LiNi0.5Mn0.5O2 powder was synthesized by a coprecipitation method. LiOH.H2O and coprecipitated [(Ni0.5Mn0.5)C2O4] precursors were mixed carefully together and then calcined at 900°C. Surface modified cathode materials were obtained by
coating LiNi0.5Mn0.5O2 with a thin layer of amorphous carbon using table sugar and starch as carbon source. Both parent and carbon-coated samples
have the characteristic layered structure of LiNi0.5Mn0.5O2 as estimated from X-ray diffractometry measurements. Transmission electron microscope showed the presence of C layer around
the prepared particles. TGA analysis emphasized and confirmed the presence of C coating around LiNi0.5Mn0.5O2. It is obvious that the carbon coating appears to be beneficial for the electrochemical performance of the LiNi0.5Mn0.5O2. A capacity of about 150 mAh/g is delivered in the voltage range 2.5–4.5 V at current density C/15 for carbon coated LiNi0.5Mn0.5O2 in comparison with about 165 mAh/g obtained for carbon free LiNi0.5Mn0.5O2 at the same current density and voltage window. About 92% and 82% capacity retention was obtained at 50th cycle for coated
LiNi0.5Mn0.5O2 using sucrose and starch, respectively; whereas, 75% was retained after only 30th cycle for carbon free LiNi0.5Mn0.5O2. This improvement is mainly attributed to the presence of thin layer of carbon layer that encapsulate the nanoparticles and
improve the conductivity and the electrochemical performance of LiNi0.5Mn0.5O2. 相似文献
Silver diiron tris(oxomolybdate), α-AgFe2(MoO4)3, was synthesized in sealed silica tubes at 1050 K and is isostructural to α-NaFe2(MoO4)3, determined by single-crystal X-ray diffraction (space group P?1, a = 6.9320(7) Å, b = 6.9266(6) Å, c = 10.9732(13) Å, α = 81.197(8)°, β = 83.456(9)°, γ = 81.352(8)° at 300 K, Z = 2). The crystal structure is built up from both monomers and edge-sharing dimers of [FeO6]-octahedra, which are linked with each other by isolated [MoO4]-tetrahedra to a three-dimensional network. Ag ions are situated on a site with four near oxygen neighbours. Thermal expansion is most pronounced along the c-axis, while the angle α decreases with increasing temperature. Antiferromagnetic ordering is indicated by a sharp maximum in the temperature dependence of magnetization at 21.5(5) K, and a magnetic moment of 5.36(1) μB per Fe-ion was derived from the Curie constant in the paramagnetic region. The collinear antiferromagnetic structure with propagation vector k = (0,½,½) and an ordered magnetic moment of 4.62(9) μB per Fe-ion were deduced from neutron powder diffraction data and give evidence for an underlying magnetic interaction mechanism, resulting in rather strong and long-ranged couplings. Mössbauer spectroscopy shows a change in the electronic configuration on the two distinct Fe sites between room temperature and 150 K, accompanied by an increase of the average Fe–O distance for one site and a shrinking one for the other as expected for charge ordering in a mixed valence compound with Fe(II) and Fe(III). 相似文献
A new polymorph of nonacopper(II) bis(orthoborate) bis(hexaoxodiborate), Cu9(BO3)2(B2O6)2, or Cu3B2O6 with Z′ = 3, has a pseudo‐layered monoclinic structure containing BO3 triangles and B2O6 units consisting of corner‐sharing BO3 triangles and BO4 tetrahedra. The compound was obtained during an investigation of the Li–Cu–B–O system. In contrast to the triclinic form of Cu3B2O6, the layers are linked to one another by BO4 tetrahedra. 相似文献
A crucial factor in choosing a porphyrin or analogous photosensitizer for photodynamic therapy (PDT) is its ability to incorporate into the cells. For hydrophobic compounds that partition passively into the cytoplasmic membrane, a partition coefficient between an organic solvent and water, P, is one factor that could be used to predict the molecule's ability to diffuse into biomembranes. We synthesized several porphyrins, modified with two, three or four meso-substituents and studied their spectroscopic and photophysical properties. The octanol-water partitioning coefficients, log P, were calculated as a parameter for hydrophobicity. We found these porphyrins to be very hydrophobic, with log P values in the range of 8.9-11.8. These were correlated with the binding constants of these porphyrins into liposomes, K(b), as well as to their uptake by cells. The correlation between the estimated log P and K(b) is nearly linear but negative, indicating, apparently, that there is lesser binding to liposomes with increased hydrophobicity. On the other hand, all of the studied porphyrins are taken up by cells, but there is no clear correlation between cellular uptake and the log P or K(b). Lipinski's pharmacological "rule of 5" predicts poor permeation of drugs into cells when log P is greater than five. This may be relevant for diffusional binding to liposomes, where aqueous aggregation can interfere strongly with cellular uptake. In such extreme conditions, neither liposome binding nor other rules seem to predict porphyrin behavior in vitro. 相似文献
The acid-base, spectroscopic, photophysical and liposome-binding properties of the recently synthesized free base, 29H,31H,1,4,8,11,15,18,22,25-octafluoro-2,3,9,10,16,17,23, 24-octakisperfluoro(isopropyl) phthalocyanine, F64PcH2, are reported. The perfluoroalkylation of the phthalocyanine core renders the hydrogen atoms acidic, with a pK(a) = 6. The F64Pc(-2) dianion is detected already at pH 3, by singular-value decomposition analysis of electronic spectra. F64Pc(-2) generates 1O2 with quantum yields phi(delta) = 0.252 (in MeOH) and 0.019 in liposomes. Metallation of the Pc macrocycle to yield F64PcZn increases phi(delta) to 0.606 and 0.126 in MeOH and liposomes, respectively. Surprisingly, F64Pc(-2) (but not F64PcH2 or F64PcZn) binds strongly to liposomes, with a binding constant K(b) = 25 (mg/mL)(-1). The fully protonated F64PcH2, but not the zwitterionic F64Pc(-2), might favor hydrogen bonding, thus reducing its lipophilicity. Similarly, the Lewis acidity of Zn in F64PcZn, and thus its ability to bind water within a hydrophobic perfluoroalkyl pocket, is significantly enhanced by the fluorinated substituents. 相似文献
We report the preparation of chiral oxygen atom-appended porphyrazines (pzs) as biomedical optical agents that absorb and emit in the near-IR wavelength range. These pzs take the form M[pz(A4-nBn)], where “A” and “B” represent moieties appended to the pz’s pyrrole entities, A = (2R,3R) 2,3-dimethyl-2,3-dimethoxy-1,4-diox-2-ene, B = β,β′-di-isopropoxybenzo, M is the incorporated metal ion (M = H2, Zn), and n =0, 1, 2 (-cis/-trans) and 3 ( Scheme 1 ). When dissolved in polar media, H2[pz(trans-A2B2)] 5a does not fluoresce and has a negligible quantum yield for singlet oxygen generation (ФΔ = 0.074 ± 0.001, methanol), as measured by the photo-oxidation of DMA. However, when sequestered in the nonpolar environment of a liposome, it displays strong NIR emission (λ max = 705 nm, Ф f = 0.087) and an extremely high singlet oxygen quantum yield (ФΔ→1). Of this series, H2[pz(trans-A2B2)] 5a is attractive as a potential optical probe, showing strongly fluorescent uptake by cells in culture, while 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide measurements of cell viability show no evidence of dark toxicity. This agent does show significant photoinduced toxicity suggesting that pzs such as 5a have promise as “theranostic” optical agents that can be visualized with fluorescence imaging while acting as a sensitizer for photodynamic therapy. Figure Scheme 1. Open in figure viewer PowerPoint Synthesis of Porphyrazines 3a – 7a , 3b – 7b . 相似文献
The problem of storing permutations in a distributed manner arises in several common scenarios, such as efficient updates of a large, encrypted, or compressed data set. This problem may be addressed in either a combinatorial or a coding approach. The former approach boils down to presenting large sets of permutations with locality, that is, any symbol of the permutation can be computed from a small set of other symbols. In the latter approach, a permutation may be coded in order to achieve locality. Both approaches must present low query complexity to allow the user to find an element efficiently. We discuss both approaches, and give a particular focus to the combinatorial one. In the combinatorial approach, we provide upper and lower bounds for the maximal size of a set of permutations with locality, and provide several simple constructions which attain the upper bound. In cases where the upper bound is not attained, we provide alternative constructions using a variety of tools, such as Reed-Solomon codes, permutation polynomials, and multi-permutations. In addition, several low-rate constructions of particular interest are discussed. In the coding approach we discuss an alternative representation of permutations, present a paradigm for supporting arbitrary powers of the stored permutation, and conclude with a proof of concept that permutations may be stored more efficiently than ordinary strings over the same alphabet. 相似文献
We study the propagation of nonlinear modulated waves in weakly dispersive media within the framework of the Korteveg- de
Vries equation. It is shown that strong generation of overtones and mean flow by the modulated packet results in asymmetry
of the wave packet envelope with respect to both horizontal and vertical axes and makes the envelope skewed. The motion of
the wave packet is accompanied by the emission of low-frequency and high-frequency waves that propagate in different directions
from the packet. As a result, the mean amplitude of the wave packet decreases with distance.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 4, pp. 354–358, April 1999. 相似文献