Outstanding room-temperature capacitance of biomass-derived microporous carbons in ionic liquid electrolyte

A remarkable capacitance of 180 F·g^− 1 (at 5 mV·s^− 1) in solvent-free room-temperature ionic liquid electrolyte, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, was achieved in symmetric supercapacitors using microporous carbons with a specific surface area of ca. 2000 m²·g^− 1 calculated from gas sorption by the 2D-NLDFT method. The efficient capacitive charge storage was ascribed to textural properties: unlike most activated carbons, high specific surface area was made accessible to the bulky ions of the ionic liquid electrolyte thanks to micropores (1–2 nm) enabled by fine-tuning chemical activation. From the industrial perspective, a high volumetric capacitance of ca. 80 F·cm^− 3 was reached in neat ionic liquid due to the absence of mesopores. The use of microporous carbons from biomass waste represents an important advantage for large-scale production of high energy density supercapacitors.     

Plasma clearance of bacteriophage Qbeta particles as a function of surface charge

Self-assembled protein capsids have gained attention as a promising class of nanoparticles for biomedical applications due to their monodisperse nature and versatile genetic and chemical tailorability. To determine the plasma clearance and tissue distribution in mice of the versatile capsid of bacteriophage Qbeta, the particles were decorated with gadolinium complexes using the CuI-mediated azide-alkyne cycloaddition reaction. Interior surface labeling was engineered by the introduction of an azide-containing unnatural amino acid into the coat protein for the first time. Clearance rates were conveniently monitored by quantitative detection of Gd using inductively coupled plasma optical emission spectroscopy and were found to be inversely proportional to the number of complexes attached to the exterior surface of the particle. This phenomenon was correlated to changes in exterior surface charge brought about by acylation of surface-exposed amine groups in the initial step of the bioconjugation protocol. When primary amine groups were reintroduced by azide-alkyne coupling, the circulation time increased accordingly. These results show that nanoparticle trafficking may be tailored in predictable ways by chemical and genetic modifications that modulate surface charge.     

Effect of surface functionalities on gas adsorption in microporous carbons: a grand canonical Monte Carlo study

In an attempt to offer a more realistic picture of adsorption in highly heterogeneous porous systems, such as oxygen functionalized porous carbons, we consider a series of carbon surfaces baring different amounts of oxygen functionalities (hydroxyl and epoxy). These surfaces are used to construct “oxidized” slit pores of varying width and functionality. With the aid of such inhomogeneous structures we study the interaction of Ar (87 K) inside “functionalized” pores and report grand canonical Monte Carlo adsorption simulations results. Based on our simulation data, we discuss the role of chemical heterogeneity on adsorbed/gas phase equilibrium properties such as density, heat of adsorption, and molecular packing within the pores. Comparisons are made with the case of the oxygen–free (completely homogeneous) slit pore models and conclusions on the suitability of Ar based pore size distributions for functionalized porous carbons are drawn.     

Light transmission study for determination of pore size distribution in microporous membranes

A new method combining light transmission and bubble pressure has been tried to determine the pore size distribution of microporous membranes. The method is based on a simple phenomenon that the light transmitivity through an opaque porous membrane increases as its pores are filled with a transparent liquid. The pore size distributions of Durapore HVHP and Sartorius PTFE membranes were tested using the new method and the results were compared with those obtained by the fluid displacement and the mercury intrusion methods.     

Optical biosensors as a tool for early determination of absorption and distribution parameters of lead candidates and drugs

Specific molecular interactions provide a fundamental mechanism for selectivity in every aspect of biological structure and function. The ability to measure quantitatively such interaction properties across a wide range of affinity, size, and purity is a growing need. A short review on the use of the optical biosensor techniques is presented, focused on its application for determining the absorption and distribution parameters of drugs and lead compounds. The basic biosensor technology principles are described together with some immobilization methods commonly used for the preparation of selective and specific biosensor surfaces for assays. Some relevant research topics in the field of small molecule recognition phenomena are presented as examples, including binding to plasma proteins, and binding to lipid membranes, in the frame of ADME (absorption, distribution, metabolism and excretion) parameter determinations. These applications demonstrate the applicability of such techniques to the study of low mass compounds and illustrates their potential for the screening of libraries of compounds with regard to their binding to target bio-molecules as part of drug development.     

Precise isotope ratio measurements as a unique tool in modern analytical chemistry

Analytical and Bioanalytical Chemistry -     

Atomic and ionic fluorescence dip spectroscopy as a tool for flame and plasma diagnostics

When two pulsed dye lasers are tuned in spatial and temporal coincidence to two connected atomic transitions in a flame or plasma, the resonance fluorescence monitored from the first excited level decreases due to the depletion of the population of that level induced by the second laser excitation step. The monitoring of such a decrease (fluorescence dip) can be shown from simple theoretical considerations to be useful for diagnostic studies and for the evaluation of some fundamental parameters of the atomic transition involved in the second-excitation step. Both steady state and transient behaviour are discussed. The information content of the fluorescence dip is similar to that of the saturated fluorescence signal. However, several distinct advantages are offered by the new technique especially when the level reached by the second excitation step is close to the ionization limit of the atom.     

Compensation effect as a tool in investigating surface reaction mechanisms

The apparent kinetic parameters for the dehydrohalogenation of 1-bromo-2-methylpropane to isopropylene on alumina modified with alkali halides have been calculated. Both true and apparent kinetic parameters give kinetic compensation effects, with different coherence of the Hv.s.S points. This leads to useful conclusions about the fitness of the two kinds of parameters for handling surface reaction mechanisms.

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Thermochemical charge generation in polymer-salt films as a function of temperature

Potential was studied as a function of temperature during charge generation in poly(vinyl alcohol) films containing ammonium heptamolybdate, copper nitrate, and polyoxometalate (NH₄)₄₂[Mo ₇₂ ^VI Mo ₆₀ ^V O₃₇₂(HCOO)₃₀(H₂O)₇₂] · 30HCOONH₄ · 250H₂O. The range of the strongest charge generation and its bounds were determined. The results are matched to thermal analysis data. Charge generation correlates with evolution of volatiles from the films.     

Electrophoretic motion of a spherical particle with a symmetric nonuniform surface charge distribution in a nanotube

The electrophoretic motion of a spherical nanoparticle, subject to an axial electric field in a nanotube filled with an electrolyte solution, has been investigated using a continuum theory, which consists of the Nernst-Planck equations for the ionic concentrations, the Poisson equation for the electric potential in the solution, and the Stokes equation for the hydrodynamic field. In particular, the effects of nonuniform surface charge distributions around the nanoparticle on its axial electrophoretic motion are examined with changes in the bulk electrolyte concentration and the surface charge of the tube's wall. A particle with a nonuniform charge distribution is shown to induce a corresponding complex ionic concentration field, which in turn influences the electric field and the fluid motion surrounding the particle and thus its electrophoretic velocity. As a result, contrary to the relatively simple dynamics of a particle with a uniform surface charge, dominated by the irradiating electrostatic force, that with a nonuniform surface charge distribution shows various intriguing behaviors due to the additional interplay of the nonuniform electro-osmotic effects.     

Streaming potential and surface charge density of microporous membranes with pore diameter in the range of thickness

A system formed by two phases bathing a microporous membrane is studied considering its behavior as a dynamic system. So, the natural frequencies for each used membrane is determined and then, applying a flow ramp with a rate sufficiently small, the streaming potential can be obtained from the slope of the pressure values versus electrical potential.The determination of the electric potential inside the pores, φ, requires to solve the Poisson–Böltzmann equation in the case of membranes with pore diameter in the range of thickness, for which the radial components of velocity of the fluid must be considered. Since there is no analytical solution, a numerical method was used to obtain φ. The electrical potential value at a distance equal to hydrodynamic radius from pore axis (zeta potential) is used to evaluate the streaming potential by the Helmholtz–Smoluchowsky relation. These values were compared with the experimental data accomplishing the suitable iterations over the surface charge density until coincidence.The values of the surface charge density for the studied membranes show a concentration dependence described by Langmuir’s model for the greatest pore diameters and Freundlich’s model for the smallest pore diameters.     

Response surface methodology (RSM) as a tool for optimization in analytical chemistry

A review about the application of response surface methodology (RSM) in the optimization of analytical methods is presented. The theoretical principles of RSM and steps for its application are described to introduce readers to this multivariate statistical technique. Symmetrical experimental designs (three-level factorial, Box-Behnken, central composite, and Doehlert designs) are compared in terms of characteristics and efficiency. Furthermore, recent references of their uses in analytical chemistry are presented. Multiple response optimization applying desirability functions in RSM and the use of artificial neural networks for modeling are also discussed.     

Ionic liquids as a tool for determination of metals and organic compounds in food analysis

Ionic liquids (ILs) are non-molecular solvents, which are mainly characterized as possessing low melting points, low-to-negligible vapor pressures, and high thermal stability. Their unique solvation properties, coupled to the fact that they can be structurally tailored for specific applications, have increased study of ILs in many areas of fundamental and applied chemistry. Thus, ILs have successfully been utilized as novel solvents in different extraction and microextraction schemes in recent years, but mainly with environmental samples.Food samples are quite complicated matrices from an analytical point of view. They contain a large range of chemical substances, and sometimes they also have a high fat content. Even with the most advanced analytical techniques, food sampling and food-sample preparation prior to the analytical determination are labor-intensive and time-consuming, and normally require relatively large amounts of organic solvents.In this review, we summarize the most recent analytical developments aimed at employing ILs as a tool in food analysis. We discuss practical applications to determine metals and organic compounds in food samples of quite different natures, with special emphasis to the extraction step at which the IL is introduced, and the advantages of the IL-based methods developed over conventional extraction methods.     

Dimensional changes as a function of charge injection in single-walled carbon nanotubes

Motivated by the central importance of charge-induced dimensional changes for carbon nanotube electromechanical actuators, we here predict changes in nanotube length and diameter as a function of charge injection for armchair and zigzag nanotubes having different diameters. Density functional theory with periodic boundary conditions is used, which we show provides results consistent with experimental observations for intercalated graphites. Strain-versus-charge relationships are predicted from dimensional changes calculated with a uniform background charge ("jellium") for representing the counterions. These jellium calculations are consistent with presented calculations that include specific counterions for intercalated graphite, showing that hybridization between the ions and the graphite sheets is unimportant. The charge-strain relationships calculated with the jellium approximation for graphite and isolated single-walled nanotubes are asymmetric with respect to the sign of charge transfer. The dependence of nanotube strain on charge approaches that for a graphite sheet for intermediate-sized metallic nanotubes and for larger diameter semiconducting nanotubes. However, the strain-charge curves strongly depend on nanotube type when the nanotube diameter is small. This reflects both the dependence of the frontier orbitals for the semiconducting nanotubes on the nanotube type and the pi-sigma mixing when the nanotube diameter is small.