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41.
del Río JC Gutiérrez A Martínez AT 《Rapid communications in mass spectrometry : RCM》2004,18(11):1181-1185
A series of non-wood plant fibers, namely kenaf, jute, sisal and abaca, have been analyzed upon pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) of the whole material. The pyrolysis products mainly arise from the carbohydrate and lignin moieties of the fibers. The lignin-derived phenols belonged to the p-hydroxyphenylpropanoid (H), guaiacylpropanoid (G) and syringylpropanoid (S) structures, and showed a high S/G ratio of between 2.0 and 5.4, the highest corresponding to kenaf. Among the lignin-derived phenols released, small amounts of sinapyl and coniferyl acetates (in both cis- and trans-forms) were identified for the first time upon Py-GC/MS of lignocellulosic materials. Acetylation of the sinapyl and coniferyl alcohols was at the gamma-position of the side chain. The release of these alcohols derived from intact acetylated lignin units upon pyrolysis seems to indicate that the native lignin in the fibers selected for this study is at least partially acetylated. Sinapyl (and coniferyl) acetates have recently been suggested to be authentic lignin precursors involved in the polymerization of lignin along with the normal sinapyl and coniferyl alcohols. Py-GC/MS will offer a convenient and rapid tool for analyzing naturally acetylated lignins, as well as to screen plant materials for the presence of acetylated units in lignin. 相似文献
42.
Six new derivatized deltahedral Zintl ions have been synthesized by reactions between the known Zintl ions Ge(9) (n-) with the halides R(3)EX and/or the corresponding anions R(3)E(-) for E=Ge or Sn. This rational approach is based on our previous discovery that these derivatization reactions are based on nucleophilic addition to the clusters. All species were structurally characterized as their salts with potassium countercations sequestered in 2,2,2-crypt or [18]crown-6 ether. The tin-containing anions were characterized also in solutions by (119)Sn NMR spectroscopy. The reaction types for such substitutions and the structures of the new anions are discussed. 相似文献
43.
García-Raso A Fiol JJ Tasada A Albertí FM Molins E Basallote MG Máñez MA Fernández-Trujillo MJ Sánchez D 《Dalton transactions (Cambridge, England : 2003)》2005,(23):3763-3772
Alkylidene-bis(2-aminopyrimidines) (pyr2Cx, x = 2-5) are useful ligands to interact with Ag(I) yielding discrete metallocycles. Crystal structures of the [(pyr2C2)Ag(NO3)]2 and [(H-pyr2C4)Ag(NO3)2]2 have been isolated where each macrocyclic moiety interacts with their surroundings through weak interactions, yielding 3D discrete structures, On the other hand, the solution study shows that the equilibrium constants for the formation of Ag(pyr2Cx)+ complexes are higher than the literature values for Ag(I) complexes with single pyrimidines, although the differences could be explained by invoking the solid-state structures of the Ag(I)-pyr2Cx complexes. 相似文献
44.
Funk T Kennepohl P Di Bilio AJ Wehbi WA Young AT Friedrich S Arenholz E Gray HB Cramer SP 《Journal of the American Chemical Society》2004,126(18):5859-5866
We show that X-ray magnetic circular dichroism (XMCD) can be employed to probe the oxidation states and other electronic structural features of nickel active sites in proteins. As a calibration standard, we have measured XMCD and X-ray absorption (XAS) spectra for the nickel(II) derivative of Pseudomonas aeruginosa azurin (NiAz). Our analysis of these spectra confirms that the electronic ground state of NiAz is high-spin (S = 1); we also find that the L(3)-centroid energy is 853.1(1) eV, the branching ratio is 0.722(4), and the magnetic moment is 1.9(4) mu(B). Density functional theory (DFT) calculations on model NiAz structures establish that orbitals 3d(x2-y2) and 3d(z2) are the two valence holes in the high-spin Ni(II) ground state, and in accord with the experimentally determined orbital magnetic moment, the DFT results also demonstrate that both holes are highly delocalized, with 3d(x2-y2) having much greater ligand character. 相似文献
45.
Luque Ruiz I García GC Gómez-Nieto MA 《Journal of chemical information and computer sciences》2004,44(6):1903-1911
The increase in the size and complexity of chemical databases necessitates the proposal and development of efficient methods of classification and recovery of information, which supposes proposal of a model of classification of database records and the use of a compatible model of screening for inspection of clusters and recovery of the molecules that satisfy the search criterion. The cycle graphs model based on consideration of all the cycles and chains (and equivalent cycles and chains) present in the molecular structure has been proven appropriate for classification of chemical databases, giving rise to a generation of different classification levels depending on the structural elements (cycles and chains) that are considered. In this paper we propose a screening model, compatible with the cycle graphs model, based on a hierarchy of levels of abstraction. The set of molecules that satisfies a screening model (or selection criterion) diminishes as we advance in the hierarchy of levels of the model, which allows filtering of records and, therefore, an increase in the efficiency of the screening process. In the following work of this series we describe and validate the screening tool developed. 相似文献
46.
Ion Gănescu Alex Popescu Magda Preoteasa 《Monatshefte für Chemie / Chemical Monthly》1970,101(6):1623-1629
Zusammenfassung Es wurden 34 neue Komplexsalze durch doppelte Umsetzung aus wäßr.-alkohol. Lösungen der folgenden Reineckeat-Analoga: [Cr(NCS)4(m-xylidin)2]–, [Cr(NCS)4(p-xyl)2]– und Hexammin-, Monoacido-pentammin- und Diacido-tetramminkobalt(III)-komplexsalze erhalten. Es wurden in einigen Fällen Unterschiede in physiko-chemischen Eigenschaften, wie Farbtönung, Kristallform, Löslichkeit und papierchromatographischeR
f-Werte, bei den stellungsisomeren Salzen vom Typus: Kation · [Cr(NCS)4(xyl)2] und auch bei den Koordinationsisomerpaaren: [Co(DH)2(m-xyl)2] [Cr(NCS)4(p-xyl)2] und [Co(DH)2(p-xyl)2] [Cr(NCS)4(m-xyl)2] usw. beobachtet.
Cobalt(III)ammine derivatives of some reineckate analogues with xylidines
34 new complex salts were prepared by double conversion of the reineckate analogues [Cr(NCS)4(m-xylidine)2]–, [Cr(NCS)4(p-xyl)2]–, with the hexammine-, monoacido-pentammine- and diacidotetrammine-complexes of Co(III). In some of the position and coordination isomeres differences of the standard physico-chemical properties, i.e. color, crystal form, solubility and paper chromatographyR f-values were observed.相似文献
47.
Esteso Ana Alemany M. M. E. Ortiz Angel Liu Shaofeng 《Central European Journal of Operations Research》2022,30(3):1101-1127
Central European Journal of Operations Research - Agri-food production must increase while food waste needs to be reduced for improving the position of farmers. To do so it is necessary to... 相似文献
48.
The framework of the paper is that of the full Fock space
and the Banach algebraF
which can be viewed as non-commutative analogues of the Hardy spacesH
2 andH
respectively.An inner-outer factorization for any element in
as well as characterization of invertible elements inF
are obtained. We also give a complete characterization of invariant subspaces for the left creation operatorsS
1
,..., S
n
of
. This enables us to show that every weakly (strongly) closed unital subalgebra of {(S
1
,..., S
n
) F
} is reflexive, extending in this way the classical result of Sarason [S]. Some properties of inner and outer functions and many examples are also considered.The first author was supported in part by NSF DMS 93-21369 1991Mathematics Subject Classification. Primary 47D25, Secondary 32A35, 47A67. 相似文献
49.
Angel Carocca 《Bulletin of the Brazilian Mathematical Society》1995,26(2):161-165
Given a finite groupG andp an odd prime number, we conclude thatO
p(G)G isp-nilpotent when for every subgroupH ofG of orderp there exists a subgroupK ofG such thatG=HK andH permutes with every subgroup ofK. 相似文献
50.