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101.
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Peptide natural products displaying a wide range of biological activities have become important drug candidates over the years. Microorganisms have been a powerful source of such bioactive peptides, and Streptomyces have yielded many novel natural products thus far. In an effort to uncover such new, meaningful compounds, the metabolome of Streptomyces acidiscabies was analyzed thoroughly. Three new compounds, scabimycins A–C (1–3), were discovered, and their chemical structures were elucidated by NMR spectroscopy. The relative and absolute configurations were determined using ROESY NMR experiments and advanced Marfey’s method.  相似文献   
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In the structure of tri­iodo­mesityl­ene (1,3,5‐tri­iodo‐2,4,6‐tri­methyl­benzene), C9H9I3, at 293 K, the benzene ring is found to be significantly distorted from ideal D6h symmetry; the average endocyclic angles facing the I atoms and the methyl groups are 123.8 (3) and 116.2 (3)°, respectively. The angle between the normal to the molecular plane and the normal to the (100) plane is 5.1°. No disorder was detected at 293 K. The thermal motion was investigated by a rigid‐body motion tensor analysis. Intra‐ and intermolecular contacts are described and topological differences compared with the isomorphous compounds tri­chloro­mesityl­ene and tri­bromo­mesityl­ene are discussed.  相似文献   
106.
Salen type complexes, CuL, the corresponding tetrahydrosalen type complexes, Cu[H4]L, and N,N′-dimethylated tetrahydrosalen type complexes, Cu[H2Me2]L, were investigated using cyclic voltammetry, and electronic and ESR spectroscopy. In addition, the analogous copper(II) complexes with a derivative of the tetradentate ligand ‘salphen’ [salphen=H2salphen=N,N′-disalicylidene-1,2-diaminobenzene] were studied. Solutions of CuL, Cu[H4]L and Cu[H2Me2]L are air-stable at ambient temperature, except for the complex Cu(tBu, Me)[H4]salphen [H2(tBu, Me)[H4]salphen=N,N′-bis(2-hydroxy-3-tert-butyl-5-methylbenzyl)-1,2-diaminobenzene]. Cu(tBu, Me)[H4]salphen interacts with dioxygen and the ligand is oxidatively dehydrogenated (–CH2–NH–→–C=N–) to form Cu(tBu, Me)[H2]salphen and finally, in the presence of base, Cu(tBu, Me)salphen. X-ray structure analysis of Cu(tBu, Me)[H2Me2]salen confirms a slightly tetrahedrally distorted planar geometry of the CuN2O2 coordination core. The complexes were subjected to spectrophotometric titration with pyridine, to determine the equilibrium constants for adduct formation. It was found that the metal center in the complexes studied is only of weak Lewis acidity. In dichlormethane, the oxidation Cu(II)/Cu(III) is quasireversible for the CuL type complexes, but irreversible for the Cu[H4]L and Cu[H2Me2]L type. A poorly defined wave was observed for the irreversible reduction Cu(II)/Cu(I) at potentials less than −1.0 V. The ESR spectra of CuL at both 77 K and room temperature reveal that very well resolved lines can be attributed to the interaction of an unpaired electron spin with the copper nuclear spin, 14N donor nuclei and to a distant interaction with two equivalent protons [ACu(iso)≈253 MHz, AN(iso)≈43 MHz, AN(iso)≈20 MHz]. These protons are attached to the carbon atoms adjacent to the 14N nuclei. In contrast to CuL, the number of lines in the spectra of the complexes Cu[H4]L and Cu[H2Me2]L is greatly reduced. At room temperature, only a quintet with a considerably smaller nitrogen shf splitting constant [AN(iso)≈27 MHz] is observed. Both factors, planarity and conjugation, are thus essential for the observation of distant hydrogen shf splitting in CuL. Due to the C=N bond hydrogenation, the coordination polyhedra of the complexes Cu[H4]L and Cu[H2Me2]L is more flexible and more sensitive to ligand modification than that of CuL. The electron-withdrawing effect of the phenyl ring of the phenylenediamine bridge is reflected in a reduction of the copper hyperfine coupling constants in Cu(tBu, Me)[H4]salphen and Cu(tBu, Me)[H2Me2]salphen complexes [ACu(iso)≈215 MHz].  相似文献   
107.
The mono‐hydrate phase as well as the water‐free RbD2PO4 (DRDP) is obtained by crystal growth from fully deuterated aqueous solution. Its crystal structure was determined by combined neutron and X‐ray single crystal diffraction. It consists of double layers of PO4 tetrahedra with D2O planes in between. The PO4 groups are linked by fully ordered deuterium bonds O‐D‐O. RbD2PO4.D2O dehydrates below 329(5)K and undergoes a phase transition to RbD2PO4 (DRDP).  相似文献   
108.
Few-cycle pulses with stable and controllable relative phase between the carrier wave and the envelope (CE phase) have become available as research tools. The actual shape of the electric field of such a pulse strongly depends on this phase, and so do the physical processes the pulse generates. Owing to its pronounced nonlinearity, above-threshold ionization (ATI) provides an excellent example. In particular, the rescattering-induced high- energy part of the ATI spectrum exhibits a dramatic dependence on the value of the CE phase. Moreover, the backward/forward symmetry of the ATI spectrum generated by a, long pulse is broken by a few-cycle pulse. Therefore, analyzing the spectrum in two opposite directions provides a very accurate means of measuring the CE phase.  相似文献   
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The purification of adenosine deaminase from human erythrocytes is reported. By means of classical procedures and by using affinity chromatography as the last step, the enzyme is purified 760,000-fold with a yield of 32%. The affinity resin is composed of purine riboside (nebularine) linked to Sepharose CL6B. Since the compound has no leaving group at the C-6 position the affinity gel is stable and the chromatography can be repeated several times (up to fifteen times in eight months). Purine riboside was chosen because its potency as a reversible inhibitor of adenosine deaminase is greater than that of inosine (a low-affinity inhibitor), but lower than that of erythro-9-(2-hydroxy-3-nonyl)adenine (a high-affinity inhibitor).  相似文献   
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