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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.

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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.

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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).

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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.

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Molecularly imprinted polymers (MIPs) were synthesized by imprinting a new template—S(-)-1,1′-binaphthalene-2,2′-diamine (S-DABN) and applied as chiral stationary phases for chiral separation of DABN racemates by high-performance liquid chromatography (HPLC). The influence of some key factors on the chiral recognition ability of MIPs, such as the type of functional monomers and porogen and the molar ratio of template to monomer, was systematically investigated. The chromatographic conditions, such as mobile phase composition, sample loading, and flow rate, were also measured. The chiral separation for DABN racemates under the optimum chromatographic conditions by using MIP chiral stationary phase (CSP) of P3, prepared with the S-DABN/MAA ratio = 1/4 and used acetonitrile (2 mL) and chloroform (4 mL) as porogen, showed the highest separation factor (2.14). Frontal analysis was used to evaluate affinity to the target molecule of MIPs. The binding sites (B t) of MIPs and dissociation constant (K d) were estimated as 4.56 μmol g−1 and 1.40 mmol L−1, respectively. In comparison with the previous studies, this approach had the advantages, such as the higher separation factor, easy preparation, and cost-effectiveness, it not only has the value for research but also has a potential in industrial application.

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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.

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

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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

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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

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