Homocoupling of arylboronic acids and potassium aryltrifluoroborates catalyzed by protein-stabilized palladium nanoparticles under air in water

Palladium nanoparticles stabilized primarily within the protein cavity of a highly thermostable Dps protein (DNA binding protein from starved cells) from the thermophilic bacterium Thermosynechoccus elongatus provide an efficient catalyst for the homocoupling of boronic acids and potassium aryltrifluoroborates in water under aerobic phosphine-free conditions. Symmetrical biaryls have been isolated in good to excellent yields. Potassium aryltrifluoroborates give similar or better results than the corresponding arylboronic acids.     

Study of Pt and Rh based supported catalysts modified with tetrabutyltin for the selective hydrogenation of 4-methoxyacetophenone

Catalysts based on Pt and Rh modified with Sn(C₄H₉)₄ were studied in the hydrogenation of 4-methoxyacetophenone. The selectivity to 1-(4-methoxyphenyl)ethanol was close to 100% at Sn/(Pt,Rh) = 1.0, however the catalytic activity decreased drastically. With respect to the balance between activity and selectivity the catalyst PtSnOM (Sn/Pt=0.4) showed the best performance.     

A polyamine coating for enhanced capillary electrophoresis-electrospray ionization-mass spectrometry of proteins and peptides

A procedure for enhanced capillary electrophoresis-electrospray ionization-mass spectrometry (CE-ESI-MS) of proteins is presented. The use of a newly presented capillary coating, PolyE-323, provided fast separations of typically a few minutes with high efficiency, good deactivation, and no bleeding into the mass spectrometer. Capillaries coated with PolyE-323 showed high stability over a range of pH 2-10, and tolerance towards methanol and acetonitrile, two modifiers commonly used in CE-ESI-MS. Due to the speed and simplicity of the coating procedure, the polymeric surface could, if necessary, easily be regenerated. This capability is especially valuable when working with samples of complex matrix, where a capillary surface cleaning step might be desired in order to eliminate possible memory effects. The potential of PolyE-323-coated capillaries in bioanalysis using CE-ESI-MS was demonstrated by analyzing peptides and proteins up to 66 kDa using time of flight (TOF)-MS. Due to the stable, anodal electroosmotic flow generated by the coating, the use of a sheathless ESI interface was enabled, demonstrated in peptide analysis with attomole sensitivity. The fast on-line CE-ESI-TOF system using PolyE-323-coated capillaries provided efficient separation and detection of a large number of peaks in a short time, exemplified by the analysis of a tryptic digest of bovine serum albumin (BSA). The capability of the developed capillary surface coating was demonstrated by the separation of human plasma and cerebrospinal fluid (CSF).     

Crystal Structure of a New Triply‐Bridged Cobalt(III) Dimer with 2, 2′‐Dipyridylamine (dipyam), [Co2(μ‐OH)2(μ‐OAc)(OAc)2(dipyam)2]AcO·EtOH

The structure of [Co₂(μ‐OH)₂(μ‐OAc)(OAc)₂(dipyam)₂]AcO · EtOH ( 1 ) has been determined by single‐crystal X‐ray analysis. The cationic complex may be described as a “di(μ‐hydroxo)(μ‐acetato)dicobalt(III)” core with chelating 2, 2′‐dipyridylamine and monodentate acetate ligands. The coordination polyhedron around each cobalt atom is a distorted octahedral. The dimers are linked in the crystal by N‐H···O_{ionic AcO} and C‐H···O_{monodentate AcO} hydrogen bonds. Spectroscopic data are also presented.     

Toward the synthesis of peloruside a: fragment synthesis and coupling studies

[reaction: see text] The asymmetric synthesis of building blocks 3, 4, and 5, corresponding to C(12)-C(19), C(7)-C(11), and C(1)-C(6) segments of peloruside A, is reported, along with boron-mediated aldol coupling studies directed toward the assembly of the complete carbon skeleton of this microtubule-stabilizing macrolide.     

Thermodynamic properties of the aqueous solution of potassium salts of some 4-((alkylcarbonyl)amino)-2-hydroxybenzoic acids at 298 and 313 K

To understand the aggregation behavior of surface-active ligands with a salycilic polar head, we undertook a systematic study of some classes of anionic surfactants where the presence and the position of the -OH and the carboxylic group differ. This paper reports the dilution heats at 298 and 313 K of aqueous solutions of potassium 4-((alkylcarbonyl)amino)-2-hydroxybenzoate (KPAS-C(n) where n stands for the number of carbon atoms in the chain) in KOH at 0.1 m, measured as a function of concentration. From the experimental data, apparent and partial molar enthalpies vs concentration were obtained. By using a pseudo-phase-transition approach, the enthalpy changes upon micelle formation (DeltaH(m)) and assuming that in the restricted range of temperature examined heat capacities are constant, the heat capacity changes have been obtained. Micelle formation enthalpies are seen to be additive with a group contribution for the methylene group of -1.5+/-0.1 kJ mol(-1) per group at 298 K and -2.3+/-0.1 kJ mol(-1) per group at 313 K, comparable with that obtained for similar anionic compounds in the same experimental conditions and for N-alkylnicotinamide chlorides (cationic surfactants). The -CH(2)- group contribution to the micelle formation heat capacities is -53+/-1 J K(-1) mol(-1).     

Biological Activity of Triazolopyrimidine Copper(II) Complexes Modulated by an Auxiliary N-N-Chelating Heterocycle Ligands

Novel complexes of type [Cu(N-N)(dmtp)₂(OH₂)](ClO₄)₂·dmtp ((1) N-N: 2,2′-bipyridine; (2) L: 1,10-phenantroline and dmtp: 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine) were designed in order to obtain biologically active compounds. Complexes were characterized as mononuclear species that crystallized in the space group P-1 of the triclinic system with a square pyramidal geometry around the copper (II). In addition to the antiproliferative effect on murine melanoma B16 cells, complex (1) exhibited low toxicity on normal BJ cells and did not affect membrane integrity. Complex (2) proved to be a more potent antimicrobial in comparison with (1), but both compounds were more active in comparison with dmtp—both against planktonic cells and biofilms. A stronger antimicrobial and antibiofilm effect was noticed against the Gram-positive strains, including methicillin-resistant Staphylococcus aureus (MRSA). Both electron paramagnetic resonance (EPR) and Saccharomyces cerevisiae studies indicated that the complexes were scavengers rather than reactive oxygen species promoters. Their DNA intercalating capacity was evidenced by modifications in both absorption and fluorescence spectra. Furthermore, both complexes exhibited nuclease-like activity, which increased in the presence of hydrogen peroxide.     

Density functional investigation of the molecular geometries,harmonic vibrational frequencies,singlet-triplet energy separations,adiabatic ionization potentials,and electron affinities of XY2 (X = Si,Ge, Sn; Y = F,Cl) systems

The geometrical and spectroscopic parameters of SiF₂, SiCl₂, GeF₂, GeCl₂, SnF₂, and SnCl₂ were determined using the linear combination of Gaussian-type orbitals-local spin density (LCGTO-LSD) method and employing both the local (LSD) and nonlocal functionals (NLSD) for the exchange-correlation energy. A general good agreement with available experimental information and with previous high-level correlated computations was found. Data on cations and anions are reported for the first time and can be used, together with those on neutral systems, to stimulate future and desirable experimental work on this significant class of molecules. © 1997 John Wiley & Sons, Inc.