Allopurinol and its interactions with Cu<Superscript>2+</Superscript> ions: radical reactions and complex structure

Allopurinol (ALP), an inhibitor of the xanthine oxidase enzime, is reported to provide protection against free-radical mediated damage by various mechanisms, including free-radical scavenging and metal chelation (i.e. Cu(II)). To obtain a wider insight into the molecular aspects of the beneficial action of ALP, free ALP and the Cu(II)- ALP system were investigated by radiation chemical and spectroscopic studies. Pulse radiolysis experiments show that ALP is a good · OH scavenger (1.8 × 10⁹ and 5.4 × 10⁹ M^-1 s^-1 at pH 6.0 and 11.0, respectively), leading to · OH-adducts and transient semi-oxidized species, such as phenoxyl radicals. The latter are also formed by the reaction of ALP with some specific one-electron oxidizing radicals (i.e. N₃ and SO₄ ^-). The semi-oxidized species are stabilized by their resonance properties and scarcely react with oxygen. In addition, the chelation of Cu(II) by ALP does not significantly affect the reactivity of the drug towards ·OH (2.5×0⁹ M^-1 s^-1). Raman and the IR spectra support the good chelating ability of ALP, indicating the formation of two Cu(II)- ALP complexes with a slightly different structure. Depending on the metal/ligand ratio, pyrimidine nitrogens may take part to the Cu(II) co-ordination in addition to the N pyrazolic atoms and the C O groups of some ALP molecules. These results suggest that ALP may inhibit oxidative damage both through the direct radical scavenging and the copper-chelation mechanism. In fact, both the conversion of a harmful radical, such as ·OH, into a less reactive transient species, and the capture of copper ions, which play a relevant role in metal-catalysed generation of reactive oxygen species, will prove beneficial for the cell protection.     

Extraction of Cu<Superscript>2+</Superscript>, Zn<Superscript>2+</Superscript>, and Co<Superscript>2+</Superscript> ions from aqueous solutions with calcium and magnesium phosphates

The efficiency of calcium and magnesium phosphates of different compositions in the extraction of Cu²⁺, Zn², and Co²⁺ ions from aqueous solutions was studied.     

Extraction of metal ions (Fe<Superscript>3+</Superscript>, Co<Superscript>2+</Superscript>, Ni<Superscript>2+</Superscript>, Cu<Superscript>2+</Superscript> and Zn<Superscript>2+</Superscript>) using immobilized-polysiloxane iminobis(n-2-aminophenylacetamide) ligand system

A new insoluble solid functionalized ligand system bearing chelating ligand group of the general formula P-(CH₂)₃-N[CH₂CONH(C₆H₄)NH₂]₂, where P represents [Si–O] _n polysiloxane network, was prepared by the reaction of the immobilized diethyliminodiacetate polysiloxane ligand system, P-(CH₂)₃N(CH₂CO₂Et)₂ with 1,2-diaminobenzene in toluene. ¹³C CP-MAS NMR, XPS and FTIR results showed that most ethylacetate groups (–COOEt) were converted into the amide groups (–N–C=O). The new functionalized ligand system exhibits high capacity for extraction and removal of the metal ions (Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺) with efficiency of 95–97% after recovery from its primary metal complexes. This functionalized ligand system formed 1:1 metal to ligand complexes.     

Thermodynamics of citrate complexation with Mn<Superscript>2+</Superscript>, Co<Superscript>2+</Superscript>, Ni<Superscript>2+</Superscript> and Zn<Superscript>2+</Superscript> ions

Isothermal titration calorimetry has been used to determine the stoichiometry, formation constants and thermodynamic parameters (ΔG ^o, ΔH, ΔS) for the formation of the citrate complexes with the Mn²⁺, Co²⁺, Ni²⁺ and Zn²⁺ ions. The measurements were run in Cacodylate, Pipes and Mes buffer solutions with a pH of 6, at 298.15 K. A constant ionic strength of 100 mM was maintained with NaClO₄. The influence of a metal ion on its interaction energy with the citrate ions and the stability of the resulting complexes have been discussed.     

Thermodynamics of resolvation of Mg<Superscript>2+</Superscript>, Ca<Superscript>2+</Superscript>, Cd<Superscript>2+</Superscript>, and Cu<Superscript>2+</Superscript> ions in aqueous-ethanol mixtures on the basis of volta potential difference method

The volta potential difference method at 298.15 K was used to determine the real primary medium effect for magnesium, calcium, cadmium, and copper ions, and also the real Gibbs transfer energy of these ions from water into a mixed water ethanol (EtOH) solution. The surface potential value at the nonaqueous solution/gas phase interface $ \Delta \chi _{H_2 O}^{EtOH} $ \Delta \chi _{H_2 O}^{EtOH} was obtained. With account for this value, chemical thermodynamic characteristics of the studied ions in the water-ethanol solvent were calculated and the effect of composition and nature of the mixed solvent on the values obtained was analyzed. The dependence of variation in the thermodynamic characteristics of cation resolvation was established on their crystallographic radius that corresponds to the following sequence: Ca²⁺ < Cd²⁺ < Cu²⁺ < Mg²⁺.     

Thermodynamics of L-valine complex formation with Cu<Superscript>2+</Superscript> ions in an aqueous solution

Heat effects of mixing of aqueous solutions of Cu(NO₃)₂ and L-valine were measured by the calorimetric method at 298.15 K and a ionic strength of 0.5–1.5 (KNO₃). The standard heat effects of formation of the Cu(II) complexes with L-valine in an aqueous solution were obtained by the extrapolation to the zero ionic strength using the equation with one individual parameter. The standard thermodynamic characteristics of complex formation in the Cu²⁺-L-valine system were calculated.     

Complex formation of maleic acid with the Zn<Superscript>2+</Superscript>, Ni<Superscript>2+</Superscript>, Co<Superscript>2+</Superscript>, Cu<Superscript>2+</Superscript> in aqueous solution

The process of complex formation of maleic acid (H₂L) with the ions Zn²⁺, Ni²⁺, Co²⁺, Cu²⁺ was studied by potentiometric titration in a wide range of concentration ratios at 298 K and I = 0.1 mol/l (NaNO₃). The moieties ZnL, CoL, NiL, NiL ₂ ^2? , CuL, and CuL ₂ ^2? were detected and their stability constants were determined.     

Sorption of Cu<Superscript>2+</Superscript> and Zn<Superscript>2+</Superscript> by Natural Biomaterial: Duck Feather

Feather fibers were modified by treatment with 5% tannic acid (TA) solution. Kinetics of the modification was investigated as a function of the reaction time. The maximum loading of TA on feather reached 8.3% after being treated by TA for 9 h. The adsorption of metal cations (Cu²⁺, Zn²⁺) by unmodified and TA-modified feather fibers was investigated as a function of fiber weight gain, temperature, and pH of the metal solution. The adsorption was enhanced at alkaline pH and ambient temperature and increased with the weight gain of TA. The maximum uptake of metal cations (Cu²⁺, 0.77 mmol/g; Zn²⁺, 0.95 mmol/g) was obtained by TA-modified feather at weight gain: 8.3%, pH 11, while at the acidic pH, the adsorption of metal cations by either unmodified or TA-modified feather was negligible. The influence of anions on the adsorption of metal cations was also studied. The uptake of Cu²⁺ from chloride was higher and faster than that from nitrate. Desorption of the metals was performed at acidic pH 2.5 for 48 h. The feather–TA–metal complexes exhibited higher stability for metal cations than the feather–metal complexes. All these experiments reveal that TA-modified feather fibers have good adsorption to metal cations and can be used as metal adsorbent in wastewater treatment.     

Specific features of absorption of Cu<Superscript>2+</Superscript>, Zn<Superscript>2+</Superscript>, Co<Superscript>2+</Superscript>, and Pb<Superscript>2+</Superscript> cations from aqueous solutions by calcium phosphates

Kinetic characteristics of the interaction of trisubstituted calcium phosphate Ca₃(PO₄)₂ · xH₂O with Cu²⁺, Zn²⁺, Co²⁺, and Pb²⁺ ions in aqueous solutions were studied.     

Two novel coordination polymers: Synthesis,structure, luminescent properties,and selective sensing of Cu<Superscript>2+</Superscript> and Mn<Superscript>2+</Superscript> ions

Two novel coordination polymers, namely {[Co(Ttac)_0.5(1,4-Bib)(H₂O)] · H₂O}_n (I) and {[La(HTtac)₂(2H₂O)] · H₂O}n (II) (H4Ttac = 4,5-di(3'-carboxylphenyl)-phthalic acid, 1,4-Bib = 1,4-bis(1-imidazoly) benzene), have been designed and successfully prepared via hydrothermal process, and characterized by elemental analyses, IR spectroscopy, and single crystal X-ray diffraction (CIF files CCDC nos. 1039298 (I), 1039300 (II)). Structural analysis reveals that the H₄Ttac ligands adopt different coordination modes in the as-synthesized I and II, and thus give rise to the targeted coordination polymers with different configurations. It is worth mentioning that, coordination polymer I is assembled from low-dimensional structures into three-dimensional (3D) via π···π stacking interactions, while three-dimensional coordination polymer II is formed by covalent bonds. Luminescent properties of coordination polymer II have been studied at ambient temperature. Significantly, luminescent measurement indicates that coordination polymer II may be acted as potential luminescent recognition sensors towards Cu²⁺ and Mn²⁺ ions.     

Thermochemical study of processes of complex formation of Cu<Superscript>2+</Superscript> ions with L-glutamine in aqueous solutions

Heats of the interaction of Cu(NO₃)₂ solutions with L-glutamine solutions were measured directly by calorimetry at a temperature of 298.15 K and ionic strength values of 0.5, 1.0, and 1.5 (KNO₃). Using RRSU universal software, the experimental data were subjected to rigorous mathematical treatment with allowances made for several concurrent processes in the system. The heats of formation of the CuL⁺ and CuL₂ complexes were calculated from the calorimetric measurements. The standard heats of the complex formation of Cu²⁺ with L-glutamine were obtained by extrapolation to zero ionic strength. The complete thermodynamic characteristic (Δ_r H ^o, Δ_r G ^o, Δ_r S ^o) of the complex formation processes in a Cu²⁺—L-glutamine system was obtained.     

Formation of coordination compounds with aniline in the interlayer space of Ca<Superscript>2+</Superscript>-, Cu<Superscript>2+</Superscript>- and Fe<Superscript>3+</Superscript>-exchanged montmorillonite

The influence of Ca²⁺-, Cu²⁺- and Fe³⁺-exchanged montmorillonite (MMT) on the type of interaction with aniline in the interlayer space of MMT has been studied by means of X-ray powder diffraction and infrared spectra. Results of X-ray diffraction showed that aniline was successfully intercalated into the interlayer space of MMT. Based on IR spectra evaluation, aniline was indirectly coordinated through a water-bridge in Ca²⁺- and Fe³⁺-MMT and it was indirectly coordinated through a water-bridge as well as protonated in Cu²⁺-MMT (the spectrum of protonated aniline showed deformation and changes in the NH ₃ ⁺ absorption at approximately 1521 cm^?1). It is important to point out that Cu²⁺-MMT indirect coordination and protonation occur simultaneously.     

Novel 1,8-naphthalimide dye for multichannel sensing of H<Superscript>+</Superscript> and Cu<Superscript>2+</Superscript>

A novel 1,8-naphthalimide dye with simple structure has been produced by a facile synthetic method for colorimetric and fluorescent sensing of H⁺ and Cu²⁺. In CH₃CN/H₂O (1/1, v/v), the dye could monitor H⁺ using dual channels (ratiometric absorbance and fluorescence intensity change) from pH 6.2 to 12.0. Meanwhile, in the pH range of 1.9–5.2, the dye could also be used to detect Cu²⁺ using triple channels [ultraviolet–visible (UV–Vis) absorption, fluorescence intensity reduction, as well as fluorescence blueshift]. The detection limits for Cu²⁺ evaluated by colorimetric and fluorescent titration were 6.10 × 10^?7 and 2.62 × 10^?7 M, respectively. The dye exhibited specific selectivity and sensitivity for H⁺ and Cu²⁺ over various coexisting metal ions. Moreover, the sensing mechanism of the dye for H⁺ and Cu²⁺ was carefully examined.     

Incorporation of Mg<Superscript>2+</Superscript>, Sr<Superscript>2+</Superscript>, Ba<Superscript>2+</Superscript> and Zn<Superscript>2+</Superscript> into aragonite and comparison with calcite

We have investigated the presence of foreign ions into the bulk structure and the external surfaces of aragonite using periodic ab-initio methods. Four cations isovalent to Ca²⁺ were studied: Mg²⁺, Sr²⁺, Ba²⁺ and Zn²⁺. The calculations were performed at structures (bulk, surface) that contain four and eight CaCO₃ units. Our results, at the Hartree-Fock level, show that the incorporation of those ions into aragonite depends strongly on their size. Mg²⁺ and Zn²⁺, due to their smaller size, can substitute Ca²⁺ ions in the crystal lattice while the incorporation of Sr²⁺ and Ba²⁺ into aragonite is energetically less favoured. Examination of the [011], [110] and [001] surfaces of aragonite revealed that the surface incorporation reduces the energetic cost for the larger ions. These systems provide challenging examples for most shape analysis methods applied in Mathematical Chemistry.     

Selective extraction of Fe<Superscript>3+</Superscript> ions from Fe<Superscript>3+</Superscript>-Zn<Superscript>2+</Superscript> mixture with phosphate sorbents

The absorption of Fe³⁺ ions from Fe³⁺-Zn²⁺ mixture with zinc and calcium phosphates was studied.     

A Cu<Superscript>2+</Superscript>ion-selective fluoroionophore with dual off/on switches

A new malonamide fluoroionophore possessing two pyrene moieties was synthesized. This bispyrene exhibited the fluorescence of the pyrene monomer (λ_em = 395 nm) and intramolecular excimer (λ_em = 467 nm) emissions. The designed derivative showed the excellent ion sensing ability to Cu²⁺. The "on-off-off" and "off-on-off" fluorescence responses were demonstrated by the addition of the variable Cu²⁺ concentration. The utilization of the dual off/on responses could apply to the estimation of the rough Cu²⁺ concentration.     

Study of complexation between Cu<Superscript>2+</Superscript> ions and <Emphasis Type="Italic">ortho</Emphasis>-azidobenzoic acid

An aqua complex of copper(II) o-azidobenzoate, [Cu(OH)ABA2H₂O]₂ (ABA is o-azidobenzoic acid), was synthesized in an aqueous solution and identified by IR and electronic absorption spectroscopy. In the complex, the azido group is not coordinated by Cu²⁺. When dissolved in dry organic solvents (DMF, DMSO, dioxane, and methanol), the complex undergoes dehydration to give a chelate complex (CC) containing the Cu²⁺-coordinated azido group as a result of the electron density redistribution at its N atoms. The IR spectrum of the chelate complex contains no absorption band at 2135 cm^–1 corresponding to the stretching vibrations of the azido group. The resulting CC is unstable in solutions and spontaneously decomposes with a release of molecular nitrogen. The interaction of a Cu²⁺ ion with o-azidobenzoic acid in dry organic solvents affords a CC similar to the complex obtained on the dissolution of [Cu(OH)ABA2H₂O]₂ in dry solvents.Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 3, 2005, pp. 195–198.Original Russian Text Copyright © 2005 by Budruev, Karyakina, Levina, Oleinik.This revised version was published online in April 2005 with a corrected cover date.This revised version was published online in April 2005 with a corrected cover date.     

Vinylimidazole copolymers: coordination chemistry,solubility, and cross-linking as function of Cu<Superscript>2+</Superscript> and Zn<Superscript>2+</Superscript> complexation

P(1-VIm-co-MMA) copolymers with 4 or 44 wt.% 1-VIm (abbreviated PVM-4 and PVM-44) where polymerized from 1-VIm (1-vinylimidazole) and methylmethacrylate with azobisisobutyronitrile as initiator and reacted with either Cu²⁺ or Zn²⁺. The resulting coordinated polymer complexes were studied using ICP-AES, CP/MAS ¹³C NMR, conductivity measurements, vibrational spectroscopy (mid-FTIR and far-FTIR), DSC, and EPR. It was established by ICP-AES, CP/MAS ¹³C NMR, conductivity, mid-FTIR and EPR measurements that the transition metal ions in the complexes were exclusively coordinated by the imidazole ligand. The coordination geometry is square planar with regard to Cu(II) complexes. The strong interaction between the polymeric imidazole ligand and the transition metal ion cross-links the system, resulting in augmentation of T _g (the glass transition temperature), especially for copolymers with high relative amount of 1-VIm. The effect of changing metal ion is more complicated and depends on both the strength of the coordinate interaction as well as the coordination number. The solubility of the coordinate polymer complex in conventional solvents is low due to the coordinate cross-links. However, the coordinate polymer complexes are soluble in strongly coordinating solvents such as acetonitrile and dimethylsulfoxide.     

1,9-Dicarbonyl-2,8-dioxo-butyne-ester Ferrocenophane: Synthesis,Structure and Recognition Properties for Co<Superscript>2+</Superscript> and Cu<Superscript>2+</Superscript> Ions

An efficient highly diluted synthetic approach to the synthesis of 1,9-dicarbonyl-2,8-dioxo-butyne ester ferrocenophane (L) has been developed. The title compound was characterized by IR, UV, FL, 1H NMR, spectroscopies, elemental analysis and so on. Further complex L shows fluorescence responses to Co²⁺ and Cu²⁺ in CH3OH, The results indicate that the complex could be applied in multianayte detection. The binding ability of receptor L CH3OH was tested for various cations (Co²⁺, Cu²⁺, Zn²⁺, and Ni²⁺ in water) and the binding constants for Co²⁺ and Cu²⁺ were the computed, having a distinct absorbance shift. The receptor is a very attractive array because its distinct absorbance shift profile in a semi-aqueous phase, making it applicable in the area of biology, environmental sciences and material chemistry.