Matrix effects in the determination of butyltin compounds in environmental samples by GC AA after hydride generation

Experiments for the determination of mono-, di and tri-butyltin (MBT, DBT and TBT) by hydride generation/gas chromatography/atomic absorption spectrometry in various matrices (sediment, suspended matter, mussel, algae and water) have revealed that poor butyltin recoveries are obtained in sediments displaying high sulphur and hydrocarbon contents; very poor recoveries were also observed for TBT in sediments with high chlorophyll pigment contents as well as in algal samples. It was however not clear whether the hydride generatin was inhibited by these infering compounds, as was previously assumed in the case of hydrocarbons, or whether interferences affected the atomization rate. Further studies were performed to solve this problem in order to validate this method in the case of analyses of, for example, oil-contaminated sediment and algae. This paper presents the results obtained. It is concluded here that the poor recoveries were due to an inhibition of hydride generation rather than to interference at the atomization stage.     

A new synthesis of ampicillin and related investigations

Quaternization of (S)-α-bromophenylacetic acid amide (8) with hexamethylentetramine (hexamine) preceded with ca. 80% inversion of configuration. Accordingly, starting from the trimethylsilylester of N-(S)-(α-bromo-α-phenylacetyl)-6-aminopenicillanic acid (4) quaternization with hexamine and subsequent hydrolysis afforded N-(R)-α-phenylglycyl-6-aminopenicillanic acid (1, ampicillin). Some other model reactions have been investigated.     

Preparation and Crystal Structure Determination of the New Intermetallic Compound RbGa3

The compound has tetragonal symmetry, space group I4 m2 with: a=b=6.315(2) and c = 15.000(2) Å and contains 6 formula units. Diffraction data with 0 < 2θ < 50° (MoKα radiation) were collected on a Nonius CAD-4 automatic diffractometer within the octant hkl. The structure was solved by Patterson synthesis and refined by full-matrix least squares to a final R(F) of 4.9% for 159 independent reflections with I > 3σ(I). The structure consists of a stacking of gallium triangular-faced dodecahedra linked to each others through direct and bifurcated Ga? Ga bonds in a non-compact netting leaving room for a sublattice of rubidium atoms with shortened Rb? Rb distances.     

Mercury(II) complex with terpyridine: structure of the 2∶1 solvate of [Hg(terpy)2](CF3SO3)2 with acetone

[Hg(terpy)₂](CF₃SO₃)₂·0.5(CH₃)₂CO crystallizes in the triclinic space group witha=14.631(6),b=15.258(4),c=18.785(7) Å, =69.66(2), =70.72(1), =88.55(1)°. The crystal structure consists of two independent [Hg(terpy)₂]²⁺ cations, four trifluoromethanesulfonate anions and an acetone molecule in the asymmetric unit. Each mercury atom is coordinated by two tridentate terpyridine ligands forming an irregular six-coordination polyhedron. The Hg–N bond lengths range from 2.27(2) to 2.53(2) Å.     

‘Face-to-Face’-Benzo-anellierte homologe Hypostrophene. Synthesen,Röntgenstrukturanalysen und PE-Spektren

‘Face-to-Face’ Benzo-anellated Homologous Hypostrophenes. Syntheses, X-Ray-Structure Analyses and PE Spectra ‘Face-to-face’ Benzo-anellated homologous hypostrophenes (series M ), of interest as substrates for [6 + 6]-photocycloaddition reactions, have been synthesized. From X-ray structural analyses of 13b and 13c shortest C? C distances of 2.80(2.76)/2.71 Å and interorbital angles (ω) of 129° (128°)/130° between the benzene rings have been determined. The PE spectra are discussed in the context of transannular π,π interactions.     

Icosahedron oligomerization and condensation in intermetallic compounds. Bonding and electronic requirements

Icosahedron-based clustering has been found to be very common in intermetallics, particularly for group 13 and early p-block icosogen elements. Linking of the icosahedral building blocks depends on the valence electron concentrations. Vertex-, edge-, or face-sharing icosahedra occur as the structure compensates for electron deficiency. Some examples of icosahedron-based clusters have been selected for an analysis of the relationships between the structural features (icosahedron oligomerization, atomic defects, etc.) and the bonding and electronic requirements. The extended Hückel method has been used with either a molecular approach or an electronic band structure calculation to rationalize bonding in the intermetallic framework.     

Analysis of aerosols at the bosporus bridge of Istanbul

Air samples collected at the second Bosporus bridge of Istanbul which carries a heavy traffic load between Asia and Europe, were analyzed for 22 elements by the INAA method. Pb, Cd and Fe concentrations in the samples were determined by AAS. Iron concentrations were used as a cross check between the two methods. In order to define the enrichment factors for the elements in the bridge area, a sample collected from our university campus which can be considered as a rural site, was also analyzed. Differences were observed especially for Br, Al, Mg, Ti, Cu and Na between the two sites. Based on the results of the samples from the bridge, we got a value of 0.58(16) for the Br/Pb-ratio.     

The effect of the counterion on water mobility in reverse micelles studied by molecular dynamics simulations

In this study, mobility and structure of water molecules in Aerosol OT (bis(2-ethylhexyl) sulfosuccinate, AOT) reverse micelles with water content w0 = 5 and Na+, K+, Cs+ counterions have been explored with molecular dynamics (MD) simulations. Using the Faeder/Ladanyi model (J. Phys. Chem. B, 2000, 104, 1033) of the reverse micelle interior, MD simulations were performed to calculate the self-intermediate scattering function, FS(Q,t), for water hydrogen atoms that could be measured in a quasielastic neutron scattering experiment. Separate intermediate scattering functions FRS(Q,t) and FCMS(Q,t) were determined for rotational and translational motion. We find that the decay of FCMS(Q,t) is nonexponential and our analysis of the MD data indicates that this behavior arises from decreased water mobility for molecules close to the interface and from confinement-induced restrictions on the range of translational displacements. Rotational relaxation also exhibits nonexponential decay, which is consistent with relatively rapid restricted rotation and slower rotational relaxation over the full angular range. Rotational relaxation is anisotropic, with the O-H bond short-time rotational mobility considerably higher than that of the molecular dipole. This behavior is related to the decreased density of water-water hydrogen bonds in the vicinity of the interface compared to core or bulk water. We find that the interfacial mobility of water molecules is quite different for the three counterion types, but that the core mobility exhibits weak counterion dependence. Differences in interfacial mobility are strongly correlated with structural features, especially ion-water coordination, and the extent of disruption by the counterions of the water hydrogen bond network.     

Solvation dynamics in acetonitrile: a study incorporating solute electronic response and nuclear relaxation

The solvent reorganization process after electronic excitation of a polar solute in a polar solvent such as acetonitrile is related mainly to the time evolution of the solute-solvent electrostatic interaction. Modern laser-based techniques have sufficient time resolution to follow this decay in real time, providing information to be confirmed and interpreted by theories and models. We present here a study aimed at the investigation of the different steps involved in the process taking place after a vertical S(0) --> S(1) excitation of a large size chromophore, coumarin 153 (C153), in acetonitrile, from both the solute and the solvent points of view. To do this, we use accurate quantum mechanical calculations for the solute properties within the polarizable continuum model (PCM) and classical molecular dynamics (MD) simulations, both equilibrium and nonequilibrium, for C153 in the presence of the solvent. The geometry of the solute is allowed to change in order to study the role of internal motions in the time-dependent solvation process. The solvent response function has been obtained from the simulation data and compared to experiment, while the comparison between equilibrium and nonequilibrium MD results for the solvation response confirms the validity of the linear response approximation in the C153-acetonitrile system. The MD trajectories have also been used to monitor the structure of the solvation shell and to determine its change in response to the change in the solute partial charges.