A Native-Like Conformation for the C-Terminal Domain of the Prion Ure2p within its Fibrillar Form

Taking a definite stance: Protein fibrils are often associated with disorder and polymorphism, but the prion fibrils of Ure2p are shown (through solid-state NMR spectroscopy) to be highly ordered, and the conformations of the globular domain to be more restricted within the fibrils (black; see scheme) than in Ure2p single crystals?(red). This finding implies that steric impairment is at the origin of the [URE3] phenotype in yeast.     

4D solid-state NMR for protein structure determination

Solid-state NMR offers the chance to extend structural studies to proteins that are otherwise difficult to study at atomic resolution, such as protein fibrils, membrane proteins or poorly diffracting crystals. As two-dimensional spatial correlation NMR spectra of proteins suffer from severe resonance overlap, we analyze in this perspective article the potential of higher-dimensional (3D and 4D) proton-detected experiments, which have an increased number of identifiable and assignable distance restraints for solid-state structural studies. We discuss practical considerations for the NMR measurements and the preparation of suitable protein samples and show results of structure calculations from 4D solid-state NMR spectra.     

Microfluidic wound-healing assay to assess the regenerative effect of HGF on wounded alveolar epithelium

We present a microfluidic epithelial wound-healing assay that allows characterization of the effect of hepatocyte growth factor (HGF) on the regeneration of alveolar epithelium using a flow-focusing technique to create a regular wound in the epithelial monolayer. The phenotype of the epithelial cell was characterized using immunostaining for tight junction (TJ) proteins and transmission electron micrographs (TEMs) of cells cultured in the microfluidic system, a technique that is reported here for the first time. We demonstrate that alveolar epithelial cells cultured in a microfluidic environment preserve their phenotype before and after wounding. In addition, we report a wound-healing benefit induced by addition of HGF to the cell culture medium (19.2 vs. 13.5 μm h(-1) healing rate).     

Multiple-state ensemble structure determination from eNOE spectroscopy

The recent investigation of an ensemble-based structure calculation using mainly a large collection of exact nuclear Overhauser enhancements (eNOEs) revealed the presence of concerted motion within the protein GB3 (B. Vögeli, S. Kazemi, P. Güntert and R. Riek, Nat. Struct. Mol. Biol., in press). Here, we discuss the method used in this study in detail. Important steps include the NMR pulse sequence, the determination of the eNOEs corrected for spin diffusion, the conversion of eNOE rates into distances, the distance-restraint classification, the use of bundling restraints to generate a compact representation of the structure and the selection of the appropriate ensemble to represent the structure. It is further demonstrated that eNOEs can be obtained between most proton types in a macromolecule. These eNOEs are then used to calculate an ensemble-based structure using CYANA that is capable to reveal long-range concerted motion in the protein. The structure ensembles are cross-validated with jackknife tests applied to the eNOEs, RDCs, scalar couplings, cross-correlated relaxation rates, and with a high-resolution structure obtained independently from X-ray diffraction and refined with RDCs.     

Polymerisierbare Ferrocene: Versuche zur Synthese von Polyferrocenen und Polyferrocenophanen

Polymerizable Ferrocenes: Synthetic Attempts towards Polyferrocenes and Polyferrocenophanes The novel polymerizable ferrocenes 8 (Scheme 2) and 11 (Scheme 3) have been synthesized, and cationic polymerization experiments towards bridged poly(1,1′-diisopropenyl)ferrocenes 1 as well as poly(1,1′,3,3′-tetraisopropenyl)ferrocenes 2 are discussed. In both cases, only oligomeric products with M¯_n ca. 1700/M¯_w of ca. 2900 ( 1 ) and M¯_n ca. 1400/M¯_w of ca. 4000 ( 2 ) have been isolated. On the other hand, synthetic attempts towards polyferrocenophanes 3 (Scheme 6) result in oligomeric products as well.     

Preparation of Polystyrene Beads with Dendritically Embedded TADDOL and Use in Enantioselective Lewis Acid Catalysis

A full account is given of the preparation and use of TADDOLates, which are dendritically incorporated in polystyrene beads (Scheme 1). A series of styryl‐substituted TADDOLs with flexible, rigid, or dendritically branching spacers between the TADDOL core and the styryl groups (2–16 in number) has been prepared ( 5 – 7, 20, 21, 26 in Schemes 2–4 and Fig. 1–3). These were used as cross‐linkers in styrene‐suspension polymerization, leading to beads of ca. 400‐μm diameter (Schemes 5 and 6, b). These, in turn, were loaded with titanate and used for the Lewis acid catalyzed addition of Et₂Zn to PhCHO as a test reaction (Scheme 6). A comparison of the enantioselectivities and degrees of conversion (both up to 99%), obtained under standard conditions, shows that these polymer‐incorporated Ti‐TADDOLates are highly efficient catalysts for this process (Table 1). In view of the effort necessary to prepare the novel, immobilized catalysts, emphasis was laid upon their multiple use. The performance over 20 cycles of the test reaction was best with the polymer obtained from the TADDOL bearing four first‐generation Fréchet branches with eight peripheral styryl groups ( 6 , p‐ 6 , p‐ 6 ⋅Ti(OⁱPr)₂): the enantioselectivity (Fig. 4), the rate of reaction (Fig. 5), and the swelling factor (Fig. 6) were essentially unchanged after numerous operations carried out with the corresponding beads of 400‐μm diameter and a degree of loading of 0.1 mmol TADDOLate/g polymer, with or without stirring (Fig. 7). The rate with the dendritically polymer‐embedded Ti‐TADDOLate (p‐ 6 ⋅Ti(OⁱPr)₂) was greater than that measured with the corresponding monomer, i.e., 6 ⋅Ti(OⁱPr)₂ (Fig. 8). Possible interpretations of this phenomenon are proposed. A polymer‐bound TADDOL, generated on a solid support (by Grignard addition to an immobilized tartrate ester ketal) did not perform well (Scheme 4 and Table 2). Also, when we prepared polystyrene beads by copolymerization of styrene, a zero‐, first‐, or second‐generation dendritic cross‐linker, and a mono‐styryl‐substituted TADDOL derivative, the performance in the test reaction did not rival that of the dendritically incorporated Ti‐TADDOLate ((p‐ 6 ⋅Ti(OⁱPr)₂) (Scheme 7 and Fig. 10). Finally, we have applied the dendritically immobilized Cl₂ and (TsO)₂Ti‐TADDOLate as chiral Lewis acid to preferentially prepare one enantiomer of the exo and the endo (3+2) cycloadduct, respectively, of diphenyl nitrone to 3‐crotonoyl‐1,3‐oxazolidinone; in one of these reaction modes, we have observed an interesting conditioning of the catalyst: with an increasing number of application cycles, the amount of polymer‐incorporated Lewis acid required to induce the same degree of enantioselectivity, decreased; the degrees of diastereo‐ and enantioselectivity were, again, comparable to those reported for homogeneous conditions (Fig. 9).     

Local velocity measurements in a thermally-stratified sodium mixing layer using a permanent-magnet probe

Mean and fluctuating velocities have been measured in a sodium mixing layer experiment, i.e. in a fluid with very low Prandtl number (Pr10⁻²), with a miniature permanent-magnet velocity probe in the presence of strong temperature gradients. A mathematical model for the probe, based upon Faraday's law of induction and including thermoelectric as well as inertia effects due to the finite response time of thermocouples, is presented together with a new dynamic method to compensate for these effects. The sensitivity of the four different probes used in this experiment is in the range of 81–65 (μV/ms⁻¹). Electrical pertubations arising from large-scale thermoelectric effects inside the test section and their influence on the velocity signal are also discussed. The electronic measurement system, combining low noise and high resolution, was specially developed to match the experimental requirements. With this system it was possible to measure velocity RMS-values down to 1 mm/s corresponding to a voltage of 100 nV, and mean velocities with an accuracy of about 6 mm/s. This paper deals with the peculiarities of the measurement technique and its performance, but does not analyze the experimental results, which will be presented in a separate publication.     

Molecular Motions in Crystalline Anthracene and Naphthalene from Multitemperature Diffraction Data

Atomic Displacement Parameters (ADPs) of anthracene (94 – 295 K), (D₁₀)anthracene (16, 295 K), naphthalene (92 – 239 K), and (D₈)naphthalene (12, 295 K) have been analyzed with the help of an Einstein‐type model of local, molecular normal modes. The low‐frequency motions are expressed in terms of molecular translations, librations, and deformations, and account for the temperature dependence of the experimental ADPs. Their frequencies decrease with increasing temperature due to crystal expansion. For anthracene, enough data of sufficient quality are available to determine two low‐frequency out‐of‐plane deformation modes. The corresponding frequencies of naphthalene are much higher and cannot be extracted from the available data, which are more limited qualitatively and quantitatively. The mean‐square amplitudes due to the high‐frequency normal modes are also extracted from the diffraction data. They agree satisfactorily with those obtained for molecules in the gas phase from density‐functional theory. Contributions to the ADPs that cannot be interpreted in terms of motion are small but significant. The case study presented here shows that dynamic aspects of molecular structure can be obtained from single‐crystal diffraction studies. For optimal results, experiments must be performed over as large a temperature and resolution range as possible, and factors affecting ADP's but not representing motion have to be kept to a minimum, e.g., by avoiding disorder, parametrizing X‐ray data with multipole models, and minimizing absorption and extinction.     

Synthesis and Structure of Linear and Cyclic Oligomers of 3-Hydroxybutanoic Acid with Specific Sequences of (R)- and (S)-Configurations

To study the stereoselectivity of enzymatic cleavage of poly(3-hydroxybutyrates) (PHB) in a well-defined system (purified depolymerase and monodisperse substrate of specific relative configuration), linear and cyclic oligomers of HB (OHBs) containing (R)- and (S)-3-hydroxybutanoate residues were synthesized. The starting material (R)-HB was prepared from natural sPHB, and (S)-HB by enantioselective reduction of 3-oxobutanoate with yeast or with H₂/Noyori-Taber catalyst (Scheme 2). The HB building blocks were then protected (O-benzyl/tert-butyl ester; Scheme 3) and coupled to give dimers 3 , 4 , tetramers 5 – 9 , and octamers 10 – 18 ; for analytical comparison, a 3mer, 5mer, 6mer, and 7mer ( 19 – 22 ) were also prepared. Two of the tetramers were subjected to macrolactonization conditions (Yamaguchi) to give the cyclic tetramers 23 and 25 and octamers 24 and 26 . All new compounds were fully characterized (m.p., [α]_D, CD, IR, ¹H- and ¹³C-NMR, MS, elemental analysis). Single-crystal X-ray structure analyses were performed with oligolides 24 and 25 (Figs. 2 and 4), and the structures, as well as the crystal packing, were compared with those of analogs containing only (R)-HB units or consisting of 3-amino- instead of 3-hydroxybutanoic-acid moieties.