A stable zerovalent palladium chain enveloped by a pi-electron sheath of conjugated polyene ligands

A surprisingly stable homoleptic Pd(0)(4) chain complex of non-activated olefins was isolated and structurally characterized by X-ray crystallographic analysis, and the unique structure and bonding are compared to those of the corresponding dicationic [Pd(4)](2+) chain sandwich complex.     

Palladium-catalyzed coupling reactions of tetrafluoroethylene with arylzinc compounds

Organofluorine compounds are widely used in all aspects of the chemical industry. Although tetrafluoroethylene (TFE) is an example of an economical bulk organofluorine feedstock, the use of TFE is mostly limited to the production of poly(tetrafluoroethylene) and copolymers with other alkenes. Furthermore, no catalytic transformation of TFE that involves carbon-fluorine bond activation has been reported to date. We herein report the first example of a palladium-catalyzed coupling reaction of TFE with arylzinc reagents in the presence of lithium iodide, giving α,β,β-trifluorostyrene derivatives in excellent yields.     

Measurements of kineic parameters of inorganic pyrophosphatase by flow-injection procedures

Two flow-injection systems were designed for characterizing the enzymatic hydrolysis of pyrophosphate by inorganic pyrophosphatase (EC 3.6.1.1). By using a molybdenum(VI) reagent the selective determination of a product, orthophosphate, in the presence of pyrophosphate was made. An anion exchange column was employed for the simultaneous determination of both the substrate and the product with a molybdenum(V)/molybdenum(VI) reagent. The effects of magnesium concentration and reaction temperature on the enzyme activity were determined. The Michaelis constant and maximum velocity at 25°C and pH 7.2 were evaluated. K_m was ca. 3 μM.     

Intramolecular hydrogen bond in enol form of 3-substituted-2,4-pentanedione

The 3-substituent effect on the enolic ring of 2,4-pentanedione has been investigated. A linear relationship between the chemical shifts of the enolic proton and the chelated carbonyl stretching vibrations has been found for the various highly enolized 3-substituted-2,4-pentanediones. The stronger electron-withdrawing resonance effect of the substituent at 3-position results in the lower magnetic field shift of the enolic proton and the lower frequency shift of the chelated carbonyl stretching. Semi-empirical Hückel calculations have been performed to enable discussion of the electronic effect of the substituents.     

Structural Characterization of Chemical Species in Solution by a Theoretical Analysis of XANES Spectra

A theoretical analysis method using a discrete variational X (DV-X) molecular orbital (MO) calculation, based on electron transition from an inner orbital to an unoccupied orbital, is introduced to analyze X-ray absorption near-edge structure (XANES) spectra in a lower energy region below the X-ray absorption edge. The computational procedure is described in detail and the evaluation of an obtained result is also explained. Applications of this method are presented for Cu(II) ions in liquid ammonia, macrocyclic Cu(II) complex in aqueous solution, and Al(III) ions in aqueous solution.     

An Artificial Receptor for Dimethyl Aspartate

[trans-5,15-Bis(2,7-dihydroxy-1-naphthyl)-2,3,7,8,12,13,17,18-octaethylporphyrinato]zinc(II) (1), a trifunctionalized porphyrin host, was prepared as a receptor for amino acid derivatives, particularly those having a hydrogen-bonding site in the side chain. The free energy changes for the binding of Leu-OMe, Asp-OMe, and Glu-OMe to 1 were -5.8 kcal/mol, -6.6 kcal/mol, and -5.9 kcal/mol, showing a selectivity for Asp-OMe. (1)H NMR titration experiments indicated that three simultaneous attractive interactions, one coordination interaction, and two hydrogen-bonding interactions, are operating in the host-guest complex. The preference for Asp-OMe over Glu-OMe was found to originate from the favorable enthalpy term for Asp-OMe. The free energy change, the enthalpy change, and the entropy change were determined and split into contributions arising from coordination interaction and from hydrogen-bonding interactions by use of reference hosts. Comparison of enthalpy and entropy changes suggests that the host-guest complex becomes more ordered as the number of recognition pairs increases.     

Efficient axial chirality induction in biphenyldiol triggered by proton-transferred hydrogen bonding with chiral amine

Axial chirality was induced in biphenyldiol upon binding chiral amines with the efficiency of chiral induction much improved at low temperature. At low temperatures, two molecules of amine were bound to biphenyldiol. The value of the dissymmetric g-factor increased as proton-transferred hydrogen bonds formed between biphenyldiol and amine. These results indicate that proton-transferred hydrogen bonding plays an important role in constructing a highly ordered chiral assembly.