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.     

Ion-pair formation in the outer-sphere electron transfer reactions between tris-(1, 10) phenanthroline iron(II) and the halopentacyanocobaltate(III) complexes in aqueous acidic solutions

The kinetics of the reactions between Fe(phen) ₃ ²⁺ [phen = tris–(1,10) phenanthroline] and Co(CN)₅X³⁻ (X = Cl, Br or I) have been investigated in aqueous acidic solutions at I = 0.1 mol dm⁻³ (NaCl/HCl). The reactions were carried out at a fixed acid concentration ([H⁺] = 0.01 mol dm⁻³) and the second-order rate constants for the reactions at 25 °C were within the range of (0.151–1.117) dm³ mol⁻¹ s⁻¹. Ion-pair constants K _ip for these reactions, taking into consideration the protonation of the cobalt complexes, were 5.19 × 10⁴, 3.00 × 10² and 4.02 × 10⁴ mol⁻¹ dm⁻³ for X = Cl, Br and I, respectively. Activation parameters measured for these systems were as follows: ΔH* (kJ K⁻¹ mol⁻¹) = 94.3 ± 0.6, 97.3 ± 1.0 and 109.1 ± 0.4; ΔS* (J K⁻¹) = 69.1 ± 1.9, 74.9 ± 3.2 and 112.3 ± 1.3; ΔG* (kJ) = 73.7 ± 0.6, 75.0 ± 1.0 and 75.7 ± 0.4; E _a (kJ) = 96.9 ± 0.3, 99.8 ± 0.4, and 122.9 ± 0.3; A (dm³ mol⁻¹ s⁻¹) = (7.079 ± 0.035) × 10¹⁶, (1.413 ± 0.011) × 10¹⁷, and (9.772 ± 0.027) × 10²⁰ for X = Cl, Br, and I respectively. An outer – sphere mechanism is proposed for all the reactions.     

Synthesis and thermal decomposition kinetics of La(III) complexwith unsymmetrical Schiff base ligand

A new unsymmetrical solid Schiff base (LLi) was synthesized using L-lysine, o-vanillin and 2-hydroxy-l-naphthaldehyde. Solid lanthanum(III) complex of this ligand [LaL(NO₃)]NO₃·2H₂O have been prepared and characterized by elemental analyses, IR, UV and molar conductance. The thermal decomposition kinetics of the complex for the second stage was studied under non-isothermal condition by TG and DTG methods. The kinetic equation may be expressed as: dα/dt=Ae^−E/RT(1−α)². The kinetic parameters (E, A), activation entropy ΔS ^# and activation free-energy ΔG ^# were also gained.     

Hydroxylamine derivatives in Purex Process

The kinetics of oxidation-reduction reaction between N,N-diethylhydroxylamine (DEHAN) and nitrous acid in nitric acid solution have been studied by spectrophotometry at 9.5°C. The rate equation is −d[HNO₂]/dt=K[HNO₂]·[DEHAN][HNO₃] and the rate constantK=12.81 (mol/l)⁻²·min⁻¹. A possible mechanism has been suggested on the basis of chemical analysis and Raman spectra. The activation energyE and the thermodynamic functions ΔH ^#, ΔG ^# and ΔS ^# are also calculated.     

Mixed complex formation of lead(II) and mercury(II) ethylenediaminetetraacetates with thiourea in an aqueous solution

The formation of mixed-ligand complexes HgEdtaThio²⁻, HgEdtaS₂O₃⁴⁻, PbEdtaThio²⁻, and Pb(Thio) _i ²⁺, i = 1, 2; Thio is thiourea) was studied by calorimetry, pH metry, and ¹H and ¹³C NMR spectroscopy. The thermodynamic parameters (logK, Δ _r G ⁰, Δ _r H, and Δ _r S) for the formation of the complexes at 298.15 K and the ionic strength I = 0.5(NaClO₄) were determined. The most probable coordination mode of the ligands in the mixed complex was considered.     

Thermal and spectral studies of palladium(II) complexes

Palladium(II) complexes of type [Pd(L)Cl₂] [where L=2-aminopyridine-N-thiohydrazide (L¹), (2-aminopyridine-N-thio)-1,3-propanediamine (L²), benzaldehyde 2-aminopyridine-N-thiohydrazone (L³) and salicylaldehyde-2-aminopyridine-N-thiohydrazone (L⁴)] have been synthesized. The thiohydrazide, thiodiamine and thiohydrazones can exist as thione-thiol tautomer and coordinate as a bidentate N-S ligand. The ligands found to act in bidentate fashion. The complexes have been characterized by elemental analysis, IR, mass, electronic, ¹H NMR spectroscopic studies, and TG/DTA study. Antifungal studies of some complexes were also carried out. Various kinetic and thermodynamic parameters like order of reaction (n), activation energy (E _a), apparent activation entropy (S ^# ) and heat of reaction (ΔH) have also been carried out for one complex.     

Oxidation of Fursemide by Diperiodatocuprate(III) in Aqueous Alkaline Medium—a Kinetic Study

Fursemide is the chemical compound 4-chloro-2-(furan-2-ylmethylamino)-5-(aminosulfonyl) benzoic acid. It was oxidized by diperiodatocuprate(III) in alkali solutions, and the oxidation products were identified as furfuraldehyde and 2-amino-4-chloro-5-(aminosulfonyl) benzoic acid. The reaction kinetics were studied spectrophotometrically. The reaction was observed to be first order in [oxidant] and fractional order each in [fursemide] and [periodate], whereas added alkali retarded the rate of reaction. The reactive form of the oxidant was inferred to be [Cu(H₃IO₆)₂]⁻. A mechanism consistent with the experimental results was proposed, in which oxidant interacts with the substrate to give a complex as a pre-equilibrium state. This complex decomposed in a slow step to give a free radical that was further oxidized by reaction with another molecule of DPC to yield 2-amino-4-chloro-5-(aminosulfonyl) benzoic acid and furfuraldehyde in a fast step. This reaction was studied at 25, 30, 35, 40 and 45 °C, and the activation parameters E _a,ΔH ^#,ΔS ^# and ΔG ^# were determined to be 51 kJ⋅mol⁻¹,48.5 kJ⋅mol⁻¹,−63.5 J⋅K⁻¹⋅mol⁻¹ and 67 kJ⋅mol⁻¹, respectively. The value of log ₁₀ A was calculated to be 6.8.     

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.     

A quantum chemical study of lead(II) thiocomplexes with mono- and bidentate ligands

Model Pb(II) thiocomplexes with mono- and bidentate ligands of the composition [Pb(L^1,2) _n ]²⁻ⁿ (L¹ is (SC₆H₅)⁻ (thiophenolate ion), L² is (S₂CN(CH₃)₂)⁻ (dithiocarbamate ion), n is the number of ligands of 2–6), which simulate fragments of the crystal structures of Pb(II) complex compounds with organic ligands, are studied within density functional theory. Geometric and energy parameters of model complexes with different coordination geometries of the Pb atom are determined and the stereochemical activity of the lone electron pair (LEP, E) of the Pb²⁺ ion is estimated in them. In the studied complexes, the highest Pb-S binding energy is found for the Pb atom surrounded by 2–4 ligands. The geometry of the Pb atom coordinated by S donor atoms can be described in terms of the valence shell electron pair repulsion (VSEPR) model with stereochemically active LEP. The coordination number (cn) of the Pb atom in the most energetically favorable complexes [Pb(SC₆H₅) _n ]²⁻ⁿ is (3+E) − (4+E), and in [Pb(S₂CN(CH₃)₂) _n ]²⁻ⁿ complexes, it is (4+E) and (6+E). Configurations with the mentioned cns are most often observed in the crystal structures of Pb(II) thiocomplex compounds.     

Thermal analysis study of imidazolinium and some benzimid azolium salts by TG

The imidazolinium and benzimidazolium bromide salts with pentafluor substituents on N atom were synthesized. The structures of imidazolinium and benzimidazolium bromide salts obtained were conformed by ¹H and ¹³C NMR, ¹⁹F NMR and elemental analysis. It was found that pyrolytic decomposition occurs with melting in salts. The imidazolinium and benzimidazolium bromide salts were studied by TG-DTG and DTA from ambient temperature to 1000°C in nitrogen atmosphere. The decomposition occurred mainly in one stage and the values of activation energy E, frequency factor A, reaction order n, enthalpy change ΔH ^#, entropy change ΔS ^# and Gibbs free energy ΔG ^#, of the thermal decomposition were calculated by means of Coats-Redfern (CR), MacCallum-Tanner (MC) and van Krevelen (vK) methods. The activation energy value obtained by CR and MC methods were in good agreement with each other while those obtained by vK were found to be 10–12 kJ mol⁻¹ larger.     

Synthesis,spectroscopic, thermal and biological aspect of mixed ligand copper(II) complexes

Derivative of 8-hydroxyquinoline i.e. Clioquinol is well known for its antibiotic properties, drug design and coordinating ability towards metal ion such as Copper(II). The structure of mixed ligand complexes has been investigated using spectral, elemental and thermal analysis. In vitro anti microbial activity against four bacterial species were performed i.e. Escherichia coli, Pseudomonas aeruginosa, Serratia marcescens, Bacillus substilis and found that synthesized complexes (15–37 mm) were found to be significant potent compared to standard drugs (clioquinol i.e. 10–26 mm), parental ligands and metal salts employed for complexation. The kinetic parameters such as order of reaction (n = 0.96–1.49), and the energy of activation (E _a = 3.065–142.9 kJ mol⁻¹), have been calculated using Freeman–Carroll method. The range found for the pre-exponential factor (A), the activation entropy (S* = −91.03 to−102.6 JK⁻¹ mol⁻¹), the activation enthalpy (H* = 0.380–135.15 kJ mol⁻¹), and the free energy (G* = 33.52–222.4 kJ mol⁻¹) of activation reveals that the complexes are more stable. Order of stability of complexes were found to be [Cu(A⁴)(CQ)OH] · 4H₂O > [Cu(A³)(CQ)OH] · 5H₂O > [Cu(A¹)(CQ)OH] · H₂O > [Cu(A²)(CQ)OH] · 3H₂O     

Kinetics and mechanism of aqua ligand substitution from cis-diaqua(cis-1,2-diaminocyclohexane)platinum(II)perchlorate by diethyldithiocarbamate anion in aqueous medium

The kinetics of the interaction of diethyldithiocarbamate (Et₂DTC) with [Pt(dach)(H₂O)₂]²⁺ (dach = cis-1,2-diaminocyclohexane) have been studied spectrophotometrically as a function of [Pt(dach)(H₂O)₂ ²⁺], [Et₂DTC] and temperature at a particular pH (4.0). The reaction proceeds via rapid outer sphere association complex formation followed by two slow consecutive steps. The first step involves the transformation of the outer sphere complex into an inner sphere complex containing a Pt–S bond and one aqua ligand, while the second step involves chelation when the second aqua ligand is replaced. The association equilibrium constant K _E and two rate constants k ₁ and k ₂ have been evaluated. Activation parameters for both the steps have been calculated (∆H ₁ ^# = 66.8 ± 3.7 kJ mol⁻¹, ∆S ₁^# = −81 ± 12 JK⁻¹ mol⁻¹ and ∆H ₂^# = 95.1 ± 2.8 kJ mol⁻¹, ∆S ₂^# = −34.4 ± 9.1 JK⁻¹ mol⁻¹). The low enthalpy of activation and negative entropy of activation indicate an associative mode of activation for both the steps.     

Kinetics and mechanism of anation of cis -diaquo- bis -oxalatochromate(III) ion byDL -alanine in ethanol-water mixtures of varying dielectric constant

The kinetics of the anation reaction of cis-diaquo-bis-oxalatochromate(III) ion by DL-alanine has been studied spectrophotometrically in the pH range 3.8 to 7.3, where DL-alanine remains in zwitterionic form. A second-order rate law has been established. Reaction rates in three different ethanol-water mixtures were measured. In each solvent medium the anation rate is higher as compared to water exchange reaction at a particular temperature. The activation parameters (gDH^# and ΔS^#) in different ethanol-water mixtures were obtained from Eyring plots. ΔG^#(ΔH^# −TΔS ^#) values were calculated in each solvent medium and compared with that of the isotopic water exchange process. A reaction mechanism involving theS _N2 path has been suggested.     

Thermal and spectral studies of 5-(phenylazo)-2-thiohydantoin and 5-(2- hydroxyphenylazo)-2-thiohydantoin complexes of cobalt(II), nickel(II) and copper(II)

Complexes of 5-(phenylazo)-2-thiohydantoin (L¹) and 5-(2-hydroxyphenylazo)-2-thiohydantoin (HL²) with Co(II), Ni(II) and Cu(II) salts have been synthesised and characterized by elemental analysis, conductivity, magnetic susceptibility, UV-Vis, IR, ESR and TG studies. The magnetic and spectral data suggested octahedral geometry for [L¹M(OAc)₂(H₂O)₂]·xH₂O {M=Ni^ll and Cu^ll} and [L¹CuCl₂(H₂O)]·H₂O (dimeric form for the latter), trigonal bipyramidal geometry for [L²Co(OAc)(H₂O)]·2H₂O, square pyramidal geometry for [L²Ni(OAc)(H₂O)]·H₂O and square planar geometry for [L²CuCl]·2H₂O. TG studies confirmed the chemical formulations of these complexes and showed that their thermal degradation takes place in three to five steps, depending on the type of the ligand and the geometry of the complex. The kinetic parameters (n, E^#, A, ΔH^#, ΔS^# and ΔG^#) of the thermal decomposition stages were computed using the Coats-Redfern and other standard equations and are discussed.     

Thermal behaviour of platinum(II) complexes of diethyl and monoethyl 2-quinolylmethylphosphonates

Summary Thermal study of the molecular and ionic platinum(II) complexes of diethyl (2-dqmp) and monoethyl (2-Hmqmp) ester of 2­quinolylmethylphosphonic acid: dihalide adducts trans-PtL₂X₂ (L=2-dqmp, X=Cl, Br; L=2-Hmqmp, X=Cl), methylquinolinium tetrahaloplatinates [LH⁺]₂[PtX₄^2-] (L=2-dqmp, X=Cl, Br; L=2­Hmqmp, X=Cl, Br), methylquinolinium hexahalodiplatinates [LH⁺]₂[Pt₂X₆^2-](L=2-Hmqmp, X=Cl, Br) and chelate complex Pt(2­mqmp)₂·2H₂O, has been carried out using TG-DTA techniques and the infrared spectroscopic study. There are great differences in the thermal behaviour between various types of complexes, especially between the molecular and the ion-pair salt complexes.     

Ligand Exchange Processes on Solvated Lithium Cations. II. Complexation by Cryptands in γ-Butyrolactone as Solvent

Kinetic studies on Li⁺ exchange between the cryptands C222 and C221, and γ-butyrolactone as solvent were performed as a function of ligand-to-metal ratio, temperature and pressure using ⁷Li NMR. The thermal rate and activation parameters are: C222: k ₂₉₈ = (3.3 ± 0.8)×10⁴ M⁻¹ s⁻¹, ΔH ^# = 35 ± 1 kJ mol⁻¹ and ΔS ^# = −41 ± 3 J K⁻¹ mol⁻¹; C221: k ₂₉₈ = 105 ± 32 M⁻¹ s⁻¹, ΔH ^# = 48 ± 1 kJ mol⁻¹ and ΔS ^# = −45 ± 2 J K⁻¹ mol⁻¹. Temperature and pressure dependence measurements were performed in the presence of an excess of Li⁺. The influence of pressure on the exchange rate is insignificant for both ligands, such that the value of activation volume is around zero within the experimental error limits. The activation parameters obtained in this study indicate that the exchange of Li⁺ between solvated and chelated Li⁺ ions follows an associative interchange mechanism. Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at . For Part I see: R. Puchta, M. Galle, N.J.R. van Hommes, E. Pasgreta and R. van Eldik: Inorg. Chem. 43, 8227 (2004).     

Spectroscopic study of protonation of oligonucleotides containing adenine and cytosine

Acidobasic properties of purine and pyrimidine bases (adenine, cytosine) and relevant nucleosides (adenosine, cytidine) were studied by means of glass-electrode potentiometry and the respective dissociation constants were determined under given experimental conditions (I = 0.1 M (NaCl), t = (25.0 ± 0.1) °C): adenine (pK _HL = 9.65 ± 0.04, pK _H2L = 4.18 ± 0.04), adenosine (pK _H2L = 3.59 ± 0.05), cytosine (pK _H2L = 4.56 ± 0.01), cytidine (pK _H2L = 4.16 ± 0.02). In addition, thermodynamic parameters for bases: adenine (ΔH ⁰ = (−17 ± 4) kJ mol⁻¹, ΔS ⁰ = (23 ± 13) J K⁻¹ mol⁻¹), cytosine (ΔH ⁰ = (−22 ± 1) kJ mol⁻¹, ΔS ⁰ = (13 ± 5) J K⁻¹ mol⁻¹) were calculated. Acidobasic behavior of oligonucleotides (5′CAC-CAC-CAC3′ = (CAC)₃, 5′AAA-CCC-CCC3′ = A₃C₆, 5′CCC-AAA-CCC3′ = C₃A₃C₃) was studied under the same experimental conditions by molecular absorption spectroscopy. pH-dependent spectral datasets were analyzed by means of advanced chemometric techniques (EFA, MCR-ALS) and the presence of hemiprotonated species concerning (C⁺-C) a non-canonical pair (i-motif) in titled oligonucleotides was proposed in order to explain experimental data obtained according to literature.     

Thermal decomposition of nickel(II), palladium(II), and platinum(II) complexes of <Emphasis Type="Italic">N</Emphasis>-allyl-<Emphasis Type="Italic">N</Emphasis>′-pyrimidin-2ylthiourea

Thermal decomposition of Ni(II), Pd(II), and Pt(II) complexes of N-pyrimidin-2ylthiourea (AllPmTu) have been studied by TG, DTG, and DTA and by electron impact (EI) mass spectra. The complexes have the molecular formulae as [Ni(AllPmTu)Cl₂(H₂O)], [Ni(AllPmTu)₂Cl₂(H₂O)₂], and [M(AllPmTu)Cl₂], where M = Pd^II or Pt^II, and [Pt(AllPmTu)₂]. The TG curves show that Ni(II) complexes decompose in three stages to yield NiO as a residue, while Pd(II) and Pt(II) decompose in two stages to yield MS residues. The initial mass losses correspond to elimination of allylamine for Pd(II) and Pt(II) complexes but, allyisothiocyanate for both Ni(II) complexes revealing that sulfur atom of thiourea part is involved in coordination to Pd(II) and Pt(II) but does not to Ni(II). Kinetic parameters (E ^#, n, ΔH ^#, ΔS ^#, ΔG ^#) of the decomposition stages are determined and correlated with bonding and structural properties of the complexes. The EI mass spectra of the complexes show fragments corresponding to the evolved and intermediate species.     

Purification, characterization, kinetic properties, and thermal behavior of extracellular polygalacturonase produced by filamentous fungus Tetracoccosporium sp

For the first time, a polygalacturonase from the culture broth of Tetracoccosporium sp. was isolated and incubated at 30°C in an orbital shaker at 160 rpm for 48h. The enzyme was purified by ammonium sulfate precipitation and two-step ion-exchange chromatography and had an apparent molecular mass of 36 kDa, as shown by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. Its optimum activity was at pH 4.3 and 40°C, and the K _m and V _max values of this enzyme (for polygalacturonic acid) were 3.23 mg/mL and 0.15 μmol/min, respectively. Ag⁺, Co²⁺, EDTA, Tween-20, Tween-80, and Triton X-100 stimulated polygalacturonase activity whereas Al³⁺, Ba²⁺, Ca²⁺, Fe²⁺, Fe³⁺, Ni²⁺, Mg²⁺, Mn²⁺, and SDS inhibited it. In addition, iodoacetamide and iodoacetic acid did not inhibit enzyme activity at a concentration of 1 mM, indicating that cysteine residues are not part of the catalytic site of polygalacturonase. We studied the kinetic properties and thermal inactivation of polygalacturonase. This enzyme exhibited a t _1/2 of 63 min at 60°C and its specific activity, turnover number, and catalytic efficiency were 6.17 U/mg, 113.64 min⁻¹, and 35.18 mL/(min·mg), respectively. The activation energy (ΔE ^#) for heat inactivation was 5.341 kJ/mol, and the thermodynamic activation parameters ΔG ^#, ΔH ^#, and ΔS ^# were also calculated, revealing a potential application for the industry.     

The study of alanine oscillating reaction catalyzed by tetraazamacrocyclic nickel(II) complex

A closed oscillation system comprised of alanine, KBrO₃, H₂SO₄ and acetone catalyzed by tetraazamacrocyclic nickel(II) complex is introduced, and quantitatively characterized with kinetic parameters, namely the rate constant (k _in, k _p), the apparent activation energy (E _in, E _p) and pre-exponential constant (A _in, A _p) and thermodynamic functions (ΔH _in, ΔG _in, ΔS _in and ΔH _p, ΔG _p, ΔS _p), where indexes “in” and “p” mean “induction period” and “oscillation period,” respectively. The results indicate that tetraazamacrocyclic nickel(II) complex can catalyze alanine oscillating reaction and the reaction corresponds exactly to the feature of irreversible thermodynamics as the entropy of system is negative.