Direct Synthesis of ZIF-8 on Transmission Electron Microscopy Grids Allows Structure Analysis and 3D Reconstruction

The first example of layer-by-layer growth of a metal–organic framework (MOF) directly on transmission electron microscopy (TEM) grids is described. ZIF-8 is deposited on thin amorphous carbon films and subjected to a structure analysis by (scanning) TEM ((S)TEM). This method serves as a two-in-one synthesis and TEM sample-preparation technique and allows straightforward analysis of ZIF-8 crystallites. Artifacts resulting from sample preparation are completely avoided by this approach. The morphological properties, crystal structure, and the chemical composition of the material are investigated with high spatial resolution by a variety of methods of (analytical) electron microscopy. Furthermore, the incorporation of metallic nanoparticles in ZIF-8 by integrating a corresponding step into the layer-by-layer deposition process is examined. The formation of ZIF-8 crystals on the film proceeds as under the absence of nanoparticle-forming synthesis steps. However, the nanoparticles rather cover the supporting amorphous carbon film than being incorporated in the ZIF-8 material. This information cannot be obtained from standard characterization techniques but requires the application of analytical (S)TEM techniques.     

Untersuchungen der Hydroxylammonium-Aluminate

Summary Two microcristalline phases have been isolated from aqueous solutions: (NH₃OH)₂AlF₅(A) and (NH₃OH)AlF₄·H₂O(B). They crystallize in the orthorhombic system with cell parameters for A:a=6.475 (3) Å,b=7.295 (3) Å,c=10.827 (5) Å, and for B:a=7.003 (3) Å,b=8.489 (4) Å,c=10.745 (5) Å. The Hydroxylammonium-aluminates were characterized by vibrational spectroscopy and their thermal decomposition studied by DSC and TG analysis.

     

Investigation of the uranil(II)—3-Hydroxyflavone complex

Summary By the application of suitable spectrophotometric methods andpH-metric measurements it has been established that uranyl ion and 3-hydroxyflavone form a [UO₂(C₁₅H₉O₃)]⁺ complex. The concentration stability constant of the complex was determined by Bent-French's (₁=8.59 atpH=3.5) and Bjerrum's (from 8.68 atpH=4 to 6.14 atpH=7) methods. Conditions are given for the spectrophotometric determination of 3-hydroxyflavone by means of the complex. The regression equation is calculated and the accuracy of the method is determined. All investigations were carried out with 80% ethanolic solutions at room temperature (20°), the spectrophotometric measurements being performed at a constantpH (3.5) and a constant ionic strength (0.01M).

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Untersuchung des Uranil(II)—3-Hydroxyflavon-Komplexes

Zusammenfassung Unter der Anwendung von geeigneten spektrophotometrischen Methoden sowiepH-metrischen Messungen wurde gefunden, daß das UO ₂ ²⁺ -Ion und 3-Hydroxyflavon den Komplex [UO₂(C₁₅H₉O₃)]⁺ bilden. Die Stabilitätskonstante des Komplexes wurde nach Bent und French (₁=8.59 beipH=3.5) und nach Bjerrum (von 8.68 beipH=4 bis 6.14 beipH=7) bestimmt. Es werden die Bedingungen für die spektrophotometrische Bestimmung des 3-Hydroxyflavons mit Hilfe des Komplexes angegeben, die Regreßgleichung berechnet und die Genauigkeit der Methode ermittelt. Alle Untersuchungen wurden in 80proz. Ethanol bei Raumtemperatur (20°), die spektrophotometrischen Untersuchungen bei konstantempH-Wert und Ionenstärke (0.01M) durchgeführt.

     

Geometry and cooperativity effects in adenosine-carboxylic acid complexes

NMR experiments and theoretical investigations were performed on hydrogen bonded complexes of specifically 1- and 7-15N-labeled adenine nucleosides with carboxylic acids. By employing a freonic solvent of CDClF2 and CDF3, NMR spectra were acquired at temperatures as low as 123 K, where the regime of slow hydrogen bond exchange is reached and several higher-order complexes were found to coexist in solution. Unlike acetic acid, chloroacetic acid forms Watson-Crick complexes with the proton largely displaced from oxygen to the nitrogen acceptor in an ion pairing structure. Calculated geometries and chemical shifts of the proton in the hydrogen bridge favorably agree with experimentally determined values if vibrational averaging and solvent effects are taken into account. The results indicate that binding a second acidic ligand at the adenine Hoogsteen site in a ternary complex weakens the hydrogen bond to the Watson-Crick bound carboxylic acid. However, substituting a second adenine nucleobase for a carboxylic acid in the trimolecular complex leads to cooperative binding at Watson-Crick and Hoogsteen faces of adenosine.     

Mesoionic dimethyl derivatives of some 1,2,4-triazinones. The course of the reaction of 3,5-dimethoxy, 3-methoxy-5-methylthio, 5-methoxy-3- methylthio and 3,5-bis(methylthio)-1,2,4-triazine with methyl iodide

Treatment of 3,5-dimethoxy-1,2,4-triazine ( 1a ) with methyl iodide was found to give depending on the reaction time triazinium iodide 2a , triaziniumolates 4a and 6a as well as methoxytriazinones 7a and 8a . Thermolysis of 2a gave triaziniumolates 4a and 6a . Reaction of 2a , 4a or methoxytriazinone 9a with methyl iodide in acetonitrile yielded as the sole product 6a . Reaction of 3-methoxy-5-methylthio-1,2,4-tri-azine (1b ) with methyl iodide gave triazinium iodide 2b and methylthio triazinone 7b . Hydrolysis of 2a,b afforded 4a . Reaction of 5-methoxy-3-methylthio-1,2,4-triazine ( 1c ) with methyl iodide gave triazinium iodide 2c , triaziniumolate 4b , triazinium iodide 5b and triazinone 8b . Hydrolysis of 2c yielded 4b and its thermolysis gave a mixture of 4b and 5b . Reaction of 2c , 4b and triazinone 9b with methyl iodide afforded 5b . Treatment of 3,5-bis(methylthio)-1,2,4-triazine ( 1d ) with methyl iodide was found to give a mixture of N1 and N2 methiodides 2d and 3d which gave on hydrolysis 4b and 8b , respectively. Methylation of 6-methyl derivatives 1c-g gave analogous results, however the proportions of N1 methylated products were lower and the reaction rates higher in comparison to their respective lower homologues 1a,c,d . The structures of the mesoionic dimethyl derivatives were assigned from uv, ir, ¹H nmr and electron impact mass spectra. The structural assignments were eventually confirmed by quantum chemical calculations of net charge distributions, bond lengths and ipso angles of the C5?O bonds.     

Evidence for deformation in <Superscript>113-116</Superscript>Cd isotopes

High-spin states in ^113-116Cd have been investigated with the fusion-fission reaction ²⁸Si +¹⁷⁶Yb at 145 > MeV. The experiment has been performed with the Eurogam2 array. New rotational bands based on two quasi-particle states have been observed for even-even cadmium isotopes. A new level scheme based on the 11/2⁻ isomeric state is proposed for ¹¹⁵Cd and the one of ¹¹³Cd has been extended to spin (31/2⁻). The decoupled bands identified in both odd-A nuclei are interpreted as being built upon a low-Ωh_11/2 quasi-neutron configuration. Microscopic Hartree-Fock + BCS calculations confirm the prolate deformation in this mass region especially for the odd cadmium isotopes. Received: 21 December 1999 / Revised version: 16 February 2000     

Annulations of isoquinoline and β-carboline ring systems: synthesis of 8-oxoprotoberberine derivatives

Annulation processes of isoquinoline and β-carboline compounds have been investigated leading to synthetic routes for the preparation of 8-oxoprotoberberine derivatives. The key steps combined a diene formation/Diels-Alder cycloaddition reaction to afford the targeted polycyclic skeletons. Further oxidative transformations of the cycloadducts produced the 8-oxoprotoberberine type products. The alkaloids of this class are important natural products with a wide range of biological activity and the synthethic methodology described in this paper could prove to be useful for the preparation of the D-ring functionalised derivatives.     

Medium-spin excitations of the neutron-rich 84Se isotope: Possible decrease in energy of the N = 50 neutron-core excitation

The ⁸⁴Se nucleus has been produced as fission fragment in the fusion reaction ¹⁸O + ²⁰⁸Pb at 85MeV bombarding energy and studied with the Euroball IV array. Medium-spin states of this neutron-rich isotope have been identified for the first time. Its level scheme has been obtained up to 4.9MeV excitation energy and spin I 7. Its structure is interpreted by analogy with those of the stable heavier isotones. The evolution of the energy of the N = 50 neutron-core excitation is discussed as a function of the proton number.     

Feeding and lifetimes of yrast levels in Hf nuclei

Feeding intensities and times, as well as lifetimes of yrast levels in doubly even ^{166, 168, 170}Hf nuclei have been measured. The reactions ^{122, 124}Sn(^{48, 50}Ti, 4n)^166–170₇₂Hf have been investigated using the recoil-distance Doppler-shift method. The lifetimes, and hence the B(E2) values measured, show the same trends of rather small deviations from the rigid rotor as in the known ₆₈Er and ₇₀Yb cases. In addition to the fast feeding component, showing behaviour rather similar to that of the Yb nuclei, another type of slow feeding, related to the low spin yrast levels, is observed.