Solubility of Lead Nitrate in Aqueous Solutions of Nitric Acid and Iron(III) Nitrate

Solubility of lead(II) nitrate in the system H₂O-Fe(NO₃)₃-HNO₃ was studied using the simplex-lattice method of experiment design.     

Solvent Effects on Complexation of Molybdenum（Ⅵ） with Nitrilotriacetic Acid in Different Aqueous Solutions of Propanol

By using spectrophotometric and potentiometric techniques the formation constants of the species formed in the systems H^＋＋ Mo（Ⅵ）＋nitrilotriacetic acid and H^＋ ＋ nitrilotriacetic acid have been determined in aqueous solutions of propanol at 25 ℃ and constant ionic strength 0.1 molodm^-3 sodium perchlorate. The composition of the complex was determined by the continuous variation method. It was shown that molybdenum（Ⅵ） forms a mononuclear 1 ： 1 complex with nitrilotriacetic acid of the type MoO3L^-3 at -lg[H^＋] =5.8. The formation constants in various media were analyzed in terms of Kamlet and Taft＇s parameters. Linear relationships were observed when lg Ks was plotted versusp. Finally, the results were discussed in terms of the effect of solvent on complexation.     

N-(1-萘基)氨基乙酸的激发态分子内电荷转移和电子转移

氨基酸是蛋白质的基本结构单位 ,水溶液中基态氨基酸分子以内盐形式存在 [1] .由于质子化氨基的正诱导效应 ,羧基的离解常数显著提高 ,如氨基乙酸的羧基离解常数 ( 4.57× 1 0 -3mol/L,2 5℃ [1] )是乙酸 ( 1 .74× 1 0 -5 mol/L[2 ] )的 2 63倍 ;同时内盐结构亦使氨基酸和肽链具有分子内电偶极 ,后者已在肽链上电荷转移过程的调控中发挥重要作用 [3,4] .激发态氨基酸或肽的诱导效应和电偶极性质的研究尚未见报道 ,其主要原因可能是难有合适的激发方式和研究方法 .然而相关研究应予重视 ,因为研究结果将可能为生物酶活性的调节提供一种新的…     

铬(III)离子催化铈(IV)离子氧化四氢糠醇的反应动力学及机理

在酸性介质中用氧化还原滴定法研究了铈(IV)离子在铬(III)离子催化作用下,于25～40℃区间氧化四氢糠醇的反应动力学.结果表明反应对铈(IV)和四氢糠醇均为一级.准一级速率常数kobs随催化剂[Cr(III)]增加而增大,亦随[H+]增加而增大,而随[HSO-4]增加而减小.在氮气保护下,反应不能引发丙烯酰胺聚合,说明在反应中没有自由基产生.提出了催化剂、底物和氧化剂间生成双核加合物的反应机理.通过kobs与HSO-4的依赖关系,并结合Ce(IV)在溶液中的平衡,找到了本反应体系的动力学活性物种是Ce(SO4)2.还计算出一些速率常数及相应的活化参数.     

铬(III)离子催化铈(IV)离子氧化四氢糠醇的反应动力学及机理

在酸性介质中用氧化还原滴定法研究了铈(IV)离子在铬(III)离子催化作用下, 于25～40 ℃区间氧化四氢糠醇的反应动力学. 结果表明反应对铈(IV)和四氢糠醇均为一级. 准一级速率常数k_obs随催化剂[Cr(III)]增加而增大, 亦随[H^＋]增加而增大, 而随增加而减小. 在氮气保护下, 反应不能引发丙烯酰胺聚合, 说明在反应中没有自由基产生. 提出了催化剂、底物和氧化剂间生成双核加合物的反应机理. 通过k_obs与的依赖关系, 并结合Ce(IV)在溶液中的平衡, 找到了本反应体系的动力学活性物种是Ce(SO₄)₂. 还计算出一些速率常数及相应的活化参数.     

The Reductions of Bis(terpyridyl) and Ethylenediaminetetraacetato Complexes of Cobalt(III) by Ascorbic Acid

The reductions of Co(terpy)₂³⁺ and Co(edta)^? complexes by ascorbic acid have been subjected to a detailed kinetic study in the range of pH =1–10.9. For each complex the rate law of the reaction is interpreted as a rate determining reaction between Co(III) complex and the ascorbic acid in the form of HA^? (k₁) and A^2? (k₂), depending on the pH of the solution, followed by a rapid scavenge of the ascorbic acid radicals by Co(III) complex. With given Ka₁ and Ka₂, the rate constants are k₁ = 0.25 and 9.87 × 10^?5 M^?1s^?1, k₂ = 1.28 × 10⁶ and 18.7 M^?1s^?1 for Co(terpy₎2³⁺and Co(edta)^? complexes, respectively, at T = 25 °C and μ = 0.50M (terpy)and 1.0 M (edta) HClO₄/LiClO₄. The mechanism of the reaction is discussed on the basis of Marcus theory for outer sphere electron transfer process. Spin change and charge effect, duly considered, account for the non‐adiabatic behavior in the reduction of Co(edta)^? complex.     

Thickening and Associating Behavior in Aqueous Solutions of a Terpolymer with Poly(ethylene oxide) Side Chains

A water-soluble terpolymer (PAVA) was synthesized by aqueous free radical copolymerization technique using acrylamide(AM), sodium 2-acrylamido-2-methylpropane-sulphonate (NaAMPS) and a macromonomer: p-vinylbenzyl-terminated octylphenoxy poly(ethylene oxide) (VPEO, degree of polymerization: 10). The remarkable intermolecular hydrophobic associations were formed in water and a brine solution for this polymer, which resulted in a good thickening effect, resistance to salt and salt-thickening. The hydrophobically associating microstructures of PAVA in aqueous solutions were measured by the fluorescent probe and scanning electron microscope. As polymer concentration was increased in water and brine solutions, the associating strength and non-polarity of hydrophobic microdomains increased remarkably. However, at the polymer concentrations higher than 0.20 g/dL, the non-polarity of hydrophobic microdomains tended to remain constant, and the I ₁/I ₃ value changed slightly in 0.5 g/dL NaCl. The continuous associating structures were formed by the expanded polymer chains in brine solutions, as well as in water. As the NaCl concentration increased, the non-polarity of associating microstructures increased slowly, but the compact degree of these microstructures increased.     

Europium(III) Catalysis for Reduction of Thionine Dye by Selenous Acid in Aqueous Sulfuric Acid Solutions: A Kinetic and Mechanistic Approach

The catalytic effect of europium(III) on the reduction of thionine dye (Th) by selenous acid has been studied by spectrophotometry in aqueous sulfuric acid solutions at a constant ionic strength of 3.0 mol dm^?3 and at different temperatures (283–313 K). A first‐order dependence with respect to both [Th] and [Eu^III] was obtained, whereas the orders with respect to [Se^IV] and [H⁺] were less than unity. Variation of ionic strength and dielectric constant of the reaction media did not affect the reaction rates. Probable mechanistic schemes for thionine reductions in both the absence and presence of europium(III) catalyst were proposed. The rate laws associated with the reaction mechanisms were derived, and the reaction constants were calculated. The activation parameters of the rate constants of the slow steps of both uncatalyzed and catalyzed reactions along with thermodynamic quantities of the equilibrium constants are computed and discussed.     

Catalytic Conversion of Xylose to Furfural by p-Toluenesulfonic Acid (pTSA) and Chlorides: Process Optimization and Kinetic Modeling

Furfural is one of the most promising precursor chemicals with an extended range of downstream derivatives. In this work, conversion of xylose to produce furfural was performed by employing p-toluenesulfonic acid (pTSA) as a catalyst in DMSO medium at moderate temperature and atmospheric pressure. The production process was optimized based on kinetic modeling of xylose conversion to furfural alongwith simultaneous formation of humin from xylose and furfural. The synergetic effects of organic acids and Lewis acids were investigated. Results showed that the catalyst pTSA-CrCl₃·6H₂O was a promising combined catalyst due to the high furfural yield (53.10%) at a moderate temperature of 120 °C. Observed kinetic modeling illustrated that the condensation of furfural in the DMSO solvent medium actually could be neglected. The established model was found to be satisfactory and could be well applied for process simulation and optimization with adequate accuracy. The estimated values of activation energies for xylose dehydration, condensation of xylose, and furfural to humin were 81.80, 66.50, and 93.02 kJ/mol, respectively.     

Electrochemistry and Spectroelectrochemistry of the Pu (III/IV) and (IV/VI) Couples in Nitric Acid Systems

The solution chemistry of Pu in nitric acid is explored via electrochemistry and spectroelectrochemistry. By utilizing and comparing these techniques, an improved understanding of Pu behavior and its dependence on nitric acid concentration can be achieved. Here the Pu (III/IV) couple is characterized using cyclic voltammetry, square wave voltammetry, and a spectroelectrochemical Nernst step. Results indicate the formal reduction potential of the couple shifts negative with increasing acid concentration and reversible electrochemistry is no longer attainable above 6 M HNO₃. Spectroelectrochemistry is also used to explore the irreversible oxidation of Pu(IV) to Pu(VI) and shine light on the mechanism and acid dependence of the redox reaction.     

Kinetics and Mechanism of Catalytic Reduction of U(VI) with Hydrazine on Platinum Catalysts in Nitric Acid Media

The kinetics of U(IV) produced by hydrazine reduction of U(VI) with platinum as a catalyst in nitric acid media was studied to reveal the reaction mechanism and optimize the reaction process. Electron spin resonance (ESR) was used to determine the influence of nitric acid oxidation. The effects of nitric acid, hydrazine, U(VI) concentration, catalyst dosage and temperature on the reaction rate were also studied. In addition, the simulation of the reaction process was performed using density functional theory. The results show that the influence of oxidation on the main reaction is limited when the concentration of nitric acid is below 0.5 mol/L. The reaction kinetics equation below the concentration of 0.5 mol/L is found as: -dc(UO₂²⁺)/dt)=kc^0.5323(UO₂²⁺)c^0.2074(N₂H₅⁺)c^-0.2009(H⁺). When the temperature is 50 ℃, and the solid/liquid ratio r is 0.0667 g/mL, the reaction kinetics constant is k=0.00199 (mol/L)^0.4712/min. Between 20 ℃ and 80 ℃, the reaction rate gradually increases with the increase of temperature, and changes from chemically controlled to diffusion-controlled. The simulations of density functional theory give further insight into the influence of various factors on the reaction process, with which the reaction mechanisms are determined according to the reaction kinetics and the simulation results.     

Modelling and Optimization of Stability Constants of Cadmium or Zinc with Biological Buffers (DIPSO or TAPS) in Aqueous Solutions by Electrochemical Techniques

The complexation behavior of four systems involving cadmium(II) or zinc(II) in aqueous solutions with the biological buffers 3-[N,N-bis(2-hydroxyethyl)amino]-2-hydroxypropanesulfonic acid (DIPSO), and [(2-hydroxy-1,1-bis(hydroxymethyl)ethyl)amino]-1-propanesulfonic acid (TAPS) was studied by direct current polarography (DCP) and glass electrode potentiometry (GEP), at 25.0 ± 0.1 °C and ionic strength 0.1 mol·dm^?3 KNO₃. Except for the Cd–TAPS system, for which full characterization of the system was possible either by DCP or GEP, full characterization of the other metal-buffer systems (Zn–DIPSO, Zn–TAPS and Cd–DIPSO) was only possible using DCP. For Zn-buffers systems, ZnL⁺ and $ {\text{ZnL(OH)}}_{2}^{ - } $ ZnL(OH) 2 ? (where L stands for buffer) were identified. For the Zn–DIPSO system, the overall stability constant values (as log₁₀ β) are 2.1 ± 0.2 and 13.4 ± 0.2, respectively. For the Zn–TAPS system, the overall stability constants values (as log₁₀ β) are 2.4 ± 0.1 and 12.9 ± 0.3, respectively. For the Cd–DIPSO system, the overall stability constants values (as log₁₀ β) of CdL⁺ and CdL(OH) are 2.9 ± 0.1 and 6.9 ± 0.3, respectively. For the Cd–TAPS system, only the species CdL⁺ was identified with log₁₀ β = 2.5 ± 0.1.     

Complexation and Electronic Spectra of Neodymium(III)–Amino Acid–1,10-Phenanthroline Systems in Aqueous Solution

Complexation of neodymium(III)-glutamate(glu)-phenanthroline(phen), neodymium(III)-aspartate(asp)-phenanthroline(phen) ternary systems and the corresponding binary systems in aqueous solution are discussed at various values of pH. Based on change regularity of hypersensitive transition intensities, the neodymium(III)-aspartate-phenanthroline ternary complex has a general formula of Nd(asp)₃phen, but the composition of the complex of Nd(III) with glutamate and phenanthroline is complicated and has not been determined. The electronic spectra of these complexes were studied, Slater-Condon parametersF _k ^s and the Lande parameter ξ_4f were obtained. The rms deviation between calculated and observed energy levels is less than 43 cm⁻¹. Bonding in these complexes are also investigated and bonding parameters calculated. The results show that Nd(III) and amino acids form complexes by ionic linkage with carboxylic oxygens, but with some weak covalency. Besides, the degrees of covalency in ternary complexes are larger than those in binary complexes.     

聚(D,L)-乳酸的合成及生理盐水降解性

聚(D; L)-乳酸的合成及生理盐水降解性;聚(D; L)-乳酸;D; L-丙交酯;生理盐水;降解性     

Kinetics and Mechanism of the Oxidation of Vanillin by Hexacyanoferrate(III) in Aqueous Alkaline Medium

The title reaction was investigated in aqueous alkaline medium. A first-order dependence in hexacyanoferrate(III) concentration and a fractional order in both vanillin and alkali were obtained at the concentrations studied. The added product, hexacyanoferrate(II), had a retarding effect on the rate of reaction. Ionic strength and dielectric constant of the reaction medium have little effect on the reaction rate. The effect of temperature on the rate of reaction has also been studied and activation parameters have been evaluated. A mechanism based on the experimental results is proposed and the rate law is derived. The reaction constants are calculated and used to regenerate the k_obs values, which are compared with the experimental values.     

Investigation of the Dissociation and Dimerization of Cyclamic Acid in Aqueous Solutions by Means of a Conductometric Method

The electrical conductivity of aqueous cyclamic acid was studied in the concentration range (0.0004<c/mol⋅dm⁻³<0.14) at temperatures ranging from 278.15 to 303.15 K. Conductivities were measured by a precise method and examined by applying extended conductivity equations taking into account dimerization and incomplete electrolyte dissociation. Limiting molar electrolyte and ionic conductivities, dissociation and dimerization constants, and thermodynamic functions associated with dissociation and dimerization of cyclamic acid are discussed.     

微波辐射下氨磺酸催化水相合成3,3-亚芳基双(4-羟基香豆素)

在水介质中, 用氨磺酸作催化剂并经微波辐射, 使芳醛与4-羟基香豆素反应合成3,3-亚芳基双(4-羟基香豆素), 具有催化剂易得、环境友好、后处理简便、反应时间短和产率高等优点.     

Determination of Hydroxy-2-ethylenediaminetriacetic Acid (HEEDTA) and Fe-HEEDTA in Nutrient Solutions by Ion-Pair Reversed-Phase High-Performance Liquid Chromatography

A reversed-phase ion-pair liquid chromatography method for the accurate detection and determination of hydroxy-2-ethylenediaminetriacetic acid (HEEDTA) and Fe-HEEDTA has been developed. Three mobile phases containing 0.05 M tetrabutylammonium hydroxide, 0.05 M tetrabutylammonium bromide, or 0.05 M tetrabutylammonium bromide + phosphate buffer were employed in this method. Iron was added to each mobile phase after addition of the selected ion pair reagent to determine the amount of HEEDTA in both the free and/or the metal chelated forms at concentrations as low as 50 μM. The method depends on the formation of the iron chelate with HEEDTA in the mobile phase at pH 7. Calculation of the amounts of chelated HEEDTA with iron in the mobile phase was verified using the Geochem-PC computer program, which showed that 99.95% of HEEDTA was chelated to iron at pH 7.     

乙酸在Rh(100)表面吸附和分散的HREELS和TDS研究

 用高分辨电子能量损失谱（HREELS）和热脱附谱（TDS）研究了乙酸在Rh（100）表面上的吸附和分解,提出了乙酸吸附和分解反应的模式．130K时,高暴露量的乙酸在Rh（100）表面上形成多层吸附的凝聚态乙酸．升温至290K时,部分乙酸以分子形式直接脱附,另一部分乙酸分子通过O—H键断裂形成乙酸根和氢吸附在表面上;在升温至400K的过程中,乙酸根在表面发生两个相互竞争的反应,即乙酸根分解成CO,CHx,O和H,以及乙酸根分解成CHx,H和CO2;升温至500K,只剩下CHx,O和CO吸附在表面上;600K后,表面吸附的CHx完全解离,同时表面吸附的碳原子和氧原子结合成CO脱附．