Development of Gradient Retention Model in Ion Chromatography. Part I: Conventional QSRR Approach

New retention methodology that integrates the conventional quantitative structure-retention relationship (QSRR) approach and gradient retention modeling based on isocratic retention data is developed and presented in this paper. Such an integrated approach removes the general QSRR limitation of highly predefined application conditions (i.e., QSRR are generally applicable only under the conditions used during model development) and allows the prediction of retentions over a wide range of different elution conditions (practically for any isocratic or gradient elution profile). At the same time, it retains the ability to predict retention of components unknown to the model, i.e., the components that have not been used in modeling. Ion-exchange chromatography (IC) analysis of carbohydrates was selected as modeling environment. Three regression techniques were applied and compared during QSRR modeling, namely: stepwise multiple linear regression, partial least squares (PLS), and uninformative variable elimination–PLS regression. The obtained prediction results of the best QSRR model (root-mean-square error of prediction = 22.69 %) were similar to those found in the literature. The upgrade from QSRR to the integrated model did not diminish the predictive ability of the model, indicating an excellent potential of the developed methodology not only in IC but also in chromatography in general.     

The dependence of critical temperature on oxygen concentration in YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>6+<Emphasis Type="Italic">x</Emphasis></Subscript> in terms of the fragmented chain model

An extended ASYNNNI model, that beside nearest-neighbour and next-nearest neighbour O-O interactions in the basal plane also includes interactions between the three nearest oxygen atoms, is used to describe the statistics of CuO chain fragmentation and to calculate doping and T _c in YBa₂Cu₃O_6+x . Calculations were made by the Monte Carlo method employing the recently proposed charge transfer model that assumes only chains whose length is equal to, or exceeds, a characteristic (critical) length, l _cr , can provide holes to the layers and contribute to doping p. The obtained p(x) is then combined with a universal T _c versus p relation to yield T _c (x) characteristics that correlate remarkably with those reported in recent experiments. The best coordination between theoretical and experimental T _c (x) characteristics has been achieved for l _cr = 2, implying that only isolated basal plane oxygen atoms (trivial chains) do not contribute holes to CuO₂ layers.     

Chemometrical Approach in Fosinopril-Sodium and its Degradation Product Fosinoprilat Analysis

In this paper the experimental design has been applied to define the optimum chromatographic conditions for the separation of fosinopril sodium and its degradation product, fosinoprilat. Fosinopril is a prodrug and after being hydrolysed, it becomes an active drug fosinoprilat. For experimental screening full factorial design 2³ was applied. Methanol content, pH of the mobile phase and column temperature were independent variables or factors to be investigated in two levels - »low« and »high«. Capacity and selectivity factors were chosen as dependent variables and matrix was applied to estimate coefficients of the linear model. After experimental screening, RSM (response surface methodology) was applied for optimization. Optimum conditions were: X Terra? 150 mm × 4.6 mm, 5 μm particle column at 45 °C; methanol-water (75 : 25 v/v) at pH 3.1 as a mobile phase, with a flow rate of 1 mL min^?1. UV detection was performed at 220 nm. Propylparaben was used as an internal standard. The proposed method is rapid, accurate, selective and because of its sensitivity and reproducibility, it may be used for the quantitative analysis of fosinopril sodium and its degradation product in Monopril^® tablets. Recovery values for fosinopril sodium were between 101.6% and 102.9% and content of degradation product fosinoprilat was lower than 5%. Applying the chemometrical approach enables a relatively limited number of experiments to define factors which affect the chromatographic behavior of investigated substances and obtain optimum conditions for their analysis.     

Synthesis and biological evaluation of two novel 2′-substituted tiazofurin analogues

Two novel tiazofurin analogues, 2-(2-benzamido-2-deoxy-β-d-ribofuranosyl)thiazole-4-carboxamide 4 and 2-(2-azido-2-deoxy-β-d-ribofuranosyl)thiazole-4-carboxamide 5, have been synthesized starting from d-glucose and evaluated for their in vitro cytotoxicity against several human leukaemia and solid tumour cell lines.     

A Simple Synthesis of Oximes

Summary. The conversion of alicyclic and aliphatic carbonyl compounds as well as aromatic aldehydes into the corresponding oximes (up to quantitative yields) was achieved by simply grinding these reactants, hydroxylamine hydrochloride and sodium hydroxide without solvent. However, this procedure was unsuccessful in the case of aromatic ketones. In this case it was necessary to add silica gel as a catalyst.     

Some integral operators acting on H ∞

Let f and g be analytic on the unit disk \({\mathbb{D}}\) . The integral operator T _g is defined by \({ T_g f(z) = \int_0^z f(t)g'(t) \,dt, z \in \mathbb{D}}\) . The problem considered is characterizing those symbols g for which T _g acting on H ^∞, the space of bounded analytic functions on \({\mathbb{D}}\) , is bounded or compact. When the symbol is univalent, these become questions in univalent function theory. The corresponding problems for the companion operator, \({ S_g f(z)= \int_0^z f'(t)g(t) \,dt}\) , acting on H ^∞ are also studied.     

Reversible interconversion of thiazolidine-tetrahydrothiazine in the thiadiazabicyclooctanone system

Summary The interconversion of thiazolidine-tetrahydrothiazine in some derivatives of thiadiazabicyclooctanone in aqueous HCl has been studied. In the case of 6- and 7-substituted hydroxy or methoxy thiadiazabicyclooctanone a reversible rearrangement was found. The sulfoxide of thiadiazabicyclooctanone under the same reaction conditions undergoes epimerisation, while reaction with PCl₅ — via a corresponding sulfenyl chloride — affords a mixture of 6-and 7-substituted hydroxy or methoxy derivatives of thiadiazabicyclooctanone.The authors dedicate this paper to Dr. B. Gapert for his 60th birthday     

Intermolecular reactions of foiled carbenes with N-H bonds: evidence for an ylidic pathway

The chemistry of endo-tricyclo[6.2.1.0 (2.7)]undec-9-en-11-ylidene (10), an archetypal foiled carbene, has been investigated. The intermolecular reactions of 10 are most conveniently performed with oxadiazoline 6 because the corresponding diazirine can be obtained only in very low yield. Furthermore, the aziridinyl imine is difficult to decompose and the tosylhydrazone sodium salt poorly soluble in common organic solvents. Photolysis of 6 in diethylamine leads merely to a reduction of the diazo group and regeneration of acetyl hydrazone 5, whereas thermolysis cleanly affords tertiary amine 12(anti) in 77% yield. Calculations show that even stabilized-nucleophilic carbenes react with amines through an ylidic pathway and not by a concerted insertion into the N-H bond. Nevertheless, in the gas phase, norbornen-7-ylidene (13) is predicted to be stabilized by one molecule of NH3 more efficiently through a hydrogen bond than by ylide formation.     

Kinetics of passivity of NiTi in an acidic solution and the spectroscopic characterization of passive films

Anodic polarization of nitinol in acetic acid under galvanostatic conditions produces oxide films composed mainly of TiO₂. An exponential current-field relation is valid during ionic conduction through the growing oxide, in which the field coefficient is related to the jump distance. Transport processes in anodic films have been discussed in terms of a cooperative mechanism developed for amorphous oxide films on valve metals, in which both metal and oxygen ions were involved in ionic conduction. For more crystalline oxide structure of passive films on nitinol, formed during a prolonged potentiostatic conditions, the charge transfer takes place only through the oxygen vacancies as mobile species via a high-field-assisted mechanism. Based on the results of the Mott–Schottky analysis, these films behave as n-type semiconductors indicating that oxygen vacancies formed during the film formation and growth act as electron donors. The barrier/protecting and electronic/semiconducting properties of the passive films as well as their chemical composition were studied using electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy.