Mixed Ligand Complex Formation Reactions and Equilibrium Studies of Cu(II) with Bidentate Heterocyclic Alcohol (N,O) and Some Bio-Relevant Ligands

The formation equilibria of copper(II) complexes and the ternary complexes Cu(HMI)L (HMI=4-Hydroxymethyl-imidazole, L=amino acid, amides or DNA constituents) have been investigated. Ternary complexes are formed by a simultaneous mechanism. The results showed the formation of Cu(HMI)L and Cu(HMI,H₋₁)(L) complexes. The stability of ternary complexes was quantitatively compared with their corresponding binary complexes in terms of the parameters Δlog ₁₀ K and log ₁₀ X. The effect of the side chains of amino acid ligands (Δ_R) on complex formation was discussed. The concentration distributions of various species formed in solution were also evaluated as a function of pH. The thermodynamic parameters ΔH° and ΔS° calculated from the temperature dependence of the equilibrium constants are investigated. The effects of dioxane as a solvent, on the protonation constant of HMI and the formation constants of Cu^II–HMI complexes, were discussed.     

A Thermodynamic Study of Bromo-Lanthanum (III) Complexes from EMF Measurements

The stability constants (for the formation) of LaBr²⁺ and LaBr₂⁺ ions were obtained potentiometrically at various ionic strengths at 20°, 25°, 30°, and 35°. The molal free energy was given by ΔG°=-2,444.04+2.67T log T+1.39T. The thermodynamic quantities for the formation of LaBr²⁺ were evaluated as ΔH_f° = ?207.9, ΔG_f° = ?199.1 kcal mole^?1 and S° = ?29.5 cal. deg^?1 mole^?1 at 25°.     

Potentiometry, Stability and Thermodynamics of Diethyltin(IV) Dichloride with Some Selected Biomolecules

The interaction of diethyltin(IV), DET, with selected bioligands having a variety of model functional groups was investigated at 25 °C and ionic strength 0.1 mol·dm^?3 NaCl using the potentiometric technique. The hydrolysis constants of the DET cation and the formation constants of the complexes formed in solution were calculated using the MINIQUAD-75 program. The stoichiometry and stability constants for the complexes formed are reported. The results show the formation of 1:1 and 1:2 complexes with amino acids and DNA constituents. The dicarboxylic acids form 1:1 complexes. The peptides form both 110 complexes and the corresponding deprotonated amide species [Et₂Sn(LH_?1)] (11-1). The participation of different ligand functional groups in binding to organotin is discussed. The concentration distributions of the various complex species were evaluated as a function of pH. The standard thermodynamic parameters ΔH° and ΔS°, calculated from the temperature dependence of the equilibrium constants, were investigated for the interaction of DET with thymine as a representative example of DNA constituents. The effect of ionic strength and solvent on hydrolysis constants of DET, protonation equilibria of thymine and its complex formation with DET were investigated and discussed.     

Kinetics of Oxygen Exchange in the System BrO - H2O (D2O)

The kinetics of oxygen exchange between water (H₂O, D₂O) and ¹⁸O-labelled bromate ion has been investigated over the range of 1.7 ≤ pH ≤ 14.3 and 20 ≤ °C ≤ 95. At 60° and ionic strength I ? 1.0M (NaNO₃), the experimental results were consistent with the rate laws (R in moll^?1 s^?1): From the temperature dependence of the rate constants the activation parameters ΔH^≠, ΔS^≠ and ΔC^≠ were derived. In the acid-catalysed region the form of the rate law and the direction of the solvent isotope effect were the same as previously found, but the numerical values of ΔH^≠ and k_2H/k_2D differ considerably. For the spontaneous and the OH^?-catalysed exchange reactions bimolecular displacement mechanisms are proposed.     

Ag(I) and Zn(II) isonicotinate complexes: design,characterization, antimicrobial effect,and CT-DNA binding studies

Trinuclear Ag(I) (1) and dinuclear and mononuclear Zn(II) isonicotinate (2 and 3) complexes were prepared and characterized by X-ray crystallography, elemental analysis, IR spectroscopy, and thermal analysis. Single-crystal analysis of the Ag(I) complex reveals two different monodentate carboxylate coordination modes, protonated and deprotonated, respectively. IR spectra showed correlations between isonicotinate coordination modes and Δ(ν_as???ν_s)_IR values. In addition, the hydrogen bonds significantly influence a position of carboxylate absorption bands. Moreover, IC₅₀ and MIC data for bacteria, yeasts, and filamentous fungi were determined and the binding of Ag(I) and Zn(II) complexes to calf thymus DNA was investigated using electronic absorption, fluorescence, and CD measurements. Biological tests showed that the Ag(I) complex is more active than commercially used Ag(I) sulfadiazine against Escherichia coli. The fluorescence spectral results indicate that the complexes can bind to DNA through an intercalative mode. The Stern–Volmer quenching constants for investigated complexes obtained from the linear quenching plot are in the range of 1.67 × 10⁴–3.42 × 10⁴ M^?1.     

Calculating the Thermodynamics of Weakly Hydrogen-Bonded Complexes from Heteronuclear NMR Data: Base-pairing stabilities of a 5-methyl(15N2)[O2, O4-17O2]uridine (= (15N2)[O2,O4-17O2]ribosylthymine) derivative,and structural implications

2′,3′-O-Isopropylidene-5-methyl(¹⁵N₂)[O²,O⁴-¹⁷O₂]uridine (= 2′,3′-O-isopropylidene (¹⁵N₂)[O²,O⁴-¹⁷O₂]-ribosylthymine; 1 ) was analyzed by ¹⁵N-and ¹⁷O-NMR spectroscopy. The ¹⁵N and ¹⁷O chemical shifts revealed, in the absence and presence of unlabelled 2′,3′-O-isopropylideneadenosine ( 2 ), the formation of thymine-thymine and thymine-adenine base pairs in CHCl₃. As expected, cyclic complexes stabilized by two H-bonds occurred at low temperatures, but at elevated temperatures, the data suggest that open complexes involving only one H-bond prevailed. The ¹⁷O-NMR data showed the cyclic thymine-adenine pair in a reverse base pair geometry. The open base pair involved contacts to the urea-derived carbonyl O-atom of thymine. The thermodynamics of complex formation of the cyclic and open forms in both homo and hetero pairs were calculated from the temperature and concentration dependence of the ¹⁵N-NMR data using a new method. It involves a fitting procedure onto the experimental isotherms using a theoretically derived function with the standard Gibbs free energy as a parameter to be optimized. ΔH° and ΔS° were derived from a linear regression of ΔG°(T) vs. T. The fitting procedure circumvents the baseline problem and could be automated and used to calculate correct thermodynamics from UV-monitored melting curves of oligonucleotides. Since titrations are not involved, this dilution method should also be a useful alternative for stability studies of supramolecular complexes in H₂O and in organic solvents.     

Synthesis,spectroscopic and thermodynamic studies of new transition metal complexes with N,N′-bis(2-hydroxynaphthalin-1-carbaldehydene)-1,2-bis(m-aminophenoxy)ethane and their determination by spectrophotometric methods

A novel tetradentate N₂O₂-type Schiff base, synthesized from 1,2-bis(m-aminophenoxy)ethane and 2-hydroxynaphthalin-1-carbaldehyde, forms stable complexes with transition metal ions such as Cu(II), VO(IV) and Zn(II) in DMF. Microanalytical data, elemental analysis, magnetic measurements, UV, visible and IR spectra as well as conductance measurements were used to confirm the structures. The stability constants of these complexes in 60% (v/v) DMF–water were determined at different ionic strengths (0.07,?0.13,?0.2?M) and at different temperatures (45,?50,?55,?60?±?0.1°C) using a spectrophotometric method. From these constants, thermodynamic stability constants and thermodynamic parameters (ΔG?⁰, ΔH?⁰, ΔS?⁰) were calculated. The values of enthalpy change are negative for all systems. The acid dissociation constant of the ligand, investigated in 60% (v/v) DMF–water, has also been calculated at different temperatures.     

Formation constants and coordination thermodynamics for binary complexes of Cu(II) and some α-amino acids in aqueous solution

In this study, the formation constants of 1?:?1 binary complexes of Cu(II) with L-glutamic acid, L-aspartic acid, glycine, L-alanine, L-valine, and L-leucine and 1?:?2 binary complexes of L-glutamic acid, glycine and the protonation macro- and microconstants of all these amino acids were determined potentiometrically in aqueous solutions at 5.0, 20.0, and 35.0°C at a constant ionic strength of I?=?0.10?mol?L^?1 (NaClO₄). The thermodynamic parameters ΔG _f°, ΔH _f°, and ΔS _f° were determined for the protonation of all amino acids used in this study and for the complex formation reactions of them with Cu(II). The results were analysed by means of Principle of hard and soft [Lewis] acids and bases. Additionally, in order to confirm the complex formation and determine the stability constants of complexes, UV-Vis spectroscopic studies were carried out. The stability constants obtained by spectrophotometrically are confirmed by those determined potentiometrically.     

Complex Formation Equilibria of Unusual Seven Coordinate Fe(III) Complexes with DNA Constituents

Seven-coordinate Fe(III) complexes [Fe(dapsox)(H₂O)₂]⁺, where [dapsox = 2,6-diacetylpyridine-bis(semioxamazide)] is an equatorial pentadentate ligand with five donor atoms (2O and 3N), were studied with regard to their acid–base properties and complex formation equilibria. Stability constants of the complexes and the pK _a values of the ligands were measured by potentiometric titration. The interaction of [Fe(dapsox)(H₂O)₂]⁺ with the DNA constituents, imidazole and methylamine·HCl were investigated at 25 °C and ionic strength 0.1 mol·dm^?3 NaNO₃. The hydrolysis constants of the [Fe(dapsox)(H₂O)₂]⁺ cation (pK _a1 = 5.94 and pK _a2 = 9.04), the induced ionization of the amide bond and the formation constants of the complexes formed in solution were calculated using the nonlinear least-squares program MINIQUAD-75. The stoichiometry and stability constants for the complexes formed are reported. The results show the formation of 1:1 and 1:2 complexes with DNA constituents supporting the hepta-coordination mode of Fe(III). The concentration distributions of the various complex species were evaluated as a function of pH. The thermodynamic parameters ΔH° and ΔS° calculated from the temperature dependence of the equilibrium constants were investigated for interaction of [Fe(dapsox)(H₂O)₂] with uridine.     

Complexation of neptunium(V) by salicylate,phthalate and citrate ligands in a pH 7.5 phosphate buffered system

Conditional stability constants, enthalpies and entropies of complexation at pH 7.5 and ionic strength 0.1 have been determined for neptunium(V) complexes of phosphate, salicylate, phthalate and citrate. Phosphate forms a complex with log β = 2.36 ± 0.42 at 25°C, ΔH°_c = ? 69.9 kJ/mole and ΔS°_c = ? 188 J/mole-K. At pH 7.5 salicylate does not form a complex with neptunium(V) due to the low charge density of the NpO₂⁺ ion and incomplete ionization of the salicylate ion. Phthalate forms a complex with log β = 3.43 ± 0.33 at 25°C, ΔH°_c = 33.5 kJ/mole and ΔS°_c = 182 J/mole-K. Citrate forms a complex with log β = 4.84 ± 0.72 at 25°C, ΔH°_c = 14.0 kJ/mole and ΔS°_c = 140 J/mole-K. In all cases, only 1:1 complexes were identified.     

Synthesis,structure, and kinetic studies on [RuCl2(NCCH3)2(cod)]

[RuCl₂(NCCH₃)₂(cod)], an alternative starting material to [RuCl₂(cod)] _n for the preparation of ruthenium(II) complexes, has been prepared from the polymer compound and isolated in yields up to 87% using a new work-up procedure. The compound has been obtained as a yellow solid without water of crystallization. The complexes [RuCl₂(NCR)₂(cod)] spontaneously transform into dimers [Ru₂Cl(μ-Cl)₃(cod)₂(NCR)] (R?=?Me, Ph). ¹H NMR kinetic experiments for these transformations evidenced first-order behavior. [RuCl₂(NCPh)₂(cod)] dimerizes slower by a factor of ten than [RuCl₂(NCCH₃)₂(cod)]. The following activation parameters, ΔH ^#?=?114?±?3?kJ?mol^?1 and ΔS ^#?=?66?±?9?J?K^?1?mol^?1 for R?=?CH₃CN (ΔG ^#?=?94?±?5?kJ?mol^?1, 298.15?K) and ΔH ^#?=?122?±?2?kJ?mol^?1 and ΔS ^#?=?75?±?6?J?K^?1?mol^?1 for R?=?Ph (ΔG ^#?=?100?±?4?kJ?mol^?1, 298.15?K), have been calculated from the first-order rate constants in the temperature range 294–323?K. The kinetic parameters are in agreement with a two-step mechanism with dissociation of acetonitrile as the rate-determining step. The molecular structures of [Ru₂Cl(μ-Cl)₃(cod)₂(NCR)] (R?=?Me, Ph) have been determined by X-ray diffraction.     

氢过碘酸）合银（III）配离子氧化L-脯氨酸的反应动力学及机理

L-脯氨酸独有的亚胺基使其在生物医药领域具有许多独特的功能,并广泛用作不对称有机化合物合成的有效催化剂。本文在碱性介质中研究了二（氢过碘酸）合银（III）配离子氧化 L-脯氨酸的反应。经质谱鉴定,脯氨酸氧化后的产物为脯氨酸脱羧生成的 γ-氨基丁酸盐;氧化反应对脯氨酸及Ag(III) 均为一级;二级速率常数 k′ 随 [IO₄^-] 浓度增加而减小,而与 [OHˉ] 的浓度几乎无关;推测反应机理应包括 [Ag(HIO₆)₂]^5-与 [Ag(HIO₆)(H₂O)(OH)]^2-之间的前期平衡,两种Ag（III）配离子均作为反应的活性组分,在速控步被完全去质子化的脯氨酸平行地还原,两速控步对应的活化参数为： k₁ (25 ^oC)＝1.87±0.04（mol·L^-1)^-1s^-1,∆ H₁^≠＝45±4 kJ · mol^-1, ∆ S₁^≠＝-90±13 J· K^-1·mol^-1 and k₂ (25 ^oC) ＝3.2±0.5（mol·L^-1)^-1s^-1, ∆ H₂^≠＝34±2 kJ · mol^-1, ∆ S₂^≠＝-122 ±10 J· K^-1·mol^-1。本文第一次发现 [Ag(HIO₆)₂]^5-配离子也具有氧化反应活性。     

Equilibrium investigation of complex formation reactions involving copper(II), nitrilo-tris(methyl phosphonic acid) and amino acids,peptides or DNA constitutents. The kinetics,mechanism and correlation of rates with complex stability for metal ion promoted hydrolysis of glycine methyl ester

The complex formation reactions of [Cu(NTP)(OH₂)]^4? (NTP?=?nitrilo-tris(methyl phosphonic acid)) with some selected bio-relevant ligands containing different functional groups, are investigated. Stoichiometry and stability constants for the complexes formed are reported. The results show that the ternary complexes are formed in a stepwise mechanism whereby NTP binds to copper(II), followed by coordination of amino acid, peptide or DNA. Copper(II) is found to form Cu(NTP)H _n species with n?=?0, 1, 2 or 3. The concentration distribution of the various complex species has been evaluated. The kinetics of base hydrolysis of glycine methyl ester in the presence of copper(II)-NTP complex is studied in aqueous solution at different temperatures. It is proposed that the catalysis of GlyOMe ester occurs by attack of OH^? ion on the uncoordinated carbonyl carbon atom of the ester group. Activation parameters for the base hydrolysis of the complex [Cu(NTP)NH₂CH₂CO₂Me]^4? are, ΔH^±?=?9.5?±?0.3?kJ?mol^?1 and ΔS^±?=??179.3?±?0.9?J?K^?1?mol^?1. These show that catalysis is due to a substantial lowering of ΔH^±.     

Solvent extraction of copper(II) from sulfate medium with N -(2-hydroxybenzylidene)aniline

Solvent extraction of copper(II) from sulfate medium with N-(2-hydroxybenzylidene)aniline is studied with the following parameters: pH, concentration of the extractant, nature of diluent, and temperature. The extraction of copper(II) proceeds by a cation exchange mechanism and the extracted species are CuL₂ in cyclohexane and toluene and CuL₂ with some CuL₂HL in chloroform. The equilibrium constants have been calculated as well as thermodynamic parameters ΔH°, ΔS°, and ΔG°. The temperature effect on the solvent extraction of copper(II) with N-(2-hydroxybenzylidene)aniline in cyclohexane is discussed.     

Spectroscopic studies and determination of the formation constants and thermodynamic parameters for a new water-soluble Co(II) Schiff-base complex and some imidazole derivatives

A new water-soluble Co(II) Schiff-base complex, sodium[{N,N′-bis(5-sulfosalicylidene)-1,8-diamino-3,6-dioxaoctan}cobalt] dihydrate, abbreviated as Na₂[Co(II)L], was synthesized and characterized. The formation constants and thermodynamic parameters for the interaction of this complex with imidazole (Im) and 1-methylimidazole (MeIm) were determined spectroscopically in aqueous solution, ethanol/water (10/90), and methanol/water (10/90) under physiological conditions (pH?=?7), constant ionic strength (I?=?0.1?mol?dm^?3 KNO₃), and various temperatures ranging from 294 to 310?K. Our spectroscopic and thermodynamic results show that this adduct formation is endothermic and the positive values of ΔS _f° make ΔG _f° negative. The trend in variation of ΔH _f° and ΔS _f° for Im is in the order water?>?methanol?>?ethanol, but for MeIm it is in the opposite order which is related to the hydrogen bonding between solvents and these donors. Formation constants between MeIm and Na₂[Co(II)L] in these three solvents are larger than for Im which depends on the electron donation of methyl on MeIm.     

Electrooxdation of Tricarbonyl(N,N-Diphenylcyclohexadienecarboxamide)Iron Complexes. Reversibility of Electron Transfer and Free Energy Change

Qualitative and quantitative criteria of irreversibility of electron transfer in cyclic voltammetry (CV) of tricarbonyl(N,N-diphenylcyclohexadienecarboxamide)iron complexes were investigated. The measurement of the heterogeneous rate constants for electron transfer according to CV data over an extended range of free energy change ( ΔG) for these complexes are described. Kinetic analyses of the electrochemical technique demonstrates that when the applied potential exceeds the standard potential E°, the experimental rate constant k_e represents an accurate measurement of the intrinsic rate constant k₁ for electron transfer. However, as the applied potential is less than E°, the reversibility of the electron-transfer process becomes increasingly more important, and the rate constants for reverse electron transfer k_-t and decomposition k₂ of the electrogenerated intermediate have to be taken into account.     

Anticancer activity of lanthanum (III) and europium (III) 5-fluorouracil complexes on Caco-2 cell line

Lanthanide complexes are of increasing importance in cancer diagnosis and therapy. In the present study 1:1 and 1:3 solid complexes of La (III)–5-FU (5-fluorouracil) were prepared and characterized. In solution, the formation of 1:1 La (III) and Eu (III) complexes enabled the enhancement of 5-FU's effectiveness. Binding constants of the 1:1 complexes of both metals were estimated using spectrophotometry and HPLC with fluorescence detection methods. The thermodynamic parameters ΔG ^° , ΔH ^° and ΔS ^° were calculated using differential scanning calorimetry. Evaluation of the cytotoxic activity of the 1:1 La (III)- and Eu (III)–5-FU complexes was performed through two methodologies, trypan blue for cell viability where La (III)- and Eu (III)–5-FU complexes were found to have 52,000 and 80,000 dead cells, respectively, and via flow cytometric analysis to measure the apoptotic values, which were found to be 59.87 and 86.86% respectively.     

Synthesis, spectroscopy, electrochemistry and thermal study of uranyl N3O2 Schiff base complexes

The new [UO₂L(CH₃OH)] [where L?=?bis(salicylaldehyde)2,6-diiminopyridine (L¹), bis(5-methoxysalicylaldehyde)2,6-diiminopyridine (L²), bis(5-bromosalicylaldehyde)2,6-diiminopyridine (L³), bis(5-nitrosalicylaldehyde)2,6-diiminopyridine (L⁴)] complexes were synthesized and characterized by IR, UV?Cvis and elemental analysis. Methanol solvent is coordinated to uranyl complexes. The electrochemical properties of the uranyl complexes were investigated by cyclic voltammetry in DMF solvent. Thermogravimetry and differential thermoanalysis of the uranyl complexes were carried out in the range of 20?C700?°C. The UO₂L⁴ complex was decomposed in two and the others were decomposed in three stages. Up to 85?°C, the coordinated solvent was released then the Schiff base ligands were decomposed in one or two steps. Decomposition of synthesized complexes is related to the Schiff base characteristics. The thermal decomposition reaction is first order for the studied complexes.     

Thermodynamic Studies on the Complexation Reactions of Copper(II) Macrocyclic Tetramine Complexes with Monodentate Ligands: Part II. A Spectrophotometric Study on the Reactions of Meso-5, 7, 7, 12, 14, 14-Hexamethyl-1, 4, 8, 11-Tetraazacyclotetradecane-Copper(II) (Blue) with Halide Ions

The stability constants for the formation of [Cu(tet a)X]⁺(blue) from [Cu(tet a)]²⁺(blue) and X- (where X=Cl, Br, I) were determined by spectrophotometric method at 15°, 25° and 35°C. The corresponding ΔH° and ΔS° values were obtained from the variations of the stability constants between 15° and 35°C. For the same halide ion, the stability constant of [Cu(tet b)X]⁺ (blue) is larger than that of [Cu(tet a)X]⁺(blue).     

Liquid-crystalline oxovanadium(IV) complexes accessed from bidentate [N,O] donor salicylaldimine Schiff-base ligands

A series of bis[4-(n-alkoxy)-N-(4′-R-phenyl)salicylideneiminato]oxovanadium(IV) complexes (n?=?6,?10,?14,?16,?18 and R?=?C₃H₇) were prepared and their mesogenic properties were investigated. The mesomorphic behaviors of the compounds were studied by polarized optical microscopy and differential scanning calorimetry. Ligands display SmA/SmC and unexpected nematic mesophases. The complexes bearing longer alkoxy carbon chain (n?=?10,?14,?16, and 18) showed both monotropic or enantiotropic transitions with smectic A and high ordered smectic E phases. However, the complex with shorter carbon chain length (n?=?6) showed monotropic transition with an unprecedented nematic (N) phase. A density functional theory study was carried out using DMol3 at BLYP/DNP level to obtain a stable optimized structure. A square-pyramidal geometry for the vanadyl complexes has been suggested. A ν_V=O stretching value of ～970?cm^?1 corroborated absence of any V?=?O?···?V?=?O interactions. Cyclic voltammetry revealed a quasireversible one-electron response at 0.61?V for the VO(IV)–VO(V) redox couple. Variable temperature magnetic susceptibility measurements of the vanadyl complexes suggested absence of any exchange interactions among the vanadyl spin centers.