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Gogolishvili OS, Reshetova EN. Chromatographic enantioseparation and adsorption thermodynamics of hydroxy acids and their derivatives on antibiotic-based chiral stationary phases as affected by eluent pH. Chromatographia 2020. [DOI: 10.1007/s10337-020-03978-w] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Asnin LD, Kopchenova MV, Vozisov SE, Klochkova MA, Klimova YA. Enantioselective retention mechanisms of dipeptides on antibiotic-based chiral stationary phases. II. Effect of the methanol content in the mobile phase. J Chromatogr A 2020; 1626:461371. [PMID: 32797850 DOI: 10.1016/j.chroma.2020.461371] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2020] [Revised: 06/22/2020] [Accepted: 06/24/2020] [Indexed: 11/28/2022]
Abstract
Effect of mobile phase (water-methanol) composition on the enantioseparation of dipeptides on the chiral stationary phase Chirobiotic R was investigated using Ala-Ala, Leu-Leu, Gly-Leu, and Leu-Gly as case studies. The lipophilicity of dipeptides was found to be an essential factor in the dependence of their retention on the methanol percentage, the retention factor of lipophobic dipeptides increasing monotonously and that of lipophilic dipeptides changing according to an asymmetric U-shaped trajectory as methanol concentration increases. The behavior of enantioselectivity as a function of the methanol content also depends on the lipophilicity of dipeptide. For lipophilic Leu-Leu, the dependence has a dome-like shape, and for more lipophobic dipeptides, Ala-Ala and Gly-Leu, it is an increasing function of the methanol concentration. The importance of solvation equilibria in the bulk liquid and on the surface of the stationary phase for the total retention is discussed from the thermodynamic point of view. Special consideration is given to the adsorption of the water-methanol mixture on the surface of the Chirobiotic R stationary phase.
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Affiliation(s)
- Leonid D Asnin
- Perm National Research Polytechnic University, 29 Komsomolsky Al., Perm 614990, Russia.
| | | | - Stepan E Vozisov
- Perm National Research Polytechnic University, 29 Komsomolsky Al., Perm 614990, Russia
| | - Mariya A Klochkova
- Perm National Research Polytechnic University, 29 Komsomolsky Al., Perm 614990, Russia
| | - Yana A Klimova
- Perm National Research Polytechnic University, 29 Komsomolsky Al., Perm 614990, Russia
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Dudowicz J, Douglas JF, Freed KF. Lattice theory for binding of linear polymers to a solid substrate from polymer melts: I. Influence of chain connectivity on molecular binding and adsorption. J Chem Phys 2019; 151:124706. [PMID: 31575160 DOI: 10.1063/1.5115400] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Most theories of the binding of molecules to surfaces or for the association between molecules treat the binding species as structureless entities and neglect their rigidity and the changes in their stiffness induced by the binding process. The binding species are also taken to be "ideal," meaning that the existence of van der Waals interactions and changes in these interactions upon molecular binding are also neglected. An understanding of the thermodynamics of these multifunctional molecular binding processes has recently come into focus in the context of the molecular binding of complex molecules, such as dendrimers and DNA grafted nanoparticles, to surfaces where the degree of binding cooperativity and selectivity, as well as the location of the binding transition, are found to be sensitive to the number of binding units constrained to a larger scale polymeric scaffold. We address the fundamental problem of molecular binding by extending classical Langmuir theory to describe the particular example of the reversible binding of semiflexible polymer chains to a solid substrate under melt conditions. The polymer chains are assumed to have a variable number N of binding units (segments) and to exhibit variable bending energies and van der Waals interactions in the bulk and on the surface, in addition to strong directional interactions with the surface. The resulting generalized Langmuir theory is applied to the examination of the influence of the chain connectivity of ideal polymers on the surface coverage Θ, transition binding temperature T1/2 at which Θ = 1/2, and on the derivative |dΘ/dT|T=T1/2 and the constant volume specific heat of binding, Cv bind, measures of the cooperativity and "sharpness" of the binding transition, respectively. Paper II is devoted to the impact of the van der Waals attractive interactions and chain stiffness on the reversible binding of nonideal polymer chains to a solid surface, including the enthalpy-entropy compensation phenomenon observed experimentally in many molecular and particle binding processes.
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Affiliation(s)
- Jacek Dudowicz
- The James Franck Institute and the Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, USA
| | - Jack F Douglas
- Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - Karl F Freed
- The James Franck Institute and the Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, USA
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Dudowicz J, Douglas JF, Freed KF. Lattice theory for binding of linear polymers to a solid substrate from polymer melts. II. Influence of van der Waals interactions and chain semiflexibility on molecular binding and adsorption. J Chem Phys 2019; 151:124709. [PMID: 31575163 DOI: 10.1063/1.5115484] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The polymeric Langmuir theory, developed in Paper I [J. Dudowicz et al., J. Chem. Phys. 151, 124706 (2019)], is employed to investigate the influence of van der Waals interactions and chain rigidity on the thermodynamics of the reversible molecular binding to interfaces in one component polymer fluids (polymer melts). Both van der Waals interactions and chain stiffness are found to influence the temperature variation of the surface coverage Θ, the binding transition itself, and the cooperativity of molecular binding. Re-entrancy of the surface coverage Θ(T) is found to arise when the intermolecular interactions are sufficiently attractive to cause a liquid-vapor like phase separation in the interfacial region, a phenomenon that can occur in the binding of both small molecules and polymer chains to surfaces.
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Affiliation(s)
- Jacek Dudowicz
- The James Franck Institute and the Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, USA
| | - Jack F Douglas
- Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - Karl F Freed
- The James Franck Institute and the Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, USA
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Reshetova EN, Kopchenova MV, Vozisov SE, Vasyanin AN, Asnin LD. Enantioselective retention mechanisms of dipeptides on antibiotic-based chiral stationary phases: Leucyl-leucine, glycyl-leucine, and leucyl-glycine as case studies. J Chromatogr A 2019; 1602:368-377. [PMID: 31213361 DOI: 10.1016/j.chroma.2019.06.025] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2019] [Revised: 06/04/2019] [Accepted: 06/10/2019] [Indexed: 11/20/2022]
Abstract
Chromatographic behaviors of dipeptides consisting of leucine and glycine were studied on two antibiotic-based chiral stationary phases (CSPs) with teicoplanin (Chirobiotic T) or ristocetin A (Chirobiotic R) as chiral selectors under reversed-phase conditions. The effect of mobile phase pH on the retention of stereoisomers of dipeptides was investigated and thermodynamic characteristic of adsorption were measured at different pH values. It was shown that the retention of dipeptides depends on the ionization of their molecules in the mobile phase, as different ionic forms have different affinity towards antibiotic selectors. Enantioselectivity of the bound antibiotics with respect to Leu-Leu stereoisomers was achieved via steric modulation of ion-ion interactions between the solute and the selector, while in the case of Gly-Leu enantiomers non-ionic interactions such as hydrogen bonding might play the key role. In both cases, the dipeptides terminating in D-Leu were retained stronger than their optical antipodes, whereas the enantiomers of Leu-Gly were hardly separated. The regression analysis of the retention data applying the Horvath-Melander-Molnar model revealed that different types of enantioselectivity resides in particular ionic forms of the compounds: cations are responsible for the separation of diastereomeric pairs and the anionic and zwitterionic forms have a universal enantioselectivity on the Chirobiotic T CSP, and the anions and zwitterions are the enantioselective forms for the Chirobiotic R CSP.
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Affiliation(s)
- Elena N Reshetova
- Institute of Technical Chemistry of the Ural Branch of the Russian Academy of Sciences, 3 Academician Korolev Str., Perm 614013, Russia
| | | | - Stepan E Vozisov
- Perm National Research Polytechnic University, 29 Komsomolsky Al., Perm 614990, Russia
| | | | - Leonid D Asnin
- Perm National Research Polytechnic University, 29 Komsomolsky Al., Perm 614990, Russia.
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Gogolishvili OS, Reshetova EN. Effect of the Concentration of an Organic Modifier in a Water–Ethanol Mobile Phase on the Retention and Thermodynamics of Adsorption of Enantiomers of Hydroxy Acids and Their Derivatives on a Chiral Adsorbent with a Grafted Antibiotic Eremomycin. RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A 2019. [DOI: 10.1134/s0036024419060128] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Žuvela P, Skoczylas M, Jay Liu J, Ba Czek T, Kaliszan R, Wong MW, Buszewski B, Héberger K. Column Characterization and Selection Systems in Reversed-Phase High-Performance Liquid Chromatography. Chem Rev 2019; 119:3674-3729. [PMID: 30604951 DOI: 10.1021/acs.chemrev.8b00246] [Citation(s) in RCA: 143] [Impact Index Per Article: 28.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Reversed-phase high-performance liquid chromatography (RP-HPLC) is the most popular chromatographic mode, accounting for more than 90% of all separations. HPLC itself owes its immense popularity to it being relatively simple and inexpensive, with the equipment being reliable and easy to operate. Due to extensive automation, it can be run virtually unattended with multiple samples at various separation conditions, even by relatively low-skilled personnel. Currently, there are >600 RP-HPLC columns available to end users for purchase, some of which exhibit very large differences in selectivity and production quality. Often, two similar RP-HPLC columns are not equally suitable for the requisite separation, and to date, there is no universal RP-HPLC column covering a variety of analytes. This forces analytical laboratories to keep a multitude of diverse columns. Therefore, column selection is a crucial segment of RP-HPLC method development, especially since sample complexity is constantly increasing. Rationally choosing an appropriate column is complicated. In addition to the differences in the primary intermolecular interactions with analytes of the dispersive (London) type, individual columns can also exhibit a unique character owing to specific polar, hydrogen bond, and electron pair donor-acceptor interactions. They can also vary depending on the type of packing, amount and type of residual silanols, "end-capping", bonding density of ligands, and pore size, among others. Consequently, the chromatographic performance of RP-HPLC systems is often considerably altered depending on the selected column. Although a wide spectrum of knowledge is available on this important subject, there is still a lack of a comprehensive review for an objective comparison and/or selection of chromatographic columns. We aim for this review to be a comprehensive, authoritative, critical, and easily readable monograph of the most relevant publications regarding column selection and characterization in RP-HPLC covering the past four decades. Future perspectives, which involve the integration of state-of-the-art molecular simulations (molecular dynamics or Monte Carlo) with minimal experiments, aimed at nearly "experiment-free" column selection methodology, are proposed.
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Affiliation(s)
- Petar Žuvela
- Department of Chemistry , National University of Singapore , Singapore 117543 , Singapore
| | - Magdalena Skoczylas
- Department of Environmental Chemistry and Bioanalytics, Center for Modern Interdisciplinary Technologies , Nicolaus Copernicus University , Wileńska 4 , 87-100 Toruń , Poland
| | - J Jay Liu
- Department of Chemical Engineering , Pukyong National University , 365 Sinseon-ro , Nam-gu, 48-513 Busan , Korea
| | | | | | - Ming Wah Wong
- Department of Chemistry , National University of Singapore , Singapore 117543 , Singapore
| | - Bogusław Buszewski
- Department of Environmental Chemistry and Bioanalytics, Center for Modern Interdisciplinary Technologies , Nicolaus Copernicus University , Wileńska 4 , 87-100 Toruń , Poland
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Dudowicz J, Douglas JF, Freed KF. Lattice theory of competitive binding: Influence of van der Waals interactions on molecular binding and adsorption to a solid substrate from binary liquid mixtures. J Chem Phys 2018; 149:044704. [PMID: 30068175 DOI: 10.1063/1.5040105] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The reversible binding of molecules to surfaces is one of the most fundamental processes in condensed fluids, with obvious applications in the molecular separation of materials, chromatographic characterization, and material processing. Motivated in particular by the ubiquitous occurrence of binding processes in molecular biology and self-assembly, we have developed a lattice type theory of competitive molecular binding to solid substrates from binary mixtures of two small molecule liquids that interact between themselves by van der Waals forces in addition to exhibiting binding interactions with the solid surface. The derived theory, in contrast to previously existing theoretical frameworks, enables us to investigate the influence of van der Waals interactions on interfacial binding and selective molecular adsorption. For reference, the classic Langmuir theory of adsorption is recovered when all van der Waals interaction energies between the molecules in the bulk liquid phase and those on the surface are formally set to zero. Illustrative calculations are performed for the binding of molecules to a solid surface from pure liquids and from their binary mixtures. The properties analyzed include the surface coverage θ, the binding transition temperature Tbind, the individual surface coverages, θA and θC, and the relative surface coverages, σAC≡θA/θC or σCA≡θC/θA. The latter two quantities coincide with the degrees of adsorption directly determined from experimental adsorption measurements. The Langmuir theory is shown to apply formally under a wide range of conditions where the original enthalpies (Δh or ΔhA and ΔhC) and entropies (Δs or ΔsA and ΔsC) of the binding reactions are simply replaced by their respective "effective" counterparts (Δheff or ΔhAeff and ΔhCeff and Δseff or ΔsAeff and ΔsCeff), whose values depend on the strength of der Waals interactions and of the "bare" free energy parameters (Δh or ΔhA and ΔhC, and Δs or ΔsA and ΔsC). Numerous instances of entropy-enthalpy compensation between these effective free energy parameters follow from our calculations, confirming previous reports on this phenomenon obtained from experimental studies of molecular binding processes in solution.
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Affiliation(s)
- Jacek Dudowicz
- Department of Chemistry, The James Franck Institute, The University of Chicago, Chicago, Illinois 60637, USA
| | - Jack F Douglas
- Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - Karl F Freed
- Department of Chemistry, The James Franck Institute, The University of Chicago, Chicago, Illinois 60637, USA
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Asnin LD, Stepanova MV. Van't Hoff analysis in chiral chromatography. J Sep Sci 2018; 41:1319-1337. [DOI: 10.1002/jssc.201701264] [Citation(s) in RCA: 47] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2017] [Revised: 12/27/2017] [Accepted: 12/28/2017] [Indexed: 11/11/2022]
Affiliation(s)
- Leonid D. Asnin
- Department of Chemistry and Biotechnology; Perm National Research Polytechnic University; Perm Russia
| | - Maria V. Stepanova
- Department of Chemistry and Biotechnology; Perm National Research Polytechnic University; Perm Russia
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Reshetova EN. Effect of the ionic strength of a mobile phase on the chromatographic retention and thermodynamic characteristics of the adsorption of enantiomers of α-phenylcarboxylic acids on a chiral adsorbent with grafted antibiotic eremomycin. RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A 2017. [DOI: 10.1134/s0036024417010228] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Dudowicz J, Freed KF, Douglas JF. Relation Between Solvent Quality and Phase Behavior of Ternary Mixtures of Polymers and Two Solvents that Exhibit Cononsolvency. J Phys Chem B 2016; 120:5753-8. [DOI: 10.1021/acs.jpcb.6b03248] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- Jacek Dudowicz
- The
James Franck Institute and the Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, United States
| | - Karl F. Freed
- The
James Franck Institute and the Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, United States
| | - Jack F. Douglas
- Materials
Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
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Reshetova E. Chromatographic retention and thermodynamics of the adsorption of α-phenylcarboxylic acid enantiomers on a chiral stationary phase with a grafted antibiotic eremomycin: Effect of eluent pH. J LIQ CHROMATOGR R T 2016. [DOI: 10.1080/10826076.2015.1137004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Affiliation(s)
- Elena Reshetova
- Institute of Technical Chemistry, The Ural Branch of the Russian Academy of Sciences, Perm, Russia
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Sykora D, Vozka J, Tesarova E. Chromatographic methods enabling the characterization of stationary phases and retention prediction in high-performance liquid chromatography and supercritical fluid chromatography. J Sep Sci 2015; 39:115-31. [DOI: 10.1002/jssc.201501023] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2015] [Revised: 10/08/2015] [Accepted: 10/08/2015] [Indexed: 11/11/2022]
Affiliation(s)
- David Sykora
- Department of Analytical Chemistry; University of Chemistry and Technology; Prague Czech Republic
| | - Jiri Vozka
- Department of Analytical Chemistry; University of Chemistry and Technology; Prague Czech Republic
- Department of Physical and Macromolecular Chemistry, Faculty of Science; Charles University in Prague; Prague Czech Republic
| | - Eva Tesarova
- Department of Physical and Macromolecular Chemistry, Faculty of Science; Charles University in Prague; Prague Czech Republic
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Medium-property relationships and compensation effect in the adsorption of heteroaromatic compounds from aqueous acetonitrile solutions. Russ Chem Bull 2015. [DOI: 10.1007/s11172-014-0787-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Dudowicz J, Freed KF, Douglas JF. Theory of competitive solvation of polymers by two solvents and entropy-enthalpy compensation in the solvation free energy upon dilution with the second solvent. J Chem Phys 2015; 142:214906. [PMID: 26049523 DOI: 10.1063/1.4921373] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Affiliation(s)
- Jacek Dudowicz
- The James Franck Institute and the Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, USA
| | - Karl F. Freed
- The James Franck Institute and the Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, USA
| | - Jack F. Douglas
- Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
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Blinov AS, Reshetova EN. Effect of the concentration of organic modifier in an aqueous-ethanol mobile phase on the chromatographic retention and thermodynamic characteristics of the adsorption of enantiomers of α-phenylcarboxylic acids on silica gel with immobilized eremomycin antibiotic. RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A 2014. [DOI: 10.1134/s0036024414100057] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Saifutdinov BR, Pimerzin AA. Effect of the nature of binary water-organic solvents on the thermodynamic characteristics of adsorption of certain 1,3,4-oxadiazoles and 1,2,4,5-tetrazines on phenyl-bonded silica gel. RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A 2013. [DOI: 10.1134/s0036024413120212] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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Thermodynamic and Extrathermodynamic Studies of Enantioseparation of Imidazolinone Herbicides on Chiralcel OJ Column. ACTA ACUST UNITED AC 2013. [DOI: 10.1155/2013/460787] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
A homologous series of chiral imidazolinone herbicide was previously resolved on Chiralcel OJ column in high performance liquid chromatography. However, the mechanism of the chiral separation remains unclear. In this study, chromatographic behaviors of five chiral imidazolinone herbicides were characterized by thermodynamic and extrathermodynamic methods in order to enhance the understanding of the chiral separation. Thermodynamic parameters of this study were derived from equilibrium constant () that was estimated from the moment analysis of the chromatographic peak. Van't Hoff plots of ( versus ) were linear at a range of 15–50°C, only nonlinear at a range of 5–15 °C with n-hexane (0.1%, trifluoroacetic acid)-2-propanol 60/40 (v/v) mobile phase. The enantiomer retention on the chiral column was entropy-driven at a lower temperature (5°C) and enthalpy-driven at a higher temperature (10 to 50°C). Enantioseparations of four of the five imidazolinone herbicides were enthalpy-driven, only entropy-driven for imazaquin. Enantioseparation mechanisms were different in between 5–10°C and 15–50°C probably due to the conformational change of the OJ phase. Enthalpy-entropy compensation showed similar mechanisms in retention and chiral separation for the five or enantiomers. Several extrathermodynamic relationships were able to be extracted to address additivity of group contribution.
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Dudowicz J, Freed KF, Douglas JF. Solvation of polymers as mutual association. I. General theory. J Chem Phys 2013; 138:164901. [DOI: 10.1063/1.4800074] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
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Lindsey RK, Rafferty JL, Eggimann BL, Siepmann JI, Schure MR. Molecular simulation studies of reversed-phase liquid chromatography. J Chromatogr A 2013; 1287:60-82. [PMID: 23489490 DOI: 10.1016/j.chroma.2013.02.040] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2013] [Revised: 02/10/2013] [Accepted: 02/11/2013] [Indexed: 11/28/2022]
Abstract
Over the past 20 years, molecular simulation methods have been applied to the modeling of reversed-phase liquid chromatography (RPLC). The purpose of these simulations was to provide a molecular-level understanding of: (i) the structure and dynamics of the bonded phase and its interface with the mobile phase, (ii) the interactions of analytes with the bonded phase, and (iii) the retention mechanism for different analytes. However, the investigation of chromatographic systems poses significant challenges for simulations with respect to the accuracy of the molecular mechanics force fields and the efficiency of the sampling algorithms. This review discusses a number of aspects concerning molecular simulation studies of RPLC systems including the historical development of the subject, the background needed to understand the two prevalent techniques, molecular dynamics (MD) and Monte Carlo (MC) methods, and the wealth of insight provided by these simulations. Examples from the literature employing MD approaches and from the authors' laboratory using MC methods are discussed. The former can provide information on chain dynamics and transport properties, whereas the latter techniques are uniquely suited for the investigation of phase and sorption equilibria that underly RPLC retention, and both can be used to elucidate the bonded-chain conformations and solvent distributions.
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Affiliation(s)
- Rebecca K Lindsey
- Department of Chemistry and Chemical Theory Center, University of Minnesota, 207 Pleasant Street SE, Minneapolis, MN 55455-0431, USA
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Saifutdinov BR. On the interrelation between the distribution constant and the retention factor in liquid chromatography. RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A 2013. [DOI: 10.1134/s0036024413030266] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Baeza-Baeza JJ, Dávila Y, Fernández-Navarro JJ, García-Álvarez-Coque MC. Measurement of the elution strength and peak shape enhancement at increasing modifier concentration and temperature in RPLC. Anal Bioanal Chem 2012; 404:2973-84. [PMID: 23007655 DOI: 10.1007/s00216-012-6387-7] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2012] [Revised: 08/22/2012] [Accepted: 08/24/2012] [Indexed: 10/27/2022]
Abstract
Two approaches are proposed to measure the effect of different experimental factors (such as the modifier concentration and temperature) on the elution strength and peak shape in reversed-phase liquid chromatography, which quantify the percentage change in the retention factor and peak width (referred to the weakest conditions) per unit change in the experimental factor. The approaches were applied to the separation of a set of flavonoids with aqueous micellar mobile phases of the surfactant Brij-35 (polyoxyethylene(23)dodecanol), in comparison with acetonitrile-water mixtures, using an Eclipse XDB-C18 column. The particular interaction of each flavonoid with the oxyethylene chains of Brij-35 molecules (adsorbed on the stationary phase or forming micelles) changed the elution window, distribution of chromatographic peaks and partitioning kinetics, depending on the hydroxyl substitution in the aromatic rings of flavonoids. At 25 °C, peak shape with Brij-35 mobile phases was significantly poorer with regard to acetonitrile-water mixtures. At increasing temperature, the efficiency of Brij-35 increased, approaching at 80 °C the values obtained at equilibrium conditions, already reached with acetonitrile at 25 °C.
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Affiliation(s)
- J J Baeza-Baeza
- Departamento de Química Analítica, Universidad de Valencia, c/Dr. Moliner 50, 46100 Burjassot, Spain.
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Forrey C, Douglas JF, Gilson MK. The Fundamental Role of Flexibility on the Strength of Molecular Binding. SOFT MATTER 2012; 8:6385-6392. [PMID: 22707976 PMCID: PMC3374587 DOI: 10.1039/c2sm25160d] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Non-covalent molecular association underlies a diverse set of biologically and technologically relevant phenomena, including the action of drugs on their biomolecular targets and self- and supra-molecular assembly processes. Computer models employed to model binding frequently use interaction potentials with atomistic detail while neglecting the thermal molecular motions of the binding species. However, errors introduced by this simplification and, more broadly, the thermodynamic consequences of molecular flexibility on binding, are little understood. Here, we isolate the fundamental relationship of molecular flexibility to binding thermodynamics via simulations of simplified molecules with a wide range of flexibilities but the same interaction potential. Disregarding molecular motion is found to generate large errors in binding entropy, enthalpy and free energy, even for molecules that are nearly rigid. Indeed, small decreases in rigidity markedly reduce affinity for highly rigid molecules. Remarkably, precisely the opposite occurs for more flexible molecules, for which increasing flexibility leads to stronger binding affinity. We also find that differences in flexibility suffice to generate binding specificity: for example, a planar surface selectively binds rigid over flexible molecules. Intriguingly, varying molecular flexibility while keeping interaction potentials constant leads to near-linear enthalpy-entropy compensation over a wide range of flexibilities, with the unexpected twist that increasing flexibility produces opposite changes in entropy and enthalpy for molecules in the flexible versus the rigid regime. Molecular flexibility is thus a crucial determinant of binding affinity and specificity and variations in flexibility can lead to strong yet non-intuitive consequences.
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Affiliation(s)
- Christopher Forrey
- Center for Devices and Radiological Health, Food and Drug Administration, 10903 New Hampshire Avenue, Silver Spring, MD 20903, USA
| | - Jack F. Douglas
- Polymers Division, National Institute of Standards and Technology, 1 Bureau Drive, Gaithersburg, MD, 20899, USA
| | - Michael K. Gilson
- Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA, 92093-0736, USA
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Causon TJ, Cortes HJ, Shellie RA, Hilder EF. Temperature Pulsing for Controlling Chromatographic Resolution in Capillary Liquid Chromatography. Anal Chem 2012; 84:3362-8. [DOI: 10.1021/ac300161b] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Tim J. Causon
- Australian
Centre for Research
on Separation Science, School of Chemistry, University of Tasmania, Private Bag 75, Hobart, Tasmania, Australia,
7001
| | - Hernan J. Cortes
- Australian
Centre for Research
on Separation Science, School of Chemistry, University of Tasmania, Private Bag 75, Hobart, Tasmania, Australia,
7001
- HJ Cortes Consulting LLC, Midland, Michigan 48642, United States
| | - Robert A. Shellie
- Australian
Centre for Research
on Separation Science, School of Chemistry, University of Tasmania, Private Bag 75, Hobart, Tasmania, Australia,
7001
| | - Emily F. Hilder
- Australian
Centre for Research
on Separation Science, School of Chemistry, University of Tasmania, Private Bag 75, Hobart, Tasmania, Australia,
7001
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26
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Dudowicz J, Freed KF, Douglas JF. Lattice cluster theory of associating polymers. II. Enthalpy and entropy of self-assembly and Flory-Huggins interaction parameter χ for solutions of telechelic molecules. J Chem Phys 2012; 136:064903. [DOI: 10.1063/1.3681256] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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27
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Asnin L, Sharma K, Park SW. Chromatographic retention and thermodynamics of adsorption of dipeptides on a chiral crown ether stationary phase. J Sep Sci 2011; 34:3136-44. [DOI: 10.1002/jssc.201100485] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2011] [Revised: 08/02/2011] [Accepted: 08/21/2011] [Indexed: 11/10/2022]
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28
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Verstraeten M, Pursch M, Eckerle P, Luong J, Desmet G. Thermal Modulation for Multidimensional Liquid Chromatography Separations Using Low-Thermal-Mass Liquid Chromatography (LC). Anal Chem 2011; 83:7053-60. [DOI: 10.1021/ac201207t] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Matthias Verstraeten
- Vrije Universiteit Brussel, Department of Chemical Engineering, Pleinlaan 2, 1050 Elsene, Belgium
| | - Matthias Pursch
- Dow Deutschand Anlagengesellschaft mbH, Analytical Technology Center, 77836 Rheinmunster, Germany
| | - Patric Eckerle
- Dow Deutschand Anlagengesellschaft mbH, Analytical Technology Center, 77836 Rheinmunster, Germany
| | - Jim Luong
- Dow Canada, Analytical Technology Center, Fort Saskatchewan, AB, Canada
| | - Gert Desmet
- Vrije Universiteit Brussel, Department of Chemical Engineering, Pleinlaan 2, 1050 Elsene, Belgium
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29
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Freed KF. Entropy−Enthalpy Compensation in Chemical Reactions and Adsorption: An Exactly Solvable Model. J Phys Chem B 2011; 115:1689-92. [DOI: 10.1021/jp1105696] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Affiliation(s)
- Karl F. Freed
- James Franck Institute and Department of Chemistry, University of Chicago, Chicago, Illinois 60637, United States
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30
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CNS delivery of L-dopa by a new hybrid glutathione-methionine peptidomimetic prodrug. Amino Acids 2010; 42:261-9. [PMID: 21080012 DOI: 10.1007/s00726-010-0804-z] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2010] [Accepted: 10/29/2010] [Indexed: 02/01/2023]
Abstract
Parkinson's disease (PD) is a neurodegenerative disorder associated primarily with loss of dopamine (DA) neurons in the nigrostriatal system. With the aim of increasing the bioavailability of L: -dopa (LD) after oral administration and of overcoming the pro-oxidant effect associated with LD therapy, we designed a peptidomimetic LD prodrug (1) able to release the active agent by enzyme catalyzed hydrolysis. The physicochemical properties, as well as the chemical and enzymatic stabilities of the new compound, were evaluated in order to check both its stability in aqueous medium and its sensitivity towards enzymatic cleavage, providing the parent LD drug, in rat and human plasma. The radical scavenging activities of prodrug 1 was tested by using both the DPPH-HPLC and the DMSO competition methods. The results indicate that the replacement of cysteine GSH portion by methionine confers resistance to oxidative degradation in gastric fluid. Prodrug 1 demonstrated to induce sustained delivery of DA in rat striatal tissue with respect to equimolar LD dosages. These results are of significance for prospective therapeutic application of prodrug 1 in pathological events associated with free radical damage and decreasing DA concentration in the brain.
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31
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Levent A, Şentürk Z. Development of an Ion-Pair HPLC Method for Determination of Acebutolol in Pharmaceuticals. ANAL LETT 2010. [DOI: 10.1080/00032710903502116] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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32
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Douglas JF, Dudowicz J, Freed KF. Crowding induced self-assembly and enthalpy-entropy compensation. PHYSICAL REVIEW LETTERS 2009; 103:135701. [PMID: 19905522 DOI: 10.1103/physrevlett.103.135701] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2009] [Indexed: 05/28/2023]
Abstract
We develop a general virial expansion to describe the influence of molecular additives on the equilibrium self-assembly of proteins or other supermolecularly assembling species M in solution. When specialized to high molar mass polymer additives, the cross-virial coefficient between the polymer and M, which dominates this effect, is found to vanish at a particular temperature T_{Theta} corresponding to an enthalpy-entropy compensation condition. Specifically, the increased stability of the assembled form of M, due to the modification of the entropy of the assembly by repulsive polymer-protein interactions, is progressively compensated by attractive interactions that alter the enthalpy of assembly.
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Affiliation(s)
- Jack F Douglas
- Polymers Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
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33
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Zhang Y, Carr PW. A visual approach to stationary phase selectivity classification based on the Snyder-Dolan Hydrophobic-Subtraction Model. J Chromatogr A 2009; 1216:6685-94. [PMID: 19700166 PMCID: PMC3195507 DOI: 10.1016/j.chroma.2009.06.048] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2009] [Revised: 06/11/2009] [Accepted: 06/16/2009] [Indexed: 11/25/2022]
Abstract
A novel type of stationary phase selectivity classification "triangle" has been developed based on the Snyder-Dolan (S-D) Hydrophobic-Subtraction Model, wherein the apices of a set of four triangles represent the relative contributions of steric hindrance (chi(S)), hydrogen-bonding acidity (chi(A)), hydrogen-bonding basicity (chi(B)), cation-exchange capacity (chi(C)) to selectivity. We found that "effective selectivity" of a stationary phase is mathematically given by the ratio of system dependent interaction coefficients but not their absolute values. Thus by normalizing the S*, A, B and C terms of the S-D model by H, we were able to obtain four parameters which fully define the chromatographic selectivity of the stationary phases. By examining the parameters in groups of three, we can represent all the result in a set of four "selectivity triangles". The distinctive feature of this approach compared to the S-D phase classification scheme is that it allows the visualization of column selectivity by plotting three-dimensional data in a two-dimensional space. Moreover, it very clearly shows that the RPLC columns thus far characterized cover only a small fraction of separation selectivity space leaving a great deal of room for researchers to develop novel RPC materials. Various applications of these "selectivity triangles" will be discussed in this paper.
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Affiliation(s)
- Yu Zhang
- Department of Chemistry, University of Minnesota, Smith and Kolthoff Hall, 207 Pleasant Street SE, Minneapolis, MN 55455
| | - Peter W. Carr
- Department of Chemistry, University of Minnesota, Smith and Kolthoff Hall, 207 Pleasant Street SE, Minneapolis, MN 55455
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34
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Reshetova EN, Asnin LD. The chromatographic behavior and thermodynamic characteristics of adsorption of profen enantiomers on silica gel with grafted eremomycin antibiotic. RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A 2009. [DOI: 10.1134/s0036024409040062] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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35
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Retention models for isocratic and gradient elution in reversed-phase liquid chromatography. J Chromatogr A 2009; 1216:1737-55. [DOI: 10.1016/j.chroma.2008.09.051] [Citation(s) in RCA: 115] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2008] [Revised: 09/11/2008] [Accepted: 09/12/2008] [Indexed: 11/20/2022]
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36
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Characterization of alkanoyl-10-O-minocyclines in micellar dispersions as potential agents for treatment of human neurodegenerative disorders. Eur J Pharm Sci 2008; 34:118-28. [DOI: 10.1016/j.ejps.2008.02.123] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2007] [Revised: 02/11/2008] [Accepted: 02/28/2008] [Indexed: 11/17/2022]
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37
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Zhu R, Zhu L. Thermodynamics of naphthalene sorption to organoclays: Role of surfactant packing density. J Colloid Interface Sci 2008; 322:27-32. [DOI: 10.1016/j.jcis.2008.02.026] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2007] [Revised: 02/16/2008] [Accepted: 02/20/2008] [Indexed: 10/22/2022]
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38
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Rafferty JL, Zhang L, Siepmann JI, Schure MR. Retention Mechanism in Reversed-Phase Liquid Chromatography: A Molecular Perspective. Anal Chem 2007; 79:6551-8. [PMID: 17668929 DOI: 10.1021/ac0705115] [Citation(s) in RCA: 114] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A detailed, molecular-level understanding of the retention mechanism in reversed-phase liquid chromatography (RPLC) has eluded analytical chemists for decades. Through validated, particle-based Monte Carlo simulations of a model RPLC system consisting of dimethyloctadecylsilanes at a coverage of 2.9 micro mol/m2 on an explicit silica substrate with unprotected residual silanols in contact with a water/methanol mobile phase, we show that the molecular-level retention processes for nonpolar and polar analytes, such as alkanes and alcohols, are much more complex than what has been previously deduced from thermodynamic and theoretical arguments. In contrast to some previous assumptions, the simulations indicate that both partitioning and adsorption play a key role in the separation process and that the stationary phase in RPLC behaves substantially different from a bulk hydrocarbon phase. The retention of nonpolar methylene segments is dominated by lipophilic interactions with the retentive phase, while solvophilic interactions are more important for the retention of the polar hydroxyl group.
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Affiliation(s)
- Jake L Rafferty
- Department of Chemistry and of Chemical Engineering, University of Minnesota, Minneapolis, MN 55455-0431, USA
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39
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Kayillo S, Dennis GR, Shalliker RA. Retention of polycyclic aromatic hydrocarbons on propyl-phenyl stationary phases in reversed-phase high performance liquid chromatography. J Chromatogr A 2007; 1148:168-76. [PMID: 17376462 DOI: 10.1016/j.chroma.2007.03.004] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2006] [Revised: 03/02/2007] [Accepted: 03/05/2007] [Indexed: 11/29/2022]
Abstract
A study on the retention of PAHs on three Propyl-phenyl stationary phases was conducted, assessing absolute retention, selectivity, retention correlation and thermodynamic behaviour. The chromatographic retention data revealed that each of the three Propyl-phenyl columns exhibited differences in absolute retention, however, comparison of the compensation temperatures derived from enthalpy-entropy compensation plots showed that the underlying processes responsible for the retention on these columns were the same.
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Affiliation(s)
- Sindy Kayillo
- Nanoscale Organisation and Dynamics Group, University of Western Sydney, NSW 1797, Australia
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40
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Kayillo S, Dennis GR, Shalliker RA. An assessment of the retention behaviour of polycyclic aromatic hydrocarbons on reversed phase stationary phases—Thermodynamic behaviour on C18 and phenyl-type surfaces. J Chromatogr A 2007; 1145:133-40. [PMID: 17306278 DOI: 10.1016/j.chroma.2007.01.131] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2006] [Revised: 01/12/2007] [Accepted: 01/15/2007] [Indexed: 11/26/2022]
Abstract
The thermodynamic retention behaviour of a linear series of polycyclic aromatic hydrocarbons (PAHs) was investigated on C18 and selected phenyl-type reversed-phase stationary phases, namely C18, C18 Aqua, Propyl-phenyl and Synergi polar-RP stationary phases, using methanol mobile phases. The Propyl-phenyl stationary phase, despite having the lowest surface coverage, was found to exhibit significantly larger enthalpic interactions to the other Phenyl-type phase (Synergi polar-RP) even though this had a much higher surface coverage. This indicated that stronger interactions between the PAHs and the stationary phase ligands were occurring on the Propyl-phenyl phase. Evaluation of the elution band profile of the PAHs in the aqueous methanol mobile phase revealed fairly symmetrical bands for the C18, C18 Aqua and Synergi polar-RP, but severe peak tailing on the Propyl-phenyl phase. A change in mobile phase from methanol to acetonitrile improved the peak shape of the PAHs on the Propyl-phenyl phase, leading to the assumption that unfavourable pi-pi interactions were occurring between the electron-rich PAHs and the electron-rich phenyl rings of the Propyl-phenyl phase.
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Affiliation(s)
- Sindy Kayillo
- Nanoscale Organisation and Dynamics Group, University of Western Sydney, NSW 1797, Australia
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41
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Chen Z, Adams MA. RETENTION BEHAVIOR AND SIMULTANEOUS SEPARATION OF CARBOXYLIC AND AROMATIC ACIDS USING ION-EXCLUSION CHROMATOGRAPHY. J LIQ CHROMATOGR R T 2007. [DOI: 10.1081/jlc-100102046] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Affiliation(s)
- ZuLiang Chen
- a Department of Botany , The University of Western Australia , Nedlands , WA , 6907 , U.S.A
| | - Mark A. Adams
- a Department of Botany , The University of Western Australia , Nedlands , WA , 6907 , U.S.A
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42
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Vailaya A. Fundamentals of Reversed Phase Chromatography: Thermodynamic and Exothermodynamic Treatment. J LIQ CHROMATOGR R T 2007. [DOI: 10.1081/jlc-200052969] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Affiliation(s)
- Anant Vailaya
- a Merck Research Laboratories , Rahway, New Jersey, USA
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43
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Kailasam K, Srinivasan G, Müller K. Solvents effects on the conformational order of triacontyl modified silica gels as evaluated by Fourier transform infrared spectroscopy. J Chromatogr A 2006; 1134:81-7. [PMID: 16965784 DOI: 10.1016/j.chroma.2006.08.062] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2006] [Revised: 08/15/2006] [Accepted: 08/21/2006] [Indexed: 11/26/2022]
Abstract
C30 alkyl modified silica gels have attracted much attention because of their enhanced shape selectivity for various types of analytes, which for instance cannot be separated with conventional C8 and C18 stationary phases. Since the retention processes strongly depend on the nature of solvents and composition of the stationary phases, a FTIR study was conducted to evaluate the influence of solvents on the conformational order of the alkyl chains in C30 alkyl modified silica gels. Variable temperature IR measurements are carried out between 273 and 353 K in the presence of polar and nonpolar solvents. Information about the conformational behavior of the tethered alkyl chains is derived from the analysis of the symmetric and antisymmetric CH2 stretching band regions. Polar solvents show both enhanced conformational order and disorder of the alkyl chains - irrespective of temperature - when compared to dry C30 alkyl modified silica gels, while nonpolar solvents in general give rise to enhanced conformational disorder in the alkyl chain region. Moreover, for polar solvents a correlation exists between the stretching band position, reflecting alkyl chain conformational order, and the solvent solvatochromic parameter pi*. Finally, both partition and adsorption models are considered to play an important role for the solvent-alkyl chain interactions which in turn determines the conformational order of the alkyl chains and thus the chromatographic properties of these phases.
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Affiliation(s)
- Kamalakannan Kailasam
- Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany
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44
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Zhang L, Rafferty JL, Siepmann JI, Chen B, Schure MR. Chain conformation and solvent partitioning in reversed-phase liquid chromatography: Monte Carlo simulations for various water/methanol concentrations. J Chromatogr A 2006; 1126:219-31. [PMID: 16820151 DOI: 10.1016/j.chroma.2006.06.003] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2006] [Revised: 05/24/2006] [Accepted: 06/01/2006] [Indexed: 11/25/2022]
Abstract
Many structural models for the stationary phase in reversed-phase liquid chromatography (RPLC) systems have been suggested from thermodynamic and spectroscopic measurements and theoretical considerations. To provide a molecular picture of chain conformation and solvent partitioning in a typical RPLC system, a particle-based Monte Carlo simulation study is undertaken for a dimethyl octadecyl (C(18)) bonded stationary phase on a model siliceous substrate in contact with mobile phases having different methanol/water concentrations. Following upon previous simulations for gas-liquid chromatography and liquid-liquid phase equilibria, the simulations are conducted using the configurational-bias Monte Carlo method in the Gibbs ensemble and the transferable potentials for phase equilibria force field. The simulations are performed for a chain surface density of 2.9 micromol/m(2), which is a typical bonded-phase coverage for mono-functional alkyl silanes. The solvent concentrations used here are pure water, approximately 33 and 67% mole fraction of methanol and pure methanol. The simulations show that the chain conformation depends only weakly on the solvent composition. Most chains are conformationally disordered and tilt away from the substrate normal. The interfacial width increases with increasing methanol content and, for mixtures, the solvent shows an enhancement of the methanol concentration in a 10 Angstrom region outside the Gibbs dividing surface. Residual surface silanol groups are found to provide hydrogen bonding sites that lead to the formation of substrate bound water and methanol clusters, including bridging clusters that penetrate from the solvent/chain interfacial region all the way to the silica surface.
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Affiliation(s)
- Ling Zhang
- Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, MN 55455-0431, USA
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45
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Vitha M, Carr PW. The chemical interpretation and practice of linear solvation energy relationships in chromatography. J Chromatogr A 2006; 1126:143-94. [PMID: 16889784 DOI: 10.1016/j.chroma.2006.06.074] [Citation(s) in RCA: 389] [Impact Index Per Article: 21.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2006] [Revised: 06/09/2006] [Accepted: 06/19/2006] [Indexed: 11/30/2022]
Abstract
This review focuses on the use of linear solvation energy relationships (LSERs) to understand the types and relative strength of the chemical interactions that control retention and selectivity in the various modes of chromatography ranging from gas chromatography to reversed phase and micellar electrokinetic capillary chromatography. The most recent, widely accepted symbolic representation of the LSER model, as proposed by Abraham, is given by the equation: SP=c + eE + sS + aA + bB + vV, in which, SP can be any free energy related property. In chromatography, SP is most often taken as logk' where k' is the retention factor. The letters E, S, A, B, and V denote solute dependent input parameters that come from scales related to a solute's polarizability, dipolarity (with some contribution from polarizability), hydrogen bond donating ability, hydrogen bond accepting ability, and molecular size, respectively. The e-, s-, a-, b-, and v-coefficients and the constant, c, are determined via multiparameter linear least squares regression analysis of a data set comprised of solutes with known E, S, A, B, and V values and which span a reasonably wide range in interaction abilities. Thus, LSERs are designed to probe the type and relative importance of the interactions that govern solute retention. In this review, we include a synopsis of the various solvent and solute scales in common use in chromatography. More importantly, we emphasize the development and physico-chemical basis of - and thus meaning of - the solute parameters. After establishing the meaning of the parameters, we discuss their use in LSERs as applied to understanding the intermolecular interactions governing various gas-liquid and liquid-liquid phase equilibria. The gas-liquid partition process is modeled as the sum of an endoergic cavity formation/solvent reorganization process and exoergic solute-solvent attractive forces, whereas the partitioning of a solute between two solvents is thermodynamically equivalent to the difference in two gas/liquid solution processes. We end with a set of recommendations and advisories for conducting LSER studies, stressing the proper chemical and statistical application of the methodology. We intend that these recommendations serve as a guide for future studies involving the execution, statistical evaluation, and chemical interpretation of LSERs.
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Affiliation(s)
- Mark Vitha
- Drake University, Department of Chemistry, 2507 University Avenue, Des Moines, IA 50311, USA
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46
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Yang B, Gao MJ, Duan GL. Ion-Pair RP-LC of Tegaserod Maleate and its Impurities in Pharmaceutical Formulations and in Dissolution Studies. Chromatographia 2006. [DOI: 10.1365/s10337-006-0778-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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47
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Liu CI, Hsu KY, Ruaan RC. Hydrophobic Contribution of Amino Acids in Peptides Measured by Hydrophobic Interaction Chromatography. J Phys Chem B 2006; 110:9148-54. [PMID: 16671727 DOI: 10.1021/jp055382f] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The adsorption behaviors of amino acids in short chain peptides were examined. Each amino acid, aliphatic or charged, was inserted between the two tryptophans of a peptide, GWWG. The capacity factors of these peptides on an Ocytl-Sepharose column were measured. The adsorption enthalpies, entropies, and the number of repelled water molecules after adsorption were estimated to analyze the contribution of each different amino acid to its hydrophobic adsorption. The peptides inserted with aliphatic amino acids owned the highest capacity factors but released the least amount of adsorption heat among all the peptides under examination. It was found that the hydrophobic contribution of aliphatic amino acids was derived from the entropy gain by repelling the ordered water surrounding them. The insertion of negatively charged amino acids greatly reduced the capacity factors but still repelled a significant number of water molecules after adsorption. This indicated that the water molecules surrounding ionic amino acids were not orderly aligned. The dehydration cost energy but the water repelling did not offer enough entropy to drive the adsorption. Subsequently, lower retention was obtained from the peptides inserted with negatively charged ionic amino acids. The insertion of lysine increased the adsorption enthalpy but repelled no water molecules after adsorption. It was speculated that the inserted lysine still interacted with hydrophobic ligands but disturbed the interaction between ligands and adjacent tryptophans. Therefore, the adsorption enthalpy increased and the capacity factors decreased. Different amino acids contributed to hydrophobic interaction in different ways. The simultaneous analysis of capacity factor, adsorption enthalpy, adsorption entropy, and the number of repelled water molecules facilitated the understanding of the adsorption processes.
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Affiliation(s)
- Chih-I Liu
- R&D Center of Membrane Technology and Department of Chemical Engineering, Chung Yuan University, Chung-Li 320, Taiwan
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48
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Meyer C, Pascui O, Reichert D, Sander LC, Wise SA, Albert K. Conformational temperature dependence of a poly(ethylene-co-acrylic acid) stationary phase investigated by nuclear magnetic resonance spectroscopy and liquid chromatography. J Sep Sci 2006; 29:820-8. [PMID: 16830494 DOI: 10.1002/jssc.200500376] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
A polymer-based RP sorbent was prepared by immobilizing a poly(ethylene-co-acrylic acid) copolymer with an acid mass fraction of 5% on silica by using a 3-glycidoxypropyl linkage. 13C cross-polarization/magic angle spinning NMR spectroscopy of the sorbent, either in the dry state or suspended in the mobile phase, showed an increase in mobility at elevated temperatures. Alkyl chain segments with gauche conformations were more mobile than chain segments with trans conformations. The strength of the 13C-1H dipolar couplings in the alkyl chains was measured using the constant time dipolar and chemical shift pulse sequence, revealing less molecular motion for the trans conformation. Non-linear van't Hoff plots were observed for separations of shape-constrained solutes (such as geometric beta-carotene isomers and polycyclic aromatic hydrocarbons). At higher temperatures, the retention behavior was similar to that of monomeric C18 sorbents, whereas at ambient and lower temperatures, enhanced shape-selective properties were exhibited similar to those of polymeric C30 sorbents.
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Affiliation(s)
- Christoph Meyer
- Institute of Organic Chemistry, University of Tuebingen, Tuebingen, Germany
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Asnin L, Guiochon G. Chromatographic separation of phenylpropanol enantiomers on a quinidine carbamate-type chiral stationary phase. J Chromatogr A 2005; 1091:11-20. [PMID: 16395788 DOI: 10.1016/j.chroma.2005.07.006] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The retention and the separation of the enantiomers of 1-phenylpropanol (1PP), 2-phenylpropanol (2PP), and 3-chloro-1-phenylpropanol (3CPP) on silica-bonded quinidine carbamate under normal phase HPLC conditions were investigated. A relatively high selectivity of the stationary phase for 3CPP and 1PP (alpha approximately 1.07-1.09) was achieved with eluents containing ethyl acetate as the polar modifier. These mobile phases were examined in detail. Based on the set of chromatographic and thermodynamic data collected, conclusions regarding the mechanism of enantioselectivity and the structure of the selector chiral center are made.
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Affiliation(s)
- Leonid Asnin
- Department of Chemistry, University of Tennessee, Knoxville, TN 37996-1600, USA
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Zhanga L, Suna L, Siepmann JI, Schure MR. Molecular simulation study of the bonded-phase structure in reversed-phase liquid chromatography with neat aqueous solvent. J Chromatogr A 2005; 1079:127-35. [PMID: 16038298 DOI: 10.1016/j.chroma.2005.03.124] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The dramatic loss of retention in reversed-phase liquid chromatography when switching to 100% aqueous solvent and stopping flow (depressurizing) has long intrigued separation scientists. Recent experimental evidence suggests that the observed loss of retention is due to the loss of pore wetting with subsequent loss of solvent penetration in the porous matrix. One of the prevalent explanations of this phenomenon has been that the bonded phase chains, typically octadecyl silane bound to porous silica, would undergo significant conformational changes, viz. collapse, under pure aqueous conditions. As a definitive means toward elucidating the conformation of bonded-phase chains under pure aqueous conditions, configurational-bias Monte Carlo simulations in the Gibbs ensemble were carried out for a system of dimethyl octadecyl silane of intermediate coverage bound to the (111) face of beta-cristobalite and immersed in pure water. The results of two sets of simulations, which were started from two entirely different starting configurations as a validity check toward reaching the same equilibrium distribution of states, show that chains are neither clustering together nor laying on the surface but rather have a broad distribution of orientations and of conformational states. The interface between the bonded and solvent phases is rough on a molecular level, and clusters of water molecules are sometimes found to adsorb at the silica surface. This computational study lends further evidence that the driving force for the loss of retention when switching to pure aqueous conditions and depressurizing is not the collapse of bonded-phase chains.
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Affiliation(s)
- Ling Zhanga
- Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, MN 55455, USA
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