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Silylated Cellulose Materials in Design of Supramolecular Structures of Ultrathin Cellulose Films

Abstract

To use the structure-forming potential and the biodegradability of cellulose and nonionic cellulose ethers, we developed synthesis pathways for soluble and regenerable silyl celluloses suitable for the design of advanced materials. A 6-0-silylation of cellulose takes place in a heterogeneous phase reaction in the presence of ammonia-saturated polar aprotic solvents at ?15°C with thexyldimethylchlorosilane. After 2,3-di-O-methylation, this type of regioselectively-substituted cellulose derivatives yields sensor matrices for the detection of halohydrocarbons in air. On the other hand, thexyldimethylsilyl celluloses and trimethylsilyl celluloses with degrees of substitution in the 2.6 to 3.0 range form mono-and multilayered supramolecular structures by applying the Langmuir–Blodgett technique and, after desilylation, oriented ultrathin cellulose films.     

Trinuclear copper(II) complexes derived from Schiff-base ligands based on a 6-amino-6-deoxyglucopyranoside: structural and magnetic characterization

The trinuclear copper(II) complexes ([CuL1)(mu-ac)Cu(mu-ac)CuL1) (1) and ([CuL2)(mu-ac)Cu(mu-ac)CuL2) (2) of the tridentate aminosaccharide-derived Schiff-base ligands H2L1 [6-N-(salicylidene)amino-6-deoxy-1,2,3-tri-O-methyl-alpha-D-glucopyranoside] and H2L2 [6-N-(3,5-di-tert-butylsalicylidene)amino-6-deoxy-1,2,3-tri-O-methyl-alpha-D-glucopyranoside] were synthesized and structurally characterized. The trinuclear complex units can be described as two terminal copper-ligand moieties bridged by a central copper acetate moiety, with the Cu centers arranged in a triangular fashion. IR and UV/vis spectroscopic studies strongly indicate that the trinuclear structure is maintained in a methanolic solution. The temperature dependence of the magnetic susceptibility of both complexes shows a moderate antiferromagnetic coupling and can be well interpreted by applying a symmetric Cua-Cub-Cua' model with linear spin topology. The fit of the magnetic data affords coupling constants J of -34 and -24 cm(-1) for 1 and 2, respectively [H = -J(SaSb + SbSa')]. For mu-alkoxo-mu-acetato-bridged copper(II) complexes with a large dihedral angle between the adjacent coordination planes, as found in 1 and 2, such an antiferromagnetic coupling is unusual. However, density functional theory calculations of 2 using BP86, B3LYP*, and B3LYP density functionals confirmed a symmetric doublet ground state.     

Chemistry of thienopyridines. XXXII. Direct introduction of C-substituents gamma to the heteronitrogen atom in the thieno[2,3-b]pyridine system

Treatment of the N-oxide 1a of thieno[2,3-b]pyridine ( 1 ) with either (a) acetic anhydride and ethyl cyanoacetate or (b) benzoyl chloride and an enamine of cyclohexanone (Hamana reactions) serves to introduce a C-substituent at the 4-position of 1 . In case (a) one obtains a yellow, isolable vinylogous N-ylide 5 (23% yield), which undergoes facile transformation into ethyl 2-(4-thieno[2,3-b]pyridyl)cyanoacetate ( 1e ) (88–93 %). Acetic anhydride reconverts 1e to 5 (95%). Case (b) produces 2-(4-thieno[2,3-b]pyridyl)cyclohexanone (39%), hydrolyzable to 6-(4-thieno[2,3-b]pyridyl)hexanoic acid (45%). The hydrochloride of 1a is also reported. Structural formulations are based on spectral studies (including ¹³C nmr data for 1 and 1e ) and chemical transformations. Major contrasts (plus some similarities) between the systems 1 and quinoline in the Hamana reactions are discussed.     

Two syntheses of 5-chloro-3-(2-thienyl)-2,1-benzisoxazole

5-Chloro-3-(2-thienyl)-2,1-benzisoxazole ( 2 ) resulted from condensation of (a) o-nitrobenzaldehyde with thiophene in the presence of hydrochloric acid and (b) p-chloronitrobenzene with 2-cyanomethylthiophene. Spectral data for ( 2 ) are presented and interpreted.     

Chemistry of thienopyridines. IV. Syntheses of 5-substituted thieno[2,3-b] pyridines

Chemical transformations on 5-acetylthieno[2,3–6] pyridine produced 5-NH₂, 5-CO₂H, and 5-CH₂ CO₂H substituents. The 5-amino compound underwent facile diazotization (plus Sand-meyer reaction), Schiff's base formation, and acylation. Treatment of the derived 5-bromo compound with potassium amide in liquid ammonia gave a mixture of 4-amino (major) and 5-amino isomers. Nmr spectral data are reported for the 5-substituted thieno [2,3-b] pyridine system.     

Stable isotopes for heavy element production

The synthesis of heavy elements and the search for new superheavy elements is one of the exciting fields in modern nuclear physics and chemistry. Heavy elements are produced by heavy-ion fusion reactions. Necessary prerequisites are intense heavy-ion beams from pure isotopic material and thin isotopically enriched targets. At GSI the elements from 107 to 112 were produced using targets of Pb and Bi and beams of the most neutron rich isotopes of Cr, Fe, Ni, and Zn.¹ We present the experimental set-up consisting of target wheel, velocity filter SHIP (Separator for Heavy Ion Reaction Products), and detector system. We shortly describe the status of the ion source techniques for delivering intense and stable beams for this kind of experiment.² The manufacturing and properties of various source - target combinations used for the synthesis of the elements by now are discussed in detail as well as the possibilities for extending the experiments into the region of superheavy elements.³     

Chemistry of thienopyridines. XXV. Comparative mass spectra of some amino and acylamino derivatives

Electron-impact mass spectral fragmentation patterns are reported for various aminothieno-pyridines (TPNH₂) and aeylaminothtenopyridines. The molecular ion TPNH₂⁺ shows loss of atomic hydrogen, hydrogen cyanide and both thioformyl radical and cation. TPNH₂⁺ is the most abundant ion in the spectrum of each acylamino compound investigated. A semiquanti-tative mass spectrum of the amine TPNH₂ can be obtained by deletion of selected peaks (for the acetylium and molecular ions) from the observed mass spectrum of the A-acetyl derivative.     

Kinetics of reduction of cinnamaldehyde by means of hydrido- and deuteridocobalt tetracarbonyl

The reaction of HCo(CO)₄ ( HT ) or DCo(CO)₄ ( DT ) with excess cinnamaldehyde ( CA ) in methylcyclohexane ( RH ) at 22.2° and under 1 atm of CO follows pseudo-first-order kinetics in HT or DT with an inverse isotopic effect of 0.54. Identified products of the reaction are hydrocinnamaldehyde ( HCA ) and styrene ( STY ). The STY is believed to be an artifact of the thermal decomposition of the true product PhCH₂CH₂C( (DOUBLE BOND) O)Co(CO)₄ ( X ) or its isomer. Reduction of the carbon-carbon double bond in CA is effected by hydrogen from both the cobalt compound and RH. It is proposed that the reaction involves a free-radical chain mechanism in which the rate of the slow step is proportional to [ CA ], the initial molar concentration of CA raised to a power of 1.5− 1.8. Additionally the rate of conversion of CA to HCA and X meets the criteria of a homocompetitive reaction with [ CA ], [ HCA ], and [ STY ] simple functions of t^0.5 (where t is reaction time) for use of DT or (in a single case) a function of (t^0.5 + t) for use of HT. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 473–481, 1997.     

Determination of Fluorescence Cross‐Sections of Biological Aerosols

Biological aerosols like pollen or bacteria can be differentiated from non‐biological aerosols as dust by fluorescence. Several organic substances contained in biological particles emit fluorescence light if they are illuminated with ultraviolet light. An instrument has been developed which generates aerosols of individual bacteria, illuminates them with light in the range of wavelengths from 220 to 570 nm and detects the spectra of fluorescence. The instrument has been tested on different species of bacteria showing that their fluorescence spectra are different.