A Schiff-Based Colorimetric Fluorescent Sensor with the Potential for Detection of Fluoride Ions

A simple Schiff-based colorimetric fluorescent receptor 1 was prepared. It exhibits a “turn-on-type” mode with high sensitivity in the presence of F^?. The change in color is very easily observed by the naked eye in the presence of F^?, whereas other anions do not induce such a change. Job plot indicated a 1:2 complexation stoichiometry between receptor 1 and F^?. The association constant for 1-F^? in CH₃CN was determined as 1.32*10⁵ M^?2 by a Hill plot.

Synthesis of Highly Selective Indole-Based Sensors for Mercuric Ion

Two indole-based fluorescent chemosensors 1 and 2 were prepared and investigated characteristic features with transition metal ions. Sensors 1 and 2 were selective for Hg²⁺ ion, among a series of metal ions, in aqueous ethanol (H₂O–EtOH, 1:2, v/v) with association constants of 5.74 × 10³ and 4.46 × 10³ M⁻¹ and detection limits of 7.4 and 6.8 μM, respectively. Computational results revealed that sensor 1 or 2 with Hg²⁺ ion formed 1:1 complex with a central, sandwich-coordinated Hg²⁺ ion. Computational calculations provided evidence that a sandwich-coordinated Hg²⁺ ion center was formed and the polyoxyethylene spacer acted as a scaffold for bringing functional ligands into a suitable geometry.     

A Quinoline Derivative as an Efficient Sensor to Detect Selectively Al3+ ion

A quinoline-based Schiff base 1 has been utilized as a fluorescence chemosensor for the selective detection of Al³⁺. The receptor 1 exhibited a high association constant (3.67?×?10⁵ M^?1) with submicromolar detection limit (0.18 ppm) towards Al³⁺ in CH₃CN solution.     

Characterization of an Isozyme of β-Glucosidase from Sweet Almond

A sweet almond β-glucosidase (EC 3.2.1.21) isozyme was purified from commercial crude product. The process of purification consisted of a Protein-Pak Q anion exchange chromatography following by a Superdex 75 HR gel filtration separation. The purified enzyme is a monomeric glycoprotein with molecular weight of 58 kDa and pI=4.55 which is distinguished from reported isozymes. The enzyme has apH optimum in the range of 5.2-5.6 when p-nitrophenyl-β-D-glycopyranosides are used as substrate and is stable up to 50 °C at that pH range. The purified protein also exhibits profound β-galactosidase and σ-L-arabinosidase activity. The study of substrate specificity revealed that lacking of hydroxymethyl group at C-5 of glycosides resulted in higher affinity for substrate binding to enzyme, whereas the chemical step of hydrolysis (k_cst) was prevented significantly. The pH activity profile displayed a bell-shaped curve for all measured p-nitrophenyl-β-D-glycopyranosides with apparent pK₁ and pK₂ values of 4.4-4.7 and 6.2-6.4, respectively. This isozyme was strongly inhibited by δ-gluconolactone (K_i = 160 μM) and 4-phenylimidazole (K_i = 17.8 μM) reversibly at pH 6.2. Among the tested glycoses, the binding affinity of N-acetyl-β-D-glucosamine to the enzyme (K_l = 52 mM) was 6 times stronger than that of glucose and its epimers.