Ueber den Nachweis und die Bestimmung des Zinns, Antimons und Arsens

Ohne Zusammenfassung     

canSAS Working Meeting

Collective action for nomadic small angle scatterers (canSAS) is an ongoing activity to help the community of users and providers of small angle scattering techniques with shared tools. This work includes providing good access to information about the method and facilities, agreeing on common reduced data formats, and working with reference samples to allow comparison of instruments and assessment of the reliability of data.     

Determination of 2-mercaptobenzothiazole in river water by HPLC

Summary A method is proposed for the determination of 2-mercaptobenzothiazole in river waters using multi-electrode electrochemical detection HPLC. 2-mercaptobenzothiazole determination is unsatisfactory by gas chromatography as it degrades readily on the column. Multielectrode electrochemical detection HPLC combines sensitivity and the ability to screen out other electrochemically active species. The development work leading up to the proposed method is discussed. The method has a limit of detection of 0.798gl^–1 2-mercaptobenzothiazole and a total standard deviation of 2.06gl^–1 2-mercaptobenzothiazole at a concentration of 7.97gl^–1 2-mercaptobenzothiazole in river water.     

Solvent-induced phase separation in polycarbonate blends PC/TMPC

Compatibility of the polycarbonates of bisphenol A (PC) and tetramethyl bisphenol A (TMPC) was studied in glassy films cast from CH₂Cl₂ at room temperature, and above the glass-transition temperature. Blends with different compositions and of different molecular weights were analyzed by DSC and small-angle neutron scattering (SANS). Solution studies were made with light scattering and microscopy. Some of the blend films were two-phased when cast at room temperature, but all films were one-phased in equilibrium above the glass transition. The SANS data demonstrated that phase separation in the cast films was not caused by inherent incompatibility of PC and TMPC, but was induced by the solvent CH₂Cl₂. The effect is caused by a closed miscibility gap in the ternary solution system PC/TMPC/CH₂Cl₂.     

The Dixmier trace and asymptotics of zeta functions

We obtain general theorems which enable the calculation of the Dixmier trace in terms of the asymptotics of the zeta function and of the trace of the heat semigroup. We prove our results in a general semi-finite von Neumann algebra. We find for p>1 that the asymptotics of the zeta function determines an ideal strictly larger than Lp,∞ on which the Dixmier trace may be defined. We also establish stronger versions of other results on Dixmier traces and zeta functions.     

A Thermodynamic Model of Auto-regulated Protein Assembly by a Supramolecular Scaffold

Ligand-mediated regulation of protein assembly occurs frequently in different cellular contexts. Auto-regulated assembly, where a ligand acts as its own competitive inhibitor, provides a mechanism for exquisite control of assembly. Unlike simple protein-ligand systems a quantification of the binding thermodynamics is not straightforward. Here, we characterize the interactions of a recently identified model system in which the oligomerization of cytochrome c is controlled by sulfonato-calix[8]arene, an anionic supramolecular scaffold. Isothermal titration calorimetry and thermodynamic modelling, in combination with Bayesian fitting, were used to quantify the ligand binding and assembly equilibria for this system. The approach and variations of this model may prove useful for the analysis of auto-regulated protein assembly in general.     

Entropy effects in the fragmentation of 1,1-dimethylhydrazine ions

The 1,1-dimethylhydrazine ion ((CH3)2NNH2+*) has two low-energy dissociation channels, the loss of a hydrogen atom to form the fragment ion m/z 59, (CH3)(CH2)NNH2+, and the loss of a methyl radical to form the fragment ion m/z 45, the methylhydrazyl cation, CH3NNH2+. The dissociation of the 1,1-dimethylhydrazine ion has been investigated using threshold photoelectron-photoion coincidence (TPEPICO) spectroscopy, in the photon energy range 8.25-31 eV, and tandem mass spectrometry. Theoretical breakdown curves have been obtained from a variational transition state theory (VTST) modeling of the two reaction channels and compared to those obtained from experiment. Seven transition states have been found at the B3-LYP/6-31+G(d) level of theory for the methyl radical loss channel in the internal energy range of 2.32-3.56 eV. The methyl loss channel transition states are found at R(N-C) = 4.265, 4.065, 3.965, 3.165, 2.765, 2.665, and 2.565 A over this internal energy range. Three transition states have been found for the hydrogen atom loss channel: R(H-C) = 2.298, 2.198, and 2.098 A. The DeltaS++(45) value, at an internal energy of 2.32 eV and a bond distance of R(N-C) = 4.265 A, is 65 J K-1 mol-1. As the internal energy increases to 3.56 eV the variational transition state moves to lower R value so that at R(N-C) = 2.565 A, the DeltaS++ decreases to 29 J K-1 mol-1. For the hydrogen atom loss channel the variation in DeltaS++ is less than that for the methyl loss channel. To obtain agreement with the experimental breakdown curves, DeltaS++(59) = 26-16 J K-1 mol-1 over the studied internal energy range. The 0 K enthalpies of formation (DeltafH0) for the two fragment ions m/z 45 and m/z 59 have been calculated from the 0 K activation energies (E0) obtained from the fitting procedure: DeltafH0[CH3NNH2+] = 906 +/- 6 kJ mol-1 and DeltafH0[(CH3)(CH2)NNH2+] = 822 +/- 7 kJ mol-1. The calculated G3 values are DeltafH0[CH3NNH2+] = 911 kJ mol-1 and DeltafH0[(CH3)(CH2)NNH2+] = 825 kJ mol-1. In addition to the two low-energy dissociation products, 21 other fragment ions have been observed in the dissociation of the 1,1-dimethylhydrazine ion as the photon energy was increased. Their appearance energies are reported.