It is shown from experiments on leucine, that is possible to obtain pure enantiomer tracers of amino acids by using radioactive racemates only. The resolution takes place in a single crystallization step after mixing the active racemate with the inactive enantiomer, due to an absolute stereoselection.
Authors:R. Pena, A. Chauvet, J. Masse, J. Ribet, and J. Maurel
The physicochemical characterization of the solid-state enantiomers and racemate of efaroxan hydrochloride (C13H17N2O+Cl-,
M=252.5 g mol-1) was performed by thermoanalytical methods (differential scanning calorimetry, thermogravimetry and thermomicroscopy)
and spectral methods (infrared spectrometry and X-ray diffractometry).
The efaroxan enantiomers and racemate were shown to be unstable near the melting point. At the beginning of the decomposition,
a loss of hydrogen chloride was observed. However when sealed pans were used, the compounds decomposed at higher temperature,
allowing a precise evaluation of the melting enthalpies by means of differential scanning calorimetry. The nature of the racemate
and its thermal stability were assessed by evaluating its free formation enthalpy. An enantiotropic solid-solid transformation
(II→I) was noted for the racemate; the reverse process (I→II) follows zero-order kinetics.
Authors:V. Drebushchak, Yulia Kovalevskaya, I. Paukov, and Elena Boldyreva
Heat capacity of D- and DL-serine was measured using adiabatic calorimetry in a temperature range of 5.5 to 300 K, and then thermodynamic functions
were calculated. The difference in heat capacity (CPD-CPDL) between two species indicates a small anomaly in D-serine near 15 K and a systematic excess over DL for temperatures > 30 K. This is much larger, than a difference in thermodynamic functions measured so far for the polymorphs
of organic molecular crystals. The excess is fitted well to Einstein contribution with characteristic temperature of 185 K
which is equivalent to vibrational mode at 129 cm−1.
Authors:A. Sykuła-Zając, E. Łodyga-Chruścińska, B. Pałecz, R. E. Dinnebier, U. J. Griesser, and V. Niederwanger
Molecular formula of bupivacaine hydrochloride (C 18 H 28 N 2 O·HCl, H 2 O, 342.99 g mol −1 )
The drug is still clinically available as a racemate which consists of “left-handed” S (−)- and “right-handed” R (+)- [ 3
Authors:Katalin Nemák, Mária Ács, D. Kozma, and E. Fogassy
The phenomena of conglomerate formation-racemic compound formation were investigated in a series of five (N-alkyl)-2′,6′-pipecoloxylidides. The optically active enantiomers were prepared by optical resolution of the racemates using 2R,3R-tartaric acid and 0,0′-dibenzoyl-2R,3R-tartaric acid as resolving agent. By DSC measurement of the racemates and the enantiomer the binary phase diagrams were determined.
Authors:Th. Beyrich, M. Schleuder, G. Mietz, H. Wulff, and M. Gruno
The 4-nitrobenzyl ester of acetylphenylhydroxyacetic acid differs in its melting behaviour from other nitrobenzyl esters of
phenylhydroxyacetic or acetylphenylhydroxyacetic acids, the racemate having a higher melting point than the enantiomers. By
means of thermal analysis, IR spectroscopy and X-ray diffractometry the ester can be shown to occur in two crystalline modifications.
In the process of solidification of the molten mass, at first a modification of higher energy is formed, obviously being caused
by an excess of one enantiomer, which is then exothermally rearranged in the lattice of the racemate.
There is no statistically significant difference in the response of the enantiomers and the racemate of -alanine to -radiation (60Co) and accelerated electrons (10 MeV). The response was measured by the yield of ammonia, one of the separated final products of solid alanine radiolysis and the concentration of free radical CH3·CH·COO–, the intermediate product of radiolysis. Some of the properties of the racemate may affect the precision of measurements. TheDL-alanine shows different crystal structure, morphology of crystals, specific density and bulk density than the enantiomers. The response ofL andDL alanines built into composites may be different because of different reactivity of the enantiomer and the racemate with components during the processing and irradiation.
Authors:V Vargha, O Vorster, Zs Finta, and G Csuka
The gelation of a powder coating and its matrix based
on a saturated carboxyl functional polyester resin and triglycidyl isocyanurate
of different diastereomer racemate composition was investigated by rotational
viscometry. The iso-Tcure
diagrams have been determined directly by isothermal viscometric measurements
and the gelation curves for the TTT-diagram
have been constructed. To the measured section of the gelation curves power
functions could be fitted and with their help the reactivity of the investigated
systems were compared. The ratio of the two diastereomer racemates of TGIC
has a significant effect on the reactivity of the coating, as it was also
supported by DSC measurements. β-TGIC is of highest reactivity, and by
increasing its ratio in TGIC, reactivity increases, and adversely effects
the performance of the powder coating. Commercial TGIC-s have similar reactivity,
comparable to that of high α-TGIC. The reactivity of the matrix is higher
than that of the powder.
Authors:H. Dong, Y. Wang, Y. Ou, J. She, X. Shen, J. Li, C. Zhang, and L. Liu
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 (Bt) of MIPs and dissociation constant (Kd) 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.
Authors:Dipshi Singh, Poonam Malik, and Ravi Bhushan
The scientific development in the area of enantioseparation during the last few decades has centered on the production of new chiral stationary phases (CSPs) and new chiral derivatizing reagents (CDRs) for use in liquid chromatography, and in particular high-performance liquid chromatography (HPLC) only. Both CSPs and CDRs have several limitations which, in general, are ignored. Little attention has been paid to thin-layer chromatography (TLC) despite its many advantages compared to HPLC in pharmaceutical and drug analysis and the areas of natural products chemistry and organic synthesis, particularly enantioselective synthesis in purification of the product prior to establishing enantiomeric ratio by different method(s). TLC provides a rapid, easy, aff ordable, and simple approach in all these situations. The demonstrated capability and effi- ciency of TLC in direct resolution of the racemate clearly establish its superiority, and the methodology should allow its application in the resolution of several other racemates, irrespective of the functional group, in a very short time along with the recovery of native enantiomers (for further use).