Sorption kinetics for the removal of aldehydes from aqueous streams with extractant impregnated resins

The sorption kinetics for the removal aldehydes from aqueous solutions with Amberlite XAD-16 and MPP particles impregnated with Primene JM-T was investigated. A model, accounting for the simultaneous mass transfer and chemical reaction, is developed to describe the process. It is based on the analogy to the diffusion and reaction in a stagnant liquid sphere, but corrected for the porosity and particle properties influencing the diffusion. The developed model describes the kinetic behavior of the process in the low concentration region rather well. However, in the high concentration region, larger discrepancies are observed. Initially, the influence of the flow rate was investigated to eliminate the effect of the external mass transfer. The influence of the particle morphology was investigated for both physical and reactive sorption. Physical sorption experiments were used to determine the factor τ that takes the particle properties influencing the diffusion into account. It was shown that the diffusion is faster in XAD-16 than in MPP impregnated systems. Reaction rate constant k _x was determined by fitting the model to the experimental data. Sorption of benzaldehyde appears to be significantly slower (k _x ∼10⁻⁴ l/mol s) than the sorption of pentanal (k _x ∼10⁻³ l/mol s) due to the slower chemical reaction. The influence of the particle size was investigated for the sorption of pentanal with XAD-16. It was observed that the particle size does influence the diffusion term, but does not have an effect on the reaction rate. On the other hand, the extractant loading influences the reaction rate slightly in the low concentration region, whereas the initial concentration of the solute has more pronounced effect.     

Ab initio molecular orbital study of the flavin-catalyzed dehydrogenation reaction of glycine - protein transport channel driving hydride-transfer mechanism

The reaction mechanism of flavin-catalyzed dehydrogenation of glycine has been studied by ab initio molecular orbital calculations using the 6-31G* basis set. 10-Methyl isoalloxazine (10-MIA) has been used as the flavin model compound. The results showed that when we assume a proton transport channel in amino acid oxidase, which is switched on by the substrate anion, the O12-protonated 10-MIA [10-MIAH⁺(O12)] is generated. The main structure of 10-MIAH⁺(O12) is one in which the central ring is expressed by an NAD⁺-like structure, which is favorable for driving the hydride-transfer reaction, i.e., the abstraction of the α-hydrogen of glycine by the hydride-transfer mechanism. We have found that this protonation results in a dramatic lowering of the activation energy of the reaction. The proposed mechanism is summarized as follows: the hydride transfer proceeds via two-electron transfer and synchronous intramolecular proton transfer → intermolecular proton transfer. Received: 10 August 1998 / Accepted: 17 September 1998 / Published online: 8 February 1999     

Investigation of copper(II) complexation by glycylglycine using isothermal titration calorimetry

Isothermal titration calorimetry (ITC) and potentiometric titration methods have been used to study the process of proton transfer in the copper(II) ion-glycylglycine reaction. The stoichiometry, conditional stability constants, and thermodynamic parameters (ΔG, ΔH, and ΔS) for the complexation reaction were determined using the ITC method. The measurements were carried out at 298.15 K in solutions with a pH of 6 and the ionic strength maintained with 100 mM NaClO₄. Carrying out the measurements in buffer solutions of equal pH but different enthalpies of ionization of its components (Mes, Pipes, Cacodylate) enabled determination of the enthalpy of complex formation, independent of the enthalpy of buffer ionization. The number of protons released by glycylglycine on account of complexation of the copper(II) ions was determined from calorimetric and potentiometric measurements.     

Effect of particle size on pyrolysis characteristics of Elbistan lignite

In this study, the relationship between particle size and pyrolysis characteristics of Elbistan lignite was examined by using the thermogravimetric (TG/DTG) and differential thermal analysis (DTA) techniques. Lignite samples were separated into different size fractions. Experiments were conducted at non-isothermal conditions with a heating rate of 10°C min⁻¹ under nitrogen atmosphere up to 900°C. Pyrolysis regions, maximum pyrolysis rates and characteristic peak temperatures were determined from TG/DTG curves. Thermogravimetric data were analyzed by a reaction rate model assuming first-order kinetics. Apparent activation energy (E) and Arrhenius constant (A _r) of pyrolysis reaction of each particle size fraction were evaluated by applying Arrhenius kinetic model. The apparent activation energies in the essential pyrolysis region were calculated as 27.36 and 28.81 kJ mol⁻¹ for the largest (−2360+2000 μm) and finest (−38 μm) particle sizes, respectively.     

Intramolecular reorganization 1. Deprotonation of toluene with the CH<Subscript>2</Subscript>CN<Superscript>−</Superscript> anion: an analysis in the framework of a gas-phase model

A mechanism is proposed of intramolecular reorganization leading to equalization of the energies of reactants and products in a nonequilibrium proton transfer reaction. The model proposed allows one to extend a conventional quantum chemical treatment to gas-phase proton transfer. Taking the reaction of toluene deprotonation with the CH₂CN⁻ anion (a conjugate base of acetonitrile) as an example, it was shown that the activation energy and its components can be determined from direct ab initio calculations. The effect of disbalance of structural changes relative to the “equilibrium” proton transfer is considered. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1808–1815, September, 2008.     

Tautomerism of quinazolin-4-ones with 2,3-annulated hydrogenated 1,3-diazaheterocycles. Synchronous and asynchronous double proton transfer in cyclic hydrogen-bonded associates

It was shown by quantum chemical methods and ¹H NMR spectroscopy that in the series of prototropic tautomeric quinazolin-4-ones with hydrogenated 1,3-diazaheterocycles annulated at positions 2 and 3, namely, imidazole, pyrimidine, or [1,3]diazepine (compounds 1–3, respectively), the 1H-tautomeric form strongly predominates in the gas phase and in solutions regardless of the nature of these cycles. Tautomerization of tricycles 1–3 occurs via the intermolecular mechanism to form as intermediates hydrogen-bonded cyclodimers of these compounds or their cyclosolvates with proton-donor solvents. The key step of the reaction is the intraassociated concerted double proton transfer, which can proceed in nearly synchronous and asynchronous modes. In particular, double proton transfer in cyclodimers of quinazolinones 1–3 is asynchronous and proceeds with the formation of solvate-stabilized polar transition states, which are similar in structure to ionic intermediates of the nonconcerted double proton transfer.     

Preparation of polyalkylcyanoacrylate nanoparticles with various morphologies

The effects of various reaction conditions on the preparation of polyalkylcyanoacrylate (PACA) nanoparticles are studied. The PACA nanoparticles with different crosslinking degrees and morphology are prepared. Addition of crosslinkers can not only adjust the particle size, but also change the morphology of PACA nanoparticles. Moreover, the loose network structure of the PACA nanoparticles with “core/shell-like” morphology is investigated by AFM and TEM in detail.     

Diffusion mechanism of water vapour in a zeolitic tuff rich in clinoptilolite

The adsorption kinetics of H₂O in a clinoptilolite rich zeolitic tuff was experimentally investigated at 18°C. In the identification of the diffusion mechanism the isothermal adsorption model equation was used. It was found out that the intraparticle mass transfer becomes more dominant over the heat transfer with increase in particle size and the adsorptive dose pressure. Although initially intraparticle mass transfer was the controlling resistance later external heat transfer also contributes to the transfer mechanism.     

Reduction mechanism in class A methionine sulfoxide reductases: a theoretical chemistry investigation

Ab initio calculations at the B3LYP/6–311 ++G(2df,2p) and B3LYP/6–31G(d) level have been carried out to investigate the reaction mechanism of methionine sulfoxide reductases of class A. These enzymes reduce oxidized methionine in vivo and therefore play an important role in repairing protein damage caused by the oxidative stress. Our calculations have been carried out for a model reaction in a model active site. Several reaction mechanisms have been explored that can roughly be described as (2H⁺ + 2e⁻) or (H⁺ + e⁻). The results suggest that the actual reaction mechanism is of the (2H⁺ + 2e⁻) type corresponding to a more or less asynchronous-concerted double-proton transfer reaction leading to the formation of methionine (dimethylthioether in our model) and a sulfenic acid Cys-SOH. The Michaelis complex would involve one deprotonated Cys and one protonated Glu residues in the active site, this protonation state being mandatory to stabilize the sulfoxide substrate. Then, proton transfer from Glu to the substrate takes place, followed by proton transfer from one Tyr residue and fast reorganization of the system. The overall activation energy barrier is estimated to fall in the range 7–9 kcal/mol, much lower than the predicted barrier in DMSO solution (29.6 kcal/mol) reported before.     

不同浸润度聚苯胺的制备及性能

采用乳液聚合的方式,分别选取十二烷基硫酸钠(SDS)、十六烷基三甲基溴化铵(CTMAB)、聚乙二醇(PEG)作为分散剂,制得了浸润度不同的聚苯胺(PANI)。研究了不同类别分散剂对PANI性能的影响。采用扫描电镜(SEM)、X射线衍射(XRD)、水接触角(WCA)、傅里叶红外光谱(FT-IR)、紫外-可见光光谱(UV-Vis)、激光粒度仪等测试方法对PANI的结构与性能进行了分析,并通过循环伏安和交流阻抗实验研究了PANI的电化学性能。结果表明所有PANI样品均处于掺杂态,以PEG为分散剂的样品亲水性最佳,CTMAB次之,SDS最差。PEG为分散剂能够降低PANI的粒度,提高PANI的规整度进而增强其导电性能。阴离子分散剂SDS亲水端带负电,容易被质子掺杂的聚苯胺吸附,SDS的疏水端向外提供了PANI疏水性。SDS存在下合成的PANI粒度较大,电导率最低。阳离子型分散剂CTMAB因为其亲水端带正电不利于质子酸掺杂PANI,电荷转移阻抗较高。     

Kinetics and mechanism of oxygen electroreduction in acidic and neutral solutions on carbon black XC-72R modified by products of pyrolysis of cobalt 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin

Cathodic oxygen reduction on the XC-72R carbon black modified by the products of pyrolysis of cobalt 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin (CoTMPP) (XC-72M) was studied in acidic and neutral electrolytes. Formation of new active centers on XC-72M is confirmed by voltammetric curves (specific charge density grows as compared to the XC-72R carbon black by 2–2.5 times) using the methods of rotating disk electrode (a shift in half-wave potential E _1/2 by 600 mV) and rotating ring-disk electrode (the fraction of the direct reaction increases to 70%). Herewith, the $\frac{{\partial E_{1/2} }} {{\partial pH}}$\frac{{\partial E_{1/2} }} {{\partial pH}} value in the range of pH 0.3–8.5 is −60 mV. It is shown that proton necessarily participates in the slow stage of the first electron transfer for the further occurrence of the direct reaction to water. At a transition from acidic solutions to neutral ones, the polarization curves converge for XC-72M and XC-72R, which is due to a decrease in the concentration of proton in the solution and variation of the mechanism of the oxygen reduction slow stage.     

Mechanisms of photoinduced protolytic interactions of 2,5-diphenyloxazoleortho-hydroxy derivatives in media of various acidities

The mechanism of photoinduced intra- and intermolecular protolytic interactions ofortho-hydroxy derivatives of 2,5-diphenyloxazole in an aqueous alcohol medium was studied over a wide range of acidity from pH ∼13 toH ₀ of ∼−7. The spectral parameters of protolytic forms and equilibrium constants were obtained, and rate constants for the primary photochemical processes (excited-state intra- and intermolecular proton transfer reactions) were evaluated. It was shown that the spectral characteristics of oxazoleortho-hydroxy derivatives in an acidic medium are formed as a result of competition and interchange of intra- and intermolecular protolytic interactions. The phototautomeric form in strongly acidic solutions was found to be produced by dissociation of the cationic form with the protonated oxazole ring.     

Numerical Modeling in Radio Frequency Suspension Plasma Spray of Zirconia Powders

A comprehensive model was developed to investigate the suspension spraying for a radio frequency (RF) inductively coupled plasma torch. Firstly, the electromagnetic field is solved with the Maxwell equations and validated by the analytical solutions. Secondly, the plasma field with different power inputs is simulated by solving the governing equations of the fluid flow coupled with the RF heating. Then, the suspension droplets embedded with nano particles are modeled in a Lagrangian manner, considering feeding, collision, heating and evaporation of the suspension droplets, as well as tracking, acceleration, melting and evaporation of the nano or agglomerate particles. The non-continuum effects and the influence of the evaporation on the heat transfer are considered. This particle model predicts the trajectory, velocity, temperature and size of the in-flight nano- or agglomerate particles. The effects of operating conditions and intial inputs on the particle characteristics are investigated. The statistical distributions of multiple particles’ size, velocity, temperature are also discussed for the cases with and without consideration of suspension droplets collision.     

Synthesis,region of existence,structural characteristics,and conductivity of BI(CR,FE)VOX solid solutions

The results of our studies of solid solutions of the general composition Bi₄V_{2 − x} Fe _x/2Cr _x/2O_{11 − δ} are presented. The crystal-chemical parameters of different polymorphic modifications of BIMEVOX were determined. The particle size distribution was determined by laser diffraction and optical microscopy. The surface of sintered preforms was studied by scanning electron microscopy. The conductivity of sintered poly-crystalline samples as a function of temperature and composition was studied by impedance spectroscopy. The conductivity was depends on the procedure for the synthesis of solid solutions. The most promising compositions were revealed.     

Investigation of sol-gel matrices containing crude metallothionein from <Emphasis Type="Italic">Scchizosaccharomyces pombe</Emphasis> for water treatment applications

The application of silica sol–gel particles containing crude metallothionein (MT) was investigated for cadmium removal from water. The metallothionein was first extracted from the yeast Scchizosaccharomyces pombe, and entrapped in the sol–gel matrices. Then sol–gel particles with the different sizes (ranging from 45 to 225 μm) were made. The effect of different flow rates as well as different particle sizes on adsorption of cadmium was investigated. The particle size has a greater effect on Cd adsorption than flow rate in the system studied. The breakthrough curves in the column were modeled using an empirical two parameter fixed-bed adsorption model. The model relates the changes of cadmium concentration in effluent to the standard deviation (σ) and characteristic of time (t ₀).     

Kinetics and thermodynamics of liquid phase isomerization of α- and β-pinene over Pd/C catalyst

The kinetics and thermodynamics of the liquid phase isomerization of an α- and β-pinene mixture on a Pd/C catalyst were studied. The effects of pinene concentration, catalyst particle size, stirring rate, reaction temperature (293–423 K) and hydrogen pressure (0.5–11 bar) on the rate of α- and β-pinene isomerization were investigated. The reaction rate of the α-pinene isomerization has the first order with respect to the α-pinene concentration and 0.5 order with respect to the hydrogen pressure. The thermodynamic parameters of the isomerization (Gibbs energy, reaction enthalpy and reaction entropy) and the equilibrium ratio of pinenes under the conditions studied were determined. The general scheme of the reaction mechanism of α- and β-pinene isomerization over the Pd/C catalyst was proposed.     

Electrochemical studies of LiMnPO4 as aqueous rechargeable lithium–ion battery electrode

A study of the electrochemical behavior of LiMnPO₄ prepared by RAPET method in different aqueous electrolytes using cyclic voltammetry (CV), galvanostatic charge–discharge experiments, and electrochemical impedance spectroscopy is reported. CV peak current is proportional to the square root of scan rate under 0.2 mV s⁻¹. The system satisfied the required conditions for a reversible system with a resistive behavior. LiMnPO₄ was found to undergo proton insertion at lower concentrations of electrolyte. At higher concentrations or saturated solutions of electrolytes, lithium insertion/de-insertion becomes the main reaction though the effect of proton insertion/de-insertion reaction cannot be ignored. Electrochemical insertion/de-insertion of lithium in LiMnPO₄ was studied using EIS technique. The kinetic parameter, charge transfer resistance (R _ct), obtained by simulating the experimental impedance data with an equivalent circuit showed a minimum at the potential close to the CV peak potential. The cell LiTi₂(PO₄)₃/5 M LiNO₃/LiMnPO₄ delivers a discharge capacity of 84 mAh g⁻¹ in the first cycle at an applied current of 0.2 mA cm⁻² and it retains its initial capacity over 50 cycles with good rate capability.     

Effects of protonation on proton transfer processes in Watson–Crick adenine–thymine base pair

Intermolecular proton transfer processes in the Watson and Crick adenine–thymine neutral and protonated base pairs have been studied using the density functional theory (DFT) with the non-local hybrid B3LYP density functional. Protonated systems subject to study are those resulting from protonation at the main basic sites of the base pair model, namely N₇ and N₃ of adenine and O₂^′ and O₄^′ of thymine. Protonation of adenine induces a strengthening by about 4–5 kcal/mol of the base pair and does not significantly modify the double proton transfer energy profile obtained for the unprotonated system. On the other hand, protonation at the O₄^′ and O₂^′ thymine moiety causes thymine’s N₃ proton to spontaneously transfer to adenine while non-transferred minima disappear at this level of theory. The different behaviour between protonated adenine– thymine and protonated guanine–cytosine is discussed. Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Contribution to the Fernando Bernardi Memorial Issue.     

Thermochemistry of solvation and complexation in the Cu(NO3)2-water-ethanol-L-α-alanine system at 298.15 K

The heats of mixing of aqueous solutions of copper(II) nitrate and sodium alaninate and the heats of dilution of an aqueous solution of sodium alaninate in water-ethanol mixtures were calorimetrically measured at 298.15 K. The enthalpies of transfer of α-alaninate from water into water-alcohol mixtures and the standard molar enthalpies of the reaction of copper(II) complexation with α-alaninate ion in the mixtures under study are calculated. The resulting enthalpy parameters are compared with those of the similar system containing synthetic β-alanine, which was studied earlier.     

Synthesis of 1,8-naphthalimide-based fluorescent nano-probes and their application in pH detection

Fluorescent nano-probes with particle sizes of 20 nm, 120 nm and 300 nm for proton were prepared through click reaction. The photophysical properties of the nano-probes were mainly affected by the particle size.