Determination of the interconversion energy barrier of 2,3-pentadienedioic acid enantiomers by HPLC. 2. On-column interconversion.

In this paper, an HPLC method is used to determine the enantiomerization barrier of 2,3-pentadienedioic acid enantiomers. The racemate of 2,3-pentadienedioic acid was separated by HPLC on a chiral CHIROBIOTIC T column with a 90:10 (100:0.5:0.5 MeOH/HOAc/TEA)/H2O mobile phase. Peak areas of enantiomers prior to (A(+)0, A(-)0) and after the separation (A(+), A(-)), were used for calculation of the rate constants and the enantiomerization barrier, as determined by computer-assisted peak deconvolution of the peak clusters on the chromatograms. The kinetic equation for irreversible reactions was used to determine the apparent enantiomerization rate constants and the interconversion energy barrier. The dependence of the apparent enantiomerization barrier (deltaG1(app), deltaG-1(app)) on temperature was used to determine the apparent activation enthalpy (deltaH1(app), deltaH(-1)app) and entropy (deltaS1(app), deltaS-1(app)) for the interconversion of 2,3-pentadienedioic acid enantiomers, where the coefficients 1 and -1 designate the interconversions (+) --> (-) and (-) --> (+), respectively.