One-electron reduction potential for oxygen- and sulfur-centered organic radicals in protic and aprotic solvents

We estimated one-electron reduction potentials of redox-active organic molecules for a spectrum of eight different functional groups (phenoxyl, p-benzoquinone, phenylthiyl, p-benzodithiyl, carboxyl, benzoyloxyl, carbthiyl, and benzoylthiyl) in protic (water) and aprotic (acetonitrile, N,N-dimethylacetamide) solvents. Electron affinities (EA) were evaluated in a vacuum with high level quantum chemical methods using Gaussian3-MP2 (G3MP2) and Becke 3 Lee, Yang, and Parr functional B3LYP with aug-cc-pVTZ basis set. To evaluate one-electron redox potentials, gas-phase free energies were combined with solvation energies obtained in a two-step computational approach. First, atomic partial charges were determined in a vacuum by the quantum chemical method B3LYP/6-31G(d,p). Second, solvation energies were determined, solving the Poisson equation with these atomic partial charges. Redox potentials computed this way, compared to experimental data for the 21 considered organic compounds in different solvents, yielded overall root-mean-square deviations of 0.058 and 0.131 V using G3MP2 or B3LYP to compute electronic energies, respectively, while B3LYP/6-31G(d,p) was used to compute solvation energies.     

Separation of noble metal ions on silica with chemically bonded ligands

The separation of noble metal ions was investigated by chemically bonded ligands based on the concept of hard and soft acids and bases according to Pearson; influences of ion pairing and chelating effects are discussed. Complexing groups containing oxygen, nitrogen and sulphur were immobilized on silica gel. Ag, Au, Ir, Os, Pd, Pt and Rh were adsorbed in the acidic range (pH 0 to pH 5) and eluted from the gel in the range from pH 0 to pH 7.5 avoiding formation of hydroxides and coprecipitation of the noble metals. The separation is dependent on the immobilized ligand, the pH-value of sorption and desorption and the eluent.     

Stereoselective synthesis of anti-1,4-diols by a BH3.THF-mediated rearrangement of 1,2-disubstituted cyclobutenes

A new stereoselective rearrangement of cyclobutylboranes, obtained by the hydroboration of 1,2-disubstituted cyclobutenes, provides anti-1,4-diols with good-to-excellent diastereoselectivity. The mechanism of the rearrangement is discussed based on theoretical calculations.     

Potential cerebral perfusion agents. Synthesis and evaluation of a 1,4-disubstituted dihydropyridine analogue

The synthesis of a 1,4-disubstituted dihydropyridine, 1-(E-1[¹²⁵I]iodo-1-penten-5-yl)-4-(β-N-acetylaminoethyl)-1,4-dihydropyridine ([¹²⁵I] 10 ), is described. Acetylation of 4-(β-aminoethylpyridine) with acetic anhydride followed by condensation with E-1-borono-5-iodo-1-pentene ( 7 ) gave 1-(E-1-borono-1-penten-5-yl)-4-(β-N-acetylaminoethyl)pyridinium iodide ( 8 ). Chloramine-T and sodium iodide iodination of 8 gave the corresponding E-1-iodo compound 9 which was reduced with sodium borohydride to furnish 1-(E-1-iodo-1-penten-5-yl)-4-(β-N-acetylaminoethyl)-1,4-dihydropyridine ( 10 ). The corresponding radioiodinated compound was prepared similarly using Na[¹²⁵I]. The tissue distribution studies in rats indicate that [¹²⁵I] 10 crosses the blood brain barrier (0.49% dose/g in the brain) but gradually washes out from the brain.     

Synthesis of the liposidomycin diazepanone nucleoside

[structure: see text] The synthesis of the liposidomycin degradation product 4 from D-glucose establishes its stereochemistry as 5'S,6'S and, by incorporation of the earlier diazepanone relative stereochemical assignment, establishes the absolute stereochemistry of the liposidomycins 1 and 2 as 5'S,6'S,2'S,3'S.     

Closed vessel microwave-assisted wet digestion with simultaneous control of pressure and temperature in all vessels

A novel system for microwave-assisted wet digestion in closed vessels is described. Six pressure vessels made of quartz or Hostaflon^® TFM are placed in a special rotor in a microwave oven. During sample decomposition the pressure and temperature are measured in each vessel, and the data are transferred from the rotor by means of infrared light to the control unit. This means that no pneumatic or electronic connections to the vessels need to be established, providing very easy handling. The temperature history of each vessel is recorded; so the progress of each sample digestion may be reconstructed later on. Thus the requirements for quality control in sample digestion are available for the first time. For sample digestion at 75 bar and up to 280°?C, quartz vessels with 50 mL volume are used. Depending on the matrix, the maximum sample loading capacity is 1.2 g. TFM-vessels with 100 mL volume work at 30 bar up to 240°?C. The performance of the digestion system was tested with twelve standard reference materials. The results closely matched the certified values.     

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Evidence of a Uranium-Paddlewheel Node in a Catecholate-Based Metal–Organic Framework

The interactions between uranium and non-innocent organic species are an essential component of fundamental uranium redox chemistry. However, they have seldom been explored in the context of multidimensional, porous materials. Uranium-based metal–organic frameworks (MOFs) offer a new angle to study these interactions, as these self-assembled species stabilize uranium species through immobilization by organic linkers within a crystalline framework, while potentially providing a method for adjusting metal oxidation state through coordination of non-innocent linkers. We report the synthesis of the MOF NU-1700 , assembled from U⁴⁺-paddlewheel nodes and catecholate-based linkers. We propose this highly unusual structure, which contains two U⁴⁺ ions in a paddlewheel built from four linkers—a first among uranium materials—as a result of extensive characterization via powder X-ray diffraction (PXRD), sorption, transmission electron microscopy (TEM), and thermogravimetric analysis (TGA), in addition to density functional theory (DFT) calculations.