Zur Methodik der Autoradiographie im Elektronenmikroskop

Die elektronenmikroskopische Autoradiographie erlaubt unter Ausmutzung des hohen Auflösungsvermögens des Elektronenmikroskops eine exakte Lokalisierung radioaktiver Verbindungen in Präparaten. Voraussetzung dafür ist die Herstellung einer Einkornschicht des Silberhalogenids aus einer vorgegebenen Filmemulsion. Diese Einkornschicht mit möglichst gleichmäßiger Silberhalogenidverteilung muß dann auf das radioaktive Objekt aufgebracht werden. Nach einer Übersicht über die Versuchsmethode werden Untersuchungen zur Präparation von Silberhalogenid-Einkornschichten aus den Emulsionen ORWO K 2, K 5, K 6, Ilford L 4 und Gevaert Nuc 7.15 für die elektronenmikroskopische Autoradiographie dargestellt.     

The regioselective C5 halogenation of quinolines using sodium halides under transition metal-free conditions

An efficient and mild halogenation of 8-acylaminoquinoline at the C5 position was described. The reaction utilized easily available sodium halides as the halogen sources and proceeded smoothly under transition metal-free conditions. Various 8-aminoquinolines with a number of functional groups were compatible in this reaction to afford the corresponding halogenated products in moderate to good yields. Moreover, the reaction conditions also tolerated the substrates without the 8-aminoquinolyl auxiliary, such as N-phenyl amide and N-naphthyl amide.     

Palladium‐Catalyzed Direct Cyclopropylation of Heterocycles

Many 1,3‐azoles and thiophenes are directly cyclopropylated in the presence of a simple palladium catalyst. The relative configuration on the three‐membered rings is retained in the products. Thus, the cyclopropyl–halide bond undergoes concerted oxidative addition to palladium(0) and cyclopropyl radicals are not involved in the productive pathway.     

Multiple-magnetic field 139La NMR and density functional theory investigation of the solid lanthanum(III) halides

Results from a solid-state ¹³⁹La NMR spectroscopic investigation of the anhydrous lanthanum(III) halides (LaX₃; X=F, Cl, Br, I) at applied magnetic fields of 7.0, 9.4, 11.7, 14.1, and 17.6 T are presented and highlight the advantages of working at high applied magnetic field strengths. The ¹³⁹La quadrupolar coupling constants are found to range from 15.55 to 24.0 MHz for LaCl₃ and LaI₃, respectively. The lanthanum isotropic chemical shifts exhibit an inverse halogen dependence with values ranging from −135 ppm for LaF₃ to 700 ppm for LaI₃, which represents nearly half of the total lanthanum chemical shift range. The spans of the magnetic shielding tensors also vary widely, from 35 to 650 ppm for the solid LaF₃ through LaI₃. DFT calculations of the ¹³⁹La electric field gradient and magnetic shielding tensors have been performed and provide a qualitative interpretation of the trends observed experimentally.     

1-(2-Iodophenyl)-1H-tetrazole as a ligand for Pd(II) catalyzed Heck reaction

1-(2-Iodophenyl)-1H-tetrazole 2 was synthesized by the reaction of 2-iodoaniline, sodium azide and triethyl orthoformate in acetic acid. The newly synthesized ligand 2 was successfully used in Heck reaction to give the cross-coupled products in excellent yields.     

The role of F A1:Ag+ defects in laser light generation and coadsorption of CO and halogen atoms at the KCl and KBr surface sites. First principles calculations

F _A1:Ag⁺ color center at the low coordination (100) and (110) surface sites of KCl and KBr thin films play an important role in providing tunable laser oscillation and adsorbatesubstrate interactions. Double-well potentials at this site are investigated using ab initio molecular electronic structure calculations. The calculated Stokes shifted (optical transition bands), opticaloptical conversion efficiencies, the probability of orientational destruction, exciton (energy) transfer and Glasner-Tompkins empirical rule suggest that laser light generation is sensitive to (i) the lattice anion, (ii) the coordination number of surface ions, and (iii) the choice of the basis set centered on the anion vacancy. The adsorbate-substrate interactions were found to be dependent on the electronegativity of the adatom and on the lattice anion. Optimised geometries and the coadsorption of CO and (F, Cl, Br, I) on KCl and KBr (100) crystals are presented. Calculated chemisorption energies for CO on the (halogen atom/defect free sites of KCl and KBr (100) crystals) showed that the coadsorption of halogen atom tends to block other adsorbate-substrate interactions at the nearest neighbour sites. Thus if halogen atom coverage increases, the CO prefers to be adsorbed on the K⁺ site of the KCl and KBr (100) surfaces and on KBr relative to KCl.      

Poly(4-vinylpyridine) catalyzed hydrolysis of methyl bromide to methanol and dimethyl ether

The hydrolysis of methyl bromide with neutral water is performed in the presence and absence of various amines in a batch reactor at different temperatures (50–125 °C). Screening of poly(4-vinylpyridine) as a potential reusable solid amine catalyst showed maximum efficiency. This significant enhancement in efficiency is due to the capture of HBr by solid PVP and remains phase-separated driving the reaction forward. The major advantage of this process is that the polymer can be easily regenerated and reused without loss of activity making it a very effective catalyst for the conversion of methyl halides to methanol and dimethyl ether.