Voltammetric sensing of triclosan in the presence of cetyltrimethylammonium bromide using a cathodically pretreated boron-doped diamond electrode

ABSTRACT

In the present study, a simple, cheap and sensitive electrochemical method based on a cathodically pretreated boron-doped diamond (CPT-BDD) electrode is described for the detection of triclosan with the cationic surfactant (cetyltrimethylammonium bromide, CTAB) media. The oxidation of triclosan was irreversible and exhibited an adsorption controlled process. The sensitivity of the adsorptive stripping voltammetric measurements was significantly improved with addition of CTAB. Using square-wave stripping mode, a linear response was obtained for triclosan determination in Britton-Robinson buffer solution at pH 9.0 containing 2.5 × 10^?4 M CTAB at around + 0.67 V (vs. Ag/AgCl) (after 30 s accumulation at open-circuit condition). The method could be used in the range of 0.01–1.0 μg mL^?1 (3.5 × 10^?8–3.5 × 10^?6 M), with a detection limit of 0.0023 μg mL^?1 (7.9 × 10^?9 M). The feasibility of the proposed method for the determination of triclosan in water samples was checked in spiked tap water.     

Heavy-metal extraction capability of chalcogenoic aminophosphines derived from 1-amino-4-methylpiperazine

Aminophosphine of the type (Ph₂PNHR) derived from 1-amino-4-methylpiperazine and its chalcogen derivatives (Ph₂P(X)NHR X = S, Se) were used as ligands in solvent extraction of metal picrates such as Cu²⁺, Ni²⁺, and Pb²⁺ from the aqueous to the organic phase. Influence of parameters such as pH of the aqueous phase, ligand concentration in the organic phase, and concentration of the extractant extracted from the aqueous to the organic phase was investigated to determine the ligands’ ability to extract metal ions. Metal picrate extraction was investigated at 25°C using UV-VIS spectrophotometry in dichloromethane in the absence and in the presence of Ph₂PNHR and chalcogenides. The extraction results revealed that the extraction percentage of Cu²⁺, Ni²⁺, and Pb²⁺ metals was much higher at lower pH values, indicating an acidity dependent complexation equilibrium.     

The Synthesis,Characterization, and Electrochemical Investigation of Novel Thio- and Alkoxy-Substituted Benzoquinone Derivatives

Abstract

Novel thio- and alkoxy-substituted benzoquinone derivatives were synthesized from the reactions of p-chloranil (1) and related nucleophiles in a sodium carbonate (Na₂CO₃) solution of acetonitrile or in chloroform with Et₃N. The structures of novel compounds were characterized by using microanalysis, FTIR, ¹H NMR, ¹³C NMR, MS, CV, and fluorescence spectroscopy.

[Supplementary materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements for the following free supplemental files: Additional text and figures.]     

New Amperometric Cholesterol Biosensors Using Poly(ethyleneoxide) Conducting Polymers

Accumulation of cholesterol in human blood can cause several health problems such as heart disease, coronary artery disease, arteriosclerosis, hypertension, cerebral thrombosis, etc. Therefore, simple and fast cholesterol determination in blood is clinically important. In this study, two types of amperometric cholesterol biosensors were designed by physically entrapping cholesterol oxidase in conducting polymers; thiophene capped poly(ethyleneoxide)/polypyrrole (PEO-co-PPy) and 3-methylthienyl methacrylate-co-p-vinyl benzyloxy poly(ethyleneoxide)/polypyrrole (CP-co-PPy). PEO-co-PPy and CP-co-PPy were synthesized electrochemically and cholesterol oxidase was immobilized by entrapment during electropolymerization. The amperometric responses of the enzyme electrodes were measured by monitoring oxidation current of H₂O₂ at +0.7 V in the absence of a mediator. Kinetic parameters, such as Km and Imax, operational and storage stabilities, effects of pH and temperature were determined for both entrapment supports. Km values were found as 1.47 and 5.16 mM for PEO-co-PPy and CP-co-PPy enzyme electrodes, respectively. By using these Km values, it can be observed that ChOx immobilized in PEO-co-PPy shows higher affinity towards the substrate.     

Upper rim-functionalized calix[4]arene-based l-proline as organocatalyst for direct asymmetric aldol reactions in water and organic media

The synthesis of upper rim-functionalized calix[4]arene-based l-proline was described, and its catalytic efficiency as organocatalyst for the enantioselective aldol reaction in water was investigated. The results showed that the nature of the hydrophobic cavity of calixarene is critical for catalytic activity in water. The products of the reaction between various ketones and aldehydes with anti-configuration were obtained in high yields (up to 94%) with high diastereo- (up to 95:5 dr) and enantioselectivities (up to 80% ee).     

Scattering of light from particles with semisoft boundaries

A three-dimensional multi-Gaussian function, being a finite sum of Gaussian functions, is adopted for modeling of a spherically symmetric scatterer with a semisoft boundary, i.e. such that has continuous and adjustable drop in the index of refraction. A Gaussian sphere and a hard sphere are the two limiting cases when the number of terms in multi-Gaussian distribution is one and infinity, respectively. The effect of the boundary's softness on the intensity distribution of the scattered wave is revealed. The generalization of the model to random scatterers with semisoft boundaries is also outlined.     

Continuous-wave, multiple-order rotational Raman generation in molecular deuterium

We demonstrate the generation of ≈10 rotational sidebands using continuous-wave stimulated Raman scattering in molecular deuterium. The generation occurs inside a high-finesse cavity at molecular gas pressures of ≈0.1?atm.     

A Robust,Precious‐Metal‐Free Dye‐Sensitized Photoanode for Water Oxidation: A Nanosecond‐Long Excited‐State Lifetime through a Prussian Blue Analogue

Herein, we establish a simple synthetic strategy affording a heterogeneous, precious metal‐free, dye‐sensitized photoelectrode for water oxidation, which incorporates a Prussian blue (PB) structure for the sensitization of TiO₂ and water oxidation catalysis. Our approach involves the use of a Fe(CN)₅ bridging group not only as a cyanide precursor for the formation of a PB‐type structure but also as an electron shuttle between an organic chromophore and the catalytic center. The resulting hetero‐functional PB‐modified TiO₂ electrode demonstrates a low‐cost and easy‐to‐construct photoanode, which exhibits favorable electron transfers with a remarkable excited state lifetime on the order of nanoseconds and an extended light absorption capacity of up to 500 nm. Our approach paves the way for a new family of precious metal‐free robust dye‐sensitized photoelectrodes for water oxidation, in which a variety of common organic chromophores can be employed in conjunction with CoFe PB structures.     

Directing the Structural Features of N2‐Phobic Nanoporous Covalent Organic Polymers for CO2 Capture and Separation

A family of azo‐bridged covalent organic polymers (azo‐COPs) was synthesized through a catalyst‐free direct coupling of aromatic nitro and amine compounds under basic conditions. The azo‐COPs formed 3D nanoporous networks and exhibited surface areas up to 729.6 m² g^?1, with a CO₂‐uptake capacity as high as 2.55 mmol g^?1 at 273 K and 1 bar. Azo‐COPs showed remarkable CO₂/N₂ selectivities (95.6–165.2) at 298 K and 1 bar. Unlike any other porous material, CO₂/N₂ selectivities of azo‐COPs increase with rising temperature. It was found that azo‐COPs show less than expected affinity towards N₂ gas, thus making the framework “N₂‐phobic”, in relative terms. Our theoretical simulations indicate that the origin of this unusual behavior is associated with the larger entropic loss of N₂ gas molecules upon their interaction with azo‐groups. The effect of fused aromatic rings on the CO₂/N₂ selectivity in azo‐COPs is also demonstrated. Increasing the π‐surface area resulted in an increase in the CO₂‐philic nature of the framework, thus allowing us to reach a CO₂/N₂ selectivity value of 307.7 at 323 K and 1 bar, which is the highest value reported to date. Hence, it is possible to combine the concepts of “CO₂‐philicity” and “N₂‐phobicity” for efficient CO₂ capture and separation. Isosteric heats of CO₂ adsorption for azo‐COPs range from 24.8–32.1 kJ mol^?1 at ambient pressure. Azo‐COPs are stable up to 350 °C in air and boiling water for a week. A promising cis/trans isomerization of azo‐COPs for switchable porosity is also demonstrated, making way for a gated CO₂ uptake.     

Interaction thermodynamics of rutin (vitamin P) with basic L-amino acids at physiological pH: the effect of temperature on the affinity order

The interactions between a flavonoid, rutin (Rt), and basic L-amino acids (BAAs) were studied at physiological pH (7.40) by UV-Visible spectroscopy and voltammetric techniques. The binding stoichiometries and constants (K) at different temperatures were measured by voltammetric method. So, the thermodynamic parameters ΔH ^○, ΔG ^○, ΔS ^○ were calculated and the results indicate that the binding reaction is mainly entropy-driven and hydrophobic forces played major role in the interactions of arginine and lysine with rutin as compared to that of histidine. Whereas, the histidine binding reaction, including with the negative enthalpy and entropy changes is entalpy-driven and this interaction primarily arise from hydrogen-bonding and van der Waals interactions. Finally, it was also observed that the affinity (that is binding constant) of hydrogen-bonding and van der Waals interactions between Rt and arginine or lysine decreased, but the stability of hydrophobic interaction of Rt with histidine increased when the temperature was raised.