Tetracyanoquinodimethanide adsorbed on a silica gel modified with titanium oxide for electrocatalytic oxidation of hydrazine

The electrocatalytical oxidation of hydrazine at low potential using tetracyanoquinodimethanide adsorbed on silica modified with titanium oxide was investigated by cyclic voltammetry and amperometry. The modified electrode was prepared modifying a carbon paste electrode employing lithium tetracyanoquinodimethanide adsorbed onto silica gel modified with titanium oxide. This electrode showed an excellent catalytic activity and stability for hydrazine oxidation. With this modified electrode, the oxidation potential of hydrazine was shifted toward less positive value, presenting a peak current much higher than those observed on a bare GC electrode. The linear response range, sensitivity and detection limit were, respectively, 2 up to 100 μmol l⁻¹, 0.36 μA l μmol⁻¹, and 0.60 μmol l⁻¹. The repeatability of the modified electrode evaluated in term of relative standard deviation was 4.2% for 10 measurements of 100 μmol l⁻¹ hydrazine solution. The number of electrons involved in hydrazine oxidation (4), the heterogenous electron transfer rate constant (1.08 × 10³ mol⁻¹ l s⁻¹), and diffusion coefficient (5.9 × 10⁻⁶ cm² s⁻¹) were evaluated with a rotating disk electrode.     

Voltammetric determination of 4-nitrophenol at a lithium tetracyanoethylenide (LiTCNE) modified glassy carbon electrode

The reduction of 4-nitrophenol (4-NP) has been carried out on a modified glassy carbon electrode using cyclic and differential pulse voltammetry (DPV). The sensor was prepared by modifying the electrode with lithium tetracyanoethylenide (LiTCNE) and poly-l-lysine (PLL) film. With this modified electrode 4-NP was reduced at −0.7 V versus SCE. The sensor presented better performance in 0.1 mol l⁻¹ acetate buffer at pH 4.0. The other experimental parameters, such as concentration of LiTCNE and PLL, pulse amplitude and scan rate were optimized. Under optimized operational conditions, a linear response range from 27 up to 23200 nmol l⁻¹ was obtained with a sensitivity of 3.057 nA l nmol⁻¹ cm⁻². The detection limit for 4-NP determination was 7.5 nmol l⁻¹. The proposed sensor presented good repeatability, evaluated in term of relative standard deviation (R.S.D.=4.4%) for n=10 and was applied for 4-NP determination in water samples. The average recovery for these samples was 103.0 (± 0.7)%.     

Absolute Conformation and Configuration of (2S, 3S)-3-Acetoxy-5-(dimethylaminoethyl)-2-(4-methoxyphenyl)-2,3-dihydro-1,5-benzothiazepin-4(5H)-one Chloride (Dilthiazem Hydrochloride)

Resolution of racemic cis-3-(2-aminophenylthio)-2-hydroxy-3-(4-methoxyphenyl) propionic acid ( 2 ) via the cinchonidine salt 3 , and brucine salt 4 , isolation of the calcium salts (+)- and (?)- 5 , as well as their cyclization to enantiomeric 1,5-benzothiazepines (+)- and (?)- 1 , are described. X-Ray single-crystal analysis reveals (2S, 3S) absolute configuration of (+)- 1 on the basis of tentative comparison of CD data with those for the 1,4-benzodiazepine derivative (+)- 8 of known absolute configuration.     

β-Cyclodextrin production by simultaneous fermentation and cyclization

Production of β-cyclodextrin (CD) with high-dextrose equivalent (DE) starch hydrolysates by simultaneous fermentation and cyclization (SFC) gives higher yields than using only the enzyme CGTase, because fermentation eliminates glucose and maltose that inhibit CD production, while at the same time, produces ethanol that increases yield. A 10% (w/v) solution of cassava starch, liquefied with α-amylase, was incubated with CGTase using: only the enzyme, added ethanol (from 1 to 5%), and added yeast,S. cerevisiae (12% w/v), plus nutrients, the latter being the SFC process. Reaction conditions were: 38αC, pH 6.0, DE from 2 to 25, and 3.3 mL of CGTase/L. The yield of β-CD has decreased with an increase in DE, and maximum reaction yields were found for DE equal to 3.54, reaching 5.6, 14.7, and 11.5 mM β-CD, respectively. For an increase of DE, of approx 6 times (from 3.54 to 23.79), β-CD yield decreased 6 times for the first, and second reaction media with 3% (v/v) ethanol, and only approx 3 times for SFC (from 11.5 to 3.73 mM), showing that this process is less sensitive to variations in the DE     

MIP models for production lot sizing problems with distribution costs and cargo arrangement

This study presents mixed integer programming (MIP) models for production lot sizing problems with distribution costs using unit load devices such as pallets and containers. Problems that integrate production lot sizing decisions and loading of the products in vehicles (bins) are also modelled, in which constraints such as weight limits, volume restrictions or the value of the cargo loaded in the bins are considered. In general, these problems involve a trade-off between production, inventory and distribution costs. Lot sizing decisions should take into account production capacity and product demand constraints. Distribution decisions are related to the loading and transport of products in unit load devices. The MIP models are solved by the branch-and-cut method of an optimization package and the results show that these approaches have the potential to address different practical situations.     

On the whole spectrum of Timoshenko beams. Part II: further applications

The problem of free vibrations of the Timoshenko beam model has been addressed in the first part of this paper. A careful analysis of the governing equations has shown that the vibration spectrum consists of two parts, separated by a transition frequency, which, depending on the applied boundary conditions, might be itself part of the spectrum. Here, as an extension, the case of a doubly clamped beam is considered. For both parts of the spectrum, the values of natural frequencies are computed and the expressions of eigenmodes are provided: this allows to acknowledge that the nature of vibration modes changes when moving across the transition frequency. This case is a meaningful example of more general ones, where the wave-numbers equation cannot be written in a factorized form and hence must be solved by general root-finding methods for nonlinear transcendental equations. These theoretical results can be used as further benchmarks for assessing the correctness of the numerical values provided by several numerical techniques, e.g. finite element models.     

Reversible Electrochemical Modulation of a Catalytic Nanosystem

A catalytic system based on monolayer‐functionalized gold nanoparticles (Au NPs) that can be electrochemically modulated and reversibly activated is reported. The catalytic activity relies on the presence of metal ions (Cd²⁺ and Cu²⁺), which can be complexed by the nanoparticle‐bound monolayer. This activates the system towards the catalytic cleavage of 2‐hydroxypropyl‐p‐nitrophenyl phosphate (HPNPP), which can be monitored by UV/Vis spectroscopy. It is shown that Cu²⁺ metal ions can be delivered to the system by applying an oxidative potential to an electrode on which Cu⁰ was deposited. By exploiting the different affinity of Cd²⁺ and Cu²⁺ ions for the monolayer, it was also possible to upregulate the catalytic activity after releasing Cu²⁺ from an electrode into a solution containing Cd²⁺. Finally, it is shown that the activity of this supramolecular nanosystem can be reversibly switched on or off by oxidizing/reducing Cu/Cu²⁺ ions under controlled conditions.     

Enhancing Hematite Photoanode Activity for Water Oxidation by Incorporation of Reduced Graphene Oxide

Two effective methods to prepare reduced graphene oxide (rGO)/hematite nanostructured photoanodes and their photoelectrochemical characterization towards water splitting reactions are presented. First, graphene oxide (GO) is reduced to rGO using hydrazine in a basic solution containing tetrabutylammonium hydroxide (TBAOH), and then deposited over the nanostructured hematite photoanodes previously treated at 750 °C for 30 min. The second method follows the deposition of a paste containing a mixture of hematite nanoparticles and rGO sheets by the doctor‐blade method, varying the rGO concentration. Since hematite suffers from low electron mobility, a low absorption coefficient, high recombination rates and slow reaction kinetics, the incorporation of rGO in the hematite can overcome such limitations due to graphene's exceptional properties. Using the first method, the rGO incorporation results in a photocurrent density increase from 0.56 to 0.82 mA cm^?2 at 1.23 V_RHE. Our results indicate that the rGO incorporation in the hematite photoanodes shows a positive effect in the reduction of the electron–hole recombination rate.     

Hematite Surface Activation by Chemical Addition of Tin Oxide Layer

In this study, the effect of tin (Sn⁴⁺) modification on the surface of hematite electrodes synthesized by an aqueous solution route at different times (2, 5, 10, 18, and 24 h) is investigated. As confirmed from X‐ray diffraction results, the as‐synthesized electrode exhibits an oxyhydroxide phase, which is converted into a pure hematite phase after being subjected to additional thermal treatment at 750 °C for 30 min. The tin‐modified hematite electrode is prepared by depositing a solution of Sn⁴⁺ precursor on the as‐synthesized electrode, followed by thermal treatment under the same abovementioned conditions. This modification results in an enhancement of the photocurrent response for all hematite electrodes investigated and attains the highest values of around 1.62 and 2.3 mA cm^?2 at 1.23 and 1.4 V versus RHE, respectively, for electrodes obtained in short synthesis times (2 h). Contact angle measurements suggest that the deposition of Sn⁴⁺ on the hematite electrode provides a more hydrophilic surface, which favors a chemical reaction at the interface between the electrode and electrolyte. This result generates new perspectives for understanding the deposition of Sn⁴⁺ on the hematite electrode surface, which is in contrast with several studies previously reported; these studies state that the enhancement in photocurrent density is related to either the induction of an increased donor charge density or shift in the flat‐band potential, which favors charge separation.     

Electrocatalysis of reduced L-glutathione oxidation by iron(III) tetra-(N-methyl-4-pyridyl)-porphyrin (FeT4MPyP) adsorbed on multi-walled carbon nanotubes

The development of a highly sensitive voltammetric sensor for reduced l-glutathione (GSH) using a basal plane pyrolytic graphite (BPPG) electrode modified with iron(III) tetra-(N-methyl-4-pyridyl)-porphyrin (FeT4MPyP) adsorbed on multi-walled carbon nanotubes (MWCNT) is described. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were used to verify the morphologies and composition of the MWCNT after modification with the FeT4MPyP complex. The modified electrode showed very efficient electrocatalytic activity for l-glutathione oxidation, substantially decreasing the oxidation peak to -0.025V vs Ag/AgCl. A linear response range from 5 micromolL(-1) to 5 mmolL(-1) was obtained with a sensitivity of 703.41 microALmmol(-1). The detection limit for GSH determination was 0.5 micromolL(-1) and the relative standard deviation (R.S.D.) for 10 determinations of 250 micromolL(-1) GSH was 1.4%. The modified electrode was applied for GSH determination in erythrocyte samples and the results were in agreement to those obtained by a comparative method described in the literature.