Enantiomers signal separation

Examination of the NMR spectrum of vinyl acetate and vinyl propionate copolymers with Eu(hfc)3 or Pr(hfc)3 indicated that linkages within the polymer were racemic in nature. The H (400 MHz) and (100 MHz) NMR spectra of 3-amino-l,2-dicarba-c/oio-dodecaboranes exhibited enantiomeric discrimination in the presence of Eu(hfc)3. The resonances broadened in the presence of the shift reagent, but it was still possible to observe signal separation for the two enantiomers. 

Chiral NMR shift reagents (CSRs) have many practical applications in chemistry, biology, medicine, and related fields. A pair of enantiomers exhibit markedly different biological properties but provide the same chemical shifts in NMR measurements. Since the diastere-omers have different chemical shifts (Wenzel and Wilcox, 2003 Jacobus and Raban, 1969 Viswanathan and Poland, 1995 Parker, 1991), the chiral anions and cations have often been mixed with pairs of enantiomers for signal separation (Jodiy and Lacour, 2000). The effective CSRs of rare earth metal complexes should have high stability in the presence of interfering... 

An overall efficiency of TRISPHAT 8 and BINPHAT 15 anions as NMR chiral shift agents for chiral cations has been demonstrated over the last few years. Additions of ammonium salts of the A or A enantiomers of 8 and 15 to solutions of racemic or enantioenriched chiral cationic substrates have generally led to efficient NMR enantiodifferentiations [112-121]. Well-separated signals are usually observed on the spectra of the diastereomeric salts generated in situ. 

Thermodynamic behaviors and retention mechanisms for SFC are unique. Low temperatures and high pressures or high densities usually favor fast separation of enantiomers in SFC. In the case that the isoelution temperature is below the working temperature, the selectivity increases as temperature increases and higher temperatures are favorable for chiral separation. Future development in SFC will likely include new chiral column technologies and instrumentation refinement. A greater variety of chiral columns packed with smaller particles will open up more areas of application for fast chiral separations. In addition, improvement in signal-to-noise ratio of... 

For expanding NMR spectra of aqueous sample solutions, lanthanide salts such as the chlorides, nitrates, or perchlorates of europium and praseodymium are used [103]. In organic solvents, tris-(/ -diketonato)-europium(III) chelates (1) are usually applied [103]. Chiral europium(III) chelates such as tris-(3-tm-butylhydroxymethylene)-D-camphora-to-europium(III) (2) separate the signals of enantiomers in the NMR spectra of racemic solutions [103],... 

Figure 10 UV chromatogram (top trace) and CD chromatogram (bottom trace) of the trfoil AMIDE KNOT. SINCE THE KNOT IS THE ONLY CHIRAL PRODUCT, THE CD TRACE, WHICH SHOWS TWO BANDS OF EQUAL INTEGRATIONS WITH OPPOSITE SIGNS OF THE CD SIGNAL, PROVIDES EVIDENCE FOR THE FORMATION AND SUCCESSFUL SEPARATION OF BOTH ENANTIOMERS BY CHIRAL HPLC.

---