Über die Darstellung von substituierten 3,4-Dihydro-2(1H)-pyrimidin-iminen und 2-Aminopyrimidinen aus Guanidin und α,β-ungesättigten Ketonen

Guanidine reacts with the 2-alken-1-ones4 a-f and5 to give the unstable dihydropyrimidinimines (or-amines respectively)8 a-f (I, II or III respectively) and the hexahydroquinazolinimine (-amine)9 (I, II or III);8 a-f lose H₂, partly in the course of the reaction, partly during recrystallization to yield the 2-pyrimidinamines10 a-c, e, f, and the 4-methyl-5,6,7,8-tetrahydro-2-quinazolinamine11. With picric acid the unstable compounds8 d, f and9, resp. are converted into the stable 2-amino-3,4-dihydro-1H-2-pyrimidinylium picrates12 d and into the 2-amino-4-methyl-3,5,6,7,8,8 a-hexahydro-1H-2-quinazolinium picrate (13 resp.14, 15)¹⁸, whereas8 e reacts with HCl to give the chloride12 e. The structures of12 d-f follow from their NMR-spectra, and of10 a-c, e, f and11 by alternative syntheses by known methods^12–17 (e.g. from -diketones and guanidine). The reaction of8 d-f and9 to10 d-f and11 respectively is compared with previously described dehydrogenation and disproportionation reactions, especially of 3,4-dihydro-2(1H)-pyrimidinones (6 d ⁴,23 ²⁰) and-thiones (30 ¹) of similar structure and formulated as a base-catalysed elimination of H₂.

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HerrnA. Fuchsgruber danken wir für die Aufnahme und Hilfe bei der Interpretation der NMR-Spektren.     

Indirect nuclear spin-spin coupling constants in 1,2-diboretane-3-ylidene, a homoaromatic system with pi and sigma 3c/2e bonds. Comparison of experimental data with calculations using density functional theory (DFT)

The non-classical 1,2-diboretane-3-ylidene 1a was studied by 13C and 29Si NMR spectroscopy in order to obtain coupling constants 1J(13C,11B) and 1J(29Si,13C). The magnitudes of 1J(13C,11B) were deduced from linewidth measurements in low-temperature 13C and 11B NMR spectra. Calculation of the coupling constants for model compounds related to 1a, using DFT methods based on optimized geometries [B3LYP/6-311+G(d,p)], gave data in agreement with the experiments. Furthermore, the calculations predict for the first time a negative sign of 1J(13C,11B) which mirrors the bonding situation in 1 as described by theory.     

NMR Microscopy—Fundamentals,Limits and Possible Applications

Alongside the numerous applications of NMR spectroscopy to structural elucidation in analytical chemistry, and to biochemical and morphological studies by NMR tomography, NMR microscopy makes possible a whole new range of applications. These include imaging, the investigation of biological objects such as plants and small animals, and also the observation of microscopic structures and structural changes in polymers and ceramics. NMR spectroscopy can also be conducted combinationally as volume-selective spectroscopy, whereby it is possible to spatially resolve the NMR-specific parameters: spin density ?, chemical shifts δ, and the relaxation times T₁ and T₂. The numerous well developed methods available make it possible to study dynamic processes by fast imaging with a temporal resolution in milliseconds. This not only allows the imaging of moving objects without incurring movement artefacts but also the measurement of diffusion constants in isotropic and anisotropic diffusion—in the latter case allowing, in principle, the determination of the complete diffusion tensor. The spatially resolved measurement of the relaxation times yields information on molecular mobility and bonding, e. g. the bonding of water, or other solvents, to polymers, the mobility of fluids in polymers or ceramics, or the three-dimensional evaluation of pore size in porous materials. In biomedicine, NMR microscopy allows the observation of growth on the cellular level, the study of embryos, and the development of therapeutic methods in animal experiments. It can lead to a drastic reduction in the number of animal experiments, and in combination with volume-selective spectroscopy gives valuable information on in-vivo metabolism.     

Die Acetalgruppe, 1. Mitt. Acetale von Halogenmethyl-arylcarbinolen

Several halomethyl-arylcarbinols were prepared, and the influence of substituents on enantiomer selectivity in the acetalisation reaction with [2S-(2,3a,4,7,7a)]-octahydro-7,8,8-trimethyl-4,7-methanobenzofuran-2-ol was examined.

Unserem sehr verehrten Lehrer, Herrn Prof. Dr.Otto Hromatka, mit den besten Wünschen zum 80. Geburtstag gewidmet.     

Neutralization of HZSM-5 Br?nsted acid sites by shaping with boehmite

The reduction of the concentration of strongly acidic Brönsted sites of HZSM-5 by neutralization due to added boehmite is reported. Strongly acidic Brönsted sites are neutralized by [AlO·(Al₂O₃)_x]⁺ isopolyoxocations proceeding during the calcination treatment.     

Synthese und Struktur eines zweikernigen Gadolinium(III)-Komplexes: Magnetische Austauschwechselwirkungen in alkoxyverbrückten Komplexen der Lanthanoiden

Synthesis and Structure of a Binuclear Gadolinium(III) Complex: Magnetic Exchange Interactions in Alkoxy Bridged Lanthanide Complexes The Schiff Base ligand N-salicylidene-2-(bis-(2-hydroxyethyl)amino)ethylamine (H₃sabhea) reacts with Gd(NO₃)₃ · 6 H₂O in methanol solution to yield the alkoxy bridged binuclear gadolinium(III) complex [{Gd(Hsabhea)(NO₃)}₂] · 2MeOH ( 1 ). 1 crystallizes in the monoclinic space group P2₁/c with a = 1014.8(2), b = 2059.2(4), c = 867.5(2) pm, β = 106.72(2)°, and Z = 2. The two gadolinium atoms are bridged by two alkoxide oxygen atoms with angles of 107.60(11)° at the oxygen bridgeheads and a Gd? Gd separation of 376.43(7) pm. A variable-temperature magnetic susceptibility study (2 to 280 K) of 1 revealed an antiferromagnetic coupling between the Gd(III) ions with J = ?0.198 cm^?1 (g = 1.975).     

Rat brain proteins: two-dimensional protein database and variations in the expression level

A two-dimensional database of rat brain proteins was constructed. Brain samples from newborn animals were analyzed by two-dimensional electrophoresis and the proteins were identified by matrix-assisted laser desorption/ionization mass spectrometry. The database comprises 210 different proteins, the majority of which are structural components, heat shock proteins and enzymes with various catalytic activities. Several minor differences in the expression level were detected, mainly of quantitative nature, which most likely represent allelic differences. The map may be useful in studies of neurological disorders in animal models of human diseases.     

A complementary cesium coolant concentration ratio for localizing defective PWR fuel rods during reactor operation

Rough techniques for pinpointing defective fuel pins during actual reactor operation were developed for nuclear power plants. These techniques are based on various fission product concentration ratios. Here, a new cesium concentration ratio,¹³⁴Cs/¹³⁶Cs, was tested in combination with the more usual cesium ratio¹³⁴Cs/¹³⁷Cs. This new cesium ratio confirmed the conclusions drawn from the ratio¹³⁴Cs/¹³⁷Cs and provided some additional information on the location of the defective fuel rods. Application of this second cesium ratio improves the reliability of the rough localization method.     

Analysis of submicroliter samples using micro thermospray flame furnace atomic absorption spectrometry

A recently described thermospray flame furnace atomic absorption spectrometric (TS-FF-AAS) system has been modified in order to extend the applicability of the method for the determination of elemental traces in very small sample volumes (microliter or submicroliter). As an easily available, effective thermospray vaporizer, a fused silica capillary was used and the liquid sample was transported by 1 MPa (10 bar) gas pressure delivered by a standard gas cylinder. A 0.3 microL sample volume can be analyzed with a higher power of detection than using 3 orders of magnitude larger sample volumes with conventional flame atomic absorption spectrometry. The relative standard deviations (N=12) for 0.3 microL volumes and 5 microg/mL Pb samples amount to 3.1% and 3.8% in signal height and signal area, respectively. The detection limit was found to be 69 ng/mL. Initial experiments with other elements (Cd, Hg, Tl, Zn) led to similar results.     

Synthesis of CO and V-containing AlPO4-5 molecular sieves and characterization of their acid properties

Co and V-containing AlPO₄-5 molecular sieves were characterized by IR spectroscopy and TPDA. The incorporation of Co²⁺ leads to the formation of additional P–OH groups. The introduction of V⁴⁺ on T-atom positions could not be observed and it seems that the VO²⁺ ions are only fixed by interaction with terminal OH-groups.