1
|
Pasquini B, Orlandini S, Caprini C, Del Bubba M, Innocenti M, Brusotti G, Furlanetto S. Cyclodextrin- and solvent-modified micellar electrokinetic chromatography for the determination of captopril, hydrochlorothiazide and their impurities: A Quality by Design approach. Talanta 2016; 160:332-339. [DOI: 10.1016/j.talanta.2016.07.038] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2016] [Revised: 07/12/2016] [Accepted: 07/20/2016] [Indexed: 10/21/2022]
|
2
|
Bouabdallah S, Ben Dhia MT, Driss MR, Touil S. Investigation of the energy barrier to the rotation of amide CN bonds in ACE inhibitors by NMR, dynamic HPLC and DFT. J Pharm Biomed Anal 2016; 128:416-425. [PMID: 27344631 DOI: 10.1016/j.jpba.2016.05.049] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2016] [Revised: 05/30/2016] [Accepted: 05/31/2016] [Indexed: 11/26/2022]
Abstract
The isomerizations of Enalapril, Perindopril, Enalaprilat and Lisinopril have been investigated using NMR spectroscopic, dynamic chromatographic, unified equation and DFT theoretical calculations. The thermodynamic parameters (ΔH, ΔS and ΔG) were determined by varying the temperature in the NMR experiments. At the coalescence temperature, we can evaluate the isomerization barrier to the rotation (ΔG(≠)) around the amide bond. Using dynamics chromatography and an unified equation introduced by Trap, we can determine isomerization rate constants and Gibbs activation energies. Molecular mechanics calculations also provided evidence for the presence of low energy conformers for the ACE due to restricted amide rotation. With the value of barriers (ΔE) between them of the order of (20kJmol(-1)), which is in agreement with the dynamic NMR results and DFT calculations.
Collapse
Affiliation(s)
- S Bouabdallah
- Laboratory of Heteroatom Organic Chemistry, Department of Chemistry, Faculty of Sciences of Bizerte, University of Carthage, 7021 Jarzouna, Tunisia.
| | - M T Ben Dhia
- Laboratory of Organic Chemistry: Synthèse et Etude Physico-Chimique, Faculty of Sciences of Tunis, University of El Manar, 1060 Tunis, Tunisia
| | - M R Driss
- Laboratory of Heteroatom Organic Chemistry, Department of Chemistry, Faculty of Sciences of Bizerte, University of Carthage, 7021 Jarzouna, Tunisia
| | - S Touil
- Laboratory of Heteroatom Organic Chemistry, Department of Chemistry, Faculty of Sciences of Bizerte, University of Carthage, 7021 Jarzouna, Tunisia
| |
Collapse
|
3
|
Shibukawa M, Miyake A, Eda S, Saito S. Determination of the cis–trans Isomerization Barriers of l-Alanyl-l-proline in Aqueous Solutions and at Water/Hydrophobic Interfaces by On-Line Temperature-Jump Relaxation HPLC and Dynamic On-Column Reaction HPLC. Anal Chem 2015; 87:9280-7. [DOI: 10.1021/acs.analchem.5b02488] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Masami Shibukawa
- Graduate School of Science
and Technology, Saitama University, 255 Shimo-Okubo, Sakura-ku, Saitama 338-8570, Japan
| | - Ayaka Miyake
- Graduate School of Science
and Technology, Saitama University, 255 Shimo-Okubo, Sakura-ku, Saitama 338-8570, Japan
| | - Sayaka Eda
- Graduate School of Science
and Technology, Saitama University, 255 Shimo-Okubo, Sakura-ku, Saitama 338-8570, Japan
| | - Shingo Saito
- Graduate School of Science
and Technology, Saitama University, 255 Shimo-Okubo, Sakura-ku, Saitama 338-8570, Japan
| |
Collapse
|
4
|
Study of a conformational equilibrium of lisinopril by HPLC, NMR, and DFT. Int J Anal Chem 2014; 2014:494719. [PMID: 24707291 PMCID: PMC3953672 DOI: 10.1155/2014/494719] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2013] [Accepted: 10/18/2013] [Indexed: 11/17/2022] Open
Abstract
The isomerization of lisinopril has been investigated using chromatographic, NMR spectroscopic, and theoretical calculations. The NMR data, particularly the NOEDIFF experiments, show that the major species that was eluted first is the trans form. The proportion was 77% and 23% for the trans and cis, respectively. The thermodynamic parameters (ΔH, ΔS, and ΔG) were determined by varying the temperature in the NMR experiments. The interpretations of the experimental data were further supported by DFT/B3LYP calculations.
Collapse
|
5
|
Wernisch S, Trapp O, Lindner W. Application of cinchona-sulfonate-based chiral zwitterionic ion exchangers for the separation of proline-containing dipeptide rotamers and determination of on-column isomerization parameters from dynamic elution profiles. Anal Chim Acta 2013; 795:88-98. [DOI: 10.1016/j.aca.2013.08.004] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2013] [Revised: 07/31/2013] [Accepted: 08/02/2013] [Indexed: 01/28/2023]
|
6
|
Interconversion of Stereochemically Labile Enantiomers (Enantiomerization). Top Curr Chem (Cham) 2013; 341:231-69. [DOI: 10.1007/128_2013_453] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
|
7
|
|
8
|
Orlandini S, Gotti R, Giannini I, Pasquini B, Furlanetto S. Development of a capillary electrophoresis method for the assay of ramipril and its impurities: an issue of cis-trans isomerization. J Chromatogr A 2011; 1218:2611-7. [PMID: 21429497 DOI: 10.1016/j.chroma.2011.02.062] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2011] [Revised: 02/22/2011] [Accepted: 02/23/2011] [Indexed: 10/18/2022]
Abstract
The development of a rapid and selective capillary electrophoresis method for the quantitation of ramipril and its eight main impurities in pharmaceutical dosage form is described. Ramipril and three of its impurities contain a proline-similar moiety which causes in solution the presence of interconverting cis-trans isomers with respect to the amide bond. The interplay between electrophoretic migration and isomerization may yield the presence of an undesired interconversion zone between the two isomer peaks in the electropherogram, depending on the experimental conditions. Different capillary electrophoresis operative modes and pseudostationary phases were evaluated, both in normal and reverse polarity, in order to find the essential analytical parameters which could make it possible to overcome this issue and thus accurately quantify the analytes. The best results were obtained by using microemulsion electrokinetic chromatography in reverse polarity, where all the compounds which undergo cis-trans interconversion migrate as a single narrow peak. Experimental design led to identification of the following optimised conditions: background electrolyte, microemulsion made by 88.95% of 90 mM phosphate pH 2.5, 1.05% of n-heptane and 10.00% of SDS/n-butanol in 1:2 ratio; voltage, -26 kV; temperature, 17°C. Applying these conditions, the baseline separation of the analytes was obtained in about 10 min. Validation of the method following ICH guidelines was carried out and the procedure was applied to a real sample of ramipril tablets.
Collapse
Affiliation(s)
- Serena Orlandini
- Department of Pharmaceutical Sciences, University of Florence, Florence, Italy.
| | | | | | | | | |
Collapse
|
9
|
Stockton AM, Tjin CC, Huang GL, Benhabib M, Chiesl TN, Mathies RA. Analysis of carbonaceous biomarkers with the Mars Organic Analyzer microchip capillary electrophoresis system: aldehydes and ketones. Electrophoresis 2010; 31:3642-9. [PMID: 20967779 DOI: 10.1002/elps.201000424] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2010] [Revised: 08/18/2010] [Accepted: 08/19/2010] [Indexed: 11/11/2022]
Abstract
A microchip CE method is developed for the analysis of two oxidized forms of carbon, aldehydes and ketones, with the Mars Organic Analyzer (MOA). Fluorescent derivitization is achieved in ∼ 15 min by hydrazone formation with Cascade Blue hydrazide in 30 mM borate pH 5-6. The microchip CE separation and analysis method is optimized via separation in 30 mM borate buffer, pH 9.5, at 20°C. A carbonyl standard consisting of ten aldehydes and ketones found in extraterrestrial matter is successfully separated; the resulting LOD depends on the reactivity of the compound and range from 70 pM for formaldehyde to 2 μM for benzophenone. To explore the utility of this method for analyzing complex samples, analyses of several fermented beverages are conducted, identifying ten aldehydes and ketones ranging from 30 nM to 5 mM. A Martian regolith simulant sample, consisting of a basalt matrix spiked with soluble ions and acetone, is designed and analyzed, but acetone is found to have a limited detectable lifetime under simulant Martian conditions. This work establishes the capability of the MOA for studying aldehydes and ketones, a critical class of oxidized organic molecules of interest in planetary and in terrestrial environmental and health studies.
Collapse
Affiliation(s)
- Amanda M Stockton
- Department of Chemistry, University of California, Berkeley, CA 94720, USA
| | | | | | | | | | | |
Collapse
|
10
|
Trapp O. Investigation of the stereodynamics of molecules and catalyzed reactions by CE. Electrophoresis 2010; 31:786-813. [DOI: 10.1002/elps.200900599] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
|
11
|
Chen Z, Weber SG. Determination of binding constants by affinity capillary electrophoresis, electrospray ionization mass spectrometry and phase-distribution methods. Trends Analyt Chem 2008; 27:738-748. [PMID: 19802330 PMCID: PMC2600677 DOI: 10.1016/j.trac.2008.06.008] [Citation(s) in RCA: 105] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Many methods for determining intermolecular interactions have been described in the literature in the past several decades. Chief among them are methods based on spectroscopic changes, particularly those based on absorption or nuclear magnetic resonance (NMR) [especially proton NMR ((1)H NMR)]. Recently, there have been put forward several new methods that are particularly adaptable, use very small quantities of material, and do not place severe requirements on the spectroscopic properties of the binding partners. This review covers new developments in affinity capillary electrophoresis, electrospray ionization mass spectrometry (ESI-MS) and phasetransfer methods.
Collapse
Affiliation(s)
- Zhi Chen
- Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - Stephen G. Weber
- Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260, USA
| |
Collapse
|
12
|
Trapp O. Unified Equation for Access to Rate Constants of First-Order Reactions in Dynamic and On-Column Reaction Chromatography. Anal Chem 2006; 78:189-98. [PMID: 16383327 DOI: 10.1021/ac051655r] [Citation(s) in RCA: 140] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A unified equation to evaluate elution profiles of reversible as well as irreversible (pseudo-) first-order reactions in dynamic chromatography and on-column reaction chromatography has been derived. Rate constants k1 and k(-1) and Gibbs activation energies are directly obtained from the chromatographic parameters (retention times tR(A) and tR(B) of the interconverting or reacting species A and B, the peak widths at half-height wA and wB, and the relative plateau height h(p)), the initial amounts A0 and B0 of the reacting species, and the equilibrium constant K(A/B). The calculation of rate constants requires only a few iterative steps without the need of performing a computationally extensive simulation of elution profiles. The unified equation was validated by comparison with a data set of 125,000 simulated elution profiles to confirm the quality of this equation by statistical means and to predict the minimal experimental requirements. Surprisingly, the recovery rate from a defined data set is on average 35% higher using the unified equation compared to the evaluation by iterative computer simulation.
Collapse
Affiliation(s)
- O Trapp
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany.
| |
Collapse
|
13
|
Newman CID, McGuffin VL. Effects of nonequilibrium on velocity and plate height in reactive capillary electrophoresis. Electrophoresis 2005; 26:4016-25. [PMID: 16252325 DOI: 10.1002/elps.200500299] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Models for velocity and plate height for reactive CE are developed under the formalism of generalized nonequilibrium theory, as described by Giddings. The resultant equations are consistent with chromatographic theory and validated with an independent stochastic simulation. Moreover, unlike prior methods for CE, this model allows calculation of thermodynamic equilibrium constants and kinetic rate constants from a single, undistorted peak. The theoretical development shows that velocity is directly dependent on the equilibrium constant and is independent of the rate constant. On the other hand, plate height varies little with equilibrium constant and is inversely proportional to rate constant. The ability to evaluate equilibrium constants from velocity and rate constants from plate height is most greatly influenced by electric field strength and mobility difference. The accuracy in calculated equilibrium constants is limited by mobility difference; however, the accuracy in rate constants is limited by plate height and equilibrium constant.
Collapse
Affiliation(s)
- Carl I D Newman
- Department of Chemistry, Michigan State University, East Lansing, MI 48824-1322, USA
| | | |
Collapse
|
14
|
Trapp O. Direct calculation of interconversion barriers in dynamic chromatography and electrophoresis: Isomerization of captopril. Electrophoresis 2005; 26:487-93. [PMID: 15657905 DOI: 10.1002/elps.200410235] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Dynamic capillary electrophoresis (DCE) and direct calculation of the rate constants of isomerization has been applied to determine the cis-trans isomerization barriers of the angiotensin-converting enzyme inhibitor captopril. The separation of the rotational cis-trans isomeric drug has been performed in an aqueous 50 mM borate buffer at pH 9.3. Interconversion profiles featuring plateau formation, peak-broadening, and peak coalescence were observed. To determine the rate constants of the forward and backward reaction (k(cis-->trans) and k(trans-->cis)) of the isomerization process in dynamic capillary electrophoresis, a novel straightforward calculation method using the experimental parameters plateau height, h(plateau), peak width at half height w(h), the total migration times of the cis-trans isomers t(R) and the electroosmotic break-through time t(0) as well as the peak ratio of the cis-trans isomers is presented for the first time. From temperature dependent measurements the rate constants k(cis-->trans) and k(trans-->cis) and the kinetic activation parameters DeltaG( not equal), DeltaH( not equal), and DeltaS( not equal) of the cis-trans isomerization of captopril were obtained. From the activation parameters the isomerization barriers of captopril at 37 degrees C under basic conditions were calculated to be DeltaG( not equal) (cis-->trans) = 90.3 kJ.mol(-1)and DeltaG( not equal) (trans-->cis) = 90.0 kJ.mol(-1*).
Collapse
Affiliation(s)
- Oliver Trapp
- Stanford University, Department of Chemistry, Roth Way, Stanford, CA 94305, USA.
| |
Collapse
|
15
|
Stellwagen E, Ledger R. Analysis of the isomeric composition of the proline peptide bond in an angiotensin-converting enzyme inhibitor using capillary electrophoresis. Anal Biochem 2003; 321:167-73. [PMID: 14511680 DOI: 10.1016/s0003-2697(03)00437-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The cis and trans isomeric composition of a proline peptide bond can be determined by routine free-solution capillary electrophoresis measurements provided that one isomeric form is preferentially stabilized by a dissociable ionic group. This capability is illustrated using the angiotensin converting enzyme (ACE) inhibitor (S)-1-N-[1-(ethoxycarbonyl)-3-phenylpropyl]-L-ala-L-pro, which has the trade name enalapril. Electropherograms indicate that the two isomeric forms of enalapril can be separated with baseline resolution at 15 degrees C using capillary buffers having pH values in the dissociation ranges of the enalapril carboxyl group, pK(cis) and pK(trans) of 2.6 and 3.1, and of the enalapril amine group, pK(cis) and pK(trans) of 5.9 and 5.6. Such baseline resolution indicates that the isomeric composition does not change during analysis, facilitating measurement of the isomer composition of a sample prior to its injection into the capillary. Thus the effect of pH, ionic strength, or an aprotic solvent on the isomeric composition of enalapril can be measured under uniform analytical conditions. The trans isomer composition changes from 68% in the cationic form, pH <2, to 50% in the isoelectric form, pH approximately 4.5, to 60% in the anionic form, pH >7. Addition of salt to the isoelectric form or addition of an aprotic solvent to any form prior to analysis increases the trans isomer composition. Similar analyses can be made using the alternative ACE inhibitors captopril and enalaprilat.
Collapse
Affiliation(s)
- Earle Stellwagen
- Department of Biochemistry, University of Iowa, Iowa City, IA 52242, USA.
| | | |
Collapse
|
16
|
Lin B, Song F, Guiochon G. Analytical solution of the ideal, nonlinear model of reaction chromatography for a reaction A-->B and a parabolic isotherm. J Chromatogr A 2003; 1003:91-100. [PMID: 12899298 DOI: 10.1016/s0021-9673(03)00656-3] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
The analytical solution of the ideal, nonlinear model of reaction chromatography for the simplest possible chemical reaction, A-->B and with a parabolic isotherm for the reagent, is derived for two types of boundary conditions, the injection of a rectangular concentration pulse of finite width (elution) and that of an instantaneous concentration jump (Riemann problem or breakthrough curve). The areas of the profiles of the reagent and of the product of the reaction are calculated in both the ideal and the nonideal cases. The effects of the nonlinear behavior of the equilibrium isotherm and of axial dispersion on the reagent profile are discussed using analytical and numerical methods.
Collapse
Affiliation(s)
- Bingchang Lin
- Center of Separation Technology, Anshan University of Science and Technology, Anshan, Liaoning 114044, China
| | | | | |
Collapse
|
17
|
Krupcik J, Oswald P, Májek P, Sandra P, Armstrong W. Determination of the interconversion energy barrier of enantiomers by separation methods. J Chromatogr A 2003; 1000:779-800. [PMID: 12877200 DOI: 10.1016/s0021-9673(03)00238-3] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Separation methods have become versatile tools for the determination of kinetic activation parameters and energy barriers to interconversion of isomers and enantiomers in the last 20 years. New computer-aided evaluation systems allow the on-line determination of these data after separating minute amount of pure compounds or mixture of isomers or enantiomers, respectively. Both dynamic interconversion during the separation process as well as static stopped-flow techniques have been applied to determine the kinetic activation parameters and interconversion energy barriers by separation methods. The use of (1) combinations of batchwise kinetic studies with enantioselective separations, (2) a continuous flow model, (3) a comparison of real chromatograms with simulated ones, (4) stopped-flow techniques, (5) stochastic methods, (6) approximation functions and (7) deconvolution methods, for the determination of interconversion energy barriers by separation methods is summarized in detail.
Collapse
Affiliation(s)
- J Krupcik
- Department of Analytical Chemistry, Slovak University of Technology, Radlinského 9, Bratislava 81237, Slovakia.
| | | | | | | | | |
Collapse
|
18
|
Bouabdallah S, Trabelsi H, Ben Dhia T, Sabbah S, Bouzouita K, Khaddar R. RP-HPLC and NMR study of cis-trans isomerization of enalaprilat. J Pharm Biomed Anal 2003; 31:731-41. [PMID: 12644200 DOI: 10.1016/s0731-7085(02)00661-1] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The angiotensin converting enzyme inhibitor, enalaprilat can exist in solution as cis and trans conformers which interconvert around the amide bond at room temperature. A HPLC with UV detection was performed to study the influence of various chromatographic operational conditions on both rotamers separation and elution of enalaprilat as a single peak. In addition nuclear overhauser enhancement difference was used for the identification of the conformers. The isomer ratio integrated from the obtained 1H NMR result were 71.5:28.5 and 76:24 at 298 and 279 K, respectively where the trans was the major form.
Collapse
Affiliation(s)
- S Bouabdallah
- Laboratoire National de Contrôle des Médicaments 11bis, rue jebel Lakhdar, Bab Saadoun 1006, Tunis, Tunisia
| | | | | | | | | | | |
Collapse
|
19
|
Bouabdallah S, Trabelsi H, Bouzouita K, Sabbah S. Reversed-phase liquid chromatography of lisinopril conformers. JOURNAL OF BIOCHEMICAL AND BIOPHYSICAL METHODS 2002; 54:391-405. [PMID: 12543514 DOI: 10.1016/s0165-022x(02)00140-9] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The effect of flow rate, temperature, pH, organic solvent and counter ion on peak shape and separation of the cis and trans conformers of lisinopril are investigated by HPLC. It was demonstrated that complete separation of the two isomers can be achieved at low temperature at either neutral or low pH together with appropriate type and concentration of organic solvent, whereas the elution of lisinopril as a single peak is favored by a decrease of flow rate, elevated temperature, choice of organic solvent (type and amount) and the use of an appropriate counter ion concentration.
Collapse
Affiliation(s)
- S Bouabdallah
- Laboratoire National de Contrôle des Médicaments 11 bis, rue jebel Lakhdar, Bab Saadoun, 1006 Tunis, Tunisia
| | | | | | | |
Collapse
|
20
|
Schoetz G, Trapp O, Schurig V. Determination of the cis-trans isomerization barrier of several L-peptidyl-L-proline dipeptides by dynamic capillary electrophoresis and computer simulation. Electrophoresis 2001; 22:2409-15. [PMID: 11519944 DOI: 10.1002/1522-2683(200107)22:12<2409::aid-elps2409>3.0.co;2-c] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Dynamic capillary electrophoresis (DCE) and computer simulation of the elution profiles with the theoretical plate and the stochastic model has been applied to determine the isomerization barriers of the three dipeptides L-alanyl-L-proline, L-leucyl-L-proline, and L-phenylalanyl-L-proline. The separation of the rotational cis-trans isomers has been performed in an aqueous 70 mM borate buffer at pH 9.5. Interconversion profiles featuring plateau formation and peak broadening were observed. To determine the rate constants k1 and k(-1) of the cis-trans isomerization in dynamic capillary electrophoresis, equations have been derived for the theoretical plate model and stochastic model. The electropherograms were simulated with the ChromWin software which uses the experimental data plateau height h(plateau), peak width at half height Wh, the total migration times of the cis-trans isomers tR and the electroosmotic break-through time t0 as well as the peak ratio [cis]/[trans]. From temperature-dependent measurements, the rate constants k1 and k(-1) and the kinetic activation parameters deltaG#, deltaH# and deltaS# of the cis-trans isomerization of the three dipeptides were obtained.
Collapse
Affiliation(s)
- G Schoetz
- Universität Tübingen, Institut für Organische Chemie, Germany
| | | | | |
Collapse
|
21
|
Trapp O, Schoetz G, Schurig V. Determination of enantiomerization barriers by dynamic and stopped-flow chromatographic methods. Chirality 2001; 13:403-14. [PMID: 11466759 DOI: 10.1002/chir.1052] [Citation(s) in RCA: 171] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
In recent years, dynamic chromatography and stopped-flow chromatographic techniques have become versatile tools for the determination of enantiomerization and isomerization barriers. Increasing demands for the stereochemical safety of chiral drugs contributed to the rapid development of new techniques. New computer-aided evaluation systems allow the on-line determination of interconversion barriers from the experimental chromatograms. Both dynamic chromatography and stopped-flow chromatography have been applied to the entire range of chromatographic methods (GC, SFC, HPLC, CE).
Collapse
Affiliation(s)
- O Trapp
- University of Tübingen, Institute of Organic Chemistry, Auf der Morgenstelle 18, 72076 Tübingen, Germany
| | | | | |
Collapse
|
22
|
Abstract
The four stereoisomers of chalcogran 1 ((2RS,SRS)-2-ethyl-1,6-di-oxaspiro[4.4]nonane), the principal component of the aggregation pheromone of the bark beetle pityogenes chalcographus, are prone to interconversion at the spiro center (C5). During diastereo- and enantioselective dynamic gas chromatography (DGC), epimerization of 1 gives rise to two independent interconversion peak profiles, each featuring a plateau between the peaks of the interconverting epimers. To determine the rate constants of epimerization by dynamic gas chromatography (DGC), equations to simulate the complex elution profiles were derived, using the theoretical plate model and the stochastic model of the chromatographic process. The Eyring activation parameters of the experimental interconversion profiles, between 70 and 120 C in the presence of the chiral stationary phase (CSP) Chirasil-beta-Dex, were then determined by computer-aided simulation with the aid of the new program Chrom-Win: (2R,5R)-1: deltaG(++) (298.15 K) = 108.0 +/-0.5 kJ mol(-1), deltaH(++) = 47.1+/-0.2 kJ mol(-1), deltaS(++) = -204+/-6 JK(-1) mol(-1): (2R,5S)-1: deltaG(++) (298.15 K) = 108.5+/-0.5 kJ mol(-1), deltaH(++) = 45.8+/-0.2 kJ mol(-1), deltaS(++) = -210 +/-6 J K mol(-1); (2S,5S)-1: deltaG(++) (298.15 K)= 108.1+/-0.5 kJ mol(-1), deltaH(++) = 49.3+/-0.3 kJ mol(-1), deltaS(++) = -197+/-8 J K(-1) mol(-1); (2S,5R)-1: deltaG(++) (298.15 K)=108.6+/-0.5 kJ mol(-1), deltaH(++) = 48.0+/-0.3 kJ mol(-1), deltaS(++) = -203+/-8 J K(-1) mol(-1). The thermodynamic Gibbs free energy of the E/Z equilibrium of the epimers was determined by the stopped-flow multidimensional gas chromatographic technique: deltaG(E/Z) (298.15 K)= -0.5 kJ mol(-1), deltaH(E/Z) = 1.4 kJ mol(-1) and deltaS(E/Z) = 6.3 J K(-1) mol(-1). An interconversion pathway proceeding through ring-opening and formation of a zwitterion and an enol ether/alcohol intermediate of 1 is proposed.
Collapse
Affiliation(s)
- O Trapp
- Institut für Organische Chemie, Universität Tübingen, Germany
| | | |
Collapse
|
23
|
Trapp O, Schurig V. Approximation function for the direct calculation of rate constants and Gibbs activation energies of enantiomerization of racemic mixtures from chromatographic parameters in dynamic chromatography. J Chromatogr A 2001; 911:167-75. [PMID: 11293578 DOI: 10.1016/s0021-9673(00)01259-0] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
An approximation function for enantioselective dynamic chromatography of racemic mixtures of interconverting enantiomers has been derived that allows the direct calculation of enantiomerization rate constants (k1 and k(-1)) and Gibbs activation energies of enantiomerization, deltaG++ , from chromatographic parameters, i.e., retention times of the enantiomers A and B ((t(A)R and t(B)R), peak widths at half height (WA and wB) and the relative plateau height (hplateau), without computer simulation. The reaction rate constants of enantiomerization, k(-1), obtained with this approximation function, have been validated by comparison with a simulated dataset of 15,625 chromatograms. The mean, standard deviation and confidence interval show a high correlation between the approximated and simulated rate constants. The average deviation from the Gibbs activation enthalpy of enantiomerization, deltaG++, has been estimated to be as small as about +/- 0.11 RT.
Collapse
Affiliation(s)
- O Trapp
- Institute of Organic Chemistry, University of Tübingen, Germany.
| | | |
Collapse
|
24
|
|
25
|
Kennedy RT, German I, Thompson JE, Witowski SR. Fast analytical-scale separations by capillary electrophoresis and liquid chromatography. Chem Rev 1999; 99:3081-132. [PMID: 11749511 DOI: 10.1021/cr980134j] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- R T Kennedy
- Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200
| | | | | | | |
Collapse
|
26
|
Abstract
This article gives a review of the recent developments in capillary electrophoresis (CE) of peptides. New approaches to the theoretical description of electromigration behavior of peptides are described, and methodological aspects of CE separations of peptides such as selection of separation conditions, sample treatment, suppression of peptide adsorption to the capillary wall and specificities of CE separation modes are discussed. Progress in application of high performance detection schemes, namely laser-induced fluorescence and mass spectrometry, in peptide separations by CE is presented. Applications of different CE techniques, zone electrophoresis, isotachophoresis, isoelectric focusing, affinity electrophoresis, electrokinetic chromatography and electrochromatography to peptide analysis, preparation and physicochemical characterization are demonstrated.
Collapse
Affiliation(s)
- V Kasicka
- Institute for Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Prague.
| |
Collapse
|