UV-Visible and IR Spectroelectrochemical Properties of V2O5 Crystalline Films Charged/Discharged in Extended Potential Range

Electrochemical properties of amorphous and crystalline V₂O₅ films, dip-coated from V-oxoisopropoxide sols and thermally treated at various temperatures (100, 150, 200 and 300°C), have been studied in extended potential range, i.e. from 1.4 to –1.6 V vs. Ag/AgCl in 1M LiClO₄/propylen carbonate (PC) electrolyte. The formation of various lithiated (-, -, - and -Li _x V₂O₅) phases was correlated with the values of insertion coefficient x obtained from cyclic voltammograms (CV) of crystalline V₂O₅ films (300°C). Reversible charging was observed when films were cycled up to –1.0 V vs. Ag/AgCl, while the extension of the potential to –1.3 V vs. Ag/AgCl change the CV of films irreversibly. Charging of crystalline V₂O₅ films was followed by the help of in-situ UV-visible spectroscopy, that revealed the intensity variations of the polaron absorption above 600 nm and the presence of the absorbing V³⁺ species between 550 and 650 nm. Ex-situ IR spectra of the crystalline films charged/discharged at –1.6V/1.4V vs. Ag/AgCl confirmed the amorphisation of the films' structure.     

Kinetic study of the reaction H2O2+H→H2O+OH by ab initio and density functional theory calculations

Theoretical investigations on the kinetics of the elementary reaction H₂O₂+H→H₂O+OH were performed using the transition state theory (TST). Ab initio (MP2//CASSCF) and density functional theory (B3LYP) methods were used with large basis set to predict the kinetic parameters; the classical barrier height and the pre-exponential factor. The ZPE and BSSE corrected value of the classical barrier height was predicted to be 4.1 kcal mol⁻¹ for MP2//CASSCF and 4.3 kcal mol⁻¹ for B3LYP calculations. The experimental value fitted from Arrhenius expressions ranges from 3.6 to 3.9 kcal mol⁻¹. Thermal rate constants of the title reaction, based on the ab initio and DFT calculations, was evaluated for temperature ranging from 200 to 2500 K assuming a direct reaction mechanism. The modeled ab initio-TST and DFT–TST rate constants calculated without tunneling were found to be in reasonable agreement with the observed ones indicating that the contribution of the tunneling effect to the reaction was predicted to be unimportant at ambient temperature.     

Oxygen binding and activation by the complexes of PY2- and TPA-appended diphenylglycoluril receptors with copper and other metals

The copper(I) complexes of diphenylglycoluril basket receptors and , appended with bis(2-ethylpyridine)amine (PY2) and tris(2-methylpyridine)amine (TPA), respectively, and their dioxygen adducts were studied with low-temperature UV-vis and X-ray absorption spectroscopy (XAS). The copper(I) complex of, [.Cu(I)2] or, forms a micro-eta2:eta2 dioxygen complex, whereas the copper(I) complex of, [.Cu(I)2] or, does not form a well defined dioxygen complex, but is oxidized to Cu(II). Dioxygen is bound irreversibly to and the formed complex is stable over time. The coordination geometries of the above complexes were determined by XAS, which revealed that pyridyl groups and amine N-donors participate in the coordination to Cu(I) ions in the complexes of both receptors. The catalytic activities of various metal complexes of and , that were designed as mimics of dinuclear copper enzymes that can activate dioxygen, were investigated. Phenolic substrates that were expected to undergo aromatic hydroxylation, showed oxidative polymerization without insertion of oxygen. The mechanism of this polymerization turns out to be a radical coupling reaction as was established by experiments with the model substrate 2,4-di-tert-butylphenol. In addition to Cu(II), the Mn(III) complex of and the Fe(II) complex of were tested as oxidation catalysts. Oxidation of catechol was observed for the Cu(II) complex of receptor but the other metal complexes did not lead to oxidation.     

Relationships between luminescent properties and structure in β-K2SO4-type orthophosphates

The conditions of a Ce³⁺ → Tb³⁺ energy transfer have been analyzed in the Na_2+x+yCa_2(1?x?y) Ce_xTb_y(PO₄)₂ orthophosphates. Terbium green emission through uv cerium excitation is characterized by a very low yield. This result is the consequence of a sodium-rare-earth short range ordering even at low rare-earth concentrations and of lack of rigidity in the anionic sublattice.     

The cocrystal of 3‐hydroxy‐2‐naphthoic acid and 4,4′‐bipyridine

4,4′‐Bipyridine cocrystallizes with 3‐hydroxy‐2‐naphthoic acid in a 1:2 ratio to give a centrosymmetric three‐component supra­molecular adduct, namely 3‐hydroxy‐2‐naphthoic acid–4,4′‐bipyridine (2/1), C₁₁H₈O₃·0.5C₁₀H₈N₂, in which 4,4′‐bipyridine is located on an inversion center. The pyridine–carboxylic acid heterosynthon generates an infinite one‐dimensional hydrogen‐bonded chain viaπ–π inter­actions between naphthyl and 4,4′‐bipyridine groups. The one‐dimensional chains are further assembled into a three‐dimensional network by weak C—H⋯π inter­actions between pyridyl and naphthyl rings, and C—H⋯O inter­actions between 3‐hydroxy‐2‐naphthoic acid mol­ecules.     

The asymmetric synthesis of (−)-pumiliotoxin C using tandem catalysis

The potent neurotoxin (−)-pumiliotoxin C has been prepared in 8 steps starting from 2-cyclohexenone. Key steps are a tandem asymmetric conjugate addition-allylic substitution reaction and a tandem Heck-allylic substitution reaction.     

Dynamic optimization of a dead-end filtration trajectory: Non-ideal cake filtration

A control strategy aimed at minimizing energy consumption is formulated for non-ideal dead-end cake filtration with an inside-out hollow fiber ultrafiltration membrane system. The non-ideal behavior was assumed to originate from cake compression, non-linear cake resistance and a variable pump efficiency.

Constant gross power, constant flux and constant pressure filtration were considered as alternatives for the optimal operating strategy. It was found that the ratio between the initial and final total resistance determines whether a large difference between these strategies occurs. This is mainly determined by the specific cake resistance, the final state and the membrane resistance.

When there is a large difference between the operating strategies, the pump characteristics determine which suboptimal strategies are attractive. For a pump with a low head and a large capacity, constant flux filtration is nearly optimal, whereas for a pump with a large head and a small capacity optimal operation is closer to constant pressure filtration. Under the investigated conditions there was no significant difference (< 0.5%) between the constant gross power and the optimal operating strategy.     

Catalytic enantioselective synthesis of (-)-prostaglandin E1 methyl ester based on a tandem 1,4-addition-aldol reaction

Catalytic enantioselective 1,4-additions and tandem 1,4-addition-aldol reactions of dialkylzinc reagents to cyclopentene-3,5-dione monoacetals in the presence of an in situ generated Cu(OTf)(2)/chiral phosphoramidite catalyst result in highly functionalized cyclopentane building blocks with ee's up to 97%. A new synthesis of cyclopentene-3,5-dione monoacetals is presented as well as its use in a tandem 1,4-addition-aldol protocol for the catalytic asymmetric total synthesis of (-)-PGE(1) methyl ester. This synthesis represents a new approach to this class of natural products. By using only 3 mol % of an enantiomerically pure catalyst in the key step, the absolute configurations at three stereocenters of the basic structure of the PGE(1) are established at once.     

Thermal decomposition of Cu(I) phosphine complexes

The thermal decomposition of Cu(I) phosphine complexes of the general types (CuXPPh₃)₄, [CuX(PPh₃)₂] and [CuX(PPh₃)₃] was investigated.The thermal decomposition of (CuXPPh₃)₄, where X denotes Cl^–, Br^–, I^–, NO ₃ ^– and PPh₃=P(C₆H₅)₃, occurs with formation of a phosphine oxide intermediate. For the remaining complexes this intermediate was not proved in the thermal decomposition.

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Zusammenfassung Die thermische Zersetzung der Cu(I)-Phosphinkomplexe vom allgemeinen Typ (CuXPPh₃)₄ und [CuX(PPh₃)₂], wie auch [CuX(PPh₃)₃] wurde untersucht. Die thermische Zersetzung von (CuXPPh₃)₄, wobei X=Cl^–, Br^–, I^– und NO ₃ ^– bedeutet und PPh₃=P(C₆H₅)₃, verläuft unter Bildung eines Phosphinoxid Zwischenproduktes, bei den übrigen Komplexen konnte dieses im Laufe der thermischen Zersetzung nicht nachgewiesen werden.

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Résumé On a étudié la décomposition thermique des complexes phosphine-Cu(I) de formule générale (CuXPPh₃)₄, [CuX(PPh₃)₂], [CuX(PPh₃)₃]. La décomposition thermique de (CuXPPh₃)₄, où X désigne Cl^–, Br^–, I^– et NO ₃ ^– , et PPh₃=P(C₆H₅)₃, s'effectue avec formation d'un oxyde de phosphine intermédiaire; avec les autres complexes, cet intermédiaire n'a pas été mis en évidence au cours de la décomposition thermique.

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(CuXPPb₃)₄ [CuX(PPh₃)₂] [CuX(PPh₃)₃]. (CuXPPh₃)₄, X=Cl^–, Br^–, I^–, NO ₃ ^– , PPh₃=(₆₅)₃ . .

     

Preparation, characterization, and solution tailored photoluminescence of all trans poly[distyrylbenzene-b-(ethylene oxide)]s

Two linear, stereoregular, and structurally defined PPV derivatives (PPVs), poly[distyrylbenzene-b-(ethylene oxide)]s, with respective 12 and 16 of ethylene oxide repeat units in the backbone, abbreviated as DE-1 and DE-2 thereinafter, have been prepared via a modified synthetic profile. Both DE-1 and -2 were soluble in organic solvents and able to form robust and transparent film upon spin casting. Instrument characterization, such as FTIR, ¹H and ¹³C NMR, UV-vis and fluorescence spectroscopy, revealed the final structures as designed and novel photophysical properties in solution. Apparent spectral evidences strongly suggested the all trans conjugated DE-1 and -2 and the successful isomeirization process adopted. It was found that the aggregates were formed for both DE-1 and -2 at approximately 60% of methanol in methanol/dichloromethane (MeOH/DCM). Both DE-1 and -2 exhibited solution tailorable absorption and emission properties. Before aggregating point, the absorption profile experienced a blue shift with the increase of MeOH and a slight increase in quantum yields (QYs). At aggregating point, however, an apparent blue shift in emission profile was observed along with a remarkable decrease of QY due to aggregate quenching.