Polyoxotungstate Archetype {P4W27} and its 3d Derivatives

The propensity of the new, phenylphosphonate-stabilized polyoxotungstate [(C₆H₅P^VO)₂P₄W₂₄O₉₂]¹⁶⁻ to act as a precursor for new 3d metal-functionalized polyanions has been investigated. Reactions with Mn^II and Cu^II induce the formation of the previously unknown polyoxotungstate archetype {P₄W₂₇}, isolated as salts of the polyanions [Na⊂{Mn^II(H₂O)}{WO(H₂O)}P₄W₂₆O₉₈]¹³⁻ ( 1 ) and [K⊂{Cu^II(H₂O)}{W(OH)(H₂O)}P₄W₂₇O₉₉]¹⁴⁻ ( 2 ), which were characterized in the solid state (single-crystal X-ray diffraction, elemental and TG analyses, IR spectroscopy, SQUID magnetometry) and in aqueous solution (UV/Vis spectroscopy, cyclic voltammetry).     

Photolysis of 3-(1-acyl-5-aryl-3-pyrazolinyl)coumarins—Effective Fluorescence Decay

Photophysical characteristics of new 3-(1-acyl-5-aryl-3-pyrazolinyl)coumarins have been measured. These coumarin derivatives are found to be effective fluorophores and show high values of quantum yields of fluorescence both in nonpolar and in polar solvents. The 3-(1-acyl-5-aryl-3-pyrazolinyl)coumarins turned to be photosensitive compounds and undergo photolysis under irradiation in the range of 310–465 nm. Photolysis is suggested to include retro-cyclization and retro-condensation steps. The process is accompanied by a sharp drop of fluorescence that can be of interest for the creation of new media in optical recording of information.     

Stabilization of High‐Valence Ruthenium with Silicotungstate Ligands: Preparation,Structural Characterization,and Redox Studies of Ruthenium(III)‐Substituted α‐Keggin‐Type Silicotungstates with Pyridine Ligands, [SiW11O39RuIII(Py)]5−

Ruthenium(III)‐substituted α‐Keggin‐type silicotungstates with pyridine‐based ligands, [SiW₁₁O₃₉Ru^III(Py)]^5?, (Py: pyridine ( 1 ), 4‐pyridine‐carboxylic acid ( 2 ), 4,4′‐bipyridine ( 3 ), 4‐pyridine‐acetamide ( 4 ), and 4‐pyridine‐methanol ( 5 )) were prepared by reacting [SiW₁₁O₃₉Ru^III(H₂O)]^5? with the pyridine derivatives in water at 80 °C and then isolated as their hydrated cesium salts. These compounds were characterized using cyclic voltammetry (CV), UV/Vis, IR, and ¹H NMR spectroscopy, elemental analysis, titration, and X‐ray absorption near‐edge structure (XANES) analysis (Ru K‐edge and L₃‐edge). Single‐crystal X‐ray analysis of compounds 2 , 3 , and 4 revealed that Ru^III was incorporated in the α‐Keggin framework and was coordinated by pyridine derivatives through a Ru? N bond. In the solid state, compounds 2 and 3 formed a dimer through π? π interaction of the pyridine moieties, whereas they existed as monomers in solution. CV indicated that the incorporated Ru^III–Py was reversibly oxidized into the Ru^IV–Py derivative and reduced into the Ru^II–Py derivative.     

Ionic liquid matrices for MALDI mass spectrometry of lignin

Analytical and Bioanalytical Chemistry - The use of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry for the study of lignin is still extremely limited due to its low...     

Side Reactions in the Liquid-Phase Cyclohexanone Ammoximation

Influence of metal ions on hydrogen peroxide decomposition on the liquid-phase ammoximation of cyclohexanone was studied in homogeneous and heterogeneous (over titanium silicalite) conditions. The latter reaction is accompanied by side reactions, which deactivate the catalyst. Deactivation behavior is discussed.     

A new mechanism of acyl group transfer in the reaction catalyzed by D-glyceraldehyde-3-phosphate dehydrogenase

D-Glyceraldehyde-3-phosphate dehydrogenase (GAPDH, EC 1.2.1.12) catalyzes the oxidative phosphorylation of its substrate in a two-step reaction. Asa result of the first, oxidativestep, the covalent intermediate where in 3-phosphoglyceroyl moiety is bound to Cys149 of the active center is subjected to nucleophilic attack by inorganic phosphate, but remains resistant to hydrolytic decomposition. This ensures tight coupling of oxidation with phosphorylation in glycolysis. In this article, we present the experimental evidence for the conversion of GAPDH into a form capable of performing the reaction in the absence of inorganic phosphate. The structural basis for this conversion is the oxidation of a cysteine residue (probably Cys 153) into a sulfenic acid derivative under mild conditions to affect the integrity of the essential Cys 149. As a result, an intram olecular transfer of 3-phosphoglyceroyl group from the active center Cys 149 to Cys 153 becomes possible with subsequent hydrolysis of the sulfenyl carboxylate intermediate.     

Variation in the regioselectivity of levulinic acid bromination in ionic liquids

The reaction of levulinic acid and its esters with bromine in ionic liquids results in the formation of 3-bromo derivatives as the major products and not the 5-bromo substituted isomers, which are typically formed in organic solvents. The bromination of levulinic acid in ionic liquids in the presence of urea leads to the formation of 5-bromolevulinic acid.