Controlled Hydrothermal Synthesis and Structural Characterization of a Nickel Selenide Series

A series of nickel selenides (NiSe₂ microcrystals, Ni_1?xSe and Ni₃Se₂ microspheres) has been successfully synthesized through a convenient, low‐temperature hydrothermal method. A good nucleation and growth environment has been created by forming a uniform and transparent solution reaction system. The compositions (including the x value of Ni_1?xSe), phase structures, as well as the morphologies of nickel selenides, can be controlled by adjusting the Ni/Se ratio of the raw materials, the pH, the reaction temperatures and times, and so forth. The newly produced Se microspheres in the system have been used as both reactant and in situ template to the Ni_1?xSe microspheres. It is found that Ni_1?xSe microspheres act as the intermediate precursor during the formation of Ni₃Se₂ microspheres. Under certain conditions, hexagonal NiSe microspheres can be converted into rhombohedral NiSe nanowires in solution. The formation mechanisms of a series of nickel selenides has been investigated in detail by means of X‐ray diffraction (XRD) and scanning electron microscopy (SEM) analyses. This work has provided a general, simple, and effective method to control the composition, phase structure, and morphology of metal selenides in aqueous solution, which will be important for inorganic synthesis methodology and further applications of selenides.     

A Spectrophotometric Study OE Zirconium Complexes of 4,5-Dihydroxyfluorescein

Zirconium (IV) ions form violet red complex with 4,5-dihydroxyfluorescein in fairly strong mineral acid medium. The reagent has been successfully applied as a metal indicator in the direct EDTA titration of zirconium. The complex formed by 4,5-dihydroxyfluorescein and zirconium ions has been studied spectrophotometrically in 0.1M HCl solution. It is found that when an excess of metal ion is present, a violet red colored complex with metal-ligand ratio of 1:1, (MR) is formed and when an excess of 4,5-dihydroxyfluorescein is present a 1:2 complex (MR₂) may be predominant. The 1:1 complex has maximum absorption at 510 mμ and the 1:2 complex has very low solubility and tends to precipitate out from the solution. Job's method, log-ratio method and gravimetric method were used to establish the composition of complexes. The apparent stability constant of the 1:1 complex is found to be log K_h = 4.46 or K_h = 2.9×10¹ at pH 1.2.     

Simple methods for the estimation of ionization constants of substituted pyridine N-oxides in polar aprotic solvents and water

A direct method for the determination of the pK _a values of acids conjugated to substituted pyridine N-oxides has been proposed which is based on the pH measurement of the solution of the basic salt. It has been experimentally shown that the method is reliable when applied to N-oxides of not too low basicity (pK _a >5). Correlation has been performed between the pK _a values in aqueous and aprotic media solutions which shows the great influence of the solvation effect on the acid-base equilibria. The good correlation between the pK _a values in aqueous and non-aqueous solutions enables the pK _a values in water to be estimated with sufficient accuracy, even in the cases when the experimental limitations make the determination impossible which is shown on the basis of selected examples.     

Differential Pulse Polarographic Determination of Nitrate in AUT Solution

A differential pulse polarographic method for the determination of nitrate ion has been developed. With 0.5 M CaCl₂ as supporting electrolyte, NO^?₃ is reduced to give a peak with E_1/2=–1.836 Volt vs. the Ag/AgCl electrode. The differential pulse polarographic peak height is proportional to the nitrate concentration from 20 to 60 ppm. The detection limit for nitrate is 2 ppm in pure aqueous solution. In the determination of 40 ppm nitrate a relative precision (relative standard deviation) of less than 2% was achieved. Nitrite interferes seriously and should be absent if accurate results are required. The method has been applied to the determination of nitrate in Ammonium Uranyl Tricarbonate (AUT) Solution, results obtained by this method are compared to those obtained by ion chromatography. The agreement between the two sets of results suggests that the DPP method can be used with a fair degree of confidence.     

Dielectric relaxation of sulfolane in benzene solution from microwave absorption data

The electric constant (ɛ′) and dielectric loss (ɛ″) for dilute solutions of sulfolane in benzene solution has been measured at 9.885 GHz at different temperatures (25, 30, 35, and 40°C) by using standard microwave techniques. Following the single frequency concentration variational method, the dielectric relaxation time (τ) and dipole moment (μ) have been calculated. It is found that dielectric relaxation process can be treated as the rate process, just like the viscous flow. Based on the above studies, monomer structure of sulfolane in benzene has been inferred. The presence of solute-solvent associations in benzene solution has been proposed. Energy parameters (ΔH _ɛ, ΔF _ɛ, ΔS _ɛ) for dielectric relaxation process of sulfolane in benzene at 25, 30, 35, and 40°C have been calculated and compared with the corresponding energy parameters (ΔH _η, ΔF _η, ΔS _η) for the viscous flow.     

Direct determination of pKa values of cationic acids conjugated to heterocyclic amine N-oxides in polar aprotic and amphiprotic solvents

The applicability of the direct method of pK_a determination in the case of protonated heterocyclic amine N-oxides in a series of polar non-aqueous (aprotic and amphiprotic) solvents has been tested. The method is based on the pH determination of the non-aqueous solution of complex salt (the semiperchlorate in this case) formed by the N-oxides studied. The direct method not only provides for quick (one data point per each pK_a determined), but also relatively accurate estimates of acidic dissociation constants. It has been experimentally shown on the example of substituted pyridine N-oxides that this method is precise enough in all studied non-aqueous solvents when applied to compounds of not too low basicity (the pK_a being of the order of 5 or higher). To prove this, the pK_a values of protonated monocyclic N-oxides obtained by the direct method have been compared with those resulting from the potentiometric titration curve. The agreement between the results found by using both methods is very good in most cases, the differences being within standard deviations. Based upon this observation it can be inferred that the pK_a values of protonated bicyclic N-oxides in solvents studied determined by using the direct method can be also considered reliable, especially in the case of polar aprotic solvents.     

Transfer of actinide ion at the interface between aqueous and nitrobenzene solutions studied by controlled-potential electrolysis at the interface

A novel electrochemical method based on controlled-potential electrolysis has been developed for the elucidation of the ion transfer at the interface between two immiscible electrolyte solutions (ITIES). A relationship between the applied interfacial potential (E_app) and the amount of the ion transferred (A_tr) was investigated after an electrolytic equilibrium was attained by controlled-potential electrolysis. The A_tr was determined chemically or radiometrically instead of by current measurement. It was found that (i) controlled-potential electrolysis was applicable to the study of the transfer of such hydrophilic ions as transition metal ions which gave no appreciable current within the potential window in voltammetry or polarography at ITIES, (ii) controlled-potential electrolysis in combination with a sensitive analytical method enabled a study of the transfer reaction of an ion of very dilute concentration, and (iii) even when the transfer reaction of an ion was irreversible or quasi-reversible, a standard ion transfer potential could be determined by controlled-potential electrolysis without using a kinetic parameter. The controlled-potential electrolysis method developed was applied to the transfer reactions of actinide ions such as UO₂ ²⁺ and Am³⁺ from aqueous solution to nitrobenzene solution in the absence or presence of an ionophore facilitating the transfer. The Gibbs energy for the transfer of actinide ion and a stability constant of the complex between an actinide ion and the ionophore in nitrobenzene solution were determined from log D versus E_app plots (D the ratio of the concentration of the ion in nitrobenzene solution to that in aqueous solution). The feasibility of controlled-potential electrolysis as a method for electrolytic separation of actinide ions is discussed.     

One - determinantal pure state versus ensemble Kohn-Sham solutions in the case of strong electron correlation: CH2 and C2

The possibility that the Kohn-Sham (KS) solution for a noninteracting auxiliary electron system is not the conventional one-determinantal pure state but a few-determinantal ensemble has been investigated. The KS solutions (the exchange-correlation potential v _xc and the orbitals) have not been approximated by local-density or density-gradient approximations but have been constructed from an accurate ab initio electron density. The lowest singlet states of the CH₂ and C₂ molecules have been selected for this investigation since for these cases the ground-state wave function Ψ is nondegenerate but has an essentially multideterminantal character (electron correlation is strong). For C₂ the dependence of the type of KS solution on the bond distance R(C–C) has been studied at the QZ level. For the shortest distance considered, R(C–C)=1.8 a.u., a pure-state KS solution has been obtained. For the equilibrium distance R _e(C–C)=2.348 a.u. and at larger distances ensemble solutions have been obtained with widely varying weights of the individual determinants, depending on the bond distance. For CH₂ the dependence of the type of KS solution on the basis has been studied: calculation in the triple zeta (TZ) basis for the KS orbitals yields an ensemble solution, while the pure-state KS solution has been obtained in the quadruple zeta (QZ) basis. The form of the KS orbitals has been compared with that of the natural orbitals (NOs). It has been shown for the model example of the stretched H₂ molecule as well as for CH₂ and C₂, that the KS orbitals of the pure state may be rather different from the corresponding NOs, while the occupied KS orbitals of the ensemble solution can be considered as plausible approximations to the corresponding NOs. Received: 10 February 1998 / Accepted: 10 June 1998 / Published online: 3 September 1998     

Dependence of the energy of surface-active substances/metal interaction on their ionization potentials. Evaluation of hydrophilicity of metal

The function Δ(ΔG _A ⁰), which is the difference of Gibbs energies characterizing surface-active substance (surfactant, SAS) adsorption at metal/solution and air/solution surfaces, has been introduced. The equation connecting the function Δ(ΔG _A ⁰) with SAS ionization potential has been obtained using the elementary theory of donor-acceptor interactions. Published experimental data on SAS adsorption at mercury, bismuth and gold have been used for Δ(ΔG _A ⁰) calculation. The dependence of Δ(ΔG _A ⁰) on ionization potentials can be described by an equation derived in this work. It has been demonstrated that the value of the hydrophilicity of gold is much higher than the values for mercury and bismuth. The lifetime of SAS molecules at a metal surface has been estimated. The question of the possibility of theoretica l estimation of standard energies ΔG _A ⁰ characterizing SAS adsorption at a metal/solution surface has been discussed. Received: 9 December 1996 / Accepted: 13 January 1997     

Influence of Surfactant and Charged Monomer Concentrations on Micro-Block Length of Associative Polymers by Micellar Polymerization

In the micellar polymerization to prepare associative polyelectrolyte, the influence of solution environment on hydrophobical micro-block length has been investigated. The results revealed that the aggregation number (N_agg) of surfactant micelles and micro-block length (N_H) of polymers closely related to electrolyte concentration in polymerization solution, and all of the surfactant and charged monomer concentration can change the free counterion concentration (C_aq) to affect N_agg and N_H. Therefore, the N_H with traditional calculation method which N_agg is looked as constant value was not accurate enough. Subsequently, we studied the attribution of N_H to rheological properties. The results indicated that the micro-block length can increase obviously the reversible network strength in solution to make a few contribution of thickening properties of associative polymer.     

Study on the nonisothermal crystallization behavior of poly(vinyl alcohol)/attapulgite nanocomposites by DSC analysis

Attapulgite (AT)‐reinforced poly(vinyl alcohol) (PVA) nanocomposite films were prepared by solution‐casting technique. The nonisothermal crystallization behaviors of PVA bulk and PVA/AT nanocomposites have been investigated by differential scanning calorimetry (DSC). It has been found that the uniformly dispersed AT nanorods in the matrix have great influence on the glass transition temperature and crystallization behavior of PVA matrix. The Jeziorny method has been employed to analyze the DSC data. The results show that Jeziorny method could describe this system very well. Comparing with the PVA bulk, PVA/AT nanocomposites have higher crystallinity X_t, shorter semicrystallization time t_1/2, and higher crystallization rate constant Z_c. It can be concluded that AT can be used as an effective nucleating agent and has effects on the growth of crystallites in the crystallization process of PVA matrix. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 534–540, 2006     

Semiempirical quantum-chemical investigation of fragmentation of O-fluorosulfonyl-N,N-difluorohydroxylamine anion-radical

The semiempirical quantum-chemical method PM3 has been used to calculate the heats of reaction for the decomposition of the anion-radical of O-fluorosulfonyl-N,N-difluorohydroxylamine in the gas phase and in solution. It has been shown that the reaction of the anion-radical leading to the formation of the radical^.NF₂ is thermodynamically favorable, either in the gas phase or in solution. For this exothermic reaction, a section of the potential energy surface along the reaction coordinate has been calculated, and it has been found that the reaction proceeds with virtually no barrier:E _a=1 kcal/mole. The O-fluorosulfonyl-N,N-difluorohydroxylamine is characterized by a high electron affinity (3 eV); i.e., its interaction with nucleophiles with a low ionization potential may proceed through anS _RN 1 mechanism.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 117913. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 4, pp. 855–860, April, 1992.     

Dependence of the frequency factor on the temperature: a new integral method of nonisothermal kinetic analysis

A new integral method of nonisothermal kinetic analysis has been developed with the dependence of the frequency factor on the temperature (A = A ₀ T ^m ). The new integral method is obtained from the newly proposed approximation for the general temperature integral, which is more accurate than the other existed approximations. For applications, nonisothermal thermoanalytical data obtained by theoretical simulation have been processed. The results have shown that the newly proposed integral method is an ideal solution for the evaluation of kinetic parameters from nonisothermal thermoanalytical data with the frequency factor dependent the temperature.     

Miscibility of bisphenol-A polycarbonate with poly(methyl methacrylate)

The miscibility of bisphenol-A polycarbonate (PC) with poly(methyl methacrylate) (PMMA) has been reexamined using differential scanning calorimetry (DSC) and optical indications for phase separation on heating, i.e., lower critical solution temperature (LCST) behavior. Various methods have been used to prepare the blends including methylene chloride (CH₂Cl₂) and tetrahydrofuran (THF) solution casting, melt mixing, and precipitation of PC and PMMA simultaneously from THF solution by using the nonsolvents methanol and heptane. It is shown that the resulting phase behavior for PC/PMMA blends is strongly affected by the blend preparation method. However, these blends are miscible over the whole blend composition range (unambiguous single composition-dependent T_g's and LCST behavior) when prepared by precipitation from solution using heptane as the nonsolvent. To the contrary, solution-cast and melt-mixed PC/PMMA blends were all phase separated, which may be attributed to the “solvent” effect and LCST behavior, respectively, not discovered in previous reports. Methanol precipitation does not lead to fully mixed blends, which demonstrates the importance of the choice of nonsolvent when using the precipitation method.     

Analysis of biomolecular chaos in aqueous solution

 The tropoelastin peptide CH₃CO-Gly-Leu-Gly-Gly-NHCH₃ has been modeled in aqueous solution by means of force-field molecular dynamics simulations and its motion characterized using nonlinear dynamics theory. The trajectory R(t) of the representative system point in configurational space has been considered. Fractional Brownian motion with anomalous diffusion is observed resulting from chaotic dynamics of molecules on fractal media. The chaos of the peptide is a consequence of nonlinear effects such as hydrodynamic interactions of the chain due to the poor solvent role of water. The viscous drag is pointed out and should be due to the percolation network of hydrogen-bonded water molecules. The method of reconstruction of the phase space using the embedding theorem is applied to the trajectory D _ee(t) of the peptide end-to-end distance. The existence of a low-dimensional chaotic attractor for dissipative systems has been demonstrated. The dynamical high-entropy state of the peptide in solution strengthens the transition-to-chaos mechanism for the elastin elasticity. Received: 14 September 1999 / Accepted: 3 February 2000 / Published online: 2 May 2000     

INVESTIGATION ON THE RELATIONSHIP BETWEEN INTRINSIC VISCOSITY AND MOLECULAR WEIGHT OF POLY (VINYL CHLORIDE-DIETHYL MALEATE)

A poly (vinyichloride-diethyl maleate) copolymer has been fractionated by repeated precipitation method. All fractions and the unfractionated sample have been characterized by viscometry, dynamic osmometry, Zimm static osmometry, light scattering and gel permeation chromatography. After correction for polydispersity, a [η]～M relationship for monodisperse polymer solutions has been obtained:[η]=1.99×10~(-3)M~(0.87) (ml/g, at 25℃, in cyclohcxanone)For the copolymer solution in THF, the second virial coefficient A_2 decreases as the molecular weight increases. The relationship isA_2=2 slope ((?)_n RT)~(-1/2).     

ITSTUDIES ON THE EFFECT OF UREA ON THE COMPATIBILITY OF PMMA/PVC MIXTURES IN DMF BY A DILUTE- SOLUTION VISCOMETRY METHOD

The interaction between poly(methymethacrylate) (PMMA) and poly(vinyl chloride) (PVC) has been studied indilute urea solutions of dimethylformamide (DMF) at 28℃ using a dilute solution viscometry method. The results show thatthe polymer mixtures are compatible in DMF solution in the absence of urea. The influence of urea addition on the degree ofcompatibility of the polymer mixtures has been studied in terms of the compatibility parameters (△b_m and △[η]_m). It wasfound that the compatibility of the polymer mixtures is decreased with increasing urea addition, passing through a minimumat 0.5 M urea.     

Comparative pharmacokinetics of prim-O-glucosylcimifugin and cimifugin by liquid chromatography-mass spectrometry after oral administration of Radix Saposhnikoviae extract, cimifugin monomer solution and prim-O-glucosylcimifugin monomer solution to rats

A sensitive and reliable liquid chromatography–mass spectrometry method has been developed and validated for simultaneous determination of cimifugin and prim‐O‐glucosylcimifugin in rat plasma after oral administration of Radix Saposhnikoviae (RS) extract, prim‐O‐glucosylcimifugin monomer solution and cimifugin monomer solution. Plasma samples were pretreated by protein precipitation with acetonitrile containing the internal standards puerarin and daidzein. LC separation was achieved on a Zorbax SB‐C₁₈ column (150 × 4.6 mm i.d., 5 µm) with 0.1% formic acid in water and methanol by isocratic elution. The detection was carried out in select‐ion‐monitoring mode with a positive electrospray ionization interface. The fully validated method was successfully applied to the pharmacokinetic study of the analytes in rats. A bimodal phenomenon appeared in the concentration–time curve of prim‐O‐glucosylcimifugin and cimifugin after oral administration of RS extract. Prim‐O‐glucosylcimifugin mainly transformed to cimifugin when it was absorbed into blood. Both absorption and elimination of cimifugin after oral administration of RS were longer than after administration of single cimifugin. The pharmacokinetic parameters (AUC_0–t, AUC_0–∞ and t_1/2) of prim‐O‐glucosylcimifugin and cimifugin by giving cimifugin monomer solution, prim‐O‐glucosylcimifugin monomer solution and RS extract had significant differences (P < 0.05). Copyright © 2012 John Wiley & Sons, Ltd.     

Multiobjective optimization of a free radical bulk polymerization reactor using genetic algorithm

A multiobjective optimization technique has been developed for free radical bulk polymerization reactors using genetic algorithm. The polymerization of methyl methacrylate in a batch reactor has been studied as an example. The two objective functions which are minimized are the total reaction time and the polydispersity index of the polymer product. Simultaneously, end‐point constraints are incorporated to attain desired values of the monomer conversion (x_m) and the number average chain length (μ_n). A nondominated sorting genetic algorithm (NSGA) has been adapted to obtain the optimal control variable (temperature) history. It has been shown that the optimal solution converges to a unique point and no Pareto set is obtained. It has been observed that the optimal solution obtained using the NSGA for multiobjective function optimization compares very well with the solution obtained using the simple genetic algorithm (SGA) for a single objective function optimization problem, in which only the total reaction time is minimized and the two end‐point constraints on x_m and μ_n are satisfied.     

Synthesis and aggregational behavior of acidic proteinoid

Polypeptide-based acidic proteinoid containing L -glutamic acid and L -aspartic acid in excess and five other neutral and basic amino acids in minor proportions have been synthesized and found that it forms organized aggregates in an aqueous solution. The proteinoid aggregate has been characterized using ¹³C-NMR, IR, and fluorescence spectroscopic techniques. The c.m.c. of the proteinoid has been determined by conductometric and pH metric methods. The aggregation studies were carried out at different temperatures and varying ionic strengths of the medium. The phase transition of the proteinoid aggregate has been determined using the fluorescence absorbance method. The aggregation behavior is shown to be dependent on the pH of the solution. This was also supported by conductivity measurements. Using methylene blue as a model drug, the drug delivery property of the proteinoid micelles were studied in acidic (pH 4.5) and neutral (pH 7.4) mediums. Using biphasic model thermochemical parameters, ΔG, ΔH, ΔS, and ΔC_p have been evaluated. © 1996 John Wiley & Sons, Inc.