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51.
Kinetico‐Mechanistic Insights on the Assembling Dynamics of Allyl‐Cornered Metallacycles: The PtNpy Bond is the Keystone 下载免费PDF全文
Dr. Inmaculada Angurell Dr. Montserrat Ferrer Dr. Albert Gutiérrez Prof. Manuel Martínez Dr. Mercè Rocamora Dr. Laura Rodríguez Prof. Oriol Rossell Dipl.‐Chem. Yvonne Lorenz Dr. Marianne Engeser 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(44):14473-14487
The square‐like homo‐ and heterometallamacrocycles [{Pd(η3‐2‐Me‐C3H4)( L n )2}2{M(dppp)}2](CF3SO3)6 (dppp=1,3‐bis(diphenylphosphino)propane) and [{Pd(η3‐2‐Me‐C3H4)( L1 )2}2{M(PPh3)2}2](CF3SO3)6 [py=pyridine, M=Pd, Pt, L n =4‐PPh2py ( L1 ), 4‐C6F4PPh2py ( L2 )] containing allyl corners were synthesised by antisymbiotic self‐assembly of the different palladium and platinum metallic corners and the ambidentate N,P ligands. All the synthesised assemblies displayed a complex dynamic behaviour in solution, the rate of which is found to be dependent on the electronic and/or steric nature of the different building blocks. A kinetico‐mechanistic study by NMR line shape analysis of the dynamics of some of these assemblies was undertaken in order to determine the corresponding thermal activation parameters. Both an enhanced thermodynamic stability and slower dynamics were observed for platinum‐pyridine‐containing species when compared with their palladium analogues. Time‐dependent NMR spectroscopy in combination with ESI mass spectrometry was used to study the exchange between the assemblies and their building blocks, as well as that occurring between different metallamacrocycles. Preliminary studies were carried out on the activity of some of the metallamacrocyclic compounds as catalytic precursors in the allylic substitution reaction, and the results compared with that of the monometallic allylic corner [Pd(η3‐2‐Me‐C3H4)( L1 )2]+. 相似文献
52.
James D. Oliver Adam A. Rosser Christopher M. Fellows Yohann Guillaneuf Jean-Louis Clement Marianne Gaborieau Patrice Castignolles 《Analytica chimica acta》2014
Direct UV detection of carbohydrates in free solution capillary electrophoresis at 270 nm is made possible by a photo-oxidation reaction. Glucose, rhamnose and xylose were shown to have unique UV absorption spectra hypothesizing different UV absorbing intermediates for their respective photo-oxidation. NMR spectroscopy of the photo-oxidation end products proved they consisted of carboxylates and not malondialdehyde as previously theorized and that oxygen thus plays a key role in the photo-oxidation pathway. Adding the photo-initiator Irgacure® 2959 in the background electrolyte increased sensitivity by 40% at an optimum concentration of 1 × 10−4 mM and 1 × 10−8 mM for conventional 50 μm i.d. capillaries and for the corresponding extended light path capillaries, respectively. 相似文献
53.
Effects of Ultraviolet Radiation (UVA+UVB) and Copper on the Morphology,Ultrastructural Organization and Physiological Responses of the Red Alga Pterocladiella capillacea 下载免费PDF全文
Éder C. Schmidt Marianne Kreusch Marthiellen R. de L. Felix Debora T. Pereira Giulia B. Costa Carmen Simioni Luciane C. Ouriques Francine L. Farias‐Soares Neusa Steiner Fungyi Chow Fernanda Ramlov Marcelo Maraschin Zenilda L. Bouzon 《Photochemistry and photobiology》2015,91(2):359-370
The effect of ultraviolet (UV) radiation and copper (Cu) on apical segments of Pterocladiella capillacea was examined under two different conditions of radiation, PAR (control) and PAR+UVA+UVB (PAR+UVAB), and three copper concentrations, ranging from 0 (control) to 0.62, 1.25 and 2.50 μm . Algae were exposed in vitro to photosynthetically active radiation (PAR) at 70 μmol photons m?2 s?1, PAR + UVB at 0.35 W m?2 and PAR +UVA at 0.70 W m?2 during a 12‐h photocycle for 3 h each day for 7 days. The effects of radiation and copper on growth rates, content of photosynthetic pigments and photosynthetic performance were analyzed. In addition, samples were processed for light and transmission electron microscopy. The content of photosynthetic pigments decreased after exposure to radiation and Cu. Compared with PAR radiation and copper treatments modified the kinetics patterns of the photosynthesis/irradiance curve. The treatments also caused changes in the ultrastructure of cortical and subcortical cells, including increased cell wall thickness and accumulation of plastoglobuli, as well as changes in the organization of chloroplasts. The results indicate that the synergistic interaction between UV radiation and Cu in P. capillacea, led to the failure of protective mechanisms and causing more drastic changes and cellular imbalances. 相似文献
54.
Ley SV Abad-Somovilla A Anderson JC Ayats C Bänteli R Beckmann E Boyer A Brasca MG Brice A Broughton HB Burke BJ Cleator E Craig D Denholm AA Denton RM Durand-Reville T Gobbi LB Göbel M Gray BL Grossmann RB Gutteridge CE Hahn N Harding SL Jennens DC Jennens L Lovell PJ Lovell HJ de la Puente ML Kolb HC Koot WJ Maslen SL McCusker CF Mattes A Pape AR Pinto A Santafianos D Scott JS Smith SC Somers AQ Spilling CD Stelzer F Toogood PL Turner RM Veitch GE Wood A Zumbrunn C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(34):10683-10704
We describe in full the first synthesis of the potent insect antifeedant azadirachtin through a highly convergent approach. An O-alkylation reaction is used to unite decalin ketone and propargylic mesylate fragments, after which a Claisen rearrangement constructs the central C8-C14 bond in a stereoselective fashion. The allene which results from this sequence then enables a second critical carbon-carbon bond forming event whereby the [3.2.1] bicyclic system, present in the natural product, is generated via a 5-exo-radical cyclisation process. Finally, using knowledge gained through our early studies into the reactivity of the natural product, a series of carefully designed steps completes the synthesis of this challenging molecule. 相似文献
55.
Sadar MD Williams DE Mawji NR Patrick BO Wikanta T Chasanah E Irianto HE Soest RV Andersen RJ 《Organic letters》2008,10(21):4947-4950
The new chlorinated peptides sintokamides A to E (1-5) have been isolated from specimens of the marine sponge Dysidea sp. collected in Indonesia. Their structures were elucidated by a combination of spectroscopic and single-crystal X-ray diffraction analyses. Sintokamide A (1) is an inhibitor of N-terminus transactivation of the androgen receptor in prostate cancer cells. 相似文献
56.
Patrice Castignolles Marianne Gaborieau Emily F. Hilder Ewan Sprong Christopher J. Ferguson Robert G. Gilbert 《Macromolecular rapid communications》2006,27(1):42-46
Summary: Oligo(acrylic acid)s, produced by RAFT polymerization, have been separated and analyzed for the first time by capillary zone electrophoresis. The resolution obtained by capillary electrophoresis in borate buffers is far higher than that currently achieved using size exclusion chromatography. This work demonstrates that capillary electrophoresis is the technique of choice for the characterization of oligomers of acrylic acid and of other water‐soluble monomers involved in emulsion polymerization processes.
57.
David M. Koshy Shucheng Chen Dong Un Lee Michaela Burke Stevens Ahmed M. Abdellah Samuel M. Dull Gan Chen Dennis Nordlund Alessandro Gallo Christopher Hahn Drew C. Higgins Zhenan Bao Thomas F. Jaramillo 《Angewandte Chemie (International ed. in English)》2020,59(10):4043-4050
Ni,N‐doped carbon catalysts have shown promising catalytic performance for CO2 electroreduction (CO2R) to CO; this activity has often been attributed to the presence of nitrogen‐coordinated, single Ni atom active sites. However, experimentally confirming Ni?N bonding and correlating CO2 reduction (CO2R) activity to these species has remained a fundamental challenge. We synthesized polyacrylonitrile‐derived Ni,N‐doped carbon electrocatalysts (Ni‐PACN) with a range of pyrolysis temperatures and Ni loadings and correlated their electrochemical activity with extensive physiochemical characterization to rigorously address the origin of activity in these materials. We found that the CO2R to CO partial current density increased with increased Ni content before plateauing at 2 wt % which suggests a dispersed Ni active site. These dispersed active sites were investigated by hard and soft X‐ray spectroscopy, which revealed that pyrrolic nitrogen ligands selectively bind Ni atoms in a distorted square‐planar geometry that strongly resembles the active sites of molecular metal–porphyrin catalysts. 相似文献
58.
Minghui Zhou Marianne Lankelma Dr. Ir. Jarl Ivar van der Vlugt Prof. Dr. Bas de Bruin 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(27):11166-11172
The metalloradical activation of o-aryl aldehydes with tosylhydrazide and a cobalt(II) porphyrin catalyst produces cobalt(III)-carbene radical intermediates, providing a new and powerful strategy for the synthesis of medium-sized ring structures. Herein we make use of the intrinsic radical-type reactivity of cobalt(III)-carbene radical intermediates in the [CoII(TPP)]-catalyzed (TPP=tetraphenylporphyrin) synthesis of two types of 8-membered ring compounds; novel dibenzocyclooctenes and unprecedented monobenzocyclooctadienes. The method was successfully applied to afford a variety of 8-membered ring compounds in good yields and with excellent substituent tolerance. Density functional theory (DFT) calculations and experimental results suggest that the reactions proceed via hydrogen atom transfer from the bis-allylic/benzallylic C−H bond to the carbene radical, followed by two divergent processes for ring-closure to the two different types of 8-membered ring products. While the dibenzocyclooctenes are most likely formed by dissociation of o-quinodimethanes (o-QDMs) which undergo a non-catalyzed 8π-cyclization, DFT calculations suggest that ring-closure to the monobenzocyclooctadienes involves a radical-rebound step in the coordination sphere of cobalt. The latter mechanism implies that unprecedented enantioselective ring-closure reactions to chiral monobenzocyclooctadienes should be possible, as was confirmed for reactions mediated by a chiral cobalt-porphyrin catalyst. 相似文献
59.
The density of neutral oxygen atoms in the MESOX set-up, one device of the PROMES-CNRS solar facilities, was determined by a fiber-optics catalytic probe (FOCP). Plasma was created in a flowing air within a quartz tube with the outer diameter of 5 cm by a 2.45 GHz microwave generator with the output power up to 1000 W. The flow of air was varied between 4 and 20 l/h. The O-atom density was found to increase monotonously with the increasing discharge power, and it decreased with the increasing flow rate. The degree of dissociation of oxygen molecules in the plasma column depended largely on the flow rate. At the air flow of 4 l/h it was about 80% but it decreased to about 20% at the flow of 20 l/h. 相似文献
60.
Tinnemans SJ Kox MH Sletering MW Nijhuis TA Visser T Weckhuysen BM 《Physical chemistry chemical physics : PCCP》2006,8(20):2413-2420
In continuation of our previous work on the applicability of the G(R(infinity)) correction factor for the quantification of Raman spectra of coke during propane dehydrogenation experiments (Phys. Chem. Chem. Phys., 2005, 7, 211), research has been carried out on the potential of this correction factor for the quantification of supported metal oxides during reduction experiments. For this purpose, supported chromium oxide catalysts have been studied by combined in situ Raman and UV-Vis spectroscopy during temperature programmed reduction experiments with hydrogen as reducing agent. The goal was to quantify on-line the amount of Cr(6+) in a reactor based on the measured in situ Raman spectra. During these experiments, a significant temperature effect was observed, which has been investigated in more detail with a thermal imaging technique. The results revealed a temperature 'on the spot' that can exceed 100 degrees C. It implies that Raman spectroscopy can have a considerable effect on the local reaction conditions and explains observed inconsistencies between the in situ UV-Vis and Raman data. In order to minimize this heating effect, reduction of the laser power, mathematical matching of the spectroscopic data, a different cell design and a change in reaction conditions has been evaluated. It is demonstrated that increasing the reactor temperature is the most feasible method to solve the heating problem. Next, it allows the application of in situ Raman spectroscopy in a reliable quantitative way without the need of an internal standard. 相似文献