Antimony(III) Oxide Film on a Cellulose Fiber Surface: Preparation and Characterization of the Composite

Cellulose/antimony(III) oxide composites, Cel/Sb(2)O(3), with oxide loadings of 1.7, 5.4, and 9.2 wt% were prepared by reacting the precursor SbCl(3) reagent with cellulose in dry ethanol solution. The reaction of the Lewis acid and the cellulose fibers occurred at the~amorphous domains of the biopolymer, increasing the crystallinity degree of the composite compared with that of the untreated cellulose. The scanning electron microscopy images and metal mapping for all samples showed that the oxide film layer uniformly covered the fiber surfaces with no detectable agglomerates of the oxide particles. The synchrotron X-ray diffraction patterns indicated that the antimony oxide film was obtained as a crystalline phase with orthorombic structure. The atomic ratios of O/Sb, determined by X-ray photoelectron spectroscopy, indicated that, for Cel/Sb(2)O(3) samples with 9.3 wt% loading, the fiber surface is nearly saturated by the oxide layer. The thermal stability of Cel/Sb(2)O(3) compared to that of untreated cellulose is practically unaffected. Copyright 2000 Academic Press.     

Zur Struktur von N-Benzoylthiobenzamid

Structure of N-Benzoylthiobenzamide N-Benzoylthiobenzamide forms two polymorphic modifications of which the crystal and molecular structures have been determined by X-ray structure analysis. In both modifications the molecules exist as NH tautomeres, but there are differences with regard to their rotameric configurations. In the monoclinic modification both symmetry independent molecules have a Z,Z′ configuration. The triclinic modification also contains two symmetry independent molecules, but now a Z,Z′ and an E,Z′ configuration exist. All four molecules deviate appreciably from planarity. The results of both structure determinations are compared with each other and with the structure of monothiodibenzoylmethane.     

Syntheses, structures, and surface aromaticity of the new carbaalane [(AlH)(6)(AlNMe(3))(2)(CCH(2)R)(6)] (R = Ph, CH(2)SiMe(3)) and a stepwise functionalization of the inner and outer sphere of the cluster

The reaction of the acetylene RC triple bond CH (R = Ph, CH(2)SiMe(3)) with an excess of AlH(3).NMe(3) in boiling toluene leads to the carbaalane [(AlH)(6)(AlNMe(3))(2)(CCH(2)R)(6)] (R = Ph 1, CH(2)SiMe(3) 2) in good yield. Treatment of 2 with BCl(3) under varying conditions gives the chlorinated products [(AlCl)(6)(AlNMe(3))(2)(CCH(2)CH(2)SiMe(3))(6)] 3 and [(AlCl)(6)(AlNMe(3))(2)(CCH(2)CH(2)SiMe(2)Cl)(6)] 4, respectively. The latter clearly demonstrates that the cluster can be stepwise functionalized within the inner and outer sphere. The X-ray single-crystal structures of 1, 2, and 4 have been determined. All compounds have in common that the central core consists of a cluster having eight aluminum and six carbon atoms. The bonding properties in this cluster are described as a new manifestation of three-dimensional surface aromaticity. Each Al(4)C fragment of the cube is formed by four bonds with three electron pairs, thus leading to a strong delocalization of the electrons. A phenomenological modeling using a three-dimensional Hückel scheme with fitted parameters to reproduce the energies from ab initio calculations revealed that the orbital scheme localized at one Al(4)C fragment possesses an orbital sextet with a large HOMO-LUMO gap. This is in line with the criteria of aromaticity. The idea of aromaticity was sustained also by qualitative valence bond reasons enumerating the different resonance structures by means of graph theoretical methods.     

Non-Born-Oppenheimer treatment of the H2 Hookean molecule

We show that the exact non-Born-Oppenheimer Schrodinger equation for the Hookean diatomic molecule H2 (a two-proton, two-electron system where the electron-proton interaction is harmonic while the proton-proton and electron-electron interactions are Coulombic) can be decoupled into equations describing the relative motion of the electrons, the relative motion of nuclei, the motion of a collective mode representing a three-dimensional harmonic oscillator, and the motion of a free particle expressed as a linear combination of the individual center-of-mass coordinates of the nuclei and electrons. Analytic solutions to the relative motion of electrons can be readily obtained for the given values of the harmonic coupling constant. However, exact analytic solutions to the equation for the relative motion of the nuclei cannot be obtained simultaneously due to the fact that the harmonic constants in these two equations are coupled. For this reason, we present for the relative nuclear motion approximate analytic wave functions, one of them obtained variationally and the other by a series solution where the coefficients are determined recursively. We also explore a variational solution to the Taylor-series expansion of the nuclear interaction potential. Properties of the electronic and nuclear intracule densities are examined at different values of the coupling constant. An interesting result of the present non-Born-Oppenheimer treatment of this harmonic model is the fact that the relative nuclear motion occurs in a highly correlated regime. This leads in a natural way to a spatial localization of the nuclei akin to Wigner electronic crystallization.     

Über Spurenelementbestimmungen in Leberproben Mittels Protoneninduzierter Röntgenfluoreszenz (Pixe)

Multi-element-analysis by PIXE in respect to medical applications is discussed. Examples of trace-element determinations in liver tissues are given, demonstrating the applicability and usefulness of this rather new analytical technique.      

Total synthesis of dictyodendrin B

A concise total synthesis of dictyodendrin B (1) is reported, a scarce marine alkaloid endowed with promising telomerase inhibitory activity. Key steps of the chosen route are a reductive cyclization of ketoamide 11 to indole 12 mediated by low-valent titanium (from TiCl3 and KC8) followed by a photochemical 6pi-electrocyclization, which was performed in the presence of Pd/C and nitrobenzene to effect concomitant dehydrogenation/aromatization of the product initially formed. Regioselective bromination of the resulting pyrrolocarbazole 13 followed by lithium/bromine exchange and quenching of the resulting organolithium species with p-methoxybenzaldehyde installed the side chain at C2. Oxidation of the benzylic alcohol 15 thus obtained to ketone 17 was best achieved with catalytic amounts of tetra-n-propylammonium perruthenate (TPAP) and N-methylmorpholine-N-oxide (NMO) in dilute CH2Cl2 solution to avoid the formation of undue amounts of the unsymmetrical dimer 16. Ketone 17 was elaborated into the natural product by selective cleavage of the isopropyl ether with BCl3, introduction of the sulfate moiety with the aid of trichloroethyl chlorosulfuric acid ester, deprotection of all lateral methyl ether groups, and final reductive cleavage of the trichloroethyl ester moiety. The spectroscopic data of synthetic dictyodendrin B thus formed matched those of an authentic sample in all regards. Moreover, it was shown that global deprotection of the peripheral -OH groups in pyrrolo[2,3-c]carbazole 13 is accompanied by spontaneous air-oxidation to form the quinone core of dictyodendrin C.