Preparation and redox properties of N,N,N-1,3,5-trialkylated flavin derivatives and their activity as redox catalysts

Eight different flavin derivatives have been synthesized and the electronic effects of substituents in various positions on the flavin redox chemistry were investigated. The redox potentials of the flavins, determined by cyclic voltammetry, correlated with their efficiency as catalysts in the H2O2 oxidation of methyl p-tolyl sulfide. Introduction of electron-withdrawing groups increased the stability of the reduced catalyst precursor.     

Sensitivity improvement in 19F NMR-based screening experiments: theoretical considerations and experimental applications

NMR-based binding and functional screening performed with FAXS (fluorine chemical shift anisotropy and exchange for screening) and 3-FABS (three fluorine atoms for biochemical screening) represents a potential alternative approach to high-throughput screening for the identification of novel potential drug candidates. The major limitation of this method in its current status is its intrinsic low sensitivity that limits the number of tested compounds. One approach for overcoming this problem is the use of a cryogenically cooled (19)F probe that reduces the thermal noise in the receiver circuitry. Sensitivity improvement in the two screening techniques achieved with the novel cryogenic (19)F probe technology permits an increased throughput, detection of weaker binders and inhibitors (relevant in a fragment-based lead discovery program), detection of slow binders, and reduction in protein and substrate consumption. These aspects are analyzed with theoretical simulations and experimental quantitative performance evaluation. Application of 3-FABS combined with the cryogenic (19)F probe technology to rapid screening at very low enzyme concentrations and the current detection limits reached with this approach are also presented.     

Probing cooperative effects in bimetallic clusters: indications of C-N coupling of CH4 and NH3 mediated by the cluster ion PtAu+ in the gas phase

The bimetallic cluster ion PtAu+ activates methane in the gas-phase, yielding the carbene PtAuCH2+ which further reacts with ammonia under C-N coupling. In contrast, neither Pt2+ nor Au2+ mediates C-N bond formation. This example demonstrates how bond activation in the gas phase can be tuned by cooperative effects in bimetallic clusters.     

Pentafluorethylschwefeltrifluorid: Synthese und Reaktionen

Pentafluorethyl Sulfurtrifluoride: Synthesis and Reactions By oxidation of (C₂F₅S?)₂ ( 1 ) with AgF₂ at 0°C a mixture of C₂F₅SF₃ ( 2 ) and C₂F₅SF₅ ( 3 ) besides C₂F₅S(O)F ( 4 ) is formed. With elemental fluorine only 3 is isolated, an intermediate in this reaction is (C₂F₅SF₄?)₂ ( 5 ). At ?40 to ?30°C the mixture of 2, 3 and 4 was reacted with TASF and AsF₅, to give TAS⁺ C₂F₅SF₄^? ( 6 ), TAS⁺ C₂F₅S(O)F₂^? ( 7 ) and C₂F₅SF₂⁺AsF₆^? ( 8 ), respectively. While 6 and 7 decompose rapidly in solution even at low temperatures, of thermally stable 8 the solid state structure was determined by x-ray diffraction.     

Extension of the Coulomb–Hole–Hartree–Fock theory to molecules

The Coulomb–Hole–Hartree–Fock method introduced by E. Clementi in the early 1960s and reparametrized more recently by S. Chakraworty and E. Clementi to compute the correlated electronic energy in atomic systems, is here extended to compute molecules. The new parametrization is obtained empirically by fitting first and second atomic ionization potentials from He to Ca and a few diatomic molecules. The present formulation makes use of either one or more determinants in order to ensure proper dissociation products, following the early proposal of G.C. Lie and E. Clementi in the context of density functional computations for molecular systems. The new formulation is tested against the dissociation energies of a large number of molecules and it is found satisfactory. © 1995 John Wiley & Sons, Inc.