Structure and Dynamics of Water Adsorbed in Carbon Nanotubes: A Joint Neutron-Scattering and Molecular-Dynamics Study

2004 ◽  
Vol 840 ◽  
Author(s):  
Nicolas R. de Souza ◽  
Alexander I. Kolesnikov ◽  
Chun-Keung Loong ◽  
Alexander P. Moravsky ◽  
Raouf O. Loutfy ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Hydrogen Bond ◽  
Freezing Point ◽  
Mean Square Displacement ◽  
Anomalous Behavior ◽  
Bulk Water ◽  
Confined Water ◽  
Hydrogen Atoms ◽  
Spatial And Temporal Scales ◽  
Wide Range

ABSTRACTThe advent of nanocarbons, from single- and multiple-walled nanotubes to nanohorns, avails model studies of confined molecules on the nanoscale. Water encapsulated inside the quasi-one-dimensional channels of these materials is expected to exhibit anomalous behavior due to the unique geometry of nanotubes and the weak interaction between the water molecules and the carbon atoms. We have employed neutron small-to-wide angle diffraction, quasielastic and inelastic scattering in conjunction with molecular-dynamics simulations to characterize the structures and dynamics of water adsorbed in open-ended single- and double-walled nanotubes over a wide range of spatial and temporal scales. We find that a square-ice sheet wrapped next to the inner nanotube wall and a water chain in the interior are the key structural elements of nanotube-confined water/ice. This configuration results in a hydrogen-bond connectivity that markedly differs from that in bulk water. This significantly softened hydrogen-bond network manifests in strong energy shifts of the observed and simulated inter- and intra-molecular vibrations. The very large mean-square displacement of hydrogen atoms observed experimentally and the strong anharmonicity inferred from simulations explain the fluid-like behavior at temperatures far below the freezing point of normal water.

scholarly journals Dynamic Properties of Water Confined in Graphene-Based Membrane: A Classical Molecular Dynamics Simulation Study

Membranes ◽  
2019 ◽  
Vol 9 (12) ◽  
pp. 165 ◽  
Author(s):  
One-Sun Lee
Keyword(s):  
Molecular Dynamics ◽  
Hydrogen Bond ◽  
Free Energy ◽  
Graphene Sheets ◽  
Water Molecules ◽  
Energy Profile ◽  
Confined Water ◽  
Graphene Surface ◽  
Dynamics Simulations ◽  
Density Of Water

We performed molecular dynamics simulations of water molecules inside a hydrophobic membrane composed of stacked graphene sheets. By decreasing the density of water molecules inside the membrane, we observed that water molecules form a droplet through a hydrogen bond with each other in the hydrophobic environment that stacked graphene sheets create. We found that the water droplet translates as a whole body rather than a dissipate. The translational diffusion coefficient along the graphene surface increases as the number of water molecules in the droplet decreases, because the bigger water droplet has a stronger van der Waals interaction with the graphene surface that hampers the translational motion. We also observed a longer hydrogen bond lifetime as the density of water decreased, because the hydrophobic environment limits the libration motion of the water molecules. We also calculated the reorientational correlation time of the water molecules, and we found that the rotational motion of confined water inside the membrane is anisotropic and the reorientational correlation time of confined water is slower than that of bulk water. In addition, we employed steered molecular dynamics simulations for guiding the target molecule, and measured the free energy profile of water and ion penetration through the interstice between graphene sheets. The free energy profile of penetration revealed that the optimum interlayer distance for desalination is ~10 Å, where the minimum distance for water penetration is 7 Å. With a 7 Å interlayer distance between the graphene sheets, water molecules are stabilized inside the interlayer space because of the van der Waals interaction with the graphene sheets where sodium and chloride ions suffer from a 3–8 kcal/mol energy barrier for penetration. We believe that our simulation results would be a significant contribution for designing a new graphene-based membrane for desalination.

scholarly journals The Anomalous Behavior of Thermodynamic Parameters in the Three Widom Deltas of Carbon Dioxide-Ethanol Mixture

2021 ◽  
Vol 22 (18) ◽  
pp. 9813
Author(s):  
Evgenii Igorevich Mareev ◽  
Alexander Petrovich Sviridov ◽  
Vyacheslav Mihailovich Gordienko
Keyword(s):  
Carbon Dioxide ◽  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Thermodynamic Parameters ◽  
Molar Fraction ◽  
Anomalous Behavior ◽  
Density Fluctuations ◽  
Ethanol Mixture ◽  
The Third ◽  
Wide Range

Using molecular dynamics, we demonstrated that in the mixture of carbon dioxide and ethanol (25% molar fraction) there are three pronounced regions on the p-T diagram characterized by not only high-density fluctuations but also anomalous behavior of thermodynamic parameters. The regions are interpreted as Widom deltas. The regions were identified as a result of analyzing the dependences of density, density fluctuations, isobaric thermal conductivity, and clustering of a mixture of carbon dioxide and ethanol in a wide range of pressures and temperatures. Two of the regions correspond to the Widom delta for pure supercritical carbon dioxide and ethanol, while the third region is in the immediate vicinity of the critical point of the binary mixture. The origin of these Widom deltas is a result of the large mixed linear clusters formation.

scholarly journals Crystalline Hydrogen Bond of Water Molecules Confined in a Metal-Organic Framework

2021 ◽  
Author(s):  
Jinhee Bae ◽  
Sun Ho Park ◽  
Dohyun Moon ◽  
Nak Cheon Jeong
Keyword(s):  
Hydrogen Bond ◽  
Metal Organic Framework ◽  
Bulk Water ◽  
Coordination Bond ◽  
Ex Situ ◽  
Water Molecules ◽  
Confined Water ◽  
Metal Organic ◽  
Cu Bonding ◽  
Organic Framework

Abstract Hydrogen bond (H-bond) of water molecules confined in nanopores is of particular interest because it is expected to exhibit chemical features different from bulk water molecules due to its interaction with the wall lining the pores. Herein, we show a crystalline behavior of hydrogen-bonded water molecules residing in the nanocages of a paddlewheel metal-organic framework, providing in situ and ex situ synchrotron single-crystal X-ray diffraction and Raman spectroscopy studies. The crystalline H-bond is demonstrated by proving the vibrational chain connectivity arising between hydrogen bonding and paddlewheel Cu−Cu bonding in sequentially connected Cu–Cu⋅⋅⋅⋅⋅coordinating H2O⋅⋅⋅⋅⋅H-bonded H2O and proving the spatial ordering of H-bonded water molecules at room temperature, where they are anticipated to be disordered with a high degree of freedom in their molecular motions. Additionally, we show a substantial distortion of the paddlewheel Cu2+ centers that arises simultaneously with water coordination. Also, we suggest the dynamic coordination bond character of the H-bond of the confined water molecules, by which an H-bond transitions to a coordination bond at the Cu2+ center instantaneously after dissociating a previously coordinated water molecule.

Molecular Dynamics Investigation of Water Behavior Through Nanopores

2020 ◽  
Author(s):  
Kimia Montazeri ◽  
Penghui Cao ◽  
Yoonjin Won
Keyword(s):  
Molecular Dynamics ◽  
Bulk Water ◽  
Energy Storage And Conversion ◽  
Water Molecules ◽  
Transport Mechanisms ◽  
Confined Water ◽  
Nanoscale Transport ◽  
Wetting Properties ◽  
Velocity Autocorrelation ◽  
Water Behavior

Abstract The transport of fluids through nanoscale pores, channels, and membranes has been of great importance in our daily life. Nanoscale transport is relevant to many applications such as agriculture, energy and environmental fields. Considering these applications, it is important to characterize detailed mechanisms of liquid transport through nanoscale defects and pores on surfaces. Such characterization requires a detailed understanding of the deviation of water behavior and its transport mechanisms in nanoscale from bulk water. Molecular dynamics provide proper means to understand the dynamics and mechanisms of motions of water molecules confined in ultra-small spaces. This work examines the water transport through an individual pore which has a nanoscale dimensions ranging from 1.0 to 1.8 nm from molecular dynamics perspective. The effects of the nanopore dimensions as well as the surface wetting properties on the behavior of confined water are studied. The translational and rotational dynamics of water molecules are characterized by examining velocity autocorrelation functions and the calculation of the density of states, which supports the presence of unusual, solid-like behaviors of water molecules. A good understanding of the transport mechanisms and their origins are crucial to address common challenges in many engineering applications such as energy storage and conversion and could pave the way towards more efficient water-energy systems.

scholarly journals Effect of Size and Temperature on Water Dynamics inside Carbon Nano-Tubes Studied by Molecular Dynamics Simulation

Molecules ◽  
2021 ◽  
Vol 26 (20) ◽  
pp. 6175
Author(s):  
Amit Srivastava ◽  
Jamal Hassan ◽  
Dirar Homouz
Keyword(s):  
Molecular Dynamics ◽  
Md Simulations ◽  
Underlying Mechanism ◽  
Bulk Water ◽  
Water Dynamics ◽  
Dynamics Simulation ◽  
Water Molecules ◽  
Wide Range ◽  
Carbon Nano Tubes ◽  
20 Nm

Water transport inside carbon nano-tubes (CNTs) has attracted considerable attention due to its nano-fluidic properties, its importance in nonporous systems, and the wide range of applications in membrane desalination and biological medicine. Recent studies show an enhancement of water diffusion inside nano-channels depending on the size of the nano-confinement. However, the underlying mechanism of this enhancement is not well understood yet. In this study, we performed Molecular Dynamics (MD) simulations to study water flow inside CNT systems. The length of CNTs considered in this study is 20 nm, but their diameters vary from 1 to 10 nm. The simulations are conducted at temperatures ranging from 260 K to 320 K. We observe that water molecules are arranged into coaxial water tubular sheets. The number of these tubular sheets depends on the CNT size. Further analysis reveals that the diffusion of water molecules along the CNT axis deviates from the Arrhenius temperature dependence. The non-Arrhenius relationship results from a fragile liquid-like water component persisting at low temperatures with fragility higher than that of the bulk water.

scholarly journals Current Understanding of Water Properties inside Carbon Nanotubes

Nanomaterials ◽  
2022 ◽  
Vol 12 (1) ◽  
pp. 174
Author(s):  
Aris Chatzichristos ◽  
Jamal Hassan
Keyword(s):  
Carbon Nanotubes ◽  
Molecular Dynamics ◽  
Nuclear Magnetic Resonance ◽  
Confined Water ◽  
Scientific Interest ◽  
Open Problems ◽  
Vast Array ◽  
Future Studies ◽  
Nanoconfined Water ◽  
Wide Range

Confined water inside carbon nanotubes (CNTs) has attracted a lot of attention in recent years, amassing as a result a very large number of dedicated studies, both theoretical and experimental. This exceptional scientific interest can be understood in terms of the exotic properties of nanoconfined water, as well as the vast array of possible applications of CNTs in a wide range of fields stretching from geology to medicine and biology. This review presents an overreaching narrative of the properties of water in CNTs, based mostly on results from systematic nuclear magnetic resonance (NMR) and molecular dynamics (MD) studies, which together allow the untangling and explanation of many seemingly contradictory results present in the literature. Further, we identify still-debatable issues and open problems, as well as avenues for future studies, both theoretical and experimental.

Anomalous behavior of confined-supercooled water near the bulk water hypothetical 2nd Critical Temperature

2003 ◽  
Vol 790 ◽  
Author(s):  
F. Mansour ◽  
R. M. Dimeo ◽  
H. Peemoeller
Keyword(s):  
Molecular Dynamics ◽  
Glass Transition ◽  
Critical Temperature ◽  
Inelastic Neutron Scattering ◽  
Supercooled Water ◽  
Inelastic Neutron ◽  
Anomalous Behavior ◽  
Bulk Water ◽  
Scattering Measurements ◽  
Mcm 41

ABSTRACTHigh resolution inelastic neutron scattering measurements of the molecular dynamics of deeply supercooled water confined to a porous host, MCM-41 are reported. Results obtained near the critical temperature of water are discussed. Anomalous behavior near and below the glass transition temperature is also presented and discussed. Results are compared to those from earlier studies on supercooled water.

Constant pH Molecular Dynamics Reveals How Proton Release Drives the Conformational Transition of a Transmembrane Efflux Pump

2017 ◽  
Author(s):  
Jana Shen ◽  
Zhi Yue ◽  
Helen Zgurskaya ◽  
Wei Chen
Keyword(s):  
Molecular Dynamics ◽  
Conformational Changes ◽  
Transmembrane Domain ◽  
Conformational Transition ◽  
Conformational Dynamics ◽  
Proton Release ◽  
Intrinsic Resistance ◽  
Constant Ph ◽  
Wide Range ◽  
Constant Ph Molecular Dynamics

AcrB is the inner-membrane transporter of E. coli AcrAB-TolC tripartite efflux complex, which plays a major role in the intrinsic resistance to clinically important antibiotics. AcrB pumps a wide range of toxic substrates by utilizing the proton gradient between periplasm and cytoplasm. Crystal structures of AcrB revealed three distinct conformational states of the transport cycle, substrate access, binding and extrusion, or loose (L), tight (T) and open (O) states. However, the specific residue(s) responsible for proton binding/release and the mechanism of proton-coupled conformational cycling remain controversial. Here we use the newly developed membrane hybrid-solvent continuous constant pH molecular dynamics technique to explore the protonation states and conformational dynamics of the transmembrane domain of AcrB. Simulations show that both Asp407 and Asp408 are deprotonated in the L/T states, while only Asp408 is protonated in the O state. Remarkably, release of a proton from Asp408 in the O state results in large conformational changes, such as the lateral and vertical movement of transmembrane helices as well as the salt-bridge formation between Asp408 and Lys940 and other sidechain rearrangements among essential residues.Consistent with the crystallographic differences between the O and L protomers, simulations offer dynamic details of how proton release drives the O-to-L transition in AcrB and address the controversy regarding the proton/drug stoichiometry. This work offers a significant step towards characterizing the complete cycle of proton-coupled drug transport in AcrB and further validates the membrane hybrid-solvent CpHMD technique for studies of proton-coupled transmembrane proteins which are currently poorly understood. <p><br></p>

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