Spectrophotometric determination of vanadium with 1,10-phenanthroline

A simple and sensitive spectrophotometric method for the determination of vanadium based upon the reaction of vanadate with 1,10-phenanthroline in the presence of sodium dithionite in ammoniacal solution is described. The absorbance of the complex measured at 645 nm follows Beer's law for solutions containing 30-400 microg of vanadium in 100 ml of solution. A 10-fold excess of molybdenum, tungsten, phosphorus or chromium does not interfere. The molar absorptivity is 8.0 x 10(3) 1 mole(-1) cm(-1). The complex is shown to be tris-1,10-phenanthroline vanadium(II). The method has been applied successfully to the determination of vanadium in bauxite.     

Synthesis and reactivity of a C3-symmetric trinuclear zinc(II) hydroxide catalyst efficient at phosphate diester transesterification

Inspired by trinuclear Zn(ii) sites in enzymatic systems, a ligand system containing three preorganized (2-pyridyl)methyl piperazine moieties anchored onto a rigid C(3)-symmetric triphenoxymethane platform has been developed for preorganizing three zinc ions into an environment conducive to intramolecular interaction. Zinc(ii) binding by this ligand has been analyzed by means of potentiometric measurements in 50% (v/v) CH(3)CN-H(2)O solutions. Subsequently a C(3)-symmetric trinuclear Zn(ii) hydroxide complex of the C(3)-symmetric ligand was synthesized and fully characterized using NMR spectroscopy and X-ray crystallography. This complex induces a 16 900-fold rate enhancement in the catalytic cyclization of the RNA model substrate, 2-hydroxypropyl-p-nitrophenyl phosphate (HPNP, pH 6.7, 25 degrees C) over the uncatalyzed reaction with multiple catalyst turnovers. The observed differences in the pH-rate profile can be attributed to the varying concentration of various trinuclear zinc species. The trinuclear Zn(ii) catalyst exhibits a higher hydrolytic activity compared to its mononuclear analogue. The reactivity and structural features of this trinuclear Zn(ii) complex will be discussed.     

Yb-doped yttria–alumino–silicate nano-particles based optical fibers: Fabrication and characterization

An efficient method to fabricate transparent glass ceramic fibers containing in-situ grown Yb³⁺ doped oxide nano-particles based on yttria–alumino–silicate glass is presented. These large-mode area Yb³⁺ doped fibers having a core diameter around 25.0 μm were drawn by a proper control over the involved process parameters; by this, the size of nano-particles was maintained within 5–10 nm. The main spectroscopic and laser properties of the fabricated fibers along with the nano-structuration results are reported. These results reveal that the developed method offers new scopes for the contemporary Yb³⁺ fiber based devices.     

Biomimetic total syntheses of flinderoles B and C

A simple and efficient biomimetic synthesis of pyrrolo[1,2-a]indoles using a highly stereo- and regioselective [3 + 2] reaction cascade was developed and then further applied in the first total synthesis of flinderoles B and C, which proceeded in 17.2% yield over the longest linear sequence of 11 steps.     

The Correct Structures of the ortho-Cyclized Products in the Cycloalkylations of 1-m-Methoxybenzyl-4,4a,5,6,7,8-Hexahydronaphthalen-2(3H)-One and 1-m-Methoxybenzyl-Octalins : X-Ray Structure Determination of (±)-4-Methoxy-9a-Carbamorphinan-16-One

The previously assigned (ref.1) ortho-cycloalkylated product from the reaction of 1 and 2 respectively, with ortho-phosphosphoric acid and polyphosphoric acid, has been corrected to (±)-4-methoxy-9a-carbamorphinan-16-one (6) and the respective ether 7 by a single crystal X-ray structure determination of 6.     

Long-Term Stability Analysis of 3D and 2D/3D Hybrid Perovskite Solar Cells Using Electrochemical Impedance Spectroscopy

Despite the remarkable progress in perovskite solar cells (PSCs), their instability and rapid degradation over time still restrict their commercialization. A 2D capping layer has been proved to overcome the stability issues; however, an in-depth understanding of the complex degradation processes over a prolonged time at PSC interfaces is crucial for improving their stability. In the current work, we investigated the stability of a triple cation 3D ([(FA_0.83MA_0.17)Cs_0.05]Pb(I_0.83Br_0.17)₃) and 2D/3D PSC fabricated by a layer-by-layer deposition technique (PEAI-based 2D layer over triple cation 3D perovskite) using a state-of-art characterization technique: electrochemical impedance spectroscopy (EIS). A long-term stability test over 24 months was performed on the 3D and 2D/3D PSCs with an initial PCE of 18.87% and 20.21%, respectively, to suggest a more practical scenario. The current-voltage (J-V) and EIS results showed degradation in both the solar cell types; however, a slower degradation rate was observed in 2D/3D PSCs. Finally, the quantitative analysis of the key EIS parameters affected by the degradation in 3D and 2D/3D PSCs were discussed.