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31.
A facile one-pot access to cone and 1,3-alternate calix[4]arene-bis(amido)crowns by the use of sodium hydride or cesium carbonate as template/base has been reported. The structures of products have been established through detailed chemical, physical, and spectroscopic data and single crystal X-ray analysis of calix[4]arene-bis-(ethyleneamido)crown, 7a. The preliminary evaluation of the obtained molecular receptors promise opportunities to design molecular capsules/carriers for toxic metal ions (i.e., Hg++) and anionic species (CrO4−−). 相似文献
32.
A series of conformationally diverse novel tetrathiacalix[4]arene(amido)crowns and amides from tetrakis((ethoxycarbonyl)methoxy)p-tert-butyl tetrathiacalix[4]arene and its debutylated analog have been prepared by their reaction with diamines [H2N(CH2)nNH2; n=2,3,4, and 6] and polyamines. It has been determined that the length of the alkyl spacer in diamines is pivotal for the formation of either the tetrathiacalix[4]arene bis(amido)crowns or tetrathiacalix[4]arene amides with pendant amine functions. The synthesized compounds represent potential building blocks for achieving sophisticated molecular assemblies for molecular organization and recognition. Single crystal X-ray analysis of tetrathiacalix[4]arene bis(amido)crown 6a revealed that it has a 1,3-alternate conformation, which forms supramolecular complexes with chloroform. 相似文献
33.
Synthesis of two ent-kaurane diterpene glycosides, steviol 19-O-β-D-glucopyranosiduronic acid (steviol glucuronide, 5), and 13-hydroxy ent-kaur-16-en-19-oic acid-β-D-glucopyranosyl ester (7) has been achieved from a common starting material, steviol, using phase transfer catalyst. Also, synthesis of an additional 17-nor-ent-kaurane glycoside, namely 13-methyl-16-oxo-17-nor-ent-kauran-19-oic acid-β-D-glucopyranosyl ester (10) was performed using the starting material isosteviol and similar synthetic methodology. Synthesis of all three steviol glycosides was performed using straightforward chemistry and their structures were characterized on the basis of 1D and 2D NMR as well as mass spectral (MS) data. 相似文献
34.
Xiao J Chernova NA Upreti S Chen X Li Z Deng Z Choi D Xu W Nie Z Graff GL Liu J Whittingham MS Zhang JG 《Physical chemistry chemical physics : PCCP》2011,13(40):18099-18106
In this paper, the influences of the lithium content in the starting materials on the final performances of as-prepared Li(x)MnPO(4) (x hereafter represents the starting Li content in the synthesis step which does not necessarily mean that Li(x)MnPO(4) is a single phase solid solution in this work.) are systematically investigated. It has been revealed that Mn(2)P(2)O(7) is the main impurity when Li < 1.0 while Li(3)PO(4) begins to form once x > 1.0. The interactions between Mn(2)P(2)O(7) or Li(3)PO(4) impurities and LiMnPO(4) are studied in terms of the structural, electrochemical, and magnetic properties. At a slow rate of C/50, the reversible capacity of both Li(0.5)MnPO(4) and Li(0.8)MnPO(4) increases with cycling. This indicates a gradual activation of more sites to accommodate a reversible diffusion of Li(+) ions that may be related to the interaction between Mn(2)P(2)O(7) and LiMnPO(4) nanoparticles. Among all of the different compositions, Li(1.1)MnPO(4) exhibits the most stable cycling ability probably because of the existence of a trace amount of Li(3)PO(4) impurity that functions as a solid-state electrolyte on the surface. The magnetic properties and X-ray absorption spectroscopy (XAS) of the MnPO(4)·H(2)O precursor, pure and carbon-coated Li(x)MnPO(4) are also investigated to identify the key steps involved in preparing a high-performance LiMnPO(4). 相似文献
35.
Here we report direct hydrothermal synthesis of a few hexagonal molybdates with composition, M
x
/+
Mo
6−x
Emphasis>/3/6+
O18−x
(OH)
x
.yH2O (M = Li, Rb, Cs, NH4). The molybdates crystallize in the space groupP6
3
/m with a r∼ 10.5 andc r∼ 3.7 ? . Unlike previous studies, our work suggests that hexagonal molybdates could be stabilized in the presence of monovalent
cations with varying ionic size (smaller lithium to larger cesium) under hydrothermal condition. The phases showed exceptional
thermal stability till 550°C.
Dedicated to Professor C N R Rao on his 70th birthday 相似文献
36.
Manganese complexes of the type [TpMn(X)] and [TpMn(μ-N3)(μ-X)MnTp] (X = acetylacetonate, acac; picolinate, pic and Tp = TpPh,Me for acac, Tp = Tpipr2 for pic complexes) having TpPh,Me (hydrotris(3-phenyl,5-methyl-pyrazol-1-yl)borate)/Tpipr2 (hydrotris(3,5-diisopropyl-pyrazol-1-yl)borate) as a supporting ligand have been synthesized and structurally characterized. IR and X-ray structures suggest that complexes 7 and 9 are binuclear with azido and bidentate ligands (acac/pic) bridging, whereas complexes 6 and 8 are mononuclear with a 5-coordinated metal center. In complex 9 the picolinate is coordinated as tridentate in a η3-fashion, but in complex 7 acac behaves as bidentate, whereas azide is coordinated in a bridging bidentate μ-1,3-manner in both 7 and 9. Since the coordination geometry of the manganese ions in complex 9 is very similar to the active site structure of manganese-containing pseudocatalase, we have tested the catalytic activity of the same towards the disproportionation of hydrogen peroxide. The catalytic results indicated that complex 9 has reasonably good catalase activity and may be suitable, structurally as well as functionally, as a model for the pseudocatalase enzyme. 相似文献
37.
Udai P. Singh Asish K. Sharma Pooja Tyagi Shailesh Upreti Raj K. Singh 《Polyhedron》2006,25(18):3628-3638
Several manganese carboxylates complexes having PziPr2H (3,5-diisopropylpyrazole), TpPh,Me (hydrotris(3-phenyl,5-methyl-pyrazol-1-yl)borate), Tpipr2 (hydrotris(3,5-diisopropyl-pyrazol-1-yl)borate) as supporting ligands have been synthesised and structurally characterized. Single-crystal X-ray diffraction studies suggest that the manganese center in complexes (PziPr2H)4Mn(NO2–OBz)2 (5) and (PziPr2H)4Mn(F–OBz)2 (6) have same coordination environment and geometry whereas the complex [TpPh,MeMn(OAc)PzPh,MeH] (7) has a five coordinate manganese center. In all these complexes, the carboxylate groups are coordinated as monodentate and the uncoordinated oxygen atom of the carboxylate groups form intramolecular hydrogen bonds with the NH group of the corresponding coordinated pyrazole (PziPr2H/PzPh,MeH). The complexes 5–8 and 10 were tested for their superoxide dismutase activity and it was found that only complex 7 has SOD activity as its structure is very similar to the active site structure of the native Mn–SOD enzyme. The SOD activity studies on these carboxylate complexes suggest that any model compound with analogous active site structure and intramolecular hydrogen bonding may be a suitable mimic for the Mn–SOD enzyme. 相似文献
38.
From a temperature variation EPR study of Mn2+ doped single crystals of Zn(ClO4)2·6H2O phase transition has been detected at T2~290 K. The phase relationships in this crystal are as follows. Phase I transforms atT2~346K to Phase II, which in turn transforms to Phase III at T2 ~ 290K. The latter exists down to at least 220 K. The space group symmetry of crystal may be the same, i.e. Pmn21 both above and below T2. The water-perchlorate sublattice symmetry below T2 is found to be lower than the P63mc symmetry determined previously by X-ray measurements. The onset of a monoclinic or lower symmetry distortion of the water octahedron around a metal ion which starts just below T2, is reflected through the observed temperature dependence of the rhombic distortion parameter E. It is felt that during this phase transition a change in the degree of configurational disorder associated with the perchlorate tetrahedra takes place, which in turn modifies the hydrogen bonded interaction in the crystal and consequently results in the onset of temperature dependent displacements of the mean positions of the oxygens of the water molecules. 相似文献
39.
On the basis of the temperature dependence of typical internal modes associated with SO2?4 and NH+4 ions it is inferred that the ferroelectric phase transition near 223°K in ammonium sulphate in primarily due to sudden distortions in the SO2?4 ions. 相似文献
40.
A series of pyridylazo calix[n]arenes (n=4, 6, 8) including the first examples of mixed hetroaryl azocalix(n)arenes have been synthesized by coupling calix[n]arenes with diazonium salts derived from amino pyridines. It has been observed that the coupling reaction of diazonium salt obtained from 3-aminopyridine with calix[n]arene gives tetrakis-, hexakis- and octakis (pyridylazo)calix[n]arenes (n=4,6,8) while those derived from 4-aminopyridine give partially substituted (4-pyridylazo)calix[n]arene analogs. There is no reaction of calix(n)arenes with diazonium salts derived from 2-aminopyridine under identical conditions of experiments. The conformational analysis of synthesized compounds have been ascertained by detailed spectral measurements and single crystal X-ray analysis of 5-(3′-pyridylazo)-25,26,27,28-tetrahydroxycalix[4]arene. A rational explanation for the observed partial and exhaustive coupling reaction in the synthesis of heteroaryl azocalix(n)arenes has been suggested. Preliminary evaluation of synthesized derivatives as molecular receptors for metal ions indicates that they have good potential to function as selective ionic filters for cesium ions. 相似文献