub><sup>3–</sup>/HPO<sub>4</sub><sup>2–</sup>/AsO<sub>4</sub><sup>3–</sup> groups,
with each bridging among four metal ions. The thermal properties of
all three complexes have been investigated by thermogravimetric analysis.
Low-temperature magnetic studies of complexes <b>1</b> and <b>2</b> disclose moderate antiferromagnetic interactions mediated
among the copper centers through alkoxide and phosphate/arsenate bridges.
Electrochemical studies of complexes <b>1</b> and <b>2</b> in dimethylformamide using cyclic voltammetry reveal the presence
of a fairly assessable one-electron metal-based irreversible reduction
and one quasireversible oxidation couple
Inorganic Phosphate and Arsenate within New Tetranuclear Copper and Zinc Complexes: Syntheses, Crystal Structures, Magnetic, Electrochemical, and Thermal Studies
Three, PO<sub>4</sub><sup>3–</sup>/HPO<sub>4</sub><sup>2–</sup> and AsO<sub>4</sub><sup>3–</sup>-incorporated, new tetranuclear
complexes of copper(II) and zinc(II) ions have been synthesized and
fully characterized. In methanol–water, reactions of H<sub>3</sub>cpdp (H<sub>3</sub>cpdp = <i>N</i>,<i>N</i>′-Bis[2-carboxybenzomethyl]-<i>N</i>,<i>N</i>′-Bis[2-pyridylmethyl]-1,3-diaminopropan-2-ol) with copper(II)
chloride in the presence of either NaOH/Na<sub>2</sub>HPO<sub>4</sub>·2H<sub>2</sub>O or KOH/Na<sub>2</sub>HAsO<sub>4</sub>·7H<sub>2</sub>O lead to the isolation of the tetranuclear complexes Na<sub>3</sub>[Cu<sub>4</sub>(cpdp)<sub>2</sub>(μ<sub>4</sub>-PO<sub>4</sub>)](OH)<sub>2</sub>·14H<sub>2</sub>O (<b>1</b>)
and K<sub>2</sub>[Cu<sub>4</sub>(cpdp)<sub>2</sub>(μ<sub>4</sub>-AsO<sub>4</sub>)](OH)·16<sup>2</sup>/<sub>3</sub>H<sub>2</sub>O (<b>2</b>), respectively. Similarly, the reaction of H<sub>3</sub>cpdp with zinc(II) chloride in the presence of NaOH/Na<sub>2</sub>HPO<sub>4</sub>·2H<sub>2</sub>O yields a tetranuclear
complex, Na(H<sub>3</sub>O)<sub>2</sub>[Zn<sub>4</sub>(cpdp)<sub>2</sub>(μ<sub>4</sub>-HPO<sub>4</sub>)]Cl<sub>3</sub>·12<sup>1</sup>/<sub>2</sub>H<sub>2</sub>O (<b>3</b>). All complexes
are characterized by single-crystal X-ray diffraction and other analytical
techniques, such as Fourier transform infrared and UV−vis spectroscopy,
thermogravimetric and electrochemical studies. The solid-state molecular
framework of each complex contains two monocationic [M<sub>2</sub>(cpdp)]<sup>+</sup> (M = Cu, Zn) units, which are exclusively coordinated
to either phosphate/hydrogen phosphate or arsenate groups in a unique
mode. All three complexes exhibit a μ<sub>4</sub>:η<sup>1</sup>:η<sup>1</sup>:η<sup>1</sup>:η<sup>1</sup> bridging mode of the PO<sub>4</sub><sup>3–</sup>/HPO<sub>4</sub><sup>2–</sup>/AsO<sub>4</sub><sup>3–</sup> groups,
with each bridging among four metal ions. The thermal properties of
all three complexes have been investigated by thermogravimetric analysis.
Low-temperature magnetic studies of complexes <b>1</b> and <b>2</b> disclose moderate antiferromagnetic interactions mediated
among the copper centers through alkoxide and phosphate/arsenate bridges.
Electrochemical studies of complexes <b>1</b> and <b>2</b> in dimethylformamide using cyclic voltammetry reveal the presence
of a fairly assessable one-electron metal-based irreversible reduction
and one quasireversible oxidation couple
Inorganic Phosphate and Arsenate within New Tetranuclear Copper and Zinc Complexes: Syntheses, Crystal Structures, Magnetic, Electrochemical, and Thermal Studies
Three, PO<sub>4</sub><sup>3–</sup>/HPO<sub>4</sub><sup>2–</sup> and AsO<sub>4</sub><sup>3–</sup>-incorporated, new tetranuclear
complexes of copper(II) and zinc(II) ions have been synthesized and
fully characterized. In methanol–water, reactions of H<sub>3</sub>cpdp (H<sub>3</sub>cpdp = <i>N</i>,<i>N</i>′-Bis[2-carboxybenzomethyl]-<i>N</i>,<i>N</i>′-Bis[2-pyridylmethyl]-1,3-diaminopropan-2-ol) with copper(II)
chloride in the presence of either NaOH/Na<sub>2</sub>HPO<sub>4</sub>·2H<sub>2</sub>O or KOH/Na<sub>2</sub>HAsO<sub>4</sub>·7H<sub>2</sub>O lead to the isolation of the tetranuclear complexes Na<sub>3</sub>[Cu<sub>4</sub>(cpdp)<sub>2</sub>(μ<sub>4</sub>-PO<sub>4</sub>)](OH)<sub>2</sub>·14H<sub>2</sub>O (<b>1</b>)
and K<sub>2</sub>[Cu<sub>4</sub>(cpdp)<sub>2</sub>(μ<sub>4</sub>-AsO<sub>4</sub>)](OH)·16<sup>2</sup>/<sub>3</sub>H<sub>2</sub>O (<b>2</b>), respectively. Similarly, the reaction of H<sub>3</sub>cpdp with zinc(II) chloride in the presence of NaOH/Na<sub>2</sub>HPO<sub>4</sub>·2H<sub>2</sub>O yields a tetranuclear
complex, Na(H<sub>3</sub>O)<sub>2</sub>[Zn<sub>4</sub>(cpdp)<sub>2</sub>(μ<sub>4</sub>-HPO<sub>4</sub>)]Cl<sub>3</sub>·12<sup>1</sup>/<sub>2</sub>H<sub>2</sub>O (<b>3</b>). All complexes
are characterized by single-crystal X-ray diffraction and other analytical
techniques, such as Fourier transform infrared and UV−vis spectroscopy,
thermogravimetric and electrochemical studies. The solid-state molecular
framework of each complex contains two monocationic [M<sub>2</sub>(cpdp)]<sup>+</sup> (M = Cu, Zn) units, which are exclusively coordinated
to either phosphate/hydrogen phosphate or arsenate groups in a unique
mode. All three complexes exhibit a μ<sub>4</sub>:η<sup>1</sup>:η<sup>1</sup>:η<sup>1</sup>:η<sup>1</sup> bridging mode of the PO<sub>4</sub><sup>3–</sup>/HPO<sub>4</sub><sup>2–</sup>/AsO<sub>4</sub><sup>3–</sup> groups,
with each bridging among four metal ions. The thermal properties of
all three complexes have been investigated by thermogravimetric analysis.
Low-temperature magnetic studies of complexes <b>1</b> and <b>2</b> disclose moderate antiferromagnetic interactions mediated
among the copper centers through alkoxide and phosphate/arsenate bridges.
Electrochemical studies of complexes <b>1</b> and <b>2</b> in dimethylformamide using cyclic voltammetry reveal the presence
of a fairly assessable one-electron metal-based irreversible reduction
and one quasireversible oxidation couple
Synthesis, Structure, Spectroscopic Characterization, and Protein Binding Affinity of New Water-Soluble Hetero- and Homometallic Tetranuclear [Cu<sup>II</sup><sub>2</sub>Zn<sup>II</sup><sub>2</sub>] and [Cu<sup>II</sup><sub>4</sub>] Clusters
Two
new water-soluble hetero- and homometallic tetranuclear clusters,
Na<sub>4</sub>[Cu<sub>2</sub>Zn<sub>2</sub>(ccdp)<sub>2</sub>(μ-OH)<sub>2</sub>]·CH<sub>3</sub>OH·6H<sub>2</sub>O (<b>1</b>) and K<sub>3</sub>[Cu<sub>4</sub>(ccdp)<sub>2</sub>(μ-OH)(μ-OH<sub>2</sub>)]·14H<sub>2</sub>O (<b>2</b>), have been
synthesized in methanol–water at room temperature by exploiting
the flexibility, chelating ability,
and bridging potential of a carboxylate-rich dinucleating ligand, <i>N</i>,<i>N</i>′-bis(2-carboxybenzomethyl)-<i>N</i>,<i>N</i>′-bis(carboxymethyl)-1,3 diaminopropan-2-ol
(H<sub>5</sub>ccdp). Complex <b>1</b> is obtained through the
self-assembly of two monoanionic [CuZn(ccdp)]<sup>−</sup> fragments,
which are, in turn, exclusively bridged by two μ-OH<sup>–</sup> groups. Similarly, complex <b>2</b> is formed through
the self-assembly of two monoanionic [Cu<sub>2</sub>(ccdp)]<sup>−</sup> species exclusively bridged by one μ-OH<sup>–</sup> and one μ-OH<sub>2</sub> groups. Complexes <b>1</b> and <b>2</b> are
fully characterized in the solid state as well as in solution using
various analytical techniques including a single-crystal X-ray diffraction
study. The X-ray crystal structure of <b>1</b> reveals that
two Cu<sup>II</sup> centers are in a distorted square-pyramidal geometry,
whereas two
Zn<sup>II</sup> centers are in a distorted trigonal-bipyramidal geometry.
The solid-state structure of <b>2</b> contains two dinuclear
[Cu<sub>2</sub>(ccdp)]<sup>−</sup> units having one Cu<sup>II</sup> center in a distorted square-pyramidal
geometry and another Cu<sup>II</sup> center in a distorted trigonal-bipyramidal
geometry within each dinuclear unit. In the powder state, the high-field
EPR spectrum of complex <b>1</b> indicates that two Cu<sup>II</sup> ions are not spin-coupled, whereas that of complex <b>2</b> exhibits at least one noninteracting Cu<sup>II</sup> center coordinated
to a nitrogen atom of the ligand.
Both complexes are investigated for their binding affinity with the
protein bovine serum albumin (BSA) in an aqueous medium at pH ∼7.2
using fluorescence spectroscopy. Synchronous fluorescence spectra
clearly reveal that complexes <b>1</b> and <b>2</b> bind
to the active sites in the protein, indicating that the effect is
more pronounced toward tyrosine than tryptophan. Density functional
theory calculations
have been carried to find the Fukui functions at the metal sites in
complexes <b>1</b> and <b>2</b> to predict the possible
metal centers involved in the binding process with BSA protein
Synthesis, Structure, Spectroscopic Characterization, and Protein Binding Affinity of New Water-Soluble Hetero- and Homometallic Tetranuclear [Cu<sup>II</sup><sub>2</sub>Zn<sup>II</sup><sub>2</sub>] and [Cu<sup>II</sup><sub>4</sub>] Clusters
Two
new water-soluble hetero- and homometallic tetranuclear clusters,
Na<sub>4</sub>[Cu<sub>2</sub>Zn<sub>2</sub>(ccdp)<sub>2</sub>(μ-OH)<sub>2</sub>]·CH<sub>3</sub>OH·6H<sub>2</sub>O (<b>1</b>) and K<sub>3</sub>[Cu<sub>4</sub>(ccdp)<sub>2</sub>(μ-OH)(μ-OH<sub>2</sub>)]·14H<sub>2</sub>O (<b>2</b>), have been
synthesized in methanol–water at room temperature by exploiting
the flexibility, chelating ability,
and bridging potential of a carboxylate-rich dinucleating ligand, <i>N</i>,<i>N</i>′-bis(2-carboxybenzomethyl)-<i>N</i>,<i>N</i>′-bis(carboxymethyl)-1,3 diaminopropan-2-ol
(H<sub>5</sub>ccdp). Complex <b>1</b> is obtained through the
self-assembly of two monoanionic [CuZn(ccdp)]<sup>−</sup> fragments,
which are, in turn, exclusively bridged by two μ-OH<sup>–</sup> groups. Similarly, complex <b>2</b> is formed through
the self-assembly of two monoanionic [Cu<sub>2</sub>(ccdp)]<sup>−</sup> species exclusively bridged by one μ-OH<sup>–</sup> and one μ-OH<sub>2</sub> groups. Complexes <b>1</b> and <b>2</b> are
fully characterized in the solid state as well as in solution using
various analytical techniques including a single-crystal X-ray diffraction
study. The X-ray crystal structure of <b>1</b> reveals that
two Cu<sup>II</sup> centers are in a distorted square-pyramidal geometry,
whereas two
Zn<sup>II</sup> centers are in a distorted trigonal-bipyramidal geometry.
The solid-state structure of <b>2</b> contains two dinuclear
[Cu<sub>2</sub>(ccdp)]<sup>−</sup> units having one Cu<sup>II</sup> center in a distorted square-pyramidal
geometry and another Cu<sup>II</sup> center in a distorted trigonal-bipyramidal
geometry within each dinuclear unit. In the powder state, the high-field
EPR spectrum of complex <b>1</b> indicates that two Cu<sup>II</sup> ions are not spin-coupled, whereas that of complex <b>2</b> exhibits at least one noninteracting Cu<sup>II</sup> center coordinated
to a nitrogen atom of the ligand.
Both complexes are investigated for their binding affinity with the
protein bovine serum albumin (BSA) in an aqueous medium at pH ∼7.2
using fluorescence spectroscopy. Synchronous fluorescence spectra
clearly reveal that complexes <b>1</b> and <b>2</b> bind
to the active sites in the protein, indicating that the effect is
more pronounced toward tyrosine than tryptophan. Density functional
theory calculations
have been carried to find the Fukui functions at the metal sites in
complexes <b>1</b> and <b>2</b> to predict the possible
metal centers involved in the binding process with BSA protein
Synthesis, Structure, Spectroscopic Characterization, and Protein Binding Affinity of New Water-Soluble Hetero- and Homometallic Tetranuclear [Cu<sup>II</sup><sub>2</sub>Zn<sup>II</sup><sub>2</sub>] and [Cu<sup>II</sup><sub>4</sub>] Clusters
Two
new water-soluble hetero- and homometallic tetranuclear clusters,
Na<sub>4</sub>[Cu<sub>2</sub>Zn<sub>2</sub>(ccdp)<sub>2</sub>(μ-OH)<sub>2</sub>]·CH<sub>3</sub>OH·6H<sub>2</sub>O (<b>1</b>) and K<sub>3</sub>[Cu<sub>4</sub>(ccdp)<sub>2</sub>(μ-OH)(μ-OH<sub>2</sub>)]·14H<sub>2</sub>O (<b>2</b>), have been
synthesized in methanol–water at room temperature by exploiting
the flexibility, chelating ability,
and bridging potential of a carboxylate-rich dinucleating ligand, <i>N</i>,<i>N</i>′-bis(2-carboxybenzomethyl)-<i>N</i>,<i>N</i>′-bis(carboxymethyl)-1,3 diaminopropan-2-ol
(H<sub>5</sub>ccdp). Complex <b>1</b> is obtained through the
self-assembly of two monoanionic [CuZn(ccdp)]<sup>−</sup> fragments,
which are, in turn, exclusively bridged by two μ-OH<sup>–</sup> groups. Similarly, complex <b>2</b> is formed through
the self-assembly of two monoanionic [Cu<sub>2</sub>(ccdp)]<sup>−</sup> species exclusively bridged by one μ-OH<sup>–</sup> and one μ-OH<sub>2</sub> groups. Complexes <b>1</b> and <b>2</b> are
fully characterized in the solid state as well as in solution using
various analytical techniques including a single-crystal X-ray diffraction
study. The X-ray crystal structure of <b>1</b> reveals that
two Cu<sup>II</sup> centers are in a distorted square-pyramidal geometry,
whereas two
Zn<sup>II</sup> centers are in a distorted trigonal-bipyramidal geometry.
The solid-state structure of <b>2</b> contains two dinuclear
[Cu<sub>2</sub>(ccdp)]<sup>−</sup> units having one Cu<sup>II</sup> center in a distorted square-pyramidal
geometry and another Cu<sup>II</sup> center in a distorted trigonal-bipyramidal
geometry within each dinuclear unit. In the powder state, the high-field
EPR spectrum of complex <b>1</b> indicates that two Cu<sup>II</sup> ions are not spin-coupled, whereas that of complex <b>2</b> exhibits at least one noninteracting Cu<sup>II</sup> center coordinated
to a nitrogen atom of the ligand.
Both complexes are investigated for their binding affinity with the
protein bovine serum albumin (BSA) in an aqueous medium at pH ∼7.2
using fluorescence spectroscopy. Synchronous fluorescence spectra
clearly reveal that complexes <b>1</b> and <b>2</b> bind
to the active sites in the protein, indicating that the effect is
more pronounced toward tyrosine than tryptophan. Density functional
theory calculations
have been carried to find the Fukui functions at the metal sites in
complexes <b>1</b> and <b>2</b> to predict the possible
metal centers involved in the binding process with BSA protein