An influenza virus inspired polymer system for the timed release of siRNA

Small interfering RNA silences specific genes by interfering with mRNA translation, and acts to modulate or inhibit specific biological pathways; a therapy that holds great promise in the cure of many diseases. However, the naked small interfering RNA is susceptible to degradation by plasma and tissue nucleases and due to its negative charge unable to cross the cell membrane. Here we report a new polymer carrier designed to mimic the influenza virus escape mechanism from the endosome, followed by a timed release of the small interfering RNA in the cytosol through a self-catalyzed polymer degradation process. Our polymer changes to a negatively charged and non-toxic polymer after the release of small interfering RNA, presenting potential for multiple repeat doses and long-term treatment of diseases.

Charge-controlled switchable CO2 capture on boron nitride nanomaterials

Increasing concerns about the atmospheric CO2 concentration and its impact on the environment are motivating researchers to discover new materials and technologies for efficient CO2 capture and conversion. Here, we report a study of the adsorption of CO2, CH4, and H2 on boron nitride (BN) nanosheets and nanotubes (NTs) with different charge states. The results show that the process of CO2 capture/release can be simply controlled by switching on/off the charges carried by BN nanomaterials. CO2 molecules form weak interactions with uncharged BN nanomaterials and are weakly adsorbed. When extra electrons are introduced to these nanomaterials (i.e., when they are negatively charged), CO2 molecules become tightly bound and strongly adsorbed. Once the electrons are removed, CO2 molecules spontaneously desorb from BN absorbents. In addition, these negatively charged BN nanosorbents show high selectivity for separating CO2 from its mixtures with CH4 and/or H2. Our study demonstrates that BN nanomaterials are excellent absorbents for controllable, highly selective, and reversible capture and release of CO2. In addition, the charge density applied in this study is of the order of 1013 cm–2 of BN nanomaterials and can be easily realized experimentally.

Gas-Phase Transformation of Phosphatidylcholine Cations to Structurally Informative Anions via Ion/Ion Chemistry

Gas-phase transformation of synthetic phosphatidylcholine (PC) monocations to structurally informative anions is demonstrated via ion/ion reactions with doubly deprotonated 1,4-phenylenedipropionic acid (PDPA). Two synthetic PC isomers, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (PC16:0/18:1) and 1-oleoyl-2-palmitoyl-sn-glycero-3-phosphocholine (PC18:1/16:0), were subjected to this ion/ion chemistry. The product of the ion/ion reaction is a negatively charged complex, \[PC + PDPA - H](-). Collisional activation of the long-lived complex causes transfer of a proton and methyl cation to PDPA, generating \[PC - CH3](-). Subsequent collisional activation of the demethylated PC anions produces abundant fatty acid carboxylate anions and low-abundance acyl neutral losses as free acids and ketenes. Product ion spectra of \[PC - CH3](-) suggest favorable cleavage at the sn-2 position over the sn-1 due to distinct differences in the relative abundances. In contrast, collisional activation of PC cations is absent of abundant fatty acid chain-related product ions and typically indicates only the lipid class via formation of the phosphocholine cation. A solution phase method to produce the gas-phase adducted PC anion is also demonstrated. Product ion spectra derived from the solution phase method are similar to the results generated via ion/ion chemistry. This work demonstrates a gas-phase means to increase structural characterization of phosphatidylcholines via ion/ion chemistry. Grant Number ARC/CE0561607, ARC/DP120102922

Ion-acoustic surface waves on a dielectric-dusty plasma interface

The theory of ion-acoustic surface wave propagation on the interface between a dusty plasma and a dielectric is presented. Both the constant and variable dust-charge cases are considered. It is found that massive negatively charged dust grains can significantly affect the propagation and damping of the surface waves. Application of the results to surface-wave generated plasmas is discussed. © 1998 IEEE.

Surface waves at the interface of a dusty plasma and a metallic wall

Electrostatic surface waves at the interface between a low-temperature nonisothermal dusty plasma and a metallic wall are investigated. The plasma contains massive negatively charged impurity or dust particles. It is shown that the impurities can significantly alter the characteristics and damping of the surface waves by reducing their phase velocity and causing charging-related damping.

Nanoparticle manipulation in plasma-assisted nanofabrication of electron field emitters based on single crystalline carbon nanotip patterns

Nanoparticle manipulation by various plasma forces in near-substrate areas of the Integrated Plasma-Aided Nanofabrication Facility (IPANF) is investigated. In the IPANF, high-density plasmas of low-temperature rf glow discharges are sustained. The model near-substrate area includes a variable-length pre-sheath, where a negatively charged nanoparticle is accelerated, and a self-consistent collisionless sheath with a repulsive electrostatic potential. Conditions enabling the nanoparticle to overcome the repulsive barrier and deposit onto the substrate are investigated numerically and experimentally. Under certain conditions the momentum gained by the nanoparticle in the pre-sheath area appears to be sufficient for the driving ion drag force to outbalance the repulsive electrostatic and thermophoretic forces. Numerical results are applied for the explanation of size-selective nanoparticle deposition in the Ar+H2+CH4 plasma-assisted chemical vapor deposition of various carbon nanostructure patterns for electron field emitters and are cross-referenced by the field emission scanning electron microscopy. It is shown that the nanoparticles can be efficiently manipulated by the temperature gradient-controlled thermophoretic force. Experimentally, the temperature gradients in the near-substrate areas are measured in situ by means of the temperature gradient probe and related to the nanofilm fabrication conditions. The results are relevant to plasma-assisted synthesis of numerous nanofilms employing structural incorporation of the plasma-grown nanoparticles, including but not limited to nanofabrication of ordered single-crystalline carbon nanotip arrays for electron field emission applications.

Ion-acoustic waves in a complex plasma with negative ions

Negative ions and negatively charged micro- to nano-meter sized dust grains are ubiquitous in astrophysical as well as industrial processing plasmas. The negative ions can appear in electro-negative plasmas as a result of elementary processes such as dissociative or non-dissociative electron attachment to neutrals. They are usually rather small in number, and in general do not affect the overall plasma behavior. On the other hand, since the dust grains are almost always highly negative, even in small numbers they can take up a considerable proportion of the total negative charge in the system. The presence of dusts can affect the characteristics of most collective processes of the plasma since the charge balance in both the steady and dynamic states can be significantly altered. Another situation that often occurs is that the electron number density becomes small because of their absorption by the dust grains or the discharge walls. In this case the negative ions in the plasma can play a very important role. Here, a self-consistent theory of linear waves in complex laboratory plasmas containing dust grains and negative ions is presented. A comprehensive model for such plasmas including source and sink effects associated with the presence of dust grains and negative ions is introduced. The stationary state of the plasma as well as the dispersion and damping characteristics of the waves are investigated. All relevant processes, such as ionization, diffusion, electron attachment, negative-positive ion recombination, dust charge relaxation, and dissipation due to electron and ion elastic collisions with neutrals and dust particles, as well as charging collisions with the dusts, are taken into consideration.

Wet hail and thunderstorm electrification

Hailstones in wet growth are commonly found in thunderclouds. While the ice-ice relative growth rate mechanism is generally accepted as the most likely cause of thunderstorm electrification, it is uncertain if this mechanism will operate under wet growth conditions because ice crystals are more likely to stick to the wet surface of a hailstone rather than bounce off it. Experiments were carried out in the laboratory to investigate if there was any charge separated when vapor-grown ice crystals bounced off a wet hailstone. A cloud of supercooled droplets, with and without ice crystals, was drawn past a simulated hailstone. In the dry growth regime, the hailstone charged strongly positive when droplets and crystals co-existed in the cloud. With only droplets in the cloud, there was no charging in the dry growth regime. However, as the hailstone attained wet growth, positive charging currents of about 0.5 and 3.5 pA were observed at 12 and 20 m s-1, respectively. We hypothesize that this observed charging was due to the evaporation of melt water. This so called Dinger-Gunn Effect is due to the ejection of negatively charged minute droplets produced by air bubbles bursting at the surface of the melt water. However the charge separated in wet growth was an order of magnitude smaller than that in dry growth and, therefore, we conclude that it is unlikely to play an important role in the electrification of thunderstorms.

Modelling CO2 adsorption and separation on experimentally-realized B40 fullerene

Searching for efficient solid sorbents for CO2 adsorption and separation is important for developing emergent carbon reduction and natural gas purification technology. This work, for the first time, has investigated the adsorption of CO2 on newly experimentally realized cage-like B40 fullerene (Zhai et al., 2014) based on density functional theory calculations. We find that the adsorption of CO2 on B40 fullerene involves a relatively large energy barrier (1.21 eV), however this can be greatly decreased to 0.35 eV by introducing an extra electron. A practical way to realize negatively charged B40 fullerene is then proposed by encapsulating a Li atom into the B40 fullerene (Li@B40). Li@B40 is found to be highly stable and can significantly enhance both the thermodynamics and kinetics of CO2 adsorption, while the adsorptions of N2, CH4 and H2 on the Li@B40 fullerene remain weak in comparison. Since B40 fullerene has been successfully synthesized in a most recent experiment, our results highlight a new promising material for CO2 capture and separation for future experimental validation.

A rapid and label-free dual detection of Hg (II) and cysteine with the use of fluorescence switching of graphene quantum dots

A simple and rapid method of analysis for mercury ions (Hg2+) and cysteine (Cys) was developed with the use of graphene quantum dots (GQDs) as a fluorescent probe. In the presence of GQDs, Hg2+ cations are absorbed on their negatively charged surface by means of electrostatic interactions. Thus, the fluorescence (FL) of the GQDs would be significantly quenched as a result of the FL charge transfer, e.g. 92% quenching at 450 nm occurs for a 5 μmol L−1 Hg2+ solution. However, when Cys was added, a significant FL enhancement was observed (510% at 450 nm for a 8.0 μmol L−1 Cys solution), and Hg2+ combined with Cys rather than with the GQDs in an aqueous solution. This occurred because a strong metalsingle bondthiol bond formed, displacing the weak electrostatic interactions, and this resulted in an FL enhancement of the GQDs. The limits of detection (LOD) for Hg2+ and Cys were 0.439 nmol L−1 and 4.5 nmol L−1, respectively. Also, this method was used successfully to analyze Hg2+ and Cys in spiked water samples.

Separate or simultaneous removal of radioactive cations and anions from water by layered sodium vanadate-based sorbents

Nanofibers of sodium vanadate, consisting of very thin negatively charged layers and exchangeable sodium ions between the layers, are efficient sorbents for the removal of radioactive 137Cs+ and 85Sr2+ cations from water. The exchange of 137Cs+ or 85Sr2+ ions with the interlayer Na+ ions eventually triggered structural deformation of the thin layers, trapping the 137Cs+ and 85Sr2+ ions in the nanofibers. Furthermore, when the nanofibers were dispersed in a AgNO3 solution at pH >7, well-dispersed Ag2O nanocrystals formed by firmly anchoring themselves on the fiber surfaces along planes of crystallographic similarity with those of Ag2O. These nanocrystals can efficiently capture I– anions by forming a AgI precipitate, which was firmly attached to the substrates. We also designed sorbents that can remove 137Cs+ and 125I– ions simultaneously for safe disposal by optimizing the Ag2O loading and sodium content of the vanadate. This study confirms that sorbent features such as fibril morphology, negatively charged thin layers and readily exchangeable Na+ ions between the layers, and the crystal planes for the formation of a coherent interface with Ag2O nanocrystals on the fiber surface are very important for the simultaneous uptake of cations and anions.

Electrochemical Reduction of Oriented Graphene Oxide Films: An in Situ Raman Spectroelectrochemical Study

Graphene oxide (GO) is assembled on a gold substrate by a layer-by-layer technique using a self-assembled cystamine monolayer. The negatively charged GO platelets are attached to the positively charged cystamine monolayer through electrostatic interactions. Subsequently, it is shown that the GO can be reduced electrochemically using applied DC bias by scanning the potential from 0 to -1 V vs a saturated calomel electrode in an aqueous electrolyte. The GO and reduced graphene oxide (RGO) are characterized by Raman spectroscopy and atomic force microscopy (AFM). A clear shift of the G band from 1610 cm-1 of GO to 1585 cm-1 of RGO is observed. The electrochemical reduction is followed in situ by micro Raman spectroscopy by carrying out Raman spectroscopic studies during the application of DC bias. The GO and RGO films have been characterized by conductive AFM that shows an increase in the current flow by at least 3 orders of magnitude after reduction. The electrochemical method of reducing GO may open up another way of controlling the reduction of GO and the extent of reduction to obtain highly conducting graphene on electrode materials.

High-Pressure Studies Of SE100-XTEX Glasses

High pressure resistivity measurements on Se100-xTex, glasses for 0≤x≤30 are reported. Two composition regions, where the transport and transformation behaviour are different, are identified. For 0≤x≤6, there is a first-order-like transformation to metallic crystalline states, while for x>6 the transformation appears to be continuous. Glass-transition temperatures also show differences in trends as a function of composition around 6% Te. An attempt is made to explain the composition-dependent trends on the basis of known structural features of selenium glasses and of the nature of tellurium bonding. At concentrations with up to 6% tellurium, Te most likely enters selenium chain terminations, substituting for negatively charged Se1- defects, while at larger concentrations, tellurium probably enters chains and rings by a random substitution.

N-Acetylglycyl-L-lysine methyl ester acetate

C llH22 N 30 + . C2H302, orthorhombic, P2~2~2~, a = 5.511(2), b = 14.588(4), c = 21.109 (4)A, Z = 4. The structure has been solved using MULTAN and refined to R = 0.079 for 993 observed reflections. The fully extended lysine side chain in the molecule is staggered between the main-chain amino and carbonyl groups. The dipeptide molecules in the crystal structure are arranged in twofold helices centred on 21 screw axes. These helices are interconnected through interactions involving the acetate and the side-chain amino groups. Each acetate group bridges two adjacent side-chain amino groups, related by an a translation, giving rise to an infinitely long chain of alternating negatively charged carboxylate and positively charged amino groups.

N-Acetylglycyl-L-lysine methyl ester acetate

C llH22 N 30 + . C2H302, orthorhombic, P2~2~2~, a = 5.511(2), b = 14.588(4), c = 21.109 (4)A, Z = 4. The structure has been solved using MULTAN and refined to R = 0.079 for 993 observed reflections. The fully extended lysine side chain in the molecule is staggered between the main-chain amino and carbonyl groups. The dipeptide molecules in the crystal structure are arranged in twofold helices centred on 21 screw axes. These helices are interconnected through interactions involving the acetate and the side-chain amino groups. Each acetate group bridges two adjacent side-chain amino groups, related by an a translation, giving rise to an infinitely long chain of alternating negatively charged carboxylate and positively charged amino groups.