Electric-field-induced wetting and dewetting in single hydrophobic nanopores

Powell, Matthew R.; Cleary, Leah; Davenport, Matt; Shea, Kenneth J.; Siwy, Zuzanna S.

doi:10.1038/nnano.2011.189

Cited by 308 publications

(327 citation statements)

References 26 publications

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“…The gate can be opened by a minor increase in polarity or radius of the pore. Recently, this principle has been used to generate voltage-gated nonbiological nanopores (32). This gating hypothesis also has been proposed for MscL (9, 10) and found support from molecular dynamics simulations (33) and flying patch clamp studies (34).…”

Section: Discussionmentioning

confidence: 64%

Hydrophobic gating of mechanosensitive channel of large conductance evidenced by single-subunit resolution

Birkner

Poolman

Koçer

2012

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

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Mechanosensitive (MS) ion channels are membrane proteins that detect and respond to membrane tension in all branches of life. In bacteria, MS channels prevent cells from lysing upon sudden hypoosmotic shock by opening and releasing solutes and water. Despite the importance of MS channels and ongoing efforts to explain their functioning, the molecular mechanism of MS channel gating remains elusive and controversial. Here we report a method that allows single-subunit resolution for manipulating and monitoring "mechanosensitive channel of large conductance" from Escherichia coli. We gradually changed the hydrophobicity of the pore constriction in this homopentameric protein by modifying a critical pore residue one subunit at a time. Our experimental results suggest that both channel opening and closing are initiated by the transmembrane 1 helix of a single subunit and that the participation of each of the five identical subunits in the structural transitions between the closed and open states is asymmetrical. Such a minimal change in the pore environment seems ideal for a fast and energyefficient response to changes in the membrane tension. from Escherichia coli (Eco-MscL) is one of the best-characterized mechanosensitive channels (1, 2). It senses membrane tension invoked by sudden hypoosmotic stress and acts as an emergency valve by opening a large, transient, nonselective aqueous pore in the membrane. The crystal structure of the closed state of MscL from Mycobacterium tuberculosis (Tb-MscL) consists of five identical subunits. Each subunit has a helical cytoplasmic N terminus (S1), two transmembrane helices (TM1 and TM2) connected by a periplasmic loop (PL), and a bundle of cytoplasmic helix (CP). The closed channel has a pore diameter of about 3.5 Å (3). The estimated open pore diameter, on the other hand, is 30-40 Å (4, 5), suggesting that significant conformational changes take place upon gating.Despite a large body of experimental and theoretical data, the gating mechanism by which MscL physically opens and closes its permeation pathway is still unknown. Various molecular rearrangements have been proposed to underlie MscL gating. These include (i) a slight counterclockwise (6) or a large clockwise rotation (7) of the TM1 helices when viewed from the periplasm; (ii) a significant preexpansion of TM1 helices forming a closed/ expanded state followed by separation of S1 bundles (8); (iii) the separation of only the TM1 domains but not S1 domains as the primary energy barrier for gating (9, 10); and (iv) the rotation and shifting of TM1-TM2 pairs as a rigid body (11,12).Despite some discrepancies in details, there are two common elements in all models of MscL gating. The first is a hydrophobic pore constriction formed by a region on TM1 helices. In the crystal structure of Tb-MscL, the pore lumen is lined mainly by TM1 helices, and it narrows toward the cytoplasm. The narrowest part is formed by the fivefold symmetry of a hydrophobic, methylterminated motif (L17xxxV21) on TM1 helices (Fig. 1). Random mutagenesi...

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Section: Discussionmentioning

confidence: 64%

Hydrophobic gating of mechanosensitive channel of large conductance evidenced by single-subunit resolution

Birkner

Poolman

Koçer

2012

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

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“…Wall defects may also lead to the following: higher CNT surface energies [39], which lead to stronger interactions with water molecules [40,41] and enable the separation of salt ions from solution [42]; altered electronic properties, [43][44][45][46] which can lead to a CNT behaving as either a metal or semi-conductor, [43] and can also lead to reversible wetting and de-wetting of water in nanopores. [47] Since wall defects can fundamentally change the CNT-water interactions, [48] their characterization is necessary.…”

Section: Cnt Surface Structure and Interaction With Adsorbatesmentioning

confidence: 99%

Exohedral Physisorption of Ambient Moisture Scales Non-monotonically with Fiber Proximity in Aligned Carbon Nanotube Arrays

et al. 2014

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Here we present a study on the presence of physisorbed water on the surface of aligned carbon nanotubes (CNTs) in ambient conditions, where the wet CNT array mass can be more than 200% larger than that of dry CNTs, and modeling indicates that a water layer > 5 nm thick can be present on the outer CNT surface. The experimentally observed non-linear and non-monotonic dependence of the mass of adsorbed water on the CNT packing (volume fraction) originates from two competing modes. Physisorbed water cannot be neglected in the design and fabrication of materials and devices using nanowires/nanofibers, especially CNTs, and further experimental and ab initio studies on the influence of defects on the surface energies of CNTs, and nanowires/nanofibers in general, are necessary to understand the underlying physics and chemistry that govern this system.One dimensional nanoscale systems, such as nanowires, nanofibers, and nanotubes, are well known for their phenomenal electrical, [1][2][3][4] thermal, [5][6][7][8] and mechanical properties, [9][10][11] which could enable the design and manufacture of next-generation materials with unprecedented properties. [12][13][14][15][16][17][18] However, while many studies have previously explored the synthesis of new architectures and devices using one dimensional nanomaterials, specifically carbon nanotubes (CNTs), the properties they reported were far lower than the properties of predicted using current theory.[12] Some of the main reasons why existing models cannot accurately predict the behavior of CNTs in scalable architectures, such as aligned CNT arrays, are the various CNT morphology and proximity effects, [13][14][15]19] which can strongly impact properties, but are not well understood and cannot be properly integrated into theoretical frameworks. Here we report the presence of a commonly neglected morphological effect, an unexpectedly large (compared to the CNT mass) amount of moisture located on the surface of CNTs in aligned CNT (A-CNT) arrays at ambient conditions; show the non-linear and non-monotonic dependence of this effect on array porosity, which suggests two competing mechanisms; and discuss the strong impact such an effect can have on the structure and properties of nanocomposite architectures composed of A-CNTs.Previous studies on how water interacts with the outer surface of a CNT illustrated that the water molecules form a layer-like shell surrounding the CNTs, [20][21][22][23] and that the water layer density varies greatly and non- * wardle@mit.edu.monotonically with its thickness. [21,22] A recent study on the physisorption of water onto the external surface of a suspended ∼ 1.1 − 1.2 nm diameter single walled CNT showed that more than one layer of water is present on the CNT surface in water vapor, and that water molecules more easily adsorb onto larger diameter CNTs.[24] However, this study was limited to isolated and defect-free CNTs, [24,25] meaning that the interaction of moisture present in ambient air with multiwalled CNTs, which normally have nativ...

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“…Instead, ionic transport through nanochannels/nanopores typically exhibits ohmic behaviour. Voltage-activated nonlinear ion transport was also observed in various systems, such as hydrophobic wetting and ion dehydration 10,11 . Here, we report for the first time the experimental observation of single-ion transport through the ionic junction of a sub-nm MoS 2 pore.…”

mentioning

confidence: 95%

“…Compared to other ions, the I -V characteristic of the divalent ions Mg 2+ and Ca 2+ shows a more suppressed current for positive voltages than the monovalent ions K + , Na + and Li + . The hydrophilic nature of MoS 2 pores owing to the Mo-rich pore surface and the pore wetting procedure we use, which involves soaking nanopores in an ethanol/water mixture, eliminates the possibility that nonlinearity originates from hydrophobic effects 10,17 . To understand the nature of the ionic transport measurements, we first used an analogy to electric transport through a quantum dot/single-molecule system 4 , shown in Supplementary Fig.…”

mentioning

confidence: 99%