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31.
Electrical microstimulation via intracortical electrodes is a widely used method for deducing functions of the brain. In this study, we compared the spatial extent and amplitude of BOLD responses evoked by intracortical electrical stimulation in primary visual cortex with BOLD activations evoked by visual stimulation. The experiments were performed in anesthetized rhesus monkeys. Visual stimulation yielded activities larger than predicted from the well-established visual magnification factor. However, electrical microstimulation yielded an even greater spread of the BOLD response. Our results confirm that the effects of electrical microstimulation extend beyond the brain region expected to be excited by direct current spread. 相似文献
32.
A New Approach for the Photosynthetic Antenna–Reaction Center Complex with a Model Organized Around an s‐Triazine Linker 下载免费PDF全文
Susanne Kuhri Dr. Georgios Charalambidis Prof. Panagiotis A. Angaridis Prof. Theodore Lazarides Dr. Georgia Pagona Dr. Nikos Tagmatarchis Prof. Dr. Athanassios G. Coutsolelos Prof. Dr. Dirk M. Guldi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(7):2049-2057
Two new artificial mimics of the photosynthetic antenna‐reaction center complex have been designed and synthesized (BDP‐H2P‐C60 and BDP‐ZnP‐C60). The resulting electron‐donor/acceptor conjugates contain a porphyrin (either in its free‐base form (H2P) or as Zn‐metalated complex (ZnP)), a boron dipyrrin (BDP), and a fulleropyrrolidine possessing, as substituent of the pyrrolidine nitrogen, an ethylene glycol chain terminating in an amino group C60‐X‐NH2 (X=spacer). In both cases, the three different components were connected by s‐triazine through stepwise substitution reactions of cyanuric chloride. In addition to the facile synthesis, the star‐type arrangement of the three photo‐ and redox‐active components around the central s‐triazine unit permits direct interaction between one another, in contrast to reported examples in which the three components are arranged in a linear fashion. The energy‐ and electron‐transfer properties of the resulting electron‐donor/acceptor conjugates were investigated by using UV/Vis absorption and emission spectroscopy, cyclic voltammetry, and femtosecond transient absorption spectroscopy. Comparison of the absorption spectra and cyclic voltammograms of BDP‐H2P‐C60 and BDP‐ZnP‐C60 with those of BDP‐H2P, BDP‐ZnP and BDP‐C60, which were used as references, showed that the spectroscopic and electrochemical properties of the individual constituents are basically retained, although some appreciable shifts in terms of absorption indicate some interactions in the ground state. Fluorescence lifetime measurements and transient absorption experiments helped to elucidate the antenna function of BDP, which upon selective excitation undergoes a rapid and efficient energy transfer from BDP to H2P or ZnP. This is then followed by an electron transfer to C60, yielding the formation of the singlet charge‐separated states, namely BDP‐H2P .+‐ C60 .? and BDP‐ZnP .+‐ C60 . ?. As such, the sequence of energy transfer and electron transfer in the present models mimics the events of natural photosynthesis. 相似文献
33.
Kinetic Modeling of α‐Hydrogen Abstractions from Unsaturated and Saturated Oxygenate Compounds by Carbon‐Centered Radicals 下载免费PDF全文
Paschalis D. Paraskevas Dr. Maarten K. Sabbe Prof. Marie‐Françoise Reyniers Prof. Dr. Nikos Papayannakos Prof. Dr. Guy B. Marin 《Chemphyschem》2014,15(9):1849-1866
Hydrogen abstractions are important elementary reactions in a variety of reacting media at high temperatures in which oxygenates and hydrocarbon radicals are present. Accurate kinetic data are obtained from CBS‐QB3 ab initio (AI) calculations by using conventional transition‐state theory within the high‐pressure limit, including corrections for hindered rotation and tunneling. From the obtained results, a group‐additive (GA) model is developed that allows the Arrhenius parameters and rate coefficients for abstraction of the α‐hydrogen from a wide range of oxygenate compounds to be predicted at temperatures ranging from 300 to 1500 K. From a training set of 60 hydrogen abstractions from oxygenates by carbon‐centered radicals, 15 GA values (ΔGAVos) are obtained for both the forward and reverse reactions. Among them, four ΔGAVos refer to primary contributions, and the remaining 11 ΔGAVos refer to secondary ones. The accuracy of the model is further improved by introducing seven corrections for cross‐resonance stabilization of the transition state from an additional set of 43 reactions. The determined ΔGAVos are validated upon a test set of AI data for 17 reactions. The mean absolute deviation of the pre‐exponential factors (log A) and activation energies (Ea) for the forward reaction at 300 K are 0.238 log(m3 mol?1 s?1) and 1.5 kJ mol?1, respectively, whereas the mean factor of deviation <ρ> between the GA‐predicted and the AI‐calculated rate coefficients is 1.6. In comparison with a compilation of 33 experimental rate coefficients, the <ρ> between the GA‐predicted values and these experimental values is only 2.2. Hence, the constructed GA model can be reliably used in the prediction of the kinetics of α‐hydrogen‐abstraction reactions between a broad range of oxygenates and oxygenate radicals. 相似文献
34.
D. Thao Nguyen Matthias Freitag Christian Gutheil Dr. Kai Sotthewes Dr. Bonnie J. Tyler Dr. Marcus Böckmann Mowpriya Das Friederike Schlüter Prof. Dr. Nikos L. Doltsinis Prof. Dr. Heinrich F. Arlinghaus Prof. Dr. Bart Jan Ravoo Prof. Dr. Frank Glorius 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(32):13754-13759
35.
36.
Ruben Canton‐Vitoria Tobias Scharl Anastasios Stergiou Alejandro Cadranel Raul Arenal Dirk M. Guldi Nikos Tagmatarchis 《Angewandte Chemie (International ed. in English)》2020,59(10):3976-3981
Molybdenum disulfide nanosheets covalently modified with porphyrin were prepared and fully characterized. Neither the porphyrin absorption nor its fluorescence was notably affected by covalent linkage to MoS2. The use of transient absorption spectroscopy showed that a complex ping‐pong energy‐transfer mechanism, namely from the porphyrin to MoS2 and back to the porphyrin, operated. This study reveals the potential of transition‐metal dichalcogenides in photosensitization processes. 相似文献
37.
D. Thao Nguyen Matthias Freitag Christian Gutheil Kai Sotthewes Bonnie J. Tyler Marcus Bckmann Mowpriya Das Friederike Schlüter Nikos L. Doltsinis Heinrich F. Arlinghaus Bart Jan Ravoo Frank Glorius 《Angewandte Chemie (International ed. in English)》2020,59(32):13651-13656
A novel photoresponsive and fully conjugated N‐heterocyclic carbene (NHC) has been synthesized that combines the excellent photophysical properties of arylazopyrazoles (AAPs) with an NHC that acts as a robust surface anchor (AAP‐BIMe). The formation of self‐assembled monolayers (SAMs) on gold was proven by ToF‐SIMS and XPS, and the organic film displayed a very high stability at elevated temperatures. This stability was also reflected in a high desorption energy, which was determined by temperature‐programmed SIMS measurements. E‐/Z‐AAP‐BIMe@Au photoisomerization resulted in reversible alterations of the surface energy (i.e. wettability), the surface potential (i.e. work function), and the conductance (i.e. resistance). The effects could be explained by the difference in the dipole moment of the isomers. Furthermore, sequential application of a dummy ligand by microcontact printing and subsequent backfilling with AAP‐BIMe allowed its patterning on gold. To the best of our knowledge, this is the first example of a photoswitchable NHC on a gold surface. These properties of AAP‐BIMe@Au illustrate its suitability as a molecular switch for electronic devices. 相似文献
38.
Georgakilas V Tagmatarchis N Pantarotto D Bianco A Briand JP Prato M 《Chemical communications (Cambridge, England)》2002,(24):3050-3051
High solubility of SWNTs and MWNTs in water is obtained by organic functionalisation; derivatisation with N-protected glycine is also easily achieved. 相似文献
39.
Tagmatarchis N Georgakilas V Prato M Shinohara H 《Chemical communications (Cambridge, England)》2002,(18):2010-2011
Electrophilic addition of chloroform to SWNTs followed by hydrolysis resulted in the addition of hydroxy groups to the surface of the nanotubes; further esterification with propionyl chloride led to the corresponding ester derivatives, which allowed us to identify their structure, also providing better solubility in organic solvents. 相似文献
40.
Nikos K. Kalfoglou 《Journal of Polymer Science.Polymer Physics》1982,20(7):1259-1267
The compatibility of poly(ethylene oxide)–poly(vinyl acetate) (PEO-PVA) blends was examined at five compositions covering the complete range. Samples were prepared by coprecipitation and solution casting. Dynamic mechanical properties were studied at 110 Hz between ?120 and 65°C for dry, quenched, and annealed samples. The study also included tensile testing at 25°C, examination of blend morphology, and DSC measurements at elevated temperatures. Optical microscopy revealed that crystallization of PEO proceeds essentially unhindered at up to 25% poly(vinyl acetate) content by weight. Higher levels of this component drastically reduce spherulite size, and at the highest PVA compositions there was no evidence of crystallization. Thermomechanical spectra of quenched and annealed samples indicate limited mixing of the two components except for the higher (>75%) PVA compositions. Tensile properties show a mutual reinforcement at 10-25% PVA content due to possible polymer segment association. The melting-point depression of PEO is significant above 25% PVA and has been attributed to morphological changes of the PEO crystalline phase. 相似文献