Influence of copper(II) catalyst on the oxidation of l-histidine by platinum(IV) in alkaline medium: a kinetic and mechanistic study

The kinetics of oxidation of l-histidine (His) by platinum(IV) in the absence and presence of copper(II) catalyst was studied using spectrophotometry in alkaline medium at a constant ionic strength of 0.1 mol dm^?3 and at 25 °C. In both cases, the reactions exhibit a 1:1 stoichiometry ([His]:[Pt^IV]). The rate of the uncatalyzed reaction is dependent on the first power of each of the concentrations of oxidant, substrate and alkali. The catalyzed path shows a first-order dependence on both [Pt^IV] and [Cu^II], but the order with respect to both [His] and [OH^?] is less than unity. The rate constants increase with increasing ionic strength and dielectric constant of the medium. The catalyzed reaction has been shown to proceed via formation of a copper(II)^_histidine intermediate complex, which reacts with the oxidant by an inner-sphere mechanism leading to decomposition of the complex in the rate-determining step. Platinum(IV) is reduced to platinum(II) by the substrate in a one-step two-electron transfer process. This is followed by other fast steps, giving rise to the oxidation products which were identified as 2-imidazole acetaldehyde, ammonia and carbon dioxide. A tentative reaction mechanism is suggested, and the associated rate laws are deduced. The activation parameters with respect to the slow step of the mechanism are reported and discussed.     

Observation of the Properties of a Single Unit of a Limited CDW Structure in a PtII/PtIV Host–Guest Binary System Based on a Square‐Shaped Complex

A macrocyclic tetranuclear platinum(II) complex [Pt(en)(4,4′‐bpy)]₄(NO₃)₈ ( 1 ?(NO₃)₈; en=ethylenediamine, 4,4′‐bpy=4,4′‐bipyridine) and a mononuclear platinum(IV) complex [Pt(en)₂Br₂]Br₂ ( 2 ?Br₂) formed two kinds of Pt^II/Pt^IV mixed valence assemblies when reacted: a discrete host–guest complex 1 ? 2 ?Br₁₀ ( 3 ) and an extended 1‐D zigzag sheet 1 ?( 2 )₃?Br₈(NO₃)₆ ( 4 ). Single crystal X‐ray analysis showed that the dimensions of the assemblies could be stoichiometrically controlled. Resonance Raman spectra suggested the presence of an intervalence interaction, which is typically observed for quasi‐1‐D halogen‐bridged M^II/M^IV complexes. The intervalence interaction indicates the presence of an isolated {Pt^II???X? Pt^IV? X???Pt^II} moiety in the structure of 4 . On the basis of electronic spectra and polarized reflectance measurements, we conclude that 4 exhibits intervalence charge transfer (IVCT) bands. A Kramers–Kronig transformation was carried out to obtain an optical conductivity spectrum, and two sub‐bands corresponding to slightly different Pt^II–Pt^IV distances were observed.     

DNA Binding and Equilibrium Investigation of the Interaction of a Model Pd(II) Complex with Some Selected Biorelevant Ligands

The Pd(DAP)Cl₂ complex, where DAP is 2,6-diaminopyridine, was synthesized and characterized. The stoichiometries and stability constants of the complexes formed between various biologically relevant ligands (amino acids, amides, DNA constituents, and dicarboxylic acids) and [Pd(DAP)(H₂O)₂]²⁺ were investigated at 25 °C and at constant 0.1 mol·dm^?3 ionic strength. The concentration distribution diagrams of the various species formed were evaluated. A further investigation of the binding properties of the diaqua complex [Pd(DAP)(H₂O)₂]²⁺ with calf thymus DNA (CT-DNA) was investigated by UV–Vis spectroscopy. The intrinsic binding constants (K _b) calculated from UV–Vis absorption studies is 1.04 × 10³ mol·dm^?3. The calculated (K _b) value was found to be of lower magnitude than that of the classical intercalator EB (ethidium bromide) (K _b = 1.23 (±0.07) × 10⁵ mol·dm^?3), suggesting an electrostatic and/or groove binding mode for the interaction with CT-DNA.     

A one‐dimensional iodine‐bridged PtII/PtIV mixed‐valence complex,catena‐poly[[[bis­(ethyl­ene­diamine)­platinum(II)]‐μ‐iodo‐[bis­(ethyl­ene­di­amine)platinum(IV)]‐μ‐iodo] hydrogenphosphate dihydrogenphosphate iodide trihydrate]

The title compound, {[Pt^IIPt^IVI₂(C₂H₈N₂)₄](HPO₄)(H₂PO₄)I·3H₂O}_n, has a chain structure composed of square‐planar [Pt(en)₂]²⁺ and elongated octa­hedral trans‐[PtI₂(en)₂]²⁺ cations (en is ethyl­ene­diamine) stacked alternately along the c axis and bridged by the I atoms; a three‐dimensionally valence‐ordered system exists with respect to the Pt sites. The title compound also has a unique cyclic tetra­mer structure composed of two hydrogenphosphate and two dihydrogenphosphate ions connected by strong hydrogen bonds [O⋯O = 2.522 (10), 2.567 (10) and 2.569 (11) Å]. The Pt and I atoms form a zigzag ⋯I—Pt^IV—I⋯Pt^II⋯ chain, with Pt^IV—I bond distances of 2.6997 (7) and 2.6921 (7) Å, inter­atomic Pt^II⋯I distances of 3.3239 (8) and 3.2902 (7) Å, and Pt^IV—I⋯Pt^II angles of 154.52 (3) and 163.64 (3)°. The structural parameters indicating the mixed‐valence state of platinum, expressed by δ = (Pt^IV—I)/(Pt^II—I), are 0.812 and 0.818 for the two independent I atoms.     

A one‐dimensional chloride‐bridged PtII/PtIV mixed‐valence complex with a 4‐[(4‐hydroxyphenyl)diazenyl]benzenesulfonate counter‐ion

The title compound, catena‐poly[[[bis(ethylenediamine‐κ²N,N′)platinum(II)]‐ μ‐chlorido‐[bis(ethylenediamine)platinum(IV)]‐μ‐chlorido] tetrakis{4‐[(4‐hydroxyphenyl)diazenyl]benzenesulfonate} dihydrate], {[Pt^IIPt^IVCl₂(C₂H₈N₂)₄](HOC₆H₄N=NC₆H₄SO₃)₄·2H₂O}_n, has a linear chain structure composed of square‐planar [Pt(en)₂]²⁺ (en is ethylenediamine) and elongated octahedral trans‐[PtCl₂(en)₂]²⁺ cations stacked alternately, bridged by Cl atoms, along the b axis. The Pt atoms are located on an inversion centre, while the Cl atoms are disordered over two sites and form a zigzag ...Cl—Pt^IV—Cl...Pt^II... chain, with a Pt^IV—Cl bond length of 2.3140 (14) Å, an interatomic Pt^II...Cl distance of 3.5969 (15) Å and a Pt^IV—Cl...Pt^II angle of 170.66 (6)°. The structural parameter indicating the mixed‐valence state of the Pt atom, expressed by δ = (Pt^IV—Cl)/(Pt^II...Cl), is 0.643.     

Electrosynthesis of Poly(azure B) from Sulfuric Acid Solution

Electrochemical polymerization of azure B from sulfuric acid solution was carried out by using cyclic voltammetry. The electrolytic solution consisted of 5.0 mmol · dm^?3 azure B and 0.3 mol · dm^?3 H₂SO₄. The temperature for polymerization was controlled at 20°C. A blue film, i.e., poly(azure B) was formed on a platinum foil and had a electrochemical reversibility, stability and a fast charge transfer ability in the 0.5 mol · dm^?3 Na₂SO₄ with pH ≤4.0 solution. The currents of both anodic and cathodic peaks are proportional to υ^1/2 at the scan rate (υ) region of 25 and 600 mV · s^?1 on the cyclic voltammograms. The conductivity of poly(azure B) is 2.8×10^?6 S · cm^?1 at 20°C. The UV‐visible spectrum and Raman spectrum of the polymer are different from those of the monomer. A possible polymerization mechanism of azure B was also proposed.     

Mechanistic Study of Oxidation of Palladium(II) by Cerium(IV) in Aqueous Acid

The kinetics of oxidation of Pd^II by Ce^IV have been studied spectrophotometrically in HClO₄ media at 40 °C. The reaction is first order each in [Ce^IV] and [Pd^II] at constant [H⁺]. Increasing [H⁺] accelerates the reaction rate with fractional order in [H⁺]. The initially added products, palladium(IV) and cerium(III) do not have any significant effect on the reaction rate. At constant acidity, increasing the added chloride concentration enhances the rate of reaction. H₃Ce(SO₄)₄⁻ and PdCl₄²⁻ are the active species of oxidant and reductant respectively. The possible mechanisms are proposed and the reaction constants involved have been determined.     

Ferric Chloride Complexes in Aqueous Solution: An EXAFS Study

A series of concentrated aqueous solutions of ferric chloride with different chloride:iron(III) ratios has been studied by means of EXAFS to determine the structure around the iron(III) ion of the dominating species in such solutions. The dominating species in dilute acidic aqueous solution of ferric chloride, at less than 1 mmol·dm^?3, are the hydrated iron(III) and chloride ions, while in concentrated aqueous solution and in solutions with an excess of chloride ions, up to 1.0 mol·dm^?3, it is the trans-[FeCl₂(H₂O)₄]⁺ complex. Possible higher chloroferrate(III) or dimeric [Fe₂Cl₆] complexes at room temperature, as proposed in the literature, were not observed in any of the studied solutions in spite of an excess of chloride ions of 1 mol·dm^?3.     

Die Fällung des PdII als [Pd(NH3)2Cl2] sowie das Verhalten verschiedener Begleitelemente

Precipitation of Pd^II as [Pd(NH₃)₂Cl₂] and the Behaviour of Various Impurities The dependence of [Pd(NH₃)₂Cl₂] precipitation upon reaction conditions (pH, Cl^? content, reaction time, temperature) has been studied. The dependence of residual Pd content in the mother liquor upon these parameters was found to be significant only for the precipitation temperature (c_Pd at 20°C: 1.65 ± 0.11 mM; at 50°C: 6.70 ± 0.58 mM). The increase of Pd concentration was due to the formation of Pd(NH₃)Cl₃^?. Among the impurities studied Cr, Ru, and Au were largely precipitated in the NH₃ medium. In subsequent precipitation of [Pd(NH₃)₂Cl₂] the following order of coprecipitation was found: The first four elements could be separated only incompletely by repeated reprecipitation. The coprecipitation of the platinum-group metals and of Au was highly dependence upon preceding formation of ammine complexes of these elements. The considerable coprecipitation of Pt^IV is presumably due to the formation of mixed Pd/Pt compounds, whereas the other impurities are adsorbed by [Pd(NH₃)₂Cl₂].     

Mixed and partial oxidation states. Photoelectron spectroscopic evidence

X-ray photoelectron spectra of the single valence platinum complexes K₂[Pt(CN)₄] · 3H₂O(1),K₂[Pt(CN)₄]Cl_0.3 · n H₂O(2) and K₂[Pt(CN)₄]Cl₂ · 3H₂O(3) and the mixed valence compound [Pt^II(C₂H₅NH₂)₄]Cl₄ · [Pt^IV (C₂H₅NH₂)₄Cl₂] · 4H₂O(4) have been measured. It is found that one can distinguish clearly between mixed and single valence compounds by electron spectroscopy. The Pt spectrum of (4) is a superposition of a Pt^II and Pt_IV spectrum. The chemical shift between (1) and (3) is normal, however (2) shows an anomalous low binding energy for the Pt 4f electrons. The importance of using reliable reference peaks for obtaining absolute binding energies is emphasized.     

cis‐[1,2‐Bis(diisopropylphosphino‐κP)‐1,2‐dicarba‐closo‐dodecaborane]dichloroplatinum(II) dichloromethane hemisolvate

The asymmetric unit of the title complex, [PtCl₂(C₁₄H₃₈B₁₀P₂)]·0.5CH₂Cl₂ or cis‐[PtCl₂{1,2‐(PⁱPr₂)₂‐1,2‐C₂B₁₀H₁₀}]·0.5CH₂Cl₂, contains one disordered solvent mol­ecule and two mol­ecules of the complex, in which each Pt^II atom displays slightly distorted square‐planar coordination geometry. The P atoms connected to the cage C atoms are coordinated to the Pt^II atom. The Pt—P distances vary slightly [2.215 (3) and 2.235 (4) Å] and the Pt—Cl distances are equal [2.348 (3) and 2.353 (5) Å].     

Palladium(II) inhibition during cerium(IV) oxidation of aldoses: a kinetic study

Summary The kinetics of oxidation of aldoses, namely xylose, arabinose, galactose and glucose, by Ce^IV have been studied in HClO₄ + H₂SO₄ medium and in the presence of Pd^II. The reactions exhibit a first order rate dependence with respect to oxidant. The rate is inversely dependent on the [HSO _inf4 ^sup– ][H⁺] ratio. The order of reaction with respect to aldose decreases at higher [aldose]. Due to the formation of a complex between Ce^IV and Pd^II, a retarding effect of [Pd^II] on the rate of disappearance of [Ce^IV] has been observed. A mechanism consistent with the observed kinetic data is proposed.     

Kinetics and mechanism of the redox reaction between malachite green and iron(III) in aqueous and micellar media

The kinetics of the oxidation of malachite green (MG⁺) by Fe(III) were investigated spectrophotometrically by monitoring the absorbance change at 618 nm in aqueous and micellar media at a temperature range 20–40 °C; I = 0.10 mol dm^?3 for [H⁺] range (2.50–15.00) × 10^?4 mol dm^?3. The rate of reaction increases with increasing [H⁺]. The reaction was carried out under pseudo-first-order conditions by taking the [Fe(III)] (>10-fold) the [MG⁺]. A mechanism of the reaction between malachite green and Fe(III) is proposed, and the rate equation derived from the mechanism was consistent with the experimental rate law as follows: Rate = (k ₄ + K ₁ k ₅[H⁺]) [MG⁺][Fe(III)]. The effect of surfactants, such as cetyltrimethylammonium bromide (CTAB, a cationic surfactant) and sodium dodecylsulfate (SDS, an anionic surfactant), on the reaction rate has been studied. CTAB has no effect on the rate of reaction while SDS inhibits it. Also, the effect of ligands on the reaction rate has been investigated. It is proposed that electron transfer proceeds through an outer-sphere mechanism. The enthalpy and the entropy of the activation were calculated using the transition state theory equation.     

Solvolysis of palladium(II) and platinum(II) complexes of asymmetric ligands: Synthesis and structural characterization of [Pd(AMP)(dmso)Cl]BF4 and [Pt(AMP)(dmso)Cl]ClO4

Treatment of [M(AMP)Cl₂] (M = Pt^II, Pd^II; AMP = 2-aminomethylpyridine) with 1 mole of AgX (X = ClO₄, BF₄, PF₆) in dmso yields [M(AMP)(dmso)Cl]X. Single crystal X-ray structure determinations of the Pd^II and Pt^II complexes indicate that dmso is S-bondedtrans to the pyridyl ring in both complexes. (2-Aminomethylpyridine)chloro(dimethylsulphoxide-S) palladium(II) tetrafluoroborate.     

Applicability of Derivative Spectrophotometry,Bivariate Calibration Algorithm,and the Vierordt Method for Simultaneous Determination of Ranitidine and Amoxicillin in Their Binary Mixtures

Abstract

Ultraviolet (UV)–derivative spectrophotometry, bivariate calibration algorithm, and Vierodt methods were applied to simultaneous determination of ranitidine (R) and amoxicillin (AMX) in binary mixtures. The first-order derivative allows determination of R in the concentration range 4.0 · 10^?6 mol · dm^?3 to 6.0 · 10^?5 mol · dm^?3. Vierordt method enables Ranitidine assaying in the presence of 2.5-fold excess of AMX and 3-fold excess of R. The bivariate calibration method obeys Beer's law in the concentration ranges 4.0 · 10^?6 mol · dm^?3 to 6.0 · 10^?5 mol · dm^?3 for R and 2.0 · 10^?6 to 2.0 · 10^?5 mol · dm^?3 for AMX.     

Kinetics and mechanism of palladium(II) catalyzed chromium(VI) oxidation of mercury(I) in aqueous sulphuric acid

The Cr^VI oxidation of Hg^I in an aqueous acid medium occurs to a modest extent only in presence of Pd^II and in H₂SO₄ above ca. 0.20 mol dm^–3. The reaction is first order in [Cr^VI] in the presence of Pd^II catalyst. The order in [Hg^I] is less than unity, whereas that in [Pd^II] is unity. Increase in [H₂SO₄] accelerates the reaction rate. The added products, Cr^III and Hg^II, do not significantly effect the reaction rate. A mechanism involving HCrO₄ ^– and PdCl⁺ as the reactive species of oxidant and catalyst respectively, is proposed. The reaction constants involved in the mechanism have been evaluated.     

Synthesis, characterization and electro-spectroelectrochemical studies of four macrocyclic Schiff-base Co(II) complexes having N2O2 set of donor atoms

Four macrocyclic Schiff-base cobalt complexes, [CoL¹][NO₃]₂ · 3H₂O, [CoL²][NO₃]₂ · 4H₂O, [CoL³][NO₃]₂ · 4H₂O and [CoL⁴][NO₃]₂ · 2H₂O, were synthesized by reaction of salicylaldehyde derivatives with 1,4-bis(3-aminopropoxy)butane or (±)-trans-1,2-diaminocyclohexane and Co(NO₃)₂ · 6H₂O by template effect in methanol. The metals to ligand ratio of the complexes were found to be 1:1. The Co(II) complexes are proposed to be tetrahedral geometry. The macrocyclic Co(II) complexes are 1:2 electrolytes as shown by their molar conductivities (Λ_M) in DMF (dimethyl formamide) at 10^?3 M. The structure of Co(II) complexes is proposed from elemental analysis, Ft-IR, UV–visible spectra, magnetic susceptibility, molar conductivity measurements and mass spectra. Electrochemical and thin-layer spectroelectrochemical studies of the complexes were comparatively studied in the same experimental conditions. The electrochemical results revealed that all complexes displayed irreversible one reduction processes and their cathodic peak potential values (E _pc) were observed in around of ?1.14 to 0.95 V. It was also seen that [CoL¹][NO₃]₂ · 3H₂O and [CoL²][NO₃]₂ · 4H₂O exhibited one cathodic wave without corresponding anodic wave but, [CoL³][NO₃]₂ · 4H₂O and [CoL⁴][NO₃]₂ · 2H₂O showed one cathodic wave with corresponding anodic wave, probably due to the presence of different ligand nature even if the complexes have the same N₂O₂ donor set. In view of spectroelectrochemical studies [CoL³][NO₃]₂ · 4H₂O showed distinctive spectral changes in which the intensity of the band (λ = at 316 nm, assigned to n → π* transitions) decreased and a new broad band in a low intensity about 391 nm appeared as a result of the reduction process based on the cobalt center in the complex.     

Mechanism of the oxidation of hydrazoic acid by tetrachloroaurate(III) ion

The oxidation of hydrazoic acid in perchloric acid in the absence of added chloride under pseudo first-order conditions ([HN₃] » [AuCl ₄ ^? ]) is first order in [Au(III)]. Michaelis–Menten type of dependence (linear plots of k _obs ^?1 vs [HN₃]^?1) is observed with respect to [HN₃]. The k _obs is independent of ionic strength and the plot between k _obs ^?1 and [H⁺] is linear. The inner-sphere mechanism is consistent with the formation of an axial complex (K = 25 dm³ mol^?1) between AuCl₃(HO)^? ion and HN₃ prior to its rate determining decomposition (k = 0.0182 s^?1). It is inferred that the free radicals N ₃ ^? do not oxidise Au(II). The reaction becomes outer-sphere in the presence of added Cl^? ions which are inferred to form a cage around the hydronium ion surrounding the AuCl ₄ ^? ions. The penetration of N ₃ ^? through the cage is rate controlling and within the cage, the electron transfer from N ₃ ^? ion to AuCl ₄ ^? is fast. The value of the rate determining constant k ₂ is 0.547 dm³ mol^?1 s^?1 and the equilibrium constant K _Cl for the cage formation is 5 dm³ mol^?1 at 25 °C. It is calculated that the minimum HN₃ concentration required before the reaction exhibits zero-order dependence in HN₃ is 0.31 mol dm^?3 when [H⁺] = 0.18 mol dm^?3 at 25 °C.     

Photolysis and Thermolysis of Platinum(IV) 2,2′‐Bipyridine Complexes Lead to Identical Platinum(II)–DNA Adducts

Two Pt^IV and two Pt^II complexes containing a 2,2′‐bipyridine ligand were treated with a short DNA oligonucleotide under light irradiation at 37 °C or in the dark at 37 and 50 °C. Photolysis and thermolysis of the Pt^IV complexes led to spontaneous reduction of the Pt^IV to the corresponding Pt^II complexes and to binding of Pt^II 2,2′‐bipyridine complexes to N7 of guanine. When the reduction product was [Pt(bpy)Cl₂], formation of bis‐oligonucleotide adducts was observed, whereas [Pt(bpy)(MeNH₂)Cl]⁺ gave monoadducts, with chloride ligands substituted in both cases. Neither in the dark nor under light irradiation was the reductive elimination process of these Pt^IV complexes accompanied by oxidative DNA damage. This work raises the question of the stability of photoactivatable Pt^IV complexes toward moderate heating conditions.     

Halometallate Complexes of Germanium(II) and (IV): Probing the Role of Cation,Oxidation State and Halide on the Structural and Electrochemical Properties

The Ge^IV chlorometallate complexes, [EMIM]₂[GeCl₆], [EDMIM]₂[GeCl₆] and [PYRR]₂[GeCl₆] (EMIM=1‐ethyl‐3‐methylimidazolium; EDMIM=2,3‐dimethyl‐1‐ethylimidazolium; PYRR=N‐butyl‐N‐methylpyrrolidinium) have been synthesised and fully characterised; the first two also by single‐crystal X‐ray diffraction. The imidazolium chlorometallates exhibited significant C?H???Cl hydrogen bonds, resulting in extended supramolecular assemblies in the solid state. Solution ¹H NMR data also showed cation–anion association. The synthesis and characterisation of Ge^II halometallate salts [EMIM][GeX₃] (X=Cl, Br, I) and [PYRR][GeCl₃], including single‐crystal X‐ray analyses for the homologous series of imidazolium salts, are reported. In these complexes, the intermolecular interactions are much weaker in the solid state and they appear not to be significantly associated in solution. Cyclic‐voltammetry experiments on the Ge^IV species in CH₂Cl₂ solution showed two distinct, irreversible reduction waves attributed to Ge^IV–Ge^II and Ge^II–Ge⁰, whereas the Ge^II species exhibited one irreversible reduction wave. The potential for the Ge^II–Ge⁰ reduction was unaffected by changing the cation, although altering the oxidation state of the precursor from Ge^IV to Ge^II does have an effect; for a given cation, reduction from the [GeCl₃]^? salts occurred at a less cathodic potential. The nature of the halide co‐ligand also has a marked influence on the reduction potential for the Ge^II–Ge⁰ couple, such that the reduction potentials for the [GeX₃]^? salts become significantly less cathodic when the halide (X) is changed Cl→Br→I.