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Peptide Enantiomers (peptide + enantiomer)
Selected AbstractsEffect of urea on analyte complexation by 2,6-dimethyl-,-CD in peptide enantioseparations by CEELECTROPHORESIS, Issue 21 2009Manuela Hammitzsch-Wiedemann Abstract The aim of the present study was the investigation of the effect of urea on analyte complexation in CD-mediated separations of peptide enantiomers by CE in the pH range of about 2,5. pH-independent complexation and mobility parameters in the absence and presence of 2,M urea were obtained by three-dimensional, non-linear curve fitting of the effective analyte mobility as a function of pH and heptakis-(2,6-di- O -methyl)-,-CD concentration. Urea led to decreased binding strength of the CD towards the protonated and neutral analyte enantiomers as well as to decreased mobilities of the free analytes. In contrast, mobilities of the fully protonated enantiomer,CD complexes as well as the pKa values of the free and complexed analytes increased. The effect of urea on separation efficiency varied with pH and CD concentration. In the case of Ala-Tyr and Ala-Phe, separations improved in the presence of urea at pH 2.2. In contrast, separations were impaired by urea at pH 3.8 and low concentrations of the CD. Decreased separation efficiency was noted for Asp-PheOMe and Glu-PheNH2 at low CD concentrations when urea was added but separations improved at higher CD concentrations over the entire pH range studied. The effect of urea on analyte complexation appeared to be primarily non-stereoselective. Furthermore, the pH-dependent reversal of the enantiomer migration order observed for Ala-Tyr and Ala-Phe can be rationalized by the complexation and mobility parameters. [source] Recent developments in peptide stereoisomer separations by capillary electromigration techniquesELECTROPHORESIS, Issue S1 2009Gerhard K. E. Scriba Abstract The stereochemistry of peptides determines their physicochemical and biological activities. Thus, analytical methods that are able to discriminate between peptide stereoisomers are important. As peptides are typically hydrophilic compounds, many methods for the separation of peptide diastereomers and enantiomers have been developed by capillary electromigration techniques. Moreover, peptide enantiomers displayed unique migration behavior such as a pH-dependent change of the enantiomer migration order in CD-mediated enantioseparations in CE making them ideal compounds to study mechanistic effects of enantioseparations. The present short review summarizes recent developments in the separation of stereoisomers of peptide and peptidomimetics by capillary electromigration techniques. Moreover, recent NMR and molecular modeling studies as well as investigation on the effect of buffer additives on complex formation will be discussed as attempts to understand mechanistic aspects of peptide enantioseparations and to analyze the structure of peptide-CD complexes. [source] Comparison of Cyclodextrin-Dipeptide Inclusion Complexes in the Absence and Presence of Urea by Means of Capillary Electrophoresis, Nuclear Magnetic Resonance and Molecular ModelingEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 18 2007Benjamin Waibel Abstract The use of capillary electrophoresis (CE) modified with cyclodextrin (CD) for the separation of stereoisomers of peptides is well established. To increase the solubility of ,-CD, urea is often added to the buffer which may influence the complexation of a CD with a guest molecule. The aim of the present study was to investigate the influence of urea on the complexation between dipeptides and ,-CD using Ala-Phe and Ala-Tyr as model compounds. For this purpose three different analytical methods were employed: capillary electrophoresis (CE), 1H-NMR spectroscopy and molecular dynamics simulations (MD). Electropherograms of the peptide enantiomers were different in the presence and absence of urea. For example, at pH,2.5 in the absence of urea the enantiomers of Ala-Tyr are not separated in contrast to the use of buffers containing urea. Applying "complexation-induced chemical shift (CICS)" in NMR spectroscopy and rotating frame Overhauser enhancement spectroscopy (ROESY) revealed differences in the complexation of the peptide enantiomers by ,-CD in the absence and presence of urea suggesting the stabilization of the complex through the phenolic hydroxyl group of tyrosine. MD simulations for different complexes were carried out with consideration of both water and urea molecules in solution. Simulations were performed for 1 ns. In conclusion, NMR spectroscopy and MD methods help to understand the structure of peptide-CD complexes and the separation and migration behavior in CE. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Enantiomer discrimination of peptides by tandem mass spectrometry: influence of the peptide sequence on chiral recognitionRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 22 2004Christoph Czerwenka The enantiomer discrimination of peptides by electrospray ionization tandem mass spectrometry is described. A cinchona alkaloid derivative, tert -butylcarbamoylquinine, is used as chiral selector. The chiral selector forms diastereomeric complexes with the peptide enantiomers in the liquid phase (methanolic solution), which are then transferred to the gas phase, where their dissociation behaviour is studied in an ion-trap mass spectrometer. Different degrees of dissociation of the diastereomeric complexes allow for the discrimination of the peptide enantiomers. The influence of the peptide sequence on enantiomer discrimination is discussed and molecular recognition information is derived by comparing the results obtained for related peptides. For dipeptides, small amino acid residues at the N-terminus and bulky side chains at the C-terminus were found to enhance chiral recognition, while for tripeptides the effects were rather irregular. Copyright © 2004 John Wiley & Sons, Ltd. [source] | ||||||||||