Purification, partial kinetic characterization and reactive sulfhydryl groups of the phosphoenolpyruvate carboxykinase from Perumytilus purpuratus adductor muscle

Phosphoenolpyruvate carboxykinase (PEPCK) from the adductor muscle of Perumytilus purpuratus was purified to homogeneity, as determined by SDS-polyacrylamide gel electrophoresis (PAGE). The purification consisted of a three-step procedure: ammonium sulphate precipitation, ion exchange chromatography on phosphocellulose and affinity chromatography on GTP-agarose. The enzyme presented a native molecular mass of 85 kDa, appearing as an active monomer. Under denaturing conditions (SDS-PAGE), the enzyme showed a relative molecular mass of 74 kDa. The specific activity of homogeneous PEPCK in the presence of 2.3 mM Mn2+ was 13.0 U/mg at 25°C. Apparent Km values at pH 7 and in the presence of 2.3 MM Mn2+ were 0.55, 2.4 and 0.045 mM for phosphoenolpyruvate, HCO3 and inosine 5′-diphosphate (IDP), respectively. Apparent Km for GDP was < 0.01 mM. ADP was not a substrate of the enzyme. Inosine 5'-triphosphate (ITP) inhibited the PEPCK activity (IC50 = 1.7 mM), and this inhibition was not reverte

Bond energy M-C/H-C correlations: dual theoretical and experimental approach to the sensitivity of M-C bond strength to substituents

DFT methods are used to quantify the relationship between M–C and H–C bond energies; for MLn = Re(5-C5H5)(CO)2H and fluorinated aryl ligands, theoretical and experimental investigations of ortho-fluorine substitution indicate a much larger increase in the M–C than in the H–C bond energy, so stabilising C–H activation products

A Dichromium(II) BiS(eta(8)-pentalene) double-sandwich complex with a spin equilibrium: Synthetic, structural, magnetic, and theoretical studies

The new bis(pentalene) complex Cr-2(eta(5):eta(5)-C8H4 (1,4-Si1Pr3))(2) has been synthesized and characterized; it is found to exhibit paramagnetism at room temperature, and solid-state magnetic studies show that the dimer is best modeled as containing a pair of antiferromagnetically interacting S = 1/2 centers with the separation between the singlet ground state and triplet excited state being 2.23 kJ mol(-1). Structural data show a Cr-Cr distance of 2.2514(15) angstrom, consistent with a strong metal-metal interaction. The bonding has been further investigated by density functional, hybrid, and CASPT2 methods. The metal-metal interaction is best described by a double bond with each metal having an 18-electron count. Theory predicts the singlet and triplet states to lie close in energy but puts the triplet state at a slightly lower energy than the singlet. The energy difference predicted by CASPT2 is closest to the experimental value

Anti-Bimetallic Complexes of Divalent Lanthanides with Silylated Pentalene and Cyclooctatetraenyl Bridging Ligands as Molecular Models for Lanthanide-Based Polymers

The new pentalene antibimetallic compounds [MCp*(THF)](2)(mu,eta(5):eta(5)-C8H41,4-SiiPr3) were prepared for M = Eu (1), Yb (2) from the one-pot reaction of MI2(THF)(x) and KCp* and the subsequent addition of 2 equiv of C8H41,4-SiiPr3[K](2) in THF. The related series of COT1,4-SiiPr3-bridged triple-deckers [MCp*(THF)(x)](2)(mu,eta(8):eta(8)-COT1,4-SiiPr3) (M = Eu, x = 0 (3); M = Yb, x = 0 (4); M = Sm, x = 1 (5)) were synthesized similarly; additionally, the base-free derivative with M = Sm and x = 0 (6) could be prepared by reaction of [SmCp*(mu-I)(THF)(2)](2) with COT1,4-SiiPr3[K](2) in toluene with heating. The solid-state structures, as determined by X-ray diffraction, show antibimetallic arrangements in which the divalent lanthanide centers are held oil opposing sides of a planar bridging ligand. The pentalene ligand coordinates in an approximate eta(5):eta(5) mode, with the metal centers slipped toward the wingtip carbons, whereas the COT ligand is bound in an eta(8):eta(8) fashion with the metal centers aligned with the centroid of the bridging ligand. Electronic spectroscopy suggests the Eu and Yb pentalene complexes have a smaller f-d gap than their COT analogues, indicating a greater extent of through-ligand metal-metal interaction in the pentalene species. [EuCp*(THF)(x)](2)(mu-COT1,4-SiiPr3) displays a weak green-yellow emission in THF solution (lambda(max) 509 nm, Phi(em) < 0.1%) upon excitation in the UV, consistent with a 4f(6)5d(1) -> 4f(7) emission process, with a short lifetime indicative of Eu-Eu coupling through the bridging COT ligand. Cyclic voltammetry reveals that 1, 3, and 4 decompose rapidly upon oxidation, although the monocation 2(+) appears to be stable in THF solution. Through-ligand Yb-Yb coupling is suggested by the electrochemical data for 2, of magnitude similar to that observed for its transition-metal analogues. However, unfortunately, attempts to further quantify this conclusion by spectroscopic investigation of 2(+) were unsuccessful