A Nitrite Electrochemical Sensor Based on Boron‐Doped Diamond Planar Electrochemical Microcells Modified with a Monolacunary Silicotungstate Polyoxoanion

A new boron doped diamond microcells (BDD) was modified, for rapid, selective and highly sensitive determination of nitrite, using a coating film of polyoxometalates (POMs), formed by cyclic voltammetry on the molecular p‐phenylenediamine (PPD) functionalized BDD. The scanning electron microscopy (SEM) technique was used to examine the morphology of (PPD/SiW₁₁) modified (BDD) electrode. It was found that (SiW₁₁) layer was uniformly formed on the electrode surface. It was observed that (BDD/PPD/SiW₁₁) showed excellent electrocatalytic activities towards nitrite ion. Under the selected conditions, the anodic peak maximum at ?0.6 V was linear versus nitrite concentration in the 40 µM–4 mM range, and the detection limit obtained was 20 µM. The newly developed electrode has been successfully applied to the determination of nitrite content in real river water samples.     

Enterprise security economics: A self‐defense versus cyber‐insurance dilemma

We propose a model that optimizes enterprise investments in cybersecurity using expected utility theory. The model allows computing (a) investment in self‐defense to reduce the risk of security breaches, (b) investment in cyber insurance to transfer the residual risk to insurance companies, and (c) investment in forensic readiness to make the insured firms capable of generating provable insurance claims about security breaches. A three‐phase–based model of vulnerability rate evolution over time is proposed and used to estimate the different planned security expenditures throughout the investment horizon. At the starting time of investment, a decision maker invests to cover the existing risk of breach and periodically spends to cover the additional risk observed due to the release of new vulnerabilities. In this work, the intermediate tranches are determined while considering three different attitudes of decision makers, namely, optimistic, pessimistic, and realistic. An analysis is conducted to assess the performance of the proposed models.     

Synthesis of NaX and NaY Zeolites from Tunisian Kaolinite as Base Catalysts: An Investigation of Knoevenagel Condensation

The synthesis of Faujasite‐type zeolites with high purity has been successfully performed from Tunisian kaolinite and the effects of different crystallization parameters on the final products were widely investigated. The alkaline fusion of kaolinite followed by hydrothermal treatment lead to zeolite NaX synthesis whereas the classic hydrothermal transformation of metakaolinite produces NaY zeolite. The results show that an increase in the synthesis temperature and time has improved the crystallization process of the zeolite NaX whereas the SiO₂/Al₂O₃ and the Na₂O/SiO₂ molar ratios were the key parameters to obtain a pure zeolite NaY. The highest specific surface areas obtained with the optimal crystallization conditions were 554 m2 g^?1 and 592 m2 g^?1 for respectively NaX and NaY zeolites. The basic properties of NaX and NaY zeolites were explored in the Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate at 140 °C as a test reaction in the absence of solvent. The influence of ion exchange with cesium cation on the catalytic activity of prepared catalysts was also investigated. It was found that the NaX provided higher activity than that of NaY catalyst due to its lower Si/Al ratio whereas a cesium exchange conferred higher basicity to the prepared Na‐faujasite.     

Perturbation of semi-Browder linear relations by commuting Riesz operators

This paper is devoted to the investigation of the stability of upper semi-Browder, lower semi-Browder and Browder linear relations which satisfy the stabilization property, under commuting Riesz operator perturbations. As applications, we infer the invariance of the corresponding Browder’s essential approximate point spectrum, Browder’s essential defect spectrum and Browder’s essential spectrum under commuting Riesz operator perturbations.     

Synergistic Effect of Polyoxometalate and Single Walled Carbon Nanotubes on Peroxidase‐like Mimics and Highly Sensitive Electrochemical Detection of Hydrogen Peroxide

A novel Keggin‐type metatungstate hybrid POMs ((APy)₆[H₂W₁₂O₄₀])/carboxylic acid functionalized single‐walled carbon nanotube based amperometric sensing platform was successfully constructed for the sensitive detection of hydrogen peroxide. A simple and reliable procedure was implemented for the synthesis of new composite materials obtained by the covalent grafting of (APy)₆[H₂W₁₂O₄₀] onto the surface of (SWCNT‐COOH). The synergistic effect of single walled carbon nanotubes on the electrochemical behavior of (APy)₆[H₂W₁₂O₄₀] was evidenced through the increase of the oxidation and reduction peaks of the polyoxometalate. The sensitivity of hydrogen peroxide detection was increased by a factor of 38.5 in presence of SWCNTs, showing their high influence on peroxidase‐like mimics of (APy)₆[H₂W₁₂O₄₀]. The detection limit, the response time, the repeatability and the shelf lifetime were respectively 0.4 μM, 10 s, <4%, 60 days.     

Et3B-mediated palladium-catalyzed direct allylic substitution reactions of Morita–Baylis–Hillman alcohols with aromatic amines

An efficient, direct allylic amination of both cyclic and acyclic Morita–Baylis–Hillman alcohols with aromatic amines, in tetrahydrofuran (THF) at room temperature, catalyzed by Pd(0)/Et₃B, is reported herein. The corresponding amines are obtained with a high α -regioselectivity in 65–87% yields.     

Transition metal-free direct nucleophilic α-substitution of Morita–Baylis–Hillman alcohols with amines and thiols

An efficient transition metal-free allylic nucleophilic α-substitution of Morita–Baylis–Hillman alcohols with both aliphatic and aromatic amines in refluxing toluene, using activated molecular sieves as additives, is described herein. The reaction proceeded with exclusive α-regioselectivity in moderate to excellent yields with the formation of water as the sole by-product. Under the same conditions, upon treatment of some thiols with the title substrates, allylic sulfides were obtained in excellent yields and high regioselectivity.