Immobilization of flavine adenine dinucleotide onto nickel oxide nanostructures modified glassy carbon electrode: fabrication of highly sensitive persulfate sensor

A simple method was used to fabricate flavin adenine dinucleotide (FAD)/NiOx nanocomposite on the surface of glassy carbon (GC) electrode. Cyclic voltammetry technique was applied for deposition nickel oxide nanostructures onto GC surface. Owing to its high biocompatibility and large surface area of nickel oxide nanomaterials with immersing the GC/NiOx-modified electrode into FAD solution for a short period of time, 10–140 s, a stable thin layer of the FAD molecules immobilized onto electrode surface. The FAD/NiOx films exhibited a pair of well-defined, stable, and nearly reversible CV peaks at wide pH range (2–10). The formal potential of adsorbed FAD onto nickel oxide nanoparticles film, E ^o′ vs. Ag/AgCl reference electrode is −0.44 V in pH 7 buffer solutions was similar to dissolved FAD and changed linearly with a slope of 58.6 mV/pH in the pH range 2–10. The surface coverage and heterogeneous electron transfer rate constant (k _s ) of FAD immobilized on NiOx film glassy carbon electrode are 4.66 × 10⁻¹¹ mol cm⁻² and 63 ± 0.1 s⁻¹, indicating the high loading ability of the nickel oxide nanoparticles and great facilitation of the electron transfer between FAD and nickel oxide nanoparticles. FAD/NiOx nanocomposite-modified GC electrode shows excellent electrocatalytic activity toward S₂O₈²⁻ reduction at reduced overpotential. Furthermore, rotated modified electrode illustrates good analytical performance for amperometric detection of S₂O₈²⁻. Under optimized condition, the concentration calibration range, detection limit, and sensitivity were 3 μM–1.5 mM, 0.38 μM and 16.6 nA/μM, respectively.     

Structure and electronic properties of amino acid ionic liquids

The interactions between eight amino acid based anions and four imidazolium-based cations have been investigated by density functional theory. The electronic and structural properties of the resulting amino acid ionic liquids (AAILs) have been unveiled by means of the atoms in molecules framework. The calculated interaction energy was found to increase in magnitude with decreasing alkyl chain length at imidazolium ring. Moreover, AAILs composed of an amino acid with some functional group such as aromatic ring had decreased interaction energy. Finally, several correlative relationships between glass transition temperature and interaction energy as well as density at bond critical point have been checked for 1-ethyl-3-methylimidazolium based ILs. Although the obtained correlations do not show excellent fits, a preliminary estimation of the glass transition temperature of different AAILs can be achieved by use of their electronic properties.     

Engineering and Kinetic Stabilization of the Therapeutic Enzyme Anabeana variabilis Phenylalanine Ammonia Lyase

Anabeana variabilis phenylalanine ammonia lyase has just recently been discovered and introduced in clinical trials of phenylketonuria enzyme replacement therapy for its outstanding kinetic properties. In the present study, kinetic stabilization of this therapeutically important enzyme has been explored by introduction of a disulfide bond into the structure. Site-directed mutagenesis was performed with quick-change PCR method. Recombinant wild-type and mutated enzymes were expressed in Escherichia coli, and his-tagged proteins were affinity purified. Formation of disulfide bond was confirmed by Ellman’s method, and then chemical unfolding, kinetic behavior, and thermal inactivation of mutated enzyme were compared with the wild type. Based on our results, the Q292C mutation resulted in a significant improvement in kinetic stability and resistance against chemical unfolding of the enzyme while kinetic parameters and pH profile of enzyme activity were remained unaffected. The results of the present study provided an insight towards designing phenylalanine ammonia lyases with higher stability.     

Ab Initio Study of the Dehydrogenation of 3-Pyrroline, 2,5-Dihydrofuran and 2,5-Dihydrothiophene

Abstract

The nature of the transition state structures of the decomposition of 3-pyrroline (1), 2,5-dihydrofuran (2) and 2,5-dihydrothiophene (3) were investigated usingab initio Molecular Orbital (MO) and Density Factional Theory (DFT) methods. The energy barrierof the decomposition of compound 1 is smaller than compound 2 and compound 2 is smaller than compound 3. The energy barriers for the decomposition of compounds 1–3 are 46.20, 50.17, and 61.34 kcal mol^?1, respectively, which is calculated by B3LYP/6-31G^*//HF/6-31G^* level of theory. Which is ingood agreement with reported experimental data. Contrary to the previously reported data, the distance between the cis-2-and-5-hydrogen atoms in compound 1 is greater than compound 2. The transition-state structures of the decomposition of compounds 1–3 are formed by interaction of the cis-2-and-5-hydrogen atoms. Also, the rings of compounds 1–3 in the transition state structures are puckered.     

One-Pot Green Synthesis of Novel Polysubstituted 1,2-Dihydronaphtho[2,1-b]furans

A simple and highly efficient one-pot protocol for the synthesis of novel polysubstituted 1,2-dihydronaphtho[2,1-b] furans has been developed by three-component coupling reaction of 2-aminopyridines, naphthols, and glyoxal in the presence of guanidinium chloride as a polyfunctional organocatalyst under solvent-free conditions. The protocol avoids the use of expensive catalysts, toxic solvents, and chromatographic separation and provides a wide range of novel dihydronaphthofurans in good to excellent yields.     

Efficient iodination of aromatic compounds using potassium ferrate supported on montmorillonite

Potassium ferrate impregnated on montmorillonite is a mild,cheap,and non-toxic reagent for the iodination of phenols, including naphthol,aromatic amines,and heterocyclic substrates in fair to excellent yields by a simple isolation procedure.     

Higher dimensional Shimura varieties in the Prym loci of ramified double covers

In this paper, we construct Shimura subvarieties of dimension bigger than one of the moduli space ${\mathsf{A}}_p^{\delta }$ of δ-polarized abelian varieties of dimension p, which are generically contained in the Prym loci of (ramified) double covers. The idea is to adapt the techniques already used to construct Shimura curves in the Prym loci to the higher dimensional case, namely, to use families of Galois covers of ${\mathbb{P}}^1$. The case of abelian covers is treated in detail, since in this case, it is possible to make explicit computations that allow to verify a sufficient condition for such a family to yield a Shimura subvariety of ${\mathsf{A}}_p^{\delta }$.