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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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Rafferty JL, Siepmann JI, Schure MR. Mobile phase effects in reversed-phase liquid chromatography: A comparison of acetonitrile/water and methanol/water solvents as studied by molecular simulation. J Chromatogr A 2011; 1218:2203-13. [DOI: 10.1016/j.chroma.2011.02.012] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2010] [Revised: 01/28/2011] [Accepted: 02/05/2011] [Indexed: 11/16/2022]
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Rafferty JL, Siepmann J, Schure MR. Influence of bonded-phase coverage in reversed-phase liquid chromatography via molecular simulation. J Chromatogr A 2008; 1204:11-9. [DOI: 10.1016/j.chroma.2008.07.037] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2008] [Revised: 06/24/2008] [Accepted: 07/04/2008] [Indexed: 10/21/2022]
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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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Sander LC, Lippa KA, Wise SA. Order and disorder in alkyl stationary phases. Anal Bioanal Chem 2005; 382:646-68. [PMID: 15827723 DOI: 10.1007/s00216-005-3127-2] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2004] [Revised: 01/21/2005] [Accepted: 01/24/2005] [Indexed: 11/28/2022]
Abstract
Covalently modified surfaces represent a unique state of matter that is not well described by liquid or solid phase models. The chemical bond in tethered alkanes imparts order to the surface in the form of anisotropic properties that are evident in chromatographic and spectroscopic studies. An understanding of the structure, conformation, and organization of alkyl-modified surfaces is requisite to the design of improved materials and the optimal utilization of existing materials. In recent years, the study of alkyl-modified surfaces has benefited from advances in modern analytical instrumentation. Aspects of alkyl chain conformation and motion have been investigated through the use of nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, fluorescence spectroscopy, and neutron scattering studies. Chromatography provides complementary evidence of alkyl chain organization through interactions with solute probes. Computational simulations offer insights into the structure of covalently modified surfaces that may not be apparent through empirical observation. This manuscript reviews progress achieved in the study of the architecture of alkyl-modified surfaces.
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Affiliation(s)
- Lane C Sander
- Chemical Science and Technology Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899-8392, USA.
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Chowdhury MAJ, Boysen RI, Ihara H, Hearn MTW. Binding Behavior of Crystalline and Noncrystalline Phases: Evaluation of the Enthalpic and Entropic Contributions to the Separation Selectivity of Nonpolar Solutes with a Novel Chromatographic Sorbent. J Phys Chem B 2002. [DOI: 10.1021/jp0200371] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- M. A. Jamil Chowdhury
- Australian Centre for Research on Separation Science, Centre of Bioprocess Technology, Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia 3168, and Graduate School of Science and Technology, College of Engineering, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan
| | - Reinhard I. Boysen
- Australian Centre for Research on Separation Science, Centre of Bioprocess Technology, Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia 3168, and Graduate School of Science and Technology, College of Engineering, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan
| | - Hirotaka Ihara
- Australian Centre for Research on Separation Science, Centre of Bioprocess Technology, Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia 3168, and Graduate School of Science and Technology, College of Engineering, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan
| | - Milton T. W. Hearn
- Australian Centre for Research on Separation Science, Centre of Bioprocess Technology, Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia 3168, and Graduate School of Science and Technology, College of Engineering, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan
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Krouskop PE, McGuffin VL. Stochastic simulation of the partition mechanism with a heterogeneous surface phase. J Chromatogr A 2002; 959:49-64. [PMID: 12141561 DOI: 10.1016/s0021-9673(02)00427-2] [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: 11/18/2022]
Abstract
A three-dimensional stochastic model of chromatography has been used to determine the effect of multiple sites on the partition mechanism. The effect of additional sites on mass transfer rates, zone profiles, and their statistical moments are investigated as a function of the partition coefficient, diffusion coefficient, and interfacial barrier to mass transfer. These studies have demonstrated that changes in the partition coefficient alone are not sufficient to alter the system response from that of a single site. Changes in the diffusion coefficient and the barrier to mass transfer do cause changes in the response compared to that of a single site. The zone profiles produced by the systems become more asymmetric as the difference between the diffusion coefficients or the barriers to mass transfer increases. The site with the slower mass transfer rate plays the dominant role in the total system response.
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Affiliation(s)
- Peter E Krouskop
- Department of Chemistry, Michigan State University, East Lansing 48824, USA
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Ban K, Jinno K. Molecular-dynamics simulation for liquid chromatographic interactions: effect of mobile phase composition. ANAL SCI 2001; 17:113-7. [PMID: 11993646 DOI: 10.2116/analsci.17.113] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
A molecular-dynamics simulation method has been applied to investigate the influence of the mobile-phase composition on the retention of solutes in HPLC. The distribution profiles of the distance between two atoms in ODS ligands were constructed to characterize the conformation of ODS ligand molecules. The distinct difference of ODS conformation is observed by comparing molecular models consisting of solvent molecules at each solvent composition. The distribution profiles of the distance between the mobile-phase solvent molecules and ODS ligand molecules were also constructed to characterize the distribution of the solvent molecules at each composition. In all distribution profiles, the difference in the distribution due to a change in the solvent compositions was very clearly found, and the facts seem to be very reasonable. The distribution profiles of the distance between the solute, n-propylbenzene, and the terminal carbon atom in the ODS ligand, and between the solute and the silicon atom in the ODS ligand have been also constructed to see the distribution of the solutes in the separation system. The calculated solute distribution in the ODS-methanol/water system is very consistent with the actual chromatographic retention behaviors.
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Affiliation(s)
- K Ban
- Toyohashi University of Technology, School of Materials Science, Aichi, Japan
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Hearn MT. Physicochemical factors in polypeptide and protein purification and analysis by high-performance liquid chromatographic techniques: current status and challenges for the future. HANDBOOK OF BIOSEPARATIONS 2000. [DOI: 10.1016/s0149-6395(00)80050-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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Purcell AW, Aguilar MI, Hearn MT. Probing the binding behavior and conformational states of globular proteins in reversed-phase high-performance liquid chromatography. Anal Chem 1999; 71:2440-51. [PMID: 10405610 DOI: 10.1021/ac9808369] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Reversed-phase high-performance liquid chromatography (RP-HPLC) is a widely used technique for the separation of proteins under low pH aquo-organic solvent gradient elution conditions, typically carried out at ambient temperatures. These conditions can however induce conformational effects with proteins as evident from changes in their biological or immunological activities. By monitoring the influence of temperature on the retention and band-broadening characteristics of proteins, the role of conformational processes in these lipophilic environments can be examined. These processes can then be interpreted in terms of a two-state model involving a native (N) and a fully unfolded species (U) or more complex folding/unfolding models. In the present study, the gradient elution RP-HPLC behavior of sperm whale myoglobin (SWMYO) and hen egg white lysozyme (HEWL) has been investigated at temperatures between 5 and 85 degrees C with n-octadecyl (C18)- and n-butyl (C4)-silica reversed-phase sorbents. The interaction of these proteins with these reversed-phase sorbents has also been examined in terms of the contributions that the heme prosthetic group of SWMYO and the disulfide bonds in HEWL make to the stabilization of the native conformation of these proteins in these hydrophobic environments. The observed interconversions of multiple peak zones of SWMYO and HEWL in the presence of C18 and C4 ligands have been subsequently analyzed in terms of the unfolding processes that these proteins can undergo at low pH and at elevated temperatures. The ability of hydrocarbonaceous ligands to trap ensemblies of partially unfolded conformational intermediates of proteins in these perturbing environments has been examined. Pseudo-first-order rate constants have been derived for these processes from analysis of the dependencies on time of the concentration of the different protein species at specified temperatures. The relationship of these processes to the conformational transitions that these proteins can undergo via molten globule-like intermediates (i.e., compact denatured states with a significant amount of residual secondary structure) in solution has also been examined. This study thus further documents an experimental strategy to assess the folding/unfolding behavior of globular proteins in the presence of hydrophobic surfaces and aquo-organic solvents, whereby the system parameters can potentially affect the preservation of native conformations, and thus the function, of the protein under these conditions.
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Affiliation(s)
- A W Purcell
- Department of Biochemistry and Molecular Biology, Monash University, Victoria, Australia
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Yarovsky I, Hearn MTW, Aguilar MI. Molecular Simulation of Peptide Interactions with an RP-HPLC Sorbent. J Phys Chem B 1997. [DOI: 10.1021/jp972232z] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- I. Yarovsky
- Department of Biochemistry & Molecular Biology, Monash University, Wellington Road, Clayton, Victoria 3168, Australia
| | - M. T. W. Hearn
- Department of Biochemistry & Molecular Biology, Monash University, Wellington Road, Clayton, Victoria 3168, Australia
| | - M. I. Aguilar
- Department of Biochemistry & Molecular Biology, Monash University, Wellington Road, Clayton, Victoria 3168, Australia
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Dorsey JG, Cooper WT, Siles BA, Foley JP, Barth HG. Liquid Chromatography: Theory and Methodology. Anal Chem 1996. [DOI: 10.1021/a19600202] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- John G. Dorsey
- Department of Chemistry, Florida State University, Tallahassee, Florida 32306-3006
| | - William T. Cooper
- Department of Chemistry, Florida State University, Tallahassee, Florida 32306-3006
| | - Barbara A. Siles
- Department of Chemistry, College of William and Mary, Williamsburg, Virginia 23187-8795
| | - Joe P. Foley
- Department of Chemistry, Villanova University, Villanova, Pennsylvania 19085-1699
| | - Howard G. Barth
- Central Research and Development Department, E. I. du Pont de Nemours & Company, P. O. Box 80228, Experimental Station, Wilmington, Delaware 19880
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Beck TL. Comment on "Influence of the chain length and surface density on the conformation and mobility of n-alkyl ligands chemically immobilized onto a silica surface". Anal Chem 1996; 68:1973-5. [PMID: 8686918 DOI: 10.1021/ac951092r] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
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Purcell AW, Aguilar MI, Hearn MT. Conformational effects in reversed-phase high-performance liquid chromatography of polypeptides. I. Resolution of insulin variants. J Chromatogr A 1995; 711:61-70. [PMID: 7496495 DOI: 10.1016/0021-9673(95)00241-e] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
In order to further characterise the role of conformation in the retention behaviour of polypeptides and proteins in reversed-phase high-performance liquid chromatography (RP-HPLC), the chromatographic properties of four different insulins have been studied as a function of temperature (over the range 5-85 degrees C) and column residence time (over the range 10-60 min). The role of the ligand structure was also investigated by comparing results obtained with a n-octadecyl (C18) and a n-butyl (C4) ligand immobilised to the same porous silica. Comparative structure-retention-stability relationships were determined from an examination of the influence of temperature on a number of chromatographic parameters including the chromatographic contact area, the affinity constant and the experimental band width. The results demonstrated that variations in temperature can be used to affect significant changes in selectivity between the different insulins despite their very high degree of sequence homology. These observations have permitted specific amino acid residues, and in particular those residues encompassing the region A8-A10, to be proposed to be directly involved in the chromatographic contact area of the insulin molecules. Overall, the analysis of the changes in various chromatographic parameters in response to variation of the amino acid sequence, temperature and other experimental parameters provides a powerful tool to elucidate the structural basis for the interfacial stability and the role of conformation on the retention behaviour of polypeptides and proteins in RP-HPLC.
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Affiliation(s)
- A W Purcell
- Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia
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A comparative study of the retention behaviour and stability of cytochrome c in reversed-phase high-performance liquid chromatography. J Chromatogr A 1994. [DOI: 10.1016/0021-9673(94)00092-1] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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