Mathematical Modeling of Kinetics of Adenosine 5"-Triphosphate Hydrolysis Catalyzed by the Zn2+ Ion in the pH Range 7.4–8.3

Kinetic data on adenosine triphosphate (ATP) hydrolysis catalyzed by the Zn²⁺ ion in the pH range 7.4–8.3 are analyzed by the method of numerical simulation. The rates of forward and reverse reactions of isomeric conversion of the open conformation of ZnATP^2– (Op), which is inactive in hydrolysis to ADP, to the active cyclic conformation ZnATP^2– (Cy) in the specified range of pH are proportional to the concentration of H₃O⁺ and characterized by the same rate constants as in the range of pH above 8.5. The mechanism of the isomeric conversion Op Cy involves the formation of a pentacovalent state at -P, pseudorotation, and the abstraction of OH^– from -P of the pentacovalent intermediate with the participation of H₃O⁺ in a slow step. The sequence of steps for the formation and transformation of intermediates, which was established earlier for the ZnATP^2– associates in the pH range 7.1–7.4, is applicable to this range of pH as well. In the analyzed range of pH, the contributions from the pH-independent channel of hydrolysis of the ZnATP^2– associates and the pH-dependent channel of CyOH^– and Op(OH^–)₂ species, which determine the formation of ADP and AMP at pH > 8.5, are comparable. Changes in the concentrations of intermediate products (monomeric and associates) in the course of hydrolysis are described. General base catalysis by a nitrogen base in the steps of formation of active centers for hydrolysis, the general acid catalysis of a coordinated water molecule, the exchange of medium OH^– with OH of -phosphate, the catalysis of conversion of the inactive conformation ZnATP^2– to the active one by a proton, and a change of the rate-limiting stage of hydrolysis with a change in pH indicate the enzyme-like mechanism of the reaction.     

Effect of preparation pH on pore structure of silica gels

Surface characterization of silica gels prepared at different gelation pH from water glass and sulphuric acid were made by argon adsorption at 77 K using continuous volumetric method. While microporous silica gels prepared in the pH range of 1–3 had BET surface areas of 504–571 m² g^–1, total pore volumes of 0.26–0.31 cm³ g^–1 and micropore volumes of 0.16–0.23 cm³ g^–1, mesoporous silica gels prepared in the pH range of 3.36–0.65 had BET surface areas of 374–530 m² g^–1 and pore volumes of 0.61–0.79 cm³ g^–1.     

Synergistic extraction behavior of samarium(III), europium(III) and dysprosium(III) with 1-nitroso-2-naphthol and 1,10-phenanthroline

The equilibrium extraction behavior of Sm(III), Eu(III) and Dy(III) from aqueous NaClO₄ solutions in the pH range of 4–9 at 0.1 M ionic strength into organic solutions of 1-nitroso-2-naphthol (HA) and 1,10-phenanthroline (Phen) has been studied. The equilibrium concentrations of Eu were assayed through the 344 keV photopeak of the¹⁵²Eu radiotracer used. The concentrations of Sm and Dy were measured by irradiating one mL portions of the organic extract and analyzing the 104 and 108 keV photopeaks of the short-lived neutron activation products,¹⁵⁵Sm and^165mDy, respectively. Quantitative extraction of Eu with 5×10^–2 M HA alone was obtained in the pH range of 6.7–7.8 with n-butanol, 7.4–8.5 with chloroform, 8.0–8.7 with ethyl acetate, 7.7–8.5 with isoamyl alcohol and 6.1–8.0 with methyl isobutyl ketone (MIBK). But, Eu was extracted only to a maximum of 78% and 83% in the pH range of 8.3–8.9 and 7.4–8.1 with carbon tetrachloride and xylene, respectively. The extraction of Sm and Dy were found quantitative in the pH range of 6.3–7.0 and 6.6–7.1, respectively, with 5×10^–2 M HA alone in MIBK solutions. The synergistic extraction of Eu was quantitative in the pH range of 6.6–9.8 with chloroform, 7.8–8.9 with ethyl acetate, 7.7–8.5 with isoamyl alcohol and 6.0–9.6 with MIBK when 1×10^–2 M each of HA and Phen were employed. Sm and Dy were quantitatively extracted into MIBK solutions containing 5×10^–2 M each of HA and Phen in the pH range 6.0–7.5 and 6.1–7.5, respectively. The distribution ratios of these lanthanides (Ln) were determined as a function of pH, and HA and Phen concentrations. The analysis of the data suggests that these Ln are extracted as LnA₃ chelates when HA alone is used. In the presence of HA and Phen, both LnA₃(Phen) and LnA₃(Phen)₂ adducts are formed only in the MIBK system while LnA₃(Phen) complexes are the predominant ones in all other solvent systems studied. The extraction constants and the adduct formation constants of these complexes have been calculated.     

Buffer Standards for the Physiological pH of Zwitterionic Compounds,MOBS and TABS from 5 to 55°C

The values of the second dissociation constant, pK₂, and related thermodynamic quantities of 4-(N-morpholino)butanesulfonic acid (MOBS) and N-tris(hydroxymethyl)-4-aminobutanesulfonic acid (TABS) have already been reported over the temperature range 5–55°C including 37{°}C. This paper reports the pH values of twelve equimolal buffer solutions at designated pH (s) with the following compositions: (a) mixtures of MOBS (0.05 mol-kg^–1) + NaMOBS (0.05 mol-kg^–1); (b) MOBS (0.08 mol-kg^–1) + NaMOBS (0.08 mol-kg^–1); (c) MOBS (0.08 mol-kg^–1) + NaMOBS (0.08 mol-kg^–1) + NaCl (0.08 mol-kg^–1); (d) TABS (0.05 mol-kg^–1) + NaTABS (0.05 mol-kg^–1); and (e) TABS (0.08 mol-kg^–1) + NaTABS (0.08 mol-kg^–1); and (f) TABS (0.08 mol-kg^–1) + NaTABS (0.08 mol-kg^–1) + NaCl (0.08 mol-kg^–1). Two buffer solutions have ionic strengths I= 0.05 mol-kg^–1, another two have I=0.08 mol-kg^–1, and the remaining two buffer solutions have I= 0.16 mol-kg^–1, which is close to that of the clinical fluids (blood serum). These buffers have been recommended as a useful pH standard for the measurements of physiological solutions. Conventional pH values of all six buffer solutions from 5–55°C, as well as those obtained from the liquid junction potential correction at 25 and 37{°}C have been calculated. The flowing-junction calomel cell has been utilized to measure E_j, the liquid junction potential.     

Solubility of particulate cadmium sulfide at pH=1–14: A radiotracer study

Cadmium sulfide particles were prepared by precipitation from acid solution. A radiotracer technique with¹⁰⁹Cd was applied to measure the solubility of cadmium sulfide at various pH's. Filtration, centrifugation, ultracentrifugation, and dialysis were used to separate the particles from the solution. Only the last two techniques proved to be successful. The solubility of cadmium sulfide in water (pH=7) is found to be: 7.9·10^–5 mol·l^–1 in contrast with the literature value of 9.0·10^–6 mol·l^–1. At low pH (1–4), the solubility agrees fairly well with the solubility calculated on the basis of generally accepted values for the solubility product and for the various complex formation constants, while at high pH (4–14) the solubility is higher than expected.     

Determination of propazine by differential pulse polarography in micellar and emulsified media

An electroanalytical study of the herbicide propazine's reduction process in micellar solutions and oil-in-water emulsions is reported. The anionic surfactant sodium pentanesulphonate was chosen as the most suitable. The differential pulse polarograms of micellar solutions had two reduction peaks below pH 2.0, whereas only one peak was obtained above pH 2.O. Ethyl acetate was chosen as the organic solvent to form propazine emulsions. Unlike in micellar solutions, the DPP polarograms of propazine emulsions showed only one peak even at pH < 2.0, suggesting that propazine hydrolysis was hindered in the emulsified medium. The limiting current is diffusion-controlled and the electrode process is irreversible. Propazine can be determined by differential pulse polarography over the 1.0 × 10^–1 – 1.0 × 10^–1moll^–1 and 1.0 × 10^–15 – 4.0 × 10^–1 moll^–1 concentration ranges and the limit of detection was 2.8 × 10^–1 moll^–1. Of the potential interferents simazine, methoprotryne and terbutryn (alls-triazines), thiram (a dithiocarbamate), dinoseb (nitrophenolic), and heptachlor (chlorinated cyclo-diene herbicide), only the first two were significant (10% error for equimolar concentrations). The method was applied to the determination of propazine in spiked drinking water. At a concentration level of 2.0 × 10^–1 moll^–1 a recovery of 94 ± 6% was obtained, after tenfold concentration on Sep-Pak.     

Polarographic determination of uranium(VI) after salting-out extraction as 8-quinolinolate in acetonitrile

Summary Uranium(VI) can be extracted as its 8-quinolinolate into acetonitrile by means of salting-out with ammonium and sodium acetates, respectively; the metal oxinates extracted give a well-defined dc polarogram with E _1/2=–0.80V and a sharp square wave (sw) polarogram with E _p=–0.96V in the extract. The dc wave height and the sw peak current are directly proportional to the uranium(VI) concentration in the range of 6.0×10^–6 to 4.0×10^–4M at pH 6.7–10.0 and 8.0×10^–7 to 2.8×10^–5M at pH 10.5–11.0, respectively. A number of ions do not interfere in the presence of EDTA.

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Polarographische Bestimmung von Uran(VI) nach Aussalz-Extraktion als 8-Hydroxychinolat mit Acetonitril

Zusammenfassung Uran(VI) kann durch Aussalzen mit Ammonium- bzw. Natriumacetat als Oxinat mit Acetonitril extrahiert werden. Das extrahierte Oxinat ergibt ein gut ausgebildetes Gleichstrompolarogramm mit E _1/2=–0,80 V bzw. ein scharfes square-wave-Polarogramm mit E _p=–0,96 V. Die Gleichstrom-Stufenhöhe bzw. der square-wave-Peakstrom sind der U(VI)-Konzentration im Bereich 6,0·10^–6-4,0· 10^–4M (pH 6,7–10,0) bzw. 8,0·10^–7-2,8·10 ^–5M (pH 10,5–11,0) direkt proportional. Durch Zusatz von EDTA kann eine Reihe von Störungen ausgeschaltet werden.

     

Kinetics and mechanism of formation of square-planar copper(II) and nickel(II) complexes of ethylenebisbiguanide in aqueous acetate buffer media

Summary The kinetics of formation of square-planar Cu^II and Ni^II complexes of the quadridentate ligand, ethylenebisbiguanide, have been studied spectrophotometrically in aqueous HOAc–NaOAc buffer, at ionic strength 0.2 mol dm^–3, in the 25–35°C temperature range. The observed rate constants for the formation reactions are independent of pH (and of OAc^– concentration) in the pH range used (3.6–4.8 for Cu^II and 5.0–5.8 for Ni^II) where the product complexes form stoichiometrically, but show first-order dependence on the ligand concentration;i.e. k_obs=k_f[L]_total. At 25°C k_f values (dm³ mol^–1s^–1) are 35.2±0.4 for Cu^II and (8.4±0.1)×10^–3 for Ni^II. The mechanism of the reactions is discussed.     

Inorganic particulates in removal of toxic heavy metal ions

Adsorption behavior of zinc ions on hydrous zirconium oxide (HZO) in aqueous solution has been studied as a function of concentration (10^–2–10^–8M), temperature (303–333 K) and pH 3–8 of adsorptive solution applying radiotracer technique. The kinetics of adsorption follows first order rate law and agrees well with the classical Freundlich isotherm in the entire range of adsorptive concentration. The removal was found to be increasing with pH of the adsorptive solution while it was suppressed in the presence of acid concentrations. The overall process is found to be endothermic and irreversible in nature.     

Differential pulse polarographic determinations of iodate, bromate and periodate

Summary The application of differential pulse polarography for quantitative trace determination of iodate, periodate and bromate has been investigated. Optimum conditions were found (pulse amplitude 100 mV, scan rate 2 mV s^–1, drop time 2 s). The detection limit for IO ₃ ^– , BrO ₃ ^– and IO ₄ ^– is ca. 2.4×10^–6M at pH 3 whereas at pH 9.3 the reduction of IO ₃ ^– and IO ₄ ^– gave concentration sensitive peak heights down to 9.9 ×10^–7M. A differential pulse polarographic method has been developed for the simultaneous determination of iodate-bromate or periodate-bromate.

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Bestimmung von Iodat, Bromat und Periodat durch Differential-Pulse-Polarographie

Zusammenfassung Optimale Bedingungen zur Bestimmung dieser Ionen im Spurenbereich wurden ausgearbeitet (Pulsamplitude 100 mV, Scangeschwindigkeit 2 mV s^–1, Tropfzeit 2 s). Die Nachweisgrenze für die drei Ionen liegt bei 2,4 · 10^–6 M für pH 3. Bei pH 9,3 ergaben sich für Iodat und Periodat konzentrationsabhängige Peakhöhen bis herab zu 9,9 · 10^–7 M. Da der Bromatpeak bei wesentlich negativerem Potential auftritt als der Iodat bzw. Periodatpeak konnten Iodat und Bromat bzw. Periodat und Bromat nebeneinander bestimmt werden.

     

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 ^. .     

Estimation of Cr(VI) in water,tannery and plating wastes

Summary Estimation of Cr(VI) in Water, Tannery and Plating Wastes A zirconium tellurite membrane exhibits good selectivity for CrO₄ ^2– or CrO₇ ^2– ions at pH 3–6 and 8–11. Membrane electrode can be used to determine the activity of Cr(VI) ions in the concentration range 10^–1 to 7×10^–5 M at specified pH. The response time is 30 s and a large number of anions and cations do not interfere with the functioning of this assembly. It has been tried for the estimation of Cr(VI) in plating and tannery waste.     

Voltammetric study of glibenclamide at carbon paste and Sephadex-modified carbon paste electrodes

The oxidative behaviour of the antidiabetic agent glibenclamide on a bare carbon paste electrode (CPE) and a Sephadex-modified carbon paste electrode (SMCPE) was explored by cyclic and differential pulse voltammetry (DPV). The analysis procedure consisted of an open circuit accumulation step in stirred sample solution of Britton-Robinson buffer (0.04 mol L^–1, pH 2.0). This was followed by medium exchange to a clean solution of Britton-Robinson buffer (0.04 mol L^–1, pH 5.0), and subsequently an anodic potential scan was effected to obtain the voltammetric peak. The glibenclamide oxidation peak current obtained by DPV was proportional to the concentration of the glibenclamide in the range of 1.0×10^–9 mol L^–1 to 5.0×10^–8 mol L^–1 for 180 s accumulation time, with a detection limit of 4.0×10^–10 mol L^–1. A method was developed for the determination of glibenclamide in formulation and spiked human serum. Moreover, the proposed procedure was used to estimate the serum concentrations after oral administration of a 5 mg tablet of glibenclamide to three diabetic subjects.     

Determination of polyphosphate ions using a lead ion-selective electrode

Summary A lead ion-selective electrode responding to polyphosphate ions, such as pyro-, hexameta- and tripolyphosphate ions, has been developed and successfully used for the determination of these ions in the concentration range of 10^–6–10^–2 Min neutral solution. Almost identical potential-activity curves were obtained and the largest potential change was observed in the concentration range of 10^–6–10^–5 M (about -35 mV per decade of the concentration of each ion at pH 7.0). The response time was 1–3 min.

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Bestimmung von Polyphosphationen mit Hilfe einer Blei-ionenselektiven Elektrode

Zusammenfassung Eine auf Polyphosphationen (Pyro-, Hexameta-, Tripolyphosphat) ansprechende Blei-ionenselektive Elektrode wurde entwickelt und mit Erfolg zur Bestimmung der genannten Ionen im Konzentrationsbereich 10^–6–10^–2 M in neutraler Lösung eingesetzt. Es wurden fast identische Potential-Aktivitäts-Kurven erhalten. Die größte Potentialänderung ergab sich im Bereich von 10^–6–10^–5 M (etwa -35 mV je Zehnerpotenz der Konzentration bei pH 7.0). Die Ansprechzeit betrug 1–3 min.

     

Electrosurface Properties of Schungite III Particles in Aqueous Electrolyte Solutions

The kinetics of electrolyte extraction into water and the electrosurface properties (adsorption of potential-determining ions H⁺ and OH⁻ and ζ potential) of five fractions of schungite III (particle sizes of < 5, 50–100, 160–400, 400–1000, and 1600–2500 µm) are studied in aqueous NaCl, CaCl₂, and AlCl₃ solutions at different pH values. It is shown that, in water and NaCl and CaCl₂ solutions, the point of zero charge (PZC) of the particles with sizes of 50–100 and 160–400 µm is observed at pH 4.0 and is independent of the electrolyte concentration. The isoelectric point (IEP) for small (<5 µm) schungite III particles is observed at pH 2.8. The IEP position is independent of CaCl₂ concentration, but it shifts to pH 2.4 when NaCl concentration increases to 0.1 M. The disclosed differences in the PZC and IEP values may be caused by different compositions of particles of different fractions. In a 10⁻⁵ M AlCl₃ solution, schungite particles demonstrate three IEPs (pH 3.0, 4.5, and 7.4) due to different degrees of AlCl₃ hydrolysis at different pH values.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 4, 2005, pp. 450–457.Original Russian Text Copyright © 2005 by Aleinikov, Lorentsson, Chernoberezhskii.     

Diphenylcarbazone as a sensitive reagent for the spectrophotometric determination of iridium(IV)

Summary The blue iridium(IV)-diphenylcarbazone complex, formed by heating the solutions in boiling water bath for 45 minutes, having an absorption maximum at 550 nm with maximum molar absorptivity of 1.90·10⁴l·cm^–1·mole^–1 (within 1.5 %) is recommended for the spectrophotometric determination of 40–240g iridium(IV) in 25–60 % ethanol medium. The complex formed in solutions at pH 3.5–7.0, after formation, is stable within the pH range 2.5 to 9.2. The effect of foreign ions has been investigated.

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Zusammenfassung Der blaue Iridium(IV)-diphenylcarbazon-Komplex entsteht beim Erwärmen der beiden Lösungen im siedenden Wasserbad für 45 Min. Er hat ein Absorptionsmaximum bei 550 nm und eine molare Extinktion von 1,90 × 10⁴ l·cm^–1·mole^–1. Diese Farbreaktion wird zur spektrophotometrischen Bestimmung von 40–240g Ir(IV) in 25-bis 60%igem Äthanol empfohlen. Der bei pH 3,5–7,0 entstandene Komplex ist zwischen pH 2,5 und 9,2 beständig. Der Einfluß von Fremdionen wurde untersucht.

     

Analysis of mercury(II), methylmercury and phenylmercury by RPHPLC with micellized dithizone post-column derivatization photometric detection

Post-column derivatization detection system based on dithizone solubilized in cetyltrimethyl-ammonium hydrogenesulfate micellar media at pH 2.0 was devised and evaluated for selective detection of mercury(II), methylmercury and phenylmercury in reversed-phase HPLC system with photometric detection at 500 nm. This reagent solution is fully compatible with acidic organo-aqueous mobile phases generally used in RPHPLC. With the aid of the detection systematic study of the retention behaviour of three mercury species on octadecylsilica sorbent was carried out. Influence of pH, acetonitrile volume fraction, complex forming additives was investigated in detail. In mobile phase consisting of 5–30% of acetonitrile in water at pH 2.0 and 2·10^–4 mol·I^–1 DCTA linear calibration curves were measured in range 20–1000 ppb with correlation coefficient better than 0.99. Detection limits were 1–5 ng for this three mercury species. Interferences of copper(II) and silver(I) are negligible.     

Electrokinetic control of fluid in plastified laser-printed poly(ethylene terephthalate)-toner microchips

The application of plastified laser-printed poly(ethylene terephthalate)(PET)-toner microchips to capillary electrophoresis was investigated. Electroosmotic flow was observed in the direction of the cathode for the buffer system studied (phosphate, pH 3–10). Average electroosmotic mobilities of 1.71×10^–4 to 4.35×10^–4 cm² V^–1 s^–1 were observed from pH 3 to 10. This variation suggests that silica fillers in the toner and on the surface of the polymer dominate the zeta potential of the material, which is also confirmed by XPS measurements. Dopamine and catechol were used as model analytes for microchip electrophoresis in combination with electrochemical detection. Results show that these two analytes can be efficiently separated and detected electrochemically with the plastified laser-printed PET-toner microchips.     

Pulse radiolysis studies on the reactions of 3-pyridinol with oxidizing radicals

Reaction rate constants for the reactions of 3-pyridinol with oxidizing radicals viz. OH, N₃, Br ₂ ^– , Cl ₂ ^– , SO ₄ ^– and O^– have been determined in aqueous solutions at different, pH's. Absorption spectra of the product transient species have been recorded in the 320–600 nm region. In the alkaline region (pH 13) the N₃ reaction product decays in two steps and O^– does not bring about one-electron oxidation. Similarly, at neutral pH, SO ₄ ^– does not cause selective one-electron oxidation of 3-pyridinol.     

Raman Spectroscopic Study of Aluminum Silicate Complexes at 20°C in Basic Solutions

Raman spectroscopic measurements were performed at ambient temperature onaqueous silica-bearing solutions (0.005 < m _Si < 0.02; 0 < pH < 14). The spectraare consistent with the formation of monomeric Si(OH)^o ₄, SiO(OH)^– ₃ andSiO₂(OH)^2– ₂ species at acid to neutral, basic, and strongly basic pH, respectively.Raman spectra of aqueous Al-bearing solutions at basic pH confirm thepredominance of the Al(OH)^– ₄ species in a wide concentration range (0.01 < m _Al < 0.1).Raman spectra of basic solutions (12.4 < pH < 14.3), containing both Al andSi, exhibit a strong decrease in intensities of SiO(OH)^– ₃, SiO₂(OH)^2– ₂, andAl(OH)^– ₄ bands in comparison with Al-free Si-bearing and Si-free Al-bearingsolutions of the same metal concentration and pH, suggesting the formation ofsoluble Al—Si complexes. The amounts of complexed Al and Si derived fromthe measurements of the Al and Si band intensities in strongly basic solutions(pH 14) are consistent with the formation, between Al(OH)^– ₄ andSiO₂(OH)^2– ₂, of the single Al—Si dimer SiAlO₃(OH)^3– ₄ according to the reactionSiO₂(OH)^2– ₂ + Al(OH)^– ₄ SiAlO₃(OH)^3– ₄ + H₂OAt lower pH ( 12.5) the changes in band intensities are consistent with theformation of several, likely more polymerized, Al—Si complexes.