Gas chromatographic determination of the interconversion energy barrier for dialkyl 2,3-pentadienedioate enantiomers.

The enantiomers of dialkyl 2,3-pentadienedioate undergo interconversion during gas chromatographic separation on chiral stationary phases. In this paper the on-column apparent interconversion kinetic and thermodynamic activation data were determined for dimethyl, diethyl, propylbutyl and dibutyl 2,3-pentadienedioate enantiomers by gas chromatographic separation of the racemic mixtures on a capillary column containing a polydimethylsiloxane stationary phase coupled to 2,3-di-O-methyl-6-O-tertbutyldimethylsilyl-beta-cyclodextrin. A deconvolution method was used to determine the individual enantiomer peak areas and retention times that are needed to calculate the interconversion rate constants and the energy barriers. The apparent rate constants and interconversion energy barriers decrease slightly with an increase in the alkyl chain length of the dialkyl 2,3-pentadienedioate esters. The optimum conformation of the dialkyl 2,3-pentadienedioate molecules, their separation selectivity factors and apparent interconversion enthalpy and entropy data changes with the alkyl chain length. The dependence of the apparent interconversion energy barrier (deltaG(app)(a-->b), deltaG(app)(b-->a)) on temperature was used to determine the apparent activation enthalpy (deltaH(app)(a-->b), deltaH(app)(b-->a)) and apparent entropy (deltaS(app)(a-->b), deltaS(app)(a-->b)) (where a denotes the first and b second eluted enantiomer). The comparison of the activation enthalpy and entropy (deltaS(app)(a-->b), deltaS(app)(a-->b)) indicated that the interconversion of dialkyl 2,3-pentadienedioate enantiomers on the HP-5+Chiraldex B-DM column series is an entropy driven process at 160 degrees C. Data obtained for dimethyl 2,3-pentadienedioate enantiomers on the HP-5+Chiraldex B-DM column series at 120 degrees C (deltaG(app)(a-->b) = 123.3 and deltaG(app)(b-->a) = 124.4 kJ mol(-1)) corresponds (at the 95% confidence interval) with the value of deltaG(#) = 128+/-1 kJ mol(-1) found at this temperature by gas chromatography using a two-dimensional stop flow technique on an empty capillary column [V. Schurig, F. Keller, S. Reich, M. Fluck, Tetrahedron: Asymmetry 8 (1997) 3475].

Transtrochanteric rotational osteotomy, section after Sugioka.

BACKGROUND: Femoral caput necrosis is an actual therapeutic problem, because it appears mainly in mid-aged people. The necrotic focus is most often localized in the proximal and ventral parts of the femoral bone capitulum, which, from the biomechanical point of view is the most loaded part. These cases can be possibly treated by transtrochanteric rotational osteotomy. By means of this operation we rotate the necrotic focus to the less loaded part of the joint in correlation with the acetabulum. PURPOSE: The aim of this paper is to inform about a rarely performed operation after Sugioka: transtrochanteric rotational osteotomy in coincidence with avascular necrosis of the femoral bone caput. We would like to point to the possibility of a joint-saving operation, which enables to postpone implantation of total endoprosthesis to older age. METHODS: We analyzed the operational therapy performed at our department in the period 1998-2000, focusing especially on joint-saving operations due to femoral caput necrosis. We turned our attention to transtrochanteric rotational osteotomy after Sugioka. In four casuistics, we describe the results of these operations. RESULTS: Transtrochanteric rotational osteotomy was performed in 12 patients. The treatment is described in four casuistics. The results after 1-3 years are good. The illness has not progressed in any of patients, pain has regressed, mobility improved and it was not necessary to implant total endoprosthesis. CONCLUSION: We consider the transtrochanteric rotational osteootomy, section after Sugioka, as one of the possible treatments in mid-aged patients. Our effort is to perform joint-saving operations in order to postpone the implantation of total endoprosthesis. (Fig. 10, Ref. 13.)

Gas chromatographic-mass spectrometric detection of trace amounts of organic compounds in the intravenous solution Infusio Darrowi.

A gas chromatographic-mass spectrometric procedure was employed to confirm the presence of trace amounts of organic compounds in the intravenous solution Infusio Darrowi. Organic contaminants in the solution analysed were concentrated by microextraction with n-pentane. The main compounds detected were 2,6-di-tert.-butyl-4-methylphenol, 2,6-di-tert.-butyl-4-ethylphenol, 2,6-di-tert.-butyl-4-methoxyphenol, benzothiazole, isomeric C9 alkyl phenols and di(n-butyl) phthalate. These impurities were leached from rubber stoppers during their sterilization into the intravenous solution at levels ranging ca. from 5 x 10(-6) to 5 x 10(-8) g/l.