Thermodynamics of mixed-ligand complexation of gadolinium ethylenediaminetetraacetate with amino acids in aqueous solution

Mixed-ligand complexation of GdEdta⁻ with glycinate, L-glutamate, DL-aspartate, iminodiacetate, and nitrilotriacetate anions in aqueous solutions at 298.15 K and the ionic strength I = 0.5 (KNO₃) was studied. The thermodynamic parameters (logK, Δ _r G, Δ _r H, Δ _r S) of these reactions were determined from calorimetric and pH-metric data. The most probable way of coordination of the amino acids in the heteroleptic complexes is discussed.     

Thermodynamics of mixed-ligand complexation of mercury(II) ethylenediaminetetraacetate with histidine and lysine in aqueous solution

The formation of mixed-ligand complexes HgEdtaIm²⁻, HgEdtaL³⁻, HgEdtaHL²⁻, and (HgEdta)₂L⁵⁻ (L is histidine, lysine; Im is imidazole) was studied by calorimetry, pH-metry, and NMR spectroscopy. The thermodynamic parameters (logK, ΔrG ⁰, ΔrH, Δr _S) for the reactions of complex formation at 298.15 K and ion strength of 0.5 (KNO₃) were determined. The most likely coordination mode for the complexone and amino acid in the mixed complexes was identified.     

Protonation of Chloro-, Bromo- and Iodo-pentacyanocobaltate(III) Complexes

The reactions between Fe(Phen)₃²⁺[phen = tris-(1,10) phenanthroline] and Co(CN)₅X³⁻ (X = Cl, Br or I) have been studied in aqueous acidic solutions at 25 °C and ionic strength in the range I = 0.001–0.02 mol dm⁻³ (NaCl/HCl). Plots of k₂ versus √I, applying Debye–Huckel Theory, gave the values −1.79 ± 0.18, −1.65 ± 0.18 and 1.81 ± 0.10 as the product of charges (Z_AZ_B) for the reactions of Fe(Phen)₃²⁺ with the chloro-, bromo- and iodo- complexes respectively. Z_AZ_B of ≈ −2 suggests that the charge on these Co^III complexes cannot be −3 but is −1. This suggests the possibility of protonation of these Co^III complexes. Protonation was investigated over the range [H⁺] = 0.0001 −0.06 mol dm⁻³ and the protonation constants K_a obtained are 1.22 × 10³, 7.31 × 10³ and 9.90 × 10² dm⁶ mol⁻³ for X = Cl, Br and I, respectively.     

Synthesis of stereoisomers of <Emphasis Type="Italic">p-tert</Emphasis>-butylthiacalix[4]arenes tetrasubstituted at the lower rim containing secondary amide groups and their complexation with a number of singly charged anions

The ability of new synthetic receptors, i.e., p-tert-butylthiacalix[4]arenes tetrasubstituted at the lower rim and containing secondary amide groups to form complexes with a number of spherical (F⁻, Cl⁻, Br⁻, I⁻), Y-shaped (MeCOO⁻), trigonal (NO₃ ⁻), and tetrahedral (H₂POO₄ ⁻) anions has been studied. It was shown that the nature of substituents on the nitrogen atom of the amide groups and configuration of the macrocycle affect the stability constant values of the forming complexes.     

Mononuclear Rare Earth Metal Complexes based on 1,10-phenanthroline Derivatives as Catalysts for Hydrolysis of p-nitrophenyl Phosphate (NPP)

Two multidentate ligands: N,N′-di-(propionic acid-2′-yl-)-2,9-diaminomethyl-1,10-phenanthroline (L1) and N,N′-di-(3′-methylbutyric acid-2′-yl-)-2,9-diaminomethyl-1,10-phenanthroline (L2) were synthesized. The hydrolytic kinetics of p-nitrophenyl phosphate (NPP) catalyzed by complexes of L1 and L2 with La(III), Gd(III) have been studied. Both LnL and LnLH₋₁ have been examined as catalysis for the hydrolysis of NPP in aqueous solution at 298 K, I = 0.10 mol dm⁻³ KNO₃ at the pH range 7.4–9.1, respectively. Kinetic studies show that both LnL and LnLH₋₁ have catalytic activity, but LnLH₋₁ is more active than LnL in the hydrolysis of NPP. The second-order rate constants for the hydrolysis of NPP are k_GdL1H−1 = 0.01399 mol⁻¹ dm³ s⁻¹, k_GdL1 = 0.0000110 mol⁻¹ dm³ s⁻¹ for complexes GdL1H₋₁ and GdL1, respectively. A new mechanism was proposed for the hydrolysis of NPP catalyzed by LnL and LnLH₋₁.     

A theoretical investigation on structures of tripodal thiourea derivatives and their anion recognition

The structural geometries of three tripodal thiourea receptors, i.e. 1,3,5-triethyl-2,4,6-tris[(N′-methylthioureido)methyl]benzene (1), tris[N′-methyl-N-(2-aminoethyl)thiourea]methane (2), tris[N′-methyl-N-(2-aminoethyl)thiourea]amine (3), and their complexes with F⁻, Cl⁻, Br⁻, I⁻, NO₃ ⁻, CO₃ ²⁻, SO₄ ²⁻, HSO₄ ⁻, PO₄ ³⁻, HPO₄ ²⁻ and H₂PO₄ ⁻ were obtained using the density functional theory calculations. Electronic and thermodynamic properties of anion binding complexes of the receptors 1, 2 and 3 were investigated. Recognition abilities of all the receptors in terms of selectivity coefficients are reported. Intermolecular interactions in all the studied complexes occurring via multi-point hydrogen bonding were found. The receptors 1, 2 and 3 were found to be excellent selectivity for phosphate ion and their binding free energy for the phosphate ion are −292.57, −291.77 and −295.01 kcal/mol, respectively.     

A new unsymmetrical vic-dioxime bearing salicylaldehyde 4-aminobenzoylhydrazone and its homo-and heterotrinuclear complexes with copper(II) and nickel(II) ions

A new vic-dioxime, N-{4-[[(2-hydroxyphenyl)methylene]hydrazinecarbonyl]phenyl}aminoglyoxime (H₃L), was prepared by the reaction of anti-chloroglyoxime with salicylaldehyde 4-aminobenzoylhydrazone. The reaction of H₃L with Cu(II) salts and an appropriate simple ligand gave only homotrinuclear complexes [Cu₃(HL)₂X₂], whereas the reaction of H₃L with Ni(II) salts gave mono-and homotrinuclear complexes [Ni(H₂L)₂ and Ni₃(HL)₂X₂]. Also, heterotrinuclear complexes of H₃L were prepared by the reaction of Ni(H₂L)₂ with Cu(II) salt and an appropriate simple ligand, [NiCu₂(HL)₂X₂], X = Cl⁻, NO ₃ ⁻ , SCN⁻, CN⁻, and N ₃ ⁻ . The new vic-dioxime and its complexes were identified by elemental analyses, IR, ¹H NMR, UV-VIS, magnetic susceptibility, and mass spectral data. The elemental analyses and spectral data indicated that the hydrazone side of H₃L acted as monobasic tridentate and the fourth position was occupied by simple ligands, such as Cl⁻, NO ₃ ⁻ , SCN⁻, CN⁻, and N ₃ ⁻ . The text was submitted by the author in English.     

Fac-mer equilibria of coordinated iminodiacetate (IDA2?) in ternary CuII(ida)(H?1B)? complex formation (B = imidazole, benzimidazole) in aqueous solution

pH potentiometric and spectrophotometric investigations on the complex formation equilibria of Cu^II with iminodiacetate (ida²⁻) and heterocyclic N-bases, viz. imidazole and benzimidazole (B), in aqueous solution in binary and ternary systems using different molar ratios of the reactants indicated the formation of complexes of the types, Cu(ida), Cu(ida)(OH)⁻, (ida)Cu(OH)Cu(ida)⁻, Cu(B)²⁺, Cu(H^-1B)⁺, Cu(ida)(H₋₁B)⁻, (ida)Cu(B)Cu(ida) and (ida)Cu(H₋₁B)Cu(ida)⁻. Formation constants of the complexes at 25 ±1° at a fixed ionic strength,I = 0.1 mol dm⁻³ (NaNO₃) in aqueous solution were evaluated and the complex formation equilibria were elucidated with the aid of speciation curves. Departure of the experimental values of the reproportionation constants(ΔlogK _cu) of ternary Cu(ida)(H₋₁B)⁻ complexes from the statistically expected values, despite their formation in appreciable amounts at equilibrium, were assigned tofac(f)-mer(m) equilibria of the ida²⁻ ligand coordinated to Cu^II, as the N-heterocyclic donors, (H₋₁B)⁻, coordinatetrans- to the N-(ida²⁻) atom in the binary Cu(ida) _f complex to form the ternary Cu(ida) _m (H₋₁B)⁻ complexes     

Potentiometric Study of the Effect of Sodium Dodecylsulfate and Dioxane on the Hydrolysis of the Aluminum(III) Ion

Hydrolytic equilibria of the aluminum(III) ion were studied in the presence of a surfactant, sodium n-dodecylsulfate (SDS) and, separately, in mixed water + dioxane and water + dioxane + surfactant media at 298.15 K, by using potentiometric measurements with a glass electrode. The concentration of SDS was between 1.25 and 25.0 mmol-dm⁻³, whereas the volume percent of dioxane was varied from 10 to 50. The supporting strong electrolyte was 0.1 mol-dm⁻³ LiCl. A general least-squares treatment of the data indicates the formation of mononuclear hydrolytic complexes of the form Al(OH)_m^{3 − m} (m = 1–3) at all studied compositions. At lower concentrations of SDS (≤ 12.5 mmol-dm⁻³) it was necessary to include polynuclear hydrolytic complexes in the hydrolytic model. On increasing the concentration of SDS, the formation of polynuclear complexes is suppressed, and at the SDS concentration of 25.0 mmol-dm⁻³, only Al(OH)²⁺ and Al(OH)₂⁺ are observed in solution. At lower volume percentages of dioxane, the speciation involved polynuclear complexes in addition to mononuclear complexes. At dioxane concentrations higher than 20 vol% only mononuclear complexes are formed. The simultaneous presence of the SDS and dioxane as ionic medium modifiers produces only the mononuclear complexes Al(OH)²⁺ and Al(OH)₂⁺, which have significantly higher stability constants than in the pure ionic medium.     

Thermodynamics of heteroligand mercury(II) complexes with nitrilotriacetic acid and ethylenediamine in aqueous solution

Formation of heteroligand complexes HgNtaEn⁻ and Hg(Nta)₂En⁴⁻, where Nta³⁻ is nitrilotriacetate ion and En is ethylenediamine, was studied by means of direct calorimetry, potentiometry, and NMR spectroscopy at 298.15 K and ionic strength I = 0.5 (KNO₃).     

Catecholase biomimetic catalytic activity of copper(II) complexes with 2-methyl-3-amino-(3H)-quinazolin-4-one

The oxidation of catechol by molecular oxygen in the presence of a catalytic amount of copper(II) complex with 2-methyl-3-amino-(3H)quinazoline-4-one (MAQ) and various anions (Cl⁻, Br⁻, ClO ₄ ⁻ , SCN⁻, NO ₃ ⁻ and SO ₄ ^– ) was studied. The catecholase biomimetic catalytic activity of the copper(II) complexes has been determined spectrophotometrically by monitoring the oxidative transformation of catechol to the corresponding light absorbing o-quinone (Q). The rate of the catalytic oxidation reaction was investigated and correlated with the catalyst structure, time, concentration of catalyst and substrate and finally solvent effects. Addition of pyridine or Et₃N showed a dramatic effect on the rate of oxidation reaction. Kinetic investigations demonstrate that the rate of oxidation reaction has a first order dependence with respect to the catalyst and catechol concentration and obeying Michaelis–Menten Kinetics. It was shown that the catalytic activity depends on the coordination environment of the catalyst created by the nature of counter anions bound to copper(II) ion in the complex molecule and follows the order: Cl⁻ > NO ₃ ⁻ > Br⁻ > SO ₄ ^– > SCN⁻ > ClO ₄ ⁻ . To further elucidate the catalytic activity of the complexes, their electrochemical properties were investigated and the catecholase mimetic activity has been correlated with the redox potential of the Cu²⁺/Cu⁺ couple in the complexes.     

Conversions of coordinated ligands by reducing thermolysis of some double complex compounds

Thermal decomposition of binary complexes [M(NH₃) _k ] _x [M′L _n ] _y (M = Ni, Co; M′ = Fe, Cr, Cu; L = CN⁻, SCN⁻, C₂O₄²⁻) in a hydrogen atmosphere showed conversion of coordinated CN⁻ groups into ammonia and hydrocarbons; SCN⁻ into ammonia, hydrogen sulfide, and hydrocarbons; and C₂O₄²⁻ into hydrocarbons and CO₂. In all cases, methane prevails in the resulting hydrocarbons; ethylene is the second in relative yield, which however strongly depends on the temperature and combination of the central ions of double complex salts. The yield of ethylene is especially high from the reduction of Co-Fe complexes at 350°C, Co₄-Fe₃ complexes at 500°C, Ni₃-Fe₂ and Ni₃-Cr₂ complexes at 350°C. The observed conversions of coordinated groups can be interpreted as arising from the catalytic effect caused by the reduced forms of the central atoms in the binary complexes to the interaction of ligands with hydrogen.     

Effects of substituents and n-donors on the energies of Si←N,Si←O,and Si=C bonds in hypervalent silenes

The effect of the nature of substituents at sp²-hybridized silicon atom in the R₂Si=CH₂ (R = SiH₃, H, Me, OH, Cl, F) molecules on the structure and energy characteristics of complexes of these molecules with ammonia, trimethylamine, and tetrahydrofuran was studied by the ab initio (MP4/6-311G(d)//MP2/6-31G(d)+ZPE) method. As the electronegativity, χ, of the substituent R increases, the coordination bond energies, D(Si← N(O)), increase from 4.7 to 25.9 kcal mol⁻¹ for the complexes of R₂Si=CH₂ with NH₃, from 10.6 to 37.1 kcal mol⁻¹ for the complexes with Me₃N, and from 5.0 to 22.2 kcal mol⁻¹ for the complexes with THF. The n-donor ability changes as follows: THF ≤ NH₃ < Me₃N. The calculated barrier to hindered internal rotation about the silicon—carbon double bond was used as a measure of the Si=C π-bond energy. As χ increases, the rotational barriers decrease from 18.9 to 5.2 kcal mol⁻¹ for the complexes with NH₃ and from 16.9 to 5.7 kcal mol⁻¹ for the complexes with Me₃N. The lowering of rotational barriers occurs in parallel to the decrease in D _π(Si=C) we have established earlier for free silenes. On the average, the D _π(Si=C) energy decreases by ∼25 kcal mol⁻¹ for NH₃· R₂Si=CH₂ and Me₃N·R₂Si=CH₂. The D(Si←N) values for the R₂Si=CH₂· 2Me₃N complexes are 11.4 (R = H) and 24.3 kcal mol⁻¹ (R = F). sp²-Hybridized silicon atom can form transannular coordination bonds in 1,1-bis[N-(dimethylamino)acetimidato]silene (6). The open form (I) of molecule 6 is 35.1 and 43.5 kcal mol⁻¹ less stable than the cyclic (II, one transannular Si←N bond) and bicyclic (III, two transannular Si←N bonds) forms of this molecule, respectively. The D(Si←N) energy for structure III was estimated at 21.8 kcal mol⁻¹. Dedicated to Academician N. S. Zefirov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1952–1961, September, 2005.     

Electrochemical behaviour of cobalta-dicarbollide sandwich complexes with different capping units

The redox aptitude of a series of cobalt(III) or cobalt(I) sandwich complexes bearing a charge compensated dicarbollide ligand ([9-L-7,8-C₂B₉H₁₀]⁻) as a constant unit and different counterparts (varying from classical [7,8-C₂B₉H₁₁]²⁻ to charge-compensated [9-L-7,8-C₂B₉H₁₀]⁻ dicarbollides, from cyclopentadienyl [C₅R₅]⁻ (R = Me, H) to cyclobutadiene [C₄Me₄]⁰ ligands) has been studied. All the Co(III) complexes display the reversible sequence Co(III)/Co(II)/Co(I). In contrast, the Co(I) complexes (namely, those capped by tetramethylcyclobutadiene) accede reversibly only to the Co(II) oxidation state, the passage to Co(III) being irreversible. When possible, the Co(II) intermediates have been characterized by EPR spectroscopy. The molecular structures of the monocation [Co(η-9-SMe₂-7,8-C₂B₉H₁₀)₂]⁺ in its DD/LL and meso diastereomeric forms as well as that of heteroleptic (η-7,8-C₂B₉H₁₁)Co(η-9-SMe₂-7,8-C₂B₉H₁₀) have been obtained by single-crystal diffraction. Presented at the 3rd Chianti Electrochemistry Meetings July 3−9, 2004, Certosa di Pontignano, Italy     

Mixed-ligand chromium(III)-oxalate-pirydinedicarboxylate complexes: potential biochromium sources: kinetic studies in NaOH solutions and effect on 3T3 fibroblasts proliferation

Base hydrolysis of [Cr(ox)₂(pda)]³⁻ (where pda is N,O-bonded 2,4- and 2,5- pyridinedicarboxylic acid dianion) causes successive ligand dissociation and leads to formation of a mixture of oligomeric chromium(III) species, known as chromates(III). The main reaction path proceeds through [Cr(ox)(pda)(OH)₂]³⁻ and [Cr(pda)(OH)₄]³⁻ complexes. The kinetics of the first oxalate dissociation was studied spectrophotometrically, within the lower energy d–d band region, at 0.4–1.0 M NaOH. The character of spectroscopic changes was consistent with a consecutive reaction model, where the chelate-ring opening and the one-end bonded oxalato liberation are the first and the second reaction stages. The pseudo-first order rate constants (k _obs0 and k _obs1) were calculated using SPECFIT software for an A → B → C reaction pattern. Additionally, kinetics of base hydrolysis of [Cr(ox)₃]³⁻ were studied. The calculated rate constants were independent of [OH ⁻ ]. Kinetic parameters for the chelate-ring opening and the first oxalate dissociation were determined. Effect of the [Cr(ox)₂(pda)]³⁻ and [Cr(2,4-pda)₃]³⁻ complexes on 3T3 fibroblasts proliferation was studied. The results manifested low cytotoxicity of these complexes, which makes them promising candidates for dietary supplements.     

Role of mononuclear rare earth metal complexes in promoting the hydrolysis of p-nitrophenyl phosphate (NPP)

Two long-chain multidentate ligands: 2,9-di-(n-2′,5′,8′-triazanonyl)-1,10-phenanthroline (L₁) and 2,9-di-(n-4′,7′,10′-triazaundecyl)-1,10-phenanthroline (L₂) were synthesized. The hydrolytic kinetics of p-nitrophenyl phosphate (NPP) catalyzed by complexes of L₁ and L₂ with La(III) and Gd(III) have been studied in aqueous solution at 298 K, I = 0.10 mol · dm⁻³ KNO₃ at pH 7.5–9.1, respectively. The study shows that the catalytic effect of GdL1 was the best in the four complexes for hydrolysis of NPP. Its k_LnLH−1, k _LnL and pK _a are 0.0127 mol⁻¹ dm³ s⁻¹, 0.000022 mol⁻¹ dm³ s⁻¹ and 8.90, respectively. This paper expounds the result from the structure of the ligands and the properties of the metal ions, and deduces the catalysis mechanism.     

Synthesis and spectral properties of titanium(iv) polynuclear hydroxo complexes stabilized in solution by the [PW11O39]7− heteropolyanion

Unsaturated heteropolyanions (HPA) [PW₁₁O₃₉]⁷⁻ stabilize Ti^IV hydroxo complexes in aqueous solutions (Ti: PW₁₁ [PW₁₁O₃₉]⁷⁻⪯12, pH 1–3). Spectral studies (optical,¹⁷O and³¹P NMR, and IR spectra) and studies by the differential dissolution method demonstrated that Ti^IV hydroxo complexes are stabilized through interactions of polynuclear Ti^IV hydroxo cations with heteropolyanions [PW₁₁TiO₄₀ ⁵⁻ formed. Depending on the reaction conditions, hydroxo cations Ti _n−1O _x H _y ^m+ either add to oxygen atoms of the W−O−Ti bridges of the heteropolyanions to form the complex [PW₁₁TiO₄₀·Ti _n−1O _x H _y ] ^k− (at [HPA]=0.01 mol L⁻¹) or interact with Ti^IV of the heteropolyanions through the terminal o atom to give the polynuclear complexes [PW₁₁O₃₉Ti−O−Ti _n−1O _x H _y ]^q− (at [HPA]=0.2 mol L⁻¹). When the complexes of the first type were treated with H₂O₂, Ti^IV ions added peroxo groups. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 914–920, May, 1997.     

Non-alkane behavior of cyclopropane and its derivatives: characterization of unconventional hydrogen bond interactions

Eight cyclopropane derivatives (Δ − R) have been modeled, with R = −H, −CH₃, −NH₂, −C ≡ CH, −C ≡ CCH₃, −OH, −F and −C ≡ N. All geometries have been fully optimized at the MP2/ AUG-cc-pVTZ level of calculations. Natural bond orbital analyses reveal extra p character (sp^λ, λ > 3) in the C-C bonds of the cyclopropyl rings. The banana-like σ _CC bonds in the rings are described in detail. Alkene-like complexes between Δ − R molecules and hydrogen fluoride are identified. These weakly bonded complexes are formed through unconventional hydrogen bond interactions between the hydrogen atom in the HF molecule and the carbon–carbon bonds in the cyclopropane ring. A topological analysis of the electronic charge density and its Laplacian has been used to characterize the interactions. The possible relevance of such complexes in the modeling of substrate–receptor interactions in some anti-AIDS drugs is discussed. Contribution to the Serafin Fraga Memorial Issue.     

Homo- and heteronuclear complexes of a new,vicinal dioxime ligand

A new symmetrical vicinal dioxime, N,N′-bis-{4-[[(2-hydroxyphenyl)methylene]hydrazinecarbonyl]phenyl}diaminoglyoxime (LH₄), was prepared by reacting anti-dichloroglyoxime with salicylaldehyde 4-aminobenzoylhydrazone. The reaction of ligand with Ni²⁺ salts gave mono-and homopentanuclear complexes, [Ni(LH₃)₂] and [Ni₅(LH)₂X₂]. Furthermore, heteropentanuclear complexes of dioxime ligand, [Cu₄Ni(LH)₂X₄], were prepared by the reaction of [Ni(LH₃)₂)] with Cu²⁺ salt and a monodentate ligand (X = SCN⁻, CN⁻, or N ₃ ⁻ ). The structures of both the new symmetrical vicinal dioxime and its complexes were identified by elemental analyses, IR, ¹H NMR, UV-VIS spectra, and magnetic susceptibility. The elemental analyses and spectral data indicate that the hydrazone side of ligand acts as a O,N,O′ tridentate and the fourth position is occupied with monodentate anion such as SCN⁻, CN⁻, N ₃ ⁻ .