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151.
Dr. Franziska K. Merkt Flaminia Mazzone Dr. Shabnam Shaneh Sazzadeh Lorand Bonda Larissa K. E. Hinz Dr. Irina Gruber Karin Buchholz Prof. Dr. Christoph Janiak Prof. Dr. Klaus Pfeffer Prof. Dr. Thomas J. J. Müller 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(38):9774-9781
A gold-catalyzed cycloisomerization of 2-indolyl-3-[(trimethylsilyl)ethynyl)]quinoxalines with concomitant 1,2-silyl shift forms 6-(trimethylsilyl)indolo[3,2-a]phenazines in moderate to excellent yield. These silylated heterocycles are readily transformed into 6-aryl-indolo[3,2-a]phenazines in moderate to good yield by one-pot ipso-iodination Suzuki coupling. The title compounds represent a novel type of tunable luminophore. Structure-property relationships for 6-aryl-indolo[3,2-a]phenazines obtained from Hammett correlations with σp+ substituent parameters indicate that emission maxima, Stokes shifts, and fluorescence quantum yields can be fine-tuned by the remote para-aryl substituent. Furthermore, indolo[3,2-a]phenazines were found to exhibit interesting activities against medically relevant pathogens such as the Apicomplexa parasite Toxoplasma gondii with an IC50 of up to 0.67±0.13 μM. Thus, these compounds are promising candidates for novel anti-parasitic therapies. 相似文献
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154.
The formation of inorganic structures in nature is commonly controlled by biogenic macromolecules. The understanding of mineralization phenomena and the nucleation and growth mechanisms involved is still a challenge in science but also of great industrial interest. This article focuses on the formation and mineralization of two archetypical inorganic materials: zinc oxide and amorphous calcium carbonate (ACC). Zinc oxide is selected as a model compound to investigate the role that polymers play in mineralization. Most of the effort has been devoted to the investigation of the effects of double-hydrophilic block and graft copolymers. Recent work has demonstrated that latex particles synthesized by miniemulsion polymerization, properly functionalized by various chemical groups, have similar effects to conventional block copolymers and are excellently suited for morphology control of ZnO crystals. Latex particles might serve as analogues of natural proteins in biomineralization. The second example presented, ACC, addresses the issue of whether this amorphous phase is an intermediate in the biomineralization of calcite, vaterite, or aragonite. Conditions under which amorphous calcium carbonate can be obtained as nanometer-sized spheres as a consequence of a liquid-liquid phase segregation are presented. Addition of specific block copolymers allows control of the particle size from the micrometer to the submicrometer length scale. The physical properties of novel materials synthesized from concentrated solution and their potential applications as a filler of polymers are also discussed. 相似文献
155.
Braun M Korff Schmising Cv Kiel M Zhavoronkov N Dreyer J Bargheer M Elsaesser T Root C Schrader TE Gilch P Zinth W Woerner M 《Physical review letters》2007,98(24):248301
Femtosecond photoexcitation of organic chromophores in a molecular crystal induces strong changes of the electronic dipole moment via intramolecular charge transfer as is evident from transient vibrational spectra. The structural response of the crystal to the dipole change is mapped directly for the first time by ultrafast x-ray diffraction or diffuse scattering. Changes of diffracted and transmitted x-ray intensity demonstrate an angular rearrangement of molecules around excited dipoles following the 10 ps kinetics of charge transfer and leaving lattice plane spacings unchanged. Transient x-ray scattering is governed by solvation, masking changes of the chromophore molecular structure. 相似文献
156.
An Exclusively trans‐Selective Chlorocarbamoylation of Alkynes Enabled by a Palladium/Phosphaadamantane Catalyst
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Christine M. Le Xiao Hou Theresa Sperger Prof. Dr. Franziska Schoenebeck Prof. Dr. Mark Lautens 《Angewandte Chemie (International ed. in English)》2015,54(52):15897-15900
Pharmaceutically relevant methylene oxindoles are synthesized by a palladium(0)‐catalyzed intramolecular chlorocarbamoylation reaction of alkynes. A relatively underexplored class of caged phosphine ligands is uniquely suited for this transformation, enabling high levels of reactivity and exquisite trans selectivity. This report entails the first transition‐metal‐catalyzed atom‐economic addition of a carbamoyl chloride across an alkyne. 相似文献
157.
Franziska Busse Christian Rehorn Markus Küppers Naira Ruiz Heike Stege Bernhard Blümich 《Magnetic resonance in chemistry : MRC》2020,58(9):830-839
Mobile nuclear magnetic resonance (NMR) is a flexible technique for nondestructive characterization of water in plants, the physical properties of polymers, moisture in porous walls, or the binder in paintings by relaxation measurements. NMR relaxation data report material properties and therefore can also help to characterize the state of tangible cultural heritage. In this work, we discuss the relaxation behavior in two series of naturally aged paint mock-up samples. First, paints with different pigment concentrations were prepared and investigated in terms of the longitudinal and transverse relaxation-time distributions. We document the evolution of both relaxation-time distributions during the initial drying stage and demonstrate the heightened importance of transverse over longitudinal relaxation measurements. Second, we observe nonlinear dependences of the relaxation times on the pigment concentration in a typical oil binder. Third, in a study of naturally aged paint samples prepared in the years between 1914 and 1951 and subsequently aged under controlled conditions, we explore the possibility of determining the age of paintings using partial least square regression (PLS) by fitting T1–T2 data with the sample age. Our results suggest some correlation, albeit with significant scatter. Estimating the age of a painting stored under unknown conditions from NMR relaxation data is therefore not feasible, as the cumulative effects of light irradiation, humidity, and biological degradation further obfuscate the chemical and physical impact of aging on the relaxation times in addition to the impact of pigment concentration. 相似文献
158.
Dr. Henning Lumpe Annika Menke Prof. Dr. Christoph Haisch Dr. Peter Mayer Dr. Anke Kabelitz Dr. Kirill V. Yusenko Dr. Ana Guilherme Buzanich Theresa Block Prof. Dr. Rainer Pöttgen Dr. Franziska Emmerling Prof. Dr. Lena J. Daumann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(44):10133-10139
Lanthanides (Ln) are critical raw materials, however, their mining and purification have a considerable negative environmental impact and sustainable recycling and separation strategies for these elements are needed. In this study, the precipitation and solubility behavior of Ln complexes with pyrroloquinoline quinone (PQQ), the cofactor of recently discovered lanthanide (Ln) dependent methanol dehydrogenase (MDH) enzymes, is presented. In this context, the molecular structure of a biorelevant europium PQQ complex was for the first time elucidated outside a protein environment. The complex crystallizes as an inversion symmetric dimer, Eu2PQQ2, with binding of Eu in the biologically relevant pocket of PQQ. LnPQQ and Ln1Ln2PQQ complexes were characterized by using inductively coupled plasma mass spectrometry (ICP-MS), infrared (IR) spectroscopy, 151Eu-Mössbauer spectroscopy, X-ray total scattering, and extended X-ray absorption fine structure (EXAFS). It is shown that a natural enzymatic cofactor is capable to achieve separation by precipitation of the notoriously similar, and thus difficult to separate, lanthanides to some extent. 相似文献
159.
Gizem Dübek Franziska Hanusch Dr. Dominik Munz Prof. Shigeyoshi Inoue 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(14):5872-5878
Air- and moisture-stable heterobimetallic tetrahedral clusters [Cp(CO)2MSiR]2 (M=Mo or W; R=SitBu3) were isolated from the reaction of N-heterocyclic carbene (NHC) stabilized silyl(silylidene) metal complexes Cp(CO)2M=Si(SitBu3)NHC with a mild Lewis acid (BPh3). Alternatively, treatment of the NHC-stabilized silylidene complex Cp(CO)2W=Si(SitBu3)NHC with stronger Lewis acids such as AlCl3 or B(C6F5)3 resulted in the reversible coordination of the Lewis acid to one of the carbonyl ligands. Computational investigations revealed that the dimerization of the intermediate metal silylidyne (M≡Si) complex to a tetrahedral cluster instead of a planar four-membered ring is due to steric bulk. 相似文献
160.
Samir Bouayad-Gervais Thomas Scattolin Prof. Dr. Franziska Schoenebeck 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(29):12006-12010
Reported herein is the first efficient strategy to synthesize a broad range of unsymmetrical N-CF3 hydrazines, which served as platform to unlock numerous currently inaccessible derivatives, such as tri- and tetra-substituted N-CF3 hydrazines, hydrazones, sulfonyl hydrazines, and valuable N-CF3 indoles. These compounds proved to be remarkably robust, being compatible with acids, bases, and a wide range of synthetic manipulations. The feasibility of RN(CF3)-NH2 to function as a directing group in C−H functionalization is also showcased. 相似文献