Zinc(II) as a versatile template for the design of dipolar and octupolar NLO-phores

Thermally stable dipolar and octupolar (D2d, D3) NLO-phores are readily accessible by combining one, two, or three 4,4'-bis(dialkylaminostyryl)-[2,2']-bipyridyl ligands with zinc(II) salts. The off-resonant beta0 values point out the superiority of octupoles versus dipoles in terms of nonlinearity/transparency tradeoff. The octahedral tris(bipyridyl)zinc(II) complex exhibits a very large beta0 value (241 x 10-30 esu), which is the largest ever reported for octupolar molecules.     

Dissipative particle dynamics simulations of polymer melts. I. Building potential of mean force for polyethylene and cis-polybutadiene

We present the derivation of coarse-grained force fields for two types of polymers, polyethylene (PE), and cis-polybutadiene (cis-PB), using the concept of potential of mean force. Coarse-grained force fields were obtained from microscopic simulations for several coarse-graining levels, i.e., different number of monomers lambda per mesoscopic unit called "bead." These force fields are then used in dissipative particle dynamics (DPD) simulations to study structural and dynamical properties of polymer melts of PE and cis-PB. The radial distribution functions g(R), the end-to-end distance R0, the end-to-end vector relaxation time tau, and the chain center of mass self-diffusion D(CM), are computed for different chain lengths at different coarse-graining factor lambda. Scaling laws typical of the Rouse regime are obtained for both polymers for chain lengths ranging from 6 to 50 beads. It is found that the end-to-end distance R0 obtained from DPD simulations agree well with values obtained from both microscopic simulations and experiments. The dependence of the friction coefficient used in DPD simulations versus the coarse-graining level is discussed in view of the overall scaling of the dynamical properties.     

Synthesis of modified Weinreb amides: N-tert-butoxy-N-methylamides as effective acylating agents

An efficient preparation of N-methyl-O-tert-butylhydroxylamine hydrochloride has been settled, which allowed the synthesis of modified Weinreb amides. Nucleophilic addition of organolithium and Grignard reagents on these N-tert-butoxy-N-methylamides afforded efficiently the corresponding ketones and reduction with DIBAL furnished the corresponding aldehydes in good yields up to 97%.     

General access to iminosugar C-glycoside building blocks by means of cross-metathesis: a gateway to glycoconjugate mimetics

[reaction: see text] Cross-metathesis reactions of alpha-1-C-allyl-1-deoxynojirimycin derivatives 7a,b and various functionalized alkenes mediated by Grubbs's catalyst 3 are reported. The reactions showed reasonable to very good yields and excellent E/Z selectivity. This methodology allows the efficient and convergent synthesis of iminosugar C-glycosides with a great degree of structural diversity in the aglycone, opening the way to a variety of new glycoconjugate mimetics of biological interest.     

Novel fluoroacrylated copolymers: synthesis, characterization and properties

The development of polymer waveguides leads to synthesis of fluorinated amorphous polymers with high transmission capacity, potential to tune their optical properties by tailoring the molecular structure, together with good processability, easy handling, good flexibility and low cost.In this work we have investigated new thermoplastic fluoroacrylated copolymers, synthesized by radical copolymerization of fluoroalkene(s) with five-membered cyclic carbonate and a third monomer or transfer agent, both containing OH group susceptible to be used for grafting of photocrosslinkable groups. The reaction of hydroxy functionalized copolymers with different acrylating agents results in fluoroacrylated resins with molecular weight in the range of 2000-3000 g mol⁻¹, yield >75% and good solubility in reactive diluents. In the presence of photoinitiator(s), they were crosslinked under UV-radiation in order to obtain optical waveguides.The copolymers synthesized were characterized by ¹H, ¹⁹F and ¹³C NMR as well as FT-IR spectroscopies and have good thermal stability (T_d > 200 °C). The refractive indeces of hydroxy functionalized fluorooligomers and acrylated resins were found to range from 1.44 to 1.45 at 23 °C and the T_gs (by DSC) varied from 40 to 110 °C depending on the content of the cyclic monomer. The optical characteristics of these thermoplastic fluoroacrylated copolymers are under progress.     

Bestimmung von Metallspuren in Polymeren mit Hilfe der Atom-Absorptionsspektrophotometrie

Zusammenfassung Die Atom-Absorptionsspektrophotometrie erlaubt die schnelle und genaue Bestimmung von Metallen in Polymeren, und zwar sowohl im ppm- als auch im Prozentbereich. Bei löslichen Polymeren werden vorzugsweise 2%ige Lösungen untersucht. Polymere, die in keinem geeigneten Lösungsmittel löslich sind, werden mit H₂SO₄/H₂O₂ aufgeschlossen. für flüchtige Metallverbindungen wird eine Umfällmethode mit anschließender Anreicherung der Metallspuren beschrieben. Untersucht werden Polystyrol, Celluloseester, Polyacrylnitril, ABS-Polymere, Polycarbonat, Polyvinylchlorid und seine Copolymeren, Polyamid, Polyäther, Wolle und Baumwolle. Nachweisgrenzen und günstigste Konzentrationsbereiche für die Elemente Li, Na, K, Mg, Ca, B, Al, Si, Sn, Pb, Sb, Cu, Ag, Au, Zn, Cd, Hg, Ti, Fe und Ni werden angegeben.

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Determination of trace metals in polymers by atomic absorption spectrophotometry

Atomic absorption spectrophotometry allows quick and exact determination of both ppm and percent quantities of metals in polymers. Preferably 2% solutions of soluble polymers are analyzed. Polymers insoluble in a suitable solvent are ashed in H₂SO₄/H₂O₂. For volatile metal compounds a double precipitating method followed by enrichment of trace metals is described. The following polymers are studied: polystyrene, cellulose esters, polyacrylonitrile, acrylonitrile-butadiene-styrene-terpolymers, polycarbonate, Polyvinylchloride and its copolymers, polyamide, polyether, wool, and cotton. Detection limits and most favourable concentration ranges are reported for the elements Li, Na, K, Mg, Ca, B, Al, Si, Sn, Pb, Sb, Cu, Ag, Au, Zn, Cd, Hg, Ti, Fe, and Ni.

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Herrn Prof. Dr. K. Hansen zum 60. Geburtstag gewidmet.

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An dieser Stelle sei Herrn Dr. A. Reichle, dem Leiter des Wissenschaftlichen Laboratoriums der Farbenfabriken Bayer AG, Werk Dormagen, für seine Unterstützung gedankt.Den Herren K. Schumann und W. Kremer danke ich für ihre sorgfältige experimentelle Mitarbeit.     

Selective functionalization at the small rim of calix[6]arene. Synthesis of novel non-symmetrical N3, N4 and N3ArO biomimetic ligands

Eight novel calix[6]arene-based biomimetic ligands for transition metal ions have been synthesized. They display a non-symmetrical N₃, N₄ or N₃ArO binding core that mimics enzyme active sites presenting histidine and tyrosine residues. The key step for their synthesis is the mono-alkylation at the small rim of the C_3v symmetrical trimethyl ether derivative of tBu-calix[6]arene with N-Boc-2-chloroethylamine to yield a novel calix[6]arene synthon. Its combined O-alkylation with a chloromethyl aromatic amine and N-deprotection or alkylation or reductive alkylation with a salicylaldehyde derivative yielded the calix[6]arene-based ligands with mixed N/O donors.     

Entrapment and release of sodium polystyrene sulfonate (SPS) from calcium alginate gel beads

The release of sodium polystyrene sulfonate (SPS) from calcium alginate hydrogel beads has been studied. It has been shown that the structure of the cross-linked calcium alginate network is of primary importance in the retention and/or release of the SPS. This has been evidenced by studying the influence of Ca²⁺ concentration, molar masses (M_n) and the ratio of mannuronic acid/guluronic acid components. A minimum in the SPS release is observed in relation with the organization of the network structure. Conditions inducing the organization of a strong gel (e.g. high Ca²⁺ concentration for example) are not always related to a low release. A good control of release is found when a compromise between a well-structured hydrogel and sterical consideration of SPS is reached.     

A study of the gold/aqueous electrolyte interphase by modulated reflection spectroscopy

The admittance and differential reflectivity of an electrode of polycrystalline gold in contact with aqueous 0.02 M NaF, KClO₄, 0.01 M Na₂SO₄ and KCl have been measured in the range of potential where the electrode is ideally polarized (?0.7 V to 0.8 V NHE). In NaF and KClO₄ evidence was obtained for the compression of the adsorbed layer of water. The increase of the number of water molecules, with respect to the number in the least original state (at?4μC cm^?2), is 3% at +8 μC cm^?2 and at?17 μC cm^?2. At the potential of zero charge the water dipoles are oriented preferentially with the oxygen towards the metal. In KCl the optical measurements confirm the existence of two types of Au?Cl^? interaction and the covalent character of the bond at the most positive charges.     

Br2 in an ar matrix: an example of complete damping of the resonance raman scattering amplitude in the discrete resonance limit

Raman scattering and relaxed fluorescence is observed upon cw laser excitation resonant with the lower vibrational manifold of the X(¹Σ_o+u) → B(³Π_o+u) transition of matrix isolated Br₂ at liquid He temperatures. The excitation profile of the relaxed fluorescence maps out the resonances, but neither detectable enhancement of Raman scattering nor resonance fluorescence is observed.