Parameters influencing the capacitive behavior of carbon composite electrodes: composition,morphology, electrical conductivity,and surface chemistry

Journal of Solid State Electrochemistry - The interplay and overlapping of several factors determine the capacitive behavior of carbon composite electrodes for capacitive energy storage...     

Preparation of HMWCNT/PLLA nanocomposite scaffolds for application in nerve tissue engineering and evaluation of their physical,mechanical and cellular activity properties

This study was aimed to prepare biodegradable and porous nanocomposite scaffolds with microtubular orientation structure as a model for nerve tissue engineering by thermally induced phase separation (TIPS) method using dioxane as the solvent, crystalline poly (L‐lactic acid) (PLLA) and multi‐walled carbon nanotubes (MWCNTs). In order to overcome dispersion of MWCNTs in the PLLA matrix, heparinization of MWCNTs was performed. Solvent crystallization, oriented structure, the mean pore diameter and porosity percentage of the scaffolds were controlled by fundamental system parameters including temperature‐gradient of the system, polymer solution concentration and carbon nanotube content. Scanning Electron Microscopy (SEM), ImageJ, software and dynamic mechanical thermal analysis (DMTA) were used to investigate the structural and mechanical properties. TEM observation was carried out for characterization of nanotube dispersion in PLLA. It was found that the scaffolds containing heparinized multi‐walled carbon nanotubes (HMWCNTs) exhibited higher storage modulus, better carbon nanotube (CNT) dispersion and tubular orientation structure than those with non heparinized MWCNTs. In‐vitro studies were also conducted by using murine P₁₉ cell line as a suitable model system to analyze neuronal differentiation over a 2‐week period. Immunofluorescence and DAPI staining were used to confirm the cells' attachment and differentiation on the PLLA/HMWCNT nanocomposite scaffolds. Based on the results, we can conclude that the PLLA/HMWCNT scaffolds enhanced the nerve cell differentiation and proliferation, and therefore, acted as a positive cue to support neurite outgrowth. Copyright © 2015 John Wiley & Sons, Ltd.     

Photochemical properties of selected flavonol dyes: Effects on their separation using capillary electrophoresis

Flavonols are naturally occurring dyes that can be extracted from plants. Because of their antioxidant properties, they are thought to have health benefits. In this study, the photochemical degradation properties of selected flavonols were investigated. Dilute solutions of dyes were exposed to light from a broadband visible light source, and the rate of photodegradation was determined by measuring the decrease in fluorescence of the dyes with respect to time. At pH 9.24, the first-order rate constants for 10?µg?mL^?1 solutions of myricetin, quercetin, kaempferol, and morin were 0.468, 0.162, 0.108, and 0.126?s^?1, respectively. Interestingly, the stability of these historical dyes was also found to be greatly affected by pH. Awareness of the photochemical properties and stability of flavonol dyes is very important for capillary electrophoresis (CE) separations. Photodegradation of the flavonol dyes under the alkaline conditions (pH 9.2) used in CE can have a profound effect on the reproducibility of repeated separations. Even a modest decrease in pH (pH 8.5) greatly improved the stability of these dyes and enabled the successful separation of these flavonol dyes with minimal degradation over time.     

Tailoring MWD of Bimodal Polyethylene in the Presence of Ziegler-Natta Catalyst

Summary: Linear poly (ethylene-co-1-butene) was produced through two-step polymerization in one reactor using a Ziegler-Natta catalyst, where in the first step, low molecular weight homopolymer of ethylene in the presence of hydrogen and in the next step, high molecular weight copolymer of ethylene with 1-butene in the absence of hydrogen were produced. Molecular weight distribution of bimodal polyethylene was tailored through adjustment of polymerization time of each stage and hydrogen concentration of the first stage. Increasing hydrogen concentration shifted the molecular weight distribution curve to the lower molecular weights and broadened molecular weight distribution while interestingly increased high molecular weight incorporation of copolymer produced in the second stage due to increasing of reaction rate in the second step. To achieve bimodal molecular weight distribution, the polymerization times of the first and the second steps, which are highly dependent on the amount of hydrogen, were adjusted properly. The effects of the mentioned parameters on the processability as well as rheological properties of some samples were investigated. The rheological results showed shear thinning behavior of all specimens and confirmed the changes in molecular weight and molecular weight distribution. It was also demonstrated that the melt miscibility between low molecular weight and high molecular weight fractions improved with increasing of chains having very low molecular weight.     

Kinetic modeling of the ethylbenzene/xylene isomerization reaction over HZSM-5 zeolites revisited

In this article, a binderless dealuminated HZSM-5 zeolite (Si/Al = 41.4) was used as a catalyst for the isomerization of a mixture of ethylbenzene and xylene. The experimental results indicated that at low residence times the catalyst is effective to isomerize the ethylbenzene into xylenes. A comprehensive kinetic model considering chemisorption, surface chemical reactions, and diffusional processes was developed for this reaction. The intrinsic activation energy (71.99 kJ mol⁻¹) for the surface reaction of ethylbenzene into m-xylene was calculated for the first time, and the corresponding intrinsic activation energies for o-xylene to m-xylene and m-xylene to p-xylene surface reactions were calculated to be 59.45 and 50.68 kJ mol⁻¹, respectively. Lower apparent values have been reported in the literature, and we rationalize that they correspond to multistep processes and intrinsically include a negative activation energy pertaining to chemisorption. The results also revealed that the ethylbenzene diffusion within the zeolite channels was four orders of magnitude smaller than p-xylene.     

Synthesis of 5-(4-aminophenyl)-2-(arylamino)-1,3,4-thiadiazoles and their schiff base derivatives as antimycobacterial agents

The condensation reaction of 5-(4-aminophenyl)-N-aryl-1,3,4-thiadiazol-2-ylamines with salicyl-aldehyde, 3-hydroxybenzaldehyde, 4-hydroxybenzaldehyde, 5-bromosalicylaldehyde, 5-chlorosalicyl-aldehyde, 4-methoxybenzaldehyde, 3-nitrobenzaldehyde, and 4-nitrobenzaldehyde results in series of new Schiff bases. The synthesized compounds were tested for their antimicrobial efficiency against Mycobacterium smegmatis PTCC 1307 in vitro. All compounds showed significant antiproliferative activity against M. smegmatis.     

Binding Studies of AICAR and Human Serum Albumin by Spectroscopic,Theoretical, and Computational Methodologies

The interactions of small molecule drugs with plasma serum albumin are important because of the influence of such interactions on the pharmacokinetics of these therapeutic agents. 5-Aminoimidazole-4-carboxamide ribonucleoside (AICAR) is one such drug candidate that has recently gained attention for its promising clinical applications as an anti-cancer agent. This study sheds light upon key aspects of AICAR’s pharmacokinetics, which are not well understood. We performed in-depth experimental and computational binding analyses of AICAR with human serum albumin (HSA) under simulated biochemical conditions, using ligand-dependent fluorescence sensitivity of HSA. This allowed us to characterize the strength and modes of binding, mechanism of fluorescence quenching, validation of FRET, and intermolecular interactions for the AICAR–HSA complexes. We determined that AICAR and HSA form two stable low-energy complexes, leading to conformational changes and quenching of protein fluorescence. Stern–Volmer analysis of the fluorescence data also revealed a collision-independent static mechanism for fluorescence quenching upon formation of the AICAR–HSA complex. Ligand-competitive displacement experiments, using known site-specific ligands for HSA’s binding sites (I, II, and III) suggest that AICAR is capable of binding to both HSA site I (warfarin binding site, subdomain IIA) and site II (flufenamic acid binding site, subdomain IIIA). Computational molecular docking experiments corroborated these site-competitive experiments, revealing key hydrogen bonding interactions involved in stabilization of both AICAR–HSA complexes, reaffirming that AICAR binds to both site I and site II.     

Catalytic Activity of Alkali Metal Cations for the Chemical Oxygen Reduction Reaction in a Biphasic Liquid System Probed by Scanning Electrochemical Microscopy

Chemical reduction of dioxygen in organic solvents for the production of reactive oxygen species or the concomitant oxidation of organic substrates can be enhanced by the separation of products and educts in biphasic liquid systems. Here, the coupled electron and ion transfer processes is studied as well as reagent fluxes across the liquid|liquid interface for the chemical reduction of dioxygen by decamethylferrocene (DMFc) in a dichloroethane-based organic electrolyte forming an interface with an aqueous electrolyte containing alkali metal ions. This interface is stabilized at the orifice of a pipette, across which a Galvani potential difference is externally applied and precisely adjusted to enforce the transfer of different alkali metal ions from the aqueous to the organic electrolyte. The oxygen reduction is followed by H₂O₂ detection in the aqueous phase close to the interface by a microelectrode of a scanning electrochemical microscope (SECM). The results prove a strong catalytic effect of hydrated alkali metal ions on the formation rate of H₂O₂, which varies systematically with the acidity of the transferred alkali metal ions in the organic phase.