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Ferchichi K, Chouchaine A, Amdouni N, Chevalier Y, Hbaieb S. Anionic Dye Removal with a Thin Cationic Polyaniline Coating on Cellulosic Biomaterial. ACS OMEGA 2024; 9:15935-15949. [PMID: 38617700 PMCID: PMC11007837 DOI: 10.1021/acsomega.3c09031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/13/2023] [Revised: 03/14/2024] [Accepted: 03/19/2024] [Indexed: 04/16/2024]
Abstract
This paper reports the development of novel adsorbent materials using polyaniline (PANI) grafted onto Posidonia (POS) fibers, aimed at efficiently removing phenol red (PSP), an anionic dye, from aqueous solutions. The synthesis involved the copolymerization of aniline grafted on the surface of the POS and aniline monomer in solution, resulting in a chemically bound thin PANI layer on the POS bioadsorbent. Structural characteristics and binding affinities of these adsorbents with PANI under its emeraldine salt (POS@PANI-ES) or emeraldine base (POS@PANI-EB) forms are reported. The rapid adsorption kinetics observed are attributed to enhanced accessibility to PANI adsorption sites on the POS surface. The binding percentages of PSP to POS@PANI-ES and POS@PANI-EB materials were found to be 97 and 50%, respectively, after 15 min of contact time. The Langmuir model for localized adsorption sites and the Volmer model for nonlocalized adsorption as a mobile layer were fitted to the experimental adsorption isotherms of PSP to POS@PANI-EB and POS@PANI-ES, yielding the thermodynamic parameters of adsorption. The adsorption capacities of PSP on POS@PANI-EB and POS@PANI-ES were 37.8 and 71.5 μmol g-1, respectively. The adsorption of PSP remained above 80% at moderate salt concentrations of around 0.1 mol L-1; however, higher concentrations of NaCl and CaCl2 in PSP solutions significantly reduced the adsorption on POS@PANI-ES.
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Affiliation(s)
- Karima Ferchichi
- Laboratoire
de Recherche: Caractérisations, Applications et Modélisation
de Matériaux, Université de
Tunis El Manar, Faculté des Sciences de Tunis, Campus Universitaire El Manar, Tunis 2092, Tunisia
| | - Amaini Chouchaine
- Laboratoire
de Recherche: Caractérisations, Applications et Modélisation
de Matériaux, Université de
Tunis El Manar, Faculté des Sciences de Tunis, Campus Universitaire El Manar, Tunis 2092, Tunisia
| | - Noureddine Amdouni
- Laboratoire
de Recherche: Caractérisations, Applications et Modélisation
de Matériaux, Université de
Tunis El Manar, Faculté des Sciences de Tunis, Campus Universitaire El Manar, Tunis 2092, Tunisia
| | - Yves Chevalier
- Laboratoire
d’Automatique, de Génie des Procédés et
de Génie Pharmaceutique, Université
de Lyon 1, UMR 5007 CNRS,
43 bd 11 Novembre, 69622 Villeurbanne, France
| | - Souhaira Hbaieb
- Laboratoire
de Recherche: Caractérisations, Applications et Modélisation
de Matériaux, Université de
Tunis El Manar, Faculté des Sciences de Tunis, Campus Universitaire El Manar, Tunis 2092, Tunisia
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Dallocchio R, Dessì A, Sechi B, Peluso P. Molecular Dynamics Simulations of Amylose- and Cellulose-Based Selectors and Related Enantioseparations in Liquid Phase Chromatography. Molecules 2023; 28:7419. [PMID: 37959839 PMCID: PMC10647714 DOI: 10.3390/molecules28217419] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2023] [Revised: 10/27/2023] [Accepted: 10/30/2023] [Indexed: 11/15/2023] Open
Abstract
In the last few decades, theoretical and technical advancements in computer facilities and computational techniques have made molecular modeling a useful tool in liquid-phase enantioseparation science for exploring enantioselective recognition mechanisms underlying enantioseparations and for identifying selector-analyte noncovalent interactions that contribute to binding and recognition. Because of the dynamic nature of the chromatographic process, molecular dynamics (MD) simulations are particularly versatile in the visualization of the three-dimensional structure of analytes and selectors and in the unravelling of mechanisms at molecular levels. In this context, MD was also used to explore enantioseparation processes promoted by amylose and cellulose-based selectors, the most popular chiral selectors for liquid-phase enantioselective chromatography. This review presents a systematic analysis of the literature published in this field, with the aim of providing the reader with a comprehensive picture about the state of the art and what is still missing for modeling cellulose benzoates and the phenylcarbamates of amylose and cellulose and related enantioseparations with MD. Furthermore, advancements and outlooks, as well as drawbacks and pitfalls still affecting the applicability of MD in this field, are also discussed. The importance of integrating theoretical and experimental approaches is highlighted as an essential strategy for profiling mechanisms and noncovalent interaction patterns.
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Affiliation(s)
| | | | | | - Paola Peluso
- Unit of Enantioselective Chromatography and Molecular Recognition, Institute of Biomolecular Chemistry ICB, Secondary Branch of Sassari, CNR, Traversa La Crucca 3, Regione Baldinca, Li Punti, 07100 Sassari, Italy; (R.D.); (A.D.); (B.S.)
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Trebel N, Höltzel A, Lutz JK, Tallarek U. Consequences of Cylindrical Pore Geometry for Interfacial Phenomena in Reversed-Phase Liquid Chromatography. J Phys Chem B 2021; 125:11320-11336. [PMID: 34610741 DOI: 10.1021/acs.jpcb.1c06732] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The interfacial phenomena behind analyte separation in a reversed-phase liquid chromatography column take place nearly exclusively inside the silica mesopores. Their cylindrical geometry can be expected to shape the properties of the chromatographic interface with consequences for the analyte density distribution and diffusivity. To investigate this topic through molecular dynamics simulations, we introduce a cylindrical pore inside a slit pore configuration, where the inner curved and outer planar silica surface bear the same bonded phase. The present model replicates an average-sized (9 nm) mesopore in an endcapped C18 column equilibrated with a mobile phase of 70/30 (v/v) water/acetonitrile. Simulations performed for ethylbenzene and acetophenone show that the surface curvature shifts the bonded phase and analyte density toward the pore center, decreases the solvent density in the bonded-phase region, increases the acetonitrile excess in the interfacial region, and considerably enhances the surface diffusivity of both analytes. Overall, the cylindrical pore provides a more hydrophobic environment than the slit pore. Ethylbenzene density is decidedly increased in the cylindrical pore, whereas acetophenone density is nearly equally distributed between the cylindrical and slit pore. The cylindrical pore geometry thus sharpens the discrimination between the apolar and moderately polar analytes while enhancing the mass transport of both.
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Affiliation(s)
- Nicole Trebel
- Department of Chemistry, Philipps-Universität Marburg, Hans-Meerwein-Strasse 4, 35032 Marburg, Germany
| | - Alexandra Höltzel
- Department of Chemistry, Philipps-Universität Marburg, Hans-Meerwein-Strasse 4, 35032 Marburg, Germany
| | - Julia K Lutz
- Department of Chemistry, Philipps-Universität Marburg, Hans-Meerwein-Strasse 4, 35032 Marburg, Germany
| | - Ulrich Tallarek
- Department of Chemistry, Philipps-Universität Marburg, Hans-Meerwein-Strasse 4, 35032 Marburg, Germany
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4
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Siders PD. Simulated molecular-scale interaction of supercritical fluid mobile and stationary phases. J Chromatogr A 2017; 1527:97-104. [DOI: 10.1016/j.chroma.2017.10.056] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2017] [Revised: 10/23/2017] [Accepted: 10/23/2017] [Indexed: 11/30/2022]
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Liyana-Arachchi TP, Sturnfield JF, Colina CM. Ultrathin Molecular-Layer-by-Layer Polyamide Membranes: Insights from Atomistic Molecular Simulations. J Phys Chem B 2016; 120:9484-94. [PMID: 27558460 DOI: 10.1021/acs.jpcb.6b02801] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In this study, we present an atomistic simulation study of several physicochemical properties of polyamide (PA) membranes formed from interfacial polymerization or from a molecular-layer-by-layer (mLbL) on a silicon wafer. These membranes are composed of meta-phenylenediamine (MPD) and benzene-1,3,5-tricarboxylic acid chloride (TMC) for potential reverse osmosis (RO) applications. The mLbL membrane generation procedure and the force field models were validated, by comparison with available experimental data, for hydrated density, membrane swelling, and pore size distributions of PA membranes formed by interfacial polymerization. Physicochemical properties such as density, free volume, thickness, the degree of cross-linking, atomic compositions, and average molecular orientation (which is relevant for the mLbL membranes) are compared for these different processes. The mLbL membranes are investigated systematically with respect to TMC monomer growth rate per substrate surface area, MPD/TMC ratio, and the number of mLbL deposition cycles. Atomistic simulations show that the mLbL deposition generates membranes with a constant film growth if both the TMC monomer growth rate and MPD/TMC monomer ratio are kept constant. The film growth rate increases with TMC monomer growth rate or MPD/TMC ratio. Furthermore, it was found on one hand that the mLbL membrane density and free volume varies significantly with respect to the TMC monomer growth rate, while on the other hand the degree of cross-linking and the atomic composition varies considerably with the MPD/TMC ratio. Additionally, it was found that both TMC and MPD orient at a tilted angle with respect to the substrate surface, where their angular distribution and average angle orientation depend on both the TMC growth rate and the number of deposition cycles. This study illustrates that molecular simulations can play a crucial role in the understanding of structural properties that can empower the design of the next generation RO membranes created from molecular-layer-by-layer (mLbL) on a silicon wafer.
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Affiliation(s)
- Thilanga P Liyana-Arachchi
- Department of Materials Science and Engineering, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
| | - James F Sturnfield
- Engineering and Process Sciences, Process Optimization, The Dow Chemical Company , North Brazosport Boulevard, Freeport, Texas 77541, United States
| | - Coray M Colina
- Department of Materials Science and Engineering, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
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Siders PD. Conformational free energy of alkylsilanes by nonequilibrium-pulling Monte Carlo simulation. MOLECULAR SIMULATION 2015. [DOI: 10.1080/08927022.2015.1083101] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Gu F, Chodavarapu K, McCreary D, Plitt TA, Tamoria E, Ni M, Burnham JJ, Peters M, Lenhoff AM. Silica-based strong anion exchange media for protein purification. J Chromatogr A 2015; 1376:53-63. [DOI: 10.1016/j.chroma.2014.11.082] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2014] [Revised: 11/24/2014] [Accepted: 11/27/2014] [Indexed: 10/24/2022]
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Fatunmbi HO, Bruch MD. Characterization of the structural morphology of chemically modified silica prepared by surface polymerization of a mixture of long and short alkyl chains using 13C and 29Si NMR spectroscopy. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:4974-4987. [PMID: 23530776 DOI: 10.1021/la3040853] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
A series of bonded phases were prepared by the chemical modification of silica using the surface polymerization of trifunctional and difunctional ligands, and the structural morphology was characterized by solid-state nuclear magnetic resonance (NMR) spectroscopy using cross-polarization and magic angle spinning (CP/MAS). Mixed-phase surfaces were prepared using mixtures of trifunctional long-chain (C18) ligands with trifunctional and difunctional short-chain (C1) ligands, and these surfaces were compared to the corresponding single-phase surfaces consisting of only long- or short-chain ligands. For both types of mixed-phase surfaces, the incorporation of short chains increases the overall ligand density, the density of long chains, and the degree of cross-linking between ligands compared to that of the single-phase surface consisting exclusively of long chains. When the percentage of long-chain ligands in the mixture is high, a horizontally polymerized monolayer of chains is formed on the silica surface for both trifunctional and difunctional short chains. However, essentially all of the long chains adopt a trans conformation when trifunctional short chains are used, and a significant number of gauche defects are observed for the long chains when mixed with difunctional short chains. Furthermore, the ligands on the mixed-phase surface are more rigid when the short chains are trifunctional. When the percentage of trifunctional short chains is increased, some vertical polymerization occurs, caused by the molecular stacking of the highly reactive short chains near the surface. However, this does not preclude cross-linking between the ligands necessary to seal the surface, and the degree of cross-linking is quite high, suggesting that the short chains cross-link both vertically, away from the surface, and horizontally, across the surface. No such vertical polymerization is observed for the bulkier difunctional short chains. For both trifunctional and difunctional short chains, the surface chains are more mobile, with a greater number of gauche conformations among the long chains when the percentage of short-chain ligands in the reaction mixture is increased.
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Affiliation(s)
- Hafeez O Fatunmbi
- Separation Methods Technologies, Inc., 31 Blue Hen Drive, Newark, Delaware 19713, United States
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Li Y, Liu D, Wang P, Zhou Z. Computational study of enantioseparation by amylose tris(3,5-dimethylphenylcarbamate)-based chiral stationary phase. J Sep Sci 2011; 33:3245-55. [PMID: 20839235 DOI: 10.1002/jssc.201000266] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The mechanism of chiral separation on amylose tris(3,5-dimethylphenylcarbamate) is studied with docking simulations of enantiomers by molecular dynamics. All-atom models of amylose tris(3,5-dimethylphenylcarbamate) on the modified silica gel surface were constructed for the docking simulations of metalaxyl and benalaxyl. The elution orders and energetic differences were also predicted based on the intermolecular interactions, which were in agreement with the experimental results. The radial distribution function was employed to analyze the structural features of the enantiomer-chiral stationary phase complex and used to elucidate the mechanism of chiral separation. The separation of metalaxyl and benalaxyl is mainly controlled by the hydrogen bond. And the binding sites had slight differences for the pair of enantiomers, but obvious differences between different chemicals.
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Affiliation(s)
- Yangyang Li
- Department of Applied Chemistry, College of Science, China Agricultural University, Beijing, PR China
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Olariu RI, Vione D, Grinberg N, Arsene C. SAMPLE PREPARATION FOR TRACE ANALYSIS BY CHROMATOGRAPHIC METHODS. J LIQ CHROMATOGR R T 2010. [DOI: 10.1080/10826076.2010.484371] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Affiliation(s)
- Romeo-Iulian Olariu
- a Department of Chemistry , Faculty of Chemistry, Laboratory of Analytical Chemistry, “Al. I. Cuza” University of Iasi , Iasi , Romania
| | - Davide Vione
- b Dipartimento di Chimica Analitica , Università di Torino , Torino , Italy
| | - Nelu Grinberg
- c Boehringer Ingelheim Pharmaceuticals Inc. , Ridgefield , Connecticut , USA
| | - Cecilia Arsene
- a Department of Chemistry , Faculty of Chemistry, Laboratory of Analytical Chemistry, “Al. I. Cuza” University of Iasi , Iasi , Romania
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11
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Zhang L, Sun Y. Molecular simulation of adsorption and its implications to protein chromatography: A review. Biochem Eng J 2010. [DOI: 10.1016/j.bej.2009.12.003] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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12
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The effects of chain length, embedded polar groups, pressure, and pore shape on structure and retention in reversed-phase liquid chromatography: Molecular-level insights from Monte Carlo simulations. J Chromatogr A 2009; 1216:2320-31. [DOI: 10.1016/j.chroma.2008.12.088] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2008] [Revised: 12/22/2008] [Accepted: 12/29/2008] [Indexed: 11/22/2022]
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13
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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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14
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Liao Z, Pemberton JE. Structure-function relationships in high-density docosylsilane bonded stationary phases by Raman spectroscopy and comparison to octadecylsilane bonded stationary phases: Effects of aromatic compounds. J Chromatogr A 2008; 1193:60-9. [DOI: 10.1016/j.chroma.2008.03.090] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2007] [Revised: 03/20/2008] [Accepted: 03/25/2008] [Indexed: 10/22/2022]
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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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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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Lippa KA, Sander LC, Mountain RD. Molecular Dynamics Simulations of Alkylsilane Stationary-Phase Order and Disorder. 1. Effects of Surface Coverage and Bonding Chemistry. Anal Chem 2005; 77:7852-61. [PMID: 16351130 DOI: 10.1021/ac0510843] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
"Shape-selective" polymeric alkylsilane stationary phases are routinely employed over the more common monomeric phases in reversed-phase liquid chromatography (RPLC) to improve the separation of geometric isomers of shape-constrained solutes. We have investigated the molecular dynamics of chromatographic models that represent both monomeric and polymeric stationary phases with alkylsilane surface coverages and bonding chemistries typical of actual materials in an effort to elucidate the molecular-level structural features that control shape-selective separations. The structural characterization of these models is consistent with previous experimental observations of alkyl chain order and disorder: (1) alkyl chain order increases with increased surface coverage; and (2) monomeric and polymeric phases with similar surface coverages yield similar alkyl chain order (although subtle differences exist). In addition, a significant portion of the alkyl chain proximal to the silica surface is disordered (primarily gauche conformations) and the distal end is most ordered. Models that represent shape-selective RPLC phases possess a significant region of distal end chain order with primarily trans dihedral angle conformations. This is consistent with the view that the alkyl chains comprising polymeric stationary phases contain a series of well-defined and rigid voids in which shape-constrained solutes can penetrate and hence be selectively retained.
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Affiliation(s)
- Katrice A Lippa
- Analytical Chemistry Division and Physical and Chemical Properties Division, Chemical Sciences and Technology Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899, 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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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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