Spectroscopy of the conformational disorder in molecular films: tetracosane and squalane on Pt(111)

The spectroscopic investigation of the molecular vibrations of adsorbed branched and unbranched alkane molecules using helium atom scattering (HAS) provides evidence for the thermal formation of gauche defects in tetracosane (C24H50) monolayers above 200 K. HAS results for the vibration of tetracosane molecules perpendicular to the Pt(111) surface reveal a strong frequency decrease and peak broadening above the transition temperature which can be related to a reduction of the force holding the molecules to the surface. This reduction of the force is interpreted as being due to the thermal formation of gauche defects within the tetracosane molecules.     

Lanthanide-mediated ligand transfer reactions--a route to late transition metal bisamido complexes

The reaction of [[O(SiMe2Ap)2)2LnLi(thf)n] 1 (Ln = Nd, n= 2) and 2 (Ln = La, n = 3) in hexane with [(dme)NiCl2] (dme = dimethoxyethane) and [(cod)PtCl2] (cod = 1,5-cyclooctadiene) leads to the dimeric Ni complex [[O(SiMe2Ap)2]2Ni2] (3) and the mononuclear platinum compound [O(SiMe2Ap)2Pt] (4). respectively (O(SiMe2ApH)2 = bis(4-methyl-2-pyridylamino)tetramethyldisiloxane). Compounds 3 and 4 have been characterized by X-ray crystal structure analysis. The ligand-transfer reactions probably proceed via heterobimetallic intermediates. A model complex of such an intermediate [[O(SiMe2Ap)2)2NdPdMe] (7) was isolated by reacting 1 with [(cod)PdMeCl]. Applications of complex 3 in ethylene oligomerization were investigated. Highly branched oligomers with a very narrow molecular weight distribution (Mn =230 gmol(-1) (relative to polystyrene standards), Mw/M= 1.14) are produced when Et3Al2Cl3 is employed as a co-catalyst and CH2Cl2 as the solvent (TOF = 122000 h(-1). Treatment of one equivalent of 1 or 2 with two equivalents of [(cod)CuCl] results in the formation of the polycyclic tetranuclear complex [[O(SiMe2Ap)2]2Cu4] (8). An X-ray crystal structure analysis of 8 shows channels formed by a series of fourteen-membered rings in the solid state.     

Spectroscopic characterization of flavin mononucleotide bound to the LOV1 domain of Phot1 from Chlamydomonas reinhardtii

The absorption and emission behavior of flavin mononucleotide (FMN) in the light-, oxygen- and voltage-sensitive (LOV) domain LOV1 of the photoreceptor Phot1 from the green alga Chlamydomonas reinhardtii was studied. The results from the wild-type (LOV1-WT) were compared with those from a mutant in which cysteine 57 was replaced by serine (LOV1-C57S), and with free FMN in aqueous solution. A fluorescence quantum yield of phi(F) = 0.30 and a fluorescence lifetime of tau(F) = 4.6 ns were determined for FMN in the mutant LOV1-C57S, whereas these quantities are reduced to about phi(F) = 0.17 and tau(F) = 2.9 ns for LOV1-WT, indicating an enhanced intersystem crossing in LOV1-WT because of the adjacent sulfur of C57. A single-exponential fluorescence decay was observed in picosecond laser time-resolved fluorescence measurements for both LOV1-WT and LOV1-C57S as expected for excited singlet state relaxation by intersystem crossing and internal conversion. An excitation intensity dependent fluorescence signal saturation was observed in steady-state fluorescence measurements for LOV1-WT, which is thought to be because of the formation of a long-lived intermediate flavin-C(4a)-cysteinyl adduct in the triplet state (few microseconds triplet lifetime, adduct lifetime around 150 s). No photobleaching was observed for LOV1-C57S, because no thiol group is present in the vicinity of FMN for an adduct formation.     

Bildung von HfSiO4-Einkristallen durch chemische Transportreaktion

On the Formation of HfSiO₄ Single Crystals by Chemical Transport Reactions The formation of synthetic hafnon single crystals, HfSiO₄, during chemical transport reactions in order to prepare CuCrHfSe₄ was observed. Characterization of the crystals was by electron microprobe analysis and X-ray methods. The crystals are tetragonal, a = 658.0(2), c = 598.0(6) pm, the space group is I4₁/amd (zircon structure). Refined atom parameters and details of preparation of these crystals by chemical transport reactions starting from mixtures of HfO₂ and SiO₂ are reported.     

Morphological studies of spin-coated films of poly(styrene-block-methyl methacrylate) copolymers by atomic force microscopy

The surface structure of very thin (15–20 nm) spin-coated films of a symmetrical poly(styrene-b-methyl-methacrylate) block copolymer on silicon and mica is analyzed by atomic force microscopy (AFM). The films show a surface corrugation of a very regular 100 nm lateral periodicity and 6–8 nm amplitude. Film thickness is measured by AFM at induced film defects and checked by ellipsometry. XPS shows that both blocks are at the film surface. Selective degradation of the methyl methacrylate block is used for contrast enhancement and allows to assign poly(styrene) to the elevated surface regions and poly(methyl methacrylate) to the substrate/film interface.Friction interactions of the AFM tip with the film surface may be used to induce high orientational ordering of the morphological pattern perpendicular to the fast scan direction.     

Ethylene oligomerization on heterogenized titanium and zirconium complexes

Besides other products, linear middle-range olefins were obtained in the low temperature oligomerization of ethylene with a selectivity of 30–58% and a linearity up to 85%. Activated ticanium and zirconium complexes as catalysts were attached to SiO₂ through surface bounded bidentate S- and N-containing ligands, the former being superior to the latter with respect to product quality.

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30–58 .% 85%. - - , , SiO₂ S- N- . , , .

     

Precise and sensitive determination of nitrite by coulometric backtitration under flow conditions

A novel method performing for coulometric backtitrations in flow channels was developed, which was applied for the precise and sensitive determination of low concentrations of nitrite. Under acid conditions nitrite is reacting stoichiometrically with hydrazine, the remained excess of which is backtitrated with electrogenerated bromine. The titration course is recorded either amperometrically or chemiluminometrically. Hydrazine can be determined precisely and accurately in the range between 0.1 microM and 1 mM without calibration. Nitrite is reduced by hydrazine according to the reaction 2 NO2- + 2 H+ + NH2-NH2 --> N2O + N2 + 3 H2O. Applying the amperometric and the chemiluminometric end-point location nitrite was determined accurately and precisely in the ranges 0.25-65 microM and 0.10-50 microM, respectively. The method was applied to the determination of nitrite in tap and river water.     

Experimental and numerical model study of the limiting current in a channel flow cell with a circular electrode

We describe first measurement in a novel thin-layer channel flow cell designed for the investigation of heterogeneous electrocatalysis on porous catalysts. For the interpretation of the measurements, a macroscopic model for coupled species transport and reaction, which can be solved numerically, is feasible. In this paper, we focus on the limiting current. We compare numerical solutions of a macroscopic model to a generalization of a Leveque-type asymptotic estimate for circular electrodes, and to measurements obtained in the aforementioned flow cell. We establish that on properly aligned meshes, the numerical method reproduces the asymptotic estimate. Furthermore, we demonstrate that the measurements are partially performed in the sub-asymptotic regime, in which the boundary layer thickness exceeds the cell height. Using the inlet concentration and the diffusion coefficient from literature, we overestimate the limiting current. On the other hand, the use of fitted parameters leads to perfect agreement between model and experiment.     

Synthesis and Crystal Structures of Copper Zinc Phenylthiolate and the First Copper Zinc Selenolate and Tellurolate Complexes

Five copper zinc phenylchalcogenolate complexes [(iPr₃PCu)₃(ZnMe₂)₂(SPh)₃] ( 1 ), [(iPr₃PCu)₂(ZnPh)₄(SPh)₆] ( 2 ), [(iPr₃PCu)₂(ZnEt)₄(SPh)₆] ( 3 ), [(iPr₃PCu)₃(ZnEt)(SePh)₄] ( 4 ), and [(iPr₃PCu)₃Cu(iPr₃PZn)(TePh)₆] ( 5 ) were synthesized by the reaction of phosphine stabilized copper phenylchalcogenolate complexes with ZnR₂ (R = Me, Et, Ph) with and without additional chalcogenol. The novel mixed metal compounds were characterized by single‐crystal X‐ray structure analysis and NMR spectroscopy. 4 and 5 are the first examples of compounds with a Zn–Se–Cu or a Zn–Te–Cu linkage, respectively.     

Comparison of Computed and Measured Temperature Distributions in the High-pressure Liquid Encapsulated Czochralski (HPLEC) Configuration

The calculations of the temperature field of the InP growth system are carried out with a stationary FEM/Newton algorithm. With regard to the radiation transparency of the B₂O₃ layer, the limiting cases transparency and non-transparency are investigated. With the thermocouples which are inserted into the crystal, the temporal temperature behavior at selected positions of the crystal is recorded. The shapes of the crystal/melt interface of further crystals are analysed by microscopy. Computational and experimental results agree.