Untersuchung der Iouenassoziation im System Natriummetavanadat-Natriumchlorid-Wasser mit der Ultrazentrifuge

Zusammenfassung Am Beispiel des Systems Na₄(VO₃)₄-NaCl-H₂O wird untersucht, in welcher Weise Ultrazentrifugenmessungen im Sedimentationsgleichgewicht durchgeführt werden müssen, um die molare Masse und die Ladungszahl von Polymerelektrolyten in ternären Systemen unter der Bedingung von nicht vernachlässigbaren Wechselwirkungen zwischen Polymerund Fremdelektrolyt zu bestimmen. Es erweist sich, daß die experimentellen scheinbaren molaren Massen nicht nur auf die Polymerkonzentration Null extrapoliert werden müssen, sondern auch auf die Fremdelektrolytkonzentration Null. Es gelingt, die Ableitung (alnyPX_z/amBx)mPX_z an der StellemPX_z = 0 mol kg_-1 mit einer scheinbaren mittleren Ladungszahlz _app des Polymeranions zu korrelieren. Zwischen dieser und der stöchiometrischen Ladungszahlz des Polymeranions besteht die Beziehungz _app = Z =az, so daß die Dissoziationskonstante des Polymerelektrolyten für die summarische Dissoziation berechnet werden kann. Die aus dieser Korrelation folgenden Abhängigkeiten der scheinbaren mittleren Ladungszahlen und der Ableitung (alnypx _z /amBX)Mpx _z = 0 von der Konzentration des Fremdelektrolyten werden experimentell bestätigt.

---

Summary The system Na₄(VO₃)₄-NaCl-H₂0 is taken as an example for ultracentrifugal measurements at sedimentation equilibrium to determine the molar mass and the valency of a polymer electrolyte in a ternary system when interactions exist between the polymer and the supporting electrolyte. The experimental apparent molar mass is obtained by extrapolation to zero value of concentration of both the polymeric and supporting electrolyte. It is possible to correlate the quantity (alnyPX _z /amBX)^mPX_z at the point ^m PX _z = 0 mole kg^-1 with the apparent valency _zapp of the polymeric anion.z _app is related to the stoichiometric valency by the equationz _app = _z =a.Z. Thus the dissociation constant can be calculated for complete dissociation of the polymer electrolyte. The dependence of _zapp and (aln _y PX _z /a ^m _BX ) ^m PX _z = 0 on concentration of the supporting electrolyte called for in the correlation is verified experimentally.

---

---

Mit 4 Abbildungen und 4 Tabellen     

X-Ray Molecular Structure of a Red Bilin Derivative from Chlorella protothecoides. 4th communication on chlorophyll catabolism

The molecular structure of a chlorophyll a catabolite isolated from the culture medium of bleached Chlorella protothecoides cells has been determined by X-ray diffraction; the crystal structure shows a distorted helical arrangement of the pyrrole rings and consists of symmetrical dimers located at a crystallographic diad, which are stabilized by six intermolecular H-bonds.     

Directed evolution of cyclic peptides for inhibition of autophagy

In recent decades it has become increasingly clear that induction of autophagy plays an important role in the development of treatment resistance and dormancy in many cancer types. Unfortunately, chloroquine (CQ) and hydroxychloroquine (HCQ), two autophagy inhibitors in clinical trials, suffer from poor pharmacokinetics and high toxicity at therapeutic dosages. This has prompted intense interest in the development of targeted autophagy inhibitors to re-sensitize disease to treatment with minimal impact on normal tissue. We utilized Scanning Unnatural Protease Resistant (SUPR) mRNA display to develop macrocyclic peptides targeting the autophagy protein LC3. The resulting peptides bound LC3A and LC3B—two essential components of the autophagosome maturation machinery—with mid-nanomolar affinities and disrupted protein–protein interactions (PPIs) between LC3 and its binding partners in vitro. The most promising LC3-binding SUPR peptide accessed the cytosol at low micromolar concentrations as measured by chloroalkane penetration assay (CAPA) and inhibited starvation-mediated GFP-LC3 puncta formation in a concentration-dependent manner. LC3-binding SUPR peptides re-sensitized platinum-resistant ovarian cancer cells to cisplatin treatment and triggered accumulation of the adapter protein p62 suggesting decreased autophagic flux through successful disruption of LC3 PPIs in cell culture. In mouse models of metastatic ovarian cancer, treatment with LC3-binding SUPR peptides and carboplatin resulted in almost complete inhibition of tumor growth after four weeks of treatment. These results indicate that SUPR peptide mRNA display can be used to develop cell-penetrating macrocyclic peptides that target and disrupt the autophagic machinery in vitro and in vivo.

SUPR peptide mRNA display was used to evolve a cell-permeable, macrocyclic peptide for autophagy inhibition.     

Mechanism of Intramolecular Photostabilization in Self‐Healing Cyanine Fluorophores

Organic fluorophores, which are popular labels for microscopy applications, intrinsically suffer from transient and irreversible excursions to dark‐states. An alternative to adding photostabilizers at high concentrations to the imaging buffer relies on the direct linkage to the fluorophore. However, the working principles of this approach are not yet fully understood. In this contribution, we investigate the mechanism of intramolecular photostabilization in self‐healing cyanines, in which photodamage is automatically repaired. Experimental evidence is provided to demonstrate that a single photostabilizer, that is, the vitamin E derivative Trolox, efficiently heals the cyanine fluorophore Cy5 in the absence of any photostabilizers in solution. A plausible mechanism is that Trolox interacts with the fluorophore through intramolecular quenching of triplet‐related dark‐states, which is a mechanism that appears to be common for both triplet‐state quenchers (cyclooctatetraene) and redox‐active compounds (Trolox, ascorbic acid, methylviologen). Additionally, the influence of solution‐additives, such as cysteamine and procatechuic acid, on the self‐healing process are studied. The results suggest the potential applicability of self‐healing fluorophores in stochastic optical reconstruction microscopy (STORM) with optical super‐resolution. The presented data contributes to an improved understanding of the mechanism involved in intramolecular photostabilization and has high relevance for the future development of self‐healing fluorophores, including their applications in various research fields.     

Determination of the impurity profile of ethyl-2-(4-[(5R)-3[4-(methoxycarboxamidoiminomethyl)-phenyl]-2- oxo-5-oxazolidinylmethyl]-1-piperazinyl) acetate, citrate, a highly active platelet aggregation inhibitor, by liquid chromatography-mass spectrometry.

Ethyl-2-(4-[(5R)-3-[4-(methoxycarboxamidoiminomethyl)-phenyl] -2-oxo-5-oxazolidinylmethyl]-1-piperazinyl) acetate, a glycoprotein IIb/IIIa antagonist, is a drug substance of the oxazolidinone type from Merck's research to be developed for the chronic oral treatment of thrombotic disorders. For the separation of the byproducts in the bulk drug substance, a reversed-phase HPLC gradient separation was developed. The eluent consisting of a nonvolatile phosphate buffer system had to be changed to a volatile acetate buffer system in order to perform on-line LC-MS coupling.With a triple quadrupole system it was possible to characterize most of the unknown byproducts occuring during synthesis and during scale-up to kg amounts of the bulk drug substance.     

The order-interval hypergraph of a finite poset and the König property

We study the hypergraph H(P) whose vertices are the points of a finite poset and whose edges are the maximal intervals in P (i.e. sets of the form I = {{v ε P: p ν q}}, p minimal, q maximal). We mention resp. show that the problems of the determination of the independence number , the point covering number τ, the matching number v and the edge covering number p are NP-complete. For interval orders we describe polynomial algorithms and prove the König property (v = τ) and the dual König property (a = p). Finally we show that the (dual) König property is preserved by product.     

Preparation of relativistic 7Li+ ion beams for precision experiments at storage rings

Heavy ion storage rings allow for tests of the structure of local space time via the Doppler effect. At the TSR/Heidelberg an experiment with high resolution laser spectroscopy at ⁷Li⁺ is performed. To gain the maximum resolution for saturation spectroscopy new methods of relativistic ion beam preparation and diagnostics have been developed. The laser cooling of the beam allows for precision determination of the mean velocity of the ions. A novel phase synchronous detection scheme, ultimately sensitive to single ions, gives insights into the cooling mechanism and dynamics. With an additional synchronous excitation scheme systematic uncertainties of the test experiment can be drastically reduced. After separation of the ground state ions from the triplet states of ⁷Li⁺ by the combination of laser and electron cooling, a bunched and cooled ensemble of fast moving high precision clocks with minimized perturbations by space charge effects and intra beam scattering is available. This revised version was published online in August 2006 with corrections to the Cover Date.     

Temperature resolved X-ray diffraction as a tool of thermal analysis

Time and temperature resolved X-ray diffraction was used for thermal analysis. Series of diffraction patterns were measured, while the samples are heated/cooled stepwise or isothermally with freely selectable temperature programs.The method was applied for the investigation of the phase transitions of ammonium nitrate and HMX (1,3,5,7-tetranitro-1,3,5,7-tetraaza-cyclooctane), when the identification of phases was required. Its capability in the field of kinetics is demonstrated with the isothermal investigation of the solid state reaction of ammonium nitrate with copper oxide and the non-isothermal investigation of the high temperature corrosion of nickel, which was performed by means of a difference procedure. For obtaining structural details peak fitting and Rietveld refinement were applied for the investigation of ammonium nitrate and HMX.We are indebted to Mr. K. O. Hartmann, Mr. H. Fietzek and Mr. H. G. Farr for their assistance during the measurements and for the maintenance of the measuring systems.