Confinement induced stochastic sensing of charged coronene and perylene aggregates in alpha-hemolysin nanochannels

Biological nanopores provide optimum dimensions and an optimal environment to study early aggregation kinetics of charged polyaromatic molecules in the nano-confined regime. It is expected that probing early stages of nucleation will enable us to design a strategy for supramolecular assembly and biocrystallization processes. Specifically, we have studied translocation dynamics of coronene and perylene based salts, through the alpha-hemolysin (alpha-HL) protein nanopore. The characteristic blocking events in the time-series signal are a function of concentration and bias voltage. We argue that different blocking events arise due to different aggregation processes as captured by all atomistic molecular dynamics (MD) simulations. These confinement induced aggregations of polyaromatic chromophores during the different stages of translocation are correlated with the spatial symmetry and charge distribution of the molecules.

Water Dispersible, Positively and Negatively Charged MoS2 Nanosheets: Surface Chemistry and the Role of Surfactant Binding

Stable aqueous dispersions of atomically thin layered MoS2 nanosheets have been obtained by sonication in the presence of ionic surfactants. The dispersions are stabilized by electrostatic repulsion between the sheets, and we show that the sign of the charge on the MoS2 nanosheets, either positive or negative, can be can be controlled by the choice of the surfactant. Using techniques from solution NMR, we show that the surfactant chains are weakly bound to the MoS2 sheets and undergo rapid exchange with free surfactant chains present in the dispersion. In situ nuclear Overhauser effect spectroscopic measurements provide direct evidence that the surfactant chains lie flat, arranged randomly on the basal plane of the MoS2 nanosheets with their charged headgroup exposed. These results provide a chemical perspective for understanding the stability of these inorganic nanosheets in aqueous dispersions and the origin of the charge on the sheets.

An Evaluation of the Effectiveness of a Charged Bilayered Conducting Fine Mesh as a Dust Filter

Aim: To develop a mesh meant to be mounted on a windowpane that will act as a barrier for dust, while allowing wind to pass freely. Materials and Methods: Two small metal meshes separated at 1 cm, connected to an electrostatic generator and holding opposite charges are used. A videographic analysis has been performed. Results: The charged bilayered mesh was able to prevent a large portion of dust from passing through. Conclusion: The device is a simple, economical, and reliable way of reducing the entry of dust into a room, easing the need for periodic cleaning, and thus creating a healthier environment for the inhabitants of the building. It also has potential space applications.

Interplay of electrostatics and lipid packing determines the binding of charged polymer coated nanoparticles to model membranes

Understanding of nanoparticle-membrane interactions is useful for various applications of nanoparticles like drug delivery and imaging. Here we report on the studies of interaction between hydrophilic charged polymer coated semiconductor quantum dot nanoparticles with model lipid membranes. Atomic force microscopy and X-ray reflectivity measurements suggest that cationic nanoparticles bind and penetrate bilayers of zwitterionic lipids. Penetration and binding depend on the extent of lipid packing and result in the disruption of the lipid bilayer accompanied by enhanced lipid diffusion. On the other hand, anionic nanoparticles show minimal membrane binding although, curiously, their interaction leads to reduction in lipid diffusivity. It is suggested that the enhanced binding of cationic QDs at higher lipid packing can be understood in terms of the effective surface potential of the bilayers which is tunable through membrane lipid packing. Our results bring forth the subtle interplay of membrane lipid packing and electrostatics which determine nanoparticle binding and penetration of model membranes with further implications for real cell membranes.

Charged pion contribution to the anomalous magnetic moment of the muon

The model dependence inherent in hadronic calculations is one of the dominant sources of uncertainty in the theoretical prediction of the anomalous magnetic moment of the muon. In this thesis, we focus on the charged pion contribution and turn a critical eye on the models employed in the few previous calculations of $a_\mu^{\pi^+\pi^-}$. Chiral perturbation theory provides a check on these models at low energies, and we therefore calculate the charged pion contribution to light-by-light (LBL) scattering to $\mathcal{O}(p^6)$. We show that the dominant corrections to the leading order (LO) result come from two low energy constants which show up in the form factors for the $\gamma\pi\pi$ and $\gamma\gamma\pi\pi$ vertices. Comparison with the existing models reveal a potentially significant omission - none include the pion polarizability corrections associated with the $\gamma\gamma\pi\pi$ vertex. We next consider alternative models where the pion polarizability is produced through exchange of the $a_1$ axial vector meson. These have poor UV behavior, however, making them unsuited for the $a_\mu^{\pi^+\pi^-}$ calculation. We turn to a simpler form factor modeling approach, generating two distinct models which reproduce the pion polarizability corrections at low energies, have the correct QCD scaling at high energies, and generate finite contributions to $a_\mu^{\pi^+\pi^-}$. With these two models, we calculate the charged pion contribution to the anomalous magnetic moment of the muon, finding values larger than those previously reported: $a_\mu^\mathrm{I} = -1.779(4)\times10^{-10}\,,\,a_\mu^\mathrm{II} = -4.892(3)\times10^{-10}$.

Pure Coulomb explosions of highly charged methane clusters investigated by a simple electrostatic model

The pure Coulomb explosions of the methane clusters (CA(4))(n), (light atom A = H or D) have been investigated by a simplified electrostatic model for both a single cluster and an ensemble of clusters with a given cluster size distribution. The dependence of the energy of ions produced from the explosions on cluster size and the charge state of the carbon ions has been analysed. It is found that, unlike the average proton energy which increases with the charge q of the carbon ions, the average deuteron energy tends to saturate as q becomes larger than 4. This implies that when the laser intensity is sufficiently high for the (CD4)(n) to be ionized to a charge state of (C4+D4+)(n), the neutron yield from a table-top laser-driven Coulomb explosion of deuterated methane clusters (CD4)(n) could be increased significantly by increasing the interaction volume rather than by increasing the laser intensity to produce the higher charge state (C6+D4+)(n). The flight-time spectra of the carbon ions and the light ions have also been studied.

Sputtering by multiply-charged ions, and preferential sputtering of isotopic mixtures

Collector-type experiments have been conducted to investigate two different aspects of sputtering induced by keV ions. The first study looked for possible ejection mechanisms related to the primary charge state of the projectile. Targets of CsI and LiNbO_3 were bombarded with 48 keV Ar^(q+), and a Au target was bombarded with 60 keV Ar^(q+), for q = 4, 8, and 11. The collectors were analyzed using heavy-ion Rutherford backscattering spectroscopy to determine the differential angular sputtering yields; these and the corresponding total yields were examined for variations as a function of projectile charge state. For the Au target, no significant changes were seen, but for the insulating targets slight (~10%) enhancements were observed in the total yields as the projectile charge state was increased from 4+ to 11+.

In the second investigation, artificial ^(92)Mo/^(100)Mo targets were bombarded with 5 and 10 keV beams of Ar^+ and Xe^+ to study the isotopic fractionation of sputtered neutrals as a function of emission angle and projectile fluence. Using secondary ion mass spectroscopy to measure the isotope ratio on the collectors, material ejected into normal directions at low bombarding fluences (~ 10^(15) ions cm^(-2)) was found to be enriched in the light isotope by as much as ~70‰ compared to steady state. Similar results were found for secondary Mo ions sputtered by 14.5 keV O^-. For low-fluence 5 keV Xe^+ bombardment, the light-isotope enrichment at oblique angles was ~20‰ less than the corresponding enrichment in the normal direction. No angular dependence could be resolved for 5 keV Ar^+ projectiles at the lowest fluence. The above fractionation decreased to steady-state values after bombarding fluences of a few times 10^(16) ions cm^(-2) , with the angular dependence becoming more pronounced. The fractionation and total sputtering yield were found to be strongly correlated, indicating that the above effects may have been related to the presence of a modified target surface layer. The observed effects are consistent with other secondary ion measurements and multiple-interaction computer simulations, and are considerably larger than predicted by existing analytic theory.

Theoretical and experimental investigations of the flocculation of charged particles in aqueous solutions by polyelectrolytes of opposite charge

An electrostatic mechanism for the flocculation of charged particles by polyelectrolytes of opposite charge is proposed. The difference between this and previous electrostatic coagulation mechanisms is the formation of charged polyion patches on the oppositely charged surfaces. The size of a patch is primarily a function of polymer molecular weight and the total patch area is a function of the amount of polymer adsorbed. The theoretical predictions of the model agree with the experimental dependence of the polymer dose required for flocculation on polymer molecular weight and solution ionic strength.

A theoretical analysis based on the Derjaguin-Landau, Verwey- Overbeek electrical double layer theory and statistical mechanical treatments of adsorbed polymer configurations indicates that flocculation of charged particles in aqueous solutions by polyelectrolytes of opposite charge does not occur by the commonly accepted polymerbridge mechanism.

A series of 1, 2-dimethyl-5 -vinylpyridinium bromide polymers with a molecular weight range of 6x10^3 to 5x10^6 was synthesized and used to flocculate dilute polystyrene latex and silica suspensions in solutions of various ionic strengths. It was found that with high molecular weight polymers and/or high ionic strengths the polymer dose required for flocculation is independent of molecular weight. With low molecular weights and/or low ionic strengths, the flocculation dose decreases with increasing molecular weight.

I. A recirculating charged-couple device. II. The mercury selenide on N-silicon Schottky barrier

A recirculating charge-coupled device structure has been devised. Entrance and exit gates allow a signal to be admitted, recirculated a given number of times, and then examined. In this way a small device permits simulation of a very long shift register without passing the signal through input and output diffusions. An oscilloscope motion picture demonstrating degradation of an actual circulating signal has been made. The performance of the device in simulating degradation of a signal by a very long shift register is well fit by a simple model based on transfer inefficiency.

Electrical properties of the mercury selenide on n-type chemically-cleaned silicon Schottky barrier have been studied. Barrier heights measured were 0.96 volts for the photoresponse technique and 0.90 volts for the current-voltage technique. These are the highest barriers yet reported on n-type silicon.