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排序方式: 共有103条查询结果,搜索用时 484 毫秒
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Angelika B. Boeer David Collison Prof. Christopher A. Muryn Dr. Grigore A. Timco Dr. Floriana Tuna Dr. Richard E. P. Winpenny Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(47):13150-13160
The synthesis and structural characterization of three heterometallic rings templated about imidazolium cations is reported. The compounds are [2,4‐DiMe‐ImidH][Cr7NiIIF8(O2CtBu)16] 1 (2,4‐DiMe‐ImidH=the cation of 2,4‐dimethylimidazole), [ImidH]2[Cr6NiII2F8(O2CCtBu)16] 2 (ImidH=the cation of imidazole), and [1‐Bz‐ImidH]2 [Cr7NiII2F9(O2CtBu)18] 3 (1‐Bz‐ImidH=the cation of 1‐benzylimidazole). The structures show the formation of octagonal arrays of metals for 1 and 2 and a nonagon of metal centers for 3 . In all cases the edges of the polygon are bridged by a single fluoride and two pivalate ligands, and the position of the divalent metal centers cannot be distinguished by X‐ray diffraction. Magnetic studies combined with EPR spectroscopy allow the characterization of the magnetic states of the compounds. In each case the exchange is antiferromagnetic with a magnetic exchange parameter J≈?5.8 cm?1, and it is not possible to differentiate the exchange between two CrIII centers (JCrCr) from the exchange between a CrIII and a NiII center (JCrNi). For 2 there is evidence for the presence of at least two, possibly four, linkage isomers of the heterometallic ring, caused by the presence of two divalent metal centers in the ring. The EPR spectroscopy of 3 suggests an S=1/2 ground state of the ring and that it is likely that only one linkage isomer is present. 相似文献
23.
Low DM Rajaraman G Helliwell M Timco G van Slageren J Sessoli R Ochsenbein ST Bircher R Dobe C Waldmann O Güdel HU Adams MA Ruiz E Alvarez S McInnes EJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(5):1385-1396
The synthesis and crystal structures of a family of decametallic Cr(III) "molecular wheels" are reported, namely [Cr10(OR)20(O2CR')10] [R' = Me, R = Me (1), Et (2); R' = Et, R = Me (3), Et (4); R' = CMe3, R = Me (5), Et (6)]. Magnetic studies on 1-6 reveal a remarkable dependence of the magnetic behaviour on the nature of R. In each pair of complexes with a common carboxylate (R') the nearest neighbour CrCr magnetic exchange coupling is more antiferromagnetic for the ethoxide-bridged (R = Et) cluster than for the methoxide analogue. In complexes 2, 4 and 6 the overall coupling is weakly antiferromagnetic resulting in diamagnetic (S = 0) ground states for the cluster, whilst in 1 and 5 it is weakly ferromagnetic thus resulting in very high-spin ground states. This ground state has been probed directly in the perdeuterated version of 1 ([D]1) by inelastic neutron scattering experiments, and these support the S = 15 ground state expected for ferromagnetic coupling of ten Cr(III) ions, and they also indicate that a single J-value model is inadequate. The ground state of 5 is large but not well defined. The trends in J on changing R are further supported by density functional calculations on 1-6, which are in excellent agreement with experiment. The very large changes in the nature of the ground state between 1 and 2, and 5 and 6 are the result of relatively small changes in J that happen to cross J = 0, hence changing the sign of J. 相似文献
24.
Magdalena Lungu Ştefania Gavriliu Elena Enescu Ioana Ion Alexandra Brătulescu Grigore Mihăescu Luminiţa Măruţescu Mariana Carmen Chifiriuc 《Journal of nanoparticle research》2014,16(1):1-15
Recent studies have revealed the existence of liver cancer stem cells (CSCs). Therefore, there is an urgent need for new and effective treatment strategies specific to liver CSCs. In this work, the poly(d,l-lactide-coglycolide) nanoparticles containing paclitaxel were prepared by emulsification-solvent evaporation method. The nanoparticles decorated with anti-CD133 antibody, termed targeted nanoparticles, were prepared by carbodiimide chemistry for liver CSCs. The physicochemical characteristics of the nanoparticles (i.e., encapsulation efficiency, particle size distribution, morphology, and in vitro release) were investigated. Cellular uptake and accumulation in tumor tissue of nanoparticles were observed. To assess anti-tumor activity of nanoparticles in vitro and in vivo, cell survival assay and tumor regression study were carried out using liver cancer cell lines (Huh7 and HepG2) and their xenografts. Particle size of targeted nanoparticles was 429.26 ± 41.53 nm with zeta potential of ?11.2 mV. Targeted nanoparticles possessed spherical morphology and high encapsulation efficiency (87.53 ± 5.9 %). The accumulation of targeted nanoparticles depends on dual effects of passive and active targeting. Drug-loaded nanoparticles showed cytotoxicity on the tumor cells in vitro and in vivo. Targeted nanoparticles resulted in significant improvement in therapeutic response through selectively eliminating CD133 positive subpopulation. These results suggested that the novel nanoparticles could be a promising candidate with excellent therapeutic efficacy for targeting liver CSCs. 相似文献
25.
This paper proposes a novel method for generating continuum spectra with possible applications in WDM access networks. This new method would allow the development of a simple continuum laser structure with better performances in terms of cost and simplicity than those of present supercontinuum sources. In this aim, we will analyze the possibility to broaden the resonant modes of a Fabry–Perot cavity by operating only on the design of one of the cavity's Bragg mirrors. Firstly we considered the conditions which a Bragg grating must satisfy in order to broaden the resonant modes of a resonant cavity. Because an exact solution is not physical possible, the genetic algorithm is the best available tool for the design of such a grating. An active medium is then added inside the cavity and its behavior below threshold is simulated. The spectra thus simulated are continuum over 5–15 nm. 相似文献
26.
Maria Mernea Octavian Calborean Oana Grigore Traian Dascalu Dan Florin Mihailescu 《Optical and Quantum Electronics》2014,46(4):505-514
Terahertz (THz) spectroscopy is a promising technique for the study of protein structure and internal flexibility. Here, we used THz spectroscopy and molecular modeling for bovine serum albumin (BSA) structure investigation. BSA molecule was built using homology modeling methods and 30 different more relaxed models were obtained by molecular dynamics simulations of the hydrated protein. As the experimental and simulated THz spectra are linear, we compared them by comparing the slopes of the lines that fit them. Six BSA structures had slope values in the range given by the slope of the experimental spectrum $\pm $ 0.2 and a total of sixteen BSA structures had slope values in the 0.6 interval near the experimental slope value. BSA average structures were calculated over the six and the sixteen identified BSA molecules. Based on the similarity with the crystal structure of BSA, we validated the average structure calculated over the sixteen BSA conformations. The comparison with the crystal structure showed that the structure validated using THz spectroscopy is a coarse model of BSA, as its root-mean-square deviation relative to the crystal structure is 1.9 Å. The regions from our model that present the highest deviation from the crystal structure are exterior loops. The results presented here show that using THz spectroscopy and molecular modeling is a promising approach to determine the structure of proteins. 相似文献
27.
Nicoleta Simona Vedeanu Dana Alina Magdas Laura Bolojan Grigore Damian 《Chemical Papers》2012,66(6):612-616
Antioxidant status of foods, plant, or fruit products is generally characterized by means of spectroscopic methods. Methods
like HPLC, UV-VIS, or MS spectroscopy are used to understand the chemical and physical properties of different samples, and
also EPR spectroscopy seems to be a valuable tool to characterize antioxidant activity of juice beverages. In this technique,
certain antioxidants present in fruit juices interact with free radicals interrupting the chain reaction that can possibly
damage essential molecules. Recording the EPR signal decay caused by the reaction with a natural or artificial reducing agent,
it is possible to draw conclusions about the antioxidant capability of materials. IRMS is a powerful tool to distinguish between
an authentic fruit juice and a juice obtained by concentrate dilution. This technique allows also the detection of commercial
C4 cane or corn derived sugar syrups in C3 fruit juices. In the present study, four commercial fruit juices were investigated using stable isotope measurements (oxygen,
hydrogen, and carbon) and EPR measurements in order to check the correct labeling in the Romanian markets and to compare antioxidant
activity of the studied juices and the reference. It was proven that the number of paramagnetic species decreases in time
with different reaction rates and this was correlated with the antioxidant activity of the studied juices. Stable isotope
ratio measurements have demonstrated that the fruit juices studied were reconstructed from concentrates with tap water, according
to their label. 相似文献
28.
We analyse some quantum multiplets associated with extended supersymmetries. We study in detail the general form of the causal (anti)commutation relations. The condition of positivity of the scalar product imposes severe restrictions on the (quantum) model. It is problematic if one can find out quantum extensions of the standard model with extended supersymmetries. 相似文献
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30.
Hybrid Organic–Inorganic Rotaxanes,Including a Hetero‐Hybrid [3]Rotaxane Featuring Two Distinct Heterometallic Rings and a Molecular Shuttle
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Dr. Grigore A. Timco Dr. Antonio Fernandez Andreas K. Kostopoulos Jodie F. Charlton Selena J. Lockyer Thomas R. Hailes Dr. Ralph W. Adams Prof. Eric J. L. McInnes Dr. Floriana Tuna Dr. Inigo J. Vitorica‐Yrezabal Dr. George F. S. Whitehead Prof. Richard E. P. Winpenny 《Angewandte Chemie (International ed. in English)》2018,57(34):10919-10922
[2] and [3] hybrid rotaxanes are reported based on {Ti7M} rings (M is a trivalent metal such as FeIII or GaIII). NMR studies show that [2]rotaxanes can act as molecular shuttles, while EPR studies of [3]rotaxanes show weak interactions between the paramagnetic components of the supramolecular assemblies. 相似文献