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991.
Ute Wild Petra Walter Dr. Olaf Hübner Dr. Elisabeth Kaifer Prof. Hans-Jörg Himmel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(69):16504-16513
Proton-coupled electron transfer (PCET) is currently intensively studied because of its importance in synthetic chemistry and biology. In recent years it was shown that redox-active guanidines are capable PCET reagents for the selective oxidation of organic molecules. In this work, the scope of their PCET reactivity regarding reactions that involve C−H activation is explored and kinetic studies carried out to disclose the reaction mechanisms. Organic molecules with potential up to 1.2 V vs. ferrocenium/ferrocene are efficiently oxidized. Reactions are initiated by electron transfer, followed by slow proton transfer from an electron-transfer equilibrium. 相似文献
992.
Dr. Christos Apostolidis Prof. Attila Kovács Dr. Olaf Walter Dr. Eric Colineau Dr. Jean-Christophe Griveau Dr. Alfred Morgenstern Dr. Jean Rebizant Prof. Roberto Caciuffo Prof. Dr. Petra J. Panak Dr. Thomas Rabung Dr. Bernd Schimmelpfennig Dr. Mauro Perfetti 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(49):11293-11306
The isostructural compounds of the trivalent actinides uranium, neptunium, plutonium, americium, and curium with the hydridotris(1-pyrazolyl)borato (Tp) ligand An[η3-HB(N2C3H3)3]3 (AnTp3) have been obtained through several synthetic routes. Structural, spectroscopic (absorption, infrared, laser fluorescence) and magnetic characterisation of the compounds were performed in combination with crystal field, density functional theory (DFT) and relativistic multiconfigurational calculations. The covalent bonding interactions were analysed in terms of the natural bond orbital (NBO) and quantum theory of atoms in molecules (QTAIM) models. 相似文献
993.
Petra Sázelová Dušan Koval Lukáš Severa Filip Teplý Gyula Vigh Václav Kašička 《Electrophoresis》2020,41(7-8):523-535
In this study, the apparent binding constants and limiting mobilities of the multiply charged complexes of the Δ− and Λ−enantiomers of Ru(II)- and Fe(II)-polypyridyl associates ([Ru(2,2′-bipyridine)3]2+, [Ru(1,10-phenanthroline)3]2+, and [Fe(1,10-phenanthroline)3]2+) with single-isomer 2,3-diacetylated-6-sulfated-cyclodextrins (CDs) (12Ac-6S-α-CD, 14Ac-7S-β-CD, and 16Ac-8S-γ-CD) were determined by ACE using uncorrected and ionic strength corrected actual mobilities of the species involved. Two limiting models were tested for the ionic strength correction of the actual mobilities based on an empirical relation for the ionic strength correction of multivalent ionic species. In model 1, the nominal values of the charge numbers (zS,nom) and analytical concentrations (cS,nom) of the above CD selectors in the BGEs were applied for calculation of the BGE ionic strength, as usual. In model 2, the CD selectors were considered as singly charged species (zS = −1) with |zS,nom|-times higher concentrations in the BGE than their analytical concentrations (cS = |zS,nom| × cS,nom) in the calculation of the BGE ionic strength. In all three cases–with uncorrected actual mobilities as well as with actual mobilities corrected according to the two limiting models–the measured effective mobilities of the above enantiomers fit well the theoretical curves of their mobility dependences on the CD selectors concentrations in the BGE, with high average coefficients of determination (R2 = 0.9890–0.9995). Nevertheless, the best physico-chemically meaningful values of the apparent binding constants and the limiting mobilities of the enantiomer-CDs complexes with low RSDs were obtained using the actual mobilities of the species involved corrected according to model 2. 相似文献
994.
Dr. Kristina A. Ganzinger Adrián Merino-Salomón Dr. Daniela A. García-Soriano A. Nelson Butterfield Thomas Litschel Dr. Frank Siedler Prof. Dr. Petra Schwille 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(48):21556-21560
The geometry of reaction compartments can affect the local outcome of interface-restricted reactions. Giant unilamellar vesicles (GUVs) are commonly used to generate cell-sized, membrane-bound reaction compartments, which are, however, always spherical. Herein, we report the development of a microfluidic chip to trap and reversibly deform GUVs into cigar-like shapes. When trapping and elongating GUVs that contain the primary protein of the bacterial Z ring, FtsZ, we find that membrane-bound FtsZ filaments align preferentially with the short GUV axis. When GUVs are released from this confinement and membrane tension is relaxed, FtsZ reorganizes reversibly from filaments into dynamic rings that stabilize membrane protrusions; a process that allows reversible GUV deformation. We conclude that microfluidic traps are useful for manipulating both geometry and tension of GUVs, and for investigating how both affect the outcome of spatially-sensitive reactions inside them, such as that of protein self-organization. 相似文献
995.
Tobias Gruber Wilhelm Seichter Petra Bombicz Ingeborg Csöregh 《Supramolecular chemistry》2013,25(6):537-547
An upper-rim dinitro-substituted calix[4]arene possessing two lower-rim ethyl ester pendant groups (1) has been shown to form solid inclusion compounds with acetone (1:1) (1a), DMF (1:1) (1b), DMSO (1:1) (1c) and n-BuOH (2:1) (1d). X-ray crystal structures of the four complexes 1a–d are reported and comparatively discussed, including isostructurality calculations. Although the solid-state conformation of the dinitrocalix[4]arene moiety, stabilized by two intramolecular O–H…O bonds, is maintained in the four inclusion compounds, and all four co-crystals have similar unit cell dimensions and identical space group symmetries, only three of them (1a–c) are homostructural. Depending on the nature of the guest molecule, either the upper or the lower rim site of the calixarene is involved in the complexation, demonstrating either cavitate- or clathrate-type of supramolecular interactions, respectively. Moreover, due to the different guest recognition modes, the calixarene host in 1d is rotated through a non-crystallographic virtual rotation of 180° within the unit cell, in relation to the host molecules in each of the other three homostructural compounds 1a–c, thus giving rise to supramolecular morphotropism – to our knowledge the first case ever described. 相似文献
996.
Jan Večeřa Žaneta Dohnalová Petr Mikulášek Petra Šulcová 《Journal of Thermal Analysis and Calorimetry》2013,113(1):61-67
Synthesis of rutile pigments is based on solid state reaction and on Hedvall effect, i.e., phase transformation from anatase to rutile. Therefore, it is important to know the thermal behavior of these compounds (the temperature of this change). The goal was to prepare rutile pigments of type Ti1?3xCrxNb2xO2+x/2 by conventional solid state method from titanium dioxide TiO2 (AV-01, anatase), to determine an influence of composition (x = 0, 0.05, 0.10, 0.20, 0.30, 0.50) and calcination temperature (850; 900; 950; 1,000; 1,050; 1,100; 1,150 °C) on color properties of these compounds and to analyze other starting compounds of titanium (hydrated anatase paste TiO2·nH2O, titanyl sulfate dihydrate TiOSO4·2H2O (VKR 611), hydrated sodium titanium oxide paste Na2Ti4O9·nH2O) and their reaction mixtures for x = 0.05 by simultaneous TG–DTA analysis. According to the highest chroma C of color, the optimal conditions for synthesis of these pigments are concentration x = 0.05 and calcination temperature 1,050 °C and higher. It was observed that initial temperature 760–830 °C is needful for a formation of rutile structure. This temperature is the lowest for hydrated Na2Ti4O9 paste (760 °C) and similar for other starting compounds of titanium. 相似文献
997.
Monika Žaludová Bedřich Smetana Simona Zlá Jana Dobrovská Vlastimil Vodárek Kateřina Konečná Vlastimil Matějka Petra Matějková 《Journal of Thermal Analysis and Calorimetry》2013,111(2):1203-1210
The paper deals with the study of phase transformation temperatures of Fe (Fe–C–O) based metallic alloys. Six model alloys with graded carbon and oxygen content were used for experimental investigation. Low-temperature region (<1000 °C) was the investigated area. Phase transformation temperatures were obtained using Differential thermal analysis and Setaram Setsys 18TM laboratory system. Controlled heating was conducted at the rates of 2, 4, 7, 10, 15, 20 °C min?1. Region of eutectoid transformation (Feα(C) + Fe3C → Feγ(C)), alpha–gamma (Feα(C) → Feγ(C)) and transformation Feα(O) + Fe0.92O → Feγ(O) + Fe0.92O was studied. New original data (phase transformation temperatures) were obtained in this study. The relationship between shift of phase transformation temperatures and chemical composition (mainly carbon and oxygen content) is investigated in this paper. To achieve good approximation to the equilibrium conditions, the extrapolation of the obtained phase transformation temperatures to the zero heating rate was performed. The influence of experimental conditions (heating rate) on temperatures of phase transformations was studied as well. Comparison of the obtained experimental data with the data presented in the accessible literature and IDS calculations (Solidification Analysis Package) was carried out. It follows from literature search that there is a lack of thermo-physical and thermo-dynamical data on Fe–C–O system. 相似文献
998.
Dr. Matteo Calvaresi Prof. Mildred Quintana Prof. Petra Rudolf Prof. Francesco Zerbetto Prof. Maurizio Prato 《Chemphyschem》2013,14(15):3447-3453
Carbon Nanotubes, CNTs, have been described as rolled‐up graphene layers. Matching this concept to experiments has been a great experimental challenge for it requires a method to exfoliate graphite, generate ordered and stable dangling carbon bonds, and roll up the layer without affecting the unpaired electrons of the dangling bonds that finally have to zip up in an orderly fashion: A tall order for any synthetic strategy. The combined use of ultrasonication of graphite in dimethylformamide and addition of ferrocene aldehyde just does it! 相似文献
999.
Hana Sklenářová Petr Chocholouš Petra Koblová Lukáš Zahálka Dalibor Šatínský Ludmila Matysová Petr Solich 《Analytical and bioanalytical chemistry》2013,405(7):2255-2263
This work describes a comparison of three types of commercial high-performance liquid chromatography silica monolithic columns with different inner diameters and generations of monolithic sorbent: a “classic” monolithic column, the first generation (Onyx? monolithic C18, 100 mm?×?4.6 mm, Phenomenex); a “narrow” monolithic column for fast separation at lower flow rates (Chromolith® Performance RP-18e, 100 mm?×?3 mm, Merck); and a recently introduced “high-resolution” monolithic column, the next generation (Chromolith® HighResolution RP-18e, 100 mm?×?4.6 mm, Merck). Separation efficiency (number of theoretical plates, height equivalent to a theoretical plate and van Deemter curves), working pressure, the symmetry factor and resolution were critical aspects of the comparison in the case of the separation of ascorbic acid, paracetamol and caffeine. The separations were performed under isocratic conditions with a mobile phase consisting of 10:90 (v/v) acetonitrile–phosphoric acid (pH 2.80). Detailed comparison of the newest-generation monolithic column (Chromolith® HighResolution) with the previously introduced monolithic sorbents was performed and proved the advantages of the Chromolith® HighResolution column. Figure
Chromatogram of separation using different flow rates (corresponded to optimal separation conditions); 1 0.5 mL?min-1; 2 0.6 mL?min-1; 3 0.3 mL?min-1 相似文献
1000.
Julia Cuers Marian Rinken Roland Adden Petra Mischnick 《Analytical and bioanalytical chemistry》2013,405(28):9021-9032
Three hydroxypropyl methylcellulose samples (HPMC1–3, DSMe?=?1.45, 1.29, and 1.36; MSHP?=?0.28, 0.46, and 0.84) were analyzed with respect to their methyl and hydroxypropyl substitution pattern in the polymer chains. Ionization yield of HPMC oligomers in electrospray ionization ion trap mass spectrometry (ESI-IT-MS) is strongly influenced by the hydroxypropyl pattern. Therefore, a sample derivatization procedure, as well as suitable measurement conditions that enable relative quantification were elaborated. Analysis was performed by negative ESI-IT-MS after per(deutero)methylation, partial depolymerization, and reductive amination with m-aminobenzoic acid. Measurement parameters like solvent, trap drive, and voltages of the ion transportation unit were studied with regard to the suitability for quantitative evaluation. Using direct infusion of the samples, strong influence of trap drive and octopole settings was observed. Optimized measurement conditions were used for the determination of the HP pattern of the permethylated samples by direct infusion. The methyl pattern was determined from the perdeuteromethylated samples by high-performance liquid chromatography–electrospray tandem mass spectrometry. For HPMC1, substituents were both found to fit the random distribution model. The other two samples showed pronounced heterogeneity which could be interpreted in more detail by extracting methyl subpatterns depending on the number of HP groups. Figure
Determination of the substituent distribution in hydroxypropyl methylcellulose oligomers by ESI-IT-MS (negative mode) after labeling with m-aminobenzoic acid 相似文献