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1.
QIU WenYuan ZHAI XinDong QIU YuanYuan Department of Chemistry State Key Laboratory of Applied Organic Chemistry Lanzhou University Lanzhou China Faculty of Arts Social Sciences The National University of Singapore SG Singapore 《中国科学B辑(英文版)》2008,51(1):13-18
A new methodology for understanding the construction of polyhedral links has been developed on the basis of the Platonic and Archimedean solids by using our method of the ‘three-cross-curve and dou- ble-twist-line covering’. There are five classes of polyhedral links that can be explored: the tetrahedral and truncated tetrahedral links; the hexahedral and truncated hexahedral links; the dodecahedral and truncated dodecahedral links; the truncated octahedral and icosahedral links. Our results show that the tetrahedral and truncated tetrahedral links have T symmetry; the hexahedral and truncated hexahedral links, as well as the truncated octahedral links, O symmetry; the dodecahedral and truncated dodeca- hedral links, as well as the truncated icosahedral links, I symmetry, respectively. This study provides further insight into the molecular design, as well as theoretical characterization, of the DNA and protein catenanes. 相似文献
2.
A new methodology for understanding the construction of polyhedral links has been developed on the basis of the Platonic solids
by using our method of the ‘n-branched curves and m-twisted double-lines covering’. There are five classes of platonic polyhedral links we can construct: the tetrahedral links;
the hexahedral links; the octahedral links; the dodecahedral links; the icosahedral links. The tetrahedral links, hexahedral
links, and dodecahedral links are, respectively, assembled by using the method of the ‘3-branched curves and m-twisted double-lines covering’, whereas the octahedral links and dodecahedral links are, respectively, made by using the
method of the ‘4-branched curves’ and ‘5-branched curves’, as well as ‘m-twisted double-lines covering’. Moreover, the analysis relating topological properties and link invariants is of considerable
importance. Link invariants are powerful tools to classify and measure the complexity of polyhedral catenanes. This study
provides further insight into the molecular design, as well as theoretical characterization, of the DNA polyhedral catenanes. 相似文献
3.
Garnets with magnetic trivalent rare earth ions (Nd, Sm, Eu, Gd, Tb, Dy) filling all or nearly all dodecahedral sites while nonmagnetic Sc3+ ions fill all octahedral sites and magnetic Fe3+ ions fill all or nearly all tetrahedral sites have recently been reported by this laboratory. They afford an opportunity to seek magnetic interaction between dodecahedral rare earth ions and tetrahedral ferric ions in the absence of the additional interaction with octahedral iron which occurs in more conventional rare earth iron garnets such as {Gd3}[Fe2](Fe3)O12. For each composition, dependence of magnetization on temperature was measured between room temperature and that of liquid helium. Measurements were also made at liquid helium temperature of the dependence of magnetization on applied field with values up to 60.7 kOe. Low temperature results are in most cases ascribed to ferrimagnetic ordering but with canting of ion moments to explain why magnetic saturation has not been attained even with the maximum field applied. As is usually the case, the magnetic behavior of the Sm compound is quite different from that of the others and the possibilities of antiferromagnetism, paramagnetism, and metastable ferrimagnetism are discussed. 相似文献
4.
Ceren Susut Thuy Dang Nguyen George B. Chapman YuYe Tong 《Journal of Cluster Science》2007,18(4):773-780
Based on a polyol process, one-step synthetic procedures were investigated for concomitant control of the shape and size of
platinum nanoparticles (Pt NPs). Cubic and octahedral/tetrahedral particles of different sizes (5–10 nm) were synthesized
using these procedures. Further attempts to control the shape of the NPs below 3–4 nm failed. It was found that 3–4 nm is
the particle size limit for Pt NPs above which the particle size and shape can be concomitantly controlled. 相似文献
5.
Alexander A. Tsirlin Evgeny V. Dikarev Yuri A. Velikodny Roman V. Shpanchenko Evgeny V. Antipov 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(7):i40-i42
In the crystal structure of the cation‐deficient garnet Pb2.63Cd2V3O12 (lead cadmium vanadium oxide), the Cd and V atoms fully occupy octahedral and tetrahedral sites, respectively, whereas the Pb atoms partially occupy a dodecahedral site. The total Pb and Cd content indicates that vanadium is slightly reduced from the +5 oxidation state. 相似文献
6.
Fruits ofPeucedanum oreoselinum (L.) Moench, were collected at three sites in 1995–1998 and contained 1.5–5.0% essential oil. Analyses were performed using
GLC and GC-MS. The main component of the essential oil is limonene (44.1–82.4%). The majority of examined samples contained
more limonene than has been reported in the literature. Only in sunny locations do plants synthesize significant quantities
of γ-terpinene (12.2–17.5%) and β-pinene (8.5–14.5%). Small quantities of α-pinene are present in all studied samples of essential
oil (4.0–8.3%). Monoterpenes comprise 97.1–98.6% of the essential oil. The remainder consists of sesquiterpenes.
Institute of Chemistry, ul. Goshtauto, 9, Vilnius, Lithuania. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 743–745,
November–December, 1999. 相似文献
7.
V. V. Sharutin V. S. Senchurin O. K. Sharutina A. P. Pakusina O. A. Fastovets 《Russian Journal of Inorganic Chemistry》2010,55(9):1415-1420
Triphenylbenzylphosphonium tetrachloroaurate (I) and triethanolammonium tetrachloroaurate hydrate (II) were prepared by reacting tetrachloroauric acid in acetone with triphenylbenzylphosphonium and triethanolammonium, respectively.
Triphenylethylphosphonium hexachlorodicuprate (III) was synthesized from triphenylethylphosphonium chloride and copper chloride in acetone. The crystal structures of complexes
I to III were determined by single-crystal X-ray diffraction. The phosphorus atoms in complex I have a nearly undistorted tetrahedral coordination (CPC, 108.3°–110.6°; P-C, 1.788–1.793 ?). The coordination of nitrogen
atoms in the cations of complex II is a distorted tetrahedron (CNC, 111.7°–112.4°). The square coordination of aurum in I and II is only slightly distorted: the ClAuCl angles are 89.6°–90.3° (I) and 89.5°–90.6° (II) and the Au-Cl distances are 2.256–2.278 ? I) and 2.280–2.285 ? (II). The phosphorus atoms in complex III are tetracoordinated (CPC, 106.34°–111.73°; P-C, 1.790–1.795 ?). The copper atoms in III have a distorted tetrahedral coordination (ClCuCl, 98.48°–144.85°; Cu-Cl, 2.1999–2.3263 ?). The central fragment Cu2Cl2 in the anion of complex III is bent relative to the Cu2 axis (the chlorine atom deviates from the Cu2Cl plane by 0.27 ?). 相似文献
8.
N. V. Kas’yan A. V. Shvets S. A. Sergienko V. G. Il’in 《Theoretical and Experimental Chemistry》2006,42(4):255-259
The zeolite IPC-3, isomorphous with germanate zeolite ASU-16, and its silicon, aluminum, and titanium analogs, were obtained
in the presence of 1,6-diaminohexane as a template. It is possible to incorporate selectively the elements in different crystallographic
positions, determined by the nature of the element, particularly its valency and its coordination number with respect to oxygen.
Silicon takes tetrahedral positions in the IPC-3 lattice, Al either tetrahedral or octahedral positions, and Ti octahedral
positions. Small amounts of the lithium cations facilitate tetrahedral coordination and increase the Al content in IPC-3.
__________
Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 4, pp. 246–251, July–August, 2006. 相似文献
9.
V. Rodríguez-González R. Gómez M. Moscosa-Santillan J. Amouroux 《Journal of Sol-Gel Science and Technology》2007,42(2):165-171
Platinum catalysts supported on indium-doped alumina were prepared by the sol–gel method. The method allows the incorporation
of In3+ in the alumina network. The indium-doped alumina supports showed narrow pore size distribution (5.4–4.0 nm) and high specific
surface areas (258–280 m2/g). The 27Al NMR-MAS spectroscopy identified aluminum in tetrahedral, pentahedral, and octahedral coordination; however, the intensity
of the signal assigned to aluminum in pentahedral coordination diminishes with the increase of the content of indium. Total
acidity determined by ammonia thermodesorption diminishes strongly in Pt/In–Al2O3 catalysts, suggesting a selective deposit of platinum over the acid sites of the support. The effect of the support in the
platinum catalytic activity was evaluated in the n-heptane dehydrocyclization reaction. The selectivity patterns for such reaction were modified substantially in the doped
Pt/In–Al2O3 catalysts, in comparison with the Pt-In/Al2O3–I coimpregnated reference catalyst. As an important result, the formation of benzene was suppressed totally over the indium-doped
alumina sol–gel supports with a high content (3 wt%) of indium. 相似文献
10.
A model of concentration transition “ions and complexes in a water structure → ionic and ionicaqueous clusters → polymer structures
of salt and crystal hydrate melts” is suggested. The appearance of cluster nanostructures outside the first zone of a waterlike
structure is regarded as a general characteristic of solutions. The characteristics of solutions, phase equilibria, and salts
of complex composition are interpreted based on this model. Investigation of the complex dielectric constant of electrolytic
solutions in the SHF and EHF bands (7–119 GHz) at high concentrations showed that there are two dispersion regions in which
the relaxation times differ by a factor of 5–10. Relaxation processes are separated, the numbers of molecules in hydration
shells are calculated, and relaxation times are determined for bulky tetrahedral water with hydration shells of ions, for
clusters, and for ionicaqueous polymer chains. It is shown that the two structure subsystems of water molecules in concentrated
solutions may be described using the limited rotator/generalized diffusion molecular model.
Translated fromZhumal Strukturnoi Khimii, Vol. 39, No. 5, pp. 851–863, September–October, 1998. 相似文献
11.
Dong Qiu Paul Guerry Jonathan C. Knowles Mark E. Smith Robert J. Newport 《Journal of Sol-Gel Science and Technology》2008,48(3):378-383
Phosphosilicate gels with high phosphorus content (P mol% > Si mol%) have been prepared using phytic acid as the phosphorus
precursor, with tetraethyl orthosilicate (TEOS). It is shown that the structure of phytic acid is maintained in both the sols
and those gels dried at a low temperature (i.e. ≤120 °C). Solid state 29Si and 31P NMR suggest that the gel network is primarily based on tetrahedral silicon and that phosphorus is not chemically incorporated
into the silicate network at this point. X-ray diffraction shows the gel to be amorphous at low temperatures. After heat treatment
at higher temperatures (i.e. up to 450 °C), P–O–Si linkages are formed and the silicon coordination changes from tetrahedral
to octahedral. At the same time, the gel crystallizes. Even after this partial calcination, 31P NMR shows that a large fraction of phytic acid remains in the network. The function of phytic acid as chelating agent is
also maintained in the gels dried at 120 °C such that its ability to absorb Ca2+ from aqueous solution is preserved. 相似文献
12.
Christie Thomas Cherian M. V. Reddy G. V. Subba Rao Chorng Haur Sow B. V. R. Chowdari 《Journal of Solid State Electrochemistry》2012,16(5):1823-1832
Sol–gel auto-combustion method is adopted to prepare solid solutions of nano-crystalline spinel oxides, (Ni1 − x
Zn
x
)Fe2O4 (0 ≤ x ≤ 1).The phases are characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy, selected
area electron diffraction, and Brunauer–Emmett–Teller surface area. The cubic lattice parameters, calculated by Rietveld refinement
of XRD data by taking in to account the cationic distribution and affinity of Zn ions to tetrahedral sites, show almost Vegard’s
law behavior. Galvanostatic cycling of the heat-treated electrodes of various compositions are carried in the voltage range
0.005–3 V vs. Li at 50 mAg−1 up to 50 cycles. Phases with high Zn content x ≥ 0.6 showed initial two-phase Li-intercalation in to the structure. Second-cycle discharge capacities above 1,000 mAh g−1 are observed for all x. However, drastic capacity fading occurs in all cases up to 10–15 cycles. The capacity fading between 10 and 50 cycles is
found to be greater than 52% for x ≤ 0.4 and for x = 0.8. For x = 0.6 and x = 1, the respective values are 40% and 18% and a capacity of 570 and 835 mAh g−1 is retained after 50 cycles. Cyclic voltammetry and ex situ transmission electron microscopy data elucidate the Li-cycling
mechanism involving conversion reaction and Li–Zn alloying–dealloying reactions. 相似文献
13.
V. P. Koropchanu F. G. Paladii S. I. Boldyrev V. Ya. Gamurar' 《Journal of Structural Chemistry》1996,37(5):707-712
The tunnel states of square-planar bielectron transfer dn-dn-dn+1-dn+1 (n=0–4) clusters are considered. The nature of the ground spin state is revealed in the limiting case of a strong double
exchange. It is shown that the magnetic properties of these systems radically differ from those of clusters with one migrating
electron (hole) and tetrameric tetrahedral bielectron transfer clusters.
Moldova State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 5, pp. 826–833, September–October, 1996.
Translated by I. Izvekova 相似文献
14.
A. A. Kashaev 《Journal of Structural Chemistry》1994,35(5):665-667
In published structures of amphiboles and pyroxenes, the edge lengths of octahedral faces, approximately parallel to (100),
are compared. The degree of distortion of octahedra is inversely proportional to the value of the SiOSi angle. Extrapolation
of the degree of distortion to zero gives an equilibrium value of 145° for the angle. This value was obtained for amphiboles
of varying composition and for six pyroxenes at different temperatures. This result confirms the previous conclusion that
the structures tend to form SiOSi and AlOSi angles of 144–148° and 136–139°; other structural features, especially the limited
availability of ternary tetrahedral rings in silicate radicals, are also evidence of this tendency.
Irkutsk State Pedagogical Institute. Translated fromZhurnal Strukturnoi Khimii, Vol 35, No. 5, pp. 105–108, September–October, 1994.
Translated by L. Smolina 相似文献
15.
Tomáš Grygar Petr Bezdička Pawel Piszora Emilia Wolska 《Journal of Solid State Electrochemistry》2001,5(7-8):487-494
Electrochemical reductive dissolution of Li–Mn–O and Li–Fe–Mn–O spinels and Li+ extraction/insertion in these oxides were performed using voltammetry of microparticles. Both electrochemical reactions are
sensitive to the Fe/(Fe+Mn) ratio, specific surface area, Li content in tetrahedral positions, and Mn valence, and can be
used for electrochemical analysis of the homogeneity of the elemental and phase composition of synthetic samples. The peak
potential (E
P) of the reductive dissolution of the Li–Mn–O spinel is directly proportional to the logarithm of the specific surface area. E
P of Li–Fe–Mn–O spinels is mainly controlled by the Fe/(Fe+Mn) ratio. Li+ insertion/extraction can be performed with Mn-rich Li–Fe–Mn–O spinels in aqueous solution under an ambient atmosphere and
it is sensitive to the regularity of the spinel structure, in particularly to the amount of Li in tetrahedral positions and
the Mn valence.
Electronic Publication 相似文献
16.
The electrochemical behaviour of the spinel-like LiMn2O4 was studied in non-aqueous and aqueous saturated alkali nitrate electrolytes in comparison with the layered manganese dioxide
δ-MnO2. The results obtained by galvanostatic and cyclic voltammetry techniques showed that the insertion of Li+/e– or H+/e– depends on both the host lattice and the type of electrolyte. The spinel-like LiMn2O4 preferably allowed the insertion of Li+/e– in non-aqueous and aqueous saturated LiNO3 electrolytes, as observed from the similarity of the electrochemical behaviour in these electrolytes and the stability of
the structure. This was explained by the presence of a three-dimensional network of vacant tetrahedral and half-filled octahedral
sites in LiMn2O4, which guarantee high mobility of Li+ ions. The layered manganese dioxide could be inserted by Li+/e– only in non-aqueous electrolytes.
The work described herein was carried out at the Institut für Anorganische und Analytische Chemie, Technische Universit?t
Berlin, Germany 相似文献
17.
The electric quadrupole interactions at the octahedral, tetrahedral, and dodecahedral sites in the Eu3?ySc2+yFe3O12 (0 ≤ y ≤ 0.5) garnet system were studied with 57Fe and 151Eu Mössbauer spectroscopy. The electric field gradient tensor at the three sites was calculated using a monopole-point-dipole model. It is shown that the dipole contribution to the electric field gradient tensor is not negligible even for very small values of the oxygen dipole polarizability. The importance of the overlap and second-order 4f contributions is discussed. 相似文献
18.
Ordered mesoporous aluminosilicate Al-SBA-15 materials with cage-like macropores have been synthesized by using micrometer-sized
aluminum balls as an Al source, tetraethyl orthosilicate (TEOS) as a silica source, and triblock copolymer Pluronic P123 as
a template. The resulting materials were fully characterized by XRD, N2 adsorption, SEM, TEM, ICP-AES, and 27Al MAS-NMR. The products (Al-SBA-15) have ordered two-dimensional (2-D) hexagonal mesostructures (space group p6mm). The calcined Al-SBA-15 materials exhibit disordered macropores with diameters of about 70–80 nm and ordered mesopores with
a diameter of ∼5 nm, a BET surface area of about 500 m2/g, Si/Al ratio of 40–80, and a ratio of tetrahedral Al to octahedral Al sites of about 2:1. This combination of properties
gives these materials potential applications in areas such as adsorption, catalysis and separation.
Supported by the National Natural Science Foundation of China (Grant Nos. 20890123 & 20721063), Shanghai Science & Technology
Committee (08DZ2270500), and Shanghai Leading Academic Discipline Project (No.B108) 相似文献
19.
A new model has been developed to account for adduct formation on multiply charged peptides observed in negative ion electrospray
mass spectrometry. To obtain a stable adduct, the model necessitates an approximate matching of apparent gas-phase basicity
(GBapp) of a given proton bearing site on the peptide with the gas-phase basicity (GB) of the anion attaching at that site. Evidence
supporting the model is derived from the fact that for [Glu] Fibrinopeptide B, higher GB anions dominated in adducts observed
at higher negative charge states, whereas lower GB anions appeared predominately in lower charge state adducts. Singly charged
adducts were only observed for lower GB anions: HSO4–, I–, CF3COO–. Ions that have medium GBs (NO3–, Br–, H2PO4–) only form adducts having −2 charge states, whereas Cl– (higher GB) can form adducts having −3 charge states. The model portends that (1) carboxylate groups are much more basic
than available amino groups; (2) apparent GBs of the various carboxylate groups on peptides do not vary substantially from
one another; and (3) apparent GBs of the individual carboxylate and amino sites do not behave independently. This model was
developed for negative ion attachment but an analogous mechanism is also proposed for the positive ion mode wherein (1) binding
of a neutral at an amino site polarizes this amino group, but hardly affects apparent GBs of other sites; (2) proton addition
(charge state augmentation) at one site can decrease the instrinsic GBs of other potential protonation sites and lower their
apparent GBs. 相似文献
20.
W. R. Fahrner G. Grabosch D. Borchert Y. Chan S. Kwong K. Man 《Journal of Solid State Electrochemistry》1999,3(5):245-250
The admittance versus frequency of a hydrogenated amorphous silicon metal oxide semiconductor capacitor is measured at a
fixed bias in inversion and for temperatures in the range of 20–50 °C. The data are fitted to theoretical capacitance and
conductance curves where the time constant of inversion is the result of the fit. In turn, the time constant can be converted
to the (minority) carrier lifetime so that a lifetime value for each measurement temperature is available. The conversion
from the time constant to the minority carrier lifetime requires the knowledge of the temperature-dependent intrinsic carrier
density or rather its activation energy. The criterion for the correct choice is a temperature-independent carrier lifetime.
Three published room temperature values of the intrinsic carrier density have been tested. The carrier lifetime activation
energy is E
a = 0.70 ± 0.03 eV.
Received: 17 June 1998 / Accepted: 23 October 1998 相似文献