Tensammetric determination of non-ionic surfactants combined with BiAS separation procedure (Wickbold) 2. Optimisation of the precipitation and investigation of interferences

The precipitation step in the developed procedure (BiAS-ITM) was optimised with the aim of achieving a lower detection limit. Losses during filtration using Triton X-100 as representative non-ionic surfactant (NS), the indirect tensammetric method (ITM) and adsorptive stripping tensammetry (AdST) for the determination of the concentration of the surfactant in the precipitate and in the filtrate were investigated. The G4 glass filter recommended up to now was found to be insufficiently effective and a source of loss. The new version of the procedure developed works within the range 2-1000 mug of NS in the sample, and thus two orders of magnitude lower than the former version of the procedure, showing satisfactory recovery and precision. The detection limit (3 x S.D.) was found to be below 1.5 mug in the sample. Interferences of anionic surfactants (ASs) e.g. sodium dodecylbenzenesulphonate and sodium lauryl sulphate, lipids, e.g. glycerol trioleate (GTO), and chlorophyll were investigated. GTO and AS show no effect on the BiAS-ITM results although strong adsorption of ASs on the glass filter as well as a slight adsorption on the precipitate was found. Chlorophyll does not interfere with the determination up to 30 mug in the sample, whereas higher concentrations produce results that are too high.     

New competitive enzyme-linked immunosorbent assay for determination of metallothionein in tissue and sera

A method for the determination of non-ionic surfactants (NS) in the presence of an excess of hydrocarbons is developed. The modified BiAS procedure combined with the indirect tensammetric method (BiAS-ITM) is applied for this purpose. The method consists of extraction of NS into ethyl acetate, precipitation of ethoxylates with modified Dragendorff reagent, removal of adsorbed hydrocarbons by washing with isooctane and the determination of NS in the dissolved precipitate by the ITM. The method is characterised by 96-100% recovery and RSD of 0.02-0.04 at a 1000-fold excess of hydrocarbons. The detection limit of the procedure is 1.5 mug and the linear dynamic range is 2-20 mug in the sample, which facilitates work within the range of 2-1000 mug through the use of aliquots. The non-modified version of the BiAS-ITM exhibits a loss of NS due to their extraction by droplets of residual hydrocarbons trapped in the precipitate. Isooctane as a washing agent is found to be the best among eight tested media: methanol, ethyl acetate, diisopropyl ether, chloroform, water, glacial acetic acid, benzene and isooctane.     

Tensammetric determination of non-ionic surfactants combined with BiAS separation procedure (wickbold)-I. precipitation of different ethoxylates with modified Dragendorff reagent in the proposed and classical BiAS procedures

The proposed procedure (BiAS-ITM) combines BiAS separation scheme of non-ionic surfactants with their determination by indirect tensammetric method (ITM). The method is based on (i) gas stripping separation of ethoxylates, (ii) their precipitation with modified Dragendorff reagent and (iii) determination of their concentration in the dissolved precipitate using ITM. Washing of the precipitate with glacial acetic acid, necessary in classical BiAS procedure which is a source of serious error, is omitted in the proposed separation scheme. The presented method determines the non-ionic surfactants instead of bismuth in the classical BiAS. The precipitation of 12 oxyethylated alcohols, four oxyethylated alkylphenols and four other ethoxylates were investigated according to the proposed procedure. Adsorptive stripping tensammery (AdST) was applied for additional control of investigated surfactants in the precipitate and in the filtrate. Simultaneously 13 ethoxylates were precipitated and determined according to classical BiAS procedure. The BiAS-ITM procedure shows significantly better recoveries and lower sensitivities vs. the chemical structure of the determined surfactants and thus BiAS-ITM is less sensitive to the composition of determined mixture than classical BiAS procedure. It enables the determination of ethoxylates having three or more oxyethylene subunits, while classical BiAS determines only those having five or more.     

Accurate and fast algorithm of the molecular incomplete gamma function with a complex argument

Several efficient algorithms for the accurate and fast calculation of the molecular incomplete gamma function Fm(z) with a complex argument z are developed. The complex incomplete gamma function is arising in molecular integrals over the gauge-including atomic orbitals. Two kinds of algorithms are recommended: (1) a high-precision version and (2) a fast version. The high-precision version is able to guarantee 15 significant figures (10(-15) in the relative error) and the fast version is able to guarantee 12 significant figures (10(-12) in the relative error), at worst, within the double-precision arithmetic. The fast version is about 5-20 times faster than the high-precision version. For most molecular calculations, the fast version will give a satisfied precision.     

Analysis of the relative strength of the singular values obtained from the non-parametric kinetic method

The non-parametric kinetic method (NPK) is a method for the processing of thermoanalytical data, which does not make any assumption about the functionality of the reaction rate with the degree of conversion or with the temperature. This method has not been widely used due to its mathematical sophistication and difficulty of automation. The original NPK method uses only the first (maximum) singular value whereas additional information could be drawn from the remaining singular values. A hypothetical application of the NPK, which uses all the significant singular values (modified version of the NPK), is the separation of two or more steps of a complex decomposition reaction. Using simulated data, we have demonstrated that the modified version of the NPK is not useful to discriminate among the decomposition steps of a consecutive complex decomposition reaction scheme. Nevertheless, the analysis of the relative strength of the singular values is useful to assess the degree of separability of the temperature and conversion functions, which are the outcome of the NPK. Taking into account the relative magnitude of the first singular value with regard to the remaining singular values, we have proposed an automated two-scan version of the NPK method which guarantees two separable functions. As the separability of both temperature and conversion functions is the imperative assumption of the single-step kinetics approximation, the two-scan NPK method can be used as a testing method for those methods based on this approximation, the model-free and model-fitting methods.     

Version of conventional thin-layer chromatography with a contact-covered sorption layer (Chamberless TLC)

A new version of TLC with a covered sorbent layer and without a free vapor volume is proposed along with a simple removable device to implement this version. The new TLC version has been tested experimentally using plates with silica gel on an aluminum substrate and ethanol, a water-24% aqueous ammonia (30:0.1) mixture, and an acetonitrile-ethanol (10:1) mixture as the mobile phases. The proposed TLC version shortens the experiment duration by 10–30% in comparison with conventional TLC; in this case, the efficiency can either slightly increase or slightly decrease. The consumption of the mobile phase and its evaporation to the environment are reduced.     

Pore classification in the characterization of porous materials: A perspective

The original version of the article was published in Cent. Eur. J. Chem., Vol. 5(2), (2007), pp. 385–395. It can be also found online at: http://dx.doi.org/10.2478/s11532-007-0017-9. Unfortunately, the original version of this article contains mistakes in the Acknowledgements section. There should be: This work was supported by Grants 240/08/0016 of Institute of Chemical Technology, 257 Prague, 104/06/1079 of Czech Science Foundation and MSM6046137308 of Ministry of Education, Youth and Sports of the Czech Republic. The online version of the original article can be found at     

Benchmarking the performance of time-dependent density functional methods

The performance of 24 density functionals, including 14 meta-generalized gradient approximation (mGGA) functionals, is assessed for the calculation of vertical excitation energies against an experimental benchmark set comprising 14 small- to medium-sized compounds with 101 total excited states. The experimental benchmark set consists of singlet, triplet, valence, and Rydberg excited states. The global-hybrid (GH) version of the Perdew-Burke-Ernzerhoff GGA density functional (PBE0) is found to offer the best overall performance with a mean absolute error (MAE) of 0.28 eV. The GH-mGGA Minnesota 2006 density functional with 54% Hartree-Fock exchange (M06-2X) gives a lower MAE of 0.26 eV, but this functional encounters some convergence problems in the ground state. The local density approximation functional consisting of the Slater exchange and Volk-Wilk-Nusair correlation functional (SVWN) outperformed all non-GH GGAs tested. The best pure density functional performance is obtained with the local version of the Minnesota 2006 mGGA density functional (M06-L) with an MAE of 0.41 eV.     

Interpretation of data obtained through the use of a version of the time-of-flight technique with a variable thickness of the generation zone

The transient-current curves recorded for molecularly doped polycarbonate are theoretically studied with a version of the time-of-flight technique with a variable thickness of the generation zone. A mixed-carrier-transport model was used, having been proposed in the literature as an alternative to the viewpoint that treats a plateau as an artifact of the optical version of the time-of-flight technique with surface carrier generation. A program for numerical calculation is developed for the model, with the hole transport being dispersive in the generation layer and Gaussian in the rest of the polymer. The model parameter values are selected according to results of independent measurements. It is shown that the mixed-transport model does not explain the experimental observations.     

Inhomogeneous polymer solutions: Theory of the interfacial free energy and the composition profile near the consolute point

The Flory–Huggins formulation of the combinatorial entropy, supplemented with residual free energy, is applied locally to obtain the interfacial free energy and the concentration profile of polymer in the interface between two demixed polymer solution phases. Two choices were investigated for the residual free energy: a “regular solution” formulation and an empirical formulation of Koningsveld for polystyrene in cyclohexane. Asymptotic, analytical solutions of the equations near the critical solution point and solutions obtained by numerical calculations are given as a function of temperature for several molecular weights. At temperatures farther below the critical temperature the equations have no solutions. The reason for this is not entirely clear. The local formulation of the free energy used here is an improved version of a previous one, which gave wrong results for asymmetric systems (polymer in a low molecular weight solvent). This newer version is consistent with our theory of critical opalescence and gives a relation between the interface “thickness” and the correlation range of the concentration fluctuations. The calculated correlation ranges were in good accord with those found experimentally by Debye, Chu, and Woerman. That the newer version of our equations for an interface gives no acceptable solutions at lower temperatures could be caused by a “collapse” of a diffuse to a sharp interface as suggested by Nose.     

An efficient improvement of the string-based direct selected CI algorithm

Summary A modified version of the Direct Selected Configuration Interaction Using Strings (DISCIUS) code is presented. From a series of test calculations it is shown that the string-based direct-CI algorithm is also very efficient in larger examples than the ones we showed in our former version. The performance of this new code with respect to the computer time is reasonable as well as its storage requirements. Hence, we present a new tool able to treat more than 10⁶ determinants of a variational space that does not have a defined structure, i.e. a selected or any way truncated CI.     

Two-Dimensional Planar Chromatography with a Closed Adsorbent Layer

A new two-dimensional chromatography process on closed plates is proposed. A previously described device with ethanol as a mobile phase is used to experimentally study two-dimensional thin-layer chromatography (2D TLC) on plates with 5 × 5 and 10 × 10 cm sizes. This work includes the experimental study and comparison of the following TLC versions: (1) the proposed 2D TLC version with a closed adsorbent layer with 1D separation on closed plates (an ascending mobile phase flow) and (2) conventional 2D TLC with an open adsorbent layer. The ascending version of 2D TLC with a closed adsorbent layer considerably (byR~55%) shortens the chromatographic time, especially with the use of 5 × 5 cm plates in the 2D separation version compared with the 1D version on 10 × 10 cm plates.     

Application of the intramolecular Yamamoto vinylogous aldol reaction to the synthesis of macrolides

An intramolecular version of the Yamamoto vinylogous aldol reaction, a method that employs the bulky Lewis acid ATPH to control the site of aldolization, is described. This macrocyclization process is effective for the construction of 10-, 12-, and 14-membered macrolides. The yields are high (70-90%), and the reaction can proceed with excellent remote stereocontrol (dr > or = 20:1) with chiral substrates.     

Solvated interaction energy (SIE) for scoring protein-ligand binding affinities. 2. Benchmark in the CSAR-2010 scoring exercise

Solvated interaction energy (SIE) is an end-point physics-based scoring function for predicting binding affinities from force-field nonbonded interaction terms, continuum solvation, and configurational entropy linear compensation. We tested the SIE function in the Community Structure-Activity Resource (CSAR) scoring challenge consisting of high-resolution cocrystal structures for 343 protein-ligand complexes with high-quality binding affinity data and high diversity with respect to protein targets. Particular emphasis was placed on the sensitivity of SIE predictions to the assignment of protonation and tautomeric states in the complex and the treatment of metal ions near the protein-ligand interface. These were manually curated from an originally distributed CSAR-HiQ data set version, leading to the currently distributed CSAR-NRC-HiQ version. We found that this manual curation was a critical step for accurately testing the performance of the SIE function. The standard SIE parametrization, previously calibrated on an independent data set, predicted absolute binding affinities with a mean-unsigned-error (MUE) of 2.41 kcal/mol for the CSAR-HiQ version, which improved to 1.98 kcal/mol for the upgraded CSAR-NRC-HiQ version. Half-half retraining-testing of SIE parameters on two predefined subsets of CSAR-NRC-HiQ led to only marginal further improvements to an MUE of 1.83 kcal/mol. Hence, we do not recommend altering the current default parameters of SIE at this time. For a sample of SIE outliers, additional calculations by molecular dynamics-based SIE averaging with or without incorporation of ligand strain, by MM-PB(GB)/SA methods with or without entropic estimates, or even by the linear interaction energy (LIE) formalism with an explicit solvent model, did not further improve predictions.     

The energy expression in the semi-empirical ham/3 method

By means of a comparison with the CNDO method we show that the HAM/3 formalism is a legitimate version of the SCF method. It is distinguished from the standard Roothaan-Hartree-Fock version of the SCF method by an unconventional exploitation of an inherent degree of freedom.     

Quasi-thin layer chromatography with forced flow of the mobile phase in microchannels packed with a sorbent

A version of the thin-layer chromatography with forced flow of the mobile phase in microchannels packed with a sorbent is proposed. The dependences of retention parametersR _f and the number of theoretical plates in the course of the elution of hydrophilic dyes (naphthol red and methyl red) on the eluent (propan-2-ol) pressure and developing time were studied. The method can be of interest as a simplified version of the forced-flow TLC and would be useful as a micropilot technique for liquid chromatography. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1538–1539, August, 1997.     

Erratum to “Two charge-transfer complex spectrophotometric methods for the determination of sulpiride in pharmaceutical formulations”

The original version of the article was published in Central European Journal of Chemistry, 2008, 7(4), 870–875, DOI: 10.2478/s11532-009-0091-2. Unfortunately, the original version of this article contains mistakes in the date section. There should be: received 13 February 2009, accepted 24 May 2009.     

Parallel computation of molecular energy gradients on the loosely coupled array of processors (LCAP)

The implementation of the HONDO program on the Loosely Coupled Array of Processors (LCAP) parallel computer system assembled in our laboratory is presented. We discuss a general strategy used to maintain a high level of compatibility between the serial version and the parallel version of the code. We report the implementation of energy-gradient calculation for SCF wavefunctions. The integral and integral derivative programs display high parallel efficiency, and so does the SCF part in the case of very large basis sets.     

Improved Iterative Version of the Coats-Redfern Method to Evaluate Non-Isothermal Kinetic Parameters

An improved version of the Coats-Redfern method of evaluating non-isothermal kinetic parameters is presented. The Coats-Redfern approximation of the temperature integral is replaced by a third-degree rational approximation, which is much more accurate. The kinetic parameters are evaluated iteratively by linear regression and, besides the correlation coefficient, the F test is suggested as a supplementary statistical criterion for selecting the most probable mechanism function. For applications, both non-isothermal data obtained by theoretical simulation and experimental data taken from the literature for the non-isothermal dehydration of Mg(OH)₂ have been processed.This revised version was published online in November 2005 with corrections to the Cover Date.     

Hydrodynamic suppression of the electroosmotic flow in capillary electrophoresis with indirect spectrophotometric detection

A version of capillary electrophoresis with indirect spectrophotometric detection and the hydrodynamic suppression of electroosmotic flow is studied. It is shown that, to improve the reliability of ion identification, one should calculate electrophoretic mobilities of ions or migration times corrected with regard to the electroosmotic flow rate. Correlations between electrophoretic peak areas of ions and their electrophoretic mobilities are derived. In the studied version of capillary electrophoresis, the accuracy of measuring anion concentrations can be improved using the internal standard method.