An XPS and Scanning Polarization Force Microscopy Study of the Exchange and Mobility of Surface Ions on Mica

Xu, Lei; Salmerón, Miquel

doi:10.1021/la980529y

Cited by 70 publications

(99 citation statements)

References 4 publications

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“…First, the adsorbed Rb þ ions appear surprisingly stable, with the same protrusion often visible in several consecutive line scans. Theory 42 and scanning polarization microscopy measurements of ions mobility on mica 43 suggest that the residence time of adsorbed ions at a given binding site should not exceed microseconds, but our IDM measurements of the residence time of Rb þ ions over a single binding site (Fig. 1c) indicate an average time in the order of 100 ms (see Supplementary Fig.…”

Section: Resultsmentioning

confidence: 86%

Water-induced correlation between single ions imaged at the solid–liquid interface

2014

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When immersed into water, most solids develop a surface charge, which is neutralized by an accumulation of dissolved counterions at the interface. Although the density distribution of counterions perpendicular to the interface obeys well-established theories, little is known about counterions' lateral organization at the surface of the solid. Here we show, by using atomic force microscopy and computer simulations, that single hydrated metal ions can spontaneously form ordered structures at the surface of homogeneous solids in aqueous solutions. The structures are laterally stabilized only by water molecules with no need for specific interactions between the surface and the ions. The mechanism, studied here for several systems, is controlled by the hydration landscape of both the surface and the adsorbed ions. The existence of discrete ion domains could play an important role in interfacial phenomena such as charge transfer, crystal growth, nanoscale self-assembly and colloidal stability.

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Section: Resultsmentioning

confidence: 86%

Water-induced correlation between single ions imaged at the solid–liquid interface

2014

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“…Under the condition of no external salt in the solution, the epitaxial binding sites on the mica surface are in equilibrium between the K + -occupied and K + -vacant states (our molecular dynamics simulations indicate that 52.3% of K + sites are open in pure water, in agreement with previous experimental findings), where GAV-9 may readily react (adsorb) onto the K + -vacant sites [for the K + -occupied sites, on the other hand, it needs to go through ion exchange reactions (34,35)]. However, once a high concentration of salt (e.g., MgCl 2 ) is added into the solution, the above equilibrium is shifted toward the K + -occupied states (or Mg 2+ -occupied states) (36,37). This can be clearly seen from the excess cation density on the mica surface in our simulation (Fig.…”

Section: Resultsmentioning

confidence: 99%

Salts drive controllable multilayered upright assembly of amyloid-like peptides at mica/water interface

Dai

Kang

Huynh

et al. 2013

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

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Surface-assisted self-assembly of amyloid-like peptides has received considerable interest in both amyloidosis research and nanotechnology in recent years. Despite extensive studies, some controlling factors, such as salts, are still not well understood, even though it is known that some salts can promote peptide selfassemblies through the so-called "salting-out" effect. However, they are usually noncontrollable, disordered, amorphous aggregates. Here, we show via a combined experimental and theoretical approach that a conserved consensus peptide NH 2 -VGGAVVAGV-CONH 2 (GAV-9) (from representative amyloidogenic proteins) can self-assemble into highly ordered, multilayered nanofilaments, with surprising all-upright conformations, under high-salt concentrations. Our atomic force microscopy images also demonstrate that the vertical stacking of multiple layers is highly controllable by tuning the ionic strength, such as from 0 mM (monolayer) to 100 mM (mainly double layer), and to 250 mM MgCl 2 (double, triple, quadruple, and quintuple layers). Our atomistic molecular dynamics simulations then reveal that these individual layers have very different internal nanostructures, with parallel β-sheets in the first monolayer but antiparallel β-sheets in the subsequent upper layers due to their different microenvironment. Further studies show that the growth of multilayered, all-upright nanostructures is a common phenomenon for GAV-9 at the mica/water interface, under a variety of salt types and a wide range of salt concentrations.amyloid peptide | atomic force microscopy | salt effect | self-assembly on mica A better understanding of the self-assembly of highly ordered peptide nanostructures is critical because it not only helps to uncover the pathogenesis of various neurodegenerative diseases (1) but provides an attractive "bottom-up" nanotechnology for de novo nanodevice design (2) and fabrication (3). In addition to a series of factors (4-6) previously discovered to modulate peptide self-assembly, solid substrates have been found to drive this process directly acting as templates (7,8), controlling both assembly kinetics and morphology of amyloid peptide aggregates (8-11). These findings emphasize the importance of the substrate surface, whether it be a cellular membrane or an inorganic solid surface, on the assembly of various peptides, which is critical in many biological processes. It has been shown recently that fibrous nanostructures form a fundamental framework ubiquitous in normal cellular metabolism, including cell division and signaling, as well as in over 27 different human amyloid diseases and 9 in animals (12).Due to the complexity of cellular membranes and associated physiological conditions (13,14), hydrophilic mica and hydrophobic highly oriented pyrolytic graphite (HOPG) are the two commonly used model substrates for the investigation of surface effects (10,11,15). For example, it was found that amyloid-β (Aβ) peptide formed oligomeric protofibrillar aggregates on mica but only 1D nanofilaments on HOPG (...

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“…However, this exchange process is rapid and leads to 100% substitution on timescales that are short compared to the timescale for the X-ray photoelectron spectroscopy (XPS) measurements used to probe this exchange (22). Nonetheless, to be certain this could not be a source of short domains, we incubated mica for overnight (i.e., approximately 21 h) in CaCl 2 solution before exposure to S-layer proteins solutions for 4 h but found no dif- A and B show unprocessed AFM images.…”

Section: Discussionmentioning

confidence: 99%

Direct observation of kinetic traps associated with structural transformations leading to multiple pathways of S-layer assembly

Shin

Chung

Sanii

et al. 2012

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

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The concept of a folding funnel with kinetic traps describes folding of individual proteins. Using in situ Atomic Force Microscopy to investigate S-layer assembly on mica, we show this concept is equally valid during self-assembly of proteins into extended matrices. We find the S-layer-on-mica system possesses a kinetic trap associated with conformational differences between a long-lived transient state and the final stable state. Both ordered tetrameric states emerge from clusters of the monomer phase, however, they then track along two different pathways. One leads directly to the final low-energy state and the other to the kinetic trap. Over time, the trapped state transforms into the stable state. By analyzing the time and temperature dependencies of formation and transformation we find that the energy barriers to formation of the two states differ by only 0.7 kT, but once the high-energy state forms, the barrier to transformation to the low-energy state is 25 kT. Thus the transient state exhibits the characteristics of a kinetic trap in a folding funnel.biological assembly | protein crystal growth | two-step crystallization | protein folding funnel P roteins that naturally self-assemble into extended ordered structures often adopt conformations that are distinct from those of the individual monomeric proteins (1-4). For example, collagen matrices, which constitute the organic scaffolds of bones and teeth in all higher organisms, are constructed from triple helices of the individual collagen monomers (4). These helices further assemble into highly organized twisted fibrils exhibiting a pseudohexagonal symmetry. In some cases, assembly is inexorably linked to folding transformations, as in the case of prion or amyloid fibrils, where misfolding of the monomers triggers assembly, which in turn drives misfolding of new monomers (1).When individual proteins transform from an unstructured state to the final equilibrium state, the concept of a folding funnel characterized by a large number of potential initial states higher in energy than the final state is often invoked (5, 6). The walls of the funnel are presumed not to be smooth and the resulting bumps and valleys define kinetic traps where the protein exhibits nonequilibrium structures for extended periods of time. These transient structures can be disordered "molten globules" or partially ordered intermediates (7). This physical picture of folding in which one fraction of a protein population promptly reaches the folded state while the remaining fraction gets trapped in metastable states has been referred as the kinetic partitioning mechanism (8). The energy landscape that defines the funnel as well as the pathways through it have been explored in some detail at the single molecule level for a number of small proteins and protein subdomains through both simulations (8-10) and experiments (11-13). However, despite the fact that conformational transformations are part and parcel of protein self-assembly into extended architectures, this concept of the folding fu...

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An XPS and Scanning Polarization Force Microscopy Study of the Exchange and Mobility of Surface Ions on Mica

Cited by 70 publications

References 4 publications

Water-induced correlation between single ions imaged at the solid–liquid interface

Water-induced correlation between single ions imaged at the solid–liquid interface

Salts drive controllable multilayered upright assembly of amyloid-like peptides at mica/water interface

Direct observation of kinetic traps associated with structural transformations leading to multiple pathways of S-layer assembly

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