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Adsorptive bubble separation methods have been used to enrich components from both heterogeneous and homogeneous solutions. These methods are particularly effective for processing large solution volumes at low cost. Previous work demonstrated that chiral, surface-active collectors could be used to enrich enantiomers from homogeneous solution in a foam fractionation process. In a significant extension of this work, the use of highly selective molecularly imprinted polymers (MIPs) and heterogeneous solutions for the bubble flotation of enantiomers was evaluated. The high selectivity and ease of recycling of the MIP make this a potentially powerful approach for process-scale separations from large-volume bulk solutions. New MIPs were produced with low swelling properties which allowed them to retain enantioselectivity after numerous recyclings.

A comparison of the solvation response functions obtained from single-wavelength and from spectral-reconstruction measurements is provided. The model used in this study is based on a linear free-energy relationship.

Nylon-6 was used as a molecularly imprinted polymer (MIP). For imprinting L-theanine (5-N-ethylglutamine) in the polymer, 2.0 g of Nylon-6, 0.8 g (MIP 1), and 1.2 g (MIP 2), respectively, of L-theanine templates and 7.2 g of formic acid was used for the phase inversion process in water. The resulting polymers, including the template molecule, were washed with acetic acid solution to extract the template from the polymers. The polymers were investigated as solid phase extraction (SPE) sorbents for the cleanup of water extracts of green tea. Various amounts of the template in the polymerization mixture had no influence on sorptive properties of MIPs in the range under study. Water was found as a suitable solvent for sample loading. The selective binding capacity of MIPs was 3.49 µg/1 g MIP. Water with addition of acetic acid (2% by volume) was used as an elution solvent. The recovery of the MISPE procedure was 87.8%±5.5%. [ABSTRACT FROM AUTHOR]

Twelve racemic substituted β-lactam compounds were examined via capillary zone electrophoresis using three chiral selectors: sulfated α-cyclodextrin (SAC), sulfated β-cyclodextrin (SBC), and carboxymethyl β-cyclodextrin (CMBC). Ten of the twelve β-lactams are separated and each of the ten compounds is baseline separated by at least one of the chiral run buffer additives under optimized conditions. SAC was found to be the most effective chiral selector, baseline separating seven of the analytes and partially separating another two. The concentration of the chiral selector had a prominent effect on the resolution, generally higher concentrations gave longer migration times and better resolutions. Addition of organic modifier also increased analyses time but gave lower resolution. Decreasing the pH of the run buffer generally decreased analyses times as well as resolution. Decreasing the applied voltage generally improved resolution. [ABSTRACT FROM AUTHOR]

Three different teicoplanin chiral stationary phases (CSPs) (native teicoplanin, teicoplanin aglycon, and methylated teicoplanin aglycon) were used to study the enantioseparation and temperature behaviour of a set of chiral sulfoxides. The chiral analytes studied were 2-, 3-, 4- toluyl methyl sulfoxides and phenyl methyl sulfoxides with different 2-, 3-, 4-halogen substituents on the aromatic ring. The effect of temperature on the LC separation of racemic aromatic sulfoxides was studied between 10 and 50°C in a methanol mobile phase. The van't Hoff plots were constructed and thermodynamic data were determined from the slope and the intercept of linear van't Hoff plots. The van't Hoff plots (ln k versus 1/T and ln α versus 1/T) were linear for all enantiomers. Given the linearity of the van't Hoff plots, thermodynamic parameters, such as the change in enthalpies Δ(ΔH2,1) and the entropies Δ(ΔS2,1) for the sulfoxide enantiomers could be calculated. In addition, the elution order did not reverse in the temperature range of this study and the mechanism of enantioseparation did not vary. [ABSTRACT FROM AUTHOR]

Four macrocyclic glycopeptide chiral stationary phases (CSPs) based on native teicoplanin (Chirobiotic T), methylated teicoplanin aglycone (Chirobiotic m‐TAG), teicoplanin aglycone (Chirobiotic TAG), and vancomycin (Chirobiotic V) were compared for the high performance liquid chromatographic (HPLC) separation of enantiomers of 1‐methyl‐2‐piperidinoethylesters of 2‐, 3‐and 4‐ alkoxyphenylcarbamic acid (potential local anaesthetic drugs). The enthalpies (Δ H i ), entropies (Δ S i ), and Gibbs energies (Δ G i ) of transfer were evaluated for the separation of these compounds. The enantiomers were separated isothermally in the range of 0–50°C with 10°C increments, in the polar organic mode. The thermodynamic parameters were calculated in order to gain an understanding of the driving forces for retention in this chromatographic system. From these results, it is evident that the elongation of the alkoxy‐chain has major influence on the values of (Δ S i ) when using the vancomycin CSP and on the values of (Δ H i ) using the teicoplanin‐type CSPs. [ABSTRACT FROM AUTHOR]

The enantiomeric separation of 12 β‐lactam compounds on 3 native cyclodextrin and 6 derivatized β‐cyclodextrin stationary phases was evaluated using high performance liquid chromatography (HPLC). The dimethylphenyl carbamate functionalized chiral stationary phase (CSP) (Cyclobond I 2000 DMP) separated 11 of the 12 β‐lactams in the reversed phase mode. The dimethylated β‐cyclodextrin column (Cyclobond I 2000 DM) was the second most effective CSP and it separated 8 of the 12 compounds. The reversed phase separation mode was the most effective approach. The effects of the composition and the flow rate on enantioseparations were studied. The effect of the structure of the substituents on the β‐lactams was examined. [ABSTRACT FROM AUTHOR]

The effect of temperature on the LC resolution of racemic aromatic sulfoxides was studied between 10 and 50°C in the polar organic mode on a teicoplanin aglycone chiral stationary phase (CSP). The set of 10 chiral sulfoxides compounds consisted of 2-,3-,4-toluyl methyl sulfoxides and phenyl methyl sulfoxides with different 2-,3-,4-halogen substituents on the aromatic ring. The van't Hoff plots were constructed to determine the thermodynamic data, and in order to promote an understanding of the mechanism of enantioseparation. The van't Hoff plots (ln k versus 1/T and ln a versus 1/T) were linear for all enantiomers. Plots of ln a versus 1/T afforded thermodynamic parameters, such as the change in enthalpies ?(?H 2,1 ) and the change in entropies ?(?S 2,1 ) for the sulfoxide enantiomers. If ?(?H 2,1 ) and ?(?S 2,1 ) are invariant with temperature, the ?(?G 2,1 ) values can be determined using the Gibbs-Helmholtz equation. The influence of different substituents and their position on the aromatic ring of the sulfoxides on their enantioseparation was correlated to the thermodynamic data. The elution order of the sulfoxide enantiomers does not reverse in the temperature range of 10 to 50°C. All chiral sulfoxides separated on teicoplanin aglycone CSP showed the (S)-(+)-enantiomer eluting first at all temperatures. [ABSTRACT FROM AUTHOR]

The enantioselectivity of native and derivatized cyclodextrin stationary phases and macrocyclic glycopeptides for chiral pterocarpans was evaluated using high performance liquid chromatography (HPLC). All enantiomers could be baseline resolved in the reverse phase mode on cyclodextrin-based Cyclobond chiral stationary phases (CSPs). The hydroxypropyl-β-cyclodextrin, acetyl-β-cyclodextrin, and gamma-cyclodextrin CSPs show the broadest enantioselectivity in the reverse phase mode. Some compounds were baseline separated on the ristocetin A and vancomycin macrocyclic glycopeptide chiral stationary phases in the reverse phase mode. Separations on the ristocetin A columns produced the highest resolutions (up to ∼7.1) in this study. The 3,5-dimethylphenyl carbamate derivatized cyclodextrin column showed the broadest enantioselectivity in normal phase LC. Of the macrocyclic glycopeptide CSPs, ristocetin A and teicoplanin aglycone (Chirobiotic R and TAG, respectively) showed enantioselectivity for the most compounds in the normal phase mode. However, baseline separations were only achieved with the teicoplanin and teicoplanin aglycone. [ABSTRACT FROM AUTHOR]

The enantiomers of 1-methyl-2-piperidinoethylesters of 3- and 4-alkoxyphenylcarbamic acid were separated on vancomycin(CHIROBIOTIC V) and teicoplanin(CHIROBIOTIC T) columns isothermally in the range of 0–50°C at 10°C increments, using methanol containing 17.5 mmol/L acetic acid and 4.8 mmol/L diethylamine as the mobile phase. Lower temperatures produced the expected increase in retention of the studied enantiomers and improved their separation. The retention factors ki(as well as the resolutions Rij) were higher on the teicoplanin chiral stationary phase(CSP) compared with the vancomycin CSP. Van't Hoff plots(dependence of ln ki on 1/T) were linear within the temperature interval studied, and they also were used to determine thermodynamic data, such as the(ΔHi) and(ΔSi) of transfer of the enantiomers between mobile and stationary phases. From these results, it is evident that the prolongation of carbon atoms in the alkoxy-chain has a major influence on the values ofΔ(ΔS2,1) using the vancomycin CSP, and on the values ofΔ(ΔH2,1) using the teicoplanin CSP. However, when the alkoxy-substituent on the phenylcarbamic acid ring system is in the 3- and 4-positions, there seems to be little difference in the thermodynamic parameters. [ABSTRACT FROM AUTHOR]