Search Results

You are looking at 11 - 20 of 20 items for :

  • "Racemates" x
  • Refine by Access: All Content x
Clear All

Abstract  

Racemic tritium-labelled amino acids were separated into optical isomers by chromatography on a chiral polyacrylamide sorbent filled with copper ions. The polyacrylamide sorbent is synthesized by Mannich's reaction through the action of formaldehyde and L-phenylalanine upon polyacrylamide Biogel P-4 in an alkali phosphate buffer. Tritiumlabelled amino acids are eluted by a weak alkali solution of ammonium carbonate. Data are presented on the ligand exchange chromatography of amino acids depending on the degree to which the sorbent is filled with copper ions and on the eluent concentration. Conditions are suggested for the quantitative separation of amino acid racemates. Amino acids are isolated from the eluent on short columns filled with sulfonated cation exchanger in the H+ form. HPLC on modified silica gel sorbents is also used for the analysis of tritium-labelled optically active amino acids. Amino acids are eluted by a weakly acidic water-methanol solution containing ammonium acetate. UV and scintillation flow type detectors are used.

Restricted access

Abstract  

Formation of conglomerates is of general interest because they offer the possibility of enantiomeric separation by preferential crystallization. A surprising result was obtained for the chiral epoxide 1a, 2, 7, 7a-tetrahydro-3-methoxynaphth-(2,3b)-oxirene, for which we have shown that the racemate crystals of a non racemic mixture can be easily transformed into a conglomerate by gentle heating and cooling within a defined temperature range. This transformation is not possible with the pure racemic mixture. Thus the enantiomeric excess seems to be the driving force for the conglomerate formation. Experiments have been carried out on analytical and preparative scale. Non racemic mixtures have been characterized by high pressure liquid chromatography on chiral stationary phase and crystal transformation has been monitored with differential scanning calorimetry (DSC) and infrared spectroscopy (IR).

Restricted access

A short survey is given of some aspects of the application of thermoanalytical methods, especially differential thermal analysis (DTA), differential scanning calorimetry (DSC) and thermogravimetry (TG), in solid-dosage technology. The usefulness of these methods in the prediction of drug-excipient compatibility, studies of solid-dispersion systems, the analysis of enantiomers and racemates, measurement of the time of tablet disintegration, the analysis of drug formulations and studies of the processes of grinding and drying of drugs is discussed.

Restricted access

Abstract  

The enantiomeric enrichment of N-methyl-amphetamine (MA) was tried by eight different preparative separation methods. The enrichment process was also studied by thermoanalitical methods (DSC,TG). There is no enantiomeric enrichment during fractional distillation and selective extraction of the liquid base. The enantiomeric mixture of MA·HCl can be enriched by crystallization or by sublimation. The most effective enrichment can be achieved by fractional crystallization or distillation of the reaction mixture after partial salt formation with hydrochloric acid. The separation is less effective in case of fractional steam distillation and selective extraction when the enantiomer and the racemate are distributed between two liquid phases. This supports the general experience that having a solid phase in the system makes enantiomer separation more efficient.

Restricted access

The metal-organic framework (MOF) is a kind of new type self-assembly porous coordination polymer, which possesses many characteristics such as homologic hole, controllable size of cave, high specific surface area, and good chemical stability. In this study, a three-dimensional framework [Zn2(d-Cam)2(4,4′-bpy)]n with large homochiral channel and the orderly arrangement of left- and right-handed helices was used as chiral stationary phases (CSPs) in gas chromatography (GC). [Zn2(d-Cam)2 (4,4′-bpy)]n-coated open tubular column was prepared by a dynamic coating method for high-resolution GC. Some racemates, isomers, linear alkanes, and alcohols are used as the targets for separation. The column coating properties efficiency, polarity, and selectivity were studied. The experimental results show that the stationary phase has outstanding selectivity and also possesses good recognition ability toward these compounds.

Open access

Enantioresolution of three active pharmaceutical ingredients (APIs), namely, atenolol, betaxolol, and orciprenaline, marketed as racemic mixture, has been achieved in a direct mode using (S)-glutamic acid as chiral additive in thin-layer chromatography. Two different approaches were adopted: (1) (S)-glutamic acid was mixed in the silica gel slurry for making thin-layer plates, or (2) it was added in the mobile phase and plain plates without any chiral additive were used. Both (1) and (2) were capable of separating enantiomers of all the three racemates, but different combinations and proportions of solvents were found successful in the two cases. Good resolution was achieved in both cases, and the results are compared for these two sets of studies among themselves and with other literature reports. Iodine was used to locate the spots of the corresponding enantiomers. The detection limits for each enantiomer were found in the range of 1.4–1.9 μg (per spot).

Restricted access

.1080/10587259608034081 . 11. Jacques , J , Collet , A , Wilen , SH Enantiomers, racemates, and resolutions Krieger Malabar 1994 . 12. Viedma , C . Experimental evidence of

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: Dhruthiman R. Mantheni, M. P. K. Maheswaram, Hany F. Sobhi, Naullage Indika Perera, Alan T. Riga, M. Ellen Matthews, and K. Alexander

–excipients compatibility, and analysis of enantiomers, and racemates [ 6 ]. Introduction of DEA as part of thermal analysis of drugs was initiated by Dr. Riga. This opened a new door for studying many more properties of drugs and other chemicals, like premelt behavior and

Restricted access

physiological pH [ 6 ]. The pharmacokinetics of Ket is linear; at the higher recommended doses, there is a proportional increase in the concentrations of free and bound racemate. It has been observed that in humans there was very little or no interconversion of

Open access

salt and the related racemate form . Food Chemistry , 136 ( 2 ): 984 – 988 . 10.1016/j.foodchem.2012.09.020 Ohrvik , V.E. and Witthoft , C.M. ( 2011 ). Human folate bioavailability . Nutrients , 3 ( 4 ), 475 – 490 . 10.3390/nu3040475

Open access