Dependence of the density of solutions of alkali metal halides on the composition of methylpyrrolidone-water mixed solvents

The densities of solutions of alkali metal halides in methylpyrrolidone (MP)-water mixtures were measured at 298.15 K over the entire range of mixed solvent compositions. The standard partial molar volumes of the electrolytes \(\overline {V_2^ \circ } \) were calculated. The \(\overline {V_2^ \circ } \) values of alkali metal halides in MP-H₂O mixtures were related linearly to the \(\overline {V_2^ \circ } \) values in aqueous solutions. These dependences were used to determine the standard partial molar volumes of ions \(\overline {V_i^ \circ } \) in the mixtures studied. The standard partial molar volumes of transfer of the ions from water into MP-water mixtures were calculated.     

Surface-plasmon-mediated single-molecule fluorescence through a thin metallic film

We demonstrate that fluorescence of single molecules in the nanometric vicinity of a thin gold film can be effectively excited and detected through the film with an epi-illumination scanning confocal microscope. A full theoretical treatment of the fluorescence signal indicates that both excitation and emission are surface-plasmon mediated. Remarkably, the number of photons detectable from chromophores perpendicular to the interface is enhanced by the presence of the metal.     

An Experimental Investigation of the Liquid Flow Induced by a Pulsed Electrical Discharge Plasma

In this work, particle image velocimetry has been used to visualize and quantify plasma-induced flow fields in liquid water. Experiments were performed in a rod-plane plasma reactor with a thin wire electrode suspended above the surface of the liquid in argon gas and a grounded plate immersed in the liquid. The velocity field has been quantified for two types of solutions: (1) aqueous NaCl solutions of varying solution conductivities and discharge frequencies and (2) aqueous NaCl solutions containing varying concentrations of the following four organic compounds: rhodamine B dye, caffeine, fluoxetine, and perfluorooctanoic acid. Results show that in neat water and aqueous caffeine solutions, the liquid is “pulled” along by the interaction of the gas molecules with the liquid molecules at the free surface and thus the direction of the liquid flow is in the direction of the gas phase flow (i.e., away from the discharge location). However, the flow was reversed (i.e., towards the discharge) for those solutions with strong surfactants such as perfluorooctanoic acid. The magnitude of the reversal depended on the initial concentration of the compound and for some compounds as time progressed the reversed flow pattern weakened and then reverted to a normal flow pattern. To determine the most likely cause of these flow reversals, a simple numerical model of the velocity field was developed to estimate relative contributions of various flow inducing mechanisms. The model indicates that in the presence of surfactants, Marangoni stresses are responsible for inducing the flow in the liquid.     

Immobilized streptavidin gradients as bioconjugation platforms

Surface density gradients of streptavidin (SAV) were created on solid surfaces and demonstrated functionality as a bioconjugation platform. The surface density of immobilized streptavidin steadily increased in one dimension from 0 to 235 ng cm(-2) over a distance of 10 mm. The density of coupled protein was controlled by its immobilization onto a polymer surface bearing a gradient of aldehyde group density, onto which SAV was covalently linked using spontaneous imine bond formation between surface aldehyde functional groups and primary amine groups on the protein. As a control, human serum albumin was immobilized in the same manner. The gradient density of aldehyde groups was created using a method of simultaneous plasma copolymerization of ethanol and propionaldehyde. Control over the surface density of aldehyde groups was achieved by manipulating the flow rates of these vapors while moving a mask across substrates during plasma discharge. Immobilized SAV was able to bind biotinylated probes, indicating that the protein retained its functionality after being immobilized. This plasma polymerization technique conveniently allows virtually any substrate to be equipped with tunable protein gradients and provides a widely applicable method for bioconjugation to study effects arising from controllable surface densities of proteins.     

Designing 1D grating for extraordinary optical transmission for TM polarization

Due to their high brightness at resonance, 1D metallo-dielectric transmission gratings have been proposed as useful in a number of applications including Scanning Near-field Optical Microscopy (SNOM), flat-panel displays, spatial light modulators and optoelectronic devices. In this article, using the Fabry–Perot resonance condition and numerical optimization, we demonstrate a design methodology of 1D grating structure that provides resonance at a desired wavelength for Transverse Magnetic (TM) polarization. Depending on grating and substrate materials and target applications under consideration, our method provides optimum grating parameters, i.e. slit width, grating period and thickness adaptively. Application specific requirements such as the bandwidth around a resonance can be adjusted by setting appropriate constraint functions. Simulations results from modal analysis show that resonances are achieved at wavelengths for which grating parameters have been optimized.     

Structural and optical properties of Er, Yb co-doped Y2O3 thin films

Thin Er³⁺, Yb³⁺ co-doped Y₂O₃ films were grown on (1 0 0) YAG substrates by pulsed laser deposition. Ceramic targets having different active ion concentration were used for ablation. The influence of the rare-earth content and oxygen pressure applied during the deposition on the structural, morphological and optical properties of the films were investigated. The films deposited at the lower pressure, 1 Pa, and at 1/10 Er to Yb doping ratio are highly textured along the (1 1 1) direction of the Y₂O₃ cubic phase. In addition to the crystalline structure, these films possess smoother surface compared to those prepared at the higher pressure, 10 Pa. All other films are polycrystalline, consisting of cubic and monoclinic phases of Y₂O₃. The rougher surface of the films produced at the higher-pressure leads to higher scattering losses and different behavior of the reflectivity spectra. Optical anisotropy in the films of less than 0.004 was measured regardless of the monoclinic structure obtained. Waveguide losses of about 1 dB/cm at 633 nm were obtained for the films produced at the lower oxygen pressure.     

Role of positive ions in determining the deposition rate and film chemistry of continuous wave hexamethyl disiloxane plasmas

New data shed light on the mechanisms of film growth from low power, low pressure plasmas of organic compounds. These data rebalance the widely held view that plasma polymer formation is due to radical/neutral reactions only and that ions play no direct role in contributing mass at the surface. Ion reactions are shown to play an important role in both the plasma phase and at the surface. The mass deposition rate and ion flux in continuous wave hexamethyl disiloxane (HMDSO) plasmas have been studied as a function of pressure and applied RF power. Both the deposition rate and ion flux were shown to increase with applied power; however, the deposition rate increased with pressure while the ion flux decreased. Positive ion mass spectrometry of the plasma phase demonstrates that the dominant ionic species is the (HMDSO-CH(3))(+) ion at m/z 147, but significant fragmentation and subsequent oligomerization was also observed. Chemical analysis of the deposits by X-ray photoelectron spectroscopy and secondary ion mass spectrometry show that the deposits were consistent with deposits reported by previous workers grown from plasma and hyperthermal (HMDSO-CH(3))(+) ions. Increasing coordination of silicon with oxygen in the plasma deposits reveals the role of ions in the growth of plasma polymers. Comparing the calculated film thicknesses after a fixed total fluence of 1.5 × 10(19) ions/m(2) to results for hyperthermal ions shows that ions can contribute significantly to the total absorbed mass in the deposits.     

Fluorescence Study of the Membrane Effects of Aggregated Lysozyme

The last decade has seen unprecedented upsurge of interest in the structural and toxic properties of particular type of protein aggregates, amyloid fibrils, associated with a number of pathological states. In the present study fluorescence spectroscopy technique has been employed to gain further insight into the membrane-related mechanisms of amyloid toxicity. To this end, erythrocyte model system composed of liposomes and hemoglobin was subjected to the action of oligomeric and fibrillar lysozyme. Acrylamide quenching of lysozyme fluorescence showed that solvent accessibility of Trp₆₂ and Trp₁₀₈ increases upon the protein fibrillization. Resonance energy transfer measurements suggested the possibility of direct complexation between hemoglobin and aggregated lysozyme. Using the novel squaraine dye SQ-1 it was demonstrated that aggregated lysozyme is capable of inhibiting lipid peroxidation processes. Fluorescent probes pyrene, Prodan and diphenylhexatriene were employed to characterize the membrane-modifying properties of hemoglobin and lysozyme. Both oligomeric and fibrillar forms of lysozyme were found to exert condensing influence on lipid bilayer structure, with the membrane effects of fibrils being less amenable to modulation by hemoglobin.     

Effect of the Loading of Metal Salts on the Formation of Fe–Co Solid Solution Nanoparticles in the IR-Pyrolyzed Chitosan Matrix

Russian Journal of General Chemistry - In this study, metal-carbon nanocomposites have been synthesized via the method of simultaneous formation of bimetallic Fe–Co nanoparticles and carbon...