Die Massenspektren einiger Arsen- und Arsenigsäureester – Kinetische Untersuchung ihres Fragmentierungsverhaltens

Mass Spectra of some Arsenic and Arsenious Esters. Kinetic Study of their Fragmentation Reactions The mass spectra of some arsenic and arsenious esters are reported. Based on a mechanistic interpretation of the kinetic of competitive and consecutive reactions correlations between mass spectra and molecular structure have been found. Conclusions: (a) molecular ions are not or very small observable; (b) fragment ions with trivalent and fivevalent arsenic (e.g. As(OCH₃)) are very abundant; (c) the first fragmentation reaction of the molecular ion is usually a simple cleavage, the second is elimination of a neutral by a rearrangement; (d) rearrangement reactions exhibit less activation energies and less frequency factors than simple cleavages, this is the reason for the differences between 70 eV and 9 eV spectra; (e) C? C cleavage in the ethoxy compounds is favoured because of the formation of mesomeric onium ions; (f) some fragmentations by electron impact are analogous to pyrolytic decompositions; (g) in the fragment ions of OAs(OCH₂C₆H₅)₃ the charge is placed on the aromatic ring.     

The use of projective limits in classical statistical mechanics and Euclidean quantum field theory

The Gibbs states of an infinite classical statistical system correspond to the states of reservoir at infinity. It is shown that its configuration space can be thought of as a generalized projective limit of configuration spaces of remote reservoirs. This notion of projective limit is defined and it is noted that it can also be used e.g. for proofs of the existence of Gibbs states in the thermodynamic limit and their decomposition into pure phase. A similar approach to (nonperturbative) Euclidean quantum field theory is suggested and connections with the concept of renormalizability are found.Dedicated to Academician Václav Votruba on the occasion of his seventieth birthday.The first-named author (R. K.) would like to express his thanks to Prof. V. Votruba for general support and constant encouragement.     

Mössbauer investigation of novel pentadentate schiff base complexes

We synthesised a series of seven mononuclear and two trinuclear Schiff base coordination compounds. All nine complexes have been analysed by Mössbauer and IR spectroscopy. The Mössbauer spectra reveal a doublet, which are related to the high spin state (S = 5/2) of the iron(III) centres.     

BV has the bounded approximation property

We prove that the space BV (ℝ ^{n) of functions with bounded variation on} ℝ ^{n has the bounded approximation property}.     

High energy electron impact ionization for elemental analysis by energy dispersive X-ray spectrometry

A method has been demonstrated in which the emission of characteristic X-rays following impact ionization by electrons of several MeV energy is used for quantitative elemental analysis. Because of the unique properties of MeV electrons with respect to their X-ray production yield and range in solids, the method has comparable sensitivity over a wide range of elements and relatively less stringent sample preparation requirements. By using energy dispersive techniques to detect the X-rays, a simultaneous determination of the weight fraction of the elements in an unknown sample is possible from a procedure based entirely on empirically determined relative X-ray yields. The method was tested by analyzing three standard metal alloy samples obtained from the National Bureau of Standards. Elements reaging from iron (Z=26) to lead (Z=82) with concentrations from 0.06% to 88% were quantitatively determined. In general, good approximate agreement was found wit the reported assays even for the minor constituents.     

Comparative studies of the leachate of an industrial landfill by gas chromatography-mass spectrometry, liquid chromatography-nuclear magnetic resonance and liquid chromatography-mass spectrometry

Nowadays, the need to have a realistic characterization of industrial effluents in the environment has become more and more recognized. A palette of different analytical methods both for sample extraction and instrumental analysis are available today, some older, others introduced more recently. The aim of this research is to compare a number of these techniques. To do this we studied a real leachate from an industrial landfill and carried out chemical analyses for organic pollutants, using different extraction methods based on solid-phase extraction and solid-phase microextraction and different instrumental techniques such as GC-MS, LC-MS, NMR and LC-NMR. Results show the performances of the different techniques, which are complementary.     

Prion protein self-peptides modulate prion interactions and conversion

Background  

Molecular mechanisms underlying prion agent replication, converting host-encoded cellular prion protein (PrP^C) into the scrapie associated isoform (PrP^Sc), are poorly understood. Selective self-interaction between PrP molecules forms a basis underlying the observed differences of the PrP^C into PrP^Sc conversion process (agent replication). The importance of previously peptide-scanning mapped ovine PrP self-interaction domains on this conversion was investigated by studying the ability of six of these ovine PrP based peptides to modulate two processes; PrP self-interaction and conversion.     

Fluorinated Weakly Coordinating Anions [M(hfip)6]– (M = Nb,Ta): Syntheses,Structural Characterizations and ­Computations

The synthesis, spectroscopic and structural characterisation of a series of [M(hfip)₆]^– (M = Nb, Ta; hfip = O–C(H)(CF₃)₂) salts that are the typical starting materials to introduce these weakly coordinating anions by metathesis reactions into a given system is described. The salts Li[Nb(hfip)₆] and Li[Ta(hfip)₆] formed in 65 to 77 % yield from freshly sublimed MCl₅ and Li[hfip]. By contrast, several attempts to synthesize Li[Sb(hfip)₆] on the similar route (replace NbCl₅ by SbCl₅) failed to yield a pure product. Upon metathesis of the Li‐niobate with AgF in CH₂Cl₂, the pure Ag[Nb(hfip)₆] formed. Mixing Li[Nb(hfip)₆] with an equimolar amount of Cl–CPh₃ in CH₂Cl₂ gave the yellow [CPh₃][Nb(hfip)₆]. Several of the compounds were characterized by X‐ray analysis. Thus, the crystal structures of the Li⁺‐ and Ag⁺‐solvates 1, 2‐C₆H₄F₂{LiNb(hfip)₆}₂, [Li(H₂O)][Ta(hfip)₆], and [Ag(C₆H₅F)][Nb(hfip)₆] as well as that of [CPh₃][Nb(hfip)₆] were solved and are described in this work.