Conducting polymer “nanogates” – Controllable diffusivities in thin films of novel tether-containing sulfonated polythiophenes

We describe a nanoscale gating effect by an atypical tether-containing polythiophene, [poly(thiophene-3-carboxylic acid 2-(2-(2-(2-ethoxy-ethoxymethyl sulfonate)-ethoxy)-ethoxy)-amide], referred to as poly(TP-OEG-SO₄). Cyclic voltammetry data permitted us to calculate liquid-phase ion diffusivities in the polymer as a function of its oxidation state. Diffusivities are more than 350 times higher in the oxidized state versus the reduced state. As a control, poly 3′,4′-dimethyl-[2,2′;5′,2″] terthiophene (DMPT) was synthesized and characterized. On comparing both polymers in the reduced state, we find diffusivities in poly(TP-OEG-SO₄) to be more than 4500 times lower than in poly(DMPT). To explain this behavior, we propose a model that features a charge-balancing mechanism by the sulfonate tethers in poly(TP-OEG-SO₄), which causes nanoporous regions around the polymer main chains to be opened and closed, leading to the large observed differences in diffusivities. These data suggest that the polymer poly(TP-OEG-SO₄) is evidently able to act as a reversible “nanogate” with an open pore structure when oxidized, and a closed one when reduced.     

Catch‐to‐stock dependence: The case of small pelagic fishery with bounded harvesting effort

Biologic characteristics of schooling fish species explain why the rates of harvesting in pelagic fisheries are not proportional to the existent stock size and may exhibit no variation between the periods of fish abundance and scarcity. Therefore, the stock‐dependent nonlinearities in catchability must be reflected in the design of flexible fishing policies, which target the sustainable exploitation of this important natural resource. In this study, such nonlinearities are expressed through eventual variability of the “catch‐to‐stock” parameter that measures the sensitivity of an additional catch yield to marginal changes in the fish‐stock level. Using the optimal control modeling framework, we establish that each value of the “catch‐to‐stock” parameter generates a unique steady‐state size of the fish stock and the latter engenders an optimal fishing policy that can be sustained as long as the “catch‐to‐stock” parameter remains unchanged. We also prove the continuous dependence of the steady‐state stock and underlying fishing policy upon the mentioned “catch‐to‐stock” parameter and then focus on the analysis of the equilibrium responses to changes in this parameter induced by external perturbations. Recommendations for Resource Managers

• Marginal catches of pelagic fish stocks do not react in a linear way to changes in existing stock level, and the latter is captured in our model by the “catch‐to‐stock” parameter . Each observable value of engenders a unique steady‐state stock size that defines an optimal fishing policy, which can be sustained as long as remains unchanged.
• The ability of fishery managers to detect variations in the levels of hyperstability expressed by the “catch‐to‐stock” parameter may help them to anticipate new equilibrium responses in stock evolution and to make timely adjustments in the fishing policy.
• Plausible estimations of the “catch‐to‐stock” parameter , as well as detection of its possible alterations, can be carried out within the framework of Management Strategy Evaluation (MSE) approach where different data collected inside and outside the fishery are contrasted via the validation of a relatively simple decision‐making model (presented in this paper) coupled with other “operation models” of higher complexity.
• If the “catch‐to‐stock” parameter cannot be reasonably assessed (), the fishery managers may rely upon the lower bound of stationary stock size, which depends on economic and biological factors (such as the present and future economic values of the exploited fish stock, its marginal productivity, and underlying dynamics of biological growth).

     

Electric field-induced nucleation and growth of focal-conic and stripe domains in a smectic A liquid crystal

We have studied the electric field-induced first order transition from a homeotropic smectic A structure to a polydomain texture that occurs through the nucleation of toric focal-conic domains (TFCDs). The process involves two steps: first, nucleation of TFCDs of a size larger than a critical radius a*, and then a steady growth of TFCDs to a secondary critical radius a**, when surface anchoring effects become dominant and cause a transition from a circular TFCD to an elongated stripe domain (SD). Studies were performed for pure smectic A materials and for smectic A doped with kunipia nanoparticles. Non-destructive 3D imaging with fluorescence confocal polarizing microscopy showed that field-induced TFCDs can nucleate in the smectic A bulk. Clay particles reduce the energy barrier for nucleation as they distort the smectic A layers and thus increase the ground state energy. Simple elastic models of the TFCD and SD allow us to describe the qualitative features of the observed phenomena.     

Reproducibility of Biomolecular Corona Experiments: A Primer for Reliable Results

The biomolecular corona is a key component controlling the identity of nanomaterials in physiological environments. Studies aimed at identifying factors shaping the biomolecular corona have proliferated in the last decade but have been performed by research groups with different backgrounds. Efforts made within the scientific community to guarantee the reproducibility of experimental data have identified protocol standardization as an indispensable step for advancing knowledge in this arena. To contribute to fulfill this gap, here the relevance of interoperator variability in biomolecular corona studies and the benefits arising from automated systems usage are explored. Moreover, the role of molecular crowding during nanoparticle-biofluid incubation and the effect of washing the pellet during corona isolation are thoroughly investigated. It is believed that the findings will help researchers enhance the accuracy of experimental design and reporting.     

Visualising mouse neuroanatomy and function by metal distribution using laser ablation-inductively coupled plasma-mass spectrometry imaging

Metals have a number of important roles within the brain. We used laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to map the three-dimensional concentrations and distributions of transition metals, in particular iron (Fe), copper (Cu) and zinc (Zn) within the murine brain. LA-ICP-MS is one of the leading analytical tools for measuring metals in tissue samples. Here, we present a complete data reduction protocol for measuring metals in biological samples, including the application of a pyramidal voxel registration technique to reproducibly align tissue sections. We used gold (Au) nanoparticle and ytterbium (Yb)-tagged tyrosine hydroxylase antibodies to assess the co-localisation of Fe and dopamine throughout the entire mouse brain. We also examined the natural clustering of metal concentrations within the murine brain to elucidate areas of similar composition. This clustering technique uses a mathematical approach to identify multiple ‘elemental clusters’, avoiding user bias and showing that metal composition follows a hierarchical organisation of neuroanatomical structures. This work provides new insight into the distinct compartmentalisation of metals in the brain, and presents new avenues of exploration with regard to region-specific, metal-associated neurodegeneration observed in several chronic neurodegenerative diseases.     

Use of Gemini surfactants to stabilize TiO2 P25 colloidal dispersions

Photocatalytically active TiO₂ P25 nanoparticles, widely used for practical applications, were investigated. The nominal size of TiO₂ P25 nanoparticles is 21 nm, but they easily agglomerate in aqueous media, depending on pH and ionic strength. TiO₂ P25 aqueous dispersions were stabilized by alkanediyl-α,ω-bis-N-dodecyl-N, N′-dimethyl-ammonium bromide, cationic Gemini surfactant. The optimal conditions required to obtain stable dispersions, without formation of large agglomerates, were experienced. The stabilization of TiO₂ P25 nanoparticles by cationic Gemini surfactant was investigated in some details. Different amounts of Gemini surfactant were used, at concentrations between 1.0 and 250 × 10⁻⁶ mol L⁻¹, well below the critical micelle concentration. Dynamic light scattering and zeta potential analyses estimated the particle size and the dispersions stability. When the proper amount of Gemini surfactant was used, the resulting nanoparticles were still poly-disperse, but large agglomerates disappeared and were remarkably redispersible.     

Sol-gel microextraction phases for sample preconcentration in chromatographic analysis

Sol-gel technology provides a simple and reliable method for solid-phase microextraction (SPME) fiber preparation through in situ creation of surface-bonded organic-inorganic hybrid coatings characterized by enhanced thermal stability and solvent-resistance properties that are important for the coupling of SPME with GC and HPLC, respectively. The sol-gel coating technology has led to the development of an extensive array of sol-gel sorbent coatings for SPME. In this article, sol-gel microextraction coatings are reviewed, with particular attention on their synthesis, characterization, and applications in conjunction with GC and HPLC analyses. In addition, the development of sol-gel-coated stir bars, their inherent advantages, and applications are discussed. Next, the development and applications of sol-gel capillary microextraction (CME) in hyphenation with GC and HPLC is extensively reviewed. The newly emerging germania- and titania-based sol-gel microextraction phases look promising, especially in terms of pH and hot solvent stability. Finally, sol-gel monolithic beds for CME are reviewed. Such monolithic beds are in a position to greatly improve the extracting capabilities and enhanced sensitivity in CME.     

Structural relationships in small molecule interactions governing gas-phase enantioselectivity and zwitterionic formation

Gas-phase zwitterionic amino acids were formed in complexes of underivatized beta-cyclodextrin through reactions with a neutral base, n-propylamine. The reaction was performed in the analyzer cell of an electrospray ionization-Fourier transform mass spectrometer. Most of the natural amino acids were studied with three cyclodextrin hosts including alpha-, beta-, and gamma-cyclodextrin to understand better the structural features that lead to the stabilization of the zwitterionic complexes. Molecular dynamics calculations were performed to provide insight into the structural features of the complexes. The rate constants of the reactions were obtained through kinetic plots. Examination of both L- and D-enantiomers of the amino acid showed that the reaction was enantioselective. The reaction was then employed to analyze mixtures of Glu enantiomers naturally occurring in the bacteria Bacillus licheniformis.