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Direct In Situ Investigation of Milling Reactions Using Combined X‐ray Diffraction and Raman Spectroscopy 下载免费PDF全文
M. Sc. Lisa Batzdorf Dipl.‐Chem. Franziska Fischer Dipl.‐Chem. Manuel Wilke Dipl.‐Ing. Klaus‐Jürgen Wenzel Dr. Franziska Emmerling 《Angewandte Chemie (International ed. in English)》2015,54(6):1799-1802
The combination of two analytical methods including time‐resolved in situ X‐ray diffraction (XRD) and Raman spectroscopy provides a new opportunity for a detailed analysis of the key mechanisms of milling reactions. To prove the general applicability of our setup, we investigated the mechanochemical synthesis of four archetypical model compounds, ranging from 3D frameworks through layered structures to organic molecular compounds. The reaction mechanism for each model compound could be elucidated. The results clearly show the unique advantage of the combination of XRD and Raman spectroscopy because of the different information content and dynamic range of both individual methods. The specific combination allows to study milling processes comprehensively on the level of the molecular and crystalline structures and thus obtaining reliable data for mechanistic studies. 相似文献
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Prof. Dr. Chao‐Jun Li 《Angewandte Chemie (International ed. in English)》2018,57(10):2616-2620
The oxidative cleavage of 1,2‐diols is a fundamental organic transformation. The stoichiometric oxidants that are still predominantly used for such oxidative cleavage, such as H5IO6 , Pb(OAc)4 , and KMnO4 , generate stoichiometric hazardous waste. Herein, we describe a widely applicable and highly selective silver(I)‐catalyzed oxidative cleavage of 1,2‐diols that consumes atmospheric oxygen as the sole oxidant, thus serving as a potentially greener alternative to the classical transformations. 相似文献
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Probing Interfacial Electronic and Catalytic Properties on Well‐Defined Surfaces by Using In Situ Raman Spectroscopy 下载免费PDF全文
Ya‐Hao Wang Miao‐Miao Liang Yue‐Jiao Zhang Shu Chen Petar Radjenovic Dr. Hua Zhang Prof. Zhi‐Lin Yang Prof. Xiao‐Shun Zhou Prof. Zhong‐Qun Tian Prof. Jian‐Feng Li 《Angewandte Chemie (International ed. in English)》2018,57(35):11257-11261
Heterogeneous metal interfaces play a key role in determining the mechanism and performance of catalysts. However, in situ characterization of such interfaces at the molecular level is challenging. Herein, two model interfaces, Pd and Pt overlayers on Au single crystals, were constructed. The electronic structures of these interfaces as well as effects of crystallographic orientation on them were analyzed by shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS) using phenyl isocyanide (PIC) as a probe molecule. A clear red shift in the frequency of the C≡N stretch (νNC) was observed, which is consistent with X‐ray photoelectron spectroscopy (XPS) data and indicates that the ultrathin Pt and Pd layers donate their free electrons to the Au substrates. Furthermore, in situ electrochemical SHINERS studies showed that the electronic effects weaken Pt?C/Pd?C bonds, leading to improved surface activity towards CO electrooxidation. 相似文献
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Prof. Dr. Suning Wang Deng‐Tao Yang Jiasheng Lu Hiroyuki Shimogawa Prof. Dr. Shaolong Gong Xiang Wang Soren K. Mellerup Prof. Dr. Atsushi Wakamiya Dr. Yi‐Lu Chang Prof. Dr. Chuluo Yang Prof. Dr. Zheng‐Hong Lu 《Angewandte Chemie (International ed. in English)》2015,54(50):15074-15078
New BN‐heterocyclic compounds have been found to undergo double arene photoelimination, forming rare yellow fluorescent BN‐pyrenes that contain two B? N units. Most significant is the discovery that the double arene elimination can also be driven by excitons generated electrically within electroluminescent (EL) devices, enabling the in situ solid‐state conversion of BN‐heterocycles to BN‐pyrenes and the use of BN‐pyrenes as emitters for EL devices. The in situ exciton‐driven elimination (EDE) phenomenon has also been observed for other BN‐heterocycles. 相似文献
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João Medeiros‐Silva Deni Mance Mark Daniëls Shehrazade Jekhmane Dr. Klaartje Houben Prof. Marc Baldus Dr. Markus Weingarth 《Angewandte Chemie (International ed. in English)》2016,55(43):13606-13610
1H detection can significantly improve solid‐state NMR spectral sensitivity and thereby allows studying more complex proteins. However, the common prerequisite for 1H detection is the introduction of exchangeable protons in otherwise deuterated proteins, which has thus far significantly hampered studies of partly water‐inaccessible proteins, such as membrane proteins. Herein, we present an approach that enables high‐resolution 1H‐detected solid‐state NMR (ssNMR) studies of water‐inaccessible proteins, and that even works in highly complex environments such as cellular surfaces. In particular, the method was applied to study the K+ channel KcsA in liposomes and in situ in native bacterial cell membranes. We used our data for a dynamic analysis, and we show that the selectivity filter, which is responsible for ion conduction and highly conserved in K+ channels, undergoes pronounced molecular motion. We expect this approach to open new avenues for biomolecular ssNMR. 相似文献
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Chensheng Ma Dr. Wai Ming Kwok Dr. Hui‐Ying An Xiangguo Guan Dr. Michael Yunyi Fu Patrick H. Toy Dr. David Lee Phillips Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(17):5102-5118
3′,5′‐Dimethoxybenzoin (DMB) is a bichromophoric system that has widespread application as a highly efficient photoremovable protecting group (PRPG) for the release of diverse functional groups. The photodeprotection of DMB phototriggers is remarkably clean, and is accompanied by the formation of a biologically benign cyclization product, 3′,5′‐dimethoxybenzofuran (DMBF). The underlying mechanism of the DMB deprotection and cyclization has, however, until now remained unclear. Femtosecond transient absorption (fs‐TA) spectroscopy and nanosecond time‐resolved resonance Raman (ns‐TR3) spectroscopy were employed to detect the transient species directly, and examine the dynamic transformations involved in the primary photoreactions for DMB diethyl phosphate (DMBDP) in acetonitrile (CH3CN). To assess the electronic character and the role played by the individual sub‐chromophore, that is, the benzoyl, and the di‐meta‐methoxybenzylic moieties, for the DMBDP deprotection, comparative fs‐TA measurements were also carried out for the reference compounds diethyl phosphate acetophenone (DPAP), and 3′,5′‐dimethoxybenzylic diethyl phosphate (DMBnDP) in the same solvent. Comparison of the fs‐TA spectra reveals that the photoexcited DMBDP exhibits distinctly different spectral character and dynamic evolution from those of the reference compounds. This fact, combined with the related steady‐state spectral and density functional theoretical results, strongly suggests the presence in DMBDP of a significant interaction between the two sub‐chromophores, and that this interaction plays a governing role in determining the nature of the photoexcitation and the reaction channel of the subsequent photophysical and photochemical transformations. The ns‐TR3 results and their correlation with the fs‐TA spectra and dynamics provide evidence for a novel concerted deprotection–cyclization mechanism for DMBDP in CH3CN. By monitoring the direct generation of the transient DMBF product, the cyclization time constant was determined unequivocally to be ≈1 ns. This indicates that there is little relevance for the long‐lived intermediates (>10 ns) in giving the DMBF product, and excludes the stepwise mechanism proposed in the literature as the major pathway for the DMB cyclization reaction. This work provides important new insights into the origin of the 3′,5′‐dimethoxy substitution effect for the DMB photodeprotection. It also helps to clarify the many different views presented in previous mechanistic studies of the DMB PRPGs. In addition to this, our fs‐TA results on the reference compound DMBnDP in CH3CN provide the first direct observation (to the best of our knowledge) showing the predominance of a prompt (≈2 ps) heterolytic bond cleavage after photoexcitation of meta‐methoxybenzylic compounds. This provides insight into the long‐term controversies about the photoinitiated dissociation mode of related substituted benzylic compounds. 相似文献
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SERS you right: The plasmon heating of gold nanoshells is exploited to yield the local conversion of amorphous TiO2 into anatase on the surface of polymeric colloidal crystals (see scheme). The resulting Au/TiO2 spots are active substrates for surface‐enhanced Raman spectroscopy and allow surface reactions and processes to be followed directly on‐site.
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Bobby Happ Dr. Georges M. Pavlov Esra Altuntas Christian Friebe Dr. Martin D. Hager Dr. Andreas Winter Dr. Helmar Görls Dr. Wolfgang Günther Prof. Dr. Ulrich S. Schubert 《化学:亚洲杂志》2011,6(3):873-880
Two 3,6‐bis(R‐1H‐1,2,3‐triazol‐4‐yl)pyridazines (R=mesityl, monodisperse (CH2 CH2O)12CH3) were synthesized by the copper(I)‐catalyzed azide–alkyne cycloaddition and self‐assembled with tetrakis(acetonitrile)copper(I) hexafluorophosphate and silver(I) hexafluoroantimonate in dichloromethane. The obtained copper(I) complexes were characterized in detail by time‐dependent 1D [1H, 13C] and 2D [1H‐NOESY] NMR spectroscopy, elemental analysis, high‐resolution ESI‐TOF mass spectrometry, and analytical ultracentrifugation. The latter characterization methods, as well as the comparison to analog 3,6‐di(2‐pyridyl)pyridazine (dppn) systems and their corresponding copper(I) and silver(I) complexes indicated that the herein described 3,6‐bis(1H‐1,2,3‐triazol‐4‐yl)pyridazine ligands form [2×2] supramolecular grids. However, in the case of the 3,6‐bis(1‐mesityl‐1H‐1,2,3‐triazol‐4‐yl)pyridazine ligand, the resultant red‐colored copper(I) complex turned out to be metastable in an acetone solution. This behavior in solution was studied by NMR spectroscopy, and it led to the conclusion that the copper(I) complex transforms irreversibly into at least one different metal complex species. 相似文献
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Reversible Single‐Crystal‐to‐Single‐Crystal Photochemical Formation and Thermal Cleavage of a Cyclobutane Ring 下载免费PDF全文
Prof. Dr. Masaki Kawano Prof. Dr. Jagadese J. Vittal 《Angewandte Chemie (International ed. in English)》2014,53(8):2143-2146
A [2+2] cycloaddition reaction has been observed in a number of solids. The cyclobutane ring in a photodimerized material can be cleaved into olefins by UV light and heat. The high thermal stability of the metal–organic salt K2SDC (H2SDC=4,4’‐stilbenedicarboxylic acid) has been successfully utilized to investigate the reversible cleavage of a cyclobutane ring. The two polymorphs of K2SDC undergo reversible cyclobutane formation by UV light and cleavage by heat in cycles. Of these, one polymorph retains its single‐crystal nature during the reversible processes. Polymorphs are known to show different physical properties and chemical reactivities. This work reveals that the retention of single‐crystal nature is strongly associated with the packing of molecules, which is controlled by kinetics and thermodynamics. The photoemissive nature of the products makes this as a promising material for photoswitches and optical data storage devices. 相似文献
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Theoretical Vibrational Raman and Surface‐Enhanced Raman Scattering Spectra of Water Interacting with Silver Clusters 下载免费PDF全文
Marta Sanchéz‐Lozano Marcos Mandado Ignacio Pérez‐Juste Dr. Jose M. Hermida‐Ramón 《Chemphyschem》2014,15(18):4067-4076
In this study, we analyzed the Raman spectrum of a water molecule adsorbed on a cluster of 20 silver atoms, and the plasmonic electromagnetic effect of the silver surface was also considered to give a theoretical prediction of the surface‐enhanced Raman scattering spectrum. The calculations were performed at the density functional theory (DFT) level by using both frozen and unfrozen silver clusters. Two different models were used to consider the plasmonic enhancement; one of them was a modified classical (dipole) model and the other was the coupled perturbed Hartree–Fock method with excitation frequencies obtained from time‐dependent DFT calculations and with proper detuning of these frequencies. The importance of small geometrical distortions of the silver surface in the orientation of the adsorbed water was shown. Moreover, it was shown how the symmetry of the transition dipole moment and the symmetry of the vibrational modes influence the Raman intensities of the SERS spectrum. 相似文献