Estimation of molecular weights of peptides by determination of height equivalent to a theoretical plate in size-exclusion chromatography

The analysis of the flow-rate required to obtain the optimum height equivalent to a theoretical plate, HETP, has been used to estimate the molecular weight, MW, of peptides in size-exclusion chromatography. A straight line is obtained when log MW is plotted against the flow-rate which gives the optimum HETP. This relationship holds even for peptides which adsorb to column packings. The typical quantity of peptide required is 1 nmol and analysis time was less than 2 h. The method is applied to peptides of 200–10,000, and the precision is ±20%. The method may be applicable to the analysis of MW for all classes of compounds.     

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.     

Facile, rapid, and high-yield synthesis of pillar[5]arene from commercially available reagents and its X-ray crystal structure

We monitored the progress of formation of dimethoxypillar[5]arene by size-exclusion chromatography. Surprisingly, the cyclization reaction completely finished in just 3 min. By improving the reaction conditions and purification process, we successfully obtained dimethoxypillar[5]arene in a short time and in high yield (71%) from commercially available reagents. By improving the deprotection reaction of the methoxy moieties, pillar[5]arene was isolated quantitatively. Single crystal X-ray analysis confirmed the structure of pillar[5]arene in the solid state.     

Regioselective CF Bond Activation of Hexafluoropropylene on Palladium(0): Formation of a Cationic η2‐Perfluoroallylpalladium Complex

A chemoselective C(sp²)? F or C(sp³)? F bond activation of hexafluoropropylene (HFP) was achieved by adopting the proper combination of a Lewis acid co‐additive with a ligand which coordinates Pd⁰. The treatment of [(η²‐HFP)Pd(PCy₃)₂] with B(C₆F₅)₃ allowed a chemoselective C(sp³)? F bond cleavage of HFP to give a unique cationic perfluoroallypalladium complex. In this complex, the coordination mode of the perfluoroallyl ligand was considered to be of the unique η²‐fashion.     

Coprecipitation of gold(III) complex ions with manganese(II) hydroxide and their stoichiometric reduction to atomic gold (Au(0)): analysis by Mössbauer spectroscopy and XPS

To elucidate the formation process of precursor of gold-supported manganese dioxide (MnO2), the coprecipitation behavior of [AuCl4-n(OH)n](-) (n=0-4) (Au(III)) complex ions with manganese(II) hydroxide (Mn(OH)2 and the change in their chemical state were examined. The Au(III) complex ions were rapidly and effectively coprecipitated with Mn(OH)(2) at pH 9. According to the M?ssbauer spectra for gold (Au) coprecipitated with Mn(OH)2, below an Au content of 60 wt% in the coprecipitates, all of the coprecipitated Au existed in the atomic state (Au(0)), while, above an Au content of 65 wt%, part of the gold existed in the Au(III) state, and the proportion increased with increasing coprecipitated Au content. Based on the results of X-ray photoelectron spectroscopy, Mn(II) in Mn(OH)2 converted to Mn(IV) in conjunction with coprecipitation of Au(III) complex ions. These results indicate that the rapid stoichiometric reduction of Au(III) to Au(0) is caused by electron transfer from Mn(II) in Mn(OH)2 to the Au(III) complex ion through an Mn-O-Au bond.     

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.     

Structures of two haptotropic isomers generated by the sliding of 1,3,5-triene ligands on a Pd-Pd-Pd chain

Two haptotropic isomers of [Pd(3)(mu(3)-DMVC)(2)(CH(3)CN)(2)][BF(4)](2) (DMVC = 1,2-di-(E)-carbomethoxyvinylcyclopentene) were structurally determined by X-ray crystallographic analyses; a monoclinic crystal contained a symmetric sandwich complex (mu(3)-eta(2):eta(2):eta(2)-coordination of DMVC ligands) and a triclinic crystal contained an unsymmetric sandwich complex (mu(3)-eta(2):eta(3):eta(1)-coordination of DMVC ligands), where the latter are connected to each other by C-HO hydrogen bonds.