Predicting equilibrium sorption of neutral organic chemicals into various polymeric sorbents with COSMO-RS

There is an increasing use of polymers in analytical chemistry as sorbents for organic chemicals in sampling, cleanup, and chromatography. In order to find the optimal polymer for a given purpose, one needs to know the equilibrium partition constants of the chemicals of interest in a wide range of polymers. COSMOtherm, a quantum-chemically based software, is designed to predict such equilibrium partition constants based only on the molecular structure as input information. In this work, literature data for such equilibrium partition constants were collected for a wide range of different polymers and used to evaluate the performance of COSMOtherm. The results show good agreement between the predicted and experimental data from water and air for most of the tested polymers. The relative preference of analytes to sorb in a given polymer represented by the molecular structure of a monomer can be predicted without any calibration. If absolute values for the partition constants are required, then a few experimental values are needed to establish a log-linear regression between the model output and the experimental values. COSMOtherm appears to be a helpful tool for selecting the best sorbent polymer for a given task or for designing new polymers. The present evaluation is limited to chemicals with a rather simple structure. Further evaluation with complex chemicals that possess multiple functionalities is still warranted.     

Differentiation of CO isotopic variants by frequency tuning a terahertz source

The transmission spectra of two CO isotopic variants, i.e., (12)CO and (13)CO, are measured with a recently developed widely tunable THz source. The pure rotational transition lines of J=6 --> 7, 10 --> 11, 11 --> 12, 12 --> 13, and 13 --> 14 have been identified in the spectra. The transition frequencies and the rotational constant of each CO isotopic variant are also presented. Experimental results indicate that the difference of the rotational constants between the two isotopic variants can be used to reliably differentiate (12)CO and (13)CO. Compared with the measurements made by using a Fourier transform infrared spectrometer, our tunable THz source has produced approximately the same accuracies for measuring transition frequencies or determining rotational constants.     

Effect of coordination on bond properties: A first principles study

We have used density functional theory to obtain the binding curves for a variety of hypothetical periodic structures of Al, Si, Pb, Sn and Au. Upon examining the resulting database of results for equilibrium bond lengths and radial force constants (within a nearest-neighbour model), we find that both decrease smoothly as coordination is reduced. The effect of dimensionality appears to be small. We find that the force constants at equilibrium vary as the inverse eighth power of the equilibrium bond length. We also find evidence that the force constants are sensitive only to the bond length, and not to the coordination number. We believe these results will be useful in formulating interatomic potentials, e.g., for nanosystems.     

Equation of state for ammonia-water mixturesEquation d'état pour les mélanges ammoniac-eau

A new correlation of equilibrium properties of ammonia-water mixtures is presented for use in the design and testing of absorption units, and especially for heat pumps. The temperature range has been extended to 500 K and the pressure range to 50 bar. The equations of state used are based on those of Schulz. Values of specific volume, vapour pressure, enthalpies and equilibrium constants for mixtures are compared with the best experimental data. The results are presented in the form of vapour pressure and enthalpy-concentration diagrams.     

Equation of state for ammonia-water mixtures

A new correlation of equilibrium properties of ammonia-water mixtures is presented for use in the design and testing of absorption units, and especially for heat pumps. The temperature range has been extended to 500 K and the pressure range to 50 bar. The equations of state used are based on those of Schulz. Values of specific volume, vapour pressure, enthalpies and equilibrium constants for mixtures are compared with the best experimental data. The results are presented in the form of vapour pressure and enthalpy-concentration diagrams.     

MOLECULAR DYNAMICS SIMULATIONS OF PREFERRED ORIENTATIONS IN THE HIGH TEMPERATURE PHASE OF C60

Molecular dynamics simulations of the high temperature phase of C₆₀ have been performed for different intermolecular potentials proposed previously for the intermolecular interactions in solid C₆₀, i.e. the van der Waals (vdW) potential and two different bond charge models. In contrast to what has been previously inferred from a mean-field theory, bond charges do lead to a much better reproduction of the experimental results, including the preferred orientations of the C₆₀ molecule, than the vdW potential.     

Disproportionation of Pu(VI) and reproportionation of Pu(V), Pu(VII) in aqueous alkali solutions

Disproportionation of Pu(VI) and reproportionation of Pu(V) and Pu(VII) in aqueous NaOH solutions was studied. With an increase in the NaOH concentration in solution over 7.5 M, the equilibrium of the reaction Pu(VII) + Pu(V)?2Pu(VI) is gradually shifted toward formation of Pu(V) and Pu(VII) as products of Pu(VI) disproportionation, and at [NaOH] + 13 M, Pu(VI) disproportionates virtually completely. At [NaOH] + 7.5 M, the equilibrium of the above reaction is shifted toward formation of Pu(VI). Based on the experimental data, the equilibrium constants of the reaction at various alkali concentrations in the solution and the formal potentials ?_{f[Pu(VII)/Pu(VI)]} were calculated. The data obtained showed that, with respect to reduction with water, Pu(VII) is stable in aqueous alkali solutions at NaOH concentrations exceeding 7.5 M.     

MOLECULAR DYNAMICS SIMULATIONS OF PREFERRED ORIENTATIONS IN THE HIGH TEMPERATURE PHASE OF C60

Molecular dynamics simulations of the high temperature phase of C₆₀ have been performed for different intermolecular potentials proposed previously for the intermolecular interactions in solid C₆₀, i.e. the van der Waals (vdW) potential and two different bond charge models. In contrast to what has been previously inferred from a mean-field theory, bond charges do lead to a much better reproduction of the experimental results, including the preferred orientations of the C₆₀ molecule, than the vdW potential.     

Adsorption mechanisms and effect of temperature in reversed-phase liquid chromatography. meaning of the classical Van't Hoff plot in chromatography

The effect of temperature on the adsorption and retention behaviors of a low molecular weight compound (phenol) on a C18-bonded silica column (C18-Sunfire, Waters) from aqueous solutions of methanol (20%) or acetonitrile (15%) was investigated. The results of the measurements were interpreted successively on the basis of the linear (i.e., overall retention factors) and the nonlinear (i.e., adsorption isotherms, surface heterogeneity, saturation capacities, and equilibrium constants) chromatographic methods. The confrontation of these two approaches confirmed the impossibility of a sound physical interpretation of the conventional Van't Hoff plot. The classical linear chromatography theory assumes that retention is determined by the equilibrium thermodynamics of analytes between a homogeneous stationary phase and a homogeneous mobile phase (although there may be two or several types of interactions). From values of the experimental retention factors in a temperature interval and estimates of the activity coefficients at infinite dilution in the same temperature interval provided by the UNIFAC group contribution method, evidence is provided that such a retention model cannot hold. The classical Van't Hoff plot appears meaningless and its linear behavior a mere accident. Results from nonlinear chromatography confirm these conclusions and provide explanations. The retention factors seem to fulfill the Van't Hoff equation, not the Henry constants corresponding to the different types of adsorption sites. The saturation capacities and the adsorption energies are clearly temperature dependent. The temperature dependence of these characteristics of the different assorption sites are different in aqueous methanol and acetonitrile solutions.     

On the dependence of the elastic properties of fcrystals on size: Simple cases

The paper aims at determining the dependence of the mechanical properties-equilibrium atomic spacing, force constants in tension and shear, as well as Poisson's ratio—of a crystal on its size. Simple configurations are considered: a plane of atoms consisting of any number of infinite atomic rows in close packing and a body consisting of any number of infinite atomic planes in h.c.p. and f.c.c. stacking, the number of rows or the number of planes being measures of its “size”.The leading assumption is that a potential energy exists which is a function of suitable generalized coordinates, and whose minimum determines a stable configuration.In Section 1 the relevant mechanical properties are expressed in terms of the potential function and its derivatives.In Section 2 the formalism developed in Section 1 is applied to Mie potentials defined in the paper. The expressions obtained have been evaluated for (m, n) equal to (6, 12) (the so-called Lennard-Jones potential) and (4, 7) (believed to be approximately applicable to copper) in the cases of h.c.p. and f.c.c. structures. The values corresponding to the two structures differ little, the maximum difference being 0.3% in the shear constants. The results for the h.c.p. structure are given in detail, showing that the equilibrium atomic spacings decrease with increasing size, while the force constants increase and Poisson's ratios oscillate. The force constant in tension is in good agreement with existing results.Similar calculations have been carried out in Section 3 using Morse potentials, where the selections of the parameters have been made to represent, respectively, the metals Ni, Cu, Al, Ag, Ca, Pb and Sr. The results, which are tabulated and illustrated graphically, are in qualitative agreement with those of the Mie potentials in Section 2.     

Electrochemical and XPS characterization of composite modified electrodes obtained by nickel deposition on noble metals

A chemically modified electrode composed of nickel oxyhydroxide film deposited on noble metals (i.e., gold or platinum) was characterized in an alkaline medium by cyclic voltammetry and XPS (X-ray photoelectron spectroscopy) techniques. The nickel was deposited on the gold substrate in an alkaline medium by various strategies: cycling the potential between -0.1 and 0.65 V vs SCE, in potentiostatic conditions at potentials comprised between 0.0 and 0.55 V and by simple immersion of the electrode in non-deaerated 0.2 M NaOH solutions containing 3 mM K2Ni(CN)4. The effects of several experimental parameters such as applied potentials, pH, tetracyanonickelate concentration, electrode substrate, etc., on the nickel film formation and growth were evaluated. The electroactivity of the resulting composite gold-nickel electrode was investigated in an alkaline medium toward the oxidation of carbohydrates using arabinose as a model compound.     

Study and application of a controlled-potential electrochemistry-electrospray emitter for electrospray mass spectrometry

This paper discusses continued studies and new analytical applications of a recently developed three-electrode controlled-potential electrochemical cell incorporated into an electrospray ion source (Van Berkel, G. J.; Asano, K. G.; Granger, M. C. Anal. Chem. 2004, 76, 1493-1499.). This cell contains a porous flow-through working electrode (i.e., the emitter electrode) with high surface area and auxiliary electrodes with small total surface area that are incorporated into the emitter electrode circuit to control the electrochemical reactions of analytes in the electrospray emitter. The current at the working and auxiliary electrodes, and current at the grounding points upstream and downstream of the emitter in the electrospray circuit, were recorded in this study, along with the respective mass spectra of model compound reserpine, under various operating conditions to better understand the electrochemical and electrospray operation of this emitter cell. In addition to the ability to control analyte oxidation in positive ion mode (or reduction in negative ion mode) in the electrospray emitter, this emitter cell system was shown to provide the ability to efficiently reduce analytes in positive ion mode and oxidize analytes in negative ion mode. This was demonstrated by the reduction of methylene blue in positive ion mode and oxidation of 3,4-dihydroxybenzoic acid in negative ion mode. Also, the ability to control electrochemical reactions via potential control was used to selectively ionize (oxidize) analytes with different standard electrochemical potentials within mixtures to different charge states to overcome overlapping molecular ion isotopic clusters. The analytical benefit of this ability was illustrated using a mixture of nickel and cobalt octaethylporphyrin.     

Isotope effects on the lattice dynamics of crystals

It seems likely that isotope effects are most clearly manifested in crystal lattice dynamics, which is evidenced by works in this field that have been published for more than half a century. A great number of stable isotopes and well-developed methods of their separation has made it possible to date to grow crystals of C, LiH, ZnO, ZnSe, CuCl, GaN, GaAs, CdS, Cu₂O, Si, Ge and -Sn with a controllable isotopic composition. The accumulated voluminous theoretical and experimental data suggest that the isotopic composition of a crystal lattice exerts some influence on the thermal, elastic, and vibrational properties of crystals. These effects are quite large and can be readily measured by modern experimental techniques (ultrasound, Brillouin and Raman scattering, and neutron scattering). For example, the change in the lattice constant is Δa/a=10⁻³ to 10⁻⁴, while the change δc_ik in the elastic constants amounts to several percent. The maximum k_m (where k_m is the maximum of thermal conductivity) measured for the most highly enriched ⁷⁰Ge (99.99%) sample is 10.5 kW/mK, one order of magnitude higher than for the natural Ge (analogous for C and Si). In addition, crystals of different isotopic compositions possess different Debye temperatures. This difference between a LiH crystal and its deuteride exceeds hundred degrees. Of the same order of magnitude is the difference between Debye temperatures for diamond crystals. Very pronounced and general effects of isotopic substitution are observed in phonon spectra. The scattering lines in isotopically mixed crystals are not only shifted (the shift of LO lines exceeds 100 cm⁻¹) but are also broadened. This broadening is related to the isotopic disorder of a crystal lattice. It is shown in this review that the degree of change in the scattering potential is different for different isotopic mixed crystals. In the case of germanium and diamond crystals, phonon scattering is weak, which allows one to successfully apply the coherent potential approximation (CPA) for describing shift and broadening of scattering lines. In the case of lithium hydride, the change in the scattering potential is so strong that it results in phonon localization, which is directly observed in experiments. Capture the thermal neutrons by isotope nuclei followed by nuclei decay produces new elements in a very large number of possibilities for isotope selective doping of different materials. The review closes with a section describing future developments and applications of isotope technology and engineering.     

Decomposition of atmospheric water content into cluster contributions based on theoretical association equilibrium constants

Water vapor is treated as an equilibrium mixture of water clusters (H₂O)_i using quantum-chemical evaluation of the equilibrium constants of water associations. The model is adapted to the conditions of atmospheric humidity, and a decomposition algorithm is suggested using the temperature and mass concentration of water as input information and used for a demonstration of evaluation of the water oligomer populations in the Earth's atmosphere. An upper limit of the populations is set up based on the water content in saturated aqueous vapor. It is proved that the cluster population in the saturated water vapor, as well as in the Earth's atmosphere for a typical temperature/humidity profile, increases with increasing temperatures.     

Determination of drug-plasma protein binding kinetics and equilibria by chromatographic profiling: exemplification of the method using L-tryptophan and albumin.

Drug-plasma protein binding may greatly influence the bioavailability and metabolism of a plasma-borne drug, the bound form being partially protected from the metabolic fate of the unbound drug. Traditionally, equilibrium values (e.g., percentage binding) for drug-protein binding have been measured to rationalize in vivo phenomena. However, such studies overlook the influence of kinetics. A rapid method of simultaneously determining kinetic rate constants and equilibrium constants from chromatographic profiles has been developed, based on the use of immobilized protein columns and HPLC. By measuring the chromatographic profiles (the position and width) of a retained and an unretained compound one can directly determine both the rate and equilibrium constants. Results are presented for the binding of L-tryptophan to human serum albumin to exemplify the method. The association equilibrium constant (Ka) and the association and dissociation rate constants (k(a) and k(d), respectively) were thereby measured in an aqueous pH 7.4 environment at 37 degrees C as 0.84 10(4) M(-1), 5.8 10(4) M(-1) s(-1), and 6.9 s(-1), respectively. These compare favorably with previously published results. The described method may be used in quantitative structure-property relationship-based rational drug discovery or for the rationalization of drug pharmacokinetics.     

An improved molecular dynamics potential for the Al-O system

Molecular dynamics (MD) simulations of aluminum oxide material and the aluminum oxidation process require a sufficiently sophisticated and well-calibrated potential, one that takes into account locally varying Al/O ratios and adaptive charge transfer between Al and O atoms. In this work we show that the Charge Transfer Ionic Potential (CTIP) by Zhou et al. [X.W. Zhou, H.N.G. Wadley, J.-S. Filhol, M.N. Neurock, Phys. Rev. B 69 (2004) 035402] in combination with a new, “Reference Free” version of the Modified Embedded Atom Method (RFMEAM) potential performs well for this purpose. This new potential has been parameterized by systematically fitting it to a large database of different Al_xO_y crystal energies, over a range of lattice constants and elastic deformations, using a recent method which separates the electrostatic and non-electrostatic fitting steps. The resulting potential yields more realistic atomic charges, crystal energies and lattice constants than earlier potentials. In particular, we show that the angular forces in the MEAM part are essential for α-Al₂O₃ to be the lowest-energy aluminum oxide. We compare the performance of our potential with the potential of Zhou et al., which lacks angular forces and was parameterized using a less involved fitting procedure, and show the results of a few molecular dynamics simulations. The two-step fitting method is generally applicable and can be adopted for constructing potentials for other metal-oxide systems.     

Optimum synthesis of solvent-based post-combustion CO2 capture flowsheets through a generalized modeling framework

A generalized framework for the optimal design of post-combustion CO₂ capture processes based on a systemic and flexible equilibrium separation model that employs orthogonal collocation on finite elements techniques is proposed. Within this context, a column section of adaptive separation capability and functionality serves as the fundamental structural block for the identification of efficient separation schemes. Separation column sections in combination with heat transfer blocks, as well as stream splitters and mixers enable the generation and evaluation of alternative flowsheet configurations within a nonlinear optimization program. The main objectives for the flowsheet evaluation involve separation and thermal efficiency that eventually impact the economics of the overall process. Vapor–liquid equilibrium calculations are performed using statistical associating fluid theory for potentials of variable range (Mac Dowell et al., Ind Eng Chem Res 49:1883–1899, 2010). The proposed design framework is used for the optimal design of five alternative flowsheet configurations for the separation of CO₂ from a flue gas stream using a 30 % weight monoethanolamine aqueous solution. These flowsheets illustrate the various connection patterns between the process units and indicate suitable distribution of process-driving forces through which the overall efficiency can be drastically enhanced.     

Mesoporous titanium–manganese dioxide for sulphur mustard and soman decontamination

Titanium(IV)–manganese(IV) nano-dispersed oxides were prepared by a homogeneous hydrolysis of potassium permanganate and titanium(IV) oxo-sulphate with 2-chloroacetamide. Synthesised samples were characterised using Brunauer–Emmett–Teller (BET) surface area and Barrett–Joiner–Halenda porosity (BJH), X-ray diffraction (XRD), infrared spectroscopy (IR), and scanning electron microscopy (SEM). These oxides were taken for an experimental evaluation of their reactivity with sulphur mustard (HD or bis(2-chloroethyl)sulphide) and soman (GD or (3,3′-dimethylbutan-2-yl)-methylphosphonofluoridate). Mn⁴⁺ content affects the decontamination activity; with increasing Mn⁴⁺ content the activity increases for sulphur mustard and decreases for soman. The best decontamination activities for sulphur mustard and soman were observed for samples TiMn_37 with 18.6 wt.% Mn and TiMn_5 with 2.1 wt.% Mn, respectively.     

单向复合材料弹性常数微观力学分析的探讨

本文所探讨的问题,由于复杂和困难,虽经过许多学者数十年的研究,取得了重大的进展,但至今还未很好解决。我们对各种简化假定的合理性、不同计算模型的差别以及不同计算方法的影响等作了简要的探讨。对前人的工作略加评述。对常见公式的适用性提出一些看法。对一些现象的机理作了解释。给出了有一定的理论背景和实验依据的半经验公式,可适用于各种纤维增强聚合物基体复合材料。