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Oxazepam undergoes reversible enantiomerization at ambient temperature. Standard solutions of this compound and extracts from tablets (both with c=0.1 mg/mL) were injected on a chiral HPLC column (Chirobiotic T) at various temperatures (273 K‐313 K, increment 5 K). The mobile phase with the composition MeOH/TEA/Hac (100/0, 1/0, 1) and flow rate 1.0 mL/min were used.1 Both the separation and the interconverson process occurred simultaneously. The various profiles obtained by a UV detector included two peaks (unreacted zone) and a plateau sandwiched between two peaks (reacted zone). These profiles could be explained by on‐column enantiomerization. The unreacted molecule zone on the profile was fused with the reacted molecule zone. The computer assisted peak deconvolution procedure (Origin 7.0 section peak fitting) was used for the determination of peak areas in peak clusters. The deconvolution of experimentally obtained chromatograms enabled the resolved and determined areas of each zones. As follo...

The dynamic HPLC was performed with the goal to estimate the influences on the configurational stability of diazepam conformers in chiral environment. The effect of sample solvent, temperature, flow rate, and pH of mobile phase on behaviour of diazepam conformers during their separation on chiral β‐cyclodextrin was studied. The separation of diazepam conformers was complicated due to simultaneous interconversion, which was the result of configurational instability of the diazepam molecule. A statistical approach was used for evaluation of the influence of individual chromatographic parameters on behaviour of diazepam in a given chiral environment. The Principal Component Analysis (PCA) and Cluster Analysis (CA) were applied for accurate interpretation of obtained results.

The HPLC analysis of diazepam conformers was carried out in the temperature range 273–313 K, increment 10 K. The pH of the mobile phase was 3.3; 5.5; 5.5 (Ic=const; 6.5; 6.5 Ic=const.). The various flow rates of 0.2; 0.5; 1.0; mL/min were used. Chiral stationary phase based on β‐cyclodextrin (ChiraDex) was used for separation of diazepam. The influence of temperature, flow rate, pH of mobile phase, and ionic strength on the retention and elution profile on two peaks of diazepam conformers were studied. After that, the chiral β‐cyclodextrin (0.001 mol/L; 0.003 mol/L; 0.005 mol/L) was added into the mobile phase. The increasing amount of β‐cyclodextrin in the mobile phase caused the disappearance of the first peak. The complete chiral separation of diazepam was not possible because of simultaneous interconversion. The plateau between two peaks of diazepam appeared in the whole range studied, any inhibitory effects of chromatographic conditions (pH of mobile phase, temperature, flow rate, ionic stre...

The thesis has analytical - interpretative nature and focuses on paradigmatic dealing with body and bodiliness motive in the prose of Slovak author Leopold Lahola. The subject of analysis is Lahola's prose collection - Posledná vec (The Last Thing). The thesis also overlaps comparatively to broader Central European context. Texts of Arnošt Lustig (Czech Republic), Imre Kertész (Hungary) and Henryk Grynberg (Poland) are reflected. The subject of comparison is the motive of body and bodiliness, means of expression, narrative point of view, and the concept of fable and sujet. Key words: the category of body and bodiliness, narrative techniques, text composition

In this paper, an HPLC method is used to determine the enantiomerization barrier of 2,3-pentadienedioic acid enantiomers. The racemate of 2,3-pentadienedioic acid was separated by HPLC on a chiral CHIROBIOTIC T column with a 90:10 (100:0.5:0.5 MeOH/HOAc/TEA)/H2O mobile phase. Peak areas of enantiomers prior to (A(+)0, A(-)0) and after the separation (A(+), A(-)), were used for calculation of the rate constants and the enantiomerization barrier, as determined by computer-assisted peak deconvolution of the peak clusters on the chromatograms. The kinetic equation for irreversible reactions was used to determine the apparent enantiomerization rate constants and the interconversion energy barrier. The dependence of the apparent enantiomerization barrier (deltaG1(app), deltaG-1(app)) on temperature was used to determine the apparent activation enthalpy (deltaH1(app), deltaH(-1)app) and entropy (deltaS1(app), deltaS-1(app)) for the interconversion of 2,3-pentadienedioic acid enantiomers, where the coefficients 1 and -1 designate the interconversions (+) --> (-) and (-) --> (+), respectively.

Chiral beta-cyclodextrin was used to separate diazepam conformers. Several mobile phases of the composition acetonitrile/acetate buffer 200 mmol/l (pH=3.3, 5.5, 6.5) were employed for this purpose. As follows, the influence of addition of chiral beta-cyclodextrin to the mobile phase on diazepam separation was studied. The interconversion was a concurrence process of separation, resulting from stereolability of the diazepam molecule. The influences of temperature, flow rate, pH, and ionic strength of the mobile phase on interconversion and chromatographic parameters (retention factor and selectivity coefficient) were studied. Complementary off-line NMR measurements were carried out with the goal to confirm the structure of diazepam in the presence of an acid mobile phase.

Enantiomerization is a first-order reaction; it means interconversion of one enantiomer into another (and vice versa). This phenomenon is a typical feature of some configurationally unstable chiral compounds and it complicates separation of racemic mixtures. For the study of enantiomerization, chromatographic separation techniques (GC, SFC, CE, MEKC, HPLC) and NMR can be used. Chromatographic methods suitable for investigation of enantiomerization include dynamic chromatography (if time scales of enantiomerization and separation are the same) and stopped-flow chromatography (time scales of both processes are different). The present paper surveys the research of enantiomerization from 1975, when papers describing enantiomerization in greater detail were published, to the present. Today, mathematical approaches and computer-assisted deconvolution procedures are commonly used for evaluation of enantiomerization--calculation of thermodynamic parameters (deltaGapp, deltaHapp, deltaSapp) and rate constants (klapp, k(-1)app). The aim of many publications was not only determination of the enantiomerization energy barrier, but the influence of the chiral stationary phase on enantiomerization was studied as well. In some cases, enantiomerization was used for preparative purposes--a pure enantiomer was obtained and thus complicated synthesis was excluded.

The paper explains the theoretical aspects of the process of enantiomerization and describes its characteristic features (generation of a plateau). In addition, some complications are presented that are produced by enantiomerization either from analytical or pharmacological points of view. It also defines the way of how to calculate energy barriers of enantiomerization according to the methods used for the separation of racemic mixtures (stopped-flow or dynamic chromatography). Mathematic models useful in deconvolution of chromatograms are also described. With the use of dynamic methods it is not possible to quantitatively evaluate the obtained chtromatograms and calculate thermodynamic parameters without computer-assisted deconvolution.