Electrochemical determination of riboflavin using a synthesized ethyl[(methythio)carbonothioyl] glycinate monolayer modified gold electrode

The surface of a gold disk electrode, for the first time, was modified with a self-assembled monolayer of a synthesized compound, ethyl [(methythio)carbonothioyl] glycinate (ECTG), for construction of an electrode sensitive to riboflavin (vitamin B₂). The electrochemical properties of the monolayer assembled on the gold disk were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. Under the optimized conditions, the voltammetric peak currents resulting from vitamin B₂ (VB₂) species were linear for VB₂ concentrations in the range from 10^–6 to 10^–2 M. The effect of pH, type of buffer solution and scan rate on the response of the modified electrode was studied. The constructed electrochemical sensor responses very well to VB₂ in the presence of most common vitamins. Finally, the performance of the Au–ECTG modified electrode was successfully tested for electrochemical detection of VB₂ in a pharmaceutical sample.     

Synthesis of 3-substituted bicyclic imidazo[1,2-d][1,2,4]thiadiazoles and tricyclic benzo[4,5]imidazo[1,2-d][1,2,4]thiadiazoles

A versatile synthetic route to potentially useful fused-ring [1,2,4]thiadiazole scaffolds (e.g., 7a and 10b) via exchange reactions of the precursor [1,2,4]thiadiazol-3-(2H)one derivatives (e.g., 6 and 9) with appropriately substituted nitriles (e.g., cyanogen bromide or p-toluenesulfonyl cyanide) under mild conditions is described. For example, the tricyclic 3-bromo [1,2,4]THD derivative (7a) underwent S(N)Ar substitution with a variety of nucleophiles, which included amines, malonate esters and alcohols. Likewise, the bicyclic 3-p-tosyl [1,2,4]THD (10b) was employed as a template in reaction with diamines, and the resulting substituted diamines (e.g., 12a or 12e) were further selectively derivatized at the N1 and/or N2 positions in a linear fashion. The X-ray crystal structure of the 3-methyl bicyclic [1,2,4]THD (21) was obtained, and selective methylation at the N1 position via a protection-alkylation-deprotection protocol, as illustrated in Scheme 6, was confirmed. Alternatively, a short convergent synthesis of N1-functionalized derivatives from the reaction of 10b with appropriately substituted secondary amines was also developed. Hence, these synthetic strategies were advantageously exploited to provide access to a variety of diversely derivatized 3-substituted fused-ring [1,2,4]thiadiazole derivatives.     

The principles of bipolar electrochemistry and its electroanalysis applications

The present study reports the wireless technique that generates asymmetric reactivity on the surface of the conducting substrate without any direct electrical connection in the electrolyte solution by inducing external power. In recent years, bipolar electrochemical systems have received special attention that they are used for new kinds of electrochemical applications ranging from electrodeposition to electroanalytical chemistry. Bipolar electrochemistry is a unique technique because of the lack of direct electrical connection to the bipolar electrode. In this perspective article, we first illustrate the concept and history of the bipolar electrochemistry as well as their application based on the open and closed bipolar configuration in different fields.     

Photocatalytic reaction of arylamines/alcohols on TiO<Subscript>2</Subscript> nano-particles

In this article, the photocatalytic reaction of aniline and 4-amino N,N-dimethyl aniline with methanol, ethanol and isopropanol on anatase TiO₂ nano-particles under UV (365-nm wavelength) irradiation was examined. The concentration of unreacted arylamines and products was measured by gas chromatography picks integration, and then the products were identified by mass spectroscopy analysis. By making a comparison within the rates of photocatalysis of each arylamine in different alcohols under various irradiation times, it was revealed that, in all cases, the sequence of photocatalysis rate was methanol > ethanol > isopropanol. In reactions where the concentrations of arylamine were lower than 10 mmol/l, imines were the main products and the alkylation of amines was not observed. In the higher concentration of arylamines, oxidation and dimerization was occurred.     

Photocatalytic reaction of aryl amines/alcohols on TiO<Subscript>2</Subscript> nanoparticles

In this article, the photocatalytic reaction of aniline and 4-amino N, N dimethyl aniline with methanol, ethanol and isopropanol on anatase TiO₂ nano-particles under UV (365 nm wavelength) irradiation was examined. The concentration of unreacted aryl amines and products was measured by gas chromatography picks integration, and then the products were identified by mass spectroscopy analysis. By making a comparison within the rates of photocatalysis of each aryl amine in different alcohols under various irradiation times, it was revealed that, in all cases, the sequence of photocatalysis rate was methanol > ethanol > isopropanol. In reactions where the concentrations of aryl amine were lower than 10 mmol/L, imines were the main products and alkylation of amines was not observed. In the higher concentration of aryl amines, oxidation and dimerization occurred.     

Facilitated ion transfer of protonated primary organic amines studied by square wave voltammetry and chronoamperometry

The transfer of the protonated forms of heptylamine, octylamine, decylamine, procaine and procainamide facilitated by dibenzo-18-crown-6 from water to a solvent polymeric membrane has been investigated by using cyclic square wave voltammetry. The experimental voltammograms obtained are in good agreement with theoretical predictions. The values of the standard ion transfer potential, complexation constant and diffusion coefficient in water have been obtained from these experiments, and have been used to draw some conclusions about the lipophilicity of these species and the relative stability of the organic ammonium complexes with dibenzo-18-crown-6. The results have been compared with those provided by linear sweep voltammetry. Calibration graphs were obtained with both techniques. An interesting chronoamperometric method for the determination of the diffusion coefficient of the target ion in the membrane has been developed and applied to all these protonated amines.     

Effect of solvent on complexation between Y3+ cation and 4,13-diaza-18-crown-6 in some binary mixed non-aqueous solvents

The complexation reaction of 4,13-diaza-18-crown-6 (DA18C6) with Y³⁺ cation was studied in some binary mixed solvent solutions of acetonitrile (AN) with methanol (MeOH), ethanol (EtOH), 2-propanol (2-PrOH) and methyl acetate (MeOAc) at different temperatures by conductometric method. The obtained data show that in all studied solutions the stoichiometry of the complex formed between DA18C6 and Y³⁺ cation is 1: 1 [ML], but in the case of pure MeOAc, a 2: 1 [ML₂] complex is formed in solution upon addition of the ligand to the metal salt solution, and further addition of the ligand results in formation of a M₂L₂ complex in solution. This results show that the stoichiometry of the composition of the macrocyclic complexes may be affected by the nature of the solvent system. The results obtained in this study show that the stability constant of the resulting 1: 1 [ML] complex in the binary solvent solutions decreases in the order: AN-MeOAc > AN-2PrOH > AN-MeOH > AN-EtOH. A non-linear relationship was observed between the stability constant (logK _f ) of [Y(DA18C6)]³⁺ complex with the composition of the binary mixed solvent solutions. The corresponding standard thermodynamic parameters (H° _c , Δ S° _c ) for 1: 1 [ML] complexation reaction between DA18C6 and Y³⁺ cation were obtained from temperature dependence of the stability constant of the complex. The results show that, in all solvent systems, the (DAI8C6.Y)³⁺ complex is entropy stabilized, but from enthalpy point of view, depending on the solvent system, it is stabilized or destabilized and the result show that the values of both thermodynamic quantities change with the nature and composition of the binary mixed solvent solutions.     

Methionine-Coated Fe3O4 Nanoparticles: An Efficient and Reusable Nanomagnetic Catalyst for the Synthesis of 5-Substituted 1H-Tetrazoles

Russian Journal of Organic Chemistry - Methionine-coated Fe3O4 nanoparticles, a magnetically reusable and environmentally friendly heterogeneous catalyst, was synthesized. The new catalyst was...     

Silica Chloride Nano Particle Catalyzed Ring Opening of Epoxides by Aromatic Amines

Silica chloride nano particle (nano SiO₂‐Cl), has been found to be heterogeneous catalyst for facile, simple and mild ring opening of epoxides with aromatic amines to afford β‐amino alcohols in dry CH₂Cl₂ at room temperature.