scholarly journals The energetic barrier to single-file water flow through narrow channels

2021 ◽  
Author(s):  
Juergen Pfeffermann ◽  
Nikolaus Goessweiner-Mohr ◽  
Peter Pohl
Keyword(s):  
Lipid Bilayers ◽  
Degrees Of Freedom ◽  
Water Channel ◽  
Water Channels ◽  
Bulk Water ◽  
State Theory ◽  
Narrow Channels ◽  
Biological Water ◽  
Free Energy Of Activation ◽  
Single File

AbstractVarious nanoscopic channels of roughly equal diameter and length facilitate single-file diffusion at vastly different rates. The underlying variance of the energetic barriers to transport is poorly understood. First, water partitioning into channels so narrow that individual molecules cannot overtake each other incurs an energetic penalty. Corresponding estimates vary widely depending on how the sacrifice of two out of four hydrogen bonds is accounted for. Second, entropy differences between luminal and bulk water may arise: additional degrees of freedom caused by dangling OH-bonds increase entropy. At the same time, long-range dipolar water interactions decrease entropy. Here, we dissect different contributions to Gibbs free energy of activation, ΔG‡, for single-file water transport through narrow channels by analyzing experimental results from water permeability measurements on both bare lipid bilayers and biological water channels that (i) consider unstirred layer effects and (ii) adequately count the channels in reconstitution experiments. First, the functional relationship between water permeabilities and Arrhenius activation energies indicates negligible differences between the entropies of intraluminal water and bulk water. Second, we calculate ΔG‡ from unitary water channel permeabilities using transition state theory. Plotting ΔG‡ as a function of the number of H-bond donating or accepting pore-lining residues results in a 0.1 kcal/mol contribution per residue. The resulting upper limit for partial water dehydration amounts to 2 kcal/mol. In the framework of biomimicry, our analysis provides valuable insights for the design of synthetic water channels. It thus may aid in the urgent endeavor towards combating global water scarcity.

Design Considerations for Artificial Water Channel–Based Membranes

2018 ◽  
Vol 48 (1) ◽  
pp. 57-82 ◽  
Author(s):  
Woochul Song ◽  
Chao Lang ◽  
Yue-xiao Shen ◽  
Manish Kumar
Keyword(s):  
Historical Perspective ◽  
Water Channel ◽  
Water Channels ◽  
Structure And Properties ◽  
High Permeability ◽  
Functional Elements ◽  
Design Considerations ◽  
Biological Water ◽  
Naturally Occurring ◽  
Artificial Water

Aquaporins (AQPs) are naturally occurring water channel proteins. They can facilitate water molecule translocation across cellular membranes with exceptional selectivity and high permeability that are unmatched in synthetic membrane systems. These unique properties of AQPs have led to their use as functional elements in membranes in recent years. However, the intricate nature of AQPs and concerns regarding their stability and processability have encouraged researchers to develop synthetic channels that mimic the structure and properties of AQPs and other biological water-conducting channels. These channels have been termed artificial water channels. This article reviews current progress and provides a historical perspective as well as an outlook toward developing scalable membranes based on artificial water channels.

Conformational dynamics and interfacial interactions of peptide-appended pillar[5]arene water channels in biomimetic membranes

2019 ◽  
Vol 21 (41) ◽  
pp. 22711-22721 ◽  
Author(s):  
Yong Liu ◽  
Harish Vashisth
Keyword(s):  
Water Purification ◽  
Conformational Dynamics ◽  
Water Channel ◽  
Water Channels ◽  
Interfacial Interactions ◽  
Biomimetic Membranes ◽  
Channel Proteins ◽  
Significant Potential ◽  
Biological Water ◽  
Artificial Water

Peptide appended pillar[5]arene (PAP) is an artificial water channel resembling biological water channel proteins, which has shown a significant potential for designing bioinspired water purification systems.

scholarly journals Targeting the Trafficking of Kidney Water Channels for Therapeutic Benefit

2020 ◽  
Vol 60 (1) ◽  
pp. 175-194 ◽  
Author(s):  
Pui W. Cheung ◽  
Richard Bouley ◽  
Dennis Brown
Keyword(s):  
Lipid Bilayers ◽  
Water Movement ◽  
Water Channel ◽  
Plasma Osmolality ◽  
Water Channels ◽  
Therapeutic Benefit ◽  
Body Volume ◽  
Pka Pathway ◽  
Complex Signaling ◽  
Urine Concentrating Ability

The ability to regulate water movement is vital for the survival of cells and organisms. In addition to passively crossing lipid bilayers by diffusion, water transport is also driven across cell membranes by osmotic gradients through aquaporin water channels. There are 13 aquaporins in human tissues, and of these, aquaporin-2 (AQP2) is the most highly regulated water channel in the kidney: The expression and trafficking of AQP2 respond to body volume status and plasma osmolality via the antidiuretic hormone, vasopressin (VP). Dysfunctional VP signaling in renal epithelial cells contributes to disorders of water balance, and research initially focused on regulating the major cAMP/PKA pathway to normalize urine concentrating ability. With the discovery of novel and more complex signaling networks that regulate AQP2 trafficking, promising therapeutic targets have since been identified. Several strategies based on data from preclinical studies may ultimately translate to the care of patients with defective water homeostasis.

Transport of water and urea in red blood cells

1984 ◽  
Vol 246 (3) ◽  
pp. C195-C203 ◽  
Author(s):  
R. I. Macey
Keyword(s):  
Red Blood Cells ◽  
Lipid Bilayers ◽  
Blood Cells ◽  
Renal Medulla ◽  
Water Channels ◽  
Facilitated Diffusion ◽  
Red Cell Membrane ◽  
Single File ◽  
Osmotic Stability ◽  
Water Transport Properties

Evidence for water channels in red blood cells is reviewed. In an entropically driven reaction, organic mercurials decrease water permeability, elevate the activation energy, and reduce the ratio of osmotic to diffusional water permeabilities to unity so that water transport properties of red blood cells are hardly distinguishable from lipid bilayers. It is concluded that mercurials close the water channels. A variety of kinetic, pharmacological, and comparative evidence converges on the conclusion that urea and other solutes are excluded from water channels. Urea apparently permeates the red cell membrane via a facilitated diffusion system, which plays an important role when red blood cells traverse the renal medulla; rapid urea transport helps preserve the osmotic stability and deformability of the cell, and it helps prevent dissipation of extracellular osmotic gradients. Water apparently traverses the channel via a single-file mechanism; the very low channel permeability of H+ is explained if the channel contains fixed charge, or alternatively, if the mobile water molecules within the channel do not form a continuum. An alternative unitary pore hypothesis for simultaneous transport of water, ions, and small solutes is also discussedl.

scholarly journals Water Dynamics in a Peptide-appended Pillar[5]arene Artificial Channel in Lipid and Biomimetic Membranes

2021 ◽  
Vol 9 ◽  
Author(s):  
Daniel Ryan Barden ◽  
Harish Vashisth
Keyword(s):  
Free Energy ◽  
Water Channel ◽  
Md Simulations ◽  
High Water ◽  
Chem Phys ◽  
Water Dynamics ◽  
Free Energy Surface ◽  
Biological Water ◽  
Single File ◽  
Single File Transport

Peptide-appended Pillar[5]arene (PAP) is an artificial water channel that can be incorporated into lipid and polymeric membranes to achieve high permeability and enhanced selectivity for angstrom-scale separations [Shen et al. Nat. Commun.9:2294 (2018)]. In comparison to commonly studied rigid carbon nanotubes, PAP channels are conformationally flexible, yet these channels allow a high water permeability [Y. Liu and H. Vashisth Phys. Chem. Chem. Phys.21:22711 (2019)]. Using molecular dynamics (MD) simulations, we study water dynamics in PAP channels embedded in biological (lipid) and biomimetic (block-copolymer) membranes to probe the effect of the membrane environment on water transport characteristics of PAP channels. We have resolved the free energy surface and local minima for water diffusion within the channel in each type of membrane. We find that water follows single file transport with low free-energy barriers in regions surroundings the central ring of the PAP channel and the single file diffusivity of water correlates with the number of hydrogen bonding sites within the channel, as is known for other sub-nm pore-size synthetic and biological water channels [Horner et al. Sci. Adv.1:e1400083 (2015)].

Radio and Electrical Measurements on Glacial Streams

1987 ◽  
Vol 33 (114) ◽  
pp. 239-242
Author(s):  
M. E. R. Walford
Keyword(s):  
Electrical Conductivity ◽  
Water Channel ◽  
Water System ◽  
Low Frequency ◽  
Water Channels ◽  
Radiative Loss ◽  
Radio Waves ◽  
Electrical Measurements ◽  
Water Conductivity ◽  
Glacier Surface

AbstractWe discuss the suggestion that small underwater transmitters might be used to illuminate the interior of major englacial water channels with radio waves. Once launched, the radio waves would naturally tend to be guided along the channels until attenuated by absorption and by radiative loss. Receivers placed within the channels or at the glacier surface could be used to detect the signals. They would provide valuable information about the connectivity of the water system. The electrical conductivity of the water is of crucial importance. A surface stream on Storglaciären, in Sweden, was found, using a low-frequency technique, to have a conductivity of approximately 4 × 10−4 S m−1. Although this is several hundred times higher than the conductivity of the surrounding glacier ice, the contrast is not sufficient to permit us simply to use electrical conductivity measurements to establish the connectivity of englacial water channels. However, the water conductivity is sufficiently small that, under favourable circumstances, radio signals should be detectable after travelling as much as a few hundred metres along an englacial water channel. In a preliminary field experiment, we demonstrated semi quantitatively that radio waves do indeed propagate as expected, at least in surface streams. We conclude that under-water radio transmitters could be of real practical value in the study of the englacial water system, provided that sufficiently robust devices can be constructed. In a subglacial channel, however, we expect the radio range would be much smaller, the environment much harsher, and the technique of less practical value.

Polymer Electrolyte Actuator Driven by Low Voltage

1999 ◽  
Vol 600 ◽  
Author(s):  
K. Oguro ◽  
K. Asaka ◽  
N. Fujiwara ◽  
K. Onishi ◽  
S. Sewa
Keyword(s):  
Polymer Electrolyte ◽  
Low Voltage ◽  
Polymer Electrolyte Membrane ◽  
Water Channel ◽  
Artificial Muscle ◽  
Ion Exchange Resin ◽  
Channel Structure ◽  
Narrow Channels ◽  
Electrolyte Membrane ◽  
Counter Ion

AbstractComposites of perfluorinated polymer electrolyte membrane and gold electrodes bend in response to low-voltage electric stimuli and work as soft actuators like muscles. The composites were prepared by chemical plating. Charge on the electrode induces electric double layer and electro-osmotic drag of water by cation from anode to cathode through narrow channels in the perfluorinated ion-exchange resin. The electro-osmotic flow of water swells the polymer near the cathode rather than anode, and the membrane bends to the anode. The actuator comprises polymer electrolyte, electrodes, counter ion, solvent, lead wires, etc. Each component affects the performance of the actuator. Surface area of electrode and species of counter ion have drastic effect on voltage-displacement response. The response may depend on water channel structure of the polymer electrolyte. Modification of these factors improved the performance and resulted in the deflection over 360 degrees at a film actuator of 10 mm length. A tubular actuator was demonstrated as a multidirectional actuator. These actuators are applicable to artificial muscle, micro robots, or micro medical equipment inside body.

Water transport across mammalian cell membranes

1996 ◽  
Vol 270 (1) ◽  
pp. C12-C30 ◽  
Author(s):  
A. S. Verkman ◽  
A. N. van Hoek ◽  
T. Ma ◽  
A. Frigeri ◽  
W. R. Skach ◽  
...  
Keyword(s):  
Water Transport ◽  
Cell Membranes ◽  
Water Channel ◽  
Water Channels ◽  
Channel Structure ◽  
Level Information ◽  
Selective Channel ◽  
Transcriptional Units ◽  
Measurement Strategies

This review summarizes recent progress in water-transporting mechanisms across cell membranes. Modern biophysical concepts of water transport and new measurement strategies are evaluated. A family of water-transporting proteins (water channels, aquaporins) has been identified, consisting of small hydrophobic proteins expressed widely in epithelial and nonepithelial tissues. The functional properties, genetics, and cellular distributions of these proteins are summarized. The majority of molecular-level information about water-transporting mechanisms comes from studies on CHIP28, a 28-kDa glycoprotein that forms tetramers in membranes; each monomer contains six putative helical domains surrounding a central aqueous pathway and functions independently as a water-selective channel. Only mutations in the vasopressin-sensitive water channel have been shown to cause human disease (non-X-linked congenital nephrogenic diabetes insipidus); the physiological significance of other water channels remains unproven. One mercurial-insensitive water channel has been identified, which has the unique feature of multiple overlapping transcriptional units. Systems for expression of water channel proteins are described, including Xenopus oocytes, mammalian and insect cells, and bacteria. Further work should be directed at elucidation of the role of water channels in normal physiology and disease, molecular analysis of regulatory mechanisms, and water channel structure determination at atomic resolution.

Progesterone inhibition of water permeability in Bufo arenarum oocytes and urinary bladder

1996 ◽  
Vol 270 (5) ◽  
pp. F880-F885 ◽  
Author(s):  
P. Ford ◽  
G. Amodeo ◽  
C. Capurro ◽  
C. Ibarra ◽  
R. Dorr ◽  
...  
Keyword(s):  
Urinary Bladder ◽  
Xenopus Laevis ◽  
Water Permeability ◽  
Water Channel ◽  
Water Channels ◽  
Toad Urinary Bladder ◽  
Osmotic Permeability ◽  
Bufo Arenarum ◽  
Mrna Extraction

The ovarian oocytes from Bufo arenarum (BAO) but not those from Xenopus laevis (XLO) would have water channels (WC). We now report that the injection of the mRNA from BAO into the oocytes from XLO increased their water osmotic permeability (Pi) (reduced by 0.3 mM HgCl2 and reversed by 5 mM beta-mercaptoethanol). A 30-min challenge with progesterone induced, 18 h later, a reduction of the mercury-sensitive fraction of Pf in the BAO (but not in XLO). The mRNA from BAO pretreated with progesterone lost its capacity to induce WC in the XLO, but the hormone did not affect the expression of the WC in XLO previously injected with the mRNA from BAO. Pf was also measured in urinary bladders of BAO. Eighteen hours after a challenge with progesterone, a reduction in the hydrosmotic response to oxytocin was observed. Finally, the mRNA from the urinary bladder of BAO was injected into XLO. An increase in Pf was observed. This was not the case if, before the mRNA extraction, the bladders were treated with progesterone. We conclude that the BAO WC share progesterone sensitivity with the oxytocin-regulated water channel present in the toad urinary bladder.

scholarly journals Rationalisation of the activities of phenolic (vitamin E-type) antioxidants

2003 ◽  
Vol 17 (4) ◽  
pp. 753-762
Author(s):  
Christopher J. Rhodes ◽  
Thuy T. Tran ◽  
Philip Denton ◽  
Harry Morris
Keyword(s):  
Free Energy ◽  
Vitamin E ◽  
Gibbs Free Energy ◽  
State Theory ◽  
Linear Free Energy Relationship ◽  
Free Energies ◽  
Gibbs Free Energy Change ◽  
Linear Free Energy ◽  
Free Energy Of Activation ◽  
Enthalpy And Entropy

Using Transition-State Theory, experimental rate constants, determined over a range of temperatures, for reactions of vitamin E type antioxidants are analysed in terms of their enthalpies and entropies of activation. It is further shown that computational methods may be employed to calculate enthalpies and entropies, and hence Gibbs Free Energies, for the overall reactions. Within the Linear Free Energy Relationship (LFER) assumption, that the Gibbs Free Energy of activation is proportional to the overall Gibbs Free Energy change for the reaction, it is possible to rationalise, and even to predict, the relative contributions of enthalpy and entropy for reactions of interest, involving potential antioxidants.

Sign in / Sign up

Export Citation Format

Share Document