In the course of our program focused on the preparation of high-nitrogen content heterocyclic compounds, we wish to report an original synthesis of the tricyclic 7-azidofurazano[3,4-b]tetrazolopyrazine via an unprecedented reaction between 2,6-dimethoxy-3,5-dinitropyrazine and hydrazine hydrate. This compound was identified by an X-ray diffraction analysis. Further studies of its structure by 15N and 13C NMR spectroscopy were carried out in different solvents. This allowed us to observe a noteworthy equilibrium involving three forms resulting from the reversible opening of a tetrazole ring. 相似文献
Al together now! A new stable aluminum aminoterephthalate system contains octameric building blocks that are connected by organic linkers to form a 12‐connected net (see picture). The structure adopts a cubic centered packing motive in which octameric units replace individual atoms, thus forming distorted octahedral (red sphere) and tetrahedral cages (green spheres) with effective accessible diameters of 1 and 0.45 nm, respectively.
The reaction of the Er3+ ion with polycarboxylate ligands in gel media leads to coordination polymers exhibiting various structural types and dimensionalities. Five Er3+/1,4-benzenedicarboxylate-based coordination polymers have been obtained in such conditions. Four out of the five are new. Their crystal structures are reported and compared herein. Compound 1, namely, Er2Ter3(H2O)6, where H2Ter symbolizes the terephthalic acid, crystallizes in the space group P1 (No. 2) with a = 7.8373(10) A, b = 9.5854(2) A, c = 10.6931(2) A, alpha = 68.7770(8) degrees, beta = 70.8710(8) degrees, and gamma = 75.3330(12) degrees. It has already been reported elsewhere. The last four compounds are new. Compound 2, namely, Er2Ter3(H2O)6 x 2 H2O, crystallizes in the space group P121/a1 (No. 14) with a = 6.7429(2) A, b = 22.4913(7) A, c = 9.6575(3) A, and beta = 91.6400(18) degrees. Compound 3, namely Er2Ter3(H2O)8 x 2 H2O crystallizes in the space group P1 (No. 2) with a = 7.5391(2) A, b = 10.0533(3) A, c = 10.4578(3) A, alpha = 87.7870(10) degrees, beta = 82.5510(11) degrees, and gamma = 86.2800(16) degrees. Compound 4, namely, Er2Ter3(H2O)6 x 2 H2O crystallizes in the space group C2/c (No. 15) with a = 38.5123(13) A, b = 11.1241(4) A, c = 7.0122(2) A, and beta = 98.634(2) degrees. Compound 5, namely, Er2Ter3(H2O)6 x H2O, crystallizes in the space group P1 (No. 2) with a = 6.8776(10) A, b = 11.0420(2) A, c = 18.5675(3) A, alpha = 84.7240(6) degrees, beta = 81.8380(6) degrees, and gamma = 84.1770(8) degrees. A computational method has also been developed to evaluate the potential porosity of the coordination polymers. This method is described and then applied to the different Er2Ter3(H2O)n coordination polymers previously described. 相似文献
A new 3-D coordination polymer containing both 3d and 4f ions has been designed. Its chemical formula is La2[Cu(pba)]3(H2O)8 . 8H2O. It crystallizes in the quadratic system, space group I41/a with a = 42.4947(9) Angstrom, c = 16.3378(3) Angstrom, and Z = 16. Its crystal structure can be described as a 3-D molecular framework exhibiting a complex network of interconnected zigzaglike channels. Once crystallization water molecules are removed, this compound presents a high potential porosity and a low density. The porosity has been evaluated using Connolly's algorithm. 相似文献
The reaction of [Ln(hfac)(3) ]?2?H(2) O and pyridine-N-oxide (PyNO) leads to isostructural dimers of the formula [Ln(hfac)(3) (PyNO)](2) (Ln=Eu, Gd, Tb, Dy). The Dy derivative shows a remarkable single-molecule magnet behavior with complex hysteresis at 1.4?K. The dynamics of the magnetization features are two relaxation regimes: a thermally activated one at high temperature (τ(0) =(5.62±0.4)×10(-11) s and Δ=(167±1)?K) and a quantum tunneling regime at low temperature with a tunneling frequency of 0.42?Hz. The analysis of the Gd derivative evidences intradimer antiferromagnetic interactions (J=(-0.034±0.001)?cm(-1) ). Moreover, the Eu, Tb, and Dy derivatives are luminescent with quantum yield of 51, 53, and 0.1?%, respectively. The thermal investigation of [Dy(hfac)(3) (PyNO)](2) shows that the dimers can be sublimated intact, suggesting their possible exploit as active materials for surface-confined nanostructures to be investigated by fluorimetry methods. 相似文献
Asthma is a heterogeneous disorder and one of the most common chronic childhood diseases. An improved characterization of asthma phenotypes would be invaluable for the understanding of the pathogenic mechanisms and the correct treatment of this disease. The aim of this pilot study was to explore the potential of metabolomics applied to urine samples in characterizing asthma, and to identify the most representative metabolites. Urine samples of 41 atopic asthmatic children (further subdivided in sub-groups according to the symptoms) and 12 age-matched controls were analyzed. Untargeted metabolic profiles were collected by LC-MS, and studied by multivariate analysis. The group of the asthmatics was differentiated by a model that proved to be uncorrelated with the chronic assumption of controller drugs on the part of the patients. The distinct sub-groups were also appropriately modeled. Further investigations revealed a reduced excretion of urocanic acid, methyl-imidazoleacetic acid and a metabolite resembling the structure of an Ile-Pro fragment in the asthmatics. The meaning of these findings was discussed and mainly correlated with the modulation of immunity in asthma. Metabolic profiles from urines have revealed the potential to characterize asthma and enabled the identification of metabolites that may have a role in the underlying inflammation. 相似文献
In this paper, we consider the estimation of the extreme value index and extreme quantiles in the presence of random right
censoring. The generalization of the peaks over threshold method is discussed and an adaptation of the moment estimator is
proposed. The corresponding extreme quantile estimators are also introduced. We make a start with the analysis of the asymptotic
properties of the moment estimator and the corresponding extreme quantile estimator. The finite sample behaviour is illustrated
with a small simulation study and through practical examples from survival data analysis.
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The average values of carbon and oxygen isotopic contents (delta(13)C and delta(18)O) of 36 glycerol samples from fats have been determined. The examined samples arise from many fats of animal and plant origin, as well as from the three Italian hard cheeses Parmigiano-Reggiano, Grana Padano and Trentingrana. The total (13)C content allows one to distinguish between glycerol from plants with the C-4 carbon fixation pathway (maize, mean delta(13)C = -14.4 per thousand) and that from plants with the C-3 pathway (mean delta(13)C = -30.7 per thousand). The delta(13)C-values of glycerols of animal origin seem to depend on the diet of the animal, as suggested by the mean values -29.6, -29.0 and -25.1 per thousand, respectively, observed for Parmigiano-Reggiano, Trentingrana and Grana Padano. Additionally, the mean total (18)O content of glycerol samples of vegetable origin is approximately 23.8 per thousand, while that from animal fat is 15.1 per thousand. However, the delta(18)O mean values relative to Parmigiano-Reggiano, Grana Padano and Trentingrana are 11.8, 16.0 and 13.8 per thousand, respectively. The combination of the (13)C and (18)O measurements relative to the fat glycerol of the three cheeses might be considered a potential criterion of authentication. 相似文献
Halido-, (2,4-pentadionato-O,O′) and (acyloxy[2-(acyloxy)ethyl]dibutylstannanes, Bu2Sn(X)CH2CHR1OCOR2 (X = halogen, 2,4- pentanedionate, or OCOR) have been prepared, either by hydrostannation of vinyl esters or by condensation of stannyllithium compounds with epoxides followed by esterification. These thermally unstable compounds are easily decomposed in diorganotin compounds with two heteroatom donors. Some are good catalyst sources for silicone curing and polyurethane preparation. 相似文献