Kinetik und Mechanismus des Ligandentausches zwischen Thallium(III)oxinat und Eisen(III) in Propylencarbonat

The transfer of oxinate ions from thallium (III)oxinate to trivalent Fe(DMF) ₆ ³⁺ in propylenecarbonate takes place via rearrangements within a rapidly formed binuclear thallium(III)—iron(III) complex. In a last rapid step this rearranged complex reacts with excess reactants to the final products whose composition accordingly depends on the ratio of the reactant concentrations.

     

Synthesis of zeolite nanocrystals at room temperature

Zeolite A nanoparticles were synthesized under room-temperature conditions from a very reactive organic-template-free gel system. The optimization of the syntheses parameters, namely, the composition of the initial system and the careful choice of the reactants, allowed the crystallization to be accomplished within 3 days. At this stage the individual zeolite crystals were in the range of 100-300 nm without well-developed crystal faces. The prolongation of the synthesis time up to 10 days led to formation of larger well-faceted cubic crystals averaging about 400-500 nm in size. The high-resolution transmission electron microscopy (HRTEM) study revealed that a thin layer of amorphous material covers the zeolite particles acting as a binder between individual zeolite crystals. The postsynthesis treatment of the product in NH(3) media under ultrasonic radiation disintegrated the loosely attached zeolite particles and decreased the fraction of zeolite A particles with low colloidal stability. The employed approach, however, did not result in complete disintegration of aggregated crystals. The zeolite crystals obtained under ambient conditions were characterized by XRD, SEM, dynamic light scattering, and N(2) adsorption measurements.     

Charge distributions in polyacetylene chains containing a positively charged defect

We present a comparative study of the AIM, CHELPG, GAPT, MK, Mulliken, NPA, and RESP charge distributions associated with a positively charged soliton on increasingly large trans‐polyacetylene chains, at HF, MP2, and DFT levels of theory. The charge storage in the soliton‐bearing systems is explored in detail, including charge magnitude, charge separation, charge alternation, and chain length effects. The grouping of the charge distributions at a given level of theory, as well as the sensitivity of a given charge distribution to the inclusion of electron correlation in its computation, are investigated using similarity analysis. Several of the charge definitions have been applied for the first time for charged soliton‐bearing systems, and there are substantial differences between the charge distributions for the charged and neutral systems. Thus, AIM charges are no longer one of the largest charge values, the AIM charges can be in counterphase with other definitions, and the GAPT charges for neutral systems are quite different from the GAPT charges for charged systems, e.g., the magnitudes of the GAPT charges are anomalously large and increase with the size of the charged system. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Stereocontrolled formation of highly substituted cis-decalins via INOC annulation. An access to the branimycin core

Quinic acid was used as a chiral scaffold for elaborating the highly substituted cis-decalin core system of branimycin via an Eschenmoser-Ireland rearrangement-INOC annulation sequence.     

Alkaloidosteroids from the starfish Lethasterias nanimensis chelifera

New ionic compounds containing an alkaloidal cation and a steroidal anion have been isolated by reverse-phase liquid chromatography from the extracts of the starfish Lethasterias nanimensis chelifera. Their structures have been elucidated by NMR and mass spectroscopy as 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinolinium salts of 3-O-sulfoasterone 1, 3-O-sulfoisoasterone 2 and 3-O-sulfothornasterol A 3. In addition, the alkaloid 1-methyl-1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid (MTCA) 4 was found in this starfish.     

Padé approximation for the polynomial representation of the correlation energy density functional

Polynomials in the one-third power of the density were recently proposed to represent approximately the correlation energy density functional [S. Liu and R.G. Parr, Phys. Rev. A 53 (1996) 2211]. Studied in the present work is a Padé-approximant in that same variable which overcomes weaknesses in the polynomial form. Numerical results for atoms and molecules show that Padé forms fairly reproduce the experimental values, and are comparable in accuracy with other commonly used local functionals for the correlation energy.     

High‐spin silicon fullerene Si60 and its oligomers

High‐spin states of the Si₆₀ fullerene and its oligomers are considered semiempirically by using sequential and parallel implementations of the AM1 codes. The states are energetically favorable and nearly degenerated over triplet, quintet, and septet spins. All atoms of the Si₆₀ fullerene are in sp³‐configuration, which is supported by atomic spin density in addition to electron density, the latter to be responsible for the formation of chemical bonds. Spotted distribution of spin density over atoms provides molecular magnetism of the molecule. A similar picture is disclosed for oligomers {Si₆₀}_n with n up to 8, which according to computational results should be magnetic with a fractal‐like distribution of spin density over atoms. Opposite the latter, composites Si₆₀C₆₀ and Si₆₀H₆₀ behave conventionally and are nonmagnetic. A way of the Si₆₀ fullerene synthesizing is suggested via the above composite product as intermediates. The considered oligomers are proposed as a model of silicon nanofibers observed recently. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Synthesis and Electrochemical Behavior of Some 1H-3-Methyl-4-ethoxycarbonyl-5-(benzylidenehydrazino)pyrazoles

Summary. 1H-3-Methyl-4-ethoxycarbonyl-5-(benzylidenehydrazino)pyrazoles are key intermediates in obtaining various heterocyclic systems including pyrazolotriazoles. We present the voltammetric behavior of these compounds in nonaqueous media, with the following para substituents grafted on the benzene ring: –N(CH₃)₂, –OH, –OCH₃, –F, –Cl, –CF₃, –NO₂, as well as of the novel compounds with –Br, –I, and –SCH₃ in the para position, in order to elucidate the influence of the various substituents on the mechanism of anodic oxidation.     

Matter–wave interference and deflection of tripeptides decorated with fluorinated alkyl chains

Studies of neutral biomolecules in the gas phase allow for the study of molecular properties in the absence of solvent and charge effects, thus complementing spectroscopic and analytical methods in solution or in ion traps. Some properties, such as the static electronic susceptibility, are best accessed in experiments that act on the motion of the neutral molecules in an electric field. Here, we screen seven peptides for their thermal stability and electron impact ionizability. We identify two tripeptides as sufficiently volatile and thermostable to be evaporated and interfered in the long‐baseline universal matter‐wave interferometer. Monitoring the deflection of the interferometric molecular nanopattern in a tailored external electric field allows us to measure the static molecular susceptibility of Ala–Trp–Ala and Ala–Ala–Trp bearing fluorinated alkyl chains at C‐ and N‐termini. The respective values are and .     

Chemical ionization of aliphatic nitro compounds

The chemical ionization mass spectra of various aliphatic nitro compounds have been studied. Almost all the nitro compounds form stable [M+H]⁺ ions in sharp contrast to the instability of their ions produced by other ionization techniques. The fragmentations of the [M+H]⁺ ions are discussed, the mechanisms and structures of fragment ions proposed being supported by quantum mechanical calculations. Correlations between chemical ionization mass spectra and structures of compounds studied are outlined. Reliable identification of mono- and polynitroalkanes and some related derivatives may be made by analysis of their chemical ionization mass spectra.