Interplay of chromatographic and electrophoretic processes in capillary electrochromatography

The separation mechanism in capillary electrochromatography (CEC) is a hybrid differential migration process, which entails the features of both high-performance liquid chromatography and capillary zone electrophoresis, i.e., chromatographic retention and electrophoretic migration. The adsorption of the different sample components on the stationary phase can be modified by the presence of the electric field across the column. Here, we use our previously published approach to decouple chromatographic retention from electrophoretic migration that allows us to investigate the "modification" of the retention process in CEC. This paper presents a methodology for characterization of changes in the retention of neutral and charged sample components, under identical conditions of stationary and mobile phase.     

Analytical aspects of organic acids

Summary Phenyl acetic acid has been found to be a selective reagent for the estimation of zirconium. The acid gives a white crystalline precipitate which is quantitative between pH values of 3.00 to 5.40. As the composition of the precipitate varies somewhat, direct weighing is not possible and the compound is ignited to the oxide. The ions Be²⁺, Ca²⁺, Sr²⁺, Zn²⁺, Hg²⁺, Pb²⁺, Mg²⁺, Ni²⁺, and Co²⁺ do not interfere, whereas the ions Fe³⁺, UO₂ ²⁺, Cr³⁺, Ba²⁺, Au⁺, Al³⁺, V₂O₄ ²⁺, Ti⁴⁺, Sn²⁺, and Ba²⁺ cause interferences in the estimation.

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Zusammenfassung Zur gravimetrischen Bestimmung von Zirkonium wird Phenylessigsäure empfohlen. Die weiße, kristalline Fällung ist im pH-Bereich 3,00–5,40 quantitativ. Infolge schwankender Zusammensetzung des Niederschlages ist eine direkte Wägung nicht möglich; er wird daher zum Oxid verglüht. Folgende Ionen stören nicht: Be²⁺, Ca²⁺, Sr²⁺, Zn²⁺, Hg²⁺, Pb²⁺, Mg²⁺, Ni²⁺ und Co²⁺; dagegen verursachen Fe³⁺, UO₂ ²⁺, Cr³⁺, Ba²⁺, Au⁺, Al³⁺, V₂O₄ ²⁺, Ti⁴⁺, Sn²⁺ und Ba²⁺ Störungen bei der Bestim mung.

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Part VI: See Z. analyt. Chem. 175, 29 (1960).     

Folding probabilities: a novel approach to folding transitions and the two-dimensional Ising-model

The theoretical concept of folding probability, p(fold), has proven to be a useful means to characterize the kinetics of protein folding. Here, we illustrate the practical importance of p(fold) and demonstrate how it can be determined theoretically. We derive a general analytical expression for p(fold) and show how it can be estimated from simulations for systems where the transition rates between the relevant microstates are not known. By analyzing the Ising model we are able to determine the scaling behavior of the numerical error in the p(fold) estimate as function of the number of analyzed Monte Carlo runs. We apply our method to a simple, newly developed protein folding model for the formation of alpha helices. It is demonstrated that our technique highly parallelizes the calculation of p(fold) and that it is orders of magnitude more efficient than conventional approaches.     

ON THE CHROMOPHORE CONFIGURATION OF METARHODOPSIN II

Abstract The nature of the chromophore configuration of metarhodopsin II (meta II) has been a subject of recent controversy. Earlier resonance Raman results from this laboratory had indicated that meta II has an unprotonated Schiff base linkage between the chromophore and apoprotein. It has been argued, on the other hand, that the Raman evidence does not exclude a non-covalently bound retinal chromophore. In this communication we present additional evidence and further arguments in favor of our earlier conclusion regarding the state of the chromophore in meta II.     

Duality for Semi-Infinite Minimax Fractional Programming Problem Involving Higher-Order (Φ, ρ)-V-Invexity

In this paper, we introduce the concept of higher-order (Φ, ρ)-V-invexity and present two types of higher-order dual models for a semi-infinite minimax fractional programming problem. Weak, strong, and strict converse duality theorems are discussed under the assumptions of higher-order (Φ, ρ)-V-invexity to establish a relation between the primal and dual problems.     

Direct calculation of the binding free energies of FKBP ligands

Direct calculations of the absolute free energies of binding for eight ligands to FKBP protein were performed using the Fujitsu BioServer massively parallel computer. Using the latest version of the general assisted model building with energy refinement (AMBER) force field for ligand model parameters and the Bennett acceptance ratio for computing free-energy differences, we obtained an excellent linear fit between the calculated and experimental binding free energies. The rms error from a linear fit is 0.4 kcal/mol for eight ligand complexes. In comparison with a previous study of the binding energies of these same eight ligand complexes, these results suggest that the use of improved model parameters can lead to more predictive binding estimates, and that these estimates can be obtained with significantly less computer time than previously thought. These findings make such direct methods more attractive for use in rational drug design.     

Protonation and solvent extraction of N-p-tolylbenzohydroxamic acid in hydrochloric acid medium

the protonation of N-p-tolylbenzohydroxamic acid (p-TBHA) in aqueous hydrochloric acid has been investigated by determination of its distribution between cyclohexane and hydrochloric acid. The pK(a) value found was - 2.30 +/- 0.02 at 30 degrees . The solubility of p-TBHA as a function of hydrochloric acid concentration has also been determined. At lower acid concentrations the solubility decreases owing to a salting-out effect, whereas at higher concentrations it increases because of formation of the more hydrophilic protonated species and a salting-in effect. Intramolecular hydrogen-bonding observed in p-TBHA provides evidence for protonation of the nitrogen atom.     

Analytical aspects of some organic acids

Summary Back titrimetric procedures for the estimation of aluminium, zirconium, and thorium have been developed, which involved the adjustment of the concentration of the metallic salts, concentration of EDTA,ph, and temperature, addition of indicator solution (namely, 2-hydroxy3-naphthoic acid and back titration with standard 0.1 M ferric chloride solution. This method is based on the fact that the excess EDTA, which is added to the metal solutions may be back titrated with iron(III), which forms a highly coloured complex with the indicator, when present in slight excess. Quantities of aluminium, zirconium and thorium as small as 10.8, 4.6, 11.6 mg respectively, can be back titrated with in experimental error, when present in a volume of 100 ml.Part IV: See Z. analyt. Chem. 172, 356 (1960).