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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]

The isocratic retention of enantiomers of chiral analytes (1-methyl-2-piperidinoethylesters of 2-, 3-, and 4-alkoxyphenylcarbamic acid, potential local anaesthetic drugs) was studied on a methylated teicoplanin CSP, at different temperatures (in the range of 0–50°C with 10°C increments) in the polar organic mode (the mobile phase composition consisted of methanol with 17.5 mmol/L acetic acid and 4.8 mmol/L diethylamine). The natural logarithms of the retention factors (ln ki) of the investigated chiral compounds depended linearly on the inverse of temperature (1/T). van't Hoff plots afforded thermodynamic parameters, such as the apparent change in enthalpy (ΔHi), the apparent change in entropy (ΔSi), and the apparent change in Gibbs free energy (ΔGi) for the transfer of analyte between the mobile phase and the stationary phase. The thermodynamic parameters were calculated in order to promote an understanding of the thermodynamic driving forces for retention in this chromatographic system. Enthalpy–entropy compensation plots showed that all of the compounds in this study separate via the same enthalpy driven chiral recognition mechanism. [ABSTRACT FROM AUTHOR]

It has been found that the teicoplanin aglycone (CHIROBIOTIC TAG) chiral stationary phase is a useful column for the high performance liquid chromatographic (HPLC) separation of enantiomers of 1-methyl-2-piperidinoethylesters of 2-, 3- and 4-alkoxy-phenylcarbamic acid (potential local anaesthetic drugs) in the polar organic mode. The enantiomers were separated on a CHIROBIOTIC TAG column, isothermally in the range of 0–50°C with 10°C increments, using methanol [100 mL (v)] containing 17.5 mmol L−1 acetic acid and 4.8 mmol L−1 diethylamine as a mobile phase. van't Hoff plots (dependence of ln ki on 1/T, where k is the retention factor of a solute i and T is the temperature) were linear in the studied temperature interval. This allowed the determination of interaction enthalpies (ΔHi), entropy (ΔSi), and Gibbs energies (ΔGi). This thermodynamic information was used to evaluate the retention and resolution of enantiomers of studied analytes in this HPLC system. [ABSTRACT FROM AUTHOR]

The Whelk-O 1 chiral stationary phase (CSP) is an useful column for the high performance liquid chromatographic (HPLC) resolution of enantiomers of 2-methoxy-1-[(4-methylpiperazino)methyl]ethyl esters of N-(2-,3-, and 4-alkoxyphenyl)carbamic acid (group of the local anaesthetic drugs) in the polar organic mode and the reversed mode. According to the results of enantiomeric separations in different mobile phases [containing organic modifiers (methanol, acetonitrile, water), with different additives of acetic acid and trimethylamine], it can be postulated that the piperazino part of the phenylcarbamic acid compound is essential because the separation of piperidino, pyrrolidino, and perhydroazepino esters of alkoxy phenylcarbamic acid were not observed. Also the influence of the environment near the analyte's stereogenic is important for enantioseparation. A comparison of the enantiomeric elution order and the configuration of the chiral selector shows that R-(−) enantiomers are more retained on the (R,R) Whelk-O 1 column and S-(+) enantiomers are more retained on the (S,S) Whelk-O 1 column. [ABSTRACT FROM AUTHOR]

Enantiomeric separation of alkoxysubstituted esters of phenylcarbamic acid (local anesthetic drugs) is carried out using high performance liquid chromatography (HPLC) with two chiral stationary phases. The teicoplanin chiral stationary phase—chirobiotic T and the teicoplanin chiral stationary phase without the pendant carbohydrate moieties—chirobiotic teicoplanin aglycone (TAG) were used. The influence of the sugar units, the concentration of the ionic modifiers (diethylamine), the influence of the position and of number of carbon atoms in the analytic alkoxychain substituent, and the composition of the mobile phase; on retention factors and resolution of enantiomers were investigated. By comparison of chromatographic parameters obtained by using both chiral stationary phases, the influence of carbohydrate moieties on the mechanism of chiral separation could be evaluated. The interaction mechanism of the enantiomeric separations is discussed. Better separation, in terms of—greater values of Rij of enantiomers—was achieved with the chirobiotic TAG column. [ABSTRACT FROM AUTHOR]

Vancomycin, immobilized on silica, served as the chiral stationary phase (CSP) in this investigation with a polar organic solvent as the mobile phase in high performance liquid chromatography (HPLC). Enantiomers of alkoxysubstituted esters of phenylcarbamic acid (local anaesthetic drugs) were examined in order to evaluate the enantiorecognition process. The chromatographic behavior was investigated in order to obtain a deeper insight into the enantiodiscrimination process. A variety of factors, including the nature and concentration of the ionic modifiers in the mobile phase were examined. Conditions for the enantioseparation of derivatives of phenylcarbamic acid were found. The interaction mechanism of the separations is discussed. [ABSTRACT FROM AUTHOR]

The macrocyclic glycopeptides, vancomycin, teicoplanin, and ristocetin A are naturally occurring chiral molecules that have been developed into one of the most useful classes of chiral stationary phases (CSPs) for HPLC. Since these chiral selectors are structurally related, they tend to have similar, but not identical, enantioselectivities for most compounds. CSPs, of this type, with opposite enantioselectivities are rare. Two exceptions have been found to this. The oxazolidiones (starting materials for asymmetric synthesis) and dansyl amino acids all show a reversal in enantioselective retention on one of these three related CSPs. By using the HPLC assays developed for these compounds, the levels of enantiomeric impurities can be measured down to ∼0.01%. The enantiomeric purity of commercial oxazolidiones was determined. [ABSTRACT FROM AUTHOR]

The enantiomeric separation of alkylaminoderivatives of aryloxypropanols using macrocyclic bonded chiral stationary phases was studied. Teicoplanin and vancomycin chiral stationary phases were used to separate a large number of derivatives of aryloxypropanol enantiomers by HPLC in the polar-organic mode. By comparison of chromatographic parameters obtained by using both chiral stationary phases (CSPs), aspects of the enantioselective separation mechanism could be discerned. Originally, the polar organic mode was developed for chiral compounds that contained a minimum of two hydrogen bonding groups, resulting in a minimum of two hydrogen bonding interactions to the CSP. This work demonstrated that a combination of one hydrogen bonding interaction and one electrostatic interaction is equally effective. The environment (i.e., functional groups) nearest to the stereogenic center of the aryloxypropanols had the greatest effect on the enantioresolution. Teicoplanin CSPs produced the greatest ΔΔG°'s and the best enantiomeric separations of these compounds. The site of a possible electrostatic interaction of these compounds is different from that found for amino acids. [ABSTRACT FROM AUTHOR]

The behaviour of teicoplanin-based chiral stationary phase (CHIROBIOTIC T) towards changes in organic and ionic modifiers in mobile phase was investigated in order to deduce suitable conditions for the liquid chromatographic enantioseparations of a series of alkoxysubstituted esters of phenylcarbamic acid. Methanol and acetonitrile were the non-ionic modifiers tested in the mobile phase, while different aliphatic carboxylic acids (formic acid, acetic acid, propionic acid, hexanoic acid) and bases (triethylamine, trimethylamine, diethylamine) were used as ionic modifiers. The influence of the nature and concentration of the modifiers on retention, selectivity, and resolution of enantiomers was investigated. Under these conditions, enantiomeric separations could be obtained for 3- and 4-alkoxysubstituted derivatives. The elution order of enantiomers was also determined. [ABSTRACT FROM AUTHOR]