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Štěpánová S, Kašička V. Determination of physicochemical parameters of (bio)molecules and (bio)particles by capillary electromigration methods. J Sep Sci 2024; 47:e2400174. [PMID: 38867483 DOI: 10.1002/jssc.202400174] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2024] [Revised: 05/03/2024] [Accepted: 05/10/2024] [Indexed: 06/14/2024]
Abstract
The review provides an overview of recent developments and applications of capillary electromigration (CE) methods for the determination of important physicochemical parameters of various (bio)molecules and (bio)particles. These parameters include actual and limiting (absolute) ionic mobilities, effective electrophoretic mobilities, effective charges, isoelectric points, electrokinetic potentials, hydrodynamic radii, diffusion coefficients, relative molecular masses, acidity (ionization) constants, binding constants and stoichiometry of (bio)molecular complexes, changes of Gibbs free energy, enthalpy and entropy and rate constants of chemical reactions and interactions, retention factors and partition and distribution coefficients. For the determination of these parameters, the following CE methods are employed: zone electrophoresis in a free solution or in sieving media, isotachophoresis, isoelectric focusing, affinity electrophoresis, electrokinetic chromatography, and electrochromatography. In the individual sections, the procedures for the determination of the above parameters by the particular CE methods are described.
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Affiliation(s)
- Sille Štěpánová
- Electromigration methods, Institute of Organic Chemistry and Biochemistry, The Czech Academy of Sciences, Prague, Czech Republic
| | - Václav Kašička
- Electromigration methods, Institute of Organic Chemistry and Biochemistry, The Czech Academy of Sciences, Prague, Czech Republic
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2
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Zhang N, Sood D, Guo SC, Chen N, Antoszewski A, Marianchuk T, Chavan A, Dey S, Xiao Y, Hong L, Peng X, Baxa M, Partch C, Wang LP, Sosnick TR, Dinner AR, LiWang A. Temperature-Dependent Fold-Switching Mechanism of the Circadian Clock Protein KaiB. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.05.21.594594. [PMID: 38826295 PMCID: PMC11142059 DOI: 10.1101/2024.05.21.594594] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2024]
Abstract
The oscillator of the cyanobacterial circadian clock relies on the ability of the KaiB protein to switch reversibly between a stable ground-state fold (gsKaiB) and an unstable fold-switched fold (fsKaiB). Rare fold-switching events by KaiB provide a critical delay in the negative feedback loop of this post-translational oscillator. In this study, we experimentally and computationally investigate the temperature dependence of fold switching and its mechanism. We demonstrate that the stability of gsKaiB increases with temperature compared to fsKaiB and that the Q10 value for the gsKaiB → fsKaiB transition is nearly three times smaller than that for the reverse transition. Simulations and native-state hydrogen-deuterium exchange NMR experiments suggest that fold switching can involve both subglobally and near-globally unfolded intermediates. The simulations predict that the transition state for fold switching coincides with isomerization of conserved prolines in the most rapidly exchanging region, and we confirm experimentally that proline isomerization is a rate-limiting step for fold switching. We explore the implications of our results for temperature compensation, a hallmark of circadian clocks, through a kinetic model.
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3
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Albreht A, Hussain H, Jiménez B, Yuen AHY, Whiley L, Witt M, Lewis MR, Chekmeneva E. Structure Elucidation and Mitigation of Endogenous Interferences in LC-MS-Based Metabolic Profiling of Urine. Anal Chem 2022; 94:1760-1768. [PMID: 35026111 DOI: 10.1021/acs.analchem.1c04378] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Liquid chromatography-mass spectrometry (LC-MS) is the main workhorse of metabolomics owing to its high degree of analytical sensitivity and specificity when measuring diverse chemistry in complex biological samples. LC-MS-based metabolic profiling of human urine, a biofluid of primary interest for clinical and biobank studies, is not widely considered to be compromised by the presence of endogenous interferences and is often accomplished using a simple "dilute-and-shoot" approach. Yet, it is our experience that broad obscuring signals are routinely observed in LC-MS metabolic profiles and represent interferences that lack consideration in the relevant metabolomics literature. In this work, we chromatographically isolated the interfering metabolites from human urine and unambiguously identified them via de novo structure elucidation as two separate proline-containing dipeptides: N,N,N-trimethyl-l-alanine-l-proline betaine (l,l-TMAP) and N,N-dimethyl-l-proline-l-proline betaine (l,l-DMPP), the latter reported here for the first time. Offline LC-MS/MS, magnetic resonance mass spectrometry (MRMS), and nuclear magnetic resonance (NMR) spectroscopy were essential components of this workflow for the full chemical and spectroscopic characterization of these metabolites and for establishing the coexistence of cis and trans isomers of both dipeptides in solution. Analysis of these definitive structures highlighted intramolecular ionic interactions as responsible for slow interconversion between these isomeric forms resulting in their unusually broad elution profiles. Proposed mitigation strategies, aimed at increasing the quality of LC-MS-based urine metabolomics data, include modification of column temperature and mobile-phase pH to reduce the chromatographic footprint of these dipeptides, thereby reducing their interfering effect on the underlying metabolic profiles. Alternatively, sample dilution and internal standardization methods may be employed to reduce or account for the observed effects of ionization suppression on the metabolic profile.
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Affiliation(s)
- Alen Albreht
- National Phenome Centre, Department of Metabolism, Digestion and Reproduction, Imperial College London, London W12 0NN, United Kingdom.,Analytical, Environmental & Forensic Sciences, Faculty of Life Sciences & Medicine, King's College London, Franklin-Wilkins Building, London SE1 9NH, United Kingdom.,Laboratory for Food Chemistry, Department of Analytical Chemistry, National Institute of Chemistry, Hajdrihova 19, 1000 Ljubljana, Slovenia
| | - Humma Hussain
- National Phenome Centre, Department of Metabolism, Digestion and Reproduction, Imperial College London, London W12 0NN, United Kingdom.,Division of Anaesthetics, Pain Medicine and Intensive Care, Department of Surgery and Cancer, Faculty of Medicine, Imperial College London, London SW7 2AZ, United Kingdom
| | - Beatriz Jiménez
- National Phenome Centre, Department of Metabolism, Digestion and Reproduction, Imperial College London, London W12 0NN, United Kingdom.,Section of Bioanalytical Chemistry, Department of Metabolism, Digestion and Reproduction, Imperial College London, London SW7 2AZ, United Kingdom
| | - Ada H Y Yuen
- National Phenome Centre, Department of Metabolism, Digestion and Reproduction, Imperial College London, London W12 0NN, United Kingdom.,Section of Bioanalytical Chemistry, Department of Metabolism, Digestion and Reproduction, Imperial College London, London SW7 2AZ, United Kingdom
| | - Luke Whiley
- National Phenome Centre, Department of Metabolism, Digestion and Reproduction, Imperial College London, London W12 0NN, United Kingdom
| | - Matthias Witt
- MRMS Solutions, Bruker Daltonics GmbH & Co. KG, MRMS Solutions, 28359 Bremen, Germany
| | - Matthew R Lewis
- National Phenome Centre, Department of Metabolism, Digestion and Reproduction, Imperial College London, London W12 0NN, United Kingdom.,Section of Bioanalytical Chemistry, Department of Metabolism, Digestion and Reproduction, Imperial College London, London SW7 2AZ, United Kingdom
| | - Elena Chekmeneva
- National Phenome Centre, Department of Metabolism, Digestion and Reproduction, Imperial College London, London W12 0NN, United Kingdom.,Section of Bioanalytical Chemistry, Department of Metabolism, Digestion and Reproduction, Imperial College London, London SW7 2AZ, United Kingdom
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4
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Steflova J, Storch G, Wiesner S, Stockinger S, Berg R, Trapp O. Investigation of Strain-Promoted Azide–Alkyne Cycloadditions in Aqueous Solutions by Capillary Electrophoresis. J Org Chem 2018; 83:604-613. [DOI: 10.1021/acs.joc.7b02092] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Affiliation(s)
- Jana Steflova
- Department
Chemie, Ludwig-Maximilians-Universität München, Butenandtstrasse
5−13, 81377 München, Germany
- Department
of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Hlavova 8, 128 40 Prague 2, Czech Republic
| | - Golo Storch
- Department
Chemie, Ludwig-Maximilians-Universität München, Butenandtstrasse
5−13, 81377 München, Germany
| | - Sarah Wiesner
- Department
Chemie, Ludwig-Maximilians-Universität München, Butenandtstrasse
5−13, 81377 München, Germany
| | - Skrollan Stockinger
- Department
Chemie, Ludwig-Maximilians-Universität München, Butenandtstrasse
5−13, 81377 München, Germany
| | - Regina Berg
- Department
Chemie, Ludwig-Maximilians-Universität München, Butenandtstrasse
5−13, 81377 München, Germany
| | - Oliver Trapp
- Department
Chemie, Ludwig-Maximilians-Universität München, Butenandtstrasse
5−13, 81377 München, Germany
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5
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Schurig V. The Reciprocal Principle of Selectand-Selector-Systems in Supramolecular Chromatography †. Molecules 2016; 21:E1535. [PMID: 27854299 PMCID: PMC6274307 DOI: 10.3390/molecules21111535] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2016] [Revised: 11/02/2016] [Accepted: 11/07/2016] [Indexed: 11/20/2022] Open
Abstract
In selective chromatography and electromigration methods, supramolecular recognition of selectands and selectors is due to the fast and reversible formation of association complexes governed by thermodynamics. Whereas the selectand molecules to be separated are always present in the mobile phase, the selector employed for the separation of the selectands is either part of the stationary phase or is added to the mobile phase. By the reciprocal principle, the roles of selector and selectand can be reversed. In this contribution in honor of Professor Stig Allenmark, the evolution of the reciprocal principle in chromatography is reviewed and its advantages and limitations are outlined. Various reciprocal scenarios, including library approaches, are discussed in efforts to optimize selectivity in separation science.
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Affiliation(s)
- Volker Schurig
- Institute of Organic Chemistry, University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany.
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6
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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.
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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
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7
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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
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8
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Native state dynamics affects the folding transition of porcine pancreatic phospholipase A2. Biophys Chem 2015; 206:12-21. [PMID: 26117657 DOI: 10.1016/j.bpc.2015.06.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2015] [Revised: 06/11/2015] [Accepted: 06/14/2015] [Indexed: 11/23/2022]
Abstract
Porcine pancreatic phospholipase A2, a small and disulfide rich protein, is extremely resistant against chemically or thermally induced unfolding. Despite this marked resistance, the protein displays broad unfolding transitions resulting in comparatively low apparent thermodynamic stability. Broad unfolding transitions may result from undetected folding intermediates, residual structures in the unfolded state or an inhomogeneity of the native state. Using circular dichroism, fluorescence, and NMR spectroscopy, we ruled out the existence of stably populated folding intermediates, whereas UV absorbance measurements hinted at stable residual structures in the unfolded state. These residual structures proved, however, to have no impact on the folding parameters. Studies by limited proteolysis, CD, and NMR spectroscopy under non-denaturing conditions suggested pronounced dynamics of the protein in the native state, which as long as unrestrained by acidic pH or bound Ca(2+) ions exert considerable influence on the unfolding transition.
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Abstract
![]()
The Crk adaptor proteins play a central
role as a molecular timer
for the formation of protein complexes including various growth and
differentiation factors. The loss of regulation of Crk results in
many kinds of cancers. A self-regulatory mechanism for Crk was recently
proposed, which involves domain–domain rearrangement. It is
initiated by a cis–trans isomerization of a specific proline
residue (Pro238 in chicken Crk II) and can be accelerated by Cyclophilin
A. To understand how the proline switch controls the autoinhibition
at the molecular level, we performed large-scale molecular dynamics
and metadynamics simulations in the context of short peptides and
multidomain constructs of chicken Crk II. We found that the equilibrium
and kinetic properties of the macrostates are regulated not only by
the local environments of specified prolines but also by the global
organization of multiple domains. We observe the two macrostates (cis
closed/autoinhibited and trans open/uninhibited) consistent with NMR
experiments and predict barriers. We also propose an intermediate
state, the trans closed state, which interestingly was reported to
be a prevalent state in human Crk II. The existence of this macrostate
suggests that the rate of switching off the autoinhibition by Cyp
A may be limited by the relaxation rate of this intermediate state.
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Affiliation(s)
- Junchao Xia
- Department of Chemistry and Chemical Biology, Rutgers, the State University of New Jersey , 610 Taylor Road, Piscataway, New Jersey 08854, United States
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10
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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]
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11
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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]
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12
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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.
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Affiliation(s)
- Serena Orlandini
- Department of Pharmaceutical Sciences, University of Florence, Florence, Italy.
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13
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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]
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14
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Doshi U, Hamelberg D. Reoptimization of the AMBER Force Field Parameters for Peptide Bond (Omega) Torsions Using Accelerated Molecular Dynamics. J Phys Chem B 2009; 113:16590-5. [DOI: 10.1021/jp907388m] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Urmi Doshi
- Department of Chemistry and The Center for Biotechnology and Drug Design, Georgia State University, Atlanta, Georgia 30302-4098
| | - Donald Hamelberg
- Department of Chemistry and The Center for Biotechnology and Drug Design, Georgia State University, Atlanta, Georgia 30302-4098
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15
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Gherghe CM, Mortimer SA, Krahn JM, Thompson NL, Weeks KM. Slow conformational dynamics at C2'-endo nucleotides in RNA. J Am Chem Soc 2008; 130:8884-5. [PMID: 18558680 PMCID: PMC4501255 DOI: 10.1021/ja802691e] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
RNA molecules undergo local conformational dynamics on timescales spanning picoseconds to minutes. Slower local motions have the greater potential to govern RNA folding, ligand recognition, and ribonucleoprotein assembly reactions but are difficult to detect in large RNAs with complex structures. RNA SHAPE chemistry employs acylation of the ribose 2'-hydroxyl position to measure local nucleotide flexibility in RNA and is well-characterized by a mechanism in which each nucleotide samples unreactive (closed) and reactive (open) states. We monitor RNA conformational dynamics over distinct time domains by varying the electrophilicity of the acylating reagent. Select C2'-endo nucleotides are nonreactive toward fast reagents but reactive toward slower SHAPE reagents in both model RNAs and in a large RNA with a tertiary fold. We conclude, first, that the C2'-endo conformation by itself does not govern SHAPE reactivity. However, some C2'-endo nucleotides undergo extraordinarily slow conformational changes, on the order of 10(-4) s(-1). Due to their distinctive local dynamics, C2'-endo nucleotides have the potential to function as rate-determining molecular switches and are likely to play central, currently unexplored, roles in RNA folding and function.
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Affiliation(s)
- Costin M. Gherghe
- Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599-3290
| | - Stefanie A. Mortimer
- Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599-3290
| | - Joseph M. Krahn
- Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599-3290
| | - Nancy L. Thompson
- Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599-3290
| | - Kevin M. Weeks
- Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599-3290
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17
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Lange J, Below E, Thede R. Separate Determination of Mobile‐Phase Rate Constants for Reversible Reactions. J LIQ CHROMATOGR R T 2007. [DOI: 10.1081/jlc-120028259] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Affiliation(s)
- Jana Lange
- a Institute of Chemistry and Biochemistry , University of Greifswald , Soldmannstrasse 23, D‐17489 , Greifswald , Germany
| | - Elke Below
- b Institute of Forensic Medicine , University of Greifswald , Greifswald , Germany
| | - Richard Thede
- a Institute of Chemistry and Biochemistry , University of Greifswald , Soldmannstrasse 23, D‐17489 , Greifswald , Germany
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18
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Newman CID, McGuffin VL. Capillary electrophoresis for thermodynamic and kinetic studies of peptidyl-proline isomerization by the theoretical plate height model. Electrophoresis 2006; 27:542-52. [PMID: 16456889 DOI: 10.1002/elps.200500645] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The theoretical plate height model, extended to include reactive CE, is used to calculate equilibrium constants and rate constants for the reversible, first-order isomerization of proline dipeptides. This model is consistent with chromatographic theory and enables calculation of equilibrium constants from velocity and calculation of rate constants from plate height. Thermodynamic and kinetic parameters for isomerization of Ala-Pro and Phe-Pro are calculated by using the plate height model, and are shown to be in good agreement with literature values. Additionally, the efficacy of the plate height model is compared to ChromWin, an existing simulation method for calculating rate constants from zone profiles. It is shown that ChromWin and the plate height model are complementary methods. ChromWin is best used for calculating rate constants for reactions that are far from steady state, where the zone profiles exhibit plateau formation. On the other hand, the plate height model is best used for calculating rate constants for reactions that are at or near steady state, where the zone profiles exhibit a single zone containing both reacting species.
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Affiliation(s)
- Carl I D Newman
- Department of Chemistry, Michigan State University, East Lansing, MI 48824-1322, USA
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19
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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.
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Affiliation(s)
- Carl I D Newman
- Department of Chemistry, Michigan State University, East Lansing, MI 48824-1322, USA
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20
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Newman CID, McGuffin VL. Stochastic simulation of reactive separations in capillary electrophoresis. Electrophoresis 2005; 26:537-47. [PMID: 15690455 DOI: 10.1002/elps.200410266] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
A stochastic (Monte Carlo) simulation is used to investigate thermodynamic and kinetic contributions from the reversible A <--> B reaction in capillary electrophoresis (CE). The effects of equilibrium constant, rate constant, and electrophoretic mobility on the molecular zone profiles and the corresponding statistical moments are evaluated. As the reaction approaches steady state, the velocity of the zone is governed by the equilibrium constant and the electrophoretic mobilities of the reacting molecules. When the equilibrium constant is less than unity, the mean zone velocity is more similar to that of the reactant A. Conversely, when the equilibrium constant is greater than unity, the velocity is more similar to that of the product B. The extent of zone-broadening and asymmetry at steady state is dependent upon the equilibrium constant, the characteristic reaction lifetime, and the electrophoretic mobility difference between reacting molecules. If all other parameters are held constant, the plate height is greatest and skew is least when the equilibrium constant is unity. The plate height increases linearly with the characteristic reaction lifetime and electrophoretic mobility difference, whereas the skew is independent of these parameters. These conclusions have important implications for the elucidation of thermodynamic and kinetic information from experimental data.
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Affiliation(s)
- Carl I D Newman
- Department of Chemistry, Michigan State University, East Lansing, MI 48824-1322, USA
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21
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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*).
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Affiliation(s)
- Oliver Trapp
- Stanford University, Department of Chemistry, Roth Way, Stanford, CA 94305, USA.
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Dugave C, Demange L. Cis-trans isomerization of organic molecules and biomolecules: implications and applications. Chem Rev 2003; 103:2475-532. [PMID: 12848578 DOI: 10.1021/cr0104375] [Citation(s) in RCA: 753] [Impact Index Per Article: 35.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Affiliation(s)
- Christophe Dugave
- CEA/Saclay, Département d'Ingénierie et d'Etudes des Protéines (DIEP), Bâtiment 152, 91191 Gif-sur-Yvette, France.
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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.
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Affiliation(s)
- J Krupcik
- Department of Analytical Chemistry, Slovak University of Technology, Radlinského 9, Bratislava 81237, Slovakia.
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Trapp O, Schurig V. Novel direct access to enantiomerization barriers from peak profiles in enantioselective dynamic chromatography: enantiomerization of dialkyl-1,3-allenedicarboxylates. Chirality 2002; 14:465-70. [PMID: 12112339 DOI: 10.1002/chir.10089] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The axially chiral allenes dimethyl-1,3-allenedicarboxylate 1 and diethyl-1,3-allenedicarboxylate 2 show characteristic plateau formation during enantioselective GC separation on the chiral stationary liquid phase Chirasil-beta-Dex. The elution profiles, obtained from temperature-dependent dynamic GC (DGC) experiments (1: 100-140 degrees C; 2: 110-150 degrees C) were evaluated with the recently derived approximation function (AF) k1(approx) = f(t(R)(A),t(R)(B),w(h)(A),h(plateau), N) to yield the enantiomerization rate constant directly k(1). These values were compared with those obtained by computer-aided simulation with ChromWin. The Eyring activation parameters of the experimental interconversion profiles were determined to be: DeltaG(#)(298.15 K) = 103.6 +/- 0.9 kJ mol(-1), DeltaH(#) = 44.7 +/- 0.4 kJ mol(-1), DeltaS(#) = -198 +/- 7 J K(1) mol(-1) for dimethyl-1,3-allenedicarboxylate 1, and DeltaG(#)(298.15 K) = 103.5 +/- 1.1 kJ mol(-1), DeltaH(#) = 44.7 +/- 0.5 kJ mol(-1), DeltaS(#) = -197 +/- 9 J K(-1) mol(-1) for diethyl-1,3-allenedicarboxylate 2. The approximation function (AF) presented here allows the fast determination of rate constants k(1) and activation barriers of enantiomerization DeltaG(#) from chromatographic parameters without extensive computer simulation.
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Affiliation(s)
- Oliver Trapp
- University of Tübingen, Institute of Organic Chemistry, Tübingen, Germany
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