Optical properties of polybutadiene in the bulk and near a gold interface

We have investigated thick films from polybutadiene on gold-coated glass using surface plasmon resonance / leaky optical waveguide spectroscopy with the aim of investigating differences in bulk and interphase properties in a single measurement. A broad range of molar masses was studied. Drying under ambient conditions leads to an exponential decay of the film thickness. Subsequent vacuum drying does not result in any further changes in the bulk part of the film but at the polymer-solid interface, indicating the absence of residual solvent. For all molar masses studied, the surface plasmon resonance is observed at angles which are incompatible with the properties of the bulk part of the film. A polymer interphase is thus present next to the gold layer which has a refractive index lower than in the bulk. Using transversal magnetic- and transversal electric polarized light, an optical anisotropy is found in the interphase which is attributed to segment alignment along the interface with gold.     

Synthesis of Boc protected block copolymers based on para-hydroxystyrene via NMRP

Nitroxide mediated free radical polymerization (NMRP) was used for the preparation of orthogonally protected block copolymers based on para-hydroxystyrene. The polymers have a low polydispersity and an active chain end. By a series of polymer analogous reactions, a partly deprotected block copolymer was synthesized consisting of a block with unprotected phenolic OH groups and a further block which is protected by the thermolabile Boc group.     

Multiplicativity factors for seminorms. II

Let S be a seminorm on an algebra . In this paper we study multiplicativity and quadrativity factors for S, i.e., constants μ > 0 and λ > 0 for which S(xy) μS(x)S(y) and S(x²) λS(x)² for all x, y A. We begin by investigating quadrativity factors in terms of the kernel of S. We then turn to the question, under what conditions does S have multiplicativity factors if it has quadrativity factors? We show that if is commutative then quadrativity factors imply multiplicativity factors. We further show that in the noncommutative case there exist both proper seminorms and norms that have quadrativity factors but no multiplicativity factors.     

Carbanion-Bildung aus Estern der Orthothiokohlensäure durch nukleophile Substitution an Schwefel

Zusammenfassung Die reaktion zwischen Butyllithium und dem Tetraphenylester der Orthothiokohlensäure C(SC₆H₅)₄ in Tetrahydrofuran bei –70° führt zum metallierten Triphenylester der Orthothioameisensäure LiC(SC₆H₅)₃ durch nukleophilen Angriff an Schwefel. Es bildet sich dabei zugleich Butylphenylsulfid C₄H₉SC₆H₅. Alkylierung der Metallverbindung mit Alkyljodid oder Allybromid gelingt glatt, ebenso die Carboxylierung mit Kohlensäuregas.Mit dem Tetraäthylester der Orthothiokohlensäure C(SC₂H₅)₄ können ähnliche Reaktionen durchgeführt werden.Wenn die metallierten Orthothioameisensäure-Ester nicht alkyliert werden, bildet sich tetrakis(phenylthio-oder-äthylthio)-äthylen (RS)₂C=C(SR)₂ (R=C₆H₅ oder C₂H₅), eine Umwandlung, bei der die Carbene (RS)₂C: Zwischenprodukt sein müssen; diese Carbene bilden sich aus (RS)₃CLi durch Abspaltung eines Lithiumthiolats RSLi. Die Bildung des Äthylen-Derivats verläuft aber nur glatt, wenn das Lithiumthiolat durch geeignete Alkylierung, z. B. mit Butylbromid, gebunden und dadurch aus dem Gleichgewicht (RS)₃CLi (RS)₂C: + RLi entfernt wird.Das Carben (C₆H₅S)₂C: ist wahrscheinlich auch verant-wortlich für das Entstehen von 1,1,2-Tris(phenylthio)-1-hexen C₄H₉C(SC₆H₅)=C(SC₆H₅)₂ aus C(SC₆H₅)₄ und Butyllithium in einem Äther—Benzol-Gemisch bei 20–50°.Herrn Prof. Dr.F. Wessely anläßlich seines 70. Geburtstages in Freund-schaft Verehrung gewidmet.     

Quantitative analysis of immobilized proteins and protein mixtures by amino acid analysis

Biomolecular surface engineering of materials often requires precise, versatile and efficient quantification of immobilized proteins at solid surfaces. Acidic hydrolysis of surface-bound proteins and subsequent HPLC analysis of fluorescence-derivatized amino acids were adapted and critically evaluated for that purpose. Contaminations and concentration-dependent amino acid retrieval during HPLC were found to influence the accuracy of the method. In addition to the choice of adequate conditions for hydrolysis, derivatization and chromatographic separation extensions of the data evaluation were suggested to improve the accuracy of the approach when applied to single protein systems: comparing the experimentally obtained amino acid ratio to the protein constitution enabled to identify the properly separated and detected amino acids. Those amino acids were selected for a more precise calculation of the amount of immobilized protein. To further increase the accuracy of the method, the retrieval of amino acids corresponding to protein amounts in the range between 0.5 and 4.0 microg was analyzed for a variety of proteins of interest to derive protein-specific correction factors. The evaluation of amino acid data was furthermore applied to quantify binary protein mixtures at similar settings. This method was proven useful to detect the composition of protein mixtures throughout a wide range of absolute and relative concentrations.     

The quadrupole moment of the 3/2+ nuclear ground state of 197Au from electric field gradient relativistic coupled cluster and density-functional theory of small molecules and the solid state

An attempt is made to improve the currently accepted muonic value for the 197Au nuclear quadrupole moment [+0.547(16)x10(-28) m2] for the 3/2+ nuclear ground state obtained by Powers et al. [Nucl. Phys. A230, 413 (1974)]. From both measured Mossbauer electric quadrupole splittings and solid-state density-functional calculations for a large number of gold compounds a nuclear quadrupole moment of +0.60x10(-28) m2 is obtained. Recent Fourier transform microwave measurements for gas-phase AuF, AuCl, AuBr, and AuI give accurate bond distances and nuclear quadrupole coupling constants for the 197Au isotope. However, four-component relativistic density-functional calculations for these molecules yield unreliable results for the 197Au nuclear quadrupole moment. Relativistic singles-doubles coupled cluster calculations including perturbative triples [CCSD(T) level of theory] for these diatomic systems are also inaccurate because of large cancellation effects between different field gradient contributions subsequently leading to very small field gradients. Here one needs very large basis sets and has to go beyond the standard CCSD(T) procedure to obtain any reliable field gradients for gold. From recent microwave experiments by Gerry and co-workers [Inorg. Chem. 40, 6123 (2001)] a significantly enhanced (197)Au nuclear quadrupole coupling constant in (CO)AuF compared to free AuF is observed. Here, these cancellation effects are less important, and relativistic CCSD(T) calculations finally give a nuclear quadrupole moment of +0.64x10(-28) m2 for 197Au. It is argued that it is currently very difficult to improve on the already published muonic value for the 197Au nuclear quadrupole moment.     

Selective Protein Hyperpolarization in Cell Lysates Using Targeted Dynamic Nuclear Polarization

Nuclear magnetic resonance (NMR) spectroscopy has the intrinsic capabilities to investigate proteins in native environments. In general, however, NMR relies on non‐natural protein purity and concentration to increase the desired signal over the background. We here report on the efficient and specific hyperpolarization of low amounts of a target protein in a large isotope‐labeled background by combining dynamic nuclear polarization (DNP) and the selectivity of protein interactions. Using a biradical‐labeled ligand, we were able to direct the hyperpolarization to the protein of interest, maintaining comparable signal enhancement with about 400‐fold less radicals than conventionally used. We could selectively filter out our target protein directly from crude cell lysate obtained from only 8 mL of fully isotope‐enriched cell culture. Our approach offers effective means to study proteins with atomic resolution in increasingly native concentrations and environments.     

Molecular motions in low cross-linked poly(N-isopropylacrylamide) microgels

Non-ionic N-isopropylacrylamide (PNIPAM) microgel is employed to investigate the molecular motion of polymer chains in the swollen and collapsed states. This study is performed using incoherent elastic (IES) and quasielastic neutron scattering (IQNS). IES measurements show an increase of both, the elastic intensity and the oscillations of the polymer network vibrational amplitude at the transition temperature. IQNS was measured at two different selected temperatures 290 K and 327 K corresponding to the swollen and collapsed states, respectively. The diffusion constant from IQNS experiments decreases nearly two orders of magnitude when the microgel de-swells and finally collapses.