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Smått JH Spliethoff B Rosenholm JB Lindén M 《Chemical communications (Cambridge, England)》2004,(19):2188-2189
Nanocrystalline cobalt oxide, Co(3)O(4), monoliths exhibiting hierarchical bimoidal porosity have been prepared by nanocasting of porous silica monoliths. 相似文献
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Robert A. Wind Jan-Henrik Ardenkjr-Larsen 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1999,141(2):347
Recently a triarylmethyl-based (TAM) radical has been developed for research in biological and other aqueous systems, and in low magnetic fields, 10 mT or less, large 1H dynamic nuclear polarization (DNP) enhancements have been reported. In this paper the DNP properties of this radical have been investigated in a considerably larger field of 1.4 T, corresponding to proton and electron Larmor frequencies of 60 MHz and 40 GHz, respectively. To avoid excessive microwave heating of the sample, an existing DNP NMR probe was modified with a screening coil, wound around the sample capillary and with its axis perpendicular to the electric component of the microwave field. It was found that with this probe the temperature increase in the sample after 4 s of microwave irradiation with an incident power of 10 W was only 16°C. For the investigations, 10 mM of the TAM radical was dissolved in deionized, but not degassed, water and put into a 1-mm i.d. and 6-mm long capillary tube. At 26°C the following results were obtained: (I) The relaxivity of the radical is 0.07 (mMs)−1, in accordance with the value extrapolated from low-field results; (II) The leakage factor is 0.63, the saturation factor at maximum power is 0.85, and the coupling factor is −0.0187. It is shown that these results agree very well with an analysis where the electron–dipolar interactions are the dominant DNP mechanism, and where the relaxation transitions resulting from these interactions are governed by translational diffusion of the water molecules. Finally, the possibilities of combining DNP with magnetic resonance microscopy (MRM) are discussed. It is shown that at 26°C the overall DNP-enhanced proton polarization should become maximal in an external field of 0.3 T and become comparable to the thermal equilibrium polarization in a field of 30 T, considerably larger than the largest high-resolution magnet available to date. It is concluded that DNP MRM in this field, which corresponds to a standard microwave frequency of 9 GHz, has the potential to significantly increase the sensitivity in NMR and MRI experiments of small aqueous samples doped with the TAM radical. 相似文献
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Dr. Anna Schwartzen Dr. Jan-Henrik Weddeling Jana Langosch Beate Neumann Dr. Hans-Georg Stammler Prof. Dr. Norbert W. Mitzel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(5):1821-1828
Tridentate Lewis acids with aligned functions were synthesized based on the rigid framework hexadehydrotribenzo[12]annulene. The backbone and its fluorinated analogue were synthesised in one-pot syntheses, with alkyne deprotection and Sonogashira cross coupling reaction being carried out in one step. Hydrosilylation of the annulene with chlorohydrosilanes proceeded highly selectively and afforded rigid poly-Lewis acids with three SiCl3 or SiCl2Me substituents perfectly oriented to one side of the molecule in a single step. The progress of hydrosilylation was investigated by time-correlated NMR spectroscopic studies. The crystal structures show that the framework is symmetrically functionalised and the silyl substituents are aligned in one direction. To increase the acidity of the Lewis acids the chlorosilyl substituents were fluorinated with SbF3. Further investigation of hydrometallation reactions (M=B, Al, Ga, Sn) did not lead to corresponding structures. 相似文献
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Dr. Andrea Capozzi M. Sc. Saket Patel M. Sc. Christine Pepke Gunnarsson Dr. Irene Marco‐Rius Dr. Arnaud Comment Dr. Magnus Karlsson Dr. Mathilde H. Lerche Dr. Olivier Ouari Prof. Jan Henrik Ardenkjær‐Larsen 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(5):1348-1353
Free radicals generated by UV‐light irradiation of a frozen solution containing a fraction of pyruvic acid (PA) have demonstrated their dissolution dynamic nuclear polarization (dDNP) potential, providing up to 30 % [1‐13C]PA liquid‐state polarization. Moreover, their labile nature has proven to pave a way to nuclear polarization storage and transport. Herein, differently from the case of PA, the issue of providing dDNP UV‐radical precursors (trimethylpyruvic acid and its methyl‐deuterated form) not involved in any metabolic pathway was investigated. The 13C dDNP performance was evaluated for hyperpolarization of [U‐13C6,1,2,3,4,5,6,6‐d7]‐d ‐glucose. The generated UV‐radicals proved to be versatile and highly efficient polarizing agents, providing, after dissolution and transfer (10 s), a 13C liquid‐state polarization of up to 32 %. 相似文献
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Difference between Extra‐ and Intracellular T1 Values of Carboxylic Acids Affects the Quantitative Analysis of Cellular Kinetics by Hyperpolarized NMR 下载免费PDF全文
Dr. Magnus Karlsson Dr. Pernille Rose Jensen Prof. Jan Henrik Ardenkjær‐Larsen Dr. Mathilde H. Lerche 《Angewandte Chemie (International ed. in English)》2016,55(43):13567-13570
Incomplete knowledge of the longitudinal relaxation time constant (T1) leads to incorrect assumptions in quantitative kinetic models of cellular systems, studied by hyperpolarized real‐time NMR. Using an assay that measures the intracellular signal of small carboxylic acids in living cells, the intracellular T1 of the carboxylic acid moiety of acetate, keto‐isocaproate, pyruvate, and butyrate was determined. The intracellular T1 is shown to be up to four‐fold shorter than the extracellular T1. Such a large difference in T1 values between the inside and the outside of the cell has significant influence on the quantification of intracellular metabolic activity. It is expected that the significantly shorter T1 value of the carboxylic moieties inside cells is a result of macromolecular crowding. An artificial cytosol has been prepared and applied to predict the T1 of other carboxylic acids. We demonstrate the value of this prediction tool. 相似文献
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Bj?rn?T?rngren Simon?Sandén Johan?O.?Nyman Armi?Tiihonen Hua?Jiang Janne?Ruokolainen Janne?Halme Ronald??sterbacka Jan-Henrik?Sm?ttEmail authorView authors OrcID profile 《Journal of nanoparticle research》2017,19(11):365
Plasmonic metal nanoparticles have shown great promise in enhancing the light absorption of organic dyes and thus improving the performance of dye-sensitized solar cells (DSSCs). However, as the plasmon resonance of spherical nanoparticles is limited to a single wavelength maximum (e.g., ~ 520 nm for Au nanoparticles), we have here utilized silica-coated gold nanorods (Au@SiO2 NRs) to improve the performance at higher wavelengths as well. By adjusting the aspect ratio of the Au@SiO2 NRs, we can shift their absorption maxima to better match the absorption spectrum of the utilized dye (here we targeted the 600–800 nm range). The main challenge in utilizing anisotropic nanoparticles in DSSCs is their deformation during the heating step required to sinter the mesoporous TiO2 photoanode and we show that the Au@SiO2 NRs start to deform already at temperatures as low as 200 °C. In order to circumvent this problem, we incorporated the Au@SiO2 NRs in a TiO2 nanoparticle suspension that does not need high sintering temperatures to produce a functional photoanode. With various characterization methods, we observed that adding the plasmonic particles also affected the structure of the produced films. Nonetheless, utilizing this low-temperature processing protocol, we were able to minimize the structural deformation of the gold nanorods and preserve their characteristic plasmon peaks. This allowed us to see a clear redshift of the maximum in the incident photon-to-current efficiency spectra of the plasmonic devices (Δλ ~ 14 nm), which further proves the great potential of utilizing Au@SiO2 NRs in DSSCs. 相似文献
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Dr. Jan-Henrik Weddeling Paul Lukas Waltersmann Beate Neumann Dr. Hans-Georg Stammler Prof. Dr. Norbert W. Mitzel 《ChemistryOpen》2021,10(10):1059-1066
Several rigid 1,3,5-tris(phenylethynyl)benzenes with different fluorination patterns were synthesized through selective Sonogashira-Hagihara coupling reactions to analyze the packing behavior in solid-state structures. The aggregation is dominated by various intermolecular interactions between aryl substituents, triple bonds, C−H bonds and H⋅⋅⋅F contacts. Co-crystallization experiments for the analysis of preferred aryl-aryl-interactions led to 1 : 1 complexes. Intermolecular phenyl-perfluorophenyl interactions with short centroid-centroid distances are dominating these co-crystal structures. They lead to melting point increases of up to 49 °C for the co-crystals compared to the pure substances. 相似文献
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