Analytical applications of ternary complexes-VI Spectrophotometric determination of trace amounts of palladium

Extremely sensitive and specific colour reactions in both aqueous and organic solutions are described for the spectrophotometric determination of palladium(II) ions. The methods are based upon ternary complex formation with 1,10-phenanthroline or pyridine, and Rose Bengal Extra. Themolar absorptivities are 5 × 10⁴ (aqueous) and 1.25 × 10⁵ (organic) in the presence of a 1000-fold molar excess of EDTA as mass masking agent. Under these conditions there is negligible interference with the pyridine-Rose Bengal Extra system from the 22 cations (including silver, gold and platinum) and seven anions investigated. Both colour reactions take place within 15 min and the complexes are stable for long periods.     

Study of the mixed-metal lanthanummagnesium-purpurin complex: spectrophotometric determination of yttrium and lanthanides

Mixtures of La(III) and Mg(II) form with purpurin (P; 1,2,4-trihydroxyanthraquinone) the mixed-metal complex LaMg₂P₅, which is extracted with methyl isobutyl ketone at pH 7.5. The molar absorptivity of the complex is 6.1 × 10⁴ l.mole⁻¹.cm⁻¹ at 570 nm and its conditional extraction constant 5 × 10¹³ l⁴.mole⁻⁴. Similar complexes have been found to be formed with yttrium, cerium, praseodymium, neodymium and samarium. The use of these complexes for the spectrophotometric determination of yttrium and lanthanides up to 15 μg has been investigated.     

Synthesis of some new o-thioazo ligands and evaluation of their metallochromic properties

The synthesis of several new o-thioazo derivatives of p-cresol and 2-naphthol is reported, as well as their spectral properties, acid dissociation constants, and potential as metallochromic reagents. All the ligands form complexes with CU²⁺ and Ni²⁺. o-Mercaptoazo complexes of Fe³⁺ and Cu²⁺ with molar absorptivities of 3.83 × 10⁴ and 3.58 × 10⁴ l.mole⁻¹ cm⁻¹, respectively, are described.     

Cobalt and nickel complexes bearing 2,6-bis (imino) phenoxy ligands: syntheses, structures and oligomerization studies

A series of new cobalt and nickel complexes LMX₂ (M=Co, X=Cl; M=Ni, X=Br) bearing 2, 6-bis(imino)phenoxy ligands were synthesized. The solid-state structures of 1 and 4 have been determined by single-crystal X-ray diffraction study. Treatment of the complexes LMX₂ with methylaluminoxane (MAO) leads to active catalysts for oligomerization of ethylene with catalytic activities in the range of 1.2×10⁵–2.1×10⁵ g mol⁻¹ h⁻¹ atm⁻¹ for Ni complexes, and 10³ g mol⁻¹ h⁻¹ atm⁻¹ for Co complexes. The oligomers were olefins from C₄ to C₁₆.     

Spectrophotometric investigation of the nature and stability of silver(II) in acidic sulphate media

A spectrophotometric study of silver(II) in sulphuric acid solution indicates the formation of two sulphate complexes, in the range 4–18M H₂SO₄, with absorbance peak maxima at 361 and 260 mμ, respectively. In 15M H₂SO₄ the molar absorptivity of silver(II) is 3.11 × 10⁴ at 361 mμ. Kinetic studies of the reduction of silver(II) by the solvent suggest a rate-determining step first order in silver(II) and yield a pseudo first-order rate constant of 1.9 × 10⁻¹min⁻¹. Further studies as a function of H₂SO₄ concentration show that the specific decomposition rate of the two complexes is identical and that changes in H₂SO₄ concentration only serve to shift the concentration equilibrium between the two complexes.     

Studies on vanadium(IV) complexes of azoxine s dyes

Comparative studies of the reaction of 7-arylazo-8-hydroxyquinoline-5-sulphonic acid (Azoxine S) dyes with vanadium(IV), show that 2:1 yellow, water-soluble complexes are formed over the pH range 2.5–6, and that the phenyl derivative is the most suitable for spectrophotometric determination of 0.2–1.4 ppm of vanadium(IV). The colour is formed instantaneously and is stable for about 8 hr. The molar absorptivity at λ_max, 400 mμ;, is 1.15 × 10⁴, and the equilibrium constant for complex formation is of the order of 10². These dyes can also be used as indicators in the direct complexometric determination of vanadium(IV). The interference of a number of anions and cations is reported.     

Acidity constants of benzidine in aqueous solutions

The acidity constants of benzidine (Bz) in aqueous solutions determined potentiometrically at 25° were K_a1 = (1.11 ± 0.08) × 10⁻⁵, K_a2 = (1.45 ± 0.12) × 10⁻⁴. The apparent mixed constants in 0.1M sodium nitrate are K_a1 = (5.37 ± 0.28) × 10⁻⁶ and K_a2 = (1.14 ± 0.09) × 10⁻⁴. The ultraviolet spectra were recorded as a function of pH and analysed with these constants to obtain the absorption spectra of H₂Bz²⁺, HBz⁺ and Bz; the corresponding wavelengths of maximal absorption are 247, 273 and 278 nm, and molar absorptivities 1.63 × 10⁴, 1.76 × 10⁴ and 2.26 × 10⁴ 1.mole⁻¹.cm⁻¹.     

Evidence for Pdx(CO)y compound formation on an alumina substrate

Although stable binary Pd carbonyls are unknown in the gas phase, we found strong evidence for a stable carbonyl-like Pd compound on an oxide surface: by in situ vapour deposition of Pd at a rate of 2 × 10¹³ atoms s⁻¹ cm⁻² onto an alumina substrate (90 K) at a pressure of 2 × 10⁻⁶ mbar CO, a binary compound of Pd and CO is formed which is stable up to 190 K. As substrate serves a well-ordered aluminium oxide film grown on a NiAl(110) single crystal surface. The system was characterized under UHV (ultrahigh vacuum) conditions by means of TDS, LEED, UPS and XPS in a coverage range between 1.4 × 10¹⁴ Pd atoms cm⁻² and 1.4 × 10¹⁶ Pd atoms cm⁻². The decomposition at 190 K results in the formation of metallic Pd particles and is accompanied by a sharp and dominant feature in the thermal desorption spectra.     

New aspects of the reaction of silver(I) cations with the ethylenediaminetetraacetate ion

The highly neutralized ethylenediaminetetraacetate (EDTA) titrant (95–99% as Y⁴⁻ anion) precipitates with Ag⁺ cations to form the Ag₄Y species, in aqueous medium, which is well characterized from conductometric titration, thermal analysis and potentiometric titration of the silver content of the solid. The precipitate dissolves in excess Y⁴⁻ to form a complex, AgY³⁻. Equilibrium studies at 25°C and ionic strength 0.50 M (NaNO₃) have shown from solubility and potentiometric measurements that the formation constant (95% confidence level) β₁ = (1.93 ± 0.07) × 10⁵ M⁻¹ and the solubility products are K_S0 = [Ag +]⁴[Y⁴⁻] = (9.0 ± 0.4) × 10⁻¹⁸ M⁵ and K_S1 = [Ag +]³[AgY³⁻] = (1.74 ± 0.08) × 10⁻¹² M⁴. The presence of Na⁺, rather than ionic strength, markedly affects the equilibrium; the data at ionic strength 0.10 M are: β₁ = (1.19 ± 0.03) × 10⁶ M⁻¹, K_S0 = (1.6 ± 0.4) × 10⁻¹⁹ M⁵ and K_S1 = (1.9 ± 0.5) × 10⁻¹³ M⁴; at ionic strength tending to zero; β₁ = (1.82 ± 0.05) × 10⁷ M⁻¹, K_S0 = (2.6 ± 0.8) × 10⁻²² M⁵ and K_S1 = (5 ± 1) × 10⁻¹⁵ M⁴. The intrinsic solubility is 2.03 mM silver (I) in 0.50 M NaNO₃. Well-defined potentiometric titration curves can be taken in the range 1–2 mM with the Ag indicator electrode. Thermal analysis revealed from differential scanning calorimetry a sharp exothermic peak at 142°C; thermal gravimetry/differential thermal gravimetry has shown mass loss due to silver formation and a brown residue, a water-soluble polymeric acid (decomposition range 135–157°C), tending to pure silver at 600°C, consistent with the original Ag₄Y salt.     

Collisional quenching of electronically excited germanium atoms, Ge[4p(S0)], by small molecules investigated by time-resolved atomic resonance absorption spectroscopy

The collisional quenching of electronically excited germanium atoms, Ge[4p²(¹S₀)], 2.029 eV above the 4p²(³P₀) ground state, has been investigated by time-resolved atomic resonance absorption spectroscopy in the ultraviolet at λ = 274.04 nm [4d(¹P₁⁰) ← 4p²(¹S₀)]. In contrast to previous investigations using the ‘single-shot mode’ at high energy, Ge(¹S₀) has been generated by the repetitive pulsed irradiation of Ge(CH₃)₄ in the presence of excess helium gas and added gases in a slow flow system, kinetically equivalent to a static system. This technique was originally developed for the study of Ge[4p²(¹D₂)] which had eluded direct quantitative kinetic study until recently. Absolute second-order rate constants obtained using signal averaging techniques from data capture of total digitised atomic decay profiles are reported for the removal of Ge(¹S₀) with the following gases (k_R in cm³ molecule⁻¹ s⁻¹, 300 K): Xe, 7.1 ± 0.4 × 10⁻¹³; N₂, 4.7 ± 0.6 × 10⁻¹²; O₂, 3.6 ± 0.9 × 10⁻¹¹; NO, 1.5 ± 0.3 × 10⁻¹¹; CO, 3.4 ± 0.5 × 10⁻¹²; N₂O, 4.5 ± 0.5 × 10⁻¹²; CO₂, 1.1 ± 0.3 × 10⁻¹¹; CH₄, 1.7 ± 0.2 × 10⁻¹¹; CF₄, 4.8 ± 0.3 × 10⁻¹²; SF₆, 9.5 ± 1.0 × 10⁻¹³; C₂H₄, 3.3 ± 0.1 × 10⁻¹⁰; C₂H₂, 2.9 ± 0.2 × 10⁻¹⁰; Ge(CH₃)₄, 5.4 ± 0.2 × 10⁻¹¹. The results are compared with previous data for Ge(¹S₀) derived in the single-shot mode where there is general agreement though with some exceptions which are discussed. The present data are also compared with analogous quenching rate data for the collisional removal of the lower lying Ge[4p²(¹D₂)] state (0.883 eV), also characterized by signal averaging methods similar to that described here.     

Simultaneous derivative spectrophotometric determination of thorium and uranium in a micellar medium

Derivative photometric methods for trace analysis of Th(IV) and UO₂(II), and their simultaneous determination in mixtures using 5,8-dihydroxy-1,4-naphthoquinone in a micellar medium are reported. Molar absorptivity and Sandell's sensitivity of 1:2 Th(IV) and 1:1 UO₂(II) complexes at their λ_max, 614.5 nm and 637.0 nm are, 1.19 × 10⁴ 1/mol/cm and 1.12 × 10⁴ 1/mol/cm and 1.95 × 10⁻² μg/cm² and 2.13 × 10⁻² μg/cm² μg/cm², respectively. Calibration graph is linear over the range 9.28 × 10⁻²−18.56 μg/ml of Th(IV) and 9.52 × 10⁻²−19.04 μg/ml of UO₂(II). Though presence of Th(IV) and UO₂(II) causes interference in each others determination, 9.28 × 10⁻¹−9.28 μg/ml Th(IV) and 9.52 × 10⁻¹−9.52 μg/ml UO₂(II) when present together, can be simultaneously determined using derivative spectra.     

四环素-Al(Ⅲ)配合物与DNA的相互作用研究

研究了四环素(TC)-Al³⁺配合物与DNA的相互作用.吸收光谱和荧光光谱研究表明,TC与DNA无明显的相互作用,但在Al³⁺离子存在下,TC能结合到小牛胸腺DNA上.TC先与Al³⁺作用,生成TC-Al二元配合物,该配合物再与DNA发生作用,形成(TC-Al)-DNA三元配合物.TC-Al二元配合物与DNA的结合常数为6.5×10⁴L/mol,其配位比n(TC):n(Al):n(DNA)=1:1:1.TC-Al配合物与DNA的键合模式主要是静电相互作用.溶液的pH值对TC-Al二元配合物和(TC-Al)-DNA三元配合物的形成有一定的影响.利用TC-Al配合物与DNA作用使体系荧光强度增强的性质测定DNA,其线性范围为1.0×10^-6～6.0×10^-5mol/L,检测限为5.0×10^-7mol/L.分别测定了天然与热变性酵母样品中DNA的含量,结果令人满意.     

Supramolecular assemblies for light-induced electron-transfer reactions

In this paper, we present a summary of our work on highly photostable supramolecular ruthenium complexes, which may be incorporated into more complex systems for artificial solar energy conversion. We have used supramolecular chemistry and photochemistry to synthesize highly photostable ruthenium bipyridine coronates and a bipyridazine podate complex and to enhance photoelectron-transfer reactions in physical model systems for artificial photosynthesis. The recent progress of covalent and non-covalent sensitizer-relay assemblies for highly efficient photoelectron transfer is described.

A detailed mechanistic investigation of the binding behavior of cationic species to crow-ether-modified bipyridine derivatives is presented as an example of supramolecular binding in systems for photoelectron transfer. The host properties of the free ligands and the derived bis-heteroleptic ruthenium complexes are compared using UV—visible, luminescence quenching and proton nuclear magnetic resonance titrations. The combination of these three methods confirms that supramolecular binding of cations and the electron relay methylviologen (MV²⁺) to the complexes can be observed. The binding constants determined are of the order of (1–6) × 10⁴ 1 mol⁻¹ for the crown-ether ruthenium complexes and 1 × 10²−4 × 10³ 1 mol⁻³ for the crown-ether ligands. Single-photon-counting (SPC) investigations give strong indications for the coexistence of different binding mechanisms. The kinetic scheme of Yekta et al. has been adapted to interpret the binding mechanism.     

Sensitive spectrophotometric method for trace amounts of uranium

A sensitive spectrophotometric method for the determination of uranium with Pyrogallol Red (PGR) and cetyltrimethylammonium bromide (CTAB) is described. The sensitivity of the colour reaction between uranium and Pyrogallol Red is greatly increased in the presence of cetyltrimethylammonium bromide. The blue ternary complex (λ_max580 nm) has composition 1:2:4 [U(VI):PGR:CTAB] at pH 5.6. Beer's law is obeyed over the range 19.0-0.24 ppm of uranium and the molar absorptivity is 3.3 × 10⁴ l.mole⁻¹.cm⁻¹ at 620 nm. A tentative structure for the ternary complex is suggested. A simple method is suggested for evaluation of stability constants of such ternary complexes.     

γ-radiolysis and pulse radiolysis of aqueous 4-chloroanisole

Using pulse radiolysis and steady state γ-radiolysis in combination with product analysis by HPLC the radiolytic degradation mechanism of 4-chloroanisole (4-ClAn) has been elucidated. Pulse radiolysis experiments show that OH radicals react in neutral aqueous N₂O saturated solutions with 4-ClAn by addition to all aromatic ring positions to yield hydroxycyclohexadienyl radicals (OH-adducts), k(OH + 4-ClAn) = 6.5 × 10⁹dm³mol⁻¹s⁻¹. Those OH-adducts formed on ipso positions of the molecule subsequently undergo HCl or CH₃OH elimination forming methoxyphenoxyl- and chlorophenoxyl radicals. Their yield corresponds to 20% of the OH-radicals, whereby the distribution is roughly 3:1 in favor of the methoxyphenoxyl radicals, which reflects the stronger ortho-, para-directing activity of the methoxy group. The OH-adducts decay second order, 2k = 1 × 10⁹dm³mol⁻¹s⁻¹. The presence of oxygen leads to its addition on the hydroxycyclohexadienyl radicals, k(OH-adduct + O₂) = 3.2 × 10⁸dm³mol⁻¹s⁻¹. In airfree solution the reaction of H-atom with the substrate, k(H + 4-ClAn) = 1.2 × 10⁹dm³mol⁻¹s⁻¹, results in H-adducts which decay in bimolecular reactions, 2k = 8.2 × 10⁸dm³mol⁻¹s⁻¹. The rate constant for the reaction of the solvated electrons has been determined to k(e_aq⁻ + 4-ClAn) = 2 × 10⁹dm³mol⁻¹s⁻¹. The absorption spectra of H- and OH-adducts were measured in the range of 280–450 nm. The products analysed by HPLC after γ-radiolysis in dependence of dose (100–600 Gy) are given for N₂O-, air-, oxygen- and argon saturated neutral aqueous solutions. In conditions favoring the OH radical oxidation 4-chlorophenol, 4-methoxyphenol, 5-chloro-2-methoxyphenol and 2-chloro-5-methoxyphenol were determined as final products. In the presence of Ar, where about equal amounts of OH and e_aq⁻ are present, additionally anisole could be detected. Under both reaction conditions the amount of identified products is about 20% of decomposed 4-ClAn. The reaction of e_aq⁻ leads to reductive dechlorination which corresponds quantitatively to the degradation of the substrate. In the presence of air or solutions saturated with pure oxygen predominantly hydroquinone, 4-chlorophenol and muconic acids are formed and the material balance is 50%. The efficient dechlorination (60% of the decomposed 4-ClAn) as well as ring fragmentation products as intermediates en route to complete mineralization in oxygenated solution indicate that high energy radiation is a promising method for degradation of halogenated aromatic compounds in water. Variation of dose rates from 79 Gy min⁻¹ to 266 Gy min⁻¹ did not show any influence on the product distribution.     

Carbon ion irradiation induced surface modification of polypropylene

Polypropylene was irradiated with ¹²C ions of 3.6 and 5.4 MeV energies in the fluence range of 5×10¹³–5×10¹⁴ ions/cm² using 3 MV tandem accelerator. Ion penetration was limited to a few microns and surface modifications were investigated by scanning electron microscopy. At the lowest ion fluence only blister formation of various sizes (1–6 μm) were observed, but at higher fluence (1×10¹⁴ ions/cm²) a three-dimensional network structure was found to form. A gradual degradation in the network structure was observed with further increase in the ion fluence. The dose dependence of the changes on surface morphology of polypropylene is discussed.     

Solid-phase extraction of metal ions and their estimation in vitamins, steel and milk using 3-hydroxy-2-methyl-1,4-naphthoquinone-immobilized silica gel

3-Hydroxy-2-methyl-1,4-naphthoquinone-immobilized silica gel has been used for the adsorption and estimation of copper, cobalt, iron and zinc by both batch and column techniques. The distribution coefficient D determined for each metal ion was as follows (ml g¹): Fe, 3.6 × 10²; Cu, 3.9 × 10²; Co, 3.8 × 10²; Zn, 4.1 × 10². Methods have been developed to estimate zinc, copper and cobalt in milk, steel and vitamin samples respectively.     

Equilibria and kinetics of the extraction of gallium with 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone

The equilibria and kinetics of the solvent extraction of gallium(III) from aqueous monochloroacetic acid [HA] media with a benzene solution of 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone [PMBP or HL] has been studied at 25 ± 0.1° and an ionic strength of 0.2. The species extracted was found to be GaL₃. The value of the acid dissociation constant of PMBP determined spectrophotometrically was 1.17 × 10⁻⁴. The values of the partition coefficient of PMBP and the extraction constant of its gallium complex between an aqueous and a benzene phase were found to be 3.72 × 10³ and 2.51 × 10⁴, respectively. The rate of extraction was first-order with respect to the concentrations of gallium(III) in the aqueous phase and PMBP in the organic phase, inversely first- and second-order with respect to the hydrogen-ion concentration and zero- and first-order with respect to the concentration of monochloroacetate ions. Two mechanisms operate for this extraction, depending on the pH of the aqueous phase, one where the formation of the first complex, GaL²⁺, between Ga³⁺ and L⁻ in the region of pH < 1.6 becomes the rate-determining step, and the other where the formation of the first complex between GaA²⁺ and L⁻ in the region of pH 2.0–2.3 is the rate-determining step. The rate constant for the first of these reactions was calculated to be 1.62 × 10⁴l.mole⁻¹.sec⁻¹, but that for the second could not be determined.     

One-electron oxidation of mitomycin C and its corresponding peroxyl radicals. A steady-state and pulse radiolysis study

The one-electron oxidation of Mitomycin C (MMC) as well as the formation of the corresponding peroxyl radicals were investigated by both steady-state and pulse radiolysis. The steady-state MMC-radiolysis by OH-attack followed at both absorption bands showed different yields: at 218 nm G_i (-MMC) = 3.0 and at 364 nm G_i (-MMC) = 3.9, indicating the formation of various not yet identified products, among which ammonia was determined, G(NH₃) = 0.81. By means of pulse radiolysis it was established a total κ (OH + MMC) = (5.8 ± 0.2) × 10⁹ dm³ mol⁻¹ s⁻¹. The transient absorption spectrum from the one-electron oxidized MMC showed absorption maxima at 295 nm (ε = 9950 dm³ mol⁻¹ cm^t-1), 410 nm (ε = 1450 dm³ mol⁻¹ cm⁻¹) and 505 nm ( ε = 5420 dm³ mol⁻¹ cm⁻¹). At 280–320 and 505 nm and above they exhibit in the first 150 μs a first order decay, κ₁ = (0.85 ± 0.1) × 10³ s⁻¹, and followed upto ms time range, by a second order decay, 2κ = (1.3 ± 0.3) × 10⁸ dm³ mol^-1 s⁻¹. Around 410 nm the kinetics are rather mixed and could not be resolved.

The steady-state MMC-radiolysis in the presence of oxygen featured a proportionality towards the absorbed dose for both MMC-absorption bands, resulting in a G_i (-MMC) = 1.5. Among several products ammonia-yield was determined G(NH₃) = 0.52. The formation of MMC-peroxyl radicals was studied by pulse radiolysis, likewise in neutral aqueous solution, but saturated with a gas mixture of 80% N₂O and 20% O₂. The maxima of the observed transient spectrum are slightly shifted compared to that of the one-electron oxidized MMC-species, namely: 290 nm (ε = 10100 dm³ mol⁻¹ cm⁻¹), 410 nm (ε = 2900 dm³ mol⁻¹ cm⁻¹) and 520 nm (ε = 5500 dm³ mol⁻¹ cm⁻¹). The O₂-addition to the MMC-one-electron oxidized transients was found to be at 290 to 410 nm gk(MMC·OH + O₂) = 5 × 10⁷ dm³ mol⁻¹ s⁻¹, around 480 nm κ = 1.6 × 10⁸ dm³ mol⁻¹ s⁻¹ and at 510 nm and above, κ = 3 × 10⁸ dm³ mol⁻¹ s⁻¹. The decay kinetics of the MMC-peroxyl radicals were also found to be different at the various absorption bands, but predominantly of first order; at 290–420 nm κ₁ = 1.5 × 10³ s⁻¹ and at 500 nm and above, κ = 7.0 × 10³ s⁻¹.

The presented results are of interest for the radiation behaviour of MMC as well as for its application as an antitumor drug in the combined radiation-chemotherapy of patients.     

Spectrophotometric determination of cadmium with 1-(2-pyridylazo)-2-naphthol and non-ionic surfactants Application to acetic acid extracts of ceramic enamels

The Cd-PAN system in the presence of non-ionic surfactants (polyoxyethylene nonylphenols), which dissolve the reagent and complex by formation of micelles, has been studied spectrophotometrically. The optimum conditions for Cd determination are pH 9 (Na₂B₄O₇-HClO₄), 2% of surfactant and measurement at 555 nm. The complex is Cd(PAN)₂ and its conditional formation constant is 3.5 × 10¹¹. The system obeys the Lambert-Beer law, with an error of 0.9% over the Cd concentration range 0.44–1.74 ppm; the molar absorptivity is 4.94 × 10⁴1·mole⁻¹.cm⁻¹ at 555 nm. The relative standard deviation is 0.7% and the limit of detection 0.009 μg/ml. The selectivity with respect to species important in the ceramic industry is adequate for application of the method to determination of Cd in acetic acid extracts of ceramic enamels.