1
|
Zeng M, Wilson KR. Experimental evidence that halogen bonding catalyzes the heterogeneous chlorination of alkenes in submicron liquid droplets. Chem Sci 2021; 12:10455-10466. [PMID: 34447538 PMCID: PMC8356749 DOI: 10.1039/d1sc02662c] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2021] [Accepted: 07/09/2021] [Indexed: 12/21/2022] Open
Abstract
A key challenge in predicting the multiphase chemistry of aerosols and droplets is connecting reaction probabilities, observed in an experiment, with the kinetics of individual elementary steps that control the chemistry that occurs across a gas/liquid interface. Here we report evidence that oxygenated molecules accelerate the heterogeneous reaction rate of chlorine gas with an alkene (squalene, Sqe) in submicron droplets. The effective reaction probability for Sqe is sensitive to both the aerosol composition and gas phase environment. In binary aerosol mixtures with 2-decyl-1-tetradecanol, linoleic acid and oleic acid, Sqe reacts 12-23× more rapidly than in a pure aerosol. In contrast, the reactivity of Sqe is diminished by 3× when mixed with an alkane. Additionally, small oxygenated molecules in the gas phase (water, ethanol, acetone, and acetic acid) accelerate (up to 10×) the heterogeneous chlorination rate of Sqe. The overall reaction mechanism is not altered by the presence of these aerosol and gas phase additives, suggesting instead that they act as catalysts. Since the largest rate acceleration occurs in the presence of oxygenated molecules, we conclude that halogen bonding enhances reactivity by slowing the desorption kinetics of Cl2 at the interface, in a way that is analogous to decreasing temperature. These results highlight the importance of relatively weak interactions in controlling the speed of multiphase reactions important for atmospheric and indoor environments.
Collapse
Affiliation(s)
- Meirong Zeng
- Chemical Sciences Division, Lawrence Berkeley National Laboratory Berkeley CA 94720 USA
| | - Kevin R Wilson
- Chemical Sciences Division, Lawrence Berkeley National Laboratory Berkeley CA 94720 USA
| |
Collapse
|
2
|
Evaluation of the solvation parameter model as a quantitative structure-retention relationship model for gas and liquid chromatography. J Chromatogr A 2020; 1626:461308. [DOI: 10.1016/j.chroma.2020.461308] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2020] [Revised: 06/02/2020] [Accepted: 06/03/2020] [Indexed: 12/14/2022]
|
3
|
Poole CF. Wayne State University experimental descriptor database for use with the solvation parameter model. J Chromatogr A 2020; 1617:460841. [DOI: 10.1016/j.chroma.2019.460841] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2019] [Revised: 12/26/2019] [Accepted: 12/31/2019] [Indexed: 01/04/2023]
|
4
|
Poole CF. Gas chromatography system constant database for 52 wall-coated, open-tubular columns covering the temperature range 60–140 °C. J Chromatogr A 2019; 1604:460482. [DOI: 10.1016/j.chroma.2019.460482] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2019] [Revised: 08/21/2019] [Accepted: 08/22/2019] [Indexed: 10/26/2022]
|
5
|
Poole CF. Gas chromatography system constant database over an extended temperature range for nine open-tubular columns. J Chromatogr A 2019; 1590:130-145. [DOI: 10.1016/j.chroma.2019.01.028] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2018] [Revised: 10/07/2018] [Accepted: 01/10/2019] [Indexed: 11/25/2022]
|
6
|
Strength of Alkane–Fluid Attraction Determines the Interfacial Orientation of Liquid Alkanes and Their Crystallization through Heterogeneous or Homogeneous Mechanisms. CRYSTALS 2017. [DOI: 10.3390/cryst7030086] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
|
7
|
Bai P, Siepmann JI. Assessment and Optimization of Configurational-Bias Monte Carlo Particle Swap Strategies for Simulations of Water in the Gibbs Ensemble. J Chem Theory Comput 2017; 13:431-440. [DOI: 10.1021/acs.jctc.6b00973] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Peng Bai
- Departments of Chemistry
and of Chemical Engineering and Materials Science and Chemical Theory
Center, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455-0431, United States
| | - J. Ilja Siepmann
- Departments of Chemistry
and of Chemical Engineering and Materials Science and Chemical Theory
Center, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455-0431, United States
| |
Collapse
|
8
|
Theoretical simulation of chromatographic separation based on random diffusion in the restricted space. Sci China Chem 2016. [DOI: 10.1007/s11426-016-5565-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
|
9
|
Tascon M, Romero LM, Acquaviva A, Keunchkarian S, Castells C. Determinations of gas–liquid partition coefficients using capillary chromatographic columns. Alkanols in squalane. J Chromatogr A 2013; 1294:130-6. [DOI: 10.1016/j.chroma.2013.04.032] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2012] [Revised: 02/18/2013] [Accepted: 04/12/2013] [Indexed: 11/28/2022]
|
10
|
Rane KS, Murali S, Errington JR. Monte Carlo Simulation Methods for Computing Liquid–Vapor Saturation Properties of Model Systems. J Chem Theory Comput 2013; 9:2552-66. [DOI: 10.1021/ct400074p] [Citation(s) in RCA: 71] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- Kaustubh S. Rane
- Department of Chemical
and Biological Engineering, University at Buffalo, The State University of New York, Buffalo, New York 14260-4200,
United States
| | - Sabharish Murali
- Department of Chemical
and Biological Engineering, University at Buffalo, The State University of New York, Buffalo, New York 14260-4200,
United States
| | - Jeffrey R. Errington
- Department of Chemical
and Biological Engineering, University at Buffalo, The State University of New York, Buffalo, New York 14260-4200,
United States
| |
Collapse
|
11
|
Rafferty JL, Siepmann JI, Schure MR. Molecular simulations of retention in chromatographic systems: use of biased Monte Carlo techniques to access multiple time and length scales. Top Curr Chem (Cham) 2012; 307:181-200. [PMID: 21898207 DOI: 10.1007/128_2011_210] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The use of configurational-bias Monte Carlo simulations in the Gibbs ensemble allows for the sampling of phenomena that occur on vastly different time and length scales. In this review, applications of this simulation approach to probe retention in gas and reversed-phase liquid chromatographic systems are discussed. These simulations provide an unprecedented view of the retention processes at the molecular-level and show excellent agreement with experimental retention data.
Collapse
Affiliation(s)
- Jake L Rafferty
- Department of Chemistry and Chemical Theory Center, University of Minnesota, 207 Pleasant Street SE, Minneapolis, MN 55455-0431, USA
| | | | | |
Collapse
|
12
|
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
| |
Collapse
|
13
|
Maerzke KA, Schultz NE, Ross RB, Siepmann JI. TraPPE-UA Force Field for Acrylates and Monte Carlo Simulations for Their Mixtures with Alkanes and Alcohols. J Phys Chem B 2009; 113:6415-25. [DOI: 10.1021/jp810558v] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Katie A. Maerzke
- Departments of Chemistry and of Chemical Engineering and Materials Science, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, and Corporate Research Materials Laboratory, 201-2E-23, 3M Company, St. Paul, Minnesota 55144
| | - Nathan E. Schultz
- Departments of Chemistry and of Chemical Engineering and Materials Science, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, and Corporate Research Materials Laboratory, 201-2E-23, 3M Company, St. Paul, Minnesota 55144
| | - Richard B. Ross
- Departments of Chemistry and of Chemical Engineering and Materials Science, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, and Corporate Research Materials Laboratory, 201-2E-23, 3M Company, St. Paul, Minnesota 55144
| | - J. Ilja Siepmann
- Departments of Chemistry and of Chemical Engineering and Materials Science, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, and Corporate Research Materials Laboratory, 201-2E-23, 3M Company, St. Paul, Minnesota 55144
| |
Collapse
|
14
|
Radak BK, Yockel S, Kim D, Schatz GC. Modeling Reactive Scattering of F(2P) at a Liquid Squalane Interface: A Hybrid QM/MM Molecular Dynamics Study. J Phys Chem A 2009; 113:7218-26. [DOI: 10.1021/jp809546r] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Brian K. Radak
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113
| | - Scott Yockel
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113
| | - Dongwook Kim
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113
| | - George C. Schatz
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113
| |
Collapse
|
15
|
Waring C, Bagot PAJ, Räisänen MT, Costen ML, McKendrick KG. Dynamics of the Reaction of O(3P) Atoms with Alkylthiol Self-assembled Monolayers. J Phys Chem A 2009; 113:4320-9. [DOI: 10.1021/jp8109868] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Carla Waring
- School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, U.K. and School of Chemistry, University of St. Andrews, St. Andrews, Fife KY16 9ST, U.K
| | - Paul A. J. Bagot
- School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, U.K. and School of Chemistry, University of St. Andrews, St. Andrews, Fife KY16 9ST, U.K
| | - Minna T. Räisänen
- School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, U.K. and School of Chemistry, University of St. Andrews, St. Andrews, Fife KY16 9ST, U.K
| | - Matthew L. Costen
- School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, U.K. and School of Chemistry, University of St. Andrews, St. Andrews, Fife KY16 9ST, U.K
| | - Kenneth G. McKendrick
- School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, U.K. and School of Chemistry, University of St. Andrews, St. Andrews, Fife KY16 9ST, U.K
| |
Collapse
|
16
|
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]
|
17
|
Kim D, Schatz GC. Theoretical Investigation of Hyperthermal Reactions at the Gas−Liquid Interface: O (3P) and Squalane. J Phys Chem A 2007; 111:5019-31. [PMID: 17511430 DOI: 10.1021/jp0700478] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Hyperthermal collisions (5 eV) of ground-state atomic oxygen [O ((3)P)] with a liquid-saturated hydrocarbon, squalane (C(30)H(62)), have been studied using QM/MM hybrid "on-the-fly" direct dynamics. The surface structure of the liquid squalane is obtained from a classical molecular dynamics simulation using the OPLS-AA force field. The MSINDO semiempirical Hamiltonian is combined with OPLS-AA for the QM/MM calculations. In order to achieve a more consistent and efficient simulation of the collisions, we implemented a dynamic partitioning of the QM and MM atoms in which atoms are assigned to QM or MM regions based on their proximity to "seed" (open-shell) atoms that determine where bond making/breaking can occur. In addition, the number of seed atoms is allowed to increase or decrease as time evolves so that multiple reactive events can be described. The results show that H abstraction is the most important process for all incident angles, with H elimination, double H abstraction, and C-C bond cleavage also being important. A number of properties of these reactive channels, as well as inelastic nonreactive scattering, are investigated, including angular and translational energy distributions, the effect of incident collision angle, variation with depth of the reactive event within the liquid, with the reaction site on the hydrocarbon, and the effect of dynamics before and after reaction (direct reaction versus trapping reaction-desorption).
Collapse
Affiliation(s)
- Dongwook Kim
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, USA
| | | |
Collapse
|
18
|
Sun L, Siepmann JI, Klotz WL, Schure MR. Retention in gas–liquid chromatography with a polyethylene oxide stationary phase: Molecular simulation and experiment. J Chromatogr A 2006; 1126:373-80. [PMID: 16814798 DOI: 10.1016/j.chroma.2006.05.084] [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] [Received: 02/28/2006] [Revised: 05/20/2006] [Accepted: 05/30/2006] [Indexed: 11/16/2022]
Abstract
Configurational-bias Monte Carlo simulations in the isobaric-isothermal Gibbs ensemble were carried out to investigate the partitioning of normal alkanes, primary and secondary alcohols, symmetric alkyl ethers and arenes between a helium vapor phase and a polyethylene oxide stationary phase (M(W)=382 g mol(-1)). The united-atom version of the transferable potentials for phase equilibria force field was used to model all solutes, polyethylene oxide and helium. The Gibbs free energies of transfer and Kovats retention indices of the solutes were calculated directly from the partition constants at two different temperatures, 353 and 393 K. Chromatographic experiments on a Carbowax 20M retentive phase were performed for the same set of solutes and temperatures ranging from 333 to 413 K. The predicted retention indices for alcohols, ethers and arenes are overestimated by about 120, 70 and 20 retention index units, respectively, pointing to an overestimation of the first-order electrostatic interactions in the model system. Molecular-level analysis shows that hydrogen-bonding and dipole-dipole interactions lead to orientational ordering for the alcohol and ether analytes, whereas the weaker dipole-quadrupole interactions for the arene solutes are not sufficient to induce orientational ordering. The retention indices of alcohols and ethers decrease with increasing temperature because of the large entropic cost of hydrogen-bonding and orientational ordering. In contrast, the retention indices for arenes increase with increasing temperature because the entropic cost of cavity formation is smaller for arenes than for comparable alkanes.
Collapse
Affiliation(s)
- Li Sun
- Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, MN 55455, USA
| | | | | | | |
Collapse
|
19
|
Zolot AM, Harper WW, Perkins BG, Dagdigian PJ, Nesbitt DJ. Quantum-state resolved reaction dynamics at the gas-liquid interface: Direct absorption detection of HF(v,J) product from F(P2)+Squalane. J Chem Phys 2006; 125:21101. [PMID: 16848566 DOI: 10.1063/1.2217016] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Exothermic reactive scattering of F atoms at the gas-liquid interface of a liquid hydrocarbon (squalane) surface has been studied under single collision conditions by shot noise limited high-resolution infrared absorption on the nascent HF(v,J) product. The nascent HF(v,J) vibrational distributions are inverted, indicating insufficient time for complete vibrational energy transfer into the surface liquid. The HF(v=2,J) rotational distributions are well fit with a two temperature Boltzmann analysis, with a near room temperature component (T(TD) approximately equal to 290 K) and a second much hotter scattering component (T(HDS) approximately equal to 1040 K). These data provide quantum state level support for microscopic branching in the atom abstraction dynamics corresponding to escape of nascent HF from the liquid surface on time scales both slow and fast with respect to rotational relaxation.
Collapse
Affiliation(s)
- Alexander M Zolot
- JILA, National Institute of Standards and Technology, University of Colorado, Boulder, CO 80309, USA
| | | | | | | | | |
Collapse
|
20
|
Janecek J, Krienke H, Schmeer G. Interfacial Properties of Cyclic Hydrocarbons: A Monte Carlo Study. J Phys Chem B 2006; 110:6916-23. [PMID: 16571003 DOI: 10.1021/jp055558d] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The Monte Carlo technique is used to study the vapor-liquid interface of cyclopentane, cyclohexane, and benzene. The OPLS and TraPPE potential fields are compared in the temperature range from 298.15 to 348.15 K (273.15-298.15 K for C5H10). A new method for the treatment of the long-range interactions in inhomogeneous simulations is used. When this new method is employed, the obtained values of saturated liquid density and of enthalpy of vaporization are equal to those obtained using the bulk isothermal-isobaric Monte Carlo technique. The values of surface tension become independent of the cutoff distance and they are significantly larger than those when only simple spherical truncation of intermolecular interactions is used.
Collapse
Affiliation(s)
- Jirí Janecek
- Physik Department, Technische Universitat München, 85748 Garching, Germany
| | | | | |
Collapse
|
21
|
Wick CD, Stubbs JM, Rai N, Siepmann JI. Transferable Potentials for Phase Equilibria. 7. Primary, Secondary, and Tertiary Amines, Nitroalkanes and Nitrobenzene, Nitriles, Amides, Pyridine, and Pyrimidine. J Phys Chem B 2005; 109:18974-82. [PMID: 16853443 DOI: 10.1021/jp0504827] [Citation(s) in RCA: 192] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The transferable potentials for phase equilibria (TraPPE) force fields are extended to amine, nitro, nitrile, and amide functionalities and to pyridine and pyrimidine. In many cases, the same parameters for a functional group are used for both united-atom and explicit-hydrogen representations of alkyl tails. Following the TraPPE philosophy, the nonbonded interaction parameters were fitted to the vapor-liquid coexistence curves for selected one-component systems. Coupled-decoupled configurational-bias Monte Carlo simulations in the Gibbs ensemble were applied to neat (methyl-, dimethyl-, trimethyl-, ethyl-, diethyl-, or triethyl-)amine, nitromethane, nitroethane, nitrobenzene, acetonitrile, propionitrile, acetamide, propanamide, butanamide, pyridine, and pyrimidine. Excellent agreement with experimental results was found, with the mean unsigned errors being less than 1% for both the critical temperature and the normal boiling temperature. Similarly, the liquid densities at low reduced temperatures are reproduced to within 1%, and the deviation for the critical densities is about 4%. Additional simulations were performed for the binary mixtures of methylamine + n-hexane, diethyl ether + acetonitrile, 1-propanol + acetonitrile, and nitroethane + ethanol. With the exception of the methylamine/n-hexane mixture for which the separation factor is substantially overestimated, agreement with experiment for the other three mixtures is very satisfactory.
Collapse
Affiliation(s)
- Collin D Wick
- Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455-0431, USA
| | | | | | | |
Collapse
|
22
|
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.
Collapse
Affiliation(s)
- Ling Zhanga
- Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, MN 55455, USA
| | | | | | | |
Collapse
|
23
|
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.
Collapse
Affiliation(s)
- Lane C Sander
- Chemical Science and Technology Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899-8392, USA.
| | | | | |
Collapse
|
24
|
Köhler SPK, Allan M, Kelso H, Henderson DA, McKendrick KG. The effects of surface temperature on the gas-liquid interfacial reaction dynamics of O(3P)+squalane. J Chem Phys 2005; 122:024712. [PMID: 15638619 DOI: 10.1063/1.1835268] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
OH/OD product state distributions arising from the reaction of gas-phase O(3P) atoms at the surface of the liquid hydrocarbon squalane C30H62/C30D62 have been measured. The O(3P) atoms were generated by 355 nm laser photolysis of NO2 at a low pressure above the continually refreshed liquid. It has been shown unambiguously that the hydroxyl radicals detected by laser-induced fluorescence originate from the squalane surface. The gas-phase OH/OD rotational populations are found to be partially sensitive to the liquid temperature, but do not adapt to it completely. In addition, rotational temperatures for OH/OD(v'=1) are consistently colder (by 34+/-5 K) than those for OH/OD(v'=0). This is reminiscent of, but less pronounced than, a similar effect in the well-studied homogeneous gas-phase reaction of O(3P) with smaller hydrocarbons. We conclude that the rotational distributions are composed of two different components. One originates from a direct abstraction mechanism with product characteristics similar to those in the gas phase. The other is a trapping-desorption process yielding a thermal, Boltzmann-like distribution close to the surface temperature. This conclusion is consistent with that reached previously from independent measurements of OH product velocity distributions in complementary molecular-beam scattering experiments. It is further supported by the temporal profiles of OH/OD laser-induced fluorescence signals as a function of distance from the surface observed in the current experiments. The vibrational branching ratios for (v'=1)/(v'=0) for OH and OD have been found to be (0.07+/-0.02) and (0.30+/-0.10), respectively. The detection of vibrationally excited hydroxyl radicals suggests that secondary and/or tertiary hydrogen atoms may be accessible to the attacking oxygen atoms.
Collapse
Affiliation(s)
- Sven P K Köhler
- School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom
| | | | | | | | | |
Collapse
|
25
|
Stubbs JM, Potoff JJ, Siepmann JI. Transferable Potentials for Phase Equilibria. 6. United-Atom Description for Ethers, Glycols, Ketones, and Aldehydes. J Phys Chem B 2004. [DOI: 10.1021/jp049459w] [Citation(s) in RCA: 362] [Impact Index Per Article: 18.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- John M. Stubbs
- Departments of Chemistry and of Chemical Engineering and Material Science, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455-0431, Department of Chemical Engineering and Materials Science, Wayne State University, 5050 Anthony Wayne Drive, Detroit, Michigan 48202-3902
| | - Jeffrey J. Potoff
- Departments of Chemistry and of Chemical Engineering and Material Science, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455-0431, Department of Chemical Engineering and Materials Science, Wayne State University, 5050 Anthony Wayne Drive, Detroit, Michigan 48202-3902
| | - J. Ilja Siepmann
- Departments of Chemistry and of Chemical Engineering and Material Science, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455-0431, Department of Chemical Engineering and Materials Science, Wayne State University, 5050 Anthony Wayne Drive, Detroit, Michigan 48202-3902
| |
Collapse
|
26
|
Abstract
The potentiality of capillary gas chromatography (GC) as a means for research on solubility phenomena is focused. Basic thermodynamic information can be obtained in a simple and direct way from this technique relying on few parameters with their associated errors tightly controlled. An unexplored field of solvation phenomenology inaccessible to other techniques is revealed by the accuracy of capillary GC, provided that relevant chromatographic variables are utilized and an adequate treatment of the experimental information performed. The present article reviews different approaches for the attainment of basic thermodynamic information through capillary GC. Some traditional concepts on the treatment of chromatographic data for physicochemical measurement are questioned. Applications of the technique to research on solubility phenomena are depicted.
Collapse
Affiliation(s)
- Francisco Rex González
- Div. Química Analítica, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, 47 y 115, 1900 La Plata, Argentina.
| |
Collapse
|
27
|
Wick CD, Siepmann JI, Schure MR. Simulation Studies on the Effects of Mobile-Phase Modification on Partitioning in Liquid Chromatography. Anal Chem 2004; 76:2886-92. [PMID: 15144201 DOI: 10.1021/ac0352225] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Various driving forces have been suggested to explain retention and selectivity in reversed-phase liquid chromatography (RPLC). To provide molecular-level information on the retention mechanism in RPLC, configurational-bias Monte Carlo simulations in the Gibbs ensemble were carried out for model systems consisting of three phases: an n-hexadecane retentive phase, a mobile phase with varying water-methanol composition, and a helium vapor phase as reference state. Liquid n-hexadecane functions as a model of a hydrophobic stationary phase, and a wealth of experimental data exists for this system. Gibbs free energies for solute transfers from gas to retentive phase, from gas to mobile phase, and from mobile to retentive phase were determined for a series of short linear alkanes and primary alcohols. Although the magnitude of the incremental Gibbs free energy of transfer for a methylene segment is always larger for the gas- to retentive-phase transfer than the gas- to mobile-phase transfer, it is found that the partitioning of alkanes and alkyl tail groups is mostly affected by the changes in the aqueous mobile phase that occur when methanol modifiers are added. In contrast, the partitioning of the alcohol headgroup is sensitive to changes in both the n-hexadecane and the mobile phases. In particular, it is found that hydrogen-bonded aggregates of methanol are present in the n-hexadecane phase for higher methanol concentrations in the mobile phase. These aggregates strongly increase alcohol partitioning into the retentive phase. The simulation data clearly demonstrate that due to modification of the retentive-phase hydrocarbons by solvent components, neither the solvophobic theory of RPLC, advocated by Horvath and co-workers, nor the lipophilic theory of RPLC, advocated by Carr and co-workers, can adequately describe the separation mechanism of the hexadecane model system of a retentive phase studied here nor the more complex situation present in actual RPLC systems.
Collapse
Affiliation(s)
- Collin D Wick
- Department of Chemistry and of Chemical Engineering and Materials Science, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455-0431, USA
| | | | | |
Collapse
|