Adsorption behavior of the +/- Troger's base enantiomers in the phase system of a silica-based packing coated with amylose tri(3,5-dimethyl carbamate) and 2-propanol and molecular modeling interpretation

Journal Article · Wed Mar 01 00:00:00 EST 2006 · Journal of Chromatography A

DOI:https://doi.org/10.1016/j.chroma.2006.02.001· OSTI ID:989610

Mihlbachler, Kathleen ^[1]; De Jesus, Marco ^[2]; Kaczmarski, Krzysztof ^[3]; Sepaniak, Michael ^[2]; Morgenstern, Andreas ^[4]; Guiochon, Georges A ^[1]

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1. ORNL
2. University of Tennessee, Knoxville (UTK)
3. University of Tennessee and Rzeszow University of Technology, Poland
4. University of Magdeburg, Germany

The binary adsorption isotherms of the enantiomers of Troeger's base in the phase system made of Chiral Technologies ChiralPak AD [a silica-based packing coated with amylose tri(3,5-dimethyl carbamate)] as the chiral stationary phase (CSP) and 2-propanol as the mobile phase were measured by the perturbation method. The more retained enantiomer exhibits a S-shaped adsorption isotherm with a clear inflection point, the concentration of the less retained enantiomer having practically no competitive influence on this isotherm: In the entire range of concentrations studied, dq{sub 2}/dC{sub 1} {approx} 0. By contrast, the less retained enantiomer has a Langmuir adsorption isotherm when pure. At constant mobile phase concentrations, however, its equilibrium concentration in the adsorbed phase increases with increasing concentration of the more retained enantiomer and dq{sub 1}/dC{sub 2} > 0. This cooperative adsorption behavior, opposed to the classical competitive behavior, is exceedingly rare but was clearly demonstrated in this case. Two adsorption isotherm equations that account for these physical observations were derived. They are based on the formation of an adsorbed multi-layer, as suggested by the isotherm data. The excellent agreement between the experimental overloaded elution profiles of binary mixtures and the profiles calculated with the equilibrium-dispersive model validates this binary isotherm model. The adsorption energies calculated by molecular mechanics (MM) and by molecular dynamics (MD) indicate that the chiral recognition arising from the different interactions between the functional groups of the CSP and the molecules of the Troeger's base enantiomers are mainly driven by their Van der Waals interactions. The MD data suggest that the interactions of the (-)-Troeger's base with the CSP are more favored by 8 {+-} (5) kJ/mol than those of (+)-Troeger's base. This difference seems to be a contributing factor to the increased retention of the - enantiomer on this chromatographic system. The modeling of the data also indicates that both enantiomers can form high stoichiometry complexes while binding onto the stationary phase, in agreement with the results of the equilibrium isotherm studies.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: DE-AC05-00OR22725
• OSTI ID: 989610
• Journal Information: Journal of Chromatography A, Vol. 1113, Issue 2006; ISSN 0021-9673
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ADSORPTION ISOTHERMS
BINARY MIXTURES
ENANTIOMORPHS
AROMATICS
MOLECULAR DYNAMICS METHOD
ADSORPTION HEAT
ORGANIC NITROGEN COMPOUNDS
Troger's base
enantioseparation
adsorption energy
adsorption isotherm
multi-layer adsorption
equilibrium-dispersive model
molecular modeling
molecular mechanics and molecular dynamics