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  • Defoliation  (1)
  • Key words Porphyrin conformation  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Correlation of macrocycle distortion with oxidation potentials of iron(III) porphyrins: molecule structure of the sterically crowded chloro-iron(III) 7,8,17,18-tetrabromo-5,10,15,20-tetraphenylporphyrin (1997)
    Springer
    JBIC 2 (1997), S. 662-666 
    Details
    ISSN: 1432-1327
    Keywords: Key words Porphyrin conformation ; Oxidation potentials ; Molecular orbital calculations ; Heme proteins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  The chloro-iron(III) complex of the tetraphenylporphyrin tetrabrominated at the antipodal β-pyrrole positions [(7,8,17,18-tetrabromo-5,10,15,20-tetraphenyl)porphyrin] has been synthesized and characterized by spectroscopy and X-ray crystallography. The iron atom is bonded to the chloride ion and the four pyrrole nitrogens. The Fe-Cl bond distance is 2.209(4) Å, and the mean value of the two opposite Fe-Np lengths at the brominated pyrrole rings is 2.079(8) Å, whereas the mean value of the two opposite Fe-Np′ bond distances at the non-brominated pyrrole rings is 2.041(8) Å. The X-ray structure determination and the analysis of the UV-Vis spectra obtained in solution and on thin films indicate that |FeCl(tpp-Br4)| (1) is principally saddle-shaped in the solid state and in solution. Variable-temperature (195–325 K) 1H NMR spectroscopy confirms the high-spin state (S=5/2) of the iron(III) center and indicates that the saddle-shaped conformation of 1 is maintained in solution. EPR spectra obtained in frozen CH2Cl2 solution and in the solid state show a rhombic symmetry with g values of 6.25, 5.70 and 1.99. Kadish et al. have shown that the one-electron oxidation potential of 1 increases only by 0.06 V relative to that of the non-brominated complex |FeCl(tpp)|. The present study indicates that the increase of the first oxidation potential of 1 is related to the non-planar distortion of the porphyrin. Relative to the unbrominated derivative |FeCl(tpp)|, this distortion destabilizes the π system of the macrocycle and thus compensates for the effects of the four electron-withdrawing bromine substituents.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007750050181
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  • 2
    Electronic Resource
    Electronic Resource
    Performance and allocation patterns of the perennial herb, Plantago lanceolata, in response to simulated herbivory and elevated CO2 environments (1991)
    Springer
    Oecologia 87 (1991), S. 37-42 
    Details
    ISSN: 1432-1939
    Keywords: Allocation ; Compensatory growth ; Defoliation ; Reproductive effort ; Seed quality
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We tested the prediction that plants grown in elevated CO2 environments are better able to compensate for biomass lost to herbivory than plants grown in ambient CO2 environments. The herbaceous perennial Plantago lanceolata (Plantaginaceae) was grown in either near ambient (380 ppm) or enriched (700 ppm) CO2 atmospheres, and then after 4 weeks, plants experienced either 1) no defoliation; 2) every fourth leaf removed by cutting; or 3) every other leaf removed by cutting. Plants were harvested at week 13 (9 weeks after simulated herbivory treatments). Vegetative and reproductive weights were compared, and seeds were counted, weighed, and germinated to assess viability. Plants grown in enriched CO2 environments had significantly greater shoot weights, leaf areas, and root weights, yet had significantly lower reproductive weights (i.e. stalks + spikes + seeds) and produced fewer seeds, than plants grown in ambient CO2 environments. Relative biomass allocation patterns further illustrated differences in plants grown in ambient CO2 environments. Relative biomass allocation patterns further illustrated differences in plant responses to enriched CO2 atmospheres: enriched CO2-grown plants only allocated 10% of their carbon resources to reproduction whereas ambient CO2-grown plants allocated over 20%. Effects of simulated herbivory on plant performance were much less dramatic than those induced by enriched CO2 atmospheres. Leaf area removal did not reduce shoot weights or reproductive weights of plants in either CO2 treatment relative to control plants. However, plants from both CO2 treatments experienced reductions in root weights with leaf area removal, indicating that plants compensated for lost above-ground tissues, and maintained comparable levels of reproductive output and seed viability, at the expense of root growth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00323777
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