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91.
Dirk Steinborn Olaf Gravenhorst Clemens Bruhn Dusan Miklo Michal Dunaj-Jur
o Alfred Kolbe 《无机化学与普通化学杂志》1997,623(12):1954-1958
Synthesis and Characterization of Aquapentachloroplatinates(IV) – Structure of [K(18-crown-6)][PtCl5(H2O)] The crown ether complex of the aquapentachloroplatinic acid of the composition [H13O6][PtCl5(H4O2)] · 2(18-cr-6) ( 2 ) reacts with K2CO3 and [NnBu4]OH in aqueous solution to give [K(18-cr-6)][PtCl5(H2O)] ( 5 a ) and [NnBu4][PtCl5(H2O)] · 1/2 (18-cr-6) · H2O ( 5 b ), respectively. Both compounds were characterized by microanalysis, vibrational (IR, Raman) and NMR (1H, 13C, 195Pt) spectroscopy. The X-ray structure analysis of 5 a (orthorhombic, pnma; a = 16,550(4), b = 18,044(3), c = 7,415(1) Å; Z = 4; R1 = 0,0183; wR2 = 0,0414) reveals that the crystal is threaded by chains built up of [PtCl5(H2O)]? and [K(18-cr-6)]+ units. There are tight K …? Cl contacts (d(K? Cl1)) = 3,0881(9) Å and OW? H? Ocr hydrogen bridges (d(O1 …? O2) = 2,806(3) Å) between these units. The coordination polyhedron [PtCl5O] has approximately C4v symmetry. 相似文献
92.
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94.
The ability to synthesize nonribosomally small bioactive peptides that find application in modern medicine is widely spread among microorganisms. As broad as the spectrum of biological activities is the structural diversity of these peptides, which are mostly cyclic or branched cyclic compounds containing non-proteinogenic amino acids, small heterocyclic rings and other unusual modifications in the peptide backbone. They are synthesized by multimodular enzymes, the so-called nonribosomal peptide synthetases (NRPSs), from simple building blocks. Biochemical and genetic studies have unveiled the key principles of nonribosomal peptide syntheses, as well as the realization of many structural features of these peptides. This review focuses on recent results in NRPS research and highlights how this knowledge can be exploited for biotechnological purposes. In addition, possibilities and limitations for prediction of structural features of uncharacterized NRPSs and approaches for their engineering are discussed. 相似文献
95.
96.
Reaction of N-benzoyl-1,2,3,4-tetrahydroquinoline-2-carboxylic acid with acetic anhydride resulted in 1H,3H,5H-oxazolo[3,4-a]quinolin-3-one derivative 13. Different cyclopropanation processes were applied to 13, but only diazomethane in the presence of water furnished the hitherto unknown methyl 1,2,7,7a-tetrahydro-1aH-cyclopropa[b]quinoline-1a-carboxylate 14, which can be considered as a doubly constrained 1-aminocyclopropane-1-carboxylic acid system. The mechanism of the cyclopropanation was studied in detail. The new ACC ester 14 was transformed into fused tetracyclic hydantoin derivatives, which comprised a new type of heterocyclic system. 相似文献
97.
Simon Smolders Tom Willhammar Andra Krajnc Kadir Sentosun Michael T. Wharmby Kirill A. Lomachenko Sara Bals Gregor Mali Maarten B. J. Roeffaers Dirk E. DeVos Bart Bueken 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(27):9258-9263
While titanium‐based metal–organic frameworks (MOFs) have been widely studied for their (photo)catalytic potential, only a few TiIV MOFs have been reported owing to the high reactivity of the employed titanium precursors. The synthesis of COK‐47 is now presented, the first Ti carboxylate MOF based on sheets of TiIVO6 octahedra, which can be synthesized with a range of different linkers. COK‐47 can be synthesized as an inherently defective nanoparticulate material, rendering it a highly efficient catalyst for the oxidation of thiophenes. Its structure was determined by continuous rotation electron diffraction and studied in depth by X‐ray total scattering, EXAFS, and solid‐state NMR. Furthermore, its photoactivity was investigated by electron paramagnetic resonance and demonstrated by catalytic photodegradation of rhodamine 6G. 相似文献
98.
Svenja M. Ackermann Dirk W. Lachenmeier Thomas Kuballa Birk Schütz Manfred Spraul Mirko Bunzel 《Magnetic resonance in chemistry : MRC》2019,57(9):579-588
Both the German and European organic food markets are growing fast, and there is also a rising demand for organic chicken eggs. Consumers are willing to pay higher prices for organic eggs produced in an animal-appropriate environment considering animal welfare. Strict labelling requirements do not prevent chicken eggs from being a subject of food fraud. Conventionally produced (barn/free-range) eggs can easily be mislabeled as organic eggs. Especially because the demand for organically produced chicken eggs is likely to exceed supply in the future, mislabeling appears to be a realistic scenario. Therefore, there is a need for analytical methods that are suitable to classify eggs as being either conventionally or organically produced. Nuclear magnetic resonance (NMR) spectroscopy in combination with multivariate data analysis is a suitable tool to screen eggs according to the different systems of husbandry. Sample preparation is based on a fat extraction method, which was optimised for application to freeze-dried egg yolk. Samples were analysed using typical q-NMR parameters. A nontargeted approach was used for the analysis of the 1H NMR data. Principal component analysis (PCA) was applied followed by a linear discriminant analysis (PCA-LDA) and Monte Carlo cross-validation. In total, 344 chicken eggs (214 barn/free-range eggs and 130 eggs from organic farms), most of them originating from Germany, were used to build and validate the prediction model. The results showed that the prediction model allowed for the correct classification of about 93% of the organic eggs. 相似文献
99.
Production and Decomposition of (NH4)[BF4] and H3N‐BF3 (NH4)[BF4] is produced as single crystals during the reaction of elemental boron and NH4HF2 (B : NH4HF2 = 1 : 2) and NH4F (B : NH4F = 1 : 4), respectively, in sealed copper ampoules at 300 °C. The crystal structure (baryte type, orthorhombic, Pnma, Z = 4) was redetermined at ambient temperature (a = 909.73(18), b = 569.77(10), c = 729.47(11) pm, Rall = 0.0361) and at 140 K (a = 887.3(2), b = 574.59(12), c = 717.10(12) pm, Rall = 0.0321). Isolated (NH4)+ and [BF4]— tetrahedra are the important building units. The thermal behaviour of (NH4)[BF4] was investigated under inert (Ar, N2) and reactive conditions (NH3) with the aid of DTA/TG and DSC measurements and with in‐situ X‐ray powder diffraction as well. Finally, (NH4)[BF4] is decomposed yielding NH3 and BF3, BN is not produced under the current conditions. Colourless single crystals of H3N‐BF3 were prepared directly from the components NH3 and BF3. The crystal structure was determined anew at 293 and 170 K (orthorhombic, Pbca, Z = 8, a = 815.12(10), b = 805.91(14), c = 929.03(12) pm, Rall = 0.0367; a = 807.26(13), b = 800.48(10), c = 924.31(11) pm, Rall = 0.0292, T = 170 K). The crystal structure contains isolated molecules H3N‐BF3 in staggered conformation with a B‐N distance of 158 pm. The thermal behaviour of H3N‐BF3 was studied likewise. 相似文献
100.
Thomas Prenveille Cyrielle Garreau Mathias Matner Dirk Dijkstra Wilhelm Oppermann Diethelm Johannsmann 《Journal of polymer science. Part A, Polymer chemistry》2019,57(5):621-629
The reactivity of urethanes based on 1,6‐hexamethylene diisocyanate (HDI) and 4,4′‐methylene diphenyl diisocyanate (MDI) was investigated at temperatures between 190 °C and 235 °C. Diurethane model compounds end‐capped with either 1‐dodecanol (D‐core‐D) or 1‐hexadecanol (H‐core‐H) were mixed and annealed at high temperature. The core was either MDI or HDI. The transurethanization reaction was followed based on the formation of the compounds (H‐core‐D). The amount of H‐core‐D and of side products, which had formed after variable annealing times, were identified with 1H NMR, FTIR, SEC, and MALDI‐TOF. Transurethanization was considerably faster for MDI‐based urethanes than for HDI‐based urethanes. Only traces of side products were formed during annealing of MDI‐based urethanes, whereas a significant amount of allophanates was formed from HDI‐based urethanes under the same conditions. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 621–629 相似文献