Single-molecule nanopore sensing of actin dynamics and drug binding

Actin is a key protein in the dynamic processes within the eukaryotic cell. To date, methods exploring the molecular state of actin are limited to insights gained from structural approaches, providing a snapshot of protein folding, or methods that require chemical modifications compromising actin monomer thermostability. Nanopore sensing permits label-free investigation of native proteins and is ideally suited to study proteins such as actin that require specialised buffers and cofactors. Using nanopores, we determined the state of actin at the macromolecular level (filamentous or globular) and in its monomeric form bound to inhibitors. We revealed urea-dependent and voltage-dependent transitional states and observed the unfolding process within which sub-populations of transient actin oligomers are visible. We detected, in real-time, filament-growth, and drug-binding at the single-molecule level demonstrating the promise of nanopore sensing for in-depth understanding of protein folding landscapes and for drug discovery.

Nanopipettes were used for real-time investigation into actin dynamics and drug binding at single-molecule resolution, showing promise for a better understanding of the mechanism of protein–protein interactions and drug discovery.     

The permeation liquid membrane as a sensor for free nickel in aqueous samples

There are currently a limited number of techniques to study nickel speciation in aqueous samples. This work reports on the use of the permeation liquid membrane (PLM) for that objective. In this paper, the composition of the organic phase was studied to maximize the Ni flux (thus the sensitivity of the device) over a wide Ni2+ concentration range (50 nM to 100 microM) in order to verify its ability to determine free Ni2+ in the presence of Ni complexes. A mixture containing 1,10-didecyl-1,10-diaza-18-crown-6 ether (22DD) and di(2-ethylhexyl)phosphoric acid (D2EHPA) in toluene/phenylhexane was selected as the optimized organic phase for the PLM. The PLM was shown to be a reliable tool to measure free nickel concentrations down to 10(-7) M. The effect of pH on Ni transport was also studied. Fluxes below pH 6 were reduced significantly, i.e. an order of magnitude smaller than fluxes above pH 7.8. Finally, as part of a broader study examining the ability of trace metals to induce antibiotic resistance in bacteria, we used the PLM to quantify the formation, at pH = 7.2, of a weak complex between Ni and Imipenem (a member of the carbapenem class of beta-lactam antibiotics) or its hydrolysis product(s).     

Novel methods for the synthesis of 5-substituted-3-carboxy-2,5- and 4,5-dihydrothiophenes and 5-substituted 2- and 3-sulfolenes

Various approaches to the syntheses of 5-substituted-3-carbomethoxy-2,5-dihydrothiophenes and their product sulfolenes, required as synthetic precursors for tangutorine, are described. An efficient route to 3,5-disubstituted-4,5-dihydrothiophenes and hence 3,5-disubstituted-2-sulfolenes by radical chemistry is also described.     

Phase modulation using different orientations of a chiral nematic in liquid crystal over silicon devices

Modulation of the intensity of light by high quality reflective micro-displays is predominantly carried out by liquid crystal over silicon (LCoS) spatial light modulator (SLM) technology for applications such as pico-projectors. Wider use of these devices, in applications such as computer-generated holography and optical correlation, is limited by their phase modulation ability and illumination polarisation state dependence. These devices rely on planar or twisted nematic liquid crystals to modulate the light, but due to their viscoelastic properties they are inherently slow. Research into the use of the polymer stabilised blue phase has already shown that it can offer high speed phase modulation. However, other chiral nematic orientations are yet to be compared in LCoS devices. In this article, we demonstrate that polymer-stabilised chiral nematic liquid crystal electro-optical effects can offer phase modulation in silicon backplane devices. The uniform standing helix and focal conic textures are shown to be independent of the input light polarisation state and the uniform lying helix is shown to be polarisation dependent. These optical responses are then compared with that of the blue phase to identify a suitable orientation for further development in LCoS technology in order to find a high-speed, full phase modulating material.     

Cooperative hydrogen-bonding effects in a water square: a single-crystal neutron and partial atomic charges and hardness analysis study

Four isomorphous complexes of formula [M(L)(4)(H(2)O)(2)]SO(4).2H(2)O (M = Co, 1a; Ni, 1b; Cu, 1c; Zn, 1d) have been isolated and characterized by single-crystal X-ray diffraction and neutron diffraction using the quasi-Laue diffractometer VIVALDI at the Institut Laue-Langevin as well as by thermogravimetric analysis. The structures contain a discrete, strongly hydrogen-bonded water tetramer which causes a significant distortion of the metal coordination sphere in each case. Partial atomic charges and hardness analysis (PACHA) calculations reveal that the shortest hydrogen bonds are not the strongest in this constrained, cyclic solid-state structure and show that the distortion at the metal center is caused by the drive to maintain the integrity of the water tetramer. The system undergoes a disorder-order transition on slow cooling that provides insight into the nature of communication between water squares.     

Wetting of surfactant solutions by alkanes.

Ellipsometry, surface tensiometry, and contact-angle measurement have been used to study the transition between partial wetting and pseudo-partial wetting of surfactant solutions by alkanes. In the partial wetting regime, the air-water surface tension is the same with and without alkane. In the pseudo-partial wetting regime, the air-water surface tension is lowered by the presence of alkane, showing that oil is solubilised into the surfactant monolayer. A discontinuous change in the coefficient of ellipticity with increasing surfactant concentration provides unequivocal evidence for the first-order nature of the wetting transitions. Ellipsometry has been used to explore the generality of wetting transitions of alkanes (dodecane, hexadecane, and squalane) on surfactant solutions [dodecyltrimethylammonium bromide, tetredecyltrimethylammonium bromide, dibucaine hydrochloride, and Aerosol OT (AOT)]. Of the systems studied, only hexadecane on AOT solutions did not show a wetting transition. Excess alkane remains as a lens on the surface of the surfactant solutions at all concentrations, but the contact angle is a minimum at the wetting transition. A semiquantitative model for the variation of the contact angle with surfactant concentration is provided.     

Dry etch damage and its effect on electronic and optical nanostructures

The creation of nano-structures in 3–5 semiconductors is currently of great interest. If the conventional route of pattern definition in a resist followed by pattern transfer is used, this implies in most cases electron beam lithography and some form of dry etching. Using electron beam lithography, patterns of 10nm width on 40nm centre to centre spacing can be transfered to metal lines on thin substrates; even on normal wafers, linewidths of 25nm on 60nm spacing are achievable with state of the art machines.If the creation of a raised structure is necessary because of the physics of the situation, it is important to consider the damage which may be introduced by dry etching. The methods by which dry etch damage can be revealed are discussed, and the ways in which it can be reduced mentioned. Progress towards understanding the microscopic nature of the damage will be reviewed. Examples are drawn from etching of GaAs/GaAlAs in Silicon tetrachloride and methane/hydrogen.     

Pronounced negative thermal expansion from a simple structure: cubic ScF(3)

Scandium trifluoride maintains a cubic ReO(3) type structure down to at least 10 K, although the pressure at which its cubic to rhombohedral phase transition occurs drops from >0.5 GPa at ～300 K to 0.1-0.2 GPa at 50 K. At low temperatures it shows strong negative thermal expansion (NTE) (60-110 K, α(l) ≈ -14 ppm K(-1)). On heating, its coefficient of thermal expansion (CTE) smoothly increases, leading to a room temperature CTE that is similar to that of ZrW(2)O(8) and positive thermal expansion above ～1100 K. While the cubic ReO(3) structure type is often used as a simple illustration of how negative thermal expansion can arise from the thermally induced rocking of rigid structural units, ScF(3) is the first material with this structure to provide a clear experimental illustration of this mechanism for NTE.