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41.
Philippe Gerbier Daniel Ruiz-Molina Neus Domingo David B. Amabilino José Vidal-Gancedo Javier Tejada David N. Hendrickson Jaume Veciana 《Monatshefte für Chemie / Chemical Monthly》2003,134(2):265-276
Summary. A new modified approach for the synthesis of Mn12 clusters, based on the use of complex [Mn12O12(O2C
t
Bu)16(H2O)4] (2) as starting material to promote the acidic ligand replacement, is presented here. This new synthetic approach allowed us
to obtain complex [Mn12O12(O2CC6H4N(O•)
t
Bu)16(H2O)4] (3), whose preparation remained elusive by direct replacement of the acetate groups of Mn12Ac (1). Complex 3 bearing open-shell radical units, was prepared to increase the total spin number of its ground state, and consequently, to
increase T
B
, with the expectation that the radical ligands may couple ferromagnetically with the Mn12 core. Unfortunately, magnetic measurements of complex 3 revealed that the sixteen radical carboxylate ligands interact antiferromagnetically with the Mn12 core to yield a S = 2 magnetic ground state.
Corresponding author. E-mail: vecianaj@icmab.es
Received March 27, 2002; accepted May 2, 2002 相似文献
42.
43.
The reactivity of N1-alkylsulfonyl- and N1-arylsulfonyl-2′,3′,5′-tri-O-acetylinosine with benzylamine and with 15NH3, regarding the attack on C2, has been shown to be in the order CF3SO2 (Tf) > 2,4-(NO2)2C6H3SO2 (DNs) ? 4-NO2C6H4SO2 (pNs) ≈ C6F5SO2 (PFBs) > 2-NO2C6H4SO2 (Ns) ? CH3SO2 (Ms) > 4-CH3C6H4SO2 (Ts) > 2,4,6-(CH3)3C6H2SO2 (Mts). In spite of its intermediate reactivity, the Ns group is the most appropriate, since in this case the formation of by-products is minimised during the ring-opening and ring-closing steps of the process. Another advantage of the Ns group is thus disclosed. 相似文献
44.
Galanthamine, an acetylcholinesterase inhibitor marketed as a hydrobromide salt for the treatment of Alzheimer's disease, is obtained from some Amaryllidaceae plants. A new method was developed and validated for its quantification by GC-MS in different plant sources: bulbs and leaves from Narcissus confusus; bulbs from N. pseudonarcissus cv. Carlton; and leaves and in vitro cultures from L. aestivum. Samples (50 mg) were extracted with methanol (1 mL) for 2 h, then aliquots of the extracts were silylated and analyzed by GC-MS. The calibration line was linear over a range of 15-800 μg galanthamine/sample, ensuring an analysis of samples with a content of 0.03-1.54% analyte referred to dry weight. The recovery was generally more than 95%. Good inter- and intra assay precision was observed (RSD < 3%). Principal component analysis of GC-MS chromatograms allowed discrimination of the plant raw material with respect to species, organs and geographical regions. The analytical method developed in this study proved to be simple, sensitive and far more informative than the routine analytical methods (GC, HPLC, CE and NMR), so it may be useful for quality control of plant raw materials in the pharmaceutical industry. 相似文献
45.
In this work we study the centers of planar analytic vector fields which are limit of linear type centers. It is proved that all the nilpotent centers are limit of linear type centers and consequently the Poincaré-Liapunov method to find linear type centers can be also used to find the nilpotent centers. Moreover, we show that the degenerate centers which are limit of linear type centers are also detectable with the Poincaré-Liapunov method. 相似文献
46.
Jaume Haro 《International Journal of Theoretical Physics》2003,42(12):2839-2846
We apply the formal W.K.B. method in the complex plane to the quantum field theory to obtain the Schwinger formula for spin and spinless particles; i.e., we obtain the probability that the vacuum state remains unchanged in presence of a constant electric field. Finally, from Schwinger formula we calculate the probability that n pairs are produced. 相似文献
47.
Maspoch D Domingo N Ruiz-Molina D Wurst K Hernández JM Vaughan G Rovira C Lloret F Tejada J Veciana J 《Chemical communications (Cambridge, England)》2005,(40):5035-5037
A metal-organic open-framework with an unprecedented (6,3)-helical topology, large channels and mixed ferro- and antiferromagnetic interactions has been synthesized using a three-connecting tricarboxylic polychlorotriphenylmethyl radical and Co(ii) ions. 相似文献
48.
Jaume Gine Jaume Llibre Claudia Valls 《Journal of Applied Analysis & Computation》2017,7(4):1534-1548
For the polynomial differential system $\dot{x}=-y$, $\dot{y}=x +Q_n(x,y)$, where $Q_n(x,y)$ is a homogeneous polynomial of degree $n$ there are the following two conjectures done in 1999. (1) Is it true that the previous system for $n \ge 2$ has a center at the origin if and only if its vector field is symmetric about one of the coordinate axes? (2) Is it true that the origin is an isochronous center of the previous system with the exception of the linear center only if the system has even degree? We give a step forward in the direction of proving both conjectures for all $n$ even. More precisely, we prove both conjectures in the case $n = 4$ and for $n\ge 6$ even under the assumption that if the system has a center or an isochronous center at the origin, then it is symmetric with respect to one of the coordinate axes, or it has a local analytic first integral which is continuous in the parameters of the system in a neighborhood of zero in the parameters space. The case of $n$ odd was studied in [8]. 相似文献
49.
50.