Flux Of Water Molecules Research Articles

PIPs from Fragaria vesca: A structural analysis of native and mutated protein

Aquaporins are an ancient family of membrane channel proteins present in all eukaryotes and most prokaryotes, and apart from water, allow the transport of neutral solutes and organic compounds through the pore. These proteins are essential role differentially expressed during ripening in Fragaria vesca fruits. Fv PIP2-1a is intensively expressed in fruits, inclusive several other proteins member are differentially expressed in fruit but also in other plant tissues. Phylogenetic analysis shows that Fv PIP2-1a grouped with other Fragaria proteins and far apart from other F. vesca PIP proteins. A structural model for Fv PIP2-1a protein was built by comparative modelling methodology, which was validated and refined by molecular dynamics simulation. Fv PIP2-1a structure consists of 6 transmembrane regions and two NPA domains. The mobilization of water was analyzed by molecular docking simulations in wildtype and two mutants. Interestingly, the mutant FvPIP2-1a_H214G allowed the prediction of an increment in the flux of water molecules. On contrary, structural analysis predicted that H214E mutation blocked passage of water associated to constriction of the pore.

Probing ice growth from vapor phase: A molecular dynamics simulation approach

We demonstrate a molecular dynamics simulation approach that can be used to investigate ice growth from water vapor. Using this approach, we explore ice/vapor interfacial systems focusing on the behavior of the quasi-liquid layer (QLL) which forms on the ice surface near its melting point. The dependence of the QLL on temperature, ice face and the flux of gas-phase water molecules are examined. We find that the thickness of the QLL increases by increasing temperature, and that the prismatic QLL is thinner than the QLL on the basal face. Both observations are consistent with previous investigations. In addition, variation in the gas densities show that an increase in the flux of water molecules in the gas vapor phase, associated with higher growth rates, results in an increased thickness of the QLL.

Water mass flow rate in a finite SWCNT under electric charge: A molecular dynamic simulation

In this paper, behavior of water flow in single-walled carbon nanotube (SWCNT) under electric charge is investigated using molecular dynamics simulation. It is shown that electric charging of SWCNT causes water flow to exhibit surprising behavior. Among water flow parameters, flow rate or flux of water molecules is of special interest. The two governing phenomena affecting flow rate in a SWCNT are resistance along the nanotube and resistance to flow at its entrance. In present study, effect of electric charging of SWCNT's carbon molecules on these two phenomena is studied in detail in SWCNTs (5, 10) with 3nm, 5nm, and 7nm lengths. Charge magnitudes between zero to 1.0e/atom are implemented along different lengths of nanotube. Charges are applied either constantly or stepwise. Based on the analysis of numerical results obtained in this paper, it is concluded that electric charging can be used to manipulate these two phenomena and therefore control the rate of water flow in a SWCNT very effectively.

Modification of the shrinking core model for hydrogen generation by reaction of aluminum particles with water

Abstract The assumptions of the traditional shrinking core model cannot be adopted for the core–shell structure formed during the reaction of aluminum particles and water. The model assumes that diffusion coefficient is constant and the particle size is unchanged during the reaction. This study modifies the traditional shrinking core model by including the effect of the growing size of the particles and the changes in porosity of the hydroxide layer on hydrogen generation. The modified model is fitted to the experimental data and the results are compared to that of the traditional model. The flux of water molecules in the hydroxide layer is calculated using the parameters obtained by the hydrogen generation data.

Molecular Dynamics Simulation of the Desalination of Sea Water by a Forward Osmosis Membrane Containing Charged Carbon Nanotubes

Spurred by traditional membrane science in which a charged membrane can improve separation efficiency,a forward osmosis membrane containing charged"armchair-type"(8,8)carbon nanotubes(CNTs)was developed and the transport phenomena of water molecules in this membrane were investigated.In the simulation,0.5 mo·lL -1 NaCl was chosen to mimic seawater,and 1 mo·lL -1 MgCl 2 was chosen as the draw solution.The effects of electric charge on the density distribution,diffusion of water molecules,and the water flux of the membrane were investigated in detail.Modifying the CNT membrane by charge significantly changes the density distribution,diffusion,and flux of water molecules. The membrane containing CNTs modified by-0.3e can achieve the highest water flux of those developed.

Evaporation of two solution droplets and a droplet located near a flat liquid surface

The mutual influence of two moderate-sized droplets of a dilute nonvolatile substance solution on the processes of their evaporation or condensation is theoretically analyzed under the assumption of a uniform concentration distribution inside the droplets. The conditions for the applicability of this approach are revealed. The evaporation or condensation of a droplet near a flat liquid surface is considered as a limiting case. The fluxes of water molecules to and from the surface of aqueous glycerol solution droplets occurring in air are numerically estimated depending on the droplet radii, distances between their surfaces, and air humidity. Analogous estimates are obtained for an aqueous glycerol solution droplet growing near a flat water surface.

Electrostatics of aquaporin and aquaglyceroporin channels correlates with their transport selectivity

Aquaporins are homotetrameric channel proteins, which allow the diffusion of water and small solutes across biological membranes. According to their transport function, aquaporins can be divided into "orthodox aquaporins", which allow the flux of water molecules only, and "aquaglyceroporins", which facilitate the diffusion of glycerol and other small solutes in addition to water. The contribution of individual residues in the pore to the selectivity of orthodox aquaporins and aquaglyceroporins is not yet fully understood. To gain insights into aquaporin selectivity, we focused on the sequence variation and electrostatics of their channels. The continuum Poisson-Boltzmann electrostatic potential along the channel was calculated and compared for ten three-dimensional-structures which are representatives of different aquaporin subfamilies, and a panel of functionally characterized mutants, for which high-accuracy three-dimensional-models could be derived. Interestingly, specific electrostatic profiles associated with the main selectivity to water or glycerol could be identified. In particular: (i) orthodox aquaporins showed a distinctive electrostatic potential maximum at the periplasmic side of the channel around the aromatic/Arg (ar/R) constriction site; (ii) aquaporin-0 (AQP0), a mammalian aquaporin with considerably low water permeability, had an additional deep minimum at the cytoplasmic side; (iii) aquaglyceroporins showed a rather flat potential all along the channel; and (iv) the bifunctional protozoan PfAQP had an unusual all negative profile. Evaluation of electrostatics of the mutants, along with a thorough sequence analysis of the aquaporin pore-lining residues, illuminated the contribution of specific residues to the electrostatics of the channels and possibly to their selectivity.

Molecular Dynamics Simulations of Hydrophilic Pores in Lipid Bilayers

Hydrophilic pores are formed in peptide free lipid bilayers under mechanical stress. It has been proposed that the transport of ionic species across such membranes is largely determined by the existence of such meta-stable hydrophilic pores. To study the properties of these structures and understand the mechanism by which pore expansion leads to membrane rupture, a series of molecular dynamics simulations of a dipalmitoylphosphatidylcholine (DPPC) bilayer have been conducted. The system was simulated in two different states; first, as a bilayer containing a meta-stable pore and second, as an equilibrated bilayer without a pore. Surface tension in both cases was applied to study the formation and stability of hydrophilic pores inside the bilayers. It is observed that below a critical threshold tension of ∼38 mN/m the pores are stabilized. The minimum radius at which a pore can be stabilized is 0.7 nm. Based on the critical threshold tension the line tension of the bilayer was estimated to be ∼3 × 10 −11 N, in good agreement with experimental measurements. The flux of water molecules through these stabilized pores was analyzed, and the structure and size of the pores characterized. When the lateral pressure exceeds the threshold tension, the pores become unstable and start to expand causing the rupture of the membrane. In the simulations the mechanical threshold tension necessary to cause rupture of the membrane on a nanosecond timescale is much higher in the case of the equilibrated bilayers, as compared with membranes containing preexisting pores.