Thermodynamic behavior of complexation of 18-crown-6 with Tl<Superscript>+</Superscript>, Pb<Superscript>2+</Superscript>, Hg<Superscript>2+</Superscript>, and Zn<Superscript>2+</Superscript> metal cations in methanol-water binary media

The equilibrium constants and thermodynamic parameters for complex formation of 18-Crown-6 (18C6) with Tl⁺, Pb²⁺, Hg²⁺, and Zn²⁺ metal cations have been determined by conductivity measurements in methanol (MeOH)-water (H₂O) binary solutions. 18-Crown-6 forms 1:1 complexes with Hg²⁺ and Zn²⁺ cations, but in the case of Tl⁺ and Pb²⁺ cations, in addition to 1:1 stoichiometry, 1:2 (ML₂) complexes are formed in some binary solvents. The thermodynamic parameters (ΔH _c⁰ and ΔS _c⁰), which were obtained from the temperature dependences of equilibrium constants, show that in most cases the complexes are enthalpy destabilized but entropy stabilized. Non-linear behavior is observed between the equilibrium constants (log K _f ) of complexes and the composition of the mixed solvent. The selectivity of the ligand for these metal cations is sensitive to the solvent composition, and, in some cases, the selectivity order is reversed in certain compositions of the mixed solvent. The results also show that the mechanism of complexation reactions and the stoichiometry of complexes of some metal cations change with the nature and even with the composition of the mixed solvent. The article was submitted by the authors in English.     

SYNTHESIS AND SOLID-STATE NMR STRUCTURAL CHARACTERIZATION OF POLYSILOXANE-IMMOBILIZED THIOL-AMINE METAL(II) COMPLEXES

Abstract

The polysiloxane-immobilized thiol, amine, and thiol-mine ligand systems P-(CH₂)₃X (where P represents the siloxane network, X[dbnd]SH,NH₂, or hybride of amine and thiol ligand groups) have been made via the sol-gel process by hydrolytic condensation of Si(OEt)₄ and (MeO)₃Si(CH₂)₃X. The immobilized polysiloxanes thiol-acetate P-(CH₂)₃SCH₂COOMe and glycinate P-(CH₂)₃NHCH₂COOMe have been prepared by the reaction of the corresponding polysiloxane system P-(CH₂)₃SH, or P-(CH₂)₃NH₃ with methylchloroacetate. The immobilized thiol-amine ligands form metal(II) complexes when treated with aqueous metal(II) ion solutions (M[dbnd]Ni²⁺, Cu²⁺, Cd²⁺. Hg²⁺). High-resolution solid state NMR studies have been used to characterize these immobilized ligand systems and their metal(II) treated samples. ²⁹Si CP-NMR spectra suggest that these ligand systems undergo some leaching(1–4%) of small oligomers when treated with aqueous acid and metal ion solutions. ¹⁵N CP-NMR results show that substantial proportion of amine groups is coordinated to metal ions.     

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.     

Synthesis of New Polysiloxane-Immobilized Ligand System Di(amidomethyl)aminetetraacetic Acid

A new chelating porous polysiloxane-immobilized tetraacetic acid ligand system has been prepared. This material was made by chemical modification of the iminodiacetic acid polysiloxane with thionyl chloride and diethyliminodiacetate, respectively. The polysiloxane functionalized with di(amidomethyl)aminetetraacetic acid of the general formula P-(CH ₂ ) ₃ N(CH ₂ C(O)N) ₂ (CH ₂ COOH) ₄ [where P represents the polysiloxane backbones (Si?O?Si) _n ] was characterized by Thermogravimetric Analysis (TGA) and FTIR spectra. The FTIR results proved that tetraacetic acid groups are successfully grafted onto the polysiloxane surface. This ligand system exhibits high potential for extraction of divalent metal ions (Co⁺², Ni⁺², Cu⁺², and Zn⁺²) from aqueous solution.     

Synthesis and Structural Characterization of a New Macrocyclic Polysiloxane-immobilized Ligand System

Summary. A new porous solid macrocyclic 1,4,7,11,14-pentaazapentadecane-3,15-dione polysiloxane ligand system of the general formula P–(CH₂)₃–C₁₁H₂₂O₂N₅ (where P represents [Si–O]_n siloxane network) has been prepared by the reaction of polysiloxane-immobilized iminobis(N-(2-aminoethyl)acetamide) with 1,3-dibromopropane. The FTIR and XPS results confirm the introduction of the macrocyclic functional ligand group into the polysiloxane network. The new macrocyclic polysiloxane ligand system exhibits high potential for the uptake of metal ions (Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺).     

Oxidative dehydrogenation of N-(2-hydroxy-3,5-R<Superscript>1</Superscript>,R<Superscript>2</Superscript>-benzyl)-4-aminoantipyrines in the complexation reaction

Reactions of N-(2-hydroxy-3,5-R¹,R²-benzyl)-4-aminoantipyrines with copper acetate in ethanol gave complexes with Schiff bases (SBs) rather than the expected complexes with reduced SBs; i.e., the starting ligands undergo oxidative dehydrogenation during the complexation reaction. The corresponding complexes with reduced SBs were obtained from sodium salts of the ligands and cupric sulfate in aqueous solutions. Kinetic measurements showed that oxidative dehydrogenation occurs in the heteroleptic complexes Cu(L ⁱ )(CH₃COO)(X) (L ⁱ H are derivatives of N-(2-hydroxy-3,5-R¹,R²-benzyl)-4-aminoantipyrines; i = 6–10; X = H₂O, CH₃OH, CH₃CH₂OH) but does not occur in the complexes CH₃OH, CH₃CH₂OH. The absence of oxidative dehydrogenation of the ligands in Cu(L ⁱ )₂ · H₂O can be explained by the octahedral environment of the Cu²⁺ ion and, accordingly, the absence of the coordination site for molecular oxygen. The molecular structures of two Cu(II) complexes with SBs were determined by X-ray diffraction.     

New Strategy for the Synthesis of Diethylenetriaminetetraacetic Acid Functionalized Polysiloxane Ligand Systems

A new rout was used for the synthesis of porous solid polysiloxane matrix of the general formula P-(CH₂)₃N(CH₂COOEt)-(CH₂)₂N(CH₂COOEt)-(CH₂)₂-N(CH₂COOEt)₂ (where P represents [Si-O]_n) by the reaction of diethylenetriaminetrimethoxysilane with ethyl chloroacetate followed by polymerization with tetraethylorthosilicate via the sol gel process. The functionalized diethylenetriaminetetraacetic acid polysiloxane system (P-DETATA) was then obtained by acid hydrolysis of the diethylenetriaminetetraethylacetate functionalized polysiloxane(P-DETATAc). FTIR, ¹³C, ²⁹Si CP-MAS NMR and XPS methods were used for characterization of their chemical structure. The new functionalized ligand system exhibits high capacity to coordinate with divalent metal ions (Co²⁺, Ni²⁺, and Cu²⁺) than its analogous ligand obtained by postmodification of triamine polysiloxane with ethyl chloroacetate.     

Study of Complex Formation between Kryptofix 21 with La<Superscript>3+</Superscript>, Y<Superscript>3+</Superscript> and Ce<Superscript>3+</Superscript> Cations in Some Binary Mixed Non-Aqueous Solvents Using the Conductometric Method

The complexation reactions between La³⁺, Y³⁺ and Ce³⁺ cations with the macrocyclic ligand, kryptofix 21, were studied in methanol-acetonitrile (MeOH-AN) and methanol-methylacetate (MeOHMeOAc) binary mixed solvent solutions at different temperatures using the conductometric method. The conductance data show that in most solvent systems, the kryptofix 21 forms a 1: 1 [M: L] complex with La³⁺, Y³⁺ and Ce³⁺ metal cations, but in the case of Y³⁺ cation in pure methylacetate, in addition of formation of a 1: 1 [ML] complex, 1: 2 [ML₂] and 1: 3 [ML₃] complexes are formed in solution. In the case of Ce³⁺cation, a 1: 1 [ML] and also a 1: 2 [ML₂] complexes are formed in this solvent system at all studied temperatures. The electrical conductance data in acetonitrile, show that a 1: 1 [ML] and also a 1: 2 [ML₂] complexes are formed between the ligand and La³⁺ and Ce³⁺ metal cations at different temperatures. The stability constants of the 1: 1 [ML] complexes were determined using the conductometric data and a computer program, GENPLOT. A non-monotonic relationship was observed between log_{K f} of the 1: 1 complexes with the composition of the binary solvent solutions which was discussed in term of solvent-solvent interactions and also preferential solvation of the metal cations and the ligand in solutions. The selectivity order of the ligand for the metal cations in MeOH–AN and MeOH–MeOAc binary solvent solutions, at 25°C was found to be: Y³⁺ > La³⁺ > Ce³⁺ and La³⁺ > Y³⁺ > Ce³⁺, respectively. The values of the standard thermodynamic quantities (ΔH _c ^° and ΔS _c ^° ) for formation of the 1: 1 complexes were obtained from temperature dependence of the stability constans of the complexes and the results show that the thermodynamics of the complexation reactions between kryptofix 21 and La³⁺, Y³⁺ and Ce³⁺ cations, is affected by the nature and composition of the mixed solvents systems.     

Uptake of Divalent Metal Ions (Cu2+, Zn2+ and Cd2+) by Polysiloxane Immobilized Monoamine Ligand System

ABSTRACT

Porous solid siloxane polymers carrying a monoamine functional group of formula P-(CH₂)₃NH₂ (Where P- represents a siloxane framework silica like ) has been prepared by polycondensation of Si(OEt)₄ and (MeO)₃Si(CH₂)₃-NH₂. Treatment of aqueous solutions of divalent metal ions with the polysiloxane monoamine ligand system demonstrates that this material has high potential for preconcentration of metal ions (Cu²⁺, Zn²⁺ and Cd²⁺). The tendency of these divalent metal ions to chemisorb by the monoamine ligand system at the optimum conditions increases in the order: Cd²⁺ <Zn²⁺ <Cu²⁺. The optimum pH is 5.5 for copper and 6-7 for zinc and cadmium. The ammonia/ ammonium chloride buffer solution gave maximum uptake for all metal ions. It is also found that the uptake of copper ions is concentration dependent and is independent of the presence of other competing ions. The monoamine ligand system suffers from leaching of ligand containing groups upon treatment with acidic solutions. The highest leaching occurs at low pH.     

Synthesis,DNA-binding and photocleavage studies of cobalt(III) complexes [Co(bpy)<Subscript>2</Subscript>(dpta)]<Superscript>3+</Superscript> and [Co(bpy)<Subscript>2</Subscript>(amtp)]<Superscript>3+</Superscript>

Two novel cobalt(III) mixed-polypyridyl complexes [Co(bpy)₂(dpta)]³⁺ and [Co(bpy)₂(amtp)]³⁺ (bpy = 2,2′-bipyridine, dpta = dipyrido-[3,2-a;2′,3′-c]-thien-[3,4-c]azine, amtp = 3-amino-1,2,4-triazino[5,6-f]-1,10-phenanthroline) have been synthesized and characterized. The interaction of Co^III complexes with calf thymus DNA was investigated by spectroscopic and viscosity measurements. Results suggest that the two complexes bind to DNA via an intercalative mode. Moreover, Co^III complexes have been found to promote the photocleavage of plasmid DNA pBR322 under irradiation at 365 nm. The mechanism studies reveal that hydroxyl radical (OH^•) is likely to be the reactive species responsible for the cleavage of plasmid DNA by [Co(bpy)₂(dpta)]³⁺ and superoxide anion radical (O ₂ ^•− ) acts as the key role in the cleavage reaction of plasmid DNA by [Co(bpy)₂(amtp)]³⁺.     

Synthesis and Structural Characterization of a New Macrocyclic Polysiloxane-immobilized Ligand System

A new porous solid macrocyclic 1,4,7,11,14-pentaazapentadecane-3,15-dione polysiloxane ligand system of the general formula P–(CH₂)₃–C₁₁H₂₂O₂N₅ (where P represents [Si–O]_n siloxane network) has been prepared by the reaction of polysiloxane-immobilized iminobis(N-(2-aminoethyl)acetamide) with 1,3-dibromopropane. The FTIR and XPS results confirm the introduction of the macrocyclic functional ligand group into the polysiloxane network. The new macrocyclic polysiloxane ligand system exhibits high potential for the uptake of metal ions (Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺).     

Synthesis and crystal structure of complex of Ce(NO<Subscript>3</Subscript>)<Subscript>3</Subscript> with N-(3-methyl-pyridin-2-yl)-formimidoyl-(3-methyl-pyridin-2-yl) hydrazone

The reaction of 3,6-di-(3-methyl-pyridin-2-yI)-s-tetrazine (DMPTZ, II) with Ce^III salt [Ce(NO₃)₃ · 6H₂O] generates a new ligand, N-(3-methyl-pyridin-2-yl)-formimidoyl-(3-methyl-pyridin-2-yl) hydrazone (L), and forms a new complex: a mononuclear complex [Ce(L)(NO₃)₂ (H₂O)₃] · NO₃ (III). Crystal data for III: space group P-1, with a = 0.7133(4) nm, b = 1.1139(2) nm, c = 1.4572(3) nm, α= 102.13(2)°, β= 99.81(3)°, γ= 91.10(3)°, Z = 2, V = 1113.6(7) nm³, μ = 2.123 mm⁻¹ and F(000) = 630. L acts as a tri-dentate chelating ligand in III. There are 10 coordination sites around Ce³⁺ of III, which are respectively occupied by seven oxygen atoms (four from two nitrate anions and three from three H₂O molecules) and three nitrogen atoms (all from L). The cerium atom and three chelating nitrogen atoms are coplanar. The mechanism of the metal assisted decomposition is discussed briefly.     

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.     

Synthesis and properties of potassium salts of per-<Emphasis Type="Italic">O</Emphasis>-carboxymethyl-calix[4]pyrogallols and their complexes with Cu<Superscript>2+</Superscript>, Fe<Superscript>3+</Superscript>, and La<Superscript>3+</Superscript>

Synthesis of water-soluble potassium salts of carboxymethyl derivatives of calix[4]pyrogallols and dodeca(carboxylatomethyl)tetramethylcalix[4]pyrogallol (L) complexes with transition metal ions (Cu²⁺, Fe³⁺, La³⁺) is described. Their structures in the solid state and in solution were characterized by NMR spectroscopy, ESR, and IR spectroscopy. Calix[4]pyrogallol dodecacarboxylates exist in the rccc-configuration. Calix[4]pyrogallol with methyl substituents at the lower rim in a wide range concentrations exists in water predominantly in the dimeric form. The obtained polynuclear transition metal complexes possess less symmetric structure than potassium salt of calix[4]pyrogallol (K₁₂L). All studied complexes contain water molecules bound by rather strong hydrogen bonds. At room temperature the Fe₄L complex is characterized by the environment of the Fe³⁺ ions close to octahedral. The absence of signals in the ESR spectrum of the Cu₆L complex indicates the strong antiferromagnetic interaction Cu²⁺-Cu²⁺.     

5-[2-(Methylthio)ethyl]-3-phenyl-2-thioxoimidazolidin-4-one and its complexes with transition metals (Co<Superscript>II</Superscript>, Ni<Superscript>II</Superscript>, and Cu<Superscript>II</Superscript>). Synthesis and electrochemical investigation

The reaction of 5-[2-(methylthio)ethyl]-3-phenyl-2-thioxoimidazolidin-4-one (LH) with salts MCl₂· xH₂O (M = Co, Ni, Cu; x = 2, 6) afforded the [M(L)Cl]_n complexes of Ni^II, Co^II, and Cu^II. The electrochemical behavior of the LH ligand and its complexes was studied using the cyclic voltammetry and rotating disk electrode techniques. The structures of the synthesized compounds were determined by the data of UV—Vis and IR spectroscopy, mass spectrometry, and electrochemical characteristics. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 339–343, February, 2007.     

Kinetic studies on H<Superscript>+</Superscript>-catalysed aquation of chromium(III)-oxalato-asparaginato and chromium(III)-oxalato-histidinato complexes

Three chromium(III) complexes with asparagine (Asn) and histidine (His) of the [Cr(ox)₂(Aa)]²⁻ type, where Aa = N,O–Asn, N,O–His or N,N′–His, were obtained and characterized in solution. The complexes with N,O–Aa undergo acid-catalysed aquation to give a free amino acid and cis-[Cr(ox)₂(H₂O)₂]⁻, whereas the complex with N,N′–His undergoes parallel reaction paths: (1) isomerization to the N,O–His complex and (2) liberation of an oxalate ligand. Kinetics of the N,O–Aa complexes in HClO₄ media were studied spectrophotometrically under pseudo-first-order conditions. The absorbance changes were attributed to the chelate ring opening at the Cr–N bond. The linear dependence of rate constants on [H⁺] was established, and a mechanism for the chelate ring cleavage was postulated. The existence of a metastable intermediate with O-monodentate Aa ligand was proved experimentally. Effect of [Cr(ox)₂(Aa)]²⁻ on 3T3 fibroblasts proliferation was studied. The tests revealed low cytotoxicity of the complexes. Complexes with Ala, His and Cys are good candidates for biochromium sources.     

Heterospin mixed-ligand heterotrinuclear Co<Superscript>II</Superscript>, Gd<Superscript>III</Superscript>, Co<Superscript>II</Superscript> complex with nitronyl nitroxide

A method was developed for the synthesis of mixed-metal heterospin compounds with the direct coordination of the nitroxide fragment based on the replacement of acetonitrile molecules in the heterotrinuclear complex [Co₂Gd(NO₃)Piv₆(CH₃CN)₂] with nitroxide molecules. The molecular and crystal structure of the heterospin mixed-ligand heterotrinuclear Co^II, Gd^III, Co^II complex [Co₂Gd(NO₃)Piv₆(NIT-Me)₂], where NIT-Me is stable nitronyl nitroxide, was established. The magnetic properties of this complex were investigated in the temperature range of 2–300 K. The coordination of nitroxide groups to Co^II ions is responsible for strong exchange interactions between the unpaired electrons in the exchange clusters {>-·O-Co^II}, resulting in the virtually complete spin coupling between each coordinated >N-·O group and one of the unpaired electrons of each Co^II ion at temperatures below 200 K. Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1742–1745, September, 2007.     

Thermodynamic study of complexation reactions between 1,7,10,16 Tetra oxa 4,13 diaza cyclo octa decane (Kryptofix22) and Ni<Superscript>2+</Superscript>, Cd<Superscript>2+</Superscript> and Ag<Superscript>+</Superscript> metal cations in some pure and binary mixed non-aqueous solvents using conductometry

The complexation reactions between Ni²⁺, Cd²⁺ and Ag⁺ metal cations with the macrocyclic ligand Kryptofix22 (K22), in pure acetonitrile (AN), ethylacetate (EtOAc), methanol (MeOH) and their binary mixtures have been studied at different temperatures using conductometric method. The obtained results show that in most solvent systems, the stoichiometry of the complexes formed between the macrocyclic ligand and the metal cations is 1: 1 [ML], but in some of the solvent systems, a 1: 2 [ML₂] complex and also [M₂L], [M₂L₂] and [M₂L₃] complexes are formed in solutions. The stability constans of the 1: 1 complexes were obtained using a computer program GENPLOT. A non-liner behavior was observed for changes of logK_f of the 1: 1 complexes versus the composition of AN–EtOAc binary solutions. The stability order of the 1: 1 complexes at 25°C in the binary solvent solution of AN–EtOAc (mol % AN = 50) was found to be: (K22.Ag)⁺ > (K22.Ni)²⁺ > (K22.Cd)²⁺. The obtained values of thermodynamic quantities (ΔH_c⁰,ΔS_c⁰) show that in most of the AN–EtOAc binary solvent solutions, the 1:1 complexation reactions are enthropy stabilized, but from the enthalpy view point, depending on the nature and composition of mixed solvents they are exothermic or athermic.     

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.     

Macrocyclic Polysiloxane Immobilized Ligand System and Its Structural Characterization

A new porous solid macrocyclic 1,4,7,10,14,17,20‐heptaazadocosane‐3,21‐dione polysiloxane ligand system of the general formula P‐(CH₂)₃‐C₁₅H₃₂O₂N₅, (where P represents [Si‐O]n siloxane network) has been prepared by the reaction of immobilized iminobis(N‐diethylenediamineacetamide)polysiloxane with 1,3 dibromopropane. The new macrocyclic polysiloxane ligand system exhibits high potential for the uptake of metal ions (Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺). Complexation with copper ions exhibits a high selectivity in which two copper ions were involved per one macrocyclic ligand group.