Flash photolytic investigations on the reaction between Pu(VI) and CO-3 in alkaline medium

Absorption spectrum of a transient species of Pu(VII), [PuO₂(CO₃)₂(OH)₂]^3-, has been obtained in the flash photolysis of solutions containing (50–500) x 10^-6 mol dm^-3 Pu(VI) and (5–30) x 10^-3 mol dm^-3 Na₂CO₃ at pH 12.5. The transient species appears to form through the reaction of CO^-₃ ion radical with [PuO₂(CO₃)(OH)₂]^2- [k = (1.45 +- 0.06) x 10⁷ mol^-1 dm³ s^-1] and decays spontaneously with a rate constant of (7.61 +- 0.09) x 10² s^-1. Evidence for the photoreduction of Pu(VI) has also been obtained and a reaction mechanism is proposed to explain the results.     

SYNTHESIS OF POLYCATECHOL WITH ELECTROCHEMICAL ACTIVITY AND ITS PROPERTIES

The electrochemical polymerization of catechol on platinum has been carried out using repeated potential cyclingbetween-0.2 and 1.1 V (versus SCE). The electrolytic solution consisted of 0.2 mol dm~(-3) catechol, 0.5 mol dm~(-3) NaCl and0.1 mol dm~(-3) Na_2HPO_4 with pH 8.72. Catechol can not be polymerized at pH≥10.12. Polycatechol has an electrochemicalactivity at pH≤4. The anodic and cathodic peak potentials of polycatechol shift towards more negative values as the pH ofthe solution increases from 1 to 4. The electrochemical activity of polycatechol hardly changes in this pH region, but itdecreases slowly with time. This is caused by oxygen in air, which leads to an irreversible oxidation of polycatechol. Thisproperty is favorable for protecting metals from corrosion. Raman and FTIR spectra of polycatechol and catechol are quitedifferent. AFM images of polycatechol films provide evidence that the image of the oxidized state of polycatechol ismarkedly different from that of the reduced one. This difference is caused by doping and dedoping of polycatechol.     

Extraction of Sm(III), Gd(III) and Ho(III) ions with picrolonic acid in methylisobutylketone

Summary Picrolonic acid (HPA) in methylisobutylketone (MIBK) (0.01 mol^. dm^-3) has been used for the extraction of lanthanide(III) ions such as Sm(III), Gd(III) and Ho(III) (Me) (~3^. 10^-6mol^. dm^-3) from pH 1-2 buffer solutions of 0.1 mol^. dm^-3(H⁺, Cl^-) ionic strength and quantitative extraction (>95%) was found at pH 2. Through slope analysis the composition of the organometallic adduct responsible for the extraction came out to be M(PA)₃. The conditional equilibrium constant values, log K_ex, were deduced to be 2.60±0.01, 2.09±0.01 and 1.44±0.03 for these lanthanide(III) ions, respectively. The metals in concentration up to ~2.5^. 10^-4mol^. dm^-3can be quantitatively extracted by the proposed system. Among the various anions, fluoride, oxalate and cyanide ions (~3.0^. 10^-4mol^. dm^-3) and, among the cations, Zn(II) Cu(II), Co(II) and Fe(III) reduced the lanthanide extraction. The extraction of various other metal ions at the optimized conditions of Me extraction for this series of lanthanide ions was also studied and high separation factors (10²-10³) were obtained showing the good selectivity of this extraction system.     

Kinetics of the photoaquation of Hexacyanoferrate(II) ion

Kinetics of the photoaquation of hexacyanoferrate(II) ion in aqueous solution were studied potentiometrically and spectrophotometrically. Supposing the simplest mechanism (see Fig. 3. in text), the photoaquation in alkaline medium can be well described. The value of the constants at pH = ll.0 are: ø = 0.8-1.0, k₆ = (3.0 ± 0.5) × 10^?8 s^?1 and k_?6 = 1.5 ± 0.2 mol^?1 dm₃ s^?1. To describe the photoaquation in neutral medium t was extended (k′ = 3.33 x 10² mol^?1 dm³s^?1). The quantum yield in acidic medium can be calculated by combination of ø values of different protonated complexes. The reversibility of photoaquation in alkaline medium is also explained by the scheme.     

Pulse-radiolysis studies of nimesulide in aqueous solution: effect of microheterogeneous media

Nimesulide, a non-steroidal anti-inflammatory drug, forms semi-oxidized species (_max = 350 nm) on reaction with N·₃ and CCl₃OO· in aqueous solution. Their oxidizing nature is confirmed by their ability to undergo an electron-transfer reaction with ABTS^2-, the rate constant for the reaction k = 4.7 × 10⁹ dm³ mol^-1 s^-1. ·OH-adduct constitutes about 94% of the species formed on reaction with ·OH radicals, the remaining 5-6% species are oxidizing in nature. The rate constant for the formation of ·OH-adduct, i.e. k(·OH + Nim-NO₂) = 2.8 × 10¹⁰ dm³ mol^-1 s^-1. Oxygen adds to both e^- _aq and ·OH-adducts of nimesulide with rate constants of 9.5 × 10⁶ dm³ mol^-1 s^-1 and 1.4 × 10⁷ dm³ mol^-1 s^-1, respectively. In the presence of cyclodextrins the nature of the transient species formed is much the same. Binding constants of the drug with CDs are generally quite low in comparison to BSA and range between 37 and 390 dm³ mol^-1. Hydrated electrons add on to nimesulide at the nitro group forming a semi-reduced species with _max = 320 and 500 nm. The rate constant k for this reaction is 1.4 × 10¹⁰ dm³ mol^-1 s^-1. The transient species formed on reaction of e^- _aq or (CH₃)·₂COH radicals with nimesulide seem to be identical, as is seen from their decay rates. The reduction potential of nimesulide for the couple (Nim-NO₂/Nim-NO·₂ ^-) is found to be -0.52 V vs. NHE at pH 7, by cyclic voltammetric and pulse radiolysis techniques.     

Development of Biosensor for Catechol Using Electrosynthesized Poly(3‐methylthiophene) and Incorporation of LAC Simultaneously

Simultaneous electropolymerization of 3‐methylthiophene and incorporation of Laccase (LAC) was carried out in the presence of propylene carbonate as a medium by amperometric method. This enzyme modified electrode was used for the sensing of polyphenol. Catechol is taken as a model compound for the study. UV‐Vis spectral studies suggest no denaturation of LAC in presence of propylene carbonate. The SEM studies reveal the surface morphology and incorporation of LAC in P3MT with agglomerated flaky masses are observed in with and without enzyme micrographs. The cyclic voltammograms were recorded for 0.01 mM catechol on plain glassy carbon, polymer and enzyme incorporated electrodes at pH 6.0 and scan rate 50 mV s^?1. The fabricated electrochemical biosensor was used for the determination of catechol in aqueous solution by Differential Pulse Voltammetry (DPV) technique. The concentration linear range of 8×10^?8 to 1.4×10^?5 M a value of Michealis? Menten constant K_m=7.67 µmol dm^?3 and activation energy is 32.75 kJ mol^?1. It retains 83 % of the original activity after 60 days which is much higher than that of other biosensors. The developed biosensor was used to quantify catechol in the determination in real samples.     

Applications of electron spin resonance in the analytical chemistry of transition metal ions: Part 3. Determination of Chromium(III) in Aqueous Solution [1]

Chromium(III) can be determined in aqueous solution at pH 1.5– 2.5 by electron spin resonance techniques. The analytical range is 2.0 x 10^-1–2.0 x 10^-6 mol dm^-3 ; the precision is± 0.3%. The effects of instrumental variables are discussed. Few commonly occurring species up to a concentration of 1.0 x 10^-1 mol dm^-3 interfered with the determination. The characteristic g value of 1.98 for chromium(III) suggests that the method may also be used to identify chromium(III).     

Radiation-induced reduction of vanadium(IV) to vanadium(II) in aqueous picolinate-formate solutions

Quantitative reduction of V(IV)(pic) to V(III)(pic)_n and then to V(II)(pic)_n(1 ⩽ n ⩽3) occurs when N₂O-saturated formate solutions (pH 4.2–6.3) containing V(IV) and picolinic acid (2-carboxypyridine) are irradiated. Pulse radiolysis measurements show that CO^-₂ reacts with picolinate only when the N-atom is protonated (k = 2.7 × 10⁸ dm³ mol^-1 s^-1). Reduction of V(IV)(pic) and V(III)(pic)_n is effected by the electron adduct of the protonated picolinate (picH)^. with rate constants at pH 4.2 of (3.5 ± 0.2) × 10⁷ dm³ mol^-1 s^-1 for V(IV)(pic) and (6.9 ± 0.4) × 10⁸ dm³ mol^-1 s^-1 for V(III)(pic)_n. No reduction of V(II)(pic)_n is observed.     

二氟沙星在中性水溶液中的光化学性质

对二氟沙星在中性水溶液中的光化学性质进行了研究. 在pH值为7.17 的水溶液中二氟沙星的紫外吸收峰位于273 nm (摩尔消光系数ε=33000 dm³·mol^-1·cm^-1), 323 nm (ε=15500 dm³·mol^-1·cm^-1), 335 nm (ε=15500 dm³·mol^-1·cm^-1)处. 荧光吸收和发射光谱均显示二氟沙星具有pH效应, 其pK_a(电离平衡常数)测定分别为5.9 和9.8. 二氟沙星的荧光量子产额较低, 在pH=3.00 时达到最大值, 为0.06. 同时对二氟沙星在中性水溶液中的激光光解和脉冲辐解进行详细研究. 激光光解研究发现在水溶液中二氟沙星的三重激发态位于620nm, 其摩尔消光系数为7900 dm³·mol^-1·cm^-1. 通过能量转移的方法得到其三重激发态的能量为263.5 kJ·mol^-1,三重激发态的量子产额为0.21. 在激光激发下, 二氟沙星进行单光子电离其量子产额为0.02. 脉冲辐解研究表明二氟沙星可以与水合电子(e_aq^-)及羟基自由基(·OH)快速反应, 其二级反应动力学常数分别为1.72×10¹⁰和1.0×10¹⁰ dm³·mol^-1·s^-1. 本文对二氟沙星光化学性质的研究有助于确定其光敏毒性的产生机理.     

Decolorization kinetics of the azo dye drimaren blue X3LR by laccase

Summary An extracellular Drimaren Blue X3LR decolorizing enzymatic activity was found in the crude filtrate of Funalia trogii grown by solid-state fermentation using wheat bran and soya bean waste. Decolorization of the azo dye Drimaren Blue X3LR by the crude filtrate and partially purified enzyme of Funalia trogii were investigated and compared. In the absence of additional redox mediator, maximum decolorization ratios of 81.33 % and 77.4 % were observed for Drimaren Blue X3LR using crude filtrate and partially purified enzyme respectively. Decolorization yield was found to be higher with crude enzyme preparations. Na₂S₂O₅ inhibited laccase and dye decolorizing enzyme activities but a significant peroxidase activity inhibition was not observed. Since the reaction was catalyzed in the absence of H₂O₂ as co-substrate, it could be concluded that this enzyme is not a peroxidase but may be a laccase.. The kinetic parameters of decolorization were calculated according to Michaelis constant (Km of 1.700 x 10^-5 mol dm^-3 and W_max = 8.02 x10^-7 mol dm^-3 sec^-1).     

Kinetics and salt effects of the reduction of octacyanomolybdate(V) and octacyanotungstate(V) by sulphite ions

The kinetics of the reduction of octacyanomolybdate(V) and octacyanotungstate(V) by sulphite ions has been studied over a wide pH range. The reaction is catalysed by alkali metal ions. The rate law is found to be of the form:

The third order rate constants at [OH^?] = 0.05 mol dm^?3 for the reduction of Mo(CN)₈^3? and W(CN)^3?₈ were determined as 6.2 x 10³dm⁶mol^?2 s^?1 and 22.3 dm⁶mol^?2s^?1 respectively at 298 K for A⁺ = Na⁺ while K_a for the hydrogen sulphite ion was determined as 2.4 x 10^?8 mol dm^?3. It was established that the reaction proceeds via an outer-sphere mechanism. An explanation for the alkali metal ion catalysis is proposed.     

Pulse radiolytic investigation of the reaction of hydroxyl radicals with gentamycin

Hydroxyl radicals were generated radiolytically in N₂O-saturated aqueous solutions of the aminoglycoside antibiotic, gentamycin. Using the pulse radiolysis technique, the rate constant of OH radicals with gentamycin determined was 1.2·10⁹ dm³·mol⁻¹·s⁻¹. Upon^.OH attack a transient species with an absorption maximum at 270 nm is observed which decays by second-order kinetics within the solute concentration range of 3.2·10⁻⁵ to 1·10⁻³mol·dm⁻³. Transient species undergoes transformation to a permanent product absorbing between 260 and 340 nm with maximum absorption at 300 nm. Rate constant of the reaction of bimolecular decay of gentamycin radicals, k (Gen^.+Gen^.) was found to be ≈ 1.4·10⁷ dm³·mol⁻¹·s⁻¹.     

Radical scavenging properties of a flavouring agent–Vanillin

Using pulse radiolysis technique, the one-electron oxidation of vanillin (V-OH) with azide radicals, at pH 6 and 9 resulted in the formation of vanillin phenoxyl radical with k = 6.7 × 10⁷ and 2.5 × 10⁹ dm³ mol^-1 s^-1, respectively. The transient absorption spectra of the vanillin phenoxyl radical (V-O) formed either at pH 6 or 9, showed a _max at 410 nm. At pH 5, the OH radicals seem to form an adduct with vanillin, _max at 430 nm and k(OH + V-OH) = 3.3 × 10⁹ dm³ mol^-1 s^-1, while at pH 9, the OH radical reaction resulted in the formation of vanillin phenoxyl radical with _max at 410 nm and k(OH + V-O-) = 6.6 × 10⁹ dm³ mol^-1 s^-1. The reactivity of NO₂radicals with vanillin is lower by orders of magnitude signifying an incomplete reaction. In general, the rate constants for the reaction of OH, N, NO radicals with vanillin were higher at pH 9 than at the lower pH. Its reactivity with other one-electron oxidants like CCl₃OO, CHCl₂OO and CH radicals and the ability to chemically repair tryptophanyl and guanosyl radicals with k = 1.5 - 4 × 10⁷ dm³ mol^-1 s^-1 indicate its antioxidative behaviour.     

Methylene Blue Poly(Vinyl Chloride) Membrane Electrode Based on the Methylene Blue-Teteraphenylborate Ion-Pair Complex and Its Application to Pharmaceutical Analysis

Abstract

A methylene blue (MB) poly (vinyl chloride) membrane electrode based on MBtetraphenylborate (TPB) ion-pair complex is described. The linear response covers the range 1x10^?2 - 1x10^?6 mol dm^?3 MB solution, with a slope of 56.5±0.5 mv/decade (pH range 3.0-1 0.0). The detection limit is 7.75x 10^?7 mol dm^?3. The electrode shows stability, good reproducibility and fast response. Interferences from common inorganic cations and some organic bases are negligible. These characteristics of the electrode enabled it to be used successfully for the determination of MB in injection.     

Organometallic complexes in ascidian embryonic development: II. Effects on different stages and larvae

The effects of the organometallic compounds Bu₂Sn-D -(?;)sorbitol, Bu₂Sn-D -(+)glucose, Bu₂Sn-D -(?)fructose and Bu₂Sn-D -(+)glyceraldehyde were tested in vivo on different stages of Ascidian development, larval movement and metamorphosis. Organotin(IV) complexes are organometallic compounds widely used as industrial biocides, antifouling agents and agricultural fungicides and are toxic to a range of organisms. Two-cell stage embryos, if incubated for one hour in the organotin (IV) solutions, stopped the cleavage, which was restored when they were transferred into normal sea water. The gastrula stage was seriously affected in 10^?4mol dm^?3 solutions of the above-mentioned complexes: 85% of the embryos were anomalous neurulae with open neural folds, 5% were twisted larvae. The gastrulae, when incubated for 1 h in 10^?5mol dm^?3 solutions, developed twisted larvae in ovular envelopes and immobile larvae with twisted tails. Larvae treated with 10^?4mol dm^?3 and 10^?5 mol dm^?3 Bu₂Sn-D -(?)sorbitol, Bu₂Sn-D -(+)glucose and Bu₂Sn-D -(+)glyceraldehyde solutions stopped swimming, did not metamorphose and afterwards underwent cytolysis. An initial hyperactivity of circular movements, followed by immobility, was observed in the larvae incubated in Bu₂Sn-D -(?;)fructose.     

ELECTROCHEMICAL SYNTHESIS AND PROPERTIES OF POLY(AZURE B)*

A blue poly(azure B) film has been synthesized using repeated potential cycling between -0.25 and 1. 10 V (versusSCE). The electrolytic solution consisted of 2.5 mmol dm~(-3) azure B, 0.5 mol dm~(-3) NaCl and 0.2 mol dm~(-3) NaH_2PO_4 at the pHrange of 2.0 to 11.0. The in situ visible spectrum during electrolysis of azure B shows that the intensity at 740 nm peakincreases with increasing numbers of potential cycles, which is attributable to the formation of poly(azure B). Thewavelength of its corresponding absorption peak is 98 nm longer than that of azure B. The polymerization rate is stronglyaffected by pH values. The anodic peak potential and cathodic peak potential of the poly(azure B) in a solution of pH 3.0 arenot affected by increasing the scan rate from 25 to 600 mV s~(-1). Poly(azure B) has good electrochemical reversibility and fastcharge transfer characteristic in the pH range of 2.0 and 11.0. The conductivity of poly(azure B) is 1.5×10~(-4) S cm~(-1).According to the differences between FTIR spectra of poly(azure B) and azure B, an electrochemical polymerizationmechanism of azure B is proposed in this paper.     

Outer-Sphere electron-transfer and the effect of linkage isomerism in the titanium(III) reduction of nitro-pentacyanocobaltate(III) and nitro-, and nitrito-pentaamminecobalt(III) complexes in aqueous acidic media

The reductions of [Co(CN)₅NO₂]³⁻, [Co(NH₃)₅NO₂]²⁺ and [Co(NH₃)₅ONO]²⁺, by Ti^III in aqueous acidic solution have been studied spectrophotometrically. Kinetic studies were carried out using conventional techniques at an ionic strength of 1.0 mol dm⁻³ (LiCl/HCl) at 25.0 ± 0.1 °C and acid concentrations between 0.015 and 0.100 mol dm⁻³. The second-order rate constant is inverse—acid dependent and is described by the limiting rate law:- k₂ ≈ k₀ + k[H⁺]⁻¹,where k=k′K_a and K_a is the hydrolytic equilibrium constant for [Ti(H₂O)₆]³⁺. Values of k₀ obtained for [Co(CN)₅NO₂]³⁻, [Co(NH₃)₅NO₂]²⁺ and [Co(NH₃)₅ONO]²⁺ are (1.31 ± 0.05) × 10⁻² dm³ mol⁻¹ s⁻¹, (4.53 ± 0.08) × 10⁻² dm³ mol⁻¹ s⁻¹ and (1.7 ± 0.08) × 10⁻² dm³ mol⁻¹ s⁻¹ respectively, while the corresponding k′ values from reductions by TiOH²⁺ are 10.27 ± 0.45 dm³ mol⁻¹ s⁻¹, 14.99 ± 0.70 dm³ mol⁻¹ s⁻¹ and 17.93 ± 0.78 dm³ mol⁻¹ s⁻¹ respectively. Values of K _a obtained for the three complexes lie in the range (1–2) × 10⁻³ mol dm⁻³ which suggest an outer-sphere mechanism.     

IONIC STRENGTH EFFECTS ON THE GROUND STATE COMPLEXATION and TRIPLET STATE ELECTRON TRANSFER REACTION BETWEEN ROSE BENGAL and METHYL VIOLOGEN

Abstract— The equilibrium constants, K_c, for complexation between methyl viologen dication (MV²+) and Rose Bengal, or Eosin Y, decrease with increasing ionic strength. At zero ionic strength K_c is 6500 (± 500) mol^?1 dm³ for Rose Bengal and 3200 (± 200) mol^?1 dm³ for Eosin Y, and these values decrease to 1500 (± 100) and 680 (± 40) mol^?1 dm³, respectively, at an ionic strength of 0.1 mol dm^?3. K_c is independent of pH between 4.5 and 10. ΔH is -25 (± 1) kJ mol^?1 for complexation with either dye, whereas ΔS is -15 (± 3) J K^?1 mol^?1 for Rose Bengal, and - 23 (± 3) J K^?1 mol^?1 for Eosin Y. The complexation constant for Rose Bengal and the neutral viologen, 4,4'-bipyridinium-N, N'-di(propylsulphonate), (4,4'-BPS), is 420 (± 35) mol^?1 dm³, and independent of ionic strength. No complexation could be observed for either Rose Bengal or Eosin with another neutral viologen, 2,2'-bipyridinium-N,N'-di(propylsulphonate), (2,2'-BPS). MV²+ quenches the triplet state of Rose Bengal with a rate constant of 7 × 10⁹ mol^?1 dm³ s^?1, and this rate constant decreases slightly as ionic strength increases. The cage escape yield following quenching, Φ_cc is very low (Φ_cc= 0.02 (± 0.005), and independent of ionic strength. 4,4'-BPS quenches the triplet state of Rose Bengal with a rate constant of 2.2 (± 0.1) × 10⁹ mol^?1 dm³ s^?1, and gives a cage escape yield of 0.033 (± 0.006). 2,2'-BPS quenches the Rose Bengal triplet with a rate constant of 6 (± 1) × 10⁸ mol^?1 dm³ s^?1 and gives a cage escape yield of 0.07 (± 0.01). Conductivity measurements indicate that MV²+(Cl^?)₂ is completely dissociated at concentrations below 2 × 10^?2 mol dm^?3.     

Formation and decay of phenoxyl radicals: Variation with pH and pulse dose

Phenoxyl type radicals were produced from tyrosine methyl ester (TME) using azide (N ₃ ^. ) radicals. The rate constant of formation increased from 2·10⁸ dm³·mol^–1·s^–1 at pH 7 to 4·10⁹ dm³·mol^–1·s^–1 at pH 11, whereas that of the decay, 2k=(6±1)·10⁸ dm³·mol^–1·s^–1, remained constant. The maximum yield of the radicals varied with pH and pulse dose consistently with the kinetic scheme, which involved a competition of the oxidation of TME by azide radicals with the natural decay of N ₃ ^. .