Water dynamics in large and small reverse micelles: From two ensembles to collective behavior

Moilanen, David E.; Fenn, Emily E.; Wong, Daryl B.; Fayer, M. D.

doi:10.1063/1.3159779

Cited by 177 publications

(369 citation statements)

References 55 publications

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“…It has been shown to provide a good fit of the measured anisotropy decays for water in reverse micelles of diameter >4 nm; for smaller diameters, the core is no longer bulk-like and its contribution progressively disappears with decreasing size. 42 A similar behavior was observed in simulations of water confined in slit pores. 35 In the context of water OH orientational dynamics, the core/shell model assumes that molecules in the interfacial layer -within a distance of the pore surface -have a modified correlation function, C shell 2 (t), while molecules in the pore interior reorient according to C core 2 (t).…”

Section: Test Of a Two-state Modelsupporting

confidence: 73%

Reorientation dynamics of nanoconfined water: Power-law decay, hydrogen-bond jumps, and test of a two-state model

Laage

Thompson

2012

The Journal of Chemical Physics

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The reorientation dynamics of water confined within nanoscale, hydrophilic silica pores are investigated using molecular dynamics simulations. The effect of surface hydrogen-bonding and electrostatic interactions are examined by comparing with both a silica pore with no charges (representing hydrophobic confinement) and bulk water. The OH reorientation in water is found to slow significantly in hydrophilic confinement compared to bulk water, and is well-described by a power-law decay extending beyond one nanosecond. In contrast, the dynamics of water in the hydrophobic pore are more modestly affected. A two-state model, commonly used to interpret confined liquid properties, is tested by analysis of the position-dependence of the water dynamics. While the two-state model provides a good fit of the orientational decay, our molecular-level analysis evidences that it relies on an over-simplified picture of water dynamics. In contrast with the two-state model assumptions, the interface dynamics is markedly heterogeneous, especially in the hydrophilic pore and there is no single interfacial state with a common dynamics.

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Section: Test Of a Two-state Modelsupporting

confidence: 73%

Reorientation dynamics of nanoconfined water: Power-law decay, hydrogen-bond jumps, and test of a two-state model

Laage

Thompson

2012

The Journal of Chemical Physics

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“…In addition, ultrafast motions of DMF are suppressed in the pores as shown by the large difference in the homogeneous line widths of the probe when it experiences DMF in the pores vs. the bulk solution ( Table 2). The slowing of DMF dynamics in nanometersized pores is consistent with slowing of dynamics in other nanoscopically confined systems, such as water in small reverse micelles (8,27). There are several molecular dynamics simulations indicating that guest molecules adsorbed in some MOFs experience strong confinement effects (28) and that the adsorbed molecules strongly interact with the organic linkers to potentially enhance ν peak is the peak position of the symmetric stretching mode.…”

supporting

confidence: 67%

Structural dynamics inside a functionalized metal–organic framework probed by ultrafast 2D IR spectroscopy

Nishida

Tamimi

Fei

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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108

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The structural elasticity of metal-organic frameworks (MOFs) is a key property for their functionality. Here, we show that 2D IR spectroscopy with pulse-shaping techniques can probe the ultrafast structural fluctuations of MOFs. 2D IR data, obtained from a vibrational probe attached to the linkers of UiO-66 MOF in low concentration, revealed that the structural fluctuations have time constants of 7 and 670 ps with no solvent. Filling the MOF pores with dimethylformamide (DMF) slows the structural fluctuations by reducing the ability of the MOF to undergo deformations, and the dynamics of the DMF molecules are also greatly restricted. Methodology advances were required to remove the severe light scattering caused by the macroscopic-sized MOF particles, eliminate interfering oscillatory components from the 2D IR data, and address Förster vibrational excitation transfer.2D IR spectroscopy | metal-organic framework | UiO-66 MOF | ultrafast structural fluctuations | solvent confinement effect M etal-organic frameworks (MOFs) are molecular architectures in which metal clusters are connected by organic linkers to yield relatively regular 3D coordination polymers with nanometer-sized pores (1, 2). MOFs have been investigated for a wide variety of chemical applications, such as adsorption of gases (3) and heterogeneous catalysts (4). Among many types of porous materials, MOFs are unique because of their structural elasticity coexisting with a high degree of spatial regularity. In some sense, MOFs are like crystals and polymers. They have relatively regular structures like a crystal, but the metal clusters are joined by organic linkers that, in some systems, produce significant structural mobility. The elasticity of MOFs is intimately related to their physical properties and behavior (5).An important goal for understanding the nature of MOFs and how their chemical composition influences their properties and applications is to develop and apply an experimental method that can measure the ultrafast structural motions of MOFs. The relatively slow motions of the framework occurring in submicrosecond to millisecond scales have been studied by NMR and neutron scattering (6). However, until now, quantitative measurements that can characterize the time dependence of MOF structural motions in ultrafast regimes have not been possible because of the lack of appropriate techniques. Here, we have accomplished the goal by applying ultrafast 2D IR spectroscopy (7) to the study of MOF structural dynamics. 2D IR is akin to 2D NMR, but it operates on the ultrafast timescales necessary to characterize the time dependence of MOF structural motions. In addition, there is the important question of the effects on MOF dynamics when guest molecules fill the MOF nanopores. The guest molecules will affect the structural fluctuations of the framework by interacting with the linkers and the metal units. Furthermore, because of the confinement of guest molecules in MOF nanopores, the dynamics of these molecules are expected to be very different from t...

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“…Computational studies show that there is a $5:5 # A shell of water with altered structure and altered rotational and translational dynamics on the picosecond time scale surrounding carbohydrates [25]. IR spectroscopy of water dynamics in nanometer-size reverse micelles show that approximately half of the water in a 4 nm diameter micelle is ''interfacial'' while the other half is bulk-like [26], implying a 5.6 Å interfacial layer thickness. NMR studies of water adsorbed to porous glass show that 2.5-3 monolayers are essentially in a ''frozen'' amorphous structure even at room temperature, and that this fraction remains amorphous as the sample is cooled to freezing temperatures [27].…”

Section: Prl 110 015703 (2013) P H Y S I C a L R E V I E W L E T T Ementioning

confidence: 99%

Critical Droplet Theory Explains the Glass Formability of Aqueous Solutions

2013

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When pure water is cooled at $10 6 K=s, it forms an amorphous solid (glass) instead of the more familiar crystalline phase. The presence of solutes can reduce this required (or ''critical'') cooling rate by orders of magnitude. Here, we present critical cooling rates for a variety of solutes as a function of concentration and a theoretical framework for understanding these rates. For all solutes tested, the critical cooling rate is an exponential function of concentration. The exponential's characteristic concentration for each solute correlates with the solute's Stokes radius. A modification of critical droplet theory relates the characteristic concentration to the solute radius and the critical nucleation radius of ice in pure water. This simple theory of ice nucleation and glass formability in aqueous solutions has consequences for general glass-forming systems, and in cryobiology, cloud physics, and climate modeling. DOI: 10.1103/PhysRevLett.110.015703 PACS numbers: 64.60.QÀ, 05.40.Àa, 64.70.dg Ice nucleation and growth are of major interest in fields ranging from cryobiology to atmospheric physics. Ice is a key issue in cryopreservation of cells and tissues [1] and in cryocooling of samples for macromolecular crystallography [2,3], where solutes like salts, sugars, alcohols, and polyols can have dramatic effects on ice formation. In atmospheric physics, models of cloud formation are sensitive to the nature of the critical nucleus of ice crystals [4] with implications for climate models [5]. Supercooled water is an interesting system in its own right [6], and the formation of crystalline phases from supercooled solutions is an active area of study [7].Previous experiments have focused on properties such as the melting and glass transition temperatures, and models to explain the data have largely been phenomenological. Similar models have been applied to explain glass formability in a wide variety ofnonaqueous systems. Here, we report measurements of the minimum cooling rates [or ''critical cooling rates'' (CCRs)] required to prevent ice formation in aqueous solutions during cooling to $100 K or below. We show that a surprisingly simple statistical modification to classical thermodynamic nucleation theory provides an excellent account of these data.We studied eight different solutes (see Fig. 1), including a salt (sodium chloride), simple alcohols (methanol, ethanol), sugars (dextrose, trehalose), polyols (glycerol, ethylene glycol), and polyethylene glycol 200 (PEG 200). All are compact and highly soluble and can have large effects on critical cooling rates required for vitrification.The effects of these solutes on ice nucleation were evaluated by measuring the critical cooling rate above which no ice was observed. Below the critical rate, a sample turns opaque on cooling, indicating the formation of polycrystalline ice. As the rate increases, a transition to transparent samples is observed. This optical transition corresponds to a transition in the x-ray diffraction patterns obtained from the cooled sam...

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Water dynamics in large and small reverse micelles: From two ensembles to collective behavior

Cited by 177 publications

References 55 publications

Reorientation dynamics of nanoconfined water: Power-law decay, hydrogen-bond jumps, and test of a two-state model

Reorientation dynamics of nanoconfined water: Power-law decay, hydrogen-bond jumps, and test of a two-state model

Structural dynamics inside a functionalized metal–organic framework probed by ultrafast 2D IR spectroscopy

Critical Droplet Theory Explains the Glass Formability of Aqueous Solutions

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