Der “thermo-stat” — eine ergänzung der verfahren zur bestimmung katalytisch wirksamer substanzen

The “Thermo-Stat” — a new device for the determination of catalyticaily active substancesA device for the determination of catalytically active substances, called a “ThermoStat”, is described. An additional heater is used to keep constant an arbitrarily preset temperature gradient between the reaction mixture and a cooling coil. Any heat produced by the catalysed reaction induces a deviation from the preset parameter and thus cuts out the additional heater. These breaks are plotted versus time by an integrating recorder. The slope of the reaction curve obtained is a measure of the concentration of the catalyst. As examples, determinations of copper in the range 0.1–2.0μg and molybdenum in the range 5–50 μg are discussed.     

Styrene emulsion polymerization: Particle-size distributions

Data are presented on the time evolution of particle-size distributions (PSDs) in seeded and ab initio styrene emulsion polymerization systems. Initiation was by chemical reagent (potassium persulfate) or γ-radiation. The unswollen PSDs at various times during interval II of the polymerization were obtained by direct measurement of calibrated electron micrographs. Experimental results were fitted with the equations that describe the time evolution of an initial PSD. Analytic solutions to these equations that allow for entry, exit, and propagation of free radicals were obtained. The values of the rate coefficients for these processes used to fit the experimental data were in excellent agreement with those obtained from dilatometric kinetics experiments.     

Strategies for measurements of pseudocontact shifts in protein NMR spectroscopy.

Paramagnetic metal ions bound to proteins generate a dipolar field that can be accurately probed by pseudocontact shifts (PCS) displayed by the protein's nuclear spins. PCS are highly useful for determining the coordinates of individual spins in the molecule and for rapid structure determinations of entire protein-protein and protein-ligand complexes. However, PCS measurements require reliable resonance assignments for the molecule in its paramagnetic state and in a diamagnetic reference state. This article discusses different approaches for pairwise resonance assignments, with emphasis on a strategy which exploits chemical exchange between the two states.     

‘Face-to-Face’-Benzo-anellierte homologe Hypostrophene. Synthesen,Röntgenstrukturanalysen und PE-Spektren

‘Face-to-Face’ Benzo-anellated Homologous Hypostrophenes. Syntheses, X-Ray-Structure Analyses and PE Spectra ‘Face-to-face’ Benzo-anellated homologous hypostrophenes (series M ), of interest as substrates for [6 + 6]-photocycloaddition reactions, have been synthesized. From X-ray structural analyses of 13b and 13c shortest C? C distances of 2.80(2.76)/2.71 Å and interorbital angles (ω) of 129° (128°)/130° between the benzene rings have been determined. The PE spectra are discussed in the context of transannular π,π interactions.     

HALORHODOPSIN and PHOTOSENSORY BEHAVIOR IN Halobacterium halobium MUTANT STRAIN L-33

Halobacterium halobium , strain L-33, which is deficient in bacteriorhodopsin (BR) but synthesizes increased amounts of halorhodopsin (HR), shows behavioral responses upon changes in fluence rate with visible light or with UV light. The observations support the earlier report (Schimz et al. , 1982). that BR is not essential for photosensing in H. halobium. In the UV-range, changes in light intensity elicit the maximal response at λ= 370 nm. In the visible range, changes in light intensity show the maximal response at Δ= 565 nm and a secondary peak at Δ= 590 nm. The latter corresponds to the absorption maximum of HR (Δ_max= 588 nm). This light-energy converting retinal pigment of H. halobium thus appears to contribute to photosensory behavior.     

Preparation and Structure of [Me3N(CF3)2BCCB(CF3)2NMe3]

Bis‐trimethylamine‐ethynyl‐di‐bis(trifluoromethyl)borane [Me₃N(CF₃)₂BCCB(CF₃)₂NMe₃] ( 1 ) has been prepared from trimethylamine‐ethynyl‐bis(trifluoromethyl)borane, [HCCB(CF₃)₂NMe₃], and dimethylamino‐bis(trifluoromethyl)borane, (CF₃)₂BNMe₂. The structure of 1 has been determined by x‐ray crystallography. In the solid state the molecule possesses crystallographic C_i symmetry. The acetylenic attachment to the boron atom is characterized by a short B–C bond length of 1.565(4) Å and an essentially linear B–C–C′ bond angle of 178.1(4)°.     

Studies of protein hydration in aqueous solution by high-resolution nuclear magnetic resonance spectroscopy

Individual hydration water molecules in aqueous protein solutions have been observed using experimental schemes for homonuclear two-dimensional and heteronuclear three-dimensional NMR experiments in H₂O solution, which do not require suppression of the solvent line by presaturation. In these experiments, the location of the hydration waters is determined from their nuclear Overhauser effects (NOE s) with individual hydrogen atoms of distinct amino acid residues. In the basic pancreatic trypsin inhibitor (BPTI ), four internal water molecules that had been reported in three different crystal forms were also found to be in the same locations in the solution structure, with lifetimes with respect to exchange of the water protons in excess of 0.3 ns. Additional NOE s with polypeptide protons located on the protein surface may involve either hydration water molecules or hydroxyl protons of amino acid side chains. Their total number is small compared to the number of NOE s expected from the hydration water molecules identified in the crystal structures of BPTI .