Kinetics of the Formation of Goethite in the Presence of Sulfates and Chlorides of Monovalent Cations

The synthesis of goethite by oxidation of Fe²⁺in presence of metallic iron was undertaken in an aqueous medium containing indifferent salts such as Na₂SO₄, (NH₄)₂SO₄, NaCl, and NH₄Cl. Temperature and bubbling air rate were maintained, respectively, at 70°C and 1 L/min. The influence of anions and cations on the kinetics of each step of the process has been followed distinctly, the iron dissolution rate has been determined by the variation of the medium acidity, and the precipitation of goethite has been determined by gravimetric measurements. With respect to Cl⁻, the SO₄²⁻anion decreases the rate of the two reactions. NH₄⁺acts as an inhibitor when it is present at low concentrations and as an accelerator for higher concentrations; the limit corresponding to the change of NH₄⁺behavior depends on the nature of the counter ion. The reaction product is composed of pure goethite in the presence of sulfate salts, whereas a mixture of goethite and lepidocrocite, respectively, 60–70 and 40–30%, was observed in the presence of chloride salts.     

Enhanced upconversion emission in Er3+-doped tellurite glass containing silver nanoparticles

Er³⁺-doped tellurite glass containing silver nanoparticles (NPs) has been synthesized. Detailed structural and optical characterizations have been carried out. Infrared to visible frequency upconversion (UC) emission has been observed in Er³⁺-doped tellurite glass on pumping with the 976 nm radiation. Further, an enhancement in UC emission intensity of green bands (²H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2) of Er³⁺ ion has been observed up to four times in presence of silver NPs in the glass annealed at 240 °C for 40 h. Though, there is enhancement in intensity in the red band (⁴F_9/2 → ⁴I_15/2) also but it is smaller. The enhancement in fluorescence intensity is attributed to local field effect due to the silver NPs.     

新型三脚架苯甲醛苯腙醋酸根选择性比色化学传感器

本文合成了一个新的基于三脚架苯甲醛苯腙的能够选择地检测醋酸根离子的比色化学传感器1。用紫外可见吸收光谱证实了受体1在二甲基亚砜溶液中对醋酸根离子高选择的键合能力超越了其它阴离子。和其他所研究的阴离子相比,其在二甲基亚砜中紫外可见吸收光谱对具有高选择性醋酸根离子的存在显示了应答,当存在（2´10^-5mol·dm^-3）醋酸根离子时其溶液的颜色也由黄色变化到蓝色。当用其他不同的客体阴离子（F^-, Cl^-, Br^-, I^-, H₂PO₄ ^–和 OH^-）处理受体1时,仅出现了很小的紫外可见吸收光谱变化。受体1对醋酸根的结合常数 K_ass为1.69´ 10⁴。     

Extraction Chromatography of Pd2+-Thiourea Complex

Abstract

The Pd²⁺-thiourea complex formed in perchloric acid medium in the presence of NaCIO₄., has been extracted quantitatively into tri-N-butyl phosphate (TBP) supported as a stationary phase on a column of Voltalef (polychloro-trifluoro ethylene). The complex was eluted with water and determined by atomic absorption spectrometry and polarography. Pd²⁺ can be estimated in the presence of Ir⁴⁺ and Au³⁺, but Pt⁴⁺ interferes seriously.     

Study on Synthesis and Binding Ability of a New Anion Receptor Containing NH Binding Sites

A new colorimetric recognition receptor 1 based on the dual capability containing NH binding sites of selectively sensing anionic guest species has been synthesized. Compared with other halide anions, its UV/Vis absorption spectrum in dimethyl sulfoxide showed the response toward the presence of fluoride anion with high selectivity, and also displayed dramatic color changes from colorless to yellow in the presence of TBAF （5 × 10^-5 mol/L）. The similar UV/Vis absorption spectrum change also occurred when 1 was treated with AcO^- while a little change with H2PO^-4 and OH^-. Receptor 1 has almost not affinity abilities to Cl^-, Br^- and I^-. The binding ability of receptor 1 to fluoride with high selectivity over other halides contributes to the anion size and the ability of forming hydrogen bonding. While the different ability of binding with geometrically triangular （AcO^-）, tetrahedral （H2PO^-4 ） and linear （OH^-） anions maybe result from their geometry configuration.     

Adsorption of51Cr(VI) on manganese dioxide from aqueous solution

Sorption of⁵¹Cr(VI) by MnO₂ has been studied as a function of pH and ionic concentration in the presence of certain added cations and anions. The findings are explained in the light of deprotonation/hydroxyl ion association reaction on oxide surface and its subsequent interaction with the tracer. Infrared spectroscopy has shown the chemical interaction of Cr(VI) on the surface of MnO₂. The influence of certain interfering ions has been shown on the sorption of⁵¹Cr(VI) on MnO₂ surface. An attempt has been made to concentrate traces of⁵¹Cr under optimum experimental conditions. The experimental observation shows that the activity sorbed under specified conditions can be recovered appreciably by leaching the pre-adsorbed carrier.     

The Influence on Interfacial Tension of the Combination of Anionic and Cationic Surfactants: Alkyl Sulfonate/Alkyltrimethylammonium Bromide

Mioellization of aqueous mixture of sodium octyl sulfonate ( C₈As )/ cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfonate (C₁₂As)( CTAB in the presence of sodium bromide has been studied by surface tension measurement. Nonideal solution theory has been used to calculate the molecular interaction parameters (β^M and β^s). The oil-aqueous interfacial tensions of C₁₂As/ CTAB, C₈As/CTAB, C₁₂As/dodecyl trimethylammonium bromide (DTAB) systems were also measured. We studied the influence of the surfactant concentration, surfactant molar fraction ratio, hydrocarbon chain length, added NaCl and alcohol concentration on the interfacial tension.     

A new solvent system for the separation of Th4+, UO 2 2+ and Zr4+ in the presence of common anions by thin-layer chromatography

Summary A TLC method has been developed for separating Th⁴⁺, UO₂ ²⁺ and Zr⁴⁺ in the presence of some common anions using a dimethylamine/acetone/formic acid mobile phase. Capacity factors, separation factors and resolution for the separation of Th⁴⁺ from UO₂ ²⁺ have been evaluated. The effect of the pH of the sample on R_F values of Th⁴⁺, UO₂ ²⁺, Ni²⁺ and Cu²⁺ has also been examined.     

472—Model reactions of nucleotide sorption: Part I. Interaction between adenine nucleotides and interface in the hydrocarbon-water-cetyltrimethyl ammonium bromide system

A study has been made of the binding between nucleotides (ATP, ADP) and other anions (HP₃O₁₀^4?, HP₂O₇^3?, HPO₄^2?, SO₄^2?) on the interface in the heptane-water-cetyltrimethylammonium bromide (CTAB) system. The binding between anions and their complexes with CTAB on the interface was registered by two methods: by change in interphase tension values and by change in the potential jump on the interface. The energies of binding of the above anions on the interface in the presence of CTAB are determined.The data obtained enabled us to assess the energy of binding of a negative charge with the interface (- ΔG ? 14.6 ± 0.7 kJ/unit charge).A model has been suggested for a study of the behaviour of the interface-CTAB-anion system and the conditions for specific nucleotide binding have been chosen.     

Adsorption of zinc(II) on hydrous iron oxides

The adsorption of Zn²⁺ ions on amorphous Fe(OH)₃ and -Fe₂O₃, as a function of pH, has been investigated. In the pH region corresponding to the formation of positively charged Zn-hydroxy complexes, an abrupt increase in adsorption was observed. The influence of EDTA and glycine on the adsorption of Zn²⁺ by -Fe₂O₃ has also been investigated. Strong suppression of the adsorption of Zn²⁺ was observed for high [EDTA or Gly]/[Zn²⁺] concentration ratios. The results of the adsorption of Zn²⁺ in the presence of an organic ligand were explained by the formation of Zn-EDTA or Zn-glycine complexes and also by the occupation of adsorption sites by the free organic ligand.     

Extraction of calcium by a nitrobenzene solution of bis-1,2-dicarbollylcobaltate in the presence of 15-crown-5

Extraction of calcium by a nitrobenzene solution of bis-1,2-dicarbollylcobaltate in the presence of 15-crown-5 (15C5, L) has been investigated. The equilibrium data and the typical maxima concerning the dependence of the Ca distribution ratios on the analytical concentration of 15C5 in the system under study can be explained assuming that the HL⁺, HL₂ ⁺ and CaL²⁺, CaL₂ ²⁺ particles are extracted into the nitrobenzene phase. The values of the corresponding extraction and stability constants of the extracted species in nitrobenzene saturated with water have been determined and the mutual Sr/Ca separation has been discussed     

Potential oscillations in the course of galvanostatic oxidation of hydrogen at platinum electrode in the presence of electrosorbing cations

An assumption has been made that in the presence of electrosorbing cations potential oscillations should be observed in the course of galvanostatic oxidation of hydrogen on platinum electrode. The reality of this assumption has been proved in the presence of Cd²⁺, Cu²⁺, Sn²⁺, Bi³⁺, Ag⁺ ions using different base electrolytes (H₂SO₄, HCl, HClO₄). Some features connected with these oscillation phenomena were considered.     

1-(d-Glucopyranosyl-2′-deoxy-2′-iminomethyl)-2-hydroxynaphthalene as chemo-sensor for Fe in aqueous HEPES buffer based on colour changes observable with the naked eye

A new glucose-based C2-derivatized colorimetric chemo-sensor (L₁) has been synthesized by a one-step condensation of glucosamine and 2-hydroxy-1-naphthaldehyde for the recognition of transition metal ions. Among the eleven metal ions studied, viz., Mg²⁺, Ca²⁺, Mn²⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺ and Hg²⁺, L₁ results in visual colour change only in the presence of Fe²⁺, Fe³⁺and Cu²⁺ in methanol. However, in an aqueous HEPES buffer (pH 7.2) it is only the Fe³⁺ that gives a distinct visual colour change even in the presence of other metal ions, up to a concentration of 280 ppb. The changes have been explained based on the complex formed, and the composition has been determined to be 2:1 between L₁ and Fe³⁺ based on Job’s plot as well as ESI MS. The structure of the proposed complex has been derived based on HF/6-31G calculations.     

Kinetics and mechanism of oxidation of anisole and substituted anisoles by acid bromate in acetic acid-water mixture

Oxidation of anisoles by acid bromate has been studied in acetic acid-water system in the presence of sulphuric acid. The reaction is first order each in [anisole] and [Br(V)]. The rate of reaction increased with increase in [H⁺] and percentage of acetic acid. The products of oxidation have been identified as ortho and para hydroxyanisoles. From the effect of [H⁺] and [acetic acid] on rate, H ₂ ⁺ BrO₃ has been established as the reactive species. Anisoles having electron-donating substituents in the benzene ring accelerate the rates and vice versa with a Hammett ρ value of −0.6. A mechanism involving the attack of H ₂ ⁺ BrO₃ on ortho/para position of the anisole in the rate-determining step has been proposed.     

Electrochemically reduced tungsten‐based active species as catalysts for cross‐metathesis reactions: cross‐metathesis of erucic acid with 2‐octene

The cross‐metathesis of erucic acid, (CH₃(CH₂)₇CH?CH(CH₂)₁₁COOH), with an excess of 2‐octene in the presence of an electrochemically produced tungsten‐based catalyst has been studied. Cross‐ and self‐hydrocarbon products, viz. 2‐undecene (C₁₁), 6‐dodecene (C₁₂) and 6‐pentadecene (C₁₅), were detected. The influence of several parameters, such as the 2‐octene/erucic acid and 2‐octene/catalyst ratios and the reaction time, on the yield of the cross‐metathesis product, 6‐pentadecene, was studied. The cross‐metathesis of functionalized olefins in the presence of an Al–e^?–WCl₆–CH₂Cl₂ system has not been reported in the literature so far. The cross‐metathesis products in the presence of this catalyst system can be obtained with high yield and high specificity. Copyright © 2004 John Wiley & Sons, Ltd.     

Reactions of Ru3(CO)12 with 2-pentynal-diethyl-acetal. The crystal structure of Ru2(CO)6[μ-η-{EtC2C(H)(OEt)2}CO{EtC2C(H)(OEt)2}] and its reactivity towards tetraethyl-orthosilicate

The title compound has been obtained in considerable yield by reacting Ru₃(CO)₁₂ with 2-pentynal-diethyl-acetal [CH₃CH₂CCC(H)(OEt)₂] (PDA) in hydrocarbon solvents. The X-ray analysis shows that the title complex belongs to the well known family of the flyover derivatives. Some X-ray structural studies have been reported, many years ago, on di-iron flyover complexes; in contrast only a few examples of diruthenium derivatives have been structurally characterized.The complex contains ethoxy-groups which could potentially undergo hydrolysis in the presence of tetraethyl-orthosilicate (TEOS) in the presence of catalysts. Reactions of complex Ru₂(CO)₆[μ-η⁴-{EtC₂C(H)(OEt)₂}CO{EtC₂C(H)(OEt)₂}] with TEOS in the presence of HCl or of NaF (as catalysts) have been attempted. An inorganic-organometallic sol-gel material containing the skeleton of the complex has been obtained and characterized with IR-Raman, XRD on powders and SEM microscopy.     

Mn(III) oxidation of peptides: A mechanistic investigation of kinetic variations in hydrophobic‐induced oxidation of tetrapeptides of elastin sequences

Four tetrapeptide analogues of elastin sequences, glycyl‐glycyl‐alanyl‐proline (GGAP), glycyl‐glycyl‐valyl‐proline (GGVP), glycyl‐glycyl‐isoleucyl‐proline (GGIP), and glycyl‐glycyl‐phenylalanyl‐proline (GGFP) were synthesized, based on their increasing order of hydrophobicity, by a classical solution phase method and were characterized. These tetrapeptides (TETPs) were oxidized using Mn(OAc)₃ in 25% acetic acid at 298 K, and the kinetics of the reaction was monitored spectrophotometrically at λ_max = 400 nm. A first‐order dependence of rate on each of [Mn(OAc)₃], [OAc^?], and substrate [TETP], an inverse order dependence on [H⁺], has been observed. The rate is independent of [Mn(II)]. However, an inverse order dependence on varying the dielectric constant using various percentages (v/v) of acetic acid has also been observed, and but addition of anions such as Cl^? and ClO₄^? has insignificant effect on the rate. Activation parameters have been evaluated using the Arrhenius and Erying plots. The oxidation products were isolated and characterized. Based on the results obtained, a plausible mechanism involving [Mn(OAc)₄]^? has been proposed. An apparent correlation was noted between the rate of oxidation of these TETPs by Mn(III) in the presence of sulfate ions in sulfuric acid medium and Mn(OAc)₃ in the acetic acid medium. The rate of oxidation with Mn(OAc)₃ was observed to be slower than with the former. The rate of oxidation of GGFP was found to be higher than GGIP, GGVP, and GGAP. This may be due to the presence of an aromatic side chain and/or because of the increased hydrophobicity. The overall order of rate of oxidation of TETPs is GGFP > GGIP > GGVP > GGAP, which also represents an increasing order of their hydrophobicity. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 115–123, 2006     

The directional reaction of hydrazine with silver complexes. Part 2. Influence of acidity and temperature

The influence of acidity and temperature on the reaction of two-coordinate silver complexes with N₂H₄ has been studied. The N₂(F)% which represents the percentage of N₂ formed by the four-electron oxidation of N₂H₄ [Reaction (A)] was greatly increased by the presence of a trace of Cu^II ion in the system. The N₂(F)% was also enhanced by increasing the pH and temperature in the absence of Cu^II ion. In addition, the N₂(F)% was linearly related to log ₂ for the silver complexes. The log of the N₂(O)% which represents the percentage of N₂ formed by the one-electron oxidation of N₂H₄ [Reaction (B)] was linearly related to the 1/log₂ value in the presence of Cu^II ions.     

Photochemical reactions of molybdenum and tungsten octacyanometallates(IV) in acidic aqueous media containing 2,2′-bipyridyl or 1,10-phenanthroline

Summary The reaction scheme of acidic photolysis of [M(CN)₈]^4– (M = Mo or W) in the presence of 2,2-bipyridyl (bipy) or 1,10-phenanthroline (phen) based on previous reports, and the present results, is given. In this scheme the formation of [M(CN)₆(N-N)]^2– (M = Mo or W), postulated in the literature to be a main product of photoexcitation of [M(CN)₈]^4– in the presence of bipy or phen, has definitively been excluded. The main cyano-polypyridyl species formed are [MO(CN)₃(N-N)]^– ions which, in acidic solution, undergo further reactions. A new product, [MoO(CN)₂(N-N)₂], resulting from thermal replacement of the cyanide ligand by polypyridyl, has been detected.Author to whom all correspondence should be directed.     

CH bond activation in the presence or absence of oxygen or nitrous oxide

The reaction of C₂H₆with lattice oxygen, O^2- (in the absence of gaseous oxygen), or “adsorbedℍ oxygen (in the presence of gaseous oxygen) over NiMoO₄ catalysts has been performed and compared to C₃H₈ activation. The results obtained indicate that adsorbed oxygen exhibits a higher reactivity to C₂H₆, while lattice oxygen is more reactive relative to C₃H₈. Kinetic studies of these two reactions in presence of molecular oxygen have indeed shown that the ethane oxidative dehydrogenation (ODH) is dependent on the oxygen partial pressure, whilst on the contrary propane ODH is not. In order to confirm the presence of “adsorbed” oxygen for ethane activation, ODH tests have been performed with N₂O. On increasing temperature, the O^- adsorbed species enhances the mild oxidation of ethane. The activation energy of ethane consumption E_C2H6, relative to propane (E_C3H8 = 133 kJ/mol) is 145 kJ/mol. A possible mechanism is proposed for the oxidative dehydrogenation of ethane. This revised version was published online in August 2006 with corrections to the Cover Date.