Influences of local polymer-solvent π-π-interaction on dynamics of phenyl ring rotation and its role on photophysics of conjugated polymer

In this report, the role of local polymer-solvent π-π-interaction on rotational dynamics of phenyl rings of poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylenevinylene] (MEH-PPV) is examined by utilizing nuclear magnetic resonance (NMR) spectroscopy. We have found that an aromatic solvent can couple strongly with the phenyl rings via favorable local π-π-interaction, causing a restriction of the ring rotation. The dynamic process takes place at much faster rate in a non-aromatic solvent. NMR line shape analysis indicates the existence of two side chain configurations with relatively long life-time in toluene and pyridine while a single time-averaged configuration is detected in chloroform and tetrahydrofuran. Addition of chloroform or cyclohexane to a solution of MEH-PPV in toluene is accompanied by an increase of the rotational dynamics. This indicates that the expansion or collapse of main chain upon varying solvent quality play a minor role on the rotational dynamics. The relationship between the dynamics of ring rotation and photophysics of MEH-PPV in solution is discussed.     

Zur Kenntnis der Hydrate M(HSeO3)2 · 4H2O (M = Mg,Co, Ni,Zn). Röntgenstrukturanalytische,schwingungsspektroskopische und thermoanalytische Untersuchungen

On the Hydrates M(HSeO₃)₂ · 4H₂O (M = Mg, Co, Ni, Zn) – Crystal Structures, IR, Raman, and Thermoanalytical Investigations From aqueous solutions of M(HSeO₃)₂ single crystals of Mg(HSeO₃)₂ · 4H₂O and of the hitherto unknown compounds Co(HSeO₃)₂ · 4H₂O, Ni(HSeO₃)₂ · 4H₂O and Zn(HSeO₃)₂ · 4H₂O could be obtained. The crystal structures, X-ray powder, IR, Raman and thermoanalytical (DTA, TG, Raman heating) data are presented and discussed. The crystal data of the isotypic compounds are: monoclinic, space group C2/c, Z = 4, Mg: a = 1 464.6(2), b = 755.3(1), c = 1 099.9(1) pm, β = 126.59(1)°, V = 0.9769(1) nm³, Co: a = 1 462.5(2), b = 756.5(2), c = 1 102.2(2) pm, β = 126.53(1)°, V = 0.9798(2) nm³, Ni: a = 1 452.2(2), b = 751.0(1), c = 1 091.5(1) pm, β = 126.28(1)°, V = 0.9595(1) nm³, Zn: a = 1 468.3(2), b = 755.8(1), c = 1 103.1(1) pm, β = 126.79(1)°, V = 0.9804(2) nm³. The crystal structures consist of hexagonal packed [M(HSeO₃)₂ · 2H₂O]_n chains of [MO₄(H₂O)₂] octahedra linked by Se atoms. They contain trigonal pyramidal SeO₂OH^?ions with “free” hydroxyl groups and also “free” molecules of water of crystallization. The hydroxyl groups build strong H-bonds (O? H …? O distances: 265–268 pm). The IR spectra show AB doublett bands in the OH stretching mode region of the hydroxyl groups. The water molecules of crystallization are linked to planar (H₂O)₄ tetramers by H-bonds with unusually short O? H …? O bond distances of 271–273 pm. DTA and TG measurements indicate that thermal decomposition results in the direct formation of the respective diselenite MSe₂O₅. Raman heating measurements show under quasi static conditions the intermediate formation of the anhydrous hydrogen selenites.     

Synthesis of 5-alkylidene-2,5-dihydropyrrol-2-ones and their ring-transformation into 5,6-dihydrobenzo[h]chromones, 5,6,7,8-tetrahydrochromones and pyran-4-ones

Acid-mediated ring-transformations of 5-alkylidene-2,5-dihydropyrrol-2-ones, available by cyclization of 1,3-diketone dianions with bis(imidoyl) dichlorides of oxalic acid, resulted in formation of functionalized pyran-4-ones, such as 5,6-dihydrobenzo[h]chromones and 5,6,7,8-tetrahydrochromones.     

Determination of alachlor and two metabolites in groundwater using solid phase and a new micro-liquid-liquid extraction method

Two different extraction procedures to determine alachlor (2-chloro-2,6-diethyl-N-methoxymethyl-acetanilide) and its metabolites 2,6-diethylaniline (DEA) and 2-chloro-2,6-diethylacetanilide (CDEA) at very low concentration levels in groundwater are compared. Both methods were performed during a field leaching study and laboratory soil column experiments. Solid phase extraction (SPE) is characterized by the enrichment of 11 water samples at 1 g RP-C18 material, while micro liquid/liquid extraction (MLLE) means that 400 ml water samples saturated with sodium chloride were extracted once with 500 l of toluene. Both methods differ in their concentration factors, i.e. 5000 for SPE and 800 for MLLE. The determination limits for alachlor determined as the lowest spiked concentration analyzed are 10 ng/l with SPE and 25 ng/l with MLLE. Even though the determination limits of the two methods are similar, the volatile metabolite 2,6-diethylaniline was not sufficiently recovered by SPE. Furthermore, SPE is more expensive and time consuming than MLLE. The latter is simple in use, rapidly performed and needs no evaporation step and clean-up before GC analysis. This is of special advantage for the analysis of 2,6-diethylaniline. The determination limits of the metabolites CDEA and DEA analyzed by MLLE are 25 ng/l. The extracts from both methods were directly analyzed by gas chromatography using electron capture and nitrogen-phosphorus detection.     

Enantioreversal in the sharpless asymmetric epoxidation reaction controlled by the molecular weight of a covalently appended achiral polymer

Polymers such as poly(ethylene glycol) (PEG) have proven use in a variety of applications including organic synthesis. We now disclose our investigations into the recently disputed report that PEG tartrate esters can reverse the enantioselectivity of the Sharpless asymmetric epoxidation reaction. The results presented herein have clarified that the enantioselectivity of this reaction can be reproducibly reversed solely as a function of the molecular weight of the appended PEG. By preparing a range of tartrate ligands with varying PEG chains lengths, the reversal was found to occur within a molecular weight change of only 800. As the PEG chain did not affect the inherent chirality of the ligand, the enantioreversal was proposed to occur as a result of two Ti-ligand complexes which differ in their molecularity of ligand, one monomeric in ligand and the other dimeric. Support for this hypothesis was given through equilibrium measurements which revealed that the predominant species in Ti/PEG tartrate ester mixtures is a distinct 2:1 Ti-ligand complex, as opposed to the 2:2 Ti-ligand complex of traditional Sharpless asymmetric epoxidations. In total, these data represent an unrecognized property of PEG-supported catalysts that could open up new venues in the control of asymmetric reactions by means of achiral appended polymers.     

Flexible matching of test ligands to a 3D pharmacophore using a molecular superposition force field: Comparison of predicted and experimental conformations of inhibitors of three enzymes

Summary A computer procedure TFIT, which uses a molecular superposition force field to flexibly match test compounds to a 3D pharmacophore, was evaluated to find out whether it could reliably predict the bioactive conformations of flexible ligands. The program superposition force field optimizes the overlap of those atoms of the test ligand and template that are of similar chemical type, by applying an attractive force between atoms of the test ligand and template which are close together and of similar type (hydrogen bonding, charge, hydrophobicity). A procedure involving Monte Carlo torsion perturbations, followed by torsional energy minimization, is used to find conformations of the test ligand which cominimize the internal energy of the ligand and the superposition energy of ligand and template. The procedure was tested by applying it to a series of flexible ligands for which the bioactive conformation was known experimentally. The 15 molecules tested were inhibitors of thermolysin, HIV-1 protease or endothiapepsin for which X-ray structures of the bioactive conformation were available. For each enzyme, one of the molecules served as a template and the others, after being conformationally randomized, were fitted. The fitted conformation was then compared to the known binding geometry. The matching procedure was successful in predicting the bioactive conformations of many of the structures tested. Significant deviation from experimental results was found only for parts of molecules where it was readily apparent that the template did not contain sufficient information to accurately determine the bioactive conformation.     

Investigations on Chemical Vapour Transport of Intermetallic Phases in the System Co/Fe/Si

The ternary phases existing on the quasi binary section CoSi/FeSi and CoSi₂/β‐FeSi₂ have been investigated by solid state reactions and chemical transport. The solid solution serie Co_xFe_1‐xSi can be described as a regular solution. The transport behaviour calculated is in good agreement with the experiments. The phases have been characterized by X‐ray powder diffraction, EDX and ICP‐OES. The temperature dependence of the resistivity has been measured from 20 K up to room temperature on single crystals.     

Synthesis and Structure of K[Cd(O2N‐C6H4‐NNN‐C6H4‐NO2)3], an Anionic 1, 3‐Bis(4‐nitrophenyl)triazenido Complex of Cadmium

The reaction of cadmium acetate in methanol with 1, 3‐bis(4‐nitrophenyl)triazene in THF in the presence of KOH yields K[Cd(O₂NC₆H₄NNNC₆H₄NO₂)₃] in form of hexagonal prismatic, red crystals with the trigonal space group R3¯ and a = 12.229(2), c = 48.988(10) Å and Z = 6. In the anionic cadmium complexes, which are located along the threefold axis, the Cd atoms are coordinated in a trigonal prismatic arrangement by the atoms N(1) and N(3) of three triazenido ligands. The potassium cations are coordinated icosahedrally by oxygen atoms of each one nitro group of six neighbouring anionic complexes. The Cd‐N distances are 2.376(4) and 2.350(4) Å, and the K‐O distances are in the range of 2.833(6) to 3.365(6) Å.     

About different types of water in swollen polyelectrolyte multilayers

The review addresses swelling of polyelectrolyte multilayers in water. Different models for the determination of the water content are compared. It is clearly shown that voids under dry conditions present cavities for water which contribute to the water content of the multilayer in the swollen state. This so-called “void water” does not lead to any changes in thickness but in scattering length density during swelling. The “swelling water” leads to both changes in scattering length density and in thickness. Depending on the preparation conditions like the type polymers, polymer charge density, ionic strength and type of salt the ratio of “void water” differs between 1 and 15 vol.% while the amount of “swelling water” is of several ten's of vol.%.