Sulfanilamide copper(II) chelates with 2-[(2-hydroxyphenyl-imino)methyl]phenolom and 1-[(2-hydroxyphenylimino)-methyl]naphthalen-2-ol

2-[(2-Hydroxyphenylimino)methyl]phenol (H²L¹) and 1-[(2-hydroxyphenylimino)methyl]naphthalen-2-ol (H²L²) reacted with copper(II) acetate hydrate and sulfanilamide (Sf¹), sulfathiazole (Sf²), sulfaethidole (Sf³), sulfadiazine (Sf⁴), and sulfadimidine (Sf⁵) in ethanol to give mixed-ligand copper chelates with the composition Cu(Sf^1–5)(L^1–2) · n H₂O (n = 1, 2). All these complexes are monomeric. Salicylaldehyde imines (H₂L¹ and H₂L²) behave as doubly deprotonated tridentate O,N,O ligands, whereas sulfanilamides (Sf^1–5) are unidentate ligands. Thermolysis of the synthesized complexes includes dehydration at 70–90°C, followed by complete thermal decomposition (290–380°C). The complexes [Cu(Sf¹)(L¹)] · 2H₂O and [Cu(Sf³)(L¹)] · H₂O at a concentration of 10⁻⁴ M inhibited growth and reproduction of 100% of human myeloid leukemia cells (HL-60). The inhibitory effect was 90 and 75%, respectively, at a concentration of 10⁻⁵ M, whereas no antitumor activity was observed at a concentration of 10⁻⁶ M.     

Kinetics and mechanism of the reaction between chromium(III) and picolinic acid in weak acidic aqueous solution

Abstract  

The interaction between chromium(III) and picolinic acid in weak acid aqueous solution was studied, resulting in the formation of a complex upon substitution of water molecules in the chromium(III) coordination sphere. Experimental results show that the reaction takes place in multiple steps. The first step is the formation of an ion pair, the second step (two consecutive steps) is the slow one corresponding to substitution of the first water molecule from the chromium aqueous complex coordination sphere by a picolinic acid molecule via oxygen atom of the carboxylic acid group and substitution of the second water molecule via nitrogen of the pyridine ring forming an 1:1 complex. Both consecutive steps were independent of chromium concentration. The rate constants of the 1st and 2nd consecutive steps were increased by increasing picolinic acid concentration. The corresponding activation parameters are ∆H _1obs ^* = 28.4 ± 4 kJ mol⁻¹, ∆S _1obs ^* = −202 ± 26 J K⁻¹ mol⁻¹, ∆H _2obs ^* = 39.6 ± 5 kJ mol⁻¹, and ∆S _2obs ^* = −175 ± 19 J K⁻¹ mol⁻¹. The third step is fast, corresponding to formation of the final complex [Cr(pic)₃]. The logarithms of the formation constants of 1:1 and 1:3 complexes were found to be 1.724 and 4.274, respectively.     

Thermal behavior and thermal safety on 3,3-dinitroazetidinium salt of perchloric acid

3,3-Dinitroazetidinium (DNAZ) salt of perchloric acid (DNAZ·HClO₄) was prepared, it was characterized by the elemental analysis, IR, NMR, and a X-ray diffractometer. The thermal behavior and decomposition reaction kinetics of DNAZ·HClO₄ were investigated under a non-isothermal condition by DSC and TG/DTG techniques. The results show that the thermal decomposition process of DNAZ·HClO₄ has two mass loss stages. The kinetic model function in differential form, the value of apparent activation energy (E _a) and pre-exponential factor (A) of the exothermic decomposition reaction of DNAZ·HClO₄ are f(α) = (1 − α)⁻¹/2, 156.47 kJ mol⁻¹, and 10^15.12 s⁻¹, respectively. The critical temperature of thermal explosion is 188.5 °C. The values of ΔS ^≠, ΔH ^≠, and ΔG ^≠of this reaction are 42.26 J mol⁻¹ K⁻¹, 154.44 kJ mol⁻¹, and 135.42 kJ mol⁻¹, respectively. The specific heat capacity of DNAZ·HClO₄ was determined with a continuous C _p mode of microcalorimeter. Using the relationship between C _p and T and the thermal decomposition parameters, the time of the thermal decomposition from initiation to thermal explosion (adiabatic time-to-explosion) was evaluated as 14.2 s.     

Evaluation of kinetic parameters of uranyl acetate complexes in ethanolic solution by cyclic voltammetry

The complexation of uranyl ion with acetate ions was investigated in 20% ethanolic solution by using cyclic voltammetry. The uranium formed 1:1 and 1:2 complexes with acetate ions. The values of log β₁ and log β₂ for uranyl acetate complexes were 2.05 ± 0.08 and 5.25 ± 0.06 respectively. The diffusion coefficient and heterogeneous rate constants for the reduction of uranyl ion at hanging mercury drop electrode in 20% ethanolic solution of acetate ions were 0.43 × 10⁻⁵ cm² s⁻¹ and 2.26 × 10⁻³ cm s⁻¹, respectively. Thermodynamic parameters were also evaluated by finding the effect of temperature on the heterogeneous rate constants. The values of ΔH ^*, ΔS ^* and \Updelta G₂₉₈^* \Updelta G_{298}^{*} were 2.52 kJ mol⁻¹, −43.8 J mol⁻¹ K⁻¹ and 15.57 kJ mol⁻¹. The positive values of ΔH ^* and \Updelta G₂₉₈^* \Updelta G_{298}^{*} indicated that electrochemical reduction of uranyl ions in ethanolic solution of acetate ions is an endothermic and non-spontaneous process.     

A kinetic investigation of the oxidation of <Emphasis Type="SmallCaps">dl</Emphasis>-pipecolinate by bis(hydrogenperiodato)argentate(III) complex anion

Kinetics of oxidation of dl-pipecolinate by bis(hydrogenperiodato)argentate(III) complex anion, [Ag(HIO₆)₂]⁵⁻, has been studied in aqueous alkaline medium in the temperature range of 25–40 °C. The oxidation kinetics is first order in the silver(III) and pipecolinate concentrations. The observed second-order rate constant, decreasing with increasing [periodate] is virtually independent of [OH⁻]. α-Aminoadipate as the major oxidation product of pipecolinate has been identified by chromatographic analysis. A reaction mechanism is proposed that involves a pre-equilibrium between [Ag(HIO₆)₂]⁵⁻ and [Ag(HIO₆)(H₂O)(OH)]²⁻, a mono-periodate coordinated silver(III) complex. Both Ag(III) complexes are reduced in parallel by pipecolinate in rate-determining steps (described by k ₁ for the former Ag(III) species and k ₂ for the latter). The determined rate constants and their associated activation parameters are k ₁ (25 °C) = 0.40 ± 0.02 M⁻¹ s⁻¹, ∆H ₁^≠ = 53 ± 2 kJ mol⁻¹, ∆S ₁^≠ = −74 ± 5 J K⁻¹ mol⁻¹ and k ₂ (25 °C) = 0.64 ± 0.02 M⁻¹ s⁻¹, ∆H ₂^≠ = 41 ± 2 kJ mol⁻¹, ∆S ₂^≠ = −110 ± 5 J K⁻¹ mol⁻¹. The time-resolved spectra, a positive dependence of the rate constants on ionic strength of the reaction medium, and the consistency of pre-equilibrium constants derived from different reaction systems support the proposed reaction mechanism.     

Multispectroscopic DNA interaction studies of a water-soluble nickel(II) complex containing different dinitrogen aromatic ligands

The water-soluble Ni(II) complex, [Ni(bipy)₂(phen-dione)](OAc)₂·2H₂O (bipy = 2,2′-bipyridine and phen-dione = 1,10-phenanthroline-5,6-dione) has been synthesized and characterized by physico-chemical and spectroscopic methods. The binding interactions of this complex with calf thymus DNA (CT-DNA) were investigated using fluorimetry, spectrophotometry, circular dichroism and viscosimetry. In fluorimetric studies, the enthalpy and entropy of the reaction between the complex and CT-DNA showed that the reaction is exothermic (ΔH = −123.9 kJ mol⁻¹; ΔS = −323.5 J mol⁻¹ K⁻¹). The competitive binding studies showed that the complex could not release methylene blue completely. The complex showed absorption hyperchromism in its UV–Vis spectrum with DNA. The calculated binding constant, K _b obtained from UV–Vis absorption studies was 2 × 10⁵ M⁻¹. Moreover, the complex induced detectable changes in the CD spectrum of CT-DNA, as well as changes in its viscosity. The results suggest that this nickel(II) complex interact with CT-DNA via a groove-binding mode.     

Thermodynamics of sodium 5-methylisophthalic acid monohydrate and sodium isophthalic acid hemihydrate

Two crystal samples, sodium 5-methylisophthalic acid monohydrate (C₉H₆O₄Na₂·H₂O, s) and sodium isophthalic acid hemihydrate (C₈H₄O₄Na₂·1/2H₂O, s), were prepared from water solution. Low-temperature heat capacities of the solid samples for sodium 5-methylisophthalic acid monohydrate (C₉H₆O₄Na₂·H₂O, s) and sodium isophthalic acid hemihydrate (C₈H₄O₄Na₂·1/2H₂O, s) were measured by a precision automated adiabatic calorimeter over the temperature range from 78 to 379 K. The experimental values of the molar heat capacities in the measured temperature region were fitted to a polynomial equation on molar heat capacities (C _p,m) with the reduced temperatures (X), [X = f(T)], by a least-squares method. Thermodynamic functions of the compounds (C₉H₆O₄Na₂·H₂O, s) and (C₈H₄O₄Na₂·1/2H₂O, s) were calculated based on the fitted polynomial equation. The constant-volume energies of combustion of the compounds at T = 298.15 K were measured by a precise rotating-bomb combustion calorimeter to be Δ_c U(C₉H₆O₄Na₂·H₂O, s) = −15428.49 ± 4.86 J g⁻¹ and Δ_c U(C₈H₄O₄Na₂·1/2H₂O, s) = −13484.25 ± 5.56 J g⁻¹. The standard molar enthalpies of formation of the compounds were calculated to be Δ _f H _m ^θ (C₉H₆O₄Na₂·H₂O, s) = −1458.740 ± 1.668 kJ mol⁻¹ and Δ _f H _m ^θ (C₈H₄O₄Na₂·1/2H₂O, s) = −2078.392 ± 1.605 kJ mol⁻¹ in accordance with Hess’ law. The standard molar enthalpies of solution of the compounds, Δ _sol H _m ^θ (C₉H₆O₄Na₂·H₂O, s) and Δ _sol H _m ^θ (C₈H₄O₄Na₂·1/2H₂O, s), have been determined as being −11.917 ± 0.055 and −29.078 ± 0.069 kJ mol⁻¹ by an RD496-2000 type microcalorimeter. In addition, the standard molar enthalpies of hydrated anion of the compounds were determined as being Δ _f H _m ^θ (C₉H₆O₄ ²⁻, aq) = −704.227 ± 1.674 kJ mol⁻¹ and Δ _f H _m ^θ (C₈H₄O₄Na₂ ²⁻, aq) = −1483.955 ± 1.612 kJ mol⁻¹, from the standard molar enthalpies of solution and other auxiliary thermodynamic data through a thermochemical cycle.     

Synthesis, structural characterization and thermal properties of three copper(II) complexes based on aryl hydrazide ligands

The thiosemicarbazide and hydrazide Cu(II) complexes, [Cu₃L₂¹(py)₄Cl₂] (1), [Cu(HL²)py] (2) and [Cu(HL³)py] (3), (H₂L¹ = 1-picolinoylthiosemicarbazide, H₃L² = N′-(2-hydroxybenzylidene)-3-hydroxy-2-naphthohydrazide, H₃L³ = 2-hydroxy-N′-((2-hydroxy-naphthalen-1-yl)methylene)benzohydrazide) have been prepared and characterized through physicochemical and spectroscopic methods as well as X-ray crystallography. Complex 1 has a centrosymmetric structure with –N–N– bridged Cu₃ skeleton. Neighboring molecules are linked into a 3D supermolecular framework by π–π stacking interactions, N–H···Cl and C–H···Cl hydrogen bonds. Complexes 2 and 3 have similar planar structures but different dimers formed by concomitant Cu···N and Cu···O interactions, respectively. Solvent accessible voids with a volume of 391 ?³ are included in the structure of complex 2, indicating that this complex is a potential host candidate. Thermogravimetric analysis shows that the three complexes are stable up to 100 °C.     

An examination of the vaporization enthalpies and vapor pressures of pyrazine, pyrimidine, pyridazine, and 1,3,5-triazine

The vaporization enthalpies and liquid vapor pressures from T = 298.15 K to T = 400 K of 1,3,5-triazine, pyrazine, pyrimidine, and pyridazine using pyridines and pyrazines as standards have been measured by correlation-gas chromatography. The vaporization enthalpies of 1,3,5-triazine (38.8 ± 1.9 kJ mol⁻¹) and pyrazine (40.5 ± 1.7 kJ mol⁻¹) obtained by these correlations are in good agreement with current literature values. The value obtained for pyrimidine (41.0 ± 1.9 kJ mol⁻¹) can be compared with a literature value of 50.0 kJ mol⁻¹. Combined with the condensed phase enthalpy of formation in the literature, this results in a gas-phase enthalpy of formation, Δ_f H _m (g, 298.15 K), of 187.6 ± 2.2 kJ mol⁻¹ for pyrimidine, compared to a value of 195.1 ± 2.1 calculated for pyrazine. Vapor pressures also obtained by correlation are used to predict boiling temperatures (BT). Good agreement with experimental BT (±4.2 K) including results for pyrimidine is observed for most compounds with the exception of the pyridazines. The results suggest that compounds containing one or two nitrogen atoms in the ring are suitable standards for correlating various heterocyclic compounds provided the nitrogen atoms are isolated from each other by carbon. Pyridazines do not appear to be evaluated correctly using pyridines and pyrazines as standards.     

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.     

Thermal behavior of 3,4,5-triamino-1,2,4-triazole dinitramide

The thermal decomposition behavior of 3,4,5-triamino-1,2,4-triazole dinitramide was measured using a C-500 type Calvet microcalorimeter at four different temperatures under atmospheric pressure. The apparent activation energy and pre-exponential factor of the exothermic decomposition reaction are 165.57 kJ mol⁻¹ and 10^18.04 s⁻¹, respectively. The critical temperature of thermal explosion is 431.71 K. The entropy of activation (ΔS ^≠), enthalpy of activation (ΔH ^≠), and free energy of activation (ΔG ^≠) are 97.19 J mol⁻¹ K⁻¹, 161.90 kJ mol⁻¹, and 118.98 kJ mol⁻¹, respectively. The self-accelerating decomposition temperature (T _SADT) is 422.28 K. The specific heat capacity of 3,4,5-triamino-1,2,4-triazole dinitramide was determined with a micro-DSC method and a theoretical calculation method. Specific heat capacity (J g⁻¹ K⁻¹) equation is C _p = 0.252 + 3.131 × 10⁻³  T (283.1 K < T < 353.2 K). The molar heat capacity of 3,4,5-triamino-1,2,4-triazole dinitramide is 264.52 J mol⁻¹ K⁻¹ at 298.15 K. The adiabatic time-to-explosion of 3,4,5-triamino-1,2,4-triazole dinitramide is calculated to be a certain value between 123.36 and 128.56 s.     

Catalytic and Thermodynamic Characterization of Endoglucanase (CMCase) from <Emphasis Type="Italic">Aspergillus oryzae</Emphasis> cmc-1

Monomeric extracellular endoglucanase (25 kDa) of transgenic koji (Aspergillus oryzae cmc-1) produced under submerged growth condition (7.5 U mg⁻¹ protein) was purified to homogeneity level by ammonium sulfate precipitation and various column chromatography on fast protein liquid chromatography system. Activation energy for carboxymethylcellulose (CMC) hydrolysis was 3.32 kJ mol⁻¹ at optimum temperature (55 °C), and its temperature quotient (Q ₁₀) was 1.0. The enzyme was stable over a pH range of 4.1–5.3 and gave maximum activity at pH 4.4. V _max for CMC hydrolysis was 854 U mg⁻¹ protein and K _m was 20 mg CMC ml⁻¹. The turnover (k _cat) was 356 s⁻¹. The pK _a1 and pK _a2 of ionisable groups of active site controlling V _max were 3.9 and 6.25, respectively. Thermodynamic parameters for CMC hydrolysis were as follows: ΔH* = 0.59 kJ mol⁻¹, ΔG* = 64.57 kJ mol⁻¹ and ΔS* = −195.05 J mol⁻¹ K⁻¹, respectively. Activation energy for irreversible inactivation ‘E _a(d)’ of the endoglucanase was 378 kJ mol⁻¹, whereas enthalpy (ΔH*), Gibbs free energy (ΔG*) and entropy (ΔS*) of activation at 44 °C were 375.36 kJ mol⁻¹, 111.36 kJ mol⁻¹ and 833.06 J mol⁻¹ K⁻¹, respectively.     

An ab initio Molecular Orbital Study of the Conformational Properties of all-(Z)-Cyclododeca-1,4,7,10-tetraene

Summary.  Ab initio HF/6-31G^* and MP2/6-31G^*//HF/6-31G^* methods were used to calculate the structure optimization and conformational interconversion pathways for all-(Z )-cyclododeca-1,4,7,10-tetraene. This compound adopts the symmetrical crown (C _4v) conformation. Ring inversion takes place via symmetrical intermediates, such as boat-chair (BC, C _s) and twist (C _2h) conformers and requires about 22.3 kJ · mol⁻¹. The calculated strain energies for BC and twist conformers are 5.9 and 13.5 kJ · mol⁻¹. The results of semiempirical AM1 calculations for structural parameters and relative energies of the important geometries of the title compound are in good agreement with the results of ab initio methods. Received July 9, 2001. Accepted September 26, 2001     

Thermodynamic Investigation of Phase Equilibria in Metal Carbonate–Water–Carbon Dioxide Systems

Summary.  Solubility measurements as a function of temperature have been shown to be a powerful tool for the determination of thermodynamic properties of sparingly-soluble transition metal carbonates. In contrast to calorimetric methods, such as solution calorimetry or drop calorimetry, the evaluation of solubility data avoids many systematic errors, yielding the enthalpy of solution at 298.15 K with an estimated uncertainty of ±3 kJ · mol⁻¹. A comprehensive set of thermodynamic data for otavite (CdCO₃), smithsonite (ZnCO₃), hydrozincite (Zn₅(OH)₆(CO₃)₂), malachite (Cu₂(OH)₂CO₃), azurite (Cu₃(OH)₂(CO₃)₂), and siderite (FeCO₃) was derived. Literature values for the standard enthalpy of formation of malachite and azurite were disproved by these solubility experiments, and revised values are recommended. In the case of siderite, data for the standard enthalpy of formation given by various data bases deviate from each other by more than 10 kJ · mol⁻¹ which can be attributed to a discrepancy in the auxiliary data for the Fe²⁺ ion. A critical evaluation of solubility data from various literature sources results in an optimized value for the standard enthalpy of formation for siderite. The Davies approximation, the specific ion-interaction theory, and the Pitzer concept are used for the extrapolation of the solubility constants to zero ionic strength in order to obtain standard thermodynamic properties valid at infinite dilution, T = 298.15 K, and p = 10⁵ Pa. The application of these electrolyte models to both homogeneous and heterogeneous (solid-solute) equilibria in aqueous solution is reviewed. Received June 26, 2001. Accepted July 2, 2001     

Studies of the reaction of the hydroxyl radical with the oxalate ion in an acidic aqueous solution by pulse radiolysis

The reaction of the · OH radical with the oxalate ion in an acidic aqueous solution was studied by pulse radiolysis. The rate constant for the reaction of formation of the radical HOOC-COO·(λ_max = 250 nm, ɛ = 1800 L mol⁻¹ cm⁻¹) is (5.0±0.5)·107 L mol⁻¹ s⁻¹. In the reaction with the hydrogen ion (k = 1.1·10⁷ L mol⁻¹ s⁻¹), the radical HOOC-COO· is transformed into a nonidentified radical designated arbitrarily as H⁺(HOOC-COO)· (λ_max = 260 nm, ɛ = 4000 L mol⁻¹ cm⁻¹). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1165–1167, June, 2008.     

Copper(II)-Catalyzed Decomposition of Hydrogen Peroxide: Catalyst Activation by Halide Ions

Summary.  The catalytic action of Cu(II) on the decomposition of H₂O₂ in near-neutrality aqueous solutions is activated by halide ions. The activation energies amount to 113±7 (parent reaction) and 69.9±1.4 (chloride-activated reaction) kJ · mol⁻¹. Free-radical chain mechanisms are proposed for both the parent reaction and the halide-activated reaction. The catalyst activation caused by halide ions is explained in terms of coordination of halide ligands by both Cu(II) and Cu(I), the coordination causing a higher stabilization of Cu(I) than of Cu(II). At low concentrations, Br⁻ causes an inhibition of the Cu(II)/H₂O₂ reaction. This is explained in terms of an increase of the rate of termination of the chain reaction due to the scavenging effect of OH radicals caused by Br⁻. Received March 27, 2001. Accepted (revised) May 25, 2001.     

Two Novel 1-D Organic–Inorganic Composite Phosphotungstates Constructed from [Ln(α-PW11O39)2]11− Units and [Cu(en)2]2+ Bridges (Ln = CeIII/ErIII)

Abstract  Two novel organic–inorganic composite phosphotungstates, [H₉{Ce(α-PW₁₁O₃₉)₂}Cu(en)₂] · 6H₂O (1) and H₇[Cu(en)₂{Er(α-PW₁₁O₃₉)₂}Cu(en)₂] · 12H₂O (2) (en = ethylenediamine) have been synthesized by the hydrothermal reaction of the trivacant Keggin polyoxoanion [α-A-PW₉O₃₄]⁹⁻ with Ce^III or Er^III ions in the presence of Cu²⁺ ions and en, and structurally characterized by IR spectra, elemental analysis and thermogravimetric analysis. X-ray crystallographic analyses indicate that they are all built by sandwich-type [Ln(α-PW₁₁O₃₉)₂]¹¹⁻ (Ln = Ce^III, Er^III) polyoxoanions and [Cu(en)₂]²⁺ cations generating infinite one-dimensional arrangements. To our knowledge, this 1-D chain structures constituted by mono-Ln sandwiched POM units and transition-metal complex cations are very rare. Graphical Abstract  Two novel organic–inorganic composite phosphotungstates, [H₉{Ce(α-PW₁₁O₃₉)₂}Cu(en)₂] · 6H₂O (1) and H₇[Cu(en)₂{Er(α-PW₁₁O₃₉)₂}Cu(en)₂] · 12H₂O (2) (en = ethylenediamine) have been synthesized by the hydrothermal reaction of the trivacant Keggin polyoxoanion [α-A-PW₉O₃₄]⁹⁻ with Ce^III or Er^III ions in the presence of Cu²⁺ ions and en, and structurally characterized by IR spectra, elemental analysis and thermogravimetric analysis. X-ray crystallographic analyses indicate that they are all built by sandwich-type [Ln(α-PW₁₁O₃₉)₂]¹¹⁻ (Ln = Ce^III, Er^III) polyoxoanions and [Cu(en)₂]²⁺ cations generating infinite one-dimensional arrangements. To our knowledge, this 1-D chain structures constituted by mono-Ln sandwiched POM units and transition-metal complex cations are very rare.      

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.     

Studies on mono- and dinuclear bisoxime copper complexes with different coordination geometries

Two new mono- and dinuclear Cu(II) complexes, namely [CuL¹]·0.5H₂O (1) and [(Cu₂(L²)₂)(DMF)]·0.5DMF (2) (H₂L¹ = 1,2-bis{[(Z)-(3-methyl-5-oxo-1-phenyl-1H-pyrazolidin-4(4H)-yl)(phenyl)]methylene-aminooxy}ethane; H₂L² = 1,3-bis{[(Z)-(3-methyl-5-oxo-1-phenyl-1H-pyrazolidin-4(4H)-yl)(phenyl)] methyleneaminooxy}propane), have been synthesized and characterized by X-ray crystallography. The unit cell of complex 1 contains two crystallographically independent but chemically identical [CuL¹] molecules and one crystalline water molecule, showing a slightly distorted square-planar coordination geometry and forming a wave-like pattern running along the a-axis via hydrogen bonding and π···π stacking interactions. Complex 2 has a dinuclear structure, comprising two Cu(II) atoms, two completely deprotonated phenolate bisoxime (L²)²⁻ moieties (in the form of enol), and both coordinated and hemi-crystalline DMF molecules. Complex 2 has square-planar and square-pyramidal geometries around the two copper centers, whose basic coordination planes are almost perpendicular and form an infinite three-dimensional supramolecular network structure involving intermolecular C–H···N, C–H···O, and C–H···π(Ph) hydrogen bonding and π···π stacking interactions of neighboring pyrazole rings.     

Synthesis, characterisation and chemical reactivity of some new dioxouranium(VI) complexes of 2-aminobenzoylhydrazone of butane-2,3-dione

A new series of dioxouranium(VI) complexes of a potential ONNO tetradentate donor 2-aminobenzoylhydrazone of butane-2,3-dione (L₁H₂) have been synthesized. At pH 2·5–4·0, the donor (L₁H₂) reacts in the keto form and complexes of the type [UO₂(L₁H₂)(X)₂] (X⁻=Cl⁻, Br⁻, NO ₃ ⁻ , NCS⁻, ClO ₄ ⁻ , CH₃COO⁻, 1/2SO ₄ ²⁻ ) are obtained. At higher pH (6·5–7), the complex of the enol form having the formula [UO₂(L₁)(H₂O)] has been isolated. On reaction with a monodentate lewis base (B), both types of complexes yield adducts of the type [UO₂(L₁)(B)]. All these complexes have been characterised adequately by elemental analyses and other standard physicochemical techniques. Location of the bonding sites of the donor molecule around the uranyl ion, status of the uranium-oxygen bond and the probable structure of the complexes have also been discussed.