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  • Author: Jozef Lehotay x
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Abstract

The HPLC by using chiral stationary phases based on macrocyclic antibiotics, dimethylphenyl carbamate cyklofructan 7 and β-cyclodextrin in terms of polar-organic separation mode (mobile phase methanol/acetonitrile/acetic acid/triethylamine) were used for enantioseparation of alkoxy derivatives of phenylcarbamic acid. The effect of the analyte structures on the efficiency of enantioseparation was investigated. The most suitable stationary phase was teicoplanin aglycone, where the separations of the enantiomers were obtained (the resolution value from 0.65 to 2.90, depending on the structure of the analyte). Significant effect on the resolution of the enantiomers has position of alkoxy substituent in the hydrophobic part of the molecule. The enantiorecognition was achieved for 3-alkoxysubstituted derivatives.

Abstract

The group selective molecularly imprinted polymers (MIPs) for coumarins, including umbelliferone, herniarin, 4-methylumbelliferone, scoparone were developed. Using umbelliferone as the template molecule, methacrylic acid as functional monomer, ethylene glycol dimethacrylate as linking agent, chloroform as porogen and bulk polymerization as synthetic method, the MIPs were synthesized and characterized with rebinding experiments. The characteristics of MIPs were evaluated by chromatographic method and frontal analysis, and demonstrating good selectivity and high binding capacity (269 μg of umbelliferone per 100 mg of polymer). The group selective MIP was used as sorbent for the SPE pretreatment of coumarins from propolis extracts prior to HPLC analysis. Analysis of the samples showed good recoveries (>70 %). The limits of quantitation (LOQs) for studied compounds were 0.3-10 ng.mL-1 (determined for fluorescence detection).

Abstract

D-amino acids can arise from endogenous microbial flora, from ingestion with the diet or from spontaneous racemization of L-amino acids during ageing. In this work, the behavior of methionine, homocysteine and cysteine enantiomers was investigated in human serum in vitro during 0-72 h at incubation temperature 37°C. The separation of enantiomers was realized in two dimensional on-line system (the connection of an achiral column Purospher RP-18 endcapped and a chiral column Chirobiotic TAG). This system allowed simultaneous monitoring all tested amino acids and their enantiomers. The possible effect D-enantiomer on the behavior of its L-enantiomer (the synergistic effect) was evaluated during incubation time. The first results have showed that no synergistic effect of D-enantiomer on its Lisomer has been observed in our experimental conditions in vitro.

Abstract

In this paper the thermodynamic analyses were used to calculate the contributions of entropic and enthalpic terms of the binding processes of selected derivatives of alkoxy-substituted phenylcarbamic acid (MEP) and phenolic acids (PAs) on the series of molecularly imprinted polymers (MIPs) and corresponding non-imprinted polymers (NIPs). All polymers were prepared by a bulk polymerization method with different porogens and functional monomers. The thermodynamic assessments were based on the quantification by HPLC measurements of the analytes tested in different mobile phases and at temperature range from 293 K to 333 K. The thermodynamic parameters were determined from the van’t Hoff plots - dependences between logarithms of the retention factors of studied analytes (ln k) and the inverse value of the temperature (1/T). Almost all data showed that enthalpic term was the dominating driving force for the investigated analytes.

Abstract

The Humulus lupulus L. is well known as necessary raw material for beer production. The main structural classes of chemical compounds identified from hop cones include terpenes, bitter acids, prenylated chalcones, and flavonol glycosides. They were subjects of presented work. The content of quercetin was found in the range 490 - 1092 μg/g and that of kaempferol from 218 to 568 μg/g of the dry hop cones. The content of isorhamnetin was very low in all varieties. From biological activities in vitro point of view, relative high level of inhibition activity was observed for six hop genotypes - Zlatan, Lučan, and the Oswald's clones 31, 70, 71, 72, 114 on both enzymes thrombin and urokinase, but without correlation to analyzed flavonols content. In spite of this, antioxidant activity, measured by both the BCLM and HPE methods, was found high and seem to be in correlation with content of analyzed flavonols. Particularly the Oswald's clone 114 expressed very potent biological activities. In general, obtained results indicate that hop cones are valuable material also for other application others than beer production.

Abstract

Methionine is a naturally occurring amino acid. Its enantiomeric separation by using high performance liquid chromatography on various types of chiral stationary phases was studied. The effect of mobile phase composition on enantioselectivity and retention was considered. The separation of the enantiomers was attained in different separation modes – reversed phase mode for the macrocyclic antibiotic chiral stationary phases (teicoplanin, teicoplanin aglycone), normal phase and polar organic phase modes for the isopropyl carbamate cyclofructan 6 chiral stationary phase. It was shown that the hydrogen bonding, dipole interactions, steric effects between methionine molecules and stationary phases play an important role in the separation of enantiomers.