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  • 1
    Electronic Resource
    Electronic Resource
    Fragmentation of vinyl triflates by electron impact. Mechanism of an unusual double hydrogen atom transfer reaction (1994)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 8 (1994), S. 427-431 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The main fragmentation pathway of vinyl triflates in mass spectra involves the loss of CF3SO2·, followed by the loss of olefin and/or CO. The loss of TfOH takes place with fragmentation of a vinylic C—H bond. TfOH2+ ions are formed via regiospecific double hydrogen transfer from five- and six-membered cyclic triflates.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290080517
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  • 2
    Electronic Resource
    Electronic Resource
    New phenylboronic esters derived from inositol [1] (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Heteroatom Chemistry 5 (1994), S. 139-143 
    Details
    ISSN: 1042-7163
    Keywords: Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have prepared two new tetracyclic phenylboronic esters 4 and 5 derived from myo-inositol and from 1,2-O-isopropylidene-myo-inositol, respectively. The structures of these compounds were established from NMR and IR spectra, elemental analyses, and an X-ray diffraction study in the case of 4. Compound 4 is a tetracyclic derivative of the less stable conformer of inositol (five axial hydroxy groups and one equatorial) with two dioxaboroline rings at opposite faces of the six-membered ring, one formed between the boron atom and the axial hydroxyl groups at C-3 and C-5 and the other between the boron atom and the hydroxyl groups at C-4 and C-6, and a dioxaborolidine ring bridging C-1 and C-2 at axial and equatorial positions. A similar structure was found for 5 with the difference that bridging C-1 and C-2 there is a dioxolane ring. The boron atoms are planar with their attached atoms, stabilized by retrocoordination between the boron and oxygen and carbon atoms, respectively. The two phenyl rings that are in the same face of the molecule are essentially parallel, with a dihedral angle between planes of 28.26 ± 0.79°.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hc.520050210
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  • 3
    Electronic Resource
    Electronic Resource
    Electron impact mass spectrometry of triterpenoids from guayuleContribution No. 998 from the Instituto de Química, UNAM, Mexico. (1990)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 25 (1990), S. 237-238 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210250411
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  • 4
    Electronic Resource
    Electronic Resource
    The number of Kα photons produced on a set of thin targets as a functional description of the fluorescence exciting x-ray beamPresented at the European Conference on EDXRS, Myconos, Greece, 30 May-6 June 1992. (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    X-Ray Spectrometry 22 (1993), S. 312-316 
    Details
    ISSN: 0049-8246
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: This work suggests a theoretical approach for the description of a primary x-ray beam by means of the K fluorescence which it excites on a set of thin targets made of pure elements. Physical quantities, defined as weighted integrals over hv of the photon spectral distribution, are obtained directly as weighted integrals of the Kα yields over the variable Ez (the ionization energy of the K shell of the element with atomic number Z), without needing any explicit reconstruction of the spectral distribution. The set of Kα yields produced by an x-ray beam as a function of Ez is a functional description of the exciting beam. Theoretically, such a description is suited to x-ray fluorescence analysis.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/xrs.1300220425
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  • 5
    Electronic Resource
    Electronic Resource
    1H, 13C, 15N, 113Cd, 2D 15N—1H and solid-state 13C CP/MAS NMR of Hg and Cd complexes of 4(1H)-quinazolinone-2,3-dihydro-2-thioxo (1993)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 31 (1993), S. 832-835 
    Details
    ISSN: 0749-1581
    Keywords: 1H, 13C, 15N and 113Cd NMR ; Two-dimensional NMR ; CP/MAS NMR ; Hg and Cd complexes 4(1H) -Quinazolinone-2,3-dihydro-2-thioxo ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Cd(II) and Hg(II) complexes of 4(1H)-quinazolinone-2,3-dihydro-2-thioxo (1) and the free ligand were studied by 1D and 2D multinuclear magnetic resonance in solution and 13C cross polarization magic angle spinning NMR in the solid state. Compound 1 adopts only one of five possible tautomeric structures in solution, namely the thiouracyl-like structure. It was found that the metal atom is linked to two molecules of deprotonated 1 by N-1 and coordinated by the sulphur atom. The compounds retain the same structure in the solid state and in dimethyl sulphoxide solution.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260310908
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  • 6
    Electronic Resource
    Electronic Resource
    Foliole movement and canopy architecture of Larrea tridentata (DC.) Cov. in Mexican deserts (1992)
    Springer
    Oecologia 92 (1992), S. 83-89 
    Details
    ISSN: 1432-1939
    Keywords: Larrea tridentata ; Mexico ; Deserts ; Canopy architecture ; Foliole movement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The creosote bush (Larrea tridentata) is a common desert perennial with bifoliate, amphistomatic, divaricate leaves. The leaves can vertically close their folioles and vary their profile with respect to direct solar radiation. Field data from different Mexican deserts showed a significant correlation between foliole aperture and mean foliole inclination: in plants in which folioles were more open, the foliole surfaces were less vertical. In a series of field experiments in the Chihuahuan Desert, foliole aperture varied significantly with the water-status of the plant and the hour of the day. In moist plants, folioles opened in the early morning and closed in the afternoon. Water-stressed plants showed significantly lower foliole apertures. A simulation of the light interception patterns of the plants showed that foliole closure in water-stressed individuals reduces direct radiation interception by around 24%. Most (64%) of the reduction in interception was due to the vertical inclination of the photosynthetic surfaces induced by foliole closure in the water-stressed plants. The rest (36%) of the reduction in interception was due to differential self-shading between foliole pairs, which was higher in the closed folioles of the water-stressed plants, but operated more towards the early hours of the day.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00317266
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  • 7
    Electronic Resource
    Electronic Resource
    Germination response to temperature, salinity, light and depth of sowing of ten tropical dune species (1992)
    Springer
    Oecologia 92 (1992), S. 343-353 
    Details
    ISSN: 1432-1939
    Keywords: Dunes ; Germination ; Mexico ; Ecophysiology ; Neotropic
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This study describes the germination responses of ten tropical dune species to several factors to which their seeds are exposed in the field. Species studied were: three sand dune endemics (Amaranthus greggii, Palafoxia lindenii, and Trachypogon gouini), three pantropical coastal species (Sesuvium portulacastrum, Sporobolus virginicus and Ipomoea stolonifera) and four cosmopolitan grasses also found inland (Panicum repens, Panicum maximum, Pappophorum vaginatum and Andropogon glomeratus). Six species germinated when exposed to different constant temperatures. Four required temperature fluctuation (S. portulacastrum, P. lindenii, S. virginicus, P. repens). Light promoted germination of three species (S. Portulacastrum, P. vaginatum, P. lindenii). Species varied in their degree of sensitivity to salinity. Seeds of T. gouini, I. stolonifera, S. portulacastrum, P. repens, P. Maximum and P. vaginatum were able to germinate under some of the salinity concentrations. Not all species were able to recover after being transferred to distilled water. Seedling emergence was inhibited when seeds were buried. This response was related to depth and to seed size. S. portulacastrum and S. virginicus were the most affected. Nitrates only affected germination response of two species. Seed age promoted germination under a wider range of conditions. P. lindenii showed very heterogeneous responses depending on seed cohort. No dormancy mechanisms were found, other than a thermoperiod and/or light requirement for some of the species. Cosmopolitan grasses tolerated both sand burial and salinity, although the endemics were the most successful in emerging from sand burial; coastal pantropicals were very tolerant to high saline concentrations and recovered completely.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00317460
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  • 8
    Electronic Resource
    Electronic Resource
    Distribution of species of Anostraca, Notostraca, Spinicaudata, and Laevicaudata in Mexico (1991)
    Springer
    Hydrobiologia 212 (1991), S. 209-219 
    Details
    ISSN: 1573-5117
    Keywords: Anostraca ; Notostraca ; Spinicaudata ; Laevicaudata ; Branchiopoda ; Mexico ; distribution ; conchostracan
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We inventorize the known distribution of the species of Anostraca, Notostraca, Spinicaudata, and Laevicaudata present in Mexico. Determinations of the species and their distribution involved: 1) Examination of Mexican collections of phyllopods, 2) Extensive sampling in 17 states, and 3) Study of laboratory cultures. The number of phyllopod species known to occur in Mexico is 27: 14 of Anostraca, including three undescribed species, 1 of Notostraca, 10 of Spinicaudata, and 2 of Laevicaudata. These results also include 44 new state records. The records of Branchinecta packardi are the first for Mexico. Some species have extensive distributions, not limited to Mexico: Streptocephalus mackini, S. texanus, Thamnocephalus platyurus, Triops longicaudatus and Leptestheria compleximanus. The species known only from Mexico are Streptocephalus kargesi, S. moorei, Paralimnetis mapimi, two undescribed species of Branchinecta, and an undescribed species of Streptocephalus. The largest number of species found to occur in the same pond at one time was eight.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00026003
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  • 9
    Electronic Resource
    Electronic Resource
    Branchinecta belki n. sp. (Branchiopoda: Anostraca), a new fairy shrimp from Mexico, hybridizing withB. packardi Pearse under laboratory conditions (1992)
    Springer
    Hydrobiologia 239 (1992), S. 151-162 
    Details
    ISSN: 1573-5117
    Keywords: Branchinecta ; Branchiopoda ; Anostraca ; Mexico ; hybridization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A new fairy shrimp,Branchinecta belki n.sp., endemic to the south of Coahuila state is described and figured. A total of nine species of phyllopods, including the new species, occur in ponds in the type area. The laboratory hybridization ofB. belki andB. packardi through ‘no-choice’ mating tests in reciprocal crosses is discussed. A mixture of characteristics of parental species is present in male F1 and F2 hybrids. This may provide a biological tool, or ‘search image’ (sensu Wiman, 1979a), for detecting male hybrids, should such exist, between theBranchinecta species of this study in nature. In addition to the reported interspecific hybridizations inStreptocephalus (Wiman, 1979a & 1979b) and inArtemia (Bowenet al., 1985) under laboratory conditions, the new evidence inBranchinecta suggests that absence of efficient premating mechanisms may be common in Anostraca.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00007672
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  • 10
    Electronic Resource
    Electronic Resource
    Contribution to the knowledge of the rotifera of Mexico (1993)
    Springer
    Hydrobiologia 255-256 (1993), S. 467-474 
    Details
    ISSN: 1573-5117
    Keywords: Rotifera ; zoogeography ; Mexico
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This faunistic survey of Mexican Rotifera, covering 32 localities, mostly in Central Mexico, has yielded 96 taxa of which 41 are new to Mexican fauna. The zoogeographic status of the rotifer fauna of Mexico was reevaluated on the basis of the present data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00025875
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