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971.
Isotypic pseudooctahedral complexes of Co, Ni, and Cu with two chelating oxalurate ligands and two water molecules, trans-[M(oxalurate)(2)(H(2)O)(2)], have been synthesized and isolated by a novel progressive crystallization technique. Diffraction analyses reveal that the three complexes form isotypic solid-state structures in which the molecular connectivity and complex network of noncovalent interactions are qualitatively identical throughout the series. The oxalurate groups form unbounded chains through two different self-recognition patterns-a typical DA-AD motif and an unusual DDA'-A'DD form (D = hydrogen bond donor, A' = double acceptor). The unsymmetrical oxalurate group possesses the topological properties necessary to form aggregates of higher symmetry, and the "M(oxalurate)(2)" fragments form a rhombic 2-D motif with hydrogen-bonded corners and with hydrogen-bond acceptors directed to the inside of the cyclic aggregate. The 2-D net is stacked to form a channeled 3-D structure, in which the coordinated aqua ligands form the principal interlayer interactions. The slanted channels are occupied by the axial waters and by waters of crystallization, which are hydrogen bonded to the channel walls to form an ordered bushing. The extensive 3-D hydrogen-bonded superstructure is flexible enough to accommodate the distortion produced by the Jahn-Teller effect in the copper compound without requiring a qualitative structural change. The bonds affected by Jahn-Teller distortion in the Cu complex [Cu-O = 2.3788(15) A] are significantly longer than their analogues in the Co and Ni complexes [Co-O = 2.175(2), Ni-O = 2.094(9) A]. 相似文献
972.
Ana C. D. Medeiros Lidiane P. Correia Mônica O. da S. Simões R. O. Macêdo 《Journal of Thermal Analysis and Calorimetry》2007,88(2):311-315
A number of disintegrants
are available on the market. They improve tablets’ disintegration. The
objective of this work is the comparison of the technological quality parameters
of disintegrants using different analytical techniques. Three batches of disintegrants
and their binary mixtures (water:disintegrants) were investigated. Cooling
experiments were used from –30 up to 200°C. The data obtained showed
calorimetric differences between the samples. In the binary mixtures water
showed different crystallization behaviour from the one found in the literature.
According to the results DSC technique helped the quality control of different
disintegrants. 相似文献
973.
J. Orbán Sz. Halasi G. Papp Szilvia Barkó Beáta Bugyi 《Journal of Thermal Analysis and Calorimetry》2005,82(1):287-290
Summary The thermodynamic properties of the cardiac and skeletal a-actin isoforms were studied to characterize the molecular bases
of the functional differences between them with the method of differential scanning calorimetry (DSC). The thermal properties
of the actin filaments were described in the presence of calcium and magnesium ions as well. Based on the calculated free
energy changes the α-cardiac actin filaments appeared to be more stable in its physiologically more relevant, magnesium saturated
form. The magnesium saturated form of the α-cardiac actin filaments seemed to be more stable compared to the calcium saturated
form of it. The enthalpy and entropy changes could differentiate between the α-cardiac and α-skeletal actin isoforms and between
the calcium and magnesium saturated cardiac actin isoforms as well. Our results can demonstrate that the few differences between
the amino acid sequences of the α-actin isoforms have an influence on the thermal properties and maybe on the function of
these proteins as well. 相似文献
974.
Zhou YanXia Tan HongWei Yang ZuoYin Jia ZongChao Liu RuoZhuang Chen GuangJu 《中国科学B辑(英文版)》2007,50(2):266-271
The insect spruce budworm(Choristoneura fumiferana) produces antifreeze protein(AFP) to assist in the protection of the over-wintering larval stage and contains multiple isoforms. Structures for two isoforms,known as CfAFP-501 and CfAFP-337,show that both possess similar left-handed β-helical structure,although thermal hysteresis activity of the longer isoform CfAFP-501 is three times that of CfAFP-337. The markedly enhanced activity of CfAFP-501 is not proportional to,and cannot be simply accounted for,by the increased ice-binding site resulting from the two extra coils in CfAFP-501. In or-der to investigate the molecular basis for the activity difference and gain better understanding of AFPs in general,we have employed several different computational methods to systematically study the structural properties and ice interactions of the AFPs and their deletion models. In the context of intact AFPs,a majority of the coils in CfAFP-501 has better ice interaction and causes stronger ice lattice disruption than CfAFP-337,strongly suggesting a cooperative or synergistic effect among β-helical coils. The synergistic effect would play a critical role and make significant contributions to the anti-freeze activity β-helical antifreeze proteins. This is the first time that synergistic effect and its implica-tion for antifreeze activity are reported for β-helical antifreeze proteins. 相似文献
975.
Małgorzata Olejnik Teresa Szprengier-Juszkiewicz Piotr Jedziniak Jan Żmudzki 《Accreditation and quality assurance》2007,12(12):637-641
In this paper, the case of FAPAS PT 0270 “Doramectin and Oxfendazole in Sheep Liver” is discussed. During evaluation of the
data received from participants (determination of total, oxidised oxfendazole residue and calculation of the sum of oxfendazole
and oxfendazole sulfone residues), significant differences were observed between the results obtained by use of two analytical
approaches. This phenomenon can be explained by the route of oxfendazole metabolism, which results in the presence of fenbendazole
in the sample. This was not predicted by the provider; consequently, not all the necessary tests on the material were conducted.
Due to the high uncertainty of the z-scores in this test, the results of the PT cannot be used for purposes of evaluation, and the benefits of participation in
PT 0270 are questionable. 相似文献
976.
With the use of the tritium monitoring network the samples of river water, air humidity and precipitation are collected and analysed for HTO in the vicinity of Temelín nuclear power plant. 相似文献
977.
A procedure for calculating the magnetic circular dichroism C/D ratio from density functional theory calculations is discussed. The method is simplified considerably through the application of group theory and the irreducible-tensor method and only requires integrals of the magnetic dipole moment operator over a few orbitals and published tables of symmetry factors. The implementation of the method is tested through application to several small and medium-sized molecules. 相似文献
978.
Metal-catalyzed di-tert-butylsilylene transfer was developed as a mild, operationally simple, functional-group-tolerant method for silacyclopropane formation. Di-tert-butylsilylene was transferred from cyclohexene silacyclopropane 1 to an alkene through the use of a metal salt. Silacyclopropanation occurred at temperatures as low as -27 degrees C when AgOTf or AgOC(O)CF(3) were used as catalysts. Complex silacyclopropanes were formed stereospecifically and diastereoselectively from functionalized alkenes. Silacyclopropanes reacted with various carbonyl compounds, including aldehydes, ketones, formate esters, and formamides, in an overall process that efficiently converts alkenes into oxasilacyclopentanes with defined stereochemistry. 相似文献
979.
The use of reduced overlap population (ROP) analysis from EHMO calculations as a means to gauge the presence of metal–metal
bonds in triosmium clusters is examined. A number of triosmium clusters containing bridging ligands have been used as test
cases, including the bis-ethoxy bridged cluster Os3(μ-OEt)2(CO)10, 1b, and some of its group 15 derivatives Os3(μ-OEt)2(CO)9(EPh3), 2. These latter clusters are newly synthesized and have been characterized completely, including by single-crystal X-ray crystallographic
studies.
In honour of Professor Dieter Fenske on his 65th birthday. 相似文献
980.
K.D. Franz H. Tom Dieck U. Krynitz I.W. Renk 《Journal of organometallic chemistry》1973,64(3):361-366
Glyoxal- and diacetyl-bis(imine)metal tetracarbonyls (RNCR′CR′NR)M(CO)4 (M = Cr, Mo, W) are reduced with potassium in DME to give paramagnetic mono-anions. Their high-resolutior, ESR spectra show the hyperfine splittings of the magnetically active ligand atoms as well as the satellites of the metal isotopes 53Cr,95,97Mo and 183W. The coupling constants are discussed with respect to π-bonding mechanisms. 相似文献