1
|
Simulations of water at the interface with hydrophilic self-assembled monolayers. Biointerphases 2010; 3:FC13-22. [PMID: 20408690 DOI: 10.1116/1.2977751] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Simulations of water at hydrophilic self-assembled monolayer (SAM) surfaces are especially relevant for biological interfaces. Well-defined, atomically smooth surfaces that can be continuously varied are possible with SAMs. These characteristics enable more accurate measurements than many other surfaces with the added advantage of tailoring the surface to treat specific chemical groups. A fundamental question is how solid surfaces affect the structure and dynamics of water. Measurements of the structure and dynamics of water at solid surfaces have improved significantly, but there remain differences among the experiments. In this article, the authors review simulations of water at the interface with hydrophilic SAMs. These simulations find that while the interfacial water molecules are slower than the bulk water molecules, the interfacial dynamics remains that of a liquid. A major biological application of SAMs is for making coatings resistant to protein adsorption. SAMs terminated with ethylene glycol monomers have proven to be excellent at resisting protein adsorption. Understanding the mechanisms behind this resistance remains an unresolved issue. Recent simulations suggest a new perspective of the role of interfacial water and the inseparable interplay between the SAM and the water.
Collapse
|
2
|
Winter N, Vieceli J, Benjamin I. Hydrogen-Bond Structure and Dynamics at the Interface between Water and Carboxylic Acid-Functionalized Self-Assembled Monolayers. J Phys Chem B 2007; 112:227-31. [PMID: 17672497 DOI: 10.1021/jp0734833] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Molecular dynamics computer simulations are used to study hydrogen-bond structure and dynamics at the interface between water and carboxylic acid-functionalized self-assembled monolayers (CAFSAMs). Water-water, water-CAFSAM, and internal CAFSAM hydrogen bonds are examined. Roughly half of all adjacent carboxylic acid-terminated hydrocarbon chains are hydrogen-bonded to one another. This is consistent with experimental results reflecting two pKa values for CAFSAMs. Hydrogen-bond dynamics are expressed in terms of hydrogen-bond population autocorrelation functions and are found to be nonexponential. The water-water hydrogen-bond dynamics are slower at the interface than in the bulk, which is similar to what was found at the interface between water and weakly polar liquids such as nitrobenzene. The water-CAFSAM hydrogen bonds are found to be long-lived, on the order of tens of picoseconds. Internal CAFSAM chain-chain hydrogen bonds show almost no relaxation on the simulation time scale.
Collapse
Affiliation(s)
- Nicolas Winter
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, California 95064
| | | | | |
Collapse
|
3
|
Pantano DA, Sonoda MT, Skaf MS, Laria D. Solvation of coumarin 314 at water/air interfaces containing anionic surfactants. I. Low coverage. J Phys Chem B 2007; 109:7365-72. [PMID: 16851843 DOI: 10.1021/jp045687e] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Through the use of molecular dynamics techniques, we analyze equilibrium and dynamical aspects of the solvation of Coumarin 314 adsorbed at water/air interfaces in the presence of sodium dodecyl sulfate surfactant molecules. Three different coverages in the submonolayer regime were considered, 500, 250, and 100 A(2)/SDS molecule. The surfactant promotes two well-differentiated solvation environments, which can be clearly distinguished in terms of their structures for the largest surfactant coverage considered. The first one is characterized by the probe lying adjacent or exterior to two-dimensional spatial domains formed by clustered surfactant molecules. A second type of solvation environment is found in which the coumarin appears embedded within compact surfactant domains. Equilibrium and dynamical aspects of the interfacial orientation of the probe are investigated. Our results show a gradual transition from parallel to perpendicular dipolar alignment of the probe with respect to the interface as the concentration of surfactant rho(s) increases. The presence of the surfactant leads to an increase in the roughness and in the characteristic width of the water/air interface. These modifications are also manifested by the decorrelation times for the probe reorientational dynamics, which become progressively slower with rho(s) in both solvation states, although much more pronounced for the embedded ones. The dynamical characteristics of the solvation responses of the charged interfaces are also analyzed, and the implications of our findings to the interpretation of available experimental measurements are discussed.
Collapse
Affiliation(s)
- Diego A Pantano
- Departamento de Química Inorganica, Analítica y Química-Física e INQUIMAE, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellón II, 1428 Buenos Aires, Argentina
| | | | | | | |
Collapse
|
4
|
Nguyen KT, Shang X, Eisenthal KB. Molecular Rotation at Negatively Charged Surfactant/Aqueous Interfaces. J Phys Chem B 2006; 110:19788-92. [PMID: 17020362 DOI: 10.1021/jp058171j] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The effect of charge on the rotational dynamics of the molecular probe coumarin 314 (C314) at air/water interfaces covered with the negatively charged surfactant sodium dodecyl sulfate (SDS) was investigated using femtosecond time-resolved second harmonic spectroscopy. The out-of-plane orientational time constant at the highest SDS surface coverage of 100 A2 per molecule is 383 +/- 9 ps. The rotational dynamics is slower than at the air/water interface where the out-of-plane reorientational time constant is 336 +/- 6 ps. At the air/water interface the rotational dynamics is over three times slower than the bulk orientational diffusion time of 100 ps. The relatively small effect of the surfactant charge density on the C314 rotation time constant is surprising, considering the marked dependence of the C314 orientation, spectra, and surfactant phase diagram on surfactant density.
Collapse
Affiliation(s)
- Kim T Nguyen
- Department of Chemistry, Columbia University, New York, New York 10027, USA
| | | | | |
Collapse
|
5
|
Affiliation(s)
- Ilan Benjamin
- Department of Chemistry, University of California, Santa Cruz, California 95064, USA
| |
Collapse
|
6
|
Chorny I, Benjamin I. Hydration Shell Exchange Dynamics during Ion Transfer Across the Liquid/Liquid Interface. J Phys Chem B 2005; 109:16455-62. [PMID: 16853092 DOI: 10.1021/jp051836x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
We examine using molecular dynamics simulations the rate and mechanism of water molecules exchange around the Li(+) and Na(+) ions during ion transfer across the interface between water and nitrobenzene. As the ions are transferred from the water to the organic phase, they keep their first hydration shell and an incomplete second shell. The rate of water exchange between the first shell and the rest of the interfacial water molecule decreases during the transfer, which is consistent with an increase in the barrier along the ion-water potential of mean force. While in bulk water the exchange of water molecules around the Li(+) follows an associative (A) or associative interchange (I(a)) type mechanism, the fraction of exchange events of type A increases at the interface. In contrast, while in bulk water the exchange of water molecules around the six coordinated Na(+) hydrated species mainly follows a dissociative mechanism, the situation at the interface involves an equilibrium interchange between the four- and five-coordinated hydrated ion. Simulation of the reversed process, in which the hydrated Li(+) ion is transferred to the aqueous phase, shows the same general behavior as a function of location from the interface.
Collapse
Affiliation(s)
- Ilya Chorny
- Department of Chemistry, University of California, Santa Cruz, California 95064, USA
| | | |
Collapse
|
7
|
Tamoto Y, Segawa H, Shirota H. Solvation dynamics in aqueous anionic and cationic micelle solutions: sodium alkyl sulfate and alkyltrimethylammonium bromide. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2005; 21:3757-3764. [PMID: 15835934 DOI: 10.1021/la046953i] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Solvation dynamics of the fluorescence probe, coumarin 102, in anionic surfactant, sodium alkyl sulfate (C(n)H(2n+1)SO(4)Na; n = 8, 10, 12, and 14), and cationic surfactant, alkyltrimethylammonium bromide (C(n)H(2n+1)N(CH(3))(3)Br; n = 10, 12, 14, and 16), micelle solutions have been investigated by a picosecond streak camera system. The solvation dynamics in the time range of 10(-10)-10(-8) s is characterized by a biexponential function. The faster solvation time constants are about 110-160 ps for both anionic and cationic micelle solutions, and the slower solvation time constants for sodium alkyl sulfate and alkyltrimethylammonium bromide micelle solutions are about 1.2-2.6 ns and 450-740 ps, respectively. Both the faster and the slower solvation times become slower with longer alkyl chain surfactant micelles. The alkyl-chain-length dependence of the solvation dynamics in both sodium alkyl sulfate and alkyltrimethylammonium bromide micelles can be attributed to the variation of the micellar surface density of the polar headgroup by the change of the alkyl chain length. The slower solvation time constants of sodium alkyl sulfate micelle solutions are about 3.5 times slower than those of alkyltrimethylammonium bromide micelle solutions for the same alkyl-chain-length surfactants. The interaction energies of the geometry optimized mimic clusters (H(2)O-C(2)H(5)SO(4)(-) and H(2)O-C(2)H(5)N(CH(3))(3)(+)) have been estimated by the density functional theory calculations to understand the interaction strengths between water and alkyl sulfate and alkyltrimethylammonium headgroups. The difference of the slower solvation time constants between sodium alkyl sulfate and alkyltrimethylammonium bromide micelle solutions arises likely from their different specific interactions.
Collapse
Affiliation(s)
- Yushi Tamoto
- Department of Applied Chemistry, Graduate School of Engineering, and Department of General Systems Sciences, Graduate School of Arts & Sciences, University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan
| | | | | |
Collapse
|
8
|
Faeder J, Ladanyi BM. Solvation Dynamics in Reverse Micelles: The Role of Headgroup−Solute Interactions. J Phys Chem B 2005; 109:6732-40. [PMID: 16851757 DOI: 10.1021/jp045202m] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
We present molecular dynamics simulation results for solvation dynamics in the water pool of anionic-surfactant reverse micelles (RMs) of varying water content, w(0). The model RMs are designed to represent water/aerosol-OT/oil systems, where aerosol-OT is the common name for sodium bis(2-ethylhexyl)sulfosuccinate. To determine the effects of chromophore-headgroup interactions on solvation dynamics, we compare the results for charge localization in model ionic diatomic chromophores that differ only in charge sign. Electronic excitation in both cases is modeled as charge localization on one of the solute sites. We find dramatic differences in the solvation responses for anionic and cationic chromophores. Solvation dynamics for the cationic chromophore are considerably slower and more strongly w(0)-dependent than those for the anionic chromophore. Further analysis indicates that the difference in the responses can be ascribed in part to the different initial locations of the two chromophores relative to the surfactant interface. In addition, slow motion of the cationic chromophore relative to the interface is the main contributor to the longer-time decay of the solvation response to charge localization in this case.
Collapse
Affiliation(s)
- James Faeder
- Theoretical Biology and Biophysics Group, MS K710, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | | |
Collapse
|
9
|
Martins LR, Skaf MS, Ladanyi BM. Solvation Dynamics at the Water/Zirconia Interface: Molecular Dynamics Simulations. J Phys Chem B 2004. [DOI: 10.1021/jp0470896] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Lucimara R. Martins
- Instituto de Química, Universidade Estadual de Campinas, Cx. P. 6154, Campinas-SP 13083-970, Brazil
| | - Munir S. Skaf
- Instituto de Química, Universidade Estadual de Campinas, Cx. P. 6154, Campinas-SP 13083-970, Brazil
| | - Branka M. Ladanyi
- Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523
| |
Collapse
|
10
|
Esenturk O, Walker RA. Surface Structure at Hexadecane and Halo-hexadecane Liquid/Vapor Interfaces. J Phys Chem B 2004. [DOI: 10.1021/jp047984p] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Okan Esenturk
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742
| | - Robert A. Walker
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742
| |
Collapse
|
11
|
Shirota H, Tamoto Y, Segawa H. Dynamic Fluorescence Probing of the Microenvironment of Sodium Dodecyl Sulfate Micelle Solutions: Surfactant Concentration Dependence and Solvent Isotope Effect. J Phys Chem A 2004. [DOI: 10.1021/jp035861j] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Hideaki Shirota
- Department of General Systems Sciences, Graduate School of Arts & Sciences, University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan, and Department of Applied Chemistry, Graduate School of Engineering, University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan
| | - Yushi Tamoto
- Department of General Systems Sciences, Graduate School of Arts & Sciences, University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan, and Department of Applied Chemistry, Graduate School of Engineering, University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan
| | - Hiroshi Segawa
- Department of General Systems Sciences, Graduate School of Arts & Sciences, University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan, and Department of Applied Chemistry, Graduate School of Engineering, University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan
| |
Collapse
|
12
|
|
13
|
Vieceli J, Benjamin I. Electron transfer at the interface between water and self-assembled monolayers. Chem Phys Lett 2004. [DOI: 10.1016/j.cplett.2003.12.050] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
|