Study of selectivity of molecularly imprinted polymers prepared under different conditions.

Molecularly imprinted polymers were prepared and tested in different ways. 1-Methyl-2-piperidinoethylester of 4-decyloxyphenylcarbamic acid was used as the template for imprints formation. Acrylamide, 4-vinylpyridine, and methacrylic acid as monomers and methanol and acetonitrile as a porogene were used. Non-imprinted polymers were prepared for each imprinted polymer by the same procedure. Polymers were employed as sorbents for solid-phase extraction. In this work the influence of polymerization mixture composition on polymer properties, such as capacity and selectivity, was investigated. The influence of alkoxy-chain length and the position on benzene ring on the selectivity of polymers was also investigated.

Gas chromatographic determination of the interconversion energy barrier for dimethyl-2,3-pentadienedioate enantiomers.

The enantiomers of dimethyl-2,3-pentadienedioate undergo interconversion during gas chromatographic separation on 2,6-di-O-methyl-3-O-pentyl-beta-, 2,6-di-O-methyl-3-O-pentyl-gamma-, and 2,3-di-O-methyl-6-O-tert butyldimethylsilyl-beta-CD chiral stationary phases. The combination of a deconvolution method with an internal standard was used to determine individual enantiomer peak areas and retention times needed for the calculation of the interconversion rate constants and the energy barrier for dimethyl-2,3-pentadienedioate enantiomers. The kinetic and thermodynamic data obtained for the interconversion data (rate constants, energy barriers, enthalpies, and entropies) were in good agreement with the published data (Trapp, O., Schurig, V., Chirality 2002, 14, 465-470) using permethylated-beta-CD (Chirasil-beta-Dex).

GC separation of 2-substituted ethyl propionate enantiomers on permethylated and 2,6-dimethyl-3-pentyl beta- and gamma-cyclodextrin stationary phases.

In this work, the capillary gas chromatographic enantiomer separation of eight congeneric compounds with general formulae CH3-HCX-COOC2H5 (where X = Cl, Br, I, CN, OH, OC2H5, OC6H5 and NHCOCF3) on four different permethyl- and 2,6-di-O-methyl-3-O-pentyl- beta- and gamma-CD stationary phases has been studied. The separation of enantiomers was evaluated in terms of the interactions of the X substituent of studied derivatives, as well as the nature of the 3-O-alkyl group in the 2,6-di-O-methyl-3-O-alkyl-CDs and the CDs cavity size. The differences in thermodynamic data [deltaH and -deltaS] obtained for studied compounds and the selectivity of modified beta- and gamma-cyclodextrin phases in gas chromatographic separation were evaluated. deltaH values were compared with a deltaH value of an achiral standard (ethyl propionate, where X = H) in order to obtain the contribution of a particular substituent to the overall interaction energy. It was shown that the variation in the enantiomeric separation with temperature and the retention order of these compounds on a given cyclodextrin capillary column depends on the nature of the substituents bonded to stereogenic carbon atom. It was found that the temperature dependencies of selectivity factors, In a on 1/T, were both linear as well as non-linear, inter alia depending on the number of glucopyranose units of the CD derivatives. The enantiospecific thermodynamic data [delta21(deltaH)] and [-delta21(deltaS)] which characterize the chiral recognition in the separation system were used to gain more insight into the mechanistic aspects of the enantioseparations on permethylated and 2,6-di-O-methyl-3-O-pentyl-beta- and gamma-cyclodextrins.

On the capillary gas chromatographic separation of enantiomers of N-trifluoroacetyl-O-alkyl esters of selected amino acids on 2,3-di-O-pentyl-6-O-acyl cyclodextrins.

In this work, the separation of enantiomers of N-TFA-O-alkyl amino acids on the 2,3-di-O-pentyl-6-O-acyl alpha-, beta- and gamma-cyclodextrin stationary phases has been studied. The influence of structure differences in the alkyl substituents bonded to the stereogenic carbon atom (R1), as well as in the ester group (R2) of the selected amino acid derivatives, and the selectivity of modified alpha-, beta- and gamma-cyclodextrin phases in gas chromatographic separation of derivatized amino acid enantiomers was studied in detail. A model set of N-TFA-alkyl esters of four amino acids was separated on five columns. The separation of enantiomers was evaluated in terms of the interactions of the alkyl substituents bonded to the stereogenic carbon (R1) and/or the ester group (R2) of the N-TFA-O-alkyl amino acid derivatives as well as the nature of the 3-O-acyl group in the 2,6-di-O-pentyl-3-O-acyl alpha-, beta- and gamma-cyclodextrins. It was shown that the variation in the enantiomeric separation with temperature and the retention order of enantiomers on a given cyclodextrin capillary column depends both on the nature of the bonded R1 and R2 alkyl groups. It was found that the temperature dependencies of selectivity factors, ln alpha on 1/T, were mostly non-linear. The thermodynamic data [delta(deltaS) and [delta(deltaH)] which characterize the chiral recognition were used to gain more insight into the mechanistic aspects of enantio separation of the N-TFA-O-alkyl amino acid derivatives on 2,6-di-O-pentyl-3-O-acyl-alpha-, beta- and gamma-cyclodextrins.

Selective extraction of derivates of p-hydroxy-benzoic acid from plant material by using a molecularly imprinted polymer.

Selective SPE of derivates of p-hydroxybenzoic acid (pHBA) from plant extract of Melissa officinalis is presented using a molecularly imprinted polymer (MIP) made with protocatechuic acid (PA) as template molecule. MIP was prepared with acrylamide as functional monomer, ethylene glycol dimethacrylate as crosslinking monomer and ACN as porogen. MIP was evaluated towards six phenolic acids: PA, gallic acid, pHBA, vanillic acid (VA), gentisic acid (GeA) and syringic acid (SyrA), and then steps of molecularly imprinted SPE (MISPE) procedure were optimized. The best specific binding capacity of MIP was obtained for PA in ACN (34.7 microg/g of MIP). Other tested acids were also bound on MIP if they were dissolved in this solvent. ACN was chosen as solvent for sample application. M. officinalis was extracted into methanol/water (4:1, v/v), the extract was then evaporated to dryness and dissolved in ACN before application on MIP. Water and ACN were used as washing solvents and elution of benzoic acids was performed by means of a mixture methanol/acetic acid (9:1, v/v). pHBA, GA, PA and VA were extracted with recoveries of 56.3-82.1% using this MISPE method. GeA was not determined in plant extract.