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61.
Carlos Sancho de Salas 《Transactions of the American Mathematical Society》2003,355(9):3651-3667
Homogeneous varieties are those whose group of automorphisms acts transitively on them. In this paper we prove that any complete homogeneous variety splits in a unique way as a product of an abelian variety and a parabolic variety. This is obtained by proving a rigidity theorem for the parabolic subgroups of a linear group. Finally, using the results of Wenzel on the classification of parabolic subgroups of a linear group and the results of Demazure on the automorphisms of a flag variety, we obtain the classification of the parabolic varieties (in characteristic different from ). This, together with the moduli of abelian varieties, concludes the classification of the complete homogeneous varieties.
62.
Barea E Navarro JA Salas JM Quirós M Willermann M Lippert B 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(18):4414-4421
A set of enantiomerically pure cyclic multinuclear complexes with the formula cis-[a(2)PdL](n) (n+) [a(2)=(R,R)-1,2-diaminocyclohexane (R,R-dach), (S,S)-1,2-diaminocyclohexane (S,S-dach); n=4, 6; LH=2-hydroxypyrimidine (2-Hpymo), 4,6-dimethyl-2-hydroxypyrimidine (2-Hdmpymo) and 4-hydroxypyrimidine (4-Hpymo)] were obtained by reaction of cis-[a(2)Pd(H(2)O)(2)](2+) and LH in aqueous media. The polynuclear complexes were studied by (1)H NMR spectroscopy and X-ray crystallography. These studies revealed that the N1,N3-bridging mode exhibited by the pyrimidine moieties is ideally suited for formation of inorganic analogues of calixarenes (metallacalixarenes) in a self-assembly process. The most stable species are the tetranuclear metallacalix[4]arenes, which are obtained in all cases. Hexanuclear species, namely, [a(2)Pd(2-dmpymo)](6) (6+), were also isolated and fully characterised. (1)H NMR experiments show conversion of [a(2)Pd(2-dmpymo)](6) (6+) to [a(2)Pd(2-dmpymo)](4) (4+) on heating. Analogously to organic calixarenes, these systems are also capable of incorporating hard metal ions at the oxo surface. Additionally, investigations on the receptor properties of these metallacalixarenes towards mononucleotides showed that enantioselective recognition processes occur in aqueous media. 相似文献
63.
Ricardo A. Tapia Claudia Carrasco Scarlet Ojeda Cristian Salas Jaime A. Valderrama Antonio Morello Yolanda Repetto 《Journal of heterocyclic chemistry》2002,39(5):1093-1096
The synthesis of new indazol‐4,7‐dione derivatives via 1,3‐dipolar cycloaddition of diazomethane with 2,3‐dimethyl‐1,4‐benzoquinone ( 2 ) and 1,4‐naphthoquinone ( 7 ) followed by N‐alkylation of the pyrazol nitrogen atom of the corresponding quinones ( 3 ) and ( 8 ) with methyl chloroacetate is described. A series of amides from esters ( 5 ) and ( 10 ) were also obtained. These compounds were tested in vitro as potential anti‐trypanosomal agents. Compounds ( 4 ) and ( 8 ) were found to have significant activity. 相似文献
64.
Olano C Wilkinson B Sánchez C Moss SJ Sheridan R Math V Weston AJ Braña AF Martin CJ Oliynyk M Méndez C Leadlay PF Salas JA 《Chemistry & biology》2004,11(1):87-97
The biosynthetic gene cluster for the angiogenesis inhibitor borrelidin has been cloned from Streptomyces parvulus Tü4055. Sequence analysis indicates that the macrolide ring of borrelidin is formed by a modular polyketide synthase (PKS) (borA1-A6), a result that was confirmed by disruption of borA3. The borrelidin PKS is striking because only seven rather than the nine modules expected for a nonaketide product are encoded by borA1-A6. The starter unit of the PKS has been verified as trans-cyclopentane-1,2-dicarboxylic acid (trans-1,2-CPDA), and the genes involved in its biosynthesis identified. Other genes responsible for biosynthesis of the nitrile moiety, regulation, and self-resistance were also identified. 相似文献
65.
Salas JA 《Chemistry & biology》2004,11(7):892-894
In this issue of Chemistry & Biology, a novel priming mechanism is proposed for aromatic polyketide biosynthesis, with an iterative type I polyketide synthase generating a starter unit primed for a type II polyketide synthase. This novel priming system participates in hedamycin biosynthesis, a DNA alkylating agent. 相似文献
66.
Francisca Barrios Juan M. Salas M. Purificación Sánchez Miguel Quirós René Faure 《Journal of chemical crystallography》1999,29(9):1009-1013
The complex [Ni(XsH–1)2(H2O)4]·6H2O (XsH–1: xanthosinate) was isolated from the reaction of nickel carbonate with xanthosine in aqueous solution. The octahedral coordination is supported by the reflectance measurements. Single-crystal X-ray diffraction studies show that the crystals belong to the triclinic P1 space group, with a = 7.152(1), b = 8.830(1),c = 13.783(1) Å, = 82.024(1)°, = 86.155(1)°, = 70.900(1)°, and D = 1.643 mg/m3, forZ = 1. Nickel is six coordinate with four water molecules, and two N7 atoms from xanthosinato ligands. A complicated hydrogen-bonding network is present, all possible donors taking part in it. 相似文献
67.
J. M. Salas E. Colacio M. N. Moreno J. Ruiz T. Debaerdemaeker J. Via M. I. Arriortua 《Journal of chemical crystallography》1989,19(4):755-763
The theophyllinium tetrabromopalladate(II), [Thph]2PdBr4, has been synthesized and its molecular structure has been determined by single crystal X-ray diffraction. The salt crystallizes in the monoclinic space group C2 with two formula units in a cell of dimensionsa=11.074(1),b=8.545(2),c=11.804(2) Å;=95.22(1)°,V=1112.3(4) Å3,D
c=2.353 mg m–3,D
exp=2.352 mg m–3,M
w=788.4, (MoK)=84.5 cm–1,F(000)=752. The structure has been refined by full-matrix least-squares techniques to a final value of theR factor of 0.058 based on 907 independent intensities. The compound consists of theophyllinium cations protonated at N(9). The [PdBr4]2– anion is planar, with distances Pd-Br(1)=2.441(12) and Pd-Br(2)=2.412(6) Å, and Br(1)-Pd-Br(2) and Br(1)-Pd-Br(3) angles of 90.34(14)° and 89.66(14)°, respectively. The1H-NMR spectrum of [Thph]2PdBr4 in DMSO-d6 (300 MHz) is consistent with the observed solid-state structure, and its thermal behavior shows two steps: (i) a dehalogenation process about 327°C and (ii) a rapid pyrolitic decomposition in the 340–575°C temperature range giving PdO as final product. 相似文献
68.
Let be the automorphism scheme of a finite purely inseparable field extension (in fact, we consider a wide class of finite ring extensions). Let be the splitting algebra of K (see 2.8) and the splitting field of K. It is proved that is integral if and only if . This may be formulated as a condition on the degree of and generalizes a result of Chase. Surprisingly, may be defined intrinsically, since is the scheme parametrizing the maximal smooth subgroups of . It is also proved that the desingularization of is the universal maximal smooth subgroup of and coincides with the blowing up along a closed subscheme canonically defined from the action of on .
Received June 4, 1997; in final form July 22, 1998 相似文献
69.
Ren Miranda Ismael Salas Catalina Salceda Luis Velasco Armando Cabrera Manuel Salmn 《Journal of mass spectrometry : JMS》1993,28(5):593-594
An electron impact mass spectral study of phosphine sulphides and selenides established the effect of the heteroatom and the role of the ortho substituent in the fragmentation pattern. 相似文献
70.