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121.
M. Sc. Markus Warnke Tobias Jung Dr. Juri Dermer Karin Hipp Dr. Nico Jehmlich Prof. Dr. Martin von Bergen Sascha Ferlaino Dr. Alexander Fries Prof. Dr. Michael Müller Prof. Dr. Matthias Boll 《Angewandte Chemie (International ed. in English)》2016,55(5):1881-1884
The hydroxylation of vitamin D3 (VD3, cholecalciferol) side chains to give 25‐hydroxyvitamin D3 (25OHVD3) is a crucial reaction in the formation of the circulating and biologically active forms of VD3. It is usually catalyzed by cytochrome P450 monooxygenases that depend on complex electron donor systems. Cell‐free extracts and a purified Mo enzyme from a bacterium anaerobically grown with cholesterol were employed for the regioselective, ferricyanide‐dependent hydroxylation of VD3 and proVD3 (7‐dehydrocholesterol) into the corresponding tertiary alcohols with greater than 99 % yield. Hydroxylation of VD3 strictly depends on a cyclodextrin‐assisted isomerization of VD3 into preVD3, the actual enzymatic substrate. This facile and robust method developed for 25OHVD3 synthesis is a novel example for the concept of substrate‐engineered catalysis and offers an attractive alternative to chemical or O2 /electron‐donor‐dependent enzymatic procedures. 相似文献
122.
Sascha Eichmann 《Journal of Geometric Analysis》2016,26(4):2563-2590
In this note Willmore surfaces of revolution with Dirichlet boundary conditions are considered. We show two nonuniqueness results by reformulating the problem in the hyperbolic half plane and solving a suitable initial value problem for the corresponding elastic curves. The behavior of such elastic curves is examined by a method provided by Langer and Singer to reduce the order of the underlying ordinary differential equation. This ensures that these solutions differ from solutions already obtained by Dall’Acqua, Deckelnick and Grunau. We will additionally provide a Bernstein-type result concerning the profile curve of a Willmore surface of revolution. If this curve is a graph on the whole real numbers it has to be a Möbius transformed catenary. We show this by a corollary of the above-mentioned method by Langer and Singer. 相似文献
123.
Frontispiece: Judicious Ligand Design in Ruthenium Polypyridyl CO2 Reduction Catalysts to Enhance Reactivity by Steric and Electronic Effects
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124.
In this study the temperature stability of several normal phase and RP columns was investigated using a water-only mobile phase. The temperature was adjusted to 120 degrees C for the bare silica stationary phases and to 185 degrees C for the metal oxide and carbon stationary phases. It could be shown that metal oxide stationary phases exhibited excellent thermal stability over the duration of the test period and are therefore suitable for high temperature LC applications. 相似文献
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Ali AA Benson RE Blumentritt S Cameron TS Linden A Wolstenholme D Thompson A 《The Journal of organic chemistry》2007,72(13):4947-4952
The diastereoselective syntheses of Zn(II) bis(dipyrrinato) helicates is reported, involving ligands templated by the incorporation of homochiral binol within the linker joining the two dipyrrinato units. The most diastereoselective formation of dinuclear bis(dipyrrinato) helicates to date is reported. The formation of either mononuclear or dinuclear helicates can be tuned by varying the length of the linker between the dipyrrinato units and by varying the complexation procedure. The neutral dipyrrinato helicates were readily analyzed by HPLC to ascertain diastereoselectivity, and circular dichroism studies revealed the helical nature of the complexes. The molar ellipticities of the helicates produced by diastereoselective complexation are very large in the visible region and typically correspond to binol moieties in the UV region. Extensive X-ray crystallographic investigations further confirmed the helicity of the mononuclear Zn(II) helicates and identified significant interlayer displacement and bending within crystals. 相似文献
129.
We present the first trans-H-bond 13C-15N 3-bond J couplings calculated from entire neutral and protonated alpha-helical polyalanines. The neutral helices considered are those of the capped peptides, acetyl(Ala)NNH2, where N = 8, 16, 17, and 18, while the protonated peptides are the uncapped (Ala)17 protonated at three different positions. The calculated J values correlate well with O...H distances and somewhat less well with N...O distances, particularly if the terminal H-bonds are eliminated from the correlation. The J values calculated using the entire helix are about 6% lower in magnitude than those recently reported for H-bonding chains whose geometries were extracted from the same helices. Aqueous solvation favors protonation of the alpha-helix on the terminal COOH. Experimental measurements of the trans-H-bond 13C-15N 3-bond J couplings in acidic solution should be interpreted with this context. 相似文献
130.
Radosaw W. Piast Rafa M. Wieczorek Nicola Marzec Maciej Garstka Aleksandra Misicka 《Molecules (Basel, Switzerland)》2021,26(19)
Chondrocalcinosis is a metabolic disease caused by the presence of calcium pyrophosphate dihydrate crystals in the synovial fluid. The goal of our endeavor was to find out whether short peptides could be used as a dissolving factor for such crystals. In order to identify peptides able to dissolve crystals of calcium pyrophosphate, we screened through a random library of peptides using a phage display. The first screening was designed to select phages able to bind the acidic part of alendronic acid (pyrophosphate analog). The second was a catalytic assay in the presence of crystals. The best-performing peptides were subsequently chemically synthesized and rechecked for catalytic properties. One peptide, named R25, turned out to possess some hydrolytic activity toward crystals. Its catalysis is Mg2+-dependent and also works against soluble species of pyrophosphate. 相似文献